The effect of implant fit on bone preservation
Message from Frank Kolisek, MD
OrthoIndy, Indiana
Registry data and clinical research shows that the number one reason for revision following Total Hip Arthroplasty (THA) is aseptic loosening1-3, with bone resorption identified as a contributing factor.4 Of particular concern is the medial calcar region, where studies show the greatest bone loss.5 The measurement of periprosthetic bone mineral density (BMD) is a useful tool to determine whether an implant has good fixation and physiologic load transfer post THA; femoral stem design is known to influence changes in BMD.5
I’d like to share a brand-new study using Dual Energy X-Ray Absorptiometry (DEXA), where my colleague Dr. Robert Barrack investigated proximal femur BMD in a growing, high-demand population 1 year after THA. I saw results that I have never seen before.
In this study, 31 young, active, patients underwent THA and received an Accolade II stem. This stem was designed using SOMA (Stryker Orthopedics Modeling and Analytics), a proprietary analytic tool containing over 16,500 globally-sourced bone scans.6 This technology allowed the ability to design and validate implant fit*, which enabled design features including a size-specific medial curvature and enhanced proximal distal proportions. It was hypothesized that these changes from traditional wedge designs would lead to an enhanced fit as well as enhanced outcomes. At one year follow up, this study showed that 100% BMD was maintained in the medial calcar region, validating this hypothesis.7 Minimizing bone loss in this region is especially important for avoiding stress transfer distally, which I’ve found can lead to thigh pain and risk stem fracture. These results are compelling, and it is believed that this new stem design is leading to more physiologic load transfer.7
The young and active represent the fastest growing subset of patients we are now treating.6,7 They demand more from their implants and it is important for us to confirm the implants we are using are designed to accommodate their needs. The results from this study give me confidence that we have done just that.
Resources:
References
*Based on 556 CT scans
1. Australian Orthopedic Association National Joint Replacement Registry, 2017 Annual Report.
2. UK National Joint Registry, 2017 Report.
3. Karrholm J, Garellick G, Rogmark C, et al. Swedish hip arthroplasty register. Annual report 2011. Sahlgrenska: Sahlgrenska University Hospital, 2012. van Loon CJ, de Waal Malefijt MC, Buma P, Verdonschot N, Veth RP. Femoral bone loss in total knee arthroplasty. A review. Acta Orthop Belg. 1999;65(2):154-163.
4. Huiskes R, Weinans H and van Rietbergen B. The relationship between stress shielding and Bone resorption around total hip stems and the effects of flexible materials. Clin Orthop Relat Res 1992; 274: 124-134.
5. Knutsen AR, Lau N, Longjohn DV, et al. Periprosthetic femoral bone loss in total hip anthroplasty: systematic analysis of the effect of stem design, Hip Int 2017; 27: 26-34.
6. Stryker Internal presentation ‘Global Bone Morphology Study –Proximal Femur’. November 10, 2016.
7. Nam D, et al. An evaluation of proximal femur bone density in young, active patients undergoing total hip arthroplasty at one year postoperatively, Hip Int May 2018; 1-7
8. Learmonth ID, Young C and Rorabeck C. The operation of the century: total hip replacement. Lancet 2007; 370: 1508–1519.
9. Kurtz SM, Lau E, Ong K, et al. Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030. Clin Orthop Relat Res 2009; 467: 2606–2612.
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