In a 68-year-old woman with severe medial right knee pain radiating down the medial leg, limited flexion to about 40°, no swelling, fever, or recent trauma, using a walking stick, unable to take NSAIDs, and only mild relief from co‑codamol (codeine/acetaminophen) and paracetamol, what is the most likely diagnosis and appropriate management?

Medial Compartment Knee Osteoarthritis: Diagnosis and Management

Most Likely Diagnosis

This presentation is classic for medial compartment knee osteoarthritis (OA), the most common cause of medial knee pain in a 68-year-old woman, affecting nearly 50% of people by age 85. 1 The medial compartment bears 70-80% of joint load during gait, making it the most frequently affected pattern in knee OA. 1, 2

Clinical Features Supporting This Diagnosis

• Age and female sex are established constitutional risk factors for OA 1
• Medial knee pain radiating down the medial leg indicates medial compartment involvement 2
• Severe limitation of knee flexion to 40 degrees reflects functional impairment from medial joint line pain and loss of range of motion 1
• Absence of swelling, fever, or acute trauma excludes infection, acute ligamentous injury, or fracture 2, 3
• Activity-related pain is characteristic, with 95% sensitivity when combined with less than 30 minutes of morning stiffness 3

Immediate Management Plan

Step 1: Non-Pharmacological Interventions (First-Line)

The optimal management requires combining non-pharmacological and pharmacological treatments, with non-pharmacological interventions forming the foundation. 4

• Refer for supervised physical therapy focusing on quadriceps strengthening exercises, which are critical as muscle weakness is both cause and consequence of knee OA 1, 2
• Require 12 or more directly supervised sessions for optimal outcomes (effect size 0.46 vs 0.28 for fewer sessions) 1
• Prescribe low-impact aerobic activity for 30-60 minutes daily at moderate intensity 1
• Recommend progressive strength training of major muscle groups 2 days/week at 60-80% of one repetition maximum for 8-12 repetitions 1
• Provide patient education about self-management, as 80% of costs are offset within a year by reduced primary care visits 4
• Continue walking stick use as an appropriate assistive device 4

Step 2: Pharmacological Management (Since NSAIDs Contraindicated)

Since she cannot take NSAIDs, the treatment algorithm must be modified from standard guidelines. 4

Current Inadequate Analgesia

• Co-codamol and paracetamol alone are providing only mild relief, indicating need for escalation 4

Recommended Pharmacological Options:

1. Optimize paracetamol dosing first: Ensure she is taking the full 4g/day in scheduled doses (not as-needed), as this is the preferred long-term oral analgesic 4, 2

2. Add topical NSAIDs as first-line adjunct therapy for localized medial knee pain, with effect size of 0.91 vs placebo and excellent safety profile in patients unable to take oral NSAIDs 4, 2

3. Consider duloxetine 30-60mg daily as a non-NSAID option that achieves significant reductions in pain and improvements in physical function in knee OA 4

4. Intra-articular corticosteroid injection is specifically indicated if clinical examination reveals an effusion, providing short-term benefit (effect size 1.27 over 7 days) 4, 2

What NOT to Use:

• Do NOT prescribe opioids (including tramadol) beyond short-term co-codamol, as current evidence shows limited benefit with high risk of adverse effects (relative risk 1.28-1.69 for adverse events) 4
• Do NOT recommend glucosamine/chondroitin, as guidelines explicitly state these should not be used 4

Step 3: Clinical Examination Priorities

Before finalizing treatment, perform focused examination to guide therapy:

• Assess for knee effusion by ballottement, as presence specifically indicates intra-articular corticosteroid injection 4, 2
• Palpate medial joint line for focal tenderness confirming medial compartment involvement 2
• Evaluate hip range of motion, as hip pathology commonly refers pain to the knee and must be excluded if knee findings are equivocal 5
• Measure actual flexion range to document baseline for monitoring response 1

Step 4: Imaging Considerations

Weight-bearing plain radiographs (AP and lateral views) should be obtained if not already done to confirm OA diagnosis and assess severity, showing expected findings of medial joint space narrowing 4, 2

Do NOT order MRI routinely, as it is not indicated for typical knee OA and should be reserved for patients with persistent pain despite adequate conservative therapy 1

Treatment Algorithm Summary

1. Immediate (Week 1-2):

   • Optimize paracetamol to 4g/day scheduled dosing 4
   • Add topical NSAID (e.g., diclofenac gel) to medial knee 4, 2
   • Refer to physical therapy for supervised quadriceps strengthening program 1, 2
   • If effusion present on exam: perform intra-articular corticosteroid injection 4, 2

2. Short-term (Week 2-6):

   • Continue physical therapy (minimum 12 sessions) 1
   • If pain remains severe despite above: add duloxetine 30mg daily, increase to 60mg after 1 week 4
   • Patient education on self-management and home exercise program 4

3. Long-term (Month 2 onwards):

   • Continue home exercise program integrating quadriceps strengthening and low-impact aerobics into daily life 1
   • Maintain paracetamol and topical NSAID as needed 4
   • Reassess annually or as needed 4

4. Surgical Referral Threshold:

   • Consider orthopedic consultation for total knee arthroplasty if she has exhausted non-operative options above, has radiographic evidence of advanced structural damage, and experiences significant functional impairment affecting valued activities 2
   • This typically means failure of 3-6 months of optimal conservative management 4

Critical Pitfalls to Avoid

• Do NOT prescribe lateral heel wedges for medial compartment OA, as guidelines explicitly recommend against this 4
• Do NOT perform arthroscopic lavage or débridement, as this is not indicated for OA 4
• Avoid prolonged high-dose opioids beyond current co-codamol due to GI, renal, and adverse event risks in elderly patients 4
• Do NOT delay physical therapy referral based on pain severity—early supervised exercise is critical for optimal outcomes 4, 1