12.55 Patella fractures and dislocations

Acute injuries to the extensor mechanism of the knee include patella fractures and dislocations and quadriceps and patella tendon ruptures. Despite their common occurrence, there is much controversy regarding the management of many aspects of patella injuries. Hardware irritation, loss of reduction, and recurrent dislocation continue to be common complications.

The patella, the largest sesamoid, is invested within the strong fascia of the extensor mechanism. Its shape is that of a pear turned upside down, with a broad proximal pole and narrower distal pole. The quadriceps insert into the proximal pole while the patella tendon originates from the inferior pole (Figure 12.55.1). The proximal three-quarters of the posterior patellar surface is composed of articular cartilage and articulates within the trochlear groove of the femur. The articular surface is divided by a vertical ridge into larger lateral and smaller medial facets. The inferior pole, which encompasses one-quarter of the patella, contains no articular surface. The patella serves four functions:

Patella fractures account for approximately 1% of fractures. Although they occur in patients of all ages, most occur in the third through fifth decades of life.

The majority of patella fractures disrupt the extensor mechanism, albeit to varying degrees. With increasing amounts of fragment separation, there is greater injury to the adjacent medial and lateral retinacula signifying a greater disruption of the extensor mechanism. Direct contact injuries are undoubtedly associated with patellar and trochlear cartilage injury.

Patella fractures result from both direct and indirect forces. A direct force applied to the anterior surface of the patella typically causes a comminuted, minimally displaced fracture pattern (Figure 12.55.2). Tensile and three-point bending forces indirectly produce patella fractures. With the knee in extension, the quadriceps transmits tensile forces to the patella. With increasing knee flexion, the patella engages in the trochlear groove. During a violent quadriceps contraction against a fixed, flexed lower extremity, as would occur from a fall from a height, the patella receives a combination of these indirect forces (tension and three-point bending) that typically creates a displaced, transverse fracture that may have a variable amount of comminution of the articular surface (Figures 12.55.3 and 12.55.4). The anterior surface fails in tension resulting in the transverse component while the posterior surface experiences compression accounting for the comminution.

A significant number of patella fractures occur as a result of combined direct and indirect forces (namely motor vehicle collisions—with the flexed knee striking the dashboard as the quadriceps contracts). These fractures also consist of both transverse and comminuted sections.

With increasing knee flexion, the patellar articular contact area shifts from distal to proximal. Therefore inferior pole fractures result from injuries that occur with the knee relatively extended and proximal fractures occur when the knee is in greater flexion.

Patella fractures are classified according to the morphology of the fracture pattern and the presence or absence of displacement. Common fracture patterns include transverse, vertical, comminuted or stellate, osteochondral, and sleeve fractures (Figure 12.55.5).

The patient usually describes the acute onset of knee pain and swelling after a direct or indirect mechanism of injury, and is often unable to bear significant weight on the injured knee.

The patient’s ability actively to extend the leg must be assessed, as the inability to extend the knee against gravity signifies a significant disruption of the extensor mechanism that may require surgical intervention. When pain is prohibitive, aspiration of fracture haematoma and intra-articular injection of local anaesthetic may be indicated to make the patient more comfortable and allow for a more accurate examination.

Plain radiographs (anteroposterior, lateral, and Merchant (45-degree axial) views) are usually all that are needed to treat patella fractures. The anteroposterior view is assessed for patella position, displacement, and comminution. A bipartite or multipartite patella (Figure 12.55.6A) is distinguished from a fracture (Figure 12.55.6B) by its typical location (superolateral), smooth borders, and frequent bilateral occurrence. The lateral projection usually provides the best view of fracture lines and should be scrutinized for patella height, displacement, and comminution. The Merchant view (Figure 12.55.7) is often the only projection that will demonstrate vertical and osteochondral fractures.

The treatment goals for most patients with patella fractures are to maintain or restore a stable extensor mechanism and a smooth articular surface.

Non-operative treatment produces excellent results in carefully selected patients; namely those with a functional extensor mechanism and minimal fracture displacement (Figure 12.55.8). The knee is immobilized in extension for 6 weeks followed by progressive active range of motion exercises. Full weight bearing and isometric quadriceps exercises are begun several days after injury. Radiographs must be obtained weekly for 3 weeks to rule out fracture displacement.

Displaced patella fractures with disrupted extensor mechanisms should be treated operatively with techniques ranging from reduction and fixation of all displaced fragments to total patellectomy.

Reduction and fixation of transverse fractures must withstand not only the considerable tension forces exerted by the quadriceps but also, if early knee motion is desired, the three-point bending forces which create additional tension along the anterior surface and compression along the articular surface. The modified tension band wiring technique as described by the AO group (Figure 12.55.8) has been clinically successful and is relatively simple and familiar to most surgeons. Two vertical 1.6-mm (0.062-inch) K-wires are placed parallel to each other across the reduced fracture. An 18-gauge wire is then placed directly posterior to the K-wires at their entrance into the superior pole, wrapped over the anterior surface of the patella in a figure-of-eight or box configuration, passed directly posterior to the K-wires at their point of exit at the inferior pole, and then twisted until appropriate compression is achieved across the fracture site.

The AO technique has been modified by replacing the K-wires with cannulated screws. The 18-gauge wire is threaded through the screws, rather than around the K-wires, before passing over the anterior surface of the patella in a similar figure-of-eight configuration (Figure 12.55.9). The screws produce interfragmentary compression across the fracture site while the wire neutralizes the tension forces across the anterior patellar surface. Mechanical testing has shown that this construct provides the strongest initial fixation. The use of an arthroscope to assess the reduction allows the possibility of a truly percutaneous approach to reduction and fixation. This technique needs further assessment but is attractive in cases where there are abrasions or other skin problems over the anterior surface of the patella.

Vertical fractures are rarely displaced. When displaced they are best treated with anatomical reduction and lag screw fixation.

When possible, vertical fracture lines should be rigidly fixed with lag screws with the objective of creating two large pole fragments. These two fragments can then be fixed like a transverse fracture (Figure 12.55.10). When comminution severity precludes this technique, all attempts should be made to save some portion of the articular surface with the hope of maintaining patella function. This frequently involves partial patellectomy and reattachment of the patella or quadriceps tendon to the salvaged fragment (Figure 12.55.11). Total patellectomy is performed when there are no large articular surface fragments that can be congruently reconstructed.

Controversy exists regarding the proper site to reattach the patella tendon when inferior pole fragments are excised. Most authors have recommended that the tendon be reattached immediately adjacent to the articular surface in order to minimize the step-off between the tendon and articular cartilage, and prevent the posterior tilting and subsequent edge loading reported to occur with anterior reattachment. However, it has been demonstrated that when the tendon is reattached anteriorly there are smaller decreases in patellofemoral contact area and smaller increases in contact pressure compared to posterior reattachment. The author reattaches the patella tendon through drill holes in the central portion of the fracture surface of the residual proximal fragment.

The knee is immobilized and rehabilitated postoperatively based on fracture configuration and stability of fixation. Patients with severely comminuted fractures, tenuously fixed fractures, partial patellectomies, and total patellectomies are treated for 4–6 weeks with the knee immobilized in extension, followed by a gradual progressive range of motion and strengthening program.

For stable well-fixed transverse fractures, the current trend is to begin early active-assisted range of motion limited to 90 degrees. Gradual and progressive strengthening is begun at 6 weeks.

Seven per cent of all patella fractures are open. Similar to other open fractures, antibiotics should be started and the fracture should be immediately irrigated, debrided, and rigidly internally fixed if the wound is clean. The wound should be closed or covered with a flap within 3–5 days of injury. The incidence of deep infection is correlated to the magnitude of soft-tissue injury with rates ranging from 0–10.7%.

Ipsilateral femoral shaft and patella fractures are not uncommon. These tend to be high-energy injuries associated with more severe soft tissue trauma. Both fractures should be stably internally fixed to allow early knee motion and prevent quadriceps adherence at the femoral fracture site.

Transverse patella fracture has been reported as a complication of bone–patellar tendon graft harvest. The fractures are usually associated with trauma and occur in the early months after the anterior cruciate ligament surgery. Standard treatment of the patella fracture leads to generally satisfactory results.

Appropriately indicated patella fractures (namely those with minimal displacement and an intact extensor mechanism) have good results when treated non-operatively, with 99% good and excellent results (average 8.9-year follow-up) reported. In a study of 40 patients (average of 30.5 months after injury), 80% were pain free and 90% had full knee range of motion.

The results of operatively-treated patella fractures are more related to the severity of injury and associated injuries than to the method of fixation. High-energy injuries, open fractures, comminution, and the presence of concomitant injuries have been found to be predictive of a poor result. Although residual articular displacement has also been associated with worse results, these findings have not been universal.

Most authors report 70–80% good and excellent results after open reduction and internal fixation of patella fractures. Perfect reduction has been found to be necessary to optimize outcomes. If precise reduction was not achieved, the results were better in patients treated with patellectomy. These results should be considered when attempting to fix comminuted cases internally. Good results after internal fixation have been reported even in elderly patients.

Despite biomechanical studies which demonstrate decreased patellofemoral contact area and increased pressure after partial patellectomy, this procedure has resulted in outcomes comparable to those after open reduction and internal fixation, and the results appear to be maintained over time. At an average 8.4-year follow-up, 78% good and excellent results and an average quadriceps strength of 85% of the opposite side, has been reported. Partial patellectomy resulted in better outcomes than total patellectomy for the treatment of comminuted displaced fractures.

Patella fractures treated by total patellectomy have less predictable outcomes than after other treatments, with reports ranging from 61–88% good and excellent results. Pain has not been a major long-term problem, and patients continue to make functional improvements for up to 2–3 years postoperatively. Most patients have some quadriceps weakness (50–75%) and are functionally limited (running, squatting, ascending and descending stairs) after patellectomy. There is some evidence that newer operative techniques (e.g. vastus medialis obliquus advancement and cruciform repair) and aggressive rehabilitation result in improved outcomes.

Operative treatment of patella fractures is often complicated by hardware irritation because the patella is located subcutaneously and stabilized with wires that become prominent. Trimming excessive length from K-wires, bending prominent wire ends away from the subcutaneous tissues, and keeping suture and wire knots off the anterior surface of the patella may help to limit these problems.

Loss of fixation is usually related to poor patient compliance, unrecognized comminution, poor bone quality, or poor surgical technique (i.e. improper placement of the tension band wire). It has been reported that fracture fragments separated (up to 2mm) in 22% of transverse fractures treated with open reduction and internal fixation. Placing the non-compliant patient in a long leg cast for a limited period of time (3–4 weeks) may prevent fixation failure. Efforts to reconstruct severely comminuted fractures should be abandoned in favour of partial patellectomy. Tension band wires must be placed in direct contact with the patellar poles, posterior to longitudinal K-wires, and over the anterior surface of the patella. When fractures widely redisplace, they must be treated with repeat open reduction and internal fixation or partial patellectomy.

In a 10- to 30-year follow-up, 45 of 64 injured knees had patellofemoral osteoarthritis compared to only 23 contralateral, uninjured knees. There is an increase in the frequency of osteoarthritis after high-energy injuries, open fractures, comminuted fractures, operatively treated fractures, and fractures with 1mm or more of articular incongruity. However, these radiographic findings often bear no relation to clinical results.

Fractures stabilized with current operative techniques and mobilized early in the postoperative period are generally considered to result in less knee stiffness and decreased range of motion. Some loss of flexion is expected after operative treatment, but is rarely of functional significance. When functionally limiting stiffness occurs, the knee should be aggressively rehabilitated. If it does not respond, it should be manipulated under anaesthesia and refractory cases should have adhesions lysed arthroscopically.

Infection following operatively-treated patella fractures is uncommon. Superficial infections should be treated with antibiotics and local wound care. Deep infections should be aggressively irrigated and debrided and the patient should be placed on intravenous antibiotics. All attempts should be made to preserve the patella, but patellectomy is inevitable is some cases of deep infection.

Although patella non-unions are considered uncommon when fractures are treated with current techniques, reported rates have ranged from 2.7–12.5% of all fractures. Minimally symptomatic patients have been successfully treated non-operatively, accepting failure of fracture healing. Symptomatic non-unions can be expected to have improved knee function when treated with open reduction and internal fixation, partial patellectomy, or total patellectomy.

Patella fractures have been treated using the same principles for the past three decades. The use of bioabsorbable implants may eliminate the need for hardware removal. The arthroscope has revolutionized surgery around the knee joint, allowing major surgery to be performed through small incisions in an almost percutaneous fashion and this technique may have increased use in fractures of the patella.

Patella fractures are common injuries caused by both direct and indirect trauma. They are classified based on the fracture pattern and presence of displacement. The status of the extensor mechanism is determined by physical examination and radiographic analysis. Surgical intervention is indicated for those patients with displaced fractures and disrupted extensor mechanisms. All attempts should be made to salvage a significant portion of the articular surface.

Acute lateral patella dislocations are relatively uncommon injuries. However, in many patients the patella relocates prior to presenting for medical care so the true incidence is unknown. Most dislocations occur in patients during their second and third decades of life and there is a slight female predominance.

The patellofemoral joint is stabilized by both bony and soft tissue restraints. Bony stability is provided by the convex shape of the patellar articular surface as it articulates within the concave trough of the femoral trochlea. The quadriceps muscle group provides dynamic stability with an essential contribution from the vastus medialis obliquus. The medial and lateral retinacula along with their associated medial and lateral patellofemoral and tibiofemoral ligaments provide static stability (see Figure 12.55.1).

Many anatomical factors can predispose a patient to sustaining a patella dislocation (Table 12.55.1). Unfortunately, no single factor or combination of factors has been shown to be predictive of dislocation, redislocation, or poor outcome after dislocation.

The medial patellofemoral ligament is a major stabilizing component of the medial retinacular complex. Several studies have shown that there is a consistent injury to the medial patellofemoral ligament after dislocation. However, whether the major injury occurs at the patellar insertion, within the midsubstance, at the femoral origin, or some combination of locations continues to be a point of controversy and is a critical piece of knowledge if one is considering operative repair. Bony injuries of the medial border of the patella represent avulsions of the medial patellofemoral ligament. Other structures commonly injured during lateral dislocation include the vastus medialis obliquus and medial patellar and lateral trochlear articular surfaces.

Most patella dislocations occur as a result of a twisting injury. Internal rotation of the femur on a fixed lower extremity while the quadriceps contracts draws the patella out of the trochlea, resulting in a lateral patella dislocation. Less commonly, a direct force applied to the medial side of the patella causes lateral dislocation.

Superior, medial, lateral, and intra-articular dislocations have been described. Lateral dislocations represent the overwhelming majority of these injuries.

The history is usually one of a twisting injury to the knee associated with collapse, acute pain, and swelling. A sensation that something ‘popped’ out of place is common. If the knee remains flexed, the patella will be visualized on the lateral side of the knee. With knee extension (by the patient or a bystander) the patella will relocate. A history of similar previous episodes along with a history of anterior knee symptoms may be elicited.

The injured knee is assessed for patella mobility and apprehension, to localize tenderness and identify tears of the medial retinaculum–vastus medialis obliquus complex, and to exclude cruciate and collateral ligament injuries. The uninjured knee is examined for anatomical factors associated with patellofemoral disorders (Table 12.55.1).

Aspiration of the knee can serve three potential functions. Firstly, evacuation of the haematoma will provide pain relief for the patient. Secondly, fat droplets within the aspirate indicate the presence of an osteochondral fracture, a consideration for operative intervention. Thirdly, removal of the haematoma may aid reapproximation of the torn edges of the medial retinacular complex.

Radiographs

Standard plain radiographs (anteroposterior, lateral, and Merchant views) are required and should be scrutinized for osteochondral fractures and the presence of any factors known to be associated with patellofemoral disorders (Table12.55.1). Medial extra-articular capsular avulsion fractures are pathognomonic and should be differentiated from osteochondral fractures.

Some surgeons obtain MRI examinations after patella dislocations to document osteochondral and chondral injuries not seen on radiographs, detect bone bruises, and characterize the injury to the medial patellofemoral ligament. In rare instances, an MRI may be indicated for diagnostic purposes in a patient with a haemarthrosis and confusing physical examination.

Patients presenting with the patella dislocated require a gentle, closed reduction as there is some evidence that the majority of osteochondral fractures occur with relocation. Using intravenous sedation to keep the quadriceps maximally relaxed, the leg is gradually extended passively until the patella reduces.

Patella dislocations have traditionally been reduced and immobilized in extension for 6 weeks followed by quadriceps rehabilitation. However, several studies have shown the treatment results to be independent of the duration of immobilization. Based on these data, many have decreased the period of immobilization and focused more on rehabilitation.

Operative procedures are most commonly indicated for patients with anatomical factors associated with patellofemoral instability (Table 12.55.1). Unfortunately, no single factor or group of factors have been shown to be highly predictive of future problems, and some patients respond well to conservative treatment despite having anatomical factors associated with instability.

Repair of the medial retinaculum–vastus medialis obliquus complex has been advocated by many, especially when a palpable defect is present on examination. The addition of a lateral release with or without a distal realignment has been advocated. An isolated lateral release can be performed arthroscopically. The indications for any one or more of these procedures are controversial and have been largely based on surgeon preference.

Post-treatment care focuses on regaining quadriceps strength, with special emphasis on the vastus medialis obliquus. This requires a prolonged rehabilitation program that lasts beyond symptomatic improvement.

Osteochondral fractures have been estimated to occur in 5–43% of all first-time patella dislocations. Plain radiographs have been reported to detect 20–82% of these injuries. Although MRI would aid in detecting these fractures, no clear benefit has been reported to addressing fractures not appreciated on plain radiographs.

Small fragments should be excised and larger fragments with adequate subchondral bone internally fixed.

Redislocation rates for conservatively treated patients range from 22–44%. Forty to seventy-five per cent of patients have persistent symptoms related to the patellofemoral joint with 25% undergoing further surgical treatment. Approximately 65% of patients are satisfied with conservative treatment alone, although 40–50% will have some limitation of function.

Arthroscopically assisted lateral release alone provides no benefit over conservative treatment. Other operative treatments (incorporating medial retinacular repair) have been reported to reduce redislocation rates to 0–10%. However, residual symptoms are common with 40–70% of patients having anterior knee pain and 20–30% having symptoms of instability. Patient satisfaction rates have been slightly higher (80–90%) with operative intervention, although there are no good controlled studies to provide definitive documentation.

Recurrent dislocations and persistent anterior knee symptomsare the major problems complicating first-time dislocation. Recurrent dislocation is associated with younger age at the time of first dislocation (less than 20 years old), non-operative treatment, and anatomical factors predisposing to instability. Surgery can reduce the rate of redislocation, but does not reduce residual symptoms of pain and instability. Furthermore, many patients with multiple predisposing factors respond well to conservative treatment alone.

The debate between operative and non-operative management of first-time dislocators will likely continue. Future work will attempt to identify specific anatomical factors predictive of redislocation and methods to more effectively treat persistent symptoms of anterior knee pain and instability.

Acute patella dislocations occur primarily in patients with anatomical predisposition. Initial treatment involves a gentle reduction. Osteochondral fractures visible on plain radiographs should be removed or replaced, depending on the size of the fragment. Non-operative treatment is indicated for most patients, emphasizing the importance of a prolonged rehabilitation program. Operative intervention is considered in those patients with large palpable medial retinaculum–vastus medialis obliquus defects along with those with persistent symptoms of pain and instability after adequate rehabilitation.