• Joost J A de Jong, Jacobus J Arts, Ursina Meyer, Paul C Willems, Piet P Geusens, Joop P W van den Bergh, and Bert van Rietbergen.
• Research Schools NUTRIM (J.J.A.d.J., U.M., and J.P.W.v.d.B.) and CAPHRI (J.J.A., P.C.W., and P.P.G.), Maastricht University, Maastricht, the Netherlands Departments of Rheumatology (J.J.A.d.J., U.M., P.P.G., and J.P.W.v.d.B.), Orthopaedic Surgery (J.J.A. and P.C.W.), and Human Movement Sciences (U.M.), Maastricht University Medical Center, Maastricht, the Netherlands joost.dejong@maastrichtuniversity.nl.
• J Bone Joint Surg Am. 2016 Mar 2; 98 (5): 356-62.

BackgroundHigh-resolution peripheral quantitative computed tomography (HR-pQCT) is a promising tool to assess the fracture-healing process at the microscale in vivo. Since casts are often used during fracture treatment, they might affect the assessment of bone density, microarchitectural, and biomechanical parameters and the short-term reproducibility of those parameters, e.g., as a result of beam-hardening. The aim of this study was to assess the effect of a plaster-of-Paris and/or fiberglass cast on bone parameters and on the short-term reproducibility of the HR-pQCT measurements of those parameters.MethodsThe effects of a cast on HR-pQCT-derived bone parameters were evaluated by comparing HR-pQCT scans of fifteen human cadaveric distal radial specimens from one male and fourteen female donors (median age, eighty-four years [range, sixty-two to ninety years] at the time of death) in three conditions: with a plaster-of-Paris cast, with a fiberglass cast, or without a cast. Short-term reproducibility was assessed using duplicate scans of the distal end of the radius in sixteen healthy volunteers without a fracture (nine men and seven women with a median age of twenty-six years; range, twenty-two to thirty-nine years) while wearing and not wearing a fiberglass cast.ResultsCompared with measurements made with no cast, the plaster-of-Paris cast introduced a systematic error in the bone parameters ranging from -2.6% in trabecular separation to -9.8% in cortical thickness. Bone parameters were affected only marginally by fiberglass, with errors between -0.6% and -1.6% in trabecular separation and cortical thickness, respectively. Short-term reproducibility with a fiberglass cast was similar to that with no cast: approximately 1% for bone density parameters, 4% to 5% for microarchitectural parameters, and 3% to 4% for biomechanical parameters.ConclusionsA plaster-of-Paris cast has a considerable effect on HR-pQCT measurements. A fiberglass cast only marginally affects the bone parameters, and the short-term reproducibility of HR-pQCT measurements in patients with a fiberglass cast is comparable with that in patients without a cast. In studies on fracture-healing using HR-pQCT, a fiberglass cast is desirable if immobilization is indicated. The use of a plaster-of-Paris cast should be avoided if possible; however, if not avoidable, corrections after the scan are desirable to adjust for the error introduced in the bone parameters.Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated.

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