Bone biopsy in the horse. 2. Evaluation of histomorphometric examination

The histomorphometrical examination of a series of bone biopsies from the wing of ilium of foals and older horses is reported. Biopsies were obtained from 20 clinically normal horses, which had previously been infused with tetracycline intravenously twice at a 7 day interval at a dose rate of 10 to 15 mg kg-1. The horses were divided into 2 groups. Group 1 consisted of 10 foals (mean age: 4 +/- 1 months) which were biopsied at 3 different sites in the wing of ilium. Group 2 comprised 10 older horses (mean age: 91 +/- 63 months) which were biopsied from only one site in the left ilium. A systematic evaluation of intra-observer, intra-core, intra-bone and inter-bone errors was made to investigate parameter variations that might affect interpretation of bone biopsies. The measurements carried out included cancellous bone volume (Cn-BV/TV), osteoid surface (OS/BS), eroded surface (ES/BS), mean wall thickness (W.Th), mean osteoid thickness (O.Th), distance between labels (Ir.L.Th) and mineralizing surface (MS/BS). The intra-observer variance, the variance between sections, the variance between adjacent biopsies and that between right and left sides proved to be smaller than the inter-individual variance. The estimate of errors associated with the histomorphometrical analysis of bone biopsies is important for correct interpretations of changes due to disease.