Loss of neuromuscular control related to motion in the acutely ACL-injured knee: an experimental study

Measuring the force perception in knee flexor/ extensor muscles in patients with anterior cruciate ligament injury and healthy subjects

BACKGROUND

Force perception as a contributor to the neuromuscular control of the knee joint may be altered after anterior cruciate ligament (ACL) injury.

OBJECTIVE

This study aimed to compare the force perception accuracy in the knee joints of patients with ACL injury and healthy subjects.

METHODS

Twenty-six patients with ACL injury and 26 healthy subjects participated in this case-control study. Participants were asked to produce 50% of the maximum voluntary isometric contraction of the knee muscles as a target force and reproduce it in their limbs in flexion and extension directions.

RESULTS

There were significant interactions between group and condition as well as group, condition, and limb in the force perception error respectively (P< 0.05). The highest amount of error was seen in the contralateral limb of the ACL injury group when the reference force was produced in the injured limb (P< 0.05).

CONCLUSION

The findings revealed that the force perception accuracy in the knee flexor/extensor muscles of individuals with ACL injury is impaired. Moreover, error is most evident when the patient produces force in the injured limb and replicates it in the uninjured limb in both flexion and extension directions. Therefore, the rehabilitation programs should encompass neuromuscular training in both quadriceps and hamstrings after ACL injury.

Diminished neuromuscular system adaptability following anterior cruciate ligament injury: Examination of knee muscle force variability and complexity

BACKGROUND

Anterior cruciate ligament (ACL) injuries impair knee extensor and flexor force generation and may alter force variability. Fractal scaling exponents quantify signal complexity and reflect neuromuscular system adaptability. The purpose of this study was to evaluate force variability magnitudes and fractal scaling exponents in persons with ACL injuries.

METHODS

Twenty-four individuals with ACL injury (time from injury: 55 ± 66 days) and 25 uninjured controls completed 10-s isometric knee extension and flexion contractions on a dynamometer at 10%, 25%, 35%, and 50% of peak force. The middle 8-s of data were used to calculate coefficients of variation and fractal exponents. Injured and non-injured limbs as well as dominant and non-dominant limbs in the control group were compared with ANOVA (P < 0.05).

FINDINGS

Peak knee extensor and flexor forces were 19% and 10% lower in the injured limb of ACL-deficient participants (P = 0.014 and P = 0.036, respectively). Fractal scaling exponents of knee extensor force signals at 25% and 35% peak force in injured limbs were higher than in non-injured limbs (P = 0.008 and P = 0.027, respectively). The fractal scaling exponent of knee extensor force signals was greater in injured limbs of ACL-deficient participants than in dominant limbs of the control group at 35% peak force (P = 0.046). The magnitude of variability did not differ between limbs in ACL-deficient participants or between the injured and control groups.

INTERPRETATION

Altered fractal exponents in knee extensor force signals represent sensorimotor and neuromuscular system deficits in individuals with ACL injury. Overall, fractal analysis identified both between-limb and between-group differences.

Permanent knee sensorimotor system changes following ACL injury and surgery

The cruciate ligaments are components of the knee capsuloligamentous system providing vital neurosensory and biomechanical function. Since most historical primary ACL repair attempts were unsuccessful, reconstruction has become the preferred surgery. However, an increased understanding of the efficacy of lesion-site scaffolding, innovative suturing methods and materials, and evolving use of biological healing mediators such as platelet-rich plasma and stem cells has prompted reconsideration of what was once believed to be impossible. A growing number of in vivo animal studies and prospective clinical studies are providing increasing support for this intervention. The significance of ACL repair rather than reconstruction is that it more likely preserves the native neurosensory system, entheses, and ACL footprints. Tissue preservation combined with restored biomechanical function increases the likelihood for premorbid neuromuscular control system and dynamic knee stability recovery. This recovery should increase the potential for more patients to safely return to sports at their desired intensity and frequency. This current concepts paper revisits cruciate ligament neurosensory and neurovascular anatomy from the perspective of knee capsuloligamentous system function. Peripheral and central nerve pathways and central cortical representation mapping are also discussed. Surgical restoration of a more physiologically sound knee joint may be essential to solving the osteoarthritis dilemma. Innovative rehabilitative strategies and outcome measurement methodologies using more holistic and clinically relevant measurements that closely link biomechanical and neurosensory characteristics of physiological ACL function are discussed. Greater consideration of task-specific patient physical function and psychobehavioral links should better delineate the true efficacy of all ACL surgical and non-surgical interventions. Level of evidence IV.

Neuromuscular efficiency of the vastus lateralis and biceps femoris muscles in individuals with anterior cruciate ligament injuries

Objective

To analyze strength and integrated electromyography (IEMG) data in order to determine the neuromuscular efficiency (NME) of the vastus lateralis (VL) and biceps femoris (BF) muscles in patients with anterior cruciate ligament (ACL) injuries, during the preoperative and postoperative periods; and to compare the injured limb at these two times, using the non-operated limb as a control.

Methods

EMG data and BF and VL strength data were collected during three maximum isometric contractions in knee flexion and extension movements. The assessment protocol was applied before the operation and two months after the operation, and the NME of the BF and VL muscles was obtained.

Results

There was no difference in the NME of the VL muscle from before to after the operation. On the other hand, the NME of the BF in the non-operated limb was found to have increased, two months after the surgery.

Conclusions

The NME provides a good estimate of muscle function because it is directly related to muscle strength and capacity for activation. However, the results indicated that two months after the ACL reconstruction procedure, at the time when loading in the open kinetic chain within rehabilitation protocols is usually started, the neuromuscular efficiency of the VL and BF had still not been reestablished.

Reduced knee joint moment in ACL deficient patients at a cost of dynamic stability during landing

The current study aimed to examine the effect of anterior cruciate ligament deficiency (ACLd) on joint kinetics and dynamic stability control after a single leg hop test (SLHT). Twelve unilateral ACLd patients and a control subject group (n=13) performed a SLHT over a given distance with both legs. The calculation of joint kinetics was done by means of a soft-tissue artifact optimized rigid full-body model. Margin of stability (MoS) was quantified by the difference between the base of support and the extrapolated center of mass. During landing, the ACLd leg showed lower external knee flexion moments but demonstrated higher moments at the ankle and hip compared to controls (p<0.05). The main reason for the joint moment redistribution in the ACLd leg was a more anterior position of the ground reaction force (GRF) vector, which affected the moment arms of the GRF acting about the joints (p<0.05). For the ACLd leg, trunk angle was more flexed over the entire landing phase compared to controls (p<0.05) and we found a significant correlation between moment arms at the knee joint and trunk angle (r² = 0.48;p<0.01). The consequence of this altered landing strategy in ACLd legs was a more anterior position of the center of mass reducing the MoS (p<0.05). The results illustrate the interaction between trunk angle, joint kinetics and dynamic stability during landing maneuvers and provide evidence of a feedforward adaptive adjustment in ACLd patients (i.e. more flexed trunk angle) aimed at reducing knee joint moments at the cost of dynamic stability control.

Extension and flexion torque variability in ACL deficiency

PURPOSE

To evaluate possible differences in knee extension and flexion torque variability in the anterior cruciate ligament-deficient (ACLD) leg and their dependence on muscle length and visual feedback (VF). Although a knee extension torque deficit is found in the ACLD leg, there is no evidence that variability in submaximal isometric knee extension and flexion torque is affected in the ACLD leg or that it depends on VF.

METHODS

All tests were performed using 13 untrained men with unilateral ACL rupture. Isometric knee extension torques at 90(o) and 120(o) and knee flexion torques at 90(o), 120(o) and 140(o) were evaluated in healthy and ACLD legs. Isometric torque variability at 20% of maximal force was evaluated with or without VF. The coefficients of variation (CV) and permutation entropies (PE) were used to calculate submaximal isometric torque variability.

RESULTS

Healthy legs had significantly greater isometric torques at 90(o) and 120(o) knee angles during knee extension compared with ACLD legs. There were no differences between healthy and ACLD legs in torque variability in knee extension and flexion with or without VF. The PE of knee extension torque at knee angles of 90(o) and 120(o) was significantly (P < 0.05) greater in healthy legs.

CONCLUSIONS

The effect of ACL deficiency on variability (CV) in submaximal isometric knee extension and flexion torque was not significant. However, PE of knee extension submaximal torque was significantly greater in the healthy leg than in the ACLD leg. When estimating ACL deficit, it is important to measure not only isometric maximal torque but also torque variability and complexity using nonlinear tool during submaximal isometric tasks.

LEVEL OF EVIDENCE

III.

Heightened flexor withdrawal responses following ACL rupture are enhanced by passive tibial translation

OBJECTIVE

Hyperexcitability of nociceptive pathways has been demonstrated with several musculoskeletal conditions but not anterior cruciate ligament (ACL) injury. The purpose was to investigate flexor withdrawal reflex (FWR) excitability following ACL rupture and determine if painless stretch of knee joint structures enhanced reflexive responses.

METHODS

Ten subjects with and 10 subjects without unilateral ACL rupture were compared. FWRs were induced through sural nerve stimulus in symmetrical stance and recumbent positions, with the knee in relaxed and stressed condition. Latencies and amplitudes of hamstring electromyographic activity were analyzed.

RESULTS

FWR thresholds were significantly diminished (p=0.05) on the injured limb (11.8±8 mA) compared to non-injured limb (18.6±13 mA) and controls (22.5±3 mA). Anterior tibial translation resulted in increased (p=0.001) amplitude of EMG hamstring response on the injured limb (70±50%) versus control (-1±20%) and decreased latency (p=0.01) of hamstring activation (82.0±13 ms).

CONCLUSIONS

Individuals with ACL rupture demonstrated increased excitability of FWR responses indicated by decreased FWR threshold and reduced hamstring muscle latency. Responses were enhanced by passive stretch of the knee joint.

SIGNIFICANCE

Subjects with ACL rupture demonstrated hyperexcitability of nociceptive pathways on the injured limb which may trigger the FWR more readily and promote the sensation of instability at the knee.

Anterior cruciate ligament deficiency causes brain plasticity: a functional MRI study

BACKGROUND

The mechanoreceptors located in anterior cruciate ligament (ACL) constitute an afferent source of information toward the central nervous system. It has been proposed that ACL deficiency causes a disturbance in neuromuscular control, affects central programs and consequently the motor response resulting in serious dysfunction of the injured limb.

PURPOSE

The objective of this study was to investigate whether chronic anterior cruciate ligament injury causes plastic changes in brain activation patterns.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Seventeen right leg-dominant male participants with chronic anterior cruciate ligament deficiency and 18 matched healthy male participants with no special sport or habitual physical activity participated in this study. Patient selection criteria comprised a complete right unilateral anterior cruciate ligament rupture > or = 6 months before testing. Brain activation was examined by using functional magnetic resonance imaging technique (1.5-T scanner).

RESULTS

Results show that patients with anterior cruciate ligament deficiency had diminished activation in several sensorimotor cortical areas and increased activation in 3 areas compared with controls: presupplementary motor area, posterior secondary somatosensory area, and posterior inferior temporal gyrus.

CONCLUSION

The current study reveals that anterior cruciate ligament deficiency can cause reorganization of the central nervous system, suggesting that such an injury might be regarded as a neurophysiologic dysfunction, not a simple peripheral musculoskeletal injury. This evidence could explain clinical symptoms that accompany this type of injury and lead to severe dysfunction. Understanding the pattern of brain activation after a peripheral joint injury such as anterior cruciate ligament injury lead to new standards in rehabilitation and motor control learning with a wide application in a number of clinical and research areas (eg, surgical procedures, patient re-education, athletic training, etc).