What This Exercise Does
Passive knee extension uses gravity to gently stretch the back of your knee and restore full straightening (0 degrees of extension). After surgery, swelling and scar tissue can quickly limit extension if not addressed.
- Restores full extension: Prevents the knee from getting "stuck" in a bent position
- Stretches posterior capsule: Lengthens tight structures at the back of the knee
- Prevents gait abnormalities: You need full extension for normal walking mechanics
- Uses gravity: Gentle, sustained stretch without forcing the joint
- Reduces long-term complications: Extension deficit is associated with poor outcomes
Step-by-Step Instructions
Prepare Your Setup
Lie on your back on a firm surface (bed, floor, or treatment table). You'll need a rolled towel or small bolster (about 4-6 inches in diameter) to prop under your ankle.
Position the Prop Under Your Ankle
Place the towel roll or bolster under your ankle (Achilles tendon area), NOT under your knee. Your heel should be elevated off the surface, allowing your knee to hang freely in space.
Important
Never put the prop under your knee. This defeats the purpose and can actually worsen extension loss. The prop goes under the ankle ONLY.
Relax Completely
Let your leg completely relax. Gravity will gently pull your knee down toward the surface. Don't actively push or force it - the key is passive stretching over time.
Add Quad Sets (Optional Enhancement)
While in this position, you can perform quad sets by tightening your thigh muscle and actively pushing the back of your knee down. Hold for 10 seconds, then relax. This combines passive and active extension work.
Hold for Extended Time
Remain in this position for 10-20 minutes per session. You can read, watch TV, or rest during this time. Perform this exercise multiple times daily.
Pro Tip
If you can tolerate it, you can add a small weight (1-2 lbs) on top of your knee for additional gentle pressure. Only do this if recommended by your physical therapist.
Common Mistakes to Avoid
- Putting the prop under the knee: This prevents extension. The prop must be under the ankle only.
- Not holding long enough: Quick stretches don't work. You need sustained time (10-20 minutes) for tissue adaptation.
- Skipping sessions: Extension can be lost quickly in early recovery. This should be done multiple times daily.
- Tensing the leg muscles: You need to fully relax for passive stretching to work. Take deep breaths and let go.
- Waiting too long to start: Begin this exercise on day 0 or 1 post-surgery. Early intervention is key.
- Stopping once you achieve extension: Continue this exercise until you're confident extension is maintained.
Goal: Match Your Other Leg
Your goal is to achieve the same extension as your non-surgical knee. Many people have slight hyperextension (beyond 0 degrees) naturally. Measure your non-surgical leg and aim to match it.
How to Check
Lie flat with both legs extended. The back of both knees should rest equally on the surface. If your surgical knee is elevated, you have an extension deficit that needs work.