Incidence and risk factors for arthrogenic muscle inhibition after ACL reconstruction

Introduction

AMI is a deficit in knee extension, which is sometimes associated fixed flexion as an antalgic response after trauma or surgery. [1] Neto T, Sayer T, Theisen D, Mierau A. Functional brain plasticity associ-ated with ACL injury: a scoping review of current evidence. Neural Plast. 2019;2019:3480512. This central reflex mechanism can persist if it is not addressed quickly with a specific treatment [2], Sonnery-Cottet B. Mise au point sur l’inhibition motrice d’origine centrale dans les suites d’une entorse du Genou. Thèse de sciences. Université Toulouse3 – Paul Sabatier; 2022 [https://www.theses.fr/2022TOU30254].[3] Delaloye JR, Murar J, Sánchez MG, Saithna A, Ouanezar H, Thaunat M, Vieira TD, Sonnery-Cottet B. How to Rapidly Abolish Knee Extension Deficit After Injury or Surgery: A Practice-Changing Video Pearl From the Scientific Anterior Cruciate Ligament Network International (SANTI) Study Group. Arthrosc Tech. 2018 May 7;7(6):e601-e605. doi: 10.1016/j.eats.2018.02.006. . Recent developments in our understanding of the pathophysiology of this complication mean that we can improve our awareness of its mechanism. The disruptions have their origin in the central nervous system and manifest in different ways [4] Rice DA, McNair PJ. Quadriceps arthrogenic muscle inhibition: neural mechanisms and treatment perspectives. Semin Arthritis Rheum. 2010 Dec;40(3):250-66. doi: 10.1016/j.semarthrit.2009.10.001. Epub 2009 Dec 2. PMID: 19954822. (Figure 1) :

• Firstly, local factors such as inflammation, swelling, pain and the destruction of mechanoreceptors appear to lead to disrupted sensory feedback. This triggers a dysfunction of spinal reflex pathways, activating the flexor reflex (contracture of the hamstrings), Ib non-reciprocal inhibition pathways and the gamma loop. All of these factors contribute to reducing quadriceps contraction.
• Potential supraspinal influences have also been described, such as increased motor threshold in the M1 region of the cerebral cortex, and the activation or inhibition of certain cortical and subcortical areas. It seems that the purpose of all these reflex mechanisms, whether of the central or peripheral nervous system, is to protect the altered joint (Figure 2).

With new surgical techniques for ACL reconstruction emerging over the past 20 years, there has been a clear improvement in outcomes. In spite of this, complications of stiffness remain a significant and common source of post-operative morbidity [5] Sonnery-Cottet B, Ripoll T, Cavaignac E. Prevention of knee stiffness following ligament reconstruction: Understanding the role of Arthrogenic Muscle Inhibition (AMI). Orthop Traumatol Surg Res. 2024 Feb;110(1S):103784. . In 2023, Sonnery-Cottet et al [6] Sonnery-Cottet B, Hopper G, Gousopoulos L, et al. Arthrogenic Muscle Inhibition Following Knee Injury or Surgery: Pathophysiology, Classification, and Treatment. Video J Sports Med. 2022;2. proposed a clinical classification for AMI, reporting that 56% of patients were presenting with a clinical picture of AMI after ACL injury. The risk factors were also identified [7] Sonnery-Cottet B, Hopper GH, Gousopoulos L, C Pioger et al. Incidence and Risk factors for Arthrogenic Muscle Inhibition in Acute Anterior Cruciate Ligament Injuries: A Cross Sectional Study and Analysis of Associated Factors From the SANTI Study Group. Am J Sports Med. 2024 Jan;52(1):60-68. doi: 10.1177/03635465231209987. However, the incidence of AMI after ACL surgery is still, to date, unknown. This study aims to evaluate the incidence of AMI in the six weeks after anterior cruciate ligament surgery and to identify the associated risk factors. The hypothesis is that AMI is common after ACL reconstruction and that the factors that are identified as important pre-operatively remain so post-operatively.

Method

This non-randomised, comparative, retrospective study was approved by the ethics committee. A consecutive series of patients who were undergoing either primary or revision ACL reconstruction surgery between January and October 2023 were invited to be included. The clinical examination and magnetic resonance imaging (MRI) confirmed ACL damage to either the native ACL or an ACL graft. Patients were excluded if they presented with a fracture of the ipsilateral or contralateral limb, had a multiligament knee injury or if they refused to participate in the study.

Patients were enrolled at the pre-operative consultation with the orthopaedic surgeons. They then had a follow-up sports medicine consultation 3 and 6 weeks after the ACL reconstruction surgery.

At each consultation: C0 (pre-surgery), C3 (3 weeks post-surgery) and C6 (6 weeks post-surgery), patients completed a monitoring questionnaire from the surgeons/doctors. There were three different questionnaires, one for each consultation, accessed via three QR codes that had been generated specifically for our study (Q0 at C0, Q3 at C3 and Q6 at C6). At each consultation, the AMI grade was determined by the practitioner based on the following clinical classification [6] Sonnery-Cottet B, Hopper G, Gousopoulos L, et al. Arthrogenic Muscle Inhibition Following Knee Injury or Surgery: Pathophysiology, Classification, and Treatment. Video J Sports Med. 2022;2. (Figure 4).

Résultats

In total, 210 patients were prospectively recruited between January and October 2023. Of these, 38.6 % of patients presented signs of AMI (n=81) in the post-operative period. Three weeks post-operatively, a total of 48.6% of patients (n=102) presented with a clinical picture of AMI. Of these, 64.7% already had AMI prior to surgery (p<0.001). The number of patients presenting with a clinical picture of AMI had fallen to 24.3% by 6 weeks post-surgery. Of these, 66.7% had presented with AMI prior to surgery (p<0.001). The incidence and grades of AMI observed are shown in table 1. It was also noted that in the vast majority of cases AMI was reversible (grade A).

The risk factors identified in a multivariate analysis were: pain that must exceed 7/10 on the numerical rating scale immediately after surgery, pre-operative AMI and no physiotherapy pre-operatively. The odds ratios are shown in figures 5 and 6.

However, based on the same statistical regressions, none of the risk factors were found to be correlated with the presence of an AMI at 6 weeks.

Discussion

Our study demonstrates that there is a high incidence of post-operative AMI after ACL surgery. More specifically, almost half (48.6%) of all patients presented with clinical signs of AMI at 3 weeks and 24.3% at 6 weeks post-operatively. Of these, 79.4% at week 3 and 72% at week 6 presented with types that are clinically reversible with specific exercises (grade 1A or 2A) [5] Sonnery-Cottet B, Ripoll T, Cavaignac E. Prevention of knee stiffness following ligament reconstruction: Understanding the role of Arthrogenic Muscle Inhibition (AMI). Orthop Traumatol Surg Res. 2024 Feb;110(1S):103784. . The risk factors identified for AMI 3 weeks after the operation were

• Pre-operative AMI (risk multiplied by 8.2)
• Pain on immediate post-operative VAS rated higher than 7 (risk multiplied by 4.6)
• Absence of any pre-operative physiotherapy (risk multiplied by 2.6).

No risk factor was identified for the presence of an AMI 6 weeks after ligament repair.

For this study, we looked exclusively at motor deficits. Nevertheless, a number of studies, including the Piskin meta-analysis, refer to cognitive involvement after ACL rupture, whether treated surgically or not [8] Piskin D, Benjaminse A, Dimitrakis P, Gokeler A. Neurocognitive and Neurophysiological Functions Related to ACL Injury: A Framework for Neurocognitive Approaches in Rehabilitation and Return-to-Sports Tests. Sports Health. 2022;14(4):549-555.. More specifically, there is evidence of deficits in reaction time, processing speed and visual and verbal memory in athletes with ACL injuries. In addition, athletes with an ACL injury were found to sacrifice their cognitive performances to maintain sufficient postural control or, in the reverse scenario, postural stability declines with additional cognitive load [9] Lisee C, Lepley AS, Birchmeier T, O’Hagan K, Kuenze C. Quadriceps Strength and Volitional Activation After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis. Sports Health. 2019;11(2):163-179..

Our study shows that when AMI is identified it can be effectively managed with simple exercises, and that this approach can begin from the first pre-operative consultation. This is important information for practitioners, whether they are doctors specialising in sports medicine or rehabilitation, surgeons or physiotherapists. They need to be vigilant when checking for AMI from the very first consultation as these patients are at high risk of post-operative AMI. Moreover, the high prevalence of AMI post-operatively underscores the importance of raising awareness of this complication and using a universal classification.

Based on the results of this study, we can put forward a number of management proposals to avoid the onset of AMI post-operatively. In addition to screening at-risk patients, i.e. those who have pre-operative AMI, it is essential to give them advice and explain the pathophysiology to them, showing them the effective exercises, which gives them the tools to reduce this motor inhibition [3], Delaloye JR, Murar J, Sánchez MG, Saithna A, Ouanezar H, Thaunat M, Vieira TD, Sonnery-Cottet B. How to Rapidly Abolish Knee Extension Deficit After Injury or Surgery: A Practice-Changing Video Pearl From the Scientific Anterior Cruciate Ligament Network International (SANTI) Study Group. Arthrosc Tech. 2018 May 7;7(6):e601-e605. doi: 10.1016/j.eats.2018.02.006. [10], Sonnery-Cottet B, Saithna A, Quelard B, Daggett M, Borade A, Ouanezar H, Thaunat M, Blakeney WG. Arthrogenic muscle inhibition after ACL reconstruction: a scoping review of the efficacy of interventions. Br J Sports Med. 2019 Mar;53(5):289-298. [11] Dos Anjos T, Gabriel F, Vieira TD, Hopper GP, Sonnery-Cottet B. Neuromotor Treatment of Arthrogenic Muscle Inhibition After Knee Injury or Surgery. Sports Health. 2024 May-Jun;16(3):383-389. doi: 10.1177/19417381231169285. . Physiotherapy prior to surgery is also important. Equally, immediate post-operative antalgic response must be controlled as far as possible through appropriate treatments. Use of a cryotherapy and compression cuff seems to be effective from the recovery room onwards, although our study was not able to prove this due to a lack of statistical power.

It is important to remember that untreated AMI can have significant repercussions. It can lead to pain, abnormal gait, quadriceps weakness and atrophy and impaired dynamic stability. In the longer term, it can result in stiffness, cyclops syndrome, chronic pain, proprioception deficits consequently impairing the motor pattern for walking, and even osteoarthritis in the long term, as demonstrated by Shelbourne et al [12], Delaloye JR, Murar J, Vieira TD, Franck F, Pioger C, Helfer L, Saithna A, Sonnery-Cottet B. Knee Extension Deficit in the Early Postoperative Period Predisposes to Cyclops Syndrome After Anterior Cruciate Ligament Reconstruction: A Risk Factor Analysis in 3633 Patients From the SANTI Study Group Database. Am J Sports Med. 2020 Mar;48(3):565-572. doi: 10.1177/0363546519897064. [13], Strum GM, Friedman MJ, Fox JM, et al. Acute anterior cruciate ligament reconstruction. Analysis of complications. Clin Orthop. 1990;(253):184-189.[14], Shelbourne KD, Benner RW, Gray T. Results of Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autografts: Objective Factors Associated With the Development of Osteoarthritis at 20 to 33 Years After Surgery. Am J Sports Med. 2017 Oct;45(12):2730-2738. doi: 1177/0363546517718827. [15] Amin S, Baker K, Niu J, et al. Quadriceps strength and the risk of cartilage loss and symptom progression in knee osteoarthritis. Arthritis Rheum. 2009;60(1):189-198. A recent study by Zunzarren found that 42% of patients had a persistent muscle deficit in the operated limb when compared to the contralateral limb [16] Zunzarren G, Garet B, Vinciguerra B, Murgier J. Persistence of neuromuscular activation deficit in the lower limb at 3-years of follow-up after ACL reconstruction surgery. Knee. 2023 Aug;43:97-105. doi: 10.1016/j.knee.2023.06.006. Epub 2023 Jun 27. PMID: 37385113.. This applies to the quadriceps but also the other lower limb muscles such as the gluteal muscles, hamstrings and so on.

There are few articles in the literature that point to the right physiotherapy management of AMI [10] Sonnery-Cottet B, Saithna A, Quelard B, Daggett M, Borade A, Ouanezar H, Thaunat M, Blakeney WG. Arthrogenic muscle inhibition after ACL reconstruction: a scoping review of the efficacy of interventions. Br J Sports Med. 2019 Mar;53(5):289-298. . Simple exercises to wake up the quadriceps, such as very rapid contraction and open kinetic circuit resistance training, and fatiguing hamstring release exercises are simple and effective strategies, as long as they are repeated every day. Similarly, electrical nerve stimulation with biofeedback (widely used for neuromuscular retraining in gynaecological indications) seems to be promising, and consists of a central action with a visual signal, although it remains to be evaluated scientifically in this indication [17] Ananías J, Vidal C, Ortiz-Muñoz L, Irarrázaval S, Besa P. Use of electromyographic biofeedback in rehabilitation following anterior cruciate ligament reconstruction: a systematic review and metaanalysis. Physiotherapy. 2024;123:19-29. doi:10.1016/ j.physio.2023.12.005.

The main limitation of our study is that is only took place at a single site. Moreover, it was not exhaustive as it did not look at all the risk factors. The section of the questionnaire completed by the patient could be subject to recall bias. In addition, the incidence of grade 3 AMI was not studied because a longer follow-up duration would be required, which was beyond the scope of this study. Finally, there was no control group that was not offered a treatment to resolve AMI because, in our view, these exercises are invaluable to reduce morbidity and it would be unethical to include a no-treatment group.

Conclusion

AMI occurs in 48.6% of patients at 3 weeks and in 24.3% at 6 weeks after ACL reconstruction. When it occurs, it is clinically reversible in the majority of patients with the use of appropriate exercises and specific physiotherapy programmes. The risk factors identified for the presence of AMI at 3 weeks post-surgery are pre-operative AMI, an immediately post-operative pain score exceeding 7/10 and no pre-operative physiotherapy.