Tarsal Coalition

Abstract

Regardless of the type of tarsal coalition present, once the condition becomes symptomatic, it rarely resolves with nonoperative care. Traditional management has been with immobilization of the foot to decrease symptoms, but the beneficial effects thus obtained usually are not long-lasting. Although this treatment may temporarily decrease the soreness in the foot, the reactive tenderness in the lateral calf musculature, and the generalized lower limb dysfunction and aching, symptoms recur. Rarely therefore do we recommend immobilization of the limb in either a child or an adult for definitive treatment purposes. If marked foot and limb tenderness is present, immobilization can be used initially until definitive surgical plans are put into effect.

Key Words

coalition, subtalar, calcaneonavicular, resection, flatfoot, rigid, ball and socket, arthrodesis

Overview

Regardless of the type of tarsal coalition present, once the condition becomes symptomatic, it rarely resolves with nonoperative care. Traditional management has been with immobilization of the foot to decrease symptoms, but the beneficial effects thus obtained are usually not long lasting. Although this treatment may temporarily decrease the soreness in the foot, the reactive tenderness in the lateral calf musculature and the generalized lower limb dysfunction and aching symptoms recur. Rarely therefore do we recommend immobilization of the limb in either a child or an adult for definitive treatment purposes. If marked foot and limb tenderness is present, immobilization can be used initially until definitive surgical plans are put into effect.

Examination and Decision Making

Tarsal coalition is one condition that the clinician can diagnose standing at the door of the examination room. Typically, when the patient is seated, the foot normally drops into a position of equinovarus. With a rigid hindfoot, the foot is held in valgus; if the deviation is unilateral, it is particularly easy to diagnose. Examination of the foot while the patient is standing, walking, sitting, and lying down is recommended. When a person with a normal foot is sitting, a natural equinovarus posture is present in the foot as it relaxes. This is not the case with a tarsal coalition because the foot is held in a more rigid position of neutral dorsiflexion with slight valgus ( Fig. 24.1 ). The peroneal tendons are often visible because of ongoing contraction, but true peroneal spasm does not occur. The peroneal musculature may be tender and certainly tight as a result of subtalar joint irritation, but true spasticity of the tendons does not occur. The decision for surgery, and for a specific type of surgery, is based on the flexibility of the foot, the presence of arthritis, the type of coalition, and function of the remaining foot. The spectrum of clinical deformity associated with coalition is very broad, and when rigidity is present, marked compensatory changes may be seen in the hindfoot and forefoot ( Fig. 24.2 ).

Arthritis of the foot is rare in a child in association with either a subtalar or calcaneonavicular coalition. The beaking of the talonavicular joint appears naturally as a result of traction on the anterior capsule of the ankle on the neck of the talus and does not in any way imply the presence of arthritis ( Fig. 24.3 ). Arthritis can occur, however, as indicated by the common finding of subtalar arthritis in adults with a middle facet coalition. Early arthritis is caused by previous surgery or may be associated with extreme rigidity, even in the child. An important point in this context is that presence of motion in the hindfoot does not rule out a coalition. Careful examination of the foot will show that most of this motion originates from either the transverse tarsal or the ankle joints. True subtalar motion is not normal and is usually absent, particularly with a middle facet coalition.

It is not easy to examine the hindfoot for true motion when the peroneal tendons are contracting. In patients who have severe stiffness, determination of how much true motion is present in the foot and how much the peroneal muscles are limiting subtalar motion is worthwhile. If the peroneal muscles are tight, we block the peroneal nerve at the fibular neck with a short-acting local anesthetic and then reexamine the foot. After peroneal nerve blockade has been achieved, the foot is frequently much easier to examine, the rigidity of the hindfoot previously noted is no longer present, and the surgery can be planned correctly. A diagnostic blockade of the subtalar joint or the sinus tarsi is not very helpful in these patients, as arthritis is not the primary pathology. Sometimes the coalition is not visible on radiologic evaluation, and, rarely, even with magnetic resonance imaging and computed tomography (CT) scanning, the coalition is difficult to visualize ( Fig. 24.4 ).

It has been stated that “a middle facet coalition in a child can be excised if it involves less than 50%.” We do not agree with this statement, and regardless of the extent of the coalition, we perform a resection of the entire coalition. The outcome with resection of the middle facet coalition depends more on the flexibility and deformity of the remainder of the foot. The problem with a complete coalition is not with the ability to resect it, but with the adaptive changes that have taken place over time in the subtalar joint and the remainder of the foot ( Fig. 24.5 ).

The question, then, is not whether to resect the coalition, but which additional procedures need to be performed to maintain motion and improve function, including calcaneal osteotomy, subtalar arthroereisis, Achilles tendon lengthening, and medial cuneiform osteotomy. The more unusual coalitions, either talonavicular or calcaneocuboid, are also encountered, and not infrequently. These present a unique set of problems, including stiffness of the hindfoot, planovalgus deformity, and a ball-and-socket ankle. The foot is always pronated, the hindfoot is fixed in valgus, and the ankle is in valgus as well.

Resection of a Middle Facet Coalition

As noted earlier, we attempt a resection of a middle facet coalition regardless of the extent noted on the radiograph or CT scan. This decision is based, however, on other factors as well, including the age of the patient, the shape of the foot, the extent of rigidity, and presence of associated deformity of the rest of the foot. An incision is made medially and extends from the undersurface of the medial malleolus distally and beyond the talonavicular joint. The incision is deepened through subcutaneous tissue, veins are cauterized, and the sheath of the flexor digitorum longus (FDL) tendon is opened ( Fig. 24.6 ). This tendon forms the upper boundary of the coalition, and the tendon is retracted dorsally. Inferior to this and under the sustentaculum tali, the sheath of the flexor hallucis longus (FHL) tendon is now carefully opened and identified. The tendon is retracted inferiorly; the FDL and FHL tendons mark the boundaries for dissection of the coalition. Elevation of all of the soft tissue, including a large periosteal flap from the sustentaculum, is useful to adequately visualize the bone to be resected. If necessary, the surgeon can proceed more distally to the talonavicular joint and then work back posteriorly after opening up the joint, but this precaution is usually not necessary.

The sustentaculum is now gradually removed until the scar of the original middle facet is visualized, which is seen slightly more posteriorly. A large, pineapple-shaped burr can be used above the sustentaculum; our preference, however, is to use a combination of a rongeur, curette, and chisel. One way of identifying the location of the anterior aspect of the coalition is to make a lateral puncture in the sinus tarsi and then insert a probe, which is advanced and pushed medially. The exit point of this probe marks the anterior aspect of the coalition. If the probe does not expose the margin of the coalition, we use a cannulated sizer from the arthroereisis screw set, and as this is advanced across the tarsal canal, the coalition opens up quite easily and the margins of posterior facet become more visible. As the bone is gradually debrided, a rongeur is now inserted once fatty tissue is observed on the medial aspect of the sinus tarsi. This point represents the apex of the cone of the tarsal canal. Once this apex can be identified, the rest of the procedure is much easier, because movement of the subtalar joint directs the dissection ( ).

A laminar spreader is inserted into the tarsal canal from the medial side, and then, with gradual distraction, the middle facet and ultimately the posterior facet become visible. Removal of most, if not all, of the middle facet is necessary until the entire posterior facet is visible. Perfect, unrestricted motion of the posterior facet should be present; passive rotatory motion is performed as a visual check. Bone wax is used on the raw cancellous surfaces of the bone to decrease the risk of recurrence.

Excision of the middle facet coalition works well for adolescents. The age limit for excision is not clear, and although we have performed resection in the young adult, the results are less predictable. Certainly, arthrodesis is to be avoided in the younger child, and although an extraarticular arthrodesis may be performed ( Fig. 24.7 ), this is not our preferred procedure. If the foot is extremely rigid, then arthrodesis of the subtalar joint may have to be performed. It is worthwhile to resect the dorsal osteophyte off the neck of the talus simultaneously because this may cause impingement against the deep peroneal nerve and pain.

There is a variant of the medial coalition that does not involve the middle facet, but the medial aspect of the posterior facet. This can be quite confusing on x-ray (XR) and CT, and one should be able to make the diagnosis with a video CT through the posterior facet. The approach to this coalition is similar to that of the middle facet, but one has to open up the posterior facet and remove the coalition. We use a dilator technique as we have described through the sinus tarsi laterally to the medial side of the foot where the guide pin exits between the middle and posterior facets. Once the guide pin has been inserted, a dilator is guided over the pin, and the medial joint distracted open. This then permits good visualization of the coalition that involves a varying amount of the far medial anterior aspect of the posterior facet ( Fig. 24.8 ; ).