Authors: Jared Topham Knee Osteoarthritis: Pathogenesis and clinical findings Reviewers: Liam Thompson, Raafi Ali Yan Yu*, Kelley DeSouza* * MD at time of publication
Primary Causes
Secondary Causes
Aging
↓ Synovial fluid in joint
Gender
Females > males
Genetics
Family history of osteoarthritis
Race
Black > Caucasian
Joint malposition (e.g. valgus or varus)
Articular trauma
Inflammatory disease or infection (e.g. Rheumatoid or septic arthritis)
Obesity and ↑leptin ↑ Chondrocytes,
inflammatory mediators, and metalloproteinases
Extracellular matrix degradation
↑ Knee joint loading forces
Metabolic syndromes (e.g. diabetes mellitus)
↑ Oxidative stress and insulin resistance
Low-grade systemic inflammation
↓ Elasticity and ↑ degradation of cartilage
↑ Friction in knee joint with movement
↓ Cartilage along femoral groove and posterior surface of patella
Pain, catching, and crepitus (crackling/clicking sound) in the patellofemoral joint
Inability/difficulty with kneeling or climbing stairs
Abnormal distribution of forces accumulate and stress articular surface
↑ Damage/laxity to soft tissue structures stabilizing knee joint
Knee Osteoarthritis
(Multifactorial entity characterized by cartilage breakdown, deterioration of connective tissue, and bone deformities)
↓ Cartilage between distal femur and proximal tibia ↓ Joint spaceàto articular dysfunction
Radiographic changes
See Osteoarthritis (OA): X-Ray Features slide
Repeated attempts to repair cartilage and joint disruption
Subchondral bone thickening (sclerosis) under joint cartilage and bone spur (osteophyte) formation around joint line
Rotational/antero-posterior instability and ↑ external adduction moments during walking
Alterations in proteoglycans, fiber arrangement, and collagen composition in soft tissue structures within/around knee joint
↑ Shear forces and medial compartment narrowing erode and pinch soft tissue structures within the knee joint
Cruciate ligament degeneration
Weakened passive stabilizers of the knee joint
Knee giving way and instability (falls)
Meniscal tears, if large àprevents knee extension/flexion
Locking of the knee
Joint line tenderness:
Patient points to area of tenderness/pain reproducible upon palpation
Anatomical axis of hip, knee, and ankle joints ↑ loading medially
Medial > lateral joint line tenderness
↑ Joint friction activating nociceptors in the surrounding anatomical tissues
Injury and inflammation ↑ nociceptive responses in soft tissue structures and subchondral bone within knee joint
Nociceptive feedback to brain inhibits activity of motor cortex neurons controlling muscles around the knee
↓ Motor output and muscle activation over time
↓ Muscle strength/endurance, lower limb muscle use, functional ability (walking, stairs, etc.)
Joint inflammationà accumulation of fluid within joint
Stiffness, swelling, redness, and pain
Limited joint space reduces range of motion for femur to roll/slide on tibia
↓ Knee flexion and extension
Flexion contracture and antalgic gait
Reduced weight acceptance of the joint and surrounding muscles/tendons
↓ Mobility and physical dysfunction
Muscular atrophy
Reduced function of active stabilizers of the knee joint (quadriceps, adductors, hamstrings)
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published July 30, 2023 on www.thecalgaryguide.com