Sprafka v. DePuy Orthopaedics, Inc.

U.S. District Court, District of Minnesota March 26, 2024

Trial Court Opinion

UNITED STATES DISTRICT COURT
DISTRICT OF MINNESOTA

Julie Sprafka, Civil No. 22-331 (DWF/TNL)

Plaintiff,

v. MEMORANDUM
OPINION AND ORDER
Medical Device Business Services, Inc.,
an Indiana Corporation formerly known
as DePuy Orthopaedics, Inc., and DePuy
Orthopaedics, Inc.,

Defendants.

INTRODUCTION
This matter is before the Court on Defendants DePuy Orthopaedics, Inc. and
Medical Device Business Services, Inc.’s (collectively, “MDBS”) motion to exclude
expert testimony (Doc. No. 91) and motion for summary judgment (Doc. No. 123).
Plaintiff Julie Sprafka opposes the motions. (Doc. Nos. 112, 137.) For the reasons set
forth below, the Court grants both motions.
BACKGROUND
Plaintiff Julie Sprafka suffered from osteoarthritis in her right knee. (Doc.
No. 127-2 (“Saterbak Dep.”) at 26-27.) Sprafka initially tried treating the pain with
conservative treatments such as anti-inflammatory drugs and cortisone injections. (Id.
at 33.) When those treatments failed, Sprafka’s doctor, Dr. Andrea Saterbak, discussed
knee replacement surgery. (Id. at 34-35.) On August 18, 2016, Sprafka underwent a
right total knee replacement, which was performed by Dr. Saterbak. (Id. at 81.) Dr.
Saterbak implanted an Attune device. (Id.) Attune devices consist of a metallic femoral
component, a metallic tibial baseplate, a tibial polyethylene insert, and a dome patella.

(Doc. No. 94-3 (“Truman Report”) at 25-26.) At issue in this case is the tibial baseplate,
which was cemented to the tibia bone. (Id. at 26.) Sprafka received an Attune with a
fixed bearing tibial baseplate. (Id. at 3.)
Following the surgery, Sprafka continued to experience pain in her right knee.
(Saterbak Dep. at 95-101.) Sprafka returned to see Dr. Saterbak in October 2018,

reporting constant pain and swelling in her right knee. (Id. at 109-11.) Dr. Saterbak
tested Sprafka’s range of motion and did a bone scan and x-ray. (Id. at 112.) Dr.
Saterbak saw no evidence of loosening and concluded that Sprafka’s range of motion
indicated moderate PCL laxity and swelling. (Id. at 113-17, 121-22.) She discussed with
Sprafka that laxity could eventually require revision surgery. (Id. at 117-18.) She told

Sprafka to return for a follow-up visit in six-months. (Id.)
Over a year and a half later, in June 2020, Sprafka saw a new orthopedic surgeon,
Dr. Kristoffer Breien. (Doc. No. 127-3 (“Breien Dep.”) at 102.) Sprafka told Dr. Breien
that she had been experiencing knee pain. (Id. at 104.) Dr. Breien was not provided with
Sprafka’s prior medical records and instead conducted an independent examination of

Sprafka. (Id. at 88-89, 93, 214.) Dr. Breien took x-rays of the knee and, after review,
concluded that Sprafka’s pain was caused by loosening. (Id. at 88-89.) Dr. Breien did a
revision surgery of Sprafka’s knee in September 2020. (Id. at 162.) During the revision
surgery, Dr. Breien put a mallet underneath the tibial baseplate and after one tap, the
baseplate came loose. (Id. at 175-77.) Based on the little effort that it took to remove the
tibial baseplate, Dr. Breien concluded that the baseplate had debonded and had caused the
device to come loose. (Id. at 128-29.) The tibial baseplate also contained little visible

cement debris and the cement mantle remained intact. (Truman Report at 22-23.)
Sprafka then sued MDBS, asserting four claims: (1) strict liability, (2) negligent
products liability; (3) breach of implied warranties; and (4) breach of express warranty.1
To support these claims, Sprafka relies on expert testimony from Mari Truman. MDBS
now moves to exclude this expert testimony and moves for summary judgment.

DISCUSSION
I. Daubert Motion
MDBS moves to exclude the testimony of Sprafka’s expert, Mari Truman. Before
accepting the testimony of an expert witness, the trial court is charged with the
“gatekeeper” function of determining whether an opinion is both relevant and reliable.

Daubert v. Merrell Dow Pharms., Inc.,

509 U.S. 579, 589-90

 (1993).        
A duly qualified expert may testify “if the proponent demonstrates to the court that 
it is more likely than not that”:  (1) “the expert’s scientific, technical, or other specialized 
knowledge will help the trier of fact to understand the evidence or to determine a fact in 
issue”; (2) “the testimony is based on sufficient facts or data”; (3) “the testimony is the 

product of reliable principles and methods”; and (4) “the expert’s opinion reflects a 

1    Sprafka’s Complaint was filed under a separate case number:  21-cv-1785.  On 
December 5, 2022, the Court consolidated Sprafka’s case with another similar case and 
ordered all future filing to be filed under the current case number:  22-cv-331.  (Doc. 
No. 40.)                                                                  
reliable application of the principles and methods to the facts of the case.”  Fed. R. 
Evid. 702.  The language of this rule changed in December 2023, but the substantive law 
did not.  The change was intended to clarify that preponderance of the evidence standard 

applies to expert opinions under this rule.  See

id.

 advisory committee’s note to 2023 
amendment (“But many courts have held that the critical questions of the sufficiency of 
an expert’s basis, and the application of the expert’s methodology, are questions of 
weight and not admissibility.  These rulings are an incorrect application of Rules 702 and 
104(a).”).                                                                

In determining whether the proposed expert testimony is reliable, the Court 
considers the following:  (1) whether the theory or technique can be and has been tested; 
(2) whether the theory or technique has been subjected to peer review and publication; 
(3) the known rate of potential error; and (4) whether the theory has been generally 
accepted.  Daubert,

509 U.S. at 593-94

.  The purpose of these requirements “is to make 

certain that an expert, whether basing testimony upon professional studies or personal 
experience, employs in the courtroom the same level of intellectual rigor that 
characterizes the practice of an expert in the relevant field.”  Kumho Tire Co. Ltd. v. 
Carmichael,

526 U.S. 137, 152

 (1999).  “[T]he trial judge must have considerable leeway 
in deciding in a particular case how to go about determining whether particular expert 

testimony is reliable.”

Id.

                                              
The Court also notes that “Rule 702 reflects an attempt to liberalize the rules 
governing the admission of expert testimony,” and it favors admissibility over exclusion.  
Lauzon v. Senco Prods., Inc.,

270 F.3d 681, 686

 (8th Cir. 2001) (internal quotations and 
citation omitted).  When examining an expert opinion, a court applies a general rule that 
“the factual basis of an expert opinion goes to the credibility of the testimony, not the 
admissibility, and it is up to the opposing party to examine the factual basis for the 

opinion in cross-examination.”  Bonner v. ISP Techs., Inc.,

259 F.3d 924, 929-30

 (8th 
Cir. 2001) (quoting Hose v. Chicago Nw. Transp. Co.,

70 F.3d 968, 974

 (8th Cir. 1995)).  
“[I]f the expert’s opinion is so fundamentally unsupported that it can offer no assistance 
to the jury,” then it must be excluded.  Id. at 929-30.                   
There is no dispute that Truman is a qualified expert.  She is a biomedical engineer 

with over forty years of experience in the fields of biomechanics and orthopedics.  
(Truman Report at 4.)  Nor is there dispute that expert testimony about the Attune 
implant would help the jury in this case.  In fact, Minnesota law requires expert testimony 
“to get a product-liability claim past summary judgment when the product at issue and 
any of its relevant inner workings are beyond the ken of a lay jury.”  Markel v. Douglas 

Techs. Grp., Inc.,

968 F.3d 888, 890

(8th Cir. 2020). The parties solely dispute whether
Truman’s testimony is reliable.
Truman offers three main opinions related to the Attune device: (1) the Attune
was defectively designed; (2) a safer alternative existed at the time Attune was
developed; and (3) MDBS’s testing of the Attune was inadequate. MDBS argues that

each opinion is unreliable and thus Truman’s testimony should be excluded in its entirety.
The Court addresses each of Truman’s opinions in turn below.
A. Design
Truman asserts that the Attune total knee replacement device was defectively
designed because the tibial baseplate had shallow pockets and a smooth surface, which

increased the prevalence of debonding. Debonding is a type of aseptic loosening. (Doc.
No. 114-1 (“Wright Dep.”) at 13.) Aseptic loosening is the loosening of the device from
the bone in the absence of infection. This case specifically focuses on debonding, or
separation, at the cement-implant interface. But loosening can also occur between the
tibia bone and cement mantle.

MDBS asserts that Truman’s opinions are speculative because Truman has no data
demonstrating what pocket depth or surface roughness would have decreased debonding,
and she admitted during her deposition that she would need to do testing in order to
determine the exact specifications that would have prevented debonding. Moreover,
MDBS argues that Truman admitted that the clinical performance of the Attune appears

to be the same or better than other devices on the market and acknowledged that people
with Attune devices seem to be happier overall than those with other competitor devices.
In sum, MDBS contends that Truman has a hypothesis based on anecdotal evidence “that
has not been tested, has not been subjected to peer review and publication, has no known
or potential rate of error and has not been accepted by or otherwise acknowledged by the

scientific community.” (Doc. No. 93 at 18.)
In response, Sprafka argues that MDBS’s challenges to Truman’s testimony goes
to weight and not admissibility. Sprafka asserts that Truman is allowed to rely on her
expertise and knowledge as a biomedical engineer when forming her opinions. In
addition, Sprafka contends that Truman identified data that showed that the Attune’s
successor, the Attune S+, significantly improved fixation using features that were feasible
when the Attune was developed. Lastly, Sprafka asserts that Truman was not required to

test her opinions for them to be admissible.
To begin, “courts have discounted the reliability of experts who formed their
opinions only within the context of litigation.” Nelson v. Am. Home Prods. Corp.,

92 F. Supp. 2d 954, 967

 (W.D. Mo. 2000).  Truman’s testimony is not based on independent 
research, and she developed these opinions expressly for the purpose of litigation.  The 

Court considers the fact that Truman’s opinions “have [not] been subjected to normal 
scientific scrutiny through peer review and publication.”  In re Bair Hugger Forced Air 
Warming Devices Prods. Liab. Litig.,

9 F.4th 768

, 783 (8th Cir. 2021).
The Court also considers the literature that Truman based her opinions on.
Truman relied heavily on anecdotal evidence to support her opinion that Attune is more

susceptible to debonding than Attune’s predecessor (the Sigma) and the Attune’s
successor (the Attune S+). Specifically, Truman relied on two published case studies,
Manufacturer and User Facility Device Experience (“MAUDE”) data, and Dr. Breien’s
testimony as the foundation for her opinion.2 (Truman Dep. at 180.) The first case study
focused on fifteen patients with an Attune device from three different hospital databases

2 Truman also cites the Hazelwood article to support her assertion that the Attune
tibial component “has been implicated in early aseptic loosening” (Truman Report at 53),
but that article concerned the Sigma device, not the Attune. See Hazelwood, et al., Case
Series Report: Early Cement-Implant Interface Fixation Failure in Total Knee
Replacement, 22 The Knee 424-28 (2015) (“Hazelwood article”).
that experienced debonding of the tibial implant-cement interface. Bonutti, et al.,
Unusually High Rate of Early Failure of Tibial Component in Attune Total Knee
Arthroplasty System at Implant-Cement Interface, 30 J. Knee Surg. 435-39 (2017)

(“Bonutti Article”). Dr. Bonutti concluded that these three hospitals experienced “an
unusually high rate of early aseptic failures as a result of failure of implant-cement
interface.”

Id.

  Dr. Bonutti’s article has received criticism because he failed to establish 
any “rate,” as the report does not indicate the size of the case series.  See Cerquiglini, et 
al., Analysis of the Attune Tibial Tray Backside: A Comparative Retrieval Study, 8 Bone 

Joint Res. 136-145 (2019).  In other words, Dr. Bonutti has a numerator (the number of 
Attune revisions due to debonding) but no denominator (the total number of Attunes 
implanted).  Truman also admitted during her deposition that, given the limited 
information in the article, she could not consider other factors, such as the cement type, 
surgeon experience, surgical technique, post-operative care, or surgeon case load.  

(Truman Dep. at 236-37.)  As Truman explained in her report, these factors have also 
been linked to debonding.  (Truman Report at 54.)                         
The second case study that Truman relied on looked at three patients with Attune 
devices who experienced debonding of the tibial implant-cement interface.  Murphy, et 
al., Early Aseptic Failure of the Tibial Component-Cement Interface in Attune Total Knee 

Arthroplasty:  A Report of Three Cases, 13 Cureus (2021).  The article similarly 
concluded that the Attune design “has led to an unusually high rate of early aseptic 
failures” again without providing the size of the case series.

Id.

  In addition, Truman 
relied on Dr. Breien’s testimony.  He testified that he and his partners observed an 
unacceptably high rate of Attune revisions.  (Breien Dep. at 41.)  Here too, Dr. Breien 
acknowledged that he did not actually know the rate of debonding; rather, he and his 
partners felt that it was higher than it should be.  (Id. at 41, 280.)  Lastly, Truman relied 

on MAUDE data and noted that there were at least eleven incidents of loosening that 
occurred at the Attune tibial implant-cement interface between 2013 and 2014.  (Truman 
Report at 64.)  Truman recognized that the MAUDE data, like the other case studies, 
cannot be used to establish rates of events.  (Truman Dep. at 192.)       
In total, Truman relied on around thirty reports of debonding to support her 

conclusion that the Attune device is unusually susceptible to debonding and is therefore 
defective.  In her deposition, Truman recognized that the anecdotal evidence that she 
relied on was at the bottom of the pyramid of reliability but asserted that she was “left 
with what [she] ha[d].”  (Id. at 220.)  While these reports establish that debonding occurs 
with the Attune, they do not establish the cause of the debonding or the rate at which 

debonding occurs.  See McClain v. Metabolife Intern., Inc.,

401 F.3d 1233, 1250

 (11th 
Cir. 2005) (“Uncontrolled anecdotal information offers one of the least reliable sources to 
justify opinions about both general and individual causation.”).  Even Dr. Bonutti 
cautioned that “[l]arger retrospective studies with longer follow-up” were warranted to 
further investigate the Attune device.  See Bonutti Article.              

In a recent case involving a different device, a court allowed expert testimony that 
relied on case reports when the expert “compared the number of medical device reports 
among different manufacturers and noted ‘the data suggests that the liner dissociation 
problem affects the DePuy AltrX at a significantly higher rate than other products.’”  
Jennings-Moline v. DePuy Orthopaedics, Inc., No. 23-cv-31,

2023 WL 7190739

, at * 2
(D. Idaho Nov. 1, 2023). In that case, liner dissociation was “rarely seen in other
products” and the failure appeared to be “specific to the [AltrX liner]” and the MAUDE

data was used to demonstrate the outsized complaints the product received when
compared to other products on the market. Id. at *5.
This case is distinguishable because debonding is not unique to the Attune. (See
Truman Dep. at 186.) Truman cited studies that have documented debonding in the
Sigma (See Truman Report at 53 (citing the Hazelwood article)) and other devices (id.

at 58 (citing Sadauskas, et al., Implant Interface Debonding After Total Knee
Arthroplasty: A New Cause for Concern? 6 Arthroplasty Today 972-75 (2020))).
Aseptic loosening is an issue for all devices and the fact that a device comes loose does
not automatically mean that the device is defective. (Truman Dep. at 235.) Without
more, the fact that there has been reports of debonding with the Attune device does not

explain how this debonding compares with other devices on the market or what caused
the debonding.
Evidence from registries seem to contradict Truman’s opinion. Truman
acknowledged during her deposition that registry data shows that the Attune performs the
same or better than the Sigma device and other similar devices on the market. (Id.

at 245-50.) In her report, Truman further noted that the Australian Orthopaedic
Association National Joint Replacement Registry, using data from 1999 to 2017,
“showed no difference in survivorship for the PFC Sigma CR [] and Attune CR.”
(Truman Report at 63.) Truman discounted this data in her report because the data “is
not specific enough to differentiate the reason for tibial loosening.” (Id. at 65.) Despite
the lack of specificity in the registry data, Truman fails to explain why the Attune’s
revision rates would not be higher given the increased rate of debonding that she alleges

should be occurring. Her only explanation for why the registry data may not reflect the
outsized incidence of debonding is because many people may experience “pain and
function loss without agreeing to revision.” (Id. at 64.) Those who decline to get a
revision would not be represented in the registry data. But Truman does not explain why
it would not be true for every device that certain people would decline to undergo a

revision surgery and thus registry data for all devices would be missing a certain subset
of people. Moreover, Truman admitted that based on the registry data, the Attune device
is “staying in longer and making patients happier in the aggregate than competing knees.”
(Truman Dep. at 250; see also id. at 203-04.)
Along with the case reports, Truman also included several articles that have found

that the Attune device experiences a higher rate of radiolucent lines than the Sigma
device. (Truman Report at 31.) Truman stated that the “analysis of radiolucent lines
represents an established modality for the prediction of component loosening.” (Id.)
During her deposition, she clarified this statement, noting that the presence of radiolucent
lines alone does not necessarily mean that the device is loose or will become loose.

(Truman Dep. at 331-32.) Radiolucent lines instead need to be “evaluated by the surgeon
in context with everything else.” (Id. at 333.) She further noted that radiolucent lines are
only an issue when they progressively widen. (Id. at 332.) Some radiolucent lines are
small and stagnant, which would not be a predictor of loosening. (Id.)
One article that Truman cited noted that the incidence of radiolucent lines was
significantly higher in the Attune, but it also concluded that the “system achieves
excellent results regarding the revision rate at very short-term follow-up.” Staats, et al.,

Modern Cemented Total Knee Arthroplasty Design Shows a Higher Incidence of
Radiolucent Lines Compared to its Predecessor, 27 Sports Traumatology, Arthroscopy
1148-1155 (2019). And other articles found no difference in radiolucent lines between
the Attune and the Sigma. See Willburger & Oberberg, Early and Mid-Term Results with
the Attune Total Knee Replacement System Compared to PFC Sigma: A Prospective

Comparative Study, 17 J. Orthop. Surg. Res. 509 (2022); Ranawat, et al., Clinical and
Radiographic Results of Attune and PFC Sigma Knee Designs at 2-Year Follow-Up: A
Prospective Matched-Pair Analysis, 32 J. Arthroplasty 431-36 (2017). As Truman noted
in her report, “[t]he clinical results from case reports are conflicting.” (Truman Report
at 53.)

Truman also relied on pullout strength data. Pullout testing involves implanting a
tibial baseplate into an artificial bone, pulling off the implant axially, and measuring the
amount of force required to separate the implant from the bone. (Doc. No. 139-1
(“Rowley Dep.”) at 102-03.) Truman stated that one article, which tested the pullout
strength of the Sigma, the Attune, and the Attune S+, concluded that certain design

features, such as the tapered keel and smooth undersurface “may have predisposed [the
Attune] baseplate to early failure.” (Truman Report at 51; Doc. No. 114-6.) This
statement, however, was made during the introductory paragraph of the article. The
authors hypothesized that because the Attune has a smooth undersurface, the Sigma
“would have a significantly higher axial pullout strength when compared to the [Attune]
with the smooth surface.” (Doc. No. 114-6 at 7.) They further hypothesized that the
Sigma “would perform comparably to the [Attune S+].” (Id.) After testing, however,

they discovered that they were wrong. The pullout strengths of the Attune and the Sigma
“were not statistically different from each other.” (Id. at 11.) And the pullout strength of
the Attune S+ was “significantly greater” than both the Sigma and the Attune, leading the
authors to deduce that the design features of the Attune S+ improved fixation. (Id.)
Contrary to Truman’s report, however, the authors could not conclude that the Attune

was “predisposed” to early failure, as the results of their testing showed that the Attune
and the Sigma performed similarly. Sprafka also mischaracterizes this article in her
briefing. (See Doc. No. 112 at 23.) Truman cited other evidence in her report that
similarly shows no difference in pullout strength between the Sigma, the Attune, and
other devices on the market. (Truman Report at 49.)

Lastly, Truman could not opine on the exact specifications of the tibial baseplate
that would have prevented debonding. (Truman Dep. at 83-84, 356-57.) While at one
point Truman mentioned that the cement pockets on the backside of the tibial baseplate
should have been 1 to 1.5 millimeters in depth (id. at 361), she also states that she would
need to do testing to figure out the exact measurements (id. at 83-84). Truman admitted

that the Sigma was a clinically successful knee device, yet her report indicates that the
Sigma devices had pockets less than one millimeter. (Id. at 256-57; Truman Report
at 55.) As for surface roughness, Truman asserted that the surface of the Attune’s tibial
baseplate needed to be rougher but stated that she could not identify a specific roughness
without further testing. (Truman Dep. at 356-57.) And again, Truman admitted that the
Sigma was clinically successful, yet prior versions of the Sigma were smoother than the
Attune. (See Truman Report at 55.)

Overall, there are several red flags with Truman’s methodology. She cannot show
that the Attune debonds at a higher rate than the Sigma or the Attune S+, she relies on
anecdotal case reports, she discounts the registry data—which overwhelmingly shows
that the Attune has the same or better revision rates than other devices on the market, she
cannot show that her opinions have an acceptable rate of error or are generally accepted,

she admits that the Sigma was clinically successful yet argues that the Attune’s design
features needed to go beyond the features in the Sigma, and she is unable, without
additional testing, to state what design features would have prevented debonding. While
Sprafka argues that challenges to Truman’s testimony should go to weight and not
admissibility, the Court should exclude expert testimony when it is “so fundamentally

unsupported that it can offer no assistance to the jury.” In re Zurn Pex Plumbing Prods.
Liab. Litig.,

644 F.3d 604, 614

 (8th Cir. 2011) (internal quotations and citation omitted).  
And while some guesswork is necessary for expert testimony, “too much is fatal to 
admission.”  Werth v. Hill-Rom, Inc.,

856 F. Supp. 2d 1051, 1063

 (D. Minn. 2012) 
(quoting Grp. Health Plan, Inc. v. Philip Morris USA, Inc.,

344 F.3d 753

, 760 (8th Cir. 

2003)).                                                                   
Truman essentially concludes based on her knowledge, experience, and certain 
anecdotal reports that the Attune should debond at a higher rate than the Sigma and the 
Attune S+ based on certain features of the Attune tibial baseplate.  (See Truman Dep. 
at 163.)  While this may be a sound hypothesis, it has not been tested or supported by 
reliable data.  “[T]he function of expert testimony is to explain how something happened, 
not to speculate as to how something could possibly have happened.”  Werth,

856 F. Supp. 2d at 1062

 (internal quotations and citation omitted).  Truman’s opinions merely 
establish that changes to the tibial baseplate could have possibly reduced instances of 
debonding.  And she cannot specify exactly what changes should have been made.  
Courts often exclude expert testimony like this when there is too great an analytical gap 
between the data and the opinion proffered.  See Gen. Elec. Co. v. Joiner,

522 U.S. 136, 146

 (1997) (holding that expert testimony may be excluded when “there is simply too 
great an analytical gap between the data and the opinion proffered”); Nelson,

92 F. Supp. 2d at 969

 (excluding expert testimony when the expert relied on case reports that were 
“mere compilations of reported occurrences” but did not “demonstrate a causal link 
sufficient for admission”); In re Baycol Prods. Litig.,

532 F. Supp. 2d 1029, 1050

(D.

Minn. 2007) (“Daubert decisions warn against leaping from an accepted scientific
premise to an unsupported one.”) (internal quotations and citation omitted).
Because Sprafka has not shown by a preponderance of the evidence the reliability
of Truman’s opinion that the Attune device is defective, the Court excludes this
testimony.

B. Safer Alternative
Similar issues arise with Truman’s opinion that a safer alternative existed.
Truman testified that MDBS could have made the following changes to the Attune tibial
baseplate to prevent debonding: (1) deepened the cement pockets; (2) increased the
cement pocket surface area; (3) provided undercuts or dovetails to the cement pockets;
and (4) increased the surface texture. (Truman Report at 33-34.) As noted above,
however, Truman cannot say what depth of pockets or level of roughness would have

prevented debonding. She also testified that the Attune S+ is the only device on the
market that she knew of that contains undercuts. (Truman Dep. at 82, 354.) Truman
asserted that deeper pockets and higher roughness is better, but she acknowledged that a
surface can be “too rough” and that the depth of the pockets can impact the integrity of
the baseplate. (Truman Dep. at 326-27, 382-83.) Ultimately, she testified that she would

need to do further testing to determine the exact specifications that she would
recommend. (Id. at 325-27, 357, 363, 380-81.)
In addition, Truman noted that one of the goals of MDBS when designing the
Attune was to limit bone loss during revision surgeries. (Truman Report at 32.) No
matter how effectively designed a knee device may be, some devices will inevitably need

to be replaced. (Wright Dep. at 74-75; Truman Dep. at 234.) Truman’s report does not
consider at all whether the Attune has resulted in less bone loss during revision surgeries.
Such analysis is necessary to properly weigh the costs and benefits of making Truman’s
suggested changes to the design of the Attune tibial baseplate.
Truman testified that she “didn’t really have to” consider the tradeoffs of making

certain changes to the Attune, because the Attune S+ incorporated her suggested changes.
(Truman Dep. at 326.) Truman relies heavily on the Attune S+ to show that certain
design features were feasible and would have improved fixation. Notably, the Attune S+
did not exist at the time Sprafka received her knee replacement. Even setting that aside,
Truman provides little data or research about the Attune S+ in her report. She admitted
that she does not actually know if the Attune S+ debonds at a lower rate than the original
Attune. (Truman Dep. at 163.) Truman’s report states that the Attune S+ has resulted in

greater pullout strength, but Truman concedes that greater pullout strength does not
necessarily translate to greater clinical results. (Truman Report at 51; Truman Dep.
at 125.) In fact, Truman criticizes MDBS for relying on pullout testing when designing
the Attune. (Truman Report at 41 (noting that the “simplistic axial pull-off” test has “low
clinical relevance”).) Truman has provided no research or data that suggests that the

Attune performs worse than the Attune S+. And one article that Truman cited in her
report suggests that the revision rates for the Attune and Attune S+ are similar. See
Torino, et al., Tibial Baseplate-Cement Interface Debonding in the Attune Total Knee
Arthroplasty System, 17 Arthroplasty Today 165-71 (2022) (“Torino article”).3
In sum, Truman asserts that the Attune S+ “should perform better than” the Attune

(Truman Dep. at 163), but she does not have any testing, data, or peer-reviewed articles
to support this proposition. Without more, Truman’s opinion that a safer alternative
existed is too speculative to be admissible. While in theory certain modifications to the
tibial baseplate should improve fixation, Truman does not know if these modifications
would lead to clinical results, nor is it generally accepted that devices need to have the

specific features that Truman proposes to be clinically successful. It is also not clear that

3 The authors, however, hypothesized that the Attune S+ improved tibial fixation
but noted that their “series was not able to demonstrate [a] statistically significant
difference in performance between [the] tibial components, likely due to a small sample
size.” See Torino article.
Truman has accounted for the costs and benefits of making such modifications. And as
noted previously, the Attune S+ was not on the market at the time of Sprafka’s surgery,
and it does not appear that any knee device existed at that time with all the features that

Truman asserts was necessary. The Court thus excludes Truman’s opinion on this issue.
C. Testing
Lastly, Truman opined that MDBS should have conducted additional testing of the
Attune. She asserted that, in addition to the pullout testing, MDBS should have
conducted a test “under reasonably foreseeable operative room and in vivo physiologic

loading conditions.” (Truman Report at 76.) Truman, however, could not specify the
parameters of such test. She also could not name any other manufacturer who has
conducted similar testing or a peer-reviewed article that outlines the need for such testing.
(Id. at 84-87, 111-12, 124, 139.) She did not conduct the test herself or explain the costs
and benefits of such a test. Without more information, Truman’s opinion is too

speculative to be admissible.
The Court stresses that its decision today does not discount Truman’s knowledge
and experience as a biomedical engineer. The issue is not that Truman’s opinions are
wrong but that Truman simply does not have the information she needs to make reliable
conclusions on whether certain design features of the Attune created an increased

prevalence of debonding, what specific design features would have prevented debonding,
and what, if any, additional testing should have been done. At best, Truman has an
educated guess. Ultimately, “[t]he courtroom is not [the] place of scientific guesswork,
even of the most inspired sort. Law lags science; it does not lead it.” Nelson,

92 F. Supp. 2d at 970

 (internal quotations and citation omitted).  For the above reasons, the Court 
excludes Truman’s opinion in its entirety.                                
II.  Summary Judgment                                                     

The Court next considers MDBS’s motion for summary judgment.  Summary 
judgment is appropriate if 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).  A dispute about a material fact is genuine “if the evidence is such that a 
reasonable jury could return a verdict for the nonmoving party.”  Anderson v. Liberty 

Lobby, Inc.,

477 U.S. 242, 248

 (1986).  A party opposing a motion for summary judgment 
“may not rest upon mere allegation or denials of his pleading, but must set forth specific 
facts showing that there is a genuine issue for trial.”

Id. at 256

.  “Conclusory arguments, 
without evidence, are insufficient as a matter of law to establish a material question of 
fact.”  Sieden v. Chipotle Mexican Grill, Inc.,

846 F.3d 1013, 1019

 (8th Cir. 2017).  The 

Court views the evidence and all reasonable inferences in the light most favorable to the 
nonmoving party.  Weitz Co., LLC v. Lloyd’s of London,

574 F.3d 885, 892

 (8th 
Cir. 2009).                                                               
Sprafka alleges four causes of action, including strict liability, negligent products 
liability, breach of implied warranty, and breach of express warranty.  In her briefing, 

Sprafka withdrew her claims for breach of implied and express warranties (see Doc. 
No. 137 at 4) and thus only Sprafka’s strict liability and negligent products liability 
claims remain.  “Where design defect cases are involved, Minnesota merges the theories 
of strict liability and negligence.”  Piotrowski v. Southworth Prods. Corp.,

15 F.3d 748, 751

 (8th Cir. 1994).  Sprafka asserts two bases for her products liability claim.  First, she 
argues that the Attune was defectively designed.  Second, she asserts that MDBS failed to 
provide adequate warnings or instructions to warn about the risks of debonding.  

Expert testimony is required under Minnesota law in products liability cases 
involving medical devices because they involve “complex medical issues with which a 
jury is unlikely to have experience.”  Rye v. Matrixx Initiatives, Inc., No. 06-cv-3288,

2007 WL 2475960

, at *4 (D. Minn. Aug. 24, 2007) (internal quotations and citation 
omitted); see also In re Baycol Prods. Litig.,

321 F. Supp. 2d 1118, 1126

 (D. Minn. 2004) 

(“[T]his Court joins with those courts that have held personal injury cases involving 
pharmaceuticals, toxins or medical devices involve complex questions of medical 
causation beyond the understanding of a lay person.”).  The Attune is a medical device 
and claims about its design and alleged failures are highly technical and complicated such 
that a jury is unlikely to understand without expert testimony.  Sprafka relies on the 

expert testimony of Truman to establish that the Attune device was defective and that 
certain design features of the Attune caused Sprafka’s Attune device to debond.  Without 
this testimony, Sprafka is unable to prove her products liability claim.  See Trost v. Trek 
Bicycle Corp.,

162 F.3d 1004, 1009

 (8th Cir. 1998) (concluding that summary judgment 
was appropriate when the only evidence the plaintiff offered of a product’s defective 

condition was expert testimony that was excluded).  The Court therefore grants summary 
judgment.                                                                 
                     CONCLUSION                                      
For the reasons outlined above, the Court grants MDBS’s motion to exclude 
testimony and motion for summary judgment.

ORDER

Based upon the foregoing, and the files, records, and proceedings herein, IT IS 
HEREBY ORDERED that:                                                      
1.   Defendants’ motion to exclude expert testimony of Mari Truman (Doc. 
No. [91]) is GRANTED.                                                     

2.   Defendants’ motion for summary judgment (Doc. No. [123]) is     
GRANTED.  Plaintiff’s claims against Defendants are DISMISSED WITH        
PREJUDICE.                                                                
LET JUDGMENT BE ENTERED ACCORDINGLY.                                 

Dated:  March 26, 2024        s/Donovan W. Frank                          
                         DONOVAN W. FRANK                            
                         United States District Judge