Tarsal coalition is a condition in which 2 or more bones in the midfoot or hindfoot are joined. The most common types of coalitions are those between the calcaneus and either the talus or the navicular bones. Patients with this congenital condition usually present during late childhood or adolescence, but presentations in adulthood have been reported. The condition usually presents as recurrent sprains and pain in the midfoot and has been associated with peroneal spastic flatfoot, fixed flatfoot, and other abnormalities of the foot (also see the eMedicine article Acquired Flatfoot and the Medscape article Flat Feet). Radiographic evaluation has been revolutionized by the use of CT scanning. Early treatment usually involves conservative modalities, including immobilization, while surgical intervention includes resection of the coalition or arthrodesis of degenerated painful joints.1,2 History of the Procedure
In 1969, Heiple and Lovejoy demonstrated the antiquity of tarsal coalition in the human gene pool by showing the presence of bilateral talocalcaneal bridging in a pre-Columbian Indian specimen.3 In 1965, Harris also mentioned the existence of the condition in Mayan archeological specimens found in Guatemala.
The earliest known mention of tarsal coalition in the literature was by Buffon in 1796. In 1829, Cruveilhier wrote the first known anatomic description of calcaneonavicular coalition.4 Zuckerkandl first described middle facet talocalcaneal coalition in 1877, while Pfitzner first described the more rare posterior facet talocalcaneal coalition in 1896. Finally, Anderson described talonavicular coalition in 1879, and Holland first described calcaneocuboid coalition. Holl first theorized a relationship between tarsal coalition and peroneal spastic flat foot in 1880.
Slomann first specifically linked calcaneonavicular coalition to peroneal spastic flatfoot in 1921 and theorized that the resection of the bar would be therapeutic. Badgley did the same in 1927 and first demonstrated the surgical technique of resection of the coalition as proper treatment.5 Finally, in 1948, Harris and Beath also linked talocalcaneal coalition to the same clinical problem.6
Kirmission performed the first radiographic demonstration of a tarsal coalition in 1898.7 Slomann, in 1921, demonstrated the usefulness of the lateral radiograph in identifying calcaneonavicular coalitions, while Korvin, in 1934, was the first to describe the special view for talocalcaneal coalition that Harris and Beath later popularized in their paper.6 In 1969, Conway and Cowell reviewed the radiographic characteristics of tarsal coalitions and first proposed the existence of an anterior facet talocalcaneal coalition.8 They also delineated the use of tomography in the evaluation of the different facets of the calcaneus. Goldman et al first suggested the use of bone scintigraphy as a screening tool for tarsal coalitions in 1982. Deutsch et al, in 1982, also evaluated bone scintigraphy along with CT scanning in 3 cases of talocalcaneal coalitions and found that the latter was better at providing detail of the coalition.9
Herzenberg et al, in 1986, attempted to identify the best CT views for evaluation of the different coalitions.10 Wechsler et al evaluated MRI as a viable tool in evaluation of fibrous or incomplete cartilaginous coalitions for which findings on CT scans might be inconclusive.11
Tarsal coalition usually presents as recurrent sprains and pain in the midfoot and has been associated with peroneal spastic flatfoot, fixed flatfoot, and other abnormalities of the foot.
The incidence of talocalcaneal coalitions in the general population is thought by most authors in the literature to be approximately 1%. Various authors have credited Pfitzner with the first incidence study but quote different percentages varying from 1.5-6% for overall incidence of tarsal coalitions to 2.9% for calcaneonavicular coalitions. Harris and Beath found 74 cases in 3600 consecutive prospective army recruits examined.6 Rankin and Baker found 24 cases in approximately 60,000 basic trainees at Fort Dix from 1971-1972 (0.4%),12 while Vaughn and Segal found 28 coalitions in 2000 cases of painful feet.13 Shands and Wentz found an incidence of 0.9% in cases of painful flat feet in a pediatric clinic.14 Leonard found in his survey of relatives of patients with symptomatic coalitions that 39% had asymptomatic coalitions.15 Snyder et al found that 91 of 223 (63%) young patients with ankle sprains had radiographic findings suggestive of tarsal coalitions.16
In an evaluation of 2982 complete skeletons collected from 1910-1940, Cooperman et al found that 26 of them had calcaneonavicular coalitions (incidence of 1.2%).17 Leonard found that all of the 76% of the first-degree relatives who had radiographic evidence of tarsal coalitions were asymptomatic.15 This would suggest that the actual incidence in the population may be higher than previously thought.
In terms of the distribution of types, Stormont and Peterson found in a review of the literature that 48.1% of the tarsal coalitions presented were talocalcaneal and 43.6% were calcaneonavicular. In their own series, the distribution was 53% calcaneonavicular and 37% talocalcaneal. The literature overall mentions a bilaterality rate of 22-60% in talocalcaneal coalitions and 40-68% in calcaneonavicular coalitions, with most being just over 50%.18
Sex ratios vary, with a male-to-female ratio of 1:1 to 4:1. No statistical difference in racial distributions has been found.
Pfitzner first proposed that the coalitions were the result of incorporation of accessory ossicles into the adjacent normal tarsal bones. This theory received some support from various authors, including Slomann, Badgley,5 and Harris and Beath.6 Leboucq first proposed in 1890 that the failure of segmentation of primitive mesenchyme was the cause of tarsal coalitions. His theory was supported by Solger (1890), Dwight (1907), Trolle (1948), and Jack (1954).19
In 1955, Harris found evidence of mesenchymal coalitions in fetal cadavers, conclusively proving Leboucq’s theory. Through the work of Leonard, Wray, Herndon, and others, it is believed today that tarsal coalition is inherited in an autosomal dominant fashion with high penetrance.
The normal motion of the subtalar joint during walking involves both rotation and gliding. The axis of motion of the subtalar joint is defined as a line deviated 42º from the horizontal surface and 16º medially or internally rotated from a line extending from the center of the calcaneus to a point between the first and second metatarsals. During stance phase, the subtalar joint rotates from a position of 4º external-valgus to 6º internal-varus. This motion compensates for the horizontal external rotation of the tibia during this phase. When the internal rotation is restricted by the coalition, the tarsal joints have to compensate, with flattening of the foot and loss of longitudinal arch and a valgus appearance in the horizontal plane. This leads to an adaptive shortening of the peroneal tendons, reactive peroneal spasm, and so-called peroneal spastic flatfoot. Prolonged restriction of motion eventually may lead to posterior facet arthrosis of the subtalar joint.
Another motion of the subtalar joint lost is the gliding motion demonstrated during foot dorsiflexion. Cineradiographic studies have demonstrated a hinge motion instead, with widening at the plantar aspect of the midtarsal joints, narrowing at the dorsal surfaces, and overriding of the navicular on the talar head at maximum dorsiflexion. The traction effect of the later motion on the ligaments and capsule of the talonavicular joint is thought to be the genesis of the talar beaking seen in many radiographs of tarsal coalition.
The pain symptoms associated with tarsal coalitions may therefore be attributed to ligament sprain, peroneal muscle spasm, sinus tarsi irritation, subtalar joint irritation, and arthritic changes. The variability of the symptoms in different patients may be due to the variability of subtalar restriction of the different coalitions. The specific but different ages of presentation of different coalitions would then be due to the different ages at which coalitions ossify and thus restrict subtalar motion.
Patients with tarsal coalition usually present during the second decade of life, but presentations in adulthood have been documented. Complaints include mild pain deep in the subtalar joint and limitation of range of motion. The patient usually presents after some traumatic event such as an ankle sprain. Indeed, what seem to be repetitive sprains should raise suspicions of tarsal coalition. Often, the symptoms are relieved by rest and aggravated by prolonged or heavy activity. In cases of calcaneonavicular coalition, pain may be more superficial and originate from the area of the coalition in the sinus tarsi. Palpation may elicit pain at the calcaneonavicular junction laterally. In cases of talonavicular coalitions, the pain is usually more vague, but tenderness may be elicited with palpation of the middle facet region, just anterior to the medial malleolus.
Different coalitions ossify at different ages, possibly explaining the difference in ages of presentation of different coalitions. Slight limitations of range of motion and mild valgus are thought to be possibly all that is present prior to ossification. Talonavicular coalitions begin to ossify in children aged 3-5 years; calcaneonavicular coalitions begin to ossify in children aged 8-12 years; and talocalcaneal ones begin to ossify in adolescents aged 12-16 years.
Loss of subtalar motion and valgus position of the hindfoot become more apparent as the coalition ossifies, leading to the appearance of pes planus. Middle facet talocalcaneal coalitions are associated with the greatest loss of subtalar motion and are the most likely to generate valgus. This loss of subtalar motion may be evaluated with the heel-tip test, wherein the examiner supinates the foot of a standing patient by raising the medial border of the forefoot and keeping the heel and lateral border in contact with the floor. In patients with limited or decreased subtalar motion, compensatory external tibial rotation is decreased and the patella is not observed to rotate outward as in a persons without tarsal coalition. Other tests include toe standing and the Jack toe-raise test; both demonstrate the fixed nature of the pes planus and the loss of hindfoot inversion.
Studies have shown that patients with neutral hindfeet have fewer symptoms; it is likely secondary to decreased peroneal shortening. Cases of hindfoot varus have been reported in the literature in conjunction with calcaneonavicular coalitions. Repeated sprains may actually mask loss of subtalar motion by allowing motion because of ligamentous laxity. Although peroneal spasticity has been attributed to tarsal coalitions in the older literature, its occurrence is actually relatively infrequent. Peroneal spasticity may be intermittent or continuous, varying with activity or stress of the ankle joint.
Differential diagnoses of tarsal coalition include tumor, rheumatologic processes, and fractures about the subtalar joint. A case report even exists of a previously asymptomatic talocalcaneal coalition that presented as a painful fracture of the talar beak. Tarsal coalitions have been shown to present as other foot deformities, including cavovarus deformity and talipes equinovarus. Syndromes that may present with tarsal coalitions include fibular hemimelia, Nievergelt-Pearlman syndrome, and Apert syndrome. In the cases of associated limb deficiency at birth, tarsal coalitions may present in association with ball-and-socket ankles,20,21,22 which has been demonstrated to allow compensatory inversion and eversion.
Surgical treatment of tarsal coalitions is indicated in cases in which conservative treatment has failed and symptoms persist (see Treatment).
Coalition resection is contraindicated when significant degenerative change is present in the joints adjacent to the coalition. Arthrodesis is preferable in such cases. Subtalar arthrodesis alone is contraindicated in cases of talocalcaneal coalitions in which midfoot joints show signs of degenerative change. Triple arthrodesis is indicated instead. Finally, in patients with multiple anomalies, individual resections are unlikely to establish a normal-appearing and a normal-functioning foot and should therefore not be pursued.