gms | German Medical Science

Objectives: Subchondral bone alterations are emerging as a considerable clinical problem associated with articular cartilage repair. Their analysis exposes a pattern of variable changes, including intra-lesional osteophytes, residual holes originating from marrow stimulation procedures, bone bridges between the holes, bone resorption, and subchondral bone cysts. Since translational investigations in this field continue to expand at a rapid pace, a precise distinction between these changes is becoming increasingly important.

Methods: A tailored algorithm based on continuous data is presented to analyse subchondral bone changes using micro-computed tomography (micro-CT) images, allowing for a clear definition of intra-lesional osteophytes, residual microfracture holes, peri-hole bone resorption, and subchondral cyst formation (Figure 1 [Fig. 1]). It was then evaluated and validated using datasets from two animal models (minipig and sheep) of cartilage repair. A comparison analysis between this algorithm and the best existing semi-quantitative evaluation method was performed. Inter-rater agreement and Cohen's kappa of this new algorithm were also calculated.

Results and Conclusion: In this algorithm, the presence of any bone bridge between microfracture holes must first be confirmed after identifying the region of the articular cartilage defect. An osseous upward overgrowth of such a bone bridge is defined as an intra-lesional osteophyte. Second, the number of microfracture holes within the osteochondral region is determined according to the relative height of the bone bridge. Third, the algorithm is used to distinguish between residual microfracture holes, peri-hole bone resorption, and subchondral bone cysts based on the suggested thresholds. The novel algorithm enables a clear definition and objective discrimination between intra-lesional osteophyte, residual microfracture holes, peri-hole bone resorption, and subchondral bone cysts. The comparison analysis with the best existing Chen score supports the enhanced precision of the present algorithm (Table 1 [Tab. 1]). With datasets from the two animal models, calculation of inter-rater agreement (90% agreement) and Cohen's kappa (kappa = 0.874) reveals that the algorithm is highly reliable and reproducible for the analysis the subchondral bone alterations in different animal models.

This novel algorithm enables a more objective, reproducible, and reliable evaluation of subchondral bone alterations following microfracture treatment in different animal models, and may serve as a basis for evaluation in patients.