A simple method for in vivo measurement of implant rod three-dimensional geometry during scoliosis surgery

Scoliosis is defined as a spinal pathology characterized as a three-dimensional deformity of the spine combined with vertebral rotation. Treatment for severe scoliosis is achieved when the scoliotic spine is surgically corrected and fixed using implanted rods and screws. Several studies performed biomechanical modeling and corrective forces measurements of scoliosis correction. These studies were able to predict the clinical outcome and measured the corrective forces acting on screws, however, they were not able to measure the intraoperative three-dimensional geometry of the spinal rod. In effect, the results of biomechanical modeling might not be so realistic and the corrective forces during the surgical correction procedure were intra-operatively difficult to measure. Projective geometry has been shown to be successful in the reconstruction of a three-dimensional structure using a series of images obtained from different views. In this study, we propose a new method to measure the three-dimensional geometry of an implant rod using two cameras. The reconstruction method requires only a few parameters, the included angle θ between the two cameras, the actual length of the rod in mm, and the location of points for curve fitting. The implant rod utilized in spine surgery was used to evaluate the accuracy of the current method. The three-dimensional geometry of the rod was measured from the image obtained by a scanner and compared to the proposed method using two cameras. The mean error in the reconstruction measurements ranged from 0.32 to 0.45 mm. The method presented here demonstrated the possibility of intra-operatively measuring the three-dimensional geometry of spinal rod. The proposed method could be used in surgical procedures to better understand the biomechanics of scoliosis correction through real-time measurement of three-dimensional implant rod geometry in vivo.     

A conductive polymer sensor for measuring external finger forces.

This paper describes the construction and use of a durable and thin force sensor that can be attached to the palmar surface of the fingers and hands for studying the biomechanics of grasp and for use in hand injury rehabilitation. These force sensors were constructed using a modified commercially available conductive polymer pressure sensing element and installing an epoxy dome for directing applied forces through a 12 mm diameter active sensing area. The installation of an epoxy dome was effective for making the sensors insensitive to contact surfaces varying from 25 to 1100 mm2 and a 16 mm radius surface curved convex towards the finger. The completed sensors were only 1.8 mm thick and capable of being taped to the distal phalangeal finger pads. They were calibrated on the hand by pinching a strain gage dynamometer. The useful range was between 0 and 30 N with an accuracy of 1 N for both static loading and normal dynamic grasp activities. The sensor time constant was 0.54 ms for a step force input. Because of varying offset voltages every time the sensors were attached, these sensors should be calibrated on the hand before each use. The sensors were used for measuring finger forces during controlled pinching and lifting tasks, and during ordinary grasping activities, such as picking up a book or a box, where the useful force range and response for these sensors were adequate.     

A new method for measuring torsional deformity in scoliosis

Background

This study evaluates the outcome and complications of decompressive cervical Laminectomy and lateral mass screw fixation in 110 cases treated for variable cervical spine pathologies that included; degenerative disease, trauma, neoplasms, metabolic-inflammatory disorders and congenital anomalies.

Methods

A retrospective review of total 785 lateral mass screws were placed in patients ages 16-68 years (40 females and 70 males). All cases were performed with a polyaxial screw-rod construct and screws were placed by using Anderson-Sekhon trajectory. Most patients had 12-14-mm length and 3.5 mm diameter screws placed for subaxial and 28-30 for C1 lateral mass. Screw location was assessed by post operative plain x-ray and computed tomography can (CT), besides that; the facet joint, nerve root foramen and foramen transversarium violation were also appraised.

Results

No patients experienced neural or vascular injury as a result of screw position. Only one patient needed screw repositioning. Six patients experienced superficial wound infection. Fifteen patients had pain around the shoulder of C5 distribution that subsided over the time. No patients developed screw pullouts or symptomatic adjacent segment disease within the period of follow up.

Conclusion

decompressive cervical spine laminectomy and Lateral mass screw stabilization is a technique that can be used for a variety of cervical spine pathologies with safety and efficiency.     

Development of a MEMS-based sensor array to characterise in situ loads during scoliosis correction surgery

Finite element analysis was implemented in three stages to design a piezoresistive, micro-electro-mechanical systems sensor array consisting of four-terminal sensors placed on deformable silicon diaphragms. This sensor array was used to retrofit the Contrel-Dubousset instrumentation in order to capture forces and moments applied by surgeons in real time during scoliosis correction surgery. Outputs from the sensor array have been designed to be compatible with a low-power wireless data transmission system that is currently being developed with a collaborating team in the biomedical industry. The designed sensor array is capable of resolving forces of up to 1000 N and moments of up to 4000 N mm in three dimensions during surgery. A process flow to produce the first prototyped version of this micro sensor with known performance characteristics is presented and tested. Acceptable correlation was found between the performance of the manufactured prototypes, numerical simulation and similar documented devices.     

Statistical assessment of two methods of measuring scoliosis before treatment.

Regression analysis has shown that the Ferguson and Cobb methods of measuring spinal curvature give comparable results, at least before the scoliosis is treated. When the Cobb angle was calculated by multiplying the Ferguson angle by 1.38, the results were accurate to within 5 degrees in 28 (76%) of 37 cases. Any further debate over the merits of the two methods should focus on their inter- and intraobserver reproducibility and their applicability after corrective treatment.     

Force plate for measuring the ground reaction forces in small animal locomotion

The importance of kinetic force plate studies of locomotion in small animals has grown recently with the increasing use of rodent models for studies of musculoskeletal diseases. However, the force plates for use with animals much smaller than a cat are difficult to design and use. Here we present data on a commercially available small force plate that accurately collects whole-body and, in a modified form, single-limb ground reaction forces in mice. The method used here is convenient, inexpensive, and readily adaptable for use with a variety of small species.     

Micro-cantilever method for measuring the tensile strength of biofilms and microbial flocs

Cohesive strength is an important factor in determining the structure and function of biofilm systems, and cohesive strength plays a key role in our ability to remove or control biofilms in engineered systems. A micro-mechanical device has been developed to directly measure the tensile strength of biofilms and other microbial aggregates. An important feature of this method is the combination of a direct measurement of force with particle separations that occur at a scale comparable to that observed for biofilm systems. The force required to separate an aggregate is determined directly from the deflection of cantilevered glass micropipettes with a 20-40-microm diameter. Combined with an estimate of the cross-sectional area of the aggregate at the point of separation this measurement indicates the cohesive strength of the aggregate. Samples of return activated sludge (RAS) and a Pseudomonas aeruginosa biofilm were tested using the device. The measured cohesive strengths of the RAS flocs ranged from 419 to 206,400 N/m(2), while many of the flocs exceeded the range of measurement of the device. Fragments of P. aeruginosa biofilm had cohesive strengths ranging from 395 to 15,640 N/m(2), with a median value of 3020 N/m(2). The median equivalent diameters of the particles detached from the aggregates were 32 microm for RAS and 30 microm for the P. aeruginosa biofilms.     

Long-term outcome of posterior spinal fusion for the correction of adolescent idiopathic scoliosis

Background

Adolescent idiopathic scoliosis (AIS) is the most common form of idiopathic scoliosis, and surgery is considered as one of the therapeutic options. However, it is associated with a variety of irreversible complications, in spite of the benefits it provides. Here, we evaluated the long-term outcome of posterior spinal fusion (PSF) of AIS to shed more light on the consequences of this surgery.

Methods

In a cross-sectional study, a total of 42 AIS patients who underwent PSF surgery were radiographically and clinically inspected for the potential post-operative complications. Radiographic assessments included the device failure, union status, and vertebral tilt below the site of fusion. Clinical outcomes were evaluated using the Oswestry disability index (ODI) and visual analogue scale (VAS).

Results

The mean age of the surgery was 14.4?±?5.1 years. The mean follow-up of the patients was 5.6?±?3.2 years. Complete union was observed in all patients, and no device failure was noticed. Pre- and post-operative vertebral tilt below the site of fusion were 11.12°?±?7.92° and 6.21°?±?5.73°, respectively (p?<?0.001). The mean post-operative ODI was 16.7?±?9.8. The mean post-operative VAS was 2.1?±?0.7. ODI value was positively correlated with follow-up periods (p?=?0.04, r?=?0.471). New degenerative disc disease (DDD) was observed in 6 out of 37 (16%) patients.

Conclusion

In spite of the efficacy and safety of PSF surgery of AIS, it might result in irreversible complications such as DDD. Moreover, the amount of post-operative disability might increase over the time and should be discussed with the patients.

     

Real time noninvasive assessment of external trunk geometry during surgical correction of adolescent idiopathic scoliosis

Study design

Retrospective study.

Objective

To evaluate the radiological results of fusion with segmental pedicle screw fixation in juvenile idiopathic scoliosis with a minimum 5-year follow-up.

Summary of background data

Progression of spinal deformity after posterior instrumentation and fusion in immature patients has been reported by several authors. Segmental pedicle screw fixation has been shown to be effective in controlling both coronal and sagittal plane deformities. However, there is no long term study of fusion with segmental pedicle screw fixation in these group of patients.

Methods

Seven patients with juvenile idiopathic scoliosis treated by segmental pedicle screw fixation and fusion were analyzed. The average age of the patients was 7.4 years (range 5–9 years) at the time of the operation. All the patients were followed up 5 years or more (range 5–8 years) and were all Risser V at the most recent follow up. Three dimensional reconstruction of the radiographs was obtained and 3DStudio Max software was used for combining, evaluating and modifying the technical data derived from both 2d and 3d scan data.

Results

The preoperative thoracic curve of 56 ± 15° was corrected to 24 ± 17° (57% correction) at the latest follow-up. The lumbar curve of 43 ± 14° was corrected to 23 ± 6° (46% correction) at the latest follow-up. The preoperative thoracic kyphosis of 37 ± 13° and the lumbar lordosis of 33 ± 13° were changed to 27 ± 13° and 42 ± 21°, respectively at the latest follow-up. None of the patients showed coronal decompensation at the latest follow-up. Four patients had no evidence of crankshaft phenomenon. In two patients slight increase in Cobb angle at the instrumented segments with a significant increase in AVR suggesting crankshaft phenomenon was seen. One patient had a curve increase in both instrumented and non instrumented segments due to incorrect strategy.

Conclusion

In juvenile idiopathic curves of Risser 0 patients with open triradiate cartilages, routine combined anterior fusion to prevent crankshaft may not be warranted by posterior segmental pedicle screw instrumentation.     

Cotrel-dubousset instrumentation for the correction of adolescent idiopathic scoliosis. Long-term results with an unexpected high revision rate

ABSTRACT: BACKGROUND: For many years, the CD instrumentation has been regarded as the standard device for the surgical correction of adolescent idiopathic scoliosis (AIS). Nevertheless, scientific long-term results on this procedure are rare. Therefore, we conducted a retrospective follow-up study of patients treated for AIS with CD instrumentation and spondylodesis. METHODS: A total of 40 patients with AIS underwent CD instrumentation in our department within 3 years and between 1990 and 1992. For the retrospective analysis, first all the patient documents were reviewed, and pre-/postoperative X-ray images as well as those at the latest follow-up were analysed. Furthermore, it was attempted to conduct a clinical survey using the SRS-24 questionnaire, which was sent to the patients after a preceding announcement on the phone. RESULTS: Radiologically, the frontal main curvature was improved from a preoperative angle of 69.2degrees to a postoperative angle of 35.4degrees, and the secondary curvature was improved from a preoperative angle of 42.6degrees to a postoperative angle of 20.5degrees. The latest radiological followup at average 57.4 months post surgery showed an average loss of correction of 9.6degrees (main curvature) and 4.6degrees (secondary curvature), respectively.Within the first 30 days post surgery, 3 out of 40 patients (7.5%) received early operative revision for the dislocation of hooks or rods.At an average of 45.7 months (range 11 to 142 months), 19 out of 40 patients (47.5%; including 2 patients with early revision) received late operative revisions: The reasons were late infection (10 out of 40 patients; 25%) with the development of fistulae (7 cases) or putrid secretion (3 cases), which was resolved with the complete removal of instrumentation after all. The average time until revision was 35.5 months (range 14 to 56 months) after CD instrumentation. Furthermore, complete implant removal was necessary in 8 out of 40 patients (20%) for late operate site pain (LOSP). The average time until removal of instrumentation was 62.7 months (range 18 to 146 months) post surgery; and one patient received partial device removal for prominent instrumentation 11 months post surgery. Altogether, only 22 out of 40 CD instrumentations (55%) were still in situ. After an average period of 14.3 years post surgery, it was possible to follow-up 14 out of 40 patients (35%) using the SRS-24 questionnaire. The average score was 93 points, without showing significant differences between patients with or without their instrumentation in situ. CONCLUSIONS: Retrospectively, we documented for the first time a very high revisions rate in patients with AIS and treated by CD instrumentation. Nearly half of the instrumentation had to be removed due to late infection and LOSP. The reasons for the high rate of late infections with or without fistulae and for LOSP were analysed and discussed in detail.     

Determination of the tensile strength of superficial passive implant materials]

The crack strength of passivating surface materials or passive layers on electroconductive substrates is determined by the electronic detection of redox reactions at the electrolyte/sample interface. A sudden increase in corrosion current under mechanical tensile loading or bending moments indicates generation or propagation of macro- and micro-cracks in the passivating layer, and exposure of the substrate. A subsequent decrease in the current indicates repassivation. Titanium oxide passivating layers generated by oxygen diffusion hardening (ODH) on titanium show crack formation at a tensile load on the substrate of more than 230 MPa. Repassivating sandwich layers of tantalum and tantalum oxide on steel substrates (AISI 31 6L) generate micro-cracks at more than 300 MPa. The crack formation of the oxide surface materials correlates with the onset of plastic deformation of the substrate.     

Micropipette suction for measuring piconewton forces of adhesion and tether formation from neutrophil membranes.

A new method for measuring piconewton-scale forces that employs micropipette suction is presented here. Spherical cells or beads are used directly as force transducers, and forces as small as 10-20 pN can be imposed. When the transducer is stationary in the pipette, the force is simply the product of the suction pressure and the cross-sectional area of the pipette minus a small correction for the narrow gap that exists between the transducer and the pipette wall. When the transducer is moving along the pipette, the force on it is corrected by a factor that is proportional to the ratio of its velocity relative to its drag-free velocity. With this technique, the minimum force required to form a membrane tether from neutrophils is determined (45 pN), and the length of the microvilli on the surface of neutrophils is inferred. The strength of this technique is in its simplicity and its ability to measure forces between cells without requiring a separate theory or a calibration against an external standard and without requiring the use of a solid surface.     

A role for metaphase spindle elongation forces in correction of merotelic kinetochore attachments

During mitosis, equal segregation of chromosomes depends on proper kinetochore-microtubule attachments. Merotelic kinetochore orientation, in which a single kinetochore binds microtubules from both spindle poles [1], is a major cause of chromosome instability [2], which is commonly observed in solid tumors [3, 4]. Using the fission yeast Schizosaccharomyces pombe, we show that a proper force balance between kinesin motors on interpolar spindle microtubules is critical for correcting merotelic attachments. Inhibition of the plus-end-directed spindle elongation motors kinesin-5 (Cut7) and kinesin-6 (Klp9) reduces spindle length, tension at kinetochores, and the frequency of merotelic attachments. In contrast, merotely is increased by deletion of the minus-end-directed kinesin-14 (Klp2) or overexpression of Klp9. Also, Cdk1 regulates spindle elongation forces to promote merotelic correction by phosphorylating and inhibiting Klp9. The role of spindle elongation motors in merotelic correction is conserved, because partial inhibition of the human kinesin-5 homolog Eg5 using the drug monastrol reduces spindle length and lagging chromosome frequency in both normal (RPE-1) and tumor (CaCo-2) cells. These findings reveal unexpected links between spindle forces and correction of merotelic attachments and show that pharmacological manipulation of spindle elongation forces might be used to reduce chromosome instability in cancer cells.     

Variability of ground reaction forces during treadmill walking.

The purpose of this study was to investigate whether or not the neuromuscular locomotor system is optimized at a unique speed by examining the variability of the ground reaction force (GRF) pattern during walking in relation to different constant speeds. Ten healthy male subjects were required to walk on a treadmill at 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 km/h. Three components [vertical (F(z)), anteroposterior (F(y)), and mediolateral (F(x)) force] of the GRF were independently measured for approximately 35 steps consecutively for each leg. To quantify the GRF pattern, five indexes (first and second peaks of F(z), first and second peaks of F(y), and F(x) peak) were defined. Coefficients of variation were calculated for these five indexes to evaluate the GRF variability for each walking speed. It became clear for first and second peaks of F(z) and F(x) peak that index variabilities increased in relation to increments in walking speed, whereas there was a speed (5.5-5.8 km/h) at which variability was minimum for first and second peaks of F(y), which were related to forward propulsion of the body. These results suggest that there is "an optimum speed" for the neuromuscular locomotor system but only for the propulsion control mechanism.     

A novel method for measuring tension generated in stress fibers by applying external forces

The distribution of contractile forces generated in cytoskeletal stress fibers (SFs) contributes to cellular dynamic functions such as migration and mechanotransduction. Here we describe a novel (to our knowledge) method for measuring local tensions in SFs based on the following procedure: 1), known forces of different magnitudes are applied to an SF in the direction perpendicular to its longitudinal axis; 2), force balance equations are used to calculate the resulting tensions in the SF from changes in the SF angle; and 3), the relationship between tension and applied force thus established is extrapolated to an applied force of zero to determine the preexisting tension in the SF. In this study, we measured tensions in SFs by attaching magnetic particles to them and applying known forces with an electromagnetic needle. Fluorescence microscopy was used to capture images of SFs fluorescently labeled with myosin II antibodies, and analysis of these images allowed the tension in the SFs to be measured. The average tension measured in this study was comparable to previous reports, which indicates that this method may become a powerful tool for elucidating the mechanisms by which cytoskeletal tensions affect cellular functions.     

Ground reaction forces during termination of human gait.

This is the first published report of the ground reaction forces during gait termination. Two mechanisms appear to be used to stop walking: increased braking forces and decreased push-off force. There appears to be a short interval of time during the gait cycle in which a decision to take an additional step is to be made.     

A treadmill ergometer for three-dimensional ground reaction forces measurement during walking.

This report describes new treadmill ergometer designed to measure the vertical and horizontal ground reaction forces produced by the left and right legs during walking. It was validated by static and dynamic tests. Non-linearity was from 0.2% (left vertical force) to 1.4% (right antero-posterior force). The resonance frequency was from 219 (right vertical direction) to 58 Hz (left medio-lateral direction). A calibration "leg", an air jack in series with a strain gauge, was developed and used to produce force signals comparable to those obtained during human locomotion. The mean differences between the force measured by the calibration leg and treadmill ergometer at 5 km h(-1) were 3.7 N (0.7%) for the left side and 6.5 N (1.2%) for the right. Measurements obtained during human walking showed that the treadmill ergometer has considerable potential for analysing human gait.