Partial Knee Replacement (Unicompartmental Knee Arthroplasty)

Overview

Partial knee replacement, also called unicompartmental knee arthroplasty, is a surgical procedure to replace only the damaged compartment of the knee joint with artificial components. Unlike total knee replacement, it preserves healthy bone, cartilage, and ligaments in the unaffected portions of the knee. The procedure may be appropriate for patients with arthritis limited to one compartment of the knee.

Indications

This procedure may be considered when:

• •Osteoarthritis or avascular necrosis limited to one compartment of the knee (medial, lateral, or patellofemoral)
• •Intact anterior cruciate ligament (ACL)
• •Adequate range of motion without severe flexion contracture
• •Stable knee without significant deformity
• •Failed conservative treatment with persistent pain and functional limitation
• •Appropriate body weight (some surgeons prefer patients who are not significantly overweight)

How It Works

The procedure typically involves several coordinated steps:

• •Preoperative evaluation includes imaging to confirm single-compartment disease and assess ligament integrity
• •The procedure is typically performed under general or regional anesthesia
• •A smaller incision is made compared to total knee replacement
• •The damaged cartilage and a small amount of bone from the affected compartment are removed
• •Metal components are placed on the femoral and tibial surfaces of the affected compartment
• •A plastic spacer is inserted between the metal components
• •The unaffected compartments and ligaments are preserved
• •Incision is closed and the patient begins recovery protocols

Risks

As with any surgical procedure, potential risks include:

• •Progression of arthritis to other compartments requiring revision to total knee replacement
• •Implant loosening or wear over time
• •Infection of the surgical site or prosthesis
• •Blood clots in the legs or lungs
• •Persistent pain despite successful surgery
• •Fracture around the implant (periprosthetic fracture)
• •Nerve or blood vessel injury
• •Stiffness or limited range of motion
• •Need for revision surgery

Recovery Expectations

Recovery follows a gradual progression:

• •Hospital stay is typically shorter than total knee replacement, often same-day or overnight
• •Weight bearing is usually allowed immediately with walker or crutches
• •Many patients report less postoperative pain compared to total knee replacement
• •Physical therapy begins early to restore motion and strength
• •Return to driving may occur within 2 to 4 weeks for many patients
• •Return to low-impact activities may be possible within 4 to 6 weeks
• •Full recovery typically occurs within 2 to 3 months
• •High-impact activities may be discouraged to prolong implant longevity

Alternatives

Depending on individual circumstances, alternatives may include:

• •Continued conservative management with physical therapy, medications, and injections
• •Total knee replacement if disease involves multiple compartments
• •High tibial osteotomy for younger patients with unicompartmental disease
• •Arthroscopic debridement (limited role in osteoarthritis)
• •Biologic treatments or cartilage restoration procedures in selected cases
• •Pain management and activity modification

Sources

• AAOS OrthoInfo – Unicompartmental Knee Replacement
• Mayo Clinic – Knee Replacement
• Cleveland Clinic – Partial Knee Replacement