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Knee Pain

Authors: Lee A. Mancini, MD; Emily J. Eshleman, DO, MS; Michael J. Maddaleni, MD

BASICS

DESCRIPTION

  • Common outpatient issue with broad differential
  • May be acute, chronic, or acute-on-chronic
  • Frequent causes: trauma, overuse, degeneration
  • Diagnostic approach: age, pain onset, location, mechanism of injury, associated symptoms

EPIDEMIOLOGY

  • 12.5 million primary care visits annually
  • Knee OA incidence: 240 cases/100,000 person-years
  • OA is:
  • 11th leading cause of global disability
  • 38th most common cause of DALYs
  • Common causes in runners: patellar tendinopathy, patellofemoral syndrome

ETIOLOGY & PATHOPHYSIOLOGY

  • Trauma: ligament/meniscal injuries, fracture, dislocation
  • Overuse: tendinopathy, PFPS, bursitis, apophysitis
  • Degenerative: OA, especially in older adults
  • Inflammatory: RA, SLE
  • Crystal arthropathies: gout, pseudogout
  • Infectious: septic arthritis, Lyme disease
  • Referred pain: hip or spine
  • Other: tumor, cyst, popliteal aneurysm

RISK FACTORS

  • Obesity, malalignment
  • Poor flexibility, muscle weakness
  • Training errors (intensity, surface, footwear)
  • High-impact activities: pivoting, jumping, kneeling
  • History of prior injuries

PREVENTION

  • Maintain BMI <25 kg/m²
  • Proper technique, equipment, and volume
  • Correct muscle imbalance and posture

ASSOCIATED CONDITIONS

  • Contusion, fracture
  • Effusion or hemarthrosis
  • Ligament injuries (ACL, PCL, MCL, LCL)
  • Meniscal tears
  • Tendinopathies, bursitis
  • Osteochondral injuries, OA
  • Patellar instability/dislocation
  • Muscle strains
  • Septic arthritis

DIAGNOSIS

HISTORY

  • Pain location and mechanism of injury critical
  • Diffuse pain: OA, PFPS, chondromalacia
  • Pain on stairs: meniscus, PFPS
  • Pain with sitting/standing: PFPS
  • Mechanical symptoms: meniscal tear
  • Effusion:
  • Rapid (within 2 hrs): ACL tear, patellar dislocation, meniscus tear, hemarthrosis
  • Delayed (24–36 hrs): sprain, arthritis, small tear
  • Posterior swelling: popliteal cyst

PHYSICAL EXAM

  • Gait, patellar tracking
  • Inspect: alignment, atrophy, swelling, ecchymosis
  • Palpation: tenderness, warmth, effusion
  • ROM, strength testing
  • Special tests:
  • Lachman, pivot shift, anterior drawer: ACL
  • Posterior drawer, sag sign: PCL
  • Valgus/varus: MCL/LCL
  • McMurray, Apley, Thessaly: meniscus
  • Grind test, patellar apprehension: PFPS, OA
  • Ober test: ITB tightness
  • Dial test: posterolateral corner

DIFFERENTIAL DIAGNOSIS

By Onset

  • Acute: fracture, ligament tears, dislocation, septic arthritis
  • Chronic: OA, PFPS, ITB syndrome, tendinopathy, loose bodies

By Pain Location

  • Anterior: PFPS, tendinopathy, bursitis, Osgood-Schlatter
  • Posterior: PCL injury, Baker cyst, DVT
  • Medial: MCL, medial meniscus, pes anserine bursitis
  • Lateral: LCL, ITB syndrome, lateral meniscus

DIAGNOSTIC TESTS

Initial Tests

  • Suspected infection/gout: arthrocentesis, Gram stain, cell count, ESR, CRP
  • Suspected RA: CBC, RF, ESR
  • Radiographs (Ottawa Knee Rules):
  • Age >55
  • Patellar or fibular head tenderness
  • Cannot flex to 90°
  • Cannot bear weight 4 steps

Imaging

  • MRI = gold standard for soft tissue
  • Ultrasound: effusions, tendons, ligaments
  • CT: fractures
  • Arthroscopy: diagnostic and therapeutic

AGE-SPECIFIC CONSIDERATIONS

Geriatrics

  • OA, degenerative meniscal tears, crystal arthropathies

Pediatrics

  • Look for physeal/apophyseal injuries
  • Acute: patellar subluxation, ACL, avulsion fractures
  • Chronic: PFPS, Osgood-Schlatter, OCD
  • Others: SCFE, Legg-Calvé-Perthes, infection, JRA

TREATMENT

GENERAL MEASURES

  • PRICEMM: Protection, Relative rest, Ice, Compression, Elevation, Medications, Modalities

MEDICATIONS

  • Acetaminophen (up to 3g/day): OA
  • NSAIDs:
  • Ibuprofen 200–800 mg TID
  • Naproxen 250–500 mg BID
  • Celecoxib 200 mg QD
  • Topical NSAIDs (preferred in OA)
  • Capsaicin: OA adjuvant
  • Injections:
  • Intra-articular corticosteroids: short-term OA relief
  • Viscosupplementation: 4–6 weeks for peak effect
  • PRP, prolotherapy (long-term benefit)
  • Not recommended: opioids, tramadol, long-term NSAIDs in fracture/healing phase

REFERRAL INDICATIONS

  • High-velocity trauma or acute athletic injury
  • Joint instability
  • Failure of conservative therapy
  • Suspected physeal fractures in children

ADDITIONAL THERAPIES

  • Physical therapy: cornerstone for PFPS, OA, tendinopathies
  • Bracing for instability
  • Orthotics, taping, acupuncture

SURGICAL OPTIONS

  • Consider in:
  • ACL/PCL injuries in athletes
  • Severe OA (grade IV)
  • Meniscal tear with mechanical symptoms
  • Refractory cases despite therapy

COMPLEMENTARY MEDICINE

  • Glucosamine 500 mg TID
  • Chondroitin 400 mg TID
  • Turmeric/Curcumin 1000 mg/day
  • Collagen hydrolysates 10g/day
  • Others: SAMe, ginger, MSM (limited evidence)
  • Acupuncture: 10 sessions minimum for effect

FOLLOW-UP & MONITORING

  • Activity modification
  • Monitor rehab progress and pain control
  • Weight loss (≥10% body weight) → 28% improvement in function

PATIENT EDUCATION

  • Role of exercise, adherence
  • Proper footwear, training technique
  • Medication risks/benefits
  • Reinforce rehab goals

PROGNOSIS

  • Depends on:
  • Diagnosis
  • Injury severity
  • Patient compliance
  • Need for surgical intervention

COMPLICATIONS

  • Chronic instability
  • Progression to OA
  • Disability, deconditioning

CODES

  • M25.569 – Pain in unspecified knee
  • M17.9 – Knee osteoarthritis, unspecified
  • M76.50 – Patellar tendinitis, unspecified knee

CLINICAL PEARLS

  • History + mechanism = essential diagnostic clues
  • Acute effusion in young = suspect ACL, patellar dislocation, septic arthritis
  • Chronic pain → consider PFPS, OA, tendinopathy, bursitis
  • Referred pain: SCFE, Perthes, hip OA → may present as knee pain