Adult ReconstructionKneeHospital

Partial Knee Replacement (Unicompartmental)

James Gardiner, MD, fellowship-trained in adult reconstruction, performs partial knee replacement for patients with single-compartment knee arthritis — preserving the healthy portions of the knee and the native ligaments.

Duration: 45–75 minutesAnesthesia: General or spinal

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What is partial knee replacement (unicompartmental)?

Partial knee replacement (unicompartmental knee arthroplasty) replaces only the damaged compartment of the knee — medial, lateral, or patellofemoral — with metal and plastic implant components while leaving the healthy compartments and ligaments intact. It is a smaller operation than total knee replacement, with faster recovery, but is only appropriate when arthritis is confined to one area of the knee.

Why this approach — at MOS

Patient selection for partial knee replacement is the critical determinant of outcome. A well-selected UKA candidate achieves an excellent result; a poorly selected one requires early revision. We apply published selection criteria rigorously and use weight-bearing radiographs and MRI where indicated to confirm that arthritis is genuinely isolated before proceeding.

We also perform a clinical examination under anesthesia to confirm ACL integrity and rule out contracture. The ACL must be intact for medial UKA to function correctly — an ACL-deficient knee loading a partial replacement develops abnormal kinematics that leads to early implant failure. Patients in Bethesda, Germantown, and the surrounding Montgomery County area with isolated medial compartment pain and appropriate anatomy are excellent candidates for this procedure.

Modern unicompartmental implant designs with mobile bearing polyethylene inserts have demonstrated excellent survivorship at 10–15 years in well-selected patients. We select implants with established long-term registry data for every case.

Who is a candidate?

Indications

Isolated single-compartment osteoarthritis confirmed on weight-bearing X-rays (medial, lateral, or patellofemoral)
Functionally significant pain in the affected compartment despite a full trial of conservative management
Intact ACL (for medial or lateral UKA) — the ACL is essential to unicompartmental kinematics
Adequate range of motion (>90° flexion, no significant fixed flexion deformity)
Varus or valgus deformity correctable to neutral under stress

Contraindications

Arthritis involving two or more compartments — total knee replacement is more appropriate
Absent or deficient ACL (for medial or lateral UKA) — ligamentous instability causes abnormal loading on the partial implant
Significant inflammatory arthritis (rheumatoid) — typically affects multiple compartments
Fixed deformity that cannot be corrected
Very high activity demands that would cause accelerated implant wear
Obesity (BMI >35–40) — increases revision risk for partial replacement

Conservative Treatment First

Partial knee replacement is indicated only after appropriate conservative management has failed. For medial compartment arthritis, this includes: weight loss, NSAIDs, supervised physical therapy focused on quadriceps and hip strengthening, corticosteroid injections for pain management, and bracing (an unloading brace that shifts weight away from the arthritic compartment is particularly effective for medial compartment disease). Hyaluronic acid injections provide variable relief. When these measures are no longer sufficient and quality of life is significantly affected, surgery is appropriate.

The procedure

What Is Partial Knee Replacement (Unicompartmental)?

Partial knee replacement (unicompartmental knee arthroplasty, or UKA) replaces only the damaged compartment of the knee — medial, lateral, or patellofemoral — with metal and plastic implant components while leaving the healthy compartments and ligaments intact. It is a smaller operation than total knee replacement, with faster recovery, but is only appropriate when arthritis is confined to one area of the knee.

The knee joint has three compartments: the medial (inner) side between the medial femoral condyle and medial tibial plateau; the lateral (outer) side; and the patellofemoral compartment between the kneecap and the front of the femur. Osteoarthritis frequently starts in one compartment — most often the medial compartment — before spreading. When arthritis is genuinely isolated to one compartment and the rest of the knee is healthy, replacing only that compartment preserves the native ACL and PCL, maintains the knee's natural feel and kinematics, and requires a smaller, less invasive operation than total replacement.

The advantages of partial over total replacement include smaller incision, less bone removal, faster recovery, and — critically — the retained native cruciate ligaments allow the knee to feel more natural after surgery. Studies comparing unicompartmental and total knee replacement consistently show that appropriately selected UKA patients report a more natural-feeling knee. The trade-off is that UKA requires strict patient selection criteria, and revision to total knee replacement is needed in approximately 5–10% of UKA patients over 10 years as arthritis progresses.

What Happens During Partial Knee Replacement?

Partial knee replacement is performed at the hospital under general or spinal anesthesia. The patient is positioned supine with the knee flexed. A shorter incision than total knee replacement is made over the affected compartment. The joint is opened with a limited approach that does not disrupt the unaffected compartments.

The damaged bone and cartilage surfaces of the arthritic compartment are removed using precision cutting guides. The amount of bone removed is significantly less than in total knee replacement. A small metal femoral component and a flat tibial tray with a polyethylene insert are placed, restoring the articular surface of the affected compartment only. The cruciate ligaments remain intact throughout and are not released.

Trial components are used to confirm stable, smooth function. The knee is taken through range of motion to verify tracking and balance. Final components are cemented and the wound is closed. Most patients stay one night in the hospital and go home the next day.

Recovery timeline

Day 0–1 (Hospital)

Physical therapy begins same day or next morning. Walking with walker. Most patients go home after one night.

Weeks 1–3

Walker or cane. Outpatient physical therapy. Swelling management.

Weeks 3–6

Progressive weight-bearing. Most patients transition off cane. Return to light daily activities.

Months 2–3

Most patients achieve functional independence. Driving at 4–6 weeks for right knee.

Months 3–4

Return to low-impact activity. Many patients walk further and with less pain than before surgery.

Partial knee replacement recovery is faster than total knee replacement — most patients feel functional within 4–6 weeks rather than 3 months. The smaller incision and less bone removal mean less tissue disruption and a shorter acute recovery. Blood clot prevention with aspirin or anticoagulant is prescribed. Infection vigilance is the same as for total knee replacement. Return to low-impact sport (golf, cycling, walking) is typically possible at 3 months. High-impact activities are discouraged for implant longevity.

Frequently Asked Questions

Am I a candidate for partial instead of total knee replacement?

Partial replacement is appropriate when arthritis is genuinely limited to one compartment, the cruciate ligaments are intact, and range of motion is adequate. X-rays and clinical examination will determine whether your disease pattern qualifies. Approximately 25–30% of patients undergoing knee replacement surgery are candidates for partial replacement, though not all elect to have it.

Does a partial knee replacement feel more natural than a total?

Most studies and patient surveys indicate that appropriately selected UKA patients report a more natural-feeling knee than total knee replacement patients. The intact cruciate ligaments preserve the natural roll-glide mechanism of the knee, allowing it to move more like a native joint. This is the primary quality-of-life advantage of partial replacement in eligible patients.

What are the chances I'll need a total knee replacement later?

Registry data shows revision rates of approximately 5–10% at 10 years for UKA in appropriate candidates. Reasons for revision include arthritis progression to other compartments (the most common cause), implant loosening, and bearing surface wear. Revision of a UKA to a total knee replacement is generally a well-tolerated procedure and produces results comparable to primary total knee replacement.

Can I be active after partial knee replacement?

Yes — low-impact activities including walking, cycling, golf, swimming, and light doubles tennis are generally appropriate. The same high-impact restrictions as total knee replacement apply to protect the implant from accelerated wear.

How long does a partial knee replacement last?

Oxford Knee registry data shows approximately 90% survival at 10 years and 85% at 15 years in appropriately selected patients at high-volume centers. Outcomes depend heavily on correct patient selection, implant design, and surgical technique.

Related conditions

Knee Osteoarthritis Unicompartmental Knee Arthritis / Partial Knee Replacement Osteonecrosis of the Knee

Medically reviewed by James S. Gardiner, MD, MD

Last reviewed May 20, 2026