Common Fractures of the Knee and Lower Leg

PART 2 OF 2 PARTS

Emerg Med 37(2):46-53, 2005

Continuing last month's discussion, the authors focus on fractures of the patella and the bones of the lower leg and provide tips on how to assess and manage these injuries for an optimal outcome.

By Jim Powers, DO, and Ioliene Boenau, MD

As noted last month in part 1 of this series, lower extremity trauma is a common presenting complaint in both emergency departments and primary care settings. Prompt diagnosis and management and timely referral are essential to improving both short- and long-term outcomes and reducing the incidence of serious complications. Last month, we discussed distal femur fractures, tibial plateau and tibial spine fractures, and epiphyseal fractures. This month, we will conclude the series by reviewing patellar fractures and fractures of the lower leg.
 

PATELLAR FRACTURES

The patella, the largest sesamoid bone in the body, is embedded in the quadriceps tendon. The ligamentum patellae, a continuation of the quadriceps tendon, runs inferiorly from the patella and attaches to the tibial tuberosity. The patella is thought to increase the extensor force of the quadriceps mechanism by increasing leverage.

Patellar fractures make up 1% of all skeletal injuries, and all such fractures except for small avulsion fractures are intra-articular fractures. Both direct trauma and indirect forces can produce patellar fractures. Indirect mechanisms are the more common cause and are usually due to sudden flexion of the knee against a forcefully contracted quadriceps. This type of mechanism usually results in a transverse patellar fracture. Direct trauma, such as the knee striking against the dashboard of an automobile or falling on a flexed knee, occurs less commonly but usually produces a comminuted fracture of the patella.

Patellar fractures are classified into four major types: transverse fractures, stellate or comminuted fractures, longitudinal or marginal fractures, and osteochondral fractures. Transverse fractures make up 50% to 80% of all patellar fractures and usually occur in young adults. The most common mechanism responsible for these fractures is a sudden, violent contractile force applied to the patella by a contracting quadriceps. This force can often produce significant displacement of the two fracture segments by pulling the superior portion of the patella cephalad. Wide displacement of the patella is associated with severe disruption in the quadriceps extensor mechanism, and active extension of the knee is usually impossible.

A small subset of transverse patellar fractures is caused by a direct blow to the anterior aspect of the knee. These fractures are usually nondisplaced, and the extensor mechanism and the ability to actively extend the knee remain intact.

Stellate or comminuted fractures are the second most common type, accounting for 30% to 35% of all patellar fractures. Comminuted patellar fractures usually result from a direct impact and are seen as multiple bony fracture fragments on X-ray.

Longitudinal or marginal vertical fractures are found along the lateral or medial edge of the patella and account for 12% to 17% of patellar fractures. These fractures are usually due to direct forces on the patella and are not associated with loss of the extensor mechanism or the ability to actively extend the knee.

The last type of patellar fracture is an osteochondral fracture, in which the articular surface of the patella separates from the subchondral and trabecular bone. These fractures usually result from patellar dislocation or indirect mechanisms of injury.
 

CLINICAL FEATURES AND DIAGNOSIS

Patellar fractures cause pain, ecchymosis, and swelling over the patella, and they often produce a knee joint hemarthrosis. Depending on the type of fracture, the extensor mechanism may be disrupted, resulting in loss of the ability to extend the knee. Evaluation of the extensor mechanism should be done with any potential patellar fracture; this can be done by having the patient perform a straight leg raise against gravity. When patellar fractures are caused by high-energy direct trauma, as in a high-speed motor vehicle accident in which the knee strikes the dashboard, a careful evaluation for associated injuries, such as femoral neck fractures, hip dislocations, and acetabular fractures, should be performed.

Most patellar fractures are easily seen on standard anteroposterior (AP) and lateral radiographs of the knee. Lateral views should be assessed for the presence of a high-riding patella, or patella alta, which is evidence of patellar tendon rupture. To evaluate for patella alta, the length of the patellar tendon, measured from the inferior pole of the patella to the tibial tuberosity, should be compared to the length of the patella itself. This ratio, called the Insall-Salvati ratio, should be 0.8 to 1.2.

The sunrise X-ray view, which specifically images the patella, can be especially helpful in identifying marginal vertical fractures that are often obscured on AP views. Bipartite and multipartite patellas, which are unfused accessory ossification centers at the upper outer quadrants of the patella, are normal variants that are sometimes mistaken for fractures. Examination of the cortical margins, which should be smooth in a bipartite patella, and comparison X-rays of the opposite extremity can help differentiate these normal variants from true fractures. Occasionally, magnetic resonance imaging (MRI) or arthrocentesis may be needed to identify small patellar fractures not seen on plain films.
 

MANAGEMENT OF PATELLAR FRACTURES

Nondisplaced patellar fractures with an intact extensor mechanism can be managed in the emergency department or primary care office with outpatient orthopedic follow-up. Management includes immobilization of the knee in full extension with a knee immobilizer, as well as the use of crutches, partial weight-bearing as tolerated, standard RICE therapy (rest, ice, compression, and elevation), and a nonsteroidal anti-inflammatory drug or narcotic analgesia. At orthopedic follow-up, these patients are usually placed in a long leg cast in full extension for four to six weeks.

Patellar fractures with disruption of the extensor mechanism or transverse fractures with more than 3 mm of displacement require early orthopedic referral for open reduction and internal fixation (ORIF). If an orthopedic surgeon is consulted first, these fractures too may be temporarily immobilized in a knee immobilizer or long leg posterior splint and the patient discharged for outpatient orthopedic follow-up.

If an open fracture is present, immediate orthopedic consultation is needed for operative debridement and repair. These patients should have their tetanus status updated and should be given an intravenous (IV) dose of an antistaphylococcal antibiotic, usually a first-generation cephalosporin such as cefazolin. If severe tissue disruption or gross contamination is present, broader coverage with an aminoglycoside or a broad-spectrum agent such as piperacillin-tazobactam or ticarcillin-clavulanate may be added.

Long-term complications from patellar fractures include persistent patellofemoral pain and osteoarthritis, which are reported in about half of all patients. Avascular necrosis of fracture fragments may also occur.
 

FRACTURES OF THE LOWER LEG

The lower leg consists of the fibula and tibia and four major compartments divided by deep fascia. These compartments contain vital structures that are frequently injured either directly by bony fracture fragments or indirectly by increased compartmental pressures from swelling. In addition to identifying and treating fractures of the lower extremity, great care must be taken to evaluate for neurovascular damage or increased compartment pressures. The major fractures of the lower extremity can be divided into proximal extra-articular tibial fractures, tibial shaft fractures, proximal fibular fractures, and stress fractures (see box).

While the lower leg consists of both the tibia and fibula, the tibia is the true weight-bearing bone, handling more than 85% of the load. The tibia has a thick cortex and significant force is required to fracture it, yet it is still the most commonly fractured long bone and the one most likely to sustain an open fracture. The three major mechanisms involved in producing a tibial fracture are torsional injury, bending forces, or direct force as in a crush injury or a direct blow from a car bumper. Also, the tibia has a paucity of overlying muscle and blood supply, which increases the risk of complications after a fracture, most notably osteomyelitis and delayed or nonunion.

The fibula is surrounded by muscle throughout its length and lies posterior and lateral to the tibia, joining it at the superior and inferior tibiofibular joints. A strong interosseous membrane connects the bodies of the tibia and fibula and is formed by obliquely oriented fibrous tissue. Due to this close relationship of the tibia and fibula, a displaced fracture of one bone usually produces a fracture of the other bone. In tibial shaft fractures, an associated fibular fracture is found 75% to 85% of the time.
 

COMPARTMENTS OF THE LOWER LEG

The major compartments of the lower leg are the anterior, lateral, superficial posterior, and deep posterior (see table below). The anterior compartment contains the anterior tibial artery, the deep peroneal nerve, and the muscles responsible for dorsiflexion of the ankle and toes. The anterior tibial artery arises from the popliteal artery, courses through the anterior compartment, and emerges as the dorsal pedal artery, which can easily be palpated on the dorsum of the foot. The deep peroneal nerve provides motor innervation to the dorsal flexors of the ankle and toes and sensory innervation to the first dorsal web space of the foot.

The lateral compartment has no major arteries but does contain the superficial peroneal nerve and the muscles responsible for eversion of the foot. The superficial peroneal nerve, also known as the fibular nerve, courses just lateral to the fibular head and can easily be injured. Assessing the integrity of the superficial peroneal nerve is done by checking its sensory innervation at the lateral dorsum of the foot and the motor function of the foot everters.

The superficial posterior compartment contains the sural nerve supplying the lateral side of the foot at the heel, as well as the strong plantar flexors of the ankle. Like the lateral compartment, it contains no major arteries.

The deep posterior compartment contains the posterior tibial and peroneal arteries, the tibial nerve, and the muscles responsible for plantar flexion of the toes. The posterior tibial artery can be assessed by palpating its pulse, located just posterior to the medial malleolus. The tibial nerve is assessed by checking sensation to the plantar surface of the foot, as well as the function of the plantar flexors of the toes.
 

HISTORY AND PHYSICAL EXAM

As in the assessment of knee injuries, obtaining a thorough history regarding the mechanism of injury is important to help predict which injuries may have occurred. Questions regarding prior injuries, orthopedic surgery, and other medical problems and comorbid conditions are also important.

A key aspect of the physical examination is the evaluation of neurologic function, vascular status, and any evidence of compartment syndrome. Findings such as an absent or decreased pulse should prompt immediate orthopedic consultation for further vascular evaluation. It is important to check and document neurologic and vascular function before and after moving the injured leg.

An important goal in the treatment of any lower extremity fracture is early splinting of the fracture. Splinting prevents movement of the fracture fragments, which decreases pain and prevents further damage, including the conversion of a closed fracture to an open fracture. Pain control may be provided with IV narcotics, as permitted by the patient's hemodynamic and respiratory status. Soft tissue trauma, including open fractures, frequently complicates lower extremity fractures; early intervention will decrease complications and improve outcome. Soft tissue wounds should be cleaned and debrided of loose tissue and foreign material.

Open fractures are common in the lower extremity, especially with tibial shaft fractures. Open fractures are fractures that communicate with an open wound and require urgent orthopedic consultation for intraoperative debridement, reduction, and fixation. A skin laceration or abrasion that does not communicate with the fracture hematoma is not an open fracture.

Four interventions are crucial in the initial management of an open fracture. First, the fracture should be covered with a sterile dressing. Next, a long leg posterior splint should be applied. Third, the patient's tetanus status must be determined and immunization with tetanus toxoid or immunoglobulin should be performed as indicated. Finally, prophylactic IV antibiotics must be given. All open fractures should be treated with a first-generation cephalosporin such as cefazolin. More complex open fractures, including those with more than 2 cm of tissue defect and severe wound contamination, require additional gram-negative coverage due to the large amount of tissue devitalization present. This additional coverage may be achieved by the addition of an aminoglycoside, such as tobramycin or gentamycin, to the cephalosporin, or by providing single-agent coverage with a drug such as ticarcillin/clavulanate or pipericillin/tazobactim.
 

PROXIMAL EXTRA-ARTICULAR TIBIAL FRACTURES

Proximal extra-articular tibial fractures include subcondylar tibial fractures and tibial tuberosity fractures. If isolated, these fractures do not extend to the joint and thus usually lack a hemarthrosis. If a hemarthrosis is present, it usually indicates an extension of the fracture into the joint, a concomitant intra-articular fracture, or an associated ligamentous injury.

Subcondylar tibial fractures. Subcondylar tibial fractures involve the tibial metaphysis and almost always occur in conjunction with tibial plateau fractures, usually bicondylar fractures. The mechanism of injury is usually a rotatory or angular stress accompanied by axial loading, which produces a transverse or oblique fracture of the metaphysis.

Subcondylar tibial fractures produce tenderness and swelling over the proximal tibia. Isolated subcondylar fractures should not have any hemarthrosis unless there is associated ligamentous injury. Because subcondylar tibial fractures usually occur in concert with tibial plateau fractures, clinical findings may include ligamentous laxity, valgus or varus deformity, and hemarthrosis. Subcondylar tibial fractures are usually easily visualized on routine AP and lateral films.

Isolated subcondylar fractures without any joint involvement or displacement can usually be treated in the emergency department, with orthopedic follow-up in three to seven days. Treatment of these fractures includes immobilization with a long leg posterior splint, crutches, and non-weight bearing, standard RICE therapy, and adequate analgesia. A comminuted or intra-articular fracture requires urgent orthopedic consultation for ORIF or placement in traction.

Tibial tuberosity fractures. The tibial tuberosity is an elevation of bone in the anterior proximal tibia approximately 5 cm distal to the inferior apex of the patella. Easily palpable, it serves as the attachment site for the patellar tendon, the inferior portion of the extensor quadriceps mechanism.

Tibial tuberosity (or tubercle) fractures are avulsion fractures that occur most commonly in boys aged 15 and 16, usually as an indirect injury sustained during a sports activity. The mechanism of injury is typically a force causing flexion of the knee against a tightly contracted quadriceps muscle. Because the patellar tendon is stronger than bone in the skeletally immature, the bone, not the tendon, fails, and an avulsion fracture results. Tibial tubercle fractures may be complete or incomplete avulsions and occasionally extend into the joint.

Tibial tubercle fractures result in pain, swelling, and tenderness to palpation over the tubercle. The knee may be held in slight flexion, and pain on passive or active extension is usually noted. The degree of functional disability depends on the extent of the fracture; it usually manifests as loss of normal active extension. If the fracture extends into the joint, a hemarthrosis may be present.

Lateral films are the most useful diagnostic tool with this type of fracture. They can show the avulsion fracture, the number of fragments present, and the degree of displacement. Occasionally, comparison films of the opposite extremity are helpful in differentiating the presence of an acute fracture from normal findings with an immature skeleton.

Tibial tubercle fractures are classified as type I, II, or III injuries, based on the degree of displacement of the fracture fragment and extension of the fracture line. Type I injuries are incomplete avulsions with the tubercle hinged upward but still attached proximally at its base. Patients with this type of fracture can usually extend the knee against gravity but not against resistance. In a type II injury, there is complete avulsion of the tubercle but no proximal retraction of the fragment and no extension of the fracture line into the joint. These patients are usually unable to actively extend their knee against gravity. Type III fractures are complete avulsion fractures with extension of the fracture into the joint. Patients with type III fractures are unable to extend the knee against gravity.

In general, types I and II injuries with less than 5 mm of displacement may be managed in the emergency department with orthopedic follow-up in three to seven days. The knee should be immobilized in extension with a knee immobilizer. The patient should maintain non-weight-bearing status with crutches until follow-up with an orthopedic surgeon. Once the patient is discharged home, standard RICE therapy and analgesia should be employed.

In a type II injury with significant displacement or any type III injury in which the fracture extends into the joint, immediate orthopedic consultation is warranted. These patients usually require ORIF.
 

TIBIAL SHAFT FRACTURES

Both direct and indirect trauma can cause tibial shaft fractures, with direct trauma being far more common. Direct trauma often involves significant force producing transverse or comminuted fractures with a large degree of displacement. Fractures caused by direct trauma are frequently open and usually have an associated fibular fracture. Low-energy indirect trauma is usually rotatory in nature and produces spiral or oblique fractures with less displacement and associated tissue damage.

Certain tibial fractures warrant special mention—namely, pathologic fractures, stress fractures, and a fracture common in children called a toddler's fracture. Pathologic fractures of the tibia are uncommon and are usually secondary to metastatic or primary bone neoplasms, osteomalacia, or metabolic bone disease. While the clinical features of these fractures are similar to other types of tibial fractures, they should be suspected in any fracture for which minimal or no mechanism of injury can be determined.

Stress fractures are common in the tibia and result from repetitive stress applied to the bone, as in activities such as running, marching, or jumping. These fractures are a common cause of patient discomfort and physician referral and will be covered later.

A toddler's fracture is a nondisplaced spiral fracture of the distal tibia, most commonly seen in children aged nine months to three years. The mechanism producing the fracture is usually external rotation of the foot with the knee flexed, as may occur in a child using a walker. The most common presentation is a child with acute onset of a limp or refusal to bear weight. Toddler's fractures are usually not indicative of child abuse, in contrast to midshaft tibial fractures, which should always raise suspicion of abuse.
 

SIGNIFICANT PAIN AND SWELLING

Tibial shaft fractures cause significant pain and swelling to the leg, often accompanied by deformity of the leg and angulation or rotation of the foot. While physical findings of a fracture are usually easily identified, close attention must be paid for any evidence of peripheral neurovascular compromise. Although vascular injuries are uncommon in these types of fractures, careful assessment of the dorsalis pedis and posterior tibial pulses as well as capillary refill should be performed. The peroneal nerve is the most commonly injured nerve, and both the superficial and deep branches of this nerve should be tested. In addition to neurovascular injuries, ligamentous damage to the knee is common in tibial shaft fractures, with almost 25% of these fractures associated with injury to at least one ligament.

One of the most feared complications of a tibial shaft fracture is compartment syndrome. The classic findings with this condition are the "four P's": pain (out of proportion to other findings and worse with passive stretching of muscle groups), pallor, paresthesia (decreased sensation to pinprick, light touch, or two-point discrimination), and paralysis.

Pain, the most important finding, is usually deep, poorly localized, and unrelieved with IV narcotics. Pulselessness is not reliable for the diagnosis of compartment syndrome; it would be a very late finding.

If compartment syndrome is suspected, compartment pressures should be measured and immediate surgical consultation should be obtained. A fasciotomy would be necessary.

Standard AP and lateral X-rays are usually sufficient to diagnose tibial shaft fractures. Due to the high frequency of concomitant injury, radiographs of the ipsilateral knee and ankle should be obtained. In addition, ipsilateral femur, hip, and pelvis X-rays may be indicated, depending on the mechanism of injury and physical findings. As a general rule, splinting of the lower extremity should be done prior to moving the patient or the extremity to obtain X-rays. This will not appreciably delay the imaging studies and will decrease the patient's pain as well as the risk of increasing tissue damage or even progression to an open fracture.
 

MANAGEMENT ISSUES

In closed tibial shaft fractures, management begins with immobilization of the extremity in a long leg posterior splint with the knee in 10 to 20 degrees of flexion. Administering parenteral narcotic analgesia prior to applying the splint may decrease the patient's discomfort and facilitate placement. If distal pulses are not palpable prior to splinting, they should be evaluated with a Doppler device to ensure arterial flow. If no flow is found, an attempt at fracture reduction should be made prior to placing the splint. If pulses are still not present after this, the limb should be splinted and immediate orthopedic consultation obtained.

Pain generally decreases after adequate reduction and splinting; its persistence following splinting may indicate limb ischemia, compartment syndrome, or nerve root compression. Circumferential casting is to be avoided early in these injuries due to swelling and the increased risk of compartment syndrome. Open tibial shaft fractures require special management with a sterile dressing, IV antibiotics, and emergent orthopedic consultation as described above.

Due to the paucity of overlying muscle and blood supply, open tibial fractures are especially prone to infection, including a fivefold risk of developing osteomyelitis. Also, tibial fractures are very slow to heal and are commonly complicated by delayed or nonunion. Other delayed complications of tibial shaft fractures include deep vein thrombosis, malrotation, re-fracture and reflex sympathetic dystrophy.
 

PROXIMAL AND MIDSHAFT FIBULAR FRACTURES

Fibular fractures occur most commonly in association with fractures of the tibia. Isolated fractures of the proximal fibula or fibular shaft are uncommon and are usually due to a direct blow producing transverse or comminuted fractures. The fibula can also be injured by indirect forces, with the proximal fibula most commonly fractured by external rotation forces and the distal fibula by internal rotation forces. While fibular fractures are clinically less significant than tibial fractures, they can result in damage to the superficial peroneal nerve and disruption of knee and ankle stability.

A Maisonneuve's fracture is a fracture of the proximal fibula that occurs with an associated distal tibial fracture, ankle fracture, or deltoid ligament tear. In this type of injury, an external rotatory force applied to the ankle fractures the tibia, partially or completely disrupts the syndesmotic interosseous membrane joining the tibia and fibula, and produces a fracture of the proximal fibula. It is important to evaluate for a fracture of the proximal fibula in any ankle or distal tibial fracture because patients will frequently complain only of pain in the ankle area.

Isolated fibular shaft fractures generally cause lateral leg pain that worsens with walking, as well as swelling and tenderness at the fracture site. In any distal tibial fracture or ankle injury, it is important to palpate along the interosseous membrane and proximal fibula for any evidence of a Maisonneuve's fracture.

In the assessment of a patient with a fibular fracture, close attention should be paid to any accompanying injuries, most notably superficial peroneal nerve injury and ligamentous injury of the knee. The common peroneal nerve passes around the proximal neck of the fibula and can be injured in a proximal fibular fracture. A characteristic finding of common peroneal nerve injury is "foot drop," in which the foot hangs down due to loss of the ability to both evert and dorsiflex the foot. In addition to these motor findings, damage to the common peroneal nerve will result in impaired sensation along the entire dorsal surface of the foot, including the first dorsal web space. Patients with proximal fibular fractures should also be evaluated for ligamentous instability of the knee, because injuries to the ligaments, especially the lateral cruciate ligament, are common.

Fibular fractures are usually easily identified on standard AP and lateral radiographs of the lower leg. In general, radiographic examination of fibular fractures should include X-rays of the ipsilateral knee and ankle to rule out an associated fracture.

Most isolated fibular fractures can be easily managed in the emergency department or primary care office, with orthopedic follow-up arranged in three to seven days. Isolated nondisplaced fractures of the fibula head, neck, or proximal fibular shaft can be immobilized with a knee immobilizer; fractures of the midshaft or distal fibula can be immobilized with a posterior splint and elastic wrap. Patients with either type of fracture should use crutches and should be told not to bear any weight on the leg.

Other general fracture care includes RICE therapy and adequate analgesia. Orthopedic consultation is required for a Maisonneuve's fracture, a severely displaced fibular shaft fracture, or any evidence of peroneal nerve injury.
 

STRESS FRACTURES OF THE LOWER EXTREMITY

Stress fractures are caused by repetitive and prolonged force applied to bone. They occur most commonly in the lower extremity and are a frequent source of pain in younger, physically active patients. Stress fractures account for 10% of all sports injuries and up to 15% of all running injuries. A higher incidence of stress fractures has been observed in Caucasians, women, and military recruits.

The tibia is the most common site for stress fractures, accounting for up to 50% of all cases. Other common sites include the femur, fibula, navicular, and metatarsal bones. Stress fractures are categorized into fatigue fractures and insufficiency fractures, depending on the underlying mechanism. Fatigue fractures occur in normal bone as a result of increased stress; they are usually found in patients who participate in running, jumping, marching, or dancing activities. Insufficiency fractures occur when normal stress is applied to abnormal bone. These fractures are typically seen in postmenopausal women whose bones are deficient in mineral content, but they may also be found in individuals with rheumatoid arthritis, diabetes, or osteodystrophy.

Patients with stress fractures frequently present with pain described as gradual in onset, progressively worsening, associated with a particular activity, and relieved with rest. They will often complain of localized pain and bony tenderness without any history of trauma. Historical features suggesting the diagnosis of stress fracture include any recent increase in the amount or intensity of physical activity, running on hard surfaces, and pain that improves with rest. The physical exam is notable for localized bony tenderness with swelling of overlying muscles, without evidence of muscular atrophy, weakness, or joint dysfunction.

Diagnosing stress fractures can be difficult, because in addition to a paucity of physical findings, only 30% of stress fractures can be seen on X-rays at the time of presentation. One approach to the diagnosis involves cessation of the physical activity suspected of being the cause and taking repeat X-rays in two weeks. Radiographic findings of new periosteal bone or sclerosis are suggestive of stress fracture and may be seen in up to 50% of patients in two to six weeks after beginning treatment.

A valuable tool in the detection of stress fractures is the bone scan, which reveals stress fractures as focal areas of increased radiotracer uptake. Technetium diphosphate bone scanning has a sensitivity for stress fractures approaching 100% and can demonstrate a stress fracture as early as three days after the onset of symptoms. However, besides its high cost, a limitation of a bone scan is that it cannot differentiate a stress fracture from infection or neoplasm. It thus lacks the specificity of plain radiographs for diagnosing stress fracture.

Most tibial and fibular stress fractures can be successfully managed with decreased physical activity for three to six weeks, along with the use of ice, elevation, and analgesics. Serial X-rays may be used to monitor the healing process but are not necessary in all cases. In extreme cases in which walking alone causes pain or in which conservative therapy has failed, casting or even surgery may be considered.

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