The extensor efficiency of unicompartmental, bicompartmental, and total knee arthroplasty

Abstract

Aims Unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BCA) have been associated with improved functional outcomes compared to total knee arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function. Methods Extensor function was measured for 16 cadaveric knees and then retested following the different arthroplasties. Eight knees underwent medial UKA then BCA, then posterior-cruciate retaining TKA, and eight underwent the lateral equivalents then TKA. Extensor efficiency was calculated for ranges of knee flexion associated with common activities of daily living. Data were analyzed with repeated measures analysis of variance (α = 0.05). Results Compared to native, there were no reductions in either extension moment or efficiency following UKA. Conversion to BCA resulted in a small decrease in extension moment between 70° and 90° flexion (p < 0.05), but when examined in the context of daily activity ranges of flexion, extensor efficiency was largely unaffected. Following TKA, large decreases in extension moment were measured at low knee flexion angles (p < 0.05), resulting in 12% to 43% reductions in extensor efficiency for the daily activity ranges. Conclusion This cadaveric study found that TKA resulted in inferior extensor function compared to UKA and BCA. This may, in part, help explain the reported differences in function and satisfaction differences between partial and total knee arthroplasty. Cite this article: Bone Joint Res 2021;10(1):1–9.

Bi-unicondylar arthroplasty

“…Partial knee arthroplasty has been shown to offer improved function over TKA using objective metrics such as gait analysis, particularly in early stance, when the quadriceps are active. 12 , 13 This correlates with observed differences in extensor biomechanics, 14 , 15 including preserved efficiency, which may also influence activities such as stair ascent and sit-to-stand. 16 Similar benefits of Bi-UKA, whether a primary or staged procedure, have not been documented.…”

“… 12 This may be explained by differences observed in extensor function in vitro: extensor efficiency was greatly reduced following TKA over the quadriceps active gait range compared to both Bi-UKA and the native knee. Although important for all activities, extensor efficiency is particularly relevant for daily activities with a high number of cycles, including stair ascent and fast walking, 12 , 14 where Bi-UKA presently outperformed TKA. This study suggests that TKA patients may expend significantly more energy to achieve the same function during these activities, corroborating findings of others, who have shown abnormal flexion-extension moments following TKA, attributing this to reduced quadriceps effectiveness.…”

“…Dissected specimens were mounted into an extension rig in accordance with a previously published protocol. 14 In short: the iliotibial band, quadriceps, and hamstring tendons were loaded with a total of 225 N in physiological directions ( Table II ). 19 Resulting knee extension caused a tibial intramedullary rod to push against a restraining bar, equipped with a calibrated full-bridge strain gauge circuit ( Figure 3 ).…”

“…Previous studies from our group have demonstrated that only minimal cementing, without pressurization or bony penetration, is needed to fix the prosthesis to withstand the experimental loading and facilitate bone-sparing revision. 14 , 15 , 24 During removal, a fine saw blade was used at the cement-bone interface. The bone bed was visually inspected both after removal of the implants (Supplementary Figure a) and after the TKA bone cuts (Supplementary Figure b).…”

Variation in the patellar tendon moment arm identified with an improved measurement framework

“…Knees were positioned in an extension rig, with the femur held stationary, so the femoral trans-epicondylar axis was aligned to the rotational axis of the rig, enabling knee kinematics to be tracked as previously described. 42,43 A manually controlled tibial restraint, which allowed secondary knee motions to freely occur, was used to control extension/flexion rates.…”