Posterior tibial tendon insufficiency (also called posterior tibial tendon dysfunction or adult acquired flatfoot) has been named literally after failure of the posterior tibial tendon. However, the condition is caused not only by the progressive failure of the posterior tibial tendon; it is also failure of associated ligaments and joints on the inner side of the ankle and foot. This results in collapse of the arch of the foot, along with the deformity which most often becomes the debilitating problem in its later stages.
Figure 1: Anatomical diagram of the foot and ankle highlighting effects of posterior tibial tendon insufficiency.
[Illustration courtesy of the Journal of Musculoskeletal Medicine]
While at the beginning the common symptom is pain over the tendon in the inner part of the hindfoot and midfoot, later on it is the deformity that can threaten a person’s ability to walk.
Just as the tendon degenerates and loses its function, other soft tissue on the same inner side of the foot - namely the ligaments - degenerate and fail. Ligaments are responsible for holding bones in place, and when they fail, bones shift to places where they shouldn’t; deformity is the result. The deformity causes malalignment, leading to more stress and failure of the ligaments.
The cause of posterior tibial tendon insufficiency is not completely understood. The condition commonly does not start from one acute trauma but is a process of gradual degeneration of the soft tissues supporting the medial (inner) side of the foot. It is most often associated with a foot that started out somewhat flat or pronated (rolled inward). This type of foot places more stress on the medial soft tissue structures, which include the posterior tibial tendon and ligaments on the inner side of the foot.
Children nearly fully grown can end up with flat feet, the majority of which are no problem. However, if the deformity is severe enough it can cause significant functional limitations at that age and later on if soft tissue failure occurs.
Also, young adults with normally aligned feet can acutely injure their posterior tibial tendon from a trauma and not develop deformity. The degenerative condition in patients beyond their twenties is different from the acute injuries in young patients or adolescent deformities, where progression of deformity is likely to occur.
Posterior tibial tendon insufficiency is divided into stages by most foot and ankle specialists:
In stage I, there is pain along the posterior tibial tendon without deformity or collapse of the arch. The patient has the somewhat flat or normal-appearing foot they have always had.
In stage II, deformity from the condition has started to occur, resulting in some collapse of the arch, which may or may not be noticeable. The patient may feel it as a weakness in the arch. Many patients initially present in stage II, as the ligament failure can occur at the same time as the tendon failure and therefore deformity can already be occurring as the tendon is becoming symptomatic.
In stage III, the deformity has progressed to the extent where the foot becomes fixed (rigid) in its deformed position.
Finally, in stage IV, deformity occurs at the ankle in addition to the deformity in the foot.
Initial treatment consists of supporting the medial longitudinal arch (running the length of the foot) to relieve strain on the medial soft tissues. The most effective way to relieve pain on the tendon is to use a boot or brace, and once tenderness and pain has resolved, an orthotic device. A boot, brace, or orthotic has not been shown to correct or even prevent the progression of deformity. Orthotics can alleviate symptoms and may slow the progression of deformity, particularly if mild. The deformity may progress despite orthotics.
The indications for surgery are persistent pain and/or significant deformity. Sometimes the foot just feels weak and the assessment of deformity is best done by a foot and ankle specialist. If surgery is appropriate, a combination of soft tissue and bony procedures may be considered to correct alignment and support the medial arch, taking strain off failing ligaments.
Depending upon the tissues involved and extent of deformity, the foot and ankle specialist will determine the necessary combination of procedures. Surgical procedures may include a medial slide calcaneal osteotomy to correct position of the heel, a lateral column lengthening to correct position in the midfoot and a medial cuneiform osteotomy or first metatarsal-tarsal fusion to correct elevation of the medial forefoot. The posterior tibial tendon may be reconstructed with a tendon transfer.
In severe cases (stage III), the reconstruction may include fusion of the hind foot,, resulting in stiffness of the hind foot but the desired pain relief.
In the most severe stage (stage IV), the deltoid ligament on the inside of the ankle fails, resulting in the deformity in the ankle. This deformity over time can result in arthritis in the ankle.