UKR spacer dislocation

Question 1

How common are dislocations of the spacers?

Answer 1

• medial UKA – rare – 1 in 200 – usually anteriorly
• lateral UKA - 10%

Question 2

Why are spacer dislocations more common in lateral UKRs?

Answer 2

• In flexion - LCL is lax and the MCL is tight
• the medial compartment is distracted by 2mm, but the lateral compartment is 7mm
• lateral compartment opens more in knee flexion allowing the spacer to dislocate

Question 3

What are the possible causes of UKR spacer dislocation?

Answer 3

-
- secondary to tibial/ femoral loosening
- instability - MCL injury intraop or progressive stretching on osteophytes
- impingement of the bearing on unresected osteophytes
- poor soft tissue balancing
- mobile bearing UKR
- unbalance flexion-extension gap
- malpositioning of the components

Question 4

What are the treatment options?

Answer 4

• replace the spacer with a larger spacer – carries risk of further dislocations
• Revision to a PS knee replacement