A clinical review based on the most recent meta-analyses and international consensus statements: Aspetar 2023, Panther Symposium 2021, Piussi 2024, Paterno 2022, Gopinatth 2025, Li 2025, van Melick 2025.

How is this injury defined, who is affected and what are the risk factors?

Rupture of the anterior cruciate ligament (ACL) is one of the most common and most disabling knee ligament injuries, particularly in young, active people.¹ It most often occurs without direct contact, during deceleration, changes of direction or a poorly controlled landing.² The sports most at risk are football, basketball, handball and alpine skiing.

The meta-analysis by Montalvo et al. 2019 (58 studies, BJSM)¹ establishes that the risk of ACL rupture in women is on average 1.7 times higher than in men (IRR 1.7; 95% CI 1.4-2.2), and that the proportion of female athletes injured is 1.5 times higher (RR 1.5; 95% CI 1.2-1.9). The gap is widest at amateur level (IRR 2.1; 95% CI 1.3-3.4); the meta-analysis gives no sport-specific estimates.

The risk factors are multifactorial and fall into two categories:

• Intrinsic :
  • Anatomical : narrow intercondylar notch, increased posterior tibial slope, wider Q angle.
  • Hormonal : oestrogen fluctuations that may modulate ligament laxity (weak evidence).
  • Neuromuscular : quadriceps/hamstring dominance, dynamic knee valgus on landing, deficient trunk control, modifiable factors through preventive training.¹²
• Extrinsic : type of footwear, playing surface, weather conditions.

In young athletes (<25 years) returning to pivoting or contact sports, the Wiggins 2016 meta-analysis documents a cumulative incidence of 23% second ACL injury (same side or opposite side).¹³ The Piussi 2024 meta-analysis (21 recent studies) updates that figure to a pooled incidence of 16.9% (CI 12.8-21.6%).¹⁴

What happens in the body and how does the graft evolve?

After reconstruction, the graft (autograft, patellar tendon or hamstrings, or allograft) does not immediately become a functional ligament. It undergoes a long biological process called « ligamentisation ».

The review of human biopsy studies by Claes et al. 2011 (AJSM)² shows that the graft remains viable throughout the process, with no agreement on the timing of the phases; the graft never entirely reproduces the histological and biomechanical properties of the native ACL (Janssen and Scheffler 2014).¹⁷ Animal and human studies describe three phases; the drop in mechanical strength is documented in animals:

1. Avascular necrosis (0-4 weeks) : central necrosis and hypocellularity of the graft, partial in humans (never more than 30% of biopsies); the graft becomes an unvascularised collagen scaffold.
2. Revascularisation (4-12 weeks) : invasion by fibroblasts and neovascularisation. Point of maximum mechanical weakness, at around 6 to 8 weeks in animal models.
3. Remodelling (3 months to 4 years) : progressive maturation of the collagen. The structure never regains its native organisation. Biomechanical maturation continues until 24-48 months (and beyond in some patients).

Beyond this local biology, the rupture and the surgery induce lasting neurocognitive disturbances . The loss of ligament mechanoreceptors leads to deafferentation and central reorganisation of motor control, documented on functional imaging.¹⁵ As a result, the following are commonly seen after surgery:

• Marked atrophy and persistent quadriceps weakness, partly through arthrogenic muscle inhibition.¹⁶
• Some biomechanical asymmetries persisting to 9-12 months after surgery and beyond (King 2018).
• A degree of kinesiophobia that can hinder progress and return to sport (Trigsted 2018).¹⁰

Assessment after ACL reconstruction must go well beyond the postoperative calendar. The modern approach, supported by the Aspetar 2023 guideline¹ and the Delaware-Oslo cohort,² is multidimensional and based on objective criteria combined with listening to the patient.

What questions should be asked to understand the patient?

The history puts the objective test results in context and identifies the barriers to successful rehabilitation.

• Goals and target level : pivoting sport? Competition? Recreational? The level of risk determines how strict the validation criteria should be.
• Pain, swelling, effusions, locking : a recurrent effusion or locking should raise suspicion of an additional intra-articular problem.
• Psychological dimension : kinesiophobia is a major predictor of successful RTS.³ Use the ACL-RSI (Anterior Cruciate Ligament-Return to Sport after Injury)⁴ scale systematically. In those aged 20 and under, a score below 76.7 at 12 months identifies with 90% sensitivity those who go on to sustain a second ACL injury; beyond the age of 20, the score does not distinguish the patients who are re-injured (McPherson 2019).³
• Adherence to the programme and the difficulties encountered: a patient who drops out is a patient at risk.

Which clinical tests should be carried out and which differential diagnoses must be ruled out?

Ligament stability : the Lachman test is, in the clinic, the most sensitive of the three manual tests studied (Sn 81%, Sp 81%; Sn 91%, Sp 78% under anaesthesia; van Eck 2013 meta-analysis).⁵ These values were established for acute complete rupture of the native ligament, not for checking a graft. The pivot shift is highly specific only under anaesthesia (Sp 98%, versus 81% in the clinic) and remains hard to perform on an awake, apprehensive patient.

Muscle strength : isokinetic dynamometry is the reference standard. The usual target is a Limb Symmetry Index (LSI) >90% for the quadriceps and the hamstrings; Aspetar 2023 aims for 100% at 60°/s before a pivoting sport.¹

Functional tests : a battery of hop tests, single hop for distance, triple hop, crossover hop, 6-metre timed hop. An LSI >90% is required for each.

Limits of the functional tests : in the meta-analysis by Webster and Hewett (2019)⁷, only 23% of patients passed the test battery. Passing it reduced the risk of graft rupture (RR 0.40; 95% CI 0.23-0.69) but was accompanied by more contralateral ACL injuries (RR 3.35; 95% CI 1.52-7.37): the risk of a further ACL injury, on either side, did not fall (RR 0.80; 95% CI 0.27-2.3). Davies et al. 2020 describe the relationship between passing the hop tests and outcome as « equivocal ».⁸

Should patients be stratified, and for what benefit?

Yes. Early stratification makes it possible to target interventions at the at-risk profiles rather than applying a « one size fits all » protocol. The landmark study Toole et al. 2017 (JOSPT, n=115 young athletes) showed that only 13.9% of young people met all the combined criteria at the time they were cleared for RTS: 27.8% for all the strength tests, 53% for all the hop tests.¹⁰ The combined criteria also included an IKDC score ≥ 90.

Early stratification on the ACL-RSI score at 3 and 6 months, the quadriceps strength deficit at 3 months and movement quality (2D analysis of dynamic valgus in a drop jump) makes it possible to steer treatment towards the patient's real deficits.¹¹

Figure 1 of 2

The recommendations of the Aspetar 2023 guideline,¹ of the Panther Symposium 2021 consensus² and of the van Melick 2025 editorial³ converge: rehabilitation must be criteria-based (and not driven by the calendar alone) and combine several complementary modalities.

Where do you start? What hierarchy of interventions?

The immediate postoperative phase lays the foundations of success. The priorities are regaining range, controlling swelling and neuromuscular activation.

• Regaining full extension : this is the absolute priority of the first 2 weeks. In the Shelbourne cohort (mean follow-up of 10.5 years), incomplete range of motion (extension more than 2° or flexion more than 5° short of the opposite knee) was associated with more radiographic osteoarthritis: 53% versus 39%.¹³
• Early weight-bearing with aids as tolerated: safe and beneficial for function (Aspetar 2023).¹
• Early neuromuscular activation of the quadriceps (isometrics, sets) to counter arthrogenic inhibition.⁵
• Cryotherapy + compression in the first few days to manage swelling and pain.

What is the place of exercise, and the optimal combination?

Therapeutic exercise is the cornerstone of rehabilitation. The historical debate between open and closed kinetic chain now leans towards combining the two, on low-certainty evidence.

The meta-analysis by Pamboris et al. 2024 (Front Sports Act Living)⁶ confirms:

• The open kinetic chain (OKC), leg extension within a protected range of 90° to 45°, is superior for isokinetic quadriceps strength gains (MD +28.1 Nm at 12 weeks). This figure comes from a single trial of 36 patients, rated very low certainty, after a 12-week programme (24 weeks after surgery).
• The closed kinetic chain (CKC) is better for early pain.
• No demonstrated difference in laxity where the open chain starts from week 4 in a limited range (90° to 45° of flexion, Aspetar 2023).¹ Three caveats: there are no data before week 4; hamstring grafts might be more vulnerable to early introduction than patellar tendon grafts; monitor anterior knee pain and effusion, and adjust the load.

The reference approach is therefore the combination of OKC + CKC, with progression in range and in load.

Manual therapies, NMES, BFR: how effective are they really?

Several adjunct modalities can speed up strength gains, particularly in the early phase.

The ratings are those published by the sources cited; the Aspetar 2023 guideline states that most of its findings rest on very low certainty of evidence. Blood flow restriction has its contraindications (cardiovascular disease, extensive swelling, skin irritation; Aspetar 2023): check them before the first session.

How do you educate the patient and address the psychological dimension?

Physical recovery alone is not enough. Psychological factors weigh as heavily as strength.

The meta-analysis by Ardern et al. 2014 (BJSM, n=7,556 patients)⁷ shows that despite good physical recovery:

The meta-analysis does not break down the gap between 81% and 55%. A positive psychological response favours a return to the pre-injury level (d = 0.3), on a par with symmetrical hopping performance (d = 0.3) and younger age; male sex (OR 1.4) and playing elite sport (OR 2.5) also carry weight. The levers available on the psychological side:

• Therapeutic education : the stages of healing, the logic behind the exercises, managing expectations.
• SMART goals (Specific, Measurable, Achievable, Realistic, Time-bound).
• ACL-RSI assessment at regular intervals (3, 6, 9 months).
• Graded exposure to anxiety-provoking sporting situations.
• Referral to a sport psychologist where kinesiophobia persists.

Return to sport (RTS) is a process, not an event. It combines three pillars, all of them necessary : a minimum biological delay, a battery of functional criteria, and psychological readiness. No pillar is enough on its own.

How do you make the patient an active participant in their recovery?

Self-management rests on three pillars:

1. Therapeutic education : understanding the injury, the stages of healing, the logic behind the exercises.
2. Setting SMART goals and patient/therapist collaboration.
3. Psychological support and strengthening self-efficacy through progressive successes.¹

When and how should a safe return to sport be planned?

The RTS decision combines three cumulative :

1. A minimum biological delay of 9 months. In the Beischer 2020 cohort² (159 athletes aged 15 to 30), returning to a knee-strenuous sport before 9 months was associated with a rate of second ACL injury about 7 times higher (HR 6.7; 95% CI 2.6-16.7). The Piussi 2024 meta-analysis³ is more guarded: patients who sustained a second injury had returned on average 25 days earlier (95% CI 9.5-40.4), with very low certainty and no difference among professional athletes. The pooled incidence of second ACL injury in that meta-analysis is 16.9% (95% CI 12.8-21.6).

2. Objective functional criteria. The study by Kyritsis et al. 2016 (BJSM, 158 male professional athletes)⁴ followed a discharge battery of six criteria; failing to meet all of them multiplied the risk of graft rupture by 4 (HR 4.1; 95% CI 1.9-9.2):

• Isokinetic quadriceps and hamstrings at 60°/s, 180°/s, 300°/s: LSI >90%
• Running T-test (agility)
• Single hop test: LSI >90%
• Triple hop
• Triple crossover hop: LSI >90%

3. Psychological readiness. The ACL-RSI scale⁵ makes it possible to quantify the patient's confidence and their fear of re-injury. Main thresholds:

• Score <56 at 4 months: predicts non-return to sport at 12 months
• Score ≥60 at 6 months: associated with return to the same sport at 2 years; optimal threshold of 65 at 2 years (Sadeqi 2018). This threshold informs return to sport, not the risk of re-injury.¹¹
• Score <76.7 in those aged ≤20: 90% sensitivity for the risk of second injury⁶

The case reports published on PubMed/PMC illustrate how the evidence-based principles translate into concrete situations.

Case 1: A professional footballer after 3 ipsilateral reconstructions (Noronha 2020)

A 32-year-old professional footballer who had sustained three successive ACL ruptures on the same side (hamstring graft, then patellar tendon, then Achilles tendon allograft).¹ The patient progressively resumed full training at 8 months and competition at the highest level at 9 months after the 3rd operation. At 36 months of follow-up: no pain, no instability, professional level maintained.

Clinical lesson: a return to the top level remains possible after a third reconstruction. The report does not describe objective return-to-play criteria: it mentions daily physiotherapy for 4 months, running in the 6th month and full training at 8 months, that is, before the 9-month delay adopted in this article. After the first two reconstructions, return to play had taken place at 6 months. A single case says nothing about the average risk after repeated revision.

Case 2: Cyclops syndrome diagnosed late (Singh 2021)

A 26-year-old patient who had undergone ACL reconstruction and presented with persistent swelling and stiffness with loss of extension (at 4 months in the body of the report, « 1 year » in its abstract).² MRI showed a lesion in the anterior intercondylar notch suggestive of a cyclops lesion. The authors advised arthroscopic excision, followed by physiotherapy: full extension was regained within 3 months.

Clinical lesson: a loss of extension that does not recover is a red flag: refer promptly to the surgeon. The « patient who plateaus » deserves a follow-up MRI.

Case 3: Multi-ligament reconstruction ACL + PCL + meniscal roots (Adi 2025)

A 19-year-old patient with a complete ACL + PCL rupture and tears of the posterior roots of both menisci.³ Simultaneous reconstruction (peroneus longus for the PCL, hamstrings for the ACL) + arthroscopic repair of the roots. At 9 months after surgery: ROM 0-140°, bi-ligamentous stability restored, no significant difference in thigh circumference compared with the uninjured side.

Clinical lesson: multi-ligament cases are biomechanically demanding (grafts under opposing constraints). The protective phases are longer and weight-bearing more cautious. Return to sport is rarely before 12-15 months.

Other notable examples:

• Joreitz 2020 (IJSPT, case series n=19): a 5-phase criterion-based protocol, 84% return to pre-injury level at 2 years, a single re-injury among 19 who completed: proof of feasibility.⁴
• Meierbachtol 2020 (OJSM, n=33 patients aged 14-30): a 5-week group RTS programme with graded exposure therapy: fear of pivoting is the most common; every fear decreases significantly after the programme; the ACL-RSI proves more discriminating than the TSK-11.⁵

Clinical application rests on two skills that are often under-invested in: knowing when to refer and knowing how to measure your own results.

When, and to which professionals, should you refer?

Yellow flags (psychosocial): referral to a psychologist / CBT: persistent kinesiophobia, catastrophising, mistaken beliefs about pain, depressive symptoms.⁵

Interprofessional collaboration : sports physician, orthopaedic surgeon, podiatrist (foot posture), nutritionist (body composition), sport psychologist. Multidisciplinary biopsychosocial management improves outcomes in chronic conditions.²

How do you measure outcomes and overcome the barriers to implementation?

Systematic use of PROMs (Patient-Reported Outcome Measures) is recommended.³ For the ACL:

• KOOS (Knee Injury and Osteoarthritis Outcome Score): function and quality of life
• IKDC (International Knee Documentation Committee): overall subjective score
• ACL-RSI: psychological readiness
• Tegner and Marx: level of sporting activity
• PSFS (Patient-Specific Functional Scale): personalised goals

The documented barriers to implementation (Scurlock-Evans 2014, SR in allied health)⁴:

• Lack of time in the consultation → integrated digital PROM tools
• Difficulty reading the literature → continuing education, podcasts (BJSM, JOSPT), CATs (critically appraised topics)
• Beliefs and habits → audit + feedback, peer mentoring
• A funding system that pays for volume, not quality: a structural fix