ACL Rehab Protocol: Evidence-Based Phases and Criteria

Phase 1 - Protection and early motion (0–2 weeks post-op)

Goals: restore full passive extension, control swelling, regain active quadriceps activation, and protect the graft. Loss of terminal extension early is a strong predictor of long-term functional limitation, so prioritise it from day one.

• Daily passive extension work (heel props, prone hangs).
• Quadriceps activation: isometric quad sets, straight leg raise without lag.
• Patellar mobilisations to maintain glide.
• Cryotherapy and elevation for effusion control.
• Weight-bearing as tolerated per surgeon protocol.

Phase 2 - Strength and neuromuscular control (2–12 weeks)

Goals: restore full active range, build quadriceps and hip strength, and re-establish single-leg control. Closed-chain exercise is well tolerated; carefully introduced open-chain quadriceps work from around week 4 (BPTB) or week 6 (hamstring graft) accelerates strength recovery without compromising the graft.

• Bilateral then unilateral leg press, squats, step-ups.
• Hip abductor and external rotator strengthening (hip drives knee mechanics).
• Open-chain knee extension within graft-appropriate range.
• Stationary cycling, then elliptical.
• Begin proprioceptive training: balance board, single-leg stance progressions.

Phase 3 - Running and plyometrics (12 weeks onward)

Running should be a milestone, not a date. Common entry criteria: at least 70% quadriceps strength symmetry (limb symmetry index, LSI), pain-free squat, and no effusion with single-leg hop attempts. Begin with straight-line running and progress to change-of-direction work only when basic plyometrics are well controlled.

• Double-leg jumps → single-leg hops → bounding.
• Linear running progression (treadmill or track).
• Continue heavy resistance training - strength gains plateau without it.

Phase 4 - Return-to-sport criteria (typically 9–12 months)

Returning to cutting and pivoting sport before 9 months is associated with substantially higher re-injury risk. Use a battery of tests rather than a single hop to gate return.

• Quadriceps and hamstring strength LSI ≥90%.
• Single-leg hop test battery LSI ≥90% (single, triple, crossover, 6m timed).
• Y-balance or similar dynamic balance LSI ≥90%.
• Movement quality on drop-jump (no dynamic valgus, controlled landing).
• Sport-specific drills completed without symptoms or compensations.
• Patient-reported confidence (ACL-RSI) above the published threshold for the patient's sport.

Pitfalls to avoid

The most common rehab failures are: under-loading the quadriceps in mid-phase, returning to sport on time alone, neglecting psychological readiness, and stopping strength work once running has resumed. Address all four explicitly with every patient.

Key takeaways

• ACL rehab is criterion-based, not time-based.
• Restore full extension immediately - losing it is a long-term problem.
• Open-chain quad work, introduced carefully, accelerates strength recovery.
• Use a test battery (strength + hops + dynamic balance + ACL-RSI) to gate return-to-sport.
• Returning before 9 months substantially raises re-injury risk.

Frequently asked questions

When can a patient start running after ACL reconstruction?

Running is a milestone, not a date. Typical entry criteria are quadriceps strength LSI ≥70%, pain-free squat, no effusion, and competent single-leg hop control. Most patients reach this between 12 and 16 weeks, but it varies.

Is open-chain knee extension safe after ACL reconstruction?

Yes, when introduced at the right time and within graft-appropriate ranges. Current evidence shows open-chain quadriceps work from around week 4 (BPTB graft) or week 6 (hamstring graft) accelerates strength recovery without compromising graft integrity.

What is a safe return-to-sport timeline?

Return to cutting and pivoting sport before 9 months is associated with substantially higher re-injury rates. Most patients should be gated to 9–12 months, contingent on passing a return-to-sport battery - not on the calendar alone.