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L P Nolte

Publications and source records attributed to L P Nolte.

At least 19 recordsLinked to original sources
PubMed1998

Moments and forces during pedicle screw insertion. In vitro and in vivo measurements.

STUDY DESIGN: Moments and forces during pedicle screw insertion were measured in vivo and in vitro and were correlated to several parameters of the screw-bone interface. OBJECTIVES: To compare the in vitro and in vivo screw insertion loads and to relate these measurements to bone mineral density, pedicle size, and other screw parameters (material, diameter). SUMMARY OF BACKGROUND DATA: The in vitro screw insertion torque has been correlated to the screw pullout forces and the number of cycles to ultimate interface failure. However, there are no comparable in vivo data. METHODS: One hundred three pedicle screws were included in the study, 43 in vivo and 60 in vitro. Duel-energy x-ray absorptiometry boen mineral density data were available for 20 in vivo and 32 in vitro specimens. A custom-made sterilizable six-axis load cell was integrated into a torque wrench, enabling the recording of the applied moments and forces during screw insertion. Statistical analysis was performed to detect differences and correlations. RESULTS: The mean in vivo insertion torque (1.29 Nm) was significantly greater than the in vitro value (0.67 Nm). The linear correlation between insertion torque and bone mineral density was significant for the in vitro data but not for the in vivo data. No correlation was observed between insertion torque and pedicle diameter. Two patterns of torque were observed during the insertion process. CONCLUSIONS: There is a significant difference between the insertion loads measured in vivo and those measured in vitro. Additional research is needed to verify whether this method provides an indication of screw fixation quality.

Absorptiometry, Photon↗
PubMed1998

Constrained testing conditions affect the axial rotation response of lumbar functional spinal units.

STUDY DESIGN: Human cadaveric spine specimens were tested in axial rotation using constrained and unconstrained methods. OBJECTIVES: To determine the degree to which constrained methods affect the response of the functional spinal unit in axial rotation at lumbar and lumbosacral levels. SUMMARY OF BACKGROUND DATA: A substantial controversy exists in the literature regarding the appropriateness of different testing methods. No study has been found in which the effect of constraint on axial rotation behavior was objectively examined. METHODS: Ten human cadaveric spine specimens (five L3-L4, five L5-S1) were tested in axial rotation, using both constrained and unconstrained methods. In the unconstrained test, pure moments were applied to the upper vertebra, and its complete three-dimensional motion was measured using an optoelectronic camera system. In the constrained test, the specimens were loaded in a fixed-axis servohydraulic test machine individually around five rotational axis positions within the vertebral body, and the rotational motion was measured. RESULTS: The rotational angles in the constrained tests were not different among the five rotational axis positions. However, the maximum rotation from the five axis positions was approximately 40% greater than the minimum rotation, a significant difference. The axial rotational motion of the unconstrained tests was always less than the maximum rotation measured in the constrained test. However, the total rotational angle using the helical axis of motion was not significantly different from the constrained angles. CONCLUSIONS: The large differences between maximum and minimum rotation angles demonstrate that the behavior of the functional spinal unit in axial rotation is sensitive to the axis's position but the location of the axis is not repeatable. This supports the use of unconstrained methods in spinal testing.

Adult↗
PubMed1998

Assessment of 3-dimensional magnetic resonance imaging fast low angle shot images for computer assisted spinal surgery.

The objective of this research was to determine whether a fast 3-dimensional (3-D) gradient echo magnetic resonance imaging (MRI) sequence could be used to acquire images suitable for image guided surgery of the spine. The main difficulty with MRI is that inhomogeneities in the static magnetic field lead to geometric distortions in the images. We used a very fast 3-D MRI sequence with a wide bandwidth and short echo time (TE) to minimize these distortions. Fiducial markers that could be localized in MRI and computed tomography (CT) images and in physical space were attached to a phantom in order to assess the accuracy of a landmark based registration method. The effect of varying the MRI parameters on image contrast was also investigated. The results demonstrate that the registration can be undertaken with an accuracy of 0.4 mm using the 3-D MRI. This is comparable to the accuracy of 0.3 mm obtained with CT and is a significant improvement over the accuracy of the 2-D MRI techniques (> 1.0 mm). In vivo images demonstrating good contrast between the spine and surrounding soft tissues such as fat, intervertebral disks, and cerebrospinal fluid were obtained. The MRI acquired using the sequence described in this article shows promise for use in computer assisted surgery of the spine.

Algorithms↗
PubMed1998

Compressive strength of interbody cages in the lumbar spine: the effect of cage shape, posterior instrumentation and bone density.

One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.

Biomechanical Phenomena↗
PubMed1998

The role of supplemental translaminar screws in anterior lumbar interbody fixation: a biomechanical study.

The immediate stabilization provided by anterior interbody cage fixation is often questioned. Therefore, the role of supplementary posterior fixation, particularly minimally invasive techniques such as translaminar screws, is relevant. The purpose of this biomechanical study was to determine the immediate three-dimensional flexibility of the lumbar spine, using six human cadaveric functional spinal units, in four different conditions: (1) intact, (2) fixed with translaminar screws (TLS), (3) instrumented with anterior interbody cage insertion with the BAK system and (4) instrumented with BAK cage with additional TLS fixation. Flexibility was determined in each testing condition by measuring the vertebral motions under applied pure moments (i.e. flexion-extension, bilateral axial rotation, bilateral lateral bending) in an unconstrained manner. Anterior fixation with the BAK alone provided significant stability in flexion and lateral bending. Additional posterior TLS significantly reduced the motion in extension and axial rotation. TLS fixation alone resulted in smaller rotations than BAK fixation in all loading directions. Based on these results, it seems that interbody cage fixation with the BAK system stabilizes the spine in some, but not all, loading directions. The problematic loading directions of extension and axial rotation can be substantially stabilized by using translaminar screw fixation. However, one should emphasize that the degree of stability needed to achieve solid fusion is not known.

Biomechanical Phenomena↗
PubMed1998

Computer assistance for pelvic osteotomies.

To assist surgeons performing pelvic osteotomies for the treatment of dysplastic hips, an image guided freehand navigation system has been developed. Preoperative computed tomographic scan images are presented in various ways to the surgeon together with real time display of the instruments and surgical action on the computer screen. The system supports the preoperative plan and provides optimized control of surgical action. The main focus of the image guidance has been placed on the execution of the different required cuts and the reorientation of the acetabular fragment. Special attention also has been given to the development of a sophisticated surgeon-machine interface. Fourteen surgeries have been performed with image guidance so far. The visualization aids provided by the system are able to help reduce potential risk and thus increase safety and accuracy for this difficult class of surgical interventions.

Acetabulum↗
PubMed1998

Interbody cage stabilisation in the lumbar spine: biomechanical evaluation of cage design, posterior instrumentation and bone density.

We performed a biomechanical study on human cadaver spines to determine the effect of three different interbody cage designs, with and without posterior instrumentation, on the three-dimensional flexibility of the spine. Six lumbar functional spinal units for each cage type were subjected to multidirectional flexibility testing in four different configurations: intact, with interbody cages from a posterior approach, with additional posterior instrumentation, and with cross-bracing. The tests involved the application of flexion and extension, bilateral axial rotation and bilateral lateral bending pure moments. The relative movements between the vertebrae were recorded by an optoelectronic camera system. We found no significant difference in the stabilising potential of the three cage designs. The cages used alone significantly decreased the intervertebral movement in flexion and lateral bending, but no stabilisation was achieved in either extension or axial rotation. For all types of cage, the greatest stabilisation in flexion and extension and lateral bending was achieved by the addition of posterior transpedicular instrumentation. The addition of cross-bracing to the posterior instrumentation had a stabilising effect on axial rotation. The bone density of the adjacent vertebral bodies was a significant factor for stabilisation in flexion and extension and in lateral bending.

Absorptiometry, Photon↗
PubMed1998

[The method of computer-assisted orthopedic surgery based on two-dimensional fluoroscopy: the principles of action].

Surgical instruments play a major role in orthopedic surgery; usually they are controlled visually at the operation. In certain situations additional device to control instrument is needed. The aim of this paper is to present theoretical foundations, create prototype and give initial assessment of computer assisted orthopedic surgery system. Two-dimensional fluoroscopy was the base for system functioning. Lab tests and first applications in the operating room are presented. Precision of the system found allows for its use in orthopedic surgery with television monitoring.

Bone Diseases↗
PubMed1998

[Computer-assisted surgical navigation with a dynamic mobile framework for the nasal fossae, sinuses and base of the skull].

Surgery of the skull base and of the paranasal sinuses is often difficult because of the complex anatomy and the delicate structures; serious complications (loss of vision, cerebral lesion) have been reported. To improve the safety of such operations, computer-assisted navigation surgery is increasingly being put to use. We introduce the system which was developed in Berne. Our computer-assisted system is based on an intraoperative pursuit of the head and instruments which are equipped with infrared diodes and registered by an opto-electronic system-camera. The CT-acquisition of the head is accomplished framelessly without a head-holding device. This allows free movement of the head during surgery. Between March and November 1997, 35 navigation operations were performed for various pathologies at the anterior and lateral skull base. The majority of the cases were endonasal operations. No surgical complications occurred inspite of the complexity of the operations. The measured accuracy of the system between the CT and the actual instrument location in the patient was 0.5-2 mm (mean : < 1 mm) for the anterior skull base and 1-2.5 mm (mean < 1.5 mm) for the lateral skull base. The intraoperative navigation system allows identification of essential anatomical structures and permits safe and efficient surgery without additional loss of time. In addition, such a system allows minimal invasive approaches, and new operations may become possible.

Adult↗
PubMed1997

Improved accuracy of pedicle screw insertion with computer-assisted surgery. A prospective clinical trial of 30 patients.

STUDY DESIGN: A prospective clinical trial was done to study the accuracy of pedicle screw placement in 30 consecutive computer-assisted orthopedic surgeries. OBJECTIVES: To determine the accuracy and clinical applicability of this new method for pedicle screw insertion. SUMMARY OF BACKGROUND DATA: Conventional screw insertion techniques have been associated with high pedicle screw malplacement rates in cadaver studies and clinical studies with postoperative computed tomography evaluation. METHODS: Thirty transpedicular, low-back, titanium instrumentations were performed with computer-assisted orthopedic surgery. The accuracy of screw placement was evaluated using a sophisticated computed tomography protocol. RESULTS: The total number of pedicle screws was 174. Of these, 139 (79.9%) could be inserted with computer-assisted orthopedic surgery. The malplacement rate of computer-assisted orthopedic surgery screws was 4.3%. In screws that were not inserted by computer-assisted orthopedic surgery, the malplacement rate was 14.3%. One malplaced screw that had not been inserted with computer-assisted orthopedic surgery caused L4 root paresis. CONCLUSIONS: The accuracy of pedicle screw placement using computer-assisted surgery proved to be superior to the accuracy obtained when using conventional techniques.

Bone Screws↗
PubMed1997

Accuracy of computer-assisted pedicle screw placement. An in vivo computed tomography analysis.

STUDY DESIGN: A computer-assisted planning and visualization system (the Orthopaedic Surgery Planning System) was tested for pedicle screw insertion in vivo. OBJECTIVES: To evaluate the system's applicability for regular intraoperative use and its accuracy for pedicle screw placement in vivo. SUMMARY OF BACKGROUND DATA: Pedicle screw placement poses considerable anatomic and biomechanical risks. The reported rates of screw misplacement with conventional insertion techniques are unacceptably high. It previously has been shown in vitro that computer assistance offers the potential to decrease the number of screws perforating the pedicular cortex. METHODS: The accuracy of 162 pedicle screws inserted with the Orthopaedic Surgery Planning System was assessed by means of postoperative computed tomography evaluation. Reconstructions of the horizontal, frontal, and sagittal planes were analyzed. Cortex perforations were graded in steps of 2 mm. RESULTS: The cortex was perforated in 2.7% of pedicles. Complete preoperative computed tomography scanning of the levels to be operated on is essential to allow for a precise image reconstruction. Initial difficulties in applying the system contribute to the malplacements. A learning curve for general handling of the Orthopaedic Surgery Planning System was observed. CONCLUSIONS: The system provides a safe and reproducible technique for pedicle screw insertion. Other applications in the field of spine surgery are under evaluation.

Bone Screws↗
PubMed1997

Man-machine interfaces in computer assisted surgery.

The clinical potential of computer assisted surgery (CAS) has been more and more widely acknowledged since CAS systems have been introduced into the operating room (OR) theater. Especially the improvements in safety and accuracy are remarkable and strengthen the ties between surgeons and engineers. Tumor stereotaxis was introduced to neurological surgery in the early 1980s, and currently systems with and without robotic navigation are in use for specific medical indications. Recently, solutions for computer assisted orthopedic surgery were developed and applied to various anatomical regions. However, with the establishment of CAS in vivo, a new complex of problems, which was not present in the laboratory setup, was introduced: the man-machine interface. Currently, the complexity of available CAS systems requires the presence of at least one system engineer (often called the "operator") in the OR. As a consequence, there is no possibility for direct communication between the surgeon and the machine or software. Most of the program steps involved in CAS and choices to be made intraoperatively have to be transferred to the software by means of communication of the surgeon with the operator. Particularly, the establishment of a relation between the virtual object (i.e., a medical image) and the surgical object (i.e., the patient), often denoted as "matching" or "skeletal registration," requires intensive interaction of the surgeon with the computer. A literature survey revealed that no CAS system in clinical use exists without a system engineer or a comparable person, and our clinical experience indicated that the matching process is a weak point in most systems. Because it appears to be contradictory to cost-reduction efforts in health care to have a highly paid specialist in the OR, this research evaluates strategies to facilitate the man-machine interface with the final goal of establishing a direct control of the system by the surgeon or the medical personnel traditionally present at surgery. Options to be investigated include 1) a CAS control panel (virtual keyboard) as an integrated component of the existing navigation system and 2) introduction of a commercial voice-recognition system. The implementation of these strategies into the existing CAS setup at the Department of Orthopaedic Surgery at the Inselspital (University of Bern) and clinical experience gained are reported.

Biomedical Engineering↗
PubMed1997

The first twelve cases of computer assisted periacetabular osteotomy.

Image guided freehand navigation of surgical instruments has been applied to the Bernese periacetabular osteotomy, a complex surgical technique for the treatment of dysplastic hips. This navigation system has been introduced into the operating room and has so far been used for 12 patients. Image data from computed tomography (CT) scans are presented in various ways to support the preoperative plan and to provide optimized control of surgical action. Special attention has been paid to the implementation of a sophisticated surgeon-machine interface. This paper describes the features of this novel surgical navigation system and its introduction into the clinical environment.

Acetabulum↗
PubMed1997

Design and evaluation of a device for measuring three-dimensional micromotions of press-fit femoral stem prostheses.

Implant micromotion is considered to be a major factor in the loosening of cementless total hip replacements. Translational micromotion at the bone-implant interface generally occurs in all three spatial directions. Under physiological loading, the interfacial micromotion consists of a cyclic amplitude and changes in the mean, which, in the cranio-caudal direction, represents subsidence of the prosthesis. Existing measurement strategies, which are based on dial gauges, extensometers, LVDTs, hall-effect transducers or strain gauge techniques provide information about only one component of the general three-dimensional micromovement. Moreover, in the majority of the studies, the data are difficult to interpret due to the measured motions being composed of interfacial micromotion and femoral strains. A new transducer was designed that allows the accurate measurement of all three isolated components of micromotion. An optoelectronic approach, based on silicon position-sensitive detectors (PSD) in combination with high precision mechanical parts, was chosen. To exclude thermodrifts during long-term testing, a thermistor was integrated in the sensor. Validation experiments on a precision positioning table indicated the high precision and resolution of the developed sensors. Furthermore, in-vitro tests on a standard press-fit prosthesis demonstrated the easy handling and reliability of the system.

Biomechanical Phenomena↗
PubMed1997

Planning and insertion of pedicle screws with computer assistance.

Transpedicular screw fixation relies on thorough knowledge of the pedicular anatomy and a reliable intraoperative technique. To enhance the safety and accuracy of screw insertion, computer-assisted systems have been introduced. Our in vitro study investigated the potential benefits of such a system for the preoperative planning and the intraoperative visualization. In part 1, the potentially possible range of screw paths (trajectories) through lumbar pedicles was analyzed. In part 2, the accuracy of actual pedicle-hole preparation with and without preoperative planning was assessed. It was shown that, especially in the lower lumbar regions, the possible range of trajectories is considerable, with inclinations of < or = 40 degrees in the transverse plane and a range of angulation in the sagittal plane of > 20 degrees. The computer assistance in preparation of 100 pedicle holes resulted in cortex perforation in only one case. Computer assistance therefore may be used as a valuable tool to minimize the risks of transpedicular screw insertion. It furthermore may assist in determining the desired screw orientation and length and transform this planning into the intraoperative pedicle-hole preparation.

Bone Screws↗
PubMed1997

[Computer-assisted orthopedic surgery. From pedicle screw insertion to further applications].

Computer assisted orthopaedic surgery is a new but rapidly evolving field. Based on previous research and development in the area of stereotactic neuronavigation a few groups have adapted these technologies for the image interactive insertion of pedicle screws. The present paper summarizes past and current work in the field of computer assisted orthopaedic surgery and describes the state of the art of research and future innovations, particularly in in vivo applications.

Bone Screws↗
PubMed1996

The relative importance of vertebral bone density and disc degeneration in spinal flexibility and interbody implant performance. An in vitro study.

STUDY DESIGN: An in vitro biomechanical investigation in the human lumbar spine focuses on the functional significance of vertebral bone density and intervertebral disc degenerations. OBJECTIVE: To determine that interrelationship between vertebral bone density and intervertebral disc degeneration, their effect on normal spine motion, and their significance in the biotechnical performance of interbody fixation techniques. SUMMARY OF BACKGROUND DATA: A relationship between vertebral bone density and intervertebral disc degeneration has been suggested, but a definitive relationship has not been established. The effect of vertebral bone density and intervertebral disc degeneration on interbody stabilization remains unknown despite the rapidly increasing use of this surgical method for patients with chronic low back pain. METHODS: The vertebral bone density and intervertebral disc degeneration of 72 functional spinal units were determined using dual energy x-ray absorptiometry scans and macroscopic grading, respectively. A three-dimensional flexibility test was performed on 24 functional spinal units in the intact and stabilised conditions. The compressive behavior of the bone-implant interface was evaluated in 48 functional spinal units. RESULTS: The vertebral bone density in moderately degenerated disc was significantly lower than at all other levels of intervertebral disc degeneration. Increasing intervertebral disc degeneration resulted in more axial rotation and less lateral bending. In flexion-extension and lateral bending, better vertebral bone resulted in significantly better stabilization. This trend was observed also in axial compression in which higher failure loads were observed with greater bone densities. CONCLUSION: The authors conclude a significant relationship exists between bone density and disc degeneration, bone density is a highly important factor in the performance of interbody stabilization, and disc degeneration, is of moderate importance in signal motion.

Biomechanical Phenomena↗