Peripheral Quantitative Computed Tomography Predicts Humeral Diaphysis Torsional Mechanical Properties With Good Short-Term Precision

Abstract

Peripheral quantitative computed tomography (pQCT) is a popular tool for non-invasively estimating bone mechanical properties. Previous studies have demonstrated pQCT provides precise estimates that are good predictors of actual bone mechanical properties at popular distal imaging sites (tibia and radius). The predictive ability and precision of pQCT at more proximal sites remains unknown. The aim of the current study was to explore the predictive ability and short-term precision of pQCT estimates of mechanical properties of the midshaft humerus, a site gaining popularity for exploring the skeletal benefits of exercise. Predictive ability was determined ex vivo by assessing the ability of pQCT-derived estimates of torsional mechanical properties in cadaver humeri (density-weighted polar moment of inertia [IP] and polar Strength Strain Index [SSIP]) to predict actual torsional properties. Short-term precision was assessed in vivo by performing six repeat pQCT scans at the level of the midshaft humerus in 30 young, healthy individuals (degrees of freedom = 150), with repeat scans performed by the same and different testers and on the same and different days to explore the influences of different testers and time between repeat scans on precision errors. IP and SSIP both independently predicted at least 90% of the variance in ex vivo midshaft humerus mechanical properties in cadaveric bones. Overall values for relative precision error (root mean squared coefficients of variation) for in vivo measures of IP and SSIP at the midshaft humerus were less than 1.5% and were not influenced by pQCT assessments being performed by different testers or on different days. These data indicate that pQCT provides very good prediction of midshaft humerus mechanical properties with good short-term precision, with measures being robust against the influences of different testers and time between repeat scans.

Progressive skeletal benefits of physical activity when young as assessed at the midshaft humerus in male baseball players

“…The throwing arm in throwers had a larger midshaft humerus (Tt.Ar) with more mass (Ct.BMC), a contracted medullary cavity (Me.Ar) and thicker cortex (Ct.Th) than the contralateral nonthrowing arm, independent of stage of somatic maturity and normal arm dominance. These mass and structural adaptations contributed to increased bone strength (SSI P ) in each maturity group, with SSI P predicting over 90% of the variance in ex vivo midshaft humerus mechanical properties [25]. These data suggest that physical activity before, during and after somatic maturation increased bone accrual on the periosteal surface, and either increased accrual or decreased resorption on the endocortical surface.…”

“…Peripheral quantitative computed tomography (pQCT) of the midshaft humerus was performed bilaterally using a Stratec XCT 3000 machine (Stratec Medizintechnik GmbH, Pforzheim, Germany) equipped with Stratec software version 6.20C, as previously described [17, 20, 24, 25]. Subjects were positioned in supine with their upper extremity positioned in 90° shoulder abduction.…”

“…Bone strength was estimated by the polar Strength Strain Index (SSI P , mm 3 ) obtained using cortical mode 2 (threshold = 400 mg/cm 3 ). SSI P represents the density-weighted section modulus and predicts over 90% of the variance in ex vivo midshaft humerus mechanical properties [25]. …”

“…A 3×3 kernel filter to filter all voxels between −500 and 500 mg/cm 3 followed by a 5×5 kernel filter to filter all voxels between −500 and 300 mg/cm 3 (F03F05 filter) was used to remove noise. Short-term precision for the pQCT scanning procedure on 30 healthy individuals scanned six times with interim repositioning showed root mean square coefficients of variation (RMS-CVs) of <1.5% for bone density, mass, structure, and estimated strength measures, and <2% for mCSA [25]. …”

Tibial Bone Strength is Enhanced in the Jump Leg of Collegiate-Level Jumping Athletes: A Within-Subject Controlled Cross-Sectional Study

“…I MIN and I MAX were estimated according to Gere and Timoshenko [31], and represent the distribution of bone material about the orthogonal planes of least and most bending resistance, respectively. I P was calculated as the sum of I MIN and I MAX , and was used to estimate the ability of the bone structure to resist torsion [32]. The ratio of I MAX to I MIN was derived to provide an indication of the directionality of diaphyseal adaptation.…”