Which Limb to Scan? Revisiting the Relationship Between Skeletal and Functional Limb Dominance

Abstract

Purpose: The typical referral for clinical or research bone densitometry requests a "non-dominant" limb exam. While hand dominance reliably predicts upper extremity skeletal dominance, our experience suggests that functional dominance does not predict lower limb skeletal dominance. In the absence of a single reliable technique to determine lower extremity functional dominance, the extrapolation of the upper extremity rule is widespread; to the extent that scanning devices such as densitometers are generally designed to facilitate scanning of the left hip rather than the right to accommodate the preponderance of right handed individuals in the population. The aim of the current work was to determine the true nature of the association between functional and skeletal dominance of the lower limb. The ultimate goal is to establish a simple and reliable determinant of lower extremity skeletal dominance. Methods: 100 healthy men and women (age 32.5 ᱰ.2 years) were recruited for anthropometry and bilateral hip densitometry (BMD; Norland XR-800), calcaneal quantitative ultrasonometry (BUA; QUS-2, Quidel) and tibial peripheral quantitative computed tomography (cortical and trabecular density and area, cortical width and stress strain indices [SSI]; XCT3000 Stratec). Side dominance questionnaires and physical tasks were completed including the Waterloo Footedness Questionnaire(Revised) (WFQ-R), hop distance test, step test, handedness and footedness questions, and side preference for a number of common postures (e.g. folding arms). Correlation analyses and chi square tests with crosstabs were run on all bone and functional dominance parameters using SPSS(17). Results: Significant negative relationships were found for handedness and WFQ-derived dominance with femoral neck BMD dominance (r = -0.35, p = 0.01 and r = -0.32, p = 0.03 respectively), as well as arm folding dominance with tibial SSI dominance at the 14% site (r = -0.62, p = 0.003). While significance was not reached for other measures, a consistent trend for lower limb skeletal dominance in the functionally non-dominant limb was observed for 70% of all bone parameters. Conclusions: Contrary to conventional thinking, the functionally dominant lower extremity exhibits lower bone mass than the functionally non-dominant lower limb. Findings bring into question the standard practice of scanning left lower extremity regions of right handed individuals when skeletally non-dominant lower limb measures are desired.