Posterior Ankle Arthroscopy: is there a Difference in Outcome between os Trigonum and Stieda Process Resection?

The etiology of posterior ankle impingement often involves either the presence of a symptomatic os trigonum or a hypertrophic posterior talar process, the so called Stieda process. Whereas an os trigonum can be removed arhthroscopically en bloc, the posterior talar process requires bony resection. We questioned whether this difference would influence the clinical outcome in a patient cohort.
Fifteen patients were operated with a posterior ankle arthroscopy for either os trigonum (Group A) or Stieda process (Group B) impingement. Two patients had bilateral involvement and were operated in both feet in two stages (a total of 17 operated feet). There were 9 patients in Group A and 6 in Group B. Patients were evaluated preoperatively and at 6 and 12 months follow up according to the AOFAS and Foot Function Index (FFI) scores.
Both groups showed significant improvement in both scores at 6 and 12 months follow up. Mean AOFAS score was 60 preoperatively, 78 at 6 months (p=0.021) and 86 at 12 months (p = 0.004). Mean FFI score was 112 preoperatively, 44 at 6 months (p=0.003), and 30 at 12 months (p=0.001) Patients continued to improve from 6 to 12 months follow up according to both AOFAS (p=0.008) and FFI (p=0.0029) scores.
Group A had a better outcome compared to Group B in both AOFAS (6 months: mean=81 vs 72, 12 months: mean 90 vs 79) and FFI (6 months: mean= 32 vs 67, 12 months: mean=16 vs 69) scores. These differences trended towards but did not reach statistical significance.
Posterior ankle arthroscopy outcome improves from 6 to 12 months postoperatively. Patients with an os trigonum impingement may have a better outcome compared to those with a posterior Stieda process.