Treatment of the Stage 4 Flatfoot

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

Long-standing arch collapse can lead to valgus tilting of the talus in the mortise, with deltoid ligament attenuation and degenerative arthritis of the ankle. Pain is often severe, and surgery will best restore function. Traditional treatment of advanced valgus ankle arthritis has been realignment and fusion of the ankle and hindfoot, but the resulting stiffness is not ideal. Realignment and arthrodesis of the hindfoot, combined with total ankle arthroplasty, represents a newer surgical option that offers the promise of better outcomes.

IMPORTANT POINTS:

1

The deformity includes dorsilateral peritalar subluxation of the hindfoot, with valgus collapse of the ankle.
2

Nonoperative treatment focuses on accommodative braces and foot wear.
3

Combined ankle and hindfoot arthrodesis require meticulous attention to restoring normal alignment.
4

Hindfoot realignment combined with total ankle arthroplasty is technically challenging, with recurrent valus tilting of the talus if perfect balance is not achieved.

SURGICAL PEARLS/PITFALLS

1

The Achilles’ tendon usually needs lengthening.
2

When realigning the hindfoot, a posterior ankle capsulotomy may be needed to dorsiflex the talus.
3

After the hindfoot is realigned, the forefoot may be supinated; plantarflexing fusion of the medial column (first metatarsal base) may be needed to get the forefoot straight.
4

It is essential to get the foot perfectly balanced under the ankle when performing total ankle arthroplasty. Occasionally, a medial sliding calcaneal osteotomy may be needed.
5

Tension in the deltoid ligament is restored with distraction during arthroplasty. An incompetent deltoid ligament is probably a contraindication to ankle arthroplasty.

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HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

Posterior tibial tendon dysfunction or insufficiency is generally regarded as the most common cause of the adult acquired flatfoot. When the posterior tibial tendon fails to lock the transverse tarsal joints in inversion before heel rise during gait, the static supports (ligaments) of the longitudinal arch become attenuated, resulting in dorsilateral peritalar subluxation. Collapse of the longitudinal arch results, along with hindfoot valgus and forefoot abduction. Over time, valgus foot alignment alters loads through the tibiotalar joint. Lateral ankle subchondral sclerosis and cartilage erosion follows. In severe cases, the deltoid is overstressed, and deltoid incompetence leads to valgus tilting of the talus in the ankle mortise ( Fig. 31-1 ).

Although some have proposed that primary, degenerative failure of the posterior tibial tendon is the underlying cause of the disease, others have cited a congenital or acquired contracture of the gastrocnemius. Such a contracture leads to failure of the arch, with secondary posterior tibial tendon fatigue. In either model, progressive weight-bearing forces lead to progressive deformity, first in the hindfoot and eventually in the ankle. A staging system has been developed for this process, in order to facilitate diagnosis and treatment ( Box 31-1 ). At present, there is little evidence that a foot progresses from one stage to the next. It remains possible that the stage 4 foot is a result of a different process than the stage 2 foot.

Box 31-1

Stage 1—Posterior tibial tendon inflammation with no deformity
Stage 2—Flexible deformity (passively can be reduced to normal alignment)
Stage 3—Rigid flatfoot, usually with degenerative changes in hindfoot
Stage 4—Rigid, arthritic hindfoot with valgus ankle collapse

Clinical Staging of Adult Acquired Flatfoot/Posterior Tibial Tendon Dysfunction

Regardless of etiology, there are some constant features of the stage 4 flatfoot. Dorsilateral peritalar subluxation of the foot usually includes deformity at the subtalar and talonavicular joints. There may be medial naviculocuneiform sag or first tarsometatarsal dorsal subluxation. There is valgus tilting of the talus in the mortise. Most or all of these joints are arthritic. The ligaments of the arch and the deltoid ligament of the ankle are attenuated or ruptured. The posterior tibial tendon is also attenuated or ruptured, and the Achilles tendon is contracted.

Symptoms vary but are often severe. If a patient has peripheral neuropathy of any cause, pain may not be present, but deformity may lead to difficulties with shoe fitting. Calluses or ulcers will appear over the medial malleolus, the medial talar head, or the navicular tuberosity.

In early posterior tibial tendon insufficiency, pain is often along the tendon itself, due to tendon inflammation. In the stage 4 foot, the tendon may have ruptured months or years earlier. In these patients pain is often related to arthritic degeneration of the ankle and hindfoot. Pain may also arise from osseus impingment between lateral process of the talus and the anterior process of the calcaneus, or between the calcaneus and the distal fibula. Pain may also arise from fatigue or other ill-defined factors.

INDICATIONS

The indications for treating a patient with stage 4 flatfoot are either pain or deformity. Most patients presenting to an orthopedist with the advanced flatfoot will have severe pain. Occasionally, patients with diabetes or rheumatoid arthritis will have severe deformity with very little pain because of neuropathy and a low activity level. But these patients are at a high risk for ulceration in routine shoes or slippers. Ulceration could lead to infection, which in turn could result in the need for an amputation, with high morbidity. All patients with an advanced flatfoot require some form of treatment.

Initial non-operative treatment is possible for those with little pain, or for those with poor distal circulation that is not reconstructable by a vascular specialist. A soft, accommodative custom orthotic is combined with an orthopedic shoe to spread weight-bearing forces evenly over the deformed foot. Severe deformities may need a custom shoe. The orthotic may be a simple foot orthosis or a bulkier ankle-foot orthosis, but in all cases the goal is to accommodate deformity, not to correct it.

The indications for surgery include pain, disability, and a foot that is not braceable or “shoeable.” There are several surgical options. The traditional treatment has been combined ankle and hindfoot arthrodesis. In other patients with ankle arthritis (such as with posttraumatic arthritis), an isolated ankle fusion is a useful procedure because the remaining hindfoot joints provide some mobility for the foot, so the perceived stiffness is not too bad. In the stage 4 flatfoot, those hindfoot joints are diseased, and a combined ankle and hindfoot fusion (pantalar fusion) is much less gratifying for the patient. In simplest terms, pantalar fusion takes a foot that is crooked, stiff, and painful and converts it into a foot that is straight, stiff, and less painful. It is however much easier to find comfortable shoes once the alignment is corrected.

In recent years, there has been increased interest in total ankle arthroplasty. An ankle fusion predictably leads to adjacent joint arthritis in long-term follow-up, arthroplasty may be better able to protect those joints. But ankle arthroplasty has a higher short-term reoperation rate and questionable long-term durability. And despite the theoretical benefits, it is not clear if an ankle arthroplasty is any better than an isolated ankle fusion in the patient with good hindfoot joints. But in those patients with pantalar arthritis, in whom a pantalar fusion is not very great, ankle arthroplasty stands to offer the most benefits.

There are several relative contraindications to ankle arthroplasty. It is generally a poor idea in a patient with severe (Charçot) neuropathy, as in any other joint. A history of previous ankle infection is also of concern, although not necessarily an absolute contraindication. Because there is a long period of convalescence, patients who are unable or unwilling to remain non–weight-bearing are poor candidates for either arthroplasty or arthrodesis.

Although rarely used, amputation remains an option for the stage 4 flatfoot. Both ankle disarticulation and trans-tibial amputation are viable choices. However, because patients with stage 4 disease are often older, less active, and less fit, their ultimate functional result with an amputation will not be as good as the younger patient. In practice, amputation is a rare choice.

SURGICAL TECHNIQUE

Preoperative Assessment

In addition to the usual medical history, physical examination, and weight-bearing radiographs of the feet and ankles, there are several factors that must be emphasized. The tightness of the Achilles should be specifically assessed, although it may be difficult to get a good assessment because the foot may be rigidly fixed in valgus. In general, the Achilles tendon, especially the gastrocnemius, is contracted.

The competence of the deltoid ligament should be assessed. Manual palpation of the ligament gives some idea, but this is difficult to determine with any certainty. A weight-bearing mortise radiograph showing medial tilting of the talus strongly suggests deltoid failure.

The other foot should be examined carefully. Often, the “good” foot is beginning to suffer the same deformity. Perhaps the most useful thing a physician can do for this patient is protect the “good” foot. In some cases, supportive orthotics may alter disease progression. Gastrocnemius lengthening, perhaps performed simultaneously with opposite foot reconstruction, may minimize deforming forces on the “good” foot.

Combined Ankle and Hindfoot Arthrodesis

When considering multiple joint fusion, it is essential to obtain precise limb alignment so that weight-bearing forces are distributed evenly and appropriately throughout the foot. Limb alignment includes static factors, such as the positions of bones and joints, and dynamic factors, mainly muscle balance. With a combined fusion, the lack of hindfoot motion will prevent the foot from compensating at all for any imbalance.

The deformity of the stage 4 flatfoot includes valgus in the ankle and valgus at the subtalar joint. Most of these feet will also have dorsilateral subluxation at the talonavicular joint. There may also be sagging at the medial naviculocuneiform or dorsal subluxation at the first metatarsocuneiform joint. Although the goal of surgery should be to fuse as few joints as possible, it is imperative to correct deformity and relieve pain from severely degenerative joints. The fusion will most commonly need to include the ankle, subtalar, and talonavicular joint. The calcaneocuboid, naviculocuneiform, and metatarsocuneiform joints may need to be included if they are a significant cause of deformity or pain.

The first step of the procedure is to expose affected joints and restore normal alignment. Next, the joints are prepared for fusion by removing granulation tissue or remaining cartilage. Fixation is then placed, and bone graft is added. Muscle balancing is performed when needed; most commonly, this requires Achilles tendon lengthening.

The patient is positioned supine with a bump under the ipsilateral hip (although the surgery can be done in the lateral or prone positions with other approaches). A tourniquet is placed on the proximal thigh, and the iliac crest can be draped for bone graft harvesting if desired. A lateral trans-fibular approach provides access to the ankle and subtalar joints. A longitudinal skin incision begins several centimeters above the ankle and extends distally and anteriorly past the tip of the fibula. An oblique osteotomy of the fibula above the ankle plafond is made, and the anterior soft tissues, including syndesmotic and lateral ankle ligaments, are transected. The fibula is rotated posteriorly on the intact posterior soft tissues.

Usually a short segment of fibula is excised at the osteotomy to facilitate later reduction, and a thin bit of medial fibular cortex is removed with the saw to facilitate fusion of the fibula to the tibia and talus.

The osteotomy provides excellent exposure to the ankle and subtalar joint, which are now prepared for fusion. Any remaining cartilage or granulation tissue is removed, leaving exposed subchondral bone. Subchondral bone is perforated with a small bur or a 2-mm drill. In the ankle, the lateral plafond will be more eroded than medially. It may be necessary to add a small structural graft to the lateral plafond, which can be done by harvesting a segment of fibula. It is imperative to restore normal tibiotalar alignment in the coronal plane. In the sagittal plane, the talus should be in neutral plantarflexion/dorsiflexion.

Anterior subluxation of the talus often occurs with other forms of ankle arthritis, but less commonly in the stage 4 foot. In any case, the talus needs to be shifted posteriorly in relation to the tibia to shorten the length of the foot. A long foot will increase the stresses on any remaining midfoot joints.

If needed, the incision is extended longitudinally along the lateral foot to reach the calcaneocuboid joint and the lateral third of the talonavicular joint.

A medial incision between the anterior and posterior tibial tendons provides access to the talonavicular joint. The joint curves around the talar head, and the bone is often soft here, so gentle preparation with curved osteotomes is helpful. Only the medial two thirds of the talonavicular joint can be reached this way, so the lateral third is prepared from the lateral incision. Failure to fully prepare this joint for fusion will increase the chance for nonunion.

As the subtalar and talonavicular joints are prepared for fusion, the capsules will be disrupted. This allows restoration of normal alignment, so the foot can be brought back under the talus. The heel will sit in slight valgus when the leg is viewed from behind. The talar head will be covered by the navicular. In advanced deformity, the talus becomes quite plantarflexed; a posterior ankle capsulotomy may be needed to restore alignment.

At this point, provisional fixation with 2-mm wires will hold the alignment while the surgeon confirms proper positioning has been achieved. In most cases, internal fixation is best achieved with 6.5-mm lag screws. The first screw passes through a small incision from the posterolateral distal tibia into the talar neck and head, effectively pulling the talus posteriorly. A screw can be passed from the calcaneal tuberosity into the talus and anterior tibial cortex. Another screw can pass from the calcaneal tuberosity into the talar neck, and it is possible to place a screw directly up from the calcaneal body, across the talus, into the distal tibial metaphysis. For the talonavicular joint, 3.5-mm or larger screws are usually placed medially from the navicular back into the talus. A screw can stabilize the calcaneocuboid joint when placed from the anterior process of the calcaneus into the cuboid.

The end goal is to have two (or more) rigid screws holding each joint. Although it is easy to spend a lot of time and effort in placing internal fixation, it is important to remember that it is more important to restore alignment and properly prepare the joints for fusion ( Fig. 31-2 ).