Knee Osteoarthritis Examination
Knee OA examination requires systematic assessment of alignment, compartmental involvement, and functional status. Examiners expect you to identify the pattern of arthritis (medial, lateral, or patellofemoral), assess severity, and evaluate the patient's suitability for different treatment options.
Quick Reference One-Pager
Alignment
- Varus (bow-legged) = medial compartment OA
- Valgus (knock-knee) = lateral compartment OA
- Measure tibiofemoral angle standing
- Note if fixed or correctable
Compartments
- Medial: Most common (60%)
- Lateral: Less common (15%)
- Patellofemoral: Anterior knee pain
- Tricompartmental: TKR indication
Key Findings
- Effusion (bulge sign, ballottement)
- Crepitus (PF more than TF)
- Fixed flexion deformity
- Range of motion (flexion and extension)
Functional Assessment
- Gait pattern (antalgic, Trendelenburg)
- Stairs (worst for PF)
- Rising from chair
- Walking distance
Classification and Patterns
OA Compartmental Patterns
Tibiofemoral OA:
- Medial compartment: Most common (60%), associated with varus
- Lateral compartment: Less common (15%), associated with valgus
- Both compartments: Pan-articular
Patellofemoral OA:
- Anterior knee pain
- Worse with stairs and rising
- May be isolated or combined
- Common after patella fracture or instability
Tricompartmental OA:
- All three compartments affected
- Usually requires TKR
Alignment and Arthritis:
- Normal tibiofemoral angle: 5-7° valgus
- Varus (bow-legged) → Medial compartment overload → Medial OA
- Valgus (knock-knee) → Lateral compartment overload → Lateral OA
Alignment determines which compartment wears first and guides treatment options.
Observation
Standing Assessment
Front View:
- Overall alignment (varus/valgus)
- Quadriceps wasting (VMO especially)
- Knee swelling (synovitis, effusion)
- Scars from previous surgery
Lateral View:
- Fixed flexion deformity (FFD)
- Hyperextension (recurvatum)
- Patella position (alta/baja)
Behind (With Patient Walking):
- Varus/valgus thrust
- Popliteal swelling (Baker's cyst)
- Gait pattern
Alignment Measurement
Clinical Assessment (Standing):
- Have patient stand with feet together
- Observe tibiofemoral angle
- Note if knees touch (valgus) or ankles touch (varus)
Inter-condylar Distance:
- Varus: Measure distance between knees when ankles together
Inter-malleolar Distance:
- Valgus: Measure distance between medial malleoli when knees together
Weight-Bearing Assessment:
- Mechanical axis: Hip center to ankle center
- Should pass through knee center
Gait Analysis
OA Gait Patterns
Antalgic Gait:
- Shortened stance phase on affected side
- Reduces weight-bearing time
Varus Thrust:
- Lateral thrust of knee during stance
- Indicates lateral ligament laxity or medial bone loss
- Important prognostic finding
Valgus Thrust:
- Medial thrust (less common)
- Indicates medial ligament laxity
Trendelenburg:
- May occur if hip also affected
- Distinguish from knee pathology
Stiff Knee Gait:
- Reduced knee flexion in swing phase
- Compensatory hip hiking or circumduction
Palpation
Systematic Palpation
Bony Landmarks:
- Joint line tenderness (medial vs lateral)
- Osteophytes (palpable around joint margin)
- Tibial tubercle
Effusion Assessment:
- Cross-fluctuance (moderate effusion)
- Patella tap/ballottement (large effusion)
- Bulge sign (small effusion)
Temperature:
- Warmth suggests active inflammation
- Cool joint = less active disease
Patellofemoral:
- Tenderness around patella edges
- Retropatellar crepitus
Special test
Patella Tap (Ballottement)
Detect moderate to large knee effusion
Technique
- 1Empty suprapatellar pouch by sliding hand distally
- 2Keep hand pressing on suprapatellar area
- 3Tap patella with other hand, pressing toward femur
Positive Sign
Patella 'clicks' against femoral trochlea (floating on fluid)
Indicates
Moderate to large knee effusion (greater than 30mL typically)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Bulge Sign (Wipe Test)
Detect small knee effusion
Technique
- 1Wipe (stroke) fluid from medial side of knee upward
- 2Quickly stroke lateral side of knee downward
- 3Observe medial side for fluid wave (bulge)
Positive Sign
Wave of fluid returns to medial side
Indicates
Small knee effusion (more sensitive than ballottement)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Range of Motion
ROM Assessment
Extension:
- Normal: 0° (some hyperextension 5-10° is normal)
- Fixed flexion deformity (FFD): Cannot reach 0°
- Document degree of FFD (e.g., "15° FFD")
Flexion:
- Normal: 135-140°
- Functional minimum for stairs: 90°
- Functional minimum for sitting: 90-110°
Assessment Technique:
- Active then passive
- Compare with contralateral
- Note crepitus during movement
- Note endpoint (hard/soft)
Record as: 0° to 130° (normal) or 15° to 110° (FFD to max flexion)
Functional ROM Requirements:
- Walking on flat: 65-70° flexion
- Climbing stairs: 85-90° flexion
- Sitting comfortably: 95-105° flexion
- Tying shoelaces: 105-110° flexion
- Deep squatting: 130-140° flexion
A patient with 0-90° ROM can walk and climb stairs but may struggle with deep bending.
Ligament Stability
Stability Assessment
Why Important in OA:
- Ligament laxity affects alignment
- Affects choice of implant (constrained vs unconstrained)
- Varus/valgus laxity may indicate bone loss
Tests:
- Varus stress (0° and 30°): Lateral ligament complex
- Valgus stress (0° and 30°): Medial ligament complex
- Lachman and anterior drawer: ACL (less relevant unless history of instability)
- Posterior drawer: PCL
Correctable vs Fixed Deformity:
- Correct varus/valgus with stress
- Fixed = bony deformity/contracture
- Correctable = ligament laxity +/- soft tissue
Patellofemoral Assessment
Special test
Patellofemoral Compression Test
Patellofemoral OA/chondromalacia
Technique
- 1Patient supine, knee extended
- 2Press patella firmly against femoral trochlea
- 3Ask patient to contract quadriceps
Positive Sign
Pain with compression or contraction
Indicates
Patellofemoral joint pathology (OA, chondromalacia)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Patellar Grind (Clarke's Test)
Patellofemoral pathology
Technique
- 1Patient supine, knee extended and relaxed
- 2Place web of hand above patella
- 3Push patella distally
- 4Ask patient to contract quadriceps
Positive Sign
Pain or inability to contract due to pain
Indicates
Patellofemoral pathology (note: high false positive rate)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
PF Specific Findings
Observation:
- J-sign (lateral tracking)
- Patellar tilt or lateral displacement
Palpation:
- Tenderness around patella facets
- Retropatellar crepitus with ROM
Functional:
- Pain worse descending stairs (eccentric load)
- Pain with prolonged sitting (movie sign)
- Pain rising from chair (high PF load)
Functional Assessment
Function Tests
Gait Assessment:
- Walking distance (meters or blocks)
- Need for walking aids
- Limp pattern
Stairs:
- Can they ascend/descend normally?
- Need for handrail?
- Step-over-step vs step-to-step?
Rising from Chair:
- Can they rise without arm support?
- Need to push up from armrests?
ADLs:
- Cutting toenails (flexion)
- Getting in/out of car
- Footwear (tying laces)
Document Pain:
- Location (medial, lateral, anterior, posterior)
- Severity (VAS score)
- Night pain (indicates severe disease)
- Starting pain (after rest)
- Walking pain
Severity Assessment
- rom
- Full or near full
- alignment
- Minimal deformity
- effusion
- None or minimal
- function
- Mild limitation
- rom
- Some limitation
- alignment
- Obvious varus/valgus
- effusion
- May be present
- function
- Moderate limitation
- rom
- Significantly limited
- alignment
- Fixed deformity
- effusion
- Often present
- function
- Significant disability
- rom
- Marked limitation, FFD
- alignment
- Severe fixed deformity
- effusion
- Variable
- function
- Unable to function normally
Treatment Considerations
Examination Implications for Treatment
Conservative Treatment Indicators:
- Mild symptoms
- Good ROM
- Minimal deformity
- Correctable alignment
Osteotomy Consideration (HTO/DFO):
- Younger patient (less than 60)
- Unicompartmental disease
- Correctable deformity
- Intact ligaments
- Good ROM
Unicompartmental Knee Replacement:
- Single compartment disease
- Correctable deformity (less than 15°)
- Intact ACL
- Range 90°+ flexion
- No inflammatory arthritis
Total Knee Replacement:
- Tricompartmental disease
- Severe symptoms
- Failed conservative treatment
- May have deformity, instability
Summary Presentation
“68-year-old man with progressive right knee pain over 5 years, now affecting sleep.”
Examiner Tips
Do
- Assess alignment standing (varus/valgus)
- Check for effusion (tap and bulge)
- Document ROM (extension AND flexion)
- Assess ligament stability
- Evaluate function (gait, stairs, aids)
Don't
- Forget to examine the hip
- Miss patellofemoral involvement
- Neglect varus/valgus thrust in gait
- Forget to ask about night pain
- Miss fixed flexion deformity