Biomechanical analysis of two insertion sites for the fixation of the sacroiliac joint via an oblique lateral approach
Introduction
The sacroiliac joint (SIJ) ensures the transmission of important forces from the spine and upper body to the lower limbs. The SIJ generates pain in 15 to 30% of patients suffering from low back pain (Cohen et al., 2013). Treatment options include anti-inflammatory medication, physical therapy, sacral belt, and in last resort, surgical fusion. For the latter, implants are inserted across the sacrum and ilium through the SIJ to allow mechanical stability. An osseointegration process begins and the opposing bony surfaces start to biologically fuse. In a meta-analysis evaluating five clinical outcome measures, minimally invasive SIJ fusion was proven effective for alleviating girdle pain (Lingutla et al., 2016). Minimally invasive SIJ surgeries limit tissue exposure during surgery and only necessitate a 3-cm long incision while offering greater pain relief than open surgeries (Smith et al., 2013). Still, the fusion rate ranges from 25 to 88% after 12 months (Cross et al., 2018; Duhon et al., 2016; Kube and Muir, 2016; Rudolf and Capobianco, 2014; Treon et al., 2016). Patients with persistent or recurrent pain may require a revision surgery, with revision rates reaching 30% after 4 years (Spain and Holt, 2017).
As the quality of the biological fusion and osseointegration is linked to the initial mechanical stability (Javed et al., 2013), researchers have investigated the effect of instrumentation on SIJ range of motion (RoM). In cadaveric studies, instrumentation with either two cylindrical and threaded implants, or three implants with a triangular cross-section significantly decreased the RoM by 27% to 54% (Lindsey et al., 2014, Lindsey et al., 2018a; Shih et al., 2018; Soriano-Baron et al., 2015). However, the SIJ RoM is not significantly reduced for all specimens. Counterintuitively, the SIJ RoM is sometimes increased following fixation (Lindsey et al., 2014, Lindsey et al., 2018a; Soriano-Baron et al., 2015). In a clinical setting, an insufficient reduction in SIJ RoM may lead to pseudarthrosis, which does not alleviate the patient's symptoms. Increased RoM could be explained by the damage to the interosseous ligament (IOL), the strongest and largest of SIJ ligaments (Vleeming et al., 2012) during implant insertion. The IOL directly connects the SIJ surfaces together, so a modification to its integrity could lead to a loss of stability greater than the stability gain provided by the implants. This hypothesis could be verified by isolating the effects of drilling and tapping on SIJ stability, which has not been done before. Decoupling instrumentation steps (drilling-tapping and implant insertion) would allow a better understanding of SIJ biomechanics and SIJ fixation.
SIJ initial mechanical stability also depends on certain surgical choices like the surgical approach and implant trajectory, as well as the type, size, and number of implants. For instance, the two main surgical approaches for minimally invasive SIJ fixation are the direct lateral and the oblique lateral approaches, respectively referred to as lateral and oblique in the text for simplicity. Compared to the oblique approach, the lateral approach requires more dissection of the gluteal muscles (medius and maximus). However, most of the recent clinical studies have used the lateral approach with triangular dowel implants and are industry-sponsored (Yson et al., 2019). Recently, two retrospective studies have compared the lateral and oblique approaches, using triangular implants and cylindrical threaded implants respectively. Majd et al. found the oblique approach to be superior for some clinical outcomes (higher rate of significant improvement on the visual analogue scale (VAS) (65% vs 45%), lower estimated blood loss (33 cm3 vs 60 cm3), lower adverse event rate (6.7% vs 20%)) (Majd, 2018). However, significance was not mentioned. Claus et al. found that both approaches led to a significant improvement of the Oswestry Disability Index (ODI) and SF-12 (Short Form-12 health survey) scores, without a significant difference between the two techniques (Claus et al., 2020). Length of stay, estimated blood loss were not statistically different between the groups but the oblique approach had a significantly longer surgery (60 min vs 41 min) (Claus et al., 2020). Revision rate was higher for the oblique approach compared to the lateral approach (6.1% vs 2.4%), but the difference was not statistically significant. Many experimental and numerical studies have been conducted on the lateral approach (Jeong et al., 2018; Lindsey et al., 2014, Lindsey et al., 2015, Lindsey et al., 2018a, Lindsey et al., 2018b; Shih et al., 2018; Soriano-Baron et al., 2015) compared to only one numerical study on the oblique approach (Bruna-Rosso et al., 2016). Bruna-Rosso et al. (2016) simulated an oblique SIJ instrumentation using a finite element model of the pelvis with one to two threaded implants and compared two insertion sites and two implant orientations. Placing the implant farther from the SIJ center of rotation (CoR) (located at the axial interosseous ligament according to Farabeuf's theory (Kapandji, 2007)) and using an orientation more parallel to the SIJ CoR led to a better stabilization of the SIJ subjected to compression loads. No cadaveric studies have been published on this approach, but such study would allow a better understanding of oblique fixation and help further reduce revision rates.
Hence, the current study aimed to experimentally measure the isolated effects of drilling and tapping as well as the effects of oblique SIJ fixation on SIJ RoM while comparing two possible insertion sites. It was hypothesized that instrumenting the SIJ with one implant would lead to significant motion reduction and that there would be a significant difference between the two tested insertion points.
Section snippets
Specimen preparation
The pelves (sacrum and iliac bones) of eight human specimens (age ranged from 73 to 94 years old; Table 1) embalmed with a zinc chloride solution were harvested. They were thawed at room temperature and cleaned of muscle tissue while keeping the ligaments of the SIJ intact (anterior, posterior, IOL, sacrotuberous and sacrospinous ligaments). CT-scans were taken to ensure there were no anomalies like bone bridging. Bone mineral density was measured with a calibration phantom (Model 062M Electron
Results
Seven specimens completed the testing protocol (Table 1). One specimen (ID1) deteriorated at the end of the second test and was therefore not included in the analysis. The age ranged from 73 to 94 years. No bone bridging was detected from the CT-scans.
Intra-articular displacements of adjoining sacrum and ilium of the “intact state” ranged from 0.08 mm to 2.20 mm for VD (translation) and from 0.15° to 2.83° for AD (rotation) (Table 2). No significant difference was found in compression or in FE
Discussion
We experimentally measured the isolated effects of drilling and tapping as well as implant insertion on SIJ stability and compared two insertion sites using image correlation methods. The VD of the intact SIJs agree with previous studies, which reported means ranging from 0.32 to 0.7 mm (Baria, 2010; Hammer et al., 2019; Jacob and Kissling, 1995). The measured AD are in line with rotations measured in vivo (means of 0.5° and 0.8°, respectively) (Kibsgard et al., 2014, Kibsgard et al., 2017) but
Conclusions
This is the first biomechanical study to investigate SIJ fusion via an oblique lateral approach. We measured the isolated effects of drilling-tapping and instrumentation on SIJ stability and compared two different insertion sites. Drilling through the IOL did not increase the intra-articular displacements of the SIJ, and thus this hypothesis is rejected. Our main hypothesis was only partly accepted, as instrumenting the SIJ with one implant significantly decreased vertical displacements in
Declaration of competing interest
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Medtronic provided the implants and surgical kit for the study. Carl-Éric Aubin – Funding: Natural Sciences and Engineering Research Council of Canada (Industrial Research Chair program with Medtronic of Canada) (grant number PCIPJ-346145). Development grant from Medtronic Canada (outside of the subject of the manuscript). The other authors have no known
Acknowledgments
The authors acknowledge the support of Dr Kathia Chaumoître, MD, and the Assistance Publique-Hôpitaux de Marseille, (Hôpital Nord, Marseille, France) for their radiologic expertise. The authors would also like to thank: the A*MIDEX foundation, France, MITACS Globalink, the Fonds de Recherche du Québec - Nature et Technologies and the Natural Sciences and Engineering Research Council of Canada (Industrial Research Chair program with Medtronic of Canada – grant number: PCIPJ-346145) for their
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