MCP Joint Replacement Flashcards
Why were early finger replacements not successful?
Migration into the bone
Loosening
Mechanical problems
What is the most frequently indicated hand joint replacement?
MCP
What are the 2 types of MCP replacement?`
Flexible hinge
Total metacarpophalangeal
What is the main indication for MCP replacement?
Pain and deformity associated with RA
Other indications for MCP replacement
Impaired hand function secondary to soft tissue imbalance but with minimum discomfort
What is the preferred treatment option for younger patients requiring a strong pinch?
Arthrodesis of the index finger
What position is the index finger fused at in arthrodesis?
40 degrees of flexion
What type of joints are MCP joints?
Condyloid (ovoid head of metacarpal + elliptical cavity of the base of the proximal phalanx
What contributes to the stability of the MCP joint?
Joint capsule
Collateral ligaments
Fibrocartilaginous palmar plate
Muscle tendons
What planes does the MCP allow motion in?
Flexion-extension
Abduction-adduction
Pronation-supination (small amount)
How much flexion does the MCP joint allow?
90 degrees
How much does the MCP joint contribute to total finger flexion?
80%
Describe the Swanson MCP prosthesis
Designed as an adjunct to resection arthroplasty
Flexible silicone elastomer hinge
Relies on encapsulation to help maintain alignment
How is the Swanson MCP prosthesis fixed?
Stems are not fixed (they freely glide within the medullary canals)
Why are the stems not fixed in the Swanson MCP prosthesis?
Mor even force transmission
Increased range of motion
Why were titanium bone liners (grommets) introduced to the Swanson MCP prosthesis?
To shield the implant from sharp bone edges after high tear rates
How are grommets fixed?
Press-fit (interference fit)
What are the clinical results of the Swanson flexible hinge prosthesis?
70-80% satisfaction
Active ROM increases only slightly but is shifted to a more functional arc of extension
80% aesthetic improvement
Infections are rare
Are fractures an issue in flexible hinge MCP prostheses?
Less than 10%
Even when they occur the prosthesis doesn’t always need replaced and joint often has pain-free motion and remains stable
3 examples of total MCP joint prostheses
Steffee
Schultz
Strickland
What are total MCP joint prostheses made of?
Metallic component and polyethylene component
Both cemented in medullary canals
What problems have been found with total MCP replacements?
Implant fracture
Migration
Loosening
Why is there a need for a total MCP joint prosthesis that produces uniformly good results?
Flexible hinge prostheses are not particularly suited to younger patients and those who would wish to perform tasks that place higher demands on the MCP joints
