Facet forces, longitudinal ligament loads, and vertebral body motion were experimentally measured in five fresh human lumbar spine segments, L1-L2. Strain gages on the bone surface were used to quantify facet loads. Buckle transducers were used to measure anterior and posterior longitudinal ligament loads. The three-dimensional motion of the motion segment was measured with an instrumented spatial linkage. The facets were found to carry no load in flexion, large loads during extension (205 N at a 10 Nm moment and a 190 N axial load), torsion (65 N at a 10 Nm moment and a 150 N axial load), and lateral bending (78 N at a 3 Nm moment and a 160 N axial load). The facet contact site on the inferior articular process of L1 was found to move inferiorly to a position of tip impingement near the lamina as extension moments increased. Impingement occurred in the range of 4-6 Nm extension. The posterior and anterior longitudinal ligaments were predominantly loaded in flexion and extension, respectively. No ligament loads occurred in lateral bending and torsion. A 1 cm strip of the anterior longitudinal ligament carried loads up to 130 N at the largest extension moment of 11.4 Nm. The posterior longitudinal ligament had a 60 N load at the largest flexion moment of 7.1 Nm. There was no pre-load in the ligament detectable with the buckle transducers (> 4 N). The facets and ligaments began carrying load immediately with applied load, without a lax region. The experimental technique developed and used provides a good tool for obtaining simultaneous facet joint loads, ligament loads, and vertebral body motion without altering the motion segment.

Adult↗

PubMedDate not supplied

Initial experience of a nephrologist-operated vascular access center.

A nephrology practice in Alabama did not feel in control of vascular access management. Scheduling delays, as well as variable techniques and outcomes, leading to high morbidity and mortality, caused frustration with the existing care system for vascular access. Our objective was to develop an integrative system of vascular access care, involving nephrologists along with the other caregivers, and to demonstrate an improvement in outcomes. Nephrology Vascular Labs (NVL), a recent RMS-Lifeline acquisition, opened a vascular access center (VAC) as an extension of the nephrology practice. Both pre-ESRD and ESRD patients are evaluated and treated in the VAC. Treatment is rendered in a timely fashion, to the benefit of the patients. Nephrologists serve as the interventionists. More than 90% of vascular access problems detected at dialysis are treated at the VAC. More than 2000 procedures have been performed over 2 years. Procedures carried out include thrombolysis with angioplasty, fluoroscopy alone or with angioplasty, placement of cuffed and noncuffed catheters, removal of cuffed catheters, and minor surgeries. Success rates have been high. Minor and major complications have been relatively low. Referrals to both surgeons and radiologists are shown to emphasize the role of the VAC as part of an integrative system of vascular access care. Results of a patient satisfaction survey were excellent. The VAC has fulfilled the vision of creating a seamless integration of care for vascular access. Hospitalization rate has been reduced and it is suspected that the global cost of access care is markedly lower than prior to the VAC. Multiple nephrologists can rotate as the VAC's interventionist and jointly obtain good outcomes and have little variability among them. Several reasons for using a nephrologists as the interventionist are discussed.

Alabama↗

PubMedDate not supplied

Load sharing and graft forces in anterior cruciate ligament reconstructions with the Ligament Augmentation Device.

Buckle transducers were used to directly measure load sharing and overall force in three segment (semitendinosus, gracilis, Ligament Augmentation Device) and two segment (patellar tendon, LAD) composite ACL grafts during the application of anteriorly directed loads to a series of five fresh knee specimens with a pneumatic load apparatus. The total graft forces generated in the two segment and three segment composite reconstructions during this immediate postoperative state were highly variable when compared to the normal ACL in each specimen, and were irreproducible among the five specimens. Load sharing among the graft components occurred and was also variable in both reconstructions, with this variation being greater in the three segment graft. The LAD carried an average of 45% of the total graft force in the three segment graft and 28% in the two segment graft. Further work is required to clarify the source of the variability in the total graft force and load sharing observed in this study.

Biomechanical Phenomena↗

PubMedDate not supplied

Graft force-setting technique in reconstruction of the anterior cruciate ligament.

The objective of this work was to present a method for controlling the mechanical state of the knee during graft fixation in an ACL reconstruction; that is, adjusting the unloaded length of the graft at the time of fixation so that the force-carrying characteristics of the graft match that of the intact ACL, when the normal and reconstructed knees are subjected to the same external load. To demonstrate the new method, an experimental knee testing system was used to measure ligament and graft forces with buckle transducers, as external loads were applied to five fresh knee specimens with a pneumatic load apparatus. ACL and collateral ligament force data were collected as anteriorly directed loads of 90 N (20 pounds) were applied at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion in the normal intact knee and the same knee following ACL excision. A composite graft was prepared, consisting of distally based semitendinosus and gracilis autogenous tissue augmented with the Kennedy Ligament Augmentation Device. Femoral fixation was obtained using a fixation plug that was inserted through the lateral femoral condyle. With a 90 N anterior tibial load applied at 30 degrees of flexion and a single buckle transducer measuring the total composite graft force, the graft length was varied using the fixation plug until the force matched that seen by the intact ACL under the same loading condition. The graft was then clamped in the fixation plug and the anterior load sequence at the four flexion angles was applied to this reconstructed knee state.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMedDate not supplied

The effect of an iliotibial tenodesis on intraarticular graft forces and knee joint motion.

Lateral extraarticular reconstructions are used as isolated procedures in knees with moderate rotatory instability and as "backups" in knees requiring primary repair or intraarticular reconstruction for major rotatory instability. We used an experimental knee testing system to analyze the immediate postoperative mechanical effect of an iliotibial band tenodesis on an intraarticular reconstruction of the ACL in fresh cadaver knees using a composite graft consisting of a bone-patellar tendonbone segment augmented with the Kennedy Ligament Augmentation Device (LAD, 3M Co., St. Paul, MN). The intraarticular graft was standardized by using a forcesetting technique. Ligament and graft forces were measured using buckle transducers, and joint motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to seven fresh knee specimens at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. The following knee states were tested in each specimen: intact ACL, excised ACL, intraarticular reconstruction, intraarticular reconstruction with the tenodesis added, and tenodesis with the intraarticular reconstruction added. Adding the iliotibial band tenodesis to an existing standardized intraarticular reconstruction significantly decreased the force in the ACL composite graft by an average of 43%. When the standardized intraarticular reconstruction was added to an existing tenodesis, the graft forces were an average of 15% below the level of when the reconstruction was performed alone. The force in the tenodesis was significantly less than the composite graft force at extension; however, the differences between the tenodesis and total graft force were not significant from 30 degrees to 90 degrees of flexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗