Distal hamstring lengthening in cerebral palsy: the influence of the proximal aponeurotic band of the semimembranosus.

We undertook a prospective review of 24 children with spastic diplegia treated by distal hamstring fractional lengthening at the Sheffield Children's Hospital. In 14 children (24 limbs) the correction achieved (popliteal angle) was inadequate and in these patients in the operating room a further correction was attained by dividing a tight band palpated in the substance of the semimembranosus muscle. Under general anaesthetic (preoperatively) the popliteal angle (a degrees ) was measured using a goniometer, then again (b degrees ) following distal hamstring fractional lengthening and finally (c degrees ) after surgically dividing the tight band. The mean preoperative popliteal angle (a degrees ) in all 24 limbs was 65 degrees (52-90). Following the standard hamstring fractional lengthening it (b degrees ) measured 37 degrees (35-50) and after division of the tight band it (c degrees ) measured 15 degrees (10-20). The reduction in popliteal angle following release of the tight band (proximal aponeurosis) was statistically significant (P<0.05). We undertook a cadaveric examination of 22 lower limbs and confirmed in all the cases that this band was the proximal aponeurosis of the semimembranosus muscle. The proximal aponeurosis is a well defined band located at the anterior aspect of the semimembranosus muscle where it arises from the tendon of the proximal attachment. It is separate from the distal aponeurosis. Division of the proximal aponeurosis during fractional lengthening of the distal hamstring in patients with cerebral palsy results in a significant reduction in the flexion deformity.