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The first thing most patients want to know after ACL surgery is when they will be back. It is an understandable question. It is also, on its own, the wrong one. The right question is what needs to be true before going back - what physical benchmarks, what strength levels, what movement quality, what psychological readiness. The timeline follows from the criteria; the criteria do not follow from the timeline.

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This page provides both: a detailed, phase-by-phase account of what each stage of ACL rehabilitation involves, what needs to be achieved before progressing, and approximately how long each phase takes when things go well. It also explains what delays the timeline, what the biology of graft healing imposes as a genuine floor, and what the most current research from the Aspetar Clinical Practice Guideline, the Isokinetic Medical Group, and the MOON Knee Group shows about modern criteria-based return-to-sport practice.

Why the Timeline Question Is the Wrong Starting Point

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ACL rehabilitation has gone through a striking historical arc. In the early 1990s, the standard timeline was 12 months. In the late 1990s and 2000s, accelerated protocols pushed return to sport to as early as four to six months, driven by improved surgical techniques and more aggressive early rehabilitation. By the 2010s, the evidence had accumulated that early return was dangerous - and the pendulum began swinging back toward longer, criteria-based programmes.

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The Delaware-Oslo data (Grindem et al., BJSM, 2016) provided the most widely cited number: each month of delay up to 9 months reduces reinjury risk by approximately 51%. The same paper found that athletes who returned to Level 1 pivoting sports had a 4.32 times higher reinjury rate than those who did not. A 2020 prospective cohort study by Beischer and colleagues (JOSPT, 2020) - following 159 athletes aged 15-30 years - found that returning to knee-strenuous sport before 9 months was associated with an approximately 7-fold higher rate of second ACL injury compared with those who returned at 9 months or later. The 2025 Aspetar data (Kotsifaki et al., BJSM, 2025) added critical nuance: for athletes who met objective criteria, time to return was not independently associated with reinjury risk. The conclusion is not that 9 months is unnecessary - it is that 9 months without meeting criteria is not sufficient, and criteria without adequate time may not be either. Both matter.

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The gap between what the evidence demands and what actually happens in practice remains significant. A 2025 nationwide study by Kooy, Grindem and colleagues (JOSPT Open, 2025) - drawing on 1,875 patients registered in the Norwegian Knee Ligament Register - found that physiotherapist-led rehabilitation ceased before 9 months in 52% of patients, and only 55% underwent any physical testing before returning to sport. The criteria that exist to protect athletes are not being applied consistently in standard care. This is the context in which Atherapy's criteria-based approach operates - not as a bureaucratic process, but as the evidence-based standard that most patients are currently not receiving.

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"The calendar tells you the minimum. The criteria tell you whether you are ready. You need both."

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The Biology That Sets the Floor

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Regardless of how well a patient performs in the gym or on the pitch, the biology of graft healing imposes a genuine time floor that no amount of rehabilitation can accelerate. After ACL reconstruction, the transplanted tendon graft undergoes a process called ligamentisation - a staged biological transformation from tendon tissue into something that functionally resembles a native ligament. This process takes time, and critically, the graft passes through its weakest period between approximately 6 and 12 weeks post-operatively.

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The ligamentisation timeline is now well-characterised in the literature. The graft undergoes initial avascular necrosis in the first few weeks as the original tendon cells die. Revascularisation and cellular repopulation follow between approximately weeks 4 and 12. The remodelling phase - during which the graft progressively acquires ligament-like mechanical properties - extends from approximately 3 months to 12 months or beyond. Two histological studies have confirmed that the graft does not appear similar to a normal ACL under light microscopy until 24 months post-operatively, with no further material changes observed after that point.

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The clinical implication is direct: a patient who achieves 90% quadriceps limb symmetry at 6 months post-operatively has a strong knee in terms of muscle strength, but may have a graft that has not completed its remodelling process. This is the argument for using 9 months as a minimum guideline for high-demand pivoting sports - not because criteria will not be met earlier, but because the biology of the graft provides a genuine reason for caution even when physical testing passes.

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Timeline at a Glance

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The table below summarises the five rehabilitation phases, their primary goals, key exercises, and progression criteria. Every criterion in this table takes precedence over the associated time range.

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Phase 1: Acute Recovery and Protection (Weeks 0-2)

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The first two weeks after surgery are not a passive recovery period - they are the most consequential two weeks of the entire rehabilitation timeline. The decisions made in this phase about swelling management, extension restoration, and early quadriceps activation directly determine the trajectory of everything that follows. A patient who emerges from week two with full passive extension, minimal effusion, and an active straight leg raise is in an entirely different position from one who has not achieved these benchmarks.

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Phase 1 Goals and Progression Criteria

Primary goal 1 - Full passive extension: This is the single most important early milestone. A knee that develops a fixed flexion deformity in the first two weeks creates downstream patellofemoral problems that are difficult to reverse. Prone hangs, heel props, and active-assisted extension work are non-negotiable from day one.

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Primary goal 2 - Effusion management: Arthrogenic muscle inhibition from joint swelling prevents quadriceps from contracting effectively regardless of effort. Cold-compression therapy (Game Ready), elevation, and avoidance of provocative loading protect the rehabilitation environment. See the Swelling Management page.

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Primary goal 3 - Quadriceps activation: Straight leg raises, terminal knee extensions (TKEs), and isometric quadriceps contractions begin immediately. The neural drive to the quadriceps must be re-established before any loaded exercise is possible. BFR from week 1 can meaningfully augment the early activation stimulus.

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Progression criteria before Phase 2: Full passive extension equal to contralateral. Effusion below trace on modified stroke test. Straight leg raise without extension lag. Comfortable weight-bearing with or without crutches as per surgeon protocol.

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Phase 2: Mobility and Foundational Strength (Weeks 2-6)

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By week two - if Phase 1 criteria have been met - the focus shifts toward restoring a normal gait pattern and building the foundational strength that will support the heavier loading of Phase 3. Range of motion should progress toward full flexion during this phase, and closed kinetic chain loading begins in earnest. The stationary bike, introduced from Phase 1 when adequate flexion allows it, becomes a primary cardiovascular and range of motion tool.

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Phase 2 Goals and Progression Criteria

Gait normalisation: Walking without limp or crutches on flat ground. This is both a functional milestone and a neuromuscular one - normal gait requires appropriate quadriceps activation, hip extension, and ankle mobility. Abnormal gait patterns that persist beyond week four reinforce compensatory movement strategies that become harder to undo later.

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Range of motion: Flexion should reach 115-120 degrees by the end of Phase 2 in most patients. Wall slides (0-60 degrees) progress to full range wall slides, heel slides, and bike-assisted flexion mobilisation. Flexion should be worked toward actively - passive stiffness resolves with loading, not just stretching.

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Foundational CKC loading: Mini squats, step-ups, leg press in a protected range, hip abductor and external rotator strengthening. The leg press is a cornerstone here - it allows meaningful quad and hamstring loading without the full compressive demands of deeper squatting. Bilateral before unilateral.

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Progression criteria before Phase 3: Walk without limp on all surfaces. Flexion 115-120 degrees. No effusion after gym sessions. Quadriceps able to maintain full extension under progressive load during straight leg raise.

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Phase 3: Heavy Strengthening (Weeks 6-16)

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Phase 3 is the longest and most physically demanding of the rehabilitation phases - and the one most commonly executed inadequately. This is where the difference between patients who achieve 90% limb symmetry and those who plateau at 70% is made. The objective is progressive overload toward the strength thresholds that protect the knee at return to sport, not maintenance exercise.

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The graft is in its ligamentisation phase during this period - biologically remodelling but not yet at full mechanical maturity. This is not a reason to avoid heavy loading; it is a reason to load progressively and systematically. The muscles around the graft provide the mechanical protection that the graft biology cannot yet provide fully on its own.

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Phase 3 Goals and Progression Criteria

Heavy CKC loading: Bulgarian split squat, rear-foot elevated split squat, barbell squat, trap bar deadlift, single-leg press at progressively increasing load. 75-85% 1RM is the working range by the end of this phase. Under-loading is the most common error - maintenance exercise does not drive the adaptations required.

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OKC introduction: Leg extension in restricted range (90-45 degrees) from weeks 4-8 for BPTB and QT grafts; delayed to week 12 for hamstring grafts. The 2025 scoping review (Forelli et al.) confirms OKC is safe when introduced per criteria - and essential for quadriceps recovery. Full range OKC follows once restricted range is well-tolerated.

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Hamstring loading: Nordic hamstring curls, Romanian deadlifts, single-leg hip hinges. For hamstring graft patients, the harvested tendons require progressive loading throughout this phase and beyond. The hamstring-to-quadriceps strength ratio is a return-to-sport criterion independent of absolute strength.

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Hip and core: Hip thrust, hip abduction under load, Copenhagen plank, Pallof press. Hip external rotation and abduction strength directly governs knee valgus during dynamic tasks. The Burnham protocol requires above 90% hip symmetry before hop testing begins.

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Progression criteria before Phase 4: Quadriceps LSI above 70-80% (MOON Phase 3 entry criterion). Single-leg squat to 90 degrees without valgus collapse. No post-session effusion. Flexion full and pain-free.

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Phase 4: Impact and Sport Preparation (Months 4-6)

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Running and plyometric loading are introduced in Phase 4, but only once the strength criteria from Phase 3 have been achieved. The return-to-running page in this series covers the criteria-based running progression in detail. The key principle here is that running is a plyometric activity - every stride involves single-leg landing and force absorption - and the knee must be able to absorb those forces before the cardiovascular and skill demands of sport are added on top.

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Phase 4 Goals and Progression Criteria

Running progression: Straight-line jogging begins when quadriceps LSI reaches 80% or above. Walking-to-running intervals, timed runs, progressive speed. Running mechanics assessment identifies compensatory movement patterns before they are reinforced at speed.

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Bilateral plyometrics: Double-leg box jumps, broad jumps, lateral hops. Focus entirely on landing mechanics: soft, hip-dominant, symmetric, quiet. Poor landing quality at bilateral level must be resolved before unilateral plyometrics begin.

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Deceleration training: E3 Rehab 5-step deceleration model - forward lunge, lunge with step back, step and land, step and land with step back, running with step back. Deceleration is the most quadriceps-demanding and ACL-loading movement in sport and must be trained explicitly.

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Progression criteria before Phase 5: Quad LSI above 80%. Straight-line running with normal mechanics. Bilateral plyometrics symmetrical and well-controlled. Cardiovascular base supporting 60+ minutes of moderate-intensity activity.

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Phase 5: On-Field Rehabilitation and Return to Competition (Months 6-12+)

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Phase 5 is where the gap between looking fit in a gym and being ready for competitive sport is bridged. On-field rehabilitation (OFR) - the structured progressive return to sport-specific environments - was systematised by Buckthorpe, Della Villa and colleagues at the Isokinetic Medical Group in the JOSPT 2019 framework. The 2025 Isokinetic GPS study (Picinini, Della Villa, Buckthorpe et al., Orthopaedic Journal of Sports Medicine) validated this approach in 100 consecutive male soccer players, demonstrating a high return-to-competition rate when OFR stages were completed according to criteria.

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The OFR framework progresses through five stages: linear movement, multidirectional movement, sport-specific technical skills, sport-specific movement patterns, and modified practice simulation. GPS and heart rate tracking are used throughout to compare the athlete's deceleration forces, high-speed running volumes, and cutting mechanics against their pre-injury baseline data - allowing the clinician to confirm that on-field physiological demands are matching those of competitive play before the athlete is returned to it. The Della Villa and Buckthorpe KSSTA 2026 study of 401 consecutive football players confirmed that OFR participation was independently associated with improved return-to-competition rates and reduced reinjury risk.

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Phase 5 Goals and Progression Criteria

Unilateral plyometrics: Single-leg hops for distance, depth drops to single-leg landing, lateral single-leg bounds. The most demanding gym-based exercises before return to competitive exposure.

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OFR stage progression: 5-stage framework (linear to modified practice). GPS tracking of deceleration forces, high-speed running volume, and cutting mechanics confirms on-field load matches competitive demands. Non-contact training integration before full contact.

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Neurocognitive challenge: Dual-task exercises integrating cognitive and physical demands simultaneously (Wilk, Ivey et al., IJSPT 2024). Reactive agility under unpredictable cues. External focus of attention cuing. Return-to-sport testing should include neurocognitive components (Grooms et al., JOSPT, 2023).

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Clearance criteria: Quad LSI 90%+. Hop tests (single-leg hop for distance, triple hop, crossover hop) all 90%+. Force plate RSI within 85% of contralateral. ACL-RSI score above 65. Minimum 9 months from surgery for high-demand pivoting sport. All OFR stages complete. Surgeon clearance received.

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The Graft-Specific Timeline

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Different graft types create different rehabilitation timelines, primarily through their effects on donor site morbidity and the timing of OKC introduction. The table below summarises the key graft-specific differences. Full detail is available on the Graft Choice page.

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Patellar Tendon / BPTB: OKC in restricted range from weeks 4-8. Anterior knee pain and kneeling discomfort are the primary donor site morbidity concerns and require active management throughout rehabilitation and after return. Sustained quadriceps conditioning post-return is particularly important for BPTB patients given the extensor mechanism involvement in the harvest site.

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Hamstring Tendon: OKC typically delayed to week 12. Knee flexion deficit up to 50% at 4 weeks - early targeted hamstring loading mandatory from week 1. Harvested tendons require progressive loading throughout Phase 3 and 4.

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Quadriceps Tendon: OKC from weeks 4-8. Harvest site tendinopathy requires progressive extensor mechanism loading (tendinopathy management principles apply). Greatest early quad strength deficit of the three options at 7 months (Holmgren et al., AJSM, 2024) - extensor mechanism work prioritised from first weeks.

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With LET augmentation: More conservative early ROM and weight-bearing. IT band harvest site adds a second donor site requirement. Surgeon protocol takes precedence over standard progressions.

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What Delays the Timeline

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Understanding what causes timelines to extend beyond the expected range helps patients and clinicians plan and respond appropriately. The most common causes of delayed progression are:

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Persistent effusion: Joint swelling inhibits quadriceps activation through arthrogenic muscle inhibition. A knee that remains swollen cannot build strength effectively, regardless of loading. Swelling management is a prerequisite, not a parallel track.

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Extension deficit: Failure to achieve full passive extension in Phase 1 creates a downstream problem that delays every subsequent phase. Patellofemoral pain, altered gait, and quadriceps inhibition all follow from fixed flexion deformity.

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Concurrent meniscal repair: Weight-bearing restrictions of 4-6 weeks for complex repairs delay Phase 2 and Phase 3 progression. The meniscal repair protocol governs over the ACL protocol. Combined timelines for complex concurrent repairs can extend to 12-18 months for high-demand sport return.

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Inadequate rehabilitation programme: Under-loading, avoidance of OKC, insufficient hamstring work, and time-based rather than criteria-based progression all produce patients who reach the nominal end date without having met the performance criteria. The programme is the variable, not just the biology.

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Psychological barriers: Kinesiophobia producing compensatory movement patterns, or overconfidence producing premature return without criteria met, both extend the safe timeline. ACL-RSI tracking from Phase 1 onwards allows early identification and intervention.

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What Accelerates the Timeline

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Within the biological floor set by ligamentisation, several factors genuinely accelerate progression through criteria and toward safe return:

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Prehabilitation: Patients who complete structured prehabilitation before surgery - achieving good strength, normal gait, and full range of motion pre-operatively - progress through Phases 1 and 2 faster. Pre-operative quadriceps strength is a strong predictor of post-operative strength trajectory: patients who are stronger before surgery recover faster after it. The prehabilitation page in this series covers this evidence in detail.

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High-quality, well-supervised rehabilitation: A programme that loads appropriately, introduces OKC at the right time, addresses hamstring and hip deficits systematically, and tracks strength objectively produces faster criteria achievement than a generic or under-supervised programme.

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BFR training: Blood flow restriction training from the first post-operative week maintains the anabolic stimulus during loading-restricted phases, attenuating early atrophy and preserving a stronger starting point for Phase 2 and 3 loading.

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Patient adherence and compliance: The single most variable factor in ACL rehabilitation timelines is how consistently and diligently the patient executes their home programme between supervised sessions. Programme quality and patient adherence are both required.

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What Timelines Look Like at Atherapy

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At Atherapy, ACL rehabilitation timelines are individualised from the first session. Graft type, concurrent procedures, prehabilitation status, age, sport, and reinjury risk profile all shape the specific progression plan for each patient. The phase structure described on this page provides the framework; the criteria govern the rate of progression through it.

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Strength testing using VALD DynaMo handheld dynamometry is performed at regular intervals throughout rehabilitation - not only at the return-to-sport assessment - providing an objective trajectory rather than a single late-stage snapshot. For patients approaching the OFR phase, GPS-assisted on-field load monitoring allows the clinical team to confirm that sport-specific physical demands are being met before full training integration. For the comprehensive return-to-sport decision, VALD ForceDecks force plate assessment is incorporated alongside the Aspetar-standard hop testing battery and ACL-RSI psychological readiness evaluation.

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Patients are given honest, specific timelines at the outset: what the expected duration of each phase is, what will determine whether they progress faster or slower, and what the full range of return-to-sport timelines looks like given their specific injury and procedure. There is no generic 9-month promise - only a commitment to getting the criteria right.

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Related Pages in the ACL Rehabilitation Series

→ Post-Operative ACL Rehabilitation

→ Quadriceps Weakness After ACL Injury

→ Return to Running After ACL Surgery

→ Gym-Based ACL Rehabilitation

→ Return to Sport Testing

→ Force PlateTesting

→ Reinjury Risk After ACL Surgery

→ Psychological Recovery After ACL Injury

→ Graft Choice Considerations

→ Football-Specific ACL Rehabilitation

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Understanding Your ACL Rehabilitation Timeline - Atherapy

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If you are at any stage of ACL rehabilitation and want an objective assessment of where you are against criteria, how long the remaining phases are likely to take, and what is needed to get you back to competitive sport safely, Atherapy offers comprehensive ACL rehabilitation assessment at Moorgate, Strand, and Chiswick. Bring your operative notes and your questions.

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Book at your nearest clinic: Moorgate | Strand | Chiswick

References

• Kotsifaki R, Korakakis V, King E, et al. Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction. British Journal of Sports Medicine. 2023;57(9):500-514.
• Kotsifaki R, King E, Bahr R, Whiteley R. Is 9 months the sweet spot for male athletes to return to sport after anterior cruciate ligament reconstruction? British Journal of Sports Medicine. 2025;59(9):667-675.
• Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. British Journal of Sports Medicine. 2016;50(13):804-808.
• Girdwood M, Culvenor AG, Rio EK, Patterson BE, et al. Tale of quadriceps and hamstring muscle strength after ACL reconstruction: a systematic review with longitudinal and multivariate meta-analysis. British Journal of Sports Medicine. 2025;59(6):423-434.
• Picinini F, Della Villa F, Tallent J, Patterson SD, et al. High return to competition rate after on-field rehabilitation in competitive male soccer players after ACL reconstruction: GPS tracking in 100 consecutive cases. Orthopaedic Journal of Sports Medicine. 2025. doi:10.1177/23259671251320093.
• Della Villa F, Buckthorpe M, Galassi L, et al. The impact of on-field rehabilitation on return to play and ACL re-injury risk after ACL reconstruction in football (soccer) players: a study on 401 consecutive cases. Knee Surgery, Sports Traumatology, Arthroscopy. 2026. doi:10.1002/ksa.70392.
• Buckthorpe M, Della Villa F, Della Villa S, Roi GS. On-field rehabilitation part 2: a 5-stage program for the soccer player. Journal of Orthopaedic and Sports Physical Therapy. 2019;49(11):570-575.
• Holmgren D, Noory S, Mostrom E, et al. Weaker quadriceps muscle strength with quadriceps tendon graft compared with patellar or hamstring tendon graft at 7 months after anterior cruciate ligament reconstruction. American Journal of Sports Medicine. 2024;52(1):69-76.
• Forelli F, Barbar W, Kersante G, et al. Criteria-based decision making for introducing open kinetic chain exercise after ACL reconstruction: a scoping review. Sports Medicine - Open. 2025.
• Kooy CEW, Grindem H, Brinchmann-Hansen A, et al. Rehabilitation, decision making, and return to pivoting sports in athletes 1-3 years after ACL reconstruction: a nationwide study. JOSPT Open. 2025;3(1):45-58. doi:10.2519/josptopen.2024.0087.
• Beischer S, Gustavsson L, Senorski EH, et al. Young athletes who return to sport before 9 months after anterior cruciate ligament reconstruction have a rate of new injury 7 times that of those who delay return. Journal of Orthopaedic and Sports Physical Therapy. 2020;50(2):83-90. doi:10.2519/jospt.2020.9071.
• Grooms DR, Chaput M, Simon JE, Criss CR, Myer GD, Diekfuss JA. Combining neurocognitive and functional tests to improve return-to-sport decisions following ACL reconstruction. Journal of Orthopaedic and Sports Physical Therapy. 2023;53(8):415-419.