What is the initial workup and treatment for a patient presenting with knee pain?

Initial Workup and Treatment for Knee Pain

Begin with acetaminophen up to 4,000 mg/day as first-line pharmacologic therapy for knee osteoarthritis, combined with exercise therapy, patient education, and weight loss if overweight. 1

Clinical Diagnosis

Key History Elements

• Age and onset pattern: Insidious, chronic pain worsening gradually suggests osteoarthritis (OA), most likely in patients ≥45 years with activity-related pain and <30 minutes of morning stiffness (95% sensitivity, 69% specificity) 2
• Age <40 years with anterior knee pain during squats: Suggests patellofemoral pain (91% sensitivity, 50% specificity) 2
• Acute twisting injury in younger patients or degenerative presentation in those ≥40 years: Consider meniscal tear 2

Physical Examination Findings

• McMurray test (knee rotation with extension): 61% sensitivity, 84% specificity for meniscal tears 2
• Joint line tenderness: 83% sensitivity, 83% specificity for meniscal tears 2
• Presence of effusion: Indicates potential need for intra-articular corticosteroid injection 3, 1

Imaging Recommendations

• Radiographs are NOT routinely recommended for all patients with suspected knee OA 2
• Consider imaging only when diagnosis is uncertain or to improve specificity 4
• Typical clinical OA findings are sufficient for diagnosis 4

First-Line Treatment Algorithm

Non-Pharmacologic Interventions (Initiate for ALL Patients)

• Exercise therapy: Strongly recommended with high-quality evidence showing sustained pain reduction and functional improvement for 2-6 months 3
• Patient education programs: Strong recommendation to improve pain 3
• Weight loss: Moderate recommendation for overweight/obese patients to improve pain and function 3
• Manual therapy plus exercise: Strong recommendation to improve pain and function 3

Pharmacologic Therapy

First-Line Medication

• Acetaminophen up to 4,000 mg/day: Strongly recommended as initial oral analgesic due to favorable safety profile (1.5% adverse events) 3, 1
• Counsel patients to avoid other acetaminophen-containing products 1
• Use full dosage before considering it ineffective 1

Important caveat: One high-quality RCT found acetaminophen no more effective than placebo for symptomatic knee OA, while diclofenac showed significant improvement 5. However, guidelines still prioritize acetaminophen first due to superior safety profile 1.

Alternative First-Line Options (if acetaminophen contraindicated/not tolerated)

• Topical NSAIDs: Conditionally recommended, especially for patients ≥75 years 3, 1
• Tramadol: Conditionally recommended alternative 1
• Intra-articular corticosteroid injection: Indicated for acute flares, especially with effusion 3, 1

Second-Line Therapy (if inadequate response to acetaminophen)

Oral NSAIDs

• Strongly recommended to improve pain and function when not contraindicated 3, 1
• For patients ≥75 years: topical NSAIDs strongly preferred over oral NSAIDs 3, 1
• For GI risk factors: Use COX-2 selective inhibitor OR nonselective NSAID with proton-pump inhibitor 3, 1
• Avoid in patients with GI bleeding history or cardiovascular disease 1

Topical Capsaicin

• May be used (0.025%-0.075%) with moderate effect, but requires 2-4 weeks of continuous use 3
• Conditionally NOT recommended by some guidelines due to limited evidence 1

Intra-articular Corticosteroids

• Consider as second-line for patients unresponsive to oral medications 1
• Particularly effective for acute exacerbations with effusion 3

Third-Line Options (if conservative measures fail)

• Opioid analgesics (with or without acetaminophen): Useful when NSAIDs contraindicated, ineffective, or poorly tolerated 3
• Radiofrequency ablation of genicular nerves: Shown to be effective when conservative treatment fails 4

Treatments NOT Recommended

• Glucosamine and chondroitin sulfate: Conditionally NOT recommended due to lack of efficacy evidence 1
• Topical capsaicin: Conditionally NOT recommended by ACR 1

Surgical Referral Indications

• Joint replacement: Consider for end-stage OA (minimal/no joint space) with refractory pain and disability after exhausting conservative options 3, 2
• Patellofemoral pain: No indication for surgery; hip/knee strengthening exercises with foot orthoses or patellar taping recommended 2
• Meniscal tears: Exercise therapy for 4-6 weeks is first-line; surgery only for severe traumatic (bucket-handle) tears with displaced tissue 2

Common Pitfalls

• Underutilizing non-pharmacologic therapy: Exercise and education have strong evidence and should be initiated immediately, not after medication failure 3
• Premature imaging: Clinical diagnosis is sufficient for most knee OA cases 2
• Inadequate acetaminophen dosing: Must use full 4,000 mg/day before declaring failure 1
• Inappropriate surgery for degenerative meniscal tears: Exercise therapy is first-line even with mechanical symptoms 2