The anatomical structures of the knee relevant to the present discussion are shown in Figures 26-1 and 26-2.

Acute injuries of the knee can cause sprains, dislocations, or fractures (Table 26-1). The anterior cruciate ligament (ACL) itself is injured most often in youth sports such as football and soccer, although this injury can happen in any sport, which involves running, cutting, or jumping. ACL injuries are more common in older adolescent athletes nearing skeletal maturity. There are also gender differences in ACL injury in adolescent athletes. One Norwegian study demonstrated a 5.4 fold increased risk of ACL injury in female athletes in matched soccer cohorts aged 15 to 18 years. In addition, the female athletes had a much lower rate of return to play following treatment than males.1 Isolated posterior cruciate ligament injuries are uncommon in skeletally immature athletes, and may occur in sports such as football. The medial collateral ligament is one of the most commonly injured structures in the knee. Meniscal tears are not common in children and adolescents. Meniscal tears are more common in sports such as soccer, football, and wrestling, but have been reported in may other sports. There is greater variability in the types of meniscus tears in the young athlete, but horizontal tears are relatively uncommon.2–4

The mechanisms of injuries are reviewed below under discussion of specific injuries.

The athlete may be seen by the pediatrician on the field or the sideline or later in the office. On the field, the athlete may present with a history of an injury to the knee or the leg following a fall, sudden twisting of the leg, or collision with another player. Rapid onset swelling, radiation of the pain, numbness, paresthesias, and sensation of cold, distal to knee may suggest neurovascular involvement, typically associated with displaced fractures or dislocations, that need urgent appropriate surgical consultation and treatment.

Most cases are seen by pediatricians in the office setting when the athlete is seen either for a follow-up after seen on the field or the emergency department, or for initial visit following the injury. Key elements of the history are listed in Table 26-2. Causes of locking and giving away are listed in Table 26-3.

History should ascertain the mechanism of the injury. Ask the athlete how the injury occurred. Determine if the athlete was running, changing direction, or stopped suddenly, and the position of the leg and the knee at the time. Sudden change in direction, especially with foot planted can result in sprain of the ACL and injury to meniscus. Landing off balance may also result in anterior cruciate sprain. Collateral ligaments are typically injured as a result of a direct impact to the medial or lateral aspect of the knee. A direct impact against tibia when the knee is flexed is associated with isolated sprain of the posterior cruciate ligament.2,5

The athlete feels immediate pain at the time of a ligamentous injury, dislocation, or fracture.2,5 The key findings on examination of acutely injured knee include swelling, tenderness, deformity, and instability. Details of examination of the knee are reviewed above.

In the setting of acute trauma to the knee encountered on the field, the initial assessment should be directed toward identifying injuries that may need immediate treatment. In the presence of gross deformity of the knee, pallor and diminished arterial pulse distally, and decreased sensation or weakness distal to the knee, a neurovascular injury, dislocation, or fracture should be suspected, that require emergent orthopedic consultation and treatment. The leg should be splinted and the athlete transported to the local hospital emergency department for further evaluation and treatment. Always examine the entire lower limb from hip to toe with the athlete in shorts or gown and not wearing socks or shoes, and compare findings to that of the uninjured limb.

Note swelling, deformity, skin break, and ecchymoses. Intra-articular effusion usually first obliterates the hollow medial to the patella, later extending superiorly, and the laterally. Causes of acute posttraumatic hemarthrosis are listed in Table 26-4.

Assess active, passive, and against manual resistance: knee flexion and extension.

Crepitus associated with anterior knee pain suggests chondromalacia patellae. Localization of tenderness may provide clue to the injured structures. Perform patellar ballottement test to assess intra-articular effusion (Figure 26-3).

Lachman

Check anterior translation of the tibia on the femur by stabilizing the femur with one hand and at 30 degrees of flexion pulling the tibia forward. This is the most sensitive and specific test for an ACL tear (Figure 26-4).

Posterior Drawer

This assesses the PCL. At 90 degrees of flexion, grasp the tibia with both hands and attempt to translate the tibia posteriorly relative to the femur (Figure 26-5).

McMurray

This test places a load and a shear force on the menisci, and is the most sensitive for assessing meniscal tears. A + McMurray is described as demonstrating popping or palpable motion of the meniscus on examination, which is likely to occur with a displaced bucket handle tear, however with many meniscal injuries the findings are not that clear cut (Figure 26-6).5

Appley

With the patient prone, the tibia and ankle are held gently, the tibia is flexed to 90 degrees and the tibia is then loaded and rotated to check the menisci. This examination is uncomfortable in many patients who do not have a meniscal tear, but this examination does reliably demonstrate focal tenderness in many patients who have a torn meniscus (Figure 26-7).

Valgus and Varus Stress

These tests assess the medial and lateral collateral ligaments respectively and are performed at 30 degrees of flexion with a gentle varus and valgus stress placed across the knee (Figure 26-8).

Patellar Apprehension

This test is performed with the patient supine and the leg extended. Gentle pressure is used to translate the patella laterally, which usually elicits discomfort in patients with retropatellar pain or subluxation. If there has been an acute dislocation, this maneuver should not be performed (Figure 26-9).

Patellar Tilt

This test is done by placing the examiners thumb beneath the lateral patella with the knee extended and using the fingers to control the patella as it is tilted up. In those with a tight lateral retinaculum or lateral patellar compression syndrome, the patella will not usually tilt above neutral. Patellar mobility measured from the center of the knee in quadrants should also be checked with gentle medial and lateral translation. Superior inferior mobility of the patella should also be assessed in the same manner.

Generally in most cases of acute knee trauma, AP, lateral, notch, and sunrise view x-rays are indicated (Table 26-5). MRI scan is indicated in some cases to assess ligament sprains, osteochondral fractures, or meniscal tears.

Based on the initial assessment, a decision is made as to the urgency of treatment as noted above when a neurovascular injury or a fracture or dislocation is identified or suspected. In nonurgent cases, the athlete should be removed from further sport participation, the knee placed in an immobilizer, and the athlete advised not to weight bear until definitive evaluation later. Treatment for specific injuries is reviewed below. Conditions that indicate orthopedic referral and consultation are listed in Box 26-1.

Definition and Epidemiology

Acute sprains of the ACL can be partial-thickness or full-thickness tears. Midsubstance tears of the ACL are uncommon before age 12. Young children are more likely to avulse the femoral attachment of the ACL (tibial spine avulsion). ACL sprains are seen most commonly in basketball, soccer, hockey, and American football.

Mechanism

In most cases, ACL sprain is a noncontact injury resulting from sudden deceleration and pivoting (external rotation) of knee (Figure 26-10). Statistically, ACL injuries are more prevalent in female than male athletes, and this may have to do with firing patterns of the quadriceps and hamstrings, overall conditioning and training, as well as leg position with the feet wider than the toes when landing from a jump.