Can Orthotics Have An Impact On Tarsal Tunnel Syndrome?
In 2002, Kinoshita and colleagues performed pronatory stress tests by dorsiflexing and everting the hindfoot with a 10-second hold on 37 patients who were diagnosed with tarsal tunnel syndrome.9 Researchers were able to reproduce plantar paresthesias in all patients. In order to confirm actual nerve impingement, all of these patients then had surgery to release the nerve and confirm the diagnosis, and nearly 100 percent (42 of 43 feet) had physical findings of nerve entrapment. The authors concluded that a positive “Kinoshita test” was very accurate in identifying tarsal tunnel syndrome.
Understanding The Anatomy And Pathomechanics Of The Tarsal Tunnel
Simply stated, the tarsal tunnel is the distal aspect of the deep posterior compartment of the leg behind the medial malleolus.3 The tarsal tunnel contains the tendons of the posterior tibial, flexor digitorum longus and the flexor hallucis longus muscles, each in their own compartments created by septae of the flexor retinaculum.2 The tarsal tunnel also contains the posterior tibial artery, nerve and vein all together in a single compartment. This is all bordered by the flexor retinaculum superficially, the posterior side of the medial malleolus anteriorly and the medial talus and calcaneus deep and posteriorly.
It is important to appreciate that each of these compartments has constantly changing volumes due to the fact that the flexor retinaculum and the included septae run from the medial malleolus to the calcaneus where they can blend with the plantar fascia.2 Therefore, tension on the fascia may create tension of the retinaculum and less volume (more pressure) on the contained structures, resulting in pain.
A 1999 article by Trepman and colleagues looked at the effect of foot position on tarsal tunnel compartment pressure.10 The authors used 10 fresh, frozen cadaver distal extremities and measured compartment pressures with the foot-ankle held in subtalar joint neutral. The foot-ankle then went into full inversion and subsequently into full eversion. It is important to note that researchers held the ankle joint in approximately 20 degrees of plantarflexion throughout testing. The tarsal tunnel compartment pressure in neutral position was 2 ± 1 mmHg while eversion yielded the greatest pressure of 32 ± 5 mmHg and inversion yielded 17 ± 5 mmHg. The authors concluded that their results might explain why neutral immobilization of the hindfoot relieves tarsal tunnel syndrome symptoms because of less pressure in the compartment and therefore less irritation to the posterior tibial nerve.
What To Consider In The Differential Diagnosis
As the clinician works up the patient with a thorough history and physical exam, and approaches the diagnosis of tarsal tunnel syndrome, it is important to appreciate what other diagnoses can mimic tarsal tunnel syndrome in order to ensure an accurate diagnosis and effective treatment.
Differential diagnoses to consider include: radiculopathy, diabetic neuropathy, peripheral neuropathy, rheumatoid arthritis, seronegative arthropathies, vascular disease, Baxter’s nerve entrapment, plantar fasciitis, scar tissue from prior injury or surgery, lower extremity edema, or a space-occupying lesion such as a ganglion, lipoma or tumor.2,3,8
Ordering nerve conduction studies and possibly magnetic resonance imaging (MRI) may assist in diagnosing the patient to allow for proper and successful treatment.