Study Confirms Knee Shapes are Highly Individualized

Think gender, body type or ethnicity influence knee joint anatomy? Think again.

A recent study found that knee shapes are individualized but not based on characteristics typically used to identify patients. Touted by Conformis Inc., the study investigated characteristic shapes of knees to determine whether typical patient identifiers such as gender, body type, or ethnicity influence the knee joint’s shape. Published in The Knee,¹ the study found that knee shape occurs independently from characteristics typically used to identify patients.  

“This new research reinforces the importance of precisely matching the implant to the individual patient,” said Mark Augusti, CEO and president of Conformis. “This is only possible with a patient-specific implant system available through our Platinum Services Program, such as our fully personalized Identity knee system. This study further supports our long-held business case that fully personalized implants provide the best fit for patients, eliminate clinically-significant overhang, minimize post-operative pain, speed recovery time, and enhance flexibility and performance.”

Led by Benjamin Hohlmann and Malte Asseln of the Helmholtz Institute for Biomedical Engineering at Aachen University in Germany, the authors conducted their analysis using a data set of computed tomography images from more than 1,000 pathological knees provided by Conformis. The company also helped fund the study.
 
Study data found that identifiers such as gender, body type, and ethnicity do not help surgeons determine the best off-the-shelf replacement system or implant size for each individual. This clinical study further underscores the value of precisely matching a replacement joint with the specific anatomy of each patient. The absence of predictable shapes or morphotypes “makes it difficult to further reduce the bone to implant mismatch with off-the-shelf implants,” the authors noted. Trying to do so, they said, might require an excessive number of sizes of standardized implants that provides significant logistical challenges for facilities. An alternative is the use of customized implants using “patient-specific implant design.” 
 
The authors used two different methodologies to analyze the knee images in an effort to find “clusters” of knees that could provide a way to standardize knee design based on patients’ gender, body type, ethnicity, or other characteristics like age. As expected, the data did not generate any clusters that could be used as predictors to better fit of off-the-shelf implants to the specific anatomies of patients undergoing total knee arthroplasty (TKA).
 
The Knee article follows a retrospective study published in The Journal of Bone & Joint Surgery Reviews (JBJS Reviews²), announced by Conformis on Feb. 28 that found patients who had undergone TKA surgery preferred their Conformis fully personalized knee compared to their bilateral off-the-shelf knee at a rate of more than 10 to one.
 
That earlier study compared patients who had a fully personalized Conformis implant in one knee after receiving a competitive off-the-shelf implant in the other knee, and found that 72.3 percent of the patients studied preferred their fully personalized Conformis knee replacement, compared to only 6.4 percent of patients who preferred their traditional off-the-shelf (OTS) implant. The remaining 21.3 percent reported no perceived difference between the two knee implants.
 
Authors of the new study concluded, “The data exhibited no morphotypes. This showed that there are no relevant identifiers, e.g., gender, body type, or ethnicity which influence the shape of the knee joint. Instead, knee shape is determined by the unique characteristics of each individual.”
 
Conformis’s product portfolio is designed to maximize surgeon and patient choice by offering fully personalized solutions through its Image-to-Implant Platinum Services Program as well as data-informed, standardized solutions that combine many benefits of personalization with the convenience and flexibility of an off-the-shelf system. Conformis’ sterile, just-in-time, Surgery-in-a-Box delivery system is available with all of its implants and personalized, single-use instruments. Conformis owns or exclusively in-licenses issued patents and pending patent applications that cover personalized implants and patient-specific instrumentation for all major joints.

References 
¹ Hohlmann, Benjamin, Asseln, Malte, Xu, Jiacheng, Radermacher, Klaus, Investigation of morphotypes of the knee using cluster analysis, The Knee 35 (2002) 157-163 https://www.thekneejournal.com/action/showPdf?pii=S0968-0160%2822%2900034-5
² Schroeder, Lennart MD1,a; Dunaway, Andrew DO2; Dunaway, Daniel MD3 A Comparison of Clinical Outcomes and Implant Preference of Patients with Bilateral TKA, JBJS Reviews: February 2022 – Volume 10 – Issue 2 – e20.00182 doi: 10.2106/JBJS.RVW.20.00182