By Robert J. Snyder, MD
There is an ephemeral “holy grail” of treatment in whatever specialty we practice, whether that be a cure for trauma-induced paralysis, cancer, diabetes, COVID-19, or multiple sclerosis. In general orthopaedics, one of those “grails” would be finding the perfect joint replacement prosthesis to ensure immediate post-surgical function restoration without a long, painful recovery. This article will discuss patient-specific joint replacement of the knee, how the technology has developed, and the benefits to the patient and the physician.
Orthopaedics is rapidly changing due to increased technology, advanced 3-D printing, computer navigation, and robotics. A few years ago, knee joint prosthetics came in maybe eight or nine sizes, were manufactured of metal and/or ceramics and used plastic spacers that could not withstand the millions of movements that a patient would be expected to perform over 10-15 years. Today, these prosthetics can be custom 3-D printed, based on the patient’s specific anatomy taken from an MRI or CT scan, and are made from space-age metal alloys and polymers that have been laboratory wear-tested to last for 30 years under normal conditions.
So, are there any benefits to this “patient-specific implant” stuff or is it all marketing hype? As an Orthopaedic surgeon who has used both the traditional and custom types of joint implants and has had two joint implant surgeries myself, why yes, there is a difference.
Here’s my experience:
The ConforMIS Company manufactures custom, patient-specific knee and hip replacement systems. However, for this article, we will confine our discussion to knees. Every part of the replacement prosthesis is custom-made, one-of-a-kind. Other joint prosthesis manufacturers advertise “custom” made; however, they still utilize mass produced, pre-made components.
For a prosthesis to be custom-made, a CT scan of the knee must first be taken, and then a virtual model of the knee can be created from the CT scan. The model is then used to manufacture the femoral and tibial components using 3-D printers for the metallic pieces and the polyethylene inserts, plus all the cutting blocks and jigs that the surgeon will use to ensure an exact fit. Extra inserts are included so that the surgeon can make on-the-spot adjustments if needed.
The benefits to the patient include less resected bone, less OR time, less blood loss, and a more anatomically accurate and functioning knee replacement, like the native knee itself. European studies have also shown the patient-specific custom knee replacements have the lowest revision rates. Unfortunately, the United States can’t perform these types of studies due to a lack of a central registry system.
Another advantage is that small changes can be incorporated immediately, unlike the pre-made implants already stocked in every hospital. Design changes for these systems take years and require trading out the entire inventory. With the customized approach, the patient always gets the LATEST model.
Patient-specific custom replacement can now be economically manufactured and in the future, this technology will extend across the entire field of joint replacement: knee, hip, shoulder, elbow and ankle.
Dr. Bob Snyder is a Board certified orthopaedic surgeon with Orthopaedic & Spine Center (OSC) in Newport News. osc-ortho.com