title: Evaluation of implant loosening following segmental pedicle screw fixation in adolescent idiopathic scoliosis: a 2 year follow-up with low-dose CT.
abstract: BACKGROUND
  The long term radiological status of screw fixation following scoliosis surgery with all pedicle screw construct is not previously studied.
  
  
  OBJECTIVE
  To evaluate the incidence of loosening (implant failure) evaluated with low-dose CT two years following scoliosis surgery.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  81 consecutive patients with adolescent idiopathic scoliosis (AIS), aged 18 ± 3 years at 2 years follow-up (83% were female), subjected for scoliosis corrective surgery with all pedicle screw construct (total of 1666 screws) has been examined with plain radiography and with low dose CT 6 weeks and 2 years postoperatively.
  
  
  RESULTS
  In 26 out of 81 (32%) patients there were signs of loosening of one or more screws, a maximum 3 screws. 47 out of 1666 (2.8%) screws showed evidence of loosening. Preoperative Cobb angle was 56° among patients with loosening compared with 53° among patients with no evidence of loosening (P = 0.288). In males there were signs of loosening in 8 out of 14 (57%) and in females 18 out of 67 (27%), (P = 0.027). Among cases with loosening, 14% had suboptimal screw placement at the first postoperative CT compared with 11% among patients with no evidence of loosening (P = 0.254). One patient with a loosened L4 screw had neurological deficit and subjected for revision of the construct. Out of 26 patients with evidence of loosening, 5 patients reported minor pain or discomfort, 1 patient had a minor proximal junctional kyphosis of about 15° and 3 patients showed evidence of pull-out of 3-5 mm at the upper end of the construct but no clinical complaint. With plain radiography loosening could be observed only in 11 out of 26 cases, 5 were in the lumbar region.
  
  
  CONCLUSIONS
  In a consecutive series of 81 cases with AIS who had underwent scoliosis surgery, one third showed, 2 years after the intervention, minor screw loosening. Males were more prone to develop screw loosening. In CT system that enables low-dose protocol, CT is recommended for the evaluation of evidence of screw loosening.
authors.affiliation: Division of Neuroradiology, Diagnostic Centre for Imaging and Functional Medicine, Faculty of Medicine, Lund University, Skåne University Hospital, Malmö 205 02, Sweden.
authors.forename: Kasim
authors.initials: K
authors.lastname: Abul-Kasim
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Lund University, Skåne University Hospital, Malmö 205 02, Sweden.
authors.forename: Acke
authors.initials: A
authors.lastname: Ohlin