Understanding How The Achilles Tendon Affects Plantar Pressure

Eleanor Wilson, DPM

   Additionally, the aforementioned study by Orendurff, et al., examined peak pressures of the forefoot for a period of time after lengthening of the Achilles and found that the ulcers healed 80 percent of the time. However, after eight months postoperatively, the peak pressure to the plantar forefoot returned.3

   While the ulcers healed, the researchers found that patients had ankle weakness/instability due to the persistence of plantar flexor torque that persisted with gait. They did note that ankle dorsiflexion flexibility continued to improve.3

   In 2005, a group of physical therapists and orthopedists compared the effects of total contact casting and tendo-Achilles lengthening (TAL) for the treatment of diabetic foot ulcers.6

   Total contact casting (TCC) offers another method of treating foot ulcers by distributing plantar pressure more evenly in the foot via offloading of the ulceration and elimination of the pull from the Achilles tendon.

   Researchers concluded that the Achilles lengthening group achieved more healed ulcers and for a longer period of time overall in comparison to the total contact cast group.6 These patients had substantial increases in dorsiflexion (9 to 19 degrees) and a short term reduction in peak plantar pressure of seven months.

   The concentric plantarflexion peak torque decreased by 31 percent following TAL and immobilization, but returned to baseline level after eight months. The study authors suspect this may have the been the result of exercise instructions the patients received.6

Choosing Between A Percutaneous TAL Or A Gastrocnemius Recession

   One can lengthen the Achilles tendon by performing a percutaneous tendo-Achilles lengthening or a gastrocnemius recession.4 The major advantage to the gastroc recession is that the procedure leaves the soleus muscle/tendon intact. This eliminates the risk of over-correction and possible calcaneal gait. There is a recurrence rate of 15 percent for the contracture of the Achilles with gastrocnemius recession. The amount of normal dorsiflexion necessary with gait is 10 degrees past neutral.

   When is a percutaneous tendo-Achilles lengthening preferable? When testing ankle dorsiflexion, if the foot is in equinus with knee flexion and extension, one would opt for the percutaneous procedure. Otherwise, a gastrocnemius recession is indicated if the necessary 10 degrees of dorsiflexion are present with knee flexion.

   There are several disadvantages to lengthening of the Achilles. One disadvantage is substantial weakening of the ankle as evidenced by decreased plantarflexory power that has been anecdotally reported after TAL and immobilization.

   Also be advised that over-lengthening of the tendon can result in a calcaneal gait with possible sequelae of heel ulceration. There is also the possibility of Achilles tendon rupture.

Other Pertinent Considerations With The Achilles Tendon

   When performing a transmetatarsal amputation, the surgeon often needs to address the Achilles tendon as well, since there may be a progressive development of an equinovarus type of deformity. The release of the Achilles tightness will greatly reduce pressure and possible breakdown under the fifth metatarsal.

   Additionally, when it comes to Charcot arthropathy, the Achilles tendon plays a vital role in decreasing stress to the midfoot. In 2002, Armstrong and Lavery studied the Achilles tendon contracture in patients with diabetic neuropathy. They found that increased load to the forefoot with plantarflexion of the heel can result in Charcot arthropathy breakdown.

   The authors theorized this occurs most often in the midfoot since it is where the foot’s superstructure is the weakest. Achilles tendon lengthening can greatly reduce stress to this area.7

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