- Email: [email protected]
Primary stability of three different iliosacral screw fixation techniques in osteoporotic cadaver specimens—a biomechanical investigation
ARTICLE IN PRESS
The Spine Journal ■■ (2015) ■■–■■
Basic Science
Primary stability of three different iliosacral screw fixation techniques in osteoporotic cadaver specimens—a biomechanical investigation Ludwig Oberkircher, MDa,b,*, Adrian Masaeli, MDa,b, Christopher Bliemel, MDa,b, Florian Debus, MDa,b, Steffen Ruchholtz, MDa,b, Antonio Krüger, MDa,b a Philipps University Marburg, Marburg, Germany Department of Trauma, Hand and Reconstructive Surgery, University Hospital Giessen and Marburg, Marburg, Germany
b
Received 23 January 2015; revised 9 July 2015; accepted 11 August 2015
Abstract
BACKGROUND: The incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is wellestablished in the operative treatment of osteoporotic posterior pelvic ring fractures. However, osteoporotic bone quality might lead to the risk of screw loosening. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended. PURPOSE: The aim of the present biomechanical study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens. STUDY DESIGN/SETTING: This study used methodical cadaver study. METHODS: A total of 15 fresh frozen human cadaveric specimens with osteoporosis were used (os sacrum). After matched pair randomization regarding bone quality (T-score), three operation technique groups were generated: screw fixation (cannulated screws) without cement augmentation (Group A); screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and screw fixation with perforated screws and cement augmentation after screw placement (Group C). In all specimens both sides of the os sacrum were used for operative treatment, resulting in a group size of 10 specimens per group. One operation technique was used on each side of the sacral bone to compare biomechanical properties in the same bone quality. Pull-out tests were performed with a rate of 6 mm/min. A load versus displacement curve was generated. RESULTS: Subgroup 1 (Group A vs. Group B): Screw fixation without cement augmentation: 594.4 N±463.7 and screw fixation with cement augmentation before screw placement: 1,020.8 N±333.3; values were significantly different (p=.025). Subgroup 2 (Group A vs. Group C): Screw fixation without cement augmentation: 641.8 N±242.0 and perforated screw fixation with cement augmentation after screw placement: 1,029.6 N±326.5; values were significantly different (p=.048). Subgroup 3 (Group B vs. Group C): Screw fixation with cement augmentation before screw placement: 804.0 N±515.3 and perforated screw fixation with cement augmentation after screw placement: 889.8 N±503.3; values were not significantly different (p=.472). CONCLUSIONS: Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques involving cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement leakage. These biomechanical results have to be transferred into clinical practice and prove their clinical value. © 2015 Elsevier Inc. All rights reserved.
Keywords:
Biomechanical; Cement augmentation; Fracture; Iliosacral fixation; Osteoporotic; Sacrum
FDA device/drug status: Investigational (modified [six 2.0 mm perforations over the first 1/2 of the thread] self-cutting lag screws made of titanium [aap Biomatterials, Dieburg, GmbH]). Author disclosures: LO: Consulting (Vexim, B), Consulting (DFine, A). AM: Nothing to disclose. CB: Nothing to disclose. FD: Nothing to disclose. SR: Nothing to disclose. AK: Consulting (Vexim, B), Consulting (DFine, A). http://dx.doi.org/10.1016/j.spinee.2015.08.016 1529-9430/© 2015 Elsevier Inc. All rights reserved.
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com. * Corresponding author. Department of Trauma, Hand and Reconstructive Surgery, University Hospital Giessen and Marburg, Baldingerstrasse, 35033 Marburg, Germany. Tel.: 0049 6421 5869125; fax: 0049 6421 5866721. E-mail address: [email protected] (L. Oberkircher)
ARTICLE IN PRESS 2
L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
Introduction Pelvic ring fractures are comparatively rare [1], with an incidence of 0.3–8%, and typically result from high-energy trauma [2]. Because of increasing life expectancy, the incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing [3–6]. Osteoporotic fractures of the pelvic ring differ substantially from high energy fractures regarding symptoms as well as treatment. Even the patient’s own body weight can be sufficient to produce such a fracture [7]. An extreme reduction of bone mass and overstressing of the already weakened bone lead to insufficiency fractures [8]. Insufficiency fractures of the sacrum are already described by Lourie et al. in 1982 [9]. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is a wellestablished therapy in the operative treatment of osteoporotic posterior pelvic ring fractures [10–12]. If elderly patients with sacral insufficiency fractures suffer from a high pain level, this minimal invasive procedure can help to both reduce pain and to recover mobility [13]. Even in unstable sacral fractures, iliosacral screw fixation is used and can be combined with lumbopelvic fixation to achieve a high biomechanical stability [14–16]. To attain even greater stability for the transverse component, lumbopelvic distraction osteosynthesis is combined with iliosacral screw osteosynthesis, resulting in a clinically sufficient multiplanar stability [16]. However, osteoporotic bone quality might lead to the risk of screw loosening [7]. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended [11,17,18]. Cement augmentation is often performed before screw placement [3]. Wähnert et al. developed a new method with perforated screws, which allows the application of cement after screw placement [19] to reduce possible complications such as cement displacement resulting in nerve compression or embolization [13]. Aim of the study The aim of the present biomechanical cadaver study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens. Our goal was to compare axial pull-out failure in the following three techniques: screw fixation without cement application, screw fixation with cement application before screw
insertion, and screw fixation with a modified, perforated screw and cement application after screw positioning. Materials and methods Specimens A total of 15 fresh frozen human cadaveric specimens were used (os sacrum). Only women donors (mean age 81.47±9.04 years) were selected, and bone density was measured in all specimens separately, which showed substantial osteoporosis (mean T-score −4.45±1.73). Osteoporosis was defined according to the World Health Organization (WHO) criteria— bone mineral density of more than 2.5 standard deviations below the mean of a young healthy reference population of the same gender (T-score). A preliminary computed tomography scan of all specimens was performed to identify any pathologies, especially preexistent sacral fractures or deformities. Soft tissue was removed and the specimens were stored at −20°C until testing. Just before the experiment, all specimens were thawed to a temperature of 37°C in a water bath to achieve realistic conditions of cement dispersion. Group generation Matched pair randomization regarding bone quality (Tscore) was performed to establish similar groups. Three operation technique groups were generated: screw fixation (cannulated screws) without cement augmentation (Group A); screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and screw fixation with perforated screws and cement augmentation after screw placement (Group C) (see Fig. 1). In all specimens both sides of the os sacrum were used for operative treatment, resulting in a group size of 10 specimens per group. One operation technique was used on each side of the sacral bone to compare biomechanical properties in the same bone quality. This allowed us to establish three comparable subgroups: subgroup 1: screw fixation without cement augmentation versus screw fixation with cement augmentation before screw placement; subgroup 2: perforated screw fixation with cement augmentation after screw placement versus screw fixation without cement augmentation; and subgroup 3: screw fixation with cement augmentation before
Fig. 1. Radiographics of the operation groups: (Left) screw fixation (cannulated screws) without cement augmentation (Group A); (Middle) screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and (Right) screw fixation with perforated screws and cement augmentation after screw placement (modified screws) (Group C).
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
screw placement versus perforated screw fixation with cement augmentation after screw placement. Operative treatment All operations were performed by the same surgeon (LO). Placement and positioning of the screw fixation as well as cement application was monitored by fluoroscopic control in three planes (a.p., lateral and craniocaudal) using an image intensifier. In Groups A and B, cannulated 7.5-mm halfthreaded, self-cutting lag screws made of titanium (aap Biomaterials GmbH, Dieburg, Germany) were used (see Fig. 1). For Group C, the same screws were modified: modification included six 2.0-mm perforations over the first 1/2 of the thread (diameter of the perforations was chosen corresponding to the inner diameter of the lag screws [2.0 mm] to allow a homogenously cement emersion through all perforations) (see Figs. 1 and 2). Group A After inserting a K-wire into S1 until the midline, the screw was positioned and drilled into S1 until the midline of the sacrum was reached. Fluoroscopic control always showed placement of the thread inside S1. Afterward the K-wire was removed. Group B After inserting a K-wire in the right position of S1 until the midline, a working cannular was placed for cement injection (Kyphon Medtronic, Sunnyvale, CA, USA). Correct
3
placement was always controlled by fluoroscopy. The K-wire was removed and 1.5 mL of bone cement (PMMA, Concept Spine VR, Radiopaque Bone Cement, Advanced Biomaterial Systems, Chatham, NJ, USA) was injected at the end of the drill hole with the use of a bone filler (Kyphon, Medtronic). The K-wire was reinserted, the working cannula was removed, and the cannulated screw was placed in S1 until the midline so that the thread was surrounded by bone cement. Afterward the K-wire was removed. Group C After inserting a K-wire into S1 until the midline, the modified screw was positioned and drilled into S1 until the midline was reached. Fluoroscopic control always showed placement of the thread inside S1. The K-wire was removed, and 1.5 mL of bone cement (PMMA, Concept Spine VR, Radiopaque Bone Cement, Advanced Biomaterial Systems, USA) was directly injected via a bone filler (Kyphon, Medtronic). Pull-out test Pull-out tests were performed by a material testing machine (Universal Testing Machine, Instron 5566, Instron® GmbH, Schenck Technologie- und Industriepark, Landwehrstraße 65, Darmstadt, D-64293, Germany). Specimens were prepared at the surface and embedded in a fixation case to allow the screw to be pulled out to its axis of insertion (see Fig. 2). Pullout tests were performed with a rate of 6 mm/min. A load versus displacement curve was generated.
Fig. 2. (Left) Pull-out procedure with Instron 5566: Specimens were prepared at the surface and embedded in a fixation case to allow the screw to be pulled out to its axis of insertion. (Top Right) Modified screw: Modification includes six 2.0-mm perforations over the first 1/2 of the thread (diameter of the perforations was chosen corresponding the inner diameter of the lag screws (2.0 mm) to allow a homogenously cement emersion through all perforations). (Bottom Right) Modified screw with cement after pull-out procedure.
ARTICLE IN PRESS 4
L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
The following values were measured in the loaddisplacement curve: maximum pull-out force (N) Newton, displacement at the point of maximum force (mm), and the E-Module (kPa). Statistics Statistics were performed by GraphPad Prism Version 5.03 (GraphPad Software, Inc., La Jolla, CA, USA). For all parameters determined, the results are expressed as means and ±SD. The test of significance between results from study pairs was conducted by using the paired Student t test with significance p<.05. Results Pull-out force The mean maximum pull-out force was 618.1 N±390.7 in Group A, 912.39 N±471.5 in Group B, and 959.7 N±453.2 in Group C (see Fig. 3). The following pull-out forces were measured in subgroups that compared two different techniques in the same specimens with respect to bone quality:
Subgroup 1 (Group A vs. Group B) Screw fixation without cement augmentation: 594.4 N±463.7 and screw fixation with cement augmentation before screw placement: 1,020.8 N±333.3; values were significantly different (p=.025) (see Fig. 3 and Table). Subgroup 2 (Group A vs. Group C) Screw fixation without cement augmentation: 641.8 N±242.0 and perforated screw fixation with cement augmentation after screw placement: 1,029.6 N±326.5; values were significantly different (p=.048) (see Fig. 3 and Table). Subgroup 3 (Group B vs. Group C) Screw fixation with cement augmentation before screw placement: 804.0 N±515.3 and perforated screw fixation with cement augmentation after screw placement: 889.8 N±503.3; values were not significantly different (p=.472) (see Fig. 3 and Table). E-Module The mean E-Module was 1,374.8 kPa±643.1 in Group A, 1,291.6 kPa±474.6 in Group B, and 1,427.5 kPa±545.5 in Group C.
Fig. 3. Graphical respresentation of the maximum pull-out force (N): Graph A: all operation groups (Group A–C) Graph B: Subgroup 1: Operation group A (screw fixation (cannulated screws) without cement augmentation) vs. Operation group B (screw fixation with cement augmentation before screw placement (cannulated screws)). Graph C: Subgroup 2: Operation group A (screw fixation (cannulated screws) without cement augmentation) vs. Operation group C (screw fixation with perforated screws and cement augmentation after screw placement (modified screws)). Graph D: Subgroup 3: Operation group B (screw fixation with cement augmentation before screw placement (cannulated screws)) vs. Operation group C (screw fixation with perforated screws and cement augmentation after screw placement (modified screws)).
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■ Table Characteristics of all operation groups (A–C) sorted by subgroup 1–3 Subgroup 1
Specimen no. 1 4 6 9 10 Mean SD
2 3 5 8 13 Mean SD
ation with cement augmentation after screw placement was 1,306.8 kPa±472.8; values were not significantly different (p=.413) (see Table).
Max. pull-out force (N)
E-Module (kPa)
DXA
Operation Group A
Operation Group B
Operation Group A
Operation Group B
Discussion
−4.0 −3.9 −6.8 −6.0 −2.1 −4.56 1.67
136 328 248 1,354 906 594.4 463.72
468.9 1,106 874 1,458 1,197 1,020.78 333.34
1,604 832 1,768 1,991 1,873 1,613.6 410.99
2,155 1,293 1,675 1,381 1,001 1,501 391.32
Increasing life expectancy in the last decades is leading to a higher incidence of osteoporotic as well as insufficiency fractures of the pelvic ring [3,4]. Trauma mechanisms as well as the resulting treatment differ from other types of pelvic ring fractures. The most common mechanism of those fractures is a low impact trauma [2], leading to severe pain and dysfunction [20]. Whereas many elderly patients are still active and have high functional demands, other elderly patients already suffer from multiple comorbidities. Nevertheless, the treatment goal for both groups should be pain reduction, improvement of function, and quality of life [2]. Various operative treatment options are discussed and performed, such as the percutaneous iliosacral screw osteosynthesis [21–24]. The compression of the fracture zone reached via the iliosacral screw fixation leads to pain reduction in elderly patients with sacral insufficieny fractures [13,25]. Iliosacral screw fixation is also used to achieve high biomechanical stability in unstable fractures of the os sacrum when combined with lumbopelvic fixation [14–16]. To attain additional stability for the transverse component, lumbopelvic distraction osteosynthesis is combined with iliosacral screw osteosynthesis, leading to a clinically sufficient multiplanar stability [16]. Nevertheless, in osteoporotic bone, a sole iliosacral screw fixation might be mechanically insufficient [14,26,27] and presents a high risk of screw loosening [7]. With respect to poor bone quality, various considerations of iliosacral screw fixation of sacral fractures have been discussed in recent years, including screw positioning as well as cement augmentation. This technique combines iliosacral screw fixation with sacroplasty and should improve stability and load sharing by increasing the supportive surface [20]. In recent years cement augmentation of iliosacral screws has been recommended in osteoporotic bone [11]; nevertheless, some remaining risks such as cement leakage and consecutive nerval compression or cement embolism should be taken into consideration [28]. To minimize complications related to cement leakage, Wähnert et al. developed a new technique with modified screws to allow cement augmentation after screw placement via perforations with low amounts of cement [19]. To our knowledge there are still no biomechanical considerations regarding this new technique, including clinical studies with a high number of patients, who underwent iliosacral screw osteosyntheses combined with cement augmentation. Spine surgery cement augmentation of pedicle screws as well as the use of fenestrated pedicle screws especially for osteoporotic bone is well described in the literature because of the knowledge of screw loosening in patients with compromised bone quality like osteoporosis [29–33]. Augmented pedicel screws showed higher pull-out forces than nonaugmented screws [29]. Using fenestrated pedicle screws may
Subgroup 2
Specimen no.
5
Max. pull-out force (N)
E-Module (kPa)
DXA
Operation Group A
Operation Group C
Operation Group A
Operation Group C
−7.4 −3.9 −2 −6.3 −4 −4.72 1.91
640 604 1,074 563 328 641.8 242.04
652 791 1,468 1,369 868 1,029.6 326.50
750 411 725 2,288 1,506 1,136 679.34
2,065 1,341 763 2,219 1,353 1,548.2 531.91
Subgroup 3 Max. pull-out force (N)
E-Module (kPa)
Specimen no.
DXA
Operation Group B
Operation Group C
Operation Group B
Operation Group C
7 11 12 14 15 Mean SD
−3.5 −6.0 −3.1 −5.2 −3.7 −4.3 1.11
419 1,647 1,090 197 667 804 515.34
663 1,419 1,455 110 802 889.8 503.34
1,418 1,557 1,136 883 417 1,082.2 405.77
757 1,963 1,769 953 1,092 1,306.8 472.83
The following E-Module values were measured in those subgroups comparing two different techniques in the same specimens with respect to bone quality Subgroup 1 (Group A vs. Group B) Screw fixation without cement augmentation was 1,613.6 kPa±411, and screw fixation with cement augmentation before screw placement was 1,501 kPa±391.3; values were not significantly different (p=.71) (see Table). Subgroup 2 (Group A vs. Group C) Screw fixation without cement augmentation was 1,136 kPa±679.3, and perforated screw fixation with cement augmentation after screw placement was 1,548.2 kPa±531.9; values were not significantly different (p=.239) (see Table). Subgroup 3 (Group B vs. Group C) Screw fixation with cement augmentation before screw placement was 1,082.2 kPa±405.8, and perforated screw fix-
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
6
lower the risk of cement leakage in the clinical setting especially in osteoporotic bone quality [29]. The goal of our biomechanical study was a comparative evaluation of the primary stability of three iliosacral screw fixations in osteoporotic bone: screw fixation without cement application; screw fixation with cement application before screw insertion; and screw fixation with a modified, perforated screw and cement application after screw positioning. Screw insertion to the midline of S1 was performed according to the recommendations in the literature. Biomechanical studies have shown better stability by placing the screws at least into the central zone of the os sacrum [34,35]. Both screw fixation techniques in combination with cement application showed a significantly higher pull-out strength than screw fixation without cement application (see Fig. 3). These findings confirm the hypotheses that screw fixation in osteoporotic spongious bone without supplementary support (eg, cement augmentation) might not be sufficient. Perforated screws are a promising alternative that have the same primary stability as that of conventional screw fixation with additional cement augmentation. Limitations of the study Our study has some limitations. Primary stabilization was measured via pull-out strength; thus, no predication regarding continuous loading can be made. Our biomechanical testing mechanism in this study does not reflect the physiologic stress and typical failure pattern observed in practice. We decided to measure pull-out forces for different screw fixation techniques. The surrounding was minimalized and standardized for all procedures to reduce differences as much as possible. Further biomechanical and clinical studies might complement our findings. Conclusions Our conclusions to screw stability in fixation techniques are based on a biomechanical evaluation. Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques using cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement leakage. References [1] Tosounidis G, Holstein JH, Culemann U, Holmenschlager F, Stuby F, Pohlemann T. Changes in epidemiology and treatment of pelvic ring fractures in Germany: an analysis on data of German Pelvic Multicenter Study Groups I and III (DGU/AO). Acta Chir Orthop Traumatol Cech 2010;6:450–6. [2] Rommens PM, Wagner D, Hofmann A. Surgical management of osteoporotic pelvic fractures: a new challenge. Eur J Trauma Emerg Surg 2012;5:499–509.
[3] Fuchs T, Rottbeck U, Hofbauer V, Raschke M, Stange R. Pelvic ring fractures in the elderly. Underestimated osteoporotic fracture. Unfallchirurg 2011;8:663–70. [4] Lin JT, Lane JM. Sacral stress fractures. J Womens Health (Larchmt) 2003;9:879–88. [5] Morris RO, Sonibare A, Green DJ, Masud T. Closed pelvic fractures: characteristics and outcomes in older patients admitted to medical and geriatric wards. Postgrad Med J 2000;900:646–50. [6] Pohlemann T, Stengel D, Tosounidis G, Reilmann H, Stuby F, Stockle U, et al. Survival trends and predictors of mortality in severe pelvic trauma: estimates from the German Pelvic Trauma Registry Initiative. Injury 2011;10:997–1002. [7] Rommens PM, Hofmann A. Comprehensive classification of fragility fractures of the pelvic ring: recommendations for surgical treatment. Injury 2013;12:1733–44. [8] Frey ME, Depalma MJ, Cifu DX, Bhagia SM, Carne W, Daitch JS. Percutaneous sacroplasty for osteoporotic sacral insufficiency fractures: a prospective, multicenter, observational pilot study. Spine J 2008;2:367–73. [9] Lourie H. Spontaneous osteoporotic fracture of the sacrum. An unrecognized syndrome of the elderly. JAMA 1982;6:715–7. [10] Rommens PM. Is there a role for percutaneous pelvic and acetabular reconstruction? Injury 2007;4:463–77. [11] Tjardes T, Paffrath T, Baethis H, Shafizadeh S, Steinhausen E, Steinbuechel T, et al. Computer assisted percutaneous placement of augmented iliosacral screws: a reasonable alternative to sacroplasty. Spine (Phila Pa 1976) 2008;13:1497–500. [12] Tsiridis E, Upadhyay N, Gamie Z, Giannoudis PV. Percutaneous screw fixation for sacral insufficiency fractures: a review of three cases. J Bone Joint Surg Br 2007;12:1650–3. [13] Stuby FM, Schaffler A, Haas T, Konig B, Stockle U, Freude T. Insufficiency fractures of the pelvic ring. Unfallchirurg 2013;4:351–64. [14] Dudda M, Hoffmann M, Schildhauer TA. Sacrum fractures and lumbopelvic instabilities in pelvic ring injuries: classification and biomechanical aspects. Unfallchirurg 2013;11:972–8. [15] Gansslen A. Biomechanical principles for treatment of osteoporotic fractures of the pelvis. Unfallchirurg 2010;4:272–80. [16] Schildhauer TA, Ledoux WR, Chapman JR, Henley MB, Tencer AF, Routt ML Jr. Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: a cadaveric and biomechanical evaluation under cyclic loads. J Orthop Trauma 2003;1:22–31. [17] Bohme J, Hoch A, Josten C. Osteoporotic fractures of the pelvis. Chirurg 2012;10:875–81. [18] Shah RV. Sacral kyphoplasty for the treatment of painful sacral insufficiency fractures and metastases. Spine J 2012;2:113–20. [19] Wähnert D, Raschke MJ, Fuchs T. Cement augmentation of the navigated iliosacral screw in the treatment of insufficiency fractures of the sacrum: a new method using modified implants. Int Orthop 2013;6:1147–50. [20] Mears SC, Sutter EG, Wall SJ, Rose DM, Belkoff SM. Biomechanical comparison of three methods of sacral fracture fixation in osteoporotic bone. Spine (Phila Pa 1976) 2010;10:E392–5. [21] Failinger MS, McGanity PL. Unstable fractures of the pelvic ring. J Bone Joint Surg Am 1992;5:781–91. [22] Matta JM, Tornetta P III. Internal fixation of unstable pelvic ring injuries. Clin Orthop Relat Res 1996;329:129–40. [23] Routt ML Jr, Kregor PJ, Simonian PT, Mayo KA. Early results of percutaneous iliosacral screws placed with the patient in the supine position. J Orthop Trauma 1995;3:207–14. [24] Ward EF, Tomasin J, Vander Griend RA. Open reduction and internal fixation of vertical shear pelvic fractures. J Trauma 1987;3:291–5. [25] Zhao Y, Li J, Wang D, Liu Y, Tan J, Zhang S. Comparison of stability of two kinds of sacro-iliac screws in the fixation of bilateral sacral fractures in a finite element model. Injury 2012;4:490–4. [26] Keating JF, Werier J, Blachut P, Broekhuyse H, Meek RN, O’Brien PJ. Early fixation of the vertically unstable pelvis: the role of iliosacral screw fixation of the posterior lesion. J Orthop Trauma 1999;2:107–13.
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■ [27] Rommens PM, Vanderschot PM, De Boodt P, Broos PL. Surgical management of pelvic ring disruptions. Indications, techniques and functional results. Unfallchirurg 1992;9:455–62. [28] Bastian JD, Keel MJ, Heini PF, Seidel U, Benneker LM. Complications related to cement leakage in sacroplasty. Acta Orthop Belg 2012;1:100– 5. [29] Choma TJ, Pfeiffer FM, Swope RW, Hirner JP. Pedicle screw design and cement augmentation in osteoporotic vertebrae: effects of fenestrations and cement viscosity on fixation and extraction. Spine (Phila Pa 1976) 2012;26:E1628–32. [30] Halvorson TL, Kelley LA, Thomas KA, Whitecloud TS III, Cook SD. Effects of bone mineral density on pedicle screw fixation. Spine (Phila Pa 1976) 1994;21:2415–20. [31] Renner SM, Lim TH, Kim WJ, Katolik L, An HS, Andersson GB. Augmentation of pedicle screw fixation strength using an injectable
[32]
[33]
[34]
[35]
7
calcium phosphate cement as a function of injection timing and method. Spine (Phila Pa 1976) 2004;11:E212–6. Soshi S, Shiba R, Kondo H, Murota K. An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine (Phila Pa 1976) 1991;11:1335–41. Wuisman PI, Van Dijk M, Staal H, Van Royen BJ. Augmentation of (pedicle) screws with calcium apatite cement in patients with severe progressive osteoporotic spinal deformities: an innovative technique. Eur Spine J 2000;6:528–33. Daum WJ, Patterson RM, Cartwright TJ, Viegas SF. Comparison of cortical and cancellous screw pull-out strengths about the posterior column and sacroiliac joint. J Orthop Trauma 1991;1:34–7. Kraemer W, Hearn T, Tile M, Powell J. The effect of thread length and location on extraction strengths of iliosacral lag screws. Injury 1994;1:5–9.
The Spine Journal ■■ (2015) ■■–■■
Basic Science
Primary stability of three different iliosacral screw fixation techniques in osteoporotic cadaver specimens—a biomechanical investigation Ludwig Oberkircher, MDa,b,*, Adrian Masaeli, MDa,b, Christopher Bliemel, MDa,b, Florian Debus, MDa,b, Steffen Ruchholtz, MDa,b, Antonio Krüger, MDa,b a Philipps University Marburg, Marburg, Germany Department of Trauma, Hand and Reconstructive Surgery, University Hospital Giessen and Marburg, Marburg, Germany
b
Received 23 January 2015; revised 9 July 2015; accepted 11 August 2015
Abstract
BACKGROUND: The incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is wellestablished in the operative treatment of osteoporotic posterior pelvic ring fractures. However, osteoporotic bone quality might lead to the risk of screw loosening. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended. PURPOSE: The aim of the present biomechanical study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens. STUDY DESIGN/SETTING: This study used methodical cadaver study. METHODS: A total of 15 fresh frozen human cadaveric specimens with osteoporosis were used (os sacrum). After matched pair randomization regarding bone quality (T-score), three operation technique groups were generated: screw fixation (cannulated screws) without cement augmentation (Group A); screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and screw fixation with perforated screws and cement augmentation after screw placement (Group C). In all specimens both sides of the os sacrum were used for operative treatment, resulting in a group size of 10 specimens per group. One operation technique was used on each side of the sacral bone to compare biomechanical properties in the same bone quality. Pull-out tests were performed with a rate of 6 mm/min. A load versus displacement curve was generated. RESULTS: Subgroup 1 (Group A vs. Group B): Screw fixation without cement augmentation: 594.4 N±463.7 and screw fixation with cement augmentation before screw placement: 1,020.8 N±333.3; values were significantly different (p=.025). Subgroup 2 (Group A vs. Group C): Screw fixation without cement augmentation: 641.8 N±242.0 and perforated screw fixation with cement augmentation after screw placement: 1,029.6 N±326.5; values were significantly different (p=.048). Subgroup 3 (Group B vs. Group C): Screw fixation with cement augmentation before screw placement: 804.0 N±515.3 and perforated screw fixation with cement augmentation after screw placement: 889.8 N±503.3; values were not significantly different (p=.472). CONCLUSIONS: Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques involving cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement leakage. These biomechanical results have to be transferred into clinical practice and prove their clinical value. © 2015 Elsevier Inc. All rights reserved.
Keywords:
Biomechanical; Cement augmentation; Fracture; Iliosacral fixation; Osteoporotic; Sacrum
FDA device/drug status: Investigational (modified [six 2.0 mm perforations over the first 1/2 of the thread] self-cutting lag screws made of titanium [aap Biomatterials, Dieburg, GmbH]). Author disclosures: LO: Consulting (Vexim, B), Consulting (DFine, A). AM: Nothing to disclose. CB: Nothing to disclose. FD: Nothing to disclose. SR: Nothing to disclose. AK: Consulting (Vexim, B), Consulting (DFine, A). http://dx.doi.org/10.1016/j.spinee.2015.08.016 1529-9430/© 2015 Elsevier Inc. All rights reserved.
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com. * Corresponding author. Department of Trauma, Hand and Reconstructive Surgery, University Hospital Giessen and Marburg, Baldingerstrasse, 35033 Marburg, Germany. Tel.: 0049 6421 5869125; fax: 0049 6421 5866721. E-mail address: [email protected] (L. Oberkircher)
ARTICLE IN PRESS 2
L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
Introduction Pelvic ring fractures are comparatively rare [1], with an incidence of 0.3–8%, and typically result from high-energy trauma [2]. Because of increasing life expectancy, the incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing [3–6]. Osteoporotic fractures of the pelvic ring differ substantially from high energy fractures regarding symptoms as well as treatment. Even the patient’s own body weight can be sufficient to produce such a fracture [7]. An extreme reduction of bone mass and overstressing of the already weakened bone lead to insufficiency fractures [8]. Insufficiency fractures of the sacrum are already described by Lourie et al. in 1982 [9]. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is a wellestablished therapy in the operative treatment of osteoporotic posterior pelvic ring fractures [10–12]. If elderly patients with sacral insufficiency fractures suffer from a high pain level, this minimal invasive procedure can help to both reduce pain and to recover mobility [13]. Even in unstable sacral fractures, iliosacral screw fixation is used and can be combined with lumbopelvic fixation to achieve a high biomechanical stability [14–16]. To attain even greater stability for the transverse component, lumbopelvic distraction osteosynthesis is combined with iliosacral screw osteosynthesis, resulting in a clinically sufficient multiplanar stability [16]. However, osteoporotic bone quality might lead to the risk of screw loosening [7]. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended [11,17,18]. Cement augmentation is often performed before screw placement [3]. Wähnert et al. developed a new method with perforated screws, which allows the application of cement after screw placement [19] to reduce possible complications such as cement displacement resulting in nerve compression or embolization [13]. Aim of the study The aim of the present biomechanical cadaver study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens. Our goal was to compare axial pull-out failure in the following three techniques: screw fixation without cement application, screw fixation with cement application before screw
insertion, and screw fixation with a modified, perforated screw and cement application after screw positioning. Materials and methods Specimens A total of 15 fresh frozen human cadaveric specimens were used (os sacrum). Only women donors (mean age 81.47±9.04 years) were selected, and bone density was measured in all specimens separately, which showed substantial osteoporosis (mean T-score −4.45±1.73). Osteoporosis was defined according to the World Health Organization (WHO) criteria— bone mineral density of more than 2.5 standard deviations below the mean of a young healthy reference population of the same gender (T-score). A preliminary computed tomography scan of all specimens was performed to identify any pathologies, especially preexistent sacral fractures or deformities. Soft tissue was removed and the specimens were stored at −20°C until testing. Just before the experiment, all specimens were thawed to a temperature of 37°C in a water bath to achieve realistic conditions of cement dispersion. Group generation Matched pair randomization regarding bone quality (Tscore) was performed to establish similar groups. Three operation technique groups were generated: screw fixation (cannulated screws) without cement augmentation (Group A); screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and screw fixation with perforated screws and cement augmentation after screw placement (Group C) (see Fig. 1). In all specimens both sides of the os sacrum were used for operative treatment, resulting in a group size of 10 specimens per group. One operation technique was used on each side of the sacral bone to compare biomechanical properties in the same bone quality. This allowed us to establish three comparable subgroups: subgroup 1: screw fixation without cement augmentation versus screw fixation with cement augmentation before screw placement; subgroup 2: perforated screw fixation with cement augmentation after screw placement versus screw fixation without cement augmentation; and subgroup 3: screw fixation with cement augmentation before
Fig. 1. Radiographics of the operation groups: (Left) screw fixation (cannulated screws) without cement augmentation (Group A); (Middle) screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and (Right) screw fixation with perforated screws and cement augmentation after screw placement (modified screws) (Group C).
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
screw placement versus perforated screw fixation with cement augmentation after screw placement. Operative treatment All operations were performed by the same surgeon (LO). Placement and positioning of the screw fixation as well as cement application was monitored by fluoroscopic control in three planes (a.p., lateral and craniocaudal) using an image intensifier. In Groups A and B, cannulated 7.5-mm halfthreaded, self-cutting lag screws made of titanium (aap Biomaterials GmbH, Dieburg, Germany) were used (see Fig. 1). For Group C, the same screws were modified: modification included six 2.0-mm perforations over the first 1/2 of the thread (diameter of the perforations was chosen corresponding to the inner diameter of the lag screws [2.0 mm] to allow a homogenously cement emersion through all perforations) (see Figs. 1 and 2). Group A After inserting a K-wire into S1 until the midline, the screw was positioned and drilled into S1 until the midline of the sacrum was reached. Fluoroscopic control always showed placement of the thread inside S1. Afterward the K-wire was removed. Group B After inserting a K-wire in the right position of S1 until the midline, a working cannular was placed for cement injection (Kyphon Medtronic, Sunnyvale, CA, USA). Correct
3
placement was always controlled by fluoroscopy. The K-wire was removed and 1.5 mL of bone cement (PMMA, Concept Spine VR, Radiopaque Bone Cement, Advanced Biomaterial Systems, Chatham, NJ, USA) was injected at the end of the drill hole with the use of a bone filler (Kyphon, Medtronic). The K-wire was reinserted, the working cannula was removed, and the cannulated screw was placed in S1 until the midline so that the thread was surrounded by bone cement. Afterward the K-wire was removed. Group C After inserting a K-wire into S1 until the midline, the modified screw was positioned and drilled into S1 until the midline was reached. Fluoroscopic control always showed placement of the thread inside S1. The K-wire was removed, and 1.5 mL of bone cement (PMMA, Concept Spine VR, Radiopaque Bone Cement, Advanced Biomaterial Systems, USA) was directly injected via a bone filler (Kyphon, Medtronic). Pull-out test Pull-out tests were performed by a material testing machine (Universal Testing Machine, Instron 5566, Instron® GmbH, Schenck Technologie- und Industriepark, Landwehrstraße 65, Darmstadt, D-64293, Germany). Specimens were prepared at the surface and embedded in a fixation case to allow the screw to be pulled out to its axis of insertion (see Fig. 2). Pullout tests were performed with a rate of 6 mm/min. A load versus displacement curve was generated.
Fig. 2. (Left) Pull-out procedure with Instron 5566: Specimens were prepared at the surface and embedded in a fixation case to allow the screw to be pulled out to its axis of insertion. (Top Right) Modified screw: Modification includes six 2.0-mm perforations over the first 1/2 of the thread (diameter of the perforations was chosen corresponding the inner diameter of the lag screws (2.0 mm) to allow a homogenously cement emersion through all perforations). (Bottom Right) Modified screw with cement after pull-out procedure.
ARTICLE IN PRESS 4
L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
The following values were measured in the loaddisplacement curve: maximum pull-out force (N) Newton, displacement at the point of maximum force (mm), and the E-Module (kPa). Statistics Statistics were performed by GraphPad Prism Version 5.03 (GraphPad Software, Inc., La Jolla, CA, USA). For all parameters determined, the results are expressed as means and ±SD. The test of significance between results from study pairs was conducted by using the paired Student t test with significance p<.05. Results Pull-out force The mean maximum pull-out force was 618.1 N±390.7 in Group A, 912.39 N±471.5 in Group B, and 959.7 N±453.2 in Group C (see Fig. 3). The following pull-out forces were measured in subgroups that compared two different techniques in the same specimens with respect to bone quality:
Subgroup 1 (Group A vs. Group B) Screw fixation without cement augmentation: 594.4 N±463.7 and screw fixation with cement augmentation before screw placement: 1,020.8 N±333.3; values were significantly different (p=.025) (see Fig. 3 and Table). Subgroup 2 (Group A vs. Group C) Screw fixation without cement augmentation: 641.8 N±242.0 and perforated screw fixation with cement augmentation after screw placement: 1,029.6 N±326.5; values were significantly different (p=.048) (see Fig. 3 and Table). Subgroup 3 (Group B vs. Group C) Screw fixation with cement augmentation before screw placement: 804.0 N±515.3 and perforated screw fixation with cement augmentation after screw placement: 889.8 N±503.3; values were not significantly different (p=.472) (see Fig. 3 and Table). E-Module The mean E-Module was 1,374.8 kPa±643.1 in Group A, 1,291.6 kPa±474.6 in Group B, and 1,427.5 kPa±545.5 in Group C.
Fig. 3. Graphical respresentation of the maximum pull-out force (N): Graph A: all operation groups (Group A–C) Graph B: Subgroup 1: Operation group A (screw fixation (cannulated screws) without cement augmentation) vs. Operation group B (screw fixation with cement augmentation before screw placement (cannulated screws)). Graph C: Subgroup 2: Operation group A (screw fixation (cannulated screws) without cement augmentation) vs. Operation group C (screw fixation with perforated screws and cement augmentation after screw placement (modified screws)). Graph D: Subgroup 3: Operation group B (screw fixation with cement augmentation before screw placement (cannulated screws)) vs. Operation group C (screw fixation with perforated screws and cement augmentation after screw placement (modified screws)).
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■ Table Characteristics of all operation groups (A–C) sorted by subgroup 1–3 Subgroup 1
Specimen no. 1 4 6 9 10 Mean SD
2 3 5 8 13 Mean SD
ation with cement augmentation after screw placement was 1,306.8 kPa±472.8; values were not significantly different (p=.413) (see Table).
Max. pull-out force (N)
E-Module (kPa)
DXA
Operation Group A
Operation Group B
Operation Group A
Operation Group B
Discussion
−4.0 −3.9 −6.8 −6.0 −2.1 −4.56 1.67
136 328 248 1,354 906 594.4 463.72
468.9 1,106 874 1,458 1,197 1,020.78 333.34
1,604 832 1,768 1,991 1,873 1,613.6 410.99
2,155 1,293 1,675 1,381 1,001 1,501 391.32
Increasing life expectancy in the last decades is leading to a higher incidence of osteoporotic as well as insufficiency fractures of the pelvic ring [3,4]. Trauma mechanisms as well as the resulting treatment differ from other types of pelvic ring fractures. The most common mechanism of those fractures is a low impact trauma [2], leading to severe pain and dysfunction [20]. Whereas many elderly patients are still active and have high functional demands, other elderly patients already suffer from multiple comorbidities. Nevertheless, the treatment goal for both groups should be pain reduction, improvement of function, and quality of life [2]. Various operative treatment options are discussed and performed, such as the percutaneous iliosacral screw osteosynthesis [21–24]. The compression of the fracture zone reached via the iliosacral screw fixation leads to pain reduction in elderly patients with sacral insufficieny fractures [13,25]. Iliosacral screw fixation is also used to achieve high biomechanical stability in unstable fractures of the os sacrum when combined with lumbopelvic fixation [14–16]. To attain additional stability for the transverse component, lumbopelvic distraction osteosynthesis is combined with iliosacral screw osteosynthesis, leading to a clinically sufficient multiplanar stability [16]. Nevertheless, in osteoporotic bone, a sole iliosacral screw fixation might be mechanically insufficient [14,26,27] and presents a high risk of screw loosening [7]. With respect to poor bone quality, various considerations of iliosacral screw fixation of sacral fractures have been discussed in recent years, including screw positioning as well as cement augmentation. This technique combines iliosacral screw fixation with sacroplasty and should improve stability and load sharing by increasing the supportive surface [20]. In recent years cement augmentation of iliosacral screws has been recommended in osteoporotic bone [11]; nevertheless, some remaining risks such as cement leakage and consecutive nerval compression or cement embolism should be taken into consideration [28]. To minimize complications related to cement leakage, Wähnert et al. developed a new technique with modified screws to allow cement augmentation after screw placement via perforations with low amounts of cement [19]. To our knowledge there are still no biomechanical considerations regarding this new technique, including clinical studies with a high number of patients, who underwent iliosacral screw osteosyntheses combined with cement augmentation. Spine surgery cement augmentation of pedicle screws as well as the use of fenestrated pedicle screws especially for osteoporotic bone is well described in the literature because of the knowledge of screw loosening in patients with compromised bone quality like osteoporosis [29–33]. Augmented pedicel screws showed higher pull-out forces than nonaugmented screws [29]. Using fenestrated pedicle screws may
Subgroup 2
Specimen no.
5
Max. pull-out force (N)
E-Module (kPa)
DXA
Operation Group A
Operation Group C
Operation Group A
Operation Group C
−7.4 −3.9 −2 −6.3 −4 −4.72 1.91
640 604 1,074 563 328 641.8 242.04
652 791 1,468 1,369 868 1,029.6 326.50
750 411 725 2,288 1,506 1,136 679.34
2,065 1,341 763 2,219 1,353 1,548.2 531.91
Subgroup 3 Max. pull-out force (N)
E-Module (kPa)
Specimen no.
DXA
Operation Group B
Operation Group C
Operation Group B
Operation Group C
7 11 12 14 15 Mean SD
−3.5 −6.0 −3.1 −5.2 −3.7 −4.3 1.11
419 1,647 1,090 197 667 804 515.34
663 1,419 1,455 110 802 889.8 503.34
1,418 1,557 1,136 883 417 1,082.2 405.77
757 1,963 1,769 953 1,092 1,306.8 472.83
The following E-Module values were measured in those subgroups comparing two different techniques in the same specimens with respect to bone quality Subgroup 1 (Group A vs. Group B) Screw fixation without cement augmentation was 1,613.6 kPa±411, and screw fixation with cement augmentation before screw placement was 1,501 kPa±391.3; values were not significantly different (p=.71) (see Table). Subgroup 2 (Group A vs. Group C) Screw fixation without cement augmentation was 1,136 kPa±679.3, and perforated screw fixation with cement augmentation after screw placement was 1,548.2 kPa±531.9; values were not significantly different (p=.239) (see Table). Subgroup 3 (Group B vs. Group C) Screw fixation with cement augmentation before screw placement was 1,082.2 kPa±405.8, and perforated screw fix-
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■
6
lower the risk of cement leakage in the clinical setting especially in osteoporotic bone quality [29]. The goal of our biomechanical study was a comparative evaluation of the primary stability of three iliosacral screw fixations in osteoporotic bone: screw fixation without cement application; screw fixation with cement application before screw insertion; and screw fixation with a modified, perforated screw and cement application after screw positioning. Screw insertion to the midline of S1 was performed according to the recommendations in the literature. Biomechanical studies have shown better stability by placing the screws at least into the central zone of the os sacrum [34,35]. Both screw fixation techniques in combination with cement application showed a significantly higher pull-out strength than screw fixation without cement application (see Fig. 3). These findings confirm the hypotheses that screw fixation in osteoporotic spongious bone without supplementary support (eg, cement augmentation) might not be sufficient. Perforated screws are a promising alternative that have the same primary stability as that of conventional screw fixation with additional cement augmentation. Limitations of the study Our study has some limitations. Primary stabilization was measured via pull-out strength; thus, no predication regarding continuous loading can be made. Our biomechanical testing mechanism in this study does not reflect the physiologic stress and typical failure pattern observed in practice. We decided to measure pull-out forces for different screw fixation techniques. The surrounding was minimalized and standardized for all procedures to reduce differences as much as possible. Further biomechanical and clinical studies might complement our findings. Conclusions Our conclusions to screw stability in fixation techniques are based on a biomechanical evaluation. Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques using cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement leakage. References [1] Tosounidis G, Holstein JH, Culemann U, Holmenschlager F, Stuby F, Pohlemann T. Changes in epidemiology and treatment of pelvic ring fractures in Germany: an analysis on data of German Pelvic Multicenter Study Groups I and III (DGU/AO). Acta Chir Orthop Traumatol Cech 2010;6:450–6. [2] Rommens PM, Wagner D, Hofmann A. Surgical management of osteoporotic pelvic fractures: a new challenge. Eur J Trauma Emerg Surg 2012;5:499–509.
[3] Fuchs T, Rottbeck U, Hofbauer V, Raschke M, Stange R. Pelvic ring fractures in the elderly. Underestimated osteoporotic fracture. Unfallchirurg 2011;8:663–70. [4] Lin JT, Lane JM. Sacral stress fractures. J Womens Health (Larchmt) 2003;9:879–88. [5] Morris RO, Sonibare A, Green DJ, Masud T. Closed pelvic fractures: characteristics and outcomes in older patients admitted to medical and geriatric wards. Postgrad Med J 2000;900:646–50. [6] Pohlemann T, Stengel D, Tosounidis G, Reilmann H, Stuby F, Stockle U, et al. Survival trends and predictors of mortality in severe pelvic trauma: estimates from the German Pelvic Trauma Registry Initiative. Injury 2011;10:997–1002. [7] Rommens PM, Hofmann A. Comprehensive classification of fragility fractures of the pelvic ring: recommendations for surgical treatment. Injury 2013;12:1733–44. [8] Frey ME, Depalma MJ, Cifu DX, Bhagia SM, Carne W, Daitch JS. Percutaneous sacroplasty for osteoporotic sacral insufficiency fractures: a prospective, multicenter, observational pilot study. Spine J 2008;2:367–73. [9] Lourie H. Spontaneous osteoporotic fracture of the sacrum. An unrecognized syndrome of the elderly. JAMA 1982;6:715–7. [10] Rommens PM. Is there a role for percutaneous pelvic and acetabular reconstruction? Injury 2007;4:463–77. [11] Tjardes T, Paffrath T, Baethis H, Shafizadeh S, Steinhausen E, Steinbuechel T, et al. Computer assisted percutaneous placement of augmented iliosacral screws: a reasonable alternative to sacroplasty. Spine (Phila Pa 1976) 2008;13:1497–500. [12] Tsiridis E, Upadhyay N, Gamie Z, Giannoudis PV. Percutaneous screw fixation for sacral insufficiency fractures: a review of three cases. J Bone Joint Surg Br 2007;12:1650–3. [13] Stuby FM, Schaffler A, Haas T, Konig B, Stockle U, Freude T. Insufficiency fractures of the pelvic ring. Unfallchirurg 2013;4:351–64. [14] Dudda M, Hoffmann M, Schildhauer TA. Sacrum fractures and lumbopelvic instabilities in pelvic ring injuries: classification and biomechanical aspects. Unfallchirurg 2013;11:972–8. [15] Gansslen A. Biomechanical principles for treatment of osteoporotic fractures of the pelvis. Unfallchirurg 2010;4:272–80. [16] Schildhauer TA, Ledoux WR, Chapman JR, Henley MB, Tencer AF, Routt ML Jr. Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: a cadaveric and biomechanical evaluation under cyclic loads. J Orthop Trauma 2003;1:22–31. [17] Bohme J, Hoch A, Josten C. Osteoporotic fractures of the pelvis. Chirurg 2012;10:875–81. [18] Shah RV. Sacral kyphoplasty for the treatment of painful sacral insufficiency fractures and metastases. Spine J 2012;2:113–20. [19] Wähnert D, Raschke MJ, Fuchs T. Cement augmentation of the navigated iliosacral screw in the treatment of insufficiency fractures of the sacrum: a new method using modified implants. Int Orthop 2013;6:1147–50. [20] Mears SC, Sutter EG, Wall SJ, Rose DM, Belkoff SM. Biomechanical comparison of three methods of sacral fracture fixation in osteoporotic bone. Spine (Phila Pa 1976) 2010;10:E392–5. [21] Failinger MS, McGanity PL. Unstable fractures of the pelvic ring. J Bone Joint Surg Am 1992;5:781–91. [22] Matta JM, Tornetta P III. Internal fixation of unstable pelvic ring injuries. Clin Orthop Relat Res 1996;329:129–40. [23] Routt ML Jr, Kregor PJ, Simonian PT, Mayo KA. Early results of percutaneous iliosacral screws placed with the patient in the supine position. J Orthop Trauma 1995;3:207–14. [24] Ward EF, Tomasin J, Vander Griend RA. Open reduction and internal fixation of vertical shear pelvic fractures. J Trauma 1987;3:291–5. [25] Zhao Y, Li J, Wang D, Liu Y, Tan J, Zhang S. Comparison of stability of two kinds of sacro-iliac screws in the fixation of bilateral sacral fractures in a finite element model. Injury 2012;4:490–4. [26] Keating JF, Werier J, Blachut P, Broekhuyse H, Meek RN, O’Brien PJ. Early fixation of the vertically unstable pelvis: the role of iliosacral screw fixation of the posterior lesion. J Orthop Trauma 1999;2:107–13.
ARTICLE IN PRESS L. Oberkircher et al. / The Spine Journal ■■ (2015) ■■–■■ [27] Rommens PM, Vanderschot PM, De Boodt P, Broos PL. Surgical management of pelvic ring disruptions. Indications, techniques and functional results. Unfallchirurg 1992;9:455–62. [28] Bastian JD, Keel MJ, Heini PF, Seidel U, Benneker LM. Complications related to cement leakage in sacroplasty. Acta Orthop Belg 2012;1:100– 5. [29] Choma TJ, Pfeiffer FM, Swope RW, Hirner JP. Pedicle screw design and cement augmentation in osteoporotic vertebrae: effects of fenestrations and cement viscosity on fixation and extraction. Spine (Phila Pa 1976) 2012;26:E1628–32. [30] Halvorson TL, Kelley LA, Thomas KA, Whitecloud TS III, Cook SD. Effects of bone mineral density on pedicle screw fixation. Spine (Phila Pa 1976) 1994;21:2415–20. [31] Renner SM, Lim TH, Kim WJ, Katolik L, An HS, Andersson GB. Augmentation of pedicle screw fixation strength using an injectable
[32]
[33]
[34]
[35]
7
calcium phosphate cement as a function of injection timing and method. Spine (Phila Pa 1976) 2004;11:E212–6. Soshi S, Shiba R, Kondo H, Murota K. An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine (Phila Pa 1976) 1991;11:1335–41. Wuisman PI, Van Dijk M, Staal H, Van Royen BJ. Augmentation of (pedicle) screws with calcium apatite cement in patients with severe progressive osteoporotic spinal deformities: an innovative technique. Eur Spine J 2000;6:528–33. Daum WJ, Patterson RM, Cartwright TJ, Viegas SF. Comparison of cortical and cancellous screw pull-out strengths about the posterior column and sacroiliac joint. J Orthop Trauma 1991;1:34–7. Kraemer W, Hearn T, Tile M, Powell J. The effect of thread length and location on extraction strengths of iliosacral lag screws. Injury 1994;1:5–9.