O2109: Indications for Relief after Lidocaine Injections and Advancement to Surgery for Pediatric Os Trigonum Syndrome

Background: Os trigonum (OT) syndrome involves an accessory bone at the posterior talus crowding the tarsal tunnel and has been frequently described in dancers. When achieving a position of extreme plantarflexion, an OT can cause a painful impingement of the posterior ankle. A low-lying flexor hallucis longus (FHL) muscle belly is thought to aggravate symptoms of posterior ankle impingement. Previous research has shown that local anesthetic injection is often used as a diagnostic measure as well as initial intervention, with >80% immediate symptom resolution. Surgical excision of an OT also results in excellent symptom resolution. We aimed to describe short-term pain relief of pediatric patients undergoing an injection of the OT and evaluate the relationship between several patient factors and progression to surgery.

Methods: Retrospective review at one institution was conducted of patients with diagnosis codes for OT syndrome between 2014 and 2023. We collected demographics, treatment details, post-injection symptom relief, and radiographic measurements: regional maturity (distal tibial physeal status), musculotendinous junction (MTJ) distance from end of tibia to end of FHL muscle belly, relative MTJ- ratio of MTJ distance to the distance from tibia to tarsal tunnel, axial area of the FHL muscle belly or tendon at the midpoint of the OT, and volume of the OT. The volume of OT was calculated by multiplying the OT length on the axial slice by the OT area on the sagittal slice. Injections and surgeries were performed by one pediatric sports medicine specialist and two orthopaedic surgeons.

Results: 76 patients (59 female) with OT syndrome of mean age 13.9 ± 2.5 years were enrolled. 24 patients (26 ankles) underwent injections for OT syndrome. 17 patients (18 ankles) underwent surgical removal of their OT. Advancement to surgery is significantly related to FHL MTJ distance (p < 0.01), relative FHL MTJ distance (p < 0.01), the relative position of the OT against the talus (p=0.02), FHL muscle belly presence at the midpoint of the OT (p < 0.01), distal tibial physeal status (p < 0.01), gender (p < 0.01), and whether the patient is a performance athlete (p < 0.01) (Table 1). None of these factors are significantly related to immediate post-injection symptom relief. The odds of advancement to surgery is significantly affected by FHL MTJ distance and relative FHL MTJ distance (p=0.009 OR=1.02, p=0.008 OR=1.13), but not by the initial level of relief from injection (p=0.453).

Conclusion: Our results suggest that a more distal FHL muscle belly, a more inferior OT, gender, and being a performance athlete are each related to progression to surgery for symptomatic OT. Initial level of relief from local injection does not predict likelihood of advancing to surgery. Clinicians may consider these patient factors when discussing treatment plans for pediatric patients with OT syndrome.