Bone resorption around the annular closure device during a postoperative follow-up of 8 years

Annular closure device (ACD) implantation is considered to be an effective means of preventing reherniation after microdiscectomy; however, there is an issue: the bone may resorb around the ACD. The causes of vertebral bone resorption remain unexplored; the dynamics of changes in bone resorption around the ACD have not yet been assessed or characterized.

One hundred thirty-three patients underwent ACD implantation after microdiscectomy, and 107 of them were followed up for 8 years after surgery (Oswestry, VAS). Lumbar CT scans helped characterize the bone resorption area around the ACD.

The median of follow-up was 85 [74; 93] months (from 73 to 105 months). The prevalence of bone resorption around the ACD was up to 63.6%, and it was mainly around the polymer mesh of the ACD (70.6%). The resorbed bone volume increased with time and reached its maximum of 5.2 cm³ (12% of the vertebral body volume) once a sclerotic rim developed around the bone resorption area. No differences in VAS pain intensity or in Oswestry Disability Index were found between patients with resorption and patients without it (p > 0.05). The volume of the intervertebral disc before surgery is a predictor of bone resorption (OR = 0.79, p = 0.009): if it is less than 13.2 cm³, the risk of bone resorption increases significantly (p < 0.05).

The majority of patients (up to 63.6%) with implanted ACDs have vertebral bone resorption around them. The bone resorption area around the ACD mesh increases with time to up to 12% of the vertebral body volume, with no clinical evidence, though. The formation of a sclerotic rim prevents the bone resorption area from further growth. If the volume of the intervertebral disc before surgery is less than 13.2 cm³, the risk of bone resorption increases significantly.