Thurs., 10/14/10 Basic Science, Paper #33, 4:11 pm OTA-2010
Biomechanical Test Load Discrepancies in the Medical Literature
Jacob L. Cartner, PhD1; Andy Whitten1; Michael Day, BS2; William M. Ricci, MD1;
1Smith & Nephew, Memphis, Tennessee, USA;
2University of Tennessee, Knoxville, Tennessee, USA
Purpose: There exist no standard loading scenarios for biomechanical studies of fracture fixation. The purpose of this investigation was to analyze the loading scenarios utilized in published reports of biomechanical fracture fixation studies. The hypothesis was that loading scenarios used in biomechanical testing are inconsistent and poorly documented.
Methods: The English-language medical literature was searched for references to lower extremity biomechanical testing related to fracture fixation that utilized “body weight” (keyword) as an orthopaedic loading scenario. Included articles were categorized based upon weight-bearing (WB) protocol, implant type, and anatomic region. These results were compared to reported body weights published by the US Department of Health and Human Services Centers for Disease Control and Prevention (CDC) and National Center for Health Statistics.
Results: 5289 publications were identified as potentially applicable. Of these, 56 articles (1%) met all inclusion conditions and were included in analyses. The majority of articles (78%) attempted to mimic full WB. Others utilized half body weight (9%), partial WB (9%), crutch-assisted WB (3%), and toe-touch–only SB (1%). A range of 31 to 980 N was chosen as a biomechanical test load, depending upon desired percentage WB. Of all studies mimicking full body weight, a mean load of 722 N was reported, but the range spanned between 562 and 932 N. Fixation with nails (46%) and plates (42%) were evenly cited, whereas there were few external fixation (12%) tests. The body weight values cited indicated no statistical difference based on implant (P = 0.24-0.77, depending on type). Pelvic studies utilized the lowest body weight justifications (668 ± 45 N), whereas proximal femur studies implemented the highest body weight loads (739 ± 93 N). The CDC reports a mean body weight for US females across all ethnicities as 74 kg (727 N) and reports a mean body weight for US males across all ethnicities as 86 kg (847 N), for an averaged total across both groups of 80 kg (787 N). When compared to the report from the CDC, the studies underestimated mean body weight).
Conclusions: Consistent loading parameters among biomechanical tests are not well documented. Biomechanical testing results should support clinical experience, and in this study we observed a discrepancy between biomechanical test parameters, which may ultimately influence our standard of care. A loading scheme of 722 to 787 N may be most appropriate for full body weight based on the literature search and reported CDC findings.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.