Posterior Tibial Tendon Dysfunction

Roger A. Mann, M.D.
Private Practice Orthopaedic Surgery
Director of Foot Fellowship Program
Oakland, California

Posterior tibial tendon dysfunction is caused by tenosynovitis of the posterior tibial tendon, which eventually results in tendinosis of the tendon. This condition presents as a spectrum of physical findings to the clinician since the patient that you see may be early in the course of the degeneration of the tendon or late. The bottom line, however, is that these patients develop an acquired flatfoot deformity. The patient will give the history that over time one of their feet has become progressively flatter than the other and has become less functional.

Posterior tibial tendon dysfunction is not the only cause of in acquired flatfoot in adults. It can also be seen in other conditions such as a Charcot foot as is in the diabetic patient, with primary arthrosis of the tarsometatarsal joints that results in an abduction dorsiflexion deformity through the mid tarsal area, residuals of a Lisfranc fracture/dislocation, or in the patient with rheumatoid arthritis.

The physical examination is very important in defining the problem that you are presented with. It begins with the patient standing and observing their feet from the front. One notes that one foot is flatter than the other foot and may be more abducted through the forefoot. Looking at the foot from the rear, the calcaneus is in more valgus on the involved side and there may be an area of swelling or fullness below the medial malleolus due to the synovitis about the posterior tibial tendon. The the patient is asked to single toe rise, they usually cannot do so because the posterior tibial tendon is necessary to stabilize the longitudinal arch to permit single limb toe rise to occur.

The next portion of the physical examination is hands-on and a determination must be made as to the range of motion of the ankle, subtalar and transverse tarsal joints. This is very important information since if the patient has normal motion through these joints then some type of an orthosis can be used to hold the foot in neutral position. If, however, there is a fixed deformity in the hindfoot or forefoot then some type of an accommodative orthotic device will be necessary.

The critical factor in examining the foot is to determine the relationship of the hindfoot to the forefoot. This is done by placing the calcaneus in line with the long axis of the tibia and covering the head of the talus with the navicular. The clinician then observes the position of the forefoot to determine the degree of forefoot varus that is present. If the patient has a fixed forefoot varus deformity of more than 10° to 15°, it will cause the calcaneus to move into valgus after initial ground contact. The degree of correction built into the forefoot portion of the orthotic device will need to compensate for this deformity if the orthotic device is to be useful.

Anterior-posterior radiographs of the foot often demonstrate lateral subluxation of the navicular on the head of the talus and on the lateral x-ray there is a sagging of the talonavicular and naviculocuneiform articulations. An MRI is sometimes useful in confirming the diagnosis, but rarely is indicated since clinically it is not very difficult to make this diagnosis. In patients who have longstanding posterior tibial tendon dysfunction, an AP x-ray of the ankle joint should also be obtained since the talus may be tilting into valgus and this will need to be taken into account when an orthotic device is made.

The pathomechanics of the deformity observed in posterior tibial tendon dysfunction results from the fact that the posterior tibial muscle and tendon are extremely strong structures whose main function is that of inversion of the transverse tarsal joint by its insertion into the plantar medial aspect of the navicular. It has a total excursion of about 2 cm, 75% of which is an inversion excursion and 25% an eversion excursion. The muscle belly itself is a bipenniform muscle, which means it has a short excursion and generates maximum power over the five insertions of the tendon into the plantar aspect of the foot. When the tendon undergoes degenerative changes it lengthens. It is this lengthening that creates muscle weakness and a muscle imbalance is created.

The main function of the tibialis posterior muscle is to adduct the transverse tarsal joint and invert the subtalar joint. This muscle is opposed by the peroneus brevis whose function is to abduct the transverse tarsal joint and evert the subtalar joint. When these two muscles are working in 'normal' balance the foot is normally aligned. However, when one of these muscles is no longer functional or is severely compromised then the other muscle takes over and a deformity results. In the case of posterior tibial tendon dysfunction it is the peroneus brevis muscle that is still functioning and this is what 'actively' creates the deformity, namely the valgus of the calcaneus and abduction of the forefoot. As this condition continues, the ligamentous supporting structures, namely the spring ligament complex, become stretched and eventually a fixed deformity of the longitudinal arch will occur. This deformity occurs over a long period of time in most cases and when in the course of the patient's problem they seek medical attention will determine the degree of deformity that is observed. This is why I stated at the beginning of this discussion that these patients present with a spectrum of problems, since it is an ongoing dynamic clinical entity.

The medical treatment of the condition consists of immobilization if the patient presents only with synovitis of the posterior tibial tendon and no structural deformity. Often, four to six weeks of immobilization followed by an ankle/foot orthosis for four to six months is sufficient. If this regimen allows the tendon to become stable, no further treatment is necessary. If the tendon continues to be inflamed and painful with resumption of normal activities, then further use of an ankle/foot orthosis or possibly surgical intervention would be indicated.

The surgical procedures that are commonly utilized to treat this condition consist of a synovectomy of the posterior tibial tendon if the tendon is structurally intact, or, if it is no longer functional, a transfer of the flexor digitorum longus tendon is used to bypass the non- or minimally functioning posterior tibial tendon in order to restore inversion and adduction to the transverse tarsal joint to balance the peroneus brevis muscle. If a flexible valgus deformity is of the calcaneus is also present a medial displacement calcaneal osteotomy is also carried our. The outcome of this type of surgery is satisfactory in about 90% of cases.

The patients that present with an inflexible foot, namely one that has fixed deformities, which usually consist of a valgus deformity of the calcaneus, abduction through the transverse tarsal joint and a fixed varus deformity, will require a procedure such as a triple arthrodesis to realign and create a plantigrade foot.

As a general rule, if a plantigrade foot can be created, then no further orthotic device is necessary, but if it cannot be achieved then some type of an accommodative orthotic device is useful.

The main advantage of carrying out a posterior tibial tendon reconstruction as opposed to an arthrodesis is that it restores active inversion, provides good pain relief, restores foot stability, the patient's functional capacity is improved, and it maintains a flexible foot as opposed to the patient that requires an arthrodesis in which the foot becomes inflexible thereby placing increased stress on the ankle and tarsometatarsal joints.

The type of orthotic device utilized in patients with this clinical problem varies depending upon the severity of the deformity, its flexibility, and the age of the patient. The orthotic device may be a short articulated ankle/foot orthosis or a long or short non-articulated ankle/foot orthosis.

References

  1. Haddad, S.L., Mann, R.A.: Flatfoot in Adults in Coughlin, M.J., Mann, R.A., Saltzman, C.L.(Eds): Surgery of the Foot and Ankle, Volume I (Ed. 8). Philadelphia, PA. Mosby Elsevier, 2007, pp 1007-1086.