Fractures of the patella are uncommon and occur primarily in patients between 20 and 50 years of age. Determining the integrity of the quadriceps extensor mechanism is crucial in the diagnosis of these fractures. Patients with nondisplaced fractures and intact knee extension heal well with immobilization and rehabilitation. Most patellar fractures in children are avulsion or osteochondral fractures
The tibia is the most frequently fractured long bone. Near-anatomic alignment is important in minimizing the risk of nonunion or malunion in these fractures. Even minimal displacement in tibial fractures necessitates referral to an orthopedist. Primary care providers must stay alert to the signs of an acute compartment syndrome when evaluating fractures of the tibia. Tibial fractures in children can result from relatively minor injuring forces. The accidental toddler’s fracture is common and must be distinguished from a fracture caused by child abuse.
Recognition of neurovascular and ligamentous injuries or compartment syndromes that may accompany fibular fractures is essential in distinguishing uncomplicated from complicated fractures. Truly isolated fractures of the fibula shaft are treated symptomatically and heal well with minimal treatment.
See Appendix for stepwise instructions for short- and long-leg casts and splints used in the treatment of patellar, tibial, and fibular fractures.
Patellar Fractures And Dislocations
The patella is the largest sesamoid bone in the body and serves to increase the leverage and efficiency of the quadriceps muscle. The patella is generally triangular, with the apex pointing distally. The rectus femoris and vastus muscles (lateralis, medialis, intermedius) all insert on the proximal pole. The patellar ligament attaches to the distal pole of the patella and inserts on the tibial tuberosity. The medial patellofemoral ligament is the primary restraint to lateral subluxation of the patella, particularly in early flexion. Other medial stabilizers include the medial retinaculum, the medial patellotibial ligament, and the vastus medialis obliquus muscle. A thin layer of quadriceps tendon passes over the patella and joins the patellar ligament distally. The medial and lateral retinacula, which are extensions of the quadriceps muscle, bypass the patella and insert directly on the tibia. If the retinacula are intact after a patellar fracture, the patient is able to extend the knee actively. The primary blood supply of the patella enters the central portion and the distal pole. Fractures through the midportion of the patella compromise the vascular supply to the proximal pole and leave it at risk for avascular necrosis (AVN).
Fractures of the patella are broadly classified as transverse, stellate or comminuted, vertical, and osteochondral. Any of these fracture types can be displaced or nondisplaced. Transverse fractures are the most common type followed by stellate fractures. The majority of transverse fractures are in the lower third of the patella. Vertical fractures usually occur along the margins of the patella. An osteochondral fracture involving the medial patellar facet can occur after a patellar dislocation or subluxation.
Mechanism of Injury
Patellar fractures result from either direct or indirect forces. Most fractures are due to direct forces such as a fall on the anterior aspect of the knee or striking the knee on the dashboard in a motor vehicle accident (MVA). Indirect injuries occur when patients stumble and attempt to prevent themselves from falling. The quadriceps muscle contracts forcefully, exceeding the intrinsic strength of the patella. The patella actually fractures before the patient strikes the ground. Continued quadriceps muscle contraction tears the medial and lateral retinacula, which results in fracture displacement. Fractures caused by direct trauma are usually stellate and nondisplaced; fractures caused by indirect forces are usually transverse and displaced.
The patient has tenderness and swelling over the anterior knee. When the fracture is displaced, a defect or separation is usually palpable if swelling is not excessive. The most important aspect of the examination is to check for the patient’s ability to actively extend the knee against gravity. If this capability is absent, the quadriceps mechanism is disrupted. Local anesthetic can be injected into the knee joint to relieve pain before testing extensor function.
Anteroposterior (AP), lateral, and sunrise views of the knee should be adequate for diagnosing most patellar fractures ( Figure 12-1 ). The lateral view is the most useful view in delineating fracture lines and determining displacement ( Figure 12-2 ). A separation of more than 3 mm between fragments or an articular stepoff of more than 2 mm constitutes a displaced fracture. Marginal vertical fractures are best visualized on the sunrise view. A bipartite patella may be mistaken for an acute fracture. This variation of ossification is best seen on the AP view and can be distinguished from an acute fracture by the well-defined zone of separation usually in the superolateral aspect of the patella ( Figure 12-3 ). A radiograph of the opposite knee can confirm this diagnosis because bipartite patella is usually a bilateral finding. Another common finding on lateral radiographs of the knee is a small sesamoid bone in the tendons posterior to the knee joint ( Figure 12-4 ). This normal variant is called the fabella and is of no clinical significance.
Indications for Orthopedic Referral
Displaced patellar fractures and avulsion fractures involving a quadriceps or patellar tendon injury require operative fixation and referral to an orthopedic surgeon. Patients with severely comminuted fractures should also be referred for consideration of partial or complete patellectomy. Quadriceps tendon repair and preservation of as much of the patella as possible are important in restoring knee extension. Total patellectomy is indicated only for highly displaced, severely comminuted fractures in which no large fragments remain. The timing of the surgery depends somewhat on the integrity of the overlying skin, which is often abraded during the injury. If the abrasions are clean and the wound is less than 8 hours old, the operative risk of infection is low. Extensive abrasions or a contaminated wound may necessitate delaying surgery until the skin heals.
Table 12-1 summarizes management guidelines for nondisplaced patellar fractures.
|Splint type and position||Knee immobilizer |
Knee in full extension
|Initial follow-up visit||5 to 7 days|
|Patient instruction||Icing and elevation of the knee |
Non–weight bearing until follow-up visit
|Cast or splint type and position||Cylinder cast above ankle to groin |
Knee in full extension, not hyperextension
Knee immobilizer brace for reliable patients
|Length of immobilization||4 to 6 weeks|
|Healing time||8 to 10 weeks|
|Follow-up visit interval||Every 3 to 4 weeks|
|Repeat radiography interval||At 2 weeks to check position |
At 4 to 6 weeks to document union
|Patient instruction||Weight bearing as tolerated and straight-leg raises while in cast or brace |
Knee ROM and strengthening exercises after the cast or brace is removed
Physical therapy referral is usually required to restore knee function
|Indications for orthopedic consult||>3 mm of separation of fragments or >2 mm of articular stepoff |
Severely comminuted fractures
Associated tendon injuries
Aspiration of the knee joint hemarthrosis with use of aseptic technique should be considered to reduce pain and swelling, especially if a tense effusion is present. The knee should be wrapped with a compressive elastic bandage and the patient placed in a knee immobilizer with the knee in full extension. Icing and elevation of the knee are important in keeping the swelling to a minimum. The patient should remain non–weight bearing until examined again 5 to 7 days later.
Patients who have nondisplaced patellar fractures that have a smooth articular surface and an intact quadriceps mechanism and who are capable of extending the knee against gravity can be treated effectively nonoperatively. A cylinder cast from the groin (not the midthigh) to just above the ankle malleoli with the knee in extension (not hyperextension) is the most reliable form of immobilization. Selected compliant patients can be treated with a removable hinged knee brace locked in extension for walking provided they wear the brace at all times except for bathing. Weight-bearing and straight-leg-raising exercises should be started in the cast or brace. The hinged brace is lighter than a cast and is an especially good choice for an elderly patient so early motion can be started to minimize loss of function.
A follow-up radiograph should be taken after 2 weeks to confirm that the fracture remains nondisplaced. Any displacement beyond the aforementioned limits warrants referral to an orthopedic surgeon. Immobilization should continue until radiographic evidence of union is apparent, which usually occurs in 4 to 6 weeks. Once the cast or brace is discontinued, the patient should be instructed in knee range of motion (ROM) exercises and quadriceps-strengthening exercises. A physical therapy referral is usually necessary to help the patient regain normal strength and motion.
Nondisplaced marginal vertical fractures do not have to be immobilized and can be treated with reduced activity for 3 to 6 weeks and progressive ROM and strengthening exercises.
Return to Work or Sports
The level of activity required by the patient’s job should be considered when deciding how soon a patient may return to work. Patients with relatively sedentary jobs could return to work after several days of elevating and icing the knee if their symptoms allow, but it may be best to wait until after the first follow-up visit (5 to 7 days after injury). Patients whose jobs involve squatting, climbing stairs, or other activities requiring knee flexion should not return until the cast or brace is discontinued and knee ROM has progressed to the point at which they can perform these activities with reasonable comfort. This level of recovery is likely to take a minimum of 6 to 8 weeks. Athletes may begin activities that require little knee flexion (e.g., walking or freestyle swimming with gentle turns) soon after immobilization ends. Patients may begin gentle running when they are able to walk with little or no discomfort and knee ROM permits. This activity can be advanced as symptoms permit, with jumping and cutting activities added last. Patients can return to active jobs or sports more quickly by performing regular weight bearing, straight-leg raises, and ankle ROM while the knee is immobilized and by working diligently on regaining leg ROM and strength after immobilization ends. Referral to a physical therapist can greatly facilitate this process.
Complications after treatment of nondisplaced patellar fractures are rare, although patellofemoral pain and post traumatic osteoarthritis may occur. Persistent patellofemoral pain after a patellar fracture should be managed with nonsteroidal antiinflammatory drugs (NSAIDs) and physical therapy. Prolonged immobilization may result in significant weakness in the extremity and loss of knee motion, and patients should work with physical therapists to restore function. Fracture fragment separation and dehiscence of fracture repair, infection, and AVN may complicate operative repair of patellar fractures.
The patella ossifies in early childhood, first becoming visible on plain radiographs between the ages of 3 and 6 years. Up to six separate ossification centers may be present, simulating the presence of a fracture. Palpation for tenderness and a comparison view of the normal knee may be used to distinguish a fracture from a growth plate.
Unlike injuries in adults, a knee effusion in a child is rarely caused by ligament injury. Patellar dislocation or fracture is far more likely. If a child has a traumatic knee effusion, a patellar dislocation that has spontaneously become reduced should be suspected. In a child with a traumatic knee effusion that was not caused by a patellar dislocation, an occult fracture is probably present. Such patients should either be referred or undergo aspiration of the joint. In the presence of normal radiographs, fat in the aspirate would indicate an occult fracture. Because the fracture may primarily involve cartilage, magnetic resonance imaging (MRI) is often required for adequate evaluation.
Most patella fractures in children are either osteochondral fractures or avulsion fractures. Osteochondral fractures occur in approximately 40% of childhood patellar dislocations. Patients with osteochondral fractures should be referred to an orthopedic surgeon.
In children, patellar avulsion fractures may appear deceptively small on radiographs. However, the fragment typically includes a portion of unossified patella, making the fracture much larger than it appears. In patellar sleeve fractures, for instance, much or all of the articular surface of the patella is avulsed along with a small fragment of bone from the inferior pole of the patella. This injury is characterized by a high-riding patella ( Figure 12-5 ), tenderness over the inferior pole, and an extensor lag when leg extension is tested. Patients with sleeve fractures should be referred, as should patients with avulsion fractures that are displaced or complicated by an inability to fully extend the knee. Nondisplaced fractures may be managed as previously described for adults. Healing is likely to be more rapid, allowing earlier discontinuation of the cast.
Transverse fractures of the patella are rare in children. They may be managed as described for adults, with special emphasis on assessing the patient’s ability to actively extend the knee. If the patient is unable to fully extend the knee, referral is indicated.
Dislocation of the patella usually occurs in patients with underlying patellofemoral malalignment. Predisposing factors that put the patient at risk of subluxation or dislocation include a shallow femoral groove, hypoplasia of the lateral femoral condyle, ligament hyperlaxity, a small or high-riding patella, genu valgum, external tibial torsion, and atrophy of the vastus medialis muscle. Nearly all patellar dislocations are lateral.
Mechanism of Injury
The usual cause of injury is an external pivotal motion on a partially flexed knee followed by a forceful contraction of the quadriceps that pulls the patella laterally. A direct blow to the medial patella, forcing it laterally, may also result in a dislocation.
If the patient reports that the knee went out of place and slipped back after extension of the knee, the patella has spontaneously become reduced. If the patella remains dislocated, the knee is obviously deformed, and a hemarthrosis may occur. Findings related to injury to the medial stabilizers include hemarthrosis, tenderness along the medial patella edge, or tenderness proximal to the medial femoral condyle. A larger hemarthrosis volume (~50 mL) suggests a more major injury to the medial stabilizers or osteochondral injury and is actually associated with a lower recurrence rate because this larger volume usually represents a more traumatic dislocation. This is in contrast to the patient with a lower energy mechanism who may have one or more predisposing risk factors and a less traumatic injury and thus a minimal hemarthrosis. The presence of fat in the knee aspirate is indicative of an osteochondral fracture.
See Expert Consult for a video on how to perform a reduction maneuver for an a patellar dislocation. Reduction of the dislocation can be preformed safely before obtaining radiographs. To reduce a laterally dislocated patella, the clinician places the patient in the supine position and flexes the hip to 90 degrees to relax the quadriceps muscle. The clinician then gradually extends the knee while gently pushing the patella medially. If moderate swelling and muscle spasm prevent relocation, aspiration of the hemarthrosis and instillation of a local anesthetic usually provide enough pain relief to accomplish the reduction. A benzodiazepine can also be used to relax the patient.
Radiographs should be obtained to rule out an accompanying fracture even if the dislocation spontaneously became reduced. The AP, lateral, and sunrise views should be examined, particularly for an osteochondral fracture of the patella, which occurs in up to 25% of cases. Unfortunately, these fractures are often missed on initial radiographs. All patients with a first-time traumatic dislocation should be considered to have an osteochondral injury until otherwise proven, and MRI is indicated to look for this injury as well as injury to the medial stabilizers. Postreduction radiographs are necessary to check patellar position.
Indications for Orthopedic Referral
If an osteochondral fracture is associated with the dislocation, the patient should be referred to an orthopedic surgeon. Other indications for operative treatment include significant injury to the medial patellar stabilizers, a persistently laterally subluxed patella, or a second dislocation.
Initial treatment includes limitation of knee flexion with a knee immobilizer, icing, and elevation of the knee. The patient should remain non–weight bearing for 2 to 3 days. The patient should remain in the knee immobilizer for the first 2 to 3 weeks for comfort.
Weight-bearing and return to work duties are allowed as soon as the patient is able. After 2 to 3 weeks, functional rehabilitation and progressive knee flexion are allowed over the next 3 weeks. Commercially available patellofemoral braces provide needed protection during this time because quadriceps strength is inadequate for full independent function. Physical therapy referral is indicated in most cases to help the patient restore strength and motion gradually. Guidelines for return to work or sports are the same as outlined previously for patellar fractures.
Redislocation is common, with those who are younger and female being at greater risk. There are some reports of higher redislocation rates with closed treatment versus operative treatment for first-time dislocators, but a well- designed, randomized, prospective trial with an adequate length of follow-up has failed to show a significant difference in rates based on initial treatment choice. Other complications after a patellar dislocation include patellar instability and patellofemoral arthritis.
The evaluation, indications for referral, and treatment of patellar dislocations in children are similar to those in adults. In children, if the patella remains dislocated when the child seeks treatment and prereduction radiographs do not reveal a fracture, reduction should be performed as previously described for adults. Films should be repeated after reduction because fracture fragments are often visible only on postreduction views.
The tibia and fibula are bound together proximally by the tibiofibular articulation, a synovial joint reinforced with strong anterior and posterior ligaments. Distally, the tibia and fibula are connected by the tibiofibular syndesmosis, which is composed of the anterior and posterior tibiofibular ligaments and the interosseous membrane. The bones and muscles of the leg are surrounded by the crural fascia. The interosseous membrane and fibrous extensions of the crural fascia separate the leg into four distinct compartments ( Figure 12-6 ).
The popliteal artery divides to form the anterior and posterior tibial arteries after it exits the popliteal fossa. The anterior tibial artery enters the anterior compartment just below the level of the fibular head and descends along the interosseous membrane. It is vulnerable to direct injury in proximal tibial fractures.
The medial and lateral tibial plateaus are the articular surfaces of the medial and lateral tibial condyles. The two plateaus are separated by the intercondylar eminence, which serves as the attachment for the anterior cruciate ligament (ACL). The outer aspect of each plateau is covered by the cartilaginous meniscus. The medial plateau and condyle are larger and stronger than on the lateral side, and fractures of the relatively weaker lateral plateau are more common.
Tibial Plateau Fractures
Mechanism of Injury
Many tibial plateau fractures occur as a result of a car–pedestrian accident in which the bumper strikes the outside of the leg with a force directed medially (valgus). This results in a depressed or split fracture of the lateral tibial plateau as the femoral condyle is driven into it. Because of the greater strength of the medial plateau, fractures on this side of the joint usually suggest a much higher energy injuring force (varus). Axial compression caused by a fall from height can also fracture the proximal tibia. Elderly patients with osteoporosis are more likely to sustain a fracture of the tibial plateau than a ligamentous or meniscal tear after a twisting injury to the knee. The intercondylar eminence can be fractured in association with an ACL tear as a result of hyperextension or rotatory forces.
Patients with a tibial plateau fracture have a painful swollen knee and are unable to bear weight. During examination, they have tenderness over the proximal tibia and limited flexion and extension of the knee. The clinician should determine whether the cause of injury was a low- or high-energy force because associated neurovascular and ligamentous injuries and compartment syndromes are much more common after high-energy injuries. Distal pulses and peroneal nerve function should be documented. The skin should be carefully examined for any evidence of abrasions or lacerations that may indicate an open fracture. Presence of an effusion suggests an osteochondral fracture or a ligament or meniscal injury.
Assessment of knee stability is an important element in the evaluation of tibial plateau injuries. Aspiration of the knee hemarthrosis and instillation of a local anesthetic may be necessary to get an accurate examination. Compared with the uninjured side, a stable knee should not have more than 10 degrees of joint widening on varus or valgus stressing at any point in the arc of motion from full extension to 90 degrees of flexion. The integrity of the ACL should be assessed by means of the Lachman test.
Tibial plateau fractures are frequently associated with soft tissue injuries around the knee. Medial collateral ligament and lateral meniscal tears often accompany lateral plateau fractures. Medial plateau fractures are associated with lateral collateral ligament and medial meniscus tears. The ACL can be injured in fractures of either plateau. Tibial plateau fractures, especially those with extension of the fracture into the tibial shaft, can lead to an acute compartment syndrome resulting from hemorrhage and edema (see discussion of acute compartment syndrome in the section on Clinical Presentation for tibial shaft fractures).
AP, lateral, and internal and external oblique views of the knee should be obtained in the evaluation of a suspected proximal tibial fracture. A tunnel (notch) view is useful in visualizing the intercondylar eminence. The tibial plateau normally slopes from anterosuperior to posteroinferior. Findings on the AP view may be subtle and fail to define fracture depression because this view does not demonstrate the normal plateau slope ( Figure 12-7 ). An area of increased bone density from fracture depression may be the only finding on the AP view ( Figure 12-8 ). Split fractures of the tibial plateau are more common in younger patients with dense cancellous bone. Depressed fractures or split fractures with depression are more common in older patients with decreased bone density. Fractures can also occur in both plateaus simultaneously.
Additional imaging with computed tomography (CT) scanning is useful in delineating the extent of articular involvement and the degree of fracture depression. MRI has replaced CT scanning in many centers because of its superior ability to detect associated ligamentous and meniscal injuries.
Indications for Orthopedic Referral
A tibial plateau fracture in association with a vascular injury or compartment syndrome requires emergent orthopedic referral and treatment. Displaced or depressed tibial plateau fractures and fractures with associated ligamentous or meniscal injuries should be referred within 24 to 48 hours. The goal in treating these fractures is to achieve a stable knee with a congruous healthy articular surface. Decisions regarding operative versus nonoperative treatment of displaced or depressed fractures must take into account the patient’s age, current and expected level of activity, presence of associated injuries, and current medical conditions.
Table 12-2 summarizes the management guidelines for nondisplaced tibial plateau fractures.