Full opinion text
MEMORANDUM AND ORDER FRANK C. DAMRELL, JR., District Judge. This matter is before the court on defendants Zimmer US, Inc. and Zimmer Inc.’s (“defendants”) motion for summary judgment pursuant to Federal Rule of Civil Procedure 56 and defendants’ motion to exclude the testimony of Martin T. Wells (“Wells”) pursuant to Federal Rule of Evidence 702. For the reasons set forth below, defendants’ motion for summary judgment is GRANTED in part and DENIED in part and defendants’ motion to exclude Wells’ testimony is DENIED. BACKGROUND Plaintiff Sara Monroe (“plaintiff’) alleges that use of a Zimmer Ambulatory Pump (“ZAP”) caused her to lose cartilage in her shoulder, resulting in unbearable pain and suffering. (Complaint, filed Oct. 16, 2008.) Plaintiff raises claims under California law for: (1) general negligence; (2) negligent products liability; and (3) strict products liability. As to the claim of general negligence, plaintiff alleges that defendants negligently designed, manufactured, and distributed a defective ZAP and negligently failed to warn doctors and patients that use of the ZAP in shoulder joints was unsafe. 1. Overview A. Anatomy of the Shoulder and the Glenohumeral Joint The ball-and-socket joint of the shoulder is called the glenohumeral joint. The area surrounding the glenohumeral joint contains articular cartilage and synovial tissue. Articular cartilage is a thin layer of tissue that covers the ends of bones in the joint and provides a smooth, gliding surface that enables the bones to move. Articular cartilage receives its nutrients exclusively from synovial fluid within the joint space. B. Glenohumeral Chondrolysis Articular cartilage cells are known as chondrocytes, is the destruction of these cells. Glenohumeral refers to rapid and permanent destruction of in the shoulder joint. See D.J. Solomon et al., Chondrolysis After Arthroscopy: A Systematic Review and Causal Pathways, 25 Arthroscopy: J. Arthroscopic & Related Surg. 1329, 1330 (Nov. 2009). Cartilage cell death may occur from the inability of chondrocytes to maintain or produce cartilage matrix. Id. If the cartilage matrix is not renewed, it wears away with normal use of the joint until all of the protective tissue is gone. This results in the bones of the joint rubbing against one another, causing debilitating pain and stiffness. C. Pain Pump A pain pump is a medical device designed to deliver targeted doses of pain management medication to a specific part of the body. A pain pump consists of a fluid reservoir that contains one or more pain medications, a mechanism that pumps the pain management medication to the patient, and a catheter that delivers the pain management medication to a specific part of the body. 2. Plaintiff’s Medical History On May 18, 2007, plaintiffs orthopedic surgeon, Dr. Richard Cross (“Cross”), performed surgery on plaintiffs left shoulder. (Deposition of Dr. Richard Cross [“Cross Dep.”], filed Sep. 23, 2010 [Docket # 80], Ex. C at 23:5-7.) The surgery involved decompression of the acromion and a resection of the distal clavicle. (Id. at 23:16-21; DUF ¶ 5.) Prior to the surgery, on May 10, 2007, Cross injected plaintiffs left shoulder with the anesthetic Marcaine. (Cross Dep. at 12:3-7.) During the surgery, Cross found that plaintiff had a “degenerative or arthritic and/or arthritic acromioclavicular joint” and “some impingement in her shoulder or crowding of her acromion.” (Id. at 23:10-13.) Cross noted that these issues were “not unusual” for a patient of plaintiffs age with plaintiffs medical background. (Id. at 23:25-24:4.) Also on May 18, 2007, Cross used a radio frequency probe on plaintiffs glenoid, within the glenohumeral joint. (Id. at 71:15-25.) He used this probe, at a low frequency, to smooth a mild amount of damaged cartilage. (Id.) Cross noted that this damage was typical wear and tear damage for someone of plaintiffs age. (Id.) Following the surgery on plaintiffs left shoulder, a ZAP was inserted into the subacromial space of plaintiffs left shoulder for a minimum of two days. (DUF ¶¶ 7-8, 10; Cross Dep. at 30:4-7.) A fluid pathway from the ZAP catheter to plaintiffs glenohumeral joint should not have been present at this time; however, it is possible that such communication occurred. (DUF ¶ 9; Cross Dep. at 54:2-25.) After plaintiffs surgery, she was involved in an altercation where she was punched in her left shoulder. (DUF ¶¶ 11-12.) This altercation delayed plaintiffs treatment and led to Cross injecting corticosteroids into plaintiffs glenohumeral joint. (DUF ¶¶ 14-15.) On August 31, 2007, Cross performed a second surgery on plaintiffs left shoulder. (DUF ¶ 16.) During this surgery, Cross noted a lesion, labral tearing, and an onset of degenerative changes in the articular cartilage of plaintiffs glenoid. (DUF ¶ 17.) Cross also noted a Hill-Sachs lesion of the humerus during this surgery. (DUF ¶ 18; Cross Dep. at 52:11-25-53:1-5.) As he did during the first surgery, Cross used a radio frequency probe on the cartilage of plaintiffs glenoid. (DUF ¶ 20.) During plaintiffs surgery on August 31, 2007, a ZAP was inserted directly into plaintiffs glenohumeral joint. (DUF ¶ 21.) The ZAP remained in plaintiffs shoulder for six days. (Cross Dep. at 62:7-21.) After this surgery, plaintiff received two additional injections of corticosteroids into her glenohumeral joint. (DUF ¶ 22.) After receiving the injections, plaintiff complained to Cross of increased pain and decreased range of motion in her shoulder. (Cross Dep. at 68:21-24.) Cross ordered an x-ray, which revealed global loss of cartilage in plaintiffs shoulder. (Id. at 69:2-6.) Plaintiff was subsequently diagnosed with chondrolysis in her left shoulder. (DUF ¶ 23.) 3. Causation A. Specific Causation Testimony on the issue of the specific cause of plaintiffs injury comes from plaintiffs treating physician, Cross. Plaintiff disclosed Cross as a non-retained expert. (DUF ¶ 25.) Cross admits that he is not an expert on the development of chondrolysis, nor is he an expert on whether chondrolysis is caused by pain pumps. (DUF ¶ 26.) As discussed below, Cross states that he implemented the “differential diagnosis” method to determine the cause of plaintiffs injury. Initially, Cross believed that plaintiffs chondrolysis resulted from her altercation. (DUF ¶ 27; Cross Dep. at 74:11-21.) It was not until January 24, 2008 that Cross determined that plaintiffs chondrolysis was “possibly” due to the ZAP. (Cross Dep. at 74:24-25-75:1-5.) Cross testifies that this change occurred because he was not previously aware of an association between chondrolysis and pain pump use. (Id. at 75:17-19.) Cross testifies that he is not entirely sure, but he believes that a “blurb” on the internet drew his attention to potential problems associated with the use of pain pumps. (Id. at 75:24-25-76:1-4.) Once he became aware of this potential association, Cross reports that it “clicked” for him, that the pain pump may be the cause of plaintiffs chondrolysis. (Id. at 76:4-7.) During his deposition, defendants’ counsel asked Cross if he ever formed an opinion that the pain pump was a substantial factor in causing plaintiffs chondrolysis. (Id. at 77:21-23.) Cross responded “[tjhats a good question. And I would say I think I have. I think I have, but it’s not science. It’s an opinion ... it’s my gut feeling with [plaintiff].” (Id. at 77:24-25, 78:2-3.) Cross later elaborated on his thought process, discussing how he considered other factors that could have caused plaintiffs injury but ultimately ruled them out, eventually deciding that the pain pump may have been a significant cause of plaintiffs injury. (Id. at 78:4-25-79:1-13.) Cross also testified that, “if I could do it all over again, I never would’ve put a pain catheter in her. Whether we would’ve had this problem or not, who’s to say? ... Certainly you can argue that point.” (Id. at 80:13-18.) Eventually, in response to questioning from plaintiffs counsel, Cross testified that it was his opinion, based on his review of medical literature, many years of orthopedic experience, and clinical experience with plaintiff, that the pain pump was “the most probable cause” of plaintiffs chondrolysis. (Id. at 102:21-25-102:1-11.) B. General Causation 1. Dr. Dragoo One of plaintiffs two retained experts on the issue of general causation is Dr. Jason Dragoo (“Dragoo”), a professor of Orthopedic Surgery at Stanford University. (Decl. of Dr. Dragoo [“Dragoo Report”], filed Feb. 19, 2010 [Docket # 29], Attachment 7 at ¶ 1.) Dragoo reviewed retrospective studies, case reports, and an in vivo animal study. Dragoo also conducted an in vitro human study, using articular cartilage from human knees and a “culture system” designed to replicate the normal physiology of the shoulder. (Dragoo Report ¶¶ 14-17.) Based on the results of his study and his review of prior studies, Dragoo determined, with a reasonable degree of medical certainty, that intra-articular pain pump usage can cause cartilage degeneration. (Id. at ¶ 31.) 2. Dr. Wells Wells, the Chair of the Department of Statistical Sciences at Cornell University, is plaintiffs other expert on the issue of general causation. (Decl. of Martin T. Wells, Ph.D. [“Wells Report I”], filed Feb. 19, 2010 [Docket # 29], Attachment 3 at ¶2.) Wells reviewed epidemiological and scientific literature relating to intra-articular pain pump use and its connection to glenohumeral chondrolysis. (Wells Report I ¶ 1.) As discussed infra, Wells conducted statistical analysis on the data reported in these studies to determine whether they reported a statistically significant causal relationship between the use of intra-articular pain pumps and the development of chondrolysis. (Id. at ¶¶ 1,14.) In his analysis, Wells employed principles set forth in Bradford Hill’s criteria of causation (“Hill analysis”), which are meant to assess the presence of a meaningful, statistically valid association between phenomena. (Id. at ¶ 14.) Wells’ statistical analysis led him to conclude that there is a substantial difference in the risk of developing chondrolysis for patients that use a pain pump versus patients who do not. Wells also analyzed the data to determine whether other potential risk factors could be responsible for the development of chondrolysis, ultimately ruling them out. STANDARD 1. Summary Judgment The Federal Rules of Civil Procedure provide for summary judgment where “the movant shows that there is no genuine dispute as to any material fact and the movant is entitled to judgment as a matter of law.” Fed.R.Civ.P. 56(a). The evidence must be viewed in the light most favorable to the nonmoving party. See Lopez v. Smith, 203 F.3d 1122, 1131 (9th Cir.2000) (en banc). The moving party bears the initial burden of demonstrating the absence of a genuine issue of fact. See Celotex Corp. v. Catrett, 477 U.S. 317, 325, 106 S.Ct. 2548, 91 L.Ed.2d 265 (1986). If the moving party fails to meet this burden, “the nonmoving party has no obligation to produce anything, even if the nonmoving party would have the ultimate burden of persuasion at trial.” Nissan Fire & Marine Ins. Co. v. Fritz Cos., 210 F.3d 1099, 1102-03 (9th Cir.2000). However, if the nonmoving party has the burden of proof at trial, the moving party only needs to show “that there is an absence of evidence to support the nonmoving party’s case.” Celotex Corp., 477 U.S. at 325, 106 S.Ct. 2548. Once the moving party has met its burden of proof, the nonmoving party must produce evidence on which a reasonable trier of fact could find in its favor viewing the record as a whole in light of the evidentiary burden the law places on that party. See Triton Energy Corp. v. Square D Co., 68 F.3d 1216, 1221 (9th Cir.1995). The nonmoving party cannot simply rest on its allegations without any significant probative evidence tending to support the complaint. See Nissan Fire & Marine, 210 F.3d at 1107. Instead, the nonmoving party must cite to “particular parts of materials in the record,” or show that moving party’s cited materials “do not establish the absence or presence of a genuine dispute, or that an adverse party cannot produce admissible evidence to support the fact.” Fed.R.Civ.P. 56(c)(1). 2. Expert Testimony The admissibility of expert testimony is governed by Federal Rule of Evidence 702 (“Rule 702”). When specialized knowledge will assist the trier of fact to understand the evidence in a case, Rule 702 permits testimony by experts with the knowledge, skill, experience, training, or education necessary to testify thereto, as long as their testimony meets several requirements. Fed.R.Evid. 702. A qualified expert’s testimony is admissible if: (1) the testimony is based upon sufficient facts or data; (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case. Id. The role of the trial judge is to act as a gatekeeper, ensuring that only relevant and reliable testimony is admitted. See Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 589, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993) {“Daubert I ”); see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 152, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999). Accordingly, the court must conduct a “preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue.” Daubert I, 509 U.S. at 592-93, 113 S.Ct. 2786. “Pertinent evidence based on scientifically valid principles will satisfy those demands.” Id. at 597,113 S.Ct. 2786. In Daubert I, the Supreme Court listed several key considerations to aid the trial court in its gatekeeping role. The trial court should consider: (1) whether the scientific knowledge can or has been tested; (2) whether the given theory or technique has been published or subjected to peer review; (3) the potential or known error rate; and (4) whether the theory or technique has gained general acceptance in the pertinent field. Daubert I, 509 U.S. at 592-94,113 S.Ct. 2786. The court’s Rule 702 analysis is flexible. Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 150, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999). The court may consider any or all of the Daubert I factors, depending on the “particular circumstances of the particular case at issue.” {Id.) The trial court may dismiss testimony that is either irrelevant or unreliable. See Stilwell v. Smith & Nephew, Inc., 482 F.3d 1187 (9th Cir.2007). In evaluating the expert’s testimony, the court must focus on the principles or methodology involved, not the conclusions that they generate. Daubert I, 509 U.S. at 595, 113 S.Ct. 2786. Thus, “the test under Daubert is not the correctness of the expert’s conelusions but the soundness of his methodology.” Daubert v. Merrell Dow Pharms., Inc., 43 F.3d 1311, 1318 (9th Cir.1995) (“Daubert II”). “Ultimately, the court must ensure that an expert employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field,” such that the expert’s “work product amounts to ‘good science.’ ” McClellan v. I-Flow Corp., 710 F.Supp.2d 1092, 1100 (D.Or.2010) (quoting Kumho, 526 U.S. at 152, 119 S.Ct. 1167 and Daubert II, 43 F.3d at 1315). ANALYSIS Defendants move for summary judgment, arguing that plaintiffs claims fail because her experts are unable to prove that the ZAP is capable of causing chondrolysis generally, or that the ZAP specifically caused plaintiffs injury. Further, defendants assert that plaintiffs claims should be dismissed because she has not demonstrated that defendants breached a specific duty of care to her. Preliminarily, defendants attack the testimony of Wells, one of plaintiffs experts on general causation. As the resolution of defendants’ motion for summary judgement turns, in large part, on whether plaintiff has sufficient, admissible evidence to establish that intra-articular use of a pain pump can cause chondrolysis, the court addresses defendants’ motion to exclude Wells’ testimony first, as without Wells’ testimony, plaintiff cannot prevail on the motion. Second, because the court denies defendants’ motion to exclude Wells’ testimony, it next considers defendants’ motion for summary judgment. 1. Motion to Exclude Wells’ Testimony Plaintiff offers Wells’ testimony as proof that intra-articular use of pain pumps can cause glenohumeral chondrolysis. Defendants move to exclude Wells’ testimony, stating that (1) he is not qualified to opine on the cause of glenohumeral chondrolysis, and (2) his testimony is unreliable because he lacks adequate scientific bases for his opinions. A. Dr. Wells’ Report At plaintiffs request, Wells reviewed statistical aspects of scientific literature relating to intra-articular pain pump use and subsequent glenohumeral chondrolysis. (Wells Report I ¶ 1.) Wells analyzed the data reported in these studies to determine whether a causal relationship existed between the use of intra-articular pain pumps and the development of chondrolysis. (Id. at ¶¶ 1,-14.) In his analysis, Wells employed principles of the Hill analysis, which are designed to assess the presence of a meaningful, statistically valid association between phenomena. (Id. at ¶ 14.) These criteria include: (1) temporality; (2) strength of association; (3) consistency; (4) consideration of alternate explanations; (5) specificity; (6) dose response; (7) plausibility; (8) coherence; and (9) experiment. (Id.) Wells reviewed a paper entitled Postarthroscopic Glenohumeral Chondrolysis (“Hansen study”). B. Hansen & C. Beck, 35 Am. J. Sports Med. 1628 (July 2007). The Hansen study examined two groups of individuals who had undergone shoulder surgery, one group that used an intraarticular pain pump (“pump group”) and another that did not (“no pump group”). (Id.) Hansen’s study reviewed the results of 177 shoulder arthroscopies performed on 152 patients. (Id.) Nineteen of the 177 shoulders received intra-articular pain pump catheters filled with bupivacaine and epinephrine. (Id.) Of these 19 shoulders, 12 developed chondrolysis. (Id.) On the other hand, none of the 158 shoulders that did not receive a pain pump developed chondrolysis. (Id.) Additionally, Wells’ review of the Hansen study included 30 shoulders that underwent arthroscopic stabilization procedures. (Supplemental Decl. of Martin T. Wells, Ph.D. [“Wells Report II”], filed July 27, 2010 [Docket #68], Attachment 2 at ¶ 3.) Of these 30 shoulders, 11 of them were not exposed to a pain pump. (Id.) None of these 11 shoulders developed chondrolysis. (Id.) Whereas, of the 19 shoulders that were exposed to a pain pump, 12 developed chondrolysis. (Id.) Accordingly, the authors of the Hansen study concluded that the “[u]se of intraarticular pain pump catheters eluting bupivaeaine with epinephrine appear highly associated with postarthroscopic glenohumeral chondrolysis.” (See Hansen Study.) Wells conducted various analyses of the Hansen study data, concluding that, “the risk difference between the pump and no pump groups with respect to chondrolysis is extremely large and is well beyond what would occur by chance and far too large to be credibly explained by any other factor that has been shown linked to chondrolysis;” “the association of postsurgieal use of intra-articular pump with chondrolysis is well beyond what would occur by chance;” and “diagnostic bias is not a viable explanation for the enormous association of intra-articular pain pump use with chondrolysis.” (Wells Report I ¶¶ 8 — 11; Wells Report II ¶ 4.) Wells explained his methodology for reaching each of these conclusions, describing numerous statistical calculations derived from accepted methodologies in this industry, including: p-values using Fisher’s exact test; the odds ratio of chondrolysis from the pump group to the no-pump group; the median unbiased odds ratio estimate; the continuity corrected odds ratio; the Fisher’s mid-p exact 95% confidence limit; and the risk difference between the two groups. (See Wells Report I, II). Wells also reviewed the data reported in an unpublished study of arthroscopic shoulder surgeries conducted by Dr. Frederick Matsen (“Matsen”). (Wells Report I ¶ 12.) Matsen reviewed 396 surgeries performed by Dr. Brooke Benz (“Benz”) from 1996 through 2008 (“Matsen study”). 281 of Benz’s surgeries did not involve the use of an intra-articular pain pump. (Id. at ¶ 13.) No instances of chondrolysis were reported after those surgeries. (Id.) Whereas, of the 115 of Benz’s surgeries that involved the use of an intra-articular pain pump, forty-eight, or 41.74%, of the shoulders developed chondrolysis. (Id.) Wells performed a similar statistical analysis for the Matsen study as he did for the Hansen study. Once again, Wells calculated the estimated risk difference between the two groups, the Fisher exact p-values, the median-unbiased estimate for the odds ratio, and the continuity corrected odds ratio. (Id.) Based on these calculations, Wells determined that the data presents “an extremely high association” between the use of an intra-articular pump and the development of chondrolysis “that is far too large to be credibly explained by any other factor that has been shown linked to chondrolysis.” (Id.) Further, based on Wells’ calculations, he found that the Matsen study results are consistent with the results of the Hansen study. (Id.) After Wells’ initial declaration was filed, a draft of Matsen’s study became available. (Wells Report II ¶ 5.) This draft was authored by Dr. Wiater, Dr. Matsen, and others (“Wiater study”). (Id.) Wells obtained the datasets and program files used in this study. (Id. ¶ 6.) Wells then conducted numerous independent data analyses, finding results that were consistent with the results of the Wiater study. (Id.) By conducting regression analyses, and examining results by chondrolysis onset date and follow-up status definitions, Wells reports that the Wiater study’s results provide strong evidence that selection bias and confounding by anchors, radiofrequency, sutures, or other factors were not viable alternative explanations for the elevated correlation between intra-articular pain pump use and chondrolysis. (Id. ¶ 7.) Wells also reports that in his view, the Wiater study is consistent with the results of the Hansen study. (Id.) Further, Wells states that his Wiater study analysis allows an inference that intra-articular pain pump use was a primary causative factor of the chondrolysis cases reported in the Hansen and Wiater studies. (Id.) Wells also analyzed a study conducted by Rapley et al. entitled Glenohumeral Chondrolysis After Shoulder Arthroscopy Associated with Continuous Bupivacaine Infusion (“Rapley study”). Rapley et al., Arthroscopy: 25 the Journal of Arthroscopic and Related Surgery 12 (2009). Rapley’s study compared a group of individuals who used a pain pump with a higher infusion flow rate (4.16 mL/h) with a group of individuals that used a pain pump with a lower infusion flow rate (2.08 mL/h). (Wells Report II ¶ 8.) The higher infusion group experienced a 19% chondrolysis rate (3/16), while the lower infusion group’s chondrolysis rate was 0% (0/13). (Id.) Wells then took the users from the pump group in Wiater’s study that reported a flow rate and divided them into one group with a flow rate higher or equal to 4.16 mL/h, and one group with a flow rate lower than 4.16 mL/h. (Id.) 75% of the higher flow group developed chondrolysis (9/12), compared to 0% of the lower flow group (0/2). (Id.) Wells then calculated the mid p-values for the Wiater and Rapley studies and determined that the association of higher flow rate intra-articular pump use with chondrolysis is higher than what could occur by chance. (Id.) Additionally, Wells compared his analysis of the Wiater and Rapley studies to the Hansen study data and found that the results regarding higher flow intra-articular pump use were consistent across all three studies. (Id.) B. Dr. Wells’Qualifications Wells is a biostatistician. He received his Ph.D. in Mathematics from the University of California. (Wells Report I, ¶ 11.) He is currently the Chair of the Department of Statistical Sciences at Cornell University, and formerly the Chair of the Department of Biological Statistics and Computational Biology at Cornell University. (Id. ¶ 2.) Wells has received numerous professional honors and has published well over one hundred scholarly articles. (Id. ¶¶ 13-20.) Defendants assert that Wells’ general causation testimony is not admissible under Rule 702 because he is not qualified to testify to whether pain pumps can cause glenohumeral chondrolysis. Based on the qualifications described above, Wells undoubtedly has the skill, experience, training, and education necessary to testify regarding mathematics and statistical analyses. Defendants argue that despite Wells’ mathematics and statistics expertise, he is not qualified to opine as to general causation because he is not a qualified expert in medicine or epidemiology- In re Welding Fume Products, No. 1:03-17000, 2005 WL 1868046 (NJD.Ohio. Aug. 8, 2005), presented issues similar to the current case. As here, the plaintiffs in In re Welding Fume Products designated Wells “to opine about the strengths and weaknesses of the statistical analyses contained in various epidemiology studies.” Id. at *15. In both cases, Wells analyzed studies to determine whether a statistical association existed between a product and a harm. Id. Defendants in In re Welding Fume Products made similar arguments to defendants in this case in moving to exclude Wells’ testimony. They argued that Wells is “ ‘simply a statistician,’ and not a medical doctor or epidemiologist.” Id. Defendants in In re Welding Fume Products further argued that Wells did not have experience with the product or harm involved. Id. Accordingly, they asked the court to “preclude Dr. Wells from testifying about any studies in the epidemiological and scientific literature discussing the existence vel non of an association between [the product and the harm].” Id. The court in In re Welding Fume Products denied the defendants’ request, determining that “ultimately the opinions offered by Dr. Wells are relevant to the central epidemiology issues in this case, and Dr. Wells is qualified to offer them.” Id. at *16. The court further noted that “[t]hat Dr. Wells is not an epidemiologist is not at all decisive, as his understanding of statistical principles and methodology relevant to the design and interpretation of epidemiological studies is thorough and clear.” Id. at *15. The court finds the same in this case. As a prolific publisher in the field of biostatistics, Wells is capable of understanding the data reported in studies conducted by medical professionals. Wells analyzed the data reported in prior studies to determine the statistical strength of the correlations that the authors report. He did not determine what data would be collected in any of these studies, nor did he collect the data himself. Nonetheless, Wells’ findings are all reported in the language of a statistician. At no time does Wells attempt to offer a medical or epidemiological opinion. Rather, he is an expert in applying statistical principles relevant to the design and interpretation of epidemiological studies. Wells is aptly qualified to provide expert testimony. Accordingly, defendants’ motion to exclude Wells’ testimony based on lack of qualifications is DENIED. C. Relevance of Dr. Wells’Statistical Analysis Defendants also argue that Wells’ testimony is inadmissible because he is not qualified to assess all of the factors of the the Hill analysis. Wells admits that he is not qualified to comment upon five of Hill’s nine criteria of causation. This issue falls under the relevance prong of the Daubert standard. Specifically, whether the four criteria of the Hill analysis that Wells purports to be qualified to comment upon are sufficient to provide relevant testimony as to general causation. Pursuant to Rule 702, the court may not admit expert testimony, unless it determines that it will “assist the trier of fact to understand the evidence or determine a fact in issue.” Daubert I, 509 U.S. at 591, 113 S.Ct. 2786. “Expert testimony which does not relate to any issue in the case is not relevant and, ergo, non-helpful.” (Id.) Accordingly, in its role as gatekeeper, the court must ensure that proffered testimony “logically advances a material aspect of the proposing party’s case.” Daubert II, 43 F.3d at 1315. Wells testifies that his analysis confirms Hill’s temporal criterion because the Hansen and Matsen studies involved pain pump use prior to the occurrence of chondrolysis, and because the incidence of chondrolysis completely ceased once the doctors stopped using pain pumps. (Id. at 15.) Wells also testifies that the “startlingly high” association and risk differences between the pump and no-pump groups confirms Hill’s strength of association criterion. (Id. at 16.) Wells then testifies that, because this association is consistent when replicated in multiple studies in multiple settings, Hill’s criterion of consistency is confirmed. (Id. at 17.) Finally, Wells testifies as to Hill’s criterion of considering alternative explanations. Defendants’ expert, Judith K. Jones, M.D., Ph.D. (“Jones”), has presented numerous factors that have been cited in medical literature as explanations for the onset of chondrolysis. Specifically, Jones declares that the use of: (1) certain diagnostic dyes; (2) irrigating solutions; (3) thermal/radiofrequency devices; (4) local anesthetics; (5) pain pumps; (6) sutures; (7) anchors; (8) pins; and (9) arthroscopic surgery, have all been reported as factors that may have played a role in the development of chondrolysis. (Report of Opinions of Judith K. Jones, M.D., Ph.D. (“Jones Report”) ¶ 8, filed February 19, 2010 [Docket # 28], Attachment 2.) Wells states that the factors cited by Jones are addressed in the discussion section of the Hansen study and ruled out by Matsen, both in his study and in Matsen’s testimony regarding his study in another case. Further, Wells states-that if one of these potential cofounders was a primary contributory cause of chondrolysis, then it would have a higher association than intraarticular pump use. This did not occur. (Wells Report I ¶ 19.) This testimony as to the four Hill analysis factors logically advances plaintiffs case (see Daubert I): (1) plaintiff must establish general causation, and the studies that Wells cites provide evidentiary support for such a finding; (2) this testimony will assist the trier of fact in understanding the evidence in order to determine a fact at issue; (3) Wells’ analysis enables the fact finder to better understand the importance of what other researchers have found; Wells’ testimony reveals that the “the association of post-surgical use of intra-artieular pump with chondrolysis is well beyond what would occur by chance,” ruling out other suggested explanations and identifying a consistency amongst multiple studies; and (4) this testimony will assist the jury in understanding whether the medical literature has found that pain pumps can cause chondrolysis. Certainly, the fact that Wells has not offered testimony as to the other five Hill analysis criteria give defendants fair grounds to attack Wells’ opinion. However, defendants’ argument as to faults in Wells’ Hill analysis go to the weight, not the admissibility of Wells’ testimony. See Kennedy v. Collagen Corp., 161 F.3d 1226 (9th Cir.1998). Accordingly, defendants’ motion to exclude Wells’ testimony based on a lack of relevance is DENIED. D. Reliability of Wells’ Statistical Analysis Defendants also argue that Wells’ testimony is inadmissible because he lacks an adequate scientific basis for his opinions. In its role as gatekeeper, the court must determine whether the reasoning and methodology underlying Wells’ testimony is scientifically valid. Daubert I, 509 U.S. at 592-593, 113 S.Ct. 2786. In doing so, the court must ensure that Wells has employed scientifically valid principles. Id. at 597, 113 S.Ct. 2786. The Supreme Court listed several key considerations to aid the trial court in this task. The trial court should consider: (1) whether the scientific knowledge can or has been tested; (2) whether the given theory or technique has been published or subjected to peer review; (3) the potential or known error rate; and (4) whether the theory or technique has gained general acceptance in the pertinent field. Daubert I, 509 U.S at 592-94, 113 S.Ct. 2786. In employing this analysis, the court must focus on the principles or methodology involved in the expert’s testimony, not the conclusions that they generate. Daubert I, 509 U.S. at 595, 113 S.Ct. 2786. Defendants argue that Wells’ analysis of the Hansen study is inadmissible due to various faults with the Hansen study itself. Defendants point out that the Hansen study was a case study, rather than a cohort study; that Wells cannot determine whether the Hansen study applied predefined screening criteria; the Hansen study does not allow for an analysis of confounding factors because it does not include nonchondrolysis patient data; and that the Hansen study did not have a follow-up monitoring period. Defendants’ reliance upon Kilpatrick v. Breg Inc., 613 F.3d 1329 (11th Cir.2010) in support of this argument, does not persuade the court to exclude Wells’ testimony regarding the Hansen study. In this pain pump negligence and products liability case, the district court determined that the plaintiffs causation expert’s methodology was not sufficiently reliable to pass Daubert muster, and the Eleventh Circuit affirmed. Id. at 1341. The expert, a medical doctor, relied in part on the Hansen study to form his conclusions regarding causation. The district court in Kilpatrick faulted the Hansen study for lacking statistical analysis, failing to (1) explain whether its results where statistically meaningful, (2) account for other causes of chondrolysis, (3) account for the shoulders that were exposed to pain pumps but did not develop chondrolysis, and (4) firmly conclude that pain pumps caused chondrolysis. Id. at 1337-38. As discussed supra, Wells accounted for the Kilpatrick court’s first three criticisms of the Hansen study. Wells analyzed the data to determine whether a statistically meaningful association between pain pump use and the development of chondrolysis was present. He also analyzed the data to determine whether any of the co-founders that Jones mentioned could have caused the shoulders to develop chondrolysis, ultimately ruling them out. As other courts have, this court disagrees with the Kilpatrick court’s determination that the Hansen study contained “an unexplained 40% error rate” because 7 out of 19 shoulders that were exposed to pain pump use did not develop chondrolysis. Kilpatrick v. Breg, Inc., No. 08-10052, 2009 WL 2058384 at *6 (S.D.Fla. Jun. 25, 2009). Just as the court found in Schott v. I-Flow Corp., 696 F.Supp.2d 898, 905 (S.D.Ohio.2010), this court is unaware of any authority for the proposition that, where 12 out of 19 shoulders developed chondrolysis, the minority of shoulders that did not, constitutes an “error rate.” Further, as the court noted in McClellan, 710 F.Supp.2d at 1106, “[i]f 100% of patients receiving continuous infusion must develop chondrolysis before an expert may reliably opine on causation, expert testimony would hardly be necessary.” Finally, unlike the Kilpatrick court, this court will not exclude testimony regarding the Hansen study for failure to conclusively determine that pain pumps cause chondrolysis. As other courts have found, this court likewise holds that excluding testimony on these grounds goes beyond the court’s gatekeeping role. See McClellan, 710 F.Supp.2d at 1106 (“I find that the district court in Kilpatrick went far beyond its gatekeeping function and ‘failed to distinguish between the threshold question of admissibility of expert testimony and the persuasive weight to be accorded such testimony by a jury.’ ”) The court must “ensure that the proffered expert testimony is sufficiently reliable to be admitted at trial for consideration by the trier of fact,” not determine whether “the proffered expert testimony sufficiently proves that continuous infusion can cause chondrolysis.” Id. Accordingly, for all the reasons discussed supra, the decision in Kilpatrick does not provide a basis for excluding testimony regarding the Hansen study in this case. The court in McClellan v. 1-Flow Corp., 710 F.Supp.2d 1092 (D.Or.2010), provides a helpful analysis of Wells’ methodology in conducting statistical analysis of the Hansen study. The analysis in McClellan is particularly pertinent in this case because, unlike in Kilpatrick, McClellan involved Wells’ analysis of the Hansen study, rather than just the Hansen study itself. The court in McClellan discussed the Hansen study’s faults, finding it “questionable whether the Hansen[] study constitutes helpful relevant evidence to support an opinion of general causation between continuous infusion and chondrolysis.” Id. at 1108. However, the court explicitly stated that it would not exclude the study for a lack of epidemiological evidence, particularly because there is no epidemiological evidence that rules out general causation. Id. Indeed, “the fact that a study is associational — rather than an epidemiological study intended to show causation— does not bar it from being used to inform an expert’s opinion.” Id. (quoting U.S. v. W.R. Grace, 504 F.3d 745, 765 (9th Cir. 2007)). Further, “‘the absence of definitive scientific studies’ should not ‘deprive a jury of having before it scientific opinions,’ though ‘less definitive and more qualified.’ ” McClellan, 710 F.Supp 2d at 1109 (quoting In re Ephedra, 393 F.Supp.2d at 189-190 (S.D.N.Y.2005)). Moreover, “[n]on-epidemiological sources are frequently utilized by experts in rendering scientific opinions and, under Daubert, should be considered by the court in assessing the reliability of those opinions.” McClellan, 710 F.Supp.2d at 1109 (quoting In re Phenylpropanolamine (PPA) Prods. Liab. Litig., 289 F.Supp.2d 1230, 1242 (W.D.Wash.2003)). Accordingly, the court will not exclude Wells’ testimony regarding the Hansen study. Next, defendants argue that Wells’ testimony should be excluded because he analyzed the work of others rather than participating in the underlying studies. In a situation such as this, the fact that the expert has not created his own published research is not dispositive. Rather, “[i]n the absence of independent research or peer review, experts must explain the process by which they reached their conclusions and identify some type of objective source demonstrating their adherence to the scientific method.” In re Phenylpropanolamine (PPA) Products Liability Litigation, 289 F.Supp.2d 1230, 1238 (W.D.Wash.2003) (citing Daubert II). Wells has met this requirement. As set forth above, Wells utilized widely accepted statistical methods to support all of his reported conclusions. Further, each of the individual statistical tests that Wells utilized were part of the Hill analysis, a larger, widely accepted statistical method. Defendants also argue that Wells’ testimony should be excluded because it was conducted solely for the purpose of litigation, at the request of plaintiffs attorneys. It is true, as defendants point out, that “independent research, rather than research conducted for the purposes of litigation, carries with it the indicia of reliability.” Carnegie Mellon University v. Hoffmann-LaRoche, Inc., 55 F.Supp.2d 1024 (N.D.Cal.1999) (citing Daubert II). However, testimony that is based directly on legitimate, preexisting research unrelated to the litigation provides the most persuasive basis for concluding that the opinions expressed were “derived by the scientific method.” Daubert II, 43 F.3d at 1317. Such is the case here. While Wells conducted his research for the purposes of litigation, his research was based directly on legitimate, albeit in part flawed, research unrelated to the litigation. Accordingly, defendants’ motion to exclude Wells’ testimony based on a lack of reliability is DENIED. For all of the above reasons, defendants’ motion to exclude Wells’ testimony is DENIED. 2. Motion for Summary Judgment A. Causation Plaintiff alleges claims under California law for: (1) general negligence; (2) negligent products liability; and (3) strict products liability. Each of these claims require plaintiff to establish causation. Defendants move for summary judgment, primarily on the basis that plaintiff lacks sufficient evidence to establish general or specific causation, and thus, none of her claims can survive. “To prevail in a negligence action, a plaintiff must show that the defendant owed a legal duty, the defendant breached that duty and the breach proximately caused injury to the plaintiff.” Garcia v. W & W Community Development, Inc., 186 Cal.App.4th 1038, 1044, 112 Cal.Rptr.3d 394 (2010). For a strict products liability claim, plaintiff must show “that the injury to the plaintiff was caused by the defective condition.” Gonzalez v. Autoliv ASP, Inc., 154 Cal.App.4th 780, 793, 64 Cal.Rptr.3d 908 (2007). Once a defendant properly raises the issue of causation on a motion for summary judgment, as defendants have here, the burden shifts to the plaintiff to demonstrate a genuine issue of material fact as to causation. Casey v. Ohio Medical Products, 877 F.Supp. 1380, 1382 (N.D.Cal.1995). Plaintiff must meet this burden as to general causation, that the product is capable of causing the harm, and specific causation, that the product caused the harm in this specific case. Id. Where demonstrating causation requires a discussion of complex medical and scientific issues, expert testimony is required. Jones v. Ortho Pharm. Corp., 163 Cal. App.3d 396, 403, 209 Cal.Rptr. 456 (1985). 1. General Causation Plaintiffs experts on the issue of general causation are Wells and Dragoo. For the reasons set forth in detail supra, Wells’ testimony regarding general causation is admissible. Wells statistically analyzed the data reported in scientific studies and determined that the risk difference with respect to chondrolysis between individuals who received a pain pump and those that did not is extremely large. Wells further determined that the association between postsurgical use of an intraarticular pump with the development of chondrolysis is well beyond what would occur by chance and far too large to be credibly explained by any other factor that has been linked to chondrolysis. Additionally, Wells testifies that his analysis rules out other possible explanations for the subjects’ chondrolysis. Accordingly,- Wells’ testimony creates a triable issue of fact as to general causation. Dragoo based his opinion upon his own research and his review of several studies conducted by others. Dragoo testifies that his opinion, to a reasonable degree of medical certainty, is that the use of intraarticular pain pumps with a local anesthetic can cause cartilage degeneration in a dose-dependent matter, regardless of whether the pump contains epinephrine. (Dragoo Report ¶ 31.) Dragoo’s study, which was published in the American Journal of Sports Medicine in August of 2008, utilized human articular cartilage taken from individuals who were undergoing total knee replacement surgery. (Id. ¶¶ 15, 23.) As a result of this study, Dragoo found that continuous infusion of local anesthetics combined with epinephrine are chondrotoxic. (Id. ¶¶ 21, 24.) He also found that local anesthetics infused without epinephrine may be chondrotoxic when infused for less then forty-eight hours and are likely to be chondrotoxic when infused for longer periods. (Id.) Defendants criticize Dragoo’s testimony for failing to present epidemiological evidence. Epidemiology is “a field that concerns itself with finding the causal nexus between external factors and disease.” Rider v. Sandoz Pharmaceuticals Corp., 295 F.3d 1194, 1198 (11th Cir.2002). As defendants point out, epidemiological studies are traditionally considered the best form of statistical evidence for proving causation. Kilpatrick v. Breg, Inc., 2009 WL 2058384 at *4. Defendants also criticize Dragoo’s human study as being in vitro rather than in vivo. However, conducting an epidemiological or in vivo human study would involve knowingly exposing the study’s subjects to harm. Dragoo has testified that there is enough underlying research demonstrating a link between pain pumps and chondrolysis, that conducting epidemiological research at this point would be unethical. (Deposition of Dragoo, filed Sep. 23, 2010 [Docket # 81], Ex. G at 128:12-18). Accordingly, Dragoo states that scientists are forced to “piecemeal” the studies that are out there to do what they can “to build a story” of causation. (Id.) Because epidemiological or in vivo research would be unethical at this point, other courts have refused to require plaintiffs to submit such studies in pain pump product liability litigation. For instance, the court in Schott, 696 F.Supp.2d at 905 found “plaintiffs’ argument persuasive that they are unable to obtain epidemiological studies, as conducting any such studies would be unethical.” Further stating that, “[i]t therefore strikes the Court as unreasonable for Defendant to clamour for such studies.” (Id.) Additionally, the court in McClellan, found that “ethical considerations preclude randomized, controlled epidemiological studies of continuous infusion given the potential for irreversible harm.” McClellan, 710 F.Supp.2d at 1109. Thus, the McClellan court found that “while epidemiological evidence is significant and can be helpful, it is not necessary to establish general causation.” Id. This court reaches the same conclusion, and thus will not require plaintiff to produce a study, which by its very nature contains a likelihood of causing harm. Accordingly, plaintiffs failure to submit an epidemiological or in vivo study is not fatal to its claim, particularly where defendants are unable to present epidemiological or in vivo evidence to “rule out” general causation. See Grace, 504 F.3d at 765 (the fact that a study is associational-rather than an epidemiological study intended to show causation-does not bar it from being used to inform an expert’s opinion.); see also McClellan, 710 F.Supp.2d at 1108 (“Regardless, the lack of epidemiological evidence is not fatal to the admission of plaintiffs’ experts’ testimony, particularly in a case where no epidemiology “rules out” continuous infusion as a cause of chondrolysis.”) Defendants then criticize the underlying studies that Dragoo relies upon. Defendants note that the Hansen study used bupivieaine combined with epinephrine, rather than strictly bupivieaine. However, Dragoo’s causation conclusion, based on his overall review of the research, was not dependent on the presence of epinephrine. He specifically states that, to a reasonable degree of medical certainty, it is his opinion that “the use of intra-articular pain pumps, with or without epinephrine, can cause cartilage degeneration.” (Dragoo Report ¶ 31.) Defendants next assert that the Hansen study cannot be used to make causation inferences because it is a case series. However, both Wells and Jones have testified that case series are helpful regarding general causation, though they do not establish causation in isolation. (Jones Report, at 7; Wells Dep. 72:11-16). As discussed supra, the Hansen study has its shortcomings. As was the case in regards to Wells’ testimony regarding the Hansen study, defendants can criticize Dragoo’s reliance upon the Hansen study at trial. However, “it is not the court’s role to decide whether the proffered expert testimony sufficiently proves that continuous infusion can cause chondrolysis; rather it is the court’s duty to ensure that the proffered expert testimony is sufficiently reliable to be admitted at trial for consideration by the trier of fact.” McClellan, 710 F.Supp.2d at 1106 (citing Primiano v. Cook, 598 F.3d 558, 565 (9th Cir.2010) (“Under Daubert, the district judge is a ‘gatekeeper, not a factfinder.’ ”)). Because defendants’ arguments against Dragoo’s Hansen study analysis go towards the weight, not the admissibility of Dragoo’s testimony, Dragoo’s Hansen study-related testimony further creates a triable issue of material fact as to general causation. Additionally, defendants criticize Dragoo’s use of an animal study to testify regarding the development of chondrolysis in humans. The “Dragoo study” involved continuous administration of Marcaine over a forty-eight hour period to live rabbits. The authors of this study concluded that “[continuous intra-articular infusion of bupivacaine, with and without epinephrine, led to significant histopathologic and metabolic changes in articular cartilage.” (Andres Gomoll et al.), Chondrolysis After Continuous Intra-Articular Bupivacaine Infusion: An Experimental Model Investigating Chondrotoxicity in the Rabbit Shoulder (“Gomoll study”), 22 Arthroscopy 813-19 (August 2006). Defendants again cite to Kilpatrick to support their argument that the Gomoll study does not provide a factual basis for Dragoo’s general causation determination. The Kilpatrick court questioned the plaintiffs expert’s reliance on the Gomoll study because the study failed to account for possible differences in dose-response relationship between humans and rabbits making the study unreliable for extrapolation to humans. Kilpatrick, 613 F.3d at 1338-39. The Kilpatrick court noted that “a dose-response relationship is ‘the single most important factor to consider in evaluating whether an alleged exposure caused a specific adverse effect.’ ” Id. at 1339 (quoting McClain v. Metabolife Intern., Inc., 401 F.3d 1233, 1242 (11th Cir.2005)). Contrary to the Kilpatrick court, the courts in both Schott and McClellan admitted expert testimony regarding the results of the Gomoll study. As the McClellan court noted, “ ‘analogy, inference and extrapolation can be sufficiently reliable’ when the expert’s opinion is the ‘kind that a reasonable scientist or physician would make in a decision of importance arising in the exercise of his profession outside the context of litigation.’ ” McClellan, 710 F.Supp.2d at 1110 (quoting In re Ephedra, 393 F.Supp.2d ,181, 189 (S.D.N.Y.2005)). Further, the Ninth Circuit has determined that animal studies can “provide useful data about human health,” and thus, should be subjected to scientific analysis just like any other scientific evidence. Metabolife Int’l, Inc. v. Womick, 264 F.3d 832, 842 (9th Cir.2001); see also Hopkins v. Dow Corning, Corp., 33 F.3d 1116, 1125 (9th Cir.1994) (finding testimony regarding “corroborating evidence found in studies conducted on animals” admissible); see also In re Silicone Gel Breast Implants Prods. Liab. Litig., 318 F.Supp.2d 879, 910-911 (C.D.Cal.2004) (noting reliance by researchers and agencies on relevant animal studies). As discussed supra, in vivo studies on the development of chondrolysis in humans are not available and cannot be ethically conducted. Accordingly, the only in vivo studies available involve animals. Under these circumstances, animal studies are particularly useful in aiding the jury in understanding chondrolysis development in humans. Such a study becomes even more valuable where, as is the case with Dragoo’s Report, an animal study is supported by human research that accounts for dose-response relationship. {See Dragoo Report ¶ 31, “it is my opinion to a reasonable degree of medical certainty that the use of intra-articular pain pumps ... can cause cartilage degeneration in a dose-duration dependent manner.”) Thus, as the courts did in McClellan and Schott, this court finds that Dragoo’s testimony regarding the Gomoll study is supported by science and will assist the trier of fact in determining general causation. Accordingly, for all of the reasons stated above, plaintiff has established a material issue of fact regarding general causation. 2. Specific Causation Plaintiffs lone expert on specific causation is Cross, plaintiffs orthopedic surgeon. Cross admits that he is not an expert on the development of chondrolysis. (Cross Dep. at 111:15-18.) However, as plaintiffs treating physician, Cross is familiar with plaintiffs medical history and treatment. Thus, he is qualified to render opinion testimony on causation, diagnosis, or other matters based on his treatment of plaintiff. First Nat’l. Mortg. Co. v. Federal Realty Inv. Trust, No. 03-02013, 2006 WL 2228941, *14 (N.D.Cal. Aug. 3, 2006). Defendants argue that Cross does not have a factual basis for determining that use of the ZAP caused plaintiffs injury. Plaintiff contends that Cross’ specific causation determination is based in fact because .he methodically ruled out other potential causes of chondrolysis. “[E]xpert’s opinions that are without factual basis and are based on speculation or conjecture are inadmissible at trial and are inappropriate material for consideration on a motion for summary judgment.” California ex rel. Brown v. Safeway, Inc., 615 F.3d 1171, 1181 (9th Cir. 2010). However, “[l]ack of certainty is not, for a qualified expert, the same thing as guesswork.” Primiano v. Cook, 598 F.3d at 565. “Expert opinion testimony is relevant if the knowledge underlying it has a valid connection to the pertinent inquiry.” Id. (quoting U.S. v. Sandoval-Mendoza, 472 F.3d 645, 655 (9th Cir.2006)). Defendants point to changes in Cross’ opinion regarding the specific causation of plaintiffs injury as evidence that Cross is unable to testify that the ZAP caused her chondrolysis. On December 27, 2007, Cross noted that it was without significant question that plaintiffs injuries were “directly and completely related to [the] injury she sustained” as a result of her May 2007 altercation. (Cross Dep. at 74:11-15.) Then on January 24, 2008, Cross wrote that plaintiffs chondrolysis may be due, in part, to the trauma she suffered, but also, in part, to the postoperative pain pump use. (Id. at 74:25-75:1-5.) Plaintiff argues, citing Cross’ testimony, that Cross’ evolving opinion coincided with his developing knowledge of a potential connection between chondrolysis and pain pump usage. Eventually, after reviewing medical literature on the association between intra-articular pain pump use and chondrolysis, Cross developed the opinion that the pain pump was “the most probable cause” of plaintiffs chondrolysis. (Id. at 102:21-25-103:1-11.) Cross testified that his determination regarding the cause of plaintiffs injury is “not science,” but “an opinion.” (Id. at 77:25.) Accordingly, defendants assert that Cross’ testimony is inadmissible because he admitted that his opinion is “not science.” Plaintiff argues that, despite Cross’ comment that his opinion is “not science,” his opinion is based in fact and is the result of an appropriate method for reaching a specific causation opinion. Plaintiff asserts that Cross implemented the “differential diagnosis” method in developing his specific causation opinion. The differential diagnosis method is a “process of elimination approach,” that “doctors routinely use to identify the most likely cause” of harm to a particular individual. In re Silicone Gel Breast Implants Products Liability Litigation, 318 F.Supp.2d 879, 916 (C.D.Cal. 2004.) This method involves an expert compiling “a comprehensive list of potential causes and then engaging] in a process of elimination to reach the most likely cause.” In re Hanford Nuclear Reservation Litigation, 534 F.3d 986, 1014 (9th Cir.2008). The differential diagnosis method has been accepted as scientifically valid methodology. Morin v. U.S., 244 Fed.Appx. 142, 143 (9th Cir.2007). However, the Ninth Circuit has determined that a district court is within its discretion in determining that an expert’s specific causation opinion is not admissible where the expert does not show whether or how he applied this method. Id. at 144 (citing Kumho Tire Co. v. Carmichael, 526 U.S. 137, 141-42, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999)). Plaintiff submits evidence to support that Cross accounted for and ruled out other potential causes of chondrolysis. Specifically, plaintiff provides evidence that Cross considered, and ruled out, single injection of steroids and local anesthetics, use of a radiofrequency probe, infection, wear and tear, and trauma suffered during plaintiffs altercation. For instance, Cross testified that he has “done hundreds and hundreds of steroid injections and Marcaine injections and ... never experienced any significant chondrolysis or seen any significant chondrolysis develop.” (Cross Dep. at 94:18-22.) Cross testified any prior cartilage damage to plaintiffs shoulder was “very typical” and that he “didn’t see anything unusual” in this regard. (Id. at 23:25-24:1-4.) Cross also testified that “there was just no clinical indication of an infection.” (Id. at 92:18.) Defendants point out that there are “multiple potential causes” for plaintiffs chondrolysis, and Cross acknowledged as much. (Id. at 95:1.) However, Cross’ lack of certainty does not mean that his analysis is not factually based or methodically sound. See Primiano, 598 F.3d at 565. Furthermore, the court’s role at this juncture is not to weigh conflicting evidence, it is to determine whether plaintiff has established an issue of material fact. See T.W. Elec. Service, Inc. v. Pacific Elec. Contractors Ass’n, 809 F.2d 626 (9th Cir.1987). Accordingly, plaintiff has submitted admissible evidence to demonstrate an issue of material fact whether the ZAP caused plaintiffs injury. B. General Negligence, Negligent Products Liability and Failure to Warn To sustain her claim of negligence or negligent products liability, plaintiff must establish that defendants owed her a cognizable legal duty. Gonzalez v. Autoliv ASP, Inc., 154 Cal.App.4th 780, 793, 64 Cal.Rptr.3d 908 (2007). As to her claim of negligent manufacture or design, plaintiff must show that defendants breached their duty of care. See id. As to plaintiffs claim of negligent failure to warn, she must show that defendants “did not warn of a particular risk for reasons which fell below the acceptable standard of care, i.e., what a reasonably prudent manufacturer would have warned about.” Anderson v. Owens-Corning Fiberglas Corp., 53 Cal.3d 987, 1002, 281 Cal.Rptr. 528, 810 P.2d 549 (1991). Accordingly, plaintiff must provide evidence that demonstrates defendants failed to give adequate warning of a risk associated with their product that defendants knew or should have known about at the time the product was distributed. See Phillippi v. Stryker Corp., No. 2:08-02445, 2010 WL 2650596 (E.D.Cal. July 1, 2010) (citing Brown v. Superior Court, 44 Cal.3d 1049, 1057, 245 Cal.Rptr. 412, 751 P.2d 470 (1988) (“The manufacturer of a ... medical device, which is available only through the prescription of a licensed physician, must give adequate warnings of dangerous propensities in its product of which the manufacturer knows or should know in the application of existing scientific knowledge at the time of distribution.”)). Plaintiff asserts defendants breached their duty to plaintiff in two respects: (1) failing to investigate the medical literature which would have put defendants on notice of the risk of pain pumps causing chondrolysis; and (2) failing to conduct required testing of the ZAP which would have revealed that the ZAP carried a risk of harm to users. 1. Medical Literature Plaintiff asserts that defendants were on notice to investigate a risk of chondrolysis based on existing medical liter