Evidence of knee extensor dysfunction during sit-to-stand following distal femoral extension osteotomy and patellar tendon advancement in young adults with cerebral palsy: A pilot study

A distal femoral extension osteotomy with patellar tendon advancement (DFEO + PTA) is a common treatment for individuals with cerebral palsy (CP) who walk in crouch. Musculoskeletal modeling suggests that the typical patella baja position post-DFEO + PTA may limit one's abilities to perform sit-to-stand (STS) tasks; however, STS function has not been assessed. Our purpose was to compare how well individuals who received a DFEO + PTA can perform a 5-times STS test (FTSST) eight or more years after surgery compared to their peers who did not receive a DFEO + PTA (non-DFEO + PTA group). Twenty-one participants completed the task (12 DFEO + PTA, 9 non-DFEO + PTA). Three-dimensional kinematics and kinetics were captured. Kinetics were non-dimensionalized to facilitate group comparisons. Non-DFEO + PTA participants performed the FTSST moderately faster than the DFEO + PTA group (median(IQR), 14.6(9.3) seconds vs. 20.3(10.1) seconds, non-parametric effect size ɣ = 0.97, p = 0.241). Peak negative knee power was larger for the non-DFEO + PTA group (Mean ± SD, −0.063 ± 0.025 vs. −0.048± 0.020, Cohen's d = 0.66, p = 0.165). A similar but weaker trend was observed for negative hip power (median(IQR) −0.120(0.066) vs. −0.105(0.044), ɣ = 0.43, p = 0.671). Both groups used their hips approximately twice as much as their knees to perform the task. The functional deficit among DFEO + PTA participants may be due to patella baja decreasing the knee extensor moment arm, which concurs with the modeling prediction. The group differences may also be due to the non-DFEO + PTA group being slightly higher functioning. Future research is warranted to determine if optimizing patella position during a DFEO + PTA may improve unaided STS function without compromising gait improvements.