How does patellar tendon advancement alter the knee extensor mechanism in children treated for crouch gait?

BACKGROUND: 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. METHODS: 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. RESULTS: 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 ±â€¯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. CONCLUSIONS: 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.

Customized therapy using distributions of reaching errors.

While there has been recent success with robotic therapy approaches, individual differences in motor impairments motivate the need for customized therapy. Our latest work with healthy participants considered the likelihood of one's error to construct a customized force field training environment, which we termed an error field. We believe error statistics could characterize individual motor impairments for stroke survivors. Here we present preliminary results from a pilot study testing this therapy technique on individuals following stroke. We tracked the changes in error for three stroke survivors across multiple days using error field training, and found that participants' errors reduced for all target directions across sessions. We also used a modeling approach to test whether the changes in error reflected the specific mathematical structure of the intervention. These results provide encouraging preliminary evidence that error field training can be valuable for both characterizing deficits and custom-tailoring therapy.