A model for evaluation of the electric activity and oxygenation in the erector spinae muscle during isometric loading adapted for spine patients.

BACKGROUND: Simultaneous measurement of electromyography (EMG) and local muscle oxygenation is proposed in an isometric loading model adjusted for patients that have undergone spinal surgery. METHODS: Twelve patients with degenerative lumbar spinal stenosis (DLSS) were included. They were subjected to a test protocol before and after surgery. The protocol consisted of two parts, a dynamic and an isometric Ito loading with a time frame of 60 s and accompanying rest of 120 s. The Ito test was repeated three times. EMG was measured bilaterally at the L4 level and L2 and was recorded using surface electrodes and collected (Biopac Systems Inc.). EMG signal was expressed as RMS and median frequency (MF). Muscle tissue oxygen saturation (MrSO2) was monitored using a near-infrared spectroscopy (NIRS) device (INVOS® 5100C Oxymeter). Two NIRS sensors were positioned bilaterally at the L4 level. The intensity of the leg and back pain and perceived exertion before, during, and after the test was evaluated with a visual analogue scale (VAS) and Borg RPE-scale, respectively. RESULTS: All patients were able to perform and complete the test protocol pre- and postoperatively. A consistency of lower median and range values was noted in the sensors of EMG1 (15.3 µV, range 4.5-30.7 µV) and EMG2 (13.6 µV, range 4.0-46.5 µV) that were positioned lateral to NIRS sensors at L4 compared with EMG3 (18.9 µV, range 6.5-50.0 µV) and EMG4 (20.4 µV, range 7.5-49.0 µV) at L2. Right and left side of the erector spinae exhibited a similar electrical activity behaviour over time during Ito test (60 s). Regional MrSO2 decreased over time during loading and returned to the baseline level during recovery on both left and right side. Both low back and leg pain was significantly reduced postoperatively. CONCLUSION: Simultaneous measurement of surface EMG and NIRS seems to be a promising tool for objective assessment of paraspinal muscle function in terms of muscular activity and local muscle oxygenation changes in response to isometric trunk extension in patients that have undergone laminectomy for spinal stenosis.

Malmö Treatment Referral and Intervention Study-High 12-Month Retention Rates in Patients Referred from Syringe Exchange to Methadone or Buprenorphine/Naloxone Treatment.

BACKGROUND: Heroin dependence is associated with high mortality. Opioid agonist treatment (OAT) with methadone or buprenorphine has strong evidence for treatment of this relapsing condition. In our setting, OAT has been associated with strict and demanding intake procedures, often with requirements of social stability, but also high, approximately 80 percent 12-month retention rates. In a recent randomized controlled trial, we demonstrated high rates of successful rapid referral from a syringe exchange programme (SEP) to treatment with methadone or buprenorphine, including actual treatment initiation. The objectives of this study were to assess 12-month retention rates, in order to assess whether a novel referral program of current drug users at a SEP would achieve retention rates comparable to more traditional intake procedures. METHODS: The present report is a 12-month follow-up of 71 patients who successfully started treatment with methadone or buprenorphine/naloxone. Patient data from baseline and at 12 months were collected. RESULTS: Out of the 71 patients who started treatment, 58 (82%) were still in treatment after 12 months. CONCLUSION: This was a population, referred from a SEP, with a high drug use severity on admission and no pretreatment requirement for social stability, but there were still high retention rates at 12 months comparable to regular opioid agonist clinics in our setting.

The effect of repetitive flexion and extension fatigue loading on the young porcine lumbar spine, a feasibility study of MRI and histological analyses.

BACKGROUND: The biomechanical mechanisms of failure of FSUs have been studied but the correlation of repetitive flexion and extension loadings to the initial phase of fatigue in young FSUs are still not known. The purpose of the study was to examine the fatigue results of low magnitude repetitive flexion and extension loading on porcine lumbar Functional Spinal Units (FSUs) with Magnetic Resonance Imaging (MRI) and histology. METHODS: Eight FSUs were subject to repetitive pivot flexion and eight to extension loading by a protocol of 20 000 cycles at 1 Hz with a load of 700 N. All loaded FSUs (N = 16) were examined with MRI and histology post loading. Three FSUs were examined with MRI as controls. Further three FSUs were non loaded histology controls. RESULTS: Fifteen (94%) of the loaded FSUs have decreased MRI signal in the growth zone of the superior vertebra and 12 (75%) in the inferior vertebrae. Fourteen (88%) FSUs have increased signal in the superior vertebral body. Fourteen (88%) FSUs have a reduced signal in all or any endplate. The histology morphometry displayed that the unstained parts of the epiphyseal growth zone were larger among the loaded FSUs (mean 29% vs 4%) and that the chondrocytes in the endplate and growth zones had abnormal structure and deformed extracellular matrix. CONCLUSION: Repetitive loading of young porcine FSUs in both extension and flexion causes concurrent MRI and histological changes in the growth zones and endplates, which could be a first sign of fatigue and an explanation for the disc, apophyseal and growth zone injuries seen among adolescent athletes.

Cyclical loading causes injury in and around the porcine proximal femoral physeal plate: proposed cause of the development of cam deformity in young athletes.

BACKGROUND: The repetitive load to which the adolescent athlete's body is exposed during training and competition affects bone growth. In previous studies, abnormalities of the spine and extremities of adolescent athletes have been described on radiographs and this also applies to the hip. The cam deformity of the hip is an extension of the physeal plate and develops during the adolescent athlete's growth. Studies of the porcine spine have shown that the vertebral endplates, apophyseal rings and intervertebral discs are susceptible to both static and repetitive loads. The proximal physeal plate of the porcine femur is susceptible to static loads, but no studies have been performed on its susceptibility to repetitive loads. The purpose of this study was to investigate the susceptibility of the proximal porcine femur to repetitive loads. METHODS: Descriptive laboratory study. Seven proximal femurs from four young (5 months) pigs were loaded repetitively (50,000 cycles) using a previously developed model. Three were loaded vertically, three antero-superiorly and one was used as a control. All femurs were examined macroscopically, histologically and with MRI after loading. RESULTS: No macroscopic injuries were detected on any of the femurs after loading. Fluid redistribution was seen in all femurs on MRI compared with the unloaded control. Injuries were seen in all loaded femurs on microscopic examination of histological samples. Injuries, perpendicularly to the physeal plate and fractures adjacent to the plate, were seen in the vertically loaded specimens. In the antero-superiorly loaded specimen, the injury in the growth plate was parallel to the plate. CONCLUSION: Repeated loading of the young porcine hip leads to histological injuries in and adjacent to the physeal plate. These injuries are likely to cause growth disturbances in the proximal femur. We propose that such injuries may be induced in adolescent athletes and offer a plausible explanation for the development of the cam deformity.

Effects of electrical nerve stimulation on force generation, oxygenation and blood volume in muscles of the immobilized human leg.

BACKGROUND: Transcutaneous electrical stimulation of the common peroneal nerve may be an additional clinical tool for enhancing venous return by active and passive mechanisms of muscle action in the immobilized leg. PURPOSES: To determine the effects of electrical stimulation of the common peroneal nerve to (1) produce force during isometric ankle joint dorsiflexion, and (2) alter muscle oxygenation and blood volume in the resting human leg. METHODS: A novel electrical stimulator was applied to 28 legs of 14 healthy subjects. The force during isometric ankle joint dorsiflexion and myoelectric responses produced by stimulation-induced leg muscle contractions were investigated. Muscle oxygen saturation, blood volume and deoxygenated haemoglobin in the tibialis anterior and medial gastrocnemius muscles were measured by near-infrared spectroscopy during venous stasis (40 mmHg thigh tourniquet), with or without electrical stimulation. Results. The force produced during ankle joint dorsiflexion at the maximal stimulation intensity was 2.25 N (0.02-14.14) in the resting leg. Changes in muscle oxygen saturation during venous stasis, with or without electrical stimulation, were similar. Electrical stimulation during venous stasis caused 4-9% and 0.2-6% less increase in total muscle blood volume and deoxygenated hemoglobin compared to venous stasis alone. CONCLUSIONS: Nerve stimulation with a newly developed device partly counteracts increases in muscle blood volume and deoxygenated hemoglobin of the resting leg during venous stasis. CLINICAL RELEVANCE: The device stimulates active and passive mechanisms of leg muscle action that seems to enhance venous return in patients with impaired function.

Strength of the porcine proximal femoral epiphyseal plate: the effect of different loading directions and the role of the perichondrial fibrocartilaginous complex and epiphyseal tubercle - an experimental biomechanical study.

BACKGROUND: The high loads on adolescent athletes' musculoskeletal system are known to cause morphological and degenerative changes in bone, intervertebral discs and joints. It has been suggested that the cam deformity of the proximal femoral head originates from a subclinical slipped capital femoral epiphysis (SCFE) as a result of non-physiological loading. The perichondrial fibrocartilaginous complex (PFC) and the epiphyseal tubercle are believed to stabilise the proximal femoral epiphysis, but their role is still unclear. The aim of the present study was to develop an experimental, biomechanical model to evaluate the strength of the porcine proximal femoral epiphysis in different loading directions and, furthermore, to investigate the stabilising role of the PFC and the epiphyseal tubercle. METHODS: A descriptive laboratory study. An in-vitro model was developed and nine young (5 months) porcine proximal femoral epiphyses were loaded to failure; three in the anterior-posterior direction, three in the lateral-medial direction and three in the vertical direction. The injured proximal femoral epiphyses were then examined both macroscopically and histologically. RESULTS: Anterior and lateral loading of the proximal femoral epiphysis resulted in failure of the epiphyseal plate, while vertical loading resulted in a fracture epiphyseolysis. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. Despite histological epiphyseolysis, the PFC was intact in 15 of 27 (56%) slices. In histological examinations, the epiphyseal tubercle appears to halt the slide of the epiphysis. CONCLUSIONS: We have developed an experimental, biomechanical model to measure the strength of the proximal femoral epiphyseal plate in different loading directions. The strength of the proximal femur was weakest through the epiphyseal plate. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. The epiphyseal tubercle and the PFC stabilise the epiphysis when the epiphyseal plate is damaged. The findings in the present study indicate that overloading the hips in growing individuals can disrupt the epiphyseal plate. These findings may have implications when it comes to understanding the pathogenesis of cam deformity of the hip.

In vivo discography in degenerate porcine spines revealed pressure transfer to adjacent discs.

STUDY DESIGN: In vivo experimental porcine study. OBJECTIVE: To investigate if discography induced pressure increase in adjacent degenerate discs. SUMMARY OF BACKGROUND DATA: Despite refinements in the past 2 decades, the validity of discography is debated. Discography in healthy pigs has shown that the pressure increase during disc injection transmits to adjacent discs, a potential source for false positive responses. METHODS: Degeneration in 1 lumbar disc was induced in 10 pigs by drilling a hole through the endplate. Intradiscal pressure was recorded using a 0.36-mm fiber-optic pressure transducer inserted into nucleus pulposus through a 22-gauge needle. The pressure was measured simultaneously in 2 adjacent discs during slow (0.03 mL/s) automated contrast injection into 1 of the discs up to 8 bar (116 psi). Ten adjacent discs were prefilled with contrast from previous discogram. A pressure increase 2 psi or more above baseline was defined as increased pressure in adjacent discs. Pressure was recorded until 15 minutes after injection. RESULTS: A total of 28 discograms were successfully performed. A pressure increase during injection was detected in 57% (16) of the 28 adjacent discs with mean 3.2 psi (1.7-8.2; standard deviation, 1.8), corresponding to a mean increase above baseline of 11%. Of those 16 adjacent discs, 4 were nondegenerate and 12 degenerate, of which 7 were prefilled. Fifteen minutes after injection, 89% of adjacent discs displayed increase in pressure of mean 14% above baseline. CONCLUSION: Discography induced pressure increase in adjacent discs in a degenerate disc model, something not reported earlier. If present, also in human spine pressure transmission, may be a potential cause for false positive discography responses.

Effect of lactoferrin peptide (PXL01) on rabbit digit mobility after flexor tendon repair.

PURPOSE: Restoration of digital function after flexor tendon injuries remains a clinical challenge. Complications such as adhesion formation and tendon rupture can lead to limited hand function. The aim of this study was to compare the effects of the lactoferrin-derived peptide, PXL01, formulated in sodium hyaluronate (SH), with SH alone on joint mobility as an indirect measure of postsurgical adhesion prevention and healing strength of the tendon and to elucidate the most optimal concentration of PXL01. METHODS: Using a rabbit flexor tendon repair model, in which the deep flexor tendon was fully transected and repaired, PXL01 in SH or SH alone was administered between the repaired tendon and the tendon sheath before closure of the surgical wound. Three concentrations of PXL01 in SH (5, 20, or 40 mg/mL) were compared to determine the lowest effective concentration. The repaired tendons were evaluated 7 weeks after surgery by measuring the proximal interphalangeal joint mobility by full range of flexion assessment and the tendon repair strength. RESULTS: Treatment with PXL01 formulated in SH resulted in improved mobility of the proximal interphalangeal joint with an average of 10°, corresponding to improvement of approximately 25% to 60% of the flexion of nonoperated toes at the different measuring points compared with SH alone. The difference was statistically significant in 5 out of 6 measuring points (0.5, 1, 2, 3, and 4 N; P < .05). The dose-response study indicated that the lowest effective concentration of PXL01 was 20 mg/mL. There was no difference in healing strength of the tendon between the groups as assessed by load-to-failure breaking strength. CONCLUSIONS: PXL01 in SH significantly improved the mobility compared with the carrier SH alone, without any negative effect on healing strength, and PXL01 at 20 mg/mL was the lowest effective concentration. CLINICAL RELEVANCE: The result provides a valuable basis for a clinical trial to assess efficacy and safety of PXL01 in clinical hand surgery.

Model for assessment of mobility of toes and healing of tendons in rabbits.

Repair of a transected flexor tendon will, despite careful technique and early rehabilitation, usually result in a restricted range of movement. This is mainly because adhesions form between the tendon and the surrounding structures. Our aim was to establish an experimental model in rabbits for future studies on new techniques to reduce the formation of adhesions after zone II repair of flexor tendons. In rabbits' hind paws the metatarsal bones II, IV, and V were removed and the flexor tendon was freed to the metatarsophalangeal (MTP) joint. The digits were secured in a specifically-designed biomechanical testing device comprising a servo-hydraulic actuator that was designed to apply controlled force or displacement. The tests were videotaped with a digital force-monitor behind the tested digit. Paper printouts from the recordings were obtained for 0, 0.5, 1, 2, 3, 4, and 5 Newton (N) and metatarsophalangeal, proximal interphalangeal, and distal interphalangeal, angles and distances between metatarsophalangeal joints and claws were measured. The tensile strength of the tendon was evaluated by a load-to-failure test. The continuous data obtained from the experiments were used to calculate functional stiffness at the selected forces. The model allows for unique continuous recordings of mobility of toes, thereby indirectly quantifying the presence of adhesions and the assessment of tensile strength. The data are reproducible, and there is little variation between the digits tested. The model is primarily intended to compare data among treated and non-treated digits of methods to limit the formation of adhesions after tendons have been repaired.

The immediate effect of repeated loading on the compressive strength of young porcine lumbar spine.

The human spine is exposed to repeated loading during daily activities and more extremely during sports. Despite this, there remains a lack of knowledge regarding the immediate effects on the spine due to this mode of loading. Age-specific spinal injury patterns has been demonstrated and this implies differences in reaction to load mode and load history The purpose of the present study was to investigate the impact of cyclic pre-loading on the biomechanical properties and fracture patterns of the adolescent spine in an experimental model. Eight functional spinal units from four young porcine spines were harvested. The functional spinal units were cyclic loaded with 20,000 cycles and then axially compressed to failure. The compression load at failure, ultimate stress and viscoelastic parameters were calculated. The functional spinal units were examined with plain radiography, computer tomography and MRI before and after the loading, and finally macroscopically and histologically. The median compression load at failure in this study was 8.3 kN (range 5.6-8.7 kN). The median deformation for all cases was 2.24 mm (range 2.30-2.7 mm) and stiffness was 3.45 N/mm (range 3.5-4.5 N/mm). A fracture was seen on radiograph in one case, on CT and macroscopically in seven, and on MRI and histologically in all eight cases. The cyclic loaded functional spinal units in the present study were not more sensitive to axial compression than non-cyclic loaded functional spinal units from young porcine. The endplate and the growth zone were the weakest part in the cyclic loaded functional spinal units. Disc signal reduction and disc height reduction was found on MRI. The E-modulus value found in this study was of the same order of magnitude as found by others using a porcine animal model.

Bulging of the inner and outer annulus during in vivo axial loading of normal and degenerated discs.

STUDY DESIGN: Comparison of in vivo biomechanical outcomes between experimental and control group animals. OBJECTIVE: To quantify the in vivo bulging response of the inner and outer annulus in animals with and without disc degeneration. SUMMARY OF BACKGROUND DATA: Prior attempts to quantify the load-deformation response of the inner annulus have most often relied on in vitro preparations. Unfortunately, to visualize the inner annulus, these in vitro approaches rely on disc modifications that may result in nonphysiologic behaviors. In response to this problem, in vivo techniques were developed to quantify regional bulging of the inner and outer annulus during applied axial loading. METHODS: Two groups of pigs were tested: a normal group and a group having disc degeneration that was induced surgically 3 months earlier. Eight adolescent pigs were evaluated and for each animal, a miniature servohydraulic actuator was attached to the third and fourth lumbar vertebrae to deliver a cyclic axial loading protocol (300 N, 1 Hz, 10 cycles) whereas regional deformations of the annulus were visualized ultrasonically via retroperitoneal access. RESULTS: For the normal animals, image analysis demonstrated a significantly greater bulging of the inner annular region when compared with the outer annular region. In animals with disc degeneration, the inner and outer annular regions were equal in their bulging response, which ranged from 0 bulging to 37% greater than the average response of the normal animals. CONCLUSIONS: This work supports prior in vitro studies that observed maximal disc bulging in the inner annulus and minimal bulging in the external annulus. Results for this in vivo study suggest that this normal bulging gradient is lost with degenerative disc disease. Compared with in vitro approaches, this new in vivo technique has the potential to demonstrate disc behavior in a variety of loading conditions and/or with a variety of induced disc pathologies.

Vertebral fractures and separations of endplates after traumatic loading of adolescent porcine spines with experimentally-induced disc degeneration.

BACKGROUND: Abnormalities of the intervertebral discs have been found in a high frequency among young elite athletes. Several studies have also reported that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. However, there is incomplete knowledge regarding the injury mechanism of the growing spine. In this study, the injury patterns of the adolescent porcine spine with disc degeneration were examined. METHODS: Twenty-four male pigs were used. A degenerative disc was created by drilling a hole through the cranial endplate of a lumbar vertebra into the disc. Two months later the animals were sacrificed and the degenerative functional spinal units (segments) were harvested. The segments were divided into three groups and exposed to axial compression, flexion compression or extension compression to failure. The load and angle at failure were measured for each group. The segments were examined with magnetic resonance imaging and plain radiography before and after the loading and finally examined macroscopically and histologically. FINDINGS: The degenerated segments required considerably more compressive load to failure than non-degenerated segments. Creating a flexion injury required significantly more load than an extension injury. Fractures and/or separations of the endplates from the vertebral bodies were seen at the margins of the endplates and in the growth zone. Only severe separations and fractures could be seen on plain radiography and magnetic resonance imaging. INTERPRETATION: The weakest part of the adolescent porcine lumbar spine with experimentally-induced degeneration, when loaded in axial compression, flexion compression or extension compression, was the growth zone, and, to a lesser extent, the endplate. Degenerated discs seem to withstand higher mechanical loads than non-degenerated discs, probably due to altered stress distribution.

Very high survival among patients defibrillated at an early stage after in-hospital ventricular fibrillation on wards with and without monitoring facilities.

BACKGROUND: The association between the interval between collapse and defibrillation and outcome is well described in out of hospital cardiac arrest but not as well in in-hospital cardiac arrest. We report the outcome among patients who suffered an in-hospital cardiac arrest and were found in ventricular fibrillation (VF) with the emphasis on the delay to defibrillation. METHODS AND RESULTS: In patients who suffered an in-hospital cardiac arrest at Sahlgrenska University Hospital in Göteborg between 1994 and 2002 there were 1.570 calls for the rescue team of which 71% had suffered a cardiac arrest. Among cardiac arrests 47% took place on monitored wards. The proportion of patients found in VF was 59% on wards with monitoring facilities and 45% on wards without (p<0.0001). Approximately 90% of these patients were defibrillated 12 min. On monitored wards, the survival was 63% if defibrillated 3 min after collapse (NS). The corresponding values for non-monitored wards were 72% and 35%, respectively (p=0.0003). Cerebral function among survivors at discharge appeared to be good among the majority of patients both in monitored and non monitored wards. CONCLUSION: If patients with in hospital VF were defibrillated early in both monitored and non monitored wards survival to hospital discharge was high. This highlights the importance of being prepared for the rapid defibrillation on wards without monitoring facilities.

Fracture patterns of the adolescent porcine spine: an experimental loading study in bending-compression.

STUDY DESIGN: To expose functional spinal units from adolescent porcine to mechanical flexion-compression and extension-compression to failure. The biomechanical, radiologic, magnetic resonance imaging, and histologic characteristics are described. OBJECTIVES: The aim of the present study was to investigate the fracture pattern of functional spinal units from adolescent porcine lumbar spines in in vitro compression loading and bending. SUMMARY OF BACKGROUND DATA: In several studies, it has been shown that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. A high frequency of abnormalities affecting the spine has been found among athletes participating in sports with high demands on the back. The etiology of these abnormalities is still a controversial issue. METHODS: Sixteen functional spinal units obtained from eight adolescent male pigs were used. Eight functional spinal units were exposed to flexion-compression and eight functional spinal units to extension-compression loading to failure. They were examined with plain radiography and magnetic resonance imaging before and after the loading. The functional spinal units were finally examined macroscopically and histologically. RESULTS: Fractures/separations were seen in the growth zone anteriorly and more frequently, posteriorly in functional spinal units exposed to flexion-compression. In the extension-compression group, such injuries occurred only anteriorly. Only large fractures could be seen on plain radiographs and on magnetic resonance imaging. Macroscopically, a fracture/separation could be seen in 15 cases and histologically in all 16 cases. The median angle at failure for the flexion group was 17 degrees (range, 12-19) and for the extension group 17 degrees (range, 13-19 degrees). The median ultimate compression load in the flexion-compression group was 1894 N (range, 1607-3138 N) and in the extension-compression group 1801 N (range, 1158-2368 N). CONCLUSIONS: The weakest part of the growing porcine lumbar spine, when compressed into flexion- or extension-compression, was the growth zone. The injury was more extensive in extension loading than during flexion loading. Growth zone injuries of the adolescent spine may go undetected on plain radiographs and magnetic resonance imaging.

Ankle arthrodesis using dowel bone graft and cancellous-bone screws: a mechanical study in cadavers.

BACKGROUND: There are numerous techniques for ankle arthrodesis. MATERIAL AND METHODS: We studied the stability of an ankle arthrodesis with the use of two cross-screws combined with dowel graft technique in 14 fresh-frozen ankles from amputees. The arthrodesis was performed by a dowel graft technique, in the coronal plane in 7 specimens (group 1) and in the diagonal plane in the remaining 7 (group 2). Allocation into the two groups took place after normalization according to the bone mineral content of the specimens. All ankles were fixed with two 6.5-mm diameter cancellous-bone screws, with the ankle in neutral position. Tibiotalar motion was measured during 5 Nm torque loading in plantar flexion-dorsiflexion, abduction-adduction and eversion-inversion planes of the ankle joint. Two testing sequences were performed and the mean value of both tests in each direction was used for the analysis. RESULTS: In all 3 planes, the torque applied caused more motion with the dowel graft in the coronal plane (group 1) than with the graft in the diagonal plane (group 2). The differences between the two groups were significant for abduction-adduction and eversion-inversion planes. Statistical analysis of differences between the first and second test showed significantly greater stiffness in group 2 than in group 1 in plantar flexion-dorsiflexion torque. INTERPRETATION: The placement of a dowel graft in the diagonal plane in comparison to the coronal plane significantly increased the initial stability of an ankle arthrodesis.

In vivo porcine intradiscal pressure as a function of external loading.

BACKGROUND: Spinal loading during daily activity as it relates to the ability of the intervertebral disc to sustain its integrity has been a major issue in spinal research. The purpose of this investigation was to establish the relationship between the intervertebral disc pressure in the nucleus and the load applied to the motion segment in an in vivo porcine model. METHODS: Nine domestic pigs were used in this study. A miniaturized servohydraulic testing machine was affixed to the lumbar spine via four intrapedicular screws, which were inserted bilaterally into the L2 and L3 vertebrae. A pressure needle was inserted through the lateral part of the L2-L3 disc annulus and into the nucleus pulposus. Force, deformation, and intradiscal pressure data were collected during a loading scheme that consisted of applying a set of constant loads in increasing order, that is, 50, 100, 150, 200, and 250 N. Each load was applied for 30 seconds followed by 30-second restitution. RESULTS: Intradiscal nucleus pressure was found to correlate to the applied load in all cases. Linear regression analyses resulted in the following equation: intradiscal pressure (MPa) = 0.08 + 1.25E(-3)(load, N), r(2) = 0.81, n = 8. Intradiscal pressure was also highly linearly dependent on the stress. The intrinsic intradiscal pressure was found to be 81 +/- 5 kPa. The results also indicated that the pressure within the disc exhibited a creep behavior. CONCLUSION: In conclusion, pressure in the nucleus of the porcine intervertebral disc was linearly related to the applied load and stress.

Experimental disc degeneration due to endplate injury.

The aim of this study was to create an experimental model of disc degeneration that closely mimicked human disc degeneration. In six domestic pigs, an L4 cranial endplate perforation into the nucleus pulposus was made. Three months postoperatively, compressive testing was performed on the L2-L4 motion segments, and intradiscal pressure was measured in the intervening discs. Histochemical and morphologic examinations were made on the excised degenerated and adjacent discs. A significant reduction in water content was observed in the outer anterior annulus of the degenerated disc. In the nucleus, the proteoglycan content was significantly reduced, as well as the cellularity, although not significantly. The nucleus lost its gel-like structure and was discolored, and there was delamination of annular layers. Intradiscal pressure in the nucleus was significantly lower in the degenerated disc. In conclusion, experimental degeneration of the intervertebral disc induced by endplate penetration resembled human disc degeneration, as exemplified by biochemical and structural changes.

32P-postlabeling of DNA adducts arising from complex mixtures: HPLC versus TLC separation applied to adducts from petroleum products.

The carcinogenicity of petroleum products is mainly due to their content of polycyclic aromatic compounds (PACs). These compounds may be activated metabolically and react with DNA to form DNA adducts, which is a critical event in the initiation of cancer. One of the most common techniques for analyzing DNA adducts is (32)P-postlabeling. The chromatographic method often used has been (32)P-TLC (thin-layer chromatography), but the more recently developed (32)P-HPLC (high-performance liquid chromatography) method has shown advantages. The aim of this study was to test the hypothesis that the (32)P-HPLC method has a better ability of detecting DNA adducts derived from petroleum products than (32)P-TLC. It was found that some DNA adducts migrated from the application point in (32)P-TLC in such a way that it is doubtful if they could be detected and quantified properly. It was also found that, when using (32)P-HPLC, it is possible to use the same protocol for substances with a wide variety of DNA adduct forming potential, whereas (32)P-TLC needs to be optimized regarding time of exposure and/or the amount of DNA applied. Further, a pattern of recognition in (32)P-HPLC enables a selective assessment of DNA adducts derived from complex mixtures whereas (32)P-TLC is very limited when analyzing complex mixtures due to poor resolution. With more knowledge about the properties of the most mutagenic DNA adducts in HPLC, it could be possible to know also which pattern corresponds to a mutagenic or carcinogenic oil. Consequently, (32)P-HPLC is a good alternative when assessing the genotoxicity of petroleum products.