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What Happens During ACL Reconstruction?

The anterior cruciate ligament (ACL) is one of the four main ligaments of the knee, responsible for rotational stability and preventing the tibia from sliding forward under the femur. An ACL tear — most commonly identified by a loud popping sound followed by immediate pain, swelling, and the knee giving way — almost always requires surgical reconstruction for patients who wish to return to sport or physically demanding activity. The surgery replaces the torn ligament with a graft, typically taken from the patellar tendon, hamstring tendon, or a cadaver. The graft is secured in place and undergoes a biological process called ligamentisation — gradually maturing and strengthening to function like a native ACL. This process takes 9–12 months, which is why ACL recovery cannot be rushed.

The First Two Weeks — Managing Swelling and Restoring Basic Movement

The immediate post-operative period focuses on controlling swelling, managing pain, and beginning gentle movement to prevent stiffness and muscle wasting. Physiotherapy begins within 24–48 hours of surgery.

• Ice, compression, and elevation to control post-surgical swelling — applied regularly throughout the day
• Quadriceps activation exercises (quad sets) to prevent the muscle shutdown that occurs rapidly after knee surgery
• Straight leg raises to maintain muscle strength without stressing the graft
• Gentle heel slides and range of motion exercises to begin restoring knee flexion
• Walking with crutches — weight-bearing as tolerated based on surgeon’s protocol

Weeks 2–6 — Progressive Loading and Range of Motion

As swelling reduces and the wound heals, rehabilitation progresses toward restoring full range of motion and beginning strength work. Most patients transition from crutches to full weight-bearing during this phase.

• Full range of motion restoration — targeting 0–120° flexion by week 6 in most protocols
• Closed kinetic chain exercises: mini-squats, leg press, step-ups — building quadriceps strength safely
• Stationary cycling for cardiovascular fitness and range of motion simultaneously
• Scar tissue mobilisation to prevent adhesions from limiting long-term movement
• Hydrotherapy exercises — walking and gentle movements in water to begin functional loading with reduced joint stress

Months 2–4 — Building Strength and Neuromuscular Control

This phase is critical for preventing re-injury. The graft is present but not yet mature — the knee has strength but lacks the neuromuscular control needed for dynamic movements. Balance and proprioception training is introduced.

• Progressive leg press and squat strengthening — moving toward symmetrical quad strength between both legs
• Single-leg exercises: single-leg squats, step-downs — building the unilateral strength and control needed for sport
• Proprioceptive training: wobble board, balance disc — restoring the joint position sense lost after ACL injury
• Running reintroduction — typically from month 3–4 depending on strength criteria: straight-line jogging at low speed on flat surfaces
• Hamstring and hip strengthening — the secondary stabilisers that protect the ACL graft from overload

Months 4–9 — Sport-Specific Training and Return to Performance

Return to sport is a gradual, criteria-based process — not a date on the calendar. Your physiotherapist will assess objective criteria before clearing you for each stage of progression.

• Agility and change of direction drills — introduced progressively as strength and confidence build
• Plyometric training: jumping, landing mechanics — essential for the dynamic control needed in sport
• Sport-specific drills: passing, kicking, lateral movements — dependent on your specific sport
• Psychological readiness: fear of re-injury is common and important to address — your physiotherapist and team will support this
• Return-to-sport clearance criteria: typically >90% limb symmetry on strength testing + functional movement screening + psychological readiness

When is it Safe to Return to Sport?

The most common cause of ACL re-injury is premature return to sport — before the graft has fully matured and before neuromuscular control has been fully restored. The current evidence-based recommendation is a minimum of 9 months post-surgery before returning to contact or pivoting sport.

• Quadriceps symmetry >90% compared to the uninjured leg on strength testing
• Full range of motion equal to the uninjured knee
• Successful completion of functional movement and jump-landing assessments
• Psychological readiness — confidence to return without protective guarding
• Surgeon and physiotherapist clearance based on clinical assessment

ACL recovery demands patience, consistency, and expert guidance. With the right rehabilitation programme — started early and progressed correctly — the vast majority of patients return to full sport at their pre-injury level or higher.