Multimodal photoacoustic arthroscopy for quantitative morphomechanical assessment of articular cartilage

Osteoarthritis (OA) involves progressive cartilage degeneration, while conventional white-light arthroscopy mainly provides surface morphological information and lacks quantitative functional contrast. Multimodal photoacoustic arthroscopy (MMPA) may strengthen intraoperative cartilage assessment by enabling earlier identification of matrix, collagen, and biomechanical alterations that are not readily visible under white light.

We developed a preclinical multimodal photoacoustic arthroscopy (MMPA) prototype integrating photoacoustic imaging, polarization-resolved photoacoustic imaging, and photoacoustic elasticity imaging to enable label-free, in situ microscopic-resolution assessment of cartilage composition, collagen-related structural anisotropy, and biomechanical response. Validation was performed on 300 human cartilage regions spanning multiple degenerative grades. A feature-based machine-learning classifier was developed mainly using cartilage regions with Mankin scores from 2 to 9, and an independent external validation cohort including 120 cartilage regions was used to assess model generalizability. Longitudinal in vivo monitoring was conducted in a large-animal model. MRI and white-light arthroscopy were used as comparative imaging modalities, whereas histopathological grading served as the reference standard.

MMPA provided additional visualization of microscopic morphomechanical changes that were less apparent on conventional white-light arthroscopy. The multimodal machine-learning model achieved AUCs of 0.93 (95% CI: 0.91-0.95) internally and 0.89 (95% CI: 0.87-0.90) externally. MMPA detected 81% of lesions, compared with 78% for MRI and 72% for white-light arthroscopy, with a significant overall difference (Cochran's $Q=21.00$ , $p=2.75\times {10}^{-5}$ ) and significant pairwise differences (MMPA vs MRI, $p=0.0313$ ; MMPA vs white-light arthroscopy, $p=0.000831$ ). MMPA-derived scores most closely tracked histopathological severity.

This study establishes a preclinical multimodal photoacoustic arthroscopy framework for quantitative intraoperative morphomechanical assessment of articular cartilage degeneration. MMPA has potential to serve as a quantitative upgrade to conventional white-light arthroscopy, assisting surgeons in earlier recognition of degenerative cartilage changes from Mankin score 2 onward, lesion evaluation, and intraoperative decision-making. The translational potential of this article : This study presents a preclinical multimodal photoacoustic arthroscopy platform that provides quantitative intraoperative assessment of cartilage composition, structural anisotropy, and biomechanical properties. Rather than replacing MRI, MMPA is intended to complement preoperative MRI by offering real-time functional assessment during arthroscopy.