The Role of Knee Flexors Hypertonia in the Decision-Making of Hamstring Lengthening Surgery for Individuals with Cerebral Palsy

Abstract

Popliteal angle (PA) and the knee position at the end of the swing phase during walking (Kts) are considered criteria for treatment selection and outcome prediction of hamstring lengthening surgery in individuals with cerebral palsy (CP). However, the relationships among Kts, PA, and hypertonia are not clear. This study aimed to determine whether hamstrings hypertonia affects the values of PA and Kts, and how it may affect the hamstring lengthening decision for CP. One hundred and twenty-six subjects with CP (male = 72, female = 54; age = 11.1 ± 3.9 years) underwent gait analysis and examination of hamstrings hypertonia (Tardieu scale) and length (PA). We found that Kts increased with PA (Kts = 5.00 + 0.31 × PA (r = 0.39; p < 0.001)). Every 10° change of PA leads to 3° improvement of knee position in walking. Kts were larger (p < 0.001) in the limbs with (20.40 ± 11.27°) than without (15.60 ± 9.99°) knee flexors hypertonia (Tardieu slow); and were larger (p < 0.001) in the limbs with (20.39 ± 11.01°) than without (14.85 ± 9.89°) knee flexors hypertonia (Tardieu fast). PAs were larger (p < 0.05) in the limbs with (42.81 ± 12.66°) than without (38.96 ± 14.38°) hypertonia (Tardieu fast). Kts = 13.93° and PA = 30° were cutoff values of the presence of hypertonia with sensitivities of 75.0% and 89.1%, respectively. Kts increased with the PA in ambulatory CP. It is estimated that pathological increase of Kts occurs at PA ≥ 40°. The hypertonia of knee flexors affected Kts and PA. The presence of knee flexors hypertonia should be considered in the decision-making of hamstring lengthening for individuals with CP if Kts ≥ 13.93° and PA ≥ 30°.