The knee is very susceptible to problems, especially from sports such as football and skiing, where the body turns fast on a fixed foot. It is the largest synovial joint in the body. The knee joint is inherently unstable, because it is not constrained by the shape of its articulating bones. It consists of two tibiofemoral and one patellofemoral compartment. The tibiofemoral articulation is a condylar joint, whereas the patellofemoral articulation is a gliding joint. The proximal tibiofibular joint is a plain synovial articulation between the lateral tibial condyle and the fibular head. The tibiofibular joint capsule is much thicker anteriorly and is reinforced by the anterior and posterior tibiofibular ligaments. Slight movements occur at the joint with lower-limb rotation and with activities involving the ankle.
Common Knee Disorders and Clinical Evaluation
Knee pain is often diffuse and difficult to localize, but if the patient is able to delineate the maximum area of pain, this can be helpful in determining which underlying structure might be injured. Knee pain may be referred from hip pathology. Occasionally, a patient is able to describe certain activities or movements that aggravate or alleviate the pain. For example, posteromedial knee-joint pain with squatting may be caused by a tear of the posterior horn of the medial meniscus. Tendinitis pain is often improved as a workout continues, whereas most other causes of pain usually increase with activity. Finally, the pain character may provide some clues as to the underlying pathology. Muscle pain is often felt as a deep, dull ache that is difficult to localize, whereas meniscus pain may be sharp, localized, and intermittent.
Clicking, Snapping, and Clunking Noises and Sensations
Normal knees often make painless, high-pitched clicking sounds during squatting. Patients with arthritis or an inflamed synovium may note a crackling sound or sensation with knee movement.
Diffuse knee-joint swelling is a nonspecific symptom that suggests knee synovitis and joint effusion.
Heat and Redness
Swelling, heat, and redness are all signs of inflammation in the knee joint or periarticular tissues.
Stiffness may accompany knee swelling, or it may be an independent symptom. With a large effusion, the knee is more comfortable in slight flexion, and patients have difficulty with both full extension and full flexion. A sense of stiffness in the morning is common with both rheumatoid arthritis and osteoarthritis.
Acute deformity after trauma suggests a major muscular, ligamentous, or bony injury that is accompanied by loss of integrity of the knee joint or the surrounding musculature sufficient to cause the deformity.
Giving Way and Instability
The knee collapses when the patient bears weight if the extensor mechanism is disrupted or inhibited by pain or muscle weakness. Patellofemoral problems often cause a sense of the knee’s giving way, especially when descending stairs, because the quadriceps muscle is contracting eccentrically with controlled lengthening of the muscle. Disruption of the ACL can cause collapse
True locking of the knee refers to sudden or recurrent inability to flex or to extend the knee. It can occur because of a mechanical block to knee-joint motion, such as a loose body, meniscus flap, cruciate ligament stump, cartilage flap, or scar tissue that interferes with knee flexion or extension by its interposition between the joint surfaces.
Inflammatory Arthritis and Osteoarthritis
Symptoms of arthritis include pain, swelling, stiffness, crepitus, and, in the late stages, deformity and instability. Physical findings include disuse atrophy of the vastus medialis, joint tenderness, joint effusion, joint instability, and decreased range of motion. There may be similar changes found in other joints, the distribution of which may provide clues for the diagnosis of inflammatory arthritis. For example, rheumatoid arthritis generally produces symmetrical swelling of small and large joints.
Ligamentous injury should be ruled out in the assessment of any patient who presents with knee pain after an acute injury. The direction of impact should be sought if possible, considering that the ligaments opposite to the impact may have been ruptured.
Significant traumatic fractures of the articular surface or metaphyseal region are obvious by the sudden loss of function with accompanying swelling and deformity. However, some types of tibial plateau fractures are quite subtle and easily missed. A lateral blow may result in a compression fracture of the lateral plateau in association with an MCL injury. The patient may be able to walk, and the MCL injury may distract the examiner from thoroughly assessing the lateral plateau.
A history of an injury with subsequent locking, clunking, and localized pain to the joint line is a classic for a meniscus tear. An acutely injured knee may be exceedingly difficult to examine for a meniscus injury. For example, it is impossible to perform a McMurray test unless the knee can be flexed to at least 90°. A repeat examination 1 or 2 weeks after the acute injury is often very helpful in establishing the correct diagnosis.
Repetitive Strain and Overuse Injuries
A number of overuse injuries, resulting from repetitive activities that place stress on the knee, have been described. Runner’s knee often refers to patellofemoral syndrome caused by abnormal patellar tracking, but it may also denote lateral knee pain resulting from iliotibial band friction syndrome. Jumper’s knee in adults refers to proximal patellar tendinitis, whereas in adolescents it denotes either distal patellar tendinitis (Larson-Johansson disease) or traction epiphysitis (Osgood-Schlatter disease). Swimmer’s knee or breaststroker’s knee denotes anserine bursitis. Carpet layer’s, miner’s, or housemaid’s knee refers to traumatic prepatellar bursitis. Gamekeeper’s knee describes medial gastrocnemius-semimembranosus bursitis caused by excessive knee flexion.
Considerations in Patients after Total Knee Replacement
In complex knee revision surgery, the extensor mechanism or the collateral ligaments may be compromised. The examiner should avoid undue force when examining for passive range of motion or when testing the integrity of the ligaments in these situations. Certain types of knee implants may click, especially during testing for stability in flexion, as the artificial components move apart a few degrees and then back together. This usually is not a sign of pathology. Some numbness around the incision site is common, but a painful trigger point near the incision may indicate the presence of a neuroma.