Osteoarthritis (OA) of the Knee - BPT Notes

1. Definition

• Pathologically - by cartilage degeneration and structural joint changes
• Radiographically - by osteophytes, joint space narrowing, sclerosis, cysts
• Clinically - by pain, stiffness, and functional limitation
• Symptomatically - pain or aching in a joint that also has radiographic OA

2. Epidemiology

• One of the most common musculoskeletal conditions worldwide
• Prevalence increases with age; more common in women, especially after menopause
• Radiographic knee OA is present in ~37% of adults >60 years
• Symptomatic knee OA affects ~12% of adults >60 years
• Annual incidence ~2.8% per year in older women (Chingford Study)
• About 15.6% of elderly individuals develop incident radiographic knee OA over 8 years (Framingham Study)

3. Risk Factors (EULAR Propositions)

4. Pathology / Pathogenesis

Articular Cartilage

• Fibrillation and fissuring of articular cartilage surface
• Progressive cartilage loss (chondrocyte death, matrix degradation)
• Collagen and proteoglycan breakdown via matrix metalloproteinases (MMPs)

Subchondral Bone

• Subchondral sclerosis (thickening/hardening)
• Subchondral bone cysts (eburnation)
• Bone marrow lesions visible on MRI

Osteophytes

• New bone formation at joint margins (enthesophytes)
• Sign of attempted repair/remodeling

Synovium

• Synovitis (low-grade inflammation) - contributes to pain
• Synovial fluid: viscosity reduced, may show mild inflammatory cells

Periarticular Structures

• Quadriceps muscle wasting and weakness
• Ligament laxity
• Capsular fibrosis

5. Compartments of Knee Involved

6. Clinical Features

Symptoms

• Pain - activity/usage-related (worse on climbing stairs, prolonged walking); relieved by rest in early stages; later occurs at rest and at night
• Morning stiffness - duration ≤30 minutes (key differentiator from RA where it is >1 hour)
• Gelling phenomenon - stiffness after prolonged inactivity (e.g. after sitting)
• Crepitus - audible/palpable grating on joint movement
• Functional limitation - difficulty walking, climbing stairs, squatting

Signs

• Bony enlargement (osteophytes) - palpable on joint margins
• Joint line tenderness - medial > lateral
• Crepitus on active/passive movement
• Effusion - soft swelling (periarticular or intra-articular)
• Restricted ROM - loss of full extension and flexion
• Varus/valgus deformity - in advanced disease
• Quadriceps wasting - due to disuse atrophy and reflex inhibition
• Antalgic gait - limping, reduced stride length

7. ACR Diagnostic Criteria for Knee OA (Clinical)

1. Age ≥38 years
2. Crepitus on active joint motion
3. Morning stiffness ≤30 minutes
4. Bony enlargement on examination
5. No palpable warmth

8. Investigations

X-Ray (Standard Weight-Bearing AP View)

• Kellgren-Lawrence (KL) Grading:

• Loss of joint space (narrowing)
• Osteophytes
• Subchondral sclerosis
• Subchondral cysts

MRI

• Detects early cartilage changes, bone marrow lesions, meniscal damage before X-ray changes appear
• Useful for research and pre-surgical planning

Lab Tests

• Usually normal in primary OA
• Used to rule out inflammatory arthritis (ESR, CRP, RF, anti-CCP)
• Synovial fluid in OA: clear, viscous, WBC <2000 cells/mm³

9. Physiotherapy Management (Central to BPT)

STRONG EVIDENCE (Must Know)

• Physical activity (any form of regular movement)
• Low-impact aerobic exercises - walking, cycling, swimming
• Strengthening exercises - especially quadriceps strengthening

Specific Exercise Programs

Electrotherapy & Physical Modalities (MODERATE to INCONCLUSIVE evidence)

• TENS (Transcutaneous Electrical Nerve Stimulation) - pain relief via gate control; inconclusive long-term evidence
• Therapeutic Ultrasound - thermal and non-thermal effects, aids tissue healing
• SWD/MWD (Short Wave/Microwave Diathermy) - deep heating, pain and stiffness relief
• LASER - low-level laser therapy for pain modulation
• IFT (Interferential Therapy) - pain reduction
• Cryotherapy - ice packs post-exercise for acute flares, reduces effusion
• Thermotherapy - hot packs for chronic pain and stiffness before exercise

Manual Therapy (MODERATE evidence per AAOS)

• Joint mobilization techniques (Maitland Grades I-IV)
• Soft tissue mobilization
• Patellar mobilization (especially in patellofemoral OA)

Taping

• Patellar taping (McConnell technique) - reduces patellofemoral pain
• Kinesio taping - reduces effusion, improves proprioception

Gait & Functional Training

• Gait re-education
• Stair training
• Transfer training (sit-to-stand)
• Activity modification and energy conservation

10. Orthotics and Assistive Devices (MODERATE evidence)

Knee Braces

• Valgus knee brace - off-loads medial tibiofemoral compartment (most common in OA)
• Varus knee brace - off-loads lateral tibiofemoral compartment
• Apply 3-point force to reduce loading on affected compartment
• Prefabricated braces as effective as custom braces in most patients

Other Aids

• Medial heel wedge - for lateral compartment OA / varus deformity
• Walking stick/cane - used on contralateral side, reduces joint loading
• Knee sleeve - provides compression, proprioceptive feedback

11. Patient Education (Critical)

• Weight reduction in patients with BMI >25 (MODERATE evidence) - every kg of weight loss reduces knee joint load by 4 kg
• Activity modification - avoid prolonged kneeling, squatting, carrying heavy loads
• Joint protection techniques
• Home exercise program (HEP) compliance

12. Medical / Pharmacological Management

• NSAIDs (Ibuprofen, Diclofenac) - first-line analgesics; strong evidence
• Paracetamol - simple analgesia
• Intra-articular corticosteroid injections - short-term pain relief in acute flares
• Intra-articular hyaluronic acid (viscosupplementation) - inconclusive evidence
• Glucosamine/Chondroitin - inconclusive evidence
• Duloxetine - for central sensitization/chronic pain

13. Surgical Management

14. Kellgren-Lawrence Grading + Physiotherapy Goals (Summary Table)

15. Differential Diagnosis (Rule Out)

• Rheumatoid arthritis (morning stiffness >1 hour, bilateral, RF positive)
• Gout/pseudogout (acute onset, crystal arthropathy)
• Meniscal tear (younger patient, trauma history)
• Bursitis (prepatellar, anserine)
• Septic arthritis (fever, acute onset, hot joint - emergency)

• Rheumatology, 2-Volume Set (2022, Elsevier), pp. 1659-1726 - Epidemiology, definitions, ACR/EULAR criteria
• Campbell's Operative Orthopaedics, 15th Ed (2026), Table 10.4 - AAOS nonoperative treatment evidence levels
• Pfenninger and Fowler's Procedures for Primary Care, 3rd Ed - Knee bracing in OA