Per Sjölander

Spinal and supraspinal effects of activity in ligament afferents.

In this paper available knowledge on effects from joint and ligament afferents on spinal neurones and pathways are briefly reviewed, and possible functional implications discussed. Ligament afferents may contribute to joint stability, muscle coordination and proprioception through direct polysynaptic reflex effects onto ascending pathways and skeletomotoneurones, and/or indirectly via reflex actions on the gamma-muscle spindle system. Theoretical and experimental evidence indicate that ligament afferents, together with afferents from other joint structures, muscles and the skin, provide the CNS with information on movements and posture through ensemble coding mechanisms, rather than via modality specific private pathways. The existence and functional relevance of ligamentomuscular protective reflexes, that are triggered when the ligament is threatened by potentially harmful loads, has been seriously questioned. It seems more likely that peripheral sensory inputs from ligament afferents participate in a continuous control of the muscle activity through feedforward, or preprogramming, mechanisms. In line with these ideas it has been suggested that ligament mechanoreceptors have an important role in muscle coordination and in the reflex regulation of the functional joint stability, by contributing to the preprogramming of the muscle stiffness through reflex modulation of the gamma-muscle spindle system.

VERTICAL POSTURE AND HEAD STABILITY IN PATIENTS WITH CHRONIC NECK PAIN

OBJECTIVE To evaluate postural performance and head stabilization of patients with chronic neck pain. DESIGN A single-blind comparative group study. SUBJECTS Patients with work-related chronic neck pain (n = 9), with chronic whiplash associated disorders (n = 9) and healthy subjects (n = 16). METHODS During quiet standing in different conditions (e.g. 1 and 2 feet standing, tandem standing, and open and closed eyes) the sway areas and the ability to maintain the postures were measured. The maximal peak-to-peak displacement of the centre of pressure and the head translation were analysed during predictable and unpredictable postural perturbations. RESULTS Patients with chronic neck pain, in particular those with whiplash-associated disorders, showed larger sway areas and reduced ability to successfully execute more challenging balance tasks. They also displayed larger sway areas and reduced head stability during perturbations. CONCLUSION The results show that disturbances of postural control in chronic neck pain are dependent on the aetiology, and that it is possible to quantify characteristic postural disturbances in different neck pain conditions. It is suggested that the dissimilarities in postural performance are a reflection of different degrees of disturbances of the proprioceptive input to the central nervous system and/or of the central processing of such input.

Activity in receptor afferents from the anterior cruciate ligament evokes reflex effects on fusimotor neurones

Responses from 2-4 muscle spindle afferents from triceps surae and/or posterior biceps and semitendinosus muscles were simultaneously recorded in cats anaesthetized with alpha-chloralose. It was demonstrated that stretch of the anterior cruciate ligament (ACL) of the ipsilateral knee causes changes in dynamic and/or static sensitivity of primary and secondary spindle afferents to sinusoidal stretching. The changes were due to reflex actions of stretch/tension-sensitive receptor afferents from ACL on dynamic and static fusimotor neurones. The findings support the hypothesis that ACL-afferents contribute to the regulation of muscular stiffness around the knee, and thereby also to dynamic knee joint stability.

Fusimotor reflexes to antagonistic muscles simultaneously assessed by multi-afferent recordings from muscle spindle afferents☆

Several single agonist/antagonist primary muscle spindle afferents were simultaneously recorded in chloralose anaesthetized cats. It was shown that their dynamic and static sensitivity to sinusoidal muscle stretches could be increased or decreased via the fusimotor system by extension and flexion of the contralateral hind limb as well as by stretch of ipsilateral muscles and stimulation of ipsilateral skin nerves. The results seem to support the hypothesis that the primary muscle spindle afferents convey complex multisensory messages to the central nervous system (CNS).

Increased intramuscular concentration of bradykinin increases the static fusimotor drive to muscle spindles in neck muscles of the cat.

Abstract The aim of the present study was to investigate if increased intramuscular concentrations of bradykinin (BK) in one muscle influence the activity in primary and secondary muscle spindle afferents (MSAs) originating from both ipsi‐ and contralateral muscles, via fusimotor reflexes. The ipsilateral trapezius (TR) and the splenius (SP) muscles were subjected to sinusoidal stretches and 2–3 MSAs were simultaneously recorded from these muscles. Responses of 29 MSAs (15 SP and 14 TR) were registered in five adult cats lightly anaesthetised with &agr;‐chloralose. Intramuscular injections of 0.5 ml BK (6–86 &mgr;g/ml) were administered to both the ipsi‐ and contralateral SP and TR muscles. Similar doses of BK (5–10 &mgr;g) have been shown to induce muscle pain when injected into the temporal muscle in man. The responsiveness of the MSAs to the injections of BK was 86% and 87.5% from the contralateral TR and SP muscles, respectively. The effects were predominantly static onto the MSAs. The duration of the effects was on average 3.5–4 min, however some effects lasted for more than 15 min. The effects were always abolished after cutting the nerve to the injected muscle. The large majority of the spindle afferents were unresponsive to i.m. Tyrode injections (23 of 29). For the afferents that were responsive to injection of Tyrode, the effects were always considerably smaller and with shorter duration than those evoked by BK injections. Thus, increased intramuscular concentrations of BK may excite primary and secondary MSAs from ipsi‐ and contralateral muscles, via fusimotor reflexes evoked most probably by activity in chemosensitive muscle afferents. The results are discussed in relation to a recent hypothesis on pathohysiological mechanisms behind genesis, spread and perpetuation of muscle tension and pain in chronic musculoskeletal pain syndromes.

Influences on the fusimotor-muscle spindle system from chemosensitive nerve endings in cervical facet joints in the cat: possible implications for whiplash induced disorders

&NA; The aim of the present study was to establish if there exists reflex connections from ligamentous structures in cervical facet joints and the fusimotor system of dorsal neck muscles. In seven cats, anaesthetized with &agr;‐chloralose, bradykinin (BK) of concentrations between 12 and 50 &mgr;g was injected into the facet joint between C1 and C2. Recordings were made from single muscle spindle afferents (MSA) originating in contralateral trapezius and splenius muscles (TrSp). Fusimotor induced changes in the sensitivity of the muscle spindle afferents were assessed by recording the responses to sinusoidal stretches of the TrSp muscles. The mean rate of discharge and the depth of modulation of a fitted sine were taken as quantitative estimates of the response. A total of 25 MSAs were recorded, and 21 of these showed clear‐cut alterations in their responses to the sinusoidal stretches following Bk. injections into contralateral facet joint. The majority of the responding afferents (13/21) showed changes in their responses indicating an increased activity of static fusimotoneurones, although responses of dynamic and mixed static and dynamic nature were also seen. Local anaesthetics applied to the intraarticular receptors abolished the effects. Injection (i.v.) of a general anaesthetic (pentobarbital) abolished the effects. The results show that there exist reflex connections between receptors in cervical facet joints and fusimotoneurones of dorsal neck muscles, and this might be of importance in the pathophysiology behind whiplash associated disorders (WAD).

Influences on the γ-muscle spindle system from muscle afferents stimulated by KCl and lactic acid

It is known that accumulation of contraction metabolites in muscles stimulates group III and IV afferents and induces excitation of gamma-efferents to the homonymous muscle. The aim of the present study was to investigate whether increased concentrations of lactic acid and KCl in one muscle may influence the activity in primary and secondary muscle spindle afferents (MSAs) from the chemically affected muscle and from surrounding muscles. The experiments were made on 7 cats anesthetized with alpha-chloralose. Recordings were made simultaneously from 2-8 single MSAs from the triceps surae (GS) and the posterior biceps and semitendinosus muscles (PBSt). The mean rate of firing and the depth of modulation of MSA responses to sinusoidal stretching of the receptor-bearing muscles were determined. Responses of 27 primary MSAs (11 from PBSt and 16 from GS) were recorded. On 24 of these clear-cut alterations in sinusoidal response were evoked by injection of 1 ml of KCl (50-600 mM) or 1 ml of lactic acid (20-200 mM) into the artery supply of the GS muscle. Also, all secondary MSAs recorded (4 from PBSt and 1 from GS) showed sizable effects to increased intramuscular concentrations of KCl and/or lactic acid. On both primary and secondary MSAs, from GS as well as from PBSt muscles, nearly all effects observed were compatible with activation of static fusimotor neurons. Effects on MSAs were completely abolished when the ipsilateral L7-L6 ventral roots were cut and when the GS nerve was anesthetized. Intravenous injections of KCl and lactic acid, as well as arterial injections of 0.9% NaCl, were ineffective in changing the MSA responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated Intramuscular Concentration of Bradykinin in Jaw Muscle Increases the Fusimotor Drive to Neck Muscles in the Cat

Patients suffering from temporomandibular dysfunction exhibit clinical findings such as fatigue, painful muscles, and muscles that are tender to palpation, not only in the temporomandibular area, but also in the neck/shoulder region. The mechanisms behind this are not known, although previous studies of similar spreading phenomena have revealed a possible involvement of the fusimotor system. In the present study, we evaluated the activity of this system by recording the activity of muscle spindle afferents from dorsal neck muscles after intramuscular injections of 6 μg to 25 μg bradykinin in the ipsilateral masseter muscle. A total of 23 muscle spindle afferents from the trapezius and splenius muscles was recorded at the C3-C4 level in 7 adult cats anesthetized with a-chloralose. Of these 23 afferents, 17 (74%) showed significantly different responses to bradykinin injections compared with control injections (dissolving agent, Tyrode), and the majority of the effects were compatible with an increased static fusimotor drive to the muscle spindle system. Thus, the results demonstrate potent reflex connections from groups III and IV masseter muscle afferents to fusimotor neurones on the C3-C4 level. It is concluded that the fusimotor system might play a significant role in the mechanisms behind the spread of muscle pain and tension from the temporomandibular region to the neck.

Influence from stretch-sensitive receptors in the collateral ligaments of the knee joint on the γ-muscle-spindle systems of flexor and extensor muscles

In lightly alpha-chloralose anaesthetized cats, activity was recorded simultaneously from 2-4 primary muscle spindle afferents from triceps surae and/or posterior biceps and semitendinosus muscles. Increased tension in medial or lateral collateral ligament was found to evoke changes in the responses of the primary spindle afferents to sinusoidal stretching of their parent muscles. It is concluded that these changes were due to reflex actions of stretch/tension-sensitive receptors in the collateral ligaments on fusimotor neurones. Thus, receptor afferents from the collateral ligaments may contribute to the regulation of the activity in the gamma-motor-muscle-spindle system, and thereby also be of importance for the control of muscular stiffness and knee joint stability.

Factors predicting pain reduction in chronic back and neck pain after multimodal treatment.

Objectives:To determine whether treatment related pain reduction on the short- and long-term is predicted by different baseline variables, and with different accuracy, in patients with chronic low back pain as compared with those with chronic neck pain. Design and Methods:A single blinded prospective cohort study based on patients with chronic musculoskeletal pain in the lower back (N = 167) or the neck (N = 136) who completed a 4-week multimodal rehabilitation program. At admission, each patient was evaluated on 17 potential predictors, including pain characteristics and physical, sociodemographic, and psychosocial-behavioral variables. Changes in self-reported pain intensity in the lower back or the neck between the pretreatment evaluation and those performed immediately after, and 12 months after the rehabilitation program, were assessed. Results:Logistic regression models revealed that change in pain intensity could be predicted with good specificity but with poor sensitivity both for patients with chronic low back pain and chronic neck pain. Significant predictors among the neck pain patients were high endurance, low age, high pain intensity, few other symptoms, low need of being social, to do things with others, and to be helped, along with optimistic attitudes on how the pain will interfere with daily life. Among the low back pain patients, high pain intensity, low levels of pain severity, and high affective distress were important predictors. Variables such as sex, sick leave history, working status, accident, pain duration, and depressive symptoms demonstrated no predictive value. Short- and long-term pain outcome was equally predictable and predicted by almost the same variables. Conclusions:Patients who reported unchanged or increased pain after multimodal treatment could be predicted with good accuracy, whereas those who reported decreased pain were more difficult to identify. Treatment-related pain alteration in chronic low back pain seems to be predicted by partly different variables than in chronic neck pain.