Standardized Three-Dimensional Volumes of Interest with Adapted Surfaces for More Precise Subchondral Bone Analyses by Micro-Computed Tomography

Abstract

Micro-computed tomography can be used to analyze subchondral bone features below treated cartilage defects in animal models. However, standardized methods for generating precise three-dimensional (3D) volumes of interest (VOI) below curved articular surfaces are lacking. The aims of this study were to develop standardized 3D VOI models adapted to the curved articular surface, and to characterize the subchondral bone specifically below a cartilage defect zone in intact and defect femoral trochlea. Skeletally mature rabbit distal femurs (N ¼ 8 intact; N ¼ 6 with acute debrided and microdrilled trochlear defects) were scanned by micro-computed tomography. Bone below the defect zone (3.5 mm width, 3.6 mm length, 1 mm deep) was quantified using simple geometric rectangular VOIs, and an optimized 3D VOI model with an adapted surface curvature, the Rectangle with Adapted Surface (RAS) model. In addition, a 250-mm-thick Curved-RAS model analyzed bone at three discrete subchondral levels. Simple geometric VOIs failed to analyze *17% of the tissue volume, mainly near the top of the curved trochlear ridges. The RAS models revealed that after debridement and drilling, only 31% of the original bone remained within the VOI and bone loss was mainly accounted for by surgical debridement. Adapted surface VOIs are better than simple geometric VOI shapes for quantifying structural features of subchondral bone below a curved articular surface. Structural differences between the bone plate and cancellous bone were best captured using the smaller, depth-dependent Curved-RAS model.

Alterations of the subchondral bone in osteochondral repair – translational data and clinical evidence

“…The subchondral bone microarchitecture can be assessed by histomorphometric (Parfitt et al, 1987) or threedimensional radiological techniques (Feldkamp et al, 1989;Marchand et al, 2011;Orth et al, 2012b).…”

“…The work of Hoemann and Buschmann (Chen et al, 2009;Chen et al, 2011a;Chen et al, 2011b;Marchand et al, 2011;Marchand et al, 2012) revealed that lapine subchondral bone surrounding drill holes remains morphologically intact at day 1, while empty osteocyte lacunae surround microfracture holes (Chen et al, 2009). Regarding the drilling instrument itself, drills may be superior to Kirschner wires, which do not remove bone The subchondral bone in cartilage repair debris -thus possibly impeding the migration of stem cells (Chen et al, 2009).…”

“…µCT showed that microfracture induces subchondral bone compaction with increased bone mineral density and trabecular thickness in rabbits, whereas drilling left a normal bone structure (Chen et al, 2009). However, only 31 % of the original lapine subchondral bone plate remained 1 day after subchondral microdrilling (Marchand et al, 2011). At 6 months, only partial restoration of the drilled subchondral bone plate was observed whereas the neighbouring subchondral plate had thickened, suggesting that drilling may also induce long-term changes in the adjacent rabbit subchondral bone (Marchand et al, 2012).…”

“…1). There is accumulating experimental evidence for these subchondral bone alterations in small (Aroen et al, 2006;Chen et al, 2009;Chen et al, 2011a;Heir et al, 2012;Marchand et al, 2011;Marchand et al, 2012;Nam et al, 2004;Qiu et al, 2003) and large preclinical animal models (Dorotka et al, 2005;Frisbie et al, 1999; Hanie et al, 1992;Hoemann et al, 2005;Howard et al, 1994;Ishimaru et al, 1992;Lane et al, 2004;Orth et al, 2012b;Vachon et al, 1986) of cartilage defects. Supporting these findings, such pathological alterations were also reported in up to one third of patients treated with microfracture (Kreuz et al, 2006;Mithoefer et al, 2005; Saris et al, 2009).…”

Issues in interstudy comparisons of bone microarchitecture

“…Hitherto, there has been no serious evaluation of the relative benefits (or risks) of considering a particular regular geometric VOI (cylindrical, spheric, cubic) vs. manually marked (adapted) scanning zone. Yet, certain advantages of using "adapted VOIs" were suggested, as simple geometric VOI shapes cannot encompass all the bone tissue within a desired zone [4].…”