Posterior tibial tendon dysfunction (PTTD) is a cause of persistent pain around the medial malleolus. It is also a leading cause of flat foot disorders, especially in seniors. The prevalence rate is 3.3% in the over 40’s, which is actually greater than that for Achilles tendinopathy in the non-athletic population (Albers et al 2014). Although the name is complicated, the condition is clearly quite common.
Although the name is complicated, the condition is clearly quite common.
Structure & Function
The tibialis posterior (TP) is the deepest of the muscles on the back of the shin, lying within the deep posterior compartment. It attaches to the back of the tibia and fibula (upper portion) and the membrane which connects the two bones (interosseous membrane). From here it passes in a groove around and beneath the medial malleolus, the latter structure acting as a pulley. Once in the foot, the muscle attaches into two block like bones on the inner surface the foot, the navicular and the inner (medial) cuneiform. The navicular is the keystone of the foot arch, and its height is maintained by the pull of the tibialis posterior. As a consequence the muscle inverts the foot at the subtalar joint, and importantly acts to maintain the height of the medial longitudinal arch. Additionally the tibialis posterior is a plantarflexor of the ankle joint. The combination of these two actions make tibialis posterior the main supinator of the foot in the stance phase of walking (Durrant 2016).
On the inside of the ankle bone (medial malleolus) a number of structures are found beneath the flexor retinaculum in a gap called the tarsal tunnel which is comparable to the carpal tunnel of the wrist. These structures are often remembered by the mneumonic from anterior to posterior ‘Tom, Dick And Very Nervous Harry’. Tom, Dick and Harry correspond to Tibialis posterior, flexor Digitorum longus, and flexor Hallucus the And Very Nervous representing the Artery (posterior tibial),Vein (posterior tibial) and Nerve (tibal nerve).
During pronation (foot flattening), the TP tendon is pressed onto the underlying bone of the groove, and in individuals who over pronate during the stance phase of walking or running, tendon or tendon sheath conditions (pathologies) may occur.
The condition may be categorised into one of four stages depending on the height of the medial foot arch and the available movement (flexible or rigid) of the rearfoot joints as shown in table 1. Early stages (1 & 2) represent a flexible flat foot deformity (FFD) and are generally managed conservatively. Later stages (3 & 4) may benefit from conservative management in the short term, but may require surgical intervention to regain foot function. Tissue changes to the tibialis posterior in PTTD suggest degeneration rather than inflammation, implying tendinopathic changes. Disruption of the in line (linear) organisation of collagen bundles occurs giving a reduction in tensile strength, with few inflammatory infiltrates found at surgery (Mosier et al 1999, Kulig et al 2009).
Subjective assessment (patient questioning) often reveals a history of slow onset over months or years with activities such as prolonged standing increasing symptoms. A recent shopping trip or standing at an event is often the trigger for a patient seeking help. Tenderness is frequently described over the inner ankle extending to the posterior portion of the inner foot edge. Pain is often dull and aching in nature and affected by choice of footwear in stages 1 and 2 especially. Soft un-supporting shoes such as ballet pumps, or slippers may make pain worse, while it can be eased when wearing supporting sports shoes or more rigid leather shoes.
Objective assessment (patient examination) should initially be made in standing. The height of the medial longitudinal arch should be assessed and the navicular drop test may be useful. The height of the navicular is assessed using a ruler placed vertically on the inside of the foot. To begin the patient stands with their weight on the unaffected leg, and then transfers the weight across to the affected leg to try to stand on one leg. Assess if the navicular height drops, and if so can the patient prevent this by trying to lift the inner edge of the foot upwards. If the inner arch has flattened, (stage 1) is the deformity correctable by passively lifting the joint up, or is it fixed. Where the arch height has lowered, has the heelbone (calcaneus) also been pulled outwards (subtalar joint valgus). A final foot position may be forefoot abduction where the front portion of the foot splays outward. A useful visual check of this when viewed from behind is that the patient appears to have too many toes (Davey 2016), demonstrating an abductor twist. Here, when looking from behind past the heel and Achilles, you should normally be able to see the 4th and 5th toes as well. However, if the forefoot has abducted (moved outwards) more of the toes are visible.
The Navicular bone may be more prominent as it presses inwards, and sometimes an accessory navicular is present, – this is an extra piece of bone or cartilage which is located within the tibialis posterior tendon as it attaches to the navicular proper, and is visible on x-ray.
Commonly with PTTD the calf muscles may be tight, limiting the amount of dorsiflexion (ankle bending forwards) at the end of the stance phase of walking. As dorsiflexion is reduced, the foot compensates by abducting the forefoot and rolling over the inner edge of the foot with each step. Raising up onto the toes (heel raise action) may also be limited or changed. Normally when a person performs a heel lift the heels swing inwards slightly (varus) but with PTTD the heelbone can begin outwards (valgus or flatfoot appearance) and fail to correct as the patient raises onto their toes. Commonly the tendon may be painful to palpation (pressing) as it travels behind the malleolus in its groove, or at its insertion to the navicular bone (navicular tuberosity).
The foot posture index (FPI-6) click here is a useful general assessment of the foot which may be used before and after treatment to assess improvement in any flexible foot disorder (FFD). Using it the clinician assesses the position of the head of talus, the curves beneath the malleolus, heel (calcaneal) position, prominence of the navicular head, height of the medial longitudinal arch and the presence of forefoot abduction. FFD is said to be present in standing when one or more of the following is shown – calcaneal valgus, medial longitudinal arch depression, and forefoot abduction (Bowring and Chockalingam 2009).
The aim of conservative management (physiotherapy and podiatry) is to reduce pain and inflammation, lessen the strain on the TP tendon and promote healing. Strength and function are enhanced and foot alignment improved to prevent the condition progressing (Bowring and Chockalingam 2009). Passive modalities (electrotherapy, acupuncture), manual therapy (massage, soft tissue manipulation), and support (taping, orthotics) all have their place in the management of this condition. Generally they are used to modify symptoms and especially to reduce pain.
Graded exercise constitutes a major part of the treatment of PTTD, as with other forms of tendinopathy. The Tibialis posterior can be exercised using a resistance band into plantarflexion and inversion. Sit with sports shoes on and your knee bent, heel in contact with the floor. Loop the band around your foot and hold your hand out to the side to take up any slack. Pull your foot in (inversion) and down (plantarflexion) against the resistance of the band. This action is a concentric muscle contraction, and an eccentric (lengthening) action is also helpful. For this movement, turn the foot in and down as before, then move your hand out to stretch the band. Holding your hand still, gradually allow your foot to turn out (eversion) and up (dorsiflexion) against the recoil of the band. Where a person has a normal arch height, this action may be performed barefoot. However, where the arch height has reduced, the action should be performed in shoes which support the arch to maintain its height as the muscle recruitment is more effective (Kulig et al 2005). Although this is a non-weightbearing movement and so not functionally specific to walking and running, it has the advantage of taking compression away from the tibialis posterior tendon, and so not exacerbating pain. Once this action is pain free dorsiflexion and plantarflexion (heel aligned) may be used against band resistance prior to double leg and single leg heel raises again with correct heel alignment. Where the heel falls outwards (valgus), gripping a ball between the heels of a double leg heel lift can be a good cue to aid correction (Davey 2016).
Graded exercise constitutes a major part of the treatment of PTTD
Arch lift exercises are also useful. These can begin in sitting, lifting the centre of the medial arch upwards (increasing the dome height) while keeping the ball of the foot pressing down on the floor to avoid forefoot supination. This action can be progressed to standing to increase load via bodyweight, and then varied by placing the outer (lateral) edge of the foot on a book or wooden block while increasing medial arch height.
Once the calf is stretched (leg straight and knee bent) a step down action may be used. The action is to keep the affected foot on the step facing forwards and to step down with the non-affected foot. The knee should pass over the centre of the foot to avoid forefoot abduction (flattening the foot and rolling over the inner edge).
The exercise response should be graded over time. The aim is to build resilience in the tissues by overloading them sufficiently to stimulate change but not so much that they are irritated or damaged. As the tissues adapt the overload (hardness of exercises) should increase to keep pace. With the aim being pain free full function.
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