Unicompartment knee replacements

Question 1

What are the indications of unicompartent knee replacements?

Answer 1

• controvesial
• alternative for TKR or osteotomy for unicompartment disease
• reserved for older >60, low demand and thin pts

Question 2

What is the epidemiology of unicomparmtent knee replacements?

Answer 2

• 5% of surgeries where knee arthoplasty is indicated
• location - medial compartment common

Question 3

What are the types of unicompartment OA?

Answer 3

• Fixed bearing
• mobile bearing
  
  • adv
    
    • Wb thru meniscus increases conformity and contact without increasing constraint
    • decrease in wear pattern
    • excellent survivorship out to second decade
  • dis
    
    • technically demanding
    • bearing can dislocate

Question 4

What are the adv to unicompartment knee replacments cf total?

Answer 4

• faster rehab
• less blood loss
• less morbidity
• less expensive
• preservation of normal kinematics
• smaller incision

Question 5

What are the adv to unicompartment knee replacments cf osteotomy?

Answer 5

• Faster rehab and quicker recovery
• improved cosmesis
• higher inital success rate
• fewer short term complications
• lasts longer
• easier to convert to TKR

Question 6

What are the contraindications to unicompartment knee replacement?

Answer 6

• Inflammatory arthritis
• ACL deficiency
  
  • absolute indication for mobile bearing UKR and lateral uKA
  • controversial for medial fixed bearing
• Fixed varus deformity > 10^o
• fixed valgus deformity >5^o
• restricted motion
  
  • arc of motion <90^o
  • flexion contracture 5-10^o
• previous meniscectomy
• tricompartmental arthritis
• overweight labourers, young high activity
  *

Question 7

What are the complications of UniKR?

Answer 7

• Stress fractures
  
  • always involve the tibia
  • assoc with high activity and pt weight
  • clinically there will be a pain free interval followed by spontaneous pain with activity
  • blood comonly found on joint aspiration
• Tibial component collapse
  
  • poor mechanical properites of bone

Question 8

What are the outcomes of uni knee replacements?

Answer 8

• Fixed bearing
  
  • 1st decade results
  • 10 yr survivorship from studies done in 1980 and 1990 ranges from 87.4% to 96%
  • the standard failure rate in the 1st decade is 1%
  • 2nd decade results
    
    • rapid decline in survivorship 79-90%
• Mobile bearing
  
  • ​excellent results with 15 yr survivorship 93%
• ​long term results
  
  • lateral compartment arthroplasties have equivalent results to medial
  • revision rates are worse than total knee revision rates
    *

Question 9

What are the causes of late failure?

Answer 9

• other degeneration - idiopathic/over-correction, more common with mobile bearing
• component failure ( overload due to under-correction)
• component loosening
• patella impingement on femoral component ( patella pain)
• polyethylene wear