Partial Knee Replacement

Patello-femoral Replacement

Overview

Degenerative arthritis can occur in any of three compartments (areas) of the knee: the medial (inside), the lateral (outside), or at the anterior (front) of the knee where the patella (kneecap) articulates with the femur.  Commonly arthritis affects more than one of these areas, in which cases a total knee replacement is recommended.  When arthritis affects only the anterior compartment of the knee (the patellofemoral space), a patella-femoral replacement may be indicated as a bone conserving partial knee replacement solution. 

Background & Rational

Patellofemoral replacements were first introduced in the 1970’s.  Many generations of implants have been introduced since that time, with the latest design incorporating science-based design features and a precise surgical technique.  The object of the procedure is to replace the painful areas of the knee where cartilage has worn away with highly engineered metal and plastic components to create a smooth and pain-free joint surface.   This option provides an opportunity to replace just the part of the knee that is causing pain, potentially delaying a total knee replacement for up to 10 years. 

Indications

The procedure is indicated in patients with osteoarthritis, traumatic arthritis, polyarthritis, and/or severe chondrocalcinosis of the patellofemoral joint, and following other surgical interventions (e.g., arthroscopy, lateral release, cartilage transplantation) that have failed to alleviate pain.  It is also indicated for patients with a history of patellar dislocation or patella fracture and dysplasia-induced patellofemoral degeneration. 

Technique

The object of the procedure is to replace the painful areas of the knee where cartilage has worn away with highly engineered metal and plastic components to create a smooth and pain-free joint surface.  To do this, the knee is exposed through an incision, which is typically smaller in size than that needed for a total knee replacement.  The worn portion of the patella is removed and the bone is prepared to accept a new plastic patellar surface, roughly the diameter of a quarter.  Removing the worn areas and preparing the bone for the metal prosthesis address the distal femur.   This is achieved using a guided milling system that precisely removes only the amount of bone necessary for the femoral implant.  This femoral implant is made of highly polished cobalt chrome.  Special care is taken to ensure proper alignment and tracking of the patella using specialized instrumentation.  Both implants are accurately sized to ensure proper fit.  The components implanted using bone cement to achieve strong and lasting fixation.

Recovery

The total time you can expect to be in the operating room is 1 to 2 hours for a Partial Knee Replacement, which is no different than a full knee replacement. In the recovery room you will be relatively comfortable, which is the advantage of a spinal anesthetic.

After surgery you will receive pain medication and begin physical therapy. Movement and mobilization is immediate.  It is important to start moving your new knee as soon as possible after surgery to promote blood flow, to regain knee motion and to facilitate the recovery process. You may be out of bed and walking with crutches or a walker within 24 hours of your surgery. Most patients are ready to go home on the first or second following surgery. Many patients will go directly home and begin supervised therapy, either at home or at an outpatient facility.

Physical therapy lasts for 2 to 3 months postoperatively. Although the knee achieves most of its recovery in the first 2 months following surgery, expect the knee to continue improve for a full year. 

Results

Though Patellofemoral Replacements have been approved and used for over 30 years, contemporary designs have been evaluated for the last 5 years.  Results have been very favorable with > 90% of patients rating themselves as highly satisfied.

With optimized patellar tracking, increased size range to achieve better fit, and superior instrumentation that is more accurate and conducive to less invasive surgical techniques1, the outlook is very promising for this implant.  Studies are currently underway to track the progress of this next generation of patella-femoral replacement.

References

Lonner, Jess H.  Patellofemoral Arthroplasty: The Impact of Design on Outcomes.  Orthopedic Clinics of North America 39 (2008) p. 347-354.