Study design: Case control study.
Objective: To compare posterior tibialis (PT) length between subjects with stage II posterior tibial tendon dysfunction (PTTD) and healthy controls during the stance phase of gait.
Background: The abnormal kinematics demonstrated by subjects with stage II PTTD are presumed to be associated with a lengthened PT musculotendon, but this relationship has not been fully explored.
Methods: Seventeen subjects with stage II PTTD and 10 healthy controls volunteered for this study. Subject-specific foot kinematics were collected using 3-D motion analysis techniques for input into a general model of PT musculotendon length (PTLength). The kinematic inputs included hindfoot eversion/inversion (HF Ev/lnv), forefoot abduction/adduction (FF Ab/Add), forefoot plantar flexion/dorsiflexion (FF Pf/Df), and ankle plantar flexion/dorsiflexion (Ankle Pf/Df). To estimate the change in PTLength from neutral the following model was used: PTLength = 0.401(HF Ev/lnv) + 0,270(FF Ab/Add) + 0.137(FF Pf/Df) + 0.057(Ankle Pf/Df). Positive values indicated lengthening from the subtalar neutral (STN) position, while negative values indicated shortening relative to the STN position. A 2-way analysis of variance (ANOVA) model was used to compare PTLength between groups across the stance phases of walking (loading response, midstance, terminal stance, and preswing). Also, a 2-way ANOVA was used to assess the foot kinematics that contributed to alterations in PTLength. The Short Musculoskeletal Functional Assessment Index and Mobility subscale were used to compare function and mobility.
Results: PTLength was significantly greater (lengthened) relative to the STN position in the PTTD group compared to the control group across all phases of stance, with the greatest between-group difference in PTLength occurring during preswing. The greater PTLength in subjects with PTTD compared to controls was principally attributed to significantly greater HF Ev/lnv during loading response (P = .014) and midstance (P = .015). During terminal stance and preswing, each kinematic input to estimate PTLength contributed to lengthening (main effect, P = .03 and P = .01, respectively). Subjects with PTTD with abnormally greater PTLength reported significantly lower function (P = .04) and mobility (P = .03) compared to subjects with PTTD with normal PTLength during walking.
Conclusions: The greater PTLength, as determined from foot kinematics, suggests that the PT musculotendon is lengthened in subjects with stage II PTTD, compared to healthy controls. The amount of lengthening is not dependent on the phase of gait; however, different foot kinematics contribute to PTLength across the stance phase. Targeting these foot kinematics may limit lengthening of the PT musculotendon. Subjects with excessive PT lengthening experience a decrease in function.