SAS journal最新文献

The incidence of osteochondroma is rare and only 2% of such tumors are found in the spine area. When they are found in the vertebral column, less than 1% of all osteochondromas and few tumors occur in the thoracic vertebrae. An osteochondroma arising from the transverse process of the vertebra is even rarer, especially following from the thoracic transverse process. Here we report a giant solitary osteochondroma arising from the thoracic transverse process of T8 vertebra and involving the corresponding transverse process and rib.

A 28-year-old man presented with a progressive thoracic node, and neuroradiological evaluation of the spine showed a giant mass lesion involving the transverse process of T8 vertebra and concomitant corresponding facet joint and rib on the left side. At surgery, a firm and cartilaginous tumor originating from the transverse process was radically excised and surgical curettage of the lesion was performed.

It is concluded that accurate and prompt diagnosis requires a high index of suspicion followed by surgical treatment to prevent severe morbidity in cases of primary spinal column tumors. The histological examination of this patient revealed the lesion was osteochondroma.

The best choice of treatment for spinal osteochondromas is surgical excision or curettage and spinal stabilization, if necessary.

Background

The increasing complexity of articulating spinal implants prohibits the use of serum-supplemented simulator fluid testing because multicomponent interfaces retain residual protein and preclude gravimetric measurement. Our original hypothesis was that simulator testing of a posterior dynamic stabilization implant that has metal-on-metal articulating bearings will not produce dramatically different wear debris when tested using pure saline versus testing in saline supplemented with 20% serum.

Methods

This hypothesis was tested using simulator testing of 12 dynamic stabilization spinal implants, 6 in 100% saline and 6 in 20%-serum saline. Gravimetric and particle analysis were performed after every million cycles up to 10 million cycles, with flexion of 11.3/extension of 5.6° coupled with axial rotation of ± 4°.

Results

The mean gravimetric weight loss was approximately 200 mg over 10 million cycles for the implants tested in 100% saline, while the mean weight loss for those tested in 20%-serum saline was below the method detection limits (< 10 mg over 10 million cycles). For the 100%-saline and 20%-serum simulator fluids, the average particle size over the course of 0 to 10 million cycles remained relatively constant at 0.2 μm-dia (saline) and 3.2 μm-dia (20%-serum saline). Testing in 100% saline generated > 1000-fold more particles, compared to testing in 20% serum-supplemented saline. Energy-dispersive X-ray (EDAX) analyses of particles demonstrated that the 100% saline debris was composed of Co-Cr-P-O (Cr-Co metal oxides), and for the 20%-serum saline debris only bulk metal Co-Cr was detected.

Conclusion

Our initial hypothesis was not supported. There were significant differences in gravimetric wear, average size, and type of wear debris that were mechanistically attributable to the type of simulator fluid used. The over-protective effect of serum proteins appears to underscore the importance of using both saline and serum when establishing upper and lower bounds of predictive implant debris generation modeling, where saline represents a worst-case scenario and as little as 20% serum masks all weight loss completely in highly modular articulating implants.

Clinical Relevance

Clinical Relevance = 5 (Oxford Centre for Evidence-based Medicine Levels of Evidence). Study findings are limited to a greater understanding of the science associated with predictive wear testing of articulating spinal implants.

Study Design

This study is a systematic review of published biomechanical studies involving pedicle screw-based posterior dynamic stabilization devices (PDS) with a special focus on kinematics and load transmission through the functional spine unit (FSU).

Methods

A literature search was performed via the PubMed online database from 1990 to 2008 using the following key words: “biomechanics,” “lumbar dynamic stabilization,” “Graf system,” “Dynesys,” and “posterior dynamic implant.” Citations were limited to papers describing biomechanics of pedicle screw-based PDS devices currently available for clinical use. Studies describing clinical experience, radiology, and in vivo testing were excluded from the review. Parameters measured included kinematics of the FSU (range of motion (ROM), neutral zone (NZ), and location of the center of rotation) and load transmission through the disk, facets, and instrumentation.

Results

A total of 27 publications were found that concerned the biomechanical evaluation of lumbar pedicle screw-based dynamic stabilization instrumentation. Nine in vitro experimental studies and 4 finite element analyses satisfied the inclusion criteria. The Dynesys implant was the most investigated pedicle screw-based PDS system. In vitro cadaveric studies mainly focused on kinematics comparing ROM of intact versus instrumented spines whereas finite element analyses allowed analysis of load transmission at the instrumented and adjacent levels.

Conclusion

Biomechanical studies demonstrate that pedicle screw-based PDS devices limit intervertebral motion while unloading the intervertebral disk. The implant design and the surgical technique have a significant impact on the biomechanical behavior of the instrumented spinal segment. The posterior placement of such devices results in non-physiologic intervertebral kinematics with a posterior shift of the axis of rotation. Biomechanical studies suggest that the difference at the adjacent level between investigated dynamic devices and rigid stabilization systems may not be as high as reported. Finally, additional investigations of semirigid devices are needed to further evaluate their biomechanical properties compared to soft stabilization PDS systems.

Background

Range of motion (ROM) has been shown to influence clinical outcomes of total disc replacement (TDR). While the parallax effect in image acquisition has been shown in the literature to influence the accuracy of a variety of measurements, this concept has not been investigated in the assessment of ROM analysis following TDR.

We performed an evaluation of the influence of radiograph beam angle on “by hand” and on “gold standard” flexion-extension ROM measurements in lumbar total disc replacement. The purpose of this study is to determine (1) the influence of X-ray beam angle on index level angle (ILA) measurements in lumbar TDR using the keel method, and (2) whether the out-of-plane radiographic beam effects cause a difference between true and calculated range of motion.

Methods

Eight blinded orthopaedic surgeons used the keel method to calculate ROM measurements from radiographs of a flexible Sawbones model (Pacific Research Laboratories, Inc., Vashon, Washington) implanted with a ProDisc-L device (Synthes Spine, West Chester, Pennsylvania). Radiographs were obtained at beam angles of 0°, 5°, 10°, and 15° in the sagittal plane from the device center. Calculations were compared to measurements obtained by a validated digitized software method (Quantitative Motion Analysis, QMA, Medical Metrics, Inc., Houston, Texas). Inter- and intraobserver precision and accuracy were determined.

Results

Compared with QMA, the radiographic keel method had an average error of 3.7°. No significant effect of variation in beam angle on interobserver precision (N = 16, P = .92) or accuracy (N = 16, P = 0.86) or intraobserver precision (N = 8, P = .09) or accuracy (N = 8, P = 0.07) of ROM measurements was identified. Repeat testing with QMA also revealed no effect of parallax and resulted in nearly identical ROM measurements.

Conclusions

Accuracy and precision of the keel method to determine ROM from index level angle measurements after TDR was not affected by increases in X-ray beam angles up to 15̊ from the device center.

Clinical Relevance

Our study demonstrates that range of motion measurements are not influenced by parallax effect when using the keel method to determine index level angle measurements in lumbar total disc replacement.

Background

Computer-assisted spinal navigation allows for real time localization of surgical instruments in multiple views. Its use decreases radiation exposure and clears the surgical field of the C-arm fluoroscope. Despite these advantages, spinal navigation has yet to gain general acceptance among spine surgeons. The purpose of this study is to survey spine surgeons about their opinions on the strengths and weaknesses of spinal navigation.

Methods

Spine surgeons from the membership of the Spine Arthroplasty Society (SAS) and the Society for Minimally Invasive Spine Surgery (SMISS) were surveyed regarding their current use of spinal navigation and their perceptions of the strengths and weaknesses of spinal navigation (N = 147). Responses were analyzed using 2-sided chi-square tests.

Results

Most spine surgeons (63.4%) have only superficial experience with spinal navigation, and 76.2% of surgeons rarely use spinal navigation in their cases. Spine surgeons have the most experience with virtual fluoroscopy spinal navigation systems (35.9%). Surgeons considered longer operating times (63.5%), increased cost (48.3%), lack of necessity (40.7%), unreliable navigation accuracy (37.9%), and too many intraoperative glitches (35.2%) to be the major weaknesses of spinal navigation.

Surgeons considered decreased radiation exposure to the surgeon (76.1%), increased screw placement accuracy (65.7%), decreased radiation exposure to the patient (41.8%), and keeping the C-arm away from the operating field (29.1%) to be the greatest advantages of spinal navigation. Among the types of procedures surgeons believe are most likely to benefit from spinal navigation are minimally invasive instrumentation and fusion (72.5%) and complex open deformity (55.6%).

Conclusion

Most spine surgeons have only superficial experience in spinal navigation. The most commonly selected weaknesses of spinal navigation are increased operative time, cost, and lack of necessity. Increased fluoroscopy and MIS use in the future may shift focus from weaknesses to the strengths of spinal navigation, including decreased radiation exposure and elimination of the C-arm from the operative field.