Clinical outcomes following Zone 2 calf lengthening surgery in children with equinus deformity

Abstract

Background and Objectives: Intervention for ankle plantarflexion contractures commonly involve lengthening of the triceps surae muscle-tendon unit. This can be performed at the level of the gastrocnemius muscle belly (Zone 1), the gastrocnemius tendon/soleus belly (Zone 2), or the Achilles tendon (Zone 3). The most frequently chosen intervention is Zone 3 lengthening, as it achieves the greatest increase in length. Investigators have showed using musculoskeletal modelling, however, that lengthening procedures that isolate the gastrocnemius preserve the length-tension relationship of the soleus and presumabley ankle push-off power during walking. Thus, if the contracture is limited to the gastrocnemius, Zone 1 or 2 surgery may be beneficial. The aim of this study was to investigate postoperative outcomes following Zone 2 lengthening. Study Design: Retrospective cohort study. Methods: An audit of the Queensland Children's Motion Analysis Service (QCMAS) database was performed to identify children diagnosed with Idiopathic Toe Walking (ITW) or cerebral palsy (CP) who had undergone calf lengthening surgery and attended gait analysis pre and post-surgery. Fourteen ITW (28 limbs) and thirteen CP (16 limbs) participants were included, with a mean (SD) age of 8.2 (2.7) and 10.4 (2.8) years respectively. Data collection followed the QCMAS standard clinical protocol. Reflective markers were attached to participants in accordance with the Plug-In-Gait model, before they were asked to perform approximately 25 gait trials. Marker trajectory reconstruction and labelling was performed in Vicon Nexus. A modified gait2392 musculoskeletal model was used to output inverse kinematics and dynamics, and to estimate muscle-tendon lengths in OpenSim (v3.3). Pre to post surgery comparisons were performed in SPSS (v22) using a repeated measures general linear model. Dependent variables included ankle joint kinematics, ankle power and muscle tendon length estimates for medial gastrocnemius. Results: Ankle dorsiflexion at initial contact increased from -27.9° (6.0) to -4.3° (8.8) in the ITW population (p<0.001), and from -36.0° (9.8) to -11.2° (5.9) in the CP population (p=0.012). Ankle power at push-off increased by on average 0.5W/kg in the ITW population (p=0.022), and 0.4W/kg in the CP population (p=0.254). Gastrocnemius muscle length increased by 2.8% of leg length for both groups (ITW=5.6cm and CP=4.5cm; p<0.05). Conclusion: The use of Zone 2 calf lengthening for children presenting with equinus deformity, was successful in increasing calf length and improving ankle dorsiflexion without diminishing ankle power during the push-off phase of gait.L6213533922018-03-27 <br />