SPORTS MEDICINE  ·  SURGERY OF THE KNEE  ·  SURGERY OF THE SHOULDER  

Torn Ligaments: ACL Print
ACL, Injuries of the Knee, Dr. Allen F. Anderson, Nashville, Orthopaedic Surgery, Sports Medicine, Figure 1
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Osteochondral Dissecans, Injuries of the Knee, Dr. Allen F. Anderson, Nashville, Orthopaedic Surgery, Sports Medicine, Figure 5
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The incidence of ACL injuries has increased dramatically over the last 2 decades. More than 200,000 new ACL injuries occur in the United States annually. These injuries are important because of the extent of disability associated with ACL tears.

Normal ACL Torn ACL

Approximately 50% of patients with ACL tears also have meniscal tears. The lateral meniscus is torn more frequently than the medial meniscus in acute ACL injuries, but in chronic ACL tears the medial meniscus is more commonly torn.

Attempts to identify athletes at greatest risk for ACL injury have identified a few predisposing factors. Individuals with a narrow intercondylar notch of the femur appear to have a higher risk of non-contact ACL injuries. Women also appear to be more susceptible to non-contact ACL injuries compared to male counterparts. A two-fold increase in ACL injuries in women collegiate soccer players and a four-fold increase in basketball players. The cause of this gender difference is not clear.

Knee instability secondary to anterior cruciate tears is the most common cause of long-term disability of the knee. The ACL is the primary restraint to hyperextension and anterior translation of the tibia on the femur. It also protects against excessive varus valgus stress and internal and external rotation as a seconary restraint. As a result of this wide range of function , a variety of injury mechanisms , most of which are non-contact in nature, may damage this ligament.

History

Patients with acute ACL injuries commonly report giving way of the knee with stopping, cutting, or jumping. A pop, immediate pain and swelling within several hours usually occurs with ACL injuries.

Physical Examination

The examination of the knee with an acute ACL injury is often difficult because the pain and swelling cause muscular guarding by the patient. . Early examination prior to the onset of the guarding is advantageous and comparison to the normal knee is mandatory.

The Lachman test is the most accurate test for diagnosis of acute ACL tears.

The Lachman test and the varus-valgus tests often are the only tests that can be reliably performed in an acute knee injury. A positive pivot shift is diagnostic for ACL tears but it can only be elicited in 25% of acute ACL tears. Examination with a knee ligament arthrometer may be helpful in diagnosis of acute knee injuries, a side to side difference of 3 mm. or more is diagnostic of an ACL tear.

 

Diagnostic Imaging

Every knee suspected of ACL damage should be evaluated with plain X-rays. Osteochondral fracture can be visualized. The Segond’s fracture , which is seen at the lateral edge of the tibia on an AP view, is diagnostic of an ACL tear.

In the chronic setting , X-ray findings associated with anterior cruciate insufficiency include intercondylar spurring and intercondylar notch narrowing .

MRI can be useful with diagnosis of ACL injuries when the clinical exam is limited because of pain and swelling. This test can also identify associated injuries to the menisci, articular cartilage or bone. The accuracy of MRI in determining acute ACL injury is approximately 90%.

MRI of a normal ACL MRI of a complete ACL Tear

Treatment

The treatment of ACL injuries should be tailored to the individual patient. Risk factors that may be used to determine treatment include age , activity level , willingness to modify activities, laxity of the joint, number of giving way episodes, and presence of associated ligament, articular cartilage, or meniscal injuries. Patients who participate in strenuous activities and have concomitant ligament or meniscal pathology are poor candidates for conservative treatment. Patients who have a greater degree to laxity or repeated episodes of giving way are also poor candidates for conservative treatment. The status of the menisci is a key determinent of long term function in the ACL deficit knee. Meniscectomy leads to decreased function with increased risk of degenerative changes. Because meniscal injury associated with ACL deficiency is in large part related to giving way episodes, treatment is directed toward eliminating functional instability.

Non Surgical Treatment

Initial nonsurgical treatment is directed at regaining range of motion, decreasing swelling, and maintaining strength. The use of functional knee braces is a part of conservative treatment for ACL insufficiency; approximately two thirds of patients feel more stable, but a substantial number of knees give way in the brace. Proprioception training using balance boards may be of benefit in a non surgical program.

Surgical Treatment

A myriad of surgical techniques for stabilizing the ACL deficient knee have been described and popularized. Extraarticular, intraarticular and combined intra and extraarticular techniques have been used. The results of ACL reconstruction have improved substantially since the 1980’s. Current arthroscopic assisted techniques emphasize anatomic placement of high strength grafts using rigid fixation techniques.

The middle one third of the patellar tendon, (bone patellar tendon bone graft), is the gold standard to which other grafts are compared. A 10 mm. wide patellar tendon graft has initial strength of more than 150% of the normal ACL. Interference screw fixation is the most popular technique for fixation of bone patellar tendon bone grafting.

Three Slides in Avoiding Complications

Quadrupled hamstring tendon is another graft with wide popularity and an increasing body of literature supports its use. Doubled looped semitendinous and gracilis tendons have been reported to be one and a half to two times as strong as the ACL. A strong graft is important because the graft loses up to 50% of its strength 6 months after surgery. By one year the graft strength increases to approximately 80% of its original strength.

Allograft (donor) tendons are occasionally used to reconstruct the ACL. The major advantage of allografts is that there is no donor site morbidity. The major disadvantages are delayed healing of the graft, a slightly lower success rate, an immunogenic response, and a slight possibility of infectious disease transmission.

Post Operative Treatment

Delaying surgery until the patient regains full knee extension and flexion to 120 degrees and obtaining full extension with early ROM after surgery has reduced the incidence of stiffness after ACL reconstruction to less than 3%. Several studies have revealed no benefit from the use of continuous passive motion. Cryotherapy (cooling) devices reduce swelling and pain but they provide no long lasting effects.

Early rehabilitation programs should protect the graft from excessive strain. Partial weight bearing progressing to full weight bearing in two weeks is recommended. Fixation of the graft is the weak link for the first six weeks after surgery. Therefore, during initial rehabilitation, stress on the graft should not exceed fixation strength (approximately 450 to 600 newtons). Three months after surgery the graft is the weakest link. Closed kinetic chain exercises are beneficial because they decrease stress on the graft from joint compression and simultaneous hamstring contraction. A randomized, controlled study showed decreased laxity, decreased anterior knee pain, and more rapid return to function when closed kinetic chain exercises were used. Several studies have confirmed that early return to athletics (by six months) can occur with no increased risk of failure, if return is based on recovery of quadriceps muscle strength (>50% for jogging, >65% for sports specific agility training, >80% for full athletics). Functional braces may decrease the strain on the graft, but inhibit the protective effect of hamstring contracture.

Proprioceptive re-education and sports specific training are the final plan of rehabilitation.

 

 
© Allen F. Anderson, M.D. 2017