Date Published: February 6, 2018
Publisher: Public Library of Science
Author(s): Helga Haberfehlner, Richard T. Jaspers, Erich Rutz, Jaap Harlaar, Johannes A. van der Sluijs, Melinda M. Witbreuk, Kim van Hutten, Jacqueline Romkes, Marie Freslier, Reinald Brunner, Jules G. Becher, Huub Maas, Annemieke I. Buizer, Andrea Martinuzzi.
To improve gait in children with spastic paresis due to cerebral palsy or hereditary spastic paresis, the semitendinosus muscle is frequently lengthened amongst other medial hamstring muscles by orthopaedic surgery. Side effects on gait due to weakening of the hamstring muscles and overcorrections have been reported. How these side effects relate to semitendinosus morphology is unknown. This study assessed the effects of bilateral medial hamstring lengthening as part of single-event multilevel surgery (SEMLS) on (1) knee joint mechanics (2) semitendinosus muscle morphology and (3) gait kinematics. All variables were assessed for the right side only. Six children with spastic paresis selected for surgery to counteract limited knee range of motion were measured before and about a year after surgery. After surgery, in most subjects popliteal angle decreased and knee moment-angle curves were shifted towards a more extended knee joint, semitendinosus muscle belly length was approximately 30% decreased, while at all assessed knee angles tendon length was increased by about 80%. In the majority of children muscle volume of the semitendinosus muscle decreased substantially suggesting a reduction of physiological cross-sectional area. Gait kinematics showed more knee extension during stance (mean change ± standard deviation: 34±13°), but also increased pelvic anterior tilt (mean change ± standard deviation: 23±5°). In most subjects, surgical lengthening of semitendinosus tendon contributed to more extended knee joint angle during static measurements as well as during gait, whereas extensibility of semitendinosus muscle belly was decreased. Post-surgical treatment to maintain muscle belly length and physiological cross-sectional area may improve treatment outcome of medial hamstring lengthening.
Medial hamstring lengthening in children with spastic paresis (SP) is commonly performed to increase the range of motion (ROM) of the knee, and thereby the ability of the child to extend the knee during walking . Medial hamstring lengthening includes lengthening of the distal semitendinosus (ST) and gracilis tendons, as well as aponeurotomy of the semimembranosus muscle [2–4]. Medial hamstring lengthening as part of single-event multilevel surgery (SEMLS) is thought to contribute to correction of flexed knee gait [4–7].
The study was approved by the Medical Ethics Committees of the VU University Medical Center (VUmc), Amsterdam (The Netherlands) and of the University of Basel Children’s Hospital (UKBB), Basel (Switzerland) and was registered in the Dutch and German trial register (NTR3042; DKRS00004723). All children and their parents gave written informed consent.
This study shows that after medial hamstring lengthening popliteal angle and minimal passive knee joint angle towards extension were both improved. In most subjects, knee moment-angle curves initially showed a shift towards more extended knee angles, while knee ROM between 0 and 4 Nm knee flexion moment increased, but recurred to pre-surgery values at medium-term follow-up. Muscle belly length decreased while tendon length increased and the change in muscle belly length from 0 to 4 Nm decreased. In gait, knee joint angles measured at medium-term follow-up were more extended in mid-stance and terminal swing, but pelvic anterior tilt increased also. There was no consistent change in hip angle. Individual data indicate that less improvement of the knee joint angles towards extension angles during gait correlated with more increase of hip flexion.