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What's New in Hip and Knee Resurfacing
An update on these tissue-sparing, bone-preserving alternatives to traditional joint replacement surgery.
Anthony Carter
Publish Date: May 13, 2008   |  Tags:   Orthopedics

Hip and knee resurfacing are generating a great deal of buzz in outpatient circles. While these alternatives to traditional joint replacement surgery are far from new, developments in instrumentation, implant systems, surgeons' skills and patients' expectations are driving resurfacing's recent resurgence. Keep these procedures on your radar. They are viable options for treating the debilitating effects of degenerative arthritis on knee and hip joints and may become mainstays in the future of orthopedic same-day surgery.

Hip resurfacing
The best way to understand the benefits of hip resurfacing is to first look at the workings of the hip joint. The ball and socket joint, comprised of a femoral head that sits in the bony socket of the pelvis, can deteriorate when diseased by degenerative arthritis, a condition that often develops in older patients or in joints injured by a prior traumatic event.

Traditional total hip replacement removes the diseased bone and cartilage by replacing the entire femoral head with an artificial ball that fits into a plastic, metal or ceramic cup placed in the pelvis. Years ago the resurfacing heads were acrylic, glass or ceramic. These materials had an unacceptable failure rate, sometimes giving out after five years. Today the artificial balls are made of enduring material that exhibits good wear and tear while also providing adequate clearance between the ball and cup.

Total hip is a proven procedure. When the artificial hip's components are well-fixed and patients are dedicated to post-op rehab assignments, normal joint function is expected to last between 16 and 20 years. Hip replacement's success has some orthopedic experts questioning the need for alternative treatment options.

That argument has some merit. The flip side, however, is also worth reviewing. Why cause more bony destruction than needed? That's the belief driving the growing interest in hip resurfacing. Instead of removing the entire femoral head, hip resurfacing focuses on removing and replacing only the diseased bone and cartilage of the hip with an artificial cap. Consider a dentist who caps a damaged molar instead of pulling the entire tooth. The concept is the same.

In the OR, hip resurfacing is performed similarly to total hip procedures. The surgeon can access the hip joint with an anterior or posterior approach. While either works, the direct anterior approach performed through a four- to five-inch incision creates an intermuscular plane to the hip. The approach preserves the muscles and tendons surrounding the joint, reducing the patient's post-op pain and recovery time.

To save bone by sacrificing more tendons and muscles is counterintuitive. Direct anterior approach hip resurfacing leaves more virgin tissue around the hip and more bone in place at the joint, offering the opportunity for successful revision surgery of the joint. The tissue spared using the anterior approach, combined with the bone preserved at the joint, makes hip resurfacing a successful, less damaging treatment option than traditional total hip.

Knee resurfacing
The knee is composed of three compartments (the medial, lateral and patella) where the femur, tibia and kneecap meet. Patients presenting with degenerative arthritis in only one compartment are candidates for partial knee resurfacing, a procedure that targets the diseased area. Like its sister procedure, resurfacing of the knee is a tissue-sparing procedure that removes diseased cartilage while leaving as much healthy cartilage as possible intact.

Focusing on individual compartments during knee resurfacing spares bone and tissue around the joint — mirroring hip resurfacing — to cause less post-op pain and faster recoveries. And like developments in partial hip implants, manufactures have advanced instrumentation and knee replacement systems, allowing for unicompartmental and bicompartmental knee procedures.

During surgery, the joint is accessed through a three-to-four-inch incision on the front of the knee. A quarter-inch segment of bone is removed from the femur on the targeted side of the knee, providing access for the removal of the damaged cartilage. The top of the tibia and bottom of the femur are then shaped to accommodate the knee prosthesis. Like hip resurfacing, this procedure is designed to treat damaged cartilage while sparing healthy tissue and bone.

The anatomy of the knee differs across individual patients, each offering unique challenges for the surgeon performing the resurfacing procedure. Physicians aim to remove only the amount of bone and tissue necessary to repair the damaged compartment. The amount that's removed must be replaced with prosthetic implants. Compartmental prostheses that match unique anatomies further the tissue sparing aims of knee resurfacing.

To that end, a recent and exciting adjunct to knee resurfacing involves the development of patient-specific compartmental implants. Custom knee systems are built to match the shape of individual knee anatomies, based on the MRI of the patient set to receive the implant. A personalized system facilitates placement of the prosthesis, aligning it with the knee's natural anatomy and restoring high-level mechanical access to the joint's healthy bone. Custom knee systems are not yet widely available and are slightly more expensive than traditional knee implants, but the technology offers tremendous promise for a more widespread application in the near future.

A future boom
Candidates for hip or knee resurfacing are typically active baby boomers who are more interested in regaining normal function of the joint than the implant's longevity. Patients can expect to return to most normal activities at six to eight weeks post-op. While the latest prostheses are implanted and secured with highly effective techniques and instrumentation, current clinical data does not address how long resurfaced knees and hips remain intact and functioning. We believe the latest implants are high quality designs, but we don't want to set unrealistic expectations or push the limits of the replaced joints' long-term functionality. The immediate results are truly promising, but we don't yet fully understand the technology's limits.

That unknown — and because candidates for hip or knee resurfacing are typically younger than total joint patients — creates the possibility that they'll need revision surgery many years after the resurfacing procedure. Resurfacing's tissue and bone sparing techniques prep patients for that possibility by leaving behind more virgin bone and tissue for surgeons to work with during subsequent surgeries on the joints.

Patients undergoing resurfacing procedures commonly require an overnight post-op stay, although regional anesthesia, new surgical instrumentation and realistic patient recovery expectations have let some facilities reduce in-house recovery to 23 hours. While Medicare now reimburses ASCs for knee resurfacing, it may be some time before the hip and knee procedures become commonplace in outpatient facilities. The procedures are moving in that direction, however, thanks to their tissue-sparing techniques. It's not the size of the incision that makes these procedures minimally invasive; it's the tissue and bone preservation going on underneath.

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