Residency · Residency · Physical Medicine Rehabilitation

Knee Osteoarthritis: Comprehensive Physiatric Management

Epidemiology and Risk Factors

Prevalence

Knee osteoarthritis (OA) is the most common form of arthritis and a leading cause of disability worldwide. Radiographic evidence of knee OA is present in over 50% of adults aged 65 and older. Symptomatic knee OA affects approximately 13% of women and 10% of men aged 60 and over. The prevalence is rising due to aging populations and increasing obesity rates.

Modifiable Risk Factors

Obesity: the strongest modifiable risk factor; each 5 kg of weight gain increases OA risk by approximately 36%. Occupational kneeling, squatting, and heavy lifting. Joint injury (post-traumatic OA after meniscal tear, ACL rupture, or intra-articular fracture). Muscle weakness, particularly quadriceps weakness. Malalignment (varus increases medial compartment loading; valgus increases lateral compartment loading).

Non-Modifiable Risk Factors

Age (strongest overall risk factor). Female sex (particularly post-menopausal). Genetics (heritability estimated at 40-65%). Prior joint surgery (meniscectomy). Bone and joint morphology.

Pathophysiology

Articular Cartilage Degeneration

OA is a disease of the entire joint, not just cartilage loss. Early changes: proteoglycan loss, collagen network disruption, increased water content. Chondrocyte apoptosis and failure of repair mechanisms. Loss of cartilage biomechanical properties (decreased compressive stiffness).

Subchondral Bone Changes

Subchondral sclerosis from increased mechanical loading. Subchondral cyst formation. Osteophyte formation at joint margins (attempted stabilization response). Bone marrow lesions on MRI correlate with pain and progression.

Synovial Inflammation

Low-grade synovitis is present in many OA joints. Release of inflammatory cytokines (IL-1, TNF-alpha, IL-6). Synovial hypertrophy and effusion. Inflammatory mediators drive further cartilage degradation.

Periarticular Changes

Meniscal degeneration and extrusion. Ligamentous laxity. Muscle weakness and inhibition (arthrogenic muscle inhibition). Capsular fibrosis and decreased range of motion.

<image>Diagram illustrating the pathophysiology of knee osteoarthritis showing articular cartilage degeneration, subchondral bone sclerosis with cyst formation, osteophyte development, synovial inflammation, and meniscal changes in a cross-sectional view of the knee joint</image>

Clinical Evaluation

History

Gradual onset of activity-related pain, classically worse with weight-bearing and stairs. Morning stiffness typically lasting less than 30 minutes (distinguishes from inflammatory arthritis). "Gelling" phenomenon: stiffness after prolonged sitting. Progressive functional limitation (difficulty with squatting, kneeling, stair climbing). Mechanical symptoms (locking, catching) suggest meniscal or loose body pathology. Night pain suggests advanced disease.

Physical Examination

Gait assessment: antalgic gait, varus or valgus thrust. Standing alignment: varus or valgus deformity. Effusion: ballottement test, bulge sign. Crepitus with range of motion (highly prevalent, moderate specificity).

Range of motion: flexion contracture is a key functional limitation. Periarticular tenderness (pes anserine bursitis is commonly associated). Quadriceps atrophy and weakness. Ligamentous stability testing.

Diagnostic Criteria

ACR clinical criteria: age >50, stiffness <30 minutes, crepitus, bony tenderness, bony enlargement, no palpable warmth. Clinical diagnosis; imaging is supportive but not required. Radiographic findings often do not correlate with symptom severity.

Imaging

Weight-Bearing Radiographs

AP standing view (ideally with fixed-flexion PA view for early detection). Lateral view for patellofemoral assessment. Sunrise/Merchant view for patellofemoral compartment. Kellgren-Lawrence grading: Grade 0 (normal) to Grade 4 (severe with bone-on-bone). Key findings: joint space narrowing, osteophytes, subchondral sclerosis, subchondral cysts.

Advanced Imaging

MRI generally not required for diagnosis but useful for evaluating concurrent pathology. Ultrasound can detect effusion, synovitis, osteophytes, and Baker cyst. Bone marrow lesions on MRI are associated with pain and rapid progression.

<image>Anteroposterior weight-bearing radiograph of both knees showing Kellgren-Lawrence grading from Grade 1 to Grade 4 osteoarthritis with progressive joint space narrowing, osteophyte formation, and subchondral sclerosis</image>

Non-Pharmacologic Management

Therapeutic Exercise

Exercise is the cornerstone of OA management and has strong evidence (Level 1A). Quadriceps strengthening: open and closed kinetic chain exercises. Aerobic exercise: walking, cycling, aquatic therapy (reduces pain and improves function). Aquatic therapy: buoyancy reduces joint loading; particularly useful in moderate-severe OA.

Flexibility and range of motion: prevent flexion contracture development. Neuromuscular training: proprioceptive and balance exercises. Exercise benefits are comparable to NSAIDs for pain reduction. Adherence is the primary challenge; supervised programs superior to home-based initially.

Weight Management

Weight loss of 5-10% of body weight produces clinically significant improvement. Combined diet and exercise programs are most effective. Bariatric surgery referral for BMI >40 or BMI >35 with comorbidities.

Physical Therapy Prescription

Manual therapy (joint mobilization) combined with exercise. Neuromuscular electrical stimulation (NMES) for quadriceps re-education. Transcutaneous electrical nerve stimulation (TENS) for pain modulation. Thermal modalities: superficial heat before exercise, ice after activity.

Bracing and Orthoses

Unloader braces: valgus-producing braces for medial compartment OA; reduce compartmental loading. Lateral heel wedge insoles: weak evidence for medial compartment OA. Medial arch supports: may help with concomitant pes planus. Patellar taping/bracing: for patellofemoral OA. Assistive devices: cane in contralateral hand reduces joint loading by 20-30%.

Self-Management Education

Arthritis self-management programs improve self-efficacy. Activity modification and joint protection principles. Pacing strategies to manage flares.

Pharmacologic Management

First-Line Agents

Topical NSAIDs (diclofenac gel): recommended as first-line, fewer systemic side effects. Oral NSAIDs (ibuprofen, naproxen, celecoxib): effective for pain and inflammation, use lowest effective dose for shortest duration. Acetaminophen: limited evidence for efficacy; AAOS and OARSI have downgraded recommendations.

Adjunctive Agents

Duloxetine: FDA-approved for OA pain, particularly with central sensitization features. Topical capsaicin: modest benefit, requires consistent application. Tramadol: weak opioid; use with caution and for short-term exacerbations only.

Agents NOT Recommended

Glucosamine and chondroitin: AAOS recommends against; conflicting evidence. Opioids: not recommended for chronic OA management. Oral corticosteroids: not indicated.

Injection Therapies

Intra-Articular Corticosteroid Injection

Provides short-term pain relief (4-8 weeks). Most effective when effusion is present. Triamcinolone 40 mg or methylprednisolone 40-80 mg. Limit to 3-4 injections per year in the same joint. Concern about accelerated cartilage loss with repeated injections (Lancet 2017 trial).

Viscosupplementation (Hyaluronic Acid)

Intra-articular injection of exogenous hyaluronic acid. AAOS: recommends against (2013 guidelines). AMSSM: conditional support for use. May have modest benefit in mild-moderate OA; peak effect at 8-12 weeks. Series of 1, 3, or 5 injections depending on formulation.

Platelet-Rich Plasma (PRP)

Emerging evidence suggesting benefit comparable to or exceeding hyaluronic acid. Proposed mechanism: growth factor-mediated cartilage repair and anti-inflammatory effects. Not covered by most insurance plans. Variable preparation protocols limit comparison across studies.

<image>Illustration demonstrating ultrasound-guided intra-articular knee injection technique showing the superolateral approach with the transducer positioned on the suprapatellar recess, needle trajectory, and intra-articular spread of injectate</image>

Surgical Referral Criteria

Indications for Total Knee Arthroplasty (TKA)

Failure of comprehensive conservative management for at least 3-6 months. Significant functional limitation affecting quality of life. Radiographic evidence of moderate-to-severe OA (KL Grade 3-4). Night pain or rest pain. Progressive deformity.

Pre-Habilitation

Exercise optimization prior to surgery improves post-operative outcomes. Quadriceps and hip abductor strengthening. Weight optimization if BMI >40 (many surgeons set a BMI threshold). Medical optimization (glycemic control, smoking cessation, nutritional status). Patient education and expectation management.

Post-TKA Rehabilitation

Early mobilization on post-operative day 0-1. Progressive ROM goals: 0-90 degrees by 2 weeks, 0-120 degrees by 6 weeks. Weight-bearing as tolerated with modern cemented TKA. Staged strengthening progression. Return to low-impact activities by 3-6 months.

Clinical Pearls

Always obtain weight-bearing radiographs; supine films underestimate joint space narrowing. Pes anserine bursitis frequently coexists with medial compartment OA and is a treatable source of pain. A flexion contracture of even 5 degrees significantly impacts gait mechanics and energy expenditure.

Consider the "triple threat" approach: exercise, weight loss, and appropriate pharmacology simultaneously. OA is frequently bilateral; treat the patient, not just the radiograph. Baker cysts in OA are secondary to effusion; treat the underlying joint pathology rather than the cyst. Duloxetine is underutilized and particularly effective when central sensitization features are present.

References

• Kolasinski SL, et al. 2019 American College of Rheumatology/Arthritis Foundation Guideline for the Management of Osteoarthritis of the Hand, Hip, and Knee. Arthritis Care Res. 2020;72(2):149-162.
• Bannuru RR, et al. OARSI Guidelines for the Non-Surgical Management of Knee, Hip, and Polyarticular Osteoarthritis. Osteoarthritis Cartilage. 2019;27(11):1578-1589.
• AAOS Clinical Practice Guideline: Treatment of Osteoarthritis of the Knee. 2nd Edition. 2013.
• McAlindon TE, et al. Effect of Intra-Articular Triamcinolone vs Saline on Knee Cartilage Volume and Pain in Patients With Knee Osteoarthritis. JAMA. 2017;317(19):1967-1975.
• Bradbury-Squires DJ, et al. DeLisa's Physical Medicine and Rehabilitation. 6th Edition. Wolters Kluwer. 2020.

Read this lecture as Markdown