First metacarpal extension-abduction osteotomy effect on joint remodeling and articular cartilage repair in thumb carpometacarpal osteoarthritis.

Abstract

The first metacarpal osteotomy is a joint-preserving surgery for thumb carpometacarpal (CMC) osteoarthritis that improves pain and function. However, its effects on joint remodeling and articular cartilage repair under physiological conditions remain unclear. This study aimed to clarify these aspects using computed tomography (CT)-based subchondral bone density analysis and arthroscopic evaluation. Fifteen hands of 14 patients who underwent a first metacarpal extension-abduction osteotomy for thumb CMC osteoarthritis were included. CT scans were performed preoperatively and one year postoperatively to assess changes in subchondral bone density (measured in Hounsfield units [HU]) across nine regions of the first metacarpal and trapezium articular surfaces. Arthroscopic evaluation of the articular cartilage was performed at the time of osteotomy and at implant removal one year postoperatively using the International Cartilage Repair Society (ICRS) grading scale. Preoperatively, higher HU values (median [interquartile range]) were observed in the palmar regions of the first metacarpal (758 [643-803] HU) and the central regions of the trapezium (898 [867-960] HU). One year after osteotomy, these values decreased significantly in these initially high-stress regions (first metacarpal palmar regions: 433 [307-475] HU, p <.001; trapezium central regions: 571 [508-649] HU, p <.001; Wilcoxon matched-pairs signed rank test), indicating a more uniform stress distribution. Arthroscopic evaluation revealed improvements in ICRS grade in five out of nine cases on the metacarpal side and four out of nine cases on the trapezium side. The first metacarpal extension-abduction osteotomy alters the abnormal stress distribution patterns in thumb CMC osteoarthritis, leading to a more uniform stress distribution across the joint. Arthroscopic findings suggest that articular cartilage repair may occur following osteotomy. These results provide new insights into the mechanisms underlying the clinical benefits of this procedure and support its use as a joint-preserving surgery for thumb CMC osteoarthritis.