POS0126 UTILITY OF THE SUBCHONDRAL BONE ATTENUATION COEFFICIENT OF THE SACROILIAC MARGINS TO DIFFERENTIATE SPONDYLOARTHRITIS AND OSTEITIS CONDENSANS ILII

Background

Differentiating ankylosing spondylitis (AS) from osteitis condensans ilii (OCI) remains challenging for clinicians.

Objectives

The aim of this study was to determine whether Subchondral Bone Attenuation Coefficient of the SacroIliac margins (SBAC-SI) is different in AS, OCI and diffuse idiopathic skeletal hyperostosis (DISH).

Methods

A monocentric retrospective observational study was performed at a French University Hospital. Patients included were followed for AS, DISH or OCI and underwent CT scan including sacroiliac joint. Patients with tumor lesion of bone or a history of pelvic radiotherapy were excluded. AS and OCI patients were matched with a control of the same age and sex. All scans were acquired on the same CT-scan unit (Somatom 64 definition AS+, Siemens Healthineers, Erlangen, Germany), with a slice thickness of 0.625 mm. In the coronal oblique plane of the SIJ, three slices (anterior, middle and posterior) and four quadrants per joint were defined. Twenty-four identical circular regions of interest (ROIs) (30 mm2), 8 per slice, were manually placed separately subcortical to the SIJ, four on the sacral side and four on the iliac side. The distance between the circle of the ROI and the cortical bone was 2 to 3 mm. An overall score was obtained from the sum of all ROIs. For every ROI, an Attenuation Coefficient was measured and expressed in Hounsfield Unit. The total SBAC-SI score was the sum of the 24 ROI. The sacral and iliac SBAC-SI scores were the sum of the sacral or the iliac ROI.

Results

Thirty AS and AS controls, 31 DISH, 29 OCI and OCI controls were included. SBAC-SI score was 9727 (±2430) in the OCI group (p<0.001), 3563 (±1860) in the AS group, 3899 (±1937) in the DISH group, 4224 (±1693) in the AS control group and 5445 (±1205) in the OCI control group. A threshold of 7500 HU had the best discriminative value between OCI and AS (youden index: 0.89). In AS, disease duration is negatively associated with SBAC-SI (r: -0.623; p< 0.01) and HLA B27 is associated with lower SBAC-SI (6523 [5198; 7137]VS 2809 [1568; 3371]; p <0.001).

Conclusion

SBAC-SI is significatively different between AS and OCI and could help to distinguish these two diseases.

Figure 1.

Distribution of the Subchondral Bone Attenuation Coefficients of the Sacroiliac Margins of the 24 ROI in the anterior (A), middle (B) and posterior (C) slices in the coronal oblique plane of the sacroiliac joints

Disclosure of Interests

None declared

Glenoid bone strain after anatomical total shoulder arthroplasty: In vitro measurements with micro-CT and digital volume correlation

Glenoid implant loosening remains a major source of failure and concern after anatomical total shoulder arthroplasty (aTSA). It is assumed to be associated with eccentric loading and excessive bone strain, but direct measurement of bone strain after aTSA is not available yet. Therefore, our objective was to develop an in vitro technique for measuring bone strain around a loaded glenoid implant. A custom loading device (1500 N) was designed to fit within a micro-CT scanner, to use digital volume correlation for measuring displacement and calculating strain. Errors were evaluated with three pairs of unloaded scans. The average displacement random error of three pairs of unloaded scans was 6.1 µm. Corresponding systematic and random errors of strain components were less than 806.0 µε and 2039.9 µε, respectively. The average strain accuracy (MAER) and precision (SDER) were 694.3 µε and 440.3 µε, respectively. The loaded minimum principal strain (8738.9 µε) was 12.6 times higher than the MAER (694.3 µε) on average, and was above the MAER for most of the glenoid bone volume (98.1%). Therefore, this technique proves to be accurate and precise enough to eventually compare glenoid implant designs, fixation techniques, or to validate numerical models of specimens under similar loading.

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis

BACKGROUND

Rotator cuff muscle degeneration is an important parameter to consider when planning shoulder arthroplasty.

HYPOTHESIS

We hypothesized that rotator cuff muscle degeneration is correlated with scapulohumeral subluxation in patients planned for anatomical total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

We developed a semi-automated quantitative CT method to measure rotator cuff muscle degeneration, and retrospectively analyzed 107 preoperative shoulder CT scans of patients with primary osteoarthritis. On a standardized sagittal-oblique CT slice perpendicular to the scapular axis, two observers measured the cross-sectional areas of residual rotator cuff muscle tissues, normalized by the estimated area of healthy muscles. Muscle degeneration was quantified in a semi-automated manner, and divided into atrophy and fatty infiltration. Scapulohumeral subluxation was determined in 3D as the distance between the humeral head center and the glenoid surface center, projected on the same CT slice, and normalized by the humeral head radius. We tested all potential correlations between muscle degeneration and scapulohumeral subluxation.

RESULTS

Muscle degeneration, primarily due to atrophy, predominated in the supraspinatus; it varied from 0.8% to 88.8%. Scapulohumeral subluxation varied from 2.5% to 72.9%, and was mainly in a posterior and postero-superior orientation. There was a significant but weak correlation between the amount of subluxation and both supraspinatus (R=0.207, P=0.032) and infraspinatus (R=0.225, P=0.020) degeneration. Inter- and intra-observer reproducibility of muscle degeneration measurements were both excellent (ICCs range=0.955-0.987 and 0.971-0.988, respectively).

CONCLUSION

This new semi-automated CT method allows to quantitatively and reproducibly measure rotator cuff muscle degeneration in shoulders with primary osteoarthritis. Muscle degeneration is weakly correlated with scapulohumeral subluxation in patients planned for anatomical TSA.

LEVEL OF EVIDENCE

Level IV.

TYPE OF STUDY

Diagnostic retrospective study.

Full-field measurement of micromotion around a cementless femoral stem using micro-CT imaging and radiopaque markers

A good primary stability of cementless femoral stems is essential for the long-term success of total hip arthroplasty. Experimental measurement of implant micromotion with linear variable differential transformers is commonly used to assess implant primary stability in pre-clinical testing. But these measurements are often limited to a few distinct points at the interface. New techniques based on micro-computed tomography (micro-CT) have recently been introduced, such as Digital Volume Correlation (DVC) or markers-based approaches. DVC is however limited to measurement around non-metallic implants due to metal-induced imaging artifacts, and markers-based techniques are confined to a small portion of the implant. In this paper, we present a technique based on micro-CT imaging and radiopaque markers to provide the first full-field micromotion measurement at the entire bone-implant interface of a cementless femoral stem implanted in a cadaveric femur. Micromotion was measured during compression and torsion. Over 300 simultaneous measurement points were obtained. Micromotion amplitude ranged from 0 to 24µm in compression and from 0 to 49µm in torsion. Peak micromotion was distal in compression and proximal in torsion. The technique bias was 5.1µm and its repeatability standard deviation was 4µm. The method was thus highly reliable and compared well with results obtained with linear variable differential transformers (LVDTs) reported in the literature. These results indicate that this micro-CT based technique is perfectly relevant to observe local variations in primary stability around metallic implants. Possible applications include pre-clinical testing of implants and validation of patient-specific models for pre-operative planning.

Measurements of three-dimensional glenoid erosion when planning the prosthetic replacement of osteoarthritic shoulders

The three-dimensional (3D) correction of glenoid erosion is critical to the long-term success of total shoulder replacement (TSR). In order to characterise the 3D morphology of eroded glenoid surfaces, we looked for a set of morphological parameters useful for TSR planning. We defined a scapular coordinates system based on non-eroded bony landmarks. The maximum glenoid version was measured and specified in 3D by its orientation angle. Medialisation was considered relative to the spino-glenoid notch. We analysed regular CT scans of 19 normal (N) and 86 osteoarthritic (OA) scapulae. When the maximum version of OA shoulders was higher than 10°, the orientation was not only posterior, but extended in postero-superior (35%), postero-inferior (6%) and anterior sectors (4%). The medialisation of the glenoid was higher in OA than normal shoulders. The orientation angle of maximum version appeared as a critical parameter to specify the glenoid shape in 3D. It will be very useful in planning the best position for the glenoid in TSR.

Importance of the subscapularis muscle after total shoulder arthroplasty

BACKGROUND

The rotator cuff muscles are the main stabilizer of the glenohumeral joint. After total shoulder arthroplasty using anterior approaches, a dysfunction of the subscapularis muscle has been reported. In the present paper we tested the hypothesis that a deficient subscapularis following total shoulder arthroplasty can induce joint instability.

METHODS

To test this hypothesis we have developed an EMG-driven musculoskeletal model of the glenohumeral joint. The model was based on an algorithm that minimizes the difference between measured and predicted muscular activities, while satisfying the mechanical equilibrium of the glenohumeral joint. A movement of abduction in the scapular plane was simulated. We compared a normal and deficient subscapularis. Muscle forces, joint force, contact pattern and humeral head translation were evaluated.

FINDINGS

To satisfy the mechanical equilibrium, a deficient subscapularis induced a decrease of the force of the infraspinatus muscle. This force decrease was balanced by an increase of the supraspinatus and middle deltoid. As a consequence, the deficient subscapularis induced an upward migration of the humeral head, an eccentric contact pattern and higher stress within the cement.

INTERPRETATION

These results confirm the importance of the suscapularis for the long-term stability of total shoulder arthroplasty.

Tightening force and torque of nonlocking screws in a reverse shoulder prosthesis

BACKGROUND

Reversed shoulder arthroplasty is an accepted treatment for glenohumeral arthritis associated to rotator cuff deficiency. For most reversed shoulder prostheses, the baseplate of the glenoid component is uncemented and its primary stability is provided by a central peg and peripheral screws. Because of the importance of the primary stability for a good osteo-integration of the baseplate, the optimal fixation of the screws is crucial. In particular, the amplitude of the tightening force of the nonlocking screws is clearly associated to this stability. Since this force is unknown, it is currently not accounted for in experimental or numerical analyses. Thus, the primary goal of this work is to measure this tightening force experimentally. In addition, the tightening torque was also measured, to estimate an optimal surgical value.

METHODS

An experimental setup with an instrumented baseplate was developed to measure simultaneously the tightening force, tightening torque and screwing angle, of the nonlocking screws of the Aquealis reversed prosthesis. In addition, the amount of bone volume around each screw was measured with a micro-CT. Measurements were performed on 6 human cadaveric scapulae.

FINDINGS

A statistically correlated relationship (p<0.05, R=0.83) was obtained between the maximal tightening force and the bone volume. The relationship between the tightening torque and the bone volume was not statistically significant.

INTERPRETATION

The experimental relationship presented in this paper can be used in numerical analyses to improve the baseplate fixation in the glenoid bone.

Targeted mechanical properties for optimal fluid motion inside artificial bone substitutes

Our goal was to develop a method to identify the optimal elastic modulus, Poisson's ratio, porosity, and permeability values for a mechanically stressed bone substitute. We hypothesized that a porous bone substitute that favors the transport of nutriments, wastes, biochemical signals, and cells, while keeping the fluid-induced shear stress within a range that stimulates osteoblasts, would likely promote osteointegration. Two optimization criteria were used: (i) the fluid volume exchange between the artificial bone substitute and its environment must be maximal and (ii) the fluid-induced shear stress must be between 0.03 and 3 Pa. Biot's poroelastic theory was used to compute the fluid motion due to mechanical stresses. The impact of the elastic modulus, Poisson's ratio, porosity, and permeability on the fluid motion were determined in general and for three different bone substitute sizes used in high tibial osteotomy. We found that fluid motion was optimized in two independent steps. First, fluid transport was maximized by minimizing the elastic modulus, Poisson's ratio, and porosity. Second, the fluid-induced shear stress could be adjusted by tuning the bone substitute permeability so that it stayed within the favorable range of 0.03 to 3 Pa. Such method provides clear guidelines to bone substitute developers and to orthopedic surgeons for using bone substitute materials according to their mechanical environment.

Comparison of polyethylene wear in anatomical and reversed shoulder prostheses

Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from in vivo recorded data.

After one year of use, the volumetric wear was 8.4 mm3 for the anatomical prosthesis, but 44.6 mm3 for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required.

Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.

Implants delivering bisphosphonate locally increase periprosthetic bone density in an osteoporotic sheep model. A pilot study

It is a clinical challenge to obtain a sufficient orthopaedic implant fixation in weak osteoporotic bone. When the primary implant fixation is poor, micromotions occur at the bone-implant interface, activating osteoclasts, which leads to implant loosening. Bisphosphonate can be used to prevent the osteoclastic response, but when administered systemically its bioavailability is low and the time it takes for the drug to reach the periprosthetic bone may be a limiting factor. Recent data has shown that delivering bisphosphonate locally from the implant surface could be an interesting solution. Local bisphosphonate delivery increased periprosthetic bone density, which leads to a stronger implant fixation, as demonstrated in rats by the increased implant pullout force. The aim of the present study was to verify the positive effect on periprosthetic bone remodelling of local bisphosphonate delivery in an osteoporotic sheep model. Four implants coated with zoledronate and two control implants were inserted in the femoral condyle of ovariectomized sheep for 4 weeks. The bone at the implant surface was 50% higher in the zoledronate-group compared to control group. This effect was significant up to a distance of 400mum from the implant surface. The presented results are similar to what was observed in the osteoporotic rat model, which suggest that the concept of releasing zoledronate locally from the implant to increase the implant fixation is not species specific. The results of this trial study support the claim that local zoledronate could increase the fixation of an implant in weak bone.

Structural abnormalities in the cerebellum and sensorimotor circuit in writer's cramp

BACKGROUND

Structural abnormalities were detected in bilateral primary sensorimotor areas in writer's cramp. Evidence in other primary dystonia, including blepharospasm and cervical dystonia, suggest that structural abnormalities may be observed in other brain areas such as the cerebellum in writer's cramp.

OBJECTIVE

To test the hypothesis that structural abnormalities are present along the sensorimotor and cerebellar circuits in patients with writer's cramp.

METHODS

Using voxel-based morphometry, the authors compared the brain structure of 30 right-handed patients with writer's cramp with that of 30 healthy control subjects matched for gender, age, and handedness.

RESULTS

Gray matter decrease was found in the hand area of the left primary sensorimotor cortex, bilateral thalamus, and cerebellum (height threshold p < 0.01, cluster significant at p < 0.05 corrected for multiple comparisons).

CONCLUSIONS

These results demonstrate in writer's cramp the presence of structural abnormalities in brain structures interconnected within the sensorimotor network including the cerebellum and the cortical representation of the affected hand. These abnormalities may be related to the pathophysiology of writer's cramp, questioning the role of the cerebellum, or to maladaptive plasticity in a task-related dystonia.

[Air embolism during lumbar discal hernia repair. Retroperioneal vessels lesions have to be suspected]

Occurrence of deep PETCO(2) drop during surgical lumbar disk repair is rare but dramatic. This case report leads to the diagnosis of retroperitoneal vessels lesions. We review the different diagnosis related to the drop of the PETCO(2) during surgery in the genupectoral position. We recommend that the diagnosis of retroperitoneal vessels lesion have to be suspected early if air embolism occurs during lumbar disk surgery.

Effects of the posterior cruciate ligament reconstruction on the biomechanics of the knee joint: a finite element analysis

BACKGROUND

Previous experimental studies have been conducted to evaluate the biomechanical effects of posterior cruciate ligament reconstruction; but no consensus has been reached on the preferred method of reconstruction.

METHODS

The 3D finite element mesh of a knee joint was reconstructed from computed tomography and magnetic resonance images. The ligaments were considered as hyperelastic materials. The tibiofemoral and patellofemoral joints were modeled with large sliding contact elements. The 3D model was used to simulate knee flexion from 0 degrees to 90 degrees in four cases: a knee with a "native" posterior cruciate ligament, a resected posterior cruciate ligament, a reconstructed single graft posterior cruciate ligament, and a reconstructed double graft posterior cruciate ligament.

FINDINGS

A resected posterior cruciate ligament induced high compressive forces in the medial tibiofemoral and patellofemoral compartments. The pressures generated in the tibiofemoral and patellofemoral compartments were nearly the same for the two reconstruction techniques (single graft and double graft). The single graft resulted in lower tensile stresses inside the graft than for the double graft.

INTERPRETATION

Firstly, a resected posterior cruciate ligament should be replaced to avoid excessive compressive forces, which are a source of cartilage degeneration. Secondly, the two types of posterior cruciate ligament reconstruction techniques partially restored the biomechanics of the knee in flexion, e.g. contact pressures were restored for pure flexion of the knee. The reconstruction techniques therefore partially restore the biomechanics of the knee in flexion. A double graft reconstruction is subjected to the highest tensile stresses.

Impact of age on both BIS values and EEG bispectrum during anaesthesia with sevoflurane in children

BACKGROUND

The aim of this study was to evaluate the potential relationship between age, BIS (Aspect), and the EEG bispectrum during anaesthesia with sevoflurane.

METHODS

BIS and raw EEG were recorded at a steady state of 1 MAC in 100 children, and during a decrease from 2 to 0.5 MAC in a sub-group of 29 children. The bispectrum of the EEG was estimated using MATLAB software. For analysis, the bispectrum was divided into 36 frequencies of coupling (P(i))--the MatBis. A multiple correspondence analysis (MCA) was used to establish an underlying structure of the pattern of each individual's MatBis at 1 MAC. Clustering of children into homogeneous groups was conducted by a hierarchical ascending classification (HAC). The level of statistical significance was set at 0.05.

RESULTS

At 1 MAC, the BIS values for all children ranged from 20 to 74 (median 40). Projection of both age and BIS value recorded at 1 MAC onto the structured model of the MCA showed them to be distributed along the same axis, demonstrating that the different values of BIS obtained in younger or older children are mainly dependent on their MatBis. At 1 MAC, six homogeneous groups of children were obtained through the HAC. Groups 5 (30 months; range 23-49) and 6 (18 months; range 6-180) were the younger children and Group 1 (97 months; range 46-162) the older. Groups 5 and 6 had the highest median values of BIS (54; range 50-59) (55; range 26-74) and Group 1 the lowest values (29; range 22-37).

CONCLUSION

The EEG bispectrum, as well as the BIS appeared to be strongly related to the age of children at 1 MAC sevoflurane.

Adaptation Models of Anisotropic Bone

A theoretical model and numerical methods were developed for testing different bone internal remodelling stimuli. The keystone of the study was the formulation of a stimulus based on the mechanical invariants of the stress tensor, which took into account bone non-homogeneity and anisotropy. A non-site specific remodelling rate equation was then used for the apparent density whereas anisotropy was fixed and evaluated from anatomic observations. An node-based semi-implicit algorithm with adaptive stepsize was implemented for solving the evolution equation. To preclude numerical artifacts (non-convergence, instability), a phase space description was proposed. As an illustration, the evolution of apparent density distribution surrounding the femoral stem after a Total Hip Replacement was simulated. Three stimuli were tested: the strain energy density stimulus, the octahedral shear stress stimulus, and an anisotropic plastic yield stress stimulus.

[Sickle cell anemia and internal cerebral vein thrombosis]

Cerebrovascular disorders are frequently associated with sickle cell disease, mainly in homozygous children. We report the case a 25-old-patient with known sickle cell disease who presented with coma inaugurated by manifestations of intracranial hypertension. CT revealed bilateral thalamic infarcts and angiography confirmed the thrombosis of internal cerebral veins. Treatment included heparin and blood transfusion. Severe cerebral oedema resulted in the lethal outcome three days later.

[Monitoring of intracranial pressure with intraparenchymal fiberoptic transducer. Technical aspects and clinical reliability]

A fiberoptic intracranial pressure transducer (Camino) was assessed prospectively in 100 patients. In all, 122 sensors were inserted intraparenchymally at the bedside, without the help of a neurosurgeon. Before the procedure, patients were given 2 to 4 mg of phenoperidine. The scalp was opened over a few millimeters in the frontal paramedian area. A burr holc was made with a 2 mm bit. The dura mater was opened and a hollow screw inserted in the diploë. When the zero of the transducer had been obtained, a 5 cm length was inserted within the screw. The transducer was then about 5 mm deep within cerebral parenchyma. The procedure took an average of about 15 min. An intracerebral haematoma around the transducer occurred five times. One had to be drained surgically. There were no infectious complications. The daily baseline drift was about 0.3 mmHg. The system seemed to be reliable: there was close agreement between the intracranial pressure (ICP), neurological status and CT scan findings. In trauma cases, there was also good correlation between mean ICP and the basal cistern obliteration score, finally, ICP became equivalent to mean arterial blood pressure in all brain dead patients. It is concluded that this system may be used in all cases where ICP requires to be monitored, even when the lateral ventricles are no longer visible, or when craniotomy has been performed. This will most probably result in a more extended use of ICP monitoring in neurosurgical intensive care.

[Treatment of ischemic cerebral edema with intracranial hypertension after neurosurgery of intracranial aneurysms]

Ischemic cerebral edema frequently develops after aneurysm surgery and may lead to severe intracranial hypertension. Of prime importance are reducing the level of ICP and preserving oligemic areas from becoming infarcted. Besides correction of factors known to worsen intracranial hypertension, several therapeutics may be of value: external CSF drainage, perfusion of mannitol, induced arterial hypertension and use of anesthetic agents with cerebral vasoconstricting capability. Hyperventilation is not recommended. Arterial hypotension and hypovolemia certainly contribute to aggravate cerebral ischemia and must be corrected. Cerebral ischemia may be reduced by two specific approaches: by improving cerebral oxygen transport in ischemic areas using arterial hypertension and calcium blockers rather than hemodilution or hypervolemia; by reducing cerebral metabolic rates with heavy anesthesia under the cover of a complete cardiovascular monitoring. In view of the large heterogenicity in cerebral lesions and physiopathological stages, a therapeutical trial appears suitable in each individual case. Criteria allowing to know if any therapeutic, used alone or in association, is beneficial include increase in blood flow in ischemic areas, reduction of ICP level and normalizing of indices like CSF or venous jugular blood lactate.

[Hyperthermia in meningeal hemorrhage. Contribution of daily determination of inflammation proteins]

This paper studies the causes of hyperthermias occurring after a subarachnoid hemorrhage by ruptured aneurysm in 54 patients, totalizing 66 febrils episodes. Only 29 episodes bacteriologically proved infections. The profile of thermic curve, the hemodynamical profile, and clinical examination are not convincing. The most convincing elements for the diagnosis of infection are the increasing number of the leucocytes counts, the increasing curve of CRP, and simultaneous decreasing curve of C4. The evolution of these parameters permit to follow the efficiency of antibiotics.

[Intracranial aneurysm and dysplasia of elastic tissue: pre- and postoperative problems]

From two cases of patients presenting a cerebral aneurysm associated with a dysplasia of elastic tissue, one a Marfan's syndrome, the other an anetoderma, this paper relate the post-operative, essentially cardio-vascularly and pulmonary complexities and define the elements of the pre-operative check-up.