The Effect of Stage II Posterior Tibial Tendon Dysfunction on Deep Compartment Muscle Strength: A New Strength Test

Background: The purpose of this study was to compare isometric subtalar inversion and forefoot adduction strength in subjects with Stage II posterior tibial tendon dysfunction (PTTD) to controls. Materials and Methods: Twenty four subjects with Stage II PTTD and fifteen matched controls volunteered for this study. A force transducer (Model SML- 200, Interface, Scottsdale, AZ) was connected with a resistance plate and oscilloscope (TDS 410A, Tektronix, Beaverton, OR) to the foot. Via the oscilloscope, subjects were given feedback on the amount of force produced and muscle activation of the anterior tibialis (AT) muscle. Subjects were instructed to maintain a plantar flexion force while performing a maximal voluntary subtalar inversion and forefoot adduction effort. A two-way ANOVA model with the factors including, side (involved/uninvolved) and group (control/PTTD) was used. Results: The PTTD group on the involved side showed signifi- cantly decreased subtalar inversion and foot adduction strength (0.70 ± 0.24 N/Kg) compared to the uninvolved side (0.94 ± 0.24 N/Kg) and controls (involved side = 0.99 ± 0.24 N/Kg, uninvolved side = 0.97 ± 0.21 N/Kg). The average AT activation was between 11% to 17% for both groups, however, considerable variability in subjects with PTTD. Conclusion: These data confirm a subtalar inversion and forefoot adduction strength deficit by 20% to 30% in subjects with Stage II PTTD. Although isolating the PT muscle is difficult, a test specific to subtalar inversion and forefoot adduction demonstrated the weakness in this population