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 long-standing 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 the following:

 

 

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 anteroposterior (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).

 

 

 

FIG 1 • A. A 45-degree oblique radiograph depicting a calcaneonavicular coalition (the anteater sign). B. CT showing an isolated calcaneonavicular coalition.

 

 

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An axial view is important because it may aid in the identification of a talocalcaneal coalition.

 

 

Computed tomography (CT) 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.

 

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 (PTT) 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 CT 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).

Preemptive 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.

 

 

 

 

TECH FIG 1 • A. Incision. B. Elevation of the extensor digitorum brevis flap. (continued)

 

 

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).

 

 

27

 

 

 

TECH FIG 1 • (continued) 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.

   

   

   

  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. (continued)

   

   

  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.

   

  28

   

   

   

  TECH FIG 2 • (continued) E. Intraoperative radiographs to confirm the adequacy of the resection. F.

  Wound closure.

   

   

  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.

• Calcaneonavicular Coalition Resection (Courtesy of Mark E. Easley, MD)

Exposure

 

 

Make a longitudinal incision from the tip of the fibula toward the base of the fifth metatarsal. Identify and protect the sural nerve and peroneal tendons.

 

Retract the extensor hallucis brevis (EHB) muscle after carefully releasing its overlying fascia.

 

The fascia may be released where it attaches immediately deep to the peroneal tendons.

 

 

 

TECH FIG 3 • Expose dorsal aspect of anterior process of calcaneus and lateral navicular through a longitudinal incision from the anterior distal fibula toward the base of the fourth metatarsal. Protect the sural nerve and peroneal tendons and retract the EHB muscle.

 

 

Expose the dorsal aspect of anterior process of calcaneus and lateral navicular (TECH FIG 3).

 

Coalition may be bony, cartilaginous, or fibrous.

 

Confirm coalition on intraoperative fluoroscopy; oblique view is most helpful.

Coalition Resection

 

Protect the soft tissues.

 

Use a chisel to resect medial aspect of coalition, which is the lateral aspect of the navicular (TECH FIG 4A).

 

Avoid injury to the lateral talar head.

 

Reposition chisel to resect lateral aspect of coalition, which is the anterior process of the calcaneus (TECH FIG 4B).

 

Avoid injury to the calcaneocuboid joint.

 

 

 

TECH FIG 4 • Calcaneonavicular coalition. A. Use a chisel to create a resection plane on the lateral aspect on the navicular. (continued)

 

 

29

 

 

 

TECH FIG 4 • (continued) B. Create the second resection plane on the medial anterior process of the calcaneus. Note that the resection demonstrated here is inadequate and needs to widen with nearly parallel resection planes, creating a trapezoidal or even rectangular resection not a wedge.

 

 

Create a wide and congruent resection.

 

Although some convergence of the two resection planes is unavoidable, the two resection planes should be nearly parallel.

 

Converging the resections creates a wedge resection with a wide dorsal base and a narrow plantar aspect that may not allow for full separation of the coalition planes.

 

The resection should be generous but without violating the lateral talar head or the medial calcaneocuboid joint.

 

At the most plantar aspect of the coalition, the planar talar head's articulation with the anterior calcaneal facet should also be protected.

Confirm Adequate Resection

 

Clinically, hindfoot motion should be reestablished.

 

Fluoroscopically, in the oblique plane, there should be a generous gap with complete separation of the navicular from the anterior process of the calcaneus.

 

Also confirm that no bone fragments remain.

 

 

 

TECH FIG 5 • A. Be sure to remove all bone fragments from deep within the resection. B. Bone wax can be used within the coalition, on the exposed cancellous surfaces, to limit bone reformation of the coalition.

Closure

 

Irrigate the wound thoroughly with sterile saline to remove any smaller residual bone fragments (TECH FIG 5A).

 

Limit bone regrowth into the coalition resection by placing bone wax on both the navicular and calcaneal cancellous (TECH FIG 5B).

 

The EHB muscle is released from retraction and repositioned in its anatomic position and its overlying fascia is reapproximated if possible.

 

The fascia and muscle may have some damage from retraction, but typically, the fascia may still be reapproximated in a satisfactory manner.

 

The subcutaneous layer and skin are carefully closed.

• Middle Facet (Subtalar) Coalition Resection (Courtesy of Mark E. Easley, MD)

Exposure

 

 

Obtain a preoperative CT to assist in guiding the middle facet coalition resection. Medial approach directly over the middle facet coalition (TECH FIG 6)

 

In most patients, the prominent coalition can be palpated. It is confluent with the sustentaculum tali.

 

Palpate the medial malleolus and the medial navicular and then identify the sustentaculum tali inferior to the medial malleolus and proximal to the navicular.

 

The dorsomedial aspect of the calcaneus is also palpable.

 

 

30

 

 

 

TECH FIG 6 • From the dorsomedial aspect of the calcaneus, make the incision immediately dorsal to the palpable sustentaculum tali, directly over the prominent coalition and inferior to the medial malleolus, ending immediately proximal to the navicular.

 

 

Course of the incision

 

Start at the dorsomedial aspect of the calcaneus, anterior to the Achilles tendon, immediately posterior to the medial malleolus.

 

Continue the incision immediately dorsal to the sustentaculum tali, over the prominent coalition and inferior to the medial malleolus.

 

Complete the incision immediately proximal to the navicular.

Exposing the Coalition

 

After the skin incision, carefully divide the flexor retinaculum.

 

Lift the retinaculum as it is divided so that the underlying tendons and neurovascular structures are not injured.

 

Interval to access the coalition

 

In most cases, the flexor digitorum longus (FDL) tendon courses directly over the coalition.

 

The posterior aspect of the coalition is accessed between the FDL and flexor hallucis longus (FHL) tendon.

 

The anterior aspect of the coalition is accessed between the FDL and the PTT.

Identifying the Coalition

 

 

The coalition is often difficult to identify, particularly when a complete bone bridge is present. Incomplete coalitions (cartilaginous or fibrous) are sometimes easier to identify.

 

Preoperative imaging, especially CT, is useful in determining the coalition orientation.

 

The coalition may not be transverse, instead having a more vertical orientation, and the preoperative CT should be used to locate the incomplete coalition.

 

The medial aspect of the posterior subtalar joint, immediately posterior to the middle facet coalition, is

typically easy to identify (TECH FIG 7).

 

In the posterior aspect of the incision, identify and carefully retract the neurovascular bundle (tibial nerve, posterior tibial artery and veins) posteriorly and inferiorly.

 

The interval will be between the FDL tendon dorsally and the FHL tendon inferiorly.

 

The medial aspect of the posterior subtalar joint may be visualized (cartilage surfaces of the inferior talus and calcaneal posterior facet).

 

 

 

TECH FIG 7 • Identify the posteromedial subtalar joint. A. The posterior subtalar joint may be identified between the FDL and FHL tendons. B. Note that the posteromedial neurovascular bundle is retracted posteriorly and inferiorly. C. The hypodermic needle is used as a guide in the posterior subtalar joint.

 

 

Carefully place a hypodermic needle in the joint.

 

If desired, fluoroscopically confirm that the needle is in the subtalar joint.

 

To outline the planned course of coalition resection, a hypodermic needle may also be placed between the talar head and the anterior calcaneal facet.

 

This is sometimes more difficult to identify but is useful in complete bony coalitions were identifying the optimal course of resection from proximal to distal cannot be readily determined.

Resection

 

Begin the coalition resection proximally, starting at the posterior calcaneal facet and advancing distally.

 

 

Use the preoperative CT to help guide the resection in the plane of an incomplete coalition. For complete bony coalitions, intraoperative fluoroscopy may be useful to guide the resection.

 

Incomplete coalitions may be identified using a curette on the coalition's medially aspect until the coalition's plane is determined.

 

On the proximal aspect, the FDL is retracted dorsally (TECH FIG 8A).

 

To advance distally, the FDL should be retracted plantarly (TECH FIG 8B).

 

 

31

 

 

 

TECH FIG 8 • A,B. Initiating the middle facet coalition resection using a curette. A. The posterior aspect of the coalition is accessed with the FDL tendon retracted dorsally. B. The anterior aspect of the coalition is accessed with the FDL tendon retracted inferiorly. C-E. Deepening the middle facet coalition resection.

C. A chisel is used to perform the deeper (more lateral) coalition resection. D. With most of the middle facet coalition resected, the posterior calcaneal facet is exposed. E. The resection should be generous to limit risk of coalition reformation.

 

 

Once the coalition plane is determined, a chisel is used (TECH FIG 8C-E).

 

From medial to lateral, the coalition is typically quite deep, often 2 or 3 cm.

 

Confirm the coalition resection has been completed anteriorly by stressing the subtalar joint and demonstrating motion.

 

The resection should be generous to optimize motion and avoid recurrence (TECH FIG 9).

 

If possible, preserve the inferior aspect of the sustentaculum tali so that the FHL maintains its anatomic course.

 

Confirm that there is no impingement medially and that inversion is reestablished.

 

Once a generous amount of bone has been resected from the coalition, thoroughly irrigate the wound and place bone wax to limit bone regrowth.

 

TECH FIG 9 • Completing the middle facet coalition resection. A. A lamina spreader is used to demonstrate complete separation of the talus from the calcaneus. B. Bone wax may be used on the exposed cancellous surfaces to limit the risk of coalition reformation.

Closure and Postoperative Care

After thorough irrigation with sterile saline, release the tourniquet and perform hemostasis. The extensor retinaculum does not need to be closed.

Use a drain to limit formation of a hematoma over the neurovascular bundle. Close the subcutaneous layer and skin.

The ankle and foot should be immobilized in a cam boot or splint to allow the wound to heal.

As soon as the soft tissues are stable, range of motion should be initiated to optimize hindfoot motion.

Weight bearing may be initiated when the wound is stable, but full weight bearing may not be tolerated for 4 to 6 weeks.

Consider physical therapy to optimize outcome.

 

 

32

PEARLS AND PITFALLS
	Preoperative ▪ Evaluate plain radiographs for the presence of significant degenerative workup changes, which would necessitate an appropriate arthrodesis. Review available CT or magnetic resonance imaging scans for the presence of any concomitant coalitions.   Coalition ▪ Osteotome cuts made in a parallel fashion will remove a rectangular block of resection bone rather than a convergent, trapezoidal segment, which may lead to recurrent pain secondary to an inadequate medial excision of the coalition.   Interpositional ▪ Preserve the fascia overlying the extensor digitorum brevis to increase the graft holding power of the Vicryl stitch.   Deformity ▪ Consider adding a lateral column lengthening procedure in the face of a correction significant pes planus.

 

 

 

 

POSTOPERATIVE CARE

 

The patient is allowed to bear weight 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 al1 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 Kumar4 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 al8 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 al9 used an interpositional material (fat or muscle) in 38 of 39 feet undergoing calcaneonavicular coalition resection and found no radiographic recurrences.

Mitchell and Gibson,7 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.

 

COMPLICATIONS

Superficial or deep infection Wound dehiscence1

Recurrence of the coalition7 Nerve damage

Inadequate resection3

Reflex sympathetic dystrophy1

 

REFERENCES

1. Cohen BE, Davis WH, Anderson RB. Success of calcaneonavicular coalition resection in the adult population. Foot Ankle Int 1996;17: 569-572.

    

    

2. Cooperman DR, Janke BE, Gilmore A, et al. A three-dimensional study of calcaneonavicular tarsal coalitions. J Pediatr Orthop 2001;21:648-651.

    

    

3. Ehrlich MG, Elmer EB. Tarsal coalition. In: Jahss M, ed. Disorders of the Foot and Ankle, ed 2. Philadelphia: Saunders, 1991:921-938.

    

    

4. Gonzalez P, Kumar SJ. Calcaneonavicular coalition treated by resection and interposition of the extensor digitorum brevis muscle. J Bone Joint Surg Am 1990;72(1):71-77.

    

    

5. Jayakumar S, Cowell HR. Rigid flatfoot. Clin Orthop Relat Res 1977;(122):77-84.

    

    

6. Kulik SA, Clanton TO. Foot fellow's review: tarsal coalition. Foot Ankle Int 1996;17:286-296.

    

    

7. Mitchell GP, Gibson JM. Excision of calcaneonavicular bar for painful spasmodic flat foot. J Bone Joint Surg Br 1967;49(2):281-287.

    

    

8. Moyes ST, Crawford EJ, Aichroth PM. The interposition of extensor digitorum brevis in the resection of calcaneonavicular bars. J Pediatr Orthop 1994;14:387-388.

    

    

9. Swiontkowski MF, Scranton PE, Hansen S. Tarsal coalitions: longterm results of surgical treatment. J Pediatr Orthop 1983;3:287-292.

    

    

10. Vincent KA. Tarsal coalition and painful flatfoot. J Am Acad Orthop Surg 1998;6:274-281.