Lower-Lying Flexor Hallucis Longus Is Associated With Advancing to Surgery in Pediatric and Adolescent Os Trigonum Syndrome

BACKGROUND: The os trigonum (OT), or Stieda process, is an accessory bone or osseous elongation at the posterolateral process of the talus. OT is one of the sources of posterior ankle impingement and pain (os trigonum syndrome), often in conjunction with the adjacent flexor hallucis longus (FHL) muscle belly. Local anesthetic injection and surgical excision are common treatments for this pathology. HYPOTHESIS/PURPOSE: We describe early pain relief among pediatric patients at a single university-affiliated hospital undergoing OT injection. We also evaluate risk factors for progression to surgery and the role that OT injection plays in that decision-making. STUDY DESIGN: Cross-sectional study. METHODS: A retrospective review of patients treated for OT syndrome over a 10-year period at a single, tertiary care pediatric hospital was performed. We collected demographics, magnetic resonance imaging (MRI) details, relative FHL location on MRI, treatment details, and symptom relief following injection. Bivariate statistical analysis using Wilcoxon Mann-Whitney, Kruskal-Wallis, ANOVA, χ2, Fisher, and T tests was performed, along with univariate logistic regression. RESULTS: Sixty patients (49 female, mean age 14.7±2.4 y) yielded 65 ankles included for analysis. All patients underwent a trial of conservative management. 31/65 (47.7%) did not complain of further symptoms, while the remaining 34/65 (52.3%) progressed to injection and/or surgical intervention. 25/65 (38.5%) underwent lidocaine injection, and 21/65 (32.3%) underwent surgical excision of OT. Early patient-reported postinjection symptom relief (median, IQR: 80.0%, 65.0% to 100.0%) was not associated with patient age, sex, performance athlete status, FHL location or size, OT location or size, nor whether steroid was injected with the lidocaine (P>0.05). Progression to surgery was unrelated to early relief from injection (P>0.05). Odds of progression to surgery were increased with FHL musculotendinous junction distance (P=0.005, OR=1.19) and relative musculotendinous junction distance (P=0.012, OR=10.48). CONCLUSION: The relative location and distal extension of the FHL muscle belly may be a risk factor for failure of nonoperative management and progression to surgical intervention in the pediatric and adolescent patient.