Researchers at a leading academic institution compared the knee motion, or kinematics, of patients implanted with a ConforMIS iTotal PS customized total knee replacement to patients implanted with an off-the-shelf Zimmer-Biomet NexGen PS total knee replacement. Similar to previously reported studies with the iTotal CR, this study demonstrated that ConforMIS iTotal PS patients’ knee motion patterns more closely resemble those of a normal knee than patients’ knee motion patterns with the traditional, off-the-shelf implant.
When a healthy knee bends, the lateral condyle, or outer portion of the end of the thigh bone or femur, rolls back on the shin bone or tibia and rotates externally, towards the outside of the knee. In this single-center study, financially supported by ConforMIS, researchers assessed the kinematics of 31 patients (13 patients with a ConforMIS iTotal PS implant and 18 patients with an off-the-shelf implant) at least six months after surgery using advanced real-time mobile x-ray imaging and 2D-3D registration. Patients who received a ConforMIS iTotal PS demonstrated greater average range of motion during a deep knee bend (112° vs. 94°*). Additionally, iTotal PS patients saw greater lateral femoral rollback (11.73mm vs. 4.69mm*), medial translation (2.8mm vs. 1.0mm*), and greater axial rotation (10.85° vs. 7.58°) during deep knee bend, which is consistent with normal knee motion.
“All findings from this study suggest that the iTotal PS has the kinematic and functional benefits that have been demonstrated with iTotal CR compared with traditional, off-the-shelf implants,” said William Kurtz, MD, chief of orthopedics at St Thomas Hospital in Nashville, Tenn. and clinical investigator in the study. “Patients want to return to everyday activities after their recovery and, in my experience, maintaining normal knee motion is critical to achieving those goals. I have found that when you alter patients’ normal kinematics, as happens with off-the-shelf implants, there’s a greater risk that the patient won’t be able to return to their regular activities.”
In addition, two studies, financially supported by ConforMIS, were presented at BASK highlighting the variability in femoral and tibial anatomy which cannot be replicated by off-the-shelf implants, which are offered in a limited number of shapes and sizes:
A retrospective review of 24,042 CT data sets used to design customized iTotal implants found that 61 percent of knees exhibited a distal femoral offset of >1mm. Additionally, 83 percent exhibited >2mm of posterior condylar offset. Off-the-shelf implants are designed with fixed condylar offsets, which are unable to retain the natural condylar shape of the knee. A similar analysis was conducted on tibial implants and found that the tibial trays were within 2mm or less of symmetrical only 12 percent of the time, while 22 percent were found to have asymmetry >5mm. The authors concluded that tibial trays that are either symmetric or have a fixed asymmetry based on medio-lateral size, as off-the-shelf implants do, may face challenges between maintaining proper rotation and adequate coverage.
“In its first year of release iTotal PS has met our expectations in terms of surgeon adoption and patient outcomes,” said Mark Augusti, MBA, chief executive officer and president of ConforMIS. “Clinical research has demonstrated our implants offer superior clinical outcomes compared with off-the-shelf implants. We are committed to continuing investing in the clinical study of our implants to demonstrate their superior clinical and economic value for patients, surgeons, hospitals, and payers across the healthcare continuum.”
* Indicates statistical significance with p≤0.05.