Shoulder Biomechanics & Assessment PDF

Orthopedic Treatment FT400 PT600 Shoulder Module Section 2 - Biomechanics Biomechanical relationships of the shoulder complex: Joint Stabilization While the other joints of the body rely on their ligaments and joint capsules to main...

Orthopedic Treatment FT400 PT600 Shoulder Module Section 2 - Biomechanics Biomechanical relationships of the shoulder complex: Joint Stabilization While the other joints of the body rely on their ligaments and joint capsules to maintain joint congruency and stabilization during movement, The shoulder joint capsule is relatively lax and must rely on muscles for active stabilization. In addition, although minimal, the shoulder joint capsule does provide some passive stability if the joint is correctly oriented. Shoulder PASSIVE stability When the arm hangs freely to the side (at neutral) there is little or no active contraction of the deltoid or rotator cuff muscles because of the way the articulating joint surfaces are situated Glenoid cavity is facing lateral, forward, and superior creating a lip for the humeral head. Shoulder PASSIVE stability The superior joint capsule and the coracohumeral ligament hold the humerus in the glenoid fossa against gravity. This is achieved because the superior joint capsule and coracohumeral ligament are usually taut creating an opposing force to the vertical weight of the humerus. This causes the pull the head of the humerus in against the upward facing glenoid cavity Shoulder ACTIVE stability When the shoulder is raised in any plane away from the side of the body, the superior joint capsule becomes lax. Therefore it is the responsibility of rotator cuff to maintain dynamic congruency and stabilization Compromised Stability - 2 conditions 1 / Excess Thoracic kyphosis - situates the scapula in a downward rotation. - this takes away the stabilizing ‘lip’ of the glenoid fossa and places the humerus into a pseudo-abduction in reference to the newly positioned scapula. - plus, the normally taut superior joint capsule and coracoacromial ligaments become lax. Dynamic ligaments (rotator cuff) take over with ACTIVE stabilization. This may lead to impingement syndrome because of the constant, increased tone in the rotator cuff group. Compromised Stability - 2 conditions 2 / Muscle Paresis The same occurs in a patient with muscle paresis. Weakness or imbalance may cause the scapular muscles to orient the scapula in the same forward rotation as thoracic kyphosis. Depending on the severity of the muscle paresis, inferior dislocation or subluxation may occur if the rotator cuff muscles are affected. Recap - GH Stability What three structures create passive stability for the GH joint? What do we mean by active stability of the GH joint? GH Joint Capsule & Movement The fibres of the GH joint capsule face anteriorly and medially. As the arm abducts this twist in the joint capsule increases and pulls the head of the humerus into the glenoid cavity. This increasing tension furthers abduction because the medial fibres become taut. This causes the capsule to pull the humerus into external rotation – untwisting of the joint capsule. Allows for further abduction b/c the external rotation also helps to prevent the greater tubercle from colliding with the acromial arch. GH Force Couples - 1/ Deltoid & Rotator Cuff The strong multipennate fibres of the deltoid act below the centre of rotation causing an upward and outward force on the humerus – this is for movement and elevation. The rotator cuff muscles act above the centre of rotation causing an inward, downward force on the humerus – this is to help maintain the congruency of the humeral head in the glenoid cavity. These muscles oppose each other & create a force coupling at the GH necessary for shoulder elevation. GH Force Couples - 2 / Traps & Serratus Anterior The three parts of the trapezius muscle and serratus anterior share a force coupling relationship to help with the rotation of the SCAPULA. With the upward rotation of the glenoid fossa, the scapula needs to track superiorly, anteriorly and laterally. GH Force Couples - 3/ Long Head Biceps The long head of the biceps helps to depress the head of the humerus with abduction of the arm in external rotation b/c of the pulley system it creates in the bicipital groove. Shoulder Abduction Biomechanics 1 / Scapulohumeral Rhythm 2 / Clavicle - SC & AC - movement 3 / Axial skeleton movement Review Qs How many joints form the shoulder complex? Which are they? How many degrees of freedom does each have? Scapulohumeral Rhythm Scapulohumeral Rhythm Phase 1: 0-30d abduction - first 30˚ “Scapular Setting” is performed by the GH - scapula is stabilized against the thorax and has minimal or no movement. The scapula does not move; therefore, there is no ratio of scapulohumeral rhythm. - 0-5˚ clavicular elevation, Scapulohumeral Rhythm Phase 2: 30-90d abduction - next 60˚ of elevation - at about 40” of humeral angulation the scapula begins to rotate (20˚) and there is a 2:1 scapulohumeral rhythm. - The clavicle continues to elevate (15˚) Scapulohumeral Rhythm Phase 3: 90-180d abduction - last 90˚ of elevation - there continues to be a 2:1 ratio of scapulohumeral movement. - In this final stage the clavicle elevates & rotates posteriorly (15*) (b/c of the pull on the conoid ligament) and the humerus laterally rotates 90˚ to clear the acromial arch. Reverse Scapulohumeral Rhythm Disruption to normal SH rhythm EG, the scapula moves more than the humerus in abduction Gross compensation/elevation of scapula to try to achieve abduction/elevation of arm Early movement of the scapula (0-30d) during abduction Clavicle movement - SC joint The clavicle moves on the manubrium The sternal facet of clavicle has an ‘apple core’ shape The superior-inferior aspects are _____________ This means when the clavicle moves inferior or superior – as happens in abduction/adduction – the joint is moving as _________________ Hence, the arthrokinematic movement (glide) is ________________ So, abduction requires ______________  Axial skeleton movement Movement of the shoulder girdle isn’t limited to only the GH, AC, SC joints and the scapulothoracic mechanism. In fact, these combined joints contribute about 160˚ to the full ROM of abduction. The remaining movement (approx. 20˚) come from other osseous components. What are the osseous structures involved to achieve full arm elevation and what movements must they perform? Upper T/S – EXT; SB and Rotation (Ipsilateral) Ribs – 1st and 2nd bodies – descend and move posteriorly Manubrium – SB and Rotate (Ipsilateral) Lower T/S – SB (contralateral) The above is for unilateral abduction. Bilateral abduction causes extension. Fixed spinal deformities cannot perform full elevation. Inferior glide & Impingement during abduction Biomechanics Review Concept 1 - Passive stability Concept 2 - Active stability Concept 3 - Compromised stability Concept 4 - 3 force couples Concept 5 - Abduction biomechanics: scapulohumeral rhythm, clavicle, axial skeleton Shoulder Assessment MOI Take time to review the grades of Sprains Strains Tendonitis Also review the stages of healing Acute Subacute Chronic Make Sure you know the duration of each stage as we will be applying it in TX & REMEX Observation & Assessment History Location: – ant brachial pain may indicate bicipital tendonitis – Lat brachial pain may indicate SupraSpin Tendonitis, bursitis, or Adhesive Caps’ – Sup/lat pain may indicate an AC sprain Mechanism of Injury: – RSI: bicipital tendonitis, supraspin tendonitis – Trauma: bursitis, AC sprain, dislocation, fracture – Insidious: Adhesive Capsulitis History Qs Does the pain spread below the elbow? Can the patient lie on the affect shoulder at night? Can the patient use the arm to comb hair? Can the patient reach back into a hip pocket or fasten a bra? Can the patient eat comfortably with the arm? Does it hurt to put on or remove your shirt? Is it difficult to perform any activities that require reaching above shoulder level? Observation Holding pattern - Posture of the arm and shoulder girdle – is the guest protecting the affected side, does the patient hold the arm close to the side or across the chest, does the Pt support the arm manually or with a sling? Functionality – ability to undress, willingness to use the arm. Observation - Anterior Head and neck in midline B shoulder height: the dominant side is usually lower due to repetitive stretch to the ligaments and capsule Muscle size and tone: dominant side larger due to repeated use. Step deformity at the distal end of clavicle: indicative of a separation. Sulcus sign: a ‘sagging’/’flattening’ below the acromion process where a rounded deltoid muscle would be; indicative of a dislocation or deltoid paralysis Mal-alignment of clavicle: fractures Observation - Posterior SICK scapula Scapular ‘winging’ – when the medial border moves away from the thorax a) Is it dynamic? This is indicative of serratus anterior injury or a compromised long thoracic nerve, possible muscle imbalance or strain to the rhomboids or upper trapezius b.) Is it static? This is indicative of structural deformity of the scapula, clavicle, spine, or ribs Scapular ‘tilting’ - when the superior or inferior angles tilt away from the chest wall. This is also indicative of weakness and instability Observation - Lateral Unilateral shoulder examination - look for anterior rounding - check curvature of the spine (kyphosis) Muscle Length Assessments Taken from Myers & Hanks, 5th ed, p460. Besides these assessments on the right, how else would you form an impression of a muscle’s length? Functional ROM Functional ROM assesses combined movements. This tells us which movements are available and pain free and which movements need to be Addressed. a. Combing the back of head (open chain) b. Reaching into the back pocket (open chain) c. Apley’s Scratch test d. Getting up out of a chair using the armrests ROM AROM a. All movement should be observed with the most painful movements performed last. b. Movements should be purely performed by the shoulder girdle. Watch to make sure the patient doesn’t ‘cheat’. Exaggerated movements of the spine should not be included either. c. With abduction, a painful arc should be observed. This pain is a result of the ‘pinching’ of inflamed structures under the acromial arch – subacromial bursitis, calcium deposits, or tendinitis of the rotator cuff muscles.  The first 45-60˚of ABD is painless b/c there is no Painful Arc pinching under the acromial arch. Abduction of 60-120˚ causes the structures to become pinched and abduction may cease. If abduction continues, pain diminishes after 120˚ bc the pinched structures have passed under the acromion process and are no longer pinched. The pain may return in the last 10-20˚ of abduction indicating possible impingement (general pain) or AC/SC joint involvement (specific pain). ROM PROM If POP wasn’t performed in AROM due to restriction or pain, determine the end feel with PROM of the shoulder complex. Determine if there is a capsular or non-capsular pattern of restriction. RROM and MMT (ISOMETRIC) General resistance in various movements tested first to isolate which movements are most affected. RROM with elbow flexion and extension should be included as triceps and biceps also cross the shoulder joint complex Note if patient complains that isotonic contraction is painful and symptomatic, these movements should also be tested. Scapula movements Referred Pain Pain associated with the shoulder is usually non-specific and is generally felt over the lateral brachial region (with the exception to AC joint lesions). Take note if pain goes past the elbows and into the hands. Pain from the shoulder joint itself very rarely refers below the elbow. Special Tests Special/Orthopedic Tests - Proficient special testing leads to higher reliability or strength in our clinical impression/conclusions (We can say that the objective findings lead to a possible condition). - Many of the structures involved in different pathologies are inter-related o (ie: impingement syndrome and shoulder instability); the RMT must be able to correlate the history with the appropriate special test and understand what a positive or negative test indicates. - An RMT must know when performing a special test is appropriate. Eg: it would be inappropriate to perform a shoulder apprehension test with a recent dislocation (10-12 days). Special Tests Special/Orthopedic Tests - Refer to PDF on Canvas