Assess & Address: Tarsal Tunnel Syndrome by Whitney Lowe

Anatomical background Pathology Assessment & Evaluation Treatment Massage Techniques

Pathology
TTS occurs when the tibial nerve is exposed to compressive or tensile stress within the tarsal tunnel. There are a number of different factors that may cause either compressive or tensile loads on the nerve. Compression may occur from extrinsic factors, which are those that come from outside the tunnel. Examples include a direct blow to the medial side of the ankle, as well as fractures or dislocations that compress the nerve.

Nerve compression in the tunnel may also occur from intrinsic factors, which are those within the tunnel itself. Space-occupying lesions or ganglions within the tunnel may press on the nerve or vascular tissues. Anatomical anomalies, such as bony prominences that protrude into the tunnel, may also compress the nerve. Each tendon that passes underneath the tunnel is encased within its own synovial sheath. A swelling of the tendon and synovial sheath (tenosynovitis) in the tunnel may compress either the tibial nerve or the nearby vascular structures. (Tenosynovitis usually occurs from repetitive overuse of the involved tendons.) The tunnel’s contents may be compressed in a calcaneal varus foot alignment as the overall space in the tarsal tunnel is decreased (Figure 3). Additional compression of the tendons within the tunnel in a varus foot alignment may lead to tenosynovitis. More than one of these factors may be in play at the same time.

Tensile forces on the nerves in the tarsal tunnel may also be a cause of symptoms. Neural tension most commonly results from either a sudden stretch of the nerves, or more commonly from a calcaneal valgus foot alignment (Figure 4). The valgus foot alignment is associated with overpronation of the foot and may be one reason why TTS appears to be more common in runners with altered foot mechanics during gait. When examining the factors responsible for TTS it is important to remember that the condition may result from compression, tension or a combination of both.

An important factor to consider in TTS is that it may not take a large amount of compression or tension within the tunnel to create symptoms. Because the tarsal tunnel is at the distal end of the lower extremity, the nerves have a long path prior to entering the tunnel. Consequently, the tibial nerve is susceptible to compression pathologies in a number of locations along its length before entering the tunnel. Distal compression or tension pathologies are increasingly common if there is a more proximal compression of the same nerve. This principle is referred to as the double- or multiple-crush phenomenon. For example, TTS is more likely to occur in a situation where there is already proximal nerve compression, such as piriformis syndrome, or disc herniation pressing on nerve roots in the lumbar region. Therefore it is important to screen for other proximal nerve conditions as well.