Knee Unicompartmental Replacement (UKR)

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Theoretical advantages

Advantages over Total Knee Replacement (TKR)

  • Increase range of movement (ROM)
    • Newman JBJS 1998 – 70% over 120° at 5 years Vs 17% of the TKR group
    • Newman JBJS 1998 – less Deep Venous thrombosis (DVT’s), Manipulation Under Anaesthesia (MUA’s).
  • More normal gait
  • Lower complication rate
  • Rapid rehabilitation
  • Preservation of bone stock
  • Preservation of native knee components (cruciates ligaments, lat compartment etc) – more normal kinematics.

Advantages over HTO

  • More rapid rehab
  • Higher earlier success rate
  • Fewer complications

Disadvantages

  • Inferior results to TKR – based on registry data (Norway, Sweden)
  • Technically difficult
  • May compromises future TKR

Indications

  • Normal lateral compartment
  • Good ROM – 10-90° at least (some say 5-120°)
  • Passively correctible varus/valgus
  • Malalignment cannot be corrected with UKR
  • Subluxation is controversial – Texts say contraindication, Coolican says not (if correctible)
  • ACL intact à anteromedial wear (no varus in flexion) and thus the MCL does not shorten and normal kinematics is maintained
  • Varus only in extension
  • Non-inflammatory OA
  • ACL deficient à more global/posterioromedial wear à varus in all positions, and thus MCL shortening and altered kinematics
    • Mobile bearing – absolute
    • Fixed bearing – relative
  • Patient factors – relative
    • Age (above 60) – controversial
    • Weight (BMI less than 30)
    • Activity level (low level of activity

Surgical principles

  • Load sharing device
  • Resurfacing, not realigning device
    • Do NOT correct alignment – if anything leave slightly under-corrected (3°)

Results

  • Specialist centres – good results
    • Oxford – 98% 7 year survival
    • Sweden – 90% 5 year survival
    • MG – 94% 10 year survival
  • Registry data – not as good
    • Norwegian registry 1994-2004 data (JBJS 2007) – Level II evidence
    • 10 year survival
      • UKR 80%
      • TKR 92%
    • Seen in ALL age categories, and no change in recent 5 years
    • UKR had:
      • higher revision due to pain
      • more tibial loosening
      • more femoral loosening
      • higher rate of periprosthetic fracture
      • BUT lower infection
    • This data matches other registry data but no that of specialist centres

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