A comparison of dynamic views using plain radiographs and thin-section three-dimensional computed tomography in the evaluation of fusion after posterior lumbar interbody fusion surgery.
BACKGROUND
Accurate evaluation of the postsurgery status of interbody fusion is important in deciding the patient's treatment. Dynamic plain radiographs are used as a convenient method, but the accuracy is not so good.


OBJECTIVE
This study aimed to evaluate the usefulness of dynamic flexion-extension radiographs as a method for evaluating fusion, by comparing it with three-dimensional thin-section computed tomography (CT).


METHODS
Prospective controlled study.


METHODS
We conducted a prospective study with 108 patients (158 levels) who, diagnosed with severe spinal stenosis and Grade I and Grade II spondylolisthesis, underwent posterior lumbar interbody fusion (PLIF) surgery, with follow-up by dynamic plain radiographs, functional rating scale, and three-dimensional (3D) thin-section CT for 1 year after surgery. In the plain radiographs, we looked for less than 3° of lordotic angle change, less than 3 mm of translation between vertebral bodies, and no presence of halo signs; satisfying all the criteria was regarded as fusion (Group A), whereas failure to satisfy any condition was referred to as probable nonfusion (Group B) and if none were satisfied as nonfusion (Group C). The patients were classified into fusion or nonfusion groups based on CT. Correlation between plain radiographs and CT groups was analyzed. Moreover, clinical assessment and cross-comparison between observers were done.


RESULTS
In 158 levels, 95 (60.8%) levels were classified into the fusion group by plain radiographs and 131 (83%) levels by CT. When we analyzed the results of each groups, in Group A, 78 (81.3%) levels belonged to the CT fusion group and 18 (18.7%) levels to the CT nonfusion group, in Group B, 51 (89.5%) and 6 (10.5%) levels, and in Group C, 2 (40%) and 3 (60%) levels, respectively. For each of the CT fusion group, a cross-comparison using dynamic radiographs reconfirmed 78 (59.5%) levels for Group A, 51 (38.9%) levels for Group B, and 2 (1.6%) levels for Group C; for the CT nonfusion groups, 18 (66.7%) levels, 6 (22.2%) levels, and 3 (11.1%) levels were for Groups A, B, and C, respectively. In clinical evaluation, all groups showed clear postsurgery improvement, but there was no statistically significant difference. In terms of observer-to-observer error and agreement between diagnoses, CT showed a statistically higher level of correlation than plain radiographs.


CONCLUSIONS
Dynamic flexion-extension radiographs cannot be seen as an objective standard in the evaluation of fusion after PLIF surgery. It would be desirable to confirm the fusion status by thin-section 3D-CT for an objective analysis.
Department of Orthopedic Surgery, Seoul National University, College of Medicine, SMG-SNU Boramae Medical Center, 425 Shindaebang-2-Dong, Seoul 156-707, Korea.
Hyeong-Seok
HS
Lee
Jae Hyup
JH
Lee
Ji-Ho
JH
Lee
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies; D011859:Radiography / Q000379:methods*; D013123:Spinal Fusion; D013168:Spondylolisthesis / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods*
3D-CT; Flexion-extension views; Interbody fusion; PLIF