目的 针对单髁膝关节置换术(UKA)内侧假体松动和外侧关节软骨退化问题,通过骨肌多体动力学方法研究不同生理活动中UKA关节线安装误差对膝关节接触力学和运动学的影响。方法 以内侧自然关节线为中性位置分别考虑了±2 mm、±4 mm、±6 mm 共六种关节线安装误差情况,建立了七个内侧UKA置换的骨肌多体动力学模型,对比研究步行和下蹲运动中膝关节接触力学和运动学的变化。结果 UKA假体关节线安装误差对行走步态摆动相和屈膝下蹲过程中的膝关节接触力学影响较大。在步态周期70%,相比于中性位置UKA假体关节线升高2mm时内侧假体接触力增大127.3%、外侧软骨接触力减少12.0%；在UKA假体关节线降低4mm时内侧假体接触力接近0N,外侧软骨接触力增大10.1%；胫股关节总接触力在关节线升高和降低2mm时分别增大19.7%和减小14.2%。在屈膝下蹲中,内侧假体接触力以及胫股关节总接触力的变化随关节线误差的增大越显著,而膝关节外侧软骨接触力变化不大。膝关节屈膝100o时,相比于中性位置膝关节内侧假体接触力和胫股关节总接触力在关节线升高2mm时分别增大31.6%和11.1%,在UKA假体关节线降低2mm时分别减小24.5%和8.5%。同时,行走步态摆动相时,随UKA假体关节线的升高膝关节内翻运动减小、内旋运动增大、关节前移,随关节线的降低而呈现相反趋势。下蹲运动中膝关节内外翻运动和前后平移运动与行走步态趋势一致,但内外旋运动则刚好相反。结论 为了降低内侧假体松动失效风险和外侧软骨退化风险,本文建议医生控制UKA假体关节线误差在 -2 mm到+2 mm范围内。研究结果为UKA假体关节线变化引起的临床失效问题提供了理论依据。
Objective Aiming at the medial prosthetic loosening failure and lateral cartilage degeneration after unicompartmental knee arthroplasty (UKA), the effects of the prosthetic installation errors of joint line in UKA on knee contact mechanics and kinematics during different activities were studied using musculoskeletal multibody dynamic method. Method On the basis of the neutral position of the medial natural joint line, six installation errors of joint line including ±2 mm, ±4 mm and ±6 mm were considered respectively, and seven musculoskeletal multibody dynamic models of medial UKA were established to comparatively study the variations in knee contact mechanics and kinematics during walking and squatting simulations. Results The prosthetic installation errors of joint line in UKA had significantly effects on the knee contact mechanics during squatting and the swing phase of walking. At the 70% of walking gait cycle, compared with the neutral position, the medial prosthetic contact force was increased by 127.3% and the contact force of the lateral cartilage was decreased by 12.0% under a +2mm joint line condition, the medial prosthetic contact force was close to 0 N but the lateral cartilage contact forces were increased by 10.1% under a -4 mm joint line condition. The tibiofemoral total contact forces were increased by 19.7% and decreased by 14.2% under the +2mm and -2mm joint line conditions, respectively. During squatting, the changes in the medial prosthetic contact force and tibiofemoral total contact force were more significant along with increased installation error of joint line, while the change in the lateral cartilage contact force was not marked. At the 100 o of knee flexion during squatting, compared with the neutral position, the medial prosthetic contact force and the tibiofemoral total contact force were increased by 31.6% and 11.1% under a +2mm joint line condition, and decreased were 24.5% and 8.5% under a -2mm joint line condition, respectively. Moreover, during the swing phase of walking, the varus angle was decreased, the internal rotation and the anterior translation were increased along with the elevation of joint line in UKA, while it was just the opposite along with the reduction of joint line in UKA. The trends of the varus-valgus movement and anterior-posterior translation during squatting were consistent with those during the swing phase of walking, but the trend of the internal-external rotation was opposite. Conclusions In order to reduce the risk of medial prosthetic loosening failure and lateral cartilage degeneration, it was recommended that the installation error of joint line in UKA should be controlled in the range of -2 mm to +2 mm. This study provided a theoretical basis for UKA clinical failure caused by the changes in joint line.