Week 8 Lecture Flashcards
Describe the mechanisms by which the glenohumeral joint maintains stability
Involves passive restraints and dynamic stabilisers
Key source of stability=concavity-compression mechanism. A stabilising mechanism in which compression of the convex humeral head into the concaved glenoid stabilises and protects it against translating forces. Its directly related to depth of concavity and magnitude of compressive force.
GHJ depth = glenoid depth + labrum
Depth is greater superior inferiorly and most shallow A-P
There is negative atmospheric pressure within the joint, the greater the depth of the labrum the greater the negative atmospheric pressure t/f greater resistance to translation.
Static stabilisers GHJ motion passively controlled by tightening of GHJ ligs and capsule at EROM Geometry of the GHJ Glenoid labrum
Dynamic stabilisers
Rotator cuff; ideally positioned biomechanically to provide a compressive force throughout the entire ROM of the GHJ.
Scapular stabilising muscles; provide a mobile yet stable BOS for GHJ functi
• Describe the functional anatomy of the glenoid labrum
A torn labrum> decreased neg atmospheric pressure, decreased concavity t/f decreased stability
Torn labrum > break in circle > channeling effect of laxity as compared to opposite side
Leads to SLAP tears, Traumatic dislocations, Atraumatic laxity
GHJ depth = glenoid depth + labrum
Depth is greater superior inferiorly and most shallow A-P
There is negative atmospheric pressure within the joint, the greater the depth of the labrum the greater the negative atmospheric pressure t/f greater resistance to translation.
• Describe the functional anatomy of glenohumeral joint ligaments.
Focal thickenings of the GHJ capsule, can be divided into 4 parts.
-Tendon of longhead of biceps,
-SGHL,Superior glenohumeral ligment
-MGHL,Middle glenohumeral ligament
-IGHL,Inferior glenohumeral ligament:
Anterior band of IGHL,auxillary pouch of IGHLC, Posterior band of IGH
*Coracohumeral ligament (CHL)
posterior band IGHL
-most important restraint to posterior subluxation
at 90° flexion and IR
-tightness leads to internal impingement and increased shear forces on superior labrum (linked to SLAP lesions)
anterior band IGHL
-primary restraint to anterior/inferior translation
90° abduction and maximum ER(late cocking phase of throwing)
-anchors into anterior labrum
forms weak link that predisposes to Bankart lesions
superior band IGHL
most important static stabilizer about the joint
100% increased strain on superior band of IGHL in presence of a SLAP lesion
*-Inferior glenohumeral ligament is like a hammock
Bands reciprocally tighen as the head is rotated in the abducted postion
Stability further enhanced by tightening ligaments increasing joint compression
External rotation winds it up so it acts like a sling
• Describe the functional anatomy of the rotator cuff
Mid-range stability(45/60-120 ) of GHJ is provided by Rotator cuff which provide a muscular compressive force which results in the concavity compression mechanism.
ER
– infraspinatus ER HOH and imparts posterior roll,
additionally holds posterior capsule relatively taut. Creates additional tensioning of passsive stability system
-Passive tension on otherside of joint by subscapularis and anterior capsular ligament when stretched during ER.
If the RC becomes damaged or weakened, the HOH may migrate upwards and forwards with a resultant increased risk of impingement of subacromial structures. (Deltoid may act unopposed)
Rotator cuff has an anti-impingement function. Deltoid pulls the humerus outward and upward towards the acromion.
Balanced action of the RC opposes this and keeps the humeral head centred, preventing upward dislocation. RC also generates ER needed to prevent impingement of the GT against the glenoid.
Describe the 2 kinds of force couples at the shoulder
GHJ force couples
Coronal force couple:
Deltoid and Supraspinatus vs Inferior cuff
Trasverse force couple:
Anterior(Subscap) vs Posterior cuff(Infraspinatus, Teres minor
* critical for providing superior-inferior stability. SA impingement often develops secondary to compromise of the transverse force couple.
Supraspinatus becomes the “victim” not the culprit.
• Describe normal scapulohumeral rhythm
Scapulohumeral rhythm
120 GHJ: 60 Scap 2:1 ratio
Initial phase (Setting phase)
30 GHJ Abduction(20-80)
Scapula mostly stable (0-30 degrees)
Midphase/critical phase 2:1
60 GHJ abduction
30 scap upwards rotation
GHJ externally rotates to clear GT from acromion and depress humeral head
Final phase 3:5:1
60 GHJ abduction
30 scap upwards rotation
Slight extension and lateral flexion of thorax to assist elevation
• Describe possible extrinsic causes of shoulder pain
Cervical spine referral (c5/6) Thoracic spine referral(upper) Heart(angina)L Liver via diaphragm R Cholecystitis (gall bladder) R Spleen L Apical lung tumours Vascular compromise( thoracic outlet syndrome)
• Discuss the difficulties associated with diagnosis in shoulder pain disorders
Diagnosis requires identification of the specific Patho anatomical source of symptoms& related pathology.
Shoulder PE tests not good at identifying structural pathology and structural pathology as seen in imaging is common in those with no pain.
Lack of specificity of common shoulder tests coz:
Morphology of RC means tendons don’t function as separate entities anatomically or functionally. Fuse to form common insertional aponeurosis t/f cant test 1 tendon in isolation.
Position and innervation of subacrominal bursa
Richly innervated and anatomically blends with GHJ capsule and RC insertions. Any test of interity and pain response from any RC tendons would inherently involve bursal tissue. No test can distinguish between them
Weakness on testing- pain inhibition vs structural failures.
Injection studies suggest weakness detected during testing may be better explained by pain inhibition rather than structural pathology.
*2/3 of RC tears are asymptomatic in general population
FTT common & commonly asymptomatic in general population
• Discuss primary and secondary sub-acromial impingement of the shoulder
PRIMARY subacromial impingement:
( true structural narrowing) Impingement leading to impingement of structures in SA space caused by outlet stenosis in Sub acromial space in a stable shoulder.
Due to Encroachment from above: Sub acromial spur/osteophytes, thickened calcified coracoacromial ligament, Acromiocalvicuar joint arthropathy/spur formation, mal-union of acromial or greater tuberosity fracture
SECONDARY subacromial impingement:
(functional narrowing
Pinching/mechanical compression of any structures between HOH ( greater tuberosisty) and acrominon/CAL as a concequency of functional narrowing. An impairment of musculoskeletal function.
Explain classification of Impingement
INTERNAL
- PSI(posterior superior)*more common
- ASI(Anterior superior)
EXTERNAL
- Subacromial (Primary or Secondary) *most common
- Subcoracoid(Primary or Secondary)
Structures potentially impinged in subacromial space:
Suacromial bursa
Superior glenohumeral capsule and superior glenohumeral ligment
Rotatorcuff tendons and most superior fibres of infraspinatus
Long head of biceps tendon
Signs of Subacromial impingement
Pain with overhead activities / activities involiving loaded shoulder IR rotation with shoulder elevation g tennis serve, swimming, throwing.
Painful arc during active shoulder elevation. Point in range where mechanical impingement of sensitised SA structures is occurring. Usually (45/60- 130 abduction) Pain commonly absent or eases in early and late ROM.May be painfull at EOR again
Pain usually worse in abduction compared to flexion
In middle range humerus needs to clear acromioclavicular space, scap needs to upwardly rotate at this point, if it cant they may get functional narrowing. @ end range scap does most of the work. If it cant glenohumeral joint may jam up to try and get more range.
Pain with loading RC ( empty can test, full can test) due to failure of RC to keep HH centred.
Othopaedic specific tests for impingement may reproduce pain: Hawkins kennedy test, Relocation test.
Common pathomechanics associated with secondary SA impingement
- Suboptimal/impaired RC function/GHJ impairment
- GHJ instability or hyperlaxity
- GHJ hypomobility
- Sub optimal scapula kinematics/MC
- Suboptimal spinal postures
- Combination of the above
• Discuss briefly glenoid (internal) impingement of the shoulder
Can be post or posterior-superior impingement(PSI)
Anterio-superior impingement(ASI) less common
PSI
Pinching/mechanical compression of articular(deeper most) fibres of subscapularis and infraspinatus & posterior labrum between greater tuberosity and posterior superior glenoid rim as consequence of FUNTIONAL NARROWING.
(during abd/ER)eg throwing motion,late cocking phase.
>Posterior shoulder pain
ASI
Impingement of under surface subscapularis and biceps pulley against anterosuperior glenoid rim in positions of horizontal adduction and IR in flexion.
Damage to pulley can lead to LHB instability
- biceps pulley is soft tissue sling that encloses LHB to stabilise it at at entrance to bicipital groove
• Discuss briefly sub-coracoid impingement of the shoulder
Structures potentially impinges
Primary or secondary narrowing of space between coracoid process and humerus and lesser tuberosity.
Structures potentially impinged:
-Subscapularis tendon
-LH biceps tendon
-Middle Glenohumeral ligament and capsule.
• Describe the pathology of
Sub-acromial pain syndrome (SAPS)
Chicken or the egg
What are the 3 limiations to the acromial irritational model
Sub-acromial pain syndrome (SAPS)
Associated with symptoms of subacromial impingement
Limitations to the acromial irritational model
1. Most AC pathology is of the deeper structures(articular side) Deeper fibres are relatively weaker and fail earlier than larger acromial side fibres. Intrinsic tendon degeneration without direct mechanical irritation.
- Acromial shape has a poor relationship to pathology and symptoms(Flat, curved, hooked)
- Subacromial spur (osteophyte) may not be primary may be secondary to chronic strain or tension in coracoacromial ligament increasing bone stress @ the acromial insertion > spur formation( seconday ossification of CAL)
Strain/ tension in CAL due to:
-Failure of RC to stop HH superior translation during elevation
-Increased tendon volumes (reactive tendonopathy)
-Increased bursal volume associated with SA bursitis
t/f type 3 acromion may not be morphological variation but a result of increased strain on CAL as a result of a degenerative process.
THEEEN failure to control superior HH migration and eventual spur formation result in irritation of bursal tissue and bursal side of RC patholgoy
Can be one or the other first
-Subacromial pathology then impingement
Injury to RC leads to superior migration of HH t/f impingement signs
-Or subacromial impingement leading to SA injury
Pathomechanics mean functional narrowing of subacromial space then subacromial strucures become sensitised and secondary SA pathology occurs
*Rotator cuff pathology is more likely due to intrinsic tendon degeneration or failure than extrinsic acromial mechanical compression.
