Metabolic kinetics of p-aminobenzoic acid in rabbits

The metabolic kinetics of p-aminobenzoic acid (PABA) in rabbits was studied. PABA is predominantly metabolized by acetylation and glycine conjugation to form p-acetamidobenzoic acid (PAABA), p-aminohippuric acid (PAHA), and p-acetamidohippuric acid (PAAHA). After PABA IV administration (20 mg/kg) to rapid (n=16) and slow (n=8) acetylation rabbits, PABA was eliminated rapidly. The half-lives of PABA were 7.01+/-0.32 min in rapid acetylation rabbits and 7.08+/-0.78 min in slow acetylation rabbits. Significant differences were obtained in formation of PAABA and PAHA formed from PABA in both acetylation phenotype rabbits. The formation fraction of PAABA, formed by acetylation of PABA, was 0.8029+/-0.0267 in rapid acetylators and 0.2385+/-0.0428 in slow acetylators (p<0.001). PAHA formed from PABA was 0.0462+/-0.0102 in rapid acetylators and 0. 6652+/-0.0562 in slow acetylators (p<0.001). Only 0.0156+/-0.0030 of PABA could be detected as PAAHA in rapid acetylation rabbits which was obtained by acetylation of PAHA. After individual IV injection of PAHA, PAAHA, and PAABA to both phenotypes of rabbits, PAABA and PAAHA were eliminated in their unchanged forms whereas PAHA was further acetylated to form PAAHA. The formation fraction of PAAHA formed from the acetylation of PAHA was 0.4408+/-0.0570 in rapid acetylators and 0.0539+/-0.0084 in slow acetylators (p=0.002). From the results obtained, metabolic pathways of PABA show significant differences in both acetylation phenotypes of rabbits. Acetylation is the major metabolic route of PABA in rapid acetylation rabbits, while glycine conjugation is more predominant in slow acetylation rabbits.

Management of aggressive benign and malignant bone tumors of the shoulder region

BACKGROUND

The shoulder girdle is one of the most common sites of aggressive malignant and benign bone tumors. Curative resections and sparing of the limb are possible. However, reconstruction methods remain a challenge and the functional results vary.

METHODS

Fourteen patients with aggressive benign or malignant bone tumors about the shoulder girdle who were treated with surgical resection with possible need for reconstructions were retrospectively analyzed. There were 8 men and 6 women. Their ages ranged from 15 to 70 years; the mean age at operation was 36 years. Ten patients had malignant bone tumors and four had extensive giant-cell tumors. A variety of reconstructive procedures were performed after resection of the tumors. The choice of procedure depended on the type of resection and the needs of the patients. Supplementary chemotherapy or radiotherapy was undertaken after surgical procedures in 9 patients.

RESULTS

The length of follow up ranged from 16 months to 10 years. The functional results were described and graded quantitatively according to the functional rating system of the Musculoskeletal Tumor Society. Overall, 6 patients achieved excellent and good shoulder functions at follow-up examination, while 8 acquired fair or poor functional results. Four patients died from lung metastasis, while 10 survived and are disease free. Resection of the glenoid cavity and the proximal part of the humerus with loss of the abductor mechanism resulted in poor function of the shoulder.

CONCLUSION

The choice of treatment options depended upon the staging of tumors, the extent of resection, the needs of individual patients, the preservation and reconstruction of rotator cuff, the experience of surgeons, and the facilities at the hospital. The functional results were related to the area of involvement and the type of resection. The preservation of the abductor mechanism provided good functional results.

Video-assisted thoracoscopic surgery to the upper thoracic spine

BACKGROUND

The standard open technique for exposure of the upper thoracic spine, T1-T4, usually requires a difficult thoracotomy. From November 1, 1995 to June 30, 1997, eight patients underwent video-assisted thoracoscopic spinal surgery in our institute to treat their upper thoracic spinal lesions endoscopically.

METHODS

A new approach, the so-called "extended manipulating channel method," was used in this series that allows the combined use of video-assisted thoracoscopy and conventional spinal instruments to enter the chest cavity freely for the procedures. Patients' ages ranged from 44 to 89 years (average, 60 years). Definitive diagnoses included two pyogenic spondylitis and six spinal metastases. Five patients presented initially with myelopathy.

RESULTS

There were no deaths or neurologic injuries associated with this technique. The mean surgical time was 3.1 h. The mean duration of chest tube retention was 3.3 days. The mean total blood loss was 1,038 ml, and two patients had a blood loss of more than 2,000 ml owing to bleeding from epidural veins or raw osseous surfaces. Complications included one superficial wound infection and one subcutaneous emphysema that resolved spontaneously. In this series, there was no need of conversion to open thoracotomy for the patients.

CONCLUSIONS

The thoracoscopy-assisted spinal technique using the extended manipulating channels, usually 2.5-3.5 cm, allows variable instrument angulations for manipulation. The mean surgical time (3.1 h) was considered no longer than for an open technique for the equivalent anterior procedure. Such an approach can achieve less procedure-related trauma and has proved to be a good alternative to other treatment modalities.

Treatment of fibrous dysplasia involving the proximal femur

Twenty-two patients with fibrous dysplasia in the femoral neck or trochanteric area were treated with curettage and bone grafting with a sliding hip compression screw and plate. Follow-up ranged from 2 to 6 years (average: 4 years). Fourteen patients had monostotic and 8 had polyostotic disease. Four patients had pathologic fractures. Bone grafting included a deep-frozen allogeneic cortical strut and cancellous bone. After implanting the lag screw and cortical strut, the remaining defect space was filled with iliac bone. Postoperatively, all patients had good bone healing and complete incorporation of the implanted graft. There were no recurrences or complications, and functional results were rated as good and excellent.

Subtalar distractional realignment arthrodesis with wedge bone grafting and lateral decompression for calcaneal malunion

BACKGROUND

The purpose of this study was to evaluate prospectively the efficacy of subtalar distractional realignment arthrodesis in the treatment of calcaneal malunion associated with subtalar arthritis, collapse of height, talonavicular subluxation, malalignment of the heel axis, and widening heel with calcaneofibular abutment.

METHODS

Thirty-four patients with severe calcaneal malunion were treated with a lateral approach, lateral decompression, medial subtalar capsulotomy, and distraction and realignment of the subtalar joint with an anteriorly and laterally tapered wedge bone graft. The patients were evaluated with a functional rating scale and radiographs, both before and after surgery.

RESULTS

Thirty-two of the 34 patients were evaluated at a mean of 71 months (range, 60-92 months) after the arthrodesis. Solid subtalar fusion was achieved in 31 of the 32 patients. The average gain of subtalar distraction was 12 mm. Neutral or mild valgus alignment was achieved in 26 of the 32 patients. The mean postoperative score (83) showed significant improvement over the mean preoperative score (47). Overall, the functional rating scale revealed excellent or good results in 26 patients and fair results in 6 patients.

CONCLUSION

Coupled with wedge bone grafting, the subtalar distractional realignment arthrodesis achieved restoration of hindfoot height and axial alignment with a good union rate and significant improvement in the majority of patients with calcaneal malunion.

Semistructural allografting in bone defects after curettage

BACKGROUND AND OBJECTIVES

A variety of aggressive benign bone tumors often require wide bone and soft tissue excision for adequate local control, but this creates a large defect and a seriously weakened extremity. Restoration of limb function presents a difficult problem.

METHODS

The treatment of 104 patients with space occupying lesions of the long bone were analyzed. Deep-frozen (-70 degrees C) cortical strut allografts with or without allogeneic cancellous bone graft were implanted into the defects after extensive intralesional curettage. Thirty-six patients had fibrous dysplasias, 29 unicameral bone cysts, 22 giant cell tumors, 12 aneurysmal bone cysts, 3 benign fibrous histiocytomas, and 2 ossifying fibromas. Fifty-six patients had pathologic fracture. The average volume after curettage was 210 ml (range 60-460 ml). The average follow-up period was 50 months.

RESULTS

At follow-up evaluation, the radiographs demonstrated complete incorporation of the allogeneic implant and new bone formation in the cavity in 83% of the patients (86/104). All fractures healed. There was no local recurrence or fracture of the cortical graft; neither were there other serious complications except one avascular necrosis of the femoral head. Good or excellent functional results were found in 97% (101/104) of the patients.

CONCLUSIONS

For large osseous defects, the reconstructive technique using cortical stent allograft provides increased strength, easy fixation, remodeling of the cystic defect, and healing of the fracture and prevents deformity. However, remodeling occurs slowly and may never be complete.

Long-term continuous infusion of propofol as a means of sedation for patients in intensive care unit: relationship between dosage and serum concentration

BACKGROUND

We studied the effect of long-term continuous propofol infusion in patients who were utilizing mechanical ventilation in intensive care unit. The purpose of our study was to identify the appropriate dosage of propofol and to monitor the relating serum level that would provide satisfactory sedative and hypnotic effects to the patients, i.e., to procure a Ramsay Sedation Scale (RSS) value between 2 and 3.

METHODS

Ten mechanically ventilated ICU patients were studied. The syringe pump was set to deliver propofol at a rate of 1 mg/kg/h without an initial loading dose. After continuous infusion of propofol for 24 h, in each patient 5 ml of whole blood was sampled daily for one week. All samples were analyzed for serum level of propofol by high performance liquid chromatography.

RESULTS

When the Ramsay Sedation Scale (RSS) value was between 2 and 3, the mean dosage of infused propofol was 0.71 +/- 0.31 mg/kg/h (ranging from 0.58 to 1.27 mg/kg/h) and the mean plasma concentration was 0.58 +/- 0.22 microgram/ml (ranging from 0.20 to 0.86 microgram/ml). The lipid serum level was measured in three patients whose infusion duration was greater than 14 days. The respective level was 321 mg/dl, 139 mg/dl, and 99 mg/dl. The first patient died from multiple organ failure as a result of multiple trauma. Four patients simultaneously received infusion of propofol and muscle relaxant.

CONCLUSIONS

We concluded that propofol infusion given at a rate of 0.71 +/- 0.31 mg/kg/h and a plasma concentration level of less than 1 microgram/ml would be sufficient to produce a sedation with RSS value between 2 and 3.

Analysis of techniques for video-assisted thoracoscopic internal fixation of the spine

Between November 1, 1995, and January 31, 1996, four separate thoracoscopic spinal fixation surgeries were performed via extended manipulating channels using the so-called three-portal technique. The diagnoses included three spinal metastases and one T11 burst fracture. All patients had myelopathy at presentation. Using the three-portal technique, the conventional spinal instruments and fixation devices could be passed freely through the extended manipulating channels (usually 3-4 cm) into the chest cavity and manipulated by techniques similar to those used in standard open procedures. A reduction-fixation spinal plate with variable screw and plate anchoring angles was successfully inserted in the procedures. The total length of the operation ranged from 3.5 to 5 h (average 4.3 h), and the total blood loss was 1000-2500 ml (average 1500 ml). There were no intraoperative deaths, and no patient showed neurological deterioration following the procedures. On the basis of these results, we believe that the combination of video-assisted thoracoscopy and conventional spinal instruments presented in this report would be an ideal method for performing these procedures. Throughout the operation, only one trocar was employed for introducing the thoracoscope. The thoracoports were used temporarily during tumor tissue retrievals. This technique makes thoracoscopy-assisted spinal fixation simple and easy. It allows greater control of intraoperative vessel bleeding and reduces the number of portals required during the procedure (on average to 3). In addition, the technique reduced the amount of endoscopic materials required for the procedure, thus reducing the cost of treatment.

Preparation and characterization of heparin-containing SBS-g-DMAEMA copolymer membrane

The grafting of dimethyl amino ethyl methacrylate (DMAEMA) onto styrene-butadiene-styrene triblock copolymer (SBS) membrane was subsequently conducted by UV-radiation induced graft copolymerization without degassing to obtain the SBS-g-DMAEMA copolymer membrane. The substituted amino groups on the SBS-g-DMAEMA graft copolymer membrane were quaternized with iodomethane, and then the membrane was treated with heparin to prepare the heparin-containing SBS-g-DMAEMA copolymer membrane (SBS-g-DMAEMA-HEP). The graft copolymer membrane (SBS-g-DMAEMA) and the heparin-containing SBS-g-DMAEMA copolymer membrane (SBS-g-DMAEMA-HEP) were characterized by FTIR spectroscopy. The heparin content was determined by toluidine blue heparin assay. Contact angle, water content, and protein adsorption of fibrinogen and albumin experiments were also performed to evaluate the effect of graft amount and heparin content on the biocompatibility of SBS-g-DMAEMA and SBS-g-DMAEMA-HEP graft copolymer membranes. By using Kaelble's equation, the surface tension of SBS-g-DMAEMA and SBS-g-DMAEMA-HEP were determined. It was found that with increasing grafting amount and the heparin content, the surface tension and water content of SBS-g-DMAEMA membrane increased, whereas the contact angle decreased. The amount of the adsorption of albumin and fibrinogen decreased with increasing graft amount and heparin content. However, there was a minimum for adsorption of proteins in the SBS-g-DMAEMA and SBS-g-DMAEMA-HEP membranes.

Video-assisted thoracoscopic treatment of spinal lesions in the thoracolumbar junction

BACKGROUND

The endoscopic treatment of spinal lesions in the thoracolumbar junction (T11-L2) poses a great challenge to the surgeon. From November 1, 1995 to December 31, 1996, we successfully used a combination of video-assisted thoracoscopy and conventional spinal instruments to treat 38 patients with anterior spinal lesions. Twelve of them had lesions in the thoracolumbar junction.

METHODS

The so-called extended manipulating channel method was used to perform vertebral biopsy, discectomy, decompressive corpectomy, interbody fusions, and/or internal fixations in these patients. The size of the thoracoscopic portals was greater than usual in order to allow conventional spinal instruments and a thoracoscope to enter the chest cavity freely and be manipulated by techniques similar to those used in standard open surgical procedures. In this series, the procedures were performed by using either a three-portal approach (2. 5-3.5 cm) or a modified two-portal technique involving a 5-6 cm larger incision and a small one for introducing the scope.

RESULTS

None of the operations resulted in injury to the great vessels, internal organs, or spinal cord. The total time for the operation ranged from 1.5 to 4.5 h (average, 3); and the total blood loss ranged from 50 to 3000 cc (average, 1050). One patient was converted to an open procedure due to severe pleural adhesion. Complications included two instances of transient intercostal neuralgia, one superfical wound infection, and one residual pneumothorax.

CONCLUSIONS

The video-assisted technique with the extended manipulating channel method presented in this report simplifies thoracoscopic spinal surgery in the thoracolumbar junction and makes it easier. It avoids division of the diaphragm, removal of the rib, and wide spread of the intercostal space, and it allows greater control of intraoperative vessel bleeding. Using this technique, the number of portals required during the procedure can be reduced. In addition, the technique reduces the endoscopic materials required, thus lowering overall cost. It is an effective and promising approach.

Low-flow anesthesia in adult orthotopic liver transplantation: a preliminary clinical experience

BACKGROUND

Anesthesia in orthotopic liver transplantation (OLT) may carry with complex hemodynamic, body temperature, and metabolic alterations. Although OLT cases increased in recent years in Taiwan, experiences remained limited. Notable advantage of low flow anesthesia may include reduced consumption of anesthetic gases and vapors, reduced environmental pollution and cost-saving. This study investigated patient profiles and the feasibility of low-flow rebreathing technique for adult orthotopic liver transplantation.

METHODS

Since June 1996, there were six OLT patients who received low flow anesthesia with isoflurane. All patients received hepatic veno-venal anastmosis (so-called piggy back procedure). Two patients were excluded from this study because of different surgical procedure (total occlusion of inferior vena cava and inferior vena cava veno-venal anastmosis). During maintenance of anesthesia, isoflurane was carried by a mixture of oxygen and air at a total fresh gas flow of 0.6 L/min. Alongside with the standard anesthesia machine and physiologic monitors, a newly designed Swan-Ganz catheter was introduced to measure and record cardiac output, systemic vascular resistance, pulmonary artery pressure, central venous pressure, and core temperature in a real-time manner. Blood samples were collected at 6 predetermined time-points in each patient for analysis of arterial blood gases, electrolytes, lactate and glucose concentrations.

RESULTS

The anesthetic time was 916 +/- 26 min (900 to 930 min). All patients regained their consciousness within 30 min after completion of surgery. The hemodynamics were relatively stable except after reperfusion of the liver. There was a significant decrease in mean arterial blood pressure, which occurred with accompaniment of a reduction of systemic vascular resistance and increased cardiac output. Arterial blood gas, electrolyte, and glucose were, however, maintained within acceptable limits. Blood lactate was progressively increased and reached its peak after reperfusion of the liver until the end of surgery. The core temperature was well maintained above 34 degrees C. No patient developed hypoxia or hypercapnia.

CONCLUSIONS

Low-flow rebreathing anesthetic technique maintained acceptable patient profiles and good body temperature preservation in orthotopic liver transplantation. These characteristics make it a promising method in maintenance of anesthesia for OLT.

Propofol anesthesia in a patient with Isaacs syndrome--report of a case and literature review

Isaacs syndrome is an unusual lower motor neuron disease characterized by myokymia (muscle twitching), muscular stiffness, and decreased tendon reflexes. We reported a patient who was affected with this rare disease, with manifestation of involuntary muscular contractions and required general anesthesia for bilateral tonsillectomies. Understanding the presentation and characterization of this unusual disease may be helpful in making choice of anesthetics or anesthetic techniques. Its possible mechanisms of action and its specific considerations in anesthesia in the literature are reviewed and discussed.

Allogeneic cortical strut for benign lesions of the humerus in adolescents

Allogeneic cortical strut associated with or without cancellous bone grafting for benign adolescent humeral shaft lesions is an alternative management option offering a good chance of stabilization and healing. This study monitored 16 patients who had been treated with this surgical method from 1988 to 1993. There were nine boys and seven girls between the ages of 11 and 16 years (average, 14). Eleven patients had unicameral bone cysts; two had aneurysmal bone cysts; and three had fibrous dysplasia. All 16 patients received fresh-frozen (-70 degrees C) cortical strut inlay grafts in the humeral shaft defect after subtotal excision of the large lesions. No intramedullary rod or plate was used. The follow-up period ranged from 26 to 58 months (average, 41). There were no local recurrences or fractures of the shaft or allograft implants. The radiographs of all humeri revealed the cortical grafts to be well incorporated with new bone formation in the cavity. The overall functional results were good and excellent. This reconstruction with biologically safe and active material provided increased strength and prevented refracture.

A dose-dependent pharmacokinetic study on caffeic acid in rabbits after intravenous administration

The dose-dependent pharmacokinetics of caffeic acid (CA) were studied in rabbits. Three different doses (5, 10, and 25 mg kg-1) were administered intravenously to six rabbits each. The concentration-time profiles for CA could be fitted by a two-compartment model for each dose. The results showed that total-body clearance and elimination rate constant from the central compartment (k10) after a 5 mg kg-1 dose were greater than those after the other two doses. Furthermore, the terminal elimination half-life (beta half-life) and mean residence time (MRT) after a 5 mg kg-1 dose were less than after the other doses. The AUC value increased linearly with dose within the range of 10-25 mg kg-1. Most of the unchanged caffeic acid was excreted in the urine within 2 h. The percentage of unchanged caffeic acid excreted in the urine was 63.4, 60.0, and 55.4% after doses of 5, 10, and 25 mg kg-1, respectively, which was not significantly different. However, significant differences in the renal clearances and renal excretion rate constants were observed with a 5 mg kg-1 dose compared to the other doses. On the other hand, nonrenal clearances and nonrenal excretion rate constants showed no dose-related differences. The differences observed in total-body clearance, k10, beta half-life, and MRT between a 5 mg kg-1 dose and the other doses can be explained on the basis of the differences in renal clearance and renal excretion rate constants.

Total knee arthroplasty in a rheumatoid arthritic knee with large geode: a case report

Geodes (subchondral cysts) are a well-known manifestation of rheumatoid arthritis. Solitary cysts or cysts larger than 2 cm are not generally found in the knee joint of patients with rheumatoid arthritis (RA). We report a case of RA involving both knees with a giant geode over the right proximal tibia. Surgical treatment was performed including synovectomy, cyst enucleation and packing of autogenous bone chips followed by primary total knee arthroplasty. The postsurgical result was excellent with the knee restored to good function and complete healing of the cystic lesion.

Preparation and properties of SBS-g-DMAEMA copolymer membrane by ultraviolet radiation

A styrene-butadiene-styrene triblock copolymer (SBS) membrane was prepared by solvent casting. Grafting of dimethyl amino ethyl methacrylate (DMAEMA) to this SBS membrane was subsequently conducted by ultraviolet radiation-induced graft copolymerization without degassing to obtain a SBS-g-DMAEMA copolymer membrane. The graft copolymer was characterized by infrared spectroscopy and scanning electron microscopy. The degree of grafting and the mechanical properties of SBS and SBS-g-DMAEMA were measured. Contact angle, water content, and protein absorption of fibrinogen and albumin experiments were also performed to evaluate the biocompatibility of SBS-g-DMAEMA graft copolymer membranes. It was found that the degree of grafting was related to the irradiation time, DMAEMA concentration, and temperature. The tensile strength of the SBS-g-DMAEMA membrane increased with an increase in the degree of grafting. By using Kaelble's equation and the contact angle data, the surface tension of SBS-g-DMAEMA was determined. It was found that with an increase in the degree of grafting, the surface tension and water content of SBS-g-DMAEMA membrane increased, whereas the contact angle decreased. The amount of absorption of albumin and fibrinogen decreased with an increase in amount of grafting. However, there was a minimum for the adsorption of proteins in the SBS-g-DMAEMA membrane.

Distal chevron osteotomy with intra-articular lateral soft-tissue release for treatment of moderate to severe hallux valgus deformity

We retrospectively reviewed the results of 32 patients (38 feet), with hallux valgus angles between 35 degrees and 60 degrees, who were treated by standard distal chevron osteotomy and intra-articular lateral soft tissue release. The average follow-up period was 5.2 years (4-7 years). The preoperative intermetatarsal angle averaged 14.4 degrees, and the postoperative angle averaged 7.7 degrees. The preoperative hallux valgus angle averaged 42.7 degrees, and the postoperative angle averaged 18.8 degrees. Subjectively, the satisfaction rate in terms of symptom improvement, cosmetic appearance and function was over 90%. Avascular necrosis of the first metatarsal head was not found in our series, which indicated that additional lateral soft tissue release is not contraindicated in combination with chevron osteotomy. Based on the level of satisfaction in our series, we conclude that the combination of distal chevron osteotomy and intraarticular lateral soft tissue release has broader application than the chevron osteotomy alone for patients with hallux valgus deformity.

Ankle arthrodesis with cross screw fixation. Good results in 36/40 cases followed 3-7 years

Tibiotalar arthrodesis by an anterior approach, using internal compression with cancellous crews, offers wide exposure, good possibilities of correcting deformities, and good bony apposition. From 1987 to 1991, we used this technique in 42 ankle joints (40 patients). The indications were posttraumatic arthrosis, sequelae of septic arthritis, necrosis of the talus and failed ankle arthrodesis. In 13 ankles with severe deformity, a bone graft was also used. 38 patients (40 ankle joints) were available for follow-up after 4 (3-7) years. Solid union was achieved in 38 ankles after an average of 13 weeks. The clinical result was good-to-excellent in 36 ankles. We conclude tha this is a simple and effective method for ankle arthrodesis in both low-risk and, coupled with bone grafting, in properly selected high-risk patients.

Contradirectional two-wave mixing with partially coherent waves in photorefractive crystals

We investigate contradirectional two-wave mixing with partially coherent waves in photorefractive crystals in the nondepleted pump regime. Equations governing the propagation of the self-coherence function and the mutual-coherence function of the signal wave and the pump wave are derived and simulated numerically. Numerical solutions of these equations are in excellent agreement with the experimental measurements.

Anatomic position of a herniated nucleus pulposus predicts the outcome of lumbar discectomy

The purpose of this study was to determine whether the anatomic position of a lumbar disc herniation has any significant effect on the clinical outcome of lumbar discectomy. Between January 1988 and March 1993, 80 patients with simple disc herniations underwent lumbar discectomy for herniated nucleus pulposus. We reviewed preoperative computed tomography scans after discography and magnetic resonance imaging of the lumbar spine. Disc herniations were classified as central, paracentral, intraforaminal, extraforaminal, or multiregional broad-based protrusions. The Smiley-Webster evaluation scale, which divided patients into groups with excellent, good, fair, and poor clinical outcome and evaluated the long-term need for pain medication, was applied. The post-operative evaluation period ranged from 6 to 48 months. The clinical outcome was then correlated with the different positions of herniations. The frequencies of the clinical outcomes were compared using the chi 2 test. We found a poorer clinical outcome that was statistically significant in patients with central herniations and with multiregional protrusions. Most herniations occurred at the L4-L5 level (58.7%). However, the level of disc herniation was not found to be a predictor of clinical outcome. Form and anatomic position of the lumbar disc herniation are of prognostic value for the outcome of lumbar discectomy. Further studies are required to confirm our preliminary results and eventually help improve surgical indications for lumbar discectomy.

Determination of p-aminobenzoic acid and its metabolites in rabbit plasma by high-performance liquid chromatography with fluorescence detection

A simple, accurate and sensitive high-performance liquid chromatographic method with fluorescence detection was used for measuring plasma concentrations of p-aminobenzoic acid (PABA) and its three metabolites: p-acetaminobenzoic acid (PAABA), p-aminohippuric acid (PAHA) and p-acetaminohippuric acid (PAAHA). A Cosmosil MS-C18 column (250 x 4.6 mm, 5 microns) was used under temperature control at 40 degrees C. The mobile phase was H2O-CH3CN-CH3COOH (100:3:1, pH 4.0) with a flow-rate of 1.5 ml/min. The excitation and emission wavelengths for fluorescence detection were set at 270 and 350 nm, respectively. Plasma samples (200 microliters) were acidified by the addition of 150 microliters of 1 m HClO4 solution containing salicylic acid (SA) as the internal standard. After centrifugation, 30 microliters of the supernatant were injected onto the column. Using this method, PABA and its three metabolites could be determined within 25 min. Within the investigated concentration ranges of PABA (0.1-50 micrograms/ml), PAABA (0.2-50 micrograms/ml), PAHA (0.1-50 micrograms/ml) and PAAHA (0.5-50 micrograms /ml), good linearity (r > 0.99) for the standard curves was obtained. The validation of this method showed coefficient of variance (C.V.) that was well below 15% for all compounds. After intravenous (i.v.) administration of PABA (20 mg/kg) to rabbits (n = 7), PABA followed a one-compartment open model elimination with a half-life of 10.90 +/- 1.03 min. The mean half lives for PAABA, PAHA and PAAHA were 24.61 +/- 6.42, 12.81 +/- 6.04 and 11.27 +/- 2.77 min, respectively.

Comparison of "inside-out" and "outside-in" interference screw fixation for anterior cruciate ligament surgery in a bovine knee

Despite numerous advances in graft fixation with anterior cruciate ligament (ACL) reconstruction, few studies have compared the fixation strength of interference screws placed "outside-in" and from "inside-out" techniques. To compare techniques, a bovine model was designed to fail at the femoral tunnel bone-screw interface. Twenty-four fresh bovine knees were stripped of all soft tissues except the ACL. The native ACL was loaded the failure at a strain rate of 50 cm/min with the knee flexed 45 degrees. One standardized femoral tunnel was created on all specimens. A 3/32-inch guide pin was drilled into the center of the ACL femoral origin and overreamed with an 11-mm reamer from inside-out until the lateral cortex was reamed. Consistently sized patellar bone blocks were created (8 x 5 x 25 mm) with an 8-mm tendon width. The bone blocks were randomized to an "inside-out" (group 1) and "outside-in" (group 2) technique. Bone blocks were secured with a 7 x 25 interference screw. Specimens were mounted with the femoral tunnel and bone block aligned parallel to the tensile force and strained to failure at 50 cm/min. Failure of the native bovine ACL occurred at a mean of 2,304 N (SD +/- 472 N; n = 24). The mode of failure for group 1 was 9 of 13 at the bone-screw interface and 4 of 13 interligamentous failures. The mode of failure for group 2 was 7 of 11 at the bone-screw interface, 3 of 11 interligamentous, and 1 bone block failure. The mean load to failure for group 1 was 1,151 N (SD +/- 320 N, n = 13) including the four ligamentous failures and 1,143 N (SD +/- 306 N, n = 9) excluding the ligamentous failures. The mean load to failure for group 2 was 1,017 N (SD +/- 262 N, n = 11), including all specimens and 843 N (SD +/- 262 N, n = 7) excluding the interligamentous and bone block failure specimens. The "inside-out" technique averaged 100 N greater fixation strength than the "outside-in" technique. Statistical analysis using two-sample Student's t-test showed no statistically significant differences between group 1 and group 2. Both techniques demonstrate comparable maximum load to failure in a bovine model tested at 50 cm/min.

Determination of caffeic acid in rabbit plasma by high-performance liquid chromatography

A simple and sensitive high-performance liquid chromatographic method involving UV detection was developed for determination of caffeic acid in rabbit plasma. A Lichrosphere CN column (250 mm x 4 mm I.D., 5 microns) was used as the stationary phase and the mobile phase consisted of 2% acetic acid solution at a flow-rate of 1.0 ml/min. The UV absorbance was monitored at 320 nm. The plasma sample was acidified by the addition of 0.01 parts of concentrated phosphoric acid (85%) to maintain caffeic acid stability. After a simple clean-up procedure, the limit of quantitation achieved was 0.1 micrograms/ml, and the standard curve was found to be linear over the concentration ranges of 0.1-2.0 micrograms/ml and 0.1-40 micrograms/ml. The coefficient of variation for within- and between-run precision and accuracy was less than 10%, and the recovery was 82.3%.

Instrumented laparoscopic spinal fusion. Preliminary Results

STUDY DESIGN

Seventeen consecutive patients underwent laparoscopic instrumented interbody fusions using custom-designed delivery instrumentation and "BAK" fusion cages; both are manufactured by Spinetech and the former was developed by the authors. The cases were performed at two spine centers under Food and Drug Administration investigational device evaluation clinical trials.

OBJECTIVES

We expect this approach will maintain a high fusion rate with diminished hospitalization time, recovery time, patient discomfort, and expense. The rehabilitative aspects of the procedure are a great improvement over traditional fusion approaches.

SUMMARY AND BACKGROUND DATA

Extraordinary advances in many endoscopic surgical fields have resulted in many endoscopic surgical fields have resulted in lowered morbidity, expense, and suffering associated with their open surgery counterparts. The authors have developed prototype of delivery instruments for the current laparoscopic fusion cage delivery system.

METHODS

The procedure is performed transperitoneally with carbon dioxide insufflation to enable video-assisted visualization through a 10-mm endoscope. Three 10-mm incisions and one 13- to 20-mm incision are required for one-level procedures. Two hollow titanium-threaded interbody implants are packed with autologous bone and inserted into the diseased interspace.

RESULTS

Seventeen patients, with an average follow-up period of 8 months and a range of 6-12 months, underwent the procedure. There were 14 single-level fusions and three two-level fusions, all involving L4-S1 levels. There were two cases that required conversion to open procedures without sequelae; two patients had remote donor site wound infections eradicated with incision and drainage and antibiotics, and one patient required subsequent posterior spinal decompression because of a displaced endplate fracture. Average hospital stay was an average of 2 days, excluding two patients with complications and very prolonged stay.

CONCLUSIONS

Although this procedure is associated with a long learning curve, the technique, once mastered, is effective and advantageous over current approaches to lumbar fusion. Operative time and hospital stay are expected to decrease with future instrumentation development and surgeon experience.