What are the recommended diagnostic steps and treatment options for a patient experiencing knee pain and increased weakness?

Diagnostic and Treatment Approach for Knee Pain with Weakness

Start with plain radiographs (AP, lateral, sunrise/Merchant, and tunnel views) as your initial imaging, then proceed to MRI only if radiographs are normal but symptoms persist or if you need to characterize a lesion found on X-ray. 1, 2

Initial Diagnostic Workup

Clinical Assessment

• Evaluate for activity-related pain, morning stiffness duration (less than 30 minutes suggests osteoarthritis with 95% sensitivity), mechanical symptoms (locking, catching, popping, giving way), and history of trauma 1, 3
• Perform physical examination checking for joint line tenderness (83% sensitivity and specificity for meniscal tears), effusion, crepitus, range of motion limitations, and quadriceps weakness particularly during eccentric contractions 1, 3, 4
• Test for patellofemoral pain with squat maneuver (91% sensitive) if patient is under 40 years and physically active 3
• Perform McMurray test with concurrent knee rotation and extension (61% sensitivity, 84% specificity for meniscal tears) 3, 5

Critical Differential Diagnosis

Do not overlook referred pain from the lumbar spine or hip—always assess these areas clinically before attributing all symptoms to knee pathology, especially if knee radiographs are unremarkable. 2, 6

Imaging Algorithm

• First-line: Weight-bearing radiographs including AP, lateral, tangential patellar, and tunnel views 1, 2, 5
• Second-line: MRI without IV contrast if radiographs are normal but pain persists, or to characterize lesions found on radiographs (such as osteochondritis dissecans) or evaluate for concomitant pathology 1, 2
• Avoid: MRI suggests against obtaining MRI for diagnosis of osteoarthritis alone 1
• Ultrasound: Consider for detecting popliteal cysts and synovial pathology 2

Treatment Algorithm Based on Diagnosis

For Osteoarthritis (Most Likely in Patients ≥45 Years)

First-line treatment is a self-management program combining exercise therapy, weight loss if overweight, and patient education—not pharmacotherapy. 1, 3

Non-Pharmacologic Management (Primary Treatment)

• Initiate physical therapy as part of comprehensive management (can be delivered via individual, group, internet-based, or telephone-based approaches) 1
• Prescribe structured exercise training to prevent cartilage degeneration, inhibit inflammation, and improve pain, stiffness, and muscle weakness 7
• Recommend weight loss for overweight patients 1
• Consider soft braces or valgus/varus knee braces to improve pain and function, but ensure concurrent exercise to prevent atrophy 1

Pharmacologic Management (Stepwise Approach)

1. Topical NSAIDs (diclofenac): Strong recommendation as first-line pharmacotherapy for knee osteoarthritis pain 1
2. Topical capsaicin: Weak recommendation as alternative option 1
3. Oral acetaminophen and/or oral NSAIDs: Weak recommendation for hip and knee osteoarthritis 1
4. Duloxetine: Weak recommendation as alternative or adjunctive therapy for inadequate response or contraindications to acetaminophen/NSAIDs 1
5. Intra-articular corticosteroid injection: Weak recommendation for persistent pain inadequately relieved by other interventions 1

What to Avoid

Do not initiate opioids (including tramadol) for osteoarthritis pain. 1

Surgical Referral

• Consider joint replacement only for end-stage osteoarthritis (minimal/no joint space with inability to cope with pain) after exhausting all appropriate conservative options 3

For Patellofemoral Pain (Typically Age <40, Physically Active)

• Prescribe hip and knee strengthening exercises combined with foot orthoses or patellar taping 3
• Focus on correcting vastus medialis/vastus lateralis imbalance before starting quadriceps exercises 4
• Implement phased rehabilitation: Phase 1 (reduce pain/swelling, restore gait), Phase 2 (improve postural control, increase strength), Phase 3 (functional exercises) 4
• Continue non-operative treatment for at least 3 months before considering other options 4
• Surgery is not indicated for patellofemoral pain 3

For Meniscal Tears

Traumatic Tears (Age <40, Acute Twisting Injury)

• Start with conservative management (exercise therapy for 4-6 weeks) for most tears 3
• Surgery is required only for severe traumatic bucket-handle tears with displaced meniscal tissue 3

Degenerative Tears (Age ≥40, Often with Concurrent OA)

• Exercise therapy is first-line treatment—surgery is not indicated even with mechanical symptoms (locking, catching) 3
• Recognize that degenerative meniscal tears are present in approximately 12% of adults and may be asymptomatic 3

For Osteochondritis Dissecans (If Found on Imaging)

• Management depends on skeletal maturity and lesion stability 8
• Use MRI to characterize the lesion and evaluate for concomitant pathology (meniscal tears, ACL injury, articular cartilage injury) 1, 8
• Surgical intervention may be necessary for unstable lesions 8

Common Pitfalls to Avoid

• Do not perform MRI without recent radiographs—approximately 20% of patients with chronic knee pain have had premature MRI 2
• Do not assume all meniscal tears seen on imaging are symptomatic, particularly in patients over 45 years 2
• Do not rush to surgery for degenerative meniscal tears even with mechanical symptoms 3
• Do not use bracing without concurrent exercise as it can lead to atrophy and functional loss 1
• Do not overlook that bilateral structural abnormalities can be present in patients over 70 years with primarily unilateral symptoms 2