Abstract
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.
Highlights
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 [1]
From baseline to the medium-term follow-up measurements, body height and body mass increased by 6.0±4.3 cm and 4.2±2.5 kg, respectively (p = 0.019, p = 0.008, Table 1), while body mass index (BMI) and femur length of the right leg did not change (p = 0.631, p = 0.580, Table 1)
In all children Gross Motor Function Classification System (GMFCS) level remained unchanged except for one child. In this child, GMFCS increased from level III to IV (Table 1)
Summary
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 [1]. The success rate is limited in some patients due to side effects of surgery (e.g. increased anterior pelvic tilt, and lumbar lordosis as well as hyperextension of the knee during gait) [4, 8,9,10] These side effects are thought to be a consequence of over-lengthening and weakening of hamstring muscles [4, 9, 10]. Detailed insight in post-surgery adaptation and function of hamstring muscles around the knee may help to increase our understanding how effects of surgery on gait, and underlying musculoskeletal structures and functions are related Such knowledge may provide indications for improvement of surgical intervention in children with SP
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