Organization of sensorimotor activity in anterior cruciate ligament reconstructed individuals: an fMRI conjunction analysis

fMRI Activation in Sensorimotor Regions at 6 Weeks After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Brain activity during knee movements is altered throughout the sensorimotor network after anterior cruciate ligament reconstruction (ACLR). Patients at 2 to 5 years after surgery appear to require greater neural activity to perform basic knee movement patterns, but it is unclear if brain activity differences within sensorimotor regions are present early after surgery. It is also unknown whether uninvolved knee movements elicit similar or unique activity compared with involved knee movements.

PURPOSE

To examine brain activity in sensorimotor regions during involved and uninvolved knee movements in patients at 6 weeks after ACLR compared with control participants.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 15 patients who underwent ACLR (mean age, 21.9 ± 4.3 years [range, 17-29 years]; 8 female) and 15 control participants performed 30-second blocks of repeated knee flexion and extension, followed by 30 seconds of rest, during functional magnetic resonance imaging. Regions of interest included the right and left primary motor cortex (M1), right and left primary somatosensory cortex (S1), supplementary motor area (SMA), precuneus, and lingual gyrus. Activity from task-relevant voxels (move > rest) was extracted, and generalized estimating equations evaluated the main effect of group and group-by-limb interaction. Effect sizes were calculated using the Cohen d.

RESULTS

Reduced brain activity during knee flexion and extension was observed in the ACLR group in the ipsilateral M1 and S1, contralateral S1, SMA, and precuneus during movements of the involved and uninvolved knees. There were no group-by-limb interaction effects, indicating no significant differences between the involved knee and uninvolved knee in the ACLR group. Medium to large effect sizes were identified for between-group differences in all regions.

CONCLUSION

At 6 weeks after ACLR, patients exhibited bilateral reductions in brain activity during knee movements in multiple sensorimotor regions. These identified regions are associated with motor planning, motor execution, somatosensory function, and sensorimotor integration. These data indicate that ACLR affected sensorimotor brain activity in both limbs during the early postoperative phase of rehabilitation.

The Neuroplastic Outcomes from Impaired Sensory Expectations (NOISE) hypothesis: How ACL dysfunction impacts sensory perception and knee stability

BACKGROUND

The anterior cruciate ligament (ACL) is integral to maintaining knee joint stability but is susceptible to rupture during physical activity. Despite surgical restoration of passive or mechanical stability, patients struggle to regain strength and prior level of function. Recent efforts have focused on understanding how ACL-related changes in the nervous system contribute to deficits in sensorimotor control following injury and reconstruction. We hypothesize that these challenges are partially due to an increase in sensorimotor uncertainty, a state that reduces the precision of movement control.

OBJECTIVES

This review proposes the ACL NOISE (Neuroplastic Outcomes from Impaired Sensory Expectations) hypothesis, reframing current literature to provide a case that increased sensory noise following ACL injury and reconstruction disrupts sensory predictions, which are anticipations of immediate sensory outcomes or motor commands. This disruption in sensory predictions may contribute to altered neurophysiology, such as cross-modal brain activity, and other persistent clinical deficits.

DESIGN

Narrative review RESULTS/FINDINGS: Following ACL injury and reconstruction, the knee and nervous system experience various neurophysiological alterations to overcome elevated sensory uncertainty and inaccurate sensory predictions, contributing to persistent motor deficits.

CONCLUSIONS

We provide a theoretical case based on compelling evidence that suggests prolonged impairment after ACL injury may be secondary to uncertainty in knee sensory perception. Future research should consider testing the NOISE hypothesis by creating a paradigm that examines dynamic joint stability in response to unexpected perturbations. This approach would help assess motor coordination errors and drive the development of clinical strategies aimed at reducing sensory uncertainty following ACL reconstruction.

Neural Activity for Uninvolved Knee Motor Control After ACL Reconstruction Differs from Healthy Controls

Recovery from anterior cruciate ligament reconstruction (ACLR) induces bilateral functional and physiological adaptations. Neurophysiologic measures of motor control have focused on the involved knee joint, limiting understanding regarding the extent of bilateral neural adaptations. Therefore, the aim of this study was to investigate differences in neural activity during uninvolved-limb motor control after ACLR compared to healthy controls.

METHODS

Fifteen participants with left ACLR (8 female and 7 male, 21.53 ± 2.7 years, 173.22 ± 10.0 cm, 72.15 ± 16.1 kg, Tegner 7.40 ± 1.1, 43.33 ± 33.1 mo. post-surgery, 2 patellar tendon, and 13 hamstring) and 15 matched controls (8 female, 23.33 ± 2.7 years, 174.92 ± 9.7 cm, 72.14 ± 15.4 kg, Tegner 7.33 ± 1.0) participated. Neural activity was evaluated using functional magnetic resonance imaging on a 3T Siemens Magnetom scanner during four 30-s cycles of a right (uninvolved) knee flexion-extension task paced with a metronome (1.2 Hz) and was completed interspersed with 30 s of rest. A significance threshold of p < 0.05 was used for all analyses, cluster corrected for multiple comparisons, and z-thresholds of >3.1 (subject level), and >2.3 (group level).

RESULTS

The ACLR group had greater neural activity in one statistically significant cluster corresponding to the left middle frontal gyrus (MFG) (834 voxels, z = 3.81, p < 0.01 multiple comparisons corrected) compared to controls.

CONCLUSIONS

These data indicate a potential contribution to uninvolved-knee neuromuscular deficits after injury and support the limitations of using the uninvolved side as a clinical reference. Uninvolved knee motor control after ACLR may require greater cognitive demand. Clinicians should be aware that the uninvolved limb might also demonstrate whole brain alterations limiting clinical inference from functional symmetry.

Knee joint pathology and efferent pathway dysfunction: Mapping muscle inhibition from motor cortex to muscle force

BACKGROUND

Dysfunction in efferent pathways after knee pathology is tied to long-term impairments in quadriceps and hamstrings muscle performance, daily function, and health-related quality of life. Understanding the underlying etiology is crucial for effective treatment and prevention of poor outcomes, such as post-traumatic osteoarthritis or joint replacement.

OBJECTIVES

To synthesize recent evidence of efferent pathway dysfunction (i.e., motor cortex, motor units) among individuals with knee pathology.

DESIGN

Commentary.

METHOD

We summarize the current literature investigating the motor cortex, corticospinal tract, and motoneuron pool in individuals with three common knee pathologies: anterior cruciate ligament (ACL) injury, anterior knee pain (AKP), and knee osteoarthritis (OA). To offer a complete perspective, we draw from studies applying a range of neuroimaging and neurophysiologic techniques.

RESULTS

Adaptations within the motor cortices, corticospinal tract, and motoneuron pool are present in those with knee pathology and underline impairments in quadriceps and hamstrings muscle function. Each pathology has evidence of altered motor system excitability and reduced volitional muscle activation and force-generating capacity, but few impairments were common across ACL injury, AKP, and OA studies. These findings underscore the central role of the motor cortex and motor unit behavior in the long-term outcomes of individuals with knee pathology.

CONCLUSIONS

Adaptations in the efferent pathways underlie persistent muscle dysfunction across three common knee pathologies. This review provides an overview of these changes and summarizes key findings from neurophysiology and neuroimaging studies, offering direction for future research and clinical application in the rehabilitation of joint injuries.

Association between seated trunk control and cortical sensorimotor white matter brain changes in patients with chronic low back pain

Trunk control involves integration of sensorimotor information in the brain. Individuals with chronic low back pain (cLBP) have impaired trunk control and show differences in brain structure and function in sensorimotor areas compared with healthy controls (HC). However, the relationship between brain structure and trunk control in this group is not well understood. This cross-sectional study aimed to compare seated trunk control and sensorimotor white matter (WM) structure in people with cLBP and HC and explore relationships between WM properties and trunk control in each group. Thirty-two people with cLBP and 35 HC were tested sitting on an unstable chair to isolate trunk control; performance was measured using the 95% confidence ellipse area (CEA95) of center-of-pressure tracing. A WM network between cortical sensorimotor regions of interest was derived using probabilistic tractography. WM microstructure and anatomical connectivity between cortical sensorimotor regions were assessed. A mixed-model ANOVA showed that people with cLBP had worse trunk control than HC (F = 12.96; p < .001; ηp2 = .091). There were no differences in WM microstructure or anatomical connectivity between groups (p = 0.564 to 0.940). In the cLBP group, WM microstructure was moderately correlated (|r| = .456 to .565; p ≤ .009) with trunk control. Additionally, the cLBP group demonstrated stronger relationships between anatomical connectivity and trunk control (|r| = .377 to .618 p < .034) compared to the HC group. Unique to the cLBP group, WM connectivity between right somatosensory and left motor areas highlights the importance of interhemispheric information exchange for trunk control. Parietal areas associated with attention and spatial reference frames were also relevant to trunk control. These findings suggest that people with cLBP adopt a more cortically driven sensorimotor integration strategy for trunk control. Future research should replicate these findings and identify interventions to effectively modulate this strategy.

Brain functional connectivity alterations in patients with anterior cruciate ligament injury

Recent advancements in neuroimaging have illustrated that anterior cruciate ligament (ACL) injuries could impact the central nervous system (CNS), causing neuroplastic changes in the brain beyond the traditionally understood biomechanical consequences. While most of previous functional magnetic resonance imaging (fMRI) studies have focused on localized cortical activity changes post-injury, emerging research has suggested disruptions in functional connectivity across the brain. However, these prior investigations, albeit pioneering, have been constrained by two limitations: a reliance on small-sample participant cohorts, often limited to two to three patients, potentially limiting the generalizability of findings, and an adherence to region of interest based analysis, which may overlook broader network interactions. To address these limitations, our study employed resting-state fMRI to assess whole-brain functional connectivity in 15 ACL-injured patients, comparing them to matched controls using two distinct network analysis methods. Using Network-Based Statistics, we identified widespread reductions in connectivity that spanned across multiple brain regions. Further modular connectivity analysis showed significant decreases in inter-modular connectivity between the sensorimotor and cerebellar modules, and intra-modular connectivity within the default-mode network in ACL-injured patients. Our results thus highlight a shift from localized disruptions to network-wide dysfunctions, suggesting that ACL injuries induce widespread CNS changes. This enhanced understanding has the potential to stimulate the development of strategies aiming to restore functional connectivity and improve recovery outcomes.