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INTRODUCTION: Adult acquired flat foot deformity (AAFD) leads to a wide spectrum of deformities in the adult foot and ankle. Spring ligament attenuation or tearing has been implicated in the pathology of AAFD. Treatment as part of a flat foot reconstruction may involve attempts to address spring ligament incompetency, either indirectly through lateral column lengthening or directly through spring ligament repair/reconstruction. When to employ these procedures is controversial. Pre-operative knowledge of the integrity of the spring ligament based on commonly used radiographic measures would be highly valuable for pre-operative planning and decision making for such procedures as part of a flat foot reconstruction. To our knowledge, there has been no attempt to correlate pre-operative radiographs with direct intra-operative evaluation of spring ligament competency.

PURPOSE: The purpose of this study is to perform a retrospective chart review to examine the relationship between pre-operative radiographic measures specific to flat foot deformity and intraoperative competency of the spring ligament during flat foot reconstruction. The goal is to find pre-operative radiographic measures that predict spring ligament attenuation intra-operatively to guide surgical decision making for the addition of procedures to address spring ligament attenuation.

METHODS: The operative reports of 3 fellowship trained orthopaedic foot and ankle surgeons were searched over a 5 year period from 2012-2017. Patients with pre-operative standing AP and lateral radiographs along with an operative report that directly visualized and commented on the integrity of the spring ligament were included in the study. Operative reports were reviewed to identify patients with either an intact or torn spring ligament. Pre-operative radiographs were evaluated and four common radiographic parameters were measured: lateral talar-first metatarsal angle, AP talar-first metatarsal angle, talonavicular coverage angle, and talonavicular coverage percentage. ANOVA and logistic regression analysis were used to evaluate which of the four radiographic parameters were predictors of spring ligament tear.

RESULTS: 58 cases were identified for the study. 29 patients had a confirmed tear intra-operatively, and 29 patients had an intact spring ligament. Increasing values for each of the 4 radiographic measures were statistically significant predictors for spring ligament tear (p=0.001). The lateral talar-first metatarsal angle was the most significant predictor for spring ligament tear (p = 0.001).

DISCUSSION: The results of this study demonstrate the predictive value of 4 different radiographic measurements in predicting the presence or absence of a spring ligament tear. The lateral talar-first metatarsal angle proved to be the best predictor of a spring ligament tear. The study also demonstrated that a lateral talar-first metatarsal angle of greater than 30 degrees is significantly sufficient at predicting a spring ligament tear.

CONCLUSION: This study is the first to correlate pre-operative radiographs with direct visualization and evaluation of spring ligament competency allowing the surgeon to predict spring ligament attenuation and make a pre-operative plan accordingly. It appears that increasing severity of common radiographic measures of flat foot deformity, particularly the lateral talar-first metatarsal angle, correlates significantly with spring ligament disruption observed intra-operatively.

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