A pilot study of four-year longitudinal bone changes following anterior cruciate ligament reconstructive surgery using DXA and HR-pQCT

Abstract

Anterior cruciate ligament reconstructive (ACLR) surgery is an effective and prevalent treatment to restore function following ACL injury. The incidence of post-traumatic osteoarthritis (PTOA) long-term is still a major problem. Longitudinal studies beyond the first year are lacking and no studies have reported high-resolution in vivo bone changes. (1) Determine longitudinal bone changes following surgery in the proximal tibia and distal femur in ACLR and contralateral knees, and (2) determine bone changes at the ACLR tunnel and surrounding region in the injured knee. Participants with acute ACL-injuries (n = 5) had DXA and HR-pQCT imaging at four timepoints: pre-surgery (baseline) and at 2-, 6- and 48-months in the injured and contralateral knees. Areal BMD in peri-articular and epiphyseal regions was evaluated using DXA. Microstructural and vBMD changes of the tibial plateau and femoral condyles and surrounding the ACLR tunnel were determined. Large initial reductions in subchondral density and microstructure within the first year were followed by a period of recovery. Although varying among participants, reduced values in the injured knee remained at 48 months. Substantial adaptations to the surrounding ACLR tunnel bone occurred resulting in a cortex-like thickening and reduced wall diameters at 48 months. Large initial reductions following ACLR surgery followed a similar pattern seen in the first year after injury, indicating the trauma of surgery may reset bone recovery. These longitudinal results are consistent with cross-sectional studies indicating irreversible bone changes following ACLR that may play a role in PTOA initiation and progression. This pilot data suggests that imaging biomarkers are persistent at 48 months, possibly reflecting early PTOA changes.