The Effect of Triceps Surae Contracture Force on Plantar Foot Pressure Distribution

Background: Triceps surae contractures have been associated with foot and ankle pathology. Achilles tendon contractures have been shown to shift plantar foot pressure from the heel to the forefoot. The purpose of this study was to determine whether isolated gastrocnemius contractures had similar effects and to assess the effects of gastrocnemius or soleus contracture on midfoot plantar pressure. Methods: Ten fresh frozen cadaver below-knee specimens were loaded to 79 pounds (350N) plantar force with the foot unconstrained on a 10-degree dorsiflexed plate. Combinations of static gastrocnemius or soleus forces were applied in 3-lb increments and plantar pressure recordings were obtained for the hindfoot, midfoot, and forefoot regions. Results: The percentage of plantar force borne by the forefoot and midfoot increased with triceps surae force, while that borne by the hindfoot decreased (p ≤ 0.005). Increasing gastrocnemius force had similar results. Increasing triceps surae force from 0 to 21 lbs (93 N) increased average percent forefoot and midfoot force 59% and 38%, respectively, and reduced average percent hindfoot force 18%. Increasing gastrocnemius force from 0 to 18 lbs increased average percent forefoot and midfoot force 50% and 32%, respectively, and reduced average percent hindfoot force 16%. For a given triceps surae force, there was no statistical difference in pressure distribution noted between different combinations of gastrocnemius and soleus force. Conclusions: In a static model, increased triceps surae or isolated gastrocnemius force shifted weightbearing plantar pressure from the hindfoot to the midfoot and forefoot. Similar results were noted whether the triceps surae force was applied through the gastrocnemius or soleus or both. The results of this study are consistent with the clinical association of triceps surae contracture with foot and ankle disorders including diabetic foot ulcers and metatarsalgia. The similar effects with triceps surae force application through the gastrocnemius or soleus suggest that patients with isolated gastrocnemius contractures may obtain similar clinical benefits with potentially less morbidity after gastrocnemius aponeurosis lengthening as compared to Achilles tendon lengthening.