Efficacy of a novel polylactic acid/nanoclay (NK-75) biodegradable composite scaffold in healing critical-size bone defects: an experimental study in a rabbit ulnar model

Background Critical-size bone defects remain a formidable challenge in orthopaedic surgery. Biodegradable polymer scaffolds represent a promising alternative to autologous bone grafting, but conventional polylactic acid (PLA) scaffolds exhibit limited osteoconductivity and generate acidic degradation products unfavorable to bone healing. Incorporation of nanoclay particles into PLA matrices may overcome these limitations. This study evaluated a novel PLA/nanoclay (NK-75) biodegradable composite scaffold for healing critical-size bone defects in a rabbit ulnar model. Methods New Zealand White rabbits underwent bilateral mid-diaphyseal ulnar osteotomy creating 3 mm extraperiosteal critical-size defects. Defects were assigned to three groups: PLA + NK-75 composite scaffold (n = 15 observations), PLA-only scaffold (n = 4), or untreated empty defect control (n = 11). Animals were sequentially sacrificed at 4, 8, 12, 16, and 20 weeks post-surgery. Radiological healing was assessed using the Lane-Sandhu scoring system (total score 0–10, comprising bone formation, proximal union, distal union, and remodeling). Data were analyzed using Kruskal-Wallis test with Dunn's post-hoc comparisons, Mann-Whitney U test, linear mixed models, generalized estimating equations, ordinal logistic regression, and permutation tests. Effect sizes and post-hoc power were calculated. Results The PLA + NK-75 group demonstrated significantly higher mean total Lane-Sandhu scores (7.20 ± 1.93) compared to PLA (4.75 ± 3.59) and control (4.00 ± 2.32; Kruskal-Wallis p = 0.0144). Post-hoc analysis confirmed PLA + NK-75 superiority over control (Dunn's p = 0.0062; Mann-Whitney p = 0.0044). Large effect sizes were observed (Hedges' g = 1.47; Cliff's delta = 0.66). The probability that a randomly selected PLA + NK-75 observation exceeds a control observation was 83.0%. Excellent healing (score ≥ 8) was achieved in 46.7% of PLA + NK-75 observations versus 0% in controls (Fisher's exact p = 0.0025). PLA + NK-75 was the only group demonstrating remodeling activity. A significant ordered trend (CONTROL < PLA < PLA + NK-75) was confirmed by the Jonckheere-Terpstra test (p = 0.0021). Results were consistent across all parametric, non-parametric, and permutation-based analyses. Achieved statistical power was 85.5%. Conclusion The PLA/NK-75 biodegradable composite scaffold significantly enhances radiological bone healing with large effect sizes and accelerated milestone achievement. These findings support nanoclay-enhanced biodegradable scaffolds as a promising strategy for orthopaedic bone regeneration.