Risk Factors for Cage Retropulsion After Posterior Lumbar Interbody Fusion

Single-center retrospective study.We examined the risk factors for cage retropulsion after posterior lumbar interbody fusion (PLIF) performed for patients with degenerative lumbar spinal diseases.Although PLIF is a widely accepted procedure, problems remain regarding perioperative and postoperative complications. There are few reported studies identifying specific risk factors for cage retropulsion, one of the implant-related complications after PLIF, although several case reports have been published.Between April 2006 and July 2010, 1070 patients with various degenerative lumbar spinal diseases underwent single- or multilevel PLIF combined with posterolateral fusion, using posterior pedicle screw fixation and box-type cages. Their medical records and preoperative radiographs were reviewed and the factors influencing the incidence of cage retropulsion were analyzed.There were 9 cases of cage retropulsion (7 men and 2 women; mean age, 68.2 yr), and it developed within 2 months after surgery in all cases. Five patients had low back pain or leg pain, 3 of whom required revision surgery. The mean fusion level was 3.9 (range, 2-5); in 6 of the 9 patients, the cage had migrated at L5/S, 2 at L4/5, and 1 at L3/4. All of the cages were inserted at the end disc level of multilevel fusion procedures. The disc heights and ranges of motion were significantly greater in patients with cage retropulsion, and patients with a pear-shaped disc space also showed a higher rate of cage retropulsion.These results indicate that PLIF at L5/S, a wide disc space with instability, multilevel fusion surgery, and a pear-shaped disc space on lateral radiographs are risk factors for cage retropulsion. The identification of these risk factors should allow us to avoid this complication, and the use of expandable cages is an effective option for such cases.