Norman A. Johanson
There are three articulations in the knee, referred to as compartments. They can be affected separately or together as part of a single process.
Medial tibiofemoral compartment.
Lateral tibiofemoral compartment.
The knee ligaments are specially designed to accommodate a wide range of motion and flexibility while providing essential stability for weight bearing.
Medial collateral ligament.
Lateral collateral ligament.
Anterior cruciate ligament.
Posterior cruciate ligament.
are crescent-shaped fibrocartilaginous structures that are peripherally situated in the medial and lateral tibiofemoral compartments. These structures are involved in the weight-bearing process and augment the stability of the knee.
IV. PERIARTICULAR STRUCTURES
Several musculotendinous structures pass across the knee to insert at or near the joint. Injury or inflammation of any of these structures can result in knee pain.
Quadriceps mechanism (quadriceps tendon and patellar tendon).
Pes anserine tendons (sartorius, gracilis, and semitendinosus).
Gastrocnemius (medial and lateral heads).
CAUSES OF KNEE PAIN
The mechanism of injury is important in formulating a differential diagnosis; however, components of several mechanisms may be present in a given injury.
Hyperextension (anterior cruciate tear).
Varus (lateral collateral ligament tear and anterior cruciate tear).
Valgus (medial collateral ligament tear and anterior cruciate tear).
Torsion (meniscal tears).
Axial impact on femur and posterior displacement of tibia (dashboard injury), patellar fracture, posterior cruciate ligament tear, femoral shaft fracture, and fracture-dislocation of hip.
Inflammation (synovitis and tendinitis).
Vascular disorder (osteonecrosis and sickle cell crisis).
Degeneration (meniscal tear and articular erosion).
Neoplasm (primary or metastatic bone tumors near the knee; soft tissue tumors around the knee).
Referred pain from hip or spine disorder.
COMMON PRESENTING SYMPTOMS ASSOCIATED WITH KNEE PAIN
Swelling —enlargement of the knee with loss of normal contour.
Locking or severe stiffness (meniscal tear and chondromalacia patellae).
Giving way or buckling (anterior cruciate tear or patellofemoral disorder).
Clicking or crackling sound in the knee (meniscal tear or chondromalacia patellae).
Audible pop at the time of knee injury (cruciate or meniscal tear).
Contour of the knee.
Alignment of the knee while the patient is standing (varus, valgus, flexed, or hyperextended).
Effusion. The presence of fluid in the knee may be demonstrated by sweeping the hand distally over the knee to empty the suprapatellar pouch. Medial and lateral bulging of the capsule can be felt and sometimes seen (as distinguished from synovial thickening).
Popliteal fullness is suggestive of Baker’s cyst.
Joint-line tenderness exacerbated by tibial rotation (Steinmann’s test) is suggestive of meniscal tear.
Tenderness on patellofemoral compression with the knee slightly flexed is suggestive of chondromalacia patellae.