Assessment of novel ureteral occlusion device and comparison with stone cone in prevention of stone fragment migration during lithotripsy

PURPOSE: To present the initial ex-vivo results of a new ureteral-occlusion device (Cook Urological, Spencer, IN) for preventing the retrograde migration of particles during ureteroscopy and its comparison with the Stone Cone (Microvasive-Boston Scientific Corp., Spencer, IN). MATERIALS AND METHODS: We designed an ex-vivo model using a porcine kidney with an intact ureter. Standardized plastic beads were placed in the proximal ureter. Each device was deployed proximal to the beads during ureteroscopy, and the number of beads impeded by each device was recorded. RESULTS: The new device was successful at preventing retrograde migration of beads > or = 1.5 mm. Furthermore, 1.0-mm beads were impeded by the center of the device, although they passed through the periphery. The Stone Cone blocked the retrograde migration of beads > or = 2.5 mm. CONCLUSION: The new occlusion device was efficacious in an ex-vivo model. It appears to prevent the migration of smaller particles than are blocked by the Stone Cone.     

The stone cone: a new generation of basketry

PURPOSE: We designed a device to minimize ureteral stone migration during intracorporeal lithotripsy, decrease the likelihood of stone and/or basket entrapment, and extract whole stones and fragments. MATERIALS AND METHODS: Nitinol and stainless steel wires were configured into expandable tapered cones, which were placed cephalad to in vitro and in vivo concretions, and used to trap and extract stones as well as other test material. Safety features were evaluated by measuring the release of ball bearings and the tension needed to unwind the coils of the cone, which were greater than 4 mm. in diameter. We treated 4 patients with ureteral calculi using the Stone Conedagger to prevent migration and extract fragments. RESULTS: The cone-shaped devices expanded to occlude the test devices and human ureters, and prevented stone migration. They extracted whole concretions and fragments greater than 1.5 mm. The cone-shaped basket released a 5.5 mm. ball bearing at an average 0.127 pounds of tension when pulled through a 5 mm. plastic orifice. Coils greater than 4 mm. in diameter were straightened at a tension of 0.10 to 0.14 pounds. Stone migration during intracorporeal lithotripsy was prevented in the 4 patients with ureteral calculi, in whom large and small fragments were safely extracted. CONCLUSIONS: The Stone Cone may be placed via a ureteral catheter and opened cephalad to a ureteral stone to prevent stone migration during intracorporeal lithotripsy. It may extract whole stones and fragments greater than 1.5 mm. It is designed, so that its coils greater than 4 mm. in diameter release concretions too wide for the ureter or ureteral orifice after approximately 0.127 pounds of tension are applied. Because of these features, the Stone Cone represents a new generation of basketry appropriate to the era of ureteroscopy and intracorporeal lithotripsy. It is worthy of further clinical study.     

Evaluation of a new multi-basket load-release ureteral stent

INTRODUCTION: A multi-basket ureteral stent was tested and modified to assess feasibility of load-release features intended to release stone(s) if resistance is encountered during stent removal. METHODS: Three versions of the stent were evaluated: (1) unaltered stent, (2) one strand of each basket partially cut to 50%, or 75% (3) tube between baskets longitudinally slit. One of the baskets was filled with multiple 3-4-mm stones or a single large 6-mm stone to 20Fr diameter. The force required to release the device through a tube with an 8Fr narrowing was determined. In a separate assessment, urologists used a string attached to the force gauge to exert the maximum force they would be comfortable using in ureteral stent removal. RESULTS: The unaltered stent was associated with higher release forces or inability to remove the stent: 18.67 +/- 8.35 N when a single large stone was present, compared to 8.46 +/- 2.75 N for multiple small stones. Modified devices with 50% and 75% cut basket strands released at 15.19 +/- 1.54 N, and 10.65 +/- 2.09 N, respectively. The longitudinal slit device released at 3.11 +/- 1.57 N. The maximum force exerted by urologists in simulated stent removal was 7.3 +/- 0.4 N. CONCLUSION: Modifications to the multi-basket ureteral stent allow for stent removal in an in vitro model with a narrowing present with stone(s) in the stent baskets. The longitudinal slit modification appears to allow for stent removal with forces low enough to prevent significant ureteral injury, even if ureteral strictures are present.     

Efficacy of dretler stone cone in the treatment of ureteral stones with pneumatic lithotripsy

INTRODUCTION: Ureteroscopic pneumatic lithotripsy has been used to treat ureteral calculi for more than 10 years. Owing to its low price and high degree of effectiveness, it has become the most popular ureteroscopic lithotripsy device in use worldwide. The major limitation of the technique is the occurrence of proximal fragment migration during intracorporeal lithotripsy. The Dretler Stone Cone is a new device developed to prevent stone migration during ureteroscopic lithotripsy. The aim of this study was to assess the efficacy and safety of this device during ureteroscopic pneumatic lithotripsy. PATIENTS AND METHODS: Twenty-three consecutive patients having ureteral stones were treated with a 10-Fr semirigid ureteroscope, a Stone Cone Nitinol Retrieval Device, and a pneumatic lithotriptor. In all patients Stone Cones were placed under visual guidance through the working channel of the ureteroscope. Outcomes of this device were then compared with the outcomes of 23 previous patients with stones of similar sizes and locations who had undergone ureteroscopic pneumatic lithotripsy prior to the Stone Cone being available at our clinic. RESULTS: All patients in the study group were stone-free after the procedure. No stone fragments were noted to migrate to proximal segments. CONCLUSIONS: The Dretler Stone Cone effectively prevents proximal stone migration and facilitates stone fragmentation during pneumatic lithotripsy with no risk of ureteral injury. It has only a small extra cost.     

Efficacy of the Stone Cone for treatment of proximal ureteral stones

BACKGROUND AND PURPOSE: Whereas ureteroscopic lithotripsy is more efficacious than SWL in treating lower-ureteral stones, the same has not been universally said of its ability to treat proximal ureteral stones. Because failed proximal lithotripsy is often attributable to the complications associated with stone migration into the renal pelvis and calices, an instrument that can prevent this migration is a potentially important tool in the ureteroscopic armamentarium. This study sought to assess the role of just such an instrument, the Stone Cone, in proximal-ureteral lithotripsy. PATIENTS AND METHODS: We treated 19 consecutive patients having proximal-ureteral stones using semirigid ureteroscopy, a Stone Cone Nitinol urologic retrieval coil, and holmium:YAG laser lithotripsy with a 200- or 365-microm fiber. In all patients, both the Stone Cone and the laser fiber were utilized under direct visual guidance through the working channel(s) of the ureteroscope. RESULTS: All 19 patients were rendered stone free after Ho:YAG laser lithotripsy in conjunction with a Stone Cone. No stone fragments were noted to migrate into the renal pelvis, and the Stone Cone did not break or become entrapped in any of the 19 cases. CONCLUSION: The Stone Cone is a powerful new tool for proximal-ureteral lithotripsy and will likely revolutionize the treatment of proximal-ureteral stones. The savings in morbidity, time, and money associated with not having to chase stone fragments using flexible ureteroscopy are considerable.     

Comparison of anterior laxity measurements in anterior cruciate deficient knees with two instrumented testing devices

We measured anterior tibial displacements in 21 anterior cruciate ligament deficient patients using two instrumented testing devices, the KT-1000 and the KSS. A comparison of values obtained from testing was done using statistical analysis. The two tests common to both devices were the 20 lb pull and the manual maximum. The involved normal (I-N) values showed that there was no significant difference between the two devices for both the manual maximum and the 20 lb force level. There was also no significant difference between devices for the manual maximum absolute values. The significant difference between the absolute values for the 20 lb force level is probably due to the different testing techniques for both devices. When testing with the KSS, the patella remains free; testing with the KT-1000 requires that the examiner maintain pressure to hold the patella down. The manual maximum absolute values showed no significant difference because the testing techniques for both devices were identical. Comparable data for both devices are the I-N values for the 20 lb and manual maximum values.     

输尿管镜下NTrap网篮配合钬激光碎石术治疗输尿管结石

目的：探讨输尿管镜下NTrap网篮配合钬激光碎石术治疗输尿管结石的疗效及其安全性。方法：2005年1月～2009年12月应用NTrap网篮输尿管镜下配合钬激光碎石术治疗输尿管结石206例,并对临床资料进行分析。结果：一次手术碎石成功195例,成功率94．7％（195／206）;10例在碎石过程中结石被冲入肾盏内形成结石残留,术后行ESWL治愈;1例双侧输尿管结石因输尿管狭窄中转开放手术取出结石并切除狭窄段输尿管。所有患者术后无严重并发症发生。结论：输尿管镜下NTrap网篮配合钬激光碎石可以有效防止碎石逆行移位,避免术后结石残留于肾盏,是一种安全、有效的工具。     

整形与美容医疗器械临床试验风险管理

整形与美容行业发展迅速，医疗器械产业规模也在逐渐扩大。但我国现阶段医疗器械临床研究 管理方案尚需进一步完善，部分科研机构管理观念较弱，导致部分伪劣商品流入市场。本文主要总结整形 与美容医疗器械临床试验发展现状及存在的问题，并提出医疗设备临床研究和临床试验管理策略，以期 提升医疗器械临床研究人员对风险的认知，健全与完善整形与美容医疗器械临床试验风险的管理。     

Controlling anterior tibial displacement under static load: a comparison of two braces

This article presents data comparing the restraining effect of the Lenox Hill and the CTi brace to static loading using the KT-1000 Knee Ligament Arthrometer. Testing was performed at 25 degrees and 90 degrees in 15 patients with documented single ligament injuries involving the anterior cruciate. The opposite knee was determined to be normal by subjective and objective testing and was used as the control. Results showed that the anterior drawer tests, both the Lenox Hill and the CTi brace improved the ACL deficient knee significantly. With 15 lb of passive loading, both the Lenox Hill and the CTi brace improved the drawer to within normal limits. However, only the CTi brace was able to return the drawer to within the normal range at the 20 lb force level. Neither brace improved the drawer to normal when subjected to the higher loads created by an active drawer test. At 90 degrees, 15 lb of passive loading could not discriminate between the braced and the unbraced knee or between the normal and ACL deficient knee. When 20 lb of force was applied, only the CTi brace improved the drawer significantly, which placed the drawer into the normal range. Under static testing condition, the CTi brace proved to be better than the Lenox Hill in controlling the anterior drawer in flexion and at 20 lb of passive loads; however, when higher loading forces were used in the active anterior drawer test, neither brace was effective in controlling anterior tibial translation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevention of retrograde calculus migration with the Stone Cone

Retrograde calculus migration during ureteroscopic lithotripsy remains a problem in 5–40% of cases. We assessed the safety and efficacy of the Stone Cone device, in comparison with the standard flat wire basket. A total of 56 consecutive patients with ureteral calculi, suitable for ureteroscopic extraction and/or lithotripsy, where included in this prospective study. Patients were randomly allocated into two groups. In group A (30 patients), we used the Stone Cone, while in group B (26 patients) we used the standard flat wire basket. The Stone Cone was placed through a cystoscope under fluoroscopic guidance, or when necessary under direct ureteroscopic control. Whenever necessary, intracorporeal electrohydraulic lithotripsy took place in both groups. Statistical significance was assessed by the paired t-test. The mean operative time was 48.5 min in group A, and 42.4 min in group B. Intact calculus extraction was possible in 16.6% in group A, and in 7.6% in group B (P<0.01). Retrograde stone migration was revealed in 23% in group B only (P<0.001). Also, residual fragments >3 mm were recorded in 30.7% in group B only (P<0.001). None of the patients in group A required auxiliary procedures, in contrary to 23% in group B (P<0.001). No major complications were recorded in group A, while in group B a case of major ureteral mucosal abrasion was recorded. The Stone Cone is safe and efficient in preventing retrograde stone migration and in minimizing residual fragments during ureteroscopic lithotripsy in comparison with the flat wire basket.     

Stone Cone取石网在输尿管镜钬激光碎石术治疗输尿管上段结石中的应用

目的 探讨Stone Cone取石网在输尿管镜钬激光碎石术治疗输尿管上段结石中的应用.方法 回顾性分析本院2015年6月至2015年12月所有诊断输尿管上段结石并使用输尿管镜钬激光联合Stone Cone取石网碎石的病例,共51例,对碎石效果进行分析.结果 所有病例中,49例患者成功粉碎结石,2例患者结石上移至肾盂,后通过体外冲击波碎石排尽结石,联合取石网碎石成功率为96.1％ (49/51),术中未发生输尿管穿孔、黏膜撕脱等并发症.结论 输尿管镜钬激光碎石术处理输尿管上段结石过程中配合使用Stone Cone取石网,可有效提高碎石率,安全性高,值得临床推广.     

Noninvasive ankle distraction: Relationship between force,magnitude of distraction,and nerve conduction abnormalities

Seven healthy volunteers (14 ankles: four males, 3 females) with no history of ankle or foot pathology were placed in a modified beach chair position on an operating table for ankle distraction using a noninvasive ankle distractor. In-line traction of 0 to 225 N (50 lb) in 22.5-N (5-lb) increments was applied to tne ankle. A direct lateral radiograph was obtained at each distraction force. The joint space was measured on the lateral radiographs using electronic microcalipers. Surface recordings of the superficial peroneal, deep peroneal dorsal digital cutaneous, and sural nerves were obtained. The ankle joint space increased progressively from an average 3.1 mm with no force applied to an average 4.2 mm with 225 N (50 lb) distraction force applied. The maximum joint distraction averaged 1.3 mm (range, 0.35 to 2.35 mm). The sensory amplitudes were diminished or absent with increasing time and force of distraction. The decreased amplitudes were most marked after 1 hour of distraction with 135 N (30 lb) or greater distraction force. This correlated with symptoms of paresthesias. The superficial and deep peroneal cutaneous nerves were affected to a much greater extent than the sural nerve. The amplitudes quickly returned to normal values with the weight being released from the ankle. The noninvasive ankle distractor safely increased ankle joint space by more than 1 mm. Distraction with 135 N (30 lb) or more for 1 hour is associated with reversible nerve conduction changes. Based on these findings, we recommend using the noninvasive ankle distraction apparatus for ankle arthroscopy, with up to 135 N (30 lb) of traction applied to the foot for up to 1 hour. Greater force, applied for longer periods, is associated with increasing nerve conduction abnormalities.     

A comparison of various angles of halo pin insertion in an immature skull model.

STUDY DESIGN: A basic science biomechanical study involving an animal model. OBJECTIVES: To evaluate the effect of varying angles of halo pin insertion on the force generated at the pin-bone interface, and thereby the stability of the halo pin-bone interaction during insertion. BACKGROUND DATA: Because of variations in the shape and size of the pediatric skull, halo pins often are inserted at various angles rather than perpendicular to the skull. Concern exists that the high complication rate associated with pediatric halo use may result in part from less than ideal structural properties at the halo pin-bone interface. METHODS: The authors used a fetal calf skull model to simulate the thickness and structural properties of the pediatric skull. Halo pins were inserted at angles of 0 degree (perpendicular), 10 degrees, 15 degrees, and 30 degrees into skull segments via a halo ring. Load generated at the pin-bone interface was measured using a modified mechanical testing device. Twenty trials were conducted per angle, with the endpoint being specimen failure, pin penetration, or maximum load. RESULTS: Mean maximum loads per unit thickness were 82.15 +/- 7.54 N/mm at 0 degree, 68.80 +/- 4.79 N/mm at 10 degrees, 51.49 +/- 5.08 N/mm at 15 degrees, and 42.38 +/- 3.51 N/mm at 30 degrees, There was a significant difference between perpendicular insertion (0 degree) and 15 degrees angles of insertion. There was also a significant difference between the 10 degrees and 30 degrees angles of insertion. CONCLUSIONS: Perpendicular halo pin insertion in an immature skull model was shown to result in increased load at the pin-bone interface. This improved structural behavior may help to reduce the incidence of complications of halo application in children.     

Bone suture anchor fixation in the lower extremity: a review of insertion principles and a comparative biomechanical evaluation

BACKGROUND: Suture anchors have been developed for the fixation of ligaments, capsules, or tendons to bone. These devices have led to improved fixation, smaller incisions, earlier limb mobility, and improved outcomes. They were originally developed for use in shoulder reconstructions but are now used in almost all extremities. In the lower leg they are used in the tibia, the talus, the calcaneus, tarsal bones, and phalanges. Nevertheless, techniques for insertion and mechanisms of failure are not well described. METHODS: Five suture anchors were studied to determine the pullout strength in four distal cadaver femurs and four proximal cadaver tibias from 55- and 62-year-old males. Eight hundred ninety Newton line was used, testing the anchors to failure with an Instron testing device (Instron, Norwood, MA). The anchor devices were inserted randomly and tested blindly (12 tests per anchor device, 60 tests in all). RESULTS: Two anchors in each group tested failed at low loads. Both types of plastic anchors had failures at the eyelet. Average pullout strength varied from 85.4 to 185.6 N. CONCLUSIONS: Insertion techniques are specific for each device, and they must be followed for optimal fixation. In this study, in all five groups of anchors tested two of the 12 anchors in each group failed with minimal force. On the basis of this finding we recommend that, if suture anchor fixation is necessary, at least two anchors should be used. Since there appears to be a percentage of failure in all devices, the second anchor can serve as a backup. It is imperative that surgeons be familiar with the insertion techniques of each device before use.     

Is it possible to train patients to limit weight bearing on a lower extremity?

Orthopedic patients are often instructed on how much weight to bear on an injured or postoperative extremity. Although specific weight-bearing instructions are given to a majority of lower-extremity orthopedic patients, the ability of patients to comply with these instructions is questioned in the medical literature. This study compared the effectiveness of new forms of clinical interventions designed to train patients on weight bearing, focusing on the use of biofeedback devices designed to offer real-time feedback to partial weight-bearing patients. Twenty healthy patients aged 20 to 30 years completed 3 interventions: (1) verbal instructions on weight bearing, (2) training with a bathroom scale, and (3) training with a biofeedback device.Patients given touchdown weight-bearing instructions (25 lb) initially bore an average of 63.57±6.24 lb when given verbal instructions. This was reduced to 44.75±5.69 lb after training with a bathroom scale (P<.001), and was further reduced to 26.2±1.57 lb with biofeedback training (P=.011). Likewise, patients given partial weight-bearing instructions (75 lb) initially bore an average of 92.28±7.85 lb. No improvement occurred with the use of a bathroom scale (at 75 lb), which showed an average of 90.82±7.19 lb (P=1.000). Training with a biofeedback device improved the average weight bearing to 69.67±3.18 lb (P=.014).Biofeedback training led to superior compliance with touchdown and partial weight-bearing instructions. Because partial weight-bearing instructions are commonly given to orthopedic patients, training with such a device may be appropriately considered.     

Fixed-angle plate fixation in simulated fractures of the proximal humerus: a biomechanical study of a new device

This study was performed to evaluate the biomechanical properties of a new device for displaced fractures of the proximal humerus. The device is a low-profile, fixed-angle plate specially designed for percutaneous application. With the use of embalmed cadaveric humeri, we simulated both noncomminuted and comminuted 2-part surgical neck fractures of the proximal humerus. Each humerus of a pair was then randomly fixed with either the new experimental device or the Association for the Study of Internal Fixation (ASIF) T-plate and mechanically tested to failure in an axial shear-loading model. The two fixation devices were evaluated in paired humeri with regard to mode of failure, stiffness, displacement at physiologic loads, and displacement, load, and energy at the point of ultimate load before failure. In the noncomminuted fracture trials the experimental device exhibited significantly greater stiffness (P <.001; P =.002 for normalized values) and ultimate load before failure (P =.015) and significantly less displacement at higher physiologic loads (P =.031). In the comminuted fracture trials the experimental device exhibited significantly greater stiffness (P =.048), ultimate load (P <.001) and energy absorbed (P =.048) before failure, and significantly less displacement at higher (P =.004) and lower physiologic loads (P =.011). The study demonstrates improved biomechanical properties for the new experimental device over the T-plate in simulated fractures of the proximal humerus. We extrapolate that these improved biomechanical properties may prove advantageous in future clinical investigation.     

What are the Predictors for Bead Shedding in Porous-Coated Hip and Knee Arthroplasties? : An Implant Retrieval Study

Bead shedding has been reported in both hip and knee arthroplasties and can result in increased polyethylene wear and metal ion release. The rates of bead loss were recorded for each device type, and the interfacial bead-substrate shear load to failure and contact areas of the beads were determined. The 3 components with the highest rate of bead loss, namely, S-Rom, Omnifit, and Optifix acetabular shells, recorded the lowest shear loads to failure. Percentage bead-substrate contact area ranged between 7% and 37% and was the most important factor affecting bead shedding. Other factors influencing bead loss in decreasing order of importance were bead fusion, bead size, component type (acetabular or knee), component loosening, and time in situ.     

Chronic rotator cuff injury and repair model in sheep

BACKGROUND: Most rotator cuff surgery is performed on chronic tears. As there is no animal model in which to examine the physiology of muscle and tendon injury and repair in this setting, we developed a chronic rotator cuff injury model in sheep. METHODS: The infraspinatus tendon was released in thirty-six female sheep. Biopsy specimens were obtained from the muscle and were analyzed for fat content. The force generated by the muscle with supramaximal stimulation was recorded intraoperatively. A control group (twelve sheep) underwent an immediate tendon repair. In the remaining twenty-four sheep, the tendon was wrapped in a dura substitute to prevent scarring and was repaired at six weeks (eight sheep) and eighteen weeks (sixteen sheep) after release. In the immediate repair group, four animals were killed at six weeks; four, at twelve weeks; and four, at twenty weeks. In the six-week delayed repair group, four animals were killed at twelve weeks and four were killed at twenty weeks after the repair. In the eighteen-week delayed repair group, eight animals were killed at twelve weeks; four, at twenty weeks; and four, at thirty weeks after the repair. Muscle biopsies and testing were repeated prior to killing of the animals. RESULTS: The average force of muscle contraction decreased 3.6 lb (1.6 kg) by six weeks after the injury and 3.9 lb (1.8 kg) by eighteen weeks after the injury. After the repair, the force of contraction in the six-week group improved by 0.8 lb (0.4 kg) at twelve weeks postoperatively and by 1.3 lb (0.6 kg) at twenty weeks postoperatively. In contrast, no improvement occurred in the eighteen-week group until thirty weeks after the repair, at which time a 0.9-lb (0.4-kg) improvement was noted. There was a twelvefold increase in intramuscular fat concentration; this lipid infiltration was partially reversed after the tendon repair. Isolated tendon samples demonstrated an increase in the modulus of elasticity after chronic detachment that partially corrected after the tendon repair in the earlier (six-week) repair group. CONCLUSIONS: We found that earlier repair of the tendon results in a more rapid recovery of both muscle function and tendon elasticity compared with a more delayed repair. We concluded that there may be a "point of no return" in rotator cuff injury after which the elasticity of the muscle-tendon unit does not return to normal.     

Does a tensioning device pinned to the tibia improve knee anterior–posterior load‐displacement compared to manual tensioning of the graft following anterior cruciate ligament reconstruction? A cadaveric study of two tibial fixation devices

Devices that are pinned to the tibia to tension an anterior cruciate ligament (ACL) graft produce joint reaction loads that in turn can affect the maintenance of graft initial tension after tibial fixation and hence knee anterior-posterior (AP) load-displacement. However, the effect of these devices on AP load-displacement is unknown. Our objectives were to determine whether tensioning by device versus tensioning by hand causes differences in AP load-displacement and intraarticular graft tension for two commonly used tibial fixation devices: a bioresorbable interference screw and a WasherLoc. AP load-displacement and intraarticular graft tension were measured in 20 cadaveric knees using a custom arthrometer. An initial tension of 110 N was applied to a double-looped tendon graft with the knee at extension using a tensioning device pinned to the tibia and a simulated method of tensioning by hand. After inserting the tibial fixation device, the 134 N anterior limit (i.e., anterior position of the tibia with respect to the femur with a 134 N anterior force applied to the tibia) and 0 N posterior limit (i.e., AP position of the tibia relative to the femur with a 0 N force applied to the tibia) were measured with the knee in 25 degrees flexion. Intraarticular graft tension was measured at extension. These limits and intraarticular graft tension were also measured after cyclically loading the knee 300 times. Compared to a simulated method of tensioning by hand, tensioning with a device pinned to the tibia did not decrease the 134 N anterior limit and did not cause posterior tibial translation. However, intraarticular graft tension was maintained better with a tensioning device pinned to the tibia for the Washerloc, but not the interference screw. For two commonly used tibial fixation devices, a tensioning device pinned to the tibia does not improve AP load-displacement at 25 degrees flexion over tensioning by hand when the graft is tensioned at full extension, but does improve the maintenance of intraarticular graft tension for the Washerloc.     

Biomechanical evaluation of spinal fixation devices: II. Stability provided by eight internal fixation devices

The three-dimensional stability provided by eight spinal fixation devices has been studied in an in vitro biomechanical model using seven-vertebrae (T9-L3) fresh cadaveric thoracolumbar specimens. An injury was created at T12-L1 by complete transection of the posterior elements and posterior half of the intervertebral disc, leaving the anterior half of the intervertebral disc and anterior longitudinal ligament intact. The three-dimensional rotational and translational motions, measures of biomechanical instabilities, were determined under physiologic loads for the intact specimen after injury and instrumentation with each of the eight fixation devices. The tested devices were: Dunn's anterior device (DD); Harrington distraction (HD); Harrington compression (HC); Harrington distraction-compression combination (HDC); Harrington distraction with sleeves (HDS); Luque rods (LQ); Luque rectangle (LR); and Luque short rectangle (LSR). The following devices were stable under the four loads: Flexion: HC, HD, HDC, HDS, LQ, and LR; Extension: HD, HDC, HDS, LQ, and LR; Lateral Bending: LQ and LR; and Axial Rotation: none.