Knee Pain

History

Onset
- Traumatic vs. Atraumatic
- Delayed pain - tendon strain, cartilage contusion, minor soft tissue tears
Activity
- Type of activity/trauma
  - Anterior knee pain associated with sprinting or jumping - patellar tendinopathy
- Playing surface
Anatomic quadrant
- Diffuse/vague secondary to intra-articular, rheumatic/infectious, or referred pain
Effusion
- Acute (<6h) after trauma - Hemarthrosis, ACL tear (Cruciate ligament), articular fracture, knee dislocation
- Delayed after trauma - Meniscal injury
- Atraumatic - Infectious, rheumatologic, crystal
Locking, clicking, catching
- Meniscus
- Knee joint loose bodies
Buckling/giving-way
- Meniscus
- ACL
- Patella subluxation
- Knee joint loose bodies
Constitutional Symptoms
- Fever/chills/night sweats/fatigue/rash - Infectious, autoimmune, neoplastic
Other joints affected - Systemic/auto-immune
PMH
- Previous injury - Predisposes injury
- History of systemic/auto-immune disease

Differential

Acute knee pain following recent trauma/overuse (contact and non-contact - eg. running, jumping, squatting)
- MCL, LCL, ACL, Meniscus tear
  - Uncommon: PCL, Quadriceps tendon tear
- Patellar dislocation/subluxation
- Patellar tendon tear
- Intra-articular, Patellar, Fibular fracture
- Osteochondral defect
Atraumatic knee pain associated with joint effusion
- Worse with activity
  - Osteochondral defects (eg. dessicans)
    - MRI/arthroscopy
  - Osteoarthritis
    - Diagnosis clinically
      - Age >30yo
      - Activity-related joint pain
      - Minimal morning stiffness
      - Functional limitations
      - One of: Crepitus, restricted ROM, bony enlargement
- NOT related to activity
  - Septic arthritis
  - Disseminated gonococcal infection (polyarthralgia, tenosynovitis, painless dermatitis)
  - Systemic rheumatic disease
  - Crystal arthropathy
Atraumatic knee pain NOT associated with joint effusion
- Anterior
  - Tibial apophysitis (Osgood-Schlatter)
    - Pain/tenderness at tibial tubercle (at insertion of patellar tendon)
    - Most common in active older children
    - Pain with activity
  - Hoffa's fat pad syndrome
    - Squatting or downward pressure of patellar tendon may reproduce pain
    - Tenderness with palpation deep to patellar tendon (but not at insertion)
    - Exam otherwise normal
  - Quadriceps/patellar tendinopathy (Jumper's knee)
    - Pain/tenderness at quadriceps or patellar tendon
    - Focal pain on knee extension, atrophy of vastus medialis
  - Bursitis
    - Localized redness, swelling with normal exam
  - Plica syndrome
    - Thickened medial plica catches medial edge of patella or medial femoral condyle causing localized anteromedial pain with movement
      - Pain/tenderness
    - Medial patellar plica test
  - Chronic patellar dislocation or subluxation
    - Anteromedial patellar discomfort, sensation of knee snapping/giving away
    - Q angle (anterior superior iliac spine to center of patella) > 15 degrees
    - Atrophy of vastus medialis and positive apprehension test
  - Patellofemoral pain (Chondromalacia patellae)
    - Vague poorly localized anterior knee pain (under patella) worse with squatting, running, sitting (theater sign), up/down stairs
    - Locking,catching and effusion are NOT associated with PFP
    - Patellofemoral tracking, crepitus during palpation of patella
    - Ultrasound of peripatellar structures to rule out other diagnoses
  - Patellar stress fracture
    - Highly active explosive jumping or plyometric activities
    - MRI needed
- Medial
  - Degenerative medial meniscus tear
    - Mechanical symptoms (catching, locking, inability to extend knee), swelling, pain with squatting
    - On exam, medial joint line tenderness (posterior to MCL), positive McMurray/Thessaly
  - Saphenous nerve entrapment
    - Allodynia, radiation along saphenous nerve, worse by palpation or tapping at entrapment site (Tinel's)
    - Not related to activity, may be positional
    - Saphenous nerve block diagnostic and therapeutic
  - Pes anserine bursitis
    - Proximal anteromedial tibia tenderness
    - Worse with exercise
- Lateral
  - Iliotibial band syndrome
    - Runners or cyclists
    - Tender lateral femoral condyle, positive Noble compression test
  - Degenerative lateral meniscus tear (as medial but more rare)
- Posterior
  - Popliteal artery aneurysm/entrapment
  - Popliteal "Baker's" cyst
    - Swelling posterior capsule, palpable cyst during knee extension but disappears on flexion, ultrasound
  - Popliteus tendinopathy
    - Worsened pain by downhill activities
    - Tenderness at insertion anterior to lateral femoral condyle and LCL, pain on resisted internal rotation (Garrick's test) or passive external rotation of tibia
Referred knee pain
- SCFE
Uncommon
- Bone tumors, systemic, medication (glucocorticoid avascular necrosis)

Physical Examination

Inspection (vastus medialis atrophy), palpation, ROM, strength, neurovascular
Special tests
- MCL/LCL: Varus/valgus stress, Apley distraction test
- ACL: Lachman's, anterior drawer, Pivot-shift/MacIntosh test, look for weak quads (low tone)
- Meniscus: McMurray, Thessaly, Apley grind, Bounce-home test
- Patellar: Patellar grind test, patellar apprehension test, Clark's/Install's maneuver
Reproduce pain
Ultrasound for effusion

Consider Investigations

Joint aspiration for cell count + differential, glucose, protein, bacterial culture, polarized light microscopy for crystals
Labs
- CBC, ESR/CRP
Imaging
- X-ray r/o #
- U/S
- MRI

Management

Knee OA
- Weight loss for BMI>25
- Exercise therapy (land-based > aquatic)
- Consider
  - Acetaminophen, NSAIDs
  - Duloxetine
  - Patellar taping with medial-directed force
- Limited data and mixed results for chondroitin sulfate, steroid injections, hyaluronic acid injection
- Minimal benefit and high risk for tramadol/opioids
Patellofemoral Pain Syndrome
- Hip and Knee exercises
  - Clam shells (side-lying hip abduction), monster walks with band
- Orthotics