CHAPTER 12 The ankle
Fig. 12.A
Anatomical Features
The ankle joint is basically a simple hinge joint, normally permitting movement in one plane (dorsiflexion and plantarflexion), but in addition, up to 18° of axial rotation of the talus in the tibial mortice may occur. Load-bearing stresses (LB) are taken by the upper articular surface of the talus and the tibia; the fibula plays no part in this.
Medial displacement (translation) of the talus is prevented by the medial malleolus (M), and lateral displacement by the lateral malleolus (L). Posterior talar shift is blocked by the downward-projecting curved articular surface of the tibia (P) behind, and the corresponding surface in front (A) prevents anterior subluxation. Any of these bony prominences may be fractured, resulting in potential instability.
When viewed from above, the articular surface of the talus may be seen to be wider anteriorly (1) than posteriorly (2). This means that as the ankle is dorsiflexed (3), the talus is gripped more firmly between the malleoli and pushes the fibula laterally (4). When the ankle is plantarflexed there is a greater degree of freedom (and instability) of the talus in the ankle mortice.
The natural congruency of the bony components of the ankle accounts for its inherent stability and this is reinforced by the disposition and strength of the associated ligaments. These include the following:
Note that a careful examination of the foot is often also required in the investigation of many ankle complaints.
Soft Tissue Injuries of the Ankle
Soft tissue injuries of the ankle are extremely common and in more severe cases difficult to differentiate from undisplaced fractures. Radiographic examination is essential in all but the most minor lesions, and is also necessary where symptoms are persistent. When fracture has been excluded after a significant injury a diagnosis has still to be made, as this manifestly affects treatment.
Injuries of the Lateral Ligament
The lateral ligament is damaged through inversion injuries. In an incomplete tear, some fibres only are ruptured (ankle sprain). Treatment is then symptomatic and a full early recovery can be expected. When the ligament is completely torn or detached from the fibula, the talus is free to tilt in the mortice of the tibia and fibula. If the lateral ligament fails to heal, chronic instability of the ankle results. If this injury is diagnosed in the acute stages, it should be treated by prolonged immobilisation in a plaster cast or orthosis, or by operative repair. In late-diagnosed cases good results generally follow lateral ligament reconstruction procedures.
In functional instability of the ankle the patient complains of frequent sensations of the ankle giving way, and pain, stiffness and swelling related to activity, but no evidence of ligament laxity can be found. It is thought that in many of these cases there is a degree of motor incoordination arising from some disorder of proprioception. Most respond to specialised physiotherapy (using tilt boards and other measures to improve muscular coordination).
Inferior Tibiofibular Ligaments
When the foot is dorsiflexed the distal end of the fibula moves laterally (and proximally) as it is engaged by the wedge-shaped upper articular surface of the talus. This movement is restricted by the inferior tibiofibular ligaments, and to a lesser extent the interosseous membrane. Damage to these structures may lead to lateral displacement of the fibula and lateral drift of the talus (diastasis). In treatment, the talus must be realigned with the tibia and any fibular displacement reduced. This reduction may be held by cross-screwing of the fibula to the tibia, or by plaster fixation.
Medial Ligament
The medial ligament is immensely strong, and if stressed in ankle joint injuries it generally avulses the medial malleolus rather than itself tearing. Nevertheless, tears do occur, and are seen particularly in conjunction with lateral malleolar fractures. Meticulous reduction of any associated fracture is essential, and this often requires an open procedure. Operative repair of the ligament may be required.
Achilles Tendon (Tendo Calcaneus)
Achilles Tendinopathy
This generally results from excessive repetitive overload of the tendon to a degree that exceeds its capacity to recover. The preferred term ‘tendinopathy’ includes a number of conditions which may only be differentiated by direct inspection and histological examination of the tendon or surrounding structures. These include tendinitis, where there is a clear inflammatory process involving the tendon; tendinosis, where there is collagen degeneration within the tendon; and paratendinitis, when there are inflammatory changes in the sheath of the tendon.
The condition is common in athletes, particularly runners and jumpers, but also in footballers, tennis players and ballet dancers. It gives rise to localised pain which is related to lower limb activity. In severe cases of tendinopathy there may be progressive weakness of plantarflexion, accompanied by impaired function and, in some cases, spontaneous rupture of the tendon.
Most cases are treated conservatively by restricting activities, supplemented when required by physiotherapy in the form of tendon stretching exercises, tendon massage, orthotic devices for the shoes, and therapeutic ultrasound. In some resistant cases surgical measures such as the removal of fibrotic nodules from within the tendon and the release of tendon adhesions may be required.
Acute Traumatic Achilles Tendon Rupture
Sudden plantarflexion of the foot may rupture the Achilles tendon, especially when it is weakened as a result of tendinosis and the degenerative changes often seen in middle age. Surgical repair may be carried out, although in most cases excellent results may be achieved by conservative management in a plaster cast or an orthosis.
Other Common Conditions Seen Around the Ankle
Tenosynovitis
Inflammatory changes in the tendon sheaths behind the malleoli may give rise to pain at the sides of the ankle joint. Tenosynovitis may follow unusual excessive activity or be associated with degenerative changes, flat foot or rheumatoid arthritis. There is puffy swelling in the line of the tendons, with tenderness extending often for several centimetres along their length. Tibialis posterior and peroneus longus are most frequently involved, and stretching of these structures during inversion and eversion of the foot gives rise to pain. Spontaneous rupture is not uncommon. Symptoms generally respond to immobilisation for short periods in a below-knee walking plaster or an orthosis.
Footballer’s Ankle
Ill-localised pain in the front of the ankle may follow repeated incidents of forced plantarflexion of the foot which result in tearing of the anterior capsule of the ankle joint. This occurs frequently in footballers, where this form of stress is common. Calcification in the resulting areas of avulsion and haemorrhage leads to the appearance of characteristic exostoses, which show in lateral radiographic projections of the ankle. These may lead to mechanical restriction of dorsiflexion.
Osteochondritis of the Talus
Although rather uncommon, this condition, which is seen most frequently in adolescents and young men, may give disabling pain in the ankle. It is now generally agreed that the condition starts as an osteochondral fracture. It is the frequent source of complaints of chronic disability following a so-called simple sprain of the ankle. The diagnosis is made on the radiological findings, although the site of the pain and local tenderness over the upper articular surface of the talus may lead one to suspect it. CT and MRI scans are invaluable in doubtful cases. If loose bodies are produced, they must be excised. The treatment of the local lesion follows in principle that of osteochondritis dissecans of the knee.
Snapping Peroneal Tendons
This is an uncommon cause of ankle pain and is due to tearing of the superior peroneal retinaculum. The patient complains of a clicking sensation in the ankle and is usually able to demonstrate the peroneal tendons riding over the lateral malleolus. The treatment is by surgical reconstruction of the retinaculum.
Osteoarthritis
Primary osteoarthritis of the ankle is rare. Secondary osteoarthritis is sometimes seen after ankle fractures, avascular necrosis of the talus, or osteochondritis of the talus.
