KIN 428 Midterm 2 Flashcards
Why model the shoulder?
- Gain insight into a closed system 2. Difficult to measure muscle forces, joint contact forces, and ligament forces 3. Test untestable hypothesis such as unsafe loading conditions and trauma 4. Test hypothesis quickly and w/o volunteers to answer “what if” questions
Types of shoulder biomechanical models?
- External models 2. Geometric Models 3. Internal (musculoskeletal models) 4. Composites
What comprises an external model?
Moments and forces…121/221 rigid link model
What comprises a geometric model?
Orthodpaedic models (has bones, not just links) and muscles capability/moment arms
What comprises an internal/musculoskeletal model?
Individual muscle forces, tissue forces (ligaments, tendons, etc), and joint contact force
What comprises a composite model?
Complete mechanisms description…a combination of an external, geometric, and internal model
What is the input for an external dynamic shoulder model?
Subject data (who), task data (what), and motion data (how)
What is the output of an external dynamic shoulder model?
Joint torques and forces
What is the input for geometric shoulder modelling?
Motion data (how)
Considerations for motion data in a geometric reconstruction?
Collection protocol–>marker placement and sampling rate
What are the geometric/orthopedic orientations for a geometric reconstruction model?
Joint center location, shoulder rhythm, and global vs. local positioning
What is the output for geometric reconstruction modeling?
Shoulder geometry
What are the considerations when doing the shoulder geometry in a geometric reconstruction model?
Muscle attachment sites, muscle wrapping, and muscle element definition
3 things to take away form shoulder modeling?
- Everyone represents muscles differently (diff # of mechanical activators of a muscle…no 2 are the same) 2. All perform differently on different criteria (depends on what you really want to look at) 3. Model is only as good as its validation
Why is it important to study muscle forces?
- can provide an objective quantitative indication of tissue loading for a given task/activity 2. This quantity can be related to pain, discomfort, or effort associated with the task 3. Assists in design of worker interfaces that minimize potentially harmful loading muscles 4. Fatigue is a major mechanism of shoulder instability and subsequent tissue damage (to estimate fatigue, you need to know what the muscle is doing)
What do optimization prediction models do?
Use inverse dynamics to calculate joint loading (moments) and minimize a quantity of muscle loading while satisfying equilibrium around all joints
What are the contraints in an optimization models?
Segment muscle composition, muscle force limits, glenohumeral contact force constraints
What are the inputs in an optimization model?
Torque model outputs and geometric model outputs
Internal muscle model outputs show an instanteous and continuous prediction of?
Muscle force, GH stability, internal joint forces (NHJRF), and ligament tension
What is the shoulder stability constraint in an optimization model?
The GH internal joint force (NHJRF) must satisfy a directional stability requirement/ratio. Other models use an ellipoid constraint
When using optimization at the shoulder, what is important to remember?
You should incorporate your knowledge of GH stability into the model to make it more realistic
What are the model limitations of optimization models?
- Assume that the body is attempting to minimize some muscular loading quantity. This has not been proven 2. Historically, do no account well for co-contraction of muscles (Joint stabilization) 3. Do not account for changes in muscle cross-sectional area for different postures when calculating stresses 4. Predict muscles as on/off and the madgitude is touchy 5. Drives by (somewhat subjective) objective function decision
What is one of the most physiologically relevant optimization models?
Soft-saturation method
What are EMG muscle force prediction models, and what do they predict?
Measure recorded surface EMG to estimate muscular loading. Estimates sholder moment generated by predicted muscle forces. Uses external forces to calculate shoulder momente and compare to predicted moment to validate muscle force predictions. Basically and in-out system.
Laursen (‘98) showed that calculated EMG model moments ___________ measured external moments?
Slightly underestimated…but overall, a positive relationship exists.
Model limitations of EMG modelling?
- Inherent limitations of the strength of the EMG/muscle force relationship (EMG does NOT equal force) 2. Confounding factors associated with EMG recording and interpretation (EMG amplitude is related to muscle length. At low levels (<10% max), EMG reliability is questionable due to cross-talk and noise levels
.How do optimization-predicted muscle forces vs EMG compare?
A fairly good/imperfect relationship exists
Models have been developed using:
optimization, EMG, hybrid (EMG-assisted optimization)
Models ________ to predict useful muscle forces to assess exertions
have been shown
What details are largely overlooked by current shoulder models?
- CO-activation (antagonistic activation for stability) 2. Joint translation (GH joint translates, which changes moment arms of muscles, which change forces and moments at the joint) 3. Variation in muscle capabilities (fibre type changes with age and fitness and therefore amount of force produced at a joint changes, too) 4. Ligaments are ignored 5. Variation in the population (no one is average…dertminism vs stochasticity)
Incidence of humeral fractures?
~4-5% of all fractures
What happens to occurence of proximal fractures with age?
Increases with age; many are osteoporosis related (degrades trabecular bone, which increases risk of humeral head fractures)
What percentage of humeral fractures do proximal fractures account for?
45% (over age 40 = 76%)
What gender is more likely to get proximal humerus fractures?
Women
What are the 3 mechanisms of proximal humerus fractures?
- Fall onto an outstretched hand (FOOSH), particularly for elderly 2. Usually something traumatic like a car accident or getting shot in younger people (sometimes overlooked because more serious injuries have also occurred) 3. Electrical shock or convulsions (bone can’t handle all the muscle contracting at once!)
What is the worst place to fracture on the humerus?
The anatomical neck because it cuts off blood supply!
4 possible fragments of a proximal humerus fracture?
greater tuberosity, lesser tuberosity, head, shaft
What fracture classification is most common?
Neer classification
What is a minimal displacement fracture in the Neer Classification system?
Most common (85%0. NO segment displaced more than 1 cm, or angulated more than 45 degrees
What is an articular segment displacement n the Neer Classification system?
Through anatomical neck of humerus (uncommon). Separation of tuberosity rare. Malunion of osteonecrosis of humeral head possible because of poor vascularization.
What is shaft displacement fracture n the Neer Classification system?
At level of surgical neck. Fragment displacement of more than 1 cm or angulations over 45 degrees. Semi neutral head posture.
What is a greater tuberosity displacement n the Neer Classification system?
Any of 3 facets/entire tuberosity retracted >1cm, or angulated >45 degrees. 2 or 3 part injury. Blood supply to humeral head at some risk.
What is a lesser tuberosity displacement n the Neer Classification system?
Uncommon 2 part lesion. Avulsion fracture of lesser tuberosity. 3 part lesion if surgical neck is also fractured. Soft tissue attachments aid in blood supply to humeral head, but some risk. 4 part lesion if both tuberosities are involved. Definite blood supply risk to humeral head.
What is fracture dislocation n the Neer Classification system?
GH dislocation with a fracture. Very complex injury. Good potential for blood supply to humeral head to be lost.
WHat does AO stand for?
Association for the Study of Internal Fixation
In the AO fracture classification, what do the letters (A,B,C) and numbers (1,2,3) stand for?
Letters are for the amount of vascular supply (A has no vascular isolation, B has partial isoaltion but necrosis is unlikely, and C has total vascular isolation with high likelihood of necrosis). The number represent the number of parts the fracture has created.
Clinical features of proximal humerus fractures?
Pain, swelling, tenderness, crepitis (popping sounds caused by bones grinding on each other), ecchymosis (bruising/skin discoloration from ruptred blood vessels around fracture sight)
How are prximal humerus fractures diagnosed?
Radiographs using 3 views (anteroposterior, lateral, and axillary)
Treatment options for a proximal humeral fracture?
- Initial immobilization and early motion 2. Closed reduction (percutaneous pins and external fixation) 3. Splints and Casts 4. Skeletal traction 5. Open reduction and internal fixation (ORIF) 6. Internal prostheses/endoprostheses
Recommended treatment sequence for a minimally displaced proximal humerus fracture?
Sling and ROM exercises within 14 days
Recommended treatment sequence for a 2 part anatomical neck proximal humerus fracture?
ORIF, prosthesis in older patients (return to mobility)
Recommended treatment sequence for a 2 part surgical neck fracture?
Closed redcution (pinning if needed), next is ORIF
In pinning, how do you want to pins placed in the bone?
Obliquely to keep the fragments together and prevent long axis rotation
Recommended treatment sequence for a 2 part greater tuberosity fracture?
ORIF and usually required a rotator cuff repair
Recommended treatment sequence for a 2 part lesser tuberosity repair?
Very rare, sometime sling, sometimes internal fixation, sometimes removal and tendon transfer
4 muscles of rotator cuff?
Supraspinatus, Infraspinatus, Subscapularis, Teres Minor
2 components that are critical in rotator cuff injuries?
Subacromial space and joint stability
Percentage of cadavers >60 that present with rotator cuff tears?
~30%
Percentage of elite swimmers with RC tears?
42%
Percentage of shoulder pain complaints that result from subacromial impingement syndrome?
44-65%
What does SAIS cause?
disability, loss of function, and pain
Signs and symptoms of SAIS?
anterosuperior pain (>at night and overhead activity), stifness, decreased ROM, crepitus (humeral head grinding on acromion)
Superior border of subacromial space?
Anterior, lateral 1/3 of acromion and coracoacromial arch
Inferior border of subacromial space?
Superior aspect of humeral head and greater tuberosity
Contents of subacromial space?
Supraspinatus tendon, LH of biceps tendon, subacromial bursa
Neutral height of a subacromial space in a healthy individual?
7-13 mm
What happens to height of subacromial space during elevation and external rotation>
It is reduced
What reduces the height of the subacromial space?
decreased size with posture, fatigue, and injury
What is SIS?
a decreased subacromial space such that tissues are compressed/”impinged”
Who was the first person to recognize SIS?
Neer in 1972
What is Stage I SIS?
Edema and haemorrhage, reversible, common in people less than 25 who do overhead sport or work
What is Stage II SIS?
Fibrosis, tendinosis, affects tendon/bursa, pain with activity, found in 25-40 year olds
What is Stage III SIS?
Bone spurs and partial or full tendon tears affecting those over the age of 40, surgery is needed
2 main theories of SIS?
Intrinsic and Extrinsic methods
What is the intrinsic theory of SIS?
Partial or full thickness tendon tears occur as a result of the degenerative process that occurs over time with overuse, tension overload, or trauma of the tendons. Osteophytes, acromial changes, muscle imbalances, and weaknesses and altered kinematics leading to impingement will subsequently follow.`
What is the extrinsic theory of SIS?
Inflammation and degeneration of the tendon occur as a result of mechanical compression by some structure external to the tendon. Potential mechanisms for EI are faulty posture, altered ST or GH kinematics, posterior capsular tightness, acromial or coracromial arch pathology.
What are some causes/risk factors for SIS?
1) Compression of supraspinatus 2) Traumatic factors 3) Degenerative factors 4)Developmental factors (acromial morphology and glenoid version) 5) Capsuloligamentous factors (instability and contractures) 6) Neuromuscular dysfunction 7) Inflammatory disease (rheumatoid arthritis and bursitis)
What are the devlopmental factors that contribute to SIS, and how do they contribute?
Acromial morphology and glenoid version…contribute because they are key in determining the subacromial space
What are the capsuloligamentous factors that contribute to SIS, and how do they contribute?
Instability and contracture…influence how humeral head sits in glenoid
What are the three types of acromions?
Flat, curved, and hooked
What is the angle of a Type I/flat acromion?
0-12 degrees
What is the angle of a Type II/curved acromion?
13-27 degrees
What is the angle of a Type III/hooked acromion>
> 27 degrees
What type of acromion causes the greatest amount and most severe rotator cuff tears?
Hooked
Order of acromion types from least severe to most severe in terms of RC injuries?
Flat, curved, hooked
What is os acromiale?
Partially unfused acromion
What does os acriomiale cause?
Hypermobile/inferiorly slanted acromion, which causes a predisposition to SIS (ligaments pulled, can cause hooked acromion)
What two parts of the acromion don’t fuse in most cases of os acromiale?
Meso and meta-acromion
What are the two mechanisms that are likely to causes translation (particularly superiorly) in the GH joint?
Gleniod degeneration and fatigue
What is scapular dyskinesis?
Abnormal movement of the scapula with humeral movement
What is does healthy/normal elevation allow at the GHJ?
Allows for upward rotation, posterior tilt, and retraction/external rotation
In SAIS, what happens to movement of the scapula during humeral movement?
It allows downward rotation, anterior tilt, and protraction/internal rotation
After a global and external rotators fatigue protocol, what happens to upward scapular rotation and posterior scapular tilt?
They increase…“impingement sparing”
Is there one cause of SIAS?
NO…a multi-factorial condition whose symptoms may be attributed to many causes
What is the progression of deterioration in RC pathology?
Supraspinatus tendon, infraspinatus tendon, suscapularis tendon, and long head of biceps tendon
What are the clinical findings of rotator cuff tears?
Stiffness, weakness/pain on contraction (esp. overhead), instability, roughness (athropathy)
What is Apley’s Scratch Test?
Can indicate rotator cuff damage if range of motion is compromies. Bend arm behind neck to touch opposite shoulder to check for GH abduction, external rotation, and scapular upward rotation. Reach behind back and touch opposite shoulder to check for GH adduction, internal rotation, and scapular retraction with downward rotation
What is Neer’s Sign?
Examiner performs maximal passive abduction in hte scapular place with internal rotation, while stabilizing the scapular. Impingement indicator. Positive test if there is anterior pain.
What is the Hawkin’s Test>
Passive internal rotation in scapular pain. Impingement indicator. Positive test if pain is felt.
How does tissue thickness relate to SIAS?
People with SAIS have increases tissue thickness and decreased subacromial space…61.7% of the space is occupied versus 54.2% space occupied in healthy people
Recommended treatment sequence for 3 part fracture?
Almost always ORIF because the joint is very unstable
Recommended treatment sequence for 4 part fracture?
Prosthesis…very hard to fix surgically
3 phases for rehab for proximal humerus fractures?
1) Passive assistive exercises to maintain ROM, avoid adhesions, and capsular tightness 2) Active and early resistive exercises 3) Maintenance through advanced stretching and strengthening
Complications of humeral fractures?
vascular injury, brachial plexus injury, frozen shoulder, avascular necrosis, nonuion, malunion
WHat is nonunion?
Bones don’t reform as a single bone (translational issues)
What is a malunion?
“New” bone that isn’t like your original…rotational issues such that the HH in the glenoid is different, which affects elbows and muscle movement at the elbow. Usually a result of rushing movement post surgery.
Incidence of scapular fractures?
2% of all fractures, 5% shoulder fractures
Reasons for infrequency of shoulder fractures?
1) Protection by soft tissues posteriorly and rib cage anteriorly 2) Scapula mobility dissipates traumatic forces
Why are scapular fractures extremely rare?
1) protection by its surrounding musculature 2) Protection by the ribcage 3) Free mobility of the scpula–gliding plane with 5 DOF
Mechanisms for body or spine fractures?
direct blow with significant force
Mechanisms for acromion fractures?
Direct blow to shoulder or force transmitted through the humeral head
Mechanisms for neck fractures?
Anterior or posterior force (lack stability in these directions). Fall with outstretched UE causing impact of the humeral head against the glenoid process.
Mechanisms for glenoid rim fracture?
Lateral force drives humeral head against the periphery of the glenoid cavity. Small avulsion fractures can also occur when dislocating humeral head impacts the anterior part of the capsule/labrum.
Mechanisms for glenoid fossa fracture?
A violent force laterally to the humerus, causing it to be driven into the center glenoid cavity, transverse fracture of the glenoid fossa occurs, fracture spreads depending on the direction of the force applied to the humerus
High shear and low compression in the glenoid causes?
dislocation
High shear and high compression in the glenoid causes?
rim/face fracture
Areas of the scapula that have the most fractures?
Scapular body (45%), glenoid neck (10%), acromial process (8%), coracoid process (7%), scapular spine (5%)
What is the biggest problem with malunion of two bones?
It changes articular version, which changes stability.
Clinical indicators of scapular fractures?
pain (with resistance, particularly abduction), local tenderness, swelling, crepitus, not much ecchymosis (so deep, so don’t see bruising)
Diagnosis of scapula fractures?
Radiographs with the scapular trauma series, AP, axillary, lateral, and weight bearing AP
3 types of extra-articular glenoid neck fractures?
Anatomical neck, surgical neck, inferior neck
Causes of glenoid neck fractures?
direct blow to shoulder, fall onto outstretched arm, force to superior aspect of shoulder
Percentage of glenoid neck fractures that are Type I fractures? Type II?
90%, 10%
Treatment for glenoid neck fractures?
conservative (non-surgical), ORIF (very traumatic to tissues so usually only done in young people), depends on the specifics of the injury.
Classification for intrarticular glenoid cavity fractures, of which 90% are nonoperative?
Classification by Goss-Ideberg…progressively more serious from Type I to Type VI
Treatment for scapular body fractures?
Usually non-operative…limited bone stock to perform surgery on, but usually heal well
Treatment for isolated acromial fractures?
depending on displacement: nonsurgical, surgical
Treatment for isolated coracoid fractures?
usually non-surgical, occasionally grafting and compression screw fixation (generates fracture site opposition, which creates some force between fragments, promoting bone growth)
What is the SSSC?
Superior Shoulder Suspensory Complex…Bony and soft tissue ring comprising the glenoid process, the coracoid process, the coracoclavicular ligaments, the distal clavicle, the AC joint and the acromion. Its integrity is essential to the normal relationship between the upper extremity and the trunk.
Treatment for a double disruption of the SSSC?
surgical intervention if displacement too large at any/either site
What is the a floating shoulder?
Ipsilateral scapular neck and clavicular shaft fractures. Unstable injury with a considerable risk of significant displacement of scapular neck and/or the clavicular fracture.
Treatment for avulsion scapular fractures?
Many are treated without surgery, but surgery is needed if there is high displacement, poor opposition, or inadequate healing/
What is scapulothoracic dissociation?
Closed traumatic forequarter amputation…extremely rare…very difficult to treat because there are no orthopedic connections and muscle attachments are completely disrupted.
Incidence of clavicular fractures?
1 in 20 fractures, 44% shoulder girdle injuries
Clavicle injury mechanisms?
Direct and indirect force (FOOSH or direct impact through axial loading (semi-direct) or superior loading). Stress fractures (usually athletic and usually resolved with change in training routine)
3 major mechanisms for clavicular fractures?
Fall directly onto shoulder (87%), direct blow to point of shoulder (7%), fall with outstretched hand (6%)
3 basic mechanisms that elevate stress levels sufficiently in slender bones that lead to fractures?
bending, torsion, compressive loading
Most likely cause of clavicular fracture out of bending, torsion and compressiON>
Compression by a force transmitted through the point of contact with the acromion (semi-direct force)
Why aren’t torsion and bending likely causes of clavicular fractures?
Freedom of the clavicle at the SCJ makes bending unlikely mechanism of clavicle fracture during clavicular impact loading. Available rotation about the longitudinal axis of the clavicle (approx. 50 degrees) eliminates torsion as the mechanism of clavicular fracture
How many times bodyweight is needed to cause a buckle fracture at the clavicle?
5x BW
What type of clavicle is most likely to buckle?
Thinner and longer
The critical force for a clavicular fracture will depend on:
speed of contact with solid object or ground, duration of collision (energy transfer through contact), body weight of individual
Clavicular fracture is most likely to occur from what type of blow?
Direct blow when the impact energy is absorbed fast vs. a glancing blow where the energy is dissipated more slowly.
Direction of applied force in a FOOSH in a clavicular fracture?
Force directed through humerus head to scapula. Fx only component that will produce clavicular compression. Fy/Fz tend to move scapula up and back away from clavicle = dislocation rather than fracture. Only when outstretched arm in coronal plane relative to the body is Fx sufficient to produce compressive buckling.
Direction of applied force in a direct blow to the shoulder that results in a clavicular fracture?
Entire impact force transmitted along the clavicular axis via the acromion. Fz/Fy are equal to zero. Critical buckling forces are reach as values apporach BW. If blow more glancing, Fx will be decreased and Fy/Fz will increase = favorable conditions for dislocation rather than fracture.
Clinical findings of clavicle fractures?
skin tenting, dropping shoulder, tenderness, ecchymosis, angles head to reduce trapezius pull
3 groups/classifications of clavicle fractures?
Group I, Group II, Group III
What is a group I clavicle fracture?
In the middle of the clavicle
What is a group II clavicle fracture?
Distal clavicle/near AC joint
What is a group III clavicle fracture?
Promximal fracture/near SC joint
Ranking of clavicle fractures from least common to most common?
Group III (5-6%) < Group II (12-15%) < Group I (80%)
As the type number of a clavicle fracture increases, what happens to severity?
It also increases
What is the worst type of clavicular fracture?
Comminuted
For group I clavicular fractures, what is A in the CCF guidelines?
Transverse fracture…one fracture sight
For group I clavicular fractures, what is B in the CCF guidelines?
Wedge…wishbone fracture with 2 fracture sights
FOr group I clavicular fractures, what is C in the CCF guidlelines?
COmminution zone separation
What does CCF stand for?
Comprehenesice Classification of Fractures
What is a Group II Type I fracture?
Clavicle fracture distal to the coracoclaviculr ligaments
What is a Group II, Type IIA fracture?
Clavicular fracture proximal to coracoclavicular joint
What is Group II, Type IIB fracture?
Clavicular fracture between the conoid and trapezoid ligaments
What types of Group II clavicular fractures are the worst?
Group II Type IIA and IIB because they cause a lost connection between the scapular and clavicle
Treatment options for clavicle fractures?
1) Arm support (simple sling) 2) Reduction (also maintain reduction) 3) ORIF 4) OREF
Type I clavicular fracture treatment?
Usually conservative…sling/figure 8 sling. If displaced or shortened, ORIF (plate fixation and intermedullary fixation via a clavicle pin)