Retrospective study.
The purpose of this study was to investigate the influence of sagittal alignment of the strut graft on graft subsidence and clinical outcomes after anterior cervical corpectomy and fusion (ACCF).
ACCF is a common technique for the treatment of various cervical pathologies. Although graft subsidence sometimes occurs after ACCF, it is one cause for poor clinical results. Malalignment of the strut graft is probably one of the factors associated with graft subsidence. However, to the best of our knowledge, no prior reports have demonstrated correlations between the alignment of the strut graft and clinical outcomes.
We evaluated 56 patients (33 men and 23 women; mean age, 59 years; range, 33–84 years; 45 with cervical spondylotic myelopathy and 11 with ossification of the posterior longitudinal ligament) who underwent one- or two-level ACCF with an autogenous fibular strut graft and anterior plating. The Japanese Orthopaedic Association (JOA) score recovery ratio for cervical spondylotic myelopathy was used to evaluate clinical outcomes. The JOA score and lateral radiograms were evaluated 1 week and 1 year postoperatively. Patients were divided into two groups (a straight group [group I] and an oblique group [group Z]) based on radiographic assessment of the sagittal alignment of the strut graft.
Group I showed a significantly greater JOA score recovery ratio (
Our findings suggest that a straight alignment of the strut graft provides better clinical outcomes and lower incidence of graft subsidence after ACCF. In contrast, an oblique strut graft can lead to significantly increased strut graft subsidence and poor clinical results.
Anterior cervical corpectomy and fusion (ACCF) is commonly
employed in patients with cervical spondylotic myelopathy (CSM), cervical ossification of the posterior longitudinal ligament (OPLL), and trauma [
Chen et al. [
We aimed to investigate the relationship between the alignment of the strut graft and strut graft subsidence by evaluating radiological and clinical results after ACCF. In addition, we investigated other potential factors that influence clinical outcomes.
This retrospective study was conducted with the approval of the Institutional Review Board. Patients received a written and verbal explanation and then underwent one- or two-level ACCF between 2004 and 2011. A total of 56 patients were included (33 men and 23 women; mean age, 59.0±11.9 years; range, 33–84 years). There were 45 patients patients with CSM and 11 patients with OPLL. All patients were followed for a minimum of 1 year postoperatively. Patients with less than 1 year of follow-up, rheumatic arthritis, dialysis-related disorders, and a history of multiple (>two) surgeries of the cervical spine were excluded from this study.
Patients were positioned supine with the neck slightly extended. All patients underwent standard anterior cervical corpectomy using a high-speed air drill through a left-sided approach. The posterior longitudinal ligament was then removed via microscopic surgery to achieve complete neural decompression. Most of the subchondral bony endplate was preserved to prevent graft subsidence. Finally, an autogenous fibular strut graft was inserted under manual cervical distraction. The location of the strut graft was confirmed using intraoperative fluoroscopy. The fusion area was stabilized with an anterior cervical plate. Postoperatively, all patients were required to wear a hard cervical collar for 2–3 months until bony callus was observed by computed tomography (CT).
We assessed a cervical plain lateral radiograph taken with the patient in the standing position preoperatively and at 1 week and 1 year postoperatively. The C2–C7 lateral Cobb angle, which was used as a global parameter to determine cervical sagittal alignment, was defined as an angle between the line on the inferior endplate of C2 and the line on the inferior endplate of C7 (
The span of the fused area was defined as the distance between the midpoint of the superior endplate of the cranial vertebra and that of the inferior endplate of the caudal vertebra (
These radiographic evaluations were performed by a trained image analyst, who measured the C2–C7 lateral Cobb angle, segmental lateral Cobb angle, and span of the fused area of 20 patients two times separately. The intraclass correlation coefficient was 0.99 (95% confidence interval [CI], 0.98–1.0) for the C2–C7 lateral Cobb angle, 0.98 (95% CI, 0.96–0.99) for the segmental lateral Cobb angle, and 1.0 (95% CI, 0.99–1.0) for the span of the fused area. Therefore, the reliabilities of the measurements were excellent.
Patients were divided into two groups (groups I and Z) according to the alignment of the autogenous fibular strut graft, as determined by the standing cervical plain lateral radiograph at 1 week and 1 year postoperatively. Group I included patients with a strut graft parallel to vertebrae, that is, the line through the axis of the strut graft was parallel to the line through the midpoints of both endplates of adjacent vertebrae (
Bony fusion was evaluated by sagittal and coronal reconstructed CT. Bony fusion in CT and plain radiographs was assessed according to the method described by Hackenberg et al. [
Radiographic evaluations with respect to the alignment of the strut graft and fusion were performed by two trained orthopedic surgeons. Intraobserver and interobserver reliability was evaluated. When intraobserver evaluations were inconsistent, the first evaluation was used. When interobserver evaluations were inconsistent, the evaluation performed by the first observer was used.
Symptoms and activities of daily life were evaluated using the Japanese Orthopaedic Association (JOA) score recovery rate for CSM, which were assessed preoperatively and at 1 year postoperatively. The complete JOA score was 17 points. The JOA score recovery ratio, a normalized value postoperatively, was calculated as follows [
Recovery ratio=(postoperative score−preoperative score)/(17−preoperative score)
We estimated the sample size to be 52 subjects based on a priori power analysis for Student's
There were 32 young (≤65 years) and 24 elderly (>65 years) patients. The young group showed a significantly greater JOA score recovery ratio than the elderly group 1 year postoperatively (young group, 0.54±0.84 and elderly group, 0.16±0.52;
No significant difference was observed in the number of resected vertebrae (number of corpectomies). The JOA score recovery ratio was 0.21±1.06 in the one-level and 0.48±0.51 in the two-level corpectomy groups (
Preoperative cervical lordosis (C2–C7 Cobb angle) did not correlate with clinical outcomes or graft subsidence. The JOA score recovery ratio was 0.43±0.94 in the non-lordosis group and 0.35±0.57 in the lordosis group (
The span of the fused area was shortened in 19, unchanged in 20, and expanded in 17 patients. There was no significant difference in the JOA score recovery ratio (
The JOA score recovery ratio 1 year postoperatively was significantly greater in group I than in group Z (0.47±0.83 and 0.25±0.58, respectively;
Bony union was radiographically observed in all patients 1 year postoperatively. The Kappa coefficient of intraobserver and interobserver agreement was 1.0. The reliability of the diagnosis was excellent.
Among the operative factors, the alignment of the strut graft 1 year postoperatively had a significant influence on graft subsidence and clinical result (OR, 10.83;
In the present study, a novel finding was that straight alignment of the strut graft provided better clinical outcomes and lower incidence of graft subsidence following ACCF. In contrast, an oblique graft may lead to increased graft subsidence and poor clinical results. Although the autogenous fibular graft is not always used because of the availability of the titanium cage and allografts, our data could indicate similar events in such patients undergoing ACCF with anterior structural support.
One advantage of the ACCF procedure is that distraction of the anterior column and correction of deformity are possible. Larger grafts can distract the anterior column, indirectly decompressing the neural elements through increased foraminal height and unbuckling of the ligamentum flavum [
A difference in the compressive forces on contacting endplates between straight and oblique strut grafts is not known. Increased pressure (force per square inch) on the endplate by an oblique graft has been suggested because the sharp edges of the oblique graft make the contacting area on the endplates smaller. However, even if the strut is set straight in vertebrae, it must be kept straight until the bony union is complete. In fact, five patients with straight strut grafts immediately postoperatively were observed to have oblique alignment 1 year postoperatively. Therefore, no significant difference was observed in the JOA score recovery rate 1 year postoperatively between those with straight and oblique strut grafts 1 week postoperatively. We believed that causative factors in the alteration of the alignment of strut grafts are complicated, and we could not identify what may have altered the alignment of the strut graft in this study. Future research should investigate the changes in the alignment of the strut graft over time.
Excessive autogenous bone graft subsidence (over 3 mm) was recently reported to be associated with poor clinical outcomes [
Other studies have shown that kyphotic deformities that accompany graft subsidence could cause further deleterious effects [
Then, which other factors induced graft subsidence? Patient age is reported to be a risk factor for graft subsidence because of low BMD, in other words, a fragile vertebral body and bony endplates are potential risk factors [
There are some limitations in this study. Although poor bone quality in the vertebra and end plate thickness should affect graft subsidence, BMD was not evaluated. However, age or sex may provide an indirect measure of BMD. In addition, there were limitations in the instrumental factors. Two types of dynamic anterior cervical plates were used in this study based on the mechanism: one as translation through the plate and the other as translation through the screw holes. We did not evaluate the differences in outcome between the types of implants. The possible impact of these differences in instruments should be evaluated in further studies.
We concluded that alignment of the strut graft significantly affected clinical outcomes and subsidence. Our results suggested that straight insertion of the strut graft in alignment with the line through adjacent vertebra and maintenance of a straight alignment until achieving bony union are important for supporting positive clinical outcomes.
Values are presented as mean±standard deviation.
JOA, Japanese Orthopaedic Association; CSM, cervical spondylotic myelopathy; OPLL, ossification of the posterior longitudinal ligament.
a)
Values are presented as mean±standard deviation.
JOA, Japanese Orthopaedic Association.
a)
Values are presented as mean±standard deviation.
JOA, Japanese Orthopaedic Association.
a)
OR, odds ratio; CI, confidence interval.