Acute Knee Injuries
Anterior Cruciate Ligament
Acute Knee Injuries
Anterior Cruciate Ligament
During the last 15 years it seems that more people have become more interested in sports and exercise even in light of the obesity epidemic that we hear about so much in the news. Possibly this increase in the participation of sports is due to the obesity awareness and aging; there are certainly more weight loss products currently on the market than in the history of weight control supplements. With this increase in physical activity there is also an increase of injuries as well. It is estimated that there are 1.3 million visits to the emergency rooms by patients with acute knee trauma and approximately 200,000 of those individuals have anterior cruciate ligament (ACL) tears. Out of those 200,000 individuals only 60,000 to 75,000 ACL reconstructions are done for patients that have complete tearing, degenerative changes in prior incomplete tearing, and meniscal injuries. Other non-surgical candidates who may have complete tearing are patients who have sedentary lifestyles or patients who only do light manual work and non-cutting sports. Another statistic to note is that there is a much greater prevalence of ACL injuries in females when activities are matched to males. It also appears that the majority of sports related ACL injuries are more often a result of contact injuries with a rotational component, and low-velocity, non-contact, deceleration injuries. Also, contact sports may produce injuries to the ACL by hyperextension, twisting, or valgus stress upon collision or contact. In acute ACL injuries the lateral meniscus is usually torn, whereas the medial meniscus is more commonly torn in chronic ACL tears.
Functional Anatomy of the Anterior Cruciate Ligament:
The Anterior Cruciate Ligament is composed of two fibrous, collagenous bundles?the anteromedial and posterolateral bands. The tension in each bundle will vary depending on the range of motion. Due to the bundles' attachments and fiber lengths of the tension of the posterolateral band will be loose while the anteromedial band will be tight during flexion. However, during extension the opposite occurs with the bands whereas the posterolateral band is tight and the anteromedial band is loose. The ACL attaches to the anterior tibial plateau where this anterior insertion point is wider and stronger than the posterior attachment to the femur. This would make sense due to a much greater requirement of tensile strength in the ligament's insert for flexion. The ACL from its insertion point in the tibial fossa courses posteriorly, medially, and distally to its posterior insertion point on the femur.
The biomechanics of the ACL provides both mechanical stability and proprioception providing an afferent or inward neural conduction arc for postural changes during motion. The mechanical stabilization role of the ACL is as follows:
Provides 85% restraint of tibial anterior (forward) translation.
Provides secondary restraint of tibial rotation.
Provides restraint of varus (inward) and valgus (outward) turning or angulation toward the midline at full extension.
Prevents the hyperextension of the knee.
The ACL has on average 2,160 newtons tensile strength, which is half of the tensile strength of the MCL (Medial Collateral Ligament) and slightly less than the tensile strength of the PCL (Posterior Cruciate Ligament). If the ACL becomes injured sufficiently a subluxation (partial dislocation) of the tibia or the femur can occur such as anterior translation and rotation.
It is important for the patient to document the history of the injury if acute or the occurrences of the problem if it is chronic so that the family physician can better determine if orthopedic referral should be necessary after examination of the injury. With a documented history the orthopedic surgeon can better understand the nature of the injury for further examination.
Causes of ACL Injuries:
1. Noncontact injuries to the ACL account for a little more than half of the ACL injuries. With noncontact injuries an audible pop can usually be heard when the injury occurs. The noncontact injuries include:
§ A change of direction in movement usually associated with twisting or a sudden pivot of the knee.
§ Running or any cutting activity usually associated with a hyperextension, pivot, or both.
§ Side stepping.
§ Landing from a jump often resulting in a hyperextension and pivot combination.
2. Contact injuries occur during sports play that either involves hits or falling such as football, basketball, skiing, and even motor vehicle accidents. Contact injuries are often associated with other ligament and meniscus injuries such as the "Terrible Triad" (ACL, MCL, and medial meniscus).
Other factors can also contribute to ACL ruptures and tears. For instance, there may be genetic predispositions in some patients, while other patients may have morphological abnormalities to either the ligament itself or the insertion points. Some patients will have ACL agenesis or improper lack of ACL development. Another ligamentous morphological abnormality will be an insufficient amount of tissue or narrow tissue heads at the insertion points. Other patients may have narrow intercondylar notches at the insertion points lending to an inability for proper attachment and weakened attachment of the ligament.
Symptoms of an ACL injury include immediate pain and fast swelling in the knee. A snapping or a popping sound is often heard audibly with an ACL tear and the patient will usually have a "trick knee" (that is, the knee gives way). Inter-articular swelling is usually due to hemarthrosis or bleeding from the vessels within the torn ligament.
A diagnosis of an ACL rupture can usually be determined by a physical examination. Typically, a physician will examine the knee looking for a gross knee effusion (swelling from blood and fluids from the torn ligament) and/or any bony abnormalities. Swelling of the knee is nearly always indicative of intra-articular trauma with a 72% correlation of an ACL injury to some degree. The patient's range of motion should always be assessed. If the patient cannot fully extend the leg, it is indicative of a bucket-handle meniscus tear that is sometimes associated with an ACL and other ligamentous injuries. A physician should also palpate the knee to feel for bone abnormalities that may suggest a tibial plateau fracture. Palpation along joint lines may also aid in determining other ligamentous or meniscal injuries.
There are a few primary physical exam tests of the knee that the primary care physician will do prior to their referral to an orthopedic surgeon. The orthopedic surgeon will normally perform the same exams prior to ordering an MRI. The Lachman Test is one exam that is done. Some physicians feel that the Lachman Test is the most sensitive but other physicians feel that the pivot-jerk test is better. With the Lachman Test, the knee is placed between 20-30 degree flexion and the physician will place his non-dominant hand to stabilize the femur from the anterior above the knee. With the dominant hand, force will be applied with an anterior motion applied to the proximal calf. The amount of displacement in millimeters and the quality of the lax endpoints of the anterior translation (soft endpoint) is usually indicative of an ACL tear, especially if there is a side-to-side difference greater than 3mm.
normal Lachman video: Lachman video - Normal
Lachman Test performed on a non-injured knee.
injured Lachman video: Lachman video - Injured
Lachman Test performed on a patient who is symptomatic for a torn ACL.
Another test that can be done is the Anterior Drawer Test. The Anterior Drawer test is less reliable because it may be influenced by hamstring spasm. The patient should be in a supine position with the hips flexed to 45 degrees and the knee in 90-degree flexion while the patient's feet are flat on the table. The physician will grab the lower leg around the shin and calf and push forward (posteriorly) and backward (anteriorally) toward the physician as if he is opening and closing a drawer. If there is a certain amount of laxicity in the anterior motion (where the physician pulls the calf toward himself) it will be indicative of an ACL tear. If there is more laxicity in the posterior motion (the pushing of the shin away from the physician) it is indicative of a Posterior Cruciate Ligament (PCL) tear.
normal Anterior Drawer video: Anterior Drawer - Normal
Anterior Drawer Test performed on a non-injured knee.
injured Anterior Drawer video: Anterior Drawer - Injured
Anterior Drawer Test performed on a patient who is symptomatic for a torn ACL.
The pivot-shift or pivot-jerk test is considered to be reliable as well for determining if there is an ACL tear. The pivot-shift test is performed while the knee is extended. If the knee becomes flexed there should be a clunk felt upon laterally pushing the lower leg with valgus stress between 20-30 degrees. This would also indicate an ACL injury.
normal pivot-shift video: Pivot-Shift - Normal
Pivot-Shift Test performed on a non-injured knee.
injured pivot-shift video: Pivot-Shift - Injured
Pivot-Shift Test performed on a patient who is symptomatic for a torn ACL.
Normally, if a patient goes to the emergency room with a knee injury, the attending physician will nearly always order X-rays to be done. This is often done as a precautionary measure for liability reasons but it is also done to primarily determine if there is a tibial plateau fracture, kneecap shift, or other bony abnormalities. Ligamentous and meniscal tears rarely appear on radiographs and therefore MRI's are more necessary to determine these types of injuries.
Magnetic Resonance Imaging (MRI):
MRI's are by far the most accurate imaging test with 90-98% accuracy for bone bruising let alone its incredible accuracy for detecting a torn ligament, tendon, or meniscus. Often an orthopedic surgeon will order a series of MRI's to be done for the patient. An MRI of the knee will allow the doctor to know precisely where the injury or injuries are located within the knee so that he or she can minimize surgical invasiveness.
MRI of a normal and uninjured ACL.
MRI of a torn ACL.
Physicians will often require physical therapy prior to surgery and some orthopedic surgeons may not even perform surgery upon the patient at all. As mentioned earlier, out of 200,000 people who have ACL injuries, only 60,000 to 75,000 surgeries are performed annually to correct ACL injuries. Surgical candidates are determined based upon other related injuries to the knee, the extent of tearing, pre-injury activity level, abnormal laxicity, and functional disability. Sometimes an orthopedic surgeon will require physical therapy prior to surgery being performed. As a patient may not understand that rationale, pre-surgery physical therapy is necessary to reduce swelling before surgery can be performed upon the patient. Roughly 15% of an ACL injury population can function normally with a completely ruptured ACL without the necessity of surgery. Even people who have an activity level such as bodybuilding can manage without surgery if he or she only has partial ligamentous tearing.
For those who are surgical candidates, surgery may be delayed as much as 3 weeks post-injury to prevent the complication of arthofibrosis. If a patient has partial tearing, primary repair may be performed but this is rarely done because ligamentous tearing and operative treatment for partial tearing is rarely successful and is prone to re-injury. Since the ACL is intra-articular, the insertion points are subjected to synovial fluids, which don't support proper ligament healing. When the intra-articular surgery is required it is done so for patients who have complete tearing of the ACL. When surgery is performed the ligament is never reattached but a new ligament is grafted instead. The most common grafts are hamstring tendon and bone-patella-bone. Allografts (from cadavers) may be done but they are best done in surgical revisions due to their higher rates of viral infections. Hamstring tendon grafts offer the least amount of anterior knee pain and offer the fastest recovery rate. Some orthopedic surgeons fell that surgery is best done during the first week of injury (as opposed to 3 weeks post-injury) to aid in revascularization of the graft. It is possible that surgical intervention lies somewhere between the first and third week of the injury to minimize arthofibrosis and encourage revascularization.
Post-surgical therapy is often performed in four phases:
§ Phase I: achieving a fuller range of motion.
§ Phase II: achieve full extension, maintain quadriceps control, and achieve 90 degree flexion.
§ Phase III: Maintain full extension while increasing the flexion to full range of motion.
§ Phase IV: Increasing of strength and agility and preparation to return to sports.
Full return to sports is generally 6-9 months post-surgery. Once the opposite leg's quadriceps reaches 65% strength, sports-specific activity can be resumed, but should be monitored; this typically occurs 5-8 weeks after surgery. Once the quadriceps has reached 80% strength, full sports activity may be done without monitoring. 82-95% of surgical candidates see success without recurrent instability and graft failure.
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