What causes knee pain when walking in a middle-aged or older adult with no known medical history?

Knee Pain When Walking: Common Causes in Middle-Aged and Older Adults

Primary Cause: Osteoarthritis

Osteoarthritis is the most common cause of knee pain when walking in middle-aged and older adults, affecting approximately 25% of persons older than age 55 years with persistent knee pain episodes. 1

The medial compartment is predominantly affected because 70-80% of joint load passes through this area during the mid-stance phase of gait, with the center of mass located medial to the knee joint center. 1 This explains why medial knee pain is far more common than lateral knee pain in this population.

Clinical Presentation of Knee OA

• Activity-related joint pain that worsens with weight-bearing activities like walking 1
• Morning stiffness lasting less than 30 minutes (95% sensitivity, 69% specificity for knee OA in patients ≥45 years) 2
• Gradual onset over months to years rather than acute trauma 1
• Medial joint line tenderness on palpation, often with reduced range of motion 1, 3

Risk Factors for Knee OA

The following modifiable and non-modifiable factors increase OA risk: 1

Non-modifiable:

• Age (prevalence increases dramatically after age 40 in women; 44% in those ≥80 years) 1
• Female gender 1
• Genetic predisposition 1

Modifiable:

• Obesity (major risk factor) 1
• Muscle weakness, particularly quadriceps weakness 1
• Joint injury or trauma 1
• Certain occupations requiring repetitive loading 1

Secondary Causes in This Population

Patellofemoral Pain Syndrome

While more common in younger adults (lifetime prevalence ~25%), patellofemoral pain can occur in middle-aged adults. 2 Key features include:

• Anterior knee pain during squatting (91% sensitivity, 50% specificity) 2
• Pain with prolonged sitting or stair navigation 1
• Pain at the inferior pole of the patella with resisted leg extension 1

Degenerative Meniscal Tears

Meniscal tears affect approximately 12% of adults and commonly occur as a degenerative condition in patients ≥40 years with concurrent knee OA. 2 Diagnostic features:

• Joint line tenderness (83% sensitivity, 83% specificity) 2
• Positive McMurray test (61% sensitivity, 84% specificity) with concurrent knee rotation and extension 2
• May present with mechanical symptoms like catching or locking 2

Patellar Tendinopathy

Though less common in older adults, patellar tendinopathy causes activity-related anterior knee pain. 1 It presents with:

• Pain at the inferior pole of the patella 1
• Pain exacerbated by stairs and prolonged sitting 1
• Positive decline squat test 1

Pain-Loading Relationship

A critical concept: patients with knee OA alter their gait mechanics in response to pain, which paradoxically may affect disease progression. 4, 5

• Decreased pain correlates with increased knee adduction moment (increased medial compartment loading) 4
• Increased pain correlates with decreased knee adduction and flexion moments (protective unloading) 4
• Experimental knee pain in healthy subjects replicates the gait patterns seen in less severe OA patients 5

This relationship suggests that pain relief interventions may inadvertently increase joint loading, highlighting the complexity of OA management. 4

Diagnostic Approach

Clinical Diagnosis Priority

For patients ≥45 years with activity-related knee pain and <30 minutes morning stiffness, clinical diagnosis of knee OA is sufficient without immediate imaging. 2

When to Image

• Plain radiographs are first-line when imaging is needed, showing joint space narrowing, osteophytes, and subchondral changes 1
• MRI is reserved for: 1
  • Suspected meniscal tears requiring surgical evaluation
  • Atypical presentations
  • Persistent symptoms after conservative treatment
  • Evaluation of bone marrow lesions or subchondral insufficiency fractures

Critical Pitfall

Do not use MRI findings alone to guide treatment decisions for degenerative meniscal tears in patients ≥40 years, as these are often incidental findings in the setting of OA. 2 Conservative management with exercise therapy is first-line even when degenerative tears are present. 2

Red Flags Requiring Alternative Diagnosis

Exclude serious pathology if present: 1, 6

• Persistent non-mechanical pain or night pain (consider malignancy)
• Progressive swelling without trauma
• Systemic symptoms (fever, weight loss)
• Acute traumatic hemarthrosis (consider ligamentous rupture or fracture) 7