Medial Compartment Osteoarthritis of the Knee
The most likely diagnosis for a 67-year-old woman presenting with medial knee pain of six-month duration is medial compartment osteoarthritis, which is the most common type of arthritis affecting the knee and predominantly involves the medial compartment in approximately 70-80% of cases. 1
Why Medial Compartment Osteoarthritis is the Primary Diagnosis
Osteoarthritis is the most common cause of knee pain in older adults, particularly in patients over age 55 years, with approximately 25% experiencing episodes of persistent knee pain 1, 2
The medial compartment is by far the most frequently affected location because during the mid-stance phase of gait, approximately 70-80% of the joint load passes through the medial compartment, as the center of mass is located medial to the knee joint center 1, 3
Age and gender are key risk factors: This patient's age of 67 years and female gender align with the typical demographic for knee osteoarthritis 2
The six-month onset indicates a chronic, progressive condition rather than an acute injury, which is consistent with the insidious nature of osteoarthritis 2
Clinical Presentation to Confirm
Early-phase symptoms include pain that appears with exercise but can be "walked off", with the joint often feeling like it creaks and grates 2
Intermittent swelling occurs, especially after unusual activity involving a flexed position 2
Tenderness to palpation over the medial joint line is a hallmark finding that represents well-localized pain matching the quality and location of pain experienced during activity 3
As the disease progresses, patients experience increasing difficulty with activities of daily living 2
Differential Considerations for Medial Knee Pain
While medial compartment osteoarthritis is the primary diagnosis, other causes of medial knee pain that should be considered include:
Medial meniscal tears, though these are often incidental findings in older patients, with the majority of people over 70 years having asymptomatic meniscal tears 1
Medial collateral ligament bursitis, which presents as a distended and inflamed bursa between the superficial and deep portions of the MCL, though this is rare 4
Medial collateral ligament calcification, an extremely rare entity 5
Crystal arthropathy (gout or pseudogout), which can affect the medial compartment 6
Diagnostic Approach
Plain radiographs are the initial imaging modality of choice to confirm osteoarthritis and assess disease severity 1
MRI is not routinely indicated for initial diagnosis but may be useful if there is diagnostic uncertainty or to evaluate for bone marrow lesions, which are associated with increased knee pain 1
Valgus stress radiographs can objectively determine the amount of medial compartment gapping in cases where the diagnosis is unclear 7
Initial Management Strategy
All patients with symptomatic knee osteoarthritis should be enrolled in an exercise program and counseled regarding weight loss if overweight, as these are strongly recommended first-line interventions 1, 8
Non-Pharmacological Management (First-Line)
Cardiovascular (aerobic) and/or resistance land-based exercise should be implemented as the cornerstone of treatment 1, 8
Aquatic exercise programs are equally efficacious and may be preferred for aerobically deconditioned patients 1
Weight reduction is strongly recommended for patients who are overweight, as even modest weight loss can significantly improve symptoms 1, 8
Self-management programs and patient education about activity modification and joint protection techniques are essential 1, 8
Laterally wedged subtalar strapped insoles should be considered for medial compartment osteoarthritis to redistribute load away from the affected compartment 1
Realignment bracing (valgus brace) can reduce medial compartment load by 11-20% and has demonstrated pain reduction in clinical trials, particularly in patients younger than 60 years 1
Pharmacological Management (Second-Line)
Topical NSAIDs should be used as first-line pharmacological therapy for localized medial knee pain 1, 8
Oral NSAIDs (including COX-2 selective inhibitors) should be used at the lowest effective dose for the shortest possible period when topical treatments provide insufficient relief 1, 8
For patients age ≥75 years, topical rather than oral NSAIDs are conditionally recommended due to safety considerations 1
Acetaminophen may be tried but has limited efficacy compared to NSAIDs 1
Intra-articular corticosteroid injections can provide short-term pain relief for acute flares, with ultrasound-guided anteromedial joint line approach being particularly effective for medial compartment pathology 6
Common Pitfalls to Avoid
Do not overrely on passive treatments without active exercise therapy, as exercise is the cornerstone of effective management 1, 8
Do not delay weight management counseling in overweight patients, as this is a critical modifiable risk factor 1, 8
Do not use opioids for long-term pain management due to risk of dependence 1
Do not order MRI routinely when plain radiographs and clinical examination are sufficient for diagnosis 1
Do not assume all meniscal tears seen on imaging are symptomatic, as they are common incidental findings in this age group 1
When to Consider Specialist Referral
Specialist referral should be considered if conservative measures fail to provide adequate symptom relief after 4-6 weeks, or if there is significant functional limitation despite appropriate conservative management 8
Joint replacement surgery should be considered for refractory pain associated with disability and radiological deterioration 1