Posterior Knee Pain
Diffuse pain in the back of the knee can present a diagnostic quandary. The anatomy and biomechanics of the area can be complicated. The differential diagnosis must take into account many possible injuries.
A thorough history of the injury or progression of the discomfort is the first step. The history should include: current injury mechanism (if known), past injuries, past surgeries, past rehabilitation, location and quality of the pain, aggravating or alleviating factors, or orthotic use.
Soft tissue injuries are the most common cause of posterior knee pain. Other, less common, injuries that can cause pain in this region are nerve or vascular in origin.
A popliteal synovial cyst is a frequent cause of posterior knee pain. The cyst is the result of a posterior herniation of the synovial membrane or by a communicating semimembranous bursa into the popliteal space. The presence of a Baker’s cyst usually points to other underlying pathology such as a meniscal tear or osteoarthritis. A ruptured cyst will display the “crescent sign”; an ecchymotic area around the malleoli. Treatment should focus on repair of the underlying pathology. Rarely, the cyst itself will have to be surgically removed.
The hamstrings consist of the semimembranosus, semitendinosus, and the biceps femoris. The most commonly injured muscle is the short head of the biceps femoris. Weakness in the hamstrings can result in muscle strains (either at the musculotendinous junction or in the muscle itself) or tendinitis. Both of these conditions are treated symptomatically: ice, rest, NSAIDs, and strength training for power and endurance.
The popliteus muscle runs a diagonal course in the posterior knee; it runs from the lateral femoral condyle distally to the posterolateral tibia. It assists in stabilizing the posterolateral corner of the knee and prevents anterior translation. Its function is especially important in downhill running. The tendon or muscle belly may exhibit point tenderness. A provocative test for a popliteal injury involves having the athlete prone, with the knee in full extension, then internally rotating the tibia. The athlete then flexes the knee against resistance. The test should reproduce the pain felt during activities. The treatment plan is the same as any muscle or tendon strain.
Meniscal tears, especially a tear of the posterior horn of the medial meniscus can produce posterior knee pain. The pain is usually reproducible with deep squatting and may be accompanied by a “pop” or “click.” A McMurray’s Test may or may not be positive. Often the physical examination results will be correlated with an MRI to determine if a meniscal tear is present. If a meniscal tear is found, surgical resection or repair is the treatment of choice.
If the meniscus is repaired rather than resected, bioabsorbable tacks may be used to secure the torn cartilage. The tacks are designed to be absorbed by the body. They retain structural integrity for 4 to 6 months and are fully absorbed within 3 years. The tacks can produce posterior knee pain for up to 6 months post-op.
Posterolateral Corner Injuries
The posterolateral corner is comprised of the popliteus muscle, lateral collateral ligament, the posterolateral capsule, and the popliteofibular ligament. Structural stability of the knee to resist excessive varus stress, external rotation, and posterior translation of the knee during the first 30° of flexion is supplied by the Posterior Cruciate Ligament and the posterolateral corner components.
Injuries to this region, in the athletic setting, usually are the result of a blow to the anteromedial aspect of the fully extended knee. If the posterolateral corner is injured the athlete may present with a varus thrust upon standing and will have pain and a feeling of “giving way” while walking. The athlete will have point tenderness along the posterolateral corner and may have tenderness at the fibular head. As these structures are extra-articular, ecchymosis will be present in the region.
A posterolateral rotary instability test can be used to ascertain the degree of joint laxity. The athlete is placed in a supine position as the examiner holds the lower extremities by the great toes, observing any differences in hyperextension, varus movement, or external tibial rotation.
The dial test can also be used to determine laxity. The athlete is supine with the knee in 30° of flexion and the foot extended over the side of the table. The foot is externally rotated, the examiner notes the amount of rotation of the tibial tubercles. If bilateral comparison results in a larger amount of rotation on the affected side, the injury must be suspected. If the dial test is performed at 90° of flexion and less roation is seen than at 30° an isolated (no PCL involvement) posterolateral corner injury is suspected. The posterior drawer test or sag tests are more provocative for an isolated PCL tear. The examiner should keep in mind that these tests quite often result in false negative findings. Due to this, the physical exam should be correlated with other diagnostic imaging tests.
Treatment of this injury varies with the degree of injury. Mild laxity may be treated with bracing and rehabilitatioin while gross instability is often treated with surgical reconstruction.
©2000 - 2009 David Edell
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Last Update for AthleticAdvisor.com: 10/24/2009 12:09:35 AM