Arthrogenic muscle inhibition after ACL reconstruction: what we now know

Arthrogenic muscle inhibition after ACL reconstruction is common and treatable with simple exercises in most cases.

Arthrogenic muscle inhibition (AMI) is a well-recognised barrier to recovery after anterior cruciate ligament (ACL) injury. This article presents findings from Professor Etienne Cavaignac’s clinical research, titled “Incidence of and Risk Factors for Arthrogenic Muscle Inhibition in Acute Anterior Cruciate Ligament Injuries”, conducted in collaboration with the SANTI Study Group.

To deepen your understanding, we invite you to explore the other scientific studies by Professor Cavaignac.

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Understanding arthrogenic muscle inhibition (ACL surgery follow-up)

Arthrogenic muscle inhibition (ACL surgery’s possible effect) refers to a reflexive neurological shutdown of the quadriceps muscle that occurs after knee injury or surgery. This phenomenon leads to difficulty fully activating the quadriceps, resulting in muscle weakness and impaired knee extension. The study found that 56.7% of patients with acute ACL injuries experienced AMI, with a significant impact on clinical scores like Lysholm, IKDC and KOOS.

This inhibitory mechanism, though protective in theory, can seriously delay or limit functional recovery. The underlying cause involves altered signals from joint receptors to the spinal cord and brain, leading to increased inhibition of quadriceps motor neurons and heightened reflex activity in the hamstrings.

The challenge of arthrogenic muscle inhibition following anterior cruciate ligament injury

The burden of arthrogenic muscle inhibition following anterior cruciate ligament injury is not only high in prevalence but also impactful in rehabilitation. Patients with AMI reported:

• Lower Lysholm and KOOS scores

• Greater pain and effusion

• Reduced knee function and mobility

Importantly, AMI is not only a postoperative issue, it is already present in the acute preoperative phase, complicating early rehabilitation and increasing the risk of persistent extension deficits and stiffness.

The consequences of unrecognised or untreated AMI include:

• Quadriceps atrophy

• Persistent gait abnormalities

• Joint stiffness and risk of cyclops lesion

• Delayed return to sport and increased osteoarthritis risk

Recognising arthrogenic muscle inhibition after ACL surgery

Arthrogenic muscle inhibition after ACL reconstruction remains a critical concern despite surgical repair. In the referenced study, AMI was classified using the Sonnery-Cottet classification, which grades the condition from 0 (no inhibition) to 3 (chronic, irreducible deficit).

Among the 170 patients with AMI:

• 79% had grades 1A or 2A, meaning the inhibition was reversible with simple exercises at the initial consultation.

• 21% had grades 1B or 2B, requiring targeted rehabilitation before surgery.

The classification system demonstrated excellent interobserver reliability (κ = 0.93), supporting its use in clinical settings. Recognising early signs, particularly in the acute phase, allows for timely and effective intervention to reverse inhibition and avoid postoperative complications.

Risk factors for arthrogenic muscle inhibition after ACL

The study identified several statistically significant predictors of arthrogenic muscle inhibition after ACL injury. These “red flags” include:

• Joint effusion: tripled the odds of developing AMI (OR = 2.22)

• High pain scores at initial assessment (OR = 2.27)

• Short interval between injury and evaluation (OR = 2.04)

• Use of crutches at first consultation (OR = 2.14)

• Sleeping with a pillow under the knee (OR = 2.67)

• Multiligament injuries seen on MRI (OR = 2.33)

Interestingly, patients with previous ACL injuries (ipsilateral or contralateral) had significantly lower odds of developing AMI. This could indicate some level of central neural adaptation from prior injury experience.

Managing AMI: an urgent but solvable issue

The most encouraging outcome of the study is that most cases of AMI are reversible. Simple clinical techniques, such as hamstring fatigue protocols and quadriceps activation exercises, reversed inhibition in nearly 80% of patients during the first consultation. For patients requiring more structured support, biofeedback techniques and neuromotor reprogramming using visual and auditory cues proved effective.

These findings reinforce the importance of early identification and intervention in managing AMI. Incorporating these strategies into initial ACL rehabilitation could prevent progression to chronic quadriceps dysfunction and facilitate a more complete recovery.

Conclusion

Arthrogenic muscle inhibition following anterior cruciate ligament injury is a common but often underdiagnosed issue that significantly impairs rehabilitation. The study by the SANTI Group confirms the high prevalence of AMI and highlights reversible patterns in most cases. Recognising risk factors early and applying targeted interventions can dramatically improve outcomes for patients with acute ACL injuries.

For patients or clinicians seeking expertise in ACL injury management, we highly recommend consulting Professor Étienne Cavaignac (lien vers accueil), a leading orthopaedic surgeon and sports trauma specialist, known for his cutting-edge research and patient-centred care.

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