Painful stress reaction in the posterior subtalar joint after resection of os trigonum or posterior talar process.

Introduction: The resection of os trigonum or posterior talar process as treatment for posterior ankle impingement is an established operation. However, the authors encountered several painful stress reactions in the posterior subtalar joint during follow-up resulting in persisting incapacity to do sports.

Methods: From March 2011 to July 2015, 29 patients with 30 feet were operated (22 endoscopic, 8 open resections). Average follow-up time was 43 ± 13 months. Complications were grouped into "none", "temporary disadvantage" and "permanent damage". The following radiographic parameters were measured: (1) length of posterior talar process or os trigonum, (2) length of the uncovered calcaneal joint surface after resection, (3) amount of resection.

Results: The rate of permanent damage was 13.3% (4 of 30 feet), and all four of these patients developed a painful stress reaction in the posterior subtalar joint. One temporary disadvantage (persistent pain for three months) was found. All patients with major complications showed retrospectively what we call the "risk configuration" -the radius of the talus ending within the subtalar joint. The length of the uncovered calcaneal joint surface was therefore significantly larger (6.4 mm ± 3.33) in feet with permanent damage than in feet without (1.06 mm ± 2.15, P < 0.001).

Conclusion: The resection of os trigonum or posterior talar process has a complication rate of 13.3% with persisting inability to do sports due to painful stress reaction in the posterior subtalar joint. The only risk factor found was the "risk configuration". In such cases, the resection has to be made not anterior into the subtalar joint and patients have to be informed about this possible complication.

Study Design: Retrospective case series; Evidence Level 4.