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🔬 Surgery Guide2024-01-21

Partial Knee Replacement: Who Is a Candidate and What to Expect

Partial knee replacement (unicompartmental arthroplasty) replaces only the damaged compartment of the knee, preserving healthy cartilage and bone. It offers faster recovery and a more natural feel for appropriate candidates.

Educational content only. This article is not medical advice. Always consult a qualified orthopedic surgeon or physician for diagnosis and treatment.

What Is Partial Knee Replacement?

Partial knee replacement (unicompartmental knee arthroplasty or UKA) is a surgical procedure that replaces only the damaged compartment of the knee while preserving the remaining healthy cartilage, ligaments, and bone. Unlike total knee replacement (TKA), which resurfaces all three compartments, UKA targets only the area of significant arthritis.

The knee has three compartments:

  • Medial (inner) compartment — most commonly replaced (medial UKA)
  • Lateral (outer) compartment — less common (lateral UKA)
  • Patellofemoral compartment — patellofemoral arthroplasty (PFA)

Medial UKA is by far the most common, as medial compartment OA is the most prevalent pattern.

Candidate Criteria

UKA produces excellent results in the right patient. Ideal candidates:

  • Isolated single-compartment osteoarthritis — arthritis limited to one compartment
  • Intact ACL — the ACL provides crucial stability in a UKA knee
  • Intact remaining compartments — no significant arthritis in the other two compartments
  • Correctable deformity — varus deformity that can be fully corrected passively
  • Age, weight, and activity considerations vary by surgeon and system

Traditional guidelines were restrictive (older, lighter patients), but modern evidence shows good outcomes in younger, more active patients with appropriate anatomy.

Advantages Over Total Knee Replacement

  • Faster recovery: Return to function typically 4–6 weeks vs. 3–6 months for TKA
  • More natural feel: Preserves the ACL and normal compartments — patients often describe a more natural feel and range of motion
  • Less blood loss
  • Lower early complication rates
  • Conversion to TKA is possible if the implant fails or other compartments develop arthritis

Limitations

  • Revision rates higher than TKA at 10–15 years (but less invasive revision)
  • Strict patient selection required — outcomes suffer with poor patient selection
  • Progression of OA to other compartments may eventually require revision to TKA
  • Technical sensitivity — proper implant sizing and alignment critical

Surgical Technique

Anesthesia: Spinal (preferred) plus adductor canal nerve block. Tourniquet on thigh.

Steps:

  1. Smaller incision than TKA (4–5 inches vs. 8–10 inches)
  2. Only the affected compartment exposed
  3. Minimal bone removal — only the diseased cartilage and underlying bone resected
  4. A metal femoral component and plastic tibial component implanted
  5. Closure; knee immobilizer or brace applied

Robotic-assisted UKA (Mako Robotic Arm) is increasingly used for highly precise bone preparation and implant positioning — particularly important given the technical demands of UKA.

Recovery: Faster Than Total Knee Replacement

  • Hospital stay: Often same-day surgery or overnight
  • Walking: With a cane by day 1–3
  • Driving: 2–3 weeks
  • Stairs: Within 2–4 weeks
  • Return to work (sedentary): 2–4 weeks
  • Return to sport: 6–12 weeks
  • Full recovery: 3–6 months

Physical therapy begins immediately but is less intensive than TKA given smaller surgical trauma.

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