What is the evaluation and management approach for an adult experiencing pain behind the knee that worsens with walking or bending?

Evaluation and Management of Pain Behind the Knee

Initial Diagnostic Approach

The most likely diagnosis in an adult with posterior knee pain worsening with walking or bending is knee osteoarthritis, particularly if the patient is over 45 years old with activity-related pain and less than 30 minutes of morning stiffness (95% sensitivity, 69% specificity). 1

Key Clinical Features to Assess

• Age and onset pattern: Patients ≥45 years with insidious, gradually worsening pain strongly suggest osteoarthritis 1, 2
• Pain characteristics: Activity-related joint pain that worsens with weight-bearing and knee flexion (walking, squatting, stair climbing) is typical of knee OA 1, 3
• Morning stiffness duration: Less than 30 minutes supports OA diagnosis 1
• Mechanical symptoms: Joint line tenderness (83% sensitivity, 83% specificity) and McMurray test (61% sensitivity, 84% specificity with concurrent knee rotation and extension) help identify meniscal tears 1
• Anterior vs posterior location: Anterior knee pain during squatting (91% sensitivity, 50% specificity) suggests patellofemoral pain syndrome, more common in patients <40 years 1

Imaging Decisions

• Radiographs are NOT routinely needed for clinical diagnosis of knee OA 1
• Order weight-bearing plain radiographs only if: chronic pain >6 weeks, considering surgical referral, or acute trauma meeting evidence-based criteria 4, 5
• MRI should be reserved for persistent pain despite adequate conservative treatment or when surgery is being considered 5

First-Line Management: Non-Pharmacological Core Treatment

All patients must begin with a combination of regular exercise, weight loss (if BMI ≥25), and patient education—this is the foundation before escalating to pharmacological interventions. 6, 7, 4

Exercise Prescription (Mandatory First Step)

• Quadriceps strengthening exercises: Perform sustained isometric exercises for both legs 5-7 repetitions, 3-5 times daily (before getting out of bed, before stairs, before sleep), holding each contraction 6-7 seconds 8
• Aerobic activity: 30-60 minutes of moderate-intensity low-impact exercise (walking, swimming, cycling, Tai Chi) most days of the week, with effect sizes of 0.52 for pain relief and 0.46 for disability reduction 7, 4
• Hip girdle strengthening: Include proximal hip muscle exercises regardless of which joint is affected 8
• Exercise principles: Start within patient's capability, build up gradually over months, link to daily activities (before shower/meals) to make it lifestyle rather than additional burden 8

Weight Management (If BMI ≥25)

• Target minimum 5% body weight reduction through combined dietary modification and exercise 7, 4
• Specific strategies: Monthly self-monitoring, regular support meetings, structured meal plans starting with breakfast, reduce saturated fat and sugar, increase fruit/vegetables (≥5 portions daily), limit portion sizes, address eating triggers 8

Patient Education and Self-Management

• Provide written information (booklets, DVDs, websites) selected by the individual, include partners/carers if appropriate 8
• Teach "small amounts often" pacing to avoid overuse of specific joints 8
• Reassure that serious disease is not present, emphasize self-management and early return to normal activities 8

Assistive Devices and Adaptations

• Walking stick on contralateral side, walking frames, wheeled walkers 8
• Home modifications: Increase height of chairs/beds/toilet seats, hand-rails for stairs, replace bath with walk-in shower 8
• Appropriate comfortable footwear (lateral-wedged insoles are NOT recommended) 8, 7

Pharmacological Treatment Algorithm

Start with acetaminophen (paracetamol) as the first-line oral analgesic, not exceeding 4000 mg daily (consider 3000 mg limit in elderly), before considering any NSAIDs. 8, 6, 7

Step 1: Acetaminophen + Topical NSAIDs

• Acetaminophen 3000-4000 mg daily (divided doses throughout the day for sustained control, not "as needed") provides pain relief comparable to oral NSAIDs in mild-to-moderate OA with superior safety profile 8, 6, 4
• Add topical NSAIDs (e.g., diclofenac gel) to the knee with clinical efficacy (effect size 0.91 vs placebo) and minimal systemic absorption, avoiding gastrointestinal and renal risks 6, 7, 4

Step 2: Oral NSAIDs (Only After Acetaminophen Failure)

• Consider oral NSAIDs only in patients unresponsive to acetaminophen 8, 7
• Mandatory gastroprotection: All patients receiving oral NSAIDs must receive proton pump inhibitor co-prescription 6
• Use selective COX-2 inhibitors in patients with increased gastrointestinal risk 8, 7
• Extreme caution in elderly: Substantially higher risks of GI bleeding, renal insufficiency, platelet dysfunction, cardiovascular complications 6
• Contraindications: Renal insufficiency, congestive heart failure, hypertension, hepatic disease 6

Step 3: Intra-Articular Corticosteroids

• Indicated for acute flares of knee pain, especially when accompanied by effusion, providing short-term relief lasting 4-8 weeks 8, 7, 4
• Particularly appropriate for elderly patients who cannot tolerate oral NSAIDs or those on anticoagulation 6

Step 4: Duloxetine (For Inadequate NSAID Response)

• Add duloxetine if pain persists despite NSAIDs, achieving significant reductions in pain and improvements in physical function 4

Medications to AVOID

Never prescribe opioids (including tramadol) for knee osteoarthritis pain—current evidence does not support their use and they carry significant adverse event risks without consistent improvement in pain or function. 4

• Do NOT prescribe glucosamine or chondroitin: Best available evidence does not support their use 6
• Do NOT combine acetaminophen with oral NSAIDs as initial therapy 6
• Do NOT use lateral-wedged insoles: Recommendation rejected by EULAR 8, 7

Reassessment and Surgical Referral

• Continue conservative management for at least 3 months before considering other options 9
• Refer for joint replacement only when: radiographic evidence of end-stage OA (minimal/no joint space), refractory pain and disability despite maximal conservative management including all appropriate non-pharmacological and pharmacological options 8, 7, 4

Critical Pitfalls to Avoid

• Never start with NSAIDs: Acetaminophen must be tried first due to superior safety profile 8, 6
• Never prescribe oral NSAIDs without gastroprotection: Mandatory PPI co-prescription 6
• Never skip exercise therapy: This is the foundation of treatment, not an optional add-on 8, 1
• Never order routine radiographs: Clinical diagnosis is sufficient; imaging only for chronic cases or surgical planning 1, 5
• Never exceed 4000 mg acetaminophen daily (3000 mg in elderly) to minimize hepatotoxicity risk 6, 4