Tendo-Achilles Lengthening: Friend Or Foe In The Diabetic Foot?
While various researchers have implicated the equinus deformity as a major deforming force in a host of foot and ankle pathologies, the exact definition of equinus remains unclear.1-4 However, Root states that “the minimal range of ankle joint dorsiflexion that is necessary for normal locomotion is 10 degrees.”5 Subsequent studies report that the ankle joint range of motion for asymptomatic patients ranges from 0 to 13.1 degrees with the knee extended and from 5 to 22.3 degrees with the knee flexed.6-9
The implication from these studies and other papers is that with a decrease in the range of motion at the ankle joint, it is more likely that pathologies will develop. Although other soft tissue and bony constraints may restrict ankle joint range of motion, the Achilles tendon appears to play the dominant role for this limitation.
Multiple factors are involved in the development of pathologies one sees in the diabetic foot. Some of these factors include neuropathy, ischemia and bony deformity. Soft tissue changes in the diabetic foot are particularly important. For example, there is a decrease in the soft tissue density on the plantar aspect of the diabetic foot, which is less tolerant of stress.10-12 We also know that patients with diabetes have less mobility available in their joints.13
In particular, the Achilles tendon undergoes structural changes. Glycation-induced collagen cross-linking causes general disorganization of the Achilles tendon, which translates to a decrease in elasticity, a decrease in tensile strength and an increase in stiffness.14-17 The changes in the substance of the Achilles tendon may explain the correlation between equinus and diabetes.18
One can indirectly measure equinus through increased peak plantar pressures on the feet of patients with diabetes.19-22 We also know there is a relationship between peak plantar pressure and diabetic ulcerations.19,20,23 Accordingly, the logical conclusion is that an equinus deformity plays a role in the production and chronicity of a diabetic wound due to these increased forces.
Should You Opt For TAL Or A Gastrocnemius Recession?
The tendo-Achilles lengthening (TAL) or a gastrocnemius recession can decrease the pathological forces due to an equinus deformity. While it is outside the scope of this column to discuss in detail the surgical techniques involved in the two types of procedures, there are some important points to consider.
The gastrocnemius recession involves the transection of the gastrocnemius aponeurosis.24-27Historically, surgeons have chosen the gastrocnemius recession over a TAL based on the Silfverskiold test.28 This examination essentially eliminates the influence of the gastrocnemius portion of the Achilles tendon by flexion at the knee. Accordingly, one can assess which component of the Achilles tendon is responsible for the equinus deformity.
The gastrocnemius recession reportedly increases ankle joint range of motion by 18.1 degrees.29 The advantages of a gastrocnemius recession include a decreased potential for an Achilles tendon rupture and faster healing due to the robust vascularity in this area.
There are some disadvantages to the gastrocnemius recession as well. This includes the potential for sural nerve entrapment or transection. This is also a relatively more technically demanding procedure in comparison to a TAL. Finally, the degree of correction may be limited with this approach.