Tendon Morphology in Stage II Tibialis Posterior Tendon Dysfunction Is Associated with a Clinical Measure of Deep Posterior Compartment Strength

Abstract

Category: Ankle Introduction/Purpose: Tibialis Posterior Tendon Dysfunction (TPTD) is thought to be a primary cause of acquired flatfoot and a result of tendon degeneration. High-frequency ultrasound has been used to measure the morphological changes associated with tendon degeneration while clinical measures of foot deformity and strength are used to identify and stage the condition. However, limited data on tendon morphology in subjects with TPTD are available to guide clinical decision making. It was hypothesized that within a group of subjects with Stage II TPTD there would be large differences in tendon cross-sectional area and these differences would be associated with clinical measures of strength. Findings from this study could be used to guide clinical examination and refine future classification schemes. Methods: Thirty-four participants (Age x?x; Sex X Female) diagnosed with unilateral stage II TPTD were included. Measures of tendon cross-sectional area were captured at the level of the medial malleolus using a Sonosite M-Turbo ultrasound unit with a 6-MHz to 13-MHz 45-mm linear transducer (Sonosite Inc. Bothell, WA). Measures of tendon cross-sectional area were completed using ImageJ software. Subjects involved and uninvolved sides were compared for both tendon area and deep posterior compartment strength. Strength was measured using a custom strength testing device to measure plantar-flexion and inversion strength of the deep posterior compartment. All subjects completed self-report measures of function (Foot and Ankle Ability Measure (FAAM)) and self-reported pain on a numerical rating scale. Group comparisons were made with a one-way ANONA comparing groups with an alpha level maintained at 0.05. Results: Tibialis Posterior Tendon cross sectional area for the group of 34 subjects averaged 31.9% larger on the involved compared to the uninvolved side consistent with signs of degeneration. However, values ranged from 110% larger on the involved side to 43% smaller on the involved side across the group. Due to the observed variance, the group was divided into an enlarged tendon group (n=16) and an average size group (n=18). The enlarged group had an average tendon cross-sectional area of 62.6%(22.2%) larger on the involved side while the average size group averaged 2.9%(22.2%) (p<0.001). Comparing the deep posterior compartment strength between groups, the enlarged group was 34.6%(32.7%) weaker on the involved side while the average tendon area group was 11.4%(34.4%) weaker on the involved side (p=0.04). Conclusion: Tendon cross sectional area varies widely despite a classification of stage II TPTD and self-report of similar pain and function across patients. Subjects tested who had greater tendon cross-sectional area, indicating more degeneration, also demonstrate greater weakness. No differences in self-reported pain, leg strength, or function were found between groups. Deep posterior compartment weakness and tendon morphology may help to inform classification systems and predict outcomes for subjects with TPTD.