Knee Implants: Customized and Personalized Options

The knee is a complex joint, and your knee differs from other’s not only in size, but also in shape. Traditional total knee replacement procedures use knee implants that are available in an assortment of six to ten standardized sizes.

Once your surgeon has selected the implant that most closely matches the size and shape of your knee, adjustments are made during surgery to fit the implant to your knee joint. This surgical technique sometimes compromises how precisely the implant fits your individual bone structure. Within a somewhat narrow tolerance, an improper implant fit may cause residual issues that could result in problems after surgery.

The theory of the need for precise implant fit has driven a new trend in the knee replacement implant industry toward customized (created for a given patient) and personalized (for example: gender-specific) implants. Research conducted in 2010 suggests that such implants help reduce sizing compromises during surgery1 and more closely replicate the curvature of your own knee joint giving you the potential for a more natural feeling replacement knee.

iFit® Image-to-Implant™ Technology (ConforMIS)

Personalized Implants

personalized knee replacement instruments (courtesy Smith & Nephew)

Custom knee replacement instruments (image courtesy of: Smith & Nephew)

Some knee replacement implant manufacturers are now offering patient-specific, or custom implants created from MRI and CT scan data that closely matches the natural shape and curves of your knee. These manufacturers use special technology to convert the scan of your knee into a 3D model which is then used to construct an implant that closely matches your own knee. Using the same scan data, computer-assisted surgical instrumentation is utilized by your surgeon during the procedure, simplifying many of the sizing and alignment steps throughout the surgery.

Gender-Specific Knee Replacement (for Women)

Narrow Femur vs. Normal Femur (MicroPort Orthopedics)

Narrow Femur vs. Normal Femur (MicroPort Orthopedics)

It is theorized that in a petite person, regular-sized implants may overhang on the bone at the sides of the knee and lead to soft tissue interference or mid-flexion instability. In many cases this can cause pain and discomfort long after the healing is complete.2 For this reason there are relatively new implants designed to accommodate the knee which may be smaller from side-to-side than from front-to-back, thereby reducing implant misfit and knee pain after surgery.

Many researchers believe that women’s knees differ from men’s not only in size, but also in shape. Due to the differences in knees between women and men, surgeons have been making tedious adjustments to traditional standardized knee implants in order to size them to fit properly for women.

The design of gender-specific implants is based on research that illustrated three distinct differences between women’s and men’s knees. A woman’s knee may have a thinner profile at the front of the knee, a distinct shape to accommodate the different angle between the hip and knee, and a different contour to allow for a more precise fit.

Some patients, surgeons and manufacturers feel strongly that these gender-specific options are necessary. Others are skeptical about the need for customized implants due to the wide variety of stock options available.

Gender-Specific Implant (Zimmer Biomet)

On the other hand, some researchers believe that differences in knee size and shape have less to do with gender and more to do with a patient’s stature in general, with possibly some ethnic influences determining size differences. Regardless, there are a number of implants available today designed to more closely match your knee size and shape, with each of the implants offering different benefits. Therefore, it is in your best interest to discuss these options with your knee surgeon, who will determine which implant will best suit your lifestyle.

Sources

  1. Bourne, et al; Patient Satisfaction after Total Knee Arthroplasty. Who is Satisfied and Who is Not? Clinical Orthopedics and Related Research; 2010, 468: 57-63.
  2. Mahoney, et al; Overhang of the Femoral Component in Total Knee Arthroplasty: Risk Factors and Clinical Consequences. The Journal of Bone and Joint Surgery; 2010, 92: 1115-1121
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