Sexual and ethnic polymorphism render prosthetic overhang and under-coverage inevitable using off-the shelf TKA implants

Abstract

Purpose Unexplained pain and stiffness after total knee arthroplasty (TKA) often result from mismatch between implant geometry and knee morphology, which depends on patient size, sex, and ethnicity. This study aimed to determine whether size, sex, or ethnicity are independently associated with distal femoral morphology in healthy Caucasian and Asian knees, and to compare anatomic ratios to those of commercially available TKA implants. Methods Two series of computed tomography (CT) angiograms from France (264 knees) and China (259 knees) were used to digitize osteometric landmarks at the level of the femoral epicondyles, to measure anteroposterior (AP) and mediolateral (ML) dimensions at the anterior, posterior, medial, and lateral zones. The aspect (ML/AP), trapezoidicity (MLp/MLa), and asymmetry (APl/APm) ratios, as well as the sulcus angle were calculated and compared to those of 9 TKA models. Multivariable analyses were performed to determine whether anatomic ratios were independently associated with sex, origin, or size. Results Multivariable analyses revealed that, independently from size, female knees were narrower (β = − 0.03; p < 0.001) and more asymmetric (β = 0.02; p < 0.001), while Chinese knees were more trapezoidal (β = 0.04; p = 0.002) and asymmetric (β = 0.02; p < 0.001) with shallower trochleae (β = 6.4°; p < 0.001). Compared to native knees, most implants were too wide, and many of the recent models too ‘trapezoidal’. Most prosthetic trochleae were too shallow compared to French knees, but within the third quartile of Chinese knees. Conclusions The morphology of the distal femur depends on sex and ethnicity independently from size. The wide spectrum of morphotypes observed cannot be covered by ‘off‐the‐shelf’ TKA models, and until customized implants become more accessible, prosthetic overhang, and under‐coverage remain inevitable. Level of evidence III, Retrospective comparative study.

Using MRI Measurement to Improve Accuracy of Femoral Component Sizing in Oxford Unicompartmental Knee Arthroplasty

“…Although our patients were quite the same ethnic groups, this algorithm only achieved 23% correct femoral size in our patient group. We only deduced in the past that the knee anatomy differs between Caucasian and Asian population groups [ 21 , 22 , 23 ]. However, even in similar populations, height- and gender-based criteria seemed to have unsatisfactory accuracy.…”

Influence of gender and age on distal femur shape. Are there any relevant differences?

“…Several studies have attempted to find in the patients' sex the explanation for unsatisfactory clinical results after TKA. 10,11 This study's main objective was to evaluate the possible sex differences in the shape of the distal femur. The secondary objective was to assess whether there is an age group influence on morphometry.…”

Biomechanical and Clinical Effect of Patient-Specific or Customized Knee Implants: A Review

“…This may lead to ML undercoverage and overcoverage, respectively, when TKA components based on the femurs of Caucasian patients are used. Moreover, the prostheses of conventional TKA cannot cover the wide spectrum of ethnic tibiofemoral morphotypes [25]. Mismatch in the angles of the sulcus between the native knees and prostheses has been proved, however, it is not clear to what extent this is true for other patellofemoral ratios [25,26].…”

“…Moreover, the prostheses of conventional TKA cannot cover the wide spectrum of ethnic tibiofemoral morphotypes [25]. Mismatch in the angles of the sulcus between the native knees and prostheses has been proved, however, it is not clear to what extent this is true for other patellofemoral ratios [25,26]. In recent studies, it was shown that four of the five measured trochlear morphometric parameters relied significantly on ethnicity, whereas only two of the measured parameters relied on gender [26].…”