Single-Incision Medial Approach for Triple Arthrodesis

Severe rigid planovalgus foot deformity may be a result of multiple underlying causes.

In long-standing rigid hindfoot valgus deformities, the lateral skin and soft tissues may become severely contracted. In these cases, adequate correction of a severe valgus deformity may stretch and compromise the lateral soft tissues if a standard two-incision approach is used for triple arthrodesis.

Previous surgical incisions, soft tissue injuries, or infections may further compromise wound healing if a lateral incision is used.

A single-medial-approach triple arthrodesis technique offers adequate exposure of the subtalar, talonavicular, and calcaneocuboid joints for preparation without putting the lateral skin at risk.

ANATOMY

The posterior and middle facets of the subtalar joint lie directly deep to the excised posterior tibial tendon (FIG 1).

The flexor digitorum longus tendon and the posterior tibial neurovascular bundle lie just posterior and plantar to the subtalar joint. These must be protected with a retractor during joint preparation.

The talonavicular joint is easily accessible through the extensile medial approach.

The calcaneocuboid joint is directly lateral to the talonavicular joint across the foot. It can be adequately accessed through the extensile medial incision after the talonavicular joint is distracted with a lamina spreader (FIG 2).

PATHOGENESIS

The medial longitudinal arch is supported by both static and dynamic anatomic structures.

The static component includes the spring ligament (calcaneonavicular ligament), the plantar fascia, and the long plantar ligament.

The dynamic component includes the posterior tibial tendon.

In the adult acquired flatfoot, the spring ligament, plantar fascia, and long plantar ligament become attenuated and the posterior tibial tendon becomes dysfunctional. It is controversial whether the static or dynamic stabilizers fail first.

In severe flatfoot patients, the peroneal tendons and the laterally shifted Achilles tendon overpower the dysfunctional posterior tibial tendon, forcing the subtalar joint into heel valgus.

The transverse tarsal joints (talonavicular and calcaneocuboid joints) are abducted by the relative overpull of the peroneus brevis, causing lateral subluxation of the talonavicular joint and uncovering of the talar head.

NATURAL HISTORY

Severe hindfoot valgus deformity, if left untreated, may lead to gradual attenuation of the deltoid ligament. Once this occurs, the tibiotalar joint becomes incongruent and tilts into valgus. This will eventually lead to ankle joint arthritis.

The association of severe hindfoot valgus and valgus tilt of the ankle is difficult to treat and generally requires either a pantalar arthrodesis or an ankle arthroplasty with an underlying triple arthrodesis.

In my opinion, it is critical to intervene in these patients with severe hindfoot valgus before the deltoid ligament becomes incompetent in order to preserve the ankle joint.

PATIENT HISTORY AND PHYSICAL FINDINGS

While a single-incision medial triple arthrodesis is feasible in most patients recommended for triple arthrodesis, I favor employing this technique in the most severe cases of hindfoot valgus or in high-risk patients.

Risk factors exist that may predispose to severe pes planovalgus or may put the patient at risk for wound healing complications. Rheumatoid arthritis is a common cause of severe hindfoot valgus. Rheumatoid patients can sometimes present with greater than 30 degrees of valgus through the subtalar joint. Many of these patients will have gross subluxation of the posterior facet of the subtalar joint on radiographs.

Likewise, diabetic patients with Charcot-like subtalar joint subluxation or dislocation may present with severe hindfoot valgus. These patients are at increased risk for wound healing complications, and in my opinion, represent patients in whom a lateral sinus tarsi approach is not advised.

Anyone with a history of previous soft tissue trauma laterally, open wounds, active infection, or recent surgical incisions that may compromise the ability of a lateral sinus tarsi incision to heal may benefit from a single-medial-incision technique.

Examination should include the following:

Standing hindfoot alignment. The examiner should visually inspect the posterior heel alignment with respect to the tibia with the patient standing. Physiologic hindfoot valgus is usually 5 to 7 degrees. Significantly greater valgus may be pathologic. In patients with severe hindfoot valgus greater than 30 degrees, a lateral sinus tarsi incision may be difficult to heal once the heel is reduced.

Subtalar range of motion. The examiner should maximally invert and evert the heel to determine the range of motion with respect to the tibial axis. Normal subtalar range of motion is 5 degrees of eversion and 20 degrees of inversion. Most severe, long-standing pes planovalgus deformities will be rigid. If the hindfoot is flexible, the surgeon may consider osteotomies or lateral column lengthening to correct the malalignment.

Peroneal tendon contracture. With the heel maximally inverted, the examiner should palpate the peroneal tendons to determine how much they are contributing to valgus contracture. If the peroneal tendons are excessively tight, they will need to be released for the heel alignment to be corrected to neutral.

Contracture of the skin overlying the lateral hindfoot. The examiner should visually inspect the lateral skin to see whether it is loose or taut. If the lateral skin is tight before correcting the heel valgus, a sinus tarsi incision will be very difficult to close once the heel is neutral.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Standard weight-bearing radiographs of both the foot and ankle are critical in evaluating severe pes planovalgus deformities. The foot films will determine the amount of subluxation or dislocation of the subtalar and transverse tarsal joints that must be corrected. They can also determine whether there is deformity or bone loss that demands the addition of structural bone grafts.

The ankle radiographs are required to confirm that the severe heel valgus is isolated to the hindfoot. Occasionally, severe valgus hindfoot deformity leads to increasing deltoid ligament incompetence, creating a valgus tilt of the talus within the ankle mortise. Deltoid ligament incompetence and valgus tilt of the ankle may necessitate surgical correction of the ankle as well should hindfoot realignment with triple arthrodesis fail to rebalance the tibiotalar joint (FIG 3).

DIFFERENTIAL DIAGNOSIS

The possible underlying causes of flatfoot in an adult include the following:

Posterior tibial tendon dysfunction

Inflammatory arthritis

Osteoarthritis

Calcaneus fracture

Navicular fracture

Spring ligament rupture

Lisfranc fracture-dislocation

Crush injury

Tarsal coalition

Accessory navicular

Charcot neuroarthropathy

Cerebral palsy

Poliomyelitis

Nerve injury

Long-standing idiopathic flatfoot

NONOPERATIVE MANAGEMENT

In patients with long-standing pes planovalgus feet, the deformity is frequently fixed, meaning that the deformity cannot be actively or passively corrected. Orthotics and braces can only help by supporting the arch, unloading prominences, or immobilizing arthritic joints. Several over-the-counter braces are available commercially that may be effective in immobilizing and supporting the painful flatfoot. The gold standard is a custom-made relatively rigid lace-up ankle brace. In-shoe orthotics for rigid flatfeet should be custom-molded to accommodate the deformity and any prominences.

Nonsteroidal anti-inflammatory medications may be helpful in alleviating arthritic pain or synovitis. Occasionally, a cortisone shot may be beneficial to relieve an acutely painful joint.

SURGICAL MANAGEMENT

Positioning

The patient is positioned supine on the operating table with a small bump beneath the contralateral hip. This places the operative foot nearly parallel to the table, which is critical because all of the exposure and preparation will be performed through the medial incision. A well-padded thigh tourniquet is placed on the proximal thigh.

Approach

An extensile medial incision affords satisfactory exposure to the talonavicular and subtalar joints. With talonavicular joint distraction, the calcaneocuboid joint may also be accessed.