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Unicompartmental knee arthroplasty

Principles and Results. Unicompartmental knee arthroplasty. Brian Le, PGY-1 January 19, 2012. Outline. Brief overview of knee biomechanics Rationale, benefits, Indications of UKA Some basic principles The Oxford UKA as a prototype Other principles Results. Knee biomechanics.

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Unicompartmental knee arthroplasty

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  1. Principles and Results Unicompartmental knee arthroplasty Brian Le, PGY-1 January 19, 2012

  2. Outline • Brief overview of knee biomechanics • Rationale, benefits, Indications of UKA • Some basic principles • The Oxford UKA as a prototype • Other principles • Results

  3. Knee biomechanics • Knee motion is more than flexion/extension • Femur “rolls back” on tibia on flexion • IR of tibia on the femur during flexion, ER during extension • Lateral femoral condyle translates posteriorly more than medial femoral condyle during flexion • Essentially pivoting about a medial base • Also ~10o abduction/adduction during gait cycle

  4. Rationale • TKA results are very good, so why bother? • 94% to >98% 15-year survival of TKAs in some studies • Australian registry data 2010 shown below TKA UKA

  5. Rationale (2) • Young patients: • 76% TKA survival at 10 years for age <60 years • Rand et al. JBJS 73-A(3), 1991 • May choose better function and lower morbidity of UKA over longevity of TKA • Can delay TKA TKA

  6. Benefits of UKA • Faster recovery • Fewer short term complications • Less invasive vs osteotomy/TKA • Spares other compartments and ligaments—preserved knee kinematics • Preserved proprioceptive function of cruciates—feels more normal • Can be simple revision to TKA

  7. Debatable Isolated single compartment involvement Pain localized to affected compartment Postponing a TKA in younger population Inflammatory arthritis Flexion contracture >15o Pre-op ROM less than 90o >10o varus from mech. axis >5o valgus from mech. axis Significant OA of other compartments ACL deficiency—relative Can be reconstructed ? obesity Indications Contraindications

  8. Basic principles • Since other compartments and ligaments are preserved, UKA is a true “resurfacing” procedure • Thus, the UKA must be anatomic to preserve normal knee motion—this is not feasible/possible • Need to find ways around this

  9. The Oxford UKA: a prototype • Designed by Goodfellow and O’Connor, first used as UKA in 1982 • spherical metal femoral component • Unconstrained fully congruent polyethylene bearing • Flat tibial base plate

  10. Oxford principles From Goodfellow and O’Connor, JBJS (Br) 60-B (3): 358, 1978 • The components should be shaped to allow distracting, sliding, and rolling movements between the bones • The components should apply only compressive stress to the juxta-articular bone • All surviving soft tissues should be kept and restored to their natural tensions • The areas of contact between the prosthetic surfaces should be large enough to maintain the pressure under load at a level which the prosthetic materials can withstand

  11. Other principles • Tibial component: larger, onlay instead of inlay designreduced subsidence and surrounding cortex # • Ligament instability, esp ACL, leads to early failure • Minimal bone resectionsimpler future revisions

  12. Tibial component • All-poly tibial components: subject to creep/cold flow resulting in breaking at bone-cement interface and loosening • Metal-backed components introduced to attempt avoiding this

  13. Constraint • Property of implant design • effect of stabilization in a deficient soft-tissue envelope •  constraint,  aseptic loosening of tibial component •  constraint,  force dissipation through ligaments but excess delamination and wear of poly More constraint Less constraint

  14. Mobile bearings • Poly slides on flat metal tibial tray • Decreases shear stresses on tibial component • Thus the Oxford 2nd principle; The components should apply only compressive stress to the juxta-articular bone

  15. Fixed vs Mobile bearings • Round on flat/slight dish, unconstrained movement • Can be all-poly or metal backed tibial components • More poly wearthicker poly needed • More contact stress • Congruent surfaces minimizing point loading • Necessarily metal-backed •  poly wear allows thinner poly, thus less bony resection • Less contact stress Fixed Bearing Mobile bearing

  16. Fixed bearing devices • Several models • Stryker PKR used here • Single radius design from 10-110 degrees of flexion • To simplify gap balancing

  17. Results

  18. Survivorship • Berger et al. JBJS (Am) 87(5): 999-1006, 2005 (duplicate data) • 98% 10 yr survival • 96% 13 yr survival • Endpoint=revision or radiographic loosening Adapted from Jamali et al. Am J Orthop 38(1):17-23, 2009.

  19. Revision rate 5% cumulative revision rate at 3 years Endpoint=any revision surgery Labek et al, JBJS (Br), 93-B(3): 293-297, 2011.

  20. Swedish Registry 2011 Report

  21. Surgeon experience • More UKA’s performed by a centreincreased success rates • Management standards • Surgical technique • Proper Indications • Robertsson et al., JBJS (Br) 83(1): 45-49, 2001.

  22. Fixed vs Mobile bearing • Mobile bearings: lower poly wear (Ashraf et al. 2004 and Psychoyios et al. 1998) • Whittaker et al. CORR 468:73-81, 2010 • Retrospective comparative study • Fixed bearing: earlier revisions for OA progression • Mobile bearing: earlier aseptic loosening—technique related? • Smith et al. Ort Tra Surg Res 95:599-605, 2009 • Meta-analysis of 5 studies • No significant difference in aseptic loosening, pain, OA progression, tib plateau fracture, subsidence, revision • Limitations: poor randomization details, low sample size, poor concealment…

  23. All-poly vs metal-backed • Equivocal results: Hyldahl et al., J Arthroplasty, 16(2):174–9, 2001 • No difference in clinical results (Hospital for Special Surgery Score) or migration of tibial component at 2 years • Other studies?

  24. UKA vs TKA: RCT UKA (St Georg Sled) TKA Prospective RCT with 15 year f/u Enrolled 52 UKA and 50 TKR Not significantly different Newman et al., JBJS (Br) 91-B(1): 52-57, 2009.

  25. UKA vs TKA: pain and function Survey study based on Norwegian registry patients Scored from 0-100 Small or no difference between UKA and TKA, no clinical significance Lygre et al., JBJS (Am) 92-A(18): 2890-7, 2010.

  26. UKA vs TKA: revision rate Labek et al, JBJS (Br), 93-B(3): 293-297, 2011. Goodfellow and O’Connor: cannot compare revision rates of UKA and TKA—relationship between clinical failure and revision rate is different for each.JBJS (Br) 92(12): 1628-31, 2010.

  27. UKA revised to TKA • Lai and Rand, CORR 287: 193-201, 1993. • 81% good/excellent results at 5.4 years • Levine et al., J Arthroplasty, 11(7): 797-801, 1996 • Comparable to primary TKA, superior to revision TKA

  28. UKA revised to TKA (2) • Ottawa Data

  29. UKA vs HTO Dettoni et al., Iowa Ort J, 30:131-40, 2010.

  30. Lateral compartment UKA • 10 times less frequently performed Retrospective case series, therapeutic level IV Heyse et al. Arch Orthop Trauma Surg 130:1539-1548, 2010

  31. Take-home messages • UKA is a good treatment option in carefully selected patients • Surgeon experience plays a role • Outcomes are excellent, comparable to TKA • UKA is an excellent alternative to HTO • UKA can delay TKA • Ongoing debate between fixed vs mobile bearings • More research needed for lateral compartment UKAs

  32. Credits • Dr. Dervin • Marie-France Rancourt • Previous presentations • Luke Gauthier • Natasha Holder • Others…

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