Biomechanics of the Sacroiliac Joint: Surgical Treatments

A comparative biomechanical study of a non-threaded triangular titanium implant versus a fully threaded screw: assessing pullout strength of two sacroiliac joint fixation implant designs

Background

Considering that implant backout is a recognized mode of failure, evaluating the pullout strength is critical for assessing anchoring efficacy. The Sacrix® fully threaded screw (TS) was designed specifically for Less Exposure Spine Surgery (LESS) to reduce incision size, surgical time, and blood loss, using two implants for sacroiliac joint (SIJ) fixation. This study compares the Sacrix® design with the SI-Bone iFuse non-threaded triangular titanium implant (TTI) design, which is widely regarded as the industry standard, and represents the first comparative biomechanical pullout strength study of these implant designs currently used in SIJ fusions.

Methods

We conducted mechanical static axial pullout tests on three 7.0 mm × 45 mm iFuse non-threaded TTIs and six 8.0 mm × 40 mm Sacrix® fully TS embedded in polyurethane foam blocks. An INSTRON 8874 Bi-Axial Tabletop Servohydraulic Dynamic Testing System was used to perform the tests by applying a 2.5 kN axial load.

Results

The effective surface areas of the iFuse non-threaded TTI and Sacrix® fully threaded TS were comparable, measuring 294.15 and 289.81 mm2, respectively. The TS exhibited a significantly higher mean static axial pullout strength of 814.90 N [standard deviation (SD), ±99.428 N] compared to the TTI 200.14 N (SD, ±14.428 N). Statistical analyses, including Welch's t-test and Mann-Whitney U test, revealed significant differences in pullout strength between the two implants (P<0.05). Variance analysis confirmed the differences in pullout strength variances between the implants (P=0.040), suggesting that the variability in pullout strength was distinct for each implant.

Conclusions

The Sacrix® fully threaded TS demonstrated a threefold increase in pullout strength compared with the SI-Bone iFuse non-threaded TTI, suggesting that future SIJ fusion designs should favor threaded over non-threaded implants for improved anchoring capability.

Fixation of the Sacroiliac Joint: A Cadaver-Based Concurrent-Controlled Biomechanical Comparison of Posterior Interposition and Posterolateral Transosseous Techniques

OBJECTIVE

Our study aimed to compare the posterior interposition technique against the posterolateral transosseous technique in the same cadaver specimens.

METHODS

Computer and cadaver models of 2 fixation techniques were developed. The computer model was constructed to analyze bone volume removed during implant placement and the bony surface area available for fusion. The cadaver model included quasi-static multidirectional bending flexibility and dynamic fatigue loading. Relative motions between the sacrum and ilium were measured intact, after joint destabilization, after fixation with direct-posterior and posterolateral techniques, and after 18,500 cycles of fatigue loading. Relative positions between each implant and the sacrum and ilium were measured after fixation and fatigue loading to ascertain the quality of the bone-implant interface. The 2 techniques were randomized to the left and right sacroiliac joints of the same cadavers.

RESULTS

The posterior interposition technique removed less bone volume and facilitated a larger surface area available for bony fusion. Posterior interposition significantly reduced the nutation/counternutation motion of the sacroiliac joint (42% ± 8%) and reduced it more than the posterolateral transosseous technique (14% ± 4%). Upon fatigue loading, the posterior interposition implant maintained the bone-implant interface across all specimens, while the posterolateral transosseous implant migrated or subsided in 20%-50% of specimens.

CONCLUSION

Posterior interposition fixation of the sacroiliac joint reduces joint motion. The amount of fixation from the posterior technique is superior and more durable than the amount of fixation achieved by the posterolateral technique.

Impact of Sacroiliac Belt Utilization on Balance in Patients with Low Back Pain

Background

Low back pain (LBP) is a common problem which can affect balance and, in turn, increase fall risk. The aim of this investigation was to evaluate the impact of a Sacroiliac Belt (SB) on balance and stability in patients with LBP.

Methods

Subjects with LBP and without LBP ("Asymptomatic") were enrolled. Baseline balance was assessed using the Berg Balance Scale. In a counterbalanced crossover design, LBP and Asymptomatic subjects were randomized to one of two groups: 1) start with wearing the SB (Serola Biomechanics, Inc.) followed by not wearing the SB or 2) start without wearing the SB followed by wearing the SB. For subjects in both groups, dynamic balance was then assessed using the Star Excursion Balance Test (SEBT) with each leg planted.

Results

Baseline balance was worse in LBP subjects (Berg 51/56) than Asymptomatic subjects (Berg 56/56) (p<0.01). SB significantly improved SEBT performance in LBP subjects regardless of which leg was planted (p<0.01). SB positively impacted Asymptomatic subjects' SEBT performance with the left leg planted (p=0.0002).

Conclusion

The Serola Sacroiliac Belt positively impacted dynamic balance for subjects with low back pain. Further research is needed to examine additional interventions and outcomes related to balance in patients with back pain, and to elucidate the mechanisms behind improvements in balance related to sacroiliac belt utilization.

A literature review of biomechanical studies on physiological and pathological sacroiliac joints: Articular surface structure, joint motion, dysfunction and treatments

BACKGROUND

Sacroiliac joints are affected by mechanical environments; the joints are formed under mechanical stimulation, receive impact of walking between the upper and lower parts of the bodies and can be a cause of pain due to non-physiological loads. However, there are so far very few studies that reviewed biomechanics of physiological and pathological sacroiliac joints. This review article aims to describe the current sacroiliac joint biomechanics.

METHODS

Previous original papers have been summarized based on three categories: articular surface structure, sacroiliac joint motion and sacroiliac joint dysfunction and treatments.

FINDINGS

Although the articular surface morphologies vary greatly from individual to individual, many researchers have tried to classify the joints into several types. It has been suggested that the surface morphologies may not change regardless of joint dysfunction, however, the relationship between the joint structure and pain are still unclear. The range of sacroiliac joint motion is demonstrated to be less than 1 mm and there is no difference between physiological and pathological joints. The sacroiliac joint absorbs shock within the pelvis by the joint structures of pelvic morphology, ligaments and fat tissues. The morphology and motion of the sacroiliac joints may be optimized for upright bipedal walking.

INTERPRETATION

There is no doubt that pelvic mechanical environments affect pain induction and treatment; however, no one has yet provided a concrete explanation. Future research could help develop treatments based on sacroiliac joint biomechanics to support joint function.

Hydroxyapatite-Coated Screws Versus Titanium Triangular Dowels for Sacroiliac Joint Fusion: Results From a Nonrandomized Prospective Outcome Study

OBJECTIVE

This is a single-surgeon series that prospectively evaluates the results of sacroiliac joint (SIJ) fusion for patients with SIJ dysfunction using hydroxyapatite-coated screws (HACSs) compared with titanium triangular dowels (TTDs).

METHODS

A total of 113 patients underwent SIJ fusion surgery between 2013 and 2018 at the University Hospital Llandough to treat symptomatic SIJ dysfunction not responding to nonoperative measures. Of the 113 patients, 40 were treated with HACSs and 73 with TTDs. Patient-reported outcomes measures (PROMs) were collected preoperatively and at 12 months postoperatively, including the 36-item short-form health survey, Oswestry disability index, EuroQol-5D-5L, and Majeed pelvic score. Patients with ongoing symptoms were followed up beyond the study period.

RESULTS

Of the 113 patients, 33 completed follow-up in the HACS group compared with 61 in the TTD group. Both groups had comparable preoperative PROMs; however, the postoperative PROMs were significantly better in the TTD group. Additionally, 21 patients (63%) in the HACS group had radiological evidence of screw lysis compared with 5 patients (9%) in the TTD group. A subgroup analysis revealed less significant improvement in PROMs for patients with screw lysis compared with those without. Four patients were offered further revision surgery.

CONCLUSIONS

Minimally invasive SIJ fusion has been shown to have good clinical outcomes for select patients. However, our experience shows that HACSs are associated with a high rate of screw lysis and poorer patient outcomes compared with TTDs. Therefore, we recommend the use of TTDs instead of HACSs for SIJ fusion surgery.

Chronic sacroiliac joint dysfunction and CT-guided percutaneous fixation: a 6-year experience

PURPOSE

Reporting the clinical outcomes, patient satisfaction, and complications following an imaging-guided percutaneous screw fixation in the treatment of sacroiliac joint dysfunction and evaluating the safety and effectiveness of this method.

METHODS

We performed a retrospective study on a prospectively gathered cohort of patients with physiotherapy-resistant pain due to sacroiliac joint incompetence that underwent percutaneous screw fixation, between 2016 and 2022 in our center. A minimum of two screws were used in all patients to obtain fixation of the sacroiliac joint, using percutaneous screw insertion under CT guidance, coupled with a C-arm fluoroscopy unit.

RESULTS

The mean visual analog scale significantly improved at 6 months of follow-up (p < 0.05). One hundred percent of the patients reported significant improvement in pain scores at the final follow-up. None of our patients experienced intraoperative or postoperative complications.

CONCLUSION

The use of percutaneous sacroiliac screws provides a safe and effective technique for the treatment of sacroiliac joint dysfunction in patients with chronic resistant pain.

Lumbar Disc Degeneration Affects the Risk of Rod Fracture Following PSO; A Finite Element Study

STUDY DESIGN

Finite element (FE) study.

OBJECTIVE

Pedicle subtraction osteotomy (PSO) is a surgical method to correct sagittal plane deformities. In this study, we aimed to investigate the biomechanical effects of lumbar disc degeneration on the instrumentation following PSO and assess the effects of using interbody spacers adjacent to the PSO level in a long instrumented spinal construct.

METHODS

A spinopelvic model (T10-pelvis) with PSO at the L3 level was used to generate 3 different simplified grades of degenerated lumbar discs (mild (Pfirrmann grade III), moderate (Pfirrmann grade IV), and severe (Pfirrmann grade V)). Instrumentation included eighteen pedicle screws and bilateral primary rods. To investigate the effect of interbody spacers, the model with normal disc height was modified to accommodate 2 interbody spacers adjacent to the PSO level through a lateral approach. For the models, the rods' stress distribution, PSO site force values, and the spine range of motion (ROM) were recorded.

RESULTS

The mildly, moderately, and severely degenerated models indicated approximately 10%, 26%, and 40% decrease in flexion/extension motion, respectively. Supplementing the instrumented spinopelvic PSO model using interbody spacers reduced the ROM by 22%, 21%, 4%, and 11% in flexion, extension, lateral bending, and axial rotation, respectively. The FE results illustrated lower von Mises stress on the rods and higher forces at the PSO site at higher degeneration grades and while using the interbody spacers.

CONCLUSIONS

Larger and less degenerated discs adjacent to the PSO site may warrant consideration for interbody cage instrumentation to decrease the risk of rod fracture and PSO site non-union.

Sacroiliac Joint Fusion: Fusion Rates and Clinical Improvement Using Minimally Invasive Approach and Intraoperative Navigation and Robotic Guidance

STUDY DESIGN

This study adopted a retrospective study design.

PURPOSE

This study was designed to describe the fusion rate and technique and patient subjective improvement after sacroiliac (SI) joint fusion using a minimally invasive surgical (MIS) approach.

OVERVIEW OF LITERATURE

The SI joint can mimic radicular or discogenic pain localized to the lower back, gluteal region, or sacral region, posing a challenge in the diagnosis and treatment. This study determines the radiological fusion rate and patient reported subjective clinical outcomes of SI joint fusion using an MIS approach, comparing the use of the Rialto SI joint fusion system (Medtronic, Minneapolis, MN, USA) with the help of the Stealth Navigation System with the use of ExcelsiusGPS Robotic Navigation Platform (Globus Medical Inc., Audubon, PA, USA) using SI-LOK screws (Globus Medical Inc.).

METHODS

In this retrospective study, 43 consecutive patients who underwent SI joint fusion between August 2017 and February 2020 were enrolled; 60 SI joints were fused. The patients' fusion was documented on computed tomography or X-rays, and Visual Analog Scale (VAS) scores were used to determine patient subjective clinical outcomes.

RESULTS

A total of 60 joints were fused, including 26 joints fused using robotic guidance and 34 joints fused using the Stealth Navigation System. Student t-test was used to compare the mean preoperative VAS score (7.52±1.3) with the mean postoperative VAS score at the 12-month follow-up (1.43±1.22) (p<0.05). The SI joint fusion rate using this technique was 61% at 6 months, 96.4% at 12 months, and 100% at 18 months.

CONCLUSIONS

The use of navigation guidance or robotic assistance enables accurate percutaneous screw placement across the SI joint. The use of bone morphogenetic protein in the screw bore hastens fusion across the joint, improving patient-perceived pain.

Minimally Invasive and Conservative Interventions for the Treatment of Sacroiliac Joint Pain: A Review of Recent Literature

Sacroiliac joint (SIJ) pain is responsible for approximately 15-25% of reported back pain. Patients with SIJ pain report some of the lowest quality of life scores of any chronic disease. Understanding of the physiology and pathology of the SI joint has changed dramatically over the years, and SI joint pain and injury can now be thought of in two broad categories: traumatic and atraumatic. Both categories of SI joint injury are thought to be caused by inflammation or injury of the joint capsule, ligaments, or subchondral bone in the SI joint. Treatment of SI joint pain usually involves a multi-pronged approach, utilizing both, multi-modal medical pain control and interventional pain/surgical techniques such as steroid injections, radiofrequency nerve ablation, and minimally invasive sacroiliac arthrodesis. Though conservative management through multi-modal pain control and physical therapy have their role as first line therapies, an increasing body of evidence supports the use of minimally invasive procedures, both as adjuvant treatments to conservative management and as second line therapies for patient's that fail first line treatment.

Minimally Invasive and Conservative Interventions for the Treatment of Sacroiliac Joint Pain: A Review of Recent Literature

Sacroiliac joint (SIJ) pain is responsible for approximately a third of reported back pain. Patients with SIJ pain report some of the lowest quality of life scores of any chronic disease. Understanding of the physiology and pathology of the SI joint has changed dramatically over the years, and SI joint pain and injury can now be thought of in two broad categories: traumatic and atraumatic. Both categories of SI joint injury are thought to be caused by inflammation or injury of the joint capsule, ligaments, or subchondral bone in the SI joint. Treatment of SI joint pain usually involves a multi-pronged approach, utilizing both, multi-modal medical pain control and interventional pain/surgical techniques such as steroid injections, radiofrequency nerve ablation, and minimally invasive sacroiliac arthrodesis. Though conservative management through multi-modal pain control and physical therapy have their role as first line therapies, an increasing body of evidence supports the use of minimally invasive procedures, both as adjuvant treatments to conservative management and as second line therapies for patient's that fail first line treatment.

Biomechanical analysis of stand-alone lumbar interbody cages versus 360° constructs: an in vitro and finite element investigation

OBJECTIVE

Low fusion rates and cage subsidence are limitations of lumbar fixation with stand-alone interbody cages. Various approaches to interbody cage placement exist, yet the need for supplemental posterior fixation is not clear from clinical studies. Therefore, as prospective clinical studies are lacking, a comparison of segmental kinematics, cage properties, and load sharing on vertebral endplates is needed. This laboratory investigation evaluates the mechanical stability and biomechanical properties of various interbody fixation techniques by performing cadaveric and finite element (FE) modeling studies.

METHODS

An in vitro experiment using 7 fresh-frozen human cadavers was designed to test intact spines with 1) stand-alone lateral interbody cage constructs (lateral interbody fusion, LIF) and 2) LIF supplemented with posterior pedicle screw-rod fixation (360° constructs). FE and kinematic data were used to validate a ligamentous FE model of the lumbopelvic spine. The validated model was then used to evaluate the stability of stand-alone LIF, transforaminal lumbar interbody fusion (TLIF), and anterior lumbar interbody fusion (ALIF) cages with and without supplemental posterior fixation at the L4-5 level. The FE models of intact and instrumented cases were subjected to a 400-N compressive preload followed by an 8-Nm bending moment to simulate physiological flexion, extension, bending, and axial rotation. Segmental kinematics and load sharing at the inferior endplate were compared.

RESULTS

The FE kinematic predictions were consistent with cadaveric data. The range of motion (ROM) in LIF was significantly lower than intact spines for both stand-alone and 360° constructs. The calculated reduction in motion with respect to intact spines for stand-alone constructs ranged from 43% to 66% for TLIF, 67%-82% for LIF, and 69%-86% for ALIF in flexion, extension, lateral bending, and axial rotation. In flexion and extension, the maximum reduction in motion was 70% for ALIF versus 81% in LIF for stand-alone cases. When supplemented with posterior fixation, the corresponding reduction in ROM was 76%-87% for TLIF, 86%-91% for LIF, and 90%-92% for ALIF. The addition of posterior instrumentation resulted in a significant reduction in peak stress at the superior endplate of the inferior segment in all scenarios.

CONCLUSIONS

Stand-alone ALIF and LIF cages are most effective in providing stability in lateral bending and axial rotation and less so in flexion and extension. Supplemental posterior instrumentation improves stability for all interbody techniques. Comparative clinical data are needed to further define the indications for stand-alone cages in lumbar fusion surgery.

Biomechanical analysis of the number of implants for the immediate sacroiliac joint fixation

PURPOSE

The fusion of the sacroiliac joint (SIJ) is the last treatment option for chronic pain resulting from sacroiliitis. With the various implant systems available, there are different possible surgical strategies in terms of the type and number of implants and trajectories. The aim was to quantify the effect of the number of cylindrical threaded implants on SIJ stabilization.

METHODS

Six cadaveric pelvises were embedded in resin simulating a double-leg stance. Compression loads were applied to the sacral plate. The pelvises were tested non-instrumented and instrumented progressively with up to three cylindrical threaded implants (12-mm diameter, 60-mm length) with a posterior oblique trajectory. Vertical (VD) and angular (AD) displacements of the SIJ were measured locally using high-precision cameras and digital image correlation.

RESULTS

Compared to the non-instrumented initial state, instrumentation with one implant significantly decreased the VD (- 24% ± 15%, p = 0.028), while the AD decreased on average by - 9% (± 15%; p = 0.345). When compared to the one-implant configuration, adding a second implant further statistically decreased VD (- 10% ± 7%, p = 0.046) and AD (- 19% ± 15, p = 0.046). Adding a third implant did not lead to additional stabilization for VD nor AD (p > 0.5).

CONCLUSION

Compared to the non-instrumented initial state, the two-implant configuration reduces both vertical and angular displacements the most, while minimizing the number of implants.

Sacroiliac joint stabilization using implants provide better fixation in females compared to males: a finite element analysis

PURPOSE

This study's objective was to assess biomechanical parameters across fused and contralateral sacroiliac joints (SIJs) and implants during all spinal motions for both sexes. Various SIJ implant devices on the market are used in minimally invasive surgeries. These implants are placed across the joint using different surgical approaches. The biomechanical effects of fusion surgical techniques in males and females have not been studied.

METHODS

The validated finite element models of a male, and a female spine-pelvis-femur were unilaterally instrumented across the SIJ using three screws for two SIJ implants, half threaded and fully threaded screws placed laterally and posteriorly to the joint, respectively.

RESULTS

Motion and peak stress data at the SIJs showed that the female model exhibited lower stresses and higher reduction in motion at the contralateral SIJ in all motions than the male model predictions with 84% and 71% reductions in motion and stresses across the SIJ.

CONCLUSION

Implants exhibited higher stresses in the female model compared to the male model. However, chances of SIJ implant failure in the female patients are still minimal, based on the calculated factor of safety which is still very high. Both lateral and posterior surgical approaches were effective in both sexes; however, the lateral approach may provide a better biomechanical response, especially for females. Moreover, implant design characteristics did not make a difference in the implants' biomechanical performance. SIJ stabilization was primarily provided by the implants which were the farthest from the sacrum rotation center.

Are Hydroxyapatite-Coated Screws a Good Option for Sacroiliac Joint Stabilization? A Prospective Outcome Study

OBJECTIVE

This is a single-surgeon series to prospectively evaluate the clinical and radiologic results of sacroiliac joint (SIJ) stabilization using hydroxyapatite (HA)-coated, fully threaded screws in patients with SIJ dysfunction.

METHODS

A total number of 40 patients underwent percutaneous SIJ stabilization using HA-coated screws between 2013 and 2015 at the University Hospital of LLandough with an age range of 33-84 years. Patients were followed up closely, and outcome scores were collected preoperative and 12 months after surgery. Preoperative and postoperative outcomes were evaluated using patient-reported outcome measures (PROMs), Short Form-36, Oswestry Disability Index, EuroQol-5D-5L, and Majeed Pelvic Scores.

RESULTS

Thirty-three patients (8 male and 32 female) out of the 40 patients completed follow-up. There was an overall improvement in all PROMs; however, only mental component of SF-36, Oswestry Disability Index, Majeed Pelvic Scores, and EuroQol-5D-5L were statistically significant. Twenty-one patients (63%) had lysis around the screw, and a subgroup analysis showed that improvement in PROMs was significantly less in patients with lysis around the screw. Four patients with lysis around the screw were offered revision due to ongoing pain. Revision was successful in only 1 patient.

CONCLUSIONS

Percutaneous SIJ fixation procedure has been shown to have good clinical outcomes, but the use of HA-coated fully threaded screws in this procedure is not recommended on the basis of patient-reported outcome measures and radiologic findings in this prospective study.