Sacral bone mineral density (BMD) assessment using opportunistic CT scans

Three-Dimensional Reconstruction of Computed Tomography Imaging Is Not Reliable in Assessing Acetabular Rim Osteophytes or Acetabular Rim Pathology in Patients With Femoroacetabular Impingement

Purpose

To determine the reliability of 3-dimensional (3D) reconstruction of computed tomography (CT) imaging in evaluating acetabular rim morphology or acetabular rim osteophyte (ARO) existence and to group patients with femoroacetabular impingement (FAI) by ARO extent on coronal sections of CT and further compare clinical differences among groups.

Methods

Patients who underwent primary hip arthroscopy for FAI by the same surgeon between August 2016 and December 2018 with minimum 2-year follow-up were enrolled. The ARO was evaluated both on the acetabular gross anatomy (AGA) and coronal sections of CT, for its position, width (unit: mm), area (unit: mm2), and CT value (unit: HU). Patients were divided into 4 groups based on the extent of ARO on coronal CT: group A (ARO anterior to 12 o'clock), group P (ARO posterior to 12 o'clock), group AP (ARO across 12 o'clock), and group N (no ARO). Inter- and intraobserver correlation was analyzed. Demographic data, FAI deformity indicators on imaging, quantitative measurements of ARO, and pre- and postoperative patient-reported outcomes were compared among groups.

Results

There were 229 patients (229 hips) enrolled in total, 122 male (53.3%) and 107 female (46.7%), with a mean age of 37.2 ± 10.2 years. The correlation between 2 observers for grouping ARO using AGA was positive but poor (Kendall Tau-b coefficient = 0.157, P = .008). Moderate correlation was found between grouping based on AGA and coronal CT by the same observer (Kendall Tau-b coefficient = 0.482, P = .000). The patients were divided into 4 groups: 84 patients (36.7%) in group N, 2 patients (0.9%) in group A, 69 patients (30.1%) in group P, and 74 patients (32.3%) in group AP. Group N was younger in age (35.4 ± 10.7 years) than group P (39.6 ± 10.2 years) (P = 0.012) and had a larger proportion of women (57.1%) than group AP (36.5%) (χ2 = 6.869, P = .032). There was a greater proportion of positive posterior wall sign in group P (52.2%) than 48.6% for group AP and 33.3% for group N (χ2 = 6.397, P = .041). Group N had 61 (72.6%) Tönnis grade 0 hips compared with 37 (50%) in group AP (P = .014). No statistical significance was found among groups in pre- and postoperative α angle, lateral center-edge angle, and patient-reported outcomes. The widths of ARO in group AP for the 3 marked points from anterior to posterior were 3.88 ± 1.86, 4.84 ± 2.72, and 6.66 ± 3.18, separately (P＜.001); 15.73 ± 21.46, 19.22 ± 18.86, and 29.96 ± 17.05 for area (P＜.01); and 652.67 ± 214.12, 677.10 ± 274.81, and 728.84 ± 232.39 for CT value (P＜.05). For the ARO posterior to 12 o'clock, the group AP showed a larger width (6.66 ± 3.18), area (29.96 ± 17.05), and CT value (728.84 ± 232.39) than group P of (4.70 ± 2.25), (20.15 ± 12.91), and (641.84 ± 183.33) (P＜.001).

Conclusions

The evaluation of ARO on AGA is poor consistent with definite double-rim sign on coronal CT. There is a tendency of size-enlarging and density-increasing for ARO from anterior to posterior along the acetabular rim. Younger age, female gender, lower Tönnis grade, and negative posterior wall sign showed lower rate of ARO development.

Level of Evidence

Level IV, diagnostic case series.

Return to Duty in Military Service Members Following Minimally Invasive Sacroiliac Joint Fusion

INTRODUCTION

As the utilization of minimally invasive sacroiliac joint fusion (SIJF) continues to expand, a better understanding of postoperative outcomes is needed, particularly in young and active individuals. The purpose of this study is to assess the outcomes of this procedure in an active duty military population by examining return-to-duty (RTD) rates.

MATERIALS AND METHODS

A retrospective review of the electronic medical record from a tertiary military medical center was performed for active duty service members undergoing SIJF from January 2013 to January 2019. The primary outcome measured was RTD at 6 months, with active duty status at 1 year, last follow-up, and revision surgery as secondary outcomes. Demographic and surgical variables recorded included patient age, gender, military rank, utilization of navigation, and implant type.

RESULTS

Sixteen service members met the inclusion criteria, with a mean age of 40.5 ± 6.7 years. The mean follow-up after surgery was 24 ± 15 months. Patients received either cylindrical (n = 6) or triangular (n = 10) implants placed with (n = 6) or without (n = 10) navigation. Within 6 months of surgery, 56% of patients were able to RTD. Patients undergoing navigation-assisted procedures were significantly more likely to RTD at 6 months (100% vs. 30%, P = .011) compared to those undergoing surgery performed with orthogonal fluoroscopic imaging. Compared to those with cylindrical implants, patients with triangular implants were also more likely to RTD at 6 months (80% vs. 17%, P = .035).

CONCLUSIONS

Following SIJF, a small majority of service members were able to return to full active duty status by 6 months. Further studies are needed to assess the potential benefits of navigation and implant selection, as our retrospective review noted differences in outcomes based on these variables.

Opportunistic screening for osteoporosis and osteopenia from CT scans of the abdomen and pelvis using machine learning

OBJECTIVES

To use multivariable machine learning using the computed tomography (CT) attenuation of each of the bones in the lumbar spine, pelvis, and sacrum, to predict osteoporosis/osteopenia.

METHODS

This was a retrospective study of 394 patients aged 50 years or older with CT scans of the abdomen and pelvis and dual-energy x-ray absorptiometry (DXA) scans obtained within 6 months of each other. Volumetric segmentations were performed for each of the bones from L1-L4 vertebrae, pelvis, and sacrum to obtain the mean CT attenuation of each bone. The data was randomly split into training/validation (n = 274, 70%) and test (n = 120, 30%) datasets. The CT attenuation of the L1 vertebrae, univariate logistic regression, least absolute shrinkage and selection operator (LASSO), and support vector machines (SVM) with radial basis function (RBF) were used to predict osteoporosis/osteopenia. The performance of using the CT attenuation at L1 to the univariate logistic regression, LASSO, and SVM models were compared using DeLong's test in the test dataset.

RESULTS

All CT attenuation measurements were predictive of osteoporosis/osteopenia (p < 0.001 for all). The SVM model (accuracy = 0.892, AUC = 0.886) outperformed the models using the CT attenuation of threshold of 173.9 Hounsfield units (HU) at L1 (accuracy = 0.725, AUC = 0.739, p = 0.010), the univariate logistic regression model (accuracy = 0.767, AUC = 0.533, p < 0.001) and the LASSO model (accuracy = 0.817, AUC = 0.711, p = 0.007) to predict osteoporosis/osteopenia.

CONCLUSION

A SVM model using the CT attenuations of multiple bones within the lumbar spine and pelvis and clinical data has a better ability to predict osteoporosis/osteopenia than using the CT attenuation of L1 or a LASSO model.

KEY POINTS

• Multivariable SVM model using the CT attenuation of multiple bones and clinical/demographic data was more predictive than using the CT attenuation at L1 only.

Risk factors for L5 pedicle fractures after single-level posterior spinal fusion

BACKGROUND CONTEXT

Pedicle fractures are a rare but potentially devastating complication of posterior instrumented spinal fusion (PSF). Preoperative awareness of the possible risk factors may help prevent these fractures by modifying the surgical plan. However, the risk factors have not yet been identified.

PURPOSE

To determine the preoperative parameters associated with postoperative L5 pedicle fracture after L4/5 PSF.

STUDY DESIGN

Case control study.

PATIENT SAMPLE

Patients undergoing L4/5 PSF at a single academic institution between 2014 and 2020.

OUTCOME MEASURES

Occurrence of postoperative L5 pedicle fracture.

METHODS

Of 253 patients (female:male, 145:108) undergoing L4/5 PSF from 2014 to 2020, patients with postoperative L5 pedicle fractures were identified retrospectively as "cases" (n = 8, all female, age: 70 ± 10.7 years). As a control group all remaining patients with a follow-up of more than 12 months were allocated (n = 184, 104 females, age: 64.27 ± 13.00 years). In all but 16 cases, anterior support with transforaminal or posterior interbody fusion was performed. Demographic and clinical data (body mass index (BMI)), surgical factors, and comorbidities) were compared. Radiological assessment of spinopelvic parameters was performed using pre- and postoperative standing lateral radiographs.

RESULTS

The overall incidence of L5 pedicle fractures after L4/5 spinal fusion was 3.16%, with a median time from index surgery to diagnosis of 25 days (range, 6-199 days) (75% within the first 32 days postoperatively). Patients with L5 pedicle fractures had higher pelvic incidence (PI) (71° ± 9° vs. 56° ± 11°; p=.001), sacral slope (SS) (45° ± 7° vs. 35° ± 8°; p=.002), L5 slope (30° ± 11° vs. 15° ± 10°, p=.001), L5 incidence (42° ± 14° vs. 26° ± 11°; p= .003), L1-S1 lumbar lordosis (LL) postop (57° ± 10° vs. 45° ± 11°; p=.006), and L4 -S1 LL postop (33° ± 7° vs. 28° ± 7°; p=.049) compared with the control group. Pelvic tilt and PI- LL mismatch were not significantly different. Female gender was a significant risk factor for L5 pedicle fractures (p=.015). BMI (kg/m²) was statistically equal in patients with or without pedicle fractures (28.37 ± 5.96 vs. 28.53 ± 16.32; p=.857). There was no significant difference between the groups for approximative bone mineral density assessment (Hounsfield units; 113 ± 60 vs. 120 ± 43; p=.396) using the L3 trabecular region of interest (ROI) measurement. The correlation analysis demonstrated that most of the identified risk factors except for the postoperative L4-S1 lordosis show significant positive associations among each other. All eight patients in the fracture group underwent revision surgery, and the instrumented fusion was extended to the sacrum, with the addition of sacral-alar-iliac or iliac screws, in six cases.

CONCLUSIONS

L5 pedicle fractures occurred in 3% of the patients after single level L4/5 PSF. Risk factors are female gender, higher PI, SS, L5 slope, L5 incidence, and LL postop but not high BMI. These findings can be used for surgical planning and decision of fusion levels.

Prediction of Sacral Screw Loosening after Lumbosacral Surgeries Involving Rigid Fixation of Sacral Bone Using Preoperative Computed Tomography Scans

Objective

To find a preoperative computed tomography-based method to predict the incidence of sacral screw loosening and assist surgical planning.

Methods

Surgically treated patients for degenerative lumbosacral disorders with rigid pedicle screw fixation of patients with L5-S1 vertebra in our center from January 2016 to January 2021 were retrospectively included in the current study. CT scan attenuation of the horizontal plane of the sacrum was measured with Hounsfield units (HU). Postoperative X-ray tests were used to diagnose screw loosening. The data was analyzed by independent sample t-tests, X² analysis, Pearson correlation analysis, and ROC curve analysis.

Results

A total of 162 (114 male, 48 female, average age 63.7 ± 7.3 years) patients were included in the final analysis. Significant differences were found between the screw loosening group and nonloosening group concerning the HU value of the sacrum at the horizontal plane (P < 0.01). In ROC curve analysis, AUC was 0.674 (95% CI: 0.592-0.756). A cutoff of 200 HU provided 64.8% sensitivity and 62.4% specificity, and a cutoff of 150 HU provided 90.2% sensitivity.

Conclusions

Analyzing 162 patients with at least 12 months of follow-up, we propose cutoff CT attenuation values of 200 HU and 150 HU to take moderate and radical measures of screw augmentation to prevent screw loosening in the sacral bone.

Distribution of hounsfield unit values in the pelvic bones: a comparison between young men and women with traumatic fractures and older men and women with fragility fractures: a retrospective cohort study

Background

The fixation strength of bone screws depends on bone mineral density (BMD), so it is important to evaluate bone strength at fracture sites. Few studies have investigated BMD in the pelvis. The aims of this study were to measure the regional Hounsfield unit (HU) values in the cancellous bone of the acetabulum and pelvic ring and to compare these values between young and older patients.

Methods

This study enrolled young patients with high-energy trauma (aged 20–44 years; young group) and older patients with low-energy trauma (aged 65–89 years; older group). Patients without pelvic computed tomography (CT) scans, those with pelvic bone implants, and those who died were excluded. The HU values on the contralateral (non-fractured) side of the pelvis were measured on CT scans. The CT data were divided into 7 areas: the pubic bone, the anterior and posterior walls and roof of the acetabulum, the ischial tuberosity, the body of the ilium, and the third lumbar vertebra. The HU values in each area were compared between the young and older groups.

Results

Sixty-one young patients and 154 older patients were included in the study. The highest HU value was in the roof of the acetabulum regardless of age and sex. HU values were significantly higher in the ischial tuberosity and body of the ilium and lower in the pubic bone and anterior wall. The HU values in all pelvic areas were significantly lower in the older group than in the young group, especially in the anterior area.

Conclusions

HU values in the 6 pelvic areas were not uniform and were strongly related to load distribution. The HU distribution and age-related differences could explain the characteristic causes and patterns of acetabular fractures in the older and may help in surgical treatment.

Three-Year Clinical Outcomes after Minimally Invasive Sacroiliac Joint Arthrodesis Using Triangular Implants in Japan: A Pilot Study of Five Cases

Introduction

Sacroiliac joint (SIJ) arthrodesis using a minimally invasive technique, particularly the triangular implant system, is performed in patients with SIJ dysfunction in the United States and Europe. We report three-year clinical outcomes of the first minimally invasive SIJ arthrodesis procedures using the implants performed in Japan.

Methods

Five patients (one man and four women; age: 56.4±16.9 years) with SIJ pain who underwent SIJ arthrodesis using a triangular implant system in 2017 were included. In addition to operation time and blood loss, pain intensity (visual analog scale [VAS]) and functional impairment (Oswestry disability index [ODI]) were assessed preoperatively and at a 36-month follow-up. Implant loosening and osseous bridging across the joint were evaluated using computed tomography images, and patients' satisfaction with the surgery was also assessed at 12 and 36 months.

Results

The surgical time was 67.7±13.1 minutes, and blood loss was 7.4±6.9 mL. The mean VAS value improved significantly from 88.0±8.4 mm to 33.6±31.9 mm at 3 months and was maintained at 46.4±30.9 mm at 36 months (P<0.05). The mean ODI improved significantly from 76.4%±3.8% to 46.2%±21.9% at 6 months postoperatively (P<0.05) but had no significant improvements thereafter: 46.94±23.7% (12 months) and 66.4±8.6% (36 months). Three of five patients presented with at least one implant loosening on the sacrum side. No patient had osseous bridging across the joint. A total of 80% (4/5) of patients reported satisfaction with the surgery at 12 months and 60% (3/5) at 36 months.

Conclusions

The mean VAS value and ODI significantly improved until 6 months after the surgery. However, the mean ODI was reaggravated at 36 months after the surgery. Osseous bridging across the joint was not observed in all patients. We should carefully keep an eye on further long-term results to evaluate the implant.

Instrumentation of the sacroiliac joint with cylindrical threaded implants: A detailed finite element study of patient characteristics affecting fixation performance

The sacroiliac joint (SIJ) is a known pain generator that, in severe cases, may require surgical fixation to reduce intra-articular displacements and allow for arthrodesis. The objective of this computational study was to analyze how the number of implants affected SIJ stabilization with patient-specific characteristics such as the pelvic geometry and bone quality. Detailed finite element models were developed to account for three pelvises of differing anatomy. Each model was tested with a normal and low bone density (LD) under two types of loading: compression only and compression with flexion and extension moments. These models were instrumented with one to three cylindrical, threaded and fenestrated implants through a posterior oblique trajectory, requiring less muscle dissection than the more common lateral trajectory used with triangular implants. Compared with the noninstrumented pelvis, the change in range of motion (ROM) and stress distribution were used to characterize joint stabilization. Noninstrumented mobility ranged from 0.86 to 2.55 mm and from 1.37° to 6.11°. Across patient-specific characteristics, the ROM reduction with one implant varied from 3% to 21% for vertical and 15% to 47% for angular displacements. With two implants, the ROM reduction ranged from 12% to 41% for vertical and from 28% to 61% for angular displacements. Three implants, however, did not further improve the joint stability (14% to 42% for vertical and 32% to 63% for angular displacements). With respect to patient characteristics, an LD led to a decreased stabilization and a higher volume of stressed bone (>75% of yield stress). A better understanding of how patient characteristics affect the implant performance could help improve surgical planning of sacroiliac arthrodesis.

Quantitative evaluation of the sacroiliac joint fixation in stress reduction on both sacroiliac joint cartilage and ligaments: A finite element analysis

BACKGROUND

The sacroiliac joint fixation is the last resort for patients with prolonged and severe joint pain. Although the clinical results of anterior fixations are conclusive, there exist several inevitable drawbacks with the surgical method such as the difficulty performing the surgery due to the presence of many organs. The posterior fixation technique has thus been developed to overcome those inconveniences. This study aims to assess in silico the mechanical environment following posterior and anterior fixations, focusing on stresses in both the sacroiliac cartilage and dorsal ligamentous part, as well as loads experienced by the pelvic ligaments.

METHODS

Sacroiliac joint cartilage, dorsal ligamentous part stresses and pelvic ligaments loads were evaluated with three types of fixation models. A vertical load of 600 N was applied, equally distributed via both acetabula when standing and sitting.

FINDINGS

Results show that the anterior sacroiliac joint fixation reduced von Mises stresses in the cartilage and dorsal ligamentous part and decreased ligaments loads more extensively than the posterior fixation when compared to the untreated model as a reference. However, the posterior fixation still remains the desirable and preferential treatment.

INTERPRETATION

The anterior sacroiliac joint fixation showed better performances compared to the posterior one; however, the lower invasive aspect of the latter is a fundamental clinical advantage which also has the possibility to be improved by considering various screws and cages configurations. This study provides a beneficial suggestion to improve the current fixation technique.

Sacral insufficiency fracture after instrumented lumbosacral fusion: Focusing pelvic deformation -A retrospective case series

The purpose of this study was to report the characteristics of SIFs after ILSF and discuss its management focusing on pelvic deformation. We retrospectively reviewed all consecutive patients who underwent ILSF for degenerative disc diseases during the period between 2000 and 2017 and were diagnosed as SIF at our institute. The clinical and radiographic data were reviewed on their medical charts. Treatment outcomes for SIF were also investigated. Eight patients (all females) were included in this study. Mean age at SIF diagnosis was 72 years, and the mean follow-up period was 3.8 years (range 1-7 years). SIF developed average 7.5 years (range 1 month-17 years) after the index ILSF. Fracture patterns were unilateral vertical in four, bilateral vertical in three, and horizontal in 1 patient. Unlike patients with unilateral vertical SIF, patients with bilateral vertical or horizontal SIF showed a marked increase of pelvic incidence (PI) by mean 17.0°±5.0° and sagittal vertical axis (SVA) by mean 4.5 ± 2.2 cm, compared to the respective values before the onset of abrupt pain. All patients with unilateral vertical SIF were treated favorably by conservative management, however sacropelvic fixation was inevitable in patients with bilateral vertical or horizontal SIF. Bilateral vertical or horizontal SIF showed marked changes on sagittal radiographic parameters including PI and SVA. Although unilateral vertical SIF has benign courses that responded well to conservative management, bilateral vertical or horizontal SIF is likely to need surgical treatment. Treatment plan should be determined depending on fracture pattern and pelvic deformation.

Comparative analysis of the lateral and posterolateral trajectories for fixation of the sacroiliac joint-a cadaveric study

Background

A number of minimally invasive sacroiliac (SI) joint fusion solutions for placing implants exist, with reduced post-operative pain and improved outcomes compared to open procedures. The objective of this study was to compare two MIS SI joint fusion approaches that place implants directly across the joint by comparing the ilium and sacrum bone characteristics and SI joint separation along the implant trajectories.

Methods

Nine cadaveric specimens (n = 9) were CT scanned and the left and right ilium and sacrum were segmented. The bone density, bone volume fraction, and SI joint gap distance were calculated along lateral and posterolateral trajectories and compared using analysis of variance between the two orientations.

Results

Iliac bone density, indicated by the mean Hounsfield Unit, was significantly greater for each lateral trajectory compared to posterolateral. The volume of cortical bone in the ilium was greater for the middle lateral trajectory compared to all others and for the top and bottom lateral trajectories compared to both posterolateral trajectories. Cortical density was greater in the ilium for all lateral trajectories compared to posterolateral. The bone fraction was significantly greater in all lateral trajectories compared to posterolateral in the ilium. No differences in cortical volume, cortical density, or cancellous density were found between trajectories in the sacrum. The ilium was significantly greater in density compared with the sacrum when compared irrespective of trajectory (p < 0.001). The posterolateral trajectories had a significantly larger SI joint gap than the lateral trajectories (p < 0.001).

Conclusion

Use of the lateral approach for minimally invasive SI fusion allows the implant to interact with bone across a significantly smaller joint space. This interaction with increased cortical bone volume and density may afford better fixation with a lower risk of pull-out or implant loosening when compared to the posterolateral approach.

Minimally Invasive Sacroiliac Joint Fusion: A Lateral Approach Using Triangular Titanium Implants and Navigation

Background:

Minimally invasive sacroiliac (SI) joint fusion is indicated for low back pain from the SI joint that is due to degenerative sacroiliitis and/or sacroiliac joint disruption. This technique is safe and effective in relieving pain uncontrolled by nonoperative management^1-4. There is some controversy, but there continues to be increasing evidence of effectiveness.

Description:

This procedure is performed, with the patient under general anesthesia and in the prone position, using fluoroscopy or 3-dimensional (3D) navigation such as cone-beam computed tomographic (CT) imaging. After navigation setup, a navigated probe is used to approximate the desired location of each implant and trajectory. These positions are marked on the skin, and the skin is incised. A 3 to 5-cm lateral incision is made. The gluteal fascia is bluntly dissected to the outer table of the ilium. A guide pin is passed across the SI joint and into the center of the sacrum lateral to the neural foramina, which is confirmed with imaging. This is then drilled and broached. Triangular titanium rods are placed. Typically, 3 implants are placed, 2 in S1 and 1 in S2. Multiplanar postplacement imaging of the pelvis is obtained. The wound is irrigated and closed in layers.

Alternatives:

Nonsurgical alternatives have been reported to include pharmacological therapies, such as nonsteroidal anti-inflammatory drugs, therapeutic SI joint blocks⁵, and physical therapy, such as core stabilization, orthotics (SI belts), and radiofrequency ablation^1,2,6-8. The surgical alternative is an open anterior or posterior approach with SI joint arthrodesis. The anterior approach differs by the resection of the SI joint cartilage, the use of a plate or screws across the joint for stabilization, and the packing of bone graft to facilitate fusion⁹. These are more morbid and have a much longer recovery.

Rationale:

Conservative management for SI joint pain is inadequate for all patients. Having 3 of 5 positive physical examination maneuvers⁷, having confirmatory diagnostic block(s)¹⁰, and ruling out the hip or spine as the pain generator provide a success rate of >80%. These patients have early and sustained clinically important and significantly improved outcomes across varying measures compared with conservative treatment^1-4,11,12.

Expected Outcomes:

Patients can expect to experience decreased pain, reduced disability, increased daily function, and improved quality of life soon after the procedure is performed. These patients typically have an improvement of ≥50% in the Oswestry Disability Index score and a clinically significant decrease in visual analog pain scores¹³. The procedure appears durable through at least 5 years¹⁴. Complete pain relief is rare, but clinically important improvement is typical.

Important Tips:

Proper setup of the navigation system or fluoroscopy is needed to ensure accurate starting points.

For 3D navigation, use a reference pin in the contralateral posterior superior iliac spine.

Although navigation is used, radiographic images are made periodically to confirm proper placement of guide pins and implants. Images provide the greatest benefit when establishing navigation, after guide-pin placement when an outlet view allows for evaluation of pin depth, and after implant placement to confirm proper placement.

Blood loss is generally low, but care should be taken to avoid vascular injury. Although rare, improper placement has led to injury of the superior gluteal artery¹⁵ and iliac artery¹⁶. This can be avoided by staying in bone.

Proper placement of the implant is imperative in this procedure. There is the potential for nerve injury with improper placement of the implant: an L5 nerve injury if the implant is too ventral or an S1 or S2 nerve injury if the implant is too deep and into the foramen. Revision surgery is commonly due to nerve root impingement and/or malpositioning.

Preoperative 3D imaging is indicated when it is necessary to rule out differential diagnoses that mimic SI joint pain. This enables the surgeon to rule out intrapelvic pathology, assess sacral bone density¹⁷, and identify dysmorphic sacra or transitional vertebrae.

The effect of obesity, diabetes, and epidural steroid injection on regional volumetric bone mineral density measured by quantitative computed tomography in the lumbosacral spine

PURPOSE

High body mass index (BMI) is positively correlated with bone mineral density (BMD) in healthy adults; however, the effect of BMI on regional segmental BMDs in the axial skeleton is unclear. In addition, obese patients often have glucose intolerance and patients with lumbar spine pathology commonly have a history of epidural steroid injections (ESIs). The purpose of this study is to evaluate the effect of these patient factors on regional differences in BMD measured by quantitative computed tomography (QCT) in a lumbar fusion patient cohort.

METHODS

The data were obtained from a database comprised of clinical and preoperative CT data from 296 patients who underwent primary posterior lumbar spinal fusion from 2014 to 2017. QCT-vBMDs of L1 to L5, S1 body, and sacral alae were measured. Multivariate linear regression analyses were performed with setting vBMDs as the response variables. As explanatory variables, age, sex, race, current smoking, categorized BMI, diabetes, and ESI were chosen a priori.

RESULTS

A total of 260 patients were included in the final analysis. Multivariate analyses demonstrated that obese and morbidly obese patients had significantly higher vBMD in the sacral alae (SA). Diabetes showed independent positive associations with vBMDs in L1, L2, and the SA. Additionally, patients with an ESI history demonstrated significantly lower vBMD in the SA.

CONCLUSIONS

Our results demonstrate that obesity, diabetes, and epidural steroids affected vBMD differently by lumbosacral spine region. The vBMD of the SA appeared to be more sensitive to various patient factors than other lumbar regions.

Opportunistic Computed Tomography and Spine Surgery: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVE

This article seeks to provide a narrative review regarding the ability of opportunistic information available from computed tomography (CT) scans to guide decisions in spine surgery related to patient bone quality.

METHODS

A review of the literature (limited to human and English language) was performed via PubMed and Google Scholar using the search terms; "osteoporosis" AND "opportunistic" AND "computed tomography" AND "spine surgery." The titles and then abstracts of all identified citations were reviewed for inclusion by 2 of the authors (MS, BAF). Relevant articles were then studied in full text.

RESULTS

A review of the literature found 25 articles that were selected for inclusion in this narrative review. These articles were broadly divided into 4 subcategories: (1) opportunistic CT (oCT) and osteoporosis detection, (2) oCT data and the quality of screw fixation, (3) utilization of Hounsfield units to assess clinical and/or radiographic outcomes following spine fusion, and (4) virtual stress testing in spine surgery.

CONCLUSION

The literature on oCT, as well as associated virtual stress-testing techniques, demonstrate the potential to enhance spine surgery outcomes by preoperatively identifying at-risk patients in need of bone health optimization and informing best techniques for performing spinal fusion surgery on patients with diminished bone quality. While our narrative summary of the limited literature to date suggests a promising future for oCT data, significant additional research and/or radiographic workflow standardization is needed to validate these methods for clinical use.

Use of Hounsfield units of S1 body to diagnose osteoporosis in patients with lumbar degenerative diseases

OBJECTIVEThe aim of this study was to evaluate the use of Hounsfield unit (HU) values of the S1 body to diagnose osteoporosis in patients with lumbar degenerative diseases.METHODSThe records of 316 patients of ages ≥ 50 years and requiring surgery for lumbar degenerative diseases were reviewed. The bone mineral density (BMD) of the S1 body and L1 was measured in HU with preoperative lumbar CT. Circular regions of interest (ROIs) were placed on midaxial and midsagittal images of the S1 body. Dual-energy x-ray absorptiometry (DXA) and the criterion of L1 HU ≤ 110 HU were used to diagnose osteoporosis. The area under the receiver operating characteristic curve (AUC) was calculated to assess the use of HUs of the S1 body to diagnose osteoporosis.RESULTSThe interobserver and intraobserver reliability of measuring HU of the S1 body was excellent with intraclass correlation coefficients over 0.8 (p < 0.001). The correlation between HUs of the S1 body and average T-score of L1-4 was significant with Pearson correlation coefficients ≥ 0.60 (p < 0.001). The AUCs for using HUs of the S1 body to diagnose osteoporosis were 0.86 and 0.88 for axial HU and sagittal HU, respectively (p < 0.001). The HU thresholds with balanced sensitivity and specificity for diagnosing osteoporosis were 202 HU for axial HU (sensitivity: 76%; specificity: 76%) and 185 HU for sagittal HU (sensitivity: 80%; specificity: 80%).CONCLUSIONSBoth sagittal and axial HUs of the S1 body are useful tools for assessing BMD and diagnosing osteoporosis. Measuring HUs of the S1 body preoperatively from lumbar CT may help with surgical planning for patients with lumbar degenerative diseases.

Radiation protection in non-ionizing and ionizing body composition assessment procedures

Body composition assessment (BCA) represents a valid instrument to evaluate nutritional status through the quantification of lean and fat tissue, in healthy subjects and sick patients. According to the clinical indication, body composition (BC) can be assessed by different modalities. To better analyze radiation risks for patients involved, BCA procedures can be divided into two main groups: the first based on the use of ionizing radiation (IR), involving dual energy X-ray absorptiometry (DXA) and computed tomography (CT), and others based on non-ionizing radiation (NIR) [magnetic resonance imaging (MRI)]. Ultrasound (US) techniques using mechanical waves represent a separate group. The purpose of our study was to analyze publications about IR and NIR effects in order to make physicians aware about the risks for patients undergoing medical procedures to assess BCA providing to guide them towards choosing the most suitable method. To this end we reported the biological effects of IR and NIR and their associated risks, with a special regard to the excess risk of death from radio-induced cancer. Furthermore, we reported and compared doses obtained from different IR techniques, giving practical indications on the optimization process. We also summarized current recommendations and limits for techniques employing NIR and US. The authors conclude that IR imaging procedures carry relatively small individual risks that are usually justified by the medical need of patients, especially when the optimization principle is applied. As regards NIR imaging procedures, a few studies have been conducted on interactions between electromagnetic fields involved in MR exam and biological tissue. To date, no clear link exists between MRI or associated magnetic and pulsed radio frequency (RF) fields and subsequent health risks, whereas acute effects such as tissue burns and phosphenes are well-known; as regards the DNA damage and the capability of NIR to break chemical bonds, they are not yet robustly demonstrated. MRI is thus considered to be very safe for BCA as well US procedures.

Biomechanics of the Sacroiliac Joint: Surgical Treatments

BACKGROUND

Fixation is one of the most common surgical techniques for the treatment of chronic pain originating from the sacroiliac joint (SIJ). Many studies have investigated the clinical outcomes and biomechanics of various SIJ surgical procedures. However, the biomechanical literature points to several issues that need to be further explored, especially for the devices used in minimally invasive surgery of the SIJ. This study (part II) aims to assess biomechanical literature to understand the existing information as it relates to efficacies of the surgical techniques and the gaps in the knowledge base. Part I reviewed basic anatomy and mechanics of the SIJ joint, including difference between males and females, and causes of pain emanating from these joints.

METHODS

A thorough literature review was performed pertaining to studies related to SIJ fixation techniques and the biomechanical outcomes of the surgical procedures.

RESULTS

Fifty-five studies matched the search criteria and were considered for the review. These articles predominantly pertained to the biomechanical outcomes of the minimally invasive surgery with different instrumentation systems and surgical settings.

CONCLUSIONS

The SIJ is one of the most overlooked sources of lower back pain. The joint is responsible for the pain in 15% to 30% of people suffering from lower back pain. Various studies have investigated the clinical outcomes of different surgical procedures intended to improve the pain and quality of life following surgery. The data show that these techniques are indeed effective. However, clinical studies have raised several issues, like optimal number and positioning of implants, unilateral versus bilateral placements, adjacent segment disease, implant designs, and optimal location of implants with respect to variations in bone density across the SIJ. Biomechanical studies using in vitro and in silico techniques have addressed some of these issues. Studies also point out the need for additional investigations for a better understanding of the underlying mechanics for the improved long-term surgical outcomes. Further long-term clinical follow-ups are essential as well. This review presents pertinent findings.

Bone density of first and second segments of normal and dysmorphic sacra

Background

Iliosacral screw fixation is safe and effective but can be complicated by loss of fixation, particularly in patients with osteopenic bone. Sacral morphology dictates where iliosacral screws may be placed when stabilizing pelvic ring injuries. In dysmorphic sacra, the safe osseous corridor of the upper sacral segment (S1) is smaller and lacks a transsacral corridor, increasing the need for fixation in the second sacral segment (S2). Previous evidence suggests that S2 is less dense than S1. The aim of this cross-sectional study is to further evaluate bone mineral density (BMD) of the S1 and S2 iliosacral osseous pathways through morphology stratification into normal and dysmorphic sacra.

Materials and methods

Pelvic computed tomography scans of 50 consecutive trauma patients, aged 18 to 50 years, from a level 1 trauma center were analyzed prospectively. Five radiographic features (upper sacral segment not recessed in the pelvis, mammillary bodies, acute alar slope, residual S1 disk, and misshapen sacral foramen) were used to identify dysmorphic characteristics, and sacra with four or five features were classified as dysmorphic. Hounsfield unit values were used to estimate the regional BMD of S1 and S2. Student’s t-test was utilized to compare the mean values at each segment, with statistical significance being set at p < 0.05. No change in clinical management occurred as a result of inclusion in this study.

Results

A statistical difference in BMD was appreciated between S1 and S2 in both normal and dysmorphic sacra (p < 0.0001), with 28.4% lower density in S2 than S1. Further, S1 in dysmorphic sacra tended to be 4% less dense than S1 in normal sacra (p = 0.047). No difference in density was appreciated at S2 based on morphology.

Conclusions

Our results would indicate that, based on BMD alone, fixation should be maximized in S1 prior to fixation in S2. In cases where S2 fixation is required, we recommend that transsacral fixation should be strongly considered if possible to bypass the S2 body and achieve fixation in the cortical bone of the ilium and sacrum.

Level of evidence

Level III.

What do we know about the biomechanics of the sacroiliac joint and of sacropelvic fixation? A literature review

The purpose of this review is to summarize the general knowledge about the biomechanics of the sacroiliac joint and sacropelvic fixation techniques. Additionally, this study aims to support biomechanical investigations in defining experimental protocols as well as numerical modeling of the sacropelvic structures. The sacroiliac joint is characterized by a large variability of shape and ranges of motion among individuals. Although the ligament network and the anatomical features strongly limit the joint movements, sacroiliac displacements and rotations are not negligible. Currently available treatments for sacroiliac joint dysfunction include physical therapy, steroid injections, Radio-frequency ablation of specific neural structures, and open or minimally invasive SIJ fusion. In long posterior construct, the most common solutions are the iliac screws and the S2 alar - iliac screws, whereas for the joint fixation alone, mini - invasive alternative system can be used. Several studies reported the clinical outcomes of the different techniques and investigated the biomechanical stability of the relative construct, but the effect of sacropelvic fixation techniques on the joint flexibility and on the stress generated into the bone is still unknown. In our opinion, more biomechanical analyses on the behavior of the sacroiliac joint may be performed in order to better predict the risk of failure or instability of the joint.

BMI and gender increase risk of sacral fractures after multilevel instrumented spinal fusion compared with bone mineral density and pelvic parameters

BACKGROUND CONTEXT

Sacral fractures are a rare but potentially devastating complication. Long-fusion constructs, including the sacrum, that do not extend to the pelvis may result in sacral fractures. Besides established risk factors including gender, age, and number of levels fused, body mass index (BMI), pelvic parameters, and bone mineral density (BMD) have also been proposed as potential risk factors for postoperative sacral fractures. The literature supporting this, however, is limited.

PURPOSE

The aim of the present study was to assess whether preoperative pelvic parameters, BMI, or BMD of patients with sacral fracture are different compared with age, gender, and fusion level-matched non-fracture controls.

STUDY DESIGN/SETTING

This is a case-control study.

PATIENT SAMPLE

Patients undergoing posterior instrumented fusion at a single academic institution between 2002 and 2016 were included in the study.

OUTCOME MEASURES

The outcome measure was occurrence of a postoperative sacral fracture.

METHODS

Patients with sacral fractures after posterior instrumented spinal fusion, including the sacrum, were retrospectively identified and matched 2:1 with non-fracture controls based on gender, age, and number of levels fused. Patients with concurrent spinopelvic fixation or missing preoperative computed tomography (CT) imaging were excluded. Preoperative sagittal balance was assessed using lateral radiographs. Quantitative computed tomography (QCT) assessment included standard measurements at L1/L2 and additional experimental measurements of the S1 body and sacral ala.

RESULTS

Twenty-one patients with sacral fracture were matched to non-fracture controls. The majority of the patients with sacral fracture was female (76.2%) and of advanced age (mean 66.4 years). Fracture and control groups were well matched with respect to gender, age, and number of levels fused. Standard measurements at L1/L2 showed no significant difference in BMD between the fracture and the control groups (109.9 mg/cm³ vs. 116.4 mg/cm³, p=.414). Similarly, there was no significant BMD differences between the groups using the experimental measurements of the S1 body (183.6 mg/cm³ vs. 176.2 mg/cm³, p=.567) and the sacral ala (8.9 mg/cm³ vs. 4.8 mg/cm³, p=.616). Mean preoperative pelvic incidence-lumbar lordosis mismatch and pelvic tilt were not significantly different between the groups. Univariate conditional logistic regression analysis revealed that the odds of experiencing a sacral fracture was approximately six times higher for obese patients compared with normal or underweight patients. After controlling for BMI in multivariate conditional logistic regression models, BMD was still not significantly associated with the odds of experiencing sacral fractures.

CONCLUSIONS

To our knowledge, this is the first study to assess the association of preoperative BMD measured by QCT, pelvic parameters, and BMI with postoperative sacral fractures in a large patient cohort. Interestingly, our data do not show any difference in preoperative pelvic parameters and BMD between the groups. This is in line with previous reports that indicate only a few patients with sacral fracture after fusion surgery have clear evidence of osteoporosis. Bone mineral density as a measure of bone quantity, rather than bone quality, may not be as important in these fractures as previously thought. Obesity, however, was associated with higher odds of experiencing postoperative sacral fractures. The present study thereby challenges the widespread concept that obesity is a protective factor against fractures in the elderly. In summary, our results suggest that BMI and gender, more than pelvic parameters and BMD, are risk factors for postoperative sacral fractures.

Opportunistic Screening for Osteoporosis Using Computed Tomography: State of the Art and Argument for Paradigm Shift

PURPOSE OF REVIEW

Osteoporosis is disproportionately common in rheumatology patients. For the past three decades, the diagnosis of osteoporosis has benefited from well-established practice guidelines that emphasized the use of dual x-ray absorptiometry (DXA). Despite these guidelines and the wide availability of DXA, approximately two thirds of eligible patients do not undergo testing. One strategy to improve osteoporosis testing is to employ computed tomography (CT) examinations obtained as part of routine patient care to "opportunistically" screen for osteoporosis, without additional cost or radiation exposure to patients. This review examines the role of opportunistic CT in the evaluation of osteoporosis.

RECENT FINDINGS

Recent evidence suggests that opportunistic measurement of bone attenuation (radiodensity) using CT has sensitivity comparable to DXA. More importantly, such an approach has been shown to predict osteoporotic fractures. The paradigm shift of using CTs obtained for other reasons to opportunistically screen for osteoporosis promises to substantially improve patient care.

Biomechanical evaluation of sacroiliac joint fixation with decortication

BACKGROUND CONTEXT

Fusion typically consists of joint preparation, grafting, and rigid fixation. Fusion has been successfully used to treat symptomatic disruptions of the sacroiliac joint (SIJ) and degenerative sacroiliitis using purpose-specific, threaded implants. The biomechanical performance of these systems is important but has not been studied.

PURPOSE

The objective of this study was to compare two techniques for placing primary (12.5 mm) and secondary (8.5 mm) implants across the SIJ.

STUDY DESIGN

This is a human cadaveric biomechanical study of SIJ fixation.

MATERIALS AND METHODS

Pure-moment testing was performed on 14 human SIJs in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) with motion measured across the SIJ. Specimens were tested intact, after destabilization (cutting the pubic symphysis), after decortication and implantation of a primary 12.5-mm implant at S1 plus an 8.5-mm secondary implant at either S1 (S1-S1, n=8) or S2 (S1-S2, n=8), after cyclic loading, and after removal of the secondary implant. Ranges of motion (ROMs) were calculated for each test. Bone density was assessed on computed tomography and correlated with age and ROM. This study was funded by Zyga Technology but was run at an independent biomechanics laboratory.

RESULTS

The mean±standard deviation intact ROM was 3.0±1.6° in FE, 1.5±1.0° in LB, and 2.0±1.0° in AR. Destabilization significantly increased the ROM by a mean 60%-150%. Implantation, in turn, significantly decreased ROM by 65%-71%, below the intact ROM. Cyclic loading did not impact ROM. Removing the secondary implant increased ROM by 46%-88% (non-significant). There was no difference between S1-S1 and S1-S2 constructs. Bone density was inversely correlated with age (R=0.69) and ROM (R=0.36-0.58).

CONCLUSIONS

Fixation with two threaded rods significantly reduces SIJ motion even in the presence of joint preparation and after initial loading. The location of the secondary 8.5-mm implant does not affect construct performance. Low bone density significantly affects fixation and should be considered when planning fusion constructs. Findings should be interpreted in the context of ongoing clinical studies.

Comparative investigation of bone mineral density using CT and DEXA in a canine femoral model

Bone density measurements using computed tomography (CT) instead of dual-energy X-ray absorptiometry (DEXA) are currently of great interest in human and veterinary medical research as it would be beneficial to use CT scans obtained for other indications also for determining bone density. For Hounsfield units (HU) measured with CT in specific regions of interests (ROIs) in one or several slice/s a correlation with bone mineral density (BMD) measured by DEXA in humans and dogs of between 0.44 and 0.77 is reported in the literature. In the present study, instead certain volumes of interest (VOIs) obtained by CT scan and the corresponding HU to the respective VOIs were compared with the bone mineral density of the corresponding areas measured by DEXA. The aim of the study was to investigate whether this procedure gives more accurate information about bone density of the bones as three-dimensional objects of the respective patient. Correlation between measured HU in the respective VOI and BMD measured with DEXA in the corresponding ROI showed a very good correlation of 0.93. Linear regression with R²  = 0.85 (p = 0.0262) was calculated. Except for VOI5, similar distribution of values and significant differences (p < 0.0001-0.0087) between ROIs/VOIs were detected. Determining HU for assessing bone mineral density in a certain volume provides more accurate results than those previously reported from two-dimensional (2D) CT measurements. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2667-2672, 2017.