Large Medial Opening Wedge High Tibial Osteotomy Increases Gastrocnemius Tension: A Cadaveric Study with Clinical Correlation to Early Knee Flexion Contracture.

Abstract

Medial opening wedge high tibial osteotomy (MOW-HTO) corrects varus malalignment and improves load distribution in the knee. Its effect on structures traversing the proximal tibia, particularly the gastrocnemius, remains unclear. This study hypothesized that large correction MOW-HTOs increase gastrocnemius tension and contribute to early postoperative knee flexion contracture. Five fresh-frozen human cadaveric lower limbs underwent MOW-HTOs with incremental opening gaps. Knee extension and ankle dorsiflexion were measured with goniometer before and after gastrocnemius recession. For clinical correlation, a retrospective matched-pair cohort of 60 MOW-HTO patients was analyzed and divided into two groups by the opening wedge sizes: SmallGap (<10 mm) and BigGap (≥10 mm). Radiological parameters including hip-knee-ankle angle, medial proximal tibial angle, lateral distal femoral angle, joint line convergence angle and posterior tibial slope were compared. Clinical outcomes (quadriceps strength and knee range of motion) and functional outcomes [Knee Society Score (KSS), Oxford Knee Score (OKS) and Short Form-36 (SF-36)] were compared preoperatively, at 6 months and at 2 years. In the cadaveric models, increasing opening gaps during MOW-HTOs resulted in progressive increase of the knee flexion (0.6˚ per 1mm, P < 0.001) and reduction of ankle dorsiflexion (0.3˚ per 1mm, P < 0.001). Gastrocnemius recession restored motion in all specimens (P < 0.001). In the clinical cohort, greater knee flexion contracture was observed in BigGap group at 6 months (P < 0.05), but not at 2 years (P = 0.432). Radiological alignments were comparable. Functional outcomes were similar except for SF-36 physical component score at 2 years (P < 0.001). Large correction MOW-HTO is associated with increased gastrocnemius tension and early postoperative knee flexion contracture. Cadaveric findings demonstrate that gastrocnemius recession improved knee extension and ankle dorsiflexion, supporting a biomechanical explanation for this transient clinical effect. Target gastrocnemius stretching may be considered during rehabilitation. Level III.