Evaluation Of Posterior Lumbar Interbody Fusion With Spinal Instrumentation

Since the initial spinal fusion operation was performed for tuberculosis, the indications for spinal fusion have expanded to a varies of disorders. The goal of any spinal fusion is to obtain a solid arthrodesis. Before one can determine whether spinal fusion is efficacious for a specific clinical condition, one must be able to assess the status of the fusion. The status of a spinal fusion also becomes important if a patient who has undergone a spinal arthrodesis presents with new or recurrent spinal symptoms or progressive spinal deformity. It is difficulty for the imaging techniques to assess the status of a spinal fusion accurately. The use of spinal instrumention such as transpedicular instrumentation or interbody devices presents new challenges in the determination of fusion status. Metal devices obscure the central bone graft, making it difficult to see if the bone graft has matured or remodeled or iftrabeculations have formed between the graft and host bone and limit segmental motion. Since the beginning of fusion surgery, there is no consensus regarding the best non-invasive method to evaluation of interbody fusion. Surgical exploration is still remains "golden standard", degree of confidence of all imaging techniques were based on results compared with surgical exploration. There is no feasible to re-operate on each patient undergoing lumbar fusion especially where post-operatively the patient has minimal or no symptoms. So, it therefore becomes imperative to have a reliable non-invasive method of assessing fusion. Over the past several years, CT has become one of the most important diagnostic modalities in evaluation of spinal fusion. To evaluate the accuracy of the interpretation of thin-section helical CT including two-dimensional (2D) multiplanar reformations (MPR) and three-dimensional reconstructions for diagnosing solid spinal arthrodesis in patients with spinal instrumentation, thirty-four patients undergoing posterior lumbar interbody fusion (PLIF) were prospectively evaluated with the thin-section helical CT scan including 2D-MPR and 3D reconstructions and compared with the results of direct surgical exploration of the solidity of the fusion at each level in every patient.Materials and Methods34 patients undergoing posterior lumbar interbody fusion (PLIF) with spinal instrumentation .There were 15 men and 19 women, with an avarage age of45.97 years. Isthmic spondylolisthesis 5 cases, disc degeneration 15cases, lumbar instability 16 cases. The average time of hardware removal was 20.26 months from time of surgury. Fusion material : autologous iliac crest grafts 30 cases, titanium mesh cage 2 cases, carbon fiber cage 2cases. Pedicle screws were all made of titanium. All patients were scanned on GE Light Speed ^?16 CT Scanners (General Electric Compony, American). The parameters of thin-section helical CT scan :16 slices /HE, 0.625mm thick, 0.625mm interval, 140KV, 200-250 MA, 1s/HE. Numerical data was dealed with AW 4.2 postprocessing software. The helical CT Scans were reformatted to produce continuos series of 2D multiplanar reformations (MPR) in the axial sagital and coronal planes or 3D reconstructions imagings. Then direct surgical exploration was performed at the time of hardware removal by an experienced spinal surgeon to evaluate status of interbody fusion. CT scans and direct surgical exploration were reviewed blind and independently by a single radiologist and a single spinal surgeon. The results of CT and direct surgical exploration were compared using KAPPA statistics to measure agreement between two rating methods of fusion. The magnitude of the KAPPA statistic was interpreted as follows:0.75 < KAPPA < 1.00 excellent agreement beyond chance. 0.40 < KAPPA <0.75 fair to good agreement beyond chance. Kappa <0.40 poor agreement.ResultsFusion rate of CT scans was 60.47%, surgical exploration 65.12%.KAPPA statistic =0.801, K < 0.05. Agreement between thin-section helical CT scan including 2D-MPR and 3D reconstructions and direct surgical exploration was excellent. The sensibility of thin-section helical CT scan evaluation of lumbar interbody fusion was 89.29%. Specificity was 93.33%. Accuracy was 90.70%. False positive rate 3.85%, false negative rate 17.65%.Conclussion1. Agreement between thin-section helical CT scan including 2D-MPR and 3D reconstructions and direct surgical exploration was excellent.2. The thin-section helical CT scans including 2D-MPR and 3D reconstructions offer the best acurracy for evaluation of lumbar interbody fusion,even when there were spinal instrumentations exsisted. Metal devices have no interfere with assessment of lumbar interbody fusion by thin-section helical CTscanning.3. Should reoperation be indicated clinically, the detailed anatomy demonstrated on the CT scan should prove very useful in planning the reoperation.4. There is still no agreement on the best way of determining fusion orther than surgical exploration, which continues toremain the "gold standard".