D. Rice

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 AMIs underlying mechanisms will allow the development of improved therapeutic strategies, enhancing the rehabilitation of patients with knee joint pathology.

Conditioned Pain Modulation in Populations With Chronic Pain: A Systematic Review and Meta-Analysis

UNLABELLED A systematic literature review and meta-analysis were undertaken to determine if conditioned pain modulation is dysfunctional in populations with chronic pain. Studies that used a standardized protocol to evaluate conditioned pain modulation in a chronic pain population and in a healthy control population were selected and reviewed. Thirty studies were included in the final review, encompassing data from 778 patients and 664 control participants. Across all studies there was a large effect size of .78, reflecting reduced conditioned pain modulation in the patient group. Analysis of moderator variables indicated a significant influence of participant gender and age on the effect size. Methodological moderator variables of type of outcome measure, type of test stimulus, type of conditioning stimulus, and the level of conditioning stimulus pain were not significant. A risk of bias assessment indicated that poor blinding of assessors and a lack of control of confounding variables were common. It is concluded that conditioned pain modulation is impaired in populations with chronic pain. Future studies should ensure adequate matching of participant age and gender between patient and control groups, blinding of the assessors obtaining the outcome measures, and more rigorous control for variables known to influence the level of modulation. PERSPECTIVE This review compared the efficacy of conditioned pain modulation between chronic pain and healthy populations. The finding of impaired modulation in the chronic pain groups highlights the dysfunction of endogenous pain modulatory mechanisms in this population.

Predictors of persistent pain after total knee arthroplasty: a systematic review and meta-analysis

BACKGROUND Several studies have identified clinical, psychosocial, patient characteristic, and perioperative variables that are associated with persistent postsurgical pain; however, the relative effect of these variables has yet to be quantified. The aim of the study was to provide a systematic review and meta-analysis of predictor variables associated with persistent pain after total knee arthroplasty (TKA). METHODS Included studies were required to measure predictor variables prior to or at the time of surgery, include a pain outcome measure at least 3 months post-TKA, and include a statistical analysis of the effect of the predictor variable(s) on the outcome measure. Counts were undertaken of the number of times each predictor was analysed and the number of times it was found to have a significant relationship with persistent pain. Separate meta-analyses were performed to determine the effect size of each predictor on persistent pain. Outcomes from studies implementing uni- and multivariable statistical models were analysed separately. RESULTS Thirty-two studies involving almost 30 000 patients were included in the review. Preoperative pain was the predictor that most commonly demonstrated a significant relationship with persistent pain across uni- and multivariable analyses. In the meta-analyses of data from univariate models, the largest effect sizes were found for: other pain sites, catastrophizing, and depression. For data from multivariate models, significant effects were evident for: catastrophizing, preoperative pain, mental health, and comorbidities. CONCLUSIONS Catastrophizing, mental health, preoperative knee pain, and pain at other sites are the strongest independent predictors of persistent pain after TKA.

Reliability of the Conditioned Pain Modulation Paradigm to Assess Endogenous Inhibitory Pain Pathways

BACKGROUND Conditioned pain modulation paradigms are often used to assess the diffuse noxious inhibitory control (DNIC) system. DNICs provide one of the main supraspinal pain inhibitory pathways and are impaired in several chronic pain populations. Only one previous study has examined the psychometric properties of the conditioned pain modulation technique and this study did not evaluate intersession reliability. OBJECTIVES To evaluate and compare the intra- and intersession reliability of two conditioned pain modulation paradigms using different conditioning stimuli, and to determine the time course of conditioned pain inhibition following stimulus removal. METHODS An electronic pressure transducer was used to determine the pressure-pain threshold at the knee during painful conditioning of the opposite hand using the ischemic arm test and the cold pressor test. Assessments were completed twice on one day and repeated once approximately three days later. RESULTS The two conditioning stimuli resulted in a similar increase in the pressure-pain threshold at the knee, reflecting presumed activation of the DNIC system. Intrasession intraclass correlation coefficients for the cold pressor (0.85) and ischemic arm tests (0.75) were excellent. The intersession intraclass correlation coefficient for the cold pressor test was good (0.66) but was poor for the ischemic arm test (-0.4). Inhibition of the pressure-pain threshold remained significant at 10 min following conditioning, but returned to baseline by 15 min. CONCLUSIONS Within-session reliability of DNIC assessment using conditioned pain modulation paradigms was excellent, but the applicability of assessing pain modulation over multiple sessions was influenced by the conditioning stimulus. The cold pressor test was the superior technique.

Effects of cryotherapy on arthrogenic muscle inhibition using an experimental model of knee swelling.

OBJECTIVE Arthrogenic muscle inhibition (AMI) contributes to quadriceps weakness and atrophy in knee arthritis and following joint injury. This laboratory-based study examined the efficacy of cryotherapy in reducing quadriceps AMI caused by intraarticular swelling. METHODS Sixteen subjects without knee pathology participated, and were randomly assigned to a cryotherapy (n = 8) or control (n = 8) group. Surface electromyography (EMG) from vastus medialis and quadriceps torque measurements were recorded during maximum effort isometric contractions. All subjects then received an experimental joint infusion, whereby dextrose saline was injected into the knee to an intraarticular pressure of 50 mm Hg. EMG and torque measurements were repeated. Thereafter, the cryotherapy group had ice applied to the knee for 20 minutes while the control group did not receive an intervention. EMG and torque measurements were again collected. Quadriceps peak torque, muscle fiber conduction velocity (MFCV), and the root mean square (RMS) of EMG signals from vastus medialis were analyzed. RESULTS Quadriceps peak torque, MFCV, and RMS decreased significantly following joint infusion (P < or = 0.001). Cryotherapy led to a significant increase in quadriceps torque and MFCV compared with controls (P < 0.05). The difference in RMS did not reach statistical significance (P = 0.13). CONCLUSION The study demonstrated that cryotherapy is effective in reducing AMI induced by swelling. Cryotherapy may allow earlier and more effective quadriceps strengthening to occur in patients with knee joint pathology.

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

IntroductionA 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.MethodsFifteen 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.ResultsPre-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).Conclusionsγ-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.

Is Motor Cortical Excitability Altered in People with Chronic Pain? A Systematic Review and Meta-Analysis

BACKGROUND Chronic pain is characterised by maladaptive neuroplasticity in many systems, including the motor system. There is evidence that patients with chronic pain demonstrate altered corticospinal and intracortical excitability; however, findings are inconsistent and existing literature in this area has not been systematically reviewed. OBJECTIVE To systematically review studies examining corticospinal and intracortical excitability using transcranial magnetic stimulation in people with chronic pain compared to healthy controls and to provide a meta-analysis of study outcomes. METHODS Databases were searched for controlled studies evaluating corticospinal and intracortical excitability in chronic pain conditions. Outcome measure data were entered into separate meta-analyses and effect sizes calculated. A subgroup analysis based on the type of chronic pain population was also performed. RESULTS Forty-three studies were included, encompassing a pooled total of 1009 people with chronic pain and 658 control participants. Significant effect sizes (P < 0.05) indicated that in chronic pain populations the duration of the silent period and the extent of short-interval intracortical inhibition were both reduced and short-interval intracortical facilitation was enhanced. The subgroup analysis revealed that only the neuropathic pain group exhibited significant effect sizes for these outcome measures. Effect sizes for the remaining outcome measures were not significant CONCLUSIONS There is evidence of motor cortex disinhibition in chronic pain populations, suggestive of a disruption in GABA-mediated intracortical inhibition. Disinhibition was more pronounced in populations with neuropathic pain. These findings provide new insights into the relationship between chronic pain and motor cortex excitability, which may have meaningful implications for the future treatment of chronic pain conditions.

Quadriceps arthrogenic muscle inhibition: the effects of experimental knee joint effusion on motor cortex excitability.

IntroductionMarked weakness of the quadriceps muscles is typically observed following injury, surgery or pathology affecting the knee joint. This is partly due to ongoing neural inhibition that prevents the central nervous system from fully activating the quadriceps, a process known as arthrogenic muscle inhibition (AMI). This study aimed to further investigate the mechanisms underlying AMI by exploring the effects of experimental knee joint effusion on quadriceps corticomotor and intracortical excitability.MethodsSeventeen healthy volunteers participated in this study. Transcranial magnetic stimulation was used to measure quadriceps motor evoked potential area, short-interval intracortical inhibition, intracortical facilitation and cortical silent period duration before and after experimental knee joint effusion. Joint effusion was induced by the intraarticular infusion of dextrose saline into the knee.ResultsThere was a significant increase in quadriceps motor evoked potential area following joint infusion, both at rest (P = 0.01) and during voluntary muscle contraction (P = 0.02). Cortical silent period duration was significantly reduced following joint infusion (P = 0.02). There were no changes in short interval intracortical inhibition or intracortical facilitation over time (all P > 0.05).ConclusionsThe results of this study provide no evidence for a supraspinal contribution to quadriceps AMI. Paradoxically, but consistent with previous observations in patients with chronic knee joint pathology, quadriceps corticomotor excitability increased after experimental knee joint effusion. The increase in quadriceps corticomotor excitability may be at least partly mediated by a decrease in gamma-aminobutyric acid (GABA)-ergic inhibition within the motor cortex.

Medicalization and marketing

Medicalization is the process by which aspects of the human condition, formerly considered nonmedical, are brought within the medical realm. Medical sociologists have asserted that medicalization is a prevalent contemporary sociocultural phenomenon that is actively promoted by pharmaceutical company marketing strategies and that has widespread negative societal effects. Medicalization has not been investigated from a business, marketing management, or macromarketing perspective. One of the principal implications of the medicalization thesis is that pharmaceutical marketing frequently acts to reduce human welfare. The central purposes of this article are to explain what evidence and argumentation has been deployed in medical sociology to implicate marketing practices in medicalization and to argue for the relevance of medicalization to the field of macromarketing. Medicalization is an intellectually robust concept of potential use when conducting macromarketing investigations into ethical and quality-of-life (QOL) aspects of the health care industries and quality of death and dying issues.

Influence of stimulation location and posture on the reliability and comfort of the nociceptive flexion reflex.

BACKGROUND The lower limb nociceptive flexion reflex (NFR) is commonly used to assess the function of the nociceptive system. Currently, there is a lack of standardized stimulation procedures to determine the NFR threshold, making comparisons of thresholds across studies difficult. OBJECTIVES To assess and compare the within- and between-session reliability of NFR threshold when elicited from two common stimulation locations: the medial arch of the foot (while standing) and the sural nerve (while seated). METHODS A staircase procedure was used to determine NFR threshold in 20 healthy participants twice within one session and once more in a separate session approximately four days later. At both sessions, NFR threshold was determined from both medial arch and sural nerve stimulation. Comparisons of NFR threshold, reliability and participant discomfort ratings were made between the two stimulation locations. RESULTS NFR thresholds were statistically equivalent at the two stimulation locations, but there were more nonresponders and ratings of participant discomfort were significantly higher during stimulation over the sural nerve. Within-session reliability measures were superior for stimulation over the sural nerve; however, between-session measures were more reliable using stimulation over the medial arch of the foot. CONCLUSIONS The authors recommend stimulation over the medial arch of the foot while standing as the preferred location for eliciting the lower limb NFR, particularly if measurements are to be compared across multiple sessions.