The most common cause of chronic knee pain and disability is arthritis, which wears away cartilage, causing pain and stiffness. When non-surgical treatments fail to correct functional limitations and relieve progressive pain, knee replacement is often the best option. In a total knee replacement, damaged cartilage and bone are removed from the surface of the knee joint and replaced with a man-made surface of metal and plastic. “The important advance in this next-generation technology for knee replacement is that now we can use computerized images to model the patient's knee and then create custom-designed cutting guides for use during surgery,” says Dr. Styles. “This enables the surgeon to preserve more of the patient's own bone and ligaments and achieve a more precise fit and alignment when inserting the prosthetic knee.”
In a traditional knee replacement procedure, the surgeon matches the patient's original knee size and alignment as closely as possible to the replacement knee model using measuring devices based on standard anatomical sizes and selecting from available replacement joints. The surgeon then makes adjustments for fit during the operation, while the patient is under anesthesia. With custom knee replacement, the process starts several weeks prior to surgery with a magnetic resonance imaging (MRI) scan and x-rays that map the exact dimensions of the patient’s knee. Computer software transforms the images into a three-dimensional model that corrects any deformity to conform the model to the patient's knee in its pre-arthritic state. The surgeon reviews the computerized model and makes any necessary adjustments. A custom surgical-grade nylon knee form is then created with pinholes and blocks that align precisely to the mechanical axis of the patient’s knee and serve as a cutting guide during surgery.
“There are several important benefits with custom knee replacement,” Dr. Styles says. “First, we can do the matching and measuring using the computerized model before surgery rather than while the patient is on the table. This makes the surgery more efficient, reducing the time the patient is under anesthesia and the knee is open to infection. Second, because the cutting blocks are molded specifically for the patient, doctors can work in a smaller area and preserve more of the patient's bone and ligaments, making the surgery less invasive and reducing recovery time. And the blocks enable greater accuracy by removing the guesswork when making cuts, enabling more precise alignment. Alignment is critical when performing knee replacement surgery; eight out of ten knee implants that fail do so because the implant is misaligned.”
Custom knee replacements are precise to within several tenths of a millimeter, whereas the traditional approach has up to five millimeters of variability in the fit. That difference in motion makes a difference particularly since more replacements are being performed on younger and more active people. Inserting a prosthesis with more precision means potentially greater longevity and improved function.
The new surgery is suitable for a wide range of patients, although it is not recommended for those who have had previous corrective knee surgery or those with damaged ligaments. It is also not recommended for patients who have hardware around the knee or other contraindications for an MRI, such as pacemakers or vascular clips.
“Every case is different,” Dr. Styles concludes. “This technique allows the surgeon a great deal of flexibility in developing the appropriate operating plan for each individual and then executing that plan efficiently and accurately, which delivers important benefits to our patients. Many of them are experiencing quicker and less painful recovery times, greater range of motion, and an easier return to daily activities.”
Stuart T. Styles, M.D., F.A.A.O.S., knee replacement specialist with Somers Orthpaedic Surgery and is a Clinical Assistant Professor of Orthopaedic Surgery at NYU School of Medicine/Hospital for Joint Disease Orthopaedic Institute. He is also on staff at Putnam General Hospital and Northern Westchester Hospital. Dr. Styles is a Board Certified Orthopaedic Surgeon and is a Fellow of the American Academy of Orthopaedic Surgeons and a Diplomate of the American Board of Orthopaedic Surgery. He is a member of the American College of Sports Medicine and Medical Society of New York State and Westchester County. Dr. Styles is a co-author of several articles and textbooks on orthopaedic subjects and attends sporting events as the orthopaedic team doctor. www.somersortho.com
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