Tarsal tunnel syndrome secondary to osteochondroma of the calcaneus: a case report

Tarsal tunnel syndrome is an entrapment neuropathy of the posterior tibial nerve or one of its branches within the tarsal tunnel on the medial aspect of the ankle [1]. Symptoms of burning, tingling, and pain along the foot plantar region can be triggered by either intrinsic or extrinsic factors that compress the posterior tibial nerve beneath the flexor retinaculum [2]. Among the rest, a bony structure protuberated within the tarsal tunnel including talocalcaneal coalition, talar or calcaneal fracture, nonunion, or os sustentaculum tali have been identified as one of the significant factors to tarsal tunnel syndrome due to its firm mass effect [1, 3‐7]. Osteochondromas, the most common benign bone tumor also characterized by a stalk or a flat protuberance emerging from the surface of the bone, however, rarely occur in tarsal bones [8‐10]. Here, we report a patient who presented with tarsal tunnel syndrome secondary to osteochondroma of the sustentaculum tali and was successfully treated through surgical decompression.

Osteochondroma is the most common benign bone tumor accounting for more than 30% of all the benign bone tumors [12]. It is defined as a cartilage capped bony projection arising on the external surface of bone containing a marrow cavity that is continuous with that of the underlying bone [8]. It tends to be found in adolescent or children and no predilection among the gender exists. Most of the lesion occur as solitary, nonhereditary lesion, which is usually located at the metaphysis of the long bones, especially near the knee joint [8, 10]. Osteochondroma is seldom found in foot or ankle, excluding the case of Multiple Hereditary Exostoses [13].

In terms of differential diagnosis of the osteochondroma near the ankle, Dysplasia epiphysealis hemimelica (DEH) could also be taken into account because it is mostly affected in ankle and knee [14]. DEH is a rare developmental disorder defined as asymmetric osteochondral overgrowth of the cartilage of epiphysis or epiphyseal equivalent [15]. It is characterized as an intra-articular, irregular bony lesion with osseous continuity to the underlying bone arising from multiple distinct ossification centers. Although the histopathologic study confirmed the lesion of this case report as osteochondroma, it is known to be difficult to discriminate osteochondroma from DEH both clinically and pathologically [16, 17]. In fact, calcaneus is an apophyseal equivalent and DEH occurs predominantly on male in developmental ages, just as the patient in this case report [18]. Despite the definite diagnostic value of the molecular assays, these are costly and radiological findings are considered to be important in discriminating these two lesions [19]. In this case, the lesion was located under the sustentaculum tali, which could be considered extra-articular. In addition, the cortical and medullary continuity between the lesion and the sustentaculum tali was apparent compared with that of DEH [15]. Lastly, no additional lesion could be detected in other ossification centers on the whole-body x-ray, excluding the generalized form of DEH. For these reasons, we thought it would be appropriate to regard the lesion as the osteochondroma.

Patients with osteochondroma usually do not have symptoms, excluding the discomfort caused by mechanical irritation of the mass. However, if osteochondroma occur near the neurovascular structure, mostly popliteal nerve and artery around knee, numbness, weakness, loss of pulse, and color change can be presented on the affected limb [20]. Patient in our case was put into a similar situation by the osteochondroma originated from the rarely affected structure, the sustentaculum tali. As a result, tarsal tunnel syndrome was provoked.

Surgical intervention for tarsal tunnel syndrome is indicated among symptomatic patients who do not respond to non-operative treatment or those who have space-occupying lesion within the tarsal tunnel [2, 21]. Besides, a positive Tine’s sign is considered one of the most predictable indicators to the satisfactory outcome after the surgery [1]. The standard surgical approach to release the compressed posterior tibial nerve in the tarsal tunnel syndrome is known to be open tarsal tunnel decompression [1]. Our surgical success in this case seems to have been derived from radical excision of the bony mass because incomplete removal of the osteochondroma and inadequate tarsal tunnel release are together related to the recurrence and residual symptoms [12, 22].

One previous case report has demonstrated a similar case of tarsal tunnel syndrome secondary to osteochondroma of the sustentaculum tali [23]. However different from our case, the patient had undergone tarsal tunnel release prior to presentation and the talocalcaneal coalition was detected along with the osteochondroma. Scar tissues resulted from the previous operation and the mass effect of the talocacaneal coalition may have affected the compression of the posterior tibial nerve in combination so the talocalcaneal bar resection was performed additionally. In this study we were able to effectively decompress the posterior tibial nerve by solitarily excising the osteochondroma followed by immediately diminished the symptoms.

In conclusion, we encountered a rare case of tarsal tunnel syndrome secondary to osteochondroma of the sustentaculum tali in pediatric patient. If the space occupying structure within the tunnel is identified with a distinct neurologic symptom, complete surgical excision of the causative structure can bring out significant improvement of preexisted symptoms without recurrence.