What are the step-by-step tests and treatment guidelines for a patient presenting with knee pain, considering age, weight, activity level, and past medical history?

Step-by-Step Approach to Knee Pain: Testing and Treatment

Step 1: Initial Clinical Assessment

Determine the acuity and severity of presentation to identify patients requiring urgent referral.

• Red flags requiring immediate evaluation: fever with joint swelling/erythema/limited range of motion (septic arthritis), severe pain with inability to bear weight after acute trauma, or gross joint instability 1, 2
• Key history elements: age (osteoarthritis most likely if ≥45 years with activity-related pain and <30 minutes morning stiffness), pain location (anterior suggests patellofemoral pain, joint line suggests meniscal pathology), mechanical symptoms (locking/catching), history of trauma, and duration (acute vs chronic >3 months) 1, 2, 3
• Physical examination findings:
  • Patellofemoral pain: anterior knee pain during squat (91% sensitive, 50% specific), typically age <40 years, physically active population 2, 4
  • Meniscal tear: McMurray test with concurrent knee rotation and extension (61% sensitive, 84% specific), joint line tenderness (83% sensitive, 83% specific) 2
  • Osteoarthritis: limited range of motion, crepitus, joint line tenderness, varus/valgus alignment 5
• Consider referred pain: examine hip and lumbar spine if knee radiographs are unremarkable, as hip or spine pathology can present as knee pain 4, 6

Step 2: Initial Imaging - Plain Radiographs

Obtain plain radiographs as the first imaging study for all patients ≥5 years old with knee pain, whether acute or chronic.

• Standard views required: anteroposterior (or Rosenberg/tunnel), lateral, and tangential patellar view 4, 7
• For acute trauma, apply Ottawa Knee Rules to determine necessity (reduces unnecessary radiographs by 23-35% while maintaining 100% fracture sensitivity) 4, 7:
  • Age ≥55 years
  • Isolated patellar tenderness
  • Fibular head tenderness
  • Cannot flex knee to 90°
  • Cannot bear weight immediately after injury or take 4 steps in emergency department
• Radiographs identify: fractures, osteoarthritis (joint space narrowing, osteophytes, subchondral sclerosis), chondrocalcinosis (pseudogout), osteochondritis dissecans, loose bodies, signs of prior injury 4, 5

Step 3: Arthrocentesis When Indicated

Perform joint aspiration immediately if infection or crystal arthropathy is suspected, particularly with joint effusion, erythema, warmth, or migratory inflammatory pattern.

• Synovial fluid analysis: cell count with differential, Gram stain and culture (infection), crystal analysis (gout/pseudogout) 8, 7
• Can be performed under ultrasound or fluoroscopic guidance if effusion is present 8, 7

Step 4: Advanced Imaging Based on Radiograph Results

If Radiographs Are Normal or Show Only Effusion with Persistent Pain:

Order MRI without IV contrast as the next appropriate study to evaluate soft tissue structures, menisci, ligaments, and occult bone pathology.

• MRI detects pathology invisible on radiographs: meniscal tears, ligament injuries (ACL/PCL/collaterals), bone marrow contusions, occult fractures (especially in osteoporotic patients), osteochondritis dissecans, articular cartilage abnormalities, popliteal cysts, tendon pathology 4, 6, 7
• Critical pitfall: approximately 20% of patients undergo MRI without recent radiographs—this is inappropriate and costly; always obtain radiographs first 4, 7

If Radiographs Show Osteoarthritis:

MRI is generally not indicated for typical osteoarthritis unless symptoms are unexplained by radiographic findings or conservative treatment fails.

• Radiographic confirmation is sufficient for diagnosis when clinical presentation aligns 7, 2

If Radiographs Show Osteochondritis Dissecans, Loose Bodies, or Prior Cartilage/Meniscal Repair:

MRI without IV contrast is appropriate to evaluate cartilage integrity, fragment stability, and repair status 4

Alternative Advanced Imaging:

• CT without IV contrast: for radiographically occult fractures, detailed patellofemoral anatomy evaluation (trochlear morphology, tibial tubercle-trochlear groove distance), or when MRI is contraindicated 4, 7
• Ultrasound: confirms effusions, guides aspiration, detects Baker cysts, evaluates superficial structures, but not comprehensive for internal derangement 7, 1

Step 5: Treatment Based on Diagnosis

Osteoarthritis (Most Common in Age ≥45):

First-line treatment consists of exercise therapy, weight loss if overweight, education, and self-management programs—not surgery or imaging.

• Exercise therapy is the cornerstone of conservative management 2, 3
• Intra-articular corticosteroid injections when conservative measures fail 3
• Radiofrequency ablation (conventional or cooled) of genicular nerves for refractory cases 3
• Hyaluronic acid injections are conditionally recommended 3
• Surgical referral for joint replacement: only after exhausting conservative options in end-stage disease (minimal/no joint space with inability to cope with pain) 2, 3

Patellofemoral Pain (Most Common Age <40, Physically Active):

Deliver hip-and-knee targeted strengthening exercises combined with prefabricated foot orthoses or patellar taping.

• Hip and knee strengthening exercises are evidence-based first-line treatment 4, 2
• Prefabricated foot orthoses should be prescribed to those responding favorably to treatment direction tests, customized for comfort 4
• Patellar taping for patients where rehabilitation is hindered by elevated symptom severity 4
• Education to challenge inaccurate beliefs, reduce fear, and promote autonomy 4
• Surgery is not indicated for patellofemoral pain 2

Meniscal Tears:

Conservative management with exercise therapy for 4-6 weeks is first-line treatment for most meniscal tears, including degenerative tears with mechanical symptoms.

• Exercise therapy is appropriate even when mechanical symptoms (locking, catching) are present in degenerative tears 2
• Surgery is indicated only for: severe traumatic bucket-handle tears with displaced meniscal tissue 2
• Surgery is NOT indicated for: degenerative meniscal tears, even with mechanical symptoms 2

Crystal Arthropathy (Gout/Pseudogout):

For acute flares: NSAIDs, colchicine, or corticosteroids (intra-articular or systemic).

• Treatment choice depends on contraindications and patient factors 8

Step 6: Reassessment and Escalation

If diagnosis remains unclear after initial workup or symptoms persist despite adequate conservative treatment (typically 4-6 weeks), consider:

• MRI if not yet performed 4, 6
• Specialty referral (orthopedics, rheumatology, sports medicine) 1, 9
• Multidisciplinary approach including psychological therapy for chronic pain 3

Critical Pitfalls to Avoid

• Never skip radiographs and proceed directly to MRI—this occurs in 20% of cases and is inappropriate 4, 7
• Never attribute migratory knee pain solely to osteoarthritis without excluding crystal disease or infection via aspiration 8
• Never perform arthroscopic surgery for degenerative meniscal tears—exercise therapy is first-line even with mechanical symptoms 2
• Never order MRI for typical osteoarthritis when radiographs confirm diagnosis and symptoms align 7, 2
• Always examine hip and lumbar spine if knee radiographs are unremarkable to exclude referred pain 4, 6