Acta Neurochir (2014) 156:229–233 DOI 10.1007/s00701-013-1954-z
CLINICAL ARTICLE - SPINE
The result of S1 double screw fixation in patients not suited for L4 and/or L5 pedicle screw insertion Il Choi & Sang Ryong Jeon
Received: 10 August 2013 / Accepted: 13 November 2013 / Published online: 28 November 2013 # Springer-Verlag Wien 2013
Abstract Background Variable methods are available for sacropelvic fixation. The usefulness of S1 double screw fixation for deformity surgery is established, but its effectiveness in cases where the L4 and/or L5 pedicle screw is not appropriate has not been reported. Methods We reviewed medical records to identify longsegment, lumbar spine fixation involving S1 double screws. Nine such patients were treated between November 2006 and November 2012 at our center: all patients had infectious spondylitis involving L4 and/or L5. Two patients were excluded due to a limited follow-up period (< 6 months). The remaining seven patients were enrolled. We used dynamic X-rays or three-dimensional computed tomography (3D-CT) to assess any change in the lumbar alignment angle and to evaluate bony fusion with the graft material. Results The mean observation period of the seven patients was 16.9 months (range: 6–25). The mean age was 63.43 years (range: 55–73). Four patients were women. The average number of fusion levels was 3.5±1.1. The ideal positioning and maintenance of the S1 double screws and bony fusion with the graft materials were confirmed using serial imaging. Lordosis in the lumbar region was immediately restored after surgery (27.0 °±10.4 to 35.1 °±10.7), and maintained with slight decrease (31.6 °±8.8) throughout the follow-up period. Conclusions S1 double screws provided stability when L4 and/ or L5 pedicle screw fixation was not possible. Our results suggest that S1 double screws are a viable option for sacropelvic fixation in selected patients. I. Choi : S. R. Jeon (*) Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Pungnap-2dongSongpa-Gu Seoul 138-736, Korea e-mail: [email protected]
Keywords Double screw . Lumbar lordosis . Sacral screw . Sacropelvic fixation . Sacrum . Spondylitis
Introduction Recently, the need for sacropelvic fixation (SPF) has increased. SPF is useful in spinal deformity surgery and revision surgery to address fusion failure for the treatment of select patients who require a lumbosacral fixation to be strengthened. However, SPF has several disadvantages, such as postoperative pain due to extensive lumbosacral muscle and soft tissue dissection, implant prominence through the skin, and fusion of the sacroiliac joint [11]. In some cases, screws cannot be inserted at the L4 and/or L5 pedicles due to a total or partial corpectomy status, infectious spondylitis, or a dysplastic pedicle with high-grade spondylolisthesis. In these cases, an extensive SPF such as iliac screw fixation could be performed; however, considering the disadvantages of iliac screw fixation, other surgical options may be more suitable. These options include S1 screw fixation with additional fixation options: S1 pedicle/S2 pedicle screws, S1 double screws or S1 pedicle/S2 alar screws [1, 2, 4, 5]. At our center, we inserted S1 double screws into both the pedicle and the alar of the S1 when the L4 and/or L5 pedicle was not available for a lumbar, long-segment fixation. The aim of this study was to describe our S1 double screw fixation technique—i.e., bilateral pedicle and alar screw insertion at the S1 entry portion—and to evaluate its long-term effect. The outcome, including screw failure and lordotic angle changes, were evaluated using serial X-ray and 3D-CT data.
230
Methods Study design and patient population We retrospectively reviewed the medical charts, operative notes, neurophysiological data, and neuroimaging results for patients treated between November 2006 and November 2012 at our institution. A total of 134 patients underwent surgery for the treatment of infectious spine disease during this period, of which 112 patients were diagnosed with pyogenic infectious spondylitis and 22 patients with tuberculosis (TB) infectious spondylitis. All patients had undergone first-line medical treatments at the department of infectious diseases. Surgery was recommended when the patient demonstrated neurological deficits due to epidural abscess formation or when the infection was medically intractable. S1 double screw fixation was performed in each of the nine patients when L4 and/or L5 pedicles were deemed to be unsuitable following debridement of the infected vertebral body. We excluded two of these nine cases from the analysis due to a follow-up period less than 6 months.
Acta Neurochir (2014) 156:229–233
except for a pathological lesion level. Each patient was placed in the prone position under general anesthesia. Through a midline skin incision, the spinal muscle was dissected to the lateral facet line. After exposing the entry point for the pedicle screw, the guide pins were inserted at all entry points under Carm fluoroscopy guidance. The pedicle screws were then drilled, tapped, and screwed at all fixation sites (SMC system; OK Medical Co., Seoul, Korea). The ideal entry points for the upper screw are at the just superolateral point of the superior facet of S1 and for the lower screw at the lowest point of the S1 body below the upper screw (Fig. 1a). The upper screw was inserted in a medial direction, and the lower screw in a lateral direction (Fig. 1b–c). The upper screw was directed just below and parallel to the upper endplate of S1 (Fig. 2a). The lower screw was inserted at the lowest point on the S1 body and directed to the upper S1 endplate (Fig. 2b). The screws used were polyaxial, 65 or 75 mm in diameter, and 30, 35, or 40 mm in length. At the week following surgery, all patients were transferred to the department of infectious diseases for continuous antibiotic treatment. We recommended an external brace for 4 months to support the thoraco-lumbo-sacral area. Outcome measures
Surgical intervention The surgical method was anterior debridement with bone grafting and staged posterior fixation. As the first-stage operation in all patients, total or partial corpectomy with autologous iliac bone grafting at L4 and/or L5 was performed via the anterior retroperitoneal approach. Posterior fixation was performed 1 week later as the second-stage operation to avoid an increased risk of surgical site infection or massive bleeding related to long procedure times for patients whose general conditions were not good due to infectious spondylitis. Screw fixation included the upper two and lower two levels, Fig. 1 Anatomical landmarks used during S1 double screw fixation. a) Insertion point, the upper screw was inserted at the superolateral point of the superior facetal process of the S1. The lower screw was inserted below the upper screw at the lowest point of the S1 body. b, c) Note that the upper screw is inserted in the medial direction, and the lower screw is inserted in the lateral direction
We evaluated dynamic and static lumbar X-rays and/or 3D-CT results data generated for the study patients during the preoperative stage, ambulation period after surgery, and outpatient clinic visits as a part of follow-up. From the X-rays, we measured lumbar lordosis at the upper T12 and S1 endplates and evaluated the displacement of each screw and instrument failure. Bony fusion was observed as bony bridge formation on 3D-CT imaging or the lack of abnormal motion on dynamic lumbar X-rays. A spine surgeon who had not attended the surgery calculated the lumbar alignment and fusion status from these imaging data using repeat measures.
Acta Neurochir (2014) 156:229–233
231
Fig. 2 Lateral view of the upper and lower S1 screws. a) The upper screw was directed just below and parallel to the upper S1 endplate in order to use the cortical portion of the sacrum. b) The lower screw is located at the lowest point of the S1 body and directed upward in order to utilize the cortical portion of the sacrum
vertebral compression fracture occurred at the adjacent level in case 3, and this patient died of lung cancer at 9 months postsurgery.
Results Patient characteristics The characteristics of our seven study patients are summarized in Table 1. There were four women and three men, with a mean age of 63.4±6.3 years (range, 55–73 years) at the time of surgery. The number of mean fusion levels was 3.5±1.1.
Clinical outcomes In all seven study patients, infectious conditions were controlled with continuous intravenous antibiotics following surgery. All patients were discharged and prescribed additional oral antibiotics. During the follow-up periods, a junctional
Radiological outcomes The mean observation period was 16.9±8.6 months (range, 6–25 months). Instrument failures such as rod or screw breakage, screw pullout, or screw loosening did not occur in any patient. The preoperative mean lumbar lordosis was 27.0 °±10.4, a value lower than normal due to a vertebral body and disc space collapse resulting from infectious spondylitis. Lumbar lordosis was restored after surgery and maintained in our patient cohort (35.1 °±10.7), demonstrating only a slight decrease during the follow-up period (31.6 °±8.8; Figs. 3 and 4).
Table 1 Demographics of the seven patients in the study cohort who received S1 double screw fixation Case
Sex
Age (y)
Fixations (no.)
Corpectomy level
Skipped pedicle screw
Preop. lordosis angle (θ)
Immediate postop. lordosis angle (θ)
Postop. lordosis angle at the last follow-up visit (θ)
Follow-up duration (months)
1 2 3 4 5 6 7 Mean±standard deviation
F F F M M F M
70 58 55 62 64 73 62 63.4±6.3
2 2 4 4 5 4 4 3.5±1.1
L5:P L4,5:P L4,5:P L4,5:P L3:P, L4:T L4,5:P L4,5:P
L5 L5 L4,5 L4,5 L4 L5 L5
24 42 34 29 8 27 25 27.0±10.4
40 33 52 31 17 33 40 35.1±10.7
40 35 30 36 15 26 39 31.6±8.8
25 7 18 12 25 25 6 16.9±68.6
no. number, F female, M male, P partial, T total, postop postoperative, preop preoperative
232
Fig. 3 Serial measurement of lumbar lordosis between the T12 and S1 upper endplates
Discussion The fusion rate of sacral fixation is lower than that of other lumbar areas because the sacrum is mainly composed of cancellous bone, and large S1 pedicles induce poor screw engagement. In addition, pullout stress can concentrate at the sacral screw under flexion along the long level of fixation in the lumbar area [12]. Hence, various instrumentation methods have been developed to reduce the instability that this would cause. Two methods for enhancing sacral screw fixation can be considered. The first entails increasing the strength of the S1 pedicle screw: a large-diameter screw demonstrates increased durability against pullout stress. In addition, the converged angle (about a medial 30 °) of the screw can enforce anti-pullout strength by about 28.6 % [10]. Bi- and tricortical screw fixation can also increase the insertion torque [9]. The second method entails an additional sacral or iliac screw (e.g., S1/S2 pedicle, S1 pedicle/S2 alar, S1 pedicle/iliac, S1 pedicle/ S2 iliac screws) [3, 11]. In previous biomechanical studies comparing lumbosacral fixation techniques, supplemental sacral fixation using S1 pedicle screws demonstrates advantages over S1 fixation alone. Iliac fixation is more effective than secondary sacral fixation, but may not be necessary in all clinical situations [8]. Moreover, iliac screw fixation has several disadvantages, including extensive muscle and soft tissue dissection, greater Fig. 4 A 73-year-old woman (case 6) with intractable back pain was referred for surgical treatment. Preoperative images revealed infectious spondylitis and discitis with epidural abscess formation at the L4 and the L5 (a-c). Anterior debridement with iliac bone grafting and staged posterior fixation using S1 double screw fixation was performed 1 week apart. Twenty-five months later, solid fusion and lordotic lumbar alignment were observed by X-ray and 3D-CT (d-f)
Acta Neurochir (2014) 156:229–233
blood loss, longer operation times, and severe postoperative pain. Some patients also report that the implant material can be prominently visible through the skin and can cause discomfort [7, 11]. In our present study, we performed bilateral, double S1 screw fixation (i.e., S1 pedicle and secondary S1 alar screw fixation). This technique provides a stronger fixation power than that of S1 pedicle screw fixation alone, does not require as extensive muscle exposure as with iliac screw fixation, and minimizes implant prominence through the skin. In addition, a minimal muscle dissection approach can reduce postoperative pain in the lumbosacral area. Furthermore, S1 double screw fixation does not need additional hardware for connections between screws, such as sacroiliac screw fixation. The predominant cancellous bone of S1 screw fixation results in a weaker fixation strength compared with an iliac screw fixation. Hence, we modified the S1 screw fixation procedure: the upper screw was inserted at the superolateral point of the superior facetal process of S1 and directed medially and parallel to the upper S1 endplate in order to use the cortical portion of the sacrum. The lower screw was inserted below the upper screw and directed superolaterally toward the upper portion of the alar in order to utilize the cortical portion of the sacrum. S1 double screw fixation was originally introduced as an option for spinal deformity surgery, and several studies have reported the usefulness of S1 double screws in such cases [6]. However, there has been no previous report of S1 double screw fixation to treat patients who are unsuitable for L4 and/or L5 pedicle screw fixation. There are several limitations to this study. Most notably, the sample size was small and there was no control group. Although S1 double screws are uncommon in clinical practice, examining a larger number of patients with a control group may provide further valuable data on their efficacy. Comparing S1 double screw fixation with other SPF methods under the same clinical conditions would also help to clarify
Acta Neurochir (2014) 156:229–233
its effectiveness. Another limitation of this study is its narrow indication. In our presented cases, double screws were inserted to treat infectious spondylitis. To validate a wider range of possible uses, further research will be needed to verify the long-term effects of double screw fixation on the fixation of degenerative spinal disorders or other comparable conditions.
Conclusions Our study findings reveal that S1 double screw fixation can be used in situations where L4 and/or L5 pedicles are unavailable for long-segment lumbar screw fixation. Our current findings also suggest that S1 double screw fixation is a viable option for sacropelvic fixation in selected patients.
Conflicts of interest None. Disclosure This research was supported by the Pioneer Research Center Program through the National Research Foundation of Korea and funded by the Ministry of Science, ICT, & Future Planning (NRF-2010-0019351)
References 1. Allen BL, Jr., Ferguson RL (1988) The Galveston experience with Lrod instrumentation for adolescent idiopathic scoliosis. Clin Orthop Relat Res:59–69 2. Bayley JC, Yuan HA, Fredrickson BE (1991) The Syracuse I-plate. Spine 16:S120–S124, Phila Pa 1976
233 3. Chang TL, Sponseller PD, Kebaish KM, Fishman EK (2009) Low profile pelvic fixation: anatomic parameters for sacral alariliac fixation versus traditional iliac fixation. Spine 34:436–440, Phila Pa 1976 4. Devlin VJ, Boachie-Adjei O, Bradford DS, Ogilvie JW, Transfeldt EE (1991) Treatment of adult spinal deformity with fusion to the sacrum using CD instrumentation. J Spinal Disord 4:1–14 5. Farcy JP, Rawlins BA, Glassman SD (1992) Technique and results of fixation to the sacrum with iliosacral screws. Spine 17:S190–S195, Phila Pa 1976 6. Kim J-H, Kim S-S, Lim D-J, Han J-I, Kim T-Y, Park C-K, Suk S-I (2010) A Comparison of Clinical Stability of Distal Instrument Fused Down to S1 with and without Sub-S1 Alar Screw in the Long Fusion using Segmental Pedicle Screw for Lumbar Degenerative Deformity. J Kor Soc Spine Surg 17:139 7. Kuklo TR, Bridwell KH, Lewis SJ, Baldus C, Blanke K, Iffrig TM, Lenke LG (2001) Minimum 2-year analysis of sacropelvic fixation and L5-S1 fusion using S1 and iliac screws. Spine 26:1976–1983, Phila Pa 1976 8. Lebwohl NH, Cunningham BW, Dmitriev A, Shimamoto N, Gooch L, Devlin V, Boachie-Adjei O, Wagner TA (2002) Biomechanical comparison of lumbosacral fixation techniques in a calf spine model. Spine 27:2312–2320, Phila Pa 1976 9. Lehman RA Jr, Kuklo TR, Belmont PJ Jr, Andersen RC, Polly DW Jr (2002) Advantage of pedicle screw fixation directed into the apex of the sacral promontory over bicortical fixation: a biomechanical analysis. Spine 27:806–811, Phila Pa 1976 10. Leong JC, Lu WW, Zheng Y, Zhu Q, Zhong S (1998) Comparison of the strengths of lumbosacral fixation achieved with techniques using one and two triangulated sacral screws. Spine 23:2289–2294, Phila Pa 1976 11. O'Brien JR, Yu W, Kaufman BE, Bucklen B, Salloum K, Khalil S, Gudipally M (2013) Biomechanical Evaluation of S2 Alar Iliac Screws: The effect of length and quad-cortical purchase as compared to iliac fixation. Spine (Phila Pa 1976) 12. Smith SA, Abitbol JJ, Carlson GD, Anderson DR, Taggart KW, Garfin SR (1993) The effects of depth of penetration, screw orientation, and bone density on sacral screw fixation. Spine 18:1006–1010, Phila Pa 1976
CLINICAL ARTICLE - SPINE
The result of S1 double screw fixation in patients not suited for L4 and/or L5 pedicle screw insertion Il Choi & Sang Ryong Jeon
Received: 10 August 2013 / Accepted: 13 November 2013 / Published online: 28 November 2013 # Springer-Verlag Wien 2013
Abstract Background Variable methods are available for sacropelvic fixation. The usefulness of S1 double screw fixation for deformity surgery is established, but its effectiveness in cases where the L4 and/or L5 pedicle screw is not appropriate has not been reported. Methods We reviewed medical records to identify longsegment, lumbar spine fixation involving S1 double screws. Nine such patients were treated between November 2006 and November 2012 at our center: all patients had infectious spondylitis involving L4 and/or L5. Two patients were excluded due to a limited follow-up period (< 6 months). The remaining seven patients were enrolled. We used dynamic X-rays or three-dimensional computed tomography (3D-CT) to assess any change in the lumbar alignment angle and to evaluate bony fusion with the graft material. Results The mean observation period of the seven patients was 16.9 months (range: 6–25). The mean age was 63.43 years (range: 55–73). Four patients were women. The average number of fusion levels was 3.5±1.1. The ideal positioning and maintenance of the S1 double screws and bony fusion with the graft materials were confirmed using serial imaging. Lordosis in the lumbar region was immediately restored after surgery (27.0 °±10.4 to 35.1 °±10.7), and maintained with slight decrease (31.6 °±8.8) throughout the follow-up period. Conclusions S1 double screws provided stability when L4 and/ or L5 pedicle screw fixation was not possible. Our results suggest that S1 double screws are a viable option for sacropelvic fixation in selected patients. I. Choi : S. R. Jeon (*) Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Pungnap-2dongSongpa-Gu Seoul 138-736, Korea e-mail: [email protected]
Keywords Double screw . Lumbar lordosis . Sacral screw . Sacropelvic fixation . Sacrum . Spondylitis
Introduction Recently, the need for sacropelvic fixation (SPF) has increased. SPF is useful in spinal deformity surgery and revision surgery to address fusion failure for the treatment of select patients who require a lumbosacral fixation to be strengthened. However, SPF has several disadvantages, such as postoperative pain due to extensive lumbosacral muscle and soft tissue dissection, implant prominence through the skin, and fusion of the sacroiliac joint [11]. In some cases, screws cannot be inserted at the L4 and/or L5 pedicles due to a total or partial corpectomy status, infectious spondylitis, or a dysplastic pedicle with high-grade spondylolisthesis. In these cases, an extensive SPF such as iliac screw fixation could be performed; however, considering the disadvantages of iliac screw fixation, other surgical options may be more suitable. These options include S1 screw fixation with additional fixation options: S1 pedicle/S2 pedicle screws, S1 double screws or S1 pedicle/S2 alar screws [1, 2, 4, 5]. At our center, we inserted S1 double screws into both the pedicle and the alar of the S1 when the L4 and/or L5 pedicle was not available for a lumbar, long-segment fixation. The aim of this study was to describe our S1 double screw fixation technique—i.e., bilateral pedicle and alar screw insertion at the S1 entry portion—and to evaluate its long-term effect. The outcome, including screw failure and lordotic angle changes, were evaluated using serial X-ray and 3D-CT data.
230
Methods Study design and patient population We retrospectively reviewed the medical charts, operative notes, neurophysiological data, and neuroimaging results for patients treated between November 2006 and November 2012 at our institution. A total of 134 patients underwent surgery for the treatment of infectious spine disease during this period, of which 112 patients were diagnosed with pyogenic infectious spondylitis and 22 patients with tuberculosis (TB) infectious spondylitis. All patients had undergone first-line medical treatments at the department of infectious diseases. Surgery was recommended when the patient demonstrated neurological deficits due to epidural abscess formation or when the infection was medically intractable. S1 double screw fixation was performed in each of the nine patients when L4 and/or L5 pedicles were deemed to be unsuitable following debridement of the infected vertebral body. We excluded two of these nine cases from the analysis due to a follow-up period less than 6 months.
Acta Neurochir (2014) 156:229–233
except for a pathological lesion level. Each patient was placed in the prone position under general anesthesia. Through a midline skin incision, the spinal muscle was dissected to the lateral facet line. After exposing the entry point for the pedicle screw, the guide pins were inserted at all entry points under Carm fluoroscopy guidance. The pedicle screws were then drilled, tapped, and screwed at all fixation sites (SMC system; OK Medical Co., Seoul, Korea). The ideal entry points for the upper screw are at the just superolateral point of the superior facet of S1 and for the lower screw at the lowest point of the S1 body below the upper screw (Fig. 1a). The upper screw was inserted in a medial direction, and the lower screw in a lateral direction (Fig. 1b–c). The upper screw was directed just below and parallel to the upper endplate of S1 (Fig. 2a). The lower screw was inserted at the lowest point on the S1 body and directed to the upper S1 endplate (Fig. 2b). The screws used were polyaxial, 65 or 75 mm in diameter, and 30, 35, or 40 mm in length. At the week following surgery, all patients were transferred to the department of infectious diseases for continuous antibiotic treatment. We recommended an external brace for 4 months to support the thoraco-lumbo-sacral area. Outcome measures
Surgical intervention The surgical method was anterior debridement with bone grafting and staged posterior fixation. As the first-stage operation in all patients, total or partial corpectomy with autologous iliac bone grafting at L4 and/or L5 was performed via the anterior retroperitoneal approach. Posterior fixation was performed 1 week later as the second-stage operation to avoid an increased risk of surgical site infection or massive bleeding related to long procedure times for patients whose general conditions were not good due to infectious spondylitis. Screw fixation included the upper two and lower two levels, Fig. 1 Anatomical landmarks used during S1 double screw fixation. a) Insertion point, the upper screw was inserted at the superolateral point of the superior facetal process of the S1. The lower screw was inserted below the upper screw at the lowest point of the S1 body. b, c) Note that the upper screw is inserted in the medial direction, and the lower screw is inserted in the lateral direction
We evaluated dynamic and static lumbar X-rays and/or 3D-CT results data generated for the study patients during the preoperative stage, ambulation period after surgery, and outpatient clinic visits as a part of follow-up. From the X-rays, we measured lumbar lordosis at the upper T12 and S1 endplates and evaluated the displacement of each screw and instrument failure. Bony fusion was observed as bony bridge formation on 3D-CT imaging or the lack of abnormal motion on dynamic lumbar X-rays. A spine surgeon who had not attended the surgery calculated the lumbar alignment and fusion status from these imaging data using repeat measures.
Acta Neurochir (2014) 156:229–233
231
Fig. 2 Lateral view of the upper and lower S1 screws. a) The upper screw was directed just below and parallel to the upper S1 endplate in order to use the cortical portion of the sacrum. b) The lower screw is located at the lowest point of the S1 body and directed upward in order to utilize the cortical portion of the sacrum
vertebral compression fracture occurred at the adjacent level in case 3, and this patient died of lung cancer at 9 months postsurgery.
Results Patient characteristics The characteristics of our seven study patients are summarized in Table 1. There were four women and three men, with a mean age of 63.4±6.3 years (range, 55–73 years) at the time of surgery. The number of mean fusion levels was 3.5±1.1.
Clinical outcomes In all seven study patients, infectious conditions were controlled with continuous intravenous antibiotics following surgery. All patients were discharged and prescribed additional oral antibiotics. During the follow-up periods, a junctional
Radiological outcomes The mean observation period was 16.9±8.6 months (range, 6–25 months). Instrument failures such as rod or screw breakage, screw pullout, or screw loosening did not occur in any patient. The preoperative mean lumbar lordosis was 27.0 °±10.4, a value lower than normal due to a vertebral body and disc space collapse resulting from infectious spondylitis. Lumbar lordosis was restored after surgery and maintained in our patient cohort (35.1 °±10.7), demonstrating only a slight decrease during the follow-up period (31.6 °±8.8; Figs. 3 and 4).
Table 1 Demographics of the seven patients in the study cohort who received S1 double screw fixation Case
Sex
Age (y)
Fixations (no.)
Corpectomy level
Skipped pedicle screw
Preop. lordosis angle (θ)
Immediate postop. lordosis angle (θ)
Postop. lordosis angle at the last follow-up visit (θ)
Follow-up duration (months)
1 2 3 4 5 6 7 Mean±standard deviation
F F F M M F M
70 58 55 62 64 73 62 63.4±6.3
2 2 4 4 5 4 4 3.5±1.1
L5:P L4,5:P L4,5:P L4,5:P L3:P, L4:T L4,5:P L4,5:P
L5 L5 L4,5 L4,5 L4 L5 L5
24 42 34 29 8 27 25 27.0±10.4
40 33 52 31 17 33 40 35.1±10.7
40 35 30 36 15 26 39 31.6±8.8
25 7 18 12 25 25 6 16.9±68.6
no. number, F female, M male, P partial, T total, postop postoperative, preop preoperative
232
Fig. 3 Serial measurement of lumbar lordosis between the T12 and S1 upper endplates
Discussion The fusion rate of sacral fixation is lower than that of other lumbar areas because the sacrum is mainly composed of cancellous bone, and large S1 pedicles induce poor screw engagement. In addition, pullout stress can concentrate at the sacral screw under flexion along the long level of fixation in the lumbar area [12]. Hence, various instrumentation methods have been developed to reduce the instability that this would cause. Two methods for enhancing sacral screw fixation can be considered. The first entails increasing the strength of the S1 pedicle screw: a large-diameter screw demonstrates increased durability against pullout stress. In addition, the converged angle (about a medial 30 °) of the screw can enforce anti-pullout strength by about 28.6 % [10]. Bi- and tricortical screw fixation can also increase the insertion torque [9]. The second method entails an additional sacral or iliac screw (e.g., S1/S2 pedicle, S1 pedicle/S2 alar, S1 pedicle/iliac, S1 pedicle/ S2 iliac screws) [3, 11]. In previous biomechanical studies comparing lumbosacral fixation techniques, supplemental sacral fixation using S1 pedicle screws demonstrates advantages over S1 fixation alone. Iliac fixation is more effective than secondary sacral fixation, but may not be necessary in all clinical situations [8]. Moreover, iliac screw fixation has several disadvantages, including extensive muscle and soft tissue dissection, greater Fig. 4 A 73-year-old woman (case 6) with intractable back pain was referred for surgical treatment. Preoperative images revealed infectious spondylitis and discitis with epidural abscess formation at the L4 and the L5 (a-c). Anterior debridement with iliac bone grafting and staged posterior fixation using S1 double screw fixation was performed 1 week apart. Twenty-five months later, solid fusion and lordotic lumbar alignment were observed by X-ray and 3D-CT (d-f)
Acta Neurochir (2014) 156:229–233
blood loss, longer operation times, and severe postoperative pain. Some patients also report that the implant material can be prominently visible through the skin and can cause discomfort [7, 11]. In our present study, we performed bilateral, double S1 screw fixation (i.e., S1 pedicle and secondary S1 alar screw fixation). This technique provides a stronger fixation power than that of S1 pedicle screw fixation alone, does not require as extensive muscle exposure as with iliac screw fixation, and minimizes implant prominence through the skin. In addition, a minimal muscle dissection approach can reduce postoperative pain in the lumbosacral area. Furthermore, S1 double screw fixation does not need additional hardware for connections between screws, such as sacroiliac screw fixation. The predominant cancellous bone of S1 screw fixation results in a weaker fixation strength compared with an iliac screw fixation. Hence, we modified the S1 screw fixation procedure: the upper screw was inserted at the superolateral point of the superior facetal process of S1 and directed medially and parallel to the upper S1 endplate in order to use the cortical portion of the sacrum. The lower screw was inserted below the upper screw and directed superolaterally toward the upper portion of the alar in order to utilize the cortical portion of the sacrum. S1 double screw fixation was originally introduced as an option for spinal deformity surgery, and several studies have reported the usefulness of S1 double screws in such cases [6]. However, there has been no previous report of S1 double screw fixation to treat patients who are unsuitable for L4 and/or L5 pedicle screw fixation. There are several limitations to this study. Most notably, the sample size was small and there was no control group. Although S1 double screws are uncommon in clinical practice, examining a larger number of patients with a control group may provide further valuable data on their efficacy. Comparing S1 double screw fixation with other SPF methods under the same clinical conditions would also help to clarify
Acta Neurochir (2014) 156:229–233
its effectiveness. Another limitation of this study is its narrow indication. In our presented cases, double screws were inserted to treat infectious spondylitis. To validate a wider range of possible uses, further research will be needed to verify the long-term effects of double screw fixation on the fixation of degenerative spinal disorders or other comparable conditions.
Conclusions Our study findings reveal that S1 double screw fixation can be used in situations where L4 and/or L5 pedicles are unavailable for long-segment lumbar screw fixation. Our current findings also suggest that S1 double screw fixation is a viable option for sacropelvic fixation in selected patients.
Conflicts of interest None. Disclosure This research was supported by the Pioneer Research Center Program through the National Research Foundation of Korea and funded by the Ministry of Science, ICT, & Future Planning (NRF-2010-0019351)
References 1. Allen BL, Jr., Ferguson RL (1988) The Galveston experience with Lrod instrumentation for adolescent idiopathic scoliosis. Clin Orthop Relat Res:59–69 2. Bayley JC, Yuan HA, Fredrickson BE (1991) The Syracuse I-plate. Spine 16:S120–S124, Phila Pa 1976
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