Clinical synthesis based on the most recent meta-analyses and international consensus statements: Dutch ACL Guideline (van Melick 2016, BJSM), KANON (Frobell 2013, BMJ), Delaware-Oslo (Grindem 2016, BJSM), Ottawa Knee Rules and PEACE & LOVE.

A knee sprain is a traumatic injury to one or more of the four ligaments that stabilise the joint: the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).¹ Understanding the definition, the populations affected, the mechanisms and the natural history directly determines the quality of the clinical assessment and of treatment choices. 🦵

How is this condition defined, who does it affect and what are the risk factors?

A knee sprain is defined by the stretching or rupture of one or more ligaments, conventionally classified into three grades: grade I (stretching without objective laxity), grade II (partial tear, moderate laxity with a firm end point) and grade III (complete tear, marked laxity with a soft end point).¹ The most frequently injured ligament is the MCL, typically through forced valgus. However, the injury most studied because of its functional impact is ACL rupture. The reference population study by Sanders et al. (AJSM 2016), based on 21 years of data from the Rochester Epidemiology Project, established an adjusted incidence of 68.6 new ACL ruptures per 100,000 person-years, with a significant increase over time. The incidence peak lies between 15 and 25 years of age, in sports involving pivoting, deceleration and changes of direction (football, basketball, skiing, handball).¹

The meta-analysis by Montalvo et al. (BJSM 2019) pooled data from prospective cohorts to answer the question “What's my risk of sustaining an ACL injury while playing sports?” Incidence is low overall at the individual level but accumulates in high-volume elite sport, and female athletes have a proportionally higher risk than men in the same sport.²

Risk factors are multiple:

• Extrinsic / modifiable : type of sport (pivoting >> linear), level of competition, type of surface, footwear and grip (shoe-surface).
• Intrinsic anatomical : increased posterior tibial slope, narrow femoral notch, increased Q angle, generalised ligamentous hyperlaxity; these anatomical factors are associated with risk but are not modifiable.
• Intrinsic neuromuscular (the most modifiable) : dynamic knee valgus on landing, poor trunk control, quadriceps dominance over the hamstrings during deceleration, and altered jump-landing motor patterns. These factors are the target of validated prevention programmes.²¹

What happens in the body, and how does a knee sprain evolve naturally?

The injury mechanism depends on the ligament. Most ACL ruptures occur through a non-contact mechanism, typically a sudden deceleration combined with rotation and valgus.¹ MCL injuries most often result from a direct blow to the lateral aspect of the knee (forced valgus). The PCL is injured by an anterior blow to the flexed tibia (“dashboard injury”) or by hyperextension. The LCL and the posterolateral corner are involved in varus + external rotation trauma. Ligament healing follows three classic phases:

1. Haemostasis & inflammation (0-72 h) : clot, cytokines, cell recruitment.
2. Proliferation (3 days to 6 weeks) : disorganised matrix, predominantly type III collagen.
3. Remodelling / maturation (6 weeks to > 1 year) : gradual replacement by type I collagen, alignment of the fibres along the lines of stress. Scar tissue, however, never reaches the biomechanical properties of the native ligament.

The natural history depends strongly on the ligament and on severity:

• MCL : excellent healing potential. Grades I and II (and most isolated grade III injuries) heal with structured conservative treatment.³
• ACL : lower healing potential, but not zero: in the KANON trial, ligament continuity was seen on MRI at 2 years in 16 of the 54 patients randomised to rehabilitation with the option of delayed surgery (30%), and in 16 of the 30 who did not go on to have surgery; this continuity is not equivalent to restored stability, and its link with outcome differs by time point (better scores at 2 years; at 11 years, worse than in reconstructed patients, continuity having been assessed at 5 years in 14 patients).^22,23 The course without treatment is variable: some patients are functional “copers”, others develop chronic instability, secondary meniscal/cartilage lesions, and an increased long-term risk of post-traumatic osteoarthritis.^4,5
• Multi-ligament injuries : often associated with knee dislocation. Major instability, guarded prognosis, near-systematic surgical management after vascular screening (see chapter 6).¹⁸

The randomised KANON trial (Frobell et al., BMJ 2013, 5-year follow-up) is central to understanding the modern course: in young active adults with acute ACL rupture, structured rehabilitation with the option of delayed reconstruction does not give functional or radiographic outcomes significantly different from rehabilitation with early reconstruction.¹¹

A third route, the flexion immobilisation protocol known as “cross-bracing” (knee at 90° for 4 weeks, then progressive mobilisation up to 12 weeks), aims at healing of the ACL. In a series of 80 patients, 90% had ligament continuity on MRI at 3 months (thinned or elongated in 40% of the series), and 14% re-ruptured, with short follow-up.²⁴ A 2026 comparative cohort (80 patients who chose their treatment, 2 years) reports much more recurrent instability than with surgery (70% versus 2.5%).²⁵ No randomised trial had been published as of October 2026; the decision is made with the surgical team and the patient.

Which questions should you ask to understand the patient and their history?

The history already points to most of the diagnosis. Four lines of questioning:

• Mechanism : non-contact deceleration + pivot/valgus → ACL. Lateral blow in valgus → MCL. Varus blow → LCL. Anterior blow to the flexed tibia (dashboard) → PCL.
• Sensations: an audible/felt “pop” is highly suggestive of an ACL rupture; rapid swelling < 12 h = haemarthrosis and intra-articular involvement (ACL, osteochondral, fracture).
• Later symptoms : subjective instability, giving way on pivoting, mechanical locking (suggesting an associated meniscal lesion).
• Past history : previous sprains, ipsilateral or contralateral surgery, comorbidities (generalised hyperlaxity, static alignment disorders).

Which clinical tests should you perform, and which other conditions must be ruled out?

Step 1: rule out a fracture. The Ottawa Knee Rules (Stiell 1996, initial validation; Bachmann 2004 meta-analysis) recommend a radiograph if at least one of the following criteria is present:

• Age ≥ 55 years
• Isolated tenderness of the patella
• Tenderness at the head of the fibula
• Inability to flex the knee to 90°
• Inability to take 4 weight-bearing steps (even limping) at the practice and in the emergency department

Pooled sensitivity is close to 100% (rare false negatives), with a reduction of about 25-30% in unnecessary radiographs.^7,8

Step 2: ligament tests, with systematic bilateral comparison.

• ACL :
  • Lachman test (knee at 20-30° flex.): the most sensitive and the most useful in the acute phase, little affected by muscle guarding;
  • Anterior drawer (at 90° flex.): less accurate, frequent false negatives in the acute phase;
  • Pivot-shift : highly specific when positive (rotatory instability), often only feasible once pain has been managed or under anaesthesia.⁹
• PCL : posterior sag sign (knees and hips at 90°), posterior drawer. Good diagnostic accuracy in combination.
• MCL : stress in valgus at 0° and 30° of flexion. Pain/laxity at 30° only isolates the MCL; laxity at 0° = more extensive ligament involvement (capsule, cruciates).
• LCL and posterolateral corner : stress in varus at 0° and 30°, dial test at 30° and 90° (external rotation asymmetry). Posterolateral corner involvement = serious injury, frequently associated with ACL/PCL injury.

Step 3: differential diagnosis. A sprain can mask or coexist with:

• Meniscal lesion (very frequently associated with acute ACL injury); McMurray and Thessaly help but have moderate accuracy;
• Patellar dislocation/subluxation can mimic a “pop” and rapid swelling; the patellar apprehension test is relevant;
• Osteochondral fracture in adolescents/young adults;
• Segond fracture on the radiograph (lateral avulsion of the tibial plateau): a quasi-pathognomonic sign of ACL rupture and frequently associated with injury to the anterolateral ligament.¹⁹

Should patients be classified, and what are the benefits?

Yes. Classification into 3 grades standardises communication, guides the initial decision and contributes to prognosis. Grade I: stretching without laxity; Grade II: partial tear, moderate laxity + firm end point; Grade III: complete tear, marked laxity + soft end point.¹

Important limitations:

• The anatomical grade does not predict functional instability. Some “coper” patients function very well with a grade III ACL injury; others with a less severe injury are severely disabled.
• MRI, often seen as the gold standard, can overdiagnose clinically insignificant lesions or miss dynamic instabilities.
• For complex injuries (multi-ligament, rotatory instability), dedicated classifications are needed (e.g. the Schenck classification for knee dislocations).

The excess risk of ACL rupture in women in pivoting sports is one of the most robust epidemiological signals in sports traumatology. The meta-analysis by Montalvo et al. (BJSM 2019) pooled prospective cohorts by sport and by sex: for equivalent exposure, incidence is proportionally higher in female athletes, particularly in basketball, football, handball and skiing.¹

Neuromuscular prevention programmes: what has been shown?

Several structured programmes (FIFA 11+ in football, PEP programme in women's football, programmes such as Knäkontroll) combine strengthening (posterior chain, hip), neuromuscular control, plyometrics, trunk stabilisation and landing technique work. Built into the warm-up and applied regularly, they are associated with a reduction in the incidence of ACL injuries and of non-contact lower limb injuries in pivoting sports.^2,3

The effect is dose-dependent: compliance > 2 sessions/week and keeping it up over the season are key conditions. Insufficient coverage explains most “negative” trials.

Where to start? What is the hierarchy of interventions?

Acute management has moved beyond RICE. Contemporary guidance follows the acronym PEACE & LOVE (Dubois & Esculier, BJSM 2020).¹

For ACL ruptures, a preoperative phase (prehabilitation) is recommended, on very low certainty evidence (Aspetar 2023 guideline),⁹ whether or not surgery is ultimately chosen: goals = full extension, oedema control, quadriceps activation, normal gait. The decision “immediate surgery vs rehabilitation alone with the option of delayed surgery” must be individualised: the KANON trial (Frobell 2013, BMJ) found no significant difference between these two strategies at 5 years in the population studied.²

What is the place of exercise, and is there a superior approach?

Therapeutic exercise is the cornerstone of rehabilitation, and is recommended as its pillar despite very low certainty of evidence for most of its components (Aspetar 2023 guideline).⁹ There is no single “best” approach but a progressive continuum structured by functional criteria and built around four pillars:

1. Muscle strengthening : focus on quadriceps and hamstrings; open kinetic chain (OKC) and closed kinetic chain (CKC) exercises are complementary.
2. Neuromuscular control : balance, perturbations, agility; integration of motor learning principles (external feedback, variable practice).
3. Progressive plyometrics : preparation for the impact and deceleration demands of the target sport.
4. Sport-specific reintegration : straight-line running, accelerations, decelerations, changes of direction, technical skills, controlled then free opposition.

The Dutch recommendations (Dutch ACL Guideline, van Melick et al., BJSM 2016) remain the practical reference: 4 phases (preop / 0-12 wk / 12-26 wk / 26-52+ wk) with progression dictated by objective criteria (full extension, quadriceps control, strength symmetry, movement quality).³ The GRADE-based Aspetar 2023 guideline makes exercise the pillar of rehabilitation after reconstruction, with very low certainty for most components, and notes that no progression or discharge criterion is evidence-based.⁹

Editorial rating applying GRADE principles; certainty of evidence and strength of recommendation are distinct: exercise remains recommended as the pillar despite low certainty. The Aspetar 2023 guideline concerns rehabilitation after reconstruction.

Manual therapies, technologies: how effective are they really?

Passive modalities have an adjunctive role, never the main one. Manual therapy can reduce pain and improve range of motion in the short term, particularly to treat post-traumatic or postoperative stiffness; it is no substitute for exercise. Cryotherapy has a useful analgesic effect in the acute phase. NMES of the quadriceps is useful in the early postoperative phase when arthrogenic muscle inhibition makes voluntary recruitment difficult. Routine ultrasound and laser are not supported by solid clinical evidence for ligament healing and should not replace an active programme.³

Beyond the physical: education and psychological factors

Adopting a biopsychosocial approach is essential. Kinesiophobia (fear of movement) is very common after ACL reconstruction. It can be measured with the ACL-RSI scale (Webster, Feller, Lambros 2008, Phys Ther Sport), which assesses psychological readiness to return to sport, and with the Tampa Scale for Kinesiophobia (TSK).⁴

Commonly proposed strategies: education about prognosis, setting shared goals (Shared Decision-Making), graded exposure to feared sporting situations, visualisation. A meta-analysis of 11 small trials (440 participants) finds an effect of psychological interventions on pain and kinesiophobia, with no effect on the ACL-RSI or on strength, evidence its authors describe as preliminary;¹¹ a trial of 161 participants testing a self-directed online programme (BANG) did not increase return to sport at 12 months (36% in each arm).¹⁰ Optimism, the “O” in LOVE, is not wishful thinking but a recognised prognostic determinant.

How do you make the patient an active participant in their recovery through self-management?

Patient empowerment is a major therapeutic lever. Three levers:

• Structured therapeutic education : the condition, the goals of each phase, the rationale for the exercises. Reduces anxiety and increases adherence.
• Shared decision-making : realistic goals defined together, an adjustable plan, a stronger therapeutic alliance.
• Systematic psychological assessment (ACL-RSI, TSK) with tailored interventions: visualisation, graded goal setting, exposure to feared situations.

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

The return-to-sport (RTS) decision must not rest on time since surgery alone. The international consensus from Bern 2016 (Ardern et al., BJSM) proposes a StARRT framework (Strategic Assessment of Risk and Risk Tolerance) and insists on a multifactorial decision integrating tissue health, risk, and personal/contextual factors.¹

The Delaware-Oslo cohort (Grindem et al., BJSM 2016, 106 patients) followed return to sport and new injuries for 2 years after ACL reconstruction: each month that return was delayed, up to 9 months, was accompanied by 51% fewer new injuries, with no further reduction beyond that; more symmetrical quadriceps strength also reduced the risk; patients who passed the criteria battery (score above 90 on all tests) had 5.6% new injuries versus 38.2%, a non-significant difference (p = 0.075).² In a cohort of 530 men in pivoting sports, among the 190 who had passed the discharge criteria, returning before or after 9 months was not associated with the risk of a new knee injury (HR 0.89; 95% CI 0.39 to 2.07), an interval too wide to rule out an excess risk.⁷ Nine months remains a maturation benchmark, neither a gate nor a sufficient criterion.

Common pitfalls :

• Relying solely on time since surgery (“6 months and you're good”): wrong and dangerous.
• Relying solely on LSI ≥ 90%: the “healthy” leg may be deconditioned, overestimating bilateral performance (Wellsandt 2017, JOSPT).³
• Neglecting psychological readiness : a patient who is physically ready but does not feel ready is not ready.
• Underestimating the context : type of sport, level of competition, team/individual sport, social support, family/club expectations.

The risk of a second ACL injury after return to sport remains high. Paterno et al. (AJSM 2014) put it at nearly 6 times that of healthy subjects over 24 months, after 15 times in the first 12 months in an earlier study by the same group, hence the importance of rehabilitation carried through to completion and of a gradual return to exposure.⁴

Analysis of a “classic” case: ACL rupture, from assessment to return to sport

The clinical pathway of an isolated ACL rupture in a pivoting-sport athlete illustrates how to link assessment, shared decision-making and criteria-based rehabilitation.

Initial assessment : suggestive history (non-contact mechanism, pop, swelling < 12 h, instability), Ottawa Knee Rules to rule out a fracture, clinical tests (Lachman, pivot-shift once pain has been managed), MRI for confirmation. Systematic search for associated injuries (meniscal, osteochondral, Segond fracture).

Shared decision : discuss the options with the patient (rehabilitation alone with the option of delayed surgery, KANON-style, vs immediate reconstruction), according to the profile (age, level and type of sport, goals, comorbidities, expectations).

Phase- and criteria-based rehabilitation (reference: Dutch ACL Guideline, van Melick 2016, BJSM):

1. Prehabilitation : full extension, oedema control, quadriceps activation.
2. Early post-op phase : graft protection, management of oedema and pain, restoring mobility, NMES if arthrogenic inhibition.
3. Intermediate phase : strengthening, neuromuscular control; progression towards return to running once the strength and movement quality criteria are met.
4. Late phase and RTS : plyometrics, agility, sport-specific work; final clearance through a multifactorial battery (strength, hop tests, ACL-RSI, movement quality) + timing, with 9 months as a benchmark.

The diagnostic challenge: Segond fracture and the anterolateral ligament

The Segond fracture is a millimetre-sized bony avulsion on the lateral aspect of the tibial plateau, visible on the initial radiograph. Long regarded as a mere marker, it is now recognised as quasi-pathognomonic of an ACL rupture and associated with involvement of the anterolateral ligament (ALL), described anatomically by Claes et al. (J Anat 2013).¹

Clinical implications :

• Any small lateral avulsion of the tibial plateau should prompt suspicion and confirmation (MRI) of an ACL rupture, without delay.
• Residual rotatory instability after ACL reconstruction may be explained by an unaddressed ALL injury; some teams propose an anterolateral augmentation procedure (tenodesis) in high-risk profiles (young, pivoting, hyperlaxity).

Study of a complex case: knee dislocation and vascular emergency

Multi-ligament injuries after high-energy trauma (road traffic accident, motorcycle fall, high-speed sports trauma) call for a very different approach. Knee dislocation can reduce spontaneously before arrival in the emergency department; it should be suspected in the face of immediate multidirectional laxity or a large post-traumatic haemarthrosis.

Priority number one: vascular screening. The systematic review by Medina et al. (Clin Orthop Relat Res 2014) pooled the published series on vascular (popliteal artery) and nerve (common fibular nerve) injuries after knee dislocation.²

The ligament management of these multi-ligament injuries is complex and outside the scope of the initial physiotherapy assessment: a multidisciplinary decision (specialist orthopaedic surgeon, vascular surgeon if needed), often staged (repair/reconstruction of the posterolateral corner then the cruciates later, or combined approaches depending on the school). Postoperative rehabilitation is itself specific, balancing protection of the structures against the fight against stiffness.

Critique and controversies: the level of evidence of clinical cases

Clinical cases are valuable to illustrate, generate hypotheses and report rare presentations. They never demonstrate effectiveness: the absence of a control group, publication bias (successes are published more than failures) and regression to the mean limit their reach. In the GRADE/Oxford CEBM hierarchy, a case report is level 5 (the weakest). When an attractive case contradicts a meta-analysis, the meta-analysis prevails.

When should you refer, and to which other health professionals?

Prompt referral is a clinical act in itself. The red flags listed below belong to knee traumatology and vascular emergencies, and do not come from a published framework of their own. The overall reasoning, however, can draw on the international framework of Finucane et al. (JOSPT 2020), which concerns serious spinal pathologies and points out that no red flag taken in isolation has established diagnostic accuracy.¹

Urgent referral (orthopaedic/vascular emergency department) :

• Knee dislocation (reduced or not), suspected popliteal artery injury.
• Common fibular nerve deficit (steppage gait, hypoaesthesia of the dorsum of the foot).
• Compartment syndrome: disproportionate pain, paraesthesia, pallor, tense haemarthrosis.
• Open fracture, bone deformity.
• Suspected septic arthritis (fever + acute swelling without trauma).

Specialist surgical referral (prompt but non-urgent consultation) :

• Complete ACL rupture in a pivoting-sport athlete with functional instability (alongside rehabilitation).
• Grade III MCL injury combined with an ACL rupture.
• Posterolateral corner involvement, confirmed Segond fracture.
• Tibial spine avulsion in a child/adolescent.

Medical collaboration : sports physician, rheumatologist (recurrent sprains with hyperlaxity, suspected EDS), general practitioner for pain relief or imaging, and psychologist/mental coach in case of persistent kinesiophobia (yellow flag).

How do you measure outcomes and overcome barriers to implementation?

The systematic use of Patient-Reported Outcome Measures (PROMs) is now a quality standard. Validated tools for ligament injuries of the knee:

• IKDC subjective form : symptoms, function and sports activity; recognised responsiveness to change.
• KOOS (Knee injury and Osteoarthritis Outcome Score), 5 subscales: pain, symptoms, ADL, sport/recreation, quality of life.
• Lysholm : general functional score.
• Tegner Activity Scale : physical activity level.
• ACL-RSI (Webster 2008): psychological readiness to return to sport.²
• Tampa Scale for Kinesiophobia (TSK-11) : fear of movement.

Common barriers to evidence-based practice : lack of time, lack of training, limited access to resources, patient expectations (passive modalities, requests for massage), pressure from the sporting context (coach, club, family). Facilitators : leadership, protected time for continuing education, communities of practice, access to PROMs integrated into the patient record.