SURGICAL TECHNIQUE
BMP-2-induced Neuroforaminal Bone Growth in the Setting of a Minimally Invasive Transforaminal Lumbar Interbody Fusion Junyoung Ahn, BS, Ehsan Tabaraee, MD, and Kern Singh, MD
Abstract: Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) has become a popular alternative to traditional methods of lumbar decompression and fusion. When compared with the open technique, the minimally invasive approach can result in decreased pain and blood loss as well as a shorter length of hospitalization. However, the narrower working channel through the tubular retractor increases the difficulty of decortication and bone grafting. Therefore, recombinant human bone morphogenetic proteins (rhBMP-2) is often utilized (although this is off-label) to create a more favorable interbody fusion environment. Recently, the use of rhBMP-2 has been associated with excessive bone growth in an MIS-TLIF. If this bone growth compresses the neighboring neural structures, patients may present with either new or recurrent radicular pain. Computed tomographic (CT) imaging can demonstrate heterotopic bone growth extending from the disk space into either the ipsilateral neuroforamen or lateral recess, which may result in the compression of the exiting or traversing root, respectively. The purpose of this article and the accompanying video is to demonstrate a technique for defining and resecting rhBMP-2induced heterotopic bone growth following a previous MIS-TLIF. Key Words: minimally invasive, transforaminal, lumbar fusion, BMP, bone growth (J Spinal Disord Tech 2015;28:186–188)
INDICATIONS The indication for resection of rhBMP-2-induced neuroforaminal bone growth after an MIS-TLIF includes intractable radicular symptoms with correlating radiographic (CT) evidence of lateral recess, foraminal, or central stenosis.
Received for publication March 23, 2015; accepted April 13, 2015. From the Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL. The authors declare no conflict of interest. Reprints: Kern Singh, MD, Department of Orthopaedic Surgery, Rush University Medical Center, 1611W. Harrison St, Suite #300, Chicago, IL 60612 (e-mail: [email protected]). Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Website, www.jspinaldisorders.com. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
186 | www.jspinaldisorders.com
OPERATING ROOM SET-UP Instruments/Materials Required
Curved microcurette Expandable versus fixed tubular retractors (22–26 mm) High-speed burr Intraoperative fluoroscopy (C-arm) Jackson table Kerrison rongeurs Surgical loupes or microscope
Positioning Endotracheal intubation is performed with the patient in supine position. Following successful intubation, the patient is positioned prone on a Jackson table. The shoulders should be abducted and the elbows flexed to 90 degrees. The pressure points are padded. The intraoperative fluoroscopy C-arm should be positioned across from the surgeon and side of pathology (Fig. 1).
SURGICAL TECHNIQUE Step 1: Localization The target level is identified with fluoroscopic imaging. Dependent on the extent of the previous decompression and fusion, the respective spinous processes and endplates may not be well visualized. Therefore, proper rotation should be determined by positioning the left and right pedicles equidistant from the midline on anteroposterior view.
Step 2: Incision The previous paramedian incision can be used. This incision should be lateral to the pedicle on the side of
FIGURE 1. Intraoperative photograph demonstrating prone positioning of patient on a Jackson table with appropriate padding. J Spinal Disord Tech
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Volume 28, Number 5, June 2015
J Spinal Disord Tech
Volume 28, Number 5, June 2015
BMP-2 Induced Neuroforaminal Bone Growth
The soft tissue over the connecting rod and set screws are cleared. The set screws are then loosened. The connecting rods and pedicle screws are also removed.
Step 4: Orientation The bony pedicle tracts above and below the operative level should be referenced for orientation in the setting of variable anatomy and the lack of protective structures such as the ligamentum flavum (Fig. 2).
Step 5: Skeletonization of the Superior Pedicle, Pars Interarticularis, and Inferior Pedicle FIGURE 2. Tubular retractor image demonstrating the bony overgrowth (outlined by dashed line). Note the location of the L4 pedicle (7 o’clock position) and the L5 pedicle (5 o’clock position).
the pathology and at least 2–3 cm in length. The scarred subcutaneous tissue and fascia should be incised with electrocautery to achieve hemostasis.
Step 3: Exposure and Visualization Previous decompressive surgeries and variable patterns of heterotopic bone growth in the setting of a revision MIS-TLIF may pose significant risks and challenges. Previous instrumentation should be palpated as the pedicle tulips and connecting rods are superficial to any previous decompression. Sequential dilation over this hardware may allow for placement of a self-retaining tubular retractor.
A high-speed burr is utilized to create troughs along the inferior aspect of the superior pedicle (L4 as demonstrated in the Supplementary Video, http://links.lww.com/JSDT/ A5; Fig. 3) and the superior aspect of the inferior pedicle (L5 in the Supplementary Video, http://links.lww.com/ JSDT/A5). By deepening the trough inferior to the superior pedicle, one can decompress the bone overlying the exiting nerve root. J This step must be approached with caution as it exposes the dorsal surface of the exiting nerve without a protective overlying ligamentum flavum.
Step 6: Establishment of the Floor of the Spinal Canal Under lateral fluoroscopic guidance, a high-speed burr is used to deepen the dorsal aspect of the bone growth until the floor of the spinal canal (posterior vertebral body) is established. J This step can be best accomplished at the site immediately superior to the trough located proximal to the inferior pedicle.
Step 7: Defining the Resection of the Bony Overgrowth A plane between the dorsomedial margins of the bone growth and the dura can be defined as this bony overgrowth often occurs in proximity to the transforaminal discectomy. Once the margins of the bone growth are identified, the bone can be thinned and resected with the use of a high-speed burr and rongeurs (Kerrison or pituitary).
Step 8: Decompression of the Traversing Nerve Root Identification and resection of the ventral bony overgrowth medially is essential to the complete decompression of the traversing nerve root. FIGURE 3. Tubular retractor image demonstrating the highspeed burr placement on the L4 pedicle (cross) and the residual L4 pars interarticularis. Note the location of the L5 pedicle indicated by the X sign. Copyright
r
J This bone growth can be the source of failed revision decompression and radiculopathy after an MIS-TLIF.
2015 Wolters Kluwer Health, Inc. All rights reserved. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
www.jspinaldisorders.com |
187
J Spinal Disord Tech
Ahn et al
Volume 28, Number 5, June 2015
Step 11: Mobilization of the Nerve Roots Complete decompression is best assessed when the nerve roots can be mobilized without residual tethering or kinking of the dural coverings (Fig. 4).
POSTOPERATIVE PROTOCOL Complications Violation of the dural sac (durotomy) may present as headaches (posture dependent) accompanied by nausea and/or vomiting.
FIGURE 4. Tubular retractor image demonstrating the completion of neurolysis and ventral decompression resulting in the mobilization of the L4 exiting nerve root (arrow). The decompressed transforaminal space is outlined (dashed line).
Step 9: Full Decompression of the Exiting Nerve Root The decompression of this ventral bony overgrowth extends in the lateral direction to fully decompress the undersurface of the exiting nerve root following visualization.
Step 10: Neurolysis of the Exiting Nerve Root Angled microcurettes are utilized to remove residual bone growth fragments and adhesions are from the exiting nerve root. J During this portion of the procedure, microcurette should be directed away from the dural sac to prevent an incidental durotomy.
188 | www.jspinaldisorders.com
J Most cases of durotomy may be adequately treated with a collagen sponge and fibrin glue. ’ If the patient is asymptomatic, early postoperative mobilization is recommended. ’ If patient is symptomatic (headaches, photophobia), 23 hours of bed rest is recommended followed by mobilization.
PEARLS AND PITFALLS Following removal of previous instrumentation, the borders of the pedicles should be referenced to orient oneself to the mediolateral and superoinferior margins of the revision decompression. Fluoroscopic guidance in the lateral view is important in identifying the floor of the spinal canal to avoid neural injury. During the neurolysis of the exiting nerve root, directing the microcurette distally helps avoid dural injury. Decompression of the ventral aspect of the exiting nerve root is crucial to free the root from any residual bone growth extending from the floor of the canal to the nerve root.
Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
BMP-2-induced Neuroforaminal Bone Growth in the Setting of a Minimally Invasive Transforaminal Lumbar Interbody Fusion Junyoung Ahn, BS, Ehsan Tabaraee, MD, and Kern Singh, MD
Abstract: Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) has become a popular alternative to traditional methods of lumbar decompression and fusion. When compared with the open technique, the minimally invasive approach can result in decreased pain and blood loss as well as a shorter length of hospitalization. However, the narrower working channel through the tubular retractor increases the difficulty of decortication and bone grafting. Therefore, recombinant human bone morphogenetic proteins (rhBMP-2) is often utilized (although this is off-label) to create a more favorable interbody fusion environment. Recently, the use of rhBMP-2 has been associated with excessive bone growth in an MIS-TLIF. If this bone growth compresses the neighboring neural structures, patients may present with either new or recurrent radicular pain. Computed tomographic (CT) imaging can demonstrate heterotopic bone growth extending from the disk space into either the ipsilateral neuroforamen or lateral recess, which may result in the compression of the exiting or traversing root, respectively. The purpose of this article and the accompanying video is to demonstrate a technique for defining and resecting rhBMP-2induced heterotopic bone growth following a previous MIS-TLIF. Key Words: minimally invasive, transforaminal, lumbar fusion, BMP, bone growth (J Spinal Disord Tech 2015;28:186–188)
INDICATIONS The indication for resection of rhBMP-2-induced neuroforaminal bone growth after an MIS-TLIF includes intractable radicular symptoms with correlating radiographic (CT) evidence of lateral recess, foraminal, or central stenosis.
Received for publication March 23, 2015; accepted April 13, 2015. From the Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL. The authors declare no conflict of interest. Reprints: Kern Singh, MD, Department of Orthopaedic Surgery, Rush University Medical Center, 1611W. Harrison St, Suite #300, Chicago, IL 60612 (e-mail: [email protected]). Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Website, www.jspinaldisorders.com. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
186 | www.jspinaldisorders.com
OPERATING ROOM SET-UP Instruments/Materials Required
Curved microcurette Expandable versus fixed tubular retractors (22–26 mm) High-speed burr Intraoperative fluoroscopy (C-arm) Jackson table Kerrison rongeurs Surgical loupes or microscope
Positioning Endotracheal intubation is performed with the patient in supine position. Following successful intubation, the patient is positioned prone on a Jackson table. The shoulders should be abducted and the elbows flexed to 90 degrees. The pressure points are padded. The intraoperative fluoroscopy C-arm should be positioned across from the surgeon and side of pathology (Fig. 1).
SURGICAL TECHNIQUE Step 1: Localization The target level is identified with fluoroscopic imaging. Dependent on the extent of the previous decompression and fusion, the respective spinous processes and endplates may not be well visualized. Therefore, proper rotation should be determined by positioning the left and right pedicles equidistant from the midline on anteroposterior view.
Step 2: Incision The previous paramedian incision can be used. This incision should be lateral to the pedicle on the side of
FIGURE 1. Intraoperative photograph demonstrating prone positioning of patient on a Jackson table with appropriate padding. J Spinal Disord Tech
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Volume 28, Number 5, June 2015
J Spinal Disord Tech
Volume 28, Number 5, June 2015
BMP-2 Induced Neuroforaminal Bone Growth
The soft tissue over the connecting rod and set screws are cleared. The set screws are then loosened. The connecting rods and pedicle screws are also removed.
Step 4: Orientation The bony pedicle tracts above and below the operative level should be referenced for orientation in the setting of variable anatomy and the lack of protective structures such as the ligamentum flavum (Fig. 2).
Step 5: Skeletonization of the Superior Pedicle, Pars Interarticularis, and Inferior Pedicle FIGURE 2. Tubular retractor image demonstrating the bony overgrowth (outlined by dashed line). Note the location of the L4 pedicle (7 o’clock position) and the L5 pedicle (5 o’clock position).
the pathology and at least 2–3 cm in length. The scarred subcutaneous tissue and fascia should be incised with electrocautery to achieve hemostasis.
Step 3: Exposure and Visualization Previous decompressive surgeries and variable patterns of heterotopic bone growth in the setting of a revision MIS-TLIF may pose significant risks and challenges. Previous instrumentation should be palpated as the pedicle tulips and connecting rods are superficial to any previous decompression. Sequential dilation over this hardware may allow for placement of a self-retaining tubular retractor.
A high-speed burr is utilized to create troughs along the inferior aspect of the superior pedicle (L4 as demonstrated in the Supplementary Video, http://links.lww.com/JSDT/ A5; Fig. 3) and the superior aspect of the inferior pedicle (L5 in the Supplementary Video, http://links.lww.com/ JSDT/A5). By deepening the trough inferior to the superior pedicle, one can decompress the bone overlying the exiting nerve root. J This step must be approached with caution as it exposes the dorsal surface of the exiting nerve without a protective overlying ligamentum flavum.
Step 6: Establishment of the Floor of the Spinal Canal Under lateral fluoroscopic guidance, a high-speed burr is used to deepen the dorsal aspect of the bone growth until the floor of the spinal canal (posterior vertebral body) is established. J This step can be best accomplished at the site immediately superior to the trough located proximal to the inferior pedicle.
Step 7: Defining the Resection of the Bony Overgrowth A plane between the dorsomedial margins of the bone growth and the dura can be defined as this bony overgrowth often occurs in proximity to the transforaminal discectomy. Once the margins of the bone growth are identified, the bone can be thinned and resected with the use of a high-speed burr and rongeurs (Kerrison or pituitary).
Step 8: Decompression of the Traversing Nerve Root Identification and resection of the ventral bony overgrowth medially is essential to the complete decompression of the traversing nerve root. FIGURE 3. Tubular retractor image demonstrating the highspeed burr placement on the L4 pedicle (cross) and the residual L4 pars interarticularis. Note the location of the L5 pedicle indicated by the X sign. Copyright
r
J This bone growth can be the source of failed revision decompression and radiculopathy after an MIS-TLIF.
2015 Wolters Kluwer Health, Inc. All rights reserved. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
www.jspinaldisorders.com |
187
J Spinal Disord Tech
Ahn et al
Volume 28, Number 5, June 2015
Step 11: Mobilization of the Nerve Roots Complete decompression is best assessed when the nerve roots can be mobilized without residual tethering or kinking of the dural coverings (Fig. 4).
POSTOPERATIVE PROTOCOL Complications Violation of the dural sac (durotomy) may present as headaches (posture dependent) accompanied by nausea and/or vomiting.
FIGURE 4. Tubular retractor image demonstrating the completion of neurolysis and ventral decompression resulting in the mobilization of the L4 exiting nerve root (arrow). The decompressed transforaminal space is outlined (dashed line).
Step 9: Full Decompression of the Exiting Nerve Root The decompression of this ventral bony overgrowth extends in the lateral direction to fully decompress the undersurface of the exiting nerve root following visualization.
Step 10: Neurolysis of the Exiting Nerve Root Angled microcurettes are utilized to remove residual bone growth fragments and adhesions are from the exiting nerve root. J During this portion of the procedure, microcurette should be directed away from the dural sac to prevent an incidental durotomy.
188 | www.jspinaldisorders.com
J Most cases of durotomy may be adequately treated with a collagen sponge and fibrin glue. ’ If the patient is asymptomatic, early postoperative mobilization is recommended. ’ If patient is symptomatic (headaches, photophobia), 23 hours of bed rest is recommended followed by mobilization.
PEARLS AND PITFALLS Following removal of previous instrumentation, the borders of the pedicles should be referenced to orient oneself to the mediolateral and superoinferior margins of the revision decompression. Fluoroscopic guidance in the lateral view is important in identifying the floor of the spinal canal to avoid neural injury. During the neurolysis of the exiting nerve root, directing the microcurette distally helps avoid dural injury. Decompression of the ventral aspect of the exiting nerve root is crucial to free the root from any residual bone growth extending from the floor of the canal to the nerve root.
Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
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