Ankle Mortise Instability in Multiple Hereditary Exostoses

CATEGORY: Ankle, Ankle Arthritis, Pediatric Foot and Ankle INTRODUCTION/PURPOSE: Ankle valgus has been reported in 50% of patients with multiple hereditary exostoses (MHE) and, untreated, results in early arthrosis. Widening of the ankle mortise has also been reported; however, there has been a lack of data regarding its natural history and management. Alterations of mortise anatomy result in poor functional outcomes and accelerated arthrosis of the ankle. The aim of our study was to report the characteristics and outcomes of mortise widening in a group of patients with MHE. METHODS: A total of 13 patients with MHE and mortise widening (16 ankles) were identified. Age, sex, BMI, laterality, origin of osteochondroma, pain, instability, clinical deformity, operative data, and complications were recorded. Mortise (M), Talocrural angle (TC), and Tibiotalar angle (TT) measurements were collected on preoperative and last follow up radiographs. The majority of patients underwent medial distal tibia hemiepiphysiodesis. Post-surgical AOFAS and SF36 scores were collected. RESULTS: Preoperatively, no patient complained of instability, however, 9/16 ankles were painful and 14/16 were clinically in valgus. Patients underwent surgery at an age of 11.8 years (9.7-15). Radiographic and clinical follow up were 2.6 years (0.2-7.3) and 6 years (1.5-11.7), respectively. There were no significant differences between pre/postoperative M, TC, TT angles. Operative patients improved mean M (5.17 to 4.63 mm) and TT (8.71 to 4.54 degrees), neither angle reached normal values. TC (fibular length) was within normal limits (82.2 to 84.8). Questionnaires were obtained for 8/16 ankles, at a mean age of 19 years (13-25.1). The average AOFAS score was 66.7 out of 100. Patients scored 8.6/10 for alignment, 32/40 for pain, 25.6/50 for function. SF-36 scores were excellent. CONCLUSION: The improvement in M and TT was modest and their values remained outside the normal limits. TC angle was within normal limits but displayed an overall fibular shortening and thus, decreased lateral buttress with potential for talar shift. This was reflected in the mean functional and overall AOFAS score. However, our patients are functionally compensating as evidenced by SF36 scores. More studies are needed to optimize the management of MHE patients with ankle malalignment. Earlier valgus correction and possible addition of fibular lengthening to simultaneously address mortise widening may need to be considered to prevent early ankle arthritis.