Unicompartment Knee Arthroplasty - Oxford




synonyms:oxford unicompartmental knee replacement, uni, partial knee replacement

Unicompartment Knee Arthroplasty CPT

Unicompartment Knee Arthroplasty Indications

  • Primary indication is anteromedial knee ostoearthritis.
  • Anteromedial knee osteoarthritis = Full thickness loss of the medial cartilage, Functionally normal ACL ,Functionally normal MCL ,Full thickness cartilage in the lateral compartment
  • Primary spontaneous osteonecrosis (secondary AVN, ie steroid use, is a contraindication)
  • ROM>90 degrees
  • Flexion contracture <5°, angular deformity <15°.

Unicompartment Knee Arthroplasty Contraindications

  • Opposit compartment athritis
  • Lateral facet patellofemoral arthritis with bone on bone contact, grooving, patellar subluxation
  • Fixed varus or valgus deformity >5°
  • Restricted ROM
  • Fixed flexion contracture
  • Joint subluxation >5mm
  • ACL deficiency 
  • MCL deficiency
  • PCL deficiency
  • Inflammatory arthritis
  • Hemochromatosis
  • Chondrocalcinosis
  • Hemophilia
  • Symptomatic instability
  • Failed HTO

Unicompartment Knee Arthroplasty Alternatives

  • Arthroscopic debridement-indicated for pt with ,1yr symptoms, normal alignment, mechanical symptoms.
  • Distal Femoral osteotomy
  • TKA
  • High Tibial osteotomy
  • Arthodesis-indicated for infection, failed TKA, young active patients, soft tissue defects, absent extensor mechanism, neuropathic joint disease.  fusion in 10-15 flexion and 0-7 valgus. complications=infection, non/malunion, pain.successful in 80-90% of failed condylar components, 55% of failed hinged prosthesis.

Unicompartment Knee Arthroplasty Pre-op Planning

  • Shorter hospital stay, fewer serious complications, improved walking ability, lower cost, more normal gait, better quadriceps function, better knee flexion than TKA
  • Arthritis progresses in other compartments which may limit long long-term outcome.  Often must deal with bone deficiency in revision to TKA
  • Goal = undercorrection of the mechanical axis by 2° -3° .
  • Do not release MCL and allow 2mm of joint laxity in extension and flexion.
  • Typically posterior cartilage in medial compartment is preserved.
  • Test MCL at 20 degrees of flexion. If ACL is not intact posterior cartilage is involved and the MCL is functionally contracted.
  • Varus deformity corrects with knee flexion and the MCL comes out to length
  • Lateral X-ray femoral chondyles should overlap. Wear defect in tibia should be anteromedial. If there is posterior wear on the tibial plateau the ACL is deficient and PKA is contraindicated.

Unicompartment Knee Arthroplasty Technique

  • Sign operative site.
  • Pre-operative antibiotics, +/- regional block.
  • General endotracheal anesthesia
  • Supine position. All bony prominences well padded.
  • Examination under anesthesia.
  • Prep and drape in standard sterile fashion.
  • Position leg in leg holder. Hip flexed 30 degrees. Knee should hang in 110 degrees of flexion
    1. Medial para patellar incision. Medial arthrotomy.
    2. Gelpi retractor
    3. resect portion of fat pad. Expose anterior portion of tibia.
    4. Inspect ACL and lateral compartment, patellofemoral compartment
    5. insert curly retractor medially.
    6. Remove osteophytes: intercondylear notch, tibial plateau, patella, posterolateral medial femoral condyle
    7. Size 1 femoral sizing spoon. Adjust if needed.
    8. Place tibial saw guide parallel with tibial shaft. Ankle piece should be pointing towards anterior superior iliac spine. (jig has 7 degrees of slope in it)
    9. Place G-clamp.  Drill one pin. (generally 3G for women, 4G for men)
    10. Perform sagital cut in line with femoral axis of knee joint just at the up slope of medial tibial spine.
    11. Perform transverse cut.
    12. Remove resected fragment with kocher and osteotome.
    13. 4mm drill 1.5 cm from origin of PCL in line with femoral shaft.
    14. Expand with awl
    15. Place femoral ligament guide.
    16. Mark center of femoral condyle.
    17. Place guide (set at 3).  Knee in 100-110 degrees flexion.
    18. Drill two holes.
    19. Insert microplasty cutting guide and retractor to protect MCL.
    20. Remove medial meniscus.
    21. Place 0 spicket and mill.
    22. Remove any bony corners.
    23. remove retractore
    24. Trial with spoons
    25. Place next spicket determined by trial.
    26. Mill.
    27. Remove any bony corners.
    28. Trial. Test in  90-100 degrees flexion and 20 degrees flexion.  If milling a second time use the spicket  which adds to the prior spicket used. If you use a 4 spicket the first time and you need to take 2 more, you would use the 6 spicket.
      The depth of the initial drill determines the depth of spicket placement.
    29. Pin tibial trial.
    30. Perform tibial notch cut and remove any residual bone with pic.
    31. Place microplasty femoral impingement guide and mill.
    32. Perform posterior osteophyte cuts with curved osteotome.
    33. Reform guides and ensure all osteophytes are cleared. 
    34. Trial final components. (flex and valgus to get bearing in)
    35. Check bearing has 2-3mm toggle.
    36. Remove trials.
    37. Inject pain cocktail and mix cement.
    38. Step drill sclerotic bone areas.
    39. Cement with antibiotic cement from front to back.
    40. Compress cement with spatula and 20 degrees. 
    41. Clean out all cement.
    42. Place bearing.
    43. Irrigate.
    44. Close arthrotomy in 45 degrees flexion with #2 Quill.
    45. Closure in layers  (0 Quill, 2-0 Quill and Dermabond)

Unicompartment Knee Arthroplasty Complications

  • Lateral Compartment arthritis progression
  • Poly dislocation
  • Pain
  • Loosening
  • Wear
  • Patellofemoral pain / arthritis (rare)
  • Tibial plateau fracture
  • Medial collateral ligament avulsion/tear
  • Stiffness
  • Infection
  • CRPS
  • DVT / PE
  • ACL rupture (related to posterior tibial slope 7°)

Unicompartment Knee Arthroplasty Follow-up care

  • Post-op:
  • 7-10 Days:
  • 6 Weeks:
  • 3 Months:
  • 6 Months:
  • 1Yr:
  • It is not uncommon for patients to have some medial proximal tibia or knee pain for the first 6-12 months post op.  This generally resolves with observation and conservative care. 

Unicompartment Knee Arthroplasty Outcomes

  • Oxford, meniscal-bearing UKa system 93% 15 year survival, 91% good/excellent clinical results (CORR 2005;435:171).
  • Cementless Oxford demonstrate 100% 5-yr survival in small British cohort. (Pandit H, JBJS 2013;95(15):1365).
  • Failure occurs from wear, loosing, and adjacent compartment degeneration.
  • UKA has higher revision rate, shorter hospital stay, lower perioperative complications when compared to TKA (Bolognesi MP, JBJS 2013;95:2049)

Unicompartment Knee Arthroplasty Review References