Response of slowly adapting articular mechanoreceptors in the cat knee joint to alterations in intra-articular volume

Arthrogenic Muscle Inhibition Following Anterior Cruciate Ligament Injury

Arthrogenic muscle inhibition (AMI) is a common impairment in individuals who sustain an anterior cruciate ligament (ACL) injury. The AMI causes decreased muscle activation, which impairs muscle strength, leading to aberrant movement biomechanics. The AMI is often resistant to traditional rehabilitation techniques, which leads to persistent neuromuscular deficits following ACL reconstruction. To better treat AMI following ACL injury and ACL reconstruction, it is important to understand the specific neural pathways involved in AMI pathogenesis, as well as the changes in muscle function that may impact movement biomechanics and long-term structural alterations to joint tissue. Overall, AMI is a critical factor that limits optimal rehabilitation outcomes following ACL injury and ACL reconstruction. This review discusses the current understanding of the: (1) neural pathways involved in the AMI pathogenesis following ACL injury; (2) consequence of AMI on muscle function, joint biomechanics, and patient function; and (3) development of posttraumatic osteoarthritis. Finally, the authors review the evidence for interventions specifically used to target AMI following ACL injury.

Mechanisms of Arthrogenic Muscle Inhibition

CONTEXT

Arthrogenic muscle inhibition (AMI) continues to be a limiting factor in joint rehabilitation as the inability to volitionally activate muscle significantly dampens recovery. New evidence acquired at higher brain centers and in clinical populations continues to reshape our perspective of what AMI is and how to treat it. This review aims to stimulate discussion about the far-reaching effects of AMI by exploring the interconnected pathways by which it evolves.

OBJECTIVES

To discuss how reflexive inhibition can lead to adaptations in brain activity, to illustrate how changes in descending motor pathways limit our ability to contract muscle following injury, and to summarize the emerging literature on the wide-reaching effects of AMI on other interconnected systems.

DATA SOURCES

The databases PubMed, SPORTDiscus, and Web of Science were searched for articles pertaining to AMI. Reference lists from appropriate articles were cross-referenced.

CONCLUSION

AMI is a sequential and cumulative neurological process that leads to complex clinical impairments. Originating with altered afferent information arising from an injured joint, patients experience changes in afferent information, reflexive muscle inhibition, deficiencies in somatosensation, neuroplastic compensations in higher brain centers, and ultimately decreased motor output to the muscle surrounding the joint. Other aspects of clinical function, like muscle structure and psychological responses to injury, are also impaired and influenced by AMI. Removing, or reducing, AMI should continue to be a focus of rehabilitation programs to assist in the optimization of health after joint injury.

Limb Segment Load Inhibits the Recovery of Soleus H-Reflex After Segmental Vibration in Humans

We investigated the effects of vertical vibration and compressive load on soleus H-reflex amplitude and postactivation depression. We hypothesized that, in the presence of a compressive load, limb vibration induces a longer suppression of soleus H-reflex. Eleven healthy adults received vibratory stimulation at a fixed frequency (30 Hz) over two loading conditions (0% and 50% of individual's body weight). H-reflex amplitude was depressed ∼88% in both conditions during vibration. Cyclic application of compression after cessation of the vibration caused a persistent reduction in H-reflex excitability and postactivation depression for > 2.5 min. A combination of limb segment vibration and compression may offer a nonpharmacologic method to modulate spinal reflex excitability in people after CNS injury.

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

Introduction

Marked 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.

Methods

Seventeen 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.

Results

There 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).

Conclusions

The 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.

Influence of Isokinetic Strength Training of Unilateral Ankle on Ipsilateral One-legged Standing Balance of Adults

[Purpose] The purpose of the current study was to investigate the changes in one-legged standing balance of the ipsilateral lower limb following unilateral isokinetic strength training. [Subjects and Methods] Thirty healthy adult volunteers were randomly assigned to either a training group or a control group, so that each group included 15 subjects. Subjects in the training group performed unilateral ankle isokinetic exercises of the dominant leg using the Biodex 3 PRO System for a period of four weeks. Ipsilateral one-legged standing balance was evaluated before and after the intervention with three stability indexes of balance using the Biodex System: Anterior-Posterior Stability Index (APSI), Medial-Lateral Stability Index (MLSI), and Overall Stability Index (OSI). [Results] Comparison of pre- and post-test data revealed significant improvements in strength values (dorsiflexion, plantarflexion, eversion, and inversion) and stability indexes (APSI, MLSI, OSI). [Conclusion] These results suggest that ankle strengthening exercise can be considered as a form of exercise that may assist individuals with improvement of balance.

Limb compressive load does not inhibit post activation depression of soleus H-reflex in indiviudals with chronic spinal cord injury

OBJECTIVE

We investigated the effect of various doses of limb compressive load on soleus H-reflex amplitude and post activation depression in individuals with/without chronic SCI. We hypothesized that SCI reorganization changes the typical reflex response to an external load.

METHODS

Ten healthy adults and 10 individuals with SCI received three doses of compressive load to the top of their knee (10%, 25%, and 50% of the body weight, BW). Soleus H-reflexes were measured before (baseline) and during the loading phase.

RESULTS

With persistent background muscle activity across all testing sessions, segment compressive load significantly decreased post activation depression in the control group, but did not change the post activation ratio in the SCI group. Normalized H2 amplitude significantly increased according to load (50%> 25%> 10%) in the control group whereas was minimally modulated to load in those with SCI.

CONCLUSIONS

Segment compressive load inhibits post activation depression in humans without SCI, but minimally modulates the reflex circuitry in people with chronic SCI. These findings suggest that spinal cord reorganization mitigates the typical response to load in people with chronic SCI.

SIGNIFICANCE

Early limb load training may impact the reorganization of the spinal cord in humans with acute SCI.

Limb segment load inhibits post activation depression of soleus H-reflex in humans

OBJECTIVE

We investigated the effect of various doses of limb segment load on soleus H-reflex amplitude and post activation depression in healthy individuals. We also explored the influence of limb segment load on spinal circuitry in one individual with chronic SCI.

METHODS

Twenty-eight healthy adults and one SCI subject received compressive loads applied to the top of their knee at varied doses of load (10%, 25%, and 50% of the body weight). Soleus H-reflexes were measured before (baseline) and during the loading phase.

RESULTS

There were no significant differences in H-reflex amplitudes during the 50% BW load-on phase as compared to either baseline session or the load-off phase. However, the post activation depression was decreased over 9% (p<0.05) during the load-on phase compared to the load-off phase and scaled according to load (50%>25%>10%). The post activation depression ratio also appears less responsive to varying loads after chronic SCI.

CONCLUSIONS

Limb segment load decreases post-activation depression in humans. These findings suggest that the mechanism associated with post activation depression is modulated by limb segment load, and may be influenced by spinal reorganization after SCI.

SIGNIFICANCE

Future studies will determine if various levels of spasticity modulate the response of limb segment load on post activation depression in those with acute and chronic SCI.

Loss of knee-extension strength is related to knee swelling after total knee arthroplasty

OBJECTIVE

To examine whether changes in knee-extension strength and functional performance are related to knee swelling after total knee arthroplasty (TKA).

DESIGN

Prospective, descriptive, hypothesis-generating study.

SETTING

A fast-track orthopedic arthroplasty unit at a university hospital.

PARTICIPANTS

Patients (N=24; mean age, 66y; 13 women) scheduled for primary unilateral TKA were investigated 1 week before surgery and on the day of hospital discharge 2.4 days postsurgery.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

We assessed all patients for knee-joint circumference, knee-extension strength, and functional performance using the Timed Up & Go, 30-second Chair Stand, and 10-m fast speed walking tests, together with knee pain during all active test procedures.

RESULTS

All investigated variables changed significantly from pre- to postsurgery independent of knee pain. Importantly, knee circumference increased (knee swelling) and correlated significantly with the decrease in knee-extension strength (r=-.51; P=.01). Reduced fast-speed walking correlated significantly with decreased knee-extension strength (r=.59; P=.003) and decreased knee flexion (r=.52; P=.011). Multiple linear regression showed that knee swelling (P=.023), adjusted for age and sex, could explain 27% of the decrease in knee-extension strength. Another model showed that changes in knee-extension strength (P=.009) and knee flexion (P=.018) were associated independently with decreased performance in fast-speed walking, explaining 57% of the variation in fast-speed walking.

CONCLUSIONS

Our results indicate that the well-known finding of decreased knee-extension strength, which decreases functional performance shortly after TKA, is caused in part by postoperative knee swelling. Future studies may look at specific interventions aimed at decreasing knee swelling postsurgery to preserve knee-extension strength and facilitate physical rehabilitation after TKA.

Warming-up before sporting activity improves knee position sense

OBJECTIVE

To evaluate the effects of a warm-up program on knee joint position sense in karatekas.

DESIGN

Repeated measures design.

SETTING

Research laboratory.

PARTICIPANTS

Ten young amateur karatekas (17.6 +/- 4.0 years of age).

MAIN OUTCOME MEASURES

Knee joint position sense evaluated before and immediately after a warm-up program through active repositioning in open kinetic chain (OKC) and closed kinetic chain (CKC).

RESULTS

At baseline testing no differences were observed between OKC and CKC in absolute (4.1 +/- 1.6 degrees vs. 3.4 +/- 2.0 degrees) and relative angular errors (2.4 +/- 3.4 degrees vs. 2.1 +/- 3.5 degrees). After the warm-up program, a significant decrease in absolute angular error was observed only in CKC (from 3.4 +/- 2.0 degrees to 1.8 +/- 0.5, p < 0.05). Additionally, in CKC the subjects reduced the relative angular error to approximately zero (from 2.1 +/- 3.5 degrees to -0.01 +/- 1.6 degrees) and decreased the variability of the responses, expressed by the decrease in standard deviation of the relative errors.

CONCLUSIONS

The warm-up program enhanced knee joint position sense only in CKC. Since no effects were detected in OKC, the evaluation of the effects of warm-up on knee joint position sense using merely an OKC technique would underestimate the valuable role of warm-up.

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.

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.

Amelioration of symptoms by enhancement of proprioception in patients with joint hypermobility syndrome

OBJECTIVE

Joint hypermobility syndrome (JHS) is characterized by an association between joint hypermobility and musculoskeletal pains, the latter occurring in the absence of any objective indicator of rheumatic disease. The lack of a recognizable disease marker makes this condition difficult to identify and manage. We previously observed that patients with JHS have impaired proprioception compared with that of a matched control group. The purpose of this study was to investigate whether a home-based exercise program could produce objective enhancement of proprioception as well as alleviate symptoms in JHS.

METHODS

A threshold detection paradigm was used to assess knee joint proprioception, balance was assessed using a balance board, and quadriceps and hamstring strength were measured by an isokinetic dynamometer. A visual analog scale was used to assess musculoskeletal pain, and quality of life was evaluated by a Short Form 36 questionnaire. Assessments were performed before and after an 8-week program of progressive closed kinetic chain exercises.

RESULTS

Following the exercise program, proprioceptive acuity increased in 16 of 18 subjects and was very significantly improved overall (P < 0.001). There was a comparable improvement in performance on the balance board (P < 0.001), and quadriceps and hamstring strength also increased significantly. Symptomatic improvement also occurred, in terms of both pain (P = 0.003) and quality-of-life (P = 0.029 for physical functioning; P = 0.008 for mental health) scores.

CONCLUSION

Appropriate exercises lead not only to symptomatic improvement, but also to demonstrable enhancement of objective parameters such as proprioception.

Pathophysiology of vascular dysfunction in a rat model of chronic joint inflammation

The impact of chronic joint inflammation on articular vascular function in rats was investigated to address whether joint swelling and the associated vascular dysfunction are dependent upon a common prostanoid mechanism. Urinary nitrate/nitrite (NO(x)) and PGE(2) excretion, knee joint diameter and body weight were measured following induction of adjuvant-induced arthritis (AIA). Ten days postinduction of AIA, joint vascular reactivity was assessed by measuring the perfusion response using a laser Doppler imager (LDI) to topical application of acetylcholine (ACh) and sodium nitroprusside (SNP). Four groups were compared: a non-inflamed control group and three AIA groups treated i.p. with vehicle, indomethacin or SC-236 (at equimolar doses). The selective cyclooxygenase-2 (COX-2) inhibitor (SC-236) was used to differentiate between COX-1 and -2-derived prostaglandins. Urinary NO(x) and PGE(2) levels increased substantially during the early phase of AIA but decreased thereafter. Toxicity to indomethacin but not SC-236 was observed, as indicated by a marked decrease in body weight. Joint swelling was similarly attenuated by indomethacin and SC-236 (P= 0.0001 cf. vehicle-treated AIA; n= 5-6 per group), indicating that this is due to COX-2 and not COX-1 inhibition. The AIA-induced changes in urinary NO(x) and PGE(2) were corrected by both COX inhibitors. While vascular reactivity to ACh and SNP was significantly attenuated by AIA (P < 0.002; n= 5-10 per group), the perfusion responses to these vasodilating agents were similar in all three AIA groups, demonstrating that the vascular dysfunction was not corrected by inhibition of either COX-1 or COX-2 enzymes. Furthermore, the attenuation of both ACh and SNP-induced responses in AIA suggest that vascular dysfunction was not exclusively endothelial in nature. In conclusion, the joint swelling and vascular dysfunction associated with AIA appear to be mediated, at least in part, by independent mechanisms. While COX-1/COX-2 inhibition reduced joint swelling, vascular dysfunction in AIA is independent of constitutive or inducible prostanoid mechanisms, and appears not to be solely endothelial-derived, but to involve other components such as the vascular smooth muscle.

Effects of loading and unloading of lower limb joints on the soleus H-reflex in standing humans

OBJECTIVE

To investigate the effects of loading and unloading of the lower limb joints on the soleus H-reflex in standing humans.

METHODS

H-reflexes were elicited in the soleus muscle in subjects standing on a force platform in a water tank under the following loading conditions of the ankle and knee joints: control condition; reduced loads of -10 and -20 N; imposed loads of 10 and 20 N. The joint loading was altered by changing the combinations of buoys and weights attached to the lower limb segments, while total body weight was kept constant.

RESULTS

As the ankle- or knee-joint load was reduced, the H-reflex was significantly enhanced compared to that under the control condition. In contrast, the H-reflex was decreased as the ankle- or knee-joint load was increased. In both cases, similar levels of background activity were recorded.

CONCLUSIONS

The present results suggest that joint afferents might mediate the suppression of the soleus H-reflex in standing humans. However, the identification of the receptors and/or the mechanisms cannot be addressed under the current experimental set up.

SIGNIFICANCE

The results of this study give some basic insights into reflex control in an upright posture.

Intra-articular knee joint effusion induces quadriceps avoidance gait patterns

OBJECTIVES

(1) To identify adaptations caused by intra-articular knee joint effusion during walking and (2) to determine if knee joint effusion may be a causative factor in promoting quadriceps avoidance gait patterns.

DESIGN

Gait testing of 14 healthy individuals who underwent incremental saline injections of the knee joint capsule.Background. Gait adaptations have been reported in the literature for knee injured and rehabilitating individuals. Knee joint capsular afferent activity can influence knee joint function.

METHODS

Gait analysis was employed in a pre- and post-test, repeated measures design to determine lower extremity joint kinematics, kinetics, energetics and thigh EMG adaptations due to intra-articular knee joint effusion.

RESULTS

Knee effusion caused an increase in hip and knee flexion through the stance phase. Knee extensor torque, impulse and negative and positive work were diminished with increased effusion levels. Quadriceps activity decreased and hamstring activity increased due to intra-articular knee joint effusion.

DISCUSSION

These adaptations cannot be attributed to an injury, surgery or rehabilitation. Thus, the results of this experiment suggest knee joint capsular distention, via knee joint effusion, may be responsible for many gait adaptations reported for knee injured individuals in previous investigations.

CONCLUSIONS

Knee joint effusion and the subsequent capsular distention can cause major alterations in the normal gait cycle and can be considered a causative factor promoting the acquisition of quadriceps avoidance gait patterns.

RELEVANCE

This study provides reference data on the effects of intra-articular knee joint effusion on gait parameters by which future studies of injured or rehabilitating individuals can be compared.

Proprioception after an acute knee ligament injury: a longitudinal study on 16 consecutive patients

A defect in proprioception has been found in selected patient groups that have an anterior cruciate ligament deficient knee at different times after the original injury. The time of development and the extent of such defects were studied longitudinally on 16 consecutive patients. During the first year after a primary knee injury, which included a complete rupture of the anterior cruciate ligament, we repeatedly performed three tests of proprioception: (a) one to determine the threshold for detecting a passive motion from starting positions of 20 and 40 degrees, (b) an active reproduction of a passive angular change, and (c) a visual estimation of a passive angular change. The injured limb was compared with the uninjured limb and with the limbs of an age-matched reference group of healthy subjects. The population did not have a normal distribution, and some patients had consistently extreme recordings in the threshold tests at the various times of testing. Significant differences were found between the groups at the starting position of 20 degrees, when the injured knee was compared with the uninjured knee, after 1 month (p = 0.05), and after 2 months (p = 0.03). There was a trend toward a higher threshold for detecting a passive motion when the injured side was compared with the knees of the reference group at 1 month (p = 0.06) but not later on. A similar pattern was found for the injured knee at the starting position of 40 degrees, but it was not significant. An impaired ability to detect a passive motion was registered for the nearly extended knee 1 and 2 months after a primary injury. In the active reproduction and visual estimation tests, no significant defects were found at any time during the first year in these consecutively studied patients.

The effects of chronic effusion on knee joint proprioception: a case study

Knee joint effusion has been shown to cause a reflex inhibition of the quadriceps musculature. However, the effect of effusion on knee joint proprioception has not been thoroughly investigated. This issue is further clouded by the debate surrounding the role of the muscle spindle and joint mechanoreceptors in providing afferent feedback to the central nervous system. This case study examines the effects of a chronic effusion on knee joint proprioception. Possible suggestions for the results are discussed, and areas for further study are offered.

Swelling of the knee joint: effects of exercise on quadriceps muscle strength

OBJECTIVE

To investigate the effects of excessive fluid in the knee joint on the performance of the quadriceps muscles and to determine whether quadriceps muscle performance can be altered by exercising the swollen joint.

DESIGN AND SETTING

A before-after trial design was used, and the procedures were performed in a laboratory setting.

SUBJECTS

A random sample of 27 adult men with no musculoskeletal problems was divided into intervention and control groups.

INTERVENTION

First, in all groups, torque generated by the quadriceps muscle was examined by isokinetic muscle testing undertaken at a joint angular velocity of 120 degrees/sec over a range of motion from 5 degrees to 80 degrees flexion. After this initial test, in group 1, 60mL saline and dextrose was injected into the knee joint and subjects repeated the maximal effort procedure. Subjects then performed submaximal exercise for 3 to 4 minutes, after which maximal effort testing was undertaken again. In group 2, subjects received no injection of fluid, undertook 2 maximum effort tests, then performed submaximal exercise for 3 to 4 minutes, after which maximum effort testing was undertaken again. In group 3 (control group), subjects undertook three maximum effort tests over a time period similar to that for the other groups.

MAIN OUTCOME MEASURE

Quadriceps muscle torque generated at 60 degrees from full knee extension.

RESULTS

Torque decreased (p < .05) 30% immediately after the injection of fluid. However, torque returned to preinjection levels after submaximal exercise (p > .05). These findings were related to joint capsule compliance and fluid movement. No significant changes (p > .05) in torque were observed for the other two groups.

CONCLUSION

Submaximal exercise of swollen knee joints can decrease artificially induced quadriceps muscle inhibition. These findings may have implications for patients with perennial effusions who at times undertake gait activities.

Knee effusion and quadriceps muscle strength

Ten healthy subjects with no musculoskeletal problems were tested using a computerized exercise dynamometer. Quadriceps femoris concentric performance was examined during maximal effort isokinetic knee extension at joint angular velocities of 2.09 and 4.18 rad s(-1). A saline and dextrose solution was injected into the knee joint cavity in 30-ml increments, and peak torque and power tests were undertaken with knee effusions of 0, 30, 60, and 90 ml. A protocol which included and excluded a local skin anaesthetic and submaximal exercise prior to the maximal effort test was also undertaken. The results showed that quadriceps peak torque and power were not significantly affected by the amount of knee effusion at either joint angular velocity when submaximal exercise was performed prior to the maximal effort test. However, peak torques were significantly decreased during isokinetic muscle action without prior submaximal muscle work. It was suggested that these findings may be related to fluid movement in the knee joint compartments, the compliance of the joint capsule, and the location that fluid was injected into the joint cavity. Joint swelling is a common symptom of individuals with osteoarthritis and rheumatoid arthritis, as well as those suffering acute joint trauma. This study has extended previous work on joint swelling by examining quadriceps function during joint movement, thus moreeffectivelysimulating joint and muscle activity which occursduring functional activities. Patients with knee joint swelling are thought to experience greater difficulty undertaking quadriceps exercises, and will not perform these exercises effectively until swelling in the joint is reduced. The current study provides some evidence to suggest that a moderate amount of swelling does not impair performance. Assuming that patients do not have other symptoms that contraindicate exercise, they can be encouraged to do more active muscle work.

Comparative study of intra-articular pressure dynamics in joints with acute traumatic and chronic inflammatory effusions: potential implications for hypoxic-reperfusion injury

It has been proposed that the process of hypoxic-reperfusion injury contributes to the persistence of synovitis in the inflamed human joint. The generation of pathological, exercise induced, intra-articular pressure leading to occlusion of the synovial microcirculation is central to this mechanism. However, acute traumatic inflammatory joint effusions rarely result in chronic synovitis, suggesting that either the basic hypothesis is incorrect, or that joints with acute traumatic effusions show different intra-articular pressure dynamics. In this study the intra-articular pressure was measured at rest and during isometric exercise in five patients with acute traumatic joint effusions and in nine patients with chronic inflammatory joint effusions. The generation of intra-articular pressure in the patients with acute traumatic effusions was significantly lower at rest (mean 2.0 v 19.6 mm Hg) and during exercise (mean 13.7 v 222.5 mm Hg) than in the patients with chronic effusions. This was due to reflex muscular inhibition around the joint, which inhibited the pathological generation of intra-articular pressure. This difference in the ability to generate intra-articular pressure might mitigate against hypoxic-reperfusion injury in joints with acute traumatic effusions, thereby explaining the paradoxical clinical observation that patients with acute traumatic inflammatory joint effusions rarely develop chronic synovitis.

Effect of flexion angle on the pressure-volume of the human knee

The objective of this study was to determine pressure-volume relationships in the human knee. Eight normal knees in eight patients undergoing elective arthroscopic surgery were studied to develop pressure-volume curves at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 80 degrees of flexion, and measure capsular volume at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 80 degrees of flexion. The results showed that capsular volume decreases with flexion, whereas capsular stiffness increases. This suggests that during arthroscopy, flexion with obstructed outflow may cause significant intraarticular pressure and potential rupture of synovial membranes. Our results support the concept of flow rates with low distension pressures for maximum safety.

Reflex actions of knee joint afferents during contraction of the human quadriceps

(1) The spinal reflex actions of afferents stimulated by knee joint distension have been investigated in man. (2) Cannulation of the knee and infusion of saline raised intra-articular pressure, especially during quadriceps contraction. High pressures did not induce any sensation of pain. Pressure was taken as an index of joint proprioceptor activation. (3) Increased pressure progressively depressed the quadriceps H-reflex, both at rest and during quadriceps contraction. There was no indication of a threshold pressure for this inhibitory action. (4) It is concluded that joint distension inhibits quadriceps motoneurons through spinal pathways that still operate during voluntary contraction. These pathways could thus contribute to pathological weakness after joint injury. (5) Joint distension produced spatial facilitation of non-reciprocal inhibition of quadriceps H-reflexes from afferents in the tibial nerve.

The interrelation of neural discharge, intra-articular pressure, and joint angle in the knee of the dog

Single- and multi-unit recordings were obtained from the medial articular nerve (m.a.n.) of knee joints in the anaesthetized dog. The single-unit recordings were confined to low threshold (group I and II) articular mechanoreceptors. Multi-unit recordings revealed that the m.a.n. discharge was maximal in extension, submaximal in flexion, and minimal at intermediate angles, i.e. a U-shaped profile. Subatmospheric intra-articular pressures do not appear to influence the m.a.n. discharge. Intra-articular infusion of even small quantities of fluid, although not affecting the U-shaped profile, reversed the m.a.n. discharge pattern with maximum neural activity occurring in flexion and being submaximal in extension. Recordings from single units indicated that the enhanced discharge after fluid infusion was a result of increased discharge frequency and 'recruitment' of individual afferents.