Technical Note
Rectangular Tubular Retractor for Microendoscopic Lumbar Decompression Motohide Shibayama1
1 Department of Orthopaedic Surgery, Aichi Spine Institute, Niwa-gun,
Aichi, Japan J Neurol Surg A
Abstract
Keywords
► paravertebral muscle ► lumbar spinal stenosis ► minimally invasive surgery
Background A cylindrical working tube with a diameter of 16 mm has been used for endoscopic posterior lumbar spinal surgery. However, intraoperative muscle resection is significant when using the current conventional tubular retractor. Objective To describe a novel tubular retractor for microendoscopic surgery and to analyze the outcomes of lumbar decompressive laminotomy using this retractor. Materials and Methods We devised a novel tubular retractor by changing the medial and lateral sides of the conventional 16-mm cylindrical tubular retractor to planes with a mediolateral dimension of 10 mm (rectangular tubular retractor hereafter). The amount of muscle resection, osteotomy angle on the approach side, and operating time were compared between 25 intervertebral levels treated by bilateral decompression through a unilateral approach using the rectangular tubular retractor and 31 intervertebral levels treated with the same surgery using a 16-mm cylindrical tubular retractor. Results Due to the short mediolateral dimension, muscle resection decreased by 86%. The rectangular tubular retractor also decreased early postoperative wound pain. Because the craniocaudal dimension of the tubular retractor was maintained, surgical difficulty did not increase, resulting in only a slight increase in operating time. The facet joint on the approach side could be sufficiently preserved. Conclusions The rectangular tubular retractor reduced surgical invasiveness without increasing surgical difficulty.
Introduction As a minimally invasive spinal surgical technique, we have performed surgery using a microendoscope and the METRx 16-mm cylindrical tubular retractor (Medtronic, Memphis, Tennessee, United States; ►Fig. 1).1–8 Serial cylindrical dilators are placed sequentially, and the tubular retractor is then placed over them. However, the multifidus muscle remains partly at the end of the tubular retractor and enters the tubular retractor when it is moved. Because these tissues must be resected, muscle damage is significant.
received November 22, 2014 accepted after revision September 30, 2015
Address for correspondence Shu Nakamura, MD, PhD, Department of Orthopaedic Surgery, Aichi Spine Institute, 41 Gouhigashi, Takao, Fuso-cho, Niwa-gun, Aichi 480-0102, Japan (e-mail: [email protected]).
If the retractor diameter is reduced, muscle damage may decrease, but operability and visibility may be compromised. Even when using the conventional 16-mm cylindrical tubular retractor, the level of surgical difficulty is high. Increased technical difficulty is associated with longer operative times and more extensive facet resection. It may also lead to increased risks of insufficient decompression and surgeryrelated complications. We devised a novel tubular retractor for microendoscopic posterior lumbar spinal surgery in an effort to reduce the extent of intraoperative muscle resection without increasing the level of surgical difficulty.
© Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0035-1570006. ISSN 2193-6315.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Shu Nakamura1
Rectangular Tubular Retractor for Lumbar Decompression
Nakamura, Shibayama
Unlike the conventional cylindrical tubular retractor, the retractor part (►Figs. 2 and 3A) is an almost rectangular tube (rectangular tubular retractor hereafter). Medial and lateral sides of the retractor part of the 16-mm cylindrical tubular retractor were changed to planes with a mediolateral dimension of 10 mm (external dimension). Cranial and caudal sides have curved surfaces to maintain the length (craniocaudal dimension) of the retractor part to 16 mm (radius of curvature is 8 mm). The upper part has a cylindrical shape, the same as that of the 16-mm cylindrical retractor, allowing application of the microendoscope attachment of the METRx system. Dilators are plates inserted serially into one side of the spinous process, and the tubular retractor is passed over them.
Patients
Fig. 1 Microendoscope and cylindrical tubular retractor of the METRx system (Medtronic, Memphis, Tennessee, United States).
This study was a prospective nonselected consecutive case series study. The subjects consisted of 31 intervertebral levels (26 patients) with lumbar spinal canal stenosis who underwent surgery using a 16-mm cylindrical tubular retractor (16-mm cylindrical tubular retractor group) and 25 intervertebral levels (21 patients) with lumbar spinal canal stenosis that underwent surgery using the rectangular tubular retractor (rectangular tubular retractor group) from October 2012 to May 2013. The former group was treated earlier than the latter group, and the subjects in each group were consecutive patients. Indications did not differ between the two groups. Mean age did not differ significantly (unpaired t test, p ¼ 0.159) between the 16-mm cylindrical tubular retractor group (68.5 9.9 years) and the rectangular tubular
Fig. 2 Rectangular tubular retractor. Medial and lateral sides of the retractor have planes with a mediolateral dimension of 10 mm. Cranial and caudal sides have curved surfaces with a craniocaudal dimension of 16 mm (radius of curvature: 8 mm). The rectangular tubular retractor can be inserted after insertion of serial plate dilators.
Journal of Neurological Surgery—Part A
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Materials and Methods
Rectangular Tubular Retractor for Lumbar Decompression
Nakamura, Shibayama
In all patients, microendoscopic bilateral decompression was performed by the first author through a unilateral approach using similar instruments except for the tubular retractor. Under general anesthesia, patients were placed in the prone position. Fluoroscopy was used to confirm the spinal level. A longitudinal paramedian skin incision was made (18 mm in length in the 16-mm cylindrical tubular retractor group and 15 mm in the rectangular tubular retractor group). The fascia immediately below was incised, and the unilateral side of the spinous process was bluntly detached. Each set of dilators and each type of tubular retractor were inserted, and the microendoscope was attached to the retractor (►Figs. 1 and 4A). The tip of the suction port of the microendoscope attachment was obliquely cut and bent to allow water injection and washing of the scope end (►Fig. 4B). A bipolar coagulator was used only to stop bleeding. Osteotomy was performed using conventional surgical burrs and an original curved chisel.9 Bone fragments resulting from osteotomy and the yellow ligament were removed using a conventional punch and 4.0-mm curved micro-rongeur (Richard Wolf, Knittlingen, Germany) for percutaneous endoscopic surgery.
Evaluation
Fig. 3 (A) A comparison of width between the rectangular tubular retractor (right) and the 16-mm cylindrical tubular retractor (left). The width of the rectangular tubular retractor is 10 mm, only two thirds the width of the cylindrical tubular retractor. (B) Endoscopic view of the 16-mm cylindrical tubular retractor. (C) Endoscopic view of the rectangular tubular retractor. The rectangular tubular retractor provides an adequate visual field. The total working portal areas of the 16mm cylindrical tubular retractor and the rectangular tubular retractor are 177 mm 2 and 124 mm2 , respectively.
retractor group (71.3 9.2 years). Mean preoperative visual analog scale (VAS) score also did not differ significantly (unpaired t test, p ¼ 0.490) between the 16-mm cylindrical tubular retractor group (75.9 22.4) and the rectangular tubular retractor group (75.8 17.2). The surgically treated levels were L3–L4 for 8 intervertebral levels, L4–L5 for 17, and L5–S1 for 6 in the 16-mm cylindrical tubular retractor group, and L2–L3 for 1 intervertebral level, L3–L4 for 8, L4–L5 for 12, and L5–S1 for 4 in the rectangular tubular retractor group.
The following items were assessed in all patients. As a parameter of muscle preservation, the amount of muscle tissue resection during surgery was measured. Muscle that entered into the retractor was removed with a punch, and all resected muscle was brought together in gauze. Blood associated with muscle was absorbed in the gauze, and only muscle was measured without drying. As a parameter of facet joint preservation, the angle of osteotomy of the medial facet joint on the approach side was measured. This angle was determined in a POP-net web server (Image ONE Co., Tokyo, Japan) of a Digital Imaging and Communications in Medicine (DICOM) viewer as that between the horizontal plane (a line connecting the ventral margins of the left and right superior articular processes) and the approach-side facet joint osteotomy line on cross-sectional computed tomography (CT) images at the middle of the intervertebral disk (►Fig. 5). Improvement rate based on VAS score (range: 0–100) for leg symptoms was calculated as follows: (preoperative score postoperative score)/(preoperative score) 100%. Severity of early postoperative wound pain was evaluated using a VAS in the evening of the day after surgery. Differences between the two groups were analyzed using the unpaired t test, and p values < 0.05 were regarded as significant. We determined the virtual segmental weight of the multifidus muscle at the operated level as a measure for judging the amount of muscle resected. Virtual segmental muscle weight was estimated as described later. On cross-sectional preoperative CT images of 20 cases selected at random, the volume of the multifidus muscle was determined unilaterally in the range of 20-mm length in the craniocaudal direction at the L4–L5 level. Then mean virtual segmental muscle weight was determined with a specific gravity of 1.1. The “20-mm length” was derived from the mean length of 19.3 mm determined for the osteotomy holes of the 20 cases. Journal of Neurological Surgery—Part A
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Surgery
Nakamura, Shibayama
Fig. 4 (A) An intraoperative picture of the rectangular tubular retractor and its assembly. (B) The tip of the suction port of the microendoscope attachment was obliquely cut and bent to allow water injection and washing of the scope end.
Fig. 5 (A) Osteotomy angle of the medial facet on the approach side was determined by the osteotomy line of the medial facet (line a) and a horizontal line (line b). (B) A case in the 16-mm cylindrical tubular retractor group, with an osteotomy angle of 73 degrees. (C) A case in the rectangular tubular retractor group, with an osteotomy angle of 74 degrees.
Results Mean amount of muscle resection (per intervertebral level) was 1.95 g in the 16-mm cylindrical tubular retractor group and 0.27 g in the rectangular tubular retractor group (p < 0.001). A decrease of 86% was shown in the rectangular tubular retractor group. Mean osteotomy angle was similar between the 16-mm cylindrical tubular retractor group (78.6 degrees) and the rectangular tubular retractor Journal of Neurological Surgery—Part A
group (77.6 degrees) (p ¼ 0.293). Mean operating time was 62.0 minutes in the 16-mm cylindrical tubular retractor group and 71.0 minutes in the rectangular tubular retractor group, demonstrating only a 9-minute prolongation in the rectangular tubular retractor group (p < 0.001). Skin incision length was 18 mm and 15 mm in the 16-mm cylindrical tubular retractor and rectangular tubular retractor groups, respectively (these are not the actual incision lengths measured postoperatively but rather that of the line drawn
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Rectangular Tubular Retractor for Lumbar Decompression
preoperatively). Mean intraoperative blood loss was similar between the 16-mm cylindrical tubular retractor group (51.0 mL) and the rectangular tubular retractor group (47.2 mL) (p ¼ 0.318). Mean follow-up time was 8.7 months (range: 3–12 months) in the 16-mm cylindrical tubular retractor group and 7.5 months (range: 3–12 months) in the rectangular tubular retractor group. Mean improvement rate of leg symptoms was similar between the 16-mm cylindrical tubular retractor group (69.7%) and the rectangular tubular retractor group (71.2%) (p ¼ 0.418). Mean VAS score for early postoperative wound pain was 20.5 in the 16-mm cylindrical tubular retractor group and 11.0 in the rectangular tubular retractor group (p < 0.005). Wound pain in the rectangular tubular retractor group was significantly less than that in the cylindrical tubular retractor group, although the difference was not large (►Table 1). Virtual segmental muscle weight was estimated to be 12.2 g.
Discussion Surgery using a 16-mm cylindrical tubular retractor and microendoscope, such as those of the METRx system, is currently considered to reduce the amount of exposure compared with the conventional technique, thereby reducing muscle damage.7,8 However, even this method requires a considerable amount of muscle resection. As shown in ►Fig. 6, when the bone surface is observed from the dorsal side, the osteotomy hole is close to a narrow rectangle. Therefore, the ratio of exposure in the lateral direction to that in the craniocaudal direction may be markedly low. The width of the osteotomy hole lateral to the spinous process is less than half of 16 mm. Because the 16-mm cylindrical tubular retractor is excessive, the amount of muscle resection increases. On the contrary, the rectangular tubular retractor has a short width (mediolateral dimension) and can reduce the amount of muscle resection. When the width of the tubular retractor is short, muscle entry into the retractor, which occurs when the retractor is tilted to the left and right, decreases. In addition, even in the presence of dorsal thickening of the lateral area due to facet joint deformation,
Nakamura, Shibayama
Fig. 6 Comparison of osteotomy hole size and the cross-section areas of the 16-mm cylindrical tubular retractor and rectangular tubular retractor. When the bone surface is observed from the dorsal side, the dotted white line indicates the 16-mm cylindrical tubular retractor; the black line indicates the rectangular tubular retractor. The crosssectional area of the 16-mm cylindrical tubular retractor is excessively wide compared with the width of the osteotomy hole lateral to the spinous process.
contact between the tubular retractor tip and the vertebral arch is less markedly obstructed due to the short width of the tubular retractor. Concerning the length (craniocaudal dimension) of the tubular retractor, that of the 16-mm cylindrical tubular retractor is even shorter than the osteotomy hole. Therefore, a reduction in tubular retractor length is not necessary. Thus to preserve muscle, a rectangular tubular retractor with a short width is more advantageous. In this study, the mean amount of muscle resection in the 16-mm cylindrical tubular retractor group was 1.95 g, which is 16% of the virtual segmental muscle weight (12.2 g). This amount is too large and needs to be reduced. It is significant that the mean amount of muscle resection in the rectangular tubular retractor group was 0.27 g, a reduction of 86% when compared with the 16-mm cylindrical tubular retractor group. If a small-caliber cylindrical tubular retractor with reduced width and length is used to further reduce invasiveness, the working space for surgical instruments decreases,
Table 1 Results 16 mm cylindrical
Rectangular
p value
Muscle resection, g
1.95 0.63
0.27 0.12
< 0.001
Osteotomy angle, degrees
78.6 7.4
77.6 6.2
0.293
NS
Operation time, min Skin incision, mm
a
62.0 6.8
71.0 5.8
< 0.001
18
15
–
–
Blood loss, mL
51.0 30.4
47.2 28.4
0.318
NS
Wound pain, VAS
20.5 12.4
11.0 9.6
Rectangular Tubular Retractor for Microendoscopic Lumbar Decompression Motohide Shibayama1
1 Department of Orthopaedic Surgery, Aichi Spine Institute, Niwa-gun,
Aichi, Japan J Neurol Surg A
Abstract
Keywords
► paravertebral muscle ► lumbar spinal stenosis ► minimally invasive surgery
Background A cylindrical working tube with a diameter of 16 mm has been used for endoscopic posterior lumbar spinal surgery. However, intraoperative muscle resection is significant when using the current conventional tubular retractor. Objective To describe a novel tubular retractor for microendoscopic surgery and to analyze the outcomes of lumbar decompressive laminotomy using this retractor. Materials and Methods We devised a novel tubular retractor by changing the medial and lateral sides of the conventional 16-mm cylindrical tubular retractor to planes with a mediolateral dimension of 10 mm (rectangular tubular retractor hereafter). The amount of muscle resection, osteotomy angle on the approach side, and operating time were compared between 25 intervertebral levels treated by bilateral decompression through a unilateral approach using the rectangular tubular retractor and 31 intervertebral levels treated with the same surgery using a 16-mm cylindrical tubular retractor. Results Due to the short mediolateral dimension, muscle resection decreased by 86%. The rectangular tubular retractor also decreased early postoperative wound pain. Because the craniocaudal dimension of the tubular retractor was maintained, surgical difficulty did not increase, resulting in only a slight increase in operating time. The facet joint on the approach side could be sufficiently preserved. Conclusions The rectangular tubular retractor reduced surgical invasiveness without increasing surgical difficulty.
Introduction As a minimally invasive spinal surgical technique, we have performed surgery using a microendoscope and the METRx 16-mm cylindrical tubular retractor (Medtronic, Memphis, Tennessee, United States; ►Fig. 1).1–8 Serial cylindrical dilators are placed sequentially, and the tubular retractor is then placed over them. However, the multifidus muscle remains partly at the end of the tubular retractor and enters the tubular retractor when it is moved. Because these tissues must be resected, muscle damage is significant.
received November 22, 2014 accepted after revision September 30, 2015
Address for correspondence Shu Nakamura, MD, PhD, Department of Orthopaedic Surgery, Aichi Spine Institute, 41 Gouhigashi, Takao, Fuso-cho, Niwa-gun, Aichi 480-0102, Japan (e-mail: [email protected]).
If the retractor diameter is reduced, muscle damage may decrease, but operability and visibility may be compromised. Even when using the conventional 16-mm cylindrical tubular retractor, the level of surgical difficulty is high. Increased technical difficulty is associated with longer operative times and more extensive facet resection. It may also lead to increased risks of insufficient decompression and surgeryrelated complications. We devised a novel tubular retractor for microendoscopic posterior lumbar spinal surgery in an effort to reduce the extent of intraoperative muscle resection without increasing the level of surgical difficulty.
© Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0035-1570006. ISSN 2193-6315.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Shu Nakamura1
Rectangular Tubular Retractor for Lumbar Decompression
Nakamura, Shibayama
Unlike the conventional cylindrical tubular retractor, the retractor part (►Figs. 2 and 3A) is an almost rectangular tube (rectangular tubular retractor hereafter). Medial and lateral sides of the retractor part of the 16-mm cylindrical tubular retractor were changed to planes with a mediolateral dimension of 10 mm (external dimension). Cranial and caudal sides have curved surfaces to maintain the length (craniocaudal dimension) of the retractor part to 16 mm (radius of curvature is 8 mm). The upper part has a cylindrical shape, the same as that of the 16-mm cylindrical retractor, allowing application of the microendoscope attachment of the METRx system. Dilators are plates inserted serially into one side of the spinous process, and the tubular retractor is passed over them.
Patients
Fig. 1 Microendoscope and cylindrical tubular retractor of the METRx system (Medtronic, Memphis, Tennessee, United States).
This study was a prospective nonselected consecutive case series study. The subjects consisted of 31 intervertebral levels (26 patients) with lumbar spinal canal stenosis who underwent surgery using a 16-mm cylindrical tubular retractor (16-mm cylindrical tubular retractor group) and 25 intervertebral levels (21 patients) with lumbar spinal canal stenosis that underwent surgery using the rectangular tubular retractor (rectangular tubular retractor group) from October 2012 to May 2013. The former group was treated earlier than the latter group, and the subjects in each group were consecutive patients. Indications did not differ between the two groups. Mean age did not differ significantly (unpaired t test, p ¼ 0.159) between the 16-mm cylindrical tubular retractor group (68.5 9.9 years) and the rectangular tubular
Fig. 2 Rectangular tubular retractor. Medial and lateral sides of the retractor have planes with a mediolateral dimension of 10 mm. Cranial and caudal sides have curved surfaces with a craniocaudal dimension of 16 mm (radius of curvature: 8 mm). The rectangular tubular retractor can be inserted after insertion of serial plate dilators.
Journal of Neurological Surgery—Part A
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Materials and Methods
Rectangular Tubular Retractor for Lumbar Decompression
Nakamura, Shibayama
In all patients, microendoscopic bilateral decompression was performed by the first author through a unilateral approach using similar instruments except for the tubular retractor. Under general anesthesia, patients were placed in the prone position. Fluoroscopy was used to confirm the spinal level. A longitudinal paramedian skin incision was made (18 mm in length in the 16-mm cylindrical tubular retractor group and 15 mm in the rectangular tubular retractor group). The fascia immediately below was incised, and the unilateral side of the spinous process was bluntly detached. Each set of dilators and each type of tubular retractor were inserted, and the microendoscope was attached to the retractor (►Figs. 1 and 4A). The tip of the suction port of the microendoscope attachment was obliquely cut and bent to allow water injection and washing of the scope end (►Fig. 4B). A bipolar coagulator was used only to stop bleeding. Osteotomy was performed using conventional surgical burrs and an original curved chisel.9 Bone fragments resulting from osteotomy and the yellow ligament were removed using a conventional punch and 4.0-mm curved micro-rongeur (Richard Wolf, Knittlingen, Germany) for percutaneous endoscopic surgery.
Evaluation
Fig. 3 (A) A comparison of width between the rectangular tubular retractor (right) and the 16-mm cylindrical tubular retractor (left). The width of the rectangular tubular retractor is 10 mm, only two thirds the width of the cylindrical tubular retractor. (B) Endoscopic view of the 16-mm cylindrical tubular retractor. (C) Endoscopic view of the rectangular tubular retractor. The rectangular tubular retractor provides an adequate visual field. The total working portal areas of the 16mm cylindrical tubular retractor and the rectangular tubular retractor are 177 mm 2 and 124 mm2 , respectively.
retractor group (71.3 9.2 years). Mean preoperative visual analog scale (VAS) score also did not differ significantly (unpaired t test, p ¼ 0.490) between the 16-mm cylindrical tubular retractor group (75.9 22.4) and the rectangular tubular retractor group (75.8 17.2). The surgically treated levels were L3–L4 for 8 intervertebral levels, L4–L5 for 17, and L5–S1 for 6 in the 16-mm cylindrical tubular retractor group, and L2–L3 for 1 intervertebral level, L3–L4 for 8, L4–L5 for 12, and L5–S1 for 4 in the rectangular tubular retractor group.
The following items were assessed in all patients. As a parameter of muscle preservation, the amount of muscle tissue resection during surgery was measured. Muscle that entered into the retractor was removed with a punch, and all resected muscle was brought together in gauze. Blood associated with muscle was absorbed in the gauze, and only muscle was measured without drying. As a parameter of facet joint preservation, the angle of osteotomy of the medial facet joint on the approach side was measured. This angle was determined in a POP-net web server (Image ONE Co., Tokyo, Japan) of a Digital Imaging and Communications in Medicine (DICOM) viewer as that between the horizontal plane (a line connecting the ventral margins of the left and right superior articular processes) and the approach-side facet joint osteotomy line on cross-sectional computed tomography (CT) images at the middle of the intervertebral disk (►Fig. 5). Improvement rate based on VAS score (range: 0–100) for leg symptoms was calculated as follows: (preoperative score postoperative score)/(preoperative score) 100%. Severity of early postoperative wound pain was evaluated using a VAS in the evening of the day after surgery. Differences between the two groups were analyzed using the unpaired t test, and p values < 0.05 were regarded as significant. We determined the virtual segmental weight of the multifidus muscle at the operated level as a measure for judging the amount of muscle resected. Virtual segmental muscle weight was estimated as described later. On cross-sectional preoperative CT images of 20 cases selected at random, the volume of the multifidus muscle was determined unilaterally in the range of 20-mm length in the craniocaudal direction at the L4–L5 level. Then mean virtual segmental muscle weight was determined with a specific gravity of 1.1. The “20-mm length” was derived from the mean length of 19.3 mm determined for the osteotomy holes of the 20 cases. Journal of Neurological Surgery—Part A
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Surgery
Nakamura, Shibayama
Fig. 4 (A) An intraoperative picture of the rectangular tubular retractor and its assembly. (B) The tip of the suction port of the microendoscope attachment was obliquely cut and bent to allow water injection and washing of the scope end.
Fig. 5 (A) Osteotomy angle of the medial facet on the approach side was determined by the osteotomy line of the medial facet (line a) and a horizontal line (line b). (B) A case in the 16-mm cylindrical tubular retractor group, with an osteotomy angle of 73 degrees. (C) A case in the rectangular tubular retractor group, with an osteotomy angle of 74 degrees.
Results Mean amount of muscle resection (per intervertebral level) was 1.95 g in the 16-mm cylindrical tubular retractor group and 0.27 g in the rectangular tubular retractor group (p < 0.001). A decrease of 86% was shown in the rectangular tubular retractor group. Mean osteotomy angle was similar between the 16-mm cylindrical tubular retractor group (78.6 degrees) and the rectangular tubular retractor Journal of Neurological Surgery—Part A
group (77.6 degrees) (p ¼ 0.293). Mean operating time was 62.0 minutes in the 16-mm cylindrical tubular retractor group and 71.0 minutes in the rectangular tubular retractor group, demonstrating only a 9-minute prolongation in the rectangular tubular retractor group (p < 0.001). Skin incision length was 18 mm and 15 mm in the 16-mm cylindrical tubular retractor and rectangular tubular retractor groups, respectively (these are not the actual incision lengths measured postoperatively but rather that of the line drawn
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Rectangular Tubular Retractor for Lumbar Decompression
preoperatively). Mean intraoperative blood loss was similar between the 16-mm cylindrical tubular retractor group (51.0 mL) and the rectangular tubular retractor group (47.2 mL) (p ¼ 0.318). Mean follow-up time was 8.7 months (range: 3–12 months) in the 16-mm cylindrical tubular retractor group and 7.5 months (range: 3–12 months) in the rectangular tubular retractor group. Mean improvement rate of leg symptoms was similar between the 16-mm cylindrical tubular retractor group (69.7%) and the rectangular tubular retractor group (71.2%) (p ¼ 0.418). Mean VAS score for early postoperative wound pain was 20.5 in the 16-mm cylindrical tubular retractor group and 11.0 in the rectangular tubular retractor group (p < 0.005). Wound pain in the rectangular tubular retractor group was significantly less than that in the cylindrical tubular retractor group, although the difference was not large (►Table 1). Virtual segmental muscle weight was estimated to be 12.2 g.
Discussion Surgery using a 16-mm cylindrical tubular retractor and microendoscope, such as those of the METRx system, is currently considered to reduce the amount of exposure compared with the conventional technique, thereby reducing muscle damage.7,8 However, even this method requires a considerable amount of muscle resection. As shown in ►Fig. 6, when the bone surface is observed from the dorsal side, the osteotomy hole is close to a narrow rectangle. Therefore, the ratio of exposure in the lateral direction to that in the craniocaudal direction may be markedly low. The width of the osteotomy hole lateral to the spinous process is less than half of 16 mm. Because the 16-mm cylindrical tubular retractor is excessive, the amount of muscle resection increases. On the contrary, the rectangular tubular retractor has a short width (mediolateral dimension) and can reduce the amount of muscle resection. When the width of the tubular retractor is short, muscle entry into the retractor, which occurs when the retractor is tilted to the left and right, decreases. In addition, even in the presence of dorsal thickening of the lateral area due to facet joint deformation,
Nakamura, Shibayama
Fig. 6 Comparison of osteotomy hole size and the cross-section areas of the 16-mm cylindrical tubular retractor and rectangular tubular retractor. When the bone surface is observed from the dorsal side, the dotted white line indicates the 16-mm cylindrical tubular retractor; the black line indicates the rectangular tubular retractor. The crosssectional area of the 16-mm cylindrical tubular retractor is excessively wide compared with the width of the osteotomy hole lateral to the spinous process.
contact between the tubular retractor tip and the vertebral arch is less markedly obstructed due to the short width of the tubular retractor. Concerning the length (craniocaudal dimension) of the tubular retractor, that of the 16-mm cylindrical tubular retractor is even shorter than the osteotomy hole. Therefore, a reduction in tubular retractor length is not necessary. Thus to preserve muscle, a rectangular tubular retractor with a short width is more advantageous. In this study, the mean amount of muscle resection in the 16-mm cylindrical tubular retractor group was 1.95 g, which is 16% of the virtual segmental muscle weight (12.2 g). This amount is too large and needs to be reduced. It is significant that the mean amount of muscle resection in the rectangular tubular retractor group was 0.27 g, a reduction of 86% when compared with the 16-mm cylindrical tubular retractor group. If a small-caliber cylindrical tubular retractor with reduced width and length is used to further reduce invasiveness, the working space for surgical instruments decreases,
Table 1 Results 16 mm cylindrical
Rectangular
p value
Muscle resection, g
1.95 0.63
0.27 0.12
< 0.001
Osteotomy angle, degrees
78.6 7.4
77.6 6.2
0.293
NS
Operation time, min Skin incision, mm
a
62.0 6.8
71.0 5.8
< 0.001
18
15
–
–
Blood loss, mL
51.0 30.4
47.2 28.4
0.318
NS
Wound pain, VAS
20.5 12.4
11.0 9.6
