What's on this Page
7 Interesting Facts of Anterior Cruciate Ligament Injury
- •The anterior cruciate ligament (ACL) is one of four major knee ligaments.
- •The ACL is the primary restraint to anterior translation of the tibia and provides rotational stability to the knee.
- •It originates on the medial lateral femoral condyle, runs obliquely, and inserts anterior to the center of the tibial intercondylar area region
- Injury to the ACL results in abnormal translation and rotation of the knee, leading to increased forces on other knee structures (e.g., menisci, articular cartilage), risking additional acute or chronic injury.
- •Approximately half of acute ACL injuries are associated with meniscal tears.
- •A triad of injuries commonly occurs in conjunction: ACL, medial collateral ligament (MCL), and lateral meniscus.
- •Rarely, ACL injuries are involved with multiple knee ligament injury that may require emergent knee reduction and confirmation of neurovascular status.
History
Acute Injury
- •Noncontact, pivoting injury to the knee
- •Associated with a “pop” sensation and results in immediate swelling
- •Unable to continue in activity
Chronic Injury
- •Recurrent swelling with activity
- •Instability with pivoting maneuvers
Physical Examination
Observation
- •Abrasions
- •Deformity
- •Effusion (intra-articular swelling)
- •Difficulty bearing weight
Palpation
- •Patellar effusion (ballottable)
- •Tenderness
Range of Motion
- •Rule out a “locked knee” (lacking full extension) from an ACL tear in conjunction with a displaced bucket handle tear of the meniscus
- •Loss of flexion can occur from an effusion
Special Tests
- •Lachman test (gold standard)
- •With knee in 20 to 30 degrees of flexion, stabilize the femur and pull forward on the tibia along the plane of the joint line
- •A positive test is excessive forward tibial translation compared to the unaffected kneeFIG 142.2(A) Lachman test is the gold standard for evaluating an anterior cruciate ligament–injured knee. It is helpful to place a pillow under the knee to relax the hamstring muscle and gain the patient’s confidence. (B) Note that the examiner faces the injured knee and uses the hand that is closer to the patient’s head to stabilize the thigh and the other hand to displace the tibia anteriorly.
- •Anterior drawer sign
- •Place knee in 70 to 90 degrees of flexion, apply an anterior force, and assess the endpoint (not as sensitive as the Lachman test)
- •Positive test is endpoint laxity in anterior direction
- •Pivot shift test
- •A valgus force is applied while knee is being flexed
- •Positive test is the appreciation of a rotational jerk or “clunk” in movement
Other Helpful Tests
- •McMurray test (to assess for an associated meniscal tear)
- •Flexion and rotation of the knee with varus and valgus forces applied
- •Positive test is pain or a “click” as the meniscus displaces
- •Posterior drawer sign (to evaluate for a posterior cruciate ligament [PCL] tear)
- •Knee in 70 to 90 degrees of flexion, apply a posterior force to assess the endpoint
- •Positive test is endpoint laxity in posterior direction
- •Dial test (associated posterolateral corner or PCL injury)
- •With patient prone and knees flexed 30 and 90 degrees, externally rotate bilateral feet
- •Asymmetrical rotation in both 30 and 90 degrees of flexion suggests a combined posterolateral corner and PCL injury
- •Asymmetrical rotation only in 30 degrees of flexion suggests an isolated posterolateral corner injury or with an associated ACL injury
- •Patellar apprehension test (to determine patellar dislocation or instability)
- •With knee in extension, attempt to displace the patella laterally or medially
- •Positive test is the provocation of patient apprehension
Imaging
Radiographs
- •Posteroanterior flexion weight-bearing view
- •Determine presence of arthritis (especially in older patients)
- •Assess for a lateral tibial avulsion (Segond fracture), which is highly associated with an ACL tear
- •Lateral view
- •Determine patellar height
- •A high-riding patella (alta) may be associated with patellar instability or a patellar tendon rupture
- •A low-riding patella (baja) is associated with a stiff knee (arthrofibrosis)
- •Assess for posterior tibial slope (slopes >12 degrees are hypothesized to correlate with greater risks of ACL injury)
- •Sunrise view
- •Evaluate for patellar subluxation/tilt
Magnetic Resonance Imaging
- •Not required for diagnosis
- •Evaluate for ligament disruption in sagittal view and classic bone bruise pattern.
Additional Tests
- •KT1000/KT2000 knee arthrometers
- •Instruments that provide objective measurement of anterior tibial translation
- •Often used after ACL reconstruction
- •Methods to test rotation are under development
Differential Diagnosis
- •Patellar instability
- •Patellar or quadriceps tendon rupture
- •PCL rupture
- •Meniscal tear
Treatment
- •At diagnosis of ACL tear, treatment focuses on:
- •Decreasing the effusion (consider aspiration, ice, compression)
- •Physical therapy with focus of closed-chain quadriceps rehabilitation. Important to maximize range of motion, quadriceps tone, and pain control In the acute period, treatment should focus on controlling the knee effusion and maintaining both strength and range of motion. To reconstruct, an autograft must be harvested, prepared, new tunnels surgically placed prior to fixation of the graft.
- •Later
- •ACL reconstruction unless otherwise contraindicated
When to Refer
- •All but sedentary, inactive patients should consult with an orthopedic surgeon.
- •The presence of a locked knee requires immediate referral with a goal to salvage as much of the associated healthy meniscus as possible.
- •Isolated ACL injuries may be referred at any time (reconstruction after improvement in effusion, range of motion is regained, and quadriceps tone restored).
- •ACL reconstruction involves first removing the torn ACL (the disrupted ends cannot be repaired, as they are immediately coated with a myofibrinous cap). A “new ACL” is created using a tendon (Autograft: typically a folded portion of the semitendinosus and gracilis hamstring tendons, or the central one-third of the patellar tendon. Alternatively, an allograft from a cadaver.). This tendon is then passed through surgically created tunnels in the tibia and femur and secured with screws or other fixation devices.
Prognosis
- •ACL reconstruction—Good, given improvement of stability and recovery of function. Patients with uncomplicated ACL reconstructions should return to sports in approximately 6 months.
- •Nonoperative treatment—Fair. Recurrent instability may occur, often resulting in additional injuries (meniscal and/or articular cartilage).
Surgical Risks and Benefits
- •Risks include bleeding, infection, nerve injury (numbness is not uncommon after patellar tendon or hamstring harvesting from incision or retraction of the infrapatellar branches of the saphenous nerve), loss of motion, and recurrence. When patellar tendon autografts are used, there is also a slight risk of a patellar fracture and late anterior knee pain typically with kneeling.
- •Benefits include restoration of stability to the knee and, in most cases, successful return to activity.
Patient Instructions
- •It is important to achieve full range of motion prior to ACL reconstruction and immediately afterward. Patients should be encouraged to use a pillow or bolster under their heel rather than under the knee to maintain full extension.
- •Control swelling with ice (apply for periods of 15 to 20 minutes several times daily).
- •Quadriceps strengthening (stationary cycle, elliptical trainer, etc.) is a crucial part of the rehabilitation process.
- •Patients should avoid running and activities involving sudden changes in direction both preoperatively and for at least 3 months after surgery.
Considerations in Special Populations
- •Inactive and sedentary patients should be treated nonoperatively. Arthroscopic management of an associated meniscal tear (and not for ACL reconstruction) may be considered.
- •Obesity can make surgery challenging, but should be performed nonetheless for any knee instability.
Suggested Readings
- Ardern CL, Webster KE, Taylor NF, et al.: Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med 2011; 45 (7): pp. 596-606.
- Benjaminse A, Gokeler A, van der Schans CP: Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther 2006; 36: pp. 267-288.
- Chhabra A, Starman JS, Ferretti M, et al.: Anatomic, radiographic, biomechanical, and kinematic evaluation of the anterior cruciate ligament and its two functional bundles. J Bone Joint Surg Am 2006; 33 (4): pp. 2-10.
- Fithian DC, Paxton EW, Stone ML, et al.: Prospective trial of a treatment algorithm for the management of the anterior cruciate ligament-injured knee. Am J Sports Med 2005; 33: pp. 333-334.
- Iobst CA, Stanitski CL: Acute knee injuries. Clin Sports Med 2000; 19: pp. 621-635.
- Sanders TG, Miller MD: A systematic approach to magnetic resonance imaging interpretation of sports medicine injuries of the knee. Am J Sports Med 2005; 33: pp. 131-148.
- Schub D: Saluan p: anterior cruciate ligament injuries in the young athlete: evaluation and treatment. Sports Med Arthrosc 2011; 19 (1): pp. 34-43.
- Solomon DH, Simel DL, Bates DW, et al.: The rational clinical examination. Does this patient have a torn meniscus or ligament of the knee? Value of the physical examination. JAMA 2001; 286: pp. 1610-1620.
- Spindler KP, Wright RW: Anterior cruciate ligament (ACL) tear. N Engl J Med 2008; 2135-2142:
- Utukuri MM, Somayaji HS, Khanduja V, et al.: Update on pediatric ACL injuries. Knee 2006; 13: pp. 345-352.