Reduction in Bone Volume Resection with a Newer Posterior Stabilized Total Knee Arthroplasty Design

Luke Pugh, MD, FRCSC
Hospital for Special Surgery

Allison Ruel, BA
Hospital for Special Surgery

Joseph Lipman, MS
Hospital for Special Surgery

Timothy Wright, PhD
Senior Scientist, Hospital for Special Surgery
F.M. Kirby Chair, Orthopaedic Biomechanics

Mark Gessell, MD
Hospital for Special Surgery


Geoffrey H. Westrich, MD

Associate Attending Orthopedic Surgeon, Hospital for Special Surgery
Research Director of Adult Reconstruction and Joint Replacement Service, Hospital for Special Surgery
Assistant Scientist, Hospital for Special Surgery
Co-Chairman, Complex Case Review Panel, Hospital for Special Surgery
Associate Professor of Clinical Orthopedic Surgery, Weill Cornell Medical College

Abstract

Background

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.

Questions/Purposes

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.

Results

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).

Conclusions

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.

This article appears in HSS Journal: Volume 9, Number 2.
View the full article at springerlink.com.

About the HSS Journal

HSS Journal, an academic peer-reviewed journal published three times a year, February, July and October. The Journal accepts and publishes peer reviewed articles from around the world that contribute to the advancement of the knowledge of musculoskeletal diseases and disorders.

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