Squat Testing After Acute Knee Injury
You can safely perform a supervised squat test 48–72 hours after acute knee injury once severe swelling, pain, and instability have subsided, but only after completing a structured examination sequence that rules out fracture, ligamentous rupture, and mechanical blocks to motion. 1
Pre-Test Requirements Before Squat Testing
Initial Exclusion Criteria (Must Be Ruled Out First)
Obtain plain radiographs (AP and lateral views) before any functional testing if the patient meets any Ottawa Knee Rule criteria: age ≥55 years, isolated patellar tenderness, fibular head tenderness, inability to flex knee to 90°, or inability to bear weight for 4 steps immediately after injury. 1, 2
Do not proceed with squat testing if red flags are present: palpable tendon gap, gross deformity, complete inability to bear weight, fever with joint effusion, or significant joint instability on ligamentous testing. 1, 3
Re-examine the patient 3–5 days after injury if initial examination was limited by excessive swelling and pain, as examination accuracy is compromised for up to 48 hours post-injury. 1
Required Baseline Assessment (48–72 Hours Post-Injury)
Confirm the patient can bear weight for at least 4 consecutive steps before attempting any squat maneuver, as inability to do so indicates ongoing structural compromise requiring imaging or specialist referral. 1, 2
Assess active and passive range of motion to ensure the patient can achieve at least 90° of knee flexion without mechanical block; the bounce test should be negative (no mechanical block to extension). 1, 4
Perform ligamentous stability testing (Lachman test for ACL, posterior drawer for PCL, valgus/varus stress for collaterals) to ensure no gross instability that would contraindicate loading. 1, 4
Palpate for joint line tenderness and assess effusion size; large tense effusions preventing flexion require aspiration before functional testing. 1, 3
Squat Test Performance Protocol
Single-Leg Squat Test (Preferred for Injury Assessment)
Position the patient standing on the injured leg with hands on hips or crossed over chest, ensuring the contralateral leg is held in slight hip and knee flexion off the ground. 5, 6
Instruct the patient to squat to 60° of knee flexion (approximately thigh at 45° angle to vertical), as forces remain low to moderate in the 0–60° functional range, minimizing stress on healing structures. 7
Observe from both frontal and lateral planes for compensatory patterns: excessive hip adduction, hip internal rotation, knee valgus collapse (frontal plane), and inadequate hip flexion or forward trunk lean (sagittal plane). 5, 6
Rate performance on a 0–2 scale for each plane: 0 = non-adequate movement with multiple compensations, 1 = moderate compensations, 2 = adequate movement with proper alignment and control. 5
Two-Leg Squat Test (Alternative for More Severe Injuries)
Use bilateral squat testing initially if single-leg testing is too demanding, limiting depth to 50° knee flexion (partial squat) to keep patellofemoral and tibiofemoral forces minimal during early rehabilitation. 7
Progress depth gradually: functional range (0–50°) for early rehabilitation, parallel squat (0–100°, thighs parallel to ground) only when the patient demonstrates full strength and stability without compensatory patterns. 7
Avoid deep squats (>100° flexion) in injured knees, as posterior shear forces on the PCL, patellofemoral compressive forces, and meniscal/ligamentous stress all increase substantially beyond 100° flexion. 7
Interpretation and Clinical Decision-Making
Indicators of Failed Test (Do Not Progress Activity)
Poor single-leg squat performance correlates with decreased hip abduction strength, decreased hop distance, and lower subjective knee scores, indicating persistent neuromuscular deficits that increase reinjury risk. 6
Knee valgus collapse, excessive hip adduction, and hip internal rotation during squat are associated with higher injury risk and indicate the need for targeted neuromuscular training before return to sport. 5, 6
Inability to control descent or maintain balance suggests inadequate quadriceps, hamstrings, or proprioceptive function requiring continued rehabilitation. 7, 8
Indicators of Passed Test (May Progress Activity)
Symmetrical performance between injured and uninjured legs with proper frontal and sagittal plane alignment, controlled descent and ascent, and no pain or instability during the movement. 5, 8
Adequate hip-to-knee extensor moment ratio (assessed clinically by observing hip flexion angle and forward trunk position) indicates proper load distribution and reduced knee stress. 5
Common Pitfalls to Avoid
Do not use time alone (e.g., 6 months post-injury) as the criterion for return to activity; nearly half of patients demonstrate persistent neuromuscular deficits on single-leg squat testing at 6 months despite following standardized rehabilitation protocols. 6
Do not skip comparison with the contralateral leg, as bilateral deficits are common (45% of poor performers also had poor contralateral performance), which may mask asymmetries if only the injured side is assessed. 6
Do not perform squat testing if the patient cannot flex the knee to 90° or bear weight comfortably, as these indicate ongoing structural issues requiring imaging (MRI if radiographs negative) or specialist evaluation. 1, 2
Recognize that older patients (mean age 33.6 years) are significantly more likely to demonstrate poor squat performance compared to younger patients (mean age 24.2 years), requiring more conservative progression criteria. 6