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.24-27 Historically, 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.

The TAL is a popular choice for the lengthening of the Achilles tendon and surgeons have utilized this procedure for the reduction of an equinus deformity for decades.4,30-33 A commonly utilized technique involves triple hemi-sectioning of the Achilles tendon through a percutaneous approach, thereby lengthening both the soleus and gastrocnemius components of the Achilles tendon. Researchers have reported that for each centimeter of lengthening, there is 3 to 12 degrees of increased ankle joint dorsiflexion.34,35 The simplicity of this approach makes this a popular choice.

Does TAL Have Adjunctive Benefits For Chronic, Diabetic Ulcers?
Surgeons have effectively used TAL as an adjunctive procedure for the treatment of chronic nonhealing ulcerations in patients with diabetes. Theoretically, the TAL should decrease the forces on the plantar aspect of the foot. Armstrong, et al., demonstrated this by reporting a significant decrease in forefoot pressures at eight weeks after performing a TAL.36 Various researchers have reported that the healing rate for chronic diabetic ulcerations after a TAL is greater than 90 percent with a low reported risk of recurrence.36-39
Mueller, et al., conducted the most robust study in examining the efficacy of a TAL for the healing of chronic diabetic ulcerations.40 This was a prospective, randomized trial that compared a TAL plus total contact casting (TCC) versus TCC alone. They reported a significant decrease in the rate of recurrence and an increase in the time for recurrence in the TAL group.

Based on the aforementioned evidence and other reported trials, the TAL appears to be an effective adjunctive procedure in healing chronic diabetic ulcerations. The perception is that one should perform TALs routinely as an adjunctive procedure. However, as we explore the literature, it becomes evident that one must conduct a more careful evaluation before performing a TAL.

Potential Complications With TAL: What You Should Know
As I noted previously, the purpose of the TAL is to increase the range of motion at the ankle joint by lengthening the Achilles tendon. A potential complication from this lengthening is overlengthening. Heel ulcerations are a consequence of this overlengthening with reported rates of 13 to 14 percent.39,40 Accordingly, we run the risk of replacing one chronic ulcer with a potentially more devastating problem.

An important addendum to this issue is raised by a study published by Shaw, et al.41 They prospectively evaluated the peak forces experienced in the foot during gait. They examined 181 patients including healthy controls, patients with diabetes, patients with diabetic neuropathy, diabetic neuropathic patients with a history of ulcerations, and patients with Charcot neuropathy. The study authors reported that all diabetic groups displayed increased peak vertical forces in comparison with the healthy controls.

However, these peak vertical forces occurred during heel strike and not at push off in the neuropathic diabetic group. This challenges the notion that patients with diabetic neuropathy are at high risk of ulceration due to increased forces in the plantar forefoot during gait. Furthermore, patients who undergo a TAL may be at an even higher risk of plantar heel ulcerations. Accordingly, the surgeon must conduct careful evaluation of the foot type and structure, including a thorough gait analysis, prior to performing a TAL.

Another potential complication of a TAL is Achilles tendon ruptures. Achilles tendon ruptures reportedly occur 10 percent of the time.39 The percutaneous approach to a TAL is essentially a blind procedure. Therefore, regardless of the deliberation by the surgeon, it is possible to compromise the Achilles tendon completely. Further, due to poor patient education or patient noncompliance, the surgically incised Achilles tendon is at risk for a complete rupture. This will significantly alter gait patterns and potentially cause new ulceration production in the area of the heel or contralateral limb.

It is important to recall the previous discussion about the soft tissue changes that occur in the diabetic Achilles tendon. The Achilles tendon is already compromised and surgery further compromises this tendon. Researchers have demonstrated that the Achilles tendon in the patient with diabetes has an altered healing cascade.42 Indeed, we are surgically incising the Achilles tendon in an already unstable environment.

Also bear in mind that it may be necessary to perform a TAL repeatedly in the future. Recurrence of an equinus deformity should not be a surprise considering that a TAL does not change the intrinsic properties of a diseased Achilles tendon. Repeated surgeries would certainly have an additive deleterious effect on an already damaged Achilles tendon, further compromising this area.

Let us revisit the prospective, randomized paper published by Mueller, et al.40 They report no difference in the number of healed ulcerations or time to healing between the TAL plus TCC group versus the TCC alone group. However, they do report a lower recurrence rate with the TAL group at seven months (15 percent) and at 2.1 years (38 percent) versus the TCC alone group at seven months (59 percent) and at 2.1 years (81 percent). Additionally, the recurrence of an ulcer happened sooner in the TCC alone group.

Interestingly, the authors report that the peak plantar pressures and the peak torque returned to baseline levels at seven months in the TAL group despite the fact that the increase in ankle joint dorsiflexion remained at the immediate postoperative levels. This appears contradictory. Why do the recurrence rates remain relatively low at seven months and 2.1 years in the TAL group despite the fact that the peak plantar pressures reverted to baseline levels? The implication is that an increase in dorsiflexion available at the ankle joint provided by the TAL is not the pivotal predictor of ulcer recurrence.

In Conclusion
An equinus deformity certainly plays a role in the development and chronicity of diabetic wounds. However, the exact mechanism of how this occurs remains unclear at this time. The TAL continues to be a popular adjunctive procedure in the treatment of equinus. There is ample evidence to support its use in this capacity. However, a TAL is not a panacea. Podiatric surgeons may be able to improve overall outcomes as long as they employ this procedure judiciously with careful consideration for the needs of the patient.
 

References:

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