Quantitative Assessment of Muscle Strength Following "slow" Surgical Lengthening of the Medial Hamstring Muscles in Children with Cerebral Palsy

Background: Classic teaching for surgical lengthening of muscle contractures in children with cerebral palsy (CP) has emphasized complete correction of the deformity acutely, with immobilization of the targeted muscles in the fully corrected position. Clinical experience has led to the impression that the muscles are invariably weakened by this approach. We have developed an alternative technique for correction of contractures called slow surgical lengthening (SSL). The goal of the study was to determine the physical examination, kinematic, and muscle strength outcomes following SSL of the medial hamstring muscles in children with CP. Methods: The study group included 41 children with CP who underwent SSL of the medial hamstring muscles as part of a comprehensive single-event multilevel surgery, who had preoperative and 1-year postoperative evaluations in our Motion Analysis Center, which included quantitative assessment of isometric and isokinetic muscle strength. Results: All subjects were Gross Motor Function Classification System I and II. Mean age at the time of surgery was 10.8 years. The mean popliteal angle improved by 16.2 degrees (P<0.001) following SSL of the medial hamstrings. Sagittal plane kinematics following SSL of the medial hamstrings showed improvement of knee extension at initial contact of 10.2 degrees (P<0.001), decrease of peak knee flexion in mid-swing of 3.6 degrees (P=0.014), improved minimum knee flexion in stance of 4.9 degrees (P=0.002), and no significant change in mean anterior pelvic tilt (P=0.123). Mean peak isometric knee flexion torque remained unchanged from preoperative to postoperative studies (P=0.154), whereas mean peak isokinetic knee flexion torque significantly increased by 0.076 Nm/kg (P=0.014) following medial hamstring SSL. Discussion: SSL was developed based upon clinical experience and improved understanding of the pathophysiology of skeletal muscle in children with CP. The SSL technique allows the tendinous tissue to separate spontaneously at the time of recession, but does not force further acute lengthening by intraoperative manipulation, thereby minimizing the damage to the underlying muscle. It is broadly believed that muscle weakness is inevitable following surgical lengthening. The current study shows that the SSL technique does not cause weakness. Level of Evidence: Level IV - therapeutic.