Achilles Tendon Reconstruction With Flexor Hallucis Longus Transfer Augmentation

Symptomatic Achilles tendon disease (signal change on magnetic resonance imaging [MRI] within the tendon) or Achilles rupture in older individuals in whom end-to-end repair would lead to excessive tightness

Examination of the Achilles tendon will often demonstrate pain and enlargement of the tendon itself or swelling around the tendon

• There is often an associated tightness of the gastrocnemius-Achilles complex. In the case of a rupture in an older patient (>38 years old), examination of the contralateral leg will often reveal similar tightness.

Radiographs

• A lateral view (in either a foot or ankle series) may show a proximal projection of bone at the insertion of the Achilles onto the tuberosity. It may also show calcification within the tendon or in the soft tissues posterior to the ankle area (synovial sarcoma). There may also be plantar tuberosity spurs, further indicating long-standing equinus contracture (calf tightness).

• There may also be a foot deformity (cavus or planus) with an associated Achilles equinus contracture.

MRI

• MRI may demonstrate tendinous degeneration by signal enhancement in the interior of the tendon. Inflammation of the tendon may be demonstrated on the T ₂ -weighted or short tau inversion recovery images. T ₁ -weighted images will demonstrate calcification or bone formation within the substance of the tendon.

• MRI will demonstrate the extent of the tendon degeneration proximal and distal to the rupture. While axial images are helpful, sagittal reconstructions are best to evaluate the tendon.

The gastrocnemius-soleus complex originates both above and below the knee ( Fig. 75.1 ).

• The gastrocnemius muscles originate behind the femoral condyles. The soleus originates from the upper third of the tibia, fibula, and interosseous membrane.

• They join to form the Achilles tendon, which inserts on the tuber of the calcaneus. The tendon is approximately 15 cm in length. It sends an aponeurosis around the tuberosity to the plantar aspect of the tuberosity, where it helps form the plantar ligaments.

  • Rerupture rate 1.4–3.7%

The Achilles tendon lies directly posterior in the leg. The overlying skin and subcutaneous layer is very thin and prone to break down if injudicious dissection is done.

The sural nerve passes superficial to the deep fascia of the posterolateral leg and onto the dorsolateral foot. The sural nerve runs lateral and anterior to the Achilles tendon at the level of the ankle joint (see Fig. 75.1A ).

A straight medial approach allows for preservation of the subcutaneous blood supply (helping to avoid wound breakdown) and access to both the Achilles (and the degenerative portion) as well as the FHL muscle belly and tendon.

To expose the FHL, dissection is carried through the deep fascia layer, at which point the neurovascular (NV) bundle sits just medial to the FHL.

In the foot, the FHL tendon is found just deep to the flexor digitorum longus (FDL) tendon at the master knot of Henry, plantar medially in the midfoot ( Fig. 75.2 ). These tendons also sit next to the NV bundle as they head distally into the forefoot. When the tendon is released at the master knot, care must be taken to avoid the NV bundle in the foot.

The patient is positioned supine with a large bump under the contralateral buttock.

A thigh tourniquet is applied but not inflated, if possible.

Medial longitudinal incision—first incision

• This incision is made just anterior to the anterior border of the Achilles profile and is carried from the midportion of the tuberosity superiorly approximately 20 cm ( Fig. 75.3 ). The incision is carried down through soft tissue in one step to maintain one thick layer from the skin through the paratenon. There is no subcutaneous dissection as this leads to wound problems.

  

• Once the Achilles tendon is encountered, the tendon can be examined. The tendon should be débrided anteriorly. As the central portion of the tendon is seen, a degenerative yellow area can be débrided. This area is not normal collagen and should be excised. If the extent of the degenerative area requires it, full removal of the tendon may be necessary.

• The fascia lies just anterior to the Achilles. The fascia is incised, exposing the underlying FHL muscle belly. The NV bundle is just superior/anterior to this, so care must be taken to avoid injury to it with a retractor.

• The FHL muscle belly is followed distally until the FHL tendon is seen (behind the talus; Fig. 75.4 ).

  

Medial utility incision—second incision

• A second incision is made to expose the master knot of Henry and the FHL tendon distally.

  • A second incision allows for increased length of tendon harvest (increase of about 3 cm [8.09 cm vs 5.16 cm])

• The incision starts 1 cm inferior to the medial malleolus ( Fig. 75.5 ). The incision is then carried distally over the prominence of the navicular and in line with the medial prominence of the first metatarsal. The distal extent of the incision is usually to the middle of the first metatarsal.

  

• The incision is deepened proximally, and the FDL tendon is identified behind the posterior tibialis tendon.