Rearfoot injuries like ankle sprains can lead to damage laterally at the anterior talofibular ligament, calcaneofibular ligament or peroneal tendon. Medially, the deltoid ligament or posterior tibialis tendon could be injured depending on the mechanism of injury. Researchers have documented that between 20 and 30 percent of ankle sprains go on to chronic pain.1 This necessitates a further workup of the ankle itself to evaluate for osteochondral defects or synovitis.
What we typically do not factor in is the disruption or aggravation of a tarsal coalition. Tarsal coalitions can arise in 0.4 to 1.2 percent of the population with calcaneonavicular and talocalcaneal coalitions accounting for 90 percent of tarsal coalitions.2-4 Jack and colleagues found 22 percent of coalitions are asymptomatic.5
Tarsal coalitions can become symptomatic after periods of trauma or aggravation to the coalition. When a patient with an osseous coalition has an ankle sprain, there is typically more initial soft tissue damage to the tendons and ligaments as the whole unit of bone has moved. When there is a fibrous component to the coalition and the patient has an ankle sprain, there is damage through the coalition as well as the soft tissues, which could lead to continued pain at the coalition site.
Why Tarsal Coalitions Go Undiagnosed
Many times patients do not present at the time of the acute injury and if they do, we treat the ligamentous or tendinous injury. Typically, it is at later follow-up appointments or when patients are seeking a second opinion (because they are still in pain) that they describe a lingering pain in their foot with weightbearing activities, standing and walking on uneven surfaces.
On a closed kinetic chain exam, patients may have collapse of the medial column, valgus rearfoot position and adduction of the forefoot on the rearfoot. On the open kinetic chain exam, patients can have limited subtalar joint range of motion. Pain may be present with palpation of the anterior process of the calcaneus or the middle facet of the talocalcaneal joint.
Rocchi and coworkers documented the “double medial malleolus” or bony prominence just inferior to the medial malleolus with limited motion of the subtalar joint present with talocalcaneal coalitions.6 If a patient has experienced multiple ankle sprains, there can be pain at the anterior talofibular and calcaneofibular ligaments as well as a positive anterior drawer sign.
Additionally, the peroneal tendon may spasm to prevent painful motion. This can create pain similar to that of sinus tarsi syndrome. If the spasm continues, there can be increased strain medially, leading to some patients developing pain to the posterior tibialis tendon. Additionally, if the patient has a flatfoot deformity with a bilateral coalition, which we have found to be present in 50 percent of patients, there can be pain along the posterior tibialis tendon.
Finally, as there is collapse of the arch, there is medial deviation of the Achilles tendon creating shortening of the tendon. Since patients can have multiple areas of pain, this can lead to missing or delaying the diagnosis of a coalition.
Key Insights On Effective Imaging
When there is a suspected tarsal coalition, obtain plain film radiographs. The classic sign of a talocalcaneal coalition is the absence of the subtalar joint, creating a halo or C-sign on the lateral view. For calcaneonavicular coalitions, the classic sign is an elongation of the anterior process on the lateral view as well as a connection between the calcaneus and navicular on the medial oblique view.
Depending on which coalition you suspect, obtain ancillary imaging. If there is a suspected talocalcaneal coalition, obtain a long leg calcaneal axial or Harris Beath view as these would show an obliquity of the middle facets in comparison to the posterior facets. If there is a suspected calcaneonavicular coalition, obtain medial oblique views at varying angles. The varying angles will show if there is osseous formation that may not appear in one view. Ancillary imaging is necessary to further evaluate the extent of the coalition as well as evaluate if there is any arthritis present.
Due to the concern for a fibrous component with the coalition, we recommend obtaining magnetic resonance imaging (MRI). At one point in time, a computed tomography (CT) scan was the gold standard for coalitions. However, in a study by Guignand and colleagues, the authors found MRI to be more effective for appreciated fibrous coalition, which they referred to as a direct sign.7 The authors also noted that MRI can let physicians appreciate if there were any indirect signs of a coalition like bone marrow edema. One could utilize CT scans if there were radiographic evidence of an osseous coalition. While clinicians may utilize ultrasound to identify a coalition, it is technically more challenging to perform and fully visualize the extent of the coalition.
A Closer Look At Treatment Options For Tarsal Coalitions
Treatment for tarsal coalitions depends on the time of diagnosis. If a patient sustained an injury that disrupted a coalition, immediately presented and got an accurate diagnosis, one can emphasize to the patient that he or she remain immobile in order to allow the coalition to coalesce. The patient can also rest and use anti-inflammatories. When the diagnosis is delayed, initial conservative treatment consists of placing the patient in custom orthotics to hold the rearfoot in a controlled position. Additionally, one should recommend a rigid-sole shoe to prevent the motion at the coalition site. Physical therapy can have an anti-inflammatory effect.
Surgical intervention depends on the type of coalition as well as the presence of arthritis. The MRI or CT scan is very helpful in determining the most appropriate procedure. Arthroscopic resection is an option for both calcaneonavicular and talocalcaneal coalitions in a variety of approaches. For posterior subtalar joint arthroscopy, the surgeon would utilize a 2.7 mm 30-degree scope with the patient in a prone position to visualize and resect the coalition. Posterior arthroscopy can be technically more challenging than a standard anterior sinus tarsi arthroscopy and it is important to keep the flexor hallucis longus tendon as the medial border in order to avoid damage to the neurovascular bundle. Additionally, Bonasia and coworkers discussed this approach and recommended evaluating the ankle joint for concomitant injuries. Employing an anterior approach can help surgeons evaluate the quality of the subtalar joint for arthritic changes as well as the extent of the coalition.8
Authors have also discussed arthroscopic resection of calcaneonavicular coalitions. Knörr and colleagues reported on the portal locations with placement of the portal for the arthroscope just posterior to the anterolateral process of the calcaneus and dorsal to the angle of Gissane, and placement of the second or working portal distal to the calcaneal process and lateral to the extensor digitorum longus tendon.9 One can perform open resection for both talocalcaneal and calcaneonavicular coalitions with good results. It is important to resect a sufficient amount of bone to prevent recurrence. Additionally, with calcaneonavicular coalitions, it is important to have parallel cuts. If the cuts converge, it will leave the plantar aspect of the coalition and can lead to a recurrence of pain.
Following the resection of the coalition, the placement of either bone wax, muscle, fat or amniotic tissue can prevent regrowth of the coalition. In other cases, the amount of osseous formation present at the coalition, arthritic changes and surrounding joint involvement may require the patient to have arthrodesis. Additionally, if the patient has a rigid flatfoot deformity due to the presence of the coalition, consider either a triple arthrodesis or a medial double arthrodesis.
While tarsal coalitions are not the most common diagnosis in podiatric medicine, clinicians frequently miss this diagnosis. When a patient sustains an ankle sprain, emphasize immobilization, anti-inflammatories and rest. If the patient continues to have chronic pain, perform a further workup to evaluate for damage to the ligaments, syndesmosis, synovitis or an osteochondral defect. Add the coalition to the list of differential diagnoses as the presence of a tarsal coalition can cause recurrent ankle sprains as well as damage to the surrounding tissues. Due to the nature of the fibrous coalition, which allows for partial motion of the subtalar joint, diagnosis may not be as obvious as an osseous bridge. Pain elicited by palpation of the lateral process of the calcaneus or the middle facet of the subtalar joint should increase suspicion. Finally, it is important to consider a coalition as earlier diagnosis could potentially allow a patient the option of initial conservative treatment at the time of injury versus requiring surgical intervention for a painful coalition.
Dr. Baravarian is an Assistant Clinical Professor at the UCLA School of Medicine, and the Director and Fellowship Director at the University Foot and Ankle Institute in Los Angeles (https://www.footankleinstitute.com/podiatrist/dr-bob-baravarian ).
Dr. Allen is a Fellow at the University Foot and Ankle Institute in Los Angeles.
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