Ankle sprains re-visited

The ankle sprain is probably the most common sport-related injury and among the most common musculoskeletal maladies the generalist is likely to face. Traditional treatment seems simple enough – rest, immobilisation, compression, elevation (RICE); ice packs and analgesia. In the last decade or so better imaging techniques like ultrasound and high resolution MRI has allowed a better understanding about the long term consequences of the injury and apparently the repercussions of the injury are not so straightforward. We present here a review of the available literature and an update on the management of the condition.

Anatomy

The ankle joint is made of three bones, the fibula and tibia (which together form a socket or mortise) and the talar dome (the ball). It is a fairly mobile joint in all planes – sagittal, coronal and axial. The principal restraints are the lateral ligaments – the anterior talo-fibular ligament (ATFL), calcaneo-fibular ligament (CFL) and posterior talo-fibular ligament (PTFL) respectively a, b and c in Figure 1. The medial joint is restrained by the deltoid ligament (d) which for all intents and purposes functions as one tough unit.

Figure 1. Medial and lateral anatomy of the ligaments of the ankle

Pathophysiology

The ATFL is most prone to injury with plantar-flexion and forced inversion forces. The CFL can rupture in a continuum of lateral ligament ruptures but this is very uncommon and the PTFL generally does not rupture. In Figure 2 below it is clear that if the ATFL ruptures, the resultant anterior translation of the talus on the tibia can only be prevented by the peroneus brevis tendon (arrowed in a). This would result in tears of this tendon. On the axial view this ligament is arrowed on the model (b) and MRI (c).

Figure 2. The ATFL in relation to the peroneal tendons around the ankle

It is also useful to revise some of the norms of biological healing. Skin and soft tissue tends to take about 2 weeks to heal. This means that bleeding and inflammation starts to settle about then and most injuries can be manipulated about then. Ligaments take about 6 weeks to heal and maybe about 6 more weeks to establish range of motion. Therefore, it is reasonable to surmise that an injury that is re-evaluated about one week after an injury would be painless enough to assess for function and yet not be too late that whatever injury there is could still be intervened on if correction is required. Within this time frame even occult fractures that only become apparent later would also be discovered.

Assessment

The main point of concern with most generalists is when should one refer such cases – the concern being that a more serious sprain has not been missed.

Clinically, in the acute phase it can be very difficult to know when an x-ray is required. In general if there has been gross deformity or significant hematoma formation then an x-ray is mandated. A simple AP and lateral x-ray of the ankle would suffice. Varus and valgus stress views are not necessary in the acute phase and can be painful to perform. Nevertheless, if a tibio-talar varus tilt is noted without fracture this may be indicative of a lateral ligament rupture. This lateral ligament rupture causes a progressively worse tilt as the ATFL, CFL and PTFL are in turn ruptured.

If at this point no fractures are seen about the ankle, then rest, immobilisation, compression, elevation (RICE); ice packs and analgesia are adequate treatment for the next 6 weeks. Depending on the swelling, an ankle brace may be too painful to fit in the acute phase. If the patient has significant pain and swelling, the patient should be seen 7 to 14 days later.

In the second week of injury swelling should have receded and pain considerably lessened. At this point, tenderness over the ATFL should be elicited and distinguished from pain that may be of a more generalised nature. An anterior drawer test can usually be performed by having the patient in a supine position, securing the leg with one hand, cupping the heel with the other hand and pulling forward (Figure 3). The foot should be internally rotated (I use my distal ulna to do this) to reduce tension on the deltoid ligament which could cause a false negative appreciation of lateral ankle instability. A subjective sense of the talus moving forward on the tibial plafond is an indication of significant instability. This manoeuvre while alarming for the patient is not generally painful at 2 weeks after injury. Such a case can then be referred for further management. All others can be managed in the community

Figure 3. The anterior drawer test in assessing ankle instability 2 weeks after a sprain

Treatment

If the ankle is found to be unstable at two weeks it should be immobilised in an ankle cast or functional brace for a further 6 weeks. These braces are only available via prescription and do not refer to the sorts used for sports (eg. aircast boot). The big advantage of these braces is they can be removed for hygiene. The disadvantage as can be guessed is patient non-compliance. Hence, a cast is often more desirable in these circumstances.

At the end of the 6-week period of immobilisation the ankle is re-assessed for stability. If the ankle is stable, physiotherapy is initiated to increase range of motion and a sport brace is used to assist in active sports. If there is persistent instability however certain undesirable effects can result (Figure 4). This patient presented with retro-malleolar pain referable to the peroneal tendons. Unlike similar medial pain which is often due to tibialis posterior tendinitis, peroneal pain is unusually primary in nature. The MRI confirmed peroneus brevis tendon thickening and tear (4a). In addition however the ATFL was noted to be chronically thickened and scarred (4b). On further probing, this patient had presented a year before to another centre with an ankle sprain. She was placed in a cast and told to return a week later but removed the cast herself one week later because there was no more pain. When this new retro-malleolar pain developed one year later she was not able to make the connection and effectively felt this was a new problem. It was not. In fact whenever significant ATFL tears are not appropriately repaired, their incompetence results in the peroneus brevis taking over this function. In the process this tendon can become torn and require a formal repair (4c and d; Arthroscopy: The Journal of Arthroscopic and Related Surgery Volume 25, Issue 11 , Pages 1288-1297, November 2009 Peroneal Tendon Tears: Associated Arthroscopic Findings and Results After Repair. Aaron Bare, M.D., Richard D. Ferkel, M.D.). They are the main cause of persistent pain after repairs of ankle instabilities. In addition, osteochondral lesions in the talar dome can result from the ankle subluxing repeatedly. This eventually results in osteoarthritis of the ankle.

Figure 4. Occult tears of the peroneus brevis tendon after neglected ankle sprains

When appropriately managed, most ankle sprains do not require surgery. Surgery may however become necessary with persistent instability in the active patient. Many procedures have been described to stabilise the ankle (Figure 5). In the past non-anatomical repairs were advocated. This involved borrowing nearby tendons to fashion an artificial lateral ligament complex. These procedures underestimated the fine balance the native ligament provides and resulted in over tightening the lateral complex and causing a non-physiological flexion extension manoeuvre even if varus stability was restored. The anatomical repairs advocated nowadays all involve some variation of reconstruction the ATFL itself and is the method of choice practiced by our surgeons.

Figure 5. Surgical techniques in restoring stability to the ankle