Thermally induced conformational changes of Ca-arachidate Langmuir-Blodgett Films at different compression.

The conformational order in Ca-arachidate Langmuir-Blodgett films on solid glass supports is investigated by means of vibrational sum-frequency generation spectroscopy (VSFG). The symmetric C-H stretching vibrations of both the terminal methyl and the methylene groups are utilized to monitor the chain conformation at various sample temperatures under ambient conditions. At room temperature the film is well-ordered consisting almost entirely of all-trans configured chains. Between 340 and 430 K we observe a marked increase in gauche-defects before oxidative degeneration starts at sample temperatures above 470 K. The temperature dependence of the data is well represented by apparent enthalpy changes for the formation of gauche-defects, sharply increasing with packing density from 29 to 62 kJ/mol; values, which are an order of magnitude larger than those of the gas phase molecule. These large apparent enthalpies do not prevent the formation of a high degree of conformational disorder at elevated temperatures.

Posterior lumbar interbody fusion using rhBMP-2.

The use of biological technologies for the treatment of degenerative spinal diseases has undergone rapid clinical and scientific development. BMP strategies have gained wide support for an inherent potential to improve the ossification process. It has been extensively studied in combination with various techniques for spinal stabilisation from both anterior and posterior approach. We studied the fusion process after implantation of rhBMP-2 in 17 patients with degenerative lumbar spine diseases in combination with dorsal fixation with pedicle screws and poly-ether-ether-ketone (PEEK) interbody cages. We used 12 mg rhBMP-2 carried by collagen sponge, 6 mg in every cage. Patient follow up consisted of pre-operative radiographic and clinical evaluation. Similar post-operative evaluations were performed at 3 and 6 months. Clinical assessment demonstrated clear improvement in all patients despite evidence of vertebral endplate osteoclastic activity in the 3-month radiographs. The 6-month radiograph, however, confirmed evidence of fusion, and no untoward results or outcomes were noted. While previous studies have shown exclusively positive results in both fusion rates and process, our study demonstrated an intermediate morphology at 3 months during the ossification process using Induct Os in combination with peek-cages using a PLIF-technique. The transient resorption of bone surrounding the peek cage did not result in subsidence, pain or complication, and fusion was reached in all cases within a 6-month-controlled evaluation. Although there was no negative influence on clinical outcome, the potential for osteoclastic or metabolic resorption bears watching during the post-surgical follow up.

Retraction Notice: Lack of Relationship Between Occupational Workload and Microscopic Alterations in Lumbar Intervertebral Disc Disease.

[This retracts the article on p. 242 in vol. 8.].

Electromyographic investigation on handling forces of mechanically counterbalanced and sensor-servomotor-supported surgical microscopes.

BACKGROUND: Recent developments in sensor-servomotor-driven microscopes again initiated a discussion on the value of such technology for practical use in neurosurgery. The need for less force in moving a motor-supported microscope is advantageous. However, questions remain if well-known difficulties in the past such as resonance phenomenon, loss of natural feeling, and unequal handling forces in different situations have been overcome by the new generation of sensor-servo-supported surgical microscopes. METHODS: Handling forces of a mechanically counterbalanced neurosurgical microscope (Zeiss NC4, Zeiss, Oberkochen, Germany) were compared with those of a sensor-servo-supported neurosurgical microscope (Moeller HiR 20-1000, Moeller, Wedel, Germany). Handling forces were correlated with the surface electromyogram measurement of the muscle activity of 4 neurosurgeons. The activity of the forearm muscles was measured while handling the 2 different microscopes in standardized tests. RESULTS: The electrophysiologic measurement revealed that significantly less muscle activity was required to handle the sensor-servo-driven microscope in all directions. The untrained surgeons profited less than the skilled ones. Differences were most evident with disbalanced microscopes. CONCLUSIONS: With this technology, the neurosurgeons exerted less effort, especially in strenuous test situations where the single-handed use of the microscope was mandatory. The reduced muscle forces that move the sensor-servo-type microscope and the continuously balanced state that might help prevent unwanted correction movements will ease intraoperative handling in general.

Lack of relationship between occupational workload and microscopic alterations in lumbar intervertebral disc disease.

OBJECTIVES: The study investigated the impact of occupational workloads on disc surgery specimens. We report the relationship between workload and histological features. METHODS: Specimens were collected prospectively from patients suffering from lumbar disc prolapse (n=90) or spinal osteochondrosis (n=19). Histomorphology and occupational workload data and histomorphological features were evaluated. Occupational data were collected in a structured, standardized patient interview assessing lifting and carrying loads. In this way the exposure was assessed for each test subject's entire working life up to surgery. RESULTS: There was no association between cumulative workload and histological patterns. In a subgroup of patients with a workload period of 12 months prior to surgery a relevant formation of chondrocyte clusters (p=0.055) was apparent. Chondrocyte cluster formation was found in 83% (n=74) of the prolapse patients and in 58% (n=11) of the osteochondrosis patients (p=0.02). Fibrocyte mediated scar formation was found in 55% of the prolapse patients and in 45% of the spinal stenosis patients. Chondrocyte clusters and their de novo collagen matrix did not integrate biomechanically sufficient with collagen fibers of the disc. Disintegration of clusters from disc matrix and formation of intra-discal sequesters were observed. CONCLUSION: Matrix degeneration was common but displayed no relationship to occupational workload or other histological features. Scar formation was observed in every second specimen. Regenerative chondrocyte cluster proliferation was a common feature in disc specimens and tended to be associated in patients with a workload one year before surgery.

Vertebral osteoporosis: perfused animal cadaver model for testing new vertebroplastic agents.

STUDY DESIGN: Experimental study. OBJECTIVE: It was aimed to establish a cadaver model to imitate osteoporotic perfused vertebral bone and to allow for transpedicular transfer of bone cement and various new materials into vertebrae. The model was perfused to simulate vertebroplasty in the presence of transvertebral blood flow. SUMMARY OF BACKGROUND DATA: The injection of bone cement into vertebrae bears the risk of irreversible discharge of material into the venous system of the spinal canal. The bovine cadaver model studied allows visual studies of material distribution in a vertebral bone, the potential spill-out of material, and quantification of washout and disintegration phenomena. METHODS: Thoracic and lumbar vertebrae from 1-year-old calves were cut transversally into 5 mm slices, macerated, and decalcified. The softened bone slices were compressed between 2 transparent plastic discs. A standard vertebroplasty cannula (outer diameter 3.5 mm, inner diameter 2.5 mm) was inserted into the vertebral body via the pedicle to transfer the different vertebroplasty materials. Arterial blood flow was simulated by means of liquid irrigation via 2 needles in the ventral part of the vertebral body slice. Metal powder was mixed with the solution to indicate the blood flow in the bone. The model was evaluated with the vertebroplasty cement polymethylmethacrylate. RESULTS: The model permitted visualization of the insertion and distribution of vertebroplasty materials. Liquid bone cement was effused into the spinal canal as in the clinical situation. Higher modulus cement acted in the same way as in clinical vertebroplasty. Rigid vertebroplasty agents led to trabecular fractures and stable mechanical interactions with the bone and eventually moved dorsal bone fragments into the spinal canal. Sedimentation of the metal powder indicated regions of perfusion. CONCLUSION: The model simulated the clinical behavior of liquid and higher modulus vertebroplasty agents in the presence of blood flow. It enabled safe ex vivo testing of the mechanical and physical properties of alternative vertebroplasty materials under flow conditions.