Bittmann Moria F, Lenhart Rachel L, Schwartz Michael H, Novacheck Tom F, Hetzel Scott, Thelen Darryl G
Department of Mechanical Engineering, University of Wisconsin-Madison, USA.
Gillette Children's Specialty Healthcare, USA; Department of Orthopaedic Surgery, University of Minnesota -Twin Cities, USA.
Gait Posture. 2018 Jul;64:248-254. doi: 10.1016/j.gaitpost.2018.06.005. Epub 2018 Jun 5.
The patellar tendon advancement (PTA) procedure, often coupled with a distal femoral extension osteotomy (DFEO), is increasingly used to treat persistent crouch gait. In this study, we investigated relationships between patella position, knee flexion, and the patellar tendon moment arm in children treated with the DFEO and PTA procedures.
We retrospectively analyzed pre- and post-operative radiographs and gait metrics from 63 knees that underwent DFEO and PTA procedures at Gillette Children's Specialty Healthcare. A computational musculoskeletal model of the knee was used to simulate the PTA procedure and predict the effects on the patellar tendon moment arm.
Approximately 80% of the knees exhibited patella alta prior to surgery. Post-operatively, 86% of the knees exhibited patella baja. The surgically altered patella position produced a 13% increase in the patellar tendon moment arm in extended knee postures, which agreed well with model predictions. However, the computational model also suggests that baja may compromise patellar tendon moment arms in flexed knee postures. Crouch gait was significantly reduced postoperatively, with a 27 ± 18° reduction in average knee flexion in stance. There was considerable inter-subject variability in outcomes with nine knees not exhibiting a meaningful enhancement of knee extension (<15° change). The subjects who improved were significantly younger and exhibited greater enhancement of the patellar tendon moment arm after surgery.
This study shows that the PTA procedure enhances the lever arm of the knee extensor mechanism, and this factor may be important in resolving crouch gait.
髌腱前移（PTA）手术通常与股骨远端延长截骨术（DFEO）联合使用，越来越多地用于治疗持续性蹲伏步态。在本研究中，我们调查了接受DFEO和PTA手术的儿童的髌骨位置、膝关节屈曲和髌腱力臂之间的关系。
我们回顾性分析了在吉列儿童专科医疗中心接受DFEO和PTA手术的63个膝关节的术前和术后X线片及步态指标。使用膝关节的计算肌肉骨骼模型来模拟PTA手术并预测对髌腱力臂的影响。
术前约80%的膝关节表现为高位髌骨。术后，86%的膝关节表现为低位髌骨。手术改变的髌骨位置使伸直膝关节姿势下的髌腱力臂增加了13%，这与模型预测结果非常吻合。然而，计算模型还表明，低位髌骨可能会损害屈膝姿势下的髌腱力臂。术后蹲伏步态明显减轻，站立时平均膝关节屈曲减少27±18°。结果存在相当大的个体间差异，有9个膝关节未表现出膝关节伸展的有意义增强（变化<15°）。改善的受试者明显更年轻，术后髌腱力臂增强更大。
本研究表明，PTA手术增强了膝关节伸肌机制的力臂，这一因素可能对解决蹲伏步态很重要。
