Knee Joint Assessment Essentials: ROM, Effusion Checks, Strength, and Functional Tests

Purpose and clinical priorities for a knee screen

This knee assessment sequence integrates observation, motion, effusion screening, strength, and simple function to quickly sort common impairment patterns. Three interpretation rules guide decision-making throughout: (1) extension loss is a priority finding because it strongly affects gait and loading tolerance; (2) effusion can inhibit quadriceps, so unexpected weakness may reflect swelling-related inhibition rather than true strength loss; (3) comparing pain with resisted extension versus pain with compression-based function helps categorize the likely driver (contractile/extensor mechanism vs load/compression intolerance).

1) Observation: swelling, alignment, quadriceps tone, and gait deviations

Step-by-step observation (standing and walking)

• Expose and compare both knees from mid-thigh to mid-calf. Look for asymmetry around the suprapatellar pouch, medial/lateral joint lines, and infrapatellar region.
• Swelling cues: loss of normal contours (patellar borders less distinct), fullness above the patella, shiny skin, or a “puffy” medial/lateral gutter.
• Alignment cues (static): note varus/valgus posture, tibial rotation, and foot position. Record what you see rather than labeling it as “bad.”
• Quadriceps tone/activation: compare vastus medialis and overall quad bulk. A visibly “quiet” quad on one side can accompany effusion or pain.
• Gait deviations (short walk): watch for reduced knee extension in stance (slight persistent bend), reduced knee flexion in swing, shortened stance time, or avoidance of loading on the involved side.

Quick interpretation notes

• Persistent knee flexion during stance often correlates with extension loss, effusion, or pain avoidance.
• Visible swelling + reduced quad tone raises suspicion for effusion-linked inhibition; plan to interpret strength findings accordingly.

2) AROM and PROM: flexion/extension with pain location and end-range notes

Use AROM first to see what the patient can do actively, then PROM to clarify whether limitation is due to pain, stiffness, or guarding. Document side-to-side differences, pain location, and what happens at end range (e.g., “tight,” “blocked,” “painful,” “springy”).

AROM: step-by-step

• Knee flexion AROM: supine or sitting. Ask the patient to slide the heel toward the buttock. Note range, pain location (anterior, medial joint line, posterior), and whether motion is smooth.
• Knee extension AROM: supine with heel supported (towel roll under heel) so the knee can fully straighten. Ask for “push the knee down/straighten fully.” Compare to the other side for any extension lag.

PROM: step-by-step

• Flexion PROM: supine. Support the heel and guide the knee into flexion. Keep the hip relaxed. Note if flexion stops due to anterior compression discomfort, posterior tightness, or a firm “block.”
• Extension PROM: supine with heel supported. Gently lift under the distal tibia to encourage extension, or apply light pressure above the knee while the heel stays supported. Note if full extension is reached and whether end range feels limited by tightness, guarding, or pain.

What to record (simple template)

Interpretation rules for ROM findings

• Extension loss priority: even a small side-to-side extension deficit can drive limping, increased patellofemoral load, and fatigue. If extension is limited, treat it as a key impairment to address and re-check after swelling management or gentle mobility.
• Flexion limited with a “full” or “boggy” feel may suggest effusion affecting capsular mechanics; correlate with effusion screen.
• Pain location matters: anterior pain at end-range flexion can align with compression sensitivity; posterior discomfort may reflect soft-tissue tightness or guarding; joint-line pain may suggest load sensitivity at the tibiofemoral joint (interpret within the full exam).

3) Beginner-friendly effusion screening and how effusion changes ROM feel

Effusion screening at the knee can be kept simple: compare visually, then use a gentle sweep concept to see whether fluid shifts. Your goal is not to “grade” precisely but to decide whether swelling is present enough to influence motion and strength.

A) Visual sweep comparisons (standing and supine)

• Standing: compare the suprapatellar area and medial/lateral gutters. Look for loss of patellar definition.
• Supine with knee relaxed: compare both knees again. Effusion may be more obvious when the quadriceps relaxes.

B) Simple stroke/sweep concept (modified for beginners)

Use gentle pressure; avoid aggressive “milking.” The concept: move potential fluid from one area to another and observe whether it returns.

• Position: patient supine, knee relaxed in slight flexion (a small towel under the knee can help relaxation).
• Step 1 (clear the medial side): with the palm/fingers, sweep upward along the medial aspect of the knee toward the suprapatellar pouch 2–3 times using light pressure.
• Step 2 (observe): pause and look at the medial gutter for refilling/fullness.
• Step 3 (lateral-to-medial sweep): gently sweep from lateral to medial across the front of the knee once and watch for a visible fluid wave or renewed medial fullness.

Positive beginner-level indicator: you see a visible shift or refilling/fullness after the sweep, or the involved knee consistently looks “puffier” than the other side in the same position.

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How effusion alters ROM feel and performance

• ROM feel: effusion often creates a boggy, springy resistance near end range, especially in flexion, and may make extension feel “not settling” into the last degrees.
• Quadriceps inhibition: even mild effusion can reduce quadriceps activation. If you find weakness that seems disproportionate to the patient’s size/effort, re-check for swelling and consider that strength may improve as effusion reduces.

4) Strength testing: quadriceps and hamstrings with safe leverage

Use positions that minimize joint irritation and avoid excessive leverage. Compare sides and note pain location and quality. If effusion is present, interpret quadriceps findings cautiously.

Quadriceps (knee extension) strength: step-by-step

• Position: seated with hips and knees at ~90°. Ensure the patient is stable (hands on table, upright posture).
• Hand placement (safe leverage): apply resistance at the distal tibia just above the ankle (not on the foot) to avoid twisting forces.
• Instruction: “Straighten your knee and hold. Don’t let me move you.” Build resistance gradually over 2–3 seconds.
• What to note: strength symmetry, ability to hold, and pain during resisted extension (anterior knee, patellar tendon region, or diffuse).

Hamstrings (knee flexion) strength: step-by-step

• Position option 1 (seated): knee at ~90°. Ask the patient to pull the heel back (flex the knee) against your resistance.
• Position option 2 (prone if comfortable): knee flexed to ~45–90°, resist at distal tibia.
• Hand placement: resist just above the ankle; stabilize the thigh to prevent hip rotation.
• What to note: posterior thigh/knee pain, cramping, or weakness compared to the other side.

Interpretation rules for strength findings

• Effusion-linked inhibition: if effusion indicators are present and quadriceps strength is reduced without clear pain reproduction, consider inhibition as a primary contributor.
• Pain during resisted extension: suggests a contractile/extensor mechanism sensitivity (quadriceps tendon/patellar tendon/patellofemoral loading with active extension). Pair this with functional findings to refine the category.

5) Simple functional tests: squat-to-chair, step-down tolerance, timed sit-to-stand

Functional tests show how the knee tolerates load, compression, and control demands. Choose tests that match the patient’s irritability and balance. Stop if pain escalates sharply, the knee feels unstable, or form deteriorates significantly.

A) Squat-to-chair (controlled sit and stand)

• Setup: use a chair of standard height. Feet hip-width, toes forward or slightly out.
• Task: “Reach your hips back, lightly touch the chair, then stand back up.”
• Observe: knee collapse inward/outward, trunk shift, unequal weight-bearing, depth tolerance, and pain location (anterior vs joint line vs diffuse).
• Interpretation: pain primarily with the compressive portion (deeper squat, chair touch) supports compression/load intolerance; difficulty rising with minimal depth may align more with extensor weakness/inhibition.

B) Step-down tolerance (low step)

• Setup: start with a low step (e.g., 10–15 cm). Use a hand support nearby for safety.
• Task: stand on the test leg, slowly lower the opposite heel toward the floor, then return up.
• Observe: control of knee position, pelvic drop, trunk lean, and whether pain appears during lowering (eccentric demand) or at the bottom (compression).
• Interpretation: pain during controlled lowering can reflect load tolerance issues and/or quadriceps inhibition; marked wobble with minimal pain may indicate motor control deficit rather than pure strength loss.

C) Timed sit-to-stand (when appropriate)

• When to use: useful for general functional capacity and tracking change over time, especially when single-leg tasks are too challenging.
• Setup: standard chair, arms crossed if safe; allow hands if needed and document the modification.
• Task options: 5x sit-to-stand (time to complete 5 reps) or 30-second sit-to-stand (count reps). Keep instructions consistent between sessions.
• Observe: symmetry of push-off, need to rock forward, pain behavior, and whether speed drops due to discomfort or fatigue.

Putting it together: quick interpretation map during the sequence

• If extension is limited: prioritize documenting the deficit, observe its effect on gait, and consider that effusion/guarding may be contributing. Re-check extension after any swelling-calming strategies or gentle mobility.
• If effusion indicators are present + quad weakness: interpret quadriceps strength as potentially inhibited; expect functional tasks to feel “heavy” or unstable even without high pain.
• If pain is reproduced mainly with resisted extension: categorize as more contractile/extensor mechanism sensitivity (then compare with squat/step-down to see if compression also provokes symptoms).
• If pain is reproduced mainly with compression-based function (squat depth, step-down bottom position): categorize as more load/compression intolerance; correlate with ROM pain location and any effusion signs.