Common Fractures of the Knee and Lower Leg

PART 1 OF 2 PARTS

Emerg Med 37(1):16-26, 2005

What is the best and safest way to approach physical examination of a knee that may be fractured? Which neurovascular injuries might accompany a distal femur fracture? What is the next step if routine films fail to confirm a tibial plateau fracture? In the first of two parts, the authors address these and many other clinical issues that arise when a patient has injured the knee area.

By Jim Powers, DO, and Ioliene Boenau, MD

Lower extremity trauma is a common presenting complaint in both emergency departments and primary care settings. In cases in which the patient has sustained a fracture, prompt diagnosis, management, and timely referral will improve both short- and long-term outcomes and reduce the incidence of serious complications. In this two-part series, we will discuss the most common fractures found in the knee and lower leg, including a review of relevant anatomy, clinical presentation, diagnostic strategies, and management of these fractures.
 

FRACTURES OF THE KNEE

The most common fractures sustained in the region of the knee include distal femur fractures, proximal intra-articular tibial fractures, and patellar fractures (see box below).

The knee is the largest and most complicated joint in the body. Its stability depends mainly on the ligamentous structures but also relies on the muscles and joint capsule. The distal end of the femur is formed by the medial and lateral condyles and is separated from the medial and lateral condyles of the tibial plateau by the menisci of the knee.

The posterior aspect of the knee contains the popliteal fossa, which includes many important structures, such as the popliteal artery, popliteal vein, and the peroneal and tibial nerves. The fact that the popliteal artery is fixed both proximally and distally within the popliteal fossa accounts for the high incidence of arterial injury that occurs in major trauma to the knee. The fibular nerve, which exits the fossa and wraps around the head of the fibula, may be injured, producing a weakness in dorsiflexion of the ankle and the characteristic "foot-drop" finding.

Obtaining a history regarding the mechanism of injury can help the clinician predict which injuries are likely to have occurred. High-energy trauma often produces comminuted and open fractures, neurovascular injury, dislocations, and the potential for multisystem trauma. Low-energy trauma produces ligamentous injuries, nondisplaced fractures, and other soft tissue damage. Important questions include any history of prior injuries or orthopedic procedures to the injured extremity, as well as the presence of any comorbid conditions such as diabetes, coagulopathy, and osteoporosis that may complicate the injury, repair of the injury, or the recovery process.
 

PHYSICAL EXAMINATION

The physical exam begins with inspection of the patient in the supine position, with both legs exposed to allow comparison of the injured and uninjured extremity. Any obvious swelling, effusion, deformity, or ecchymosis should be noted. Small knee effusions may be difficult to detect; a loss of the concavity in the medial patellar area may be the only sign. Milking the fluid from the suprapatellar pouch inferiorly into the knee joint may help to demonstrate a small effusion.

A large effusion is usually obvious, with the presence of fluid elevating the patella off the femur and obliterating the normal contour of the knee. In this situation, direct pressure over the elevated patella will produce a ballottement of the patella against the femur. Immediate hemarthrosis of the knee following an injury is an important physical finding that usually indicates an intra-articular fracture or an anterior cruciate ligament (ACL) disruption. This is in contrast to the delayed onset of swelling in a torn meniscus that occurs 12 to 24 hours after an injury.

Following inspection, the knee should be palpated to identify an area of maximum point tenderness. Palpation should always begin in the least tender area of the knee and progress to the most tender area last to avoid increased pain, anxiety, and loss of patient cooperation early in the exam. While point tenderness is classically one of the most reliable signs of an underlying fracture, it does have its limitations. In the acutely injured knee, the presence of a large effusion, muscle spasm, or patient guarding may limit its utility. Also, it has been suggested that in children, point tenderness may not be a good predictor of knee fracture.

Range-of-motion testing, while important in the assessment of nontraumatic knee pain and overall knee function, is less important in the detection of fractures and is contraindicated in any obvious deformity or open fracture. It can be beneficial in the evaluation of the extensor mechanism in patellar and tibial tubercle fractures, as well as in quadriceps and patellar tendon rupture. Loss of active extension of the knee and an inability to maintain knee extension against gravity are evidence of loss of the normal extensor mechanism, which requires immediate orthopedic consultation.

Stability testing is the most important aspect in the assessment of ligamentous injuries that often accompany fractures of the knee. For example, an avulsion fracture of the lateral tibial plateau, also known as a Segond fracture, predicts the presence of an ACL rupture in 75% to 100% of cases. In the acutely injured knee, Lachman's test, not the anterior drawer test, is the test of choice for the evaluation of ACL integrity. The posterior cruciate ligament (PCL) is evaluated by the posterior drawer test; the collateral ligaments are evaluated with valgus and varus stress testing. When examining the injured knee, it is always important to also examine the hip and ankle on the same side.

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RADIOGRAPHIC EVALUATION OF THE KNEE

Guidelines for the use of X-rays in cases of potential knee fracture have been established and have widespread, though not universal, acceptance. Perhaps the most widely known set of guidelines for the use of X-rays is the Ottawa Knee Rules (see box below). Stiell and colleagues found that one or more of these findings has a sensitivity of 100% and a specificity of 54% for the presence of a fracture. Studies have shown that these decision rules reduced the number of X-rays obtained in acute knee injuries from 68.6% to 49.4% and the time spent in the emergency department by almost 40 minutes. Acute hemarthrosis is another indication for obtaining an X-ray, due to the high likelihood of an intra-articular fracture with this finding.

Routine views utilized when evaluating for a fracture around the knee include the anterior-posterior (AP), lateral, and oblique views. The AP view can identify many common fractures and can also show a joint effusion. The lateral view may demonstrate an abnormally positioned patella, a tibial tubercle fracture, a fat-fluid level, or lipohemarthrosis in the knee joint, suggestive of an intra-articular fracture. Oblique views are helpful when a tibial plateau fracture is suspected but not seen on the AP or lateral films.

In addition to these routine views, there are the tunnel or intercondylar view and the sunrise or skyline view. The tunnel view images the intercondylar notch and is useful in detecting tibial spine fractures or avulsion fractures at the site of ACL or PCL attachment. The sunrise view is utilized to image the patella when a patellar fracture or subluxation is suspected.

When examining a plain film of the knee, it is useful to follow the mnemonic ABC for alignment, bony cortical defects, and cartilage radiolucency. When examining the film for alignment, the clinician should look for any joint space narrowing, rotational abnormalities in the femur or tibia, and the position of the patella. A plain film should also be evaluated for soft tissue findings such as hemarthrosis or lipohemarthrosis.
 

ADDITIONAL STUDIES

In addition to plain films, other imaging studies, including computed tomography (CT), magnetic resonance imaging (MRI), or a bone scan, may be useful in the evaluation of knee fractures. A CT scan is especially helpful to guide operative intervention or when the diagnosis is unclear or a specific fracture classification is needed. While an MRI is most often used to evaluate injuries of the cartilage, menisci, and ligaments, it can also be used to detect occult fractures or contusions to the bone. The utility of bone scans is in detecting suspected stress fractures that are not apparent on plain films.

In the setting of an acute knee injury, arthrocentesis can be both diagnostic and therapeutic. If joint aspiration reveals the presence of fat globules, it is diagnostic of an intra-articular fracture. Arthrocentesis is also therapeutic in that it drains the effusion that contributes to the patient's pain. In addition, this procedure can be used to instill analgesic agents to reduce the pain and need for systemic analgesics. Both intra-articular morphine and bupivacaine have been shown to be useful for this purpose. Morphine 1 to 5 mg diluted in normal saline solution to a total volume of 30 ml can provide up to 24 hours of pain relief.

Vascular studies are indicated for all knee injuries in which evidence of arterial insult (including pale color), delayed capillary refill, or absent pulses exists. In general, these studies should also be performed for all knee dislocations or fractures with severe instability, regardless of any evidence of good peripheral perfusion, to rule out an occult injury. Studies that may be performed initially at the bedside include a Doppler exam of pulses and measurement of the ankle-brachial index. However, because increased morbidity is associated with delays in vascular repair, consultation with an orthopedic surgeon should be obtained immediately in any patient with evidence of vascular insult.

In cases of impaired arterial flow in which surgical exploration and repair of the fracture is not planned, an arteriogram should be obtained. It is also important to remember that the presence of normal pulses does not rule out an occult vascular injury.
 

DISTAL FEMUR FRACTURES

About 4% of all femur fractures are distal fractures, which are usually caused by high-energy forces involving axial loading and direct blows. Distal femur fractures are divided into supracondylar fractures, intercondylar fractures, condylar fractures, and distal epiphyseal fractures. Supracondylar fractures are considered extra-articular fractures and involve the femur from the metaphysis, just proximal to the femoral condyles, to the diaphysis at the junction of the femoral shaft. Both intercondylar and condylar fractures are considered intra-articular fractures and, unlike supracondylar fractures, are associated with a hemarthrosis. Also, fractures of the femoral condyles often produce a notable knee joint incongruity.

The hallmarks of a distal femur fracture are pain and swelling in the area of the distal femur and suprapatellar region and an inability to bear weight. With a supracondylar fracture, there may be a shortening, external rotation, and angulation of the extremity. Another common finding is an acute hemarthrosis, indicative of an intra-articular fracture or a ligamentous rupture. The clinician must be alert to the presence of any soft tissue defect in the region of the fracture, which may represent an open fracture warranting special care.

While neurovascular injuries are relatively uncommon in distal femur fractures, a careful assessment of peripheral circulatory, motor, and sensory function should be performed. As previously discussed, the popliteal artery is anchored firmly in the popliteal fossa and is at risk for injury in fractures of the knee. Careful assessment of the dorsal pedal pulse, posterior tibial pulse, and capillary refill is mandatory. If pulses are not palpable, a bedside Doppler ultrasound may be able to detect pulsatile blood flow. In the case of suspected circulatory compromise, emergency orthopedic consultation is warranted.

The most common nerve injury is to the deep peroneal nerve, which can be assessed by testing sensation in the first dorsal web space as well as the function of the dorsiflexors of the ankle and toes. Due to the major forces involved in distal femur fractures, a careful examination for ipsilateral hip, lower extremity, or pelvic fractures should also be conducted.
 

DIAGNOSIS AND MANAGEMENT

Distal femur fractures are usually seen easily on routine AP and lateral films. Because the energy required to cause these injuries is significant, X-rays of the pelvis, hip, and lower leg should also be considered.

The most important aspect of acute management of distal femur fractures is to attain adequate stabilization of the fracture using a properly applied splint. A long leg posterior mold splint is easily applied and should prevent excessive motion of the fracture and help reduce the pain. Systemic analgesia, titrated to the patient's pain and hemodynamic status, should be administered.

Distal femur fractures warrant early orthopedic consultation, and patients with any significant displacement or joint incongruity usually require open reduction and internal fixation (ORIF). Complications of distal femur fractures include fat emboli, deep vein thrombosis (DVT), delayed union or malunion, angulation deformity, and osteoarthritis. While these complications may not be evident at the time of injury, they may be a reason for future visits to the emergency department or primary care office.
 

TIBIAL PLATEAU FRACTURES

Tibial plateau fractures are fractures occurring above the tibial tuberosity and involving the tibial condyles. They represent 1% of all fractures overall but are more common in the elderly, comprising 8% of all fractures in that population. Tibial plateau fractures are intra-articular fractures most commonly involving the lateral plateau.

When they occur in younger patients, most of these fractures are due to high-energy trauma. The most common mechanism is a strong valgus force coupled with axial loading, which subsequently drives the femoral condyles into the tibial plateau, producing the fracture. These injuries are sometimes referred to as "car bumper injuries," because the most common setting in which they occur is when the bumper of a car strikes the lower leg.

While high-energy trauma is the rule in tibial plateau fractures in the young, the elderly may sustain fatigue and stress fractures of the tibial plateau with minimal or even no identified trauma. These fractures are usually the result of compressive forces acting on osteoporotic bone. In fact, any hemarthrosis of the knee occurring in an elderly person should be assumed to be a tibial plateau fracture until proven otherwise.

Fractures of the tibial plateau are commonly accompanied by damage to the collateral ligaments, a fact easily explained by examining the major mechanisms of injury. Avulsion fractures of the lateral tibial plateau, also known as Segond fractures, are accompanied by a concurrent ACL rupture in 75% to 100% of cases. This special type of tibial plateau fracture usually occurs in sporting events and is due to mechanisms of injury that produce knee flexion, excessive internal rotation, and varus stress.
 

CLINICAL FEATURES

As expected, tibial plateau fractures produce pain and swelling around the knee, with proximal tibial pain and point tenderness over the fracture site. The site of impact to the knee may be marked by a bruise, abrasion, or laceration, which should raise suspicion for an open fracture. Because tibial plateau fractures are intra- articular fractures, an acute hemarthrosis is present.

The patient is usually unable to bear weight, and the knee may be slightly flexed and may have a decreased range of motion. The presence of a valgus or varus deformity is not uncommon and indicates a depressed condylar fracture or concomitant additional leg fracture.

Tibial plateau fractures are accompanied by ligamentous injuries in 20% to 25% of cases, resulting in knee instability. Lateral plateau fractures will have ACL and medial cruciate ligament (MCL) injuries, whereas medial plateau fractures typically involve the PCL and lateral cruciate ligament (LCL). Fractures of the tibial plateau are at significant risk for vascular complications, especially damage to the popliteal artery, and assessment of peripheral vascular status is mandatory.

In addition, peroneal nerve injury and paralysis may occur, particularly with displaced fractures of the lateral condyle. The mechanism in these cases is usually stretching rather than transection of the nerve, and function usually returns. Assessment of the distal peroneal nerve should be performed by checking for sensation in the first dorsal web space and the function of dorsiflexors of the ankle and toes.

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DIAGNOSING TIBIAL PLATEAU FRACTURES

Tibial plateau fractures are usually identified with routine AP and lateral films. In some cases, however, the fracture may not be obvious because the fracture is small and nondisplaced or because the normal contour of the tibial plateau hides a subtle fracture line. In cases in which routine films are negative but clinical suspicion for a tibial plateau fracture remains high, a cross-table lateral or oblique view of the knee may reveal the fracture. The cross-table lateral view may show a fat-fluid level or lipohemarthrosis, which is highly suggestive of an occult intra-articular fracture.

In addition, oblique films are useful in further characterizing a fracture that was identified on routine views. When reviewing radiographs for a possible tibial plateau fracture, the clinician should look for any bony avulsion fragments indicative of concomitant ligamentous injury. In a Segond fracture, there is a bony avulsion of the lateral tibial plateau that appears as an oval-shaped fragment adjacent to the lateral tibial plateau. This finding, known as the "lateral capsule sign," is an important marker of ACL disruption and the hallmark of a Segond fracture.

Another radiographic finding that may suggest damage to the collateral ligaments is a condyle fracture associated with a widened joint space on the side of the joint opposite the fracture. In addition to plain radiographs, a CT scan, MRI, and a bone scan have a role in the evaluation of tibial plateau fractures. Both CT and MRI are useful in localizing occult lesions, imaging both nondisplaced and severely comminuted fractures, and quantifying the amount of condylar depression present.

An MRI has the additional benefit of evaluating concomitant ligamentous and meniscal injuries. A bone scan, although not routinely performed in the evaluation of tibial plateau fractures, can be utilized to detect occult compression fractures.
 

STABILIZATION MEASURES

While orthopedic consultation is usually recommended at the time of injury, most tibial plateau fractures can be stabilized in the emergency department or primary care office, and the patient can be discharged with orthopedic follow-up in three to seven days. A knee immobilizer with crutches and non-weight-bearing usually provides adequate stabilization of nondisplaced single plateau fractures as well as stable bicondylar fractures. Casting is not generally recommended at the time of injury because of increased swelling over the first 48 hours and an associated incidence of knee stiffness that occurs with early casting.

Standard RICE therapy (rest, ice, compression, and elevation) is recommended. Arthrocentesis with aspiration of hematoma and installation of morphine and bupivacaine can provide good pain relief. Severely displaced fracture fragments usually require ORIF, and depressed fractures greater than 8 mm need surgical elevation and bone graft support. The prognosis for tibial plateau fractures is usually good but depends on four factors: the degree of articular depression, the extent and separation of the condylar fracture lines, diaphyseal-metaphyseal comminution and dissociation, and whether the fracture is open or closed.

The most common early complications of a tibial plateau fracture are wound infection, loss of reduction, DVT, and angular deformity of the knee. Compartment syndrome can also occur, usually in association with high-energy fractures, and typically within the first 24 to 48 hours after the injury. Osteoarthritis is the most common late complication, occurring in approximately 50% of patients 10 years after the initial injury.
 

FRACTURES OF THE TIBIAL SPINE

The tibial spine, or intercondylar eminence, is the central portion of the proximal tibial surface and fits into the intercondylar notch between the condyles of the femur. It is composed of two prominences, the medial spine (tubercle) and lateral spine, separated by the intercondylar fossa. The medial spine is the larger of the two spines and, along with the anterior portion of the intercondylar fossa, serves as the attachment site for the ACL. As a result, fractures of the intercondylar eminence often result in cruciate ligament injury.

Approximately 60% of all tibial spine fractures occur in children and adolescents. This is because the ligamentous structures in these age groups are stronger than their adjacent physeal attachments, so a force applied to the ligament will result in fracture of the tibial spine at the attachment site rather than rupture of the ligament. A tibial spine fracture should be suspected in any child or adolescent who has a positive Lachman test, an acute hemarthrosis, or an inability to ambulate, or who has sustained any mechanism of injury that would be expected to produce an ACL injury in an adult.

In children with immature skeletons, tibial spine fractures are often isolated, whereas in adults they are often accompanied by additional intra-articular fractures. Most tibial spine injuries occur due to a combination of high-energy forces, including knee twisting, hyperflexion, hyperextension, and valgus-varus stresses, such as those that may occur during sporting activities or auto-pedestrian injuries.

Tibial spine fractures produce pain and swelling of the knee, decreased range of motion, and an inability to bear weight, which is an important distinguishing factor between a tibial spine fracture and an isolated ACL injury. While both injuries characteristically result in knee instability, a positive Lachman test, and swelling, the ability to bear weight should be preserved in an isolated ACL injury. Also, because tibial spine fractures are intra-articular fractures, an acute, tense hemarthrosis is usually present.
 

APPROPRIATE X-RAYS

In addition to the standard AP and lateral X-rays, a tunnel view may be utilized to image the intercondylar region. Close attention should be paid to the joint margins for any evidence of bony avulsion from ligament attachment sites. A normal finding often mistaken for a fracture fragment is a fabella, a sesamoid bone located in the lateral head of the gastrocnemius muscle. As with other fractures of the knee, a CT scan may be useful to demonstrate a subtle fracture or further delineate a fracture and aid in developing an appropriate treatment plan. Arthroscopy can also be used to establish the diagnosis and is especially useful in children in whom skeletal immaturity can make radiographic diagnosis difficult.

Most nondisplaced or incomplete fractures can usually be managed in the emergency department, with orthopedic follow-up in three to seven days. The knee should be immobilized in full extension with a knee immobilizer; crutches and non-weight-bearing are also mandatory until the orthopedic follow-up. Standard RICE therapy should be utilized, and the patient should be provided with adequate analgesia for pain control at home. Aspiration of a hemarthrosis and instillation of morphine or bupivacaine is an option.

Completely displaced tibial spine fractures require early orthopedic evaluation and often will need ORIF or arthroscopic reduction. The prognosis for tibial spine fractures is good once they have adequately healed and ligamentous function is restored.
 

EPIPHYSEAL FRACTURES

The epiphyseal plate, or physis, is the area of growth cartilage at the ends of long bones in children and is responsible for longitudinal growth of the bone through the process of endochondral ossification. While the two largest physes in the body are found at the distal femur and proximal tibia, fractures there are relatively uncommon.

Epiphyseal fractures are classified using the Salter-Harris system, which is based on the degree of involvement of the epiphysis and metaphysis. Type I fractures produce growth plate separation, with complete separation of the epiphysis from the metaphysis without any associated fracture. It is usually caused by shearing, torsion, or avulsion forces and is commonly encountered in infants and toddlers. Treatment of type I fractures is generally with complete limb immobilization for six to eight weeks, and the prognosis is very good.

Type II fractures, the most common epiphyseal fractures, involve a fracture that extends from the physis proximally through the metaphysis. They occur most commonly in children over the age of eight and also have a good prognosis with complete limb immobilization for six to eight weeks.

Type III fractures are intra-articular fractures, with the fracture extending from the epiphyseal plate distally through the epiphysis to the joint surface. These fractures are uncommon but occur with increased frequency at the proximal and distal tibial epiphysis. Treatment is directed at accurate reduction in order to restore the joint surface and function.

Type IV fractures are also intra-articular fractures, with the fracture extending from the joint surface through the epiphyseal plate into the metaphysis. Unless displacement is minimal, this type of fracture almost always requires open reduction.

Type V fractures are crush injuries to the physis that can be very difficult to detect on standard X-rays. While uncommon, they can lead to severe growth disturbance if not detected and treated appropriately. Therefore, even with a normal X-ray, point tenderness over the physis should raise suspicion of this type of fracture and appropriate treatment with immobilization and non-weight-bearing should be initiated.
 

SIGNS AND SYMPTOMS

Clinical features of an epiphyseal fracture include severe pain and swelling in the area of the epiphysis. Overlying abrasions, contusions, or lacerations are sometimes seen, and angular deformity may also be present if there is displacement of the fracture. In general, an epiphyseal fracture should be suspected in any child who limps, refuses to bear weight, or has tenderness in the area of the growth plate.

There is a relatively high incidence of associated injuries in epiphyseal fractures, with damage to the ACL and MCL, popliteal artery, and, most commonly, the peroneal nerve. A meticulous physical examination to exclude these injuries is essential, as is thorough documentation of such findings.

Lateral and AP radiographs commonly reveal the fracture, although oblique views may be required to visualize some nondisplaced fractures. In general, radiographic findings suggesting an epiphyseal fracture include epiphyseal displacement, widening of the epiphysis, and loss of the normally sharp and well- defined margins between the epiphysis and metaphysis. Comparison views of the opposite extremity may be useful in attempting to differentiate a fracture from a normal epiphysis. If the suspicion for an epiphyseal fracture is high but X-ray findings are normal, a CT scan or MRI may be useful in delineating the fracture.

Proper management of epiphyseal fractures is essential to reduce the possibility of growth disturbance or arrest. Because epiphyseal fractures often go undetected on the initial X-rays, any child with juxta-articular tenderness at the knee should be assumed to have an epiphyseal injury and treated appropriately. General care includes immobilization in a long leg posterior splint with non-weight-bearing for at least three weeks or until the patient is cleared by an orthopedic surgeon. RICE therapy and orthopedic follow-up should be arranged. A common strategy is to obtain a second set of X-rays after two weeks of immobilization to look for any evidence of a healing fracture, such as new periosteal bone or epiphyseal thickening. If displacement of the distal femur or proximal tibia is noted, an orthopedic consultation should be obtained for anatomical reduction, which will reduce the risk of growth disturbance or poor functional outcome.

While most epiphyseal fractures have a good prognosis, complications can occur, especially with improper treatment. The most common complication is growth disturbance, most cases of which do not result in clinically significant dysfunction. Late complications include angular deformity of the extremity, leg length discrepancy, and persistent knee instability.

Next month: Patellar fractures and fractures of the lower leg.

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