Optoelectronic Tracking Research Articles

Biomechanics of a multisegmental lumbar spine with a prosthetic nucleus

Andrew Dooris, Iowa City, IA, USA; Garryl Hudgins, Minnetonka, MD, USA; Vijay Goel, Toledo, OH, USA; Qi-Bin Bao, Minnetonka, MN, USA; Shinichiro Kubo, Miyazaki, JapanPurpose: Recent developments in intervertebral disc replacements offer surgeons new tools for treating degenerative disc disease. Reports of adverse effects of fusion on adjacent motion segments have been a primary motive for developing these devices as means for facilitating motion while retaining stability and restoring disc height. Some reports have described the mechanical performance of these devices, but little attention has been paid to how they affect adjacent motion segments despite this being a major factor for their use. Many such devices require considerable surgical resection, potentially disrupting normal spine load sharing. This experiment characterized in vitro multisegment biomechanics in a lumbar spine implanted with an in situ curable prosthetic intervertebral disc nucleus. We quantified changes in bending, torsional and compression stiffness of both the implanted and adjacent motion segments, as well as disc height distraction during implantation.Methods: Five fresh-frozen osteoligamentous three-segment human lumbar spines, screened for abnormal radiograph and low bone density, were prepared by potting the bottom vertebral body in a stiff polymer mixture and the top in a steel loading frame. Vertebral body rotations were tracked with an optoelectronic tracking system while specimens were loaded to 6 Nm in left/right torsion, left/right bending and flexion and extension. Displacement gauges monitored the motion of the top and bottom disc heights (one gauge each) and the implanted middle disc height (three gauges, front and left/right) when loading from 50 to 750 N in axial compression. The spines were tested under four conditions: intact, denucleated, implanted and fatigued. Fatiguing was produced by cyclic loading from 250 to 750 N at 2 Hz for at least 100,000 cycles. Nuclectomy was performed through a 5.5-mm trephine hole in the right lateral side of the middle annulus. The device consists of a compliant balloon connected to a catheter. This was inserted and liquid polymer injected into the balloon under controlled pressure (150 to 180 psi), inflating the balloon and filling the cavity. A compressive axial load of 200 N was maintained while implanting the device. Within 5 minutes the polymer cured; loads were applied after 2 hours set at room temperature.Results: Rotations generally increased with discectomy but decreased with implantation on the middle segment. After fatiguing, rotations increased again but not more than, and often less, than the adjacent segments. During polymer injection, the segment distracted approximately +1.8 mm at the disc center. Test repeatability was set at 0.25, significance at p<.05, trend at p<.10 using paired t test (d=0.25) (Tables 1 and 2)Table 1Rotation change from intact (6 Nm)Left torsionRight torsionLeft bendingMiddle segment, nuclectomized+0.47°*+0.80°+1.35°†Middle segment, implanted−0.33°‡−0.09°‡−0.32°‡Superior segment, implanted+0.23°+0.30°+0.37°Inferior segment, implanted+0.13°+0.16°+0.30°Right bendingFlexionExtensionMiddle segment, nuclectomized+1.68°†+1.22°+1.45°†Middle segment, implanted+0.43°‡+0.42°−1.12°§Superior segment, implanted+0.92°+0.03°−0.53°Inferior segment, implanted+0.36∥°+0.29°+0.77°*Significance between intact and nuclectomized.†Significance between nuclectomized and implanted.‡Trend between intact and nuclectomized.§Trend between nuclectomized and implanted.∥Trend between intact and implanted.Table 2Mean disc height change under compression from 50 N to 750 N (compression < 0, distraction > 0)Left center (mm)Front center (mm)Right center (mm)Superior (mm)Inferior (mm)Middle segment, intact−0.190.240.100.38−1.55Middle segment nuclectomized−0.56−0.840.280.35−0.80Middle segment, implanted−0.400.530.070.21−1.79.Discussion: The immediate goal of a disc replacement system is restoration of disc height and providing segment mobility without causing instability. This experiment showed that this device could reverse the destabilizing effects of a nuclectomy and restore normal segment stiffness. Significant increases in disc height can also be achieved. Long-term success of a disc replacement system, however, depends not only on mechanical endurance of the device but also on how the device affects the rest of the spine. In this test adjacent motion segments had minimal kinematic changes after implantation of the nucleus prosthesis, suggesting a normal load-sharing relationship. After fatiguing, the implanted segment behaved similar to adjacent segments, further evidence of a normal load-sharing condition. No implant extrusion or end-plate fracture was observed on any of implanted disc levels in the fatigue test. Lastly, whereas the majority of disc replacement systems require a significant annular resection for implantation, this system has the advantage of minimal surgical compromise and has the potential to be performed arthoscopically.

Principles of computer-assisted arthroscopy of the temporomandibular joint with optoelectronic tracking technology

Purpose: This preliminary clinical study evaluated the applicability, accuracy, and benefits of computer-assisted arthroscopy of the temporomandibular joint (TMJ) with optoelectronic tracking technology. Material And Methods: A hybrid of reality and virtual reality is built as a composite-reality environment by extracting 3-dimensional anatomical structures through use of computed tomography, magnetic resonance imaging, radiography, and other types of imaging procedures commonly used in clinical praxis. These various independent sources of imaging data of a particular patient can be combined with and complemented by complex graphic simulations. Intraoperatively they are merged with online position data of surgical instruments inside the patient’s TMJ. This hybrid model of detailed anatomical structures, guidelines, and real-time instrument positions allows the surgeon to accurately plan the arthroscopic intervention as well as to navigate effectively intraoperatively. Results: In the first 10 cases of computer-assisted TMJ arthroscopy, composite reality environment technology permitted the online visualization of TMJ structures, puncture sites, instrument positions, and virtual pathways in relation to anatomical landmarks with high spatial accuracy (minimum, 0.0 mm; maximum, 2.5 mm; mean, 1.4 mm; SD, 0.6 mm) and high temporal resolution (100 ms). Past, present, and possible future instrument positions can be displayed. The application of computer-assisted arthroscopy caused little immobility for either surgeon or patient. Conclusion: Even experienced surgeons profit from improved precision in the handling of the arthroscope; thus this technology was found to be particularly useful in degenerative temporomandibular disorders and for triangulation procedures. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92:30-7)

Subclinical cerebellar impairment in the common types of migraine: A three‐dimensional analysis of reaching movements

Mutations in the CACNA1A gene can cause familial hemiplegic migraine (FHM) and/or cerebellar ataxia. CACNA1A codes for the α1 subunit of P/Q-Ca2+ channels and is highly expressed in the cerebellum. Using a pointing paradigm and infrared optoelectronic tracking system, we found subclinical hypermetria and other subtle cerebellar signs in the common forms of migraine. These were more pronounced in migraine with than without aura. Whether this reflects involvement of Ca2+ channel genes in the common types of migraine needs to be investigated by genetic analyses.

Subclinical cerebellar impairment in the common types of migraine: A three‐dimensional analysis of reaching movements

Mutations in the CACNA1A gene can cause familial hemiplegic migraine (FHM) and/or cerebellar ataxia CACNA1A codes for the alpha1 subunit of P/Q-Ca2+ channels and is highly expressed in the cerebellum. Using a pointing paradigm and infrared optoelectronic tracking system, we found subclinical hypermetria and other subtle cerebellar signs in the common forms of migraine. These were more pronounced in migraine with than without aura. Whether this reflects involvement of Ca2+ channel genes in the common types of migraine needs to be investigated by genetic analyses.

Computer-Assisted Fluoroscopy-Based Reduction of Femoral Fractures and Antetorsion Correction

Objective: Intra-operative fluoroscopy is a valuable tool for visualizing underlying bone, implant, and surgical tool positions in orthopedics. It has brought about the minimally invasive surgical technique of intramedullar nailing to fix femoral shaft fractures. However, the limited field of view and two-dimensional property of fluoroscopic images aggravate intra-operative control of surgical parameters. The purpose of this article is to introduce a surgical navigation System based on fluoroscopy that provides missing information for the procedure of femoral fracture fixation.Materials and Methods: Optoelectronic markers are placed on a surgical drill, involved bone fragments, the femoral nail, and the fluoroscope to track their positions. Projection properties of the fluoroscope are acquired through an initial precalibration. The relative positions of bone fragments, implants, and surgical tools are displayed superimposed simultaneously and in real time on multi-planar intra-operative fluoroscopic images. This is achieved by computer simulation of X-ray projections that have taken place with acquisition of the fluoroscopic images. in addition, a method has been developed that allows contactless measurement of three-dimensional anatomic landmarks, based on their representation in fluoroscopic images. in combination with optoelectronic tracking, this enables dynamic calculacion of important surgical parameters such as femoral antetorsion.Results: A pilot surgery showed that fracture reduction can benefit from the developed computer-assisted method. An in-vitro study on computer-assisted measurement of femoral antetorsion demonstrated the high degree of precision of this technique.

Computer-assisted fluoroscopy-based reduction of femoral fractures and antetorsion correction.

Intra-operative fluoroscopy is a valuable tool for visualizing underlying bone, implant, and surgical tool positions in orthopedics. It has brought about the minimally invasive surgical technique of intramedullar nailing to fix femoral shaft fractures. However, the limited field of view and two-dimensional property of fluoroscopic images aggravate intra-operative control of surgical parameters. The purpose of this article is to introduce a surgical navigation system based on fluoroscopy that provides missing information for the procedure of femoral fracture fixation. Optoelectronic markers are placed on a surgical drill, involved bone fragments, the femoral nail, and the fluoroscope to track their positions. Projection properties of the fluoroscope are acquired through an initial precalibration. The relative positions of bone fragments, implants, and surgical tools are displayed superimposed simultaneously and in real time on multi-planar intra-operative fluoroscopic images. This is achieved by computer simulation of X-ray projections that have taken place with acquisition of the fluoroscopic images. In addition, a method has been developed that allows contactless measurement of three-dimensional anatomic landmarks, based on their representation in fluoroscopic images. In combination with optoelectronic tracking, this enables dynamic calculation of important surgical parameters such as femoral antetorsion. A pilot surgery showed that fracture reduction can benefit from the developed computer-assisted method. An in-vitro study on computer-assisted measurement of femoral antetorsion demonstrated the high degree of precision of this technique.

Load-sharing characteristics of stabilized lumbar spine segments.

Load sharing in stabilized spinal segments was evaluated using sequential injury and stabilization with a posterior instrumentation system under an in vitro flexibility protocol. To analyze the partitioning of applied loads between anatomic and implanted structures of lumbar functional spinal units stabilized with a posterior instrumentation system. To identify surgical indications for which the risk of fixator breakage in vivo is high. Relatively few groups have experimentally measured the in vitro and in vivo forces and/or moments supported by posterior instrumentation systems, and no analysis, of the load sharing in these systems has been performed. This information will provide novel insight into implant fatigue life, and the degree to which the spinal anatomy is shielded from the applied load and will allow the verification of mathematical models for new injury scenarios. Specimen kinematics were determined using an optoelectronic tracking system. Intradiscal pressure and the forces and moments supported by the implants were measured using, respectively, a needle-mounted pressure sensor and strain gauges mounted on the spinal implants. A large majority of the applied moments were supported by an equal and opposite force pair between the intervertebral disc and fixator rods in flexion and extension and an equal and opposite force pair between the left and right fixator rods in lateral bending. Torsional moments were shared approximately equally between the posterior elements, intervertebral disc, an equal and opposite shear force pair in the transverse plane between the right and left fixators and internal fixator moments. When posterior instrumentation devices are used to stabilize severe anterior column injuries, they are at risk of fracture secondary to reversed bending moments.

Identification of axial rigidity during locomotion in parkinson disease

Objectives: To identify coordination changes and stability in the movements of the trunk during locomotion in Parkinson disease (PD) as a function of walking velocity. Study Design: Comparison of treadmill locomotion with an opto-electronic tracking device. Patients: Newly diagnosed patients with PD ( n = 27) and a group of healthy control subjects ( n = 11). Results: Coordination between transversal pelvic and thoracic rotations showed significantly smaller changes in mean relative phase ( p < .0001) and lower variability in relative phase ( p < .0001) in the PD group. No significant differences were found in stride duration and variability in stride duration. Conclusions: The relative phase data contradict traditional notions of increased variability in motor control in PD and pinpoint the importance of the trunk in identifying axial rigidity. This discrepancy may be due to lack of control for walking velocity in earlier studies. It is concluded that systematic manipulation of walking velocity can identify coordination deficits and rigidity in trunk movement. This coordination of trunk movement can also be a sensitive measure for (early) diagnosis and the assessment of movement and pharmacological therapy in PD.

Gait initiation in Parkinson's disease.

We studied the kinematic patterns of gait initiation in 31 patients with Parkinson's disease and in 20 age- and sex-matched normals by using an optoelectronic tracking system (ELITE). Position markers were attached to the skin overlying the ankle, knee, hip, elbow, shoulder, and zygomatic bone. Subjects were instructed to start walking immediately after an acoustic go signal. Gait initiation was defined as the phase between standing motionless and steady-state locomotion. This phase was subdivided into a movement preparation period (the time between go signal and movement onset) and a movement execution period (the time between movement onset and the end of the first stride). Onset and duration of ankle, knee, hip, trunk, and arm motion within the first stride were analyzed. Movement preparation time was significantly increased in Parkinson's disease (p = 0.01), whereas movement execution times were similar in both groups (p = 0.23). Initiation of ankle, knee, hip, arm, and trunk movements was delayed in patients as compared with healthy subjects, but the relative timing and the sequence of submovements was comparable in both groups, indicating that the overall pattern of submovements was preserved in the patients. Our data suggest that gait initiation deficits in Parkinson's disease cannot be explained by a disordered sequence of limb and trunk submovements. More likely, gait initiation problems originate from the basal ganglia's internal cueing deficit for movement sequences, delaying onset and slowing the execution of all subcomponents.

Three-dimensional unilateral method for the bilateral measurement of condylar movements

Using a unilateral optoelectronic tracking system (JAWS-3D), a method was developed for the simultaneous measurement of the three-dimensional kinematics of both ipsilateral and contralateral human condyles, the latter being represented by virtual points bcyond the field of vision of the camera system during the actual recording. The method leaves the subject's head unrestrained while measuring the movements of two sets of three light-emitting diodes rigidly attached to the upper and lower tech. The Tait-Bryan angles method was employed for calculating the jaw rotations in three dimensions. Movements were referenced to both a skeletal and a dental coordinate system. The worst-case static measurement errors were 0.24 mm for a 20 mm translation and 0.71° for a 35° rotation. The mean dynamic measurement errors were 9.73 μm s −1 at a constant linear velocity of 200 μm s −1 and 0.73° s −1 at a constant angular velocity of 149° s −1. The utility of the method was demonstrated in a subject who was asked to open and close the mouth in a cyclic fashion.

Some timing constraints in the productionof bilabial stops

The timing of lip and jaw movements and acoustic events was studied for one subject producing six Aku pseudo words, such as /papa/ and /baba/, at two speaking rates. Movement data from the upper and lower lips and the jaw were obtained via an opto-electronic tracking device, together with a simultaneous audio recording. The acoustic duration of the medial bilabial closure served as a temporal base for analyzing articulatory timing. Within this temporal base, a phase was defined as the interval between peak raising or lowering velocity for an articulator and the acoustic onset of the following vowel. The proportion of time taken by each phase in the temporal base provides a measure of the anticipatory influence from the vowel on the consonant. Results suggest that as speech rate increases, this influence from the vowel either remains stable or increases. Thus, these results show that a speaker can show both stability and variability in timing across speaking rates.

Timing of lip and jaw movements in the production of vowel types /i, a, u/ and voicing contrast /p, b/

The temporal organization of lip and jaw movements was investigated for one subject, producing six pseudowords. The words, produced at two speech rates, normal and fast, were: /pipi/, /papa/, /pupu/, /bibi/, /baba/, /bubu/. Movement data from the upper and lower lips, and the jaw were obtained via an optoelectronic tracking device, together with an audio recording. Based on articulatory and acoustic events in the velocity and audio signals, respectively, four cycles were identified in the movement of each articulator, and two cycles in the acoustic waveform. The movement cycles are: (1) maximum vocalic velocity; (2) vocalic cycle onset; (3) maximum consonantal velocity; and (4) consonantal cycle onset. Velocity cycles were determined, as the interval between successive positive or negative peaks associated with the raising or lowering gesture in the production of either a vowel or a consonant. Onset cycles were defined as the recurrence of zero-crossings on velocity traces, reflecting the onset of a lowering or a raising gesture to produce a vowel or a consonant. The acoustic cycles are: (1) release cycle; and (2) closure cycle. Vocalic and consonantal phases were defined, within vocalic and consonantal movement cycles, respectively, as specific timing relations of articulator lowering or raising gestures, and within the appropriate acoustic cycle, as the interval that presents a stable formant structure for the vocalic phase, and as the obstruent portion, for the consonantal phase. Gestural and acoustic phasing patterns obtained within the cycles suggest that: (1) the lower lip is an efficient articulator in distinguishing the front vowels /i, a/ from the back vowel /u/, in both consonantal contexts and in all four cycles; (2) the upper lip distinguishes all vowel types in both consonantal contexts in the vocalic cycle onset, and voicing contrast in the maximum consonantal velocity; (3) distinct phasing patterns in normal speech tend to merge with increased speech rate; (4) the jaw, although a carrier articulator, does not contribute actively to separating the phonetic tasks required in this study; (5) the closure cycle is the better of the two acoustic cycles in separating vocalic and consonantal classes. Results are analyzed and discussed in terms of cognitive tasks and emergent properties of the speech production system. [Work supported by the Fyssen Foundation and NIH.]

Lip protrusion in sibilant production

While anecdotal reports of lip protrusion contributing to sibilant production in a variety of languages exist, little attention has been paid to quantifying its contribution. In the present study, lip position was monitored using a modified SELSPOT optoelectronic tracking system, and location of oral constriction was simultaneously monitored by means of a RION artificial palate. Subjects (speakers of Catalan, English, German, and Italian) produced 50 tokens each of 6 (8) symmetrical VCV utterances, where V ranged over /iau(ü)/ and C over /sš/. As expected, /s/ has a more anterior constriction than /š/, with the constriction for /usu/ being the most anterior; and, there is more lip protrusion for /š/ than for /s/, except for in the /u_u/ context. Across utterance types, the combination of lip protrusion and constriction location is a better predictor of the frequency of a sibilant's centroid than is either parameter alone; within utterance types, lip protrusion and aperture are, in general, better predictors of centroid frequency than is constriction location. [Work supported by NIH Grant NS‐07237.]

Sun Seeker System

An opto-electronic tracking system has been developed to track the sun accurately at one place only. The system has three modes of operation viz scan, track and suspend modes. When the system is sw...

Cerebellar ablation and mastication in the guinea pig ( Cavia porcellus)

The jaw movements of 3 subadult guinea pigs were recorded before and after cerebellar ablation with the aid of an optoelectronic tracking system. Despite overall ataxia of the animals' body and limbs, masticatory patterns were essentially normal. The major effects of cerebellar ablation upon Cavia mastication were a statistically significant ( P < 0.01) increase in chew cycle duration and a decrease in chew duration variability.

Temporomandibular joint meniscectomy — Effects on joint structure and masticatory function in Macaca fascicularis

The postoperative effects of unilateral temporomandibular joint meniscectomy on joint structure and masticatory function were evaluated in four mature Macaca fascicularis and compared with one control. Mandibular movement during mastication was monitored objectively with an optoelectronic tracking system within four months and again within twelve months postmeniscectomy in each animal. Temporomandibular joint structure was documented radiographically and histologically. Results showed that degenerative joint disease was produced in the postsurgical joint, and that the morphological changes were location-dependent. Fibrous ankylosis was observed histologically in three animals. The contralateral joints were not affected morphologically, except for bony resorption of the articular eminence noted microscopically in one animal. Radiographically, however, the joint appeared normal. Variable alterations in masticatory patterns were observed following unilateral meniscectomy. While there appeared to be an association between temporomandibular joint structure and masticatory function, radiographic and microscopic observation of morphological alterations in the joint did not result in predictable functional limitations in chewing pattern.