UKA — Unicompartmental Knee Arthroplasty

I offer my patients the Oxford UKA when appropriate.

Medial UKA (unicompartmental knee arthroplasty, also known as a partial knee replacement) resurfaces only the medial (inner) compartment of the knee with prosthetic components. When arthritis is confined to a single compartment, UKA is the better operation, because it is less invasive than total knee replacement, preserves more bone, maintains both cruciate ligaments, and results in a more natural feeling knee.

Differences between a TKA and UKA

Feature Total Knee Replacement Unicompartmental (UKA)
Bone removed All three compartments resurfaced Only the affected compartment
Ligaments Anterior cruciate ligament removed Anterior cruciate ligament preserved
Feel Highly reliable; some patients notice it feels mechanical Feels more natural
Recovery Typically 3–6 months to full function Often faster; less surgical trauma
Candidates Arthritis affecting multiple compartments Arthritis confined to one compartment with intact ligaments

Is UKA Right for Me?

I apply the Nuffield criteria to determine whether UKA is the correct operation for a given patient, including obtaining stress X-rays of the knee.

Generally speaking, pain at rest and pain involving the entire knee make it less likely that UKA is the appropriate operation. Patients who benefit most from medial UKA have pain that is limited to the medial (inner) side of the knee and that occurs primarily with weight bearing.

The Oxford UKA

  1. The defining characteristic of the Oxford UKA is its mobile bearing.
  2. It is ligament-sparing: both the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL) are kept intact.
  3. Biological kinematics: Because the ACL is preserved and the articular bearing is mobile, the knee retains its natural "roll-and-glide" motion and proprioception (the brain's ability to sense joint position).
  4. Outcome: Patients often report that a partial knee feels significantly more "normal" and stable during activity than a total knee replacement.

Is the Oxford UKA performed with the robot?

No. The Oxford UKA is a well established successful procedure that is performed with highly accurate mechanical calipers.

How long does a partial knee replacement last?

Patients are often concerned about needing additional surgery, such as a full replacement, later in life. While the odds of revision surgery are slightly higher than with TKA, in appropriately selected patients, the Oxford UKA has a 10-year survival rate of approximately 90–95%. Long-term data show that 20 years after surgery, 91% of Oxford® Knee patients still had their original partial knee replacement implants. Revision from UKA to a total knee replacement, if ever needed, is generally straightforward.

Recovery Timeline

  • Day of surgery: Surgery is typically performed under spinal anesthesia with sedation. Most patients are up and walking with assistance on the same day. Because UKA is less invasive than TKA, same-day discharge is the rule.
  • Weeks 0–2: Physical therapy begins immediately. Maintaining range of motion in this early window is critical. Perform range-of-motion exercises after every meal, despite surgical pain.
  • Weeks 3–6 (Avoid setbacks): Continue range-of-motion exercises. Transition to a cane, then wean off. Driving is typically not permitted for the first 4-6 weeks.
  • Weeks 6–12 (Early Function): Most patients are walking independently and returning to light daily activities. Therapy transitions to strengthening.
  • Months 3–6 (Strengthening): Focused rehabilitation to restore strength, endurance, and confidence on the knee.
  • Months 6–12 (Full Recovery): Final maturation. Most patients reach maximum improvement by the one-year mark.
  • The Ultimate Goal: A "forgotten joint" — returning to daily life without thinking about your knee.

Outcomes of Partial Knee Replacement

  1. Longevity: In appropriately selected patients, the Oxford UKA has a 10-year survival rate of approximately 90–95%.
  2. Satisfaction: Because the ACL is preserved, this procedure has the highest likelihood of achieving the "forgotten joint," where the patient no longer notices the prosthesis during daily life.
  3. Risks: While rare, risks include "bearing dislocation" or the potential for arthritis to develop in the other compartments later in life, which may require a conversion to a TKA.

Surgery Risks

  • Infection: The most serious complication, occurring in approximately 1% of cases. Treatment often requires additional surgery.
  • Bearing dislocation: Specific to mobile-bearing designs; rare with proper implantation and patient selection.
  • Stiffness: Less common than with TKA given the less invasive nature of the procedure, but early rehabilitation remains important.
  • Blood clots (DVT/PE): Blood thinners and early mobilization are used routinely to reduce this risk.
  • Progression of arthritis: Arthritis may develop in the remaining compartments over time, potentially requiring conversion to a total knee replacement.
  • Component loosening: Wear over time may eventually require revision surgery.
  • Nerve or vessel injury: Rare, but can affect sensation or circulation around the knee.