- Email: [email protected]
Minimally invasive surgical options for adolescent idiopathic scoliosis
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Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Minimally invasive surgical options for adolescent idiopathic scoliosis Firoz Miyanji, MD, FRCSCa,b,n, and Sameer Desai, BScb a
Pediatric Spine Surgeon, Division of Orthopedics, British Columbia Children's Hospital, Vancouver, British Columbia Canada b Clinical Assistant Professor, Department of Orthopedics, University of British Columbia, Vancouver, British Columbia Canada
article info
abstra ct Early results of MIS in AIS have been promising; however, longer-term follow-up data remains limited. Our objective was to compare perioperative outcomes as well as radiographic and clinical outcomes between MIS and standard open posterior spinal instrumentation and fusion (PSIF) at 2-year follow-up. Advantages of MIS in AIS were related to intra-operative blood loss, cell saver transfusion rates, and LOS; however, significant increases in ORT, lower mean percent curve correction, and a higher complication rate of MIS in AIS were also noted. Despite these variations, no clinical differences in SRS-22 scores were found at 2 years postop between the groups. & 2015 Published by Elsevier Inc.
1.
Introduction
Traditional open spine surgery is often associated with significant perioperative morbidity.1–5 Previous authors have reported on the significant soft tissue and muscle morbidity of standard open spine procedures leading to increases in long-term pain and limited functional recovery.1,6–12 Minimally invasive surgery (MIS) in spine has been gaining increasing popularity in an effort to decrease the approachrelated morbidity associated with conventional open spine techniques. Encouraging results of MIS in adult patients have lead to its widespread use in the setting of adult trauma and degenerative conditions.1,2,11,13–15 MIS application in deformity has also been reported to have potential favorable outcomes at least in the early postoperative period. Feasibility studies of MIS in deformity along with reported advantages in blood loss and length of hospital stay
have led deformity surgeons to strongly consider its potential application in adolescent idiopathic scoliosis (AIS).16–19 Despite the encouraging early postoperative results of MIS in AIS, longer-term follow-up data remains limited in attempting to address the raised theoretical concerns of curve correction, fusion, and possible future junctional issues following MIS techniques. The aim of our study was therefore to compare perioperative outcomes, as well as radiographic and clinical outcomes between MIS and standard open posterior spinal instrumentation and fusion (PSIF) at 2-year follow-up.
2.
Methods
After IRB approval, a retrospective analysis of prospectively collected data of all consecutive patients who underwent MIS for the treatment of AIS was performed. All patients are
Disclosure: Dr. Miyanji receives research support directed to his institution from the Setting Scoliosis Straight Foundation. Dr. Miyanji has a consultancy agreement with Depuy Synthes Spine. n Correspondence to: Dr. Miyanji, Division of Orthopaedics British Columbia Children's and Women's Hospital, 1D65-4480 Oak St, Vancouver, BC, Canada V6H 3V4. E-mail address: [email protected] (F. Miyanji). http://dx.doi.org/10.1053/j.semss.2015.01.009 1040-7383/& 2015 Published by Elsevier Inc.
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followed up prospectively within a multicenter, longitudinal AIS surgical database registry. MIS cases were matched for age, sex, weight, Lenke classification, curve size, and single surgeon with conventional open PSIF from the database registry. All patients had 2-year follow-up data available and were treated between 2009 and 2012. Preoperative, perioperative, and 2-year post-operative data were evaluated. An independent observer made all radiographic data measurements. A priori defined perioperative outcome variables of interest included operative time (ORT), length of hospital stay (LOS), estimated blood loss (EBL), mean volume of cell saver blood transfused, and postoperative day switch to oral pain medication. At 2-year follow-up, mean percentage major coronal and sagittal Cobb correction, SRS-22 scores, and any complication identified within the 2-year follow-up period were also compared between the 2 groups. Complications were included in this study if inpatient hospitalization, prolonged hospitalization, or unplanned additional surgery was required. Data normality was determined using the Shapiro–Wilk test and significance was tested using Independent Samples T-tests and Mann–Whitney U tests. SPSS V.18 was used for statistical analysis.
2.1.
MIS surgical technique
Three separate midline skin incisions are planned using fluoroscopy (Fig. 1A). In our practice, fluoroscopy is limited to preoperative planning of the incisions. The skin is then undermined laterally to make paramedian fascial incisions approximately 1 fingerbreadth from midline (Fig. 1B). A blunt muscle-sparing approach is used down to the facet joints, which are visualized with the aid of handheld retractors. Wide facetectomies are performed, and the pedicles are cannulated using a freehand technique (Fig. 2A). They are localized by placement of guide wires or cannulated bone pegs. This facilitates bilateral facetectomies without committing to passage of a single rod before fully mobilizing the spinal column. The facet joints are then meticulously decorticated with a high-speed burr. Bone graft comprising autograft and freeze-dried allograft is placed before screw insertion to help augment fusion (Fig. 2B and C). An appropriately sized pedicle screw is inserted, and the guide wire is
27 (2015) 39–44
removed. Once the screws are placed at all levels, a rod of appropriate length that is contoured to the correct sagittal profile is introduced. The rod is passed from distal to proximal below the soft tissues and under the skin bridges to be captured within the tulips of the pedicle screws (Fig. 3). The cylinders are made collinear to allow most of the deformity to be corrected before placement of the rod. The rod is reduced to the pedicle screws using the reduction instruments and secured using set screws. Further correction is obtained with rod derotation into the appropriate sagittal plane. Before placement of the second rod, en bloc direct vertebral apical derotation can be performed using available instruments. The second convex rod is then undercontoured in the sagittal plane and placed from distal to proximal. Undercontouring of this rod allows further deformity correction in the axial plane (Fig. 4). Uniaxial screws are primarily used.
3.
Results
A total of 23 MIS patients with 2-year follow-up data were matched with 23 standard open PSIF patients. Patient demographics of age, sex, weight distribution as well as Lenke classification, mean preoperative major coronal, and lateral Cobb angles are summarized in Table 1. There were no significant differences in these preoperative variables. The number of levels fused in the MIS group was on average 2 levels shorter than the open group. In terms of perioperative variables we found significant differences between the 2 groups in ORT, LOS, EBL, and volume of cell saver blood transfused. In the MIS patients, the average ORT was 475.3 7 13.25 min compared to 346.4 7 15.64 min in the PSIF group (p ¼ 0.000). LOS was noted to be significantly shorter on average by 1.5 7 0.05 days in the MIS group compared to the PSIF patients (4.4 7 0.15 days versus 5.9 7 0.20 days; p ¼ 0.000). In addition, EBL and subsequent mean volume of cell saver transfused was also significantly lower in the MIS group (p ¼ 0.000, p ¼ 0.005, respectively). In the MIS group no patients received cell saver blood transfusions. There were no significant differences between MIS patients and PSIF patients with respect to postoperative day switch to oral pain medication (p ¼ 0.419).
Fig.1 – (A) Skin incisions marked with fluoroscopic guidance. (B) Paramedian fascial incisions.
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Fig. 2 – (A) Facetectomy and pedicle cannulation for pedicle screw. (B) Morselized bone graft placement. (C) Bone peg placement to keep cannulated pedicle localized while graft is placed. When comparing the outcome variables, we found a statistically significant difference in the mean postoperative major coronal Cobb at 2-year follow-up between the 2 groups. The average Cobb in the PSIF group was 18.71 7 1.021 compared to 23.91 7 1.681 in the MIS group. The mean percent major coronal Cobb correction was therefore 68.0% 7 1.45% in the PSIF group and 58.1% 7 2.41% in the MIS group. This difference was statistically significant (p ¼ 0.001). The mean postoperative lateral Cobb was not significantly different between the groups with the MIS patients on average having a T5–T12 sagittal profile of 22.91 7 1.901 compared to the PSIF group having 21.01 7 1.321 (p ¼ 0.552). Although not reaching statistical significance, the number of complications in this case–control study was slightly higher in the MIS group compared to the PSIF group. There were 5 complications that were documented within the 2-year follow-up period in the MIS group of patients compared to 1 complication noted in the PSIF group. In the MIS group, there was 1 pseudarthrosis requiring revision PSIF, 3 chronic infections (priopionibacterium acnes), and 1 hardware failure at 6 weeks following surgery which was dislodgement of distal set screws. In the PSIF group, there was 1 chronic infection (priopionibacterium acnes).
We found no differences between the 2 groups in SRS-22 outcomes scores at 2-year follow-up (p ¼ 0.715). Table 2 summarizes the results.
4.
Discussion
We present a comparative study of AIS patients treated by either MIS or standard open PSIF techniques at minimum 2-year follow-up and found important differences between the 2 groups of patients. There was a significantly better percentage coronal Cobb correction with open PSIF compared to MIS; however, no differences were noted in the sagittal plane measurements. We did find MIS patients to have a significantly lower LOS (p ¼ 0.000), EBL (p ¼ 0.000), and mean volume of cell saver blood transfused (p ¼ 0.005) compared to the PSIF group; however, this was potentially at the expense of increased ORT in the MIS group by an average 128.9 7 2.39 min compared to the PSIF group (p ¼ 0.000). Complications were also higher in the MIS group although not statistically significant. Despite these differences in radiographic and perioperative variables, no differences in the SRS-22
Fig. 3 – (A) Rod placement from distal to proximal. (B) Rod placement below skin and soft tissue bridges seated within the tulips of the pedicle screw marked by the cylinders.
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Fig. 4 – (A–C) Differential rod contouring. functional outcome scores were noted at 2 years postop between the 2 groups. The rationale of MIS techniques in spine surgery has focused on reducing approach-related morbidity associated with conventional open procedures. Previous authors have reported on significant soft tissue and muscle morbidity, including denervation, ischemia, atrophy, scarring, and decreased extensor strength likely contributing to increased perioperative and long-term pain.2,20–31 Recent advances in MIS technologies have led to the application of MIS in all regions of the spine for decompression, instrumentation, and arthrodesis. Its widespread use in spinal trauma and degenerative disorders is now well established.1,3,5,10,13,15,32 Blood loss, LOS, and return to activity have been documented advantages of MIS in these settings compared to standard open surgery.4,5,14,32–35 Currently data focusing on outcomes of MIS in deformity remains limited, despite its purported advantages. Initial studies reported on the feasibility of MIS in adult deformity. Anand et al.16 reported on a series of 12 adult patients with degenerative scoliosis who had on average 3.64 segments fused. They reported a feasibility study in which patients underwent a lateral retroperitoneal approach followed by percutaneous pedicle screw placements. Functional or longterm data was not available in this series. Similarly Hsieh et al.12 have described MIS procedures on a heterogeneous group of patients with complex spine disorders but only 1 patient was treated for deformity. Samdani et al.17 retrospectively reviewed their experience with MIS in 15 patients and
had on average a preoperative major Cobb angle of 541 correcting to 181, noting a 67% correction. The average blood loss in their series was 254 cc and OR time was on average 470 min. There was a lack of a comparative standard open posterior surgical arm in this reported case series. Sarwahi et al.18 also reported a feasibility study of 7 patients with idiopathic scoliosis treated with MIS. They reported a mean ORT of 8.7 hours, mean EBL of 564.3 cc, and an encouraging mean percentage curve correction of 81.7%. More recently Miyanji et al.19 reported on a matched comparative study of MIS to standard open posterior techniques in AIS. This study emphasized early postoperative results primarily of perioperative outcomes and noted that advantages of MIS in AIS over standard open PSIF were a decrease in blood loss and LOS. Our current study expands on these previous reports with a larger sample size, a matched cohort of patients who underwent conventional open PSIF, and all cases having minimum 2-year follow-up data. Similar to the previous reports, we found MIS in AIS to help decrease perioperative morbidity namely blood loss, volume of cell saver transfused, and LOS. The ORT, however, was significantly longer in patients treated with MIS. It is also important to note that curve correction remained significantly better in the open PSIF at 2year follow-up. The differences in ORT and curve correction may be the effect of a learning curve when applying new techniques, nonetheless they should be emphasized as potential limitations of MIS in the setting of AIS. Although in this study, the differences in the number of complications was not statistically significant, we did find a
Table 1 – MIS and PSIF patient demographics. Patient demographics
MIS (n ¼ 23)
PSIF (n ¼ 23)
Gender, M:F Lenke class classification (n)
3:20 1:20 2:2 4:1 16.8 59.1 56.7 20.5 10.2
4:19 1:12 2:8 3:3 16.4 56.4 58.1 22.6 12.2
Mean Mean Mean Mean Mean
age (yr) weight (kg) preop major Cobb (1) preop lat (T5–T12) number of fusion levels
7 7 7 7
0.40 1.74 1.62 2.08
(14–20) (43–72) (45–77) (2 to 39)
7 7 7 7
0.28 1.57 1.57 3.38
(13–19) (44.6–76.2) (46–71) (4 to 54)
p-Value (α ¼ 0.05)
0.553
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Table 2 – Perioperative, 2-year radiographic, and clinical outcomes comparison between MIS and PSIF groups. Outcome variables of interest
MIS (n ¼ 23)
PSIF (n ¼ 23)
p-Value (α ¼ 0.05)
Mean postop major Cobb at 2-year follow-up Mean postop lat (T5–T12) at 2-year follow-up Mean %, major Cobb correction at 2-year follow-up Mean postop SRS-22 scores at 2-year follow-up Mean OR time (min) Mean LOS (days) Mean EBL (mL) Mean volume of cell saver blood transfused (mL) Switch to PO pain medication (POD) Complications (n)
23.9 7 1.68 (12–46) 22.9 7 1.90 (10–49) 58.1 7 2.41 (30.4–78.9) 4.23 7 0.14 475.3 7 13.25 (350–618) 4.4 7 0.15 (3–6) 261.5 7 20.89 (100–500) 0 3.4 7 0.19 (2–5) 5 (21.7%)
18.7 7 21.0 7 68.0 7 4.34 7 346.4 7 5.9 7 471.7 7 69.0 7 3.7 7 1 (4.3%)
0.017* 0.552 0.001* 0.715 0.000* 0.000* 0.000* 0.005* 0.419 0.080
n
Indicates point at which a significant difference (po0.05) found.
larger number of complications in the MIS group (5) compared to the standard open PSIF (1) at minimum 2-year follow-up. The MIS group had 3 chronic infections that appeared greater than 1 year following the index procedure. All cases had priopionibacterium acnes isolated from intraoperative cultures and the infections were successfully eradicated with hardware removal (1 complete and 2 partial) and appropriate antibiotics. The pseudarthrosis case presented 10 months following surgery in a patient with a smoking history who was poorly compliant with the postoperative, graduated return to activity protocol. The final complication was dislodgement of distal set screws noted acutely 6 weeks following surgery after routine outpatient x-rays. Our matched case–control series did highlight the potential limitation of MIS in AIS with respect to curve correction. Although a number of correction techniques exist for open procedures, not all are applicable in the setting of MIS. Greater emphasis is placed on rod rotation, differential rod contouring, and more recently intra-operative traction with MIS cases. Application of compression, distraction, and in situ contouring is very limited both because of the approach and available instrumentation to date. Although statistically significant, the mean postoperative major coronal Cobb difference between the 2 groups in this comparative study was 5.21 (23.91 7 1.681 in the MIS group compared to 18.71 7 1.021 in the PSIF group). Whether a difference on average of 5.21 has any clinical significance remains debatable.
5.
1.02 (8–28) 1.32 (12–41) 1.45 (56.9–84.6) 0.10 15.64 (223–510) 0.20 (4–8) 36.09 (150–800) 23.33 (0–300) 0.21 (2–5)
Conclusions
Advantages of MIS over standard open posterior surgery for AIS relate to intra-operative blood loss, cell saver transfusion rates, and LOS; this needs to be carefully weighed against the significant increase in ORT, limited mean percentage curve correction and a higher noted complication rate of MIS in AIS at 2-year follow-up compared to standard open posterior surgery. Despite these variations, no clinical differences in SRS-22 scores were found at 2 years postop in this comparative study. Our study supports the evolution of MIS as an effort to decrease perioperative morbidity in the setting of AIS. However, we found MIS to have a limited scope in providing significant advantages over standard open posterior procedures at 2-year follow-up.
refere nces
1. German JW, Adamo MA, Hoppenot RG, et al. Perioperative results following lumbar discectomy: comparison of minimally invasive discectomy and standard microdiscectomy. Neurosurg Focus. 2008;25(2):E20. 2. Jackson RK. The long-term effects of wide laminectomy for lumbar disc excision. A review of 130 patients. J Bone Joint Surg Br. 1971;53:609–616. 3. Ryang YM, Oertel MF, Mayfrank L, et al. Standard open microdiscectomy versus minimal access trocar microdiscectomy: result of a prospective randomized study. Neurosurgery. 2008;62:174–181. 4. Righesso O, Falavigna S, Avanzi O, et al. Comparison of open disectomy with microscopic disectomy in lumbar disc herniations: results of a randomized controlled trial. Neurosurgery. 2007;61:174–181. 5. Peng CW, Yue WM, Poh SY, et al. Clinical and radiographic outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine. 2009;24:1385–1389. 6. Maroon JC. Current concepts in minimally invasive discectomy. Neurosurgery. 2002;51(suppl 5):S137–S145. 7. Oppenheimer JH, DeCastro I, McDonnell DE. Minimally invasive spine technology and minimally invasive spine surgery: a historical review. Neurosurg Focus. 2009;27(3):E9. 8. Samartzis D, Shen FH, Perez-cruet MJ, et al. Minimally invasive spine surgery: a historical perspective. Orthop Clin North Am. 2007;38:305–326. 9. Thongtrangan I, Le H, Park J, et al. Minimally invasive spinal surgery: a historical perspective. Neurosurg Focus. 2004;16(1):E13. 10. Fessler RG, O'Toole JE, Eichholz KM, et al. The development of minimally invasive spine surgery. Neurosurg Clin N Am. 2006;17:401–409. 11. Jaikumar S, Kim DH, Kam AC. History of minimally invasive spine surgery. Neurosurgery. 2002;51(suppl 5):S1–S14. 12. Hsieh PC, Koski TR, Sciubba DM, et al. Maximizing the potential of minimally invasive spine surgery in complex spinal disorders. Neurosurg Focus. 2008;25(2):E19. 13. Katayama Y, Matsuyama Y, Yoshishara H, et al. Comparison of surgical outcomes between macro discectomy and micro discectomy for lumbar disc herniation: a prospective randomized study with surgery performed by the same spine surgeon. J Spinal Disord Tech. 2006;19:344–347. 14. Rampersaud YR, Annand N, Dekutoski MB. Use of minimally invasive surgical techniques in the management of thoracolumbar trauma: current concepts. Spine. 2006;31(suppl11):S96–S104. 15. Smith JS, Ogden AT, Fessler RG. Minimally invasive posterior thoracic fusion. Neurosurg Focus. 2008;25(2):E9. 16. Anand N, Baron EM, Thaiyananthan G, et al. Minimally invasive multilevel percutaneous correction and fusion for
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adult lumbar degenerative scoliosis: a technique and feasibility study. J Spinal Disord Tech. 2008;21:459–467. Samdani AF, Asghar J, Miyanji F, et al. Minimally invasive treatment of pediatric spinal deformity. Semin Spine Surg. 2011;23:72–75. Sarwahi V, Wollowick AL, Sugarman EP, et al. Minimally invasive scoliosis surgery: an innovative technique in patients with adolescent idiopathic scoliosis. Scoliosis. 2011;6:16. Miyanji F, Samdani AF, Marks M, et al. Minimally invasive surgery for AIS: an early prospective comparison with standard open posterior surgery. J Spine. 2013;S5:001. Kawaguchi Y, Matsui H, Tsuji H. Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis. Spine. 1996;21:941–944. Kawaguchi Y, Matsui H, Tsuji H. Back muscle injury after posterior lumbar spine surgery. Part 1: histologic and histochemical analyses in rats. Spine. 1994;19:2590–2597. Kawaguchi Y, Matsui H, Tsuji H. Back muscle injury after posterior lumbar spine surgery. Part 2: histologic and histochemical analyses in humans. Spine. 1994;19:2598–2602. Kawaguchi Y, Yakubi S, Styf J, et al. Back muscle injury after posterior lumbar spine surgery. Topographic evaluation of intramuscular pressure and blood flow in the porcine back muscle during surgery. Spine. 1996;21:2683–2688. Kim DY, Lee SH, Chung SK, et al. Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation. Spine. 2005;30:123–129. Macnab I, Cuthbert H, Godfrey CM. The incidence of denervation of the sacrospinales muscle following spinal surgery. Spine. 1977;2:294–298. Mayer TG, Vanharanta H, Gatchel RJ, et al. Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients. Spine. 1989;14:33–36.
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27. Naylor A. Late results of laminectomy for lumbar disc prolapse. A review after ten to twenty-five years. J Bone Joint Surg Br. 1974;56:17–29. 28. Rantanen J, Hurme M, Falck B, et al. The lumbar multifidus muscle five years after surgery for a lumbar intervertebral disc herniation. Spine. 1993;18:568–574. 29. Sihvonen T, Herno A, Paljärvi L, et al. A local denervation atrophy of paraspinal muscles in postoperative failed back syndrome. Spine. 1993;18:575–581. 30. Styf JR, Willén J. The effects of external compression by three different retractors on pressure in the erector spine muscles during and after posterior lumbar spine surgery in humans. Spine. 1998;23:354–358. 31. Weber BR, Grob D, Dvorák J, et al. Posterior surgical approach to the lumbar spine and its effect on the multifidus muscle. Spine. 1997;22:1765–1772. 32. Khoo LT, Beisse R, Potulski M. Thoracoscopic-assisted treatment of thoracic and lumbar fractures: a series of 371 consecutive cases. Neurosurgery. 2002;51(5): 104–117. 33. Dhall SS, Wang MY, Memmaneni PV. Clinical and radiographic comparison of mini-open transforaminal lumbar interbody fusion with open transforaminal lumbar interbody fusion in 42 patients with long-term follow-up. J Neurosurg Spine. 2008;9:560–565. 34. Park P, Upadhyaya C, Garton HJ, et al. The impact of minimally invasive spine surgery on perioperative complications in overweight or obese patients. Neurosurg. 2008;62: 693–699. 35. Korovessis P, Hadjipavlou A, Repantis T. Minimally invasive short posterior instrumentation plus balloon kyphoplasty with calcium phosphate for burst and severe compression lumbar fractures. Spine. 2008;33:658–667.
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Available online at www.sciencedirect.com
www.elsevier.com/locate/semss
Minimally invasive surgical options for adolescent idiopathic scoliosis Firoz Miyanji, MD, FRCSCa,b,n, and Sameer Desai, BScb a
Pediatric Spine Surgeon, Division of Orthopedics, British Columbia Children's Hospital, Vancouver, British Columbia Canada b Clinical Assistant Professor, Department of Orthopedics, University of British Columbia, Vancouver, British Columbia Canada
article info
abstra ct Early results of MIS in AIS have been promising; however, longer-term follow-up data remains limited. Our objective was to compare perioperative outcomes as well as radiographic and clinical outcomes between MIS and standard open posterior spinal instrumentation and fusion (PSIF) at 2-year follow-up. Advantages of MIS in AIS were related to intra-operative blood loss, cell saver transfusion rates, and LOS; however, significant increases in ORT, lower mean percent curve correction, and a higher complication rate of MIS in AIS were also noted. Despite these variations, no clinical differences in SRS-22 scores were found at 2 years postop between the groups. & 2015 Published by Elsevier Inc.
1.
Introduction
Traditional open spine surgery is often associated with significant perioperative morbidity.1–5 Previous authors have reported on the significant soft tissue and muscle morbidity of standard open spine procedures leading to increases in long-term pain and limited functional recovery.1,6–12 Minimally invasive surgery (MIS) in spine has been gaining increasing popularity in an effort to decrease the approachrelated morbidity associated with conventional open spine techniques. Encouraging results of MIS in adult patients have lead to its widespread use in the setting of adult trauma and degenerative conditions.1,2,11,13–15 MIS application in deformity has also been reported to have potential favorable outcomes at least in the early postoperative period. Feasibility studies of MIS in deformity along with reported advantages in blood loss and length of hospital stay
have led deformity surgeons to strongly consider its potential application in adolescent idiopathic scoliosis (AIS).16–19 Despite the encouraging early postoperative results of MIS in AIS, longer-term follow-up data remains limited in attempting to address the raised theoretical concerns of curve correction, fusion, and possible future junctional issues following MIS techniques. The aim of our study was therefore to compare perioperative outcomes, as well as radiographic and clinical outcomes between MIS and standard open posterior spinal instrumentation and fusion (PSIF) at 2-year follow-up.
2.
Methods
After IRB approval, a retrospective analysis of prospectively collected data of all consecutive patients who underwent MIS for the treatment of AIS was performed. All patients are
Disclosure: Dr. Miyanji receives research support directed to his institution from the Setting Scoliosis Straight Foundation. Dr. Miyanji has a consultancy agreement with Depuy Synthes Spine. n Correspondence to: Dr. Miyanji, Division of Orthopaedics British Columbia Children's and Women's Hospital, 1D65-4480 Oak St, Vancouver, BC, Canada V6H 3V4. E-mail address: [email protected] (F. Miyanji). http://dx.doi.org/10.1053/j.semss.2015.01.009 1040-7383/& 2015 Published by Elsevier Inc.
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followed up prospectively within a multicenter, longitudinal AIS surgical database registry. MIS cases were matched for age, sex, weight, Lenke classification, curve size, and single surgeon with conventional open PSIF from the database registry. All patients had 2-year follow-up data available and were treated between 2009 and 2012. Preoperative, perioperative, and 2-year post-operative data were evaluated. An independent observer made all radiographic data measurements. A priori defined perioperative outcome variables of interest included operative time (ORT), length of hospital stay (LOS), estimated blood loss (EBL), mean volume of cell saver blood transfused, and postoperative day switch to oral pain medication. At 2-year follow-up, mean percentage major coronal and sagittal Cobb correction, SRS-22 scores, and any complication identified within the 2-year follow-up period were also compared between the 2 groups. Complications were included in this study if inpatient hospitalization, prolonged hospitalization, or unplanned additional surgery was required. Data normality was determined using the Shapiro–Wilk test and significance was tested using Independent Samples T-tests and Mann–Whitney U tests. SPSS V.18 was used for statistical analysis.
2.1.
MIS surgical technique
Three separate midline skin incisions are planned using fluoroscopy (Fig. 1A). In our practice, fluoroscopy is limited to preoperative planning of the incisions. The skin is then undermined laterally to make paramedian fascial incisions approximately 1 fingerbreadth from midline (Fig. 1B). A blunt muscle-sparing approach is used down to the facet joints, which are visualized with the aid of handheld retractors. Wide facetectomies are performed, and the pedicles are cannulated using a freehand technique (Fig. 2A). They are localized by placement of guide wires or cannulated bone pegs. This facilitates bilateral facetectomies without committing to passage of a single rod before fully mobilizing the spinal column. The facet joints are then meticulously decorticated with a high-speed burr. Bone graft comprising autograft and freeze-dried allograft is placed before screw insertion to help augment fusion (Fig. 2B and C). An appropriately sized pedicle screw is inserted, and the guide wire is
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removed. Once the screws are placed at all levels, a rod of appropriate length that is contoured to the correct sagittal profile is introduced. The rod is passed from distal to proximal below the soft tissues and under the skin bridges to be captured within the tulips of the pedicle screws (Fig. 3). The cylinders are made collinear to allow most of the deformity to be corrected before placement of the rod. The rod is reduced to the pedicle screws using the reduction instruments and secured using set screws. Further correction is obtained with rod derotation into the appropriate sagittal plane. Before placement of the second rod, en bloc direct vertebral apical derotation can be performed using available instruments. The second convex rod is then undercontoured in the sagittal plane and placed from distal to proximal. Undercontouring of this rod allows further deformity correction in the axial plane (Fig. 4). Uniaxial screws are primarily used.
3.
Results
A total of 23 MIS patients with 2-year follow-up data were matched with 23 standard open PSIF patients. Patient demographics of age, sex, weight distribution as well as Lenke classification, mean preoperative major coronal, and lateral Cobb angles are summarized in Table 1. There were no significant differences in these preoperative variables. The number of levels fused in the MIS group was on average 2 levels shorter than the open group. In terms of perioperative variables we found significant differences between the 2 groups in ORT, LOS, EBL, and volume of cell saver blood transfused. In the MIS patients, the average ORT was 475.3 7 13.25 min compared to 346.4 7 15.64 min in the PSIF group (p ¼ 0.000). LOS was noted to be significantly shorter on average by 1.5 7 0.05 days in the MIS group compared to the PSIF patients (4.4 7 0.15 days versus 5.9 7 0.20 days; p ¼ 0.000). In addition, EBL and subsequent mean volume of cell saver transfused was also significantly lower in the MIS group (p ¼ 0.000, p ¼ 0.005, respectively). In the MIS group no patients received cell saver blood transfusions. There were no significant differences between MIS patients and PSIF patients with respect to postoperative day switch to oral pain medication (p ¼ 0.419).
Fig.1 – (A) Skin incisions marked with fluoroscopic guidance. (B) Paramedian fascial incisions.
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Fig. 2 – (A) Facetectomy and pedicle cannulation for pedicle screw. (B) Morselized bone graft placement. (C) Bone peg placement to keep cannulated pedicle localized while graft is placed. When comparing the outcome variables, we found a statistically significant difference in the mean postoperative major coronal Cobb at 2-year follow-up between the 2 groups. The average Cobb in the PSIF group was 18.71 7 1.021 compared to 23.91 7 1.681 in the MIS group. The mean percent major coronal Cobb correction was therefore 68.0% 7 1.45% in the PSIF group and 58.1% 7 2.41% in the MIS group. This difference was statistically significant (p ¼ 0.001). The mean postoperative lateral Cobb was not significantly different between the groups with the MIS patients on average having a T5–T12 sagittal profile of 22.91 7 1.901 compared to the PSIF group having 21.01 7 1.321 (p ¼ 0.552). Although not reaching statistical significance, the number of complications in this case–control study was slightly higher in the MIS group compared to the PSIF group. There were 5 complications that were documented within the 2-year follow-up period in the MIS group of patients compared to 1 complication noted in the PSIF group. In the MIS group, there was 1 pseudarthrosis requiring revision PSIF, 3 chronic infections (priopionibacterium acnes), and 1 hardware failure at 6 weeks following surgery which was dislodgement of distal set screws. In the PSIF group, there was 1 chronic infection (priopionibacterium acnes).
We found no differences between the 2 groups in SRS-22 outcomes scores at 2-year follow-up (p ¼ 0.715). Table 2 summarizes the results.
4.
Discussion
We present a comparative study of AIS patients treated by either MIS or standard open PSIF techniques at minimum 2-year follow-up and found important differences between the 2 groups of patients. There was a significantly better percentage coronal Cobb correction with open PSIF compared to MIS; however, no differences were noted in the sagittal plane measurements. We did find MIS patients to have a significantly lower LOS (p ¼ 0.000), EBL (p ¼ 0.000), and mean volume of cell saver blood transfused (p ¼ 0.005) compared to the PSIF group; however, this was potentially at the expense of increased ORT in the MIS group by an average 128.9 7 2.39 min compared to the PSIF group (p ¼ 0.000). Complications were also higher in the MIS group although not statistically significant. Despite these differences in radiographic and perioperative variables, no differences in the SRS-22
Fig. 3 – (A) Rod placement from distal to proximal. (B) Rod placement below skin and soft tissue bridges seated within the tulips of the pedicle screw marked by the cylinders.
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Fig. 4 – (A–C) Differential rod contouring. functional outcome scores were noted at 2 years postop between the 2 groups. The rationale of MIS techniques in spine surgery has focused on reducing approach-related morbidity associated with conventional open procedures. Previous authors have reported on significant soft tissue and muscle morbidity, including denervation, ischemia, atrophy, scarring, and decreased extensor strength likely contributing to increased perioperative and long-term pain.2,20–31 Recent advances in MIS technologies have led to the application of MIS in all regions of the spine for decompression, instrumentation, and arthrodesis. Its widespread use in spinal trauma and degenerative disorders is now well established.1,3,5,10,13,15,32 Blood loss, LOS, and return to activity have been documented advantages of MIS in these settings compared to standard open surgery.4,5,14,32–35 Currently data focusing on outcomes of MIS in deformity remains limited, despite its purported advantages. Initial studies reported on the feasibility of MIS in adult deformity. Anand et al.16 reported on a series of 12 adult patients with degenerative scoliosis who had on average 3.64 segments fused. They reported a feasibility study in which patients underwent a lateral retroperitoneal approach followed by percutaneous pedicle screw placements. Functional or longterm data was not available in this series. Similarly Hsieh et al.12 have described MIS procedures on a heterogeneous group of patients with complex spine disorders but only 1 patient was treated for deformity. Samdani et al.17 retrospectively reviewed their experience with MIS in 15 patients and
had on average a preoperative major Cobb angle of 541 correcting to 181, noting a 67% correction. The average blood loss in their series was 254 cc and OR time was on average 470 min. There was a lack of a comparative standard open posterior surgical arm in this reported case series. Sarwahi et al.18 also reported a feasibility study of 7 patients with idiopathic scoliosis treated with MIS. They reported a mean ORT of 8.7 hours, mean EBL of 564.3 cc, and an encouraging mean percentage curve correction of 81.7%. More recently Miyanji et al.19 reported on a matched comparative study of MIS to standard open posterior techniques in AIS. This study emphasized early postoperative results primarily of perioperative outcomes and noted that advantages of MIS in AIS over standard open PSIF were a decrease in blood loss and LOS. Our current study expands on these previous reports with a larger sample size, a matched cohort of patients who underwent conventional open PSIF, and all cases having minimum 2-year follow-up data. Similar to the previous reports, we found MIS in AIS to help decrease perioperative morbidity namely blood loss, volume of cell saver transfused, and LOS. The ORT, however, was significantly longer in patients treated with MIS. It is also important to note that curve correction remained significantly better in the open PSIF at 2year follow-up. The differences in ORT and curve correction may be the effect of a learning curve when applying new techniques, nonetheless they should be emphasized as potential limitations of MIS in the setting of AIS. Although in this study, the differences in the number of complications was not statistically significant, we did find a
Table 1 – MIS and PSIF patient demographics. Patient demographics
MIS (n ¼ 23)
PSIF (n ¼ 23)
Gender, M:F Lenke class classification (n)
3:20 1:20 2:2 4:1 16.8 59.1 56.7 20.5 10.2
4:19 1:12 2:8 3:3 16.4 56.4 58.1 22.6 12.2
Mean Mean Mean Mean Mean
age (yr) weight (kg) preop major Cobb (1) preop lat (T5–T12) number of fusion levels
7 7 7 7
0.40 1.74 1.62 2.08
(14–20) (43–72) (45–77) (2 to 39)
7 7 7 7
0.28 1.57 1.57 3.38
(13–19) (44.6–76.2) (46–71) (4 to 54)
p-Value (α ¼ 0.05)
0.553
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Table 2 – Perioperative, 2-year radiographic, and clinical outcomes comparison between MIS and PSIF groups. Outcome variables of interest
MIS (n ¼ 23)
PSIF (n ¼ 23)
p-Value (α ¼ 0.05)
Mean postop major Cobb at 2-year follow-up Mean postop lat (T5–T12) at 2-year follow-up Mean %, major Cobb correction at 2-year follow-up Mean postop SRS-22 scores at 2-year follow-up Mean OR time (min) Mean LOS (days) Mean EBL (mL) Mean volume of cell saver blood transfused (mL) Switch to PO pain medication (POD) Complications (n)
23.9 7 1.68 (12–46) 22.9 7 1.90 (10–49) 58.1 7 2.41 (30.4–78.9) 4.23 7 0.14 475.3 7 13.25 (350–618) 4.4 7 0.15 (3–6) 261.5 7 20.89 (100–500) 0 3.4 7 0.19 (2–5) 5 (21.7%)
18.7 7 21.0 7 68.0 7 4.34 7 346.4 7 5.9 7 471.7 7 69.0 7 3.7 7 1 (4.3%)
0.017* 0.552 0.001* 0.715 0.000* 0.000* 0.000* 0.005* 0.419 0.080
n
Indicates point at which a significant difference (po0.05) found.
larger number of complications in the MIS group (5) compared to the standard open PSIF (1) at minimum 2-year follow-up. The MIS group had 3 chronic infections that appeared greater than 1 year following the index procedure. All cases had priopionibacterium acnes isolated from intraoperative cultures and the infections were successfully eradicated with hardware removal (1 complete and 2 partial) and appropriate antibiotics. The pseudarthrosis case presented 10 months following surgery in a patient with a smoking history who was poorly compliant with the postoperative, graduated return to activity protocol. The final complication was dislodgement of distal set screws noted acutely 6 weeks following surgery after routine outpatient x-rays. Our matched case–control series did highlight the potential limitation of MIS in AIS with respect to curve correction. Although a number of correction techniques exist for open procedures, not all are applicable in the setting of MIS. Greater emphasis is placed on rod rotation, differential rod contouring, and more recently intra-operative traction with MIS cases. Application of compression, distraction, and in situ contouring is very limited both because of the approach and available instrumentation to date. Although statistically significant, the mean postoperative major coronal Cobb difference between the 2 groups in this comparative study was 5.21 (23.91 7 1.681 in the MIS group compared to 18.71 7 1.021 in the PSIF group). Whether a difference on average of 5.21 has any clinical significance remains debatable.
5.
1.02 (8–28) 1.32 (12–41) 1.45 (56.9–84.6) 0.10 15.64 (223–510) 0.20 (4–8) 36.09 (150–800) 23.33 (0–300) 0.21 (2–5)
Conclusions
Advantages of MIS over standard open posterior surgery for AIS relate to intra-operative blood loss, cell saver transfusion rates, and LOS; this needs to be carefully weighed against the significant increase in ORT, limited mean percentage curve correction and a higher noted complication rate of MIS in AIS at 2-year follow-up compared to standard open posterior surgery. Despite these variations, no clinical differences in SRS-22 scores were found at 2 years postop in this comparative study. Our study supports the evolution of MIS as an effort to decrease perioperative morbidity in the setting of AIS. However, we found MIS to have a limited scope in providing significant advantages over standard open posterior procedures at 2-year follow-up.
refere nces
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