Pre-synaptic modulation of quadriceps arthrogenic muscle inhibition

Sensorimotor control of functional joint stability: Scientific concepts, clinical considerations, and the articuloneuromuscular cascade paradigm in peripheral joint injury

Human movement depends on sensorimotor control. Sensorimotor control refers to central nervous system (CNS) control of joint stability, posture, and movement, all of which are effected via the sensorimotor system. Given the nervous, muscular, and skeletal systems function as an integrated "neuromusculoskeletal system" for the purpose of executing movement, musculoskeletal conditions can result in a cascade of impairments that affect negatively all three systems. The purpose of this article is to revisit concepts in joint stability, sensorimotor control of functional joint stability (FJS), joint instability, and sensorimotor impairments contributing to functional joint instability. This article differs from historical work because it updates previous models of joint injury and joint instability by incorporating more recent research on CNS factors, skeletal muscle factors, and tendon factors. The new 'articuloneuromuscular cascade paradigm' presented here offers a framework for facilitating further investigation into physiological and biomechanical consequences of joint injury and, in turn, how these follow on to affect physical activity (functional) capability. Here, the term 'injury' represents traumatic joint injury with a focus is on peripheral joint injury. Understanding the configuration of the sensorimotor system and the cascade of post-injury sensorimotor impairments is particularly important for clinicians reasoning rational interventions for patients with mechanical instability and functional instability. Concurrently, neurocognitive processing and neurocognitive performance are also addressed relative to feedforward neuromuscular control of FJS. This article offers itself as an educational resource and scientific asset to contribute to the ongoing research and applied practice journey for developing optimal peripheral joint injury rehabilitation strategies.

Quadriceps strength, patellar tendon quality, relative load exposure, and knee symptoms in male athletes before the anterior cruciate ligament reconstruction

Introduction

Anterior cruciate ligament (ACL) injuries cause knee instability, knee pain, weight-bearing adjustments, and functional deficits but their association to patellar tendon quality is unknown. Our purpose was to investigate quadriceps strength, patellar tendon quality, relative load exposure, perceived knee stability, knee pain, extension angle, and time from ACL injury; in addition to examining their relative associations.

Methods

Injured and uninjured legs of 81 male athletes of different sports with a unilateral ACL injury (18-45 years) were examined. Participants reported location and intensity of knee pain and their perceived stability using a numerical rating scale (NRS 0-10). Strength was tested with an isokinetic device. Tendon quality was measured using ultrasound tissue characterization. Means ± standard deviation (SD) of perceived knee stability, knee extension angle, knee pain, isokinetic quadriceps strength in relation to body mass, proportion of echo-types (I-IV), tendon volume, and number of days from ACL injury to assessment are reported. Values of effect sizes (ES) and correlations (rs) were calculated.

Results

ACL injured leg demonstrated reduced reported knee stability (6.3 ± 2.5), decreased knee extension angle (-0.7 ± 3.1° vs. -2.7 ± 2.2°; ES = 0.7; P < 0.001), greater knee pain (NRS 3.1 ± 2.2 vs. 0.0 ± 0.1; ES = 2.0; P < 0.001), and 22% lower quadriceps strength (228.0 ± 65.0 vs. 291.2 ± 52.9 Nm/kg: ES = 1.2; P < 0.001) as compared to the uninjured leg. However, patellar tendons in both legs displayed similar quality. Quadriceps strength was associated with stability (rs = -0.54; P < 0.001), pain (rs = -0.47; P < 0.001), extension angle (rs = -0.39; P < 0.001), and relative load exposure (rs = -0.34; P < 0.004). Echo-types distribution was beneficially associated with time from ACL injury (rs range: -0.20/ -0.32; P < 0.05).

Discussion

ACL injured athletes displayed knee pain, extension deficit, and weaker quadriceps in the injured leg. While there were no differences in patellar tendon quality between legs, longer time from ACL injury showed better tendon quality.

The effects of pain relief on proprioception and muscle strength for tibial plateau fractures: A randomized controlled trial

OBJECTIVES

To investigate the effect of transcutaneous electrical acupoint stimulation (TEAS) combined with proprioceptive neuromuscular facilitation (PNF) on postural stability, muscle strength and pain in patients with tibial plateau fracture.

METHOD

A 3-arm randomized controlled trial was conducted in 60 patients with tibial plateau fracture. Participants received one of the following interventions: standard treatment (ST group, n = 20), ST + PNF training (ST + PNF group, n = 20), ST + PNF training + TEAS intervention (ST + PNF + TEAS group, n = 20). All treatments lasted for six weeks. Participants' postural stability, muscle strength and pain were evaluated at baseline, after 3 and 6 weeks of intervention.

RESULTS

After 3 weeks of intervention, Between-group comparisons showed that both the ST + PNF group and ST + PNF + TEAS group showed significantly greater performance than the ST group in the postural stability measure (P < 0.02) and pain score(P < 0.05). The peak torque of quadriceps extensors and flexors at the velocity of 60°/s was significantly higher in the ST + PNF + TEAS group than in the ST group (P < 0.02). After 6 weeks of intervention, only the ST + PNF + TEAS group was superior to the ST group in postural stability measure(P < 0.04) and in pain score (P < 0.05). The ST + PNF + TEAS group was significantly higher than the ST + PNF group and the ST group in the peak torque of quadriceps extensors at the velocity of 60°/s and 180°/s (P < 0.01).

CONCLUSION

PNF training could improve dynamic postural stability and relieve pain at three weeks, while TEAS combined with PNF was more effective in relieving pain, strengthening muscle strength and improving dynamic postural stability at six weeks post-intervention.

"But it feels swollen!": the frequency and clinical characteristics of people with knee osteoarthritis who report subjective knee swelling in the absence of objective swelling

Supplemental Digital Content is Available in the Text.

The present results support the coexistence of altered body image (subjective without objective swelling) and pain, disability, and maladaptive beliefs in people with knee osteoarthritis.

Introduction:

There are complex interactions between pain and perceptions of the painful body part in musculoskeletal disorders, and disruption of various body representations in people with chronic pain.

Objectives:

The purpose of this study was to investigate how frequently people with knee osteoarthritis (OA) complain of swelling without objective evidence of swelling, and describe the clinical characteristics of this population.

Methods:

Forty-six people with knee OA (68.1 ± 8.8 years) participated in this cross-sectional study. Subjective and objective swelling was evaluated by knee-specific body perception questionnaire and ultrasonography, respectively. Pain intensity, disability, pain-related beliefs, 2-point discrimination threshold, and quadriceps muscle strength were also evaluated.

Results:

Approximately 1/3 of participants (n = 15) had subjective feelings of knee swelling in the absence of objective swelling (S only). Fifteen participants had both subjective and objective knee swelling (S + O group) and 16 had neither subjective nor objective knee swelling (No S/O group). Participants in the S only group had similar pain or disability as those in the S + O group but had more severe pain or disability than those with in the No S/O group. Those in the S only group also had larger 2-point discrimination distance threshold at the medial knee (impaired tactile acuity) than those in the S + O group and had more dysfunctional pain catastrophizing and pain-related self-efficacy than both other groups.

Conclusion:

Our results suggest that about 30% of people with knee OA perceive swelling of the knee in the absence of any objective swelling and that this is accompanied by severe pain and functional disability. Considering altered body image of the knee may reveal relevant treatment-based subgroups in people with knee OA.

Rupture, reconstruction, and rehabilitation: A multi-disciplinary review of mechanisms for central nervous system adaptations following anterior cruciate ligament injury

BACKGROUND

Despite surgical reconstruction and extensive rehabilitation, persistent quadriceps inhibition, gait asymmetry, and functional impairment remain prevalent in patients after anterior cruciate ligament (ACL) injury. A combination of reports have suggested underlying central nervous system adaptations in those after injury govern long-term neuromuscular impairments. The classic assumption has been to attribute neurophysiologic deficits to components of injury, but other factors across the continuum of care (e.g. surgery, perioperative analgesia, and rehabilitative strategies) have been largely overlooked.

OBJECTIVE

This review provides a multidisciplinary perspective to 1) provide a narrative review of studies reporting neuroplasticity following ACL injury in order to inform clinicians of the current state of literature and 2) provide a mechanistic framework of neurophysiologic deficits with potential clinical implications across all phases of injury and recovery (injury, surgery, and rehabilitation) RESULTS: Studies using a variety of neurophysiologic modalities have demonstrated peripheral and central nervous system adaptations in those with prior ACL injury. Longitudinal investigations suggest neurophysiologic changes at spinal-reflexive and corticospinal pathways follow a unique timecourse across injury, surgery, and rehabilitation.

CONCLUSION

Clinicians should consider the unique injury, surgery, anesthesia, and rehabilitation on central nervous system adaptations. Therapeutic strategies across the continuum of care may be beneficial to mitigate maladaptive neuroplasticity in those after ACL injury.

Slacklining as therapy to address non-specific low back pain in the presence of multifidus arthrogenic muscle inhibition

Low back pain (LBP) represents the most prevalent, problematic and painful of musculoskeletal conditions that affects both the individual and society with health and economic concerns. LBP is a heterogeneous condition with multiple diagnoses and causes. In the absence of consensus definitions, partly because of terminology inconsistency, it is further referred to as non-specific LBP (NSLBP). In NSLBP patients, the lumbar multifidus (MF), a key stabilizing muscle, has a depleted role due to recognized myocellular lipid infiltration and wasting, with the potential primary cause hypothesized as arthrogenic muscle inhibition (AMI). This link between AMI and NSLBP continues to gain increasing recognition. To date there is no 'gold standard' or consensus treatment to alleviate symptoms and disability due to NSLBP, though the advocated interventions are numerous, with marked variations in costs and levels of supportive evidence. However, there is consensus that NSLBP management be cost-effective, self-administered, educational, exercise-based, and use multi-modal and multi-disciplinary approaches. An adjuvant therapy fulfilling these consensus criteria is 'slacklining', within an overall rehabilitation program. Slacklining, the neuromechanical action of balance retention on a tightened band, induces strategic indirect-involuntary therapeutic muscle activation exercise incorporating spinal motor control. Though several models have been proposed, understanding slacklining's neuro-motor mechanism of action remains incomplete. Slacklining has demonstrated clinical effects to overcome AMI in peripheral joints, particularly the knee, and is reported in clinical case-studies as showing promising results in reducing NSLBP related to MF deficiency induced through AMI (MF-AMI). Therefore, this paper aims to: rationalize why and how adjuvant, slacklining therapeutic exercise may positively affect patients with NSLBP, due to MF-AMI induced depletion of spinal stabilization; considers current understandings and interventions for NSLBP, including the contributing role of MF-AMI; and details the reasons why slacklining could be considered as a potential adjuvant intervention for NSLBP through its indirect-involuntary action. This action is hypothesized to occur through an over-ride or inhibition of central down-regulatory induced muscle insufficiency, present due to AMI. This subsequently allows neuroplasticity, normal neuro-motor sequencing and muscle re-activation, which facilitates innate advantageous spinal stabilization. This in-turn addresses and reduces NSLBP, its concurrent symptoms and functional disability. This process is hypothesized to occur through four neuro-physiological processing pathways: finite neural delay; movement-control phenotypes; inhibition of action and the innate primordial imperative; and accentuated corticospinal drive. Further research is recommended to investigate these hypotheses and the effect of slacklining as an adjuvant therapy in cohort and control studies of NSLBP populations.

Using neuromuscular electrical stimulation in conjunction with ultrasound imaging technique to investigate lumbar multifidus muscle activation deficit

Lumbar multifidus muscle (LM) activation deficit has been proposed as a potential underlying mechanism responsible for recurrence episode of low back pain (LBP). The quantification of voluntary LM activation can provide a better understanding of the role of muscle activation deficit in LBP. The objective of this technical report is to propose a new approach using neuromuscular electrical stimulation (NMES) in combination with the ultrasound imaging technique (USI) to investigate the ability of individual to voluntarily activate the LM. We recruited ten participants with a recurrent LBP (rLBP) and twelve participants with no history of LBP (NoLBP). Theoretically, the superimposition of NMES on the LM during maximum voluntary isometric contraction (MVIC) should activate all motor units available in the LM. The percentage of LM activation (%LM) can be calculated by the changes of LM thickness during MVIC, divided by the changes of LM thickness during the combination of MVIC and NMES. This %LM was used to compare between groups. The individuals with rLBP had significantly lower %LM (p < 0.05) compared with the NoLBP counterpart (%LM = 72.4 and 92.9, respectively). Results demonstrate that this new approach can potentially differentiate %LM among individuals with rLBP and NoLBP. This new approach can be potentially used to 1) determine the extent of LM activation deficit, 2) identify the existence of muscle activation deficit in the LM, and 3) objectively measure the effect of the intervention designed to address the LM activation deficit.

Single bout of vibration-induced hamstrings fatigue reduces quadriceps inhibition and coactivation of knee muscles after anterior cruciate ligament (ACL) reconstruction

Persistent quadriceps strength deficits in individuals with anterior cruciate ligament reconstruction (ACLr) have been attributed to arthrogenic muscle inhibition (AMI). The purpose of the present study was to investigate the effect of vibration-induced hamstrings fatigue on AMI in patients with ACLr. Eight participants with unilateral ACLr (post-surgery time: M = 46.5, SD = 23.5 months; age: M = 21.4, SD = 1.4 years) and eight individuals with no previous history of knee injury (age: M = 22.5, SD = 2.5 years) were recruited. A fatigue protocol, consisting of 10 min of prolonged local hamstrings vibration, was applied to both the ACLr and control groups. The central activation ratio (CAR) of the quadriceps was measured with a superimposed burst of electrical stimulation, and hamstrings/quadriceps coactivation was assessed using electromyography (EMG) during isometric knee extension exercises, both before and after prolonged local vibration. For the ACLr group, the hamstrings strength, measured by a load cell on a purpose-built chair, was significantly (P = 0.016) reduced about 14.5%, indicating fatigue was actually induced in the hamstrings. At baseline, the ACLr group showed a trend (P = 0.051) toward a lower quadriceps CAR (M = 93.2%, SD = 6.2% versus M = 98.1%, SD = 1.1%) and significantly (P = 0.001) higher hamstrings/quadriceps coactivation (M = 15.1%, SD = 6.2% versus M = 7.5%, SD = 4.0%) during knee extension compared to the control group. The fatigue protocol significantly (P = 0.001) increased quadriceps CAR (from M = 93.2%, SD = 6.2% to M = 97.9%, SD = 2.8%) and significantly (P = 0.006) decreased hamstrings/quadriceps coactivation during knee extension (from M = 15.1%, SD = 6.2% to M = 9.5%, SD = 4.5%) in the ACLr group. In conclusion, vibration-induced hamstrings fatigue can alleviate AMI of the quadriceps in patients with ACLr. This finding has clinical implications in the management of recovery for ACLr patients with quadriceps strength deficits and dysfunction.

Femoral nerve block at time of ACL reconstruction causes lasting quadriceps strength deficits and may increase short-term risk of re-injury

PURPOSE

To determine whether femoral nerve blockade (FNB) at the time of primary ACL reconstruction is associated with meeting isokinetic extension strength return to sport criteria near completion of physical therapy and whether FNB affects 1-year or 2-year risk of ipsilateral ACL graft rupture or contralateral native ACL injury.

METHODS

Three-hundred and sixty patients (n = 244 with FNB, n = 116 no FNB) underwent primary ACL reconstruction. All patients completed rehabilitation and underwent functional strength testing towards the end of knee rehabilitation (mean 5.6 months post-surgery). Association between FNB and isokinetic extension strength limb symmetry index (LSI) (goal LSI ≥ 90% for return to sport) as well as risk of recurrent ACL injury within first or second year after surgery was evaluated.

RESULTS

Ipsilateral or contralateral ACL injury within 2 years occurred in 11.2% of patients with FNB and 5.7% without FNB (p = 0.01). Patients with FNB had higher incidence of ipsilateral graft rupture within the first year after surgery but no difference in graft rupture during the second. Two-year risk of contralateral ACL injury was similar in both groups. At the time of initial testing, patients who received FNB had lower fast isokinetic extension LSI versus patients without FNB and were less likely achieve a goal ≥ 90% LSI; slow extension LSI was unaffected.

CONCLUSION

Use of FNB at the time of primary ACL reconstruction can negatively affect achievement of isokinetic extension strength return to sport criteria. FNB increases risk of graft rupture within the first year after surgery but does not affect re-injury risk during the second. FNB may not be appropriate for use in patients already at high risk of ACL re-injury.

LEVEL OF EVIDENCE

III.

Risk factors and the natural history of accelerated knee osteoarthritis: a narrative review

BACKGROUND

Osteoarthritis is generally a slowly progressive disorder. However, at least 1 in 7 people with incident knee osteoarthritis develop an abrupt progression to advanced-stage radiographic disease, many within 12 months. We summarize what is known - primarily based on findings from the Osteoarthritis Initiative - about the risk factors and natural history of accelerated knee osteoarthritis (AKOA) - defined as a transition from no radiographic knee osteoarthritis to advanced-stage disease < 4 years - and put these findings in context with typical osteoarthritis (slowly progressing disease), aging, prior case reports/series, and relevant animal models. Risk factors in the 2 to 4 years before radiographic manifestation of AKOA (onset) include older age, higher body mass index, altered joint alignment, contralateral osteoarthritis, greater pre-radiographic disease burden (structural, symptoms, and function), or low fasting glucose. One to 2 years before AKOA onset people often exhibit rapid articular cartilage loss, larger bone marrow lesions and effusion-synovitis, more meniscal pathology, slower chair-stand or walking pace, and increased global impact of arthritis than adults with typical knee osteoarthritis. Increased joint symptoms predispose a person to new joint trauma, which for someone who develops AKOA is often characterized by a destabilizing meniscal tear (e.g., radial or root tear). One in 7 people with AKOA onset subsequently receive a knee replacement during a 9-year period. The median time from any increase in radiographic severity to knee replacement is only 2.3 years. Despite some similarities, AKOA is different than other rapidly progressive arthropathies and collapsing these phenomena together or extracting results from one type of osteoarthritis to another should be avoided until further research comparing these types of osteoarthritis is conducted. Animal models that induce meniscal damage in the presence of other risk factors or create an incongruent distribution of loading on joints create an accelerated form of osteoarthritis compared to other models and may offer insights into AKOA.

CONCLUSION

Accelerated knee osteoarthritis is unique from typical knee osteoarthritis. The incidence of AKOA in the Osteoarthritis Initiative and Chingford Study is substantial. AKOA needs to be taken into account and studied in epidemiologic studies and clinical trials.

Pathomechanics Underlying Femoroacetabular Impingement Syndrome: Theoretical Framework to Inform Clinical Practice

Over the last decade, there has been a marked increase in attention to, and interest in, femoroacetabular impingement syndrome (FAIS). Despite continued efforts by researchers and clinicians, the development, progression, and appropriate treatment of FAIS remains unclear. While research across various disciplines has provided informative work in various areas related to FAIS, the underlying pathomechanics, time history, and interaction between known risk factors and symptoms remain poorly understood. The purpose of this perspective is to propose a theoretical framework that describes a potential pathway for the development and progression of FAIS. This paper aims to integrate relevant knowledge and understanding from the growing literature related to FAIS to provide a perspective that can inform future research and intervention efforts.

The effect of a single high velocity low amplitude hip mobilization on strength in subjects with knee injuries

BACKGROUND

Manual therapy have been used as a disinhibitory intervention to increase muscle activation before performing functional tasks that are limited by weakness. Knee injuries are commonly associated with weakness in quadriceps and gluteus. Currently, there is no evidence to support anecdotal experience that a hip distraction mobilization improves muscle performance in subjects with knee injuries and lower extremity weakness.

OBJECTIVES

To determine if a hip distraction mobilization would result in an immediate change of maximal force output of the quadriceps and gluteus.

DESIGN

Non-controlled observational pre-post design.

METHODS

Forty individuals with knee pathology were included. Subjects underwent quadriceps, gluteus maximus, and gluteus medius muscle strength assessment before a single hip distraction of the symptomatic side. An immediate re-assessment of muscle strength of both symptomatic and asymptomatic sides followed the mobilization.

RESULTS

/findings: Comparing pre-to post-mobilization strength on the symptomatic side, a significant increase was found with the gluteus maximus (average change = 2.0 kg [95%CI 0.6-3.4]; p < 0.01) but not gluteus medius (0.2 kg [-0.7-1.0]; p = 0.71) or quadriceps (0.1 kg [-1.4-1.7]; p = 0.86). When comparing the strength on the symptomatic side in subjects with weakness greater than the MDD₉₅ (0.7-2.9 kg), a significant increase was again found for gluteus maximus (4.7 kg [2.6-6.8]; p < 0.01) but not for gluteus medius (0.2 kg [-1.0-1.4]; p = 0.71) or quadriceps (1.6 kg [-0.7-3.9]; p = 0.15).

CONCLUSION

A single hip distraction resulted in a significant increase in gluteus maximus strength but did not produce a change in gluteus medius or quadriceps strength in subjects with knee injuries.

Peripheral Nociception Is Associated with Voluntary Activation Deficits and Quadriceps Weakness Following Total Knee Arthroplasty

BACKGROUND

Quadriceps weakness is a hallmark of total knee arthroplasty and is driven by reduced voluntary muscle activation following the surgical procedure. The mechanisms underlying postoperative activation deficits are not well established, although nociception has been implicated via both spinal reflex and supraspinal pathways. The purpose of this study was to assess the role of nociception in postoperative recovery of strength and activation.

METHODS

A total of 53 participants were assessed prior to total knee arthroplasty and at 6 weeks postoperatively. Quadriceps strength was measured by maximum voluntary isometric contraction, and activation was measured by the doublet interpolation technique. The pressure-pain threshold was used to measure local sensitization (at the knee joint) and systemic sensitization (at the forearm). Changes in outcomes (strength and activation) were regressed against pressure-pain threshold measurements. Mediation analyses were planned for significant associations to investigate whether deficits in voluntary activation were implicated on a causal pathway between pressure-pain threshold measures and postoperative strength loss.

RESULTS

Knee pressure-pain threshold measures were significantly associated with reduced voluntary quadriceps activation (beta = -0.04; p = 0.009) and diminished quadriceps strength after total knee arthroplasty (beta = -0.07; p = 0.001). There was also a mediation effect of voluntary activation on the relationship between the knee pressure-pain threshold and quadriceps strength. After correcting for multiple comparisons, relationships between the forearm pressure-pain threshold and strength and activation did not reach significance.

CONCLUSIONS

The measures of local nociceptor sensitization were related to reduced strength and activation following total knee arthroplasty. This is consistent with a causal pathway linking increased firing of knee joint nociceptors to reduced activation and reduced strength. Future randomized studies should investigate whether peripherally directed pain therapies reduce pain while also promoting the recovery of quadriceps strength via an improved capacity for voluntary activation.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Experimental muscle pain of the vastus medialis reduces knee joint extensor torque and alters quadriceps muscle contributions as revealed through musculoskeletal modeling

BACKGROUND

Voluntary activation deficit of the quadriceps muscle group is a common symptom in populations with knee joint injury. Musculoskeletal modeling and simulations can improve our understanding of pathological conditions; however, they are mathematically complex which can limit their clinical application. A practical subject-specific modeling framework is introduced to evaluate knee extensor inhibition and muscle force contributions to isometric knee joint torques in healthy adults with and without experimentally induced quadriceps muscle pain.

METHODS

A randomized cross-over placebo controlled study design was used. Subject-specific maximum knee joint extension torque and quadriceps electromyographic data from 13 uninjured young adults were combined in a modeling framework to determine optimal muscle strength scaling parameters and ideal torque. Strength deficit ratios (experimental torque/ideal torque) and individual muscle contribution to experimental torque was computed before and after intramuscular hypertonic (pain inducing) and isotonic (sham) saline was injected to the vastus medialis.

FINDINGS

Decreased experimental knee extension torque (-8%) and vastus medialis electromyography (-26%) amplitude pre- to post- hypertonic injection was observed. Correspondingly, significant decreases in the knee extensor strength deficit ratio (-18%) and percent contribution of vastus medialis to experimental torque (-24%) was observed pre- to post- hypertonic injection. No differences were observed with isotonic injections, confirming the validity of the model.

INTERPRETATION

Our practical method to estimate strength ratios can be easily implemented within a musculoskeletal modeling framework to improve the validity of model estimates. This, in turn, can increase our understanding of the relationship between neuromuscular deficits and functional outcomes in patient populations.

The hamstring/quadriceps ratio is an indicator of function in ACL-deficient, but not in ACL-reconstructed knees

PURPOSE

The purpose of this study was to investigate the isokinetic, eccentric and isometric hamstring/quadriceps (HQ) ratios in patients before and after ACL reconstruction (ACLR) using bone-patellar tendon grafts and to establish the relationships between HQ ratio and knee function.

METHODS

Forty-four patients (mean age of 26.6 years) underwent isokinetic testing of quadriceps and hamstring muscles before and after ACLR and HQ ratios were calculated. Lysholm, IKDC and Cincinnati Scores were used to assess function. Isokinetic concentric and eccentric peak torque (Nm/kg) was measured at three different speeds: 60, 120, and 180°/s. Isometric strength was tested at 30° and 60° of knee flexion.

RESULTS

For the isometric tests, the HQ ratio between the involved and non-involved limb was not different for the ACLD knee (p = 0.28) at 30° knee flexion, but significant at the 60° flexion angle (p = 0.02) and for the ACLR knees at 30° and 60° (p = 0.02). For the isokinetic tests, the ratio between involved and non-involved limb was significant for ACL-deficient knees at both 60 (p = 0.039) and 120°/s (p = 0.05). There were significant differences between limbs for all speeds in ACLR knees (p = 0.0003-0.01). For the eccentric tests, the HQ ratio between the involved and non-involved limbs was not significant for both the ACLD (p = 0.19) and ACLR knees (p = 0.29) at the speed of 60°/s. At 120 and 180°/s, there were significant differences between limbs for both the ACLD (p = 0.02) and ACLR knees (p = 0.003). Linear regression did not reveal significant relationships between Cincinnati, Lysholm, and IKDC scores and HQ ratios in the ACLD (R² = 0.35, p = 0.58; R² = 0.34, p = 0.63; R² = 0.38, p = 0.49). In contrast, there were significant correlations between the Lysholm and IKDC scores and HQ ratios in the ACLR knees (R² = 0.84, p = 0.002; R² = 0.86, p = 0.001).

CONCLUSIONS

The findings of this study suggest that the HQ ratio in ACLD patients was not a predictor, but an indicator of patient-perceived knee function following ACLR.

LEVEL OF EVIDENCE

Level IV, case series.

Single-Shot Femoral Nerve Block Does Not Cause Long-Term Strength and Functional Deficits Following Anterior Cruciate Ligament Reconstruction

PURPOSE

To determine if patients treated with a single-shot femoral nerve block have strength and functional deficits at 9-month follow-up.

METHODS

Forty-three patients who underwent primary anterior cruciate ligament reconstructions were randomized to receive either a preoperative single-shot femoral nerve block or local infiltration anesthesia for primary pain control. All patients underwent a standardized comprehensive rehabilitation program postoperatively. Isokinetic strength and function was tested using a Biodex machine at 9 months or more postoperatively comparing the operative and nonoperative extremity.

RESULTS

No significant difference in strength was found at an average of 10.6 months postoperatively (range, 9-15 months) between the femoral nerve block and control groups. In comparing strength deficits, we found no difference in slow isokinetic extension strength (22.4% vs 27.8%, P = .51), fast isokinetic extension strength (18.5% vs 12.5%, P = .41), slow isokinetic flexion strength (11.0% vs 15.1%, P = .55), and fast isokinetic flexion strength (8.2% vs 4.9%, P = .56) in the femoral nerve block versus control groups, respectively. In terms of functional outcomes, there also was no difference in deficits for single-leg hop distance (P = .12), timed single-leg hop (P = .74), and single-leg triple hop distance (P = .94). Maximal strength noted to be within 15% of the contralateral limb was achieved in 40% of patients and maximal function in 63% of patients at an average of 10.6 months postoperatively. A 13% complication rate was found in patients who received a femoral nerve block (1 with prolonged quadriceps inhibition and 2 with prolonged sensory disturbances).

CONCLUSIONS

Our study found a 13% motor/sensory complication rate in patients who underwent femoral nerve block for pain control after anterior cruciate ligament reconstruction. Although these deficits may persist, they are not permanent and are not different when compared with controls at 9-month follow-up. However, maximal strength and function are not fully restored at normal return to play time and rehabilitation should continue long term to maximize recovery.

LEVEL OF EVIDENCE

Level I, prospective randomized trial.

Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability

PURPOSE

Persistent voluntary quadriceps activation deficits are common after anterior cruciate ligament reconstruction (ACLR), but the direct causes are unclear. The primary purpose of this study was to determine whether spinal reflex excitability deficits are present in individuals with a history of ACLR, and secondarily to determine whether spinal reflex excitability predicts which individuals possess full voluntary quadriceps activation.

METHODS

One hundred and forty-seven individuals (74 healthy and 73 ACLR) participated in this cross-sectional case-control study. Quadriceps spinal reflex excitability was quantified using the Hoffmann reflex normalized to the maximal muscle response (H:M ratio). Voluntary quadriceps activation was evaluated with the burst superimposition technique and calculated via the central activation ratio (CAR). Separate 2 × 2 ANCOVA tests were used to compare between-limb and between-group differences for H:M ratio and CAR. A receiver operating characteristic curve was used to determine the accuracy of H:M ratio to predict if ACLR participants present with full voluntary activation (CAR ≥ 0.95).

RESULTS

The ACLR H:M ratio was not different between limbs or compared with the healthy group (P > 0.05). Although ACLR CAR was lower bilaterally compared with the healthy group (P < 0.001), it did not differ between limbs. The H:M ratio has poor accuracy for predicting which individuals exhibit full voluntary activation (receiver operating characteristic area under the curve = 0.52, 95% CI = 0.37,0.66; odds ratio = 2.2, 95% CI = 0.8, 5.9).

CONCLUSIONS

Spinal reflex excitability did not differ between limbs in individuals with ACLR or compared with healthy participants. The level of quadriceps spinal reflex excitability has poor accuracy at predicting which ACLR individuals would demonstrate full voluntary quadriceps activation.

Performance on a Clinical Quadriceps Activation Battery Is Related to a Laboratory Measure of Activation and Recovery After Total Knee Arthroplasty

OBJECTIVE

To determine the relation between performance on a clinical quadriceps activation battery with (1) activation measured by doublet interpolation and (2) recovery of quadriceps strength and functional performance after total knee arthroplasty (TKA).

DESIGN

Planned secondary analysis of a randomized controlled trial.

SETTING

University research laboratory.

PARTICIPANTS

Patients (N=162; mean age, 63±7y; 89 women) undergoing TKA.

MAIN OUTCOME MEASURES

Patients were classified as high (quadriceps activation battery ≥4/6) or low (quadriceps activation battery ≤3/6) based on performance on the quadriceps activation battery measured 4 days after TKA. Differences between groups in activation and recovery at 1, 2, 3, 6, and 12 months after TKA were compared using a repeated-measures maximum likelihood model.

RESULTS

The low quadriceps activation battery group demonstrated poorer quadriceps activation via doublet interpolation (P=.01), greater quadriceps strength loss (P=.01), and greater functional performance decline (all P<.001) at 1 month after TKA compared with the high quadriceps activation battery group. Differences between low and high quadriceps activation battery groups on all measures did not persist at 3 and 12 months (all P>.05).

CONCLUSIONS

Poor performance on the quadriceps activation battery early after TKA is related to poor quadriceps activation and poor recovery in the early postoperative period. Patients in the low quadriceps activation battery group took 3 months to recover to the same level as the high quadriceps activation battery group. The quadriceps activation battery may be useful in identifying individuals who need specific interventions to target activation deficits or different care pathways in the early postoperative period to speed recovery after TKA.

Anterior cruciate ligament reconstruction does not induce further gamma loop abnormalities on the intact side of the quadriceps femoris: A longitudinal study

This study aimed to investigate the effect of surgery on the gamma loop of the quadriceps on the side with an intact knee in patients with anterior cruciate ligament (ACL) injuries. We compared longitudinally the response of alpha motor neurons to vibration stimulation of the quadriceps on the side with an intact knee before and after ACL reconstruction. To evaluate alpha motor neuron response, we measured the maximal knee extension strength and integrated electromyography of the vastus medialis, vastus lateralis, and rectus femoris. After obtaining pre-vibration data from each subject, vibration stimulation was applied to the infrapatellar tendon, and the same measurements were performed immediately after stimulation. The results of this study showed that the response to prolonged vibration stimulation on the intact side of the quadriceps did not differ pre- and post-surgery. As vibration stimuli normally elicit a decrease in alpha motor neuron activity in normal individuals, abnormal responses to prolonged vibration stimulation of the quadriceps on the side with an intact knee might be observed in patients with ACL injuries. The abnormality of the gamma loop of the quadriceps on the side with an intact knee was probably induced by the rupture. Based on these results, we conclude that surgery does not induce further gamma loop abnormalities on the intact side of the quadriceps.

Neural Excitability and Joint Laxity in Chronic Ankle Instability, Coper, and Control Groups

CONTEXT

Neuromuscular and mechanical deficiencies are commonly studied in participants with chronic ankle instability (CAI). Few investigators have attempted to comprehensively consider sensorimotor and mechanical differences among people with CAI, copers who did not present with prolonged dysfunctions after an initial ankle sprain, and a healthy control group.

OBJECTIVE

To determine if differences exist in spinal reflex excitability and ankle laxity among participants with CAI, copers, and healthy controls.

DESIGN

Case-control study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-seven participants with CAI, 30 participants categorized as copers, and 26 healthy control participants.

MAIN OUTCOME MEASURE(S)

We assessed spinal reflex excitability of the soleus using the Hoffmann reflex protocol. Participants' ankle laxity was measured with an instrumented ankle arthrometer. The maximum Hoffmann reflex : maximal muscle response ratio was calculated. Ankle laxity was measured as the total displacement in the anterior-posterior directions (mm) and total rotation in the inversion and eversion directions (°).

RESULTS

Spinal reflex excitability was diminished in participants with CAI compared with copers and control participants (P = .01). No differences were observed among any of the groups for ankle laxity.

CONCLUSION

Changes in the spinal reflex excitability of the soleus that likely affect ankle stability were seen only in the CAI group, yet no mechanical differences were noted across the groups. These findings support the importance of finding effective ways to increase spinal reflex excitability for the purpose of treating neural excitability dysfunction in patients with CAI.

Whole-Body and Local Muscle Vibration Immediately Improve Quadriceps Function in Individuals With Anterior Cruciate Ligament Reconstruction

OBJECTIVE

To determine the immediate effects of a single session of whole-body vibration (WBV) and local muscle vibration (LMV) on quadriceps function in individuals with anterior cruciate ligament reconstruction (ACLR).

DESIGN

Singe-blind, randomized crossover trial.

SETTING

Research laboratory.

PARTICIPANTS

Population-based sample of individuals with ACLR (N=20; mean age ± SD, 21.1±1.2y; mean mass ± SD, 68.3±14.9kg; mean time ± SD since ACLR, 50.7±21.3mo; 14 women; 16 patellar tendon autografts, 3 hamstring autografts, 1 allograft).

INTERVENTIONS

Participants performed isometric squats while being exposed to WBV, LMV, or no vibration (control). Interventions were delivered in a randomized order during separate visits separated by 1 week.

MAIN OUTCOME MEASURES

Quadriceps active motor threshold (AMT), motor-evoked potential (MEP) amplitude, Hoffmann reflex (H-reflex) amplitude, peak torque (PT), rate of torque development (RTD), electromyographic amplitude, and central activation ratio (CAR) were assessed before and immediately after a WBV, LMV, or control intervention.

RESULTS

There was an increase in CAR (+4.9%, P=.001) and electromyographic amplitude (+16.2%, P=.002), and a reduction in AMT (-3.1%, P<.001) after WBV, and an increase in CAR (+2.7%, P=.001) and a reduction in AMT (-2.9%, P<.001) after LMV. No effect was observed after WBV or LMV in H-reflex, RTD, or MEP amplitude. AMT (-3.7%, P<.001), CAR (+5.7%, P=.005), PT (+.31Nm/kg, P=.004), and electromyographic amplitude (P=.002) in the WBV condition differed from the control condition postapplication. AMT (-3.0% P=.002), CAR (+3.6%, P=.005), and PT (+.30Nm/kg, P=.002) in the LMV condition differed from the control condition postapplication. No differences were observed between WBV and LMV postapplication in any measurement.

CONCLUSIONS

WBV and LMV acutely improved quadriceps function and could be useful modalities for restoring quadriceps strength in individuals with knee pathologies.

Influence of Anterior Cruciate Ligament Tear on Thigh Muscle Strength and Hamstring-to-Quadriceps Ratio: A Meta-Analysis

Theoretical compensation after anterior cruciate ligament (ACL) tear could cause quadriceps weakness and hamstring activation, preventing anterior tibial subluxation and affecting the expected hamstring-to-quadriceps ratio. Although quadriceps weakness often occurs after ACL tears, it remains unclear whether hamstring strength and hamstring-to-quadriceps ratio increase in ACL deficient knees. This meta-analysis compared the isokinetic muscle strength of quadriceps and hamstring muscles, and the hamstring-to-quadriceps ratio, of the injured and injured limbs of patients with ACL tears. This meta-analysis included all studies comparing isokinetic thigh muscle strengths and hamstring-to-quadriceps ratio in the injured and uninjured legs of patients with ACL tear, without or before surgery. Thirteen studies were included in the meta-analysis. Quadriceps and hamstring strengths were 22.3 N∙m (95% CI: 15.2 to 29.3 N∙m; P<0.001) and 7.4 N∙m (95% CI: 4.3 to 10.5 N∙m; P<0.001) lower, respectively, on the injured than on the uninjured side. The mean hamstring-to-quadriceps ratio was 4% greater in ACL deficient than in uninjured limbs (95% CI: 1.7% to 6.3%; P<0.001). Conclusively, Decreases were observed in both the quadriceps and hamstring muscles of patients with ACL tear, with the decrease in quadriceps strength being 3-fold greater. These uneven reductions slightly increase the hamstring-to-quadriceps ratio in ACL deficient knees.

Is Hip Abduction Strength Asymmetry Present in Female Runners in the Early Stages of Patellofemoral Pain Syndrome?

BACKGROUND

The current literature indicates that hip abduction weakness in female patients is associated with ipsilateral patellofemoral pain syndrome (PFPS) as part of the weaker hip abductor complex. Thus, it has been suggested that clinicians should consider screening female athletes for hip strength asymmetry to identify those at risk of developing PFPS to prevent the condition. However, no study to date has demonstrated that hip strength asymmetry exists in the early stages of PFPS.

PURPOSE

To determine whether hip abduction strength asymmetry exists in female runners with early unilateral PFPS, defined as symptoms of PFPS not significant enough to cause patients to seek medical attention or prevent them from running at least 10 miles per week.

STUDY DESIGN

Controlled laboratory study.

METHODS

This study consisted of 21 female runners (mean age, 30.5 years; range, 18-45 years) with early unilateral PFPS, who had not yet sought medical care and who were able to run at least 10 miles per week, and 36 healthy controls comparably balanced for age, height, weight, and weekly running mileage (mean, 18.5 mi/wk). Study volunteers were recruited using flyers and from various local running events in the metropolitan area. Bilateral hip abduction strength in both a neutral and extended hip position was measured using a handheld dynamometer in each participant by an examiner blinded to group assignment.

RESULTS

Patients with early unilateral PFPS demonstrated no significant side-to-side difference in hip abduction strength, according to the Hip Strength Asymmetry Index, in both a neutral (mean, 83.5 ± 10.2; P = .2272) and extended hip position (mean, 96.3 ± 21.9; P = .6671) compared with controls (mean, 87.0 ± 8.3 [P = .2272] and 96.6 ± 16.2 [P = .6671], respectively). Hip abduction strength of the affected limb in patients with early unilateral PFPS (mean, 9.9 ± 2.2; P = .0305) was significantly stronger than that of the weaker limb of control participants (mean, 8.9 ± 1.4; P = .0305) when testing strength in a neutral hip position; however, no significant difference was found when testing the hip in an extended position (mean, 7.0 ± 1.4 [P = .1406] and 6.6 ± 1.5 [P =.1406], respectively).

CONCLUSION

The study data show that early stages of unilateral PFPS in female runners is not associated with hip abduction strength asymmetry and that hip abduction strength tested in neutral is significantly greater in the affected limb in the early stages of PFPS compared with the unaffected limb. However, when tested in extension, no difference exists. Further studies investigating the early stages of PFPS are warranted.

CLINICAL RELEVANCE

Unlike patients with PFPS seeking medical care, early PFPS does not appear to be significantly associated with hip abduction strength asymmetry.

Effects of transcutaneous electrical nerve stimulation on quadriceps function in individuals with experimental knee pain

Knee joint pain (KJP) is a cardinal symptom in knee pathologies, and quadriceps inhibition is commonly observed among KJP patients. Previously, KJP independently reduced quadriceps strength and activation. However, it remains unknown how disinhibitory transcutaneous electrical nerve stimulation (TENS) will affect inhibited quadriceps motor function. This study aimed at examining changes in quadriceps maximum voluntary contraction (MVC) and central activation ratio (CAR) before and after sensory TENS following experimental knee pain. Thirty healthy participants were assigned to either the TENS or placebo groups. All participants underwent three separate data collection sessions consisting of two saline infusions and one no infusion control in a crossover design. TENS or placebo treatment was administered to each group for 20 min. Quadriceps MVC and CAR were measured at baseline, infusion, treatment, and post-treatment. Perceived knee pain intensity was measured on a 100-mm visual analogue scale. Post-hoc analysis revealed that hypertonic saline infusion significantly reduced the quadriceps MVC and CAR compared with control sessions (P < 0.05). Sensory TENS, however, significantly restored inhibited quadriceps motor function compared with placebo treatment (P < 0.05). There was a negative correlation between changes in MVC and knee pain (r = 0.33, P < 0.001), and CAR and knee pain (r = 0.62, P < 0.001), respectively.

The Time Course of Knee Swelling Post Total Knee Arthroplasty and Its Associations with Quadriceps Strength and Gait Speed

This study examines the time course of knee swelling post total knee arthroplasty (TKA) and its associations with quadriceps strength and gait speed. Eighty-five patients with unilateral TKA participated. Preoperatively and on post-operative days (PODs) 1, 4, 14, and 90, knee swelling was measured using bioimpedance spectrometry. Preoperatively and on PODs 14 and 90, quadriceps strength was measured using isokinetic dynamometry while fast gait speed was measured using the timed 10-meter walk. On POD1, knee swelling increased ~35% from preoperative levels after which, knee swelling reduced but remained at ~11% above preoperative levels on POD90. In longitudinal, multivariable analyses, knee swelling was associated with quadriceps weakness (P<0.01) and slower gait speed (P=0.03). Interventions to reduce post-TKA knee swelling may be indicated to improve quadriceps strength and gait speed.

Immediate Effects of Therapeutic Ultrasound on Quadriceps Spinal Reflex Excitability in Patients With Knee Injury

OBJECTIVE

To investigate the effects of nonthermal therapeutic ultrasound on quadriceps spinal reflex excitability in patients with knee joint injury.

DESIGN

Double-blind, randomized controlled laboratory study with a pretest posttest design.

SETTING

University laboratory.

PARTICIPANTS

Recreationally active volunteers with a self-reported history of diagnosed intra-articular knee joint injury and documented quadriceps dysfunction (N=30).

INTERVENTIONS

A nonthermal ultrasound, or sham, treatment was applied to the anteromedial knee.

MAIN OUTCOME MEASURES

Hoffmann reflex measurements were recorded at baseline, immediately postintervention, and 20 minutes post-intervention. The peak Hoffmann reflex amplitude was normalized by the peak motor response (H/M ratio) measured from the vastus medialis using surface electromyography as an estimate of quadriceps motorneuron pool excitability. A repeated-measures analysis of variance was used for comparisons.

RESULTS

A significant group-by-time interaction was observed for mean (P=.016) and change (P=.044) in H/M ratio. The ultrasound group demonstrated significantly higher mean (P=.015) and change (P=.028) in H/M ratio 20 minutes postintervention than did the sham ultrasound group.

CONCLUSIONS

Quadriceps motoneuron pool excitability was facilitated 20 minutes after a nonthermal therapeutic ultrasound treatment, and not a sham treatment. These data provide supporting evidence of the contribution of peripheral receptors in modulation of the arthrogenic response in patients with persistent quadriceps dysfunction. Future research in this area should attempt to identify optimal treatment parameters and translate them to clinical outcomes.

Chronic Low Back Pain: Restoration of Dynamic Stability

OBJECTIVES

Electrical stimulation for multifidus muscle contraction is a novel approach for treating chronic low back pain (CLBP). A multicenter, open-label feasibility study investigated this modality in patients with continuing CLBP despite medical management and no prior back surgery and no known pathological cause of CLBP.

METHODS

Twenty-six patients with continuing CLBP despite physical therapy and medication were implanted with commercially-available implantable pulse generators and leads positioned adjacent to the medial branch of the dorsal ramus as it crosses the L3 transverse process such that electrical stimulation resulted in contraction of the lumbar multifidus (LM) muscle. Patients self-administered stimulation twice daily for 20 min. Low back pain (VAS), Oswestry Disability Index (ODI) and Quality of Life (EQ-5D) scores were collected at three and five months and compared to baseline. Stimulation was withdrawn between months 4 and 5 to test durability of effect.

RESULTS

At three months, 74% of patients met or exceeded the minimally important change (MIC) in VAS and 63% for disability. QoL improved in 84% of patients (N = 19) and none got worse. Five of the 11 patients on disability for CLBP (45%) resumed work by three months. Half the patients reported ≥50% VAS reduction by month 5. Twenty-one lead migration events occurred in 13 patients, of which 7 patients are included in the efficacy cohort.

CONCLUSIONS

Episodic stimulation to induce LM contraction can reduce CLBP and disability, improve quality of life and enable return to work. A dedicated lead design to reduce risk of migration is required.

Neuromechanical characteristics in the knees of patients who had primary conservative treatment for a torn cruciate ligament and reconstruction afterward

BACKGROUND/PURPOSE

To compare the neuromechanical characteristics and subjective outcomes for knees of patients with a cruciate ligament tear and reconstruction with those for knees of controls at three time intervals, and to determine correlations between the characteristics and subjective outcomes.

METHODS

Ten participants with a cruciate ligament tear and at least a 12-week conservative treatment prior to ligament reconstruction were prospectively measured prior to and 3 months and 6 months after surgery. Ten healthy individuals were recruited as controls. Questionnaire surveys regarding the injured knee were conducted, as were bilateral measurements of root mean square electromyography (EMG), the rate of EMG rise, the median frequency in the vastus medialis of the quadriceps muscles and antagonist coactivation from the semitendinosus muscle, and force capacities, including peak torque, rate of force development, and total works of the knee extension. Correlations between the EMG variables (of the vastus medialis and semitendinosus) and the force capacities, and between the EMG variables and the knee injury and osteoarthritis outcome scores (KOOS), and between force capacities and the KOOS were assessed in the participants with a ligament reconstruction.

RESULTS

Pre- and postoperative results of EMG variable and force capacities were lower in both knees of the experimental group participants than in the control group participants (all p < 0.05). Correlations between EMG and force capacities, and between these parameters and the KOOS were found.

CONCLUSION

There were bilateral neuromechanical defects in the knees of the participants who had undergone conservative treatment as well as reconstruction after a cruciate ligament tear.

Intra-articular pressures and joint mechanics: should we pay attention to effusion in knee osteoarthritis?

What factors play a role to ensure a knee joint does what it should given the demands of moving through the physical environment? This paper aims to probe the hypothesis that intra-articular joint pressures, once a topic of interest, have been left aside in contemporary frameworks in which we now view knee joint function. The focus on ligamentous deficiencies and the chondrocentric view of osteoarthritis, while important, have left little attention to the consideration of other factors that can impair joint function across the lifespan. Dynamic knee stability is required during every step we take. While there is much known about the role that passive structures and muscular activation play in maintaining a healthy knee joint, this framework does not account for the role that intra-articular joint pressures may have in providing joint stability during motion and how these factors interact. Joint injuries invariably result in some form of intra-articular fluid accumulation. Ultimately, it may be how the knee mechanically responds to this fluid, of which pressure plays a significant role that provides the mechanisms for continued function. Do joint pressures provide an important foundation for maintaining knee function? This hypothesis is unique and argues that we are missing an important piece of the puzzle when attempting to understand implications that joint injury and disease have for joint function.

Muscle force and movement variability before and after total knee arthroplasty: A review

Variability in muscle force output and movement variability are important aspects of identifying individuals with mobility deficits, central nervous system impairments, and future risk of falling. This has been investigated in elderly healthy and impaired adults, as well as in adults with osteoarthritis (OA), but the question of whether the same correlations also apply to those who have undergone a surgical intervention such as total knee arthroplasty (TKA) is still being investigated. While there is a growing body of literature identifying potential rehabilitation targets for individuals who have undergone TKA, it is important to first understand the underlying post-operative impairments to more efficiently target functional deficits that may lead to improved long-term outcomes. The purpose of this article is to review the potential role of muscle force output and movement variability in TKA recipients. The narrative review relies on existing literature in elderly healthy and impaired individuals, as well as in those with OA before and following TKA. The variables that may predict long-term functional abilities and deficits are discussed in the context of existing literature in healthy older adults and older adults with OA and following TKA, as well as the role future research in this field may play in providing evidence-based data for improved rehabilitation targets.

Manual therapy directed at the knee or lumbopelvic region does not influence quadriceps spinal reflex excitability

Manual therapies, directed to the knee and lumbopelvic region, have demonstrated the ability to improve neuromuscular quadriceps function in individuals with knee pathology. It remains unknown if manual therapies may alter impaired spinal reflex excitability, thus identifying a potential mechanism in which manual therapy may improve neuromuscular function following knee injury.

AIM

To determine the effect of local and distant mobilisation/manipulation interventions on quadriceps spinal reflex excitability.

METHODS

Seventy-five individuals with a history of knee joint injury and current quadriceps inhibition volunteered for this study. Participants were randomised to one of five intervention groups: lumbopelvic manipulation (grade V), lumbopelvic manipulation positioning (no thrust), grade IV patellar mobilisation, grade I patellar mobilisation, and control (no treatment). Changes in spinal reflex excitability were quantified by assessing the Hoffmann reflex (H-reflex), presynaptic, and postsynaptic excitability. A hierarchical linear-mixed model for repeated measures was performed to compare changes in outcome variables between groups over time (pre, post 0, 30, 60, 90 min).

RESULTS

There were no significant differences in H-reflex, presynaptic, or postsynaptic excitability between groups across time.

CONCLUSIONS

Manual therapies directed to the knee or lumbopelvic region did not acutely change quadriceps spinal reflex excitability. Although manual therapies may improve impairments and functional outcomes the underlying mechanism does not appear to be related to changes in spinal reflex excitability.

Disinhibitory interventions and voluntary quadriceps activation: a systematic review

OBJECTIVE

To determine the effects of various therapeutic interventions on increasing voluntary quadriceps muscle activation.

BACKGROUND

Decreased voluntary quadriceps activation is commonly associated with knee injury. Recently, research has focused on developing specific disinhibitory interventions to improve voluntary quadriceps activation; yet, it remains unknown which interventions are most effective in promoting this improvement.

DATA SOURCES

We searched Web of Science from January 1, 1965 through September 27, 2012, using the key words quadriceps activation and transcutaneous electrical nerve stimulation, transcranial magnetic stimulation, cryotherapy, focal joint cooling, joint mobilization, joint mobilisation, joint manipulation, manual therapy, and neuromuscular electrical stimulation.

STUDY SELECTION

Studies evaluating the effect of disinhibitory interventions on volitional quadriceps activation were used in our review. Standardized effect sizes (Cohen d) and 95% confidence intervals (CIs) were calculated from voluntary quadriceps activation means and standard deviations measured at baseline and at all available postintervention time points from each study.

DATA SYNTHESIS

Ten studies were grouped into 5 categories based on intervention type: manual therapy (4 studies), transcutaneous electrical nerve stimulation (2 studies), cryotherapy (2 studies), neuromuscular electrical stimulation (2 studies), and transcranial magnetic stimulation (1 study). Transcutaneous electrical nerve stimulation demonstrated the strongest immediate effects (d = 1.03; 95% CI = 0.06, 1.92) and long-term effects (d = 1.93; 95% CI = 0.91, 2.83). Cryotherapy (d = 0.76; 95% CI = -0.13, 1.59) and transcranial magnetic stimulation (d = 0.54; 95% CI = -0.33, 1.37) had moderate immediate effects in improving voluntary quadriceps activation, whereas manual therapy (d = 0.38; 95% CI = -0.35, 1.09) elicited only weak immediate effects. Neuromuscular electrical stimulation produced weak negative to strong positive effects (range of d values = -0.50 to 1.87) over a period of 3 weeks to 6 months.

CONCLUSIONS

Transcutaneous electrical nerve stimulation demonstrated the strongest and most consistent effects in increasing voluntary quadriceps activation and may be the best disinhibitory intervention for improving the same.

The effects of repetitive haemarthrosis on postural balance in children with haemophilia

Sensory information from visual, vestibular and proprioceptive systems is necessary to control posture and balance. Impairment in proprioception due to repetitive joints bleeding may lead to a deficit in postural balance which, in turn, leads to high joint stress and risk of bleeding recurrence. Despite the increase in attention in this field during the past few years, the data concerning to how bleeds can affect postural control in children with haemophilia (CWH) remain scarce. This study aimed to evaluate the postural balance in CWH. Twenty CWH Haemophilia Group (HG) and 20 age-matched children Control Group (CG) were recruited to this study. A force plate was used to record centre of pressure (COP) displacement under four different postural conditions during quiet standing: eyes open on firm surface, eyes open on foam surface, eyes closed on firm surface and eyes closed on a foam surface. Variables of COP as sway area and mean velocity and in anterior-posterior (y) medio-lateral (x) direction were processed and for each variable sensory, quotients were calculated and compared between groups. No differences were found in visual and vestibular quotients variables between groups. A higher value was found in sway area variable on proprioception quotient in the HG when compared with CG (P = 0.042). CWH with repetitive joint bleed on lower limbs showed differences in postural balance when compared with non-haemophiliac children. The identification of early balance impairments in CWH can help us understand better the effects of bleeds inside joints on postural control and plan a more effective preventive and rehabilitative treatment.

Arthrogenic neuromusculature inhibition: a foundational investigation of existence in the hip joint

BACKGROUND

Patients and athletes with diminished gluteal muscle activation are thought to have 'gluteal inhibition'. This may be a component of arthrogenic neuromuscular inhibition, which has been well documented in the knee and generalized to all joints. While clinical evidence surrounding gluteal inhibition increases, supportive research is non-existent. This study investigated whether arthrogenic neuromuscular inhibition occurred about the hip following instillation of intra-articular fluid during functional hip extension tasks.

METHODS

Data was collected in a biomechanics laboratory (control) and hospital setting (intervention). Nine healthy individuals (4M/5F) comprised the control group. The intervention group contained twelve patients (4M/8F) with hip pathology requiring a magnetic resonance arthrogram (capsular distension via intra-articular fluid injection) procedure. The participants performed a pelvic bridge (PB) and active hip extension (EXT) before and after the control time or injection. Peak EMG from the gluteus maximus (GM) was collected bilaterally.

FINDINGS

The findings of this study provide substantial support for arthrogenic inhibition following hip intra-articular fluid instillation during functional tasks. Two-way repeated measures ANOVA revealed a significant group by session interaction effect (PB,EXT: affected/unaffected=0.0192/0.9654 P=0.05, <0.0001/0.0826 P=0.05). Tukey post hoc revealed decreases in ipsilateral peak GM EMG following intervention were significant (0.0238/<0.0001 P=0.025). No changes were observed in the control group.

INTERPRETATION

These concepts are of clinical importance to both patient and athletic populations. Understanding the role of gluteal inhibition in the injury process is essential to the development of rehabilitation and prevention protocols. Restoration and promotion of optimal recruitment patterns are crucial to enhancing athletic performance.

Knee effusion affects knee mechanics and muscle activity during gait in individuals with knee osteoarthritis

OBJECTIVE

To test the hypothesis that knee effusion presence in those with knee osteoarthritis (OA) alters knee joint muscle activation patterns and sagittal plane mechanics during gait.

METHODS

Thirty-five patients with medial compartment knee OA were assessed for the presence of effusion using a brush test. Based on the results, they were assigned to the knee effusion (n = 17) and no knee effusion (n = 18) groups. Electromyograms from seven lower extremity muscles (lateral and medial gastrocnemius, vastus lateralis and medialis, rectus femoris and the lateral and medial hamstrings), leg motion and ground reaction forces were recorded during self-selected walking. Isometric knee extensor, plantar flexor and knee flexor strength were measured. Discrete measures from angular knee motion and net external moment of force waveforms were identified. Principal component analysis extracted electromyographic waveform features. Analysis of variance models tested for main effects (group, muscle) and interactions (α = 0.05). Bonferroni post-hoc testing was employed.

RESULTS

No differences in age, body mass index, knee pain, Western Ontario McMaster Osteoarthritis Index scores, gait velocity and muscle strength were found between groups (P > 0.05). Individuals with effusion had a greater overall quadriceps activation and prolonged hamstring activation into mid-stance (P < 0.05). Knee joint flexion angles were higher (P < 0.05) and net external knee extension (KE) moments in mid to late stance lower in the effusion group.

CONCLUSION

Quadriceps and hamstrings activation during walking were altered when effusions were present. Increased knee flexion (KF) angles and decreased KE moment in mid-late stance provide a mechanical explanation for the effect of joint effusion on muscle activation in those with knee OA.

Quadriceps activation failure after anterior cruciate ligament rupture is not mediated by knee joint effusion

STUDY DESIGN

Descriptive prospective cohort study.

OBJECTIVES

To investigate the relationships between knee joint effusion, quadriceps activation, and quadriceps strength. These relationships may help clinicians better identify impaired quadriceps activation.

BACKGROUND

After anterior cruciate ligament (ACL) injury, the involved quadriceps may demonstrate weakness. Experimental data have shown that quadriceps activation and strength may be directly mediated by intracapsular joint pressure created by saline injection. An inverse relationship between quadriceps activation and the amount of saline injected has been reported. This association has not been demonstrated for traumatic effusion. We hypothesized that traumatic joint effusion due to ACL rupture and postinjury quadriceps strength would correlate well with quadriceps activation, allowing clinicians to use effusion and strength measurement as a surrogate for electrophysiological assessment of quadriceps activation.

METHODS

Prospective data were collected on 188 patients within 100 days of ACL injury (average, 27 days) referred from a single surgeon. A complete clinical evaluation of the knee was performed, including ligamentous assessment and assessment of range of motion and effusion. Quadriceps function was electrophysiologically assessed using maximal volitional isometric contraction and burst superimposition techniques to quantify both strength and activation.

RESULTS

Effusion grade did not correlate with quadriceps central activation ratio (CAR) (zero effusion: mean ± SD CAR, 93.5% ± 5.8%; trace effusion: CAR, 93.8% ± 9.5%; 1+ effusion: CAR, 94.0% ± 7.5%; 2+/3+ effusion: CAR, 90.6% ± 11.1%). These values are lower than normative data from healthy subjects (CAR, 98% ± 3%).

CONCLUSION

Joint effusion after ACL injury does not directly mediate quadriceps activation failure seen after injury. Therefore, it should not be used as a clinical substitute for electrophysiological assessment of quadriceps activation. Patients presenting to physical therapy after ACL injury should be treated with high-intensity neuromuscular electrical stimulation to help normalize this activation.

Mechanisms of quadriceps muscle weakness in knee joint osteoarthritis: the effects of prolonged vibration on torque and muscle activation in osteoarthritic and healthy control subjects

INTRODUCTION

A consequence of knee joint osteoarthritis (OA) is an inability to fully activate the quadriceps muscles, a problem termed arthrogenic muscle inhibition (AMI). AMI leads to marked quadriceps weakness that impairs physical function and may hasten disease progression. The purpose of the present study was to determine whether γ-loop dysfunction contributes to AMI in people with knee joint OA.

METHODS

Fifteen subjects with knee joint OA and 15 controls with no history of knee joint pathology participated in this study. Quadriceps and hamstrings peak isometric torque (Nm) and electromyography (EMG) amplitude were collected before and after 20 minutes of 50 Hz vibration applied to the infrapatellar tendon. Between-group differences in pre-vibration torque were analysed using a one-way analysis of covariance, with age, gender and body mass (kg) as the covariates. If the γ-loop is intact, vibration should decrease torque and EMG levels in the target muscle; if dysfunctional, then torque and EMG levels should not change following vibration. One-sample t tests were thus undertaken to analyse whether percentage changes in torque and EMG differed from zero after vibration in each group. In addition, analyses of covariance were utilised to analyse between-group differences in the percentage changes in torque and EMG following vibration.

RESULTS

Pre-vibration quadriceps torque was significantly lower in the OA group compared with the control group (P = 0.005). Following tendon vibration, quadriceps torque (P < 0.001) and EMG amplitude (P ≤0.001) decreased significantly in the control group but did not change in the OA group (all P > 0.299). Hamstrings torque and EMG amplitude were unchanged in both groups (all P > 0.204). The vibration-induced changes in quadriceps torque and EMG were significantly different between the OA and control groups (all P < 0.011). No between-group differences were observed for the change in hamstrings torque or EMG (all P > 0.554).

CONCLUSIONS

γ-loop dysfunction may contribute to AMI in individuals with knee joint OA, partially explaining the marked quadriceps weakness and atrophy that is often observed in this population.

Transcranial magnetic stimulation and volitional quadriceps activation

CONTEXT

Quadriceps-activation deficits have been reported after meniscectomy. Transcranial magnetic stimulation (TMS) in conjunction with maximal contractions affects quadriceps activation in patients after meniscectomy.

OBJECTIVE

To determine the effect of single-pulsed TMS on quadriceps central activation ratio (CAR) in patients after meniscectomy.

DESIGN

Randomized controlled clinical trial.

SETTING

University laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty participants who had partial meniscectomy and who had a CAR less than 85% were assigned randomly to the TMS group (7 men, 4 women; age  =  38.1 ± 16.2 years, height  =  176.8 ± 11.5 cm, mass  =  91.8 ± 27.5 kg, postoperative time  =  36.7 ± 34.9 weeks) or the control group (7 men, 2 women; age  =  38.2 ± 17.5 years, height  =  176.5 ± 7.9 cm, mass  =  86.2 ± 15.3 kg, postoperative time  =  36.6 ± 37.4 weeks).

INTERVENTION(S)

Participants in the experimental group received TMS over the motor cortex that was contralateral to the involved leg and performed 3 maximal quadriceps contractions with the involved leg. The control group performed 3 maximal quadriceps contractions without the TMS.

MAIN OUTCOME MEASURE(S)

Quadriceps activation was assessed using the CAR, which was measured in 70° of knee flexion at baseline and at 0, 10, 30, and 60 minutes posttest. The CAR was expressed as a percentage of full activation.

RESULTS

Differences in CAR were detected over time (F(4,72)  =  3.025, P  = .02). No interaction (F(4,72)  =  1.457, P  =  .22) or between-groups differences (F(1,18)  =  0.096, P  =  .76) were found for CAR. Moderate CAR effect sizes were found at 10 (Cohen d  =  0.54, 95% confidence interval [CI]  =  -0.33, 1.37) and 60 (Cohen d  =  0.50, 95% CI  =  -0.37, 1.33) minutes in the TMS group compared with CAR at baseline. Strong effect sizes were found for CAR at 10 (Cohen d  =  0.82, 95% CI  =  -0.13, 1.7) and 60 (Cohen d  =  1.06, 95% CI  =  0.08, 1.95) minutes in the TMS group when comparing percentage change scores between groups.

CONCLUSIONS

No differences in CAR were found between groups at selected points within a 60-minute time frame, yet moderate to strong effect sizes for CAR were found at 10 and 60 minutes in the TMS group, indicating increased activation after TMS.

Relationship between transcranial magnetic stimulation and percutaneous electrical stimulation in determining the quadriceps central activation ratio

OBJECTIVE

To determine the relationship between quadriceps central activation ratios (CARs) derived from a percutaneous electrical stimulation (CAR(SIB)) and a transcranial magnetic stimulation (CAR(TMS)) in healthy participants.

DESIGN

Nineteen healthy participants (5 men, 14 women, 23.7 ± 4.8 yrs, 66.8 ± 10.0 kg, and 170.1 ± 7.0 cm) qualified for this descriptive study. Muscle activation, using both methods (CAR(SIB) and CAR(TMS)), was measured at days 1, 14, and 28. All participants performed both methods in a counterbalanced order. Correlation coefficients and Bland-Altman plots were used to assess relationships and agreement between the two methods. For both methods, reliability was assessed at 14 and 28 days using Bland-Altman plots and intraclass correlation coefficients.

RESULTS

CAR(TMS) scores were higher than CAR(SIB) scores for all three sessions, with mean differences between CAR scores of -0.06 (95% confidence interval, -0.19-0.07), -0.03 (95% confidence interval, -0.14-0.08), and -0.03 (95% confidence interval, -0.11-0.05). There was a significant moderate positive correlation between CAR(SIB) and CAR(TMS) at 14 days from baseline (ρ = 0.45, P = 0.05). Intersession reliability was strong for CAR(SIB) at 14 and 28 days from baseline (intraclass correlation coefficients = 0.80 [P = 0.001] and 0.85 [P < 0.001], respectively). Intersession reliability for CAR(TMS) was moderate from baseline to 14 days (intraclass correlation coefficients = 0.68 [P = 0.01]).

CONCLUSIONS

It does not seem that the CAR(TMS) and CAR(SIB) methods are interchangeable measurements for evaluating volitional quadriceps activation; however, both measurements seem to have acceptable agreement at 14 and 28 days compared with day 1.

Voluntary quadriceps activation deficits in patients with tibiofemoral osteoarthritis: a meta-analysis

The objective of this study was to assess the magnitude of quadriceps activation deficits in the involved extremity and contralateral extremity of patients with knee joint osteoarthritis (OA), as well as matched controls. An exhaustive search of the literature was performed using Web of Science between 1970 and February 24, 2010, using the search terms "osteoarthritis" AND "quadriceps activation" OR "quadriceps inhibition" and cross-referencing pertinent articles. Studies written in English reporting quadriceps activation means and standard deviations in patients with tibiofemoral OA via a method using an exogenous electrical stimulation were evaluated for methodological quality and were included for data analysis. Fourteen individual studies met the criteria for inclusion into data analysis. The number of participants and mean activation levels were used to calculate weighted means for the involved limb (14 studies), the contralateral limb (from a subset of 6 studies), and an involved limb subset from only the studies evaluating the contralateral limb and population of control subjects (5 studies). Weighted means from the involved limb (82.2; 95% CI = 81.4-83.3%), contralateral limb (81.7; 80.1-83.3%), and involved limb subset (76.8; 74.8-78.8%) groups were found to have lower volitional quadriceps activation compared with the control groups (90; 88.9-91.7%). Although the weighted involved limb mean was not different from that of the contralateral limb, the mean and 95% confidence intervals for the involved limb subset were lower than that of the contralateral limb group, suggesting that the involved limb had less volitional activation within OA subjects. This provides evidence that bilateral quadriceps volitional activation deficits are present in persons with knee OA.

Effects of transcutaneous electrical nerve stimulation and therapeutic exercise on quadriceps activation in people with tibiofemoral osteoarthritis

STUDY DESIGN

Blinded, randomized controlled trial.

OBJECTIVES

To determine if the combination of transcutaneous electrical nerve stimulation (TENS) set to a sensory level and therapeutic exercise would be more effective than the combination of placebo TENS and therapeutic exercises or therapeutic exercises only to increase quadriceps activation in individuals with tibiofemoral osteoarthritis.

BACKGROUND

Quadriceps activation deficits are common in those with tibiofemoral osteoarthritis, and TENS has been reported to immediately increase quadriceps activation. Yet the long-term benefits of TENS for motor neuron activation have yet to be determined.

METHODS

Thirty-six individuals with radiographically assessed tibiofemoral osteoarthritis were randomly assigned to the TENS and exercise, placebo and exercise, and exercise only groups. All participants completed a supervised 4-week lower extremity exercise program. TENS and placebo TENS were worn throughout the therapeutic exercise sessions, as well as during daily activities. Our primary outcome measures, quadriceps central activation ratio, and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were evaluated at baseline and at 2 weeks and 4 weeks of the intervention.

RESULTS

Quadriceps activation was significantly higher in the TENS with exercise group compared to the exercise only group at 2 weeks (0.94 ± 0.04 versus 0.82 ± 0.12, P<.05) and the placebo and exercise group at 4 weeks (0.94 ± 0.06 versus 0.81 ± 0.15, P<.05). WOMAC scores improved in all 3 groups over time, with no significant differences among groups.

CONCLUSION

This study provides evidence that TENS applied in conjunction with therapeutic exercise and daily activities increases quadriceps activation in patients with tibiofemoral osteoarthritis and, while function improved for all participants, effects were greatest in the group treated with a combination of TENS and therapeutic exercises.

LEVEL OF EVIDENCE

Therapy, level 1b-.

Cryotherapy to treat persistent muscle weakness after joint injury

Cryotherapy is a widely used modality following acute joint injury. It is considered helpful in reducing pain and swelling, and there is a growing body of evidence to suggest that it may have additional benefits in muscle function. Following joint injury, it is common for patients to experience persistent muscle weakness that is resistant to traditional strengthening exercises. This may be due to a reflex inhibition of musculature surrounding the injured joint. The underlying cause of this reflex inhibition may arise from aberrant sensory information from the joints' neural receptors, which result in a neural inhibition of motor neurons. This inhibition is beyond conscious control, is ongoing, and impedes normal joint function via a disruption of normal muscle function. Cryotherapy treatments targeted at peripheral joints have been shown to result in transient resolution of reflex inhibition, which thereby provide an environment where injured patients can benefit from a more thorough motorneuron pool during controlled rehabilitation exercises. This article presents current evidence-based recommendations regarding the use of joint cryotherapy for maximizing the effectiveness of commonly used rehabilitation exercises in patients recovering from joint injury.

Effects of disinhibitory transcutaneous electrical nerve stimulation and therapeutic exercise on sagittal plane peak knee kinematics and kinetics in people with knee osteoarthritis during gait: a randomized controlled trial

Objective: To determine whether sensory transcutaneous electrical nerve stimulation (TENS) augmented with therapeutic exercise and worn for daily activities for four weeks would alter peak gait kinetics and kinematics, compared with placebo electrical stimulation and exercise, and exercise only.

Design: Randomized controlled trial.

Setting: Motion analysis laboratory.

Subjects: Thirty-six participants with radiographically assessed knee osteoarthritis and volitional quadriceps activation below 90% were randomly assigned to electrical stimulation, placebo and comparison (exercise-only) groups.

Interventions: Participants in all three groups completed a four-week quadriceps strengthening programme directed by an experienced rehabilitation clinician. Active electrical stimulation units and placebo units were worn in the electrical stimulation and placebo groups throughout the rehabilitation sessions as well as during all activities of daily living.

Main measures: Peak external knee flexion moment and angle during stance phase were analysed at a comfortable walking speed before and after the intervention.

Findings: Comfortable walking speed increased for all groups over time (TENS 1.16 ± 0.15 versus 1.32 ± 0.16 m/s; placebo 1.21 ± 0.34 versus 1.3 ± 0.24 m/s; comparison 1.27 ± 0.18 versus 1.5 ± 0.14 m/s), yet no group differences in speed were found. No differences were found for peak flexion moment or angle between groups overtime.

Conclusions: TENS in conjunction with therapeutic exercise does not seem to affect peak flexion moment and angle during stance over a four-week period in participants with tibiofemoral osteoarthritis.

Introduction to rehabilitation

Rehabilitation plays an integral role when it comes to managing sports injuries in a safe and timely manner. Doing so competently allows for a greater chance of quick recovery and ultimate success on and off the field. Understanding the goals of rehabilitation and how to enhance communication between all providers who are involved with athlete care is critical to the process. The purpose of this article is to thoroughly explain the steps and critical components of a rehabilitation process designed specifically for each athlete's needs.

Quadriceps arthrogenic muscle inhibition: neural mechanisms and treatment perspectives

OBJECTIVES

Arthritis, surgery, and traumatic injury of the knee joint are associated with long-lasting inability to fully activate the quadriceps muscle, a process known as arthrogenic muscle inhibition (AMI). The goal of this review is to provide a contemporary view of the neural mechanisms responsible for AMI as well as to highlight therapeutic interventions that may help clinicians overcome AMI.

METHODS

An extensive literature search of electronic databases was conducted including AMED, CINAHL, MEDLINE, OVID, SPORTDiscus, and Scopus.

RESULTS

While AMI is ubiquitous across knee joint pathologies, its severity may vary according to the degree of joint damage, time since injury, and knee joint angle. AMI is caused by a change in the discharge of articular sensory receptors due to factors such as swelling, inflammation, joint laxity, and damage to joint afferents. Spinal reflex pathways that likely contribute to AMI include the group I nonreciprocal (Ib) inhibitory pathway, the flexion reflex, and the gamma-loop. Preliminary evidence suggests that supraspinal pathways may also play an important role. Some of the most promising interventions to counter the effects of AMI include cryotherapy, transcutaneous electrical nerve stimulation, and neuromuscular electrical stimulation. Nonsteroidal anti-inflammatory drugs and intra-articular corticosteroids may also be effective when a strong inflammatory component is present with articular pathology.

CONCLUSIONS

AMI remains a significant barrier to effective rehabilitation in patients with arthritis and following knee injury and surgery. Gaining a better understanding of AMI's underlying mechanisms will allow the development of improved therapeutic strategies, enhancing the rehabilitation of patients with knee joint pathology.

A neuromuscular mechanism of posttraumatic osteoarthritis associated with ACL injury

Anterior cruciate ligament (ACL) injury leads to early-onset osteoarthritis. Quadriceps weakness is a consequence of ACL injury and is considered to result from arthrogenic inhibition (AMI). AMI is the neurological "shutdown" of muscles surrounding an injured joint, preventing full activation, reducing strength, and promoting atrophy. As quadriceps function is critical for energy absorption, its dysfunction may contribute to posttraumatic osteoarthritis.