Internal Derangement of the Knee (Knee Injury)
Anterior Cruciate Ligament Sprains
• Anterior cruciate ligament (ACL) injuries occur most commonly in basketball, soccer, American football, and downhill skiing.
• Typical mechanism of injury is a valgus or rotational force to the knee with the foot planted, or hyperextension
• More than 70% of ACL injuries occur without body contact (ie, have a noncontact mechanism).
— Landing from a jump
— Decelerating quickly
— Changing direction suddenly
• ACL injuries are being diagnosed in patients younger than 11 years with increasing frequency because of increased awareness, better diagnostic tools, and more children participating in high-intensity sports training at younger ages.
— A high index of suspicion is necessary for ACL injuries, especially for younger children in whom such injuries were previously thought to be uncommon. Long delays in treatment affect outcomes.
— Children may experience an intrasubstance ACL tear or an avulsion injury of the ACL tibial attachment (see “Tibial Eminence Fracture” section in this chapter). The diagnosis and treatment of each is markedly different.
• After 11 years of age, the incidence increases steadily with age and skill level, with an overall incidence of 1 per 100 high school athletes.
• Girls who play sports that involve running and cutting are 2 to 8 times more likely to injure their ACL than boys, probably because of any of the following factors:
— Increasing ACL laxity due to an increase in estrogen
— The tendency to have a smaller intercondylar notch, a smaller ACL, a higher incidence of generalized ligamentous laxity, knee valgus, femoral internal rotation, and greater strength imbalances in the lower extremities
— Most importantly, poor neuromuscular control of knee motion during landing and cutting
■Reduced activation of the hamstring muscles
■Reduced knee and hip flexion
■Greater dynamic knee valgus
SIGNS AND SYMPTOMS
• Sensation of a painful pop, followed by immediate swelling, a feeling of instability, and difficulty bearing weight
• Physical examination reveals a significant effusion and limited range of motion.
— About 67% of acute hemarthrosis in children is caused by an ACL tear, but in children younger than 10 years hemarthrosis may not occur with ACL rupture.
• There may not be any tenderness unless associated injuries are present.
• Sprain of the posterior cruciate ligament (PCL) or collateral ligaments
• Meniscal tear
• Chondral injury
• Distal femoral or proximal tibia fracture
• Patellar sleeve avulsion
• Tibial eminence fracture
• Patellar subluxation
• “Giving way” due to patellofemoral pain
• Posterior drawer test, varus and valgus stress tests, and Apley and McMurray tests should be performed to evaluate for other ligamentous or meniscus injuries (Table 35-1) (see also Figures 4-30–4-34).
|Injured Structure||Mechanism of Injury||Physical Examination Test|
|ACL||Hyperextension, twisting||Lachman test|
|MCL||Valgus force||Valgus stress test|
|Patellar dislocation||Direct blow to the patella or twisting injury to the extended knee||Apprehension test|
|PCL||Posterior force to the tibia or hyperextension|
Posterior drawer test
Quadriceps active test
Apley compression test
|LCL||Varus force||Varus stress test|
Abbreviations: ACL, anterior cruciate ligament; LCL, lateral collateral ligament; MCL, medial collateral ligament; PCL, posterior cruciate ligament.
• Radiographs (anteroposterior [AP], lateral, skyline, and tunnel views) should be obtained to rule out other injuries.
— AP view may reveal a small fleck of bone avulsed from the lateral tibia (Segond fracture) (Figure 35-1), which is pathognomonic of an ACL injury.
• Magnetic resonance imaging (MRI) may be performed to evaluate for associated soft tissue injuries, as suggested by history and physical examination. Although it is not always necessary, MRI is also helpful to confirm an ACL injury (Figure 35-2), especially when surgery is being considered.
Figure 35-1. Segond fracture, anteroposterior view. Black arrows point to a small avulsion (flake) fracture of the lateral tibia just below the articular surface of the tibia.
From Johnson TR, Steinbach LS, eds. Essentials of Musculoskeletal Imaging. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2004:515. Reproduced with permission.
Figure 35-2. A, Magnetic resonance imaging (MRI) scan of normal anterior cruciate ligament (ACL). B, Sagittal T2-weighted MRI scan showing disruption of the proximal fibers of the ACL (black arrows), typical of an ACL tear.
A courtesy of Cynthia LaBella, MD. B from Johnson TR, Steinbach LS, eds. Essentials of Musculoskeletal Imaging. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2004:548. Reproduced with permission.
• Initial treatment consists of protection, rest, ice, elevation, and mobilization (PRICEM).
— Protection is provided with crutches or a knee immobilizer.
— Nonsteroidal anti-inflammatory drugs are helpful for control of pain and swelling.
— If there is a large hemarthrosis, aspiration can improve patient comfort and facilitate early rehabilitation.
• A rehabilitation program, starting with early weight-bearing and range of motion exercises, is initiated as soon as possible after the pain begins to subside, usually within 5 to 7 days after injury.
• Whether to pursue nonoperative or operative treatment is a complex decision that depends on the patient’s age, symptoms, degree of laxity on examination, associated injuries, and future sports demands. An orthopaedic surgeon or a pediatric sports medicine physician can provide information to help the patient and family choose the most appropriate treatment.
• Nonoperative treatment consists of a comprehensive rehabilitation program to build lower extremity and core strength, balance, and endurance, which can take 6 to 12 weeks.
— After nonoperative treatment, patients are advised to avoid high-demand sports (Box 35-1) because of the risk for recurrent instability and secondary meniscal and chondral injuries.
— May be appropriate for patients who do not intend to pursue high-demand sports. This is controversial because playground activities are often high demand.
— May be used as a temporizing treatment of skeletally immature athletes who intend to pursue high-demand sports in the future but want to delay surgical treatment until the physes have closed. However, physeal-sparing surgical techniques are available to avoid these delays.
• Operative treatment in skeletally mature patients
— Operative treatment is advisable for
■Patients with an associated meniscus tear or other ligament injury
■Skeletally mature athletes who intend to pursue high-demand sports
— A variety of arthroscopic techniques and graft types are available for reconstructing the ACL in skeletally mature athletes.
■Bone-patellar tendon-bone and hamstring autografts have been used with success, and quadriceps autograft is becoming increasingly common; the choice is surgeon dependent.
■A variety of allografts are also available, although these are generally thought to be at higher risk of failure than autograft in young athletes.
— After surgery, rehabilitation follows the same protocol as for nonoperative treatment, but it takes longer to complete.
— Return to sports typically takes 9 to 12 months.
• Treatment of skeletally immature athletes with isolated ACL injuries is controversial.
— Surgical treatment using standard techniques creates a risk of growth disturbance. The tunnel site for the new ligament would traverse the tibial and femoral physes.
Box 35-1. Anterior Cruciate Ligament Demands of Various Sports
• American football
• Ice hockey
• Field hockey
• Track (non-jumping field events)
• Tennis (doubles)
Adapted from Dorizas JA, Stanitski CL. Anterior cruciate ligament injury in the skeletally immature. Orthop Clin North Am. 2003;34:355–363. © 2003, with permission from Elsevier.
— Physeal-sparing techniques may be used to allow very young athletes to return to high-demand sports and are being used with increasing frequency.
■A large number of techniques have been described. Some of these techniques closely resemble adult-type reconstruction, but the tunnels remain within the epiphysis.
■The risk of associated meniscal tears and cartilage injury is significantly increased if surgical treatment is delayed beyond 3 months; however, no study has shown that surgical treatment slows the progression of radiographic arthritis.
■Although the risk of physeal arrest is extremely low, long-term stability after these modified procedures is unproven. Skeletally immature patients may eventually require standard ACL reconstruction on reaching skeletal maturity.
• Despite disparity in injury rates, treatment outcomes are generally similar for boys and girls.
• After nonoperative treatment
— An ACL-deficient knee is prone to episodes of instability and risk of secondary meniscus tears and cartilage injury.
— Twenty percent to 27% of patients develop patellofemoral pain.
• After ACL reconstruction
— Patellofemoral pain is reported by 32% of patients.
— Risk factors include persistent quadriceps weakness, knee flexion contracture after rehabilitation, and use of a patellar tendon autograft.
• After surgical treatment of an ACL tear
— Many athletes are able to return to their previous level of competition.
— Recurrence rate after surgery (ie, graft rupture) is approximately 10% to 15%.
— After ACL injury, the frequency of ACL injury in the opposite knee is about 7% to 10%. Girls and younger children are at highest risk.
• Unfortunately, regardless of treatment, an ACL sprain is associated with a 10-fold increased risk for osteoarthritis later in life. This is probably because of intra-articular damage suffered at the time of the injury and the neuromuscular deficits that follow.
• Partial tears, especially in the skeletally immature athlete, may have satisfactory outcomes after nonoperative treatment.
— Some partial tears may heal sufficiently to provide knee stability for high-demand sports.
WHEN TO REFER
• Patients with ACL sprains should be referred to an orthopaedic surgeon with expertise in pediatric sports injuries or a pediatric sports medicine physician to evaluate and discuss treatment options.
• Neuromuscular training programs that include progressive strengthening and plyometrics (repetitive jumping exercises) while teaching safe landing mechanics have been shown to reduce ACL injury risk in female adolescent athletes by 72%. Resources for evidence-based neuromuscular training programs can be found at www.aap.org/cosmf.
• A functional knee brace (Figure 35-3