Imp Tech U5 Flashcards
What is the order of priority of upper limb replacement? Why?
C-spine first (limits nerve damage)
Then Distal to proximal
More functional movement is gained from the more distal joints, impairment of distal joint may compromise physio of a more proximal joint
Why do some surgeons prefer to do the shoulder first?
- Can cause pain radiating to the elbow
- Can cause abnormal loading at elbow which an compromise an elbow prosthesis
- Rehab of other joints better with a pain free shoulder
What are the types of shoulder replacement? How is the type decided
Unconstrained, semiconstrained, constrained
Depends upon the quality of soft tissues which provide joint stability
Why would a hemiarthroplasty be considered for an unconstrained shoulder replacement?
Less risk of loosening of glenoid component (main cause of failure) - good in younger patients to avoid revisions despite compromise of pain/functional relief
What are the pros/cons of an unconstrained shoulder replacement?
Pros;
- allows max function as follows natural anatomical shape
- minimal bone removal (soft tissue attachments well preserved)
- best pain and functional relief
Cons;
- dependent upon fully intact + functioning rotator cuff
What is replaced in a hemi vs total arthroplasty of shoulder?
Hemi; just humeral head replaced
Total; humeral head + glenoid fossa
When is a semiconstrained shoulder prosthesis used?
Rotator cuff muscles intact but weak (prosthesis prevents upward subluxation when muscles are weak)
What are the pros/cons of a semiconstrained shoulder prosthesis?
Pros;
- resists shear forces upwards when arm elevated
- prevents upwards subluxation
Cons;
- Limited ROM compared to unconstrained
- greater forces through glenoid component so more likely to loosen
Why is ROM reduced in a semiconstrained shoulder prosthesis?
Hooded glenoid component (int/ext rot most limited)
What are the 2 types of constrained shoulder prosthesis?
Normal anatomy (humeral ball & glenoid socket) Reversed Anatomy (humeral socket & glenoid ball)
What are the complications of the stanmore constrained shoulder prosthesis?
Unsnapping of components
Instability
Glenoid loosening
How does the trispherical constrained shoulder prosthesis work?
Humeral ball + glenoid ball contained within a third larger ball
Allows greater ROM (not limited by joint space) + avoids impingement
What are the cons of constrained shoulder prostheses?
- Higher rate of loosening than unconstrained
- dislocations more common
- mechanical failure of components problematic
How does the reversed anatomy (kessel) shoulder prosthesis work?
Large screw into glenoid with a ball on it
Larger radius of ball = increased ROM
Better lever arm for deltoid (but more stress at bone-cement junction)
Why is it difficult to attach glenoid component?
Very little bone in scapula (mostly use cement)
What are the different methods of glenoid component fixation?
Triangular shaped keel Extended keel Stem Wedge Large screw Flanges bolted to base of spine of scapula
What are the 3 articulations in the elbow joint?
Humeroulnar (trocheo-ulnar)
Humeroradial (radiocapitellar)
Proximal radioulnar
Why is a uniaxial hinge problematic at the elbow?
Does not follow a simply hinge, the coronal plane between forearm and upper arm varies throughout flexion
Uniaxial hinge maintains same coronal plane = high shearing forces at bone-cement interface (loosening)
Where does most of the stability of the elbow joint come from?
Medial collateral ligament (50%)
Why should surrounding tissues be protected in elbow joint replacement?
Stability mostly comes from soft tissues (esp if bony structure removed)
If removed then bone-cement interface stresses much higher
Why should shoulder replacement sometimes be done before elbow?
Stiff shoulder = all force through elbow for int/ext rot which increases bone-cement interface stresses
What are first generation elbow prostheses also called?
Constrained, uniaxial hinged
What are the results of first generation elbow prostheses?
Good short term but poor long term
Due to loosening from restricted single axis of motion
(elbow not a simple hinge so high shear forces)
High metal wear debris also caused loosening
Why are the cons of first generation elbow prostheses?
Significant removal of bone stock necessary
- Loss of attachments for soft tissues
- Difficult to replace if failure (high failure rate)
What are the 2 types of second generation elbow prostheses?
Semi-constrained (hinge)
Unconstrained (resurfacing)
What are the advantages of semi-constrained elbow prostheses?
Some lateral laxity (5º varus, 6º valgus)
Extra stability as partially constrained (compared to unconstrained)
Can be used when there is loss of bone stock
How do unconstrained elbow prostheses work?
Resurfacing of humerus + olecranon
(humerus = metal, ulnar = HDP)
Requires fully functioning collateral ligaments
Why is resurfacing of the radial head done? What are the results like?
To gain load transmission stability from humeroradial articulation
Variable results as difficult to balance the 3 articulations at the same time
If there is arthritis of the radoiocarpal joint what is done?
Arthrodesis
What is more important for activities of daily living; flexion or extension of the wrist?
Extension
What type of joint is the radoiocarpal?
Condyloid
Very important to overall motion
How does a flexible hinge prostheses of the wrist attach?
One stem in distal radius, one in 3rd metacarpal
Barrel shaped midsection
Made of rubber (silicone elastomer)
What are grommets used for in flexible hinge prostheses? How successful are they?
Used to protect the prosthesis from sharp bone edges
shown to have the same tear rate with or without grommets
How do flexible hinge prostheses work during motion?
Not fixed so slide in and out of intramedullary canals during motion
What is a Meuli prosthesis?
Total wrist prosthesis (radial ball and metacarpal socket)
Is a flexible hinge prosthesis and true prosthesis?
No
Resection arthroplasty with interposition of a silicone rubber spacer
What are the advantages/disadvantages of the Meuli prosthesis?
Pros;
- no rotational failures from ball and socket
- very little stresses on components as impingement can only occur at the extremes of motion
Cons
- rely on good soft tissue stability to prevent excess rotary motion
What is a Voltz prosthesis?
Total wrist prosthesis
non spherical metacarpal ball and shallower radial cup
What type of deformities do patients with total wrist prostheses develop and why?
Ulnar deviation deformity
Due to increased moment arms of ulnar wrist tendons (centre of rotation more radial)
What are the key features of the Voltz prosthesis?
Has a larger radius for abduction-adduction than flex/ext (similar to natural radiocarpal joint)
Which type of total wrist prosthesis has better results for loosening? How much?
Voltz = 25% loosening Meuli = 50% loosening
What is the best option if a MCP prosthesis is required in young patients?
Fusion at 40º flexion
What are the 2 types of MCP prosthesis?
Flexible hinge
Total MCP
What are grommets?
Titanium bone liners to protect flexible hinge prostheses
What is the fracture rate of MCP flexible hinge prostheses and what are the consequences of this?
20% fracture rate
Doesn’t need to be replaced - can continue with high pain free motion and stability
What are total MCP prostheses made from? How do they compare to flexible hinge?
Metallic component articulating with polyethylene component
Similar performance to flexible hinge
What are the risks of failure of total MCP prostheses?
Implant fracture
Migration
Loosening
What is the main method of treatment of IP pain/deformity?
Arthrodesis
What type of prosthesis can be used for IP joints?
Flexible hinge prosthesis
What are the results for IP flexible hinge prostheses?
98% complete pain relief
