10:30
Medical Instruments - Surgery I
Chair: John van den Dobbelsteen
10:30
15 mins
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WATERJET DRILLING IN BONE: A MODEL TO PREDICT DRILLING DEPTH USING BONE ARCHITECTURE AND NOZZLE DIAMETER
Steven den Dunnen, Lars Mulder, Gino Kerkhoffs, Jenny Dankelman, Gabrielle Tuijthof
Abstract: The use of waterjets in orthopaedic surgical drilling can be beneficial over conventional rigid instruments, because it allows the design of flexible instruments for easy manoeuvring in joints. For safe application, the drill depth should be controlled, which is challenging as the heterogeneous characteristics of bone tissue can cause variations in hole dimensions despite waterjet drilling under similar circumstances. The bone heterogeneity can be identified by determining the bone density or volume fraction (BV/TV). An increase in BV/TV increases the maximum stress bone can endure, and is therefore expected to reduce the depth of a water jet drilled hole. The goal of this study is to determine whether a correlation is present between BV/TV and drilling depth (Ldepth), which can be used to describe a hole depth prediction model for safe waterjet drilling in various types of articular bone.
Two hundred and ten holes were drilled in the articular surfaces of 10 pig tali and 10 femora (4-6 months) by waterjet diameters (dwaterjet) of 0.3 (femora only), 0.4, 0.5 and 0.6mm. Pressure, standoff distance and jet time were kept constant at 700 bar, 8 mm and 5 seconds, respectively. All tests were performed submerged in water to mimic regular arthroscopic treatment. MicroCT scans were used to measure hole depths and the local BV/TV. A Pearson test was used to correlate the BV/TV and nozzle diameters to the drilling depths (p<0.05).
A significant linear correlation (R2=0.90, p<0.001) was found for predicting the drilling depth: Ldepth = -18.3 x BV/TV + 31.5 x dwaterjet + 4.1, with Ldepth and dwaterjet in mm. An increase in BV/TV and nozzle diameter will result in shallower and deeper holes, respectively.
The results allow prediction of the drilling depth for a given BV/TV and chosen nozzle diameter, which is an important finding for the safe application of waterjet drilling in orthopaedic surgery. Orthopaedic procedures where holes are drilled in bone such as microfracturing treatments and screw fixations can now be considered to be performed with waterjet drilling. Future developments will concentrate on miniaturization of the waterjet instrument for performing minimally invasive surgery.
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10:45
15 mins
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MECHANICAL BEHAVIOUR OF A NOVEL NON-FUSION SCOLIOSIS CORRECTION SYSTEM
Martijn Wessels, Edsko Hekman, Bart Verkerke
Abstract: Introduction - Surgical treatment of scoliosis generally consists of performing spondylo-desis, a technique which invokes vertebral fusion [Deyo, 2004]. Complications related to this technique are inhibition of spinal flexibility and growth. For that reason, non-fusion surgery is increasingly explored [Maruyama, 2008], however results are still not satisfying. The University of Twente developed a novel revolutionary non-fusion correction system which consists of two functional implants that are extremely flexible and extendable. The first implant (XS-TOR) generates a torque to correct the axial rotation of the spine. The second implant (XS-LAT) generates a lateral bending moment to correct the lateral curvature. Application of torque and bending moment is achieved by using cross-bridges that are anchored to three different vertebrae, using a three-point-bending mechanism. To deliver the appropriate moment, both implants are pre-stressed before final anchoring to the spine.
Methods - For animal experiment applications, inverse versions of the implants were tested, which means that the systems were designed to induce scoliosis. The XS-TOR and XS-LAT were measured using an apparatus that simulates different spinal configurations. The implants were anchored to three metal vertebrae containing 6D force sensors, after which the vertebrae were rotated and translated e.g. axially and laterally towards the demanded position. The reaction forces and moments were recorded in all configurations.
Results - The XS-TOR generates a torque which increases during growth of the system. Similarly, the XS-LAT generates a bending moment that slightly increases during growth of the system. The contribution to the spinal stiffness is limited, between 0.01 and 0.03 Nm/° in bending and between 0.04 and 0.08 Nm/° in torsion.
Discussion - Although the inverse functionality of the implants results in altered behaviour, the magnitudes of moments are similar. The actual applied bending moment is dependent on the obtained correction and will reduce during correction. However, the decrease of the correction moment will be much less than observed in conventional fusion constructs which generally have a 300 to 400% higher bending stiffness. The contribution of XS-TOR and XS-LAT on spinal stiffness is very low since the stiffness of vertebral region is approximated between 2 and 3 Nm/° in (lateral) flexion and torsion [Panjabi, 1976], thus allowing flexibility of the spine, which will prevent fusion
References
Deyo et al, Spine J 4(S1): 138, 2004;
Maruyama et al, Scoliosis 3(1): 6, 2008;
Panjabi et al, JBJS Am 58(5): 642-652, 1976.
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11:00
15 mins
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BONE MINERAL DENSITY HAS DIRECT EFFECT ON THE FIXATION STRENGTH OF CEMENTLESS FEMORAL KNEE COMPONENT
Sanaz Berahmani, Dennis Janssen, David Wolfson, Maarten de Waal Maelfijt, Nico Verdonschot
Abstract: To achieve desirable outcomes in cementless total knee arthroplasty (TKA), sufficient primary stability is essential. The primary stability inhibits excessive motions at the bone-implant interface, hence providing the necessary condition for osseointegration [1]. Primary stability for cementless TKA is provided by press-fit forces between the bone and implant. The press-fit forces depend on several factors including interference fit, friction between bone and implant surface, and the bone material properties. It is expected that bone mineral density (BMD) will affect the stability of cementless TKA [2]. However, the effect of BMD on the primary stability of cementless femoral knee component has not been investigated in vitro.
Calibrated CT-scans of 9 distal femora were obtained after the surgical cuts were made by an experienced surgeon. Since the press-fit forces of the femoral component mainly occur in the AP-direction, the BMD was measured in the anterior and posterior faces for a depth of 5mm; this depth was based on stress distributions from a Finite Element Analysis of the same implant design. In addition, four strain gauges were connected to different locations on the implant’s outer surface to measure strain as representative of bone relaxation. A cementless Sigma CR femoral component (DePuy International, Leeds, UK) was then implanted using an MTS machine. In order to simulate a ‘normal’ bone condition, the implanted bone was pre conditioned for one hour at a cyclic load of 300-1500 N, and a rate of 1Hz. In addition, two waiting periods of 30 minutes were included before and after the dynamic loading. Finally, the implants were pushed-off from the bone in a high-flex position. Forces and displacements were recorded both during insertion and push-off tests.
Strong correlations were found for insertion and push-off forces with BMD (R2=0.82 and R2=0.88, respectively). A strong linear correlation was also found between final strain and push-off forces (R2=0.90). BMD also showed strong correlation with final strain corrected for maximum strain measured during insertion (R2=0.80).
There is no consensus on the best fixation method for the TKA but some surgeons prefer a cementless design for young and active patients. The results of our study showed that the primary stability of a cementless femoral component depends on the bone mineral density. Therefore, patient selection based on bone quality may increase the likelihood of good osseointegration and adequate long-term fixation for cementless femoral knee components.
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11:15
15 mins
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PATIENT-TAILORED PLATE FOR BONE FIXATION AND ACCURATE 3-D POSITIONING IN CORRECTIVE OSTEOTOMY
Johannes Dobbe, Joy Vroemen, Simon Strackee, Geert Streekstra
Abstract: A bone fracture may lead to malunion of bone segments, which gives discomfort to the patient and may lead to chronic pain, reduced function and finally to early osteoarthritis. A treatment option to realign the bone segments is a corrective osteotomy [1]. In this procedure the surgeon tries to improve alignment by cutting the bone at, or near, the fracture location and fixates the bone segments in an improved position, using a plate and screws. Three-dimensional positioning is very complex and difficult to plan, perform and evaluate using standard 2-D fluoroscopy imaging [2].
We present a new technique that uses preoperative 3-D imaging to plan positioning and to design a patient-tailored fixation plate that only fits in one way and realigns the bone segments as planned in six degrees of freedom. The method is evaluated for distal radius osteotomy using artificial bones and renders realignment highly accurate and very reproducible (derr < 1.2 ± 0.8 mm and φerr < 1.8 ± 2.1°).
Besides using a patient-tailored plate for corrective distal radius osteotomy, the method may be of interest for corrective osteotomy of other long bones, mandibular reconstruction and clavicular reconstruction as well. In all of these cases the contralateral side can equally be used as reference for reconstruction of the affected side. Even if a healthy reference is missing, the surgeon can plan the position of one (distal) bone segment with respect to another (proximal) bone segment in a manual fashion, e.g., guided by surrounding anatomy. A patient-tailored plate can thus generally be used to fixate bone segments in a planned position. The patient-tailored plating technology is expected to have a great impact on future corrective osteotomy surgery.
REFERENCES
[1] M. W. Patton, “Distal Radius Malunion”, J Am Soc Surg Hand, 4(4):266-274, (2004).
[2] D. Paley D Principles of Deformity Correction, 1st edn, Springer-Verlag, Berlin, Heidelberg, New York, 2005, ISBN 3-540-41665-X
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11:30
15 mins
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CLINICAL FEASIBILITY OF SOLO-SURGERY USING IN MINIMALLY INVASIVE SURGERY A TROCAR HOLDING SYSTEM
Joris Jaspers, Jesse Bosma, Arto Boeken Kruger
Abstract: Holding an endoscope or other static instrumentation during Minimally Access Surgery (MAS) can be a rather fatiguing, boring and cumbersome job. Usually an assistant is in charge of this task, so that the surgeon has no direct control over his viewing direction. This easily results in communication problems and disturbance of the surgeon’s eye-hand co-ordination. Moreover, it is hard to obtain a sustained stable endoscopic view. A few systems with an endoscope holding function have been assessed, but most of these systems are expensive, complex, not intuitive to use or bulky. Previous studies showed that passive holders perform as well as or even better than active holders and as well as human control [1,2]
The University Medical Center (UMC) Utrecht has developed a new holding device for endoscopic instruments. It features a simple construction that aims at user friendly operation of the device. This includes easy one-handed operation of the device and a slender design that minimizes the interference with other instruments in the sterile field. The device actually fixates all degrees of freedom of the trocar and the instrument going through it simultaneously, in a drag ‘n drop manner. Engaging the operating button of the device removes the fixation of trocar and instrument, releasing the button fixates the instrument in the desired position immediately. The button of the system can easily be attached to the instrument, which improves the intuitive way of interacting with the device even more.
A prototype for clinically evaluation has been produced using a reusable holder in combination with an adjusted disposable trocar. A feasibility study in a number of Minimally Access Nefrectomies (kidney removal) showed the ease of use, the stable image and showed that solo surgery is possible, improving the operational effectiveness of the OR-team
The trocar holding system showed to be a user friendly, single-hand operated device that helps to provide a stable endoscopic view and may be able to reduce OR costs for MAS.
REFERENCES
[1] Arezzo et al, Surgical Endoscopy 2000
[2] Den Boer et al, Surgical Endoscopy, 2001
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11:45
15 mins
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CONTROLLED SURGERY USING CW 2 µm LASER SYSTEMS WITH MODIFIED FIBER TIPS
Ruud Verdaasdonk, Albert van der Veen, Ivo van Eibergen Santhagens, Tjeerd de Boorder
Abstract: The continuous wave 2 µm laser has proven to be a versatile tool for controlled ablation or cutting of tissue with hemostasis and minimal carbonisation due to effective tissue water vaporisation. The 2 µm wavelength can be considered ‘eye safe’ and fiber delivery enables endoscopic application in both air and water.
To improve the practical application in various endoscopic and robotic surgical procedures, the fiber delivery system was adapted by shaping the fiber tip for better control of the beam direction and enhancement of the tissue effect.
The optical characteristics of tapered, ball shaped and angled fiber tips and the ablation effects in tissues were studied using high speed and thermal imaging techniques. Beam properties were also analysed by ray-tracing. The modified tips were applied during surgery in the lungs to ablate diseased mucosa on the trachea wall, resection of tumors in the tongue and, in neurosurgery for 3rd ventriculostomy to treat hydrocephalus.
Due to an instant cyclic phase change between water and vapour, the beam direction can change dramatically and has to be accounted for in tip design and potential damage during clinical application. The tapered shape enabled precise contact surgery. An angled ball shape provides controlled side irradiation of the wall during endoscopic procedures e.g. in the trachea.
Modified fiber tips improve the control and versatility of the cw 2 µm laser for various clinical applications.
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