Symptomatic Neuroforaminal Bony Overgrowth after Transforaminal Lumbar Interbody Fusion with BMP

Presented at SMISS Annual Forum 2014
By Anton Jorgensen MD
With Kern Singh MD, Sreeharsha Nandyala BA, Alejandro Marquez-Lara MD, Islam Elboghdady , Eric Sundberg MD, Abbas Naqvi BS, Hamid Hassanzadeh MD, Khaled Aboushaala MD, Spencer Leblang ,

Disclosures: Anton Jorgensen MD None Kern Singh MD A; CSRS Resident Grant. B; DePuy, Zimmer, Stryker, CSRS, ISASS, AAOS, SRS, Vertebral Column - ISASS. D; Avaz Surgical, LLC, Vital 5, LLC. F; Zimmer, Stryker, Pioneer, Lippincott Williams & Wilkins, Th, Sreeharsha Nandyala BA None, Alejandro Marquez-Lara MD None, Islam Elboghdady None, Eric Sundberg MD None, Abbas Naqvi BS None, Hamid Hassanzadeh MD None, Khaled Aboushaala MD None, Spencer Leblang None,

Introduction:
BMP has been demonstrated to induce differentiation of osteoblasts leading to new bone formation. This study radiographically characterizes BMP associated heterotopic bone formation associated with radiculopathy following an MIS TLIF.

Aims/Objectives:
To identify patterns of symptomatic neuroforaminal bony overgrowth in patients who have undergone a minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) augmented with bone morphogenetic protein (BMP).

Methods:
A radiographic analysis of patients who underwent TLIF with a cage and BMP performed by a single surgeon between the years of 2008 and 2012 was performed. Medical records were reviewed to identify patients who developed recalcitrant postoperative radiculopathy. CT scans of the symptomatic patients were analyzed in order to identify patterns of bony overgrowth. An asymptomatic control group that also underwent postoperative CT scan was analyzed for comparison. The patterns of bony overgrowth were characterized on axial and sagittal images. Unpaired t-tests were performed comparing the amount of bony neuroforaminal overgrowth in symptomatic and asymptomatic patients.

Results:
A total of 360 patients were identified of which thirty patients developed intractable radiculopathy. Post-operative CT scans in twenty of those patients were compared to post-operative CT scans in a group of thirteen asymptomatic controls. The mean area of bony overgrowth in the foraminal level was 30 mm2 in symptomatic patients versus 0 mm2 in controls (p=0.12). The mean area of overgrowth in the disc level was 149 mm2 in symptomatic patients versus 84 mm2 in controls (p=0.08). The mean area of overgrowth in the pedicle level was 91 mm2 in symptomatic patients versus 16 mm2 in controls (p=0.03). Sagittal differences in areas between symptomatic and asymptomatic patients did not reach statistical significance.

Conclusions:
In patients who have undergone MIS TLIF with BMP, there is an association between recalcitrant post-operative radiculopathy and neuroforaminal bony overgrowth as measured on axial CT scan imaging at the pedicle level.