Ankle Mortise Instability in Multiple Hereditary Exostoses

Abstract

Ankle valgus is commonly reported in patients with multiple hereditary exostoses (MHE). We report the characteristics of mortise widening in MHE, its progression over time, and the resultant ankle pain and function at skeletal maturity. Mortise medial space (M), talocrural angle (TC), and tibiotalar angle (TT) measurements were collected on preoperative and last follow-up radiographs. Operative data and complications were recorded. American Orthopaedic Foot and Ankle Society (AOFAS) and short form-36 scores at skeletal maturity were collected. A total of 16 patients (19 ankles) had MHE and mortise widening. Thirteen patients had surgery. Preoperatively, no patient complained of instability. However, 11 ankles (57.9%) were painful and 15 (78.9%) were clinically in valgus. Patients underwent surgery at a mean age of 11.8 ± 2.2 y. Operative interventions included medial distal tibia hemiepiphysiodesis for the majority of patients. There were no statistically significant differences between pre and postoperative M, TC, TT angles. Operative patients showed an improved mean M (5.17 ± 1.17 to 4.63 ± 1.06 mm) and TT (8.71 ± 5.40° to 4.54 ±7.58°), however, neither angle reached normal values. TC representing fibular length-maintained measurements within normal limits (82.2 ± 5.3° to 84.8 ±5.8°). Questionnaires were obtained for 10 (52.6%) ankles. Mean age at questionnaires collection was 19.0 ± 3.6 y. Mean AOFAS score was 74.8 ± 17.6 out of 100. Patients scored 6.5 ± 4.1 out of 10 for alignment, 33.0 ± 6.7 out of 40 for pain, 35.3 ± 9.5 out of 50 for function. All short form-36 scores were above the national mean. Improvement of M and TT angles was modest. TC angle was within normal limits but showed an overall fibular shortening and decreased lateral buttress and potential for talar shift, as reflected in AOFAS score. The underwhelming amount of mortise widening correction achieved may not provide for a stable ankle joint.