Managing Equinus In Patients With Diabetes
If the ankle joint dorsiflexes greater than 90 percent with both the knee extended and flexed, there is no equinus. If the ankle joint dorsiflexes greater than 90 percent with the knee flexed by less than 90 degrees with the knee extended, the result is gastrocnemius equinus. If the ankle dorsiflexion is less than 90 percent with both the knee flexed and extended, then it can either be gastroc-soleus equinus or osseous equinus.
One can determine this by the quality of the end range of motion and with a charger view or dorsiflexion stress lateral ankle X-ray. A soft end range of motion is more likely associated with a gasctroc-soleus equinus, especially if no anterior ankle impingement is present on the X-ray.
The pathologies associated with equinus are numerous and consist of proximal and distal pathologies. The proximal pathologies associated with equinus are numerous and easily overlooked due to the profound distal pathologies that often overshadow these proximal deformities. Lumbar lordosis, hip flexion, knee flexion, genu recurvatum and hamstring contractures have all been attributed to equinus. We will discuss the more obvious distal pathologies that directly result from or have a relationship to equinus with some of the well documented literature.
The study by Aronow and colleagues was one of the first to not only explore the changes on forefoot and rearfoot pressures associated with equinus, but also examined the midfoot changes as well.5 Researchers applied a load to the gastroc-soleus complex and then applied a load to just the gastrocnemius muscle. They subsequently measured the changes in pressures. In the gastroc-soleus group, the rearfoot pressures decreased by 18 percent and the midfoot and forefoot pressures increased by 38 and 59 percent respectively. In the gastrocnemius group, the rearfoot pressures decreased by 16 percent and the midfoot and forefoot pressures increased by 32 and 50 percent respectively.
These numbers were very consistent with other studies on the effect of equinus and forefoot pressure changes.6,7 When researchers removed the loads, the pressures on the forefoot decreased 32 percent and the rearfoot pressures increased 32 percent. These additional findings were similar to those of Mueller and co-workers, who measured the effect of a tendo-Achilles lengthening on pressure changes in the foot.8 In the study by Mueller and colleagues, the forefoot pressures decreased 31 percent and the rearfoot pressures increased by 34 percent.
In 1997, Grant and colleagues examined the effects of diabetes on the Achilles tendon.9 They took Achilles tendon samples from 12 patients with diabetes and five non-diabetic patients with foot pathology undergoing foot surgery. Researchers subsequently examined these specimens under an electron microscope.
The findings showed the patients with diabetes had increased packing density of collagen fibrils, decreases in fibrillar diameter and abnormal fibril morphology.9 The researchers theorized that the cause of these findings is non-enzymatic glycation over many years. In the non-diabetic patients, the fine structure of the Achilles tendon remained normal. These changes in the patients with diabetes lead to extreme shortening of the gastroc-soleal complex.
The effect that this extreme shortening of the Achilles tendon has on the diabetic foot is what Lavery, Armstrong and Boulton examined in their study in 2002.10 They reviewed 1,666 patients with diabetes over two years, placed patients in risk categories and treated them according to risk-based protocols. The authors defined equinus as ankle joint dorsiflexion of less than 0 degrees. Their findings showed the equinus group had peak plantar pressures in the forefoot that were three times higher in the forefoot in comparison to the non-equinus group.