Abstract: BACKGROUND: There is no consensus on the optimal bone tunnel position in the lateral clavicle, which guides coracoclavicular ligament reconstruction. Postoperative complications such as enlargement of the lateral clavicle bone tunnel, bone osteolysis, clavicle fracture, and failure of internal fixation are likely to occur. Bone mass density plays an important role in the strength and stability of endophytic fixation. Regional differences in the bone mass density of the distal clavicle should not be overlooked in the repair and reconstruction of acromioclavicular dislocation. Currently, there are no quantitative clinical studies in humans regarding the bone mass density of the distal clavicle.
OBJECTIVE: To measure the magnitude of bone mass density in different regions of the distal clavicle by quantitative CT to provide a reference for surgeons to repair and reconstruct the coracoclavicular ligament.
METHODS: 101 patients undergoing quantitative CT checking in Fuyang People’s Hospital Affiliated to Anhui Medical University from October to December 2022 were enrolled, from which 1 616 samples of subdivisional bone mass density of the distal clavicle were measured. For each of the quantitative CT samples, firstly, the distal clavicle was divided medially to laterally into the following four regions: conical nodal region (region A), inter-nodal region (region B), oblique crest region (region C) and distal clavicular region (region D). Secondly, each region was divided into the first half and the second half to determine eight subdivisions, then setting semiautomatic region of interest (ROI) in each subdivision: (ROI A1, A2, B1, B2, C1, C2, D1, and D2). Thirdly, each quantitative CT scan was transferred to the quantitative CT pro analysis workstation, and cancellous bone mass density was measured in the distal clavicle ROI. Finally, the clavicular cortex was avoided when measuring. 
RESULTS AND CONCLUSION: (1) There was no statistically significant difference in bone mineral density on the different sides of the shoulder (P > 0.05). (2) The analysis of bone mineral density in eight sub-areas of the distal clavicle A1, A2, B1, B2, C1, C2, D1, and D2 showed statistically significant differences (P < 0.05). It could be considered that there were differences in bone mineral density in different areas of the distal clavicle. After pairwise comparison, there was no statistically significant difference in bone mineral density between A1 and A2, D1 and D2, A2 and B1 (P > 0.05), and there was a statistically significant difference in bone mineral density between the other sub-areas (P < 0.05). (3) The bone mineral density in the region A2 of the anatomical insertion of the conical ligament was significantly higher than that in the inter-nodular area (region B) (P < 0.05). The bone mineral density in the region A1 was higher than that in the region A2, but the difference was not statistically significant (P > 0.05). The bone mineral density in the region C1 of the anatomical insertion of the trapezium ligament was higher than that in regions C2, D1 and D2, and the bone mineral density in the inter-nodular area (region B) was significantly higher than that in regions C and D (P < 0.05). (4) These results have suggested that there are differences in bone mass density in different regions of the distal clavicle; regional differences in bone mass density in the distal clavicle during repair and reconstruction of acromioclavicular dislocation cannot be ignored. Consideration should be given not only to biomechanical factors but also to the placement of implants or bone tunnels in regions of higher bone mass density, which could improve the strength and stability of implant fixation and reduce the risk of complications such as bone tunnel enlargement, osteolysis, fracture and implant failure.

Key words: acromioclavicular joint dislocation, repair, reconstruction, clavicle, bone mass density, quantitative CT, region, bone tunnel, coracoclavicular ligament