The durability of small-diameter rods in lumbar spinal fusion

The use of a small-diameter rod in lumbar fusion offers a lower hardware profile and reduced implant bulk. Concern has been raised, however, about the ability of smaller rods to withstand the cyclic loads placed on them until fusion is achieved. This study is a retrospective radiographic review designed to evaluate the durability of a 4.75-mm diameter rod in the early postoperative period before fusion healing. Examination of postoperative radiographs revealed two instances of rod failure that occurred more than 24 months after operation among 85 cases of pedicle screw instrumentation followed for an average of 32 months. Based on these preliminary data, the benefits of a small-diameter rod can be obtained without an increased incidence of rod failure during the initial healing period.