Design and test of a MEMS strain-sensing device for monitoring artificial knee implants.

This paper describes the development of a polyimide-based MEMS strain-sensing device. Finite element analysis was used to investigate an artificial knee implant and assist on device design and to optimize sensing characteristics. The sensing element of the device was fabricated using polyimide micromachining with embedded thin-metallic wires and placed into a knee prosthesis. The device was evaluated experimentally in a mechanical knee simulator using static and dynamic axial load conditions similar to those encountered in vivo. Results indicates the sensor is capable of measuring the strain associated to the total axial forces in the range of approximately 4 times body weight with a good sensitivity and accuracy for events happening within 1 s time window.

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 µÎµ and 2039.9 µÎµ, respectively. The average strain accuracy (MAER) and precision (SDER) were 694.3 µÎµ and 440.3 µÎµ, respectively. The loaded minimum principal strain (8738.9 µÎµ) was 12.6 times higher than the MAER (694.3 µÎµ) 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.

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.

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.

Importance of trabecular anisotropy in finite element predictions of patellar strain after Total Knee Arthroplasty.

Patellar fracture and anterior knee pain remain major complications after Total Knee Arthroplasty (TKA). Patient-specific finite element (FE) models should help improve understanding of these complications through estimation of joint and bone mechanics. However, sensitivity of predictions on modeling techniques and approaches is not fully investigated. In particular, the importance of patellar bone anisotropy, usually omitted in FE models, on strain prediction is still unknown. The objective of this study was thus to estimate the influence of modeling patellar trabecular anisotropy on prediction of patellar strain in TKA models. We compared FE-derived strain predictions with isotopic and anisotropic material properties using 17 validated FE models of the patella after TKA. We considered both non-resurfaced and resurfaced patellae, in a load-bearing TKA joint. We evaluated and compared the bone volume above a strain threshold and, in addition, estimated if the difference in isotopic and anisotropic predictions was consistent between patellae of different average bone volume fraction. Compared to the anisotropic reference, the isotropic prediction of strained volume was 3.7±1.8 times higher for non-resurfaced patellae and 1.5±0.4 times for resurfaced patellae. This difference was higher for patellae with lower average bone volume fraction. This study indicates that strain predictions acquired via isotropic patellar FE models should be interpreted with caution, especially when patellae of different average bone volume fraction are compared.

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.

Patients with primary localized high-grade sarcomas of the digestive tract excluding GIST : a retrospective study from the French sarcoma group.

INTRODUCTION: The natural history of localized high-grade sarcomas of the digestive tract (SDT) excluding GIST has been rarely considered owing to their low incidence and heterogeneity. We describe the histoclinical characteristics of SDT and correlate them with patients' outcomes. METHODS: We retrospectively collected medical files from a European database covering connective tissue tumors listed in Europe for about twenty years. Only untreated localized primary high-grade SDT were included. A central histological review was performed for each case. Patients' characteristics were compared and correlated with clinical outcomes. RESULTS: A total of 45 patients were identified. Leiomyosarcomas (LMS) and undifferentiated sarcomas (UDS) were predominant, the former having better overall survival (OS) and progressionfree survival (PFS) while the latter having a worse outcome than the other histological types. Complete remission was obtained in 34 patients (75%) and was associated with male sex, age over 40 years and monofocal tumor. Complete surgery and LMS histology were associated with a better prognosis without any significant difference in baseline characteristics or in treatment modalities. CONCLUSION: Complete surgery and histological type seem to be prognostic indicators of SDT. These results suggest the importance of treating these patients in a reference center.

[Air embolism during lumbar discal hernia repair. Retroperioneal vessels lesions have to be suspected]. / Symptomatologie d'embolie gazeuse au cours d'une chirurgie de hernie discale lombaire: suspecter une plaie vasculaire rétropéritonéale.

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.

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.

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.

[Unilateral hydrocephalus caused by abscess of the choroid plexus]. / Hydrocéphalie unilatérale par abcès des plexus choroïdes.

A case of unilateral hydrocephalus due to an abscess in the ipsilateral choroid plexuses, and revealed by intracranial hypertension is reported. Treatment with ceftriaxone, metronidazol and thiophenicol was clinically and radiographically successful, without surgery 3 weeks later. Management and mechanisms are discussed.

[Sickle cell anemia and internal cerebral vein thrombosis]. / Drépanocytose et thrombose des veines cérébrales internes.

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.

[Electrophoresis of cholinesterases of the cerebrospinal fluid in the Guillain-Barré syndrome]. / Electrophorèse des cholinestérases du liquide céphalorachidien dans le syndrome de Guillain-Barré.

Polyacrylamide gel electrophoresis of cholinesterase from cerebrospinal fluid was performed in 22 patients with Guillain-Barré syndrome. Fifteen of these patients had an abnormal cerebrospinal fluid with emergence of a second electrophoretic migration band corresponding to non-specific cholinesterase. Among 182 patients with a variety of diseases who served as controls, only one presented with this abnormality. From these data the sensitivity and specificity of cerebrospinal fluid cholinesterase electrophoresis were calculated at 68 and 99 percent respectively. The second migration band seems to appear early in the course of the disease and disappears when the patient is cured. Moreover, the occurrence of this band is correlated with the severity of the condition, as shown by a greater number of patients under artificial ventilation and by a longer stay in intensive care unit. Cerebrospinal fluid electrophoresis could be used as a prognosis factor.

[Monitoring of intracranial pressure with intraparenchymal fiberoptic transducer. Technical aspects and clinical reliability]. / Monitorage de la pression intracrânienne par capteur intraparenchymateux à fibres optiques: aspects techniques et fiabilité clinique.

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.

[A prospective study of 180 percutaneous catheterizations of the axillary vein during resuscitation]. / Etude prospective de 180 cathétérismes percutanés de la veine axillaire en réanimation.

Central venous catheterization via the axillary vein was performed in 180 comatose patients with a success rate of 91%. The scarcity of serious nervous (none), thrombotic (6%), hemorrhagic (9.4%), infectious (1.8%), or thoracic (none) complications, the preservation of cerebral venous drainage, a longer distance between puncture site and tracheostomy or intubation tube make this safe and easy procedure perfectly convenient for comatose patients.

[A comparative study of CPK during spinal surgery in the knee-chest position. Apropos of 93 patients]. / Etude comparée des CPK au cours de la chirurgie du rachis en position génupectorale. A propos de 93 patients.

A number of severe rhabdomyolysis with acute renal failure have been reported following spine surgery in knee chest position. CPK were measured postoperatively in 93 patients (A group), comparatively with two groups in which respectively neurosurgery without any muscle stretching (B group) and abdominal surgery with aid of retractors (C group) were performed. CPK were significantly and similarly increased in A and C groups only. This postoperative increase of CPK appears to be related more to the muscle stretching than to the posture itself. Intraoperative low blood pressure and an operating time longer than 4 hrs contribute probably to rhabdomyolysis. No renal failure was observed in our series. Low limb vascular insufficiency is the main contra-indication of knee chest position. Postoperative diuresis surveillance is mandatory in all cases, CPK analysis is not.

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.

Translation of biomechanical concepts in bone tissue engineering: from animal study to revision knee arthroplasty.

Bone defects in revision knee arthroplasty are often located in load-bearing regions. The goal of this study was to determine whether a physiologic load could be used as an in situ osteogenic signal to the scaffolds filling the bone defects. In order to answer this question, we proposed a novel translation procedure having four steps: (1) determining the mechanical stimulus using finite element method, (2) designing an animal study to measure bone formation spatially and temporally using micro-CT imaging in the scaffold subjected to the estimated mechanical stimulus, (3) identifying bone formation parameters for the loaded and non-loaded cases appearing in a recently developed mathematical model for bone formation in the scaffold and (4) estimating the stiffness and the bone formation in the bone-scaffold construct. With this procedure, we estimated that after 3 years mechanical stimulation increases the bone volume fraction and the stiffness of scaffold by 1.5- and 2.7-fold, respectively, compared to a non-loaded situation.

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.