SLR - February 2020 - Jacob M. Jones

Subluxation of the Middle Facet of the Subtalar Joint as a Marker of Peritalar Subluxation in Adult Acquired Flatfoot Deformity: A Case-Control Study

Reference: Netto C, Godoy-Santos A, Saito G, Lintz F, Siegler S, O’Malley M, Deland J, Ellis S. Subluxation of the Middle Facet of the Subtalar Joint as a Marker of Peritalar Subluxation in Adult Acquired Flatfoot Deformity: A Case-Control Study. J Bone Joint Surg Am. 2019 Oct. 101 (20)

Scientific Literature Review

Reviewed By: Jacob M. Jones, DPM
Residency Program: West Penn Hospital – Pittsburgh, PA

Podiatric Relevance: A common condition treated by foot and ankle surgeons is adult acquired flat foot deformity (AAFD). Evaluation of and staging of AAFD is critical in determining treatment options. Peritalar subluxation has been well described in the literature with the utilization of simulated weight-bearing CT or physiological standing, weight-bearing CT in an effort to better understand the extent of the deformity. These studies have evaluated the subluxation of the posterior facet. The purpose of this study was to evaluate middle facet subluxation on weight bearing CT of patients with AAFD compared to a control group of patients without deformity. This evaluation may provide better insight to the extent of such deformities in our patient population.

Methods: This study is a retrospective case control study of 30 patients that underwent weight-bearing CT examinations with a clinical diagnosis of stage II AAFD and 30 control patients without an AAFD diagnosis that were matched to the study group. The CT images were analyzed by two fellowship trained foot and ankle orthopedic surgeons to determine the degree of peritalar subluxation at the middle facet in the coronal-plane images which they reported as percentage of un-coverage.  

Results: In the AAFD group the mean percentage of un-coverage was 45.3 percent with an incongruence angle of 17.3 degrees while the control group had an average percentage of un-coverage of 4.8 percent and incongruence angle of 0.3 degrees. Both of these measurements were found to be statistically significant with a p-value of less than 0.0001 for both. Both of these measurements were also found to be strong, significant predictors for diagnosis of symptomatic stage II AAFD. The study determined that middle facet uncoverage percentage of 17.9 percent had a specificity of 100 percent and a sensitivity of 96.7 percent for symptomatic stage II AAFD. The study also found that an angle of incongruence of 8.4 degrees or greater was diagnostic for symptomatic stage II AAFD with 100 percent specificity and sensitivity.

Conclusions: This study shows a clear correlation between middle facet subluxation and symptomatic stage II AAFD. The study supports the use of weight bearing CT to evaluate AAFD in the symptomatic patient population. While peritalar subluxation has been well described in the literature utilizing subluxation of the posterior facet this is the first study to evaluate subluxation of the middle facet for a predictor of the deformity. Further research into middle facet subluxation may provide us with a better predictor for symptomatic AAFD or early stages of more severe cases of AAFD which will allow us to better treat our patients. 

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