Indirect foraminal decompression after anterior lumbar interbody fusion: a prospective radiographic study using a new pedicle-to-pedicle technique

Background contextA frequently quoted advantage of anterior lumbar interbody fusion (ALIF) is indirect foraminal decompression, although there are few studies substantiating this statement. Also, there are no clinical studies using a standardized method to measure the foraminal area (FA) and the correlation with disc height (DH) parameters. This study is proposed to measure the degree of indirect foraminal decompression radiologically using a standardized method and correlate with the intervertebral disc parameters.PurposeTo standardize the foramen measurement technique. To measure indirect neural foraminal decompression in surgically operated patients after ALIF using radiographic measurement and elucidate factors affecting foraminal restoration.Study designA prospective cohort study.Patient sampleA continuous cohort of patients undergoing ALIF surgery.Outcome measuresIt included FA, foraminal height (FH), and foraminal width.MethodsThis is a prospective analysis of a single surgeon series of consecutive patients undergoing an ALIF from 2011 to 2013. Pre- and postoperative computed tomography scans were used to obtain a standardized foramen snapshot using the pedicle-to-pedicle (P-P) technique, and measurements were obtained using image j software. Radiologic parameters such as DH, local disc angle (LDA), and lumbar lordosis (LL) were measured using radiographs and Surgimap software.ResultsOne-hundred forty patients with 184 levels were operated. Anterior lumbar interbody fusion resulted in a statistically significant (p<.01) improvement in foraminal dimensions (area=67%, height=21%, and width=38%). Other parameters also significantly improved, including anterior DH (90%), posterior DH (77%), LDA, and LL (6%). Posterior DH correlated significantly with FH improvement. Statistically, the P-P technique presented with high intra- and interclass reliabilities.ConclusionsAnterior lumbar interbody fusion results in significant indirect foraminal decompression based on the new P-P technique. Posterior DH is a significant factor in the restoration of the FH.