Jhurani Anoop, Agarwal Piyush, Ardawatia Gaurav, Sahni Hardik, Srivastava Mudit
Joint Replacement Unit, Fortis Escorts Hospital, Jaipur, Rajasthan, India.
J Clin Orthop Trauma. 2025 Apr 19;65:103023. doi: 10.1016/j.jcot.2025.103023. eCollection 2025 Jun.
Downsizing of femur is often considered during TKA to increase the flexion space or to reduce the mediolateral overhang of the femoral component. This leads to an obvious opening up of flexion space by 2-3 mm. However, the effect of downsizing of the femur component on knee extension and final sagittal correction are unknown. This CAS based prospective study aims to find out change in knee extension caused as a result of downsizing the femur component through objective data from computer navigation.
Out of a total 1811 CAS knees operated between 2020 and 2022. 152 knees required downsizing of which 112 knees were included after applying exclusion criteria. The patients had average BMI of 28.2 ± 4.6 kg/m and average age of 62.5 ± 8 years.
The average preoperative deformity was fixed flexion of 7.7 ± 4.3 (0.5-14) and varus of 8.6 ± 2.7 (3-13). The average difference of deformity in sagittal plane in extension between larger and downsized femur trial was 5.8° which was statistically significant (p = 0.001). Knee achieves more extension after downsizing possibly because of decrease in metallic volume in the joint capsule and soft tissue envelope. There was significant correction in coronal plane alignment (1°) on downsizing as the soft tissue envelope on the medial side relaxed due to decreased impingement (p = 0.001).
Surgeons should be aware that downsizing of the femur may increase the knee extension by 5.8° and this can be a strategy to increase both gaps specially when there is significant mediolateral overhang of the femoral component.
Type IV.
全膝关节置换术（TKA）中常考虑对股骨进行缩径，以增加屈曲间隙或减少股骨假体的内外侧悬垂。这会使屈曲间隙明显增大2 - 3毫米。然而，股骨部件缩径对膝关节伸展及最终矢状面矫正的影响尚不清楚。这项基于计算机辅助手术（CAS）的前瞻性研究旨在通过计算机导航的客观数据，找出股骨部件缩径导致的膝关节伸展变化。
在2020年至2022年期间接受CAS手术的1811例膝关节中，有152例需要进行股骨缩径，应用排除标准后纳入112例。患者的平均体重指数（BMI）为28.2±4.6千克/平方米，平均年龄为62.5±8岁。
术前平均畸形为固定屈曲7.7±4.3（0.5 - 14）度和内翻8.6±2.7（3 - 13）度。较大尺寸和缩径后的股骨试件在伸展时矢状面畸形的平均差异为5.8°，具有统计学意义（p = 0.001）。股骨缩径后膝关节伸展增加，可能是因为关节囊和软组织包膜内金属体积减少。由于内侧软组织包膜因撞击减少而松弛，缩径时冠状面排列有显著矫正（1°）（p = 0.001）。
外科医生应意识到，股骨缩径可能使膝关节伸展增加5.8°，这可作为增加两个间隙的一种策略，特别是当股骨部件存在明显的内外侧悬垂时。
IV型。
