Neuropathology of the Shoulder What can we learn from SCI? BESS 2009

Transcription

1 Neuropathology of the Shoulder What can we learn from SCI? BESS 2009 Sue Paddison Lead Clinical Specialist Physiotherapist Spinal Cord Injury Centre, RNOH,Stanmore

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3 Learning objectives Identify neural & non neural components of motor control Biomechanical influences on motor control Relevance of muscle properties: fibres types, Size Principle of Recruitment Postural control Motor Control Systems- feedback and feedforward Motor Learning Central Pattern Generators/ learned motor programmes Sensory processing Clinical Application FES in motor learning Your Treatments Conclusion

4 SCI Rehab - Shoulder instability? Shoulders part of whole body and not a joint in isolation Is the shoulder the only area of instabilty? Hypermobility - proprioceptive impairment, a component of another syndrome? Motor sequencing problems

5 Components of Motor Control Consider Neural components- Motor, Sensory, Perceptual, Cognitive Non-neural components- Biomechanical factors Effects of CNS on both these systems?

6 These negative phenomena are characterised by a reduction in motor activity and are the principle cause of disability in the neurological dysfunction. - Many of these features are present in patient s presenting with shoulder instability. Neuro rehabilitation of the negative phenomenon is usually directed towards maximising function of weakened areas and maintaining effective joint and soft tissue integrity.

7 Impairments Over-activity in muscles Muscle shortening/soft tissue changes. Deformity/altered posture. Joint contractures. Low toned muscles Overstretch of muscle & Joints. Altered of joint position sense Reduced exercise tolerance. Pain

8 The Role of Biomechanical Changes. In addition to neural factors, the biomechanical contribution to muscle tone may also be pathologically increased eg. Marfans syndrome Muscles and tendons become stiff, with reduced compliance, which results in fixed contractures. This occurs if muscles are not moved through a full range of movement, due to weakness or poor positioning, or excessive abnormal muscle patterning. Altered alignment is a consequence of muscle imbalance+/- ligamentous incompetence. Altered movement patterns - neurological or non neurological.

9 Therefore: Muscle tone is the combined result of neural and biomechanical factors. This is central to understanding and managing patients. Increase in muscle stiffness may involve changes in connective tissue, and stiffness in the muscle fibre itself (Thixotrophy) and fibre type.

10 Muscle Physiology QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture.

11 Reduced Muscle Compliance Versus Contracture. Reduced Compliance: Remodelling of connective tissue within muscle. Contracture: Persistent and involuntary shortening of muscle due to a reduced number of sarcomeres. Muscle tone may or may not be normal within a ROM reduced by contractures.

12 Hennman Size Principle Small motor units (slow) recruited 1 st at 30% MVC Larger motor units (fast) recruited last Muscle specificity - fibre type - position - speed - function Muscle are recruited most easily during a functional task

13 Properties of Muscle Fibre Type I IIa IIb Motor Unit Fibre Diameter Slow oxidative Fast oxidative glycolytic Small Small / medium Fast fatiguable glycolytic Large Recruitment order First Middle Last

14 Changes in function, imposed through movement impairment - disuse, hypertonia, dystonia, will produce changes in muscle type. Single lower motor neuron can innervate a single muscle fibre or many muscle fibres. Motor neuron pool- all motor neurons that innervate a muscle Re-myelination and axon growth is dependant on activity. (McDonald et al 2002, Howe 2003) Disuse atrophy- All muscle fibre types change. Extent depends on the normal function of the muscle.

15 The elastic compliance of muscle depends on the concentration of collagen (major component of connective tissue). Type I (S/O): High collagen content : Reduced compliance Type II (F/G): Low collagen content : Higher compliance. If a muscle alters from F/G to S/O elastic compliance will reduce. - Demonstrated on length tension curves. (Lieber 2004)

16 Therefore if a muscle is immobilised in a shortened position Fewer sarcomeres. in a lengthened position More sarcomeres. Either may occur in patients due to prevalence of abnormal tone/altered posture/pain. Weakness is a consequence of either. The muscle develops maximum tension in the immobilised position - too long or too short. Eccentric lengthening requires more neural activation than concentric - de-recruitment under active CNS control.

17 Movement Problems of the Shoulder Girdle Muscle balance around the shoulder, on which the joint relies for stability is altered by: Muscle weakness/ tear altered active control Abnormal muscle tone Inflammation Trauma altered passive control

18 Problems that could result from Trauma: Ability of the arm to abduct may be compromised as the joint capsule and muscles become progressively more fibrous. Future efforts to restore range of movement meet with increased resistance and pain. Altered alignment and pain leads to: Decreased selectivity of movement Impaired co-ordination of shoulder girdle musculature

19 Upper Limb Function Stability v Mobility Selective UL function depends upon normal innervation of the arm; shoulder; trunk and legs. The shoulder complex is the most mobile joint in the body with no fixed origin and insertion, being dependent on co-ordinated muscle activity for stability. Functional movement depends on thoracic spine mobility as well as UL mobility and compliance on a background of stability.

20 Trunk Stability What is it?

21 Trunk muscle recruitment in upper limb activity EMG recording, intra abdominal pressure and movement analysis. Short latency response in TrA to unexpected loading of UL. Likely due to afferent receptors in the UL? (Hodges 2001)

22 Trunk stability and upper limb function Activity (Feedforward) in lumbar spine stability changes patterns when bringing in the limbs (Hodges 2001) - Some judgement of task - Thought planning- lateral cerebellum -?Spinal segmental reflexes -stretch

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24 Feedforward Mechnism Central control Innate Ongoing experience Demonstrated activity in the brain before movement begins (Kristeva 1994) Initiation+ / - and anticipatory

25 Feedback Mechanism New task no experience, needs feedback mechanism Less efficient Slower ms Regulates and adapts

26 Feedback and Feedforward Systems IDEA PLAN EXECUTE APPRAISAL Need Extrinsic Command to muscles Desire Intrinsic Sensory Feedback During task After task Motivation Posture & Task Activity Internal Feedback (Cognitive) Adjust Feedforward

27 Bilateral reflex control of Trapezius Initial response 1a stretch reflex Second response CNS and back (like the H reflex in soleus) Demonstrates muscle twitch afferents on ipsilateral side and also monosynaptically activate motorneurones on contralateral side. If feedback systems are disrupted this also changes feedback to the opposite side. (Alexander et al 2002)

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29 Central Command for Posture and Movement Central Command Limb Movement Postural Accompanying APAs Disturbance? Feedforward for Postural Adjustment Feedback anticipation for unexpected Postural disturbance Preparatory APAs

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31 Postural Control and Afferent Input from the Upper Limb Light touch - feeds to vestibular system Somatosensory input from the hands provides feedforward for postural control (Jekka 1997 and McLoughlin et al 2005)

32 Proposed that group I muscle afferents from the forearm or hand evoke a supraspinal reflex to trapezius and serratus anterior. It seems that the functional significance of these reflexes aids in the stability of the shoulder girdle. (Alexander CM, Harrison PJ. 2003)

33 Position of the arm in relation to the body The human brain has two body part representations Body Schema- codes body parts in space Body Structural Description- codes position of body parts relative to standard body. fmri used to identify neural mechanisms involved in different areas of the brain -specific. (Corradi-Dell Acqua C. et al 2009) 2-3 weeks after loss of afferent input - lose the body schema (De-chunking)

34 Active vs Passive Positioning Position sense acuity varies across shoulder complex ROM (Janwantanakul P et al) Hand position sense reproduced more accurately when a movement has been encoded by active compared to passive. (Laufer Y et al)

35 Bracing Stabilisation Effect on repositioning sense: Compressive bracing improves passive positioning (Ulkar B et al) In unstable shoulders, active end range of external rotation is improved by wearing brace. (Chu JC et al)

36 Motor Learning.a set of processes associated with practice or experience leading to relatively permanent changes in the capability of responding (Schmidt & Lee 1999) PERFORMANCE How do we retain the ability to do what is learned? Train to create adaptation Perfect Practice (Winstein CJ 2009) Increase synaptic connections (overload the system) - strength Cells that fire together, wire together.

37 Motor Programmes Complex patterns of movement can be generated by the CNS without specific input from the limbs.set of muscle commands structured before a movement begins. ( Keele 1968) Based on prior experience (stored in cerebellum). Joint instability- habitual patterns -Type III muscle.

38 Central Pattern Generators Evidence that neural networks in the isolated spinal cord - generating rhythmic motor bursts output - reciprocally organised between agonists and antagonists - in the absence of efferent descending and all movement related afferent sources. (Grillner 1985) Afferents- Spinal and supraspinal levels feedback to the CPGs

39 Key areas in clinical application Task analysis-goals Specificity of training- FITT principles Importance of biomechanics, muscle strength, extensibility Attentiveness cognitive /perceptual Feedback/ guidance Practice

40 Treatment principles in clinical application Incorporate all relevant principles Muscle imbalance Stabilise 1 st then mobilise Neural Dynamics Address structures affecting the nerves Can the patient achieve the functional range? Affects quality and memory of movement

41 Skill Learning Preparation- Feedforward Lengthening of muscles to gain alignment and improve efficiency: Tension/ length ratio- Motor patterns Optimum length = optimum function Practice task Retrain holding and alignment- sensory mapping Functional position to generate power in correct range- feedback

42 How can FES contribute to motor control? Activates muscle directly via the nerve Stimulation is electrical (voltage gate) at the axon not chemical via the soma Fusion frequency is high Multiple synaptic depletion at the same time - fatigue. Training increases in muscle resistance to fatigue Increases muscle size and capillary circulation with regular training. (Chillibeck 1999) Create background of stability.

43 Treatment Toolkit Motivation- goals/ visualise/ video Practice speed of activity/kineasthetic sense for function -Specific Synchrony Soft tissue techniques- inhibitory/facilitatory techniques FES Biofeedback Taping/ bracing Be Creative!

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45 Concepts of retraining Activity driver causes change becomes the driver neurological reorganisation structural change Success breeds success Avoid purist approach Bombardment of unaffected systems Access other areas, joints, other UL for contributory afferent sources.

46 Conclusion Evidence of complex systems that are integrated and modulated in the CNS to produce postural control Active movements at speed or loading the upper limb demonstrates feedforward and feedback mechanisms Theories of motor control incorporate these ideas Rehabilitation should utilise all these systems Treatments must be tailored and the patient engaged

47 Thank You