Aaron T. Scott and H. Robert Tuten
DEFINITION
A tarsal coalition is an abnormal fusion between two adjacent tarsal bones.
Less than 2% of the general population is affected, and there appears to be no gender or racial predisposition.2,6,10
Nearly 90% of all tarsal coalitions involve either the subtalar joint or the intervening space between the calcaneus and the navicular, with nearly an equal distribution between these two areas.1
Although most calcaneonavicular coalitions are identified in children or adolescents, there does exist a subset of patients who become symptomatic in adulthood.
ANATOMY
Unlike other tarsal coalitions, the calcaneonavicular coalition forms between two bones that normally do not articulate with each other.
A calcaneonavicular coalition generally occurs between the anterior process of the calcaneus and the inferolateral aspect of the navicular.
Histologically, these coalitions may be fibrous, cartilaginous, or osseous in nature, and may progress through these stages as the patient matures.
PATHOGENESIS
Tarsal coalitions are most likely secondary to a failure of segmentation of the primitive mesenchyme.2,3
In adolescents and young adults, the time at which the coalition becomes symptomatic appears to coincide with its ossification.5
Although most coalitions are idiopathic, a dominant trait has been suggested.10
NATURAL HISTORY
The natural history of a calcaneonavicular coalition is one of progressive disability.
As the coalition ossifies in adolescence, the lack of subtalar range of motion may lead to hindfoot or midfoot pain, recurrent ankle sprains, and difficulty ambulating on uneven surfaces.
In longstanding coalitions, the increased stresses imposed on the remaining mobile tarsal joints secondary to absent subtalar inversion and eversion may contribute to degenerative arthritic changes elsewhere in the foot.
PATIENT HISTORY AND PHYSICAL FINDINGS
Symptomatic adults with calcaneonavicular coalitions generally present with hindfoot or midfoot pain, recurrent ankle sprains, or difficulty ambulating on uneven surfaces.
In contrast to the often insidious onset of symptoms in adolescents with a calcaneonavicular coalition, onset in adults with this condition is abrupt and often coincides with a specific traumatic event, such as a severe ankle sprain.
Other adults may simply present with a planovalgus foot deformity.
Physical examination findings consistent with a calcaneonavicular coalition may include:
Planovalgus foot deformity (rarely, a cavovarus deformity)
Decreased or absent subtalar and transverse tarsal joint range of motion
Tenderness in the region of the coalition
Pain with inversion or eversion of the hindfoot
Antalgic gait
Instability secondary to multiple ankle sprains (as determined by anterior drawer testing)
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs should be obtained in every patient suspected of having a tarsal coalition and should include AP, lateral, 45-degree oblique, and axial views of the foot.
The 45-degree oblique view of the foot is the most useful plain radiograph for identifying a calcaneonavicular coalition. On this oblique view, the coalition may be seen as a discrete bony bridge between the calcaneus and the navicular, or this may simply be suggested by the presence of an extended, narrow beak of bone projecting from the anterior process of the calcaneus in the direction of the navicular (the “anteater sign”; FIG 1A).
An axial view is important because it may aid in the identification of a talocalcaneal coalition.
Computed tomographic scans should be obtained in all patients preoperatively to rule out a concomitant talocalcaneal coalition and to further evaluate for degenerative changes that may alter the surgical plan (FIG 1B).
Magnetic resonance imaging may help identify a fibrous or cartilaginous coalition but is not necessary in the workup and treatment of most calcaneonavicular coalitions in adults.
FIG 1 • A. A 45-degree oblique radiograph depicting a calcaneonavicular coalition (the “anteater sign”). B. Computed tomographic scan showing an isolated calcaneonavicular coalition.
DIFFERENTIAL DIAGNOSIS
Talocalcaneal (subtalar) coalition
Trauma or fracture of the hindfoot
Arthritis (primary osteoarthrosis, posttraumatic arthritis, or inflammatory arthritis)
Flatfoot secondary to posterior tibial tendon insufficiency
Chronic ankle instability
NONOPERATIVE MANAGEMENT
Initially, all patients with symptomatic calcaneonavicular coalition should be managed nonoperatively.
Patients are first treated with nonsteroidal anti-inflammatory medications and custom orthotics that support the medial longitudinal arch.
The UCBL brace is another orthotic option that acts to limit hindfoot motion.
If patients fail this early conservative treatment, they are immobilized in a fiberglass short leg walking cast for 4 to 6 weeks.
Symptomatic coalitions that are recalcitrant to casting in feet that display no degenerative changes may require surgical resection for relief of symptoms.
SURGICAL MANAGEMENT
For patients who do not achieve relief with an adequate trial of nonoperative management, surgical intervention is warranted.
Preoperative Planning
Plain radiographs, as well as computed tomographic or magnetic resonance imaging scans, are reviewed.
All images are evaluated for additional pathology, including concomitant coalitions or degenerative arthritic changes that may alter the surgical treatment plan.
Positioning
Thirty to 90 minutes before the incision is made, the patient is given an appropriate intravenous antibiotic.
The patient is placed supine on the operating table, and a bump is placed under the ipsilateral sacrum to internally rotate the foot.
A pneumatic tourniquet is placed around the upper thigh, and the extremity is prepped and draped in a standard, sterile fashion.
TECHNIQUES
INCISION AND EXPOSURE
After exsanguination with an Esmarch bandage and inflation of the tourniquet, a standard Ollier incision is created.
This incision is centered directly over the dorsal aspect of the coalition and extends along a transverse Langer line plantarly to the peroneal tendon sheath and dorsally to the most lateral of the extensor digitorum longus tendons (TECH FIG 1A).
Pre-emptive cauterization of any crossing vessels is performed.
The sural cutaneous nerve and dorsal intermediate branch of the superficial peroneal nerve are identified and protected, as are the peroneal tendons.
The extensor digitorum brevis muscle is visualized in the depths of the wound and subsequently elevated as a distally based flap using a scalpel and a Cobb elevator, with great care taken to preserve the overlying fascia, which will increase the suture-holding capacity of the flap (TECH FIG 1B).
The elevated origin of the brevis is then grasped with a modified Mason-Allen stitch using 0-Vicryl (TECH FIG 1C).
As the flap is retracted distally, the calcaneonavicular coalition is easily identified (TECH FIG 1D).
TECH FIG 1 • A. Incision. B. Elevation of the extensor digitorum brevis flap. C. Grasping of the extensor digitorum brevis with Vicryl suture. D. Flap retraction and visualization of calcaneonavicular coalition.
RESECTION OF CALCANEONAVICULAR COALITION WITH INTERPOSITION OF THE EXTENSOR DIGITORUM BREVIS
After adequate visualization of the coalition, a straight osteotome is used to remove a 1-cm block to include the entire coalition.
The osteotome cuts are made parallel to prevent the removal of a convergent, trapezoidal block of bone (TECH FIG 2A).
Any remaining soft tissue within the resection site is cleared with a rongeur.
The two limbs of the previously placed Vicryl suture attached to the extensor digitorum brevis flap are passed through the void created by coalition resection with the use of a free Keith needle (TECH FIG 2B).
The tips of the Keith needles should pass just dorsal to the glabrous skin of the medial arch (TECH FIG 2C).
The two limbs of the Vicryl suture are then tied over a soft dental bolster (no button; TECH FIG 2D).
Alternatively, the raw bony surfaces of the resection site may be covered with bone wax, the void filled with gelfoam or autologous fat graft, and the brevis reattached to its origin.
Radiographs are taken to confirm the adequacy of the resection (TECH FIG 2E).
The wound is thoroughly irrigated, the tourniquet is released, and hemostasis is secured.
Closure of the wound is performed using 2-0 Vicryl for the deep subcutaneous layer and 4-0 nylon horizontal mattress sutures for the skin (TECH FIG 2F).
Finally, the wound is covered with a nonadherent dressing, sterile gauze, sterile cast padding, and a short leg fiberglass walking cast.
TECH FIG 2 • Resection and interposition. A. Removal of a rectangular block of bone using parallel osteotome cuts. B. Interposition of the extensor digitorum brevis flap into the void created by the resection. C. Passage of Keith needles through the skin of the medial arch. D. Flap sutures tied over soft dental bolster. E. Intraoperative radiographs to confirm the adequacy of the resection. F. Wound closure.
POSTOPERATIVE CARE
The patient is allowed to weight bear as tolerated in the cast on postoperative day 1.
At 3 weeks, the patient returns to clinic for removal of the cast, wound sutures, and bolster stitch. At this point, the patient is placed in a walking boot.
Following removal of the cast, physical therapy is initiated for ankle and hindfoot range-of-motion exercises.
OUTCOMES
In the absence of significant degenerative changes that may necessitate an appropriate arthrodesis, resection of a calcaneonavicular coalition can be a successful procedure in symptomatic adults or adolescents.
Cohen et al reviewed results of calcaneonavicular coalition resection in 12 adult patients. Subjective relief was attained in 10 patients and the average increase in total subtalar range of motion was 10 degrees.1
In a group of 48 child and adolescent patients, Gonzalez and Kumar achieved 77% good to excellent results following calcaneonavicular coalition resection with interposition of the extensor digitorum brevis. The results did not deteriorate with time in those patients followed up for more than 10 years.4
The importance of using an interpositional material has been reinforced in several publications.
No recurrences of a calcaneonavicular coalition were noted by Moyes et al on oblique radiographs when an extensor digitorum brevis interposition was performed. However, in this same study, three of seven patients who underwent resection without interposition displayed radiographic evidence of a recurrence.8
Swiontkowski et al used an interpositional material (fat or muscle) in 38 of 39 feet undergoing calcaneonavicular coalition resection and found no radiographic recurrences.9
Mitchell and Gibson, on the other hand, found a recurrence of the coalition in nearly two thirds of their 41 patients who had undergone a simple coalition resection without interposition of the extensor digitorum brevis.7
COMPLICATIONS
Superficial or deep infection
Wound dehiscence1
Recurrence of the coalition7
Nerve damage
Inadequate resection3
Reflex sympathetic dystrophy1
REFERENCES
· Cohen BE, Davis WH, Anderson RB. Success of calcaneonavicular coalition resection in the adult population. Foot Ankle Int 1996;17: 569–572.
· Cooperman DR, Janke BE, Gilmore A, et al. A three-dimensional study of calcaneonavicular tarsal coalitions. J Pediatr Orthop 2001; 21:648–651.
· Ehrlich MG, Elmer EB. Tarsal coalition. In: Jahss M, ed. Disorders of the Foot and Ankle, ed 2. Philadelphia: Saunders, 1991:921–938.
· Gonzalez P, Kumar SJ. Calcaneonavicular coalition treated by resection and interposition of the extensor digitorum brevis muscle. J Bone Joint Surg Am 1990;72A:71–77.
· Jayakumar S, Cowell HR. Rigid flatfoot. Clin Orthop Relat Res 1977;122:77–84.
· Kulik SA, Clanton TO. Foot fellow's review: tarsal coalition. Foot Ankle Int 1996;17:286–296.
· Mitchell GP, Gibson JMC. Excision of calcaneonavicular bar for painful spasmodic flatfoot. J Bone Joint Surg Br 1967;49B:281–287.
· Moyes ST, Crawford EJP, Aichroth PM. The interposition of extensor digitorum brevis in the resection of calcaneonavicular bars. J Pediatr Orthop 1994;14:387–388.
· Swiontkowski MF, Scranton PE, Hansen S. Tarsal coalitions: longterm results of surgical treatment. J Pediatr Orthop 1983;3:287–292.
· Vincent KA. Tarsal coalition and painful flatfoot. J Am Acad Orthop Surg 1998;6:274–281.