NONUNION OF A FRACTURE OF THE SUSTENTACULUM TALI CAUSING A TARSAL TUNNEL SYNDROME: A CASE REPORT
July 19th, 1995
Mark S. Myerson, MD and Barry I. Berger, MD
A middle-aged man sustained an isolated sustentaculum tali fracture that formed a stable nonunion. He subsequently developed tarsal tunnel syndrome when this sustentacular fragment migrated superiorly to cause tibial nerve impingement and presented with a history of long-standing foot and ankle pain. He was pain-free 2 weeks after excision of the bony mass encased in fibrous tissue.
Tarsal tunnel syndrome is an entrapment neuropathy of the tibial nerve or one of its terminal branches as it crosses beneath the medial retinaculum of the ankle. This syndrome is often caused by various space-occupying lesions, trauma, collagen, or vascular and systemic disease states.3-6,10 In this report, we present a case of tarsal tunnel syndrome arising in a middle-aged man who had sustained an isolated sustentaculum tali fracture that formed a stable nonunion. This sustentacular fragment eventually migrated superiorly to cause tibial nerve impingement.
A 42-year-old physician was referred to our facility for treatment of long-standing foot and ankle pain. The patient had sustained multiple minor injuries to his foot and ankle during young adulthood; they were all treated nonsurgically. No radiographs of the ankle were obtained at the time of these injuries. He had been slowly forced to curtail nearly all athletic activities because of medial ankle and foot pain. He had been aware of a palpable lump near his right medial malleolus for 13 years, but it had not previously caused any particular problems.
His presenting complaint was an aching and sensitivity with some burning and paresthesia over the right medial foot, hallux, and second toe. The pain was exacerbated by passive and active dorsiflexion of the ankle.
Vascular examination of the entire lower extremity was normal. He was able to bear weight with no forefoot or hindfoot deformity. Posterior tibial tendon function was normal bilaterally. He had a palpable 2- to 3-cm firm mass at the location of the sustentaculum tali. Motion of the great toe was not painful and muscle strength testing of the foot revealed no weakness. Passive dorsiflexion of the ankle was unimpeded and there were no signs of ankle arthrosis. Subtalar motion was present and painless. Static and moving two-point discrimination was normal in all toes. A markedly positive percussion test was elicited over the tibial nerve in the tarsal tunnel, reproducing his pain; it was associated with severe paresthesias in the medial forefoot and medial toes.
Weight-bearing radiographs and a computerized tomography scan were obtained. There was a fracture of the sustentaculum noted by computerized tomography with complete loss of bony continuity between the sustentaculum and the calcaneus (Fig. 1). The sustentaculum fragment had displaced medially and superiorly from its original position. The findings were interpreted as a displaced nonunion of the sustentaculum with resulting compression on the tibial nerve or one of the terminal branches in the tarsal tunnel.
The surgical approach was through the standard tarsal tunnel incision. The bony mass encountered in the tunnel was encased in fibrous tissue and was found lying directly over the medial plantar branch of the tibial nerve. There were no gross changes evident in the medial plantar nerve. The final pathologic diagnosis was cortical bone with articular cartilage. Postoperatively, the patient was placed in a compressive dressing and range of motion exercises were begun at 10 days. By 2 weeks, the patient was free of pain. At 3 months, he was participating in his usual athletic activities and was completely pain free.
Isolated fractures of the sustentaculum tali are rare injuries, accounting for less than 1% of all calcaneal fractures.1 The sustentaculum tali is a part of the subtalar joint, forming the middle subtalar facet. The flexor hallucis longus tendon courses under the sustentaculum in a groove along its base. Superiorly, fibers of the deltoid ligament insert onto the sustentaculum. This anatomic arrangement has been thought to be responsible for the infrequent incidence of displacement of these fractures.1 Uneventful healing of these fractures is the usual result clinically. Numerous mechanisms of injury have been described and the usual history is one of minimal trauma and initial misdiagnosis. Frequently, the initial symptoms are attributed to medial soft-tissue injury and the patient is managed symptomatically. The long-standing symptoms in our patient, along with the history of a mass and the radiographic findings, all suggest a stable fibrous nonunion. The stability of the nonunion was probably compromised by a minor trauma, after which the patient began experiencing pain.
A coalition of the subtalar joint is one of the more common diagnoses in patients with an identifiable cause of tarsal tunnel syndrome.6,10 The onset of symptoms is usually much earlier, however, and our radiographic workup revealed no evidence of coalition. Likewise, osteophytic margination and spurring of an arthritic subtalar joint are common definable etiologies.1 Evidence of subtalar arthrosis was not present in our patient. It was quite clear that migration of the sustentaculum fragment had caused direct compression on the tibial nerve at the junction of the terminal bifurcation into the medial and lateral plantar nerves.
Tarsal tunnel syndrome is usually secondary to extrinsic compression within the tunnel.
Many authors feel that tarsal tunnel syndrome is underdiagnosed. Good results with operative decompression of extrinsically compressed nerves have been reported to approach 90%10 (Fig. 2). Since the clinical symptoms usually begin insidiously, and the initial findings are limited to localized pain without a neuritic component, other conditions are ruled out first. Peripheral vascular disease, plantar fascitis, longitudinal arch sprain, interdigital neuroma, sciatica, prolapsed metatarsal heads with metatarsalgia, and rheumatologic diseases are initially sought. Intrinsic nerve disorders (such as neurilemmoma), metabolic abnormalities (such as ankylosing spondylitis), and diabetes have been implicated in the development of the disease.4,8,9 Three to 4 months of nonoperative treatment, with treatment for associated medical conditions when present, are indicated in the absence of anatomic impingement.
The role of electrodiagnostic studies in the workup of tarsal tunnel is unclear; some authors recommend them for all patients before operative treatment, whereas others feel the studies should be obtained on an individual basis.2,7 In the current case report, our clinical and radiographic evidence was strong enough to support operative decompression.
This case report supports the contention that relief of extrinsic compression in the rigidly bound tarsal tunnel is usually met with clinical success. The nearly complete resolution of symptoms in our patient is somewhat surprising because of the length of time during which he had exhibited symptoms. The mobility of the mass may have been responsible for intermittent compression of the nerve and therefore damage to the neural elements was not irrevocable. To our knowledge, isolated fracture of the sustentaculum tali with formation of a nonunion and subsequent migration and impingement has not been encountered.
1. DeLee, J.C. Fractures and dislocations of the foot. In Surgery of the Foot and Ankle, Ed. 6, Mann, R.A. and Coughlin, M.J. (eds.). St. Louis, Mosby-Year Book Inc, 1993, pp. 1465-1703.
2. DeLisa, J.A. and Saeed, M.A. The tarsal tunnel syndrome. Muscle Nerve, 6:664-670, 1983.
3. Edwards, W.G., Lincoln, C.R., Bassett, F.H., III, and Goldner, J.L. The tarsal tunnel syndrome. Diagnosis and treatment. JAMA, 207(4):716-720, 1969.
4. Jackson, D.L. and Haglund, B. Tarsal tunnel syndrome in athletes. Case reports and literature review. Am. J. Sports Med. 19:61-65, 1991.
5. Keck, C. The tarsal-tunnel syndrome. J. Bone Joint Surg. 44A:180-182, 1962.
6. Lam, S.J.S. Tarsal tunnel syndrome. J. Bone Joint Surg. 49B(1):87-92, 1967.
7. MacKinnon, S.E. and Dellon, A.L. Surgery of the Peripheral Nerve, p. 305. New York, Thieme Medical Publishers, 1988.
8. Mann, R.A. and Baxter, D.E. Diseases of the nerves. In Surgery of the Foot and Ankle, Ed. 6, Mann, R.A. and Coughlin, M.J. (eds.). St. Louis, Mosby-Year Book Inc, 1993, pp. 543-573.
9. Pratt, T.C. Gangrene and infection in the diabetic. Med. Clin. North Am. 49:987-1004, 1975.
10. Takakura, Y., Kitada, C., Sugimoto, K., Tanaka, Y., and Tamai, S. Tarsal tunnel syndrome. Causes and results of operative treatment. J. Bone Joint Surg. 73B:125-128, 1991.
Fig. 1. CT scan illustrating the nonunion. Note rounded margins, suggesting a long-standing displacement with superomedial migration.
Fig. 2. Tarsal tunnel compression.