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extensor muscle contraction pulls it firmly into the groove; and the extensor retinacula and patellofemoral ligaments guide it centrally as it tracks along the trochlea groove. The most important static checkrein on the medial side is the medial patellofemoral ligament, a more or less distinct structure extending from the superomedial border of the patella towards the medial femoral condyle deep to vastus medialis. Additional restraint is provided by the medial patellomeniscal and patellotibial ligaments and the associated medial retinacular fibres. In a typical knee, considerable force is required to wrench the patella out of its track. However, if the intercondylar groove is unusually shallow (trochlea dysplasia), or the patella is seated higher than usual (patella alta), or the ligaments are abnormally lax (hypermobility), dislocation occurs more easily.

Mechanism of injury

Patella dislocation may be traumatic or atraumatic. The patella dislocates laterally and the medial patellofemoral ligament and retinacular fibres may be torn. Atraumatic dislocations occur in patients with predisposing factors as discussed, such as trochlea dysplasia, patella alta or hypermobility. Traumatic dislocations are rarely caused by direct violence while the knee is flexed and the quadriceps muscle relaxed, although the patella may be forced laterally by direct violence. More often, traumatic dislocation is due to indirect force: sudden, severe contraction of the quadriceps muscle while the knee is stretched in valgus and external rotation. Typically this occurs in field sports when a runner dodges to one side.

The rate of first-time dislocation is highest among female adolescents. Following a first event, 17% of patients will experience subsequent instability. The younger a patient is at the time of first dislocation and the more severe the dislocation, the greater the risk of subsequent dislocation. If the patient has an established history of subluxation or dislocation, the risk of subsequent episodes rises to 50%.

Clinical features

In a ‘first-time’ dislocation the patient may experience a tearing sensation and a feeling that the knee has gone ‘out of joint.’ Often the patella springs back into position spontaneously; however, if it remains unreduced,

there is an obvious (if somewhat misleading) deformity: the displaced patella, seated on the lateral side of the knee, is not easily noticed but the uncovered medial femoral condyle is unduly prominent and may be mistaken for the patella. Neither active nor passive movement is possible (Figure 31.13). If the dislocation has reduced spontaneously, the knee may be swollen and there may be bruising and tenderness on the medial side.

With recurrent dislocation the symptoms and signs are much less marked, though still unpleasant. After spontaneous reduction the knee looks normal, but the apprehension test is positive, i.e. the patient experiences pain and apprehension of attempts to push the patella laterally.

Imaging

Anteroposterior (AP), lateral and tangential (‘patella skyline’) X-rays are needed. In an unreduced dislocation, the patella is seen to be laterally displaced and tilted or rotated. In 5% of cases there is an associated osteochondral fracture. The lateral radiograph enables assessment for patella alta and trochlear dysplasia. A shallow trochlea and a crossing sign are features of dysplasia.

MRI provides invaluable information on the multifactorial aspects of patellofemoral instability and is the investigation of choice for patients being considered for surgical intervention. The cartilage contour in the trochlea typically varies from that of the underlying bone and accentuates the dysplasia. This is not appreciable on conventional radiographs or CT.

Treatment

If unreduced, dislocations can in most cases be pushed back into place without much difficulty. There is no need for immobilization or bracing and it is safe to weight-bear on the knee as soon as it is comfortable to do so.

First-time dislocations are generally managed non-operatively in the first instance. Non-operative therapy initially aims to reducing swelling and increase the range of motion of the knee. This is followed by muscle-strengthening exercises. Physiotherapy is directed towards closed chain exercises and vastus medialis oblique (VMO) strengthening (the main dynamic stabilizer of the patella).

Figure 31.13 Dislocation of the patella (a) The right patella has dislocated laterally; the flattened appearance is typical. (b,c) AP and lateral X-rays of lateral patella dislocation.

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With the higher grades of injury there is a risk of complete growth arrest at the proximal tibia. If the predicted leg length discrepancy is greater than 2.5 cm, tibial lengthening (or epiphysiodesis of the opposite limb) may be needed. Epiphysiodesis is surgical damage to the physis leading to growth arrest.

PROXIMAL TIBIAL METAPHYSEAL

FRACTURES

This rare injury (Cozen’s fracture) usually occurs between the ages of 4 and 8 years, resulting in fracture of the medial cortex with valgus angulation at the fracture site. Most fractures can be managed nonoperatively with reduction and immobilization. It is vital to ensure that any valgus angulation is corrected with careful varus moulding of the cast and this must be monitored while the fracture heals. Open reduction is rarely required, usually due to failed reduction because of interposed soft tissues.

A unique complication seen with this fracture type is a progressive valgus deformity after bony healing and possible tibial overgrowth resulting in leg lengthening.

TIBIAL TUBEROSITY INJURIES

Fracture or avulsion of the tibial tubercle usually occurs as a sports injury in young people. The knee is suddenly forced into flexion while the quadriceps is contracting, and a fragment of the tubercle – or sometimes the entire apophysis – may be wrenched from the bone. The diagnosis is suggested by the history. The area over the tubercle is swollen and tender; active extension causes pain.

The lateral radiograph shows the fracture, although this can be subtle. Patella alta may be present (the patella is abnormally high), having lost part of its distal attachment. CT/MRI may help delineate anatomy of the injury.

An incomplete fracture can be treated by applying a long-leg cast or extension brace with the knee in extension. Complete separation requires open reduction and fixation.

PATELLA SLEEVE FRACTURES

Sleeve fractures occur between the cartilage ‘sleeve’ and main part of the patella and ossific nucleus. The causative mechanism is similar to that of tibial tubercle avulsions, i.e. a forced quadriceps contraction on a flexed knee. These fractures occur most commonly in children aged 8–12 years when patella ossification is nearly complete.

Lateral radiographs may reveal small flecks of bone adjacent to the distal pole of the patella and patella alta. CT/MRI may help delineate anatomy of the injury.

Undisplaced fractures with intact extensor mechanisms may be treated in long-leg casts or extension braces. Displaced fractures require open reduction and internal fixation.

FRACTURES OF THE TIBIA

AND FIBULA

TIBIAL PLATEAU FRACTURES

Mechanism of injury

Fractures of the tibial plateau are caused by a varus or valgus force combined with axial loading (a pure valgus force is more likely to rupture the ligaments). This is sometimes the result of a car striking a pedestrian (hence the term ‘bumper fracture’); more often it is due to a fall from a height in which the knee is forced into valgus or varus. The tibial condyle is crushed or split by the opposing femoral condyle, which remains intact.

Pathological anatomy

The fracture pattern and degree of displacement depend on the type and direction of force as well as the quality of the bone at the upper end of the tibia. A useful classification is that of Schatzker (Figure 31.14):

•Type 1 – a vertical split of the lateral condyle

This is a fracture through dense bone, usually in younger people. It may be virtually undisplaced, or the condylar fragment may be pushed inferiorly and tilted; the damaged lateral meniscus may be trapped in the crevice.

•Type 2 – a vertical split of the lateral condyle combined with depression of an adjacent load-bearing part of the condyle

The wedge fragment, which varies in size from a portion of the rim to a sizeable part of the lateral condyle, is displaced laterally; the joint is widened and, if the fracture is not reduced, may later develop a valgus deformity.

•Type 3 – depression of the articular surface with an intact condylar rim

Unlike type 2, the split to the edge of the plateau is absent. The depressed fragments may be wedged firmly into the subchondral bone. The joint is usually stable and may tolerate early movement.

•Type 4 – fracture of the medial tibial condyle

Two types of fracture are seen: (1) a depressed, crush fracture of osteoporotic bone in an elderly

person (a low-energy lesion); and (2) a high-energy fracture resulting in a condylar split that runs obliquely from the intercondylar eminence to the medial cortex. The momentary varus angulation may be severe enough to cause a rupture of the lateral collateral ligament and a traction injury of the peroneal nerve. The severity of these injuries should not be underestimated.

•Type 5 – fracture of both condyles

Both condyles are split but there is a column of the metaphysis wedged in between that remains in continuity with the tibial shaft.

•Type 6 – combined condylar and subcondylar fractures

This is a high-energy injury that may result in severe comminution. Unlike type 5 fractures, the tibial shaft is effectively disconnected from the tibial condyles.

Figure 31.14 Tibial plateau fractures - Schatzker classification (a) Type 1: simple split of the lateral condyle. (b) Type 2: a split of the lateral condyle with a more central area of depression. (c) Type 3: depression of the lateral condyle with an intact rim.

(d) Type 4: a fracture of the medial condyle. (e) Type

5:fractures of both condyles, but with the central portion of the metaphysis still connected to the tibial shaft. (f) Type 6: combined condylar and subcondylar fractures; effectively a disconnection of the shaft from the metaphysis.

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TRAUMA

Clinical features

The knee is swollen and may be deformed. Bruising is usually extensive and the tissues feel ‘doughy’ because of haemarthrosis. Examining the knee may suggest medial or lateral instability but this is usually painful and adds little to the radiographic diagnosis. More importantly, the leg and foot should be carefully examined for signs of vascular or neurological injury. Traction injury of the peroneal or tibial nerves is not uncommon and it is important to establish the extent of any neurological injury at the time of admission and before surgery.

Imaging

Anteroposterior, lateral and oblique X-rays will usually show the fracture, but the amount of comminution or plateau depression may not be appreciated without CT. This provides information on the location of the main fracture lines, the site and size of the portion of condyle that is depressed and the position of major parts of articular surface that have been displaced. Software-generated reassembly of the axial images can provide sagittal and coronal views that aid in surgical planning (Figure 31.15). It is important not to miss a posterior condylar component in high-energy fractures because this may require a separate posteromedial or posterolateral exposure for internal fixation.

Treatment

TYPE 1 FRACTURES

Undisplaced type 1 fractures can be treated conservatively. As soon as the acute pain and swelling have subsided (usually within 1 week), a hinged cast-brace or ROM brace is fitted to allow early mobilization. Weight-bearing is restricted initially.

Displaced fractures should be treated by open reduction and internal fixation. The condylar surface

is examined (open or arthroscopically) and trapped fragments are released or removed. The aim is for an accurate reduction and fixation; lag screws alone or in combination with a buttress plate are usually sufficient for fixation.

TYPE 2 FRACTURES

If depression is slight (less than 5 mm) and the knee is not unstable, or if the patient is old and frail or osteoporotic, the fracture can be treated non-operatively with the aim of regaining mobility and function rather than anatomical restitution. In younger patients, and more so in those with a central depression of more than 5 mm, open reduction with elevation of the plateau and internal fixation is required. The joint is seen to allow a check on the quality of reduction (either with a submeniscal arthrotomy or arthroscopically). After elevation and restoration of the joint line bone graft may be needed to support the elevated fragments. Screws can be placed in parallel just beneath the subchondral bone to hold up the elevated fragments well. These are sometimes referred to as ‘raft’ screws, describing the arrangement of parallel screws (Figure 31.16). The wedge of lateral condyle is then fixed with a buttress plate (Figure 31.17). Newer designs of anatomically contoured and angle-stable locking plates (using screws that lock into the plate) are available and increasingly used but are not always necessary. Early knee movement is encouraged after surgery to minimize joint stiffness.

TYPE 3 FRACTURES

The principles of treatment are similar to those applying to type 2 fractures. However, the fact that the lateral rim of the condyle is intact means that the knee is usually stable and a satisfactory outcome is more predictable. The depressed fragments may need to be elevated through a window in the metaphysis; reduction should be checked by X-ray or arthroscopy. The elevated fragments can be supported with

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3be gauged by comparing the width of the tibiofibular interspace above and below the fracture.

Management

The main objectives are:

(a)

(b)

Figure 31.20 Fractured tibia and fibula – closed treatment (a) The position is held while an assistant applies plaster from the knee downwards. When the plaster has set, the leg is lifted and the above-knee plaster completed; note that the foot is plantigrade, the knee slightly bent and the plaster moulded round the patella. A rockered boot can be fitted for walking (b).

commonly performed and is an excellent way of managing these injuries. Care must be taken: there may be existing intra-articular extensions of metaphyseal fracture lines and there is the potential for propagation of a fracture into the joint when the nail is passed.

Plate fixation Plating can be used for metaphyseal fractures deemed unsuitable for nailing. It is also sometimes used for unstable tibial shaft fractures in children as it avoids the potential damage to the growth plate from passing an intramedullary nail through an open physis. Previously, the disadvantages of plate fixation included the need to expose the fracture site and, in so doing, stripping the soft tissues around the fracture, which could increase the risk of introducing infection and delaying union. Newer techniques of plating overcome these disadvantages. The plate is slid across the fracture through proximal and distal ‘access incisions’ on the anterolateral aspect

Figure 31.21 Fractured tibia and fibula – intramedullary nailing Closed intramedullary nailing is now the preferred treatment for unstable tibial fractures. This series of X-rays shows the fracture before (a) and after (b,c) nailing. Active movements and partial weight-bearing were started soon after operation.

of the tibia and then fixed to the bone only at these levels. This method of ‘submuscular’ plating preserves the soft tissues around the fracture site better than conventional open plating, and it provides a relative stability that appears to hasten union. The soft tissues are still at risk using this technique, however, and considerable care is required in tissue handling to minimize the risk of wound complications.

External fixation This is a more rarely used alternative to closed nailing; it avoids exposure of the fracture site and allows further adjustments to be made if this should be needed. It has a particular role in long, segmental, multifragmentary fractures. Monolateral external fixation is most commonly used as a temporizing method of fixation in the context of an open injury in adults but can be used as a definitive method. It is more commonly used in children. Disadvantages include the need to span joints for sufficient stability, which can cause stiffness and the potential for pinsite infection. Circular external fixators confer greater stability and often negate the need to span joints (Figure 31.22). In both cases the tissues around the fracture are left undisturbed.

HIGH-ENERGY FRACTURES

Initially, the most important consideration is the viability of the damaged soft tissues and underlying

bone. Tissues around the fracture should be disturbed as little as possible.

Comminuted and segmental fractures, those associated with bone loss, and indeed any high-energy fracture that is inherently unstable, require early surgical stabilization. For closed fractures, most commonly this is done by intramedullary nailing hence the tissues around the fracture are left undisturbed.

In cases of bone loss, small defects can be treated by delayed bone grafting as required; limb salvage options for larger defects include either bone transport or compression-distraction (acute shortening to close the defect, with subsequent lengthening at a different level) with a circular external fixator (see Chapter 12).

OPEN FRACTURES

For open fractures, the use of internal fixation has to be accompanied by judicious and expert debridement and prompt cover of the exposed bone and implant; alternatively, initial temporary external (or internal) fixation can be safer if these prerequisites cannot be met and definitive fixation can be delayed until coverage can be achieved. In the UK all high-energy open fractures are managed in Major Trauma Centres where orthopaedic and plastic surgeons can jointly manage these injuries to provide the highest standards of care according to BOA Standards for Trauma (BOAST 4) guidelines.

A suitable mantra for the treatment of open tibial fractures is:

•antibiotics

•debridement

•stabilization

•prompt soft-tissue cover

•rehabilitation.

Antibiotics are started immediately. A firstor secondgeneration cephalosporin or co-amoxiclav is suitable in most cases and should be continued until softtissue closure or for a maximum of 72 hours, whichever is sooner. The evidence for prolonged antibiotic use is lacking. Good debridement of the fracture and prompt cover remain the strongest defence against infection.

The wound should be photographed on first inspection in the Emergency Department by medical photography or using a hospital-registered camera, and then covered with a sterile dressing. The photograph can then be printed for inclusion in the patient’s case notes to serve as a record and prevent further disturbance to the wound.

Adequate debridement is possible only if the original wound is extended. Wounds should be reviewed and discussed with plastic surgeons, especially if there appears to be a need for local or free skin or muscle flaps. Ideally the debridement should be performed

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Figure 31.22 Circular external fixation (a–d) This method of fixation offers the benefit of multilevel stability and can be carried out with little additional damage to the soft tissues around the injury.

POSTOPERATIVE MANAGEMENT

Swelling is common after tibial fractures; even after skeletal fixation the soft tissues continue to swell for several days. The limb should be elevated and frequent checks made for signs of compartment syndrome.

After intramedullary nailing of a transverse or short oblique fracture, weight-bearing can be started within a few days and increased to full weight when this is comfortable. If the fracture is comminuted or segmental, meaning that almost the entire load will be taken by the nail initially, only partial weightbearing is permitted until some callus is seen on X-ray.

Early complications

VASCULAR INJURY

Fractures of the proximal half of the tibia may damage the popliteal artery. This is an emergency of the first order, requiring exploration and repair. Damage to one of the two major tibial vessels may also occur and go unnoticed if there is no critical ischaemia.

COMPARTMENT SYNDROME

Tibial fractures – both open and closed – are among the commonest causes of compartment syndrome in the leg. The combination of tissue oedema and bleeding (oozing) causes swelling in the muscle compartments and this may precipitate ischaemia. Additional risk factors are proximal tibial fractures, severe crush injury, a long ischaemic period before revascularization (in type IIIC open fractures), a long delay to treatment, haemorrhagic shock, difficult and prolonged operation and a fracture fixed in distraction.