Knee Replacement

Partial Knee Replacement
in San Diego, CA

Not every arthritic knee requires full replacement. When arthritis is limited to just one compartment of the knee and the rest of the joint remains healthy, partial knee replacement — also called unicompartmental knee arthroplasty (UKA) — may offer a less invasive surgical option with a faster recovery, smaller incision, and a more natural-feeling result. At Grossmont Orthopedic Medical Group in La Mesa, our surgeons use the Mako robotic-assisted system to bring exceptional precision to every partial knee replacement.

The knee has three compartments: the medial (inner side), the lateral (outer side), and the patellofemoral (the joint between the kneecap and thigh bone). In many patients, arthritis affects primarily one of these compartments — most often the medial compartment — while the remaining cartilage stays relatively intact. For carefully selected patients, resurfacing only that damaged compartment may address the pain at its source while preserving the healthy structures that make a natural knee feel like a natural knee.

What Is Partial Knee Replacement?

In partial (unicompartmental) knee replacement, the surgeon resurfaces only the damaged compartment of the knee with metal and plastic implant components, leaving the healthy cartilage and bone in the other compartments completely untouched. Critically, the cruciate ligaments — which are removed in total knee replacement — are preserved, which may contribute to more natural knee motion and proprioception (your brain's sense of where your knee is in space).

Because only a portion of the joint is addressed, the surgical incision is typically smaller, less bone is removed, and the surrounding muscles and soft tissues experience less disruption. This may translate to less post-operative pain, a shorter hospital stay, and a faster return to daily activities compared to total knee replacement.

At GOMG, partial knee replacement is performed using the Mako robotic-assisted system, which is particularly well-suited to this procedure because the precision required for a single-compartment implant is even greater than for a total replacement — there is less margin for error when only part of the joint is being resurfaced.

Who May Be a Candidate for Partial Knee Replacement?

Patient selection is the most critical factor in achieving a good outcome with partial knee replacement. The procedure may work best for patients whose arthritis meets specific criteria that point toward a single compartment as the primary source of pain and disability:

Factors That May Make You a Good Candidate

  • Arthritis confirmed by X-ray and/or MRI to be localized to primarily one compartment (medial or lateral)
  • Intact anterior and posterior cruciate ligaments (ACL and PCL)
  • Relatively preserved range of motion with no severe flexion contracture
  • Pain that is well localized to the affected side of the knee (inner or outer)
  • Failed conservative treatment (physical therapy, injections, medications) for that compartment
  • Good overall health for an elective surgical procedure

Factors That May Favor Total Knee Replacement Instead

  • Arthritis affecting two or more compartments (bicompartmental or tricompartmental disease)
  • Absent or non-functional cruciate ligaments
  • Significant inflammatory arthritis such as rheumatoid arthritis affecting the entire joint
  • Severe leg malalignment that cannot be corrected with a single-compartment implant alone
  • Severe pre-operative stiffness or significant loss of range of motion

Medial vs. Lateral Compartment

Medial (Inner) Compartment

The medial compartment — the inner side of the knee — is by far the most common location for unicompartmental arthritis and the most frequently resurfaced compartment in partial knee replacement. Medial compartment arthritis often causes pain along the inner knee that worsens with walking and climbing stairs. Patients may also notice a progressive bow-legged appearance as cartilage on the inner side wears away.

Medial unicompartmental replacement is a well-established procedure with an extensive long-term track record, and the Mako robotic system may further improve the consistency and precision of implant placement in this compartment.

Lateral (Outer) Compartment

Lateral compartment arthritis — affecting the outer side of the knee — is less common than medial disease but may also be addressed with a unicompartmental replacement in appropriately selected patients. Lateral compartment arthritis may cause pain along the outer knee and can sometimes be associated with a knock-kneed leg alignment.

Lateral unicompartmental replacement requires careful patient selection and precise implant positioning due to the anatomic differences between the medial and lateral sides of the knee. Robotic assistance may be particularly valuable in lateral compartment cases.

Benefits of Partial Knee Replacement

Compared to total knee replacement, partial knee replacement may offer several potential advantages for appropriately selected patients:

  • Smaller incision — The surgical approach is more limited, which may reduce post-operative pain and minimize disruption to surrounding soft tissues
  • Faster recovery — Many patients may return to light activity and driving within two to three weeks, versus six or more weeks with total replacement
  • More natural-feeling knee — Preserving the cruciate ligaments and healthy cartilage may allow more natural motion patterns and better proprioception after surgery
  • Less bone removal — Only the arthritic compartment is addressed, preserving healthy bone that may be used if a future revision is ever needed
  • Potentially shorter hospital stay — Many partial knee replacement patients may be candidates for same-day or next-day discharge
  • Revision option remains open — If arthritis progresses to other compartments years later, the partial replacement may be converted to a total knee replacement

Treatment: The Mako Robotic Advantage for Partial Replacement

Precision matters in any knee replacement, but it may matter even more in a partial replacement. When only one compartment is being resurfaced, the implant must integrate seamlessly with the native cartilage and ligaments on either side. Even a small error in implant alignment or sizing could affect the balance of the knee and lead to suboptimal outcomes. The Mako robotic-assisted system addresses this challenge directly.

Patient-Specific Pre-Operative Planning

A CT scan of your knee is taken before surgery and used to generate a 3D digital model of your exact bone anatomy. Your surgeon uses this model to plan every detail of the procedure — the implant size, the precise amount of bone to be removed, and the target implant position — all customized to your unique anatomy before you arrive at the operating room.

Haptic Robotic Guidance During Surgery

During surgery, the Mako arm provides real-time tactile (haptic) resistance that keeps the surgical instruments within the surgeon's precisely planned bone-removal zone. This helps ensure that only the intended amount of bone is removed from the arthritic compartment — protecting healthy tissue in adjacent compartments — which may contribute to a more accurate and reproducible result.

Intraoperative Adjustability

The Mako system allows the surgeon to make real-time adjustments to the plan during surgery if intraoperative findings warrant it. This flexibility — combined with the pre-operative 3D model — may result in more reliable achievement of the intended implant position compared to freehand techniques.

Deep Robotic Experience at GOMG

Dr. Hacker, a designated Surgeon of Excellence in Robotic Surgery, performs Mako robotic partial knee replacement, and Dr. Yoo completed advanced fellowship training in robotic arthroplasty at UT Houston. GOMG was among the first practices in San Diego to adopt the Mako platform, so our patients benefit from both a mature robotic workflow and the refined judgment that comes with high-volume robotic practice.

Conservative Options Tried Before Surgery

As with total knee replacement, our surgeons explore appropriate non-operative approaches before recommending partial replacement. These may include:

What to Expect: Recovery from Partial Knee Replacement

One of the most frequently cited advantages of partial over total knee replacement is the potential for a faster recovery. While individual outcomes vary, many patients may experience a recovery along the following general timeline:

Frequently Asked Questions

Who is a good candidate for partial knee replacement?

A good candidate for partial knee replacement typically has arthritis confined to only one compartment of the knee — most commonly the medial (inner) compartment — with the remaining compartments relatively preserved. Other important factors include intact cruciate ligaments, a stable knee, a relatively normal range of motion, and a body weight that does not place excessive mechanical stress on a single-compartment implant. Your surgeon will evaluate your X-rays and MRI to determine whether the pattern of your arthritis may make you a suitable candidate.

What is the difference between partial and total knee replacement?

In a partial (unicompartmental) knee replacement, only the damaged compartment of the knee is resurfaced — the healthy cartilage and bone in the other compartments, along with the cruciate ligaments, are preserved. In a total knee replacement, all three compartments are resurfaced. Because partial replacement preserves more of the patient's natural anatomy, many patients report a more natural-feeling knee. Recovery may also be faster with a partial replacement due to the smaller incision, less bone removal, and reduced surgical trauma to surrounding tissues.

How long is recovery from partial knee replacement?

Recovery from partial knee replacement is generally faster than from total knee replacement. Many patients may walk with minimal assistance within the first few days and may be able to drive within two to three weeks if the operative leg is not needed for braking. A return to most daily activities may be possible within four to six weeks for many patients, and return to low-impact recreational activities may occur within two to three months. Individual recovery timelines can vary based on age, overall health, and adherence to the physical therapy program.

Can a partial knee replacement be converted to a total if needed?

Yes. If arthritis progresses over time to affect other compartments of the knee, a partial knee replacement may be converted to a total knee replacement in a revision procedure. Studies suggest that patients who require conversion from a partial to a total replacement tend to do well with the revision surgery, with outcomes that may be comparable to patients undergoing a primary total knee replacement. This potential future conversion is one of the factors your surgeon will discuss when helping you weigh the options.

Your Partial Knee Replacement Surgeons

Our fellowship-trained joint replacement specialists apply the same robotic precision and personalized approach to partial knee replacement that they bring to every joint procedure at GOMG.

Dr. Scott A. Hacker, MD — Robotic Joint Replacement & Sports Medicine, Grossmont Orthopedic Medical Group

Dr. Scott A. Hacker, MD, MS

Robotic Joint Replacement, Sports Medicine & Arthroscopy

  • Mako robotic partial & total knee replacement
  • Fellowship-trained at the Steadman-Hawkins Clinic
  • Team surgeon, U.S. Olympic Team
  • Specializes in ACL reconstruction, meniscus repair, and arthroscopic knee surgery
Meet Dr. Hacker
Dr. Andrew E. Yoo, MD — Hip and Knee Specialist, Grossmont Orthopedic Medical Group

Dr. Andrew E. Yoo, MD

Hip & Knee Specialist

  • Fellowship-trained in robotic-assisted total & revision hip/knee arthroplasty, UT Houston
  • Chief Resident Teaching Award, UC San Diego
  • Advanced expertise in unicompartmental and complex revision knee surgery
  • Specialized training in Mako robotic knee arthroplasty
Meet Dr. Yoo
Dr. Peter B. Hanson, MD — Hip and Knee Specialist, Grossmont Orthopedic Medical Group

Dr. Peter B. Hanson, MD

Hip & Knee Specialist

  • 3,000+ direct anterior hip replacements since 2005
  • Board Certified, American Board of Orthopaedic Surgery (ABOS)
Meet Dr. Hanson

Find Out If Partial Knee Replacement Is Right for You

Schedule a consultation at our La Mesa office. Our surgeons will review your X-rays, evaluate your symptoms, and help you understand whether partial or total knee replacement — or a non-surgical approach — may best address your condition.

Call 619.462.3131 Request an Appointment