Threaded cortical bone dowels for lumbar interbody fusion: over 1-year mean follow up in 28 patients

The authors retrospectively reviewed a series of 35 patients with mechanical low-back or one- to two-level discogenic pain; the patients underwent lumbar interbody fusion in which threaded cortical bone dowels (TCBDs) were placed to treat degenerative disc disease. The purpose of the study was to delineate fusion rates and outcome data in this series of patients.

The series was composed of 18 women and 17 men whose mean age was 46 years (range 17-76 years). There were nine active cigarette smokers. All patients presented with symptoms consistent with mechanical low-back or discogenic pain, and magnetic resonance imaging revealed degenerative changes related to disc collapse at one or two vertebral levels. For placement of the TCBDs, 23 patients underwent posterior lumbar interbody fusion (PLIF), whereas 12 patients underwent anterior lumbar interbody fusion (ALIF). In all except one patient undergoing PLIF, pedicle screw and rod constructs were used without posterolateral fusion. In all patients undergoing ALIF except one, TCBDs were used as stand-alone devices without supplemental fixation. At follow up the success of fusion was determined by static lumbar radiography and/or computerized tomography scanning. The degree of lumbar lordosis at the diseased level was measured immediately postoperatively and compared with that documented on follow-up radiological studies. Outcomes were assessed using a modified Prolo Scale. Excellent and good outcomes were considered satisfactory, and fair or poor outcomes were considered unsatisfactory. In 28 patients (eight ALIF and 20 PLIF) radiological and clinical follow-up data were considered adequate. The mean follow-up duration was 12.3 months. Overall satisfactory outcome was 60%; 70% satisfactory outcome was noted in PLIF patients and 38% in ALIF patients. Osseous fusion was present in 95% of the patients in the PLIF group and in 13% of those in the ALIF group. Complications included one L-5 nerve root injury and two postoperative wound infections, all in patients who underwent PLIF; in an ALIF patient lateral breakout of one implant occurred at 8 months postoperatively.

Analysis of the mean 12.3 month follow-up data indicates that there is a dramatically higher fusion rate in PLIF compared with ALIF procedures when TCBDs are used. The authors believe that it is important to note that in all the PLIF procedures except one, supplemental pedicle screw/rod constructs were used, whereas in ALIF procedures no supplemental fixation was performed. The results thus suggest that TCBDs are best used in PLIF in conjunction with pedicle screw and rod constructs.