Posterior stabilized total knee arthroplasty requires an intercondylar notch to accommodate the cam housing that articulates with the tibial post to create femoral rollback required for deep flexion. The volume of bone resected for the intercondylar notch varies with implant design, and newer designs may accommodate high flexion with less bone resection.
This study aims to analyze the bone volume and density resected from the intercondylar notch for three posterior stabilized implants from a single company: a Posterior Stabilized (PS) system, a Hi-Flex system (HF), and a rounded new box-reamer (RB) system and to further assess whether the newer RB with a cylindrical cutting tool would preserve more native bone.
Materials and Methods
Using a computer model, the PS, HF, and RB femoral components were digitally implanted into CT scans of 19 cadaver femurs. Nine cadavers were fit with a size 4 implant, six with size 3, and four with a size 2. The volume of intercondylar bone resected digitally for femoral preparation was measured. Bone density was measured by CT scans in Hounsfield units (HU). A paired t test was used to compare the mean volume of bone resected for each implant.
For the size 4 femurs, the newer RB design removed 8% less intercondylar bone than the PS design (7,832 ± 501 vs. 8,547 ± 377 mm3, p < 0.001) and 28% less bone than the HF design (7,832 ± 501 vs. 10,897 ± 444 mm3, p < 0.001). The average HU for size 4 femurs for RB design was 427 ± 72 (PS = 399 ± 69, p < 0.001; HF = 379 ± 66, p < 0.001). For the size 3 femurs, the RB design removed 12% less intercondylar bone than the PS (6,664 ± 786 vs. 7,516 ± 648 mm3, p < 0.001) and 27% less bone than the HF (6,664 ± 786 vs. 9,078 ± 713 mm3, p < 0.001). HU for size 3 femurs for the RB design was 452 ± 70 (PS = 422 ± 53, p < 0.1; HF = 410 ± 59, p < 0.01). For the size 2 femurs, the RB design removed 5% less intercondylar bone than the PS (5,730 ± 552 vs. 6,009 ± 472 mm3, p < 0.01) and 22% less bone than the HF (5,730 ± 552 vs. 7,380 ± 532 mm3, p < 0.001). HU for size 2 femurs for the RB design was 430 ± 48 (PS = 408 ± 55, p < 0.01; HF = 385 ± 56, p < 0.01).
The newer RB design removes less bone from the intercondylar notch than the classic PS and HF designs in all sizes tested. The bone-conserving cuts incorporated into this newer implant design appear to preserve native bone without compromising design objectives.
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Conflict of Interest:
Timothy Wright, PhD, is a board member of the Knee Society and receives royalties from Orthopaedic Research Society and Mathys ABG, stock payments from Exactech, and research support from Synthes Spine, outside the work. Geoffrey Westrich, MD, is a board member of Eastern Orthopaedic Association and receives research support from Exactech and Stryker, outside the work. Luke Pugh, MD, FRCSC, Allison Ruel, BA, and Mark Gessell, MD, have declared that they have no conflict of interest. Joseph D. Lipman, MS is a paid consultant for Ivy Sport Medicine; employee of Hospital for Special Surgery; has received payment for manuscript preparation from Stryker; has the following patents: Posterior Stabilized Knee Prosthesis, Self‐aligning knee prosthesis, Dual radius glenoid prosthetic component for total shoulder arthroplasty, Pelvic Positioner, Trochlear Clamp, Patella Resection Drill and Prosthesis Implantation Device; has pending patents for Constrained Condylar Knee Device, Prosthetic Condylar Joints With Articulating Bearing Surfaces Having A Translating Contact Point During Rotation Thereof, Elbow Replacement Apparatus And Methods, Expanding Cannula And Retractor Device And Methods Of Use and External fixation devices and methods of use; receives royalties payment from Mathys Inc. and Ortho Development Corp; has received travel support for travel to meetings from Chinese Orthopaedic Association, outside the work.
This article does not contain any studies with human or animal subjects performed by any of the authors.
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Pugh, L., Ruel, A., Lipman, J. et al. Reduction in Bone Volume Resection with a Newer Posterior Stabilized Total Knee Arthroplasty Design. HSS Jrnl 9, 157–160 (2013). https://doi.org/10.1007/s11420-013-9340-1
- total knee arthroplasty
- bone resection
- posterior stabilized