Knee Pain

Definition: The knee joint is the largest and most frequently affected peripheral joint. This primarily relates to its importance in ambulation and weight bearing and its numerous supportive periarticular structures.

Anatomic Considerations: The knee is often divided into the medial compartment, lateral (femorotibial) compartment, and patellofemoral compartment. Articular structures within these compartments include the synovium, synovial effusion, articular cartilage, meniscal cartilage, cruciate ligaments, and joint capsule. The term internal derangement of the knee implies mechanical damage to one of these structures. Outside the joint, periarticular structures that are common sources of pain may include a variety of bursae (e.g., anserine, prepatellar, superficial and deep infrapatellar), ligaments (e.g., collateral), tendons (e.g., semimembranosus, semitendinosus), bones (e.g., patella, femur, tibia), muscles (e.g., quadriceps), vessels (e.g., popliteal artery), and other soft tissue structures (e.g., popliteal cysts) (see Fig. 1, Section 1.2).

Etiology: Pain in the knee may result from traumatic, mechanical/degenerative, inflammatory, reactive, infectious, or neoplastic disorders affecting the joint or juxtaarticular structures.

Cardinal Findings: Knee pain in middle-aged and elderly individuals is likely caused by periarticular bursitis, traumatic or degenerative meniscal cartilage tears, or degenerative arthritis of the knee. In children, disorders commonly involving the knee may include Osgood-Schlatter disease (osteochondritis at the insertion of the patellar tendon on the tibial tubercle), benign growing pains, or juvenile arthritis. Young adults are most likely to complain of pain from chondromalacia patellae or trauma-induced internal derangement, with possible damage to menisci and cruciate or collateral ligaments.

It is important to ask about the presence of low back or hip pain with referred pain to, or below, the knee. A history of recent trauma may suggest fracture, internal derangement, bursitis, tendinitis, or even septic bursitis or arthritis. A history of remote, repetitive trauma and occupational or athletic contributions to knee pain should be sought. Although many individuals complain of fine or coarse joint crepitus, this is rarely associated with pain and thus has little diagnostic significance. However, pain associated with a sudden pop or snap may indicate severe ligamentous or tendinous injury or rupture. Most chronic articular disorders are accompanied by stiffness. However, prolonged morning stiffness (>1 hour) may indicate an inflammatory process.

Often patients complain of locking, buckling, or giving way. Such complaints suggests a meniscal tear but may also result from loose bodies, cruciate tear, severe quadriceps weakness, or patellar dislocation.

Acute monarticular presentations should lead the examiner to consider urgent noninflammatory (e.g., fracture) or inflammatory (e.g., crystal-induced or septic arthritis) causes.

Pain involving articular structures is likely to be diffuse and deep, whereas periarticular disorders may manifest focal or “point” tenderness. A careful search of periarticular bursae may disclose point tenderness, with or without local signs of inflammation, possibly indicating a bursal or tendinous condition. Palpation should also include examination of the popliteal fossa to detect any fluctuant mass indicating a Baker cyst. The examination should identify limb alignment or the presence of contracture. A contracture may indicate antecedent trauma or undiagnosed articular inflammation. Range of motion is best assessed with the patient supine. Hypermobility of the patella and hyper-extension at the knee may indicate a hypermobility syndrome. Ligamentous laxity may lead to excessive medial, lateral, forward, or posterior “play” at the knee. A series of specific maneuvers (i.e., Drawer sign or McMurray test) may be used to detect damage to the meniscal cartilage or cruciate ligaments (see Evaluation of Musculoskeletal Complaints, Table 7). Synovial effusion or proliferation is best palpated on either side of the patella and, if large enough, causes a “bulge sign” or distention of the suprapatellar pouch.

Diagnostic Testing: Laboratory testing should be guided by clinical findings. The examiner should avoid using routine laboratory screening tests. If an acute or chronic monarthritis exists, synovial fluid aspiration and analysis should be strongly considered.

Imaging: For nontraumatic acute presentations, radiographs are not indicated because they seldom reveal more than soft tissue swelling or effusion. Acute trauma and knee pain may benefit from imaging. The Ottawa knee rules propose who should undergo radiography. These include injury from trauma and age >55 years, tenderness at the head of the fibula or the patella, inability to bear weight for four steps, or inability to flex the knee to 90 degrees. Anteroposterior and lateral views of the knees should be obtained in those with trauma or who have undiagnosed chronic knee pain. If tolerable, weight-bearing films are preferred because they yield information on articular alignment and the degree of cartilage loss (resulting in uni- or bicompartmental joint space narrowing). Arthroscopy and MRI are powerful imaging tools best reserved for those with severe internal derangement of the knee. MRI may be indicated to diagnose osteonecrosis, osteomyelitis, pigmented villonodular synovitis, or early fractures not yet apparent by routine radiography.

Therapy: Depending on the condition, nonpharmacologic modalities of cold or warm compresses, immobilization, and quadriceps-strengthening exercises may be indicated. Symptomatic control of pain may be achieved with NSAIDs or simple analgesics (e.g., acetaminophen). In selected instances, infrequent use of local corticosteroid injections may enhance therapeutic results. Surgery (e.g., arthroscopy) may be indicated with acute internal derangement or fractures or chronically with advanced joint and cartilage damage.

Adapted from: RheumaKnowledgy
 

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