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Biomedical subjects

S A Banks

Publications and source records attributed to S A Banks.

At least 19 recordsLinked to original sources
PubMed2006

A kinematic comparison of fixed- and mobile-bearing knee replacements.

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur. We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.

Arthroplasty, Replacement, Knee↗
PubMed2003

Dynamic in-vivo tibio-femoral and bearing motions in mobile bearing knee arthroplasty.

To determine the tibio-femoral and bearing motions in well functioning mobile bearing total knee arthroplasties, a quantitative analysis by means of fluoroscopy was carried out during stair ascending, chair rising-sitting and step up-down motor tasks. Femoral and tibial component positions were obtained using a CAD-model-based shape matching technique. Direct measurement of mobile bearing motion was carried out by tracking previously inserted tantalum beads. A relatively small motion of the bearing was observed. The advantage of self-alignment claimed for the mobile bearing arthroplasty seems to be confirmed by subject-specific ranges of motion exhibited by these patients. It has also been demonstrated that these total knee arthroplasties, which are not fully conforming in flexion, provide little constraint to antero-posterior motion, leading to a kinematic pattern very similar to an ACL deficient knee.

Activities of Daily Living↗
PubMed2001

Polyethylene damage and knee kinematics after total knee arthroplasty.

This study characterizes the relationship between in vivo knee kinematics and polyethylene damage by combining fluoroscopic analysis of tibiofemoral contact during dynamic activities and implant retrieval analysis in the same patients. Six patients (eight knees) underwent posterior cruciate ligament-retaining total knee arthroplasty. All patients participated in fluoroscopic analysis during a stair-rise and descent activity and treadmill gait an average of 18 months after arthroplasty, and articular contact was measured. Subsequently, all polyethylene tibial inserts were retrieved after an average of 26 months in vivo function: three at autopsy and five at revision. There was a statistically significant correlation between the damage location on the retrieved inserts and the articular contact location measured fluoroscopically during the activities. The femoral contact and polyethylene damage occurred predominantly on the posterior half of the tibial articular surface, and the damage pattern was largest in the compartment with the greatest range of in vivo femoral contact for each patient. This study showed that in vivo fluoroscopic analysis can predict the damage location on the polyethylene articular surface.

Aged↗
PubMed2000

Sagittal plane imaging parameters for computer-assisted fluoroscopic anterior cruciate ligament reconstruction.

Reproducible graft placement in anterior cruciate ligament (ACL) reconstructions is considered to be a critical factor affecting the successful clinical outcome of the procedure. Many current ACL instrument systems rely on intra-articular landmarks to guide the ACL tunnel placement. However, most of these instrument systems use mobile soft tissues as landmarks. We hypothesize that consistently identifiable radiographic contour landmarks can be established that can be used to improve the reproducibility of graft tunnel placement in fluoroscopically and computer-assisted ACL reconstructions. For the tibia, magnetic resonance imaging (MRI) scans showed the average ACL attachment site to be projected at 46% on a line extending from the anterior to the posterior cortices. Intraoperative fluoroscopic images were checked for the reproducibility of this line and its clinical use. For the femur, lateral radiographs demonstrated a consistent relationship between the intercondylar roof line (Blumensaat's line) and the nearly circular profile of the posterior and inferior contour of the lateral femoral condyle. The middle of this circular profile is consistently projected on Blumensaat's line at 66% of its anterior-to-posterior direction. Intraoperative images were used, which showed the aiming drill at the point of entering the lateral femoral condyle. Instead of determining the femoral attachment site relative to Blumensaat's line, we can thus determine its position relative to the center of the circle. Based on intraoperative x-rays, the proposed femoral ACL attachment site can be projected on a line parallel with the Blumensaat's line from the circle center in the posterior direction. Our results indicate that there are consistently identifiable radiographic features on the tibia and femur contours that can be used for fluoroscopic and computer-assisted guidance of ACL graft placement.

Anterior Cruciate Ligament↗
PubMed2000

Distribution of renal medullary hyaluronan in lean and obese rabbits.

BACKGROUND: Obese individuals have an expanded interstitium in the renal inner medulla (IM), which stains positively with periodic acid-Schiff and Alcian blue. In obese dogs, the IM is also expanded, with hyaluronan (HA) content being 2.4 times control. METHODS: We determined the anatomic pattern of renal HA deposition following weight gain, using an animal model of obesity consisting of young rabbits (N = 10), representing animals entering into the study, lean rabbits (N = 19), fed a control diet, and obese rabbits (N = 19), fed a high-fat diet (15% fat, by fortifying with corn oil and lard, in a ratio of 2:1) for two to three months. Tissue was papain digested, and HA was recovered in a phosphate or a Tris buffer and detected by an indirect immunoabsorbent competition assay. RESULTS: Rabbits fed a high-fat diet for 8 to 12 weeks gained weight (37%) and became mildly hypertensive (10 mm Hg). In lean rabbits, HA was low in the renal cortex (6 +/- 30 microg/g tissue), increased steadily across the outer medulla (OM; 79 +/- 28 microg/g tissue) and was uniformly high in the IM (192 +/- 28 microg/g tissue) when recovered in a Tris buffer; these levels of tissue HA did not change during the three-month period of dietary intervention. In obese rabbits, the renal medullary interstitium was expanded and stained intensely with periodic acid Schiff and Alcian blue, and tissue HA was elevated in the IM (448 +/- 25 microg/g tissue) but not the cortex (5 +/- 25 microg/g tissue) or the OM (85 +/- 25 microg/g tissue). The significant difference was due to those IM samples taken from the renal papilla; IM samples from the body of the kidney did not significantly differ among the lean, obese, and young rabbits. CONCLUSION: The elevated renal HA associated with weight gain is limited to the IM and occurs most consistently in the papilla, which is the region of the kidney that is most vulnerable to distention caused by elevated renal interstitial hydrostatic pressure.

Age Factors↗
PubMed1999

Active responses decrease impact forces at the hip and shoulder in falls to the side.

Active responses, such as using the arm to break the fall, may be an effective means of decreasing likelihood of injury in a fall and may help explain why only a small percentage of falls result in a fracture. We quantified the impact force at the hip and shoulder in falls to the side from a kneeling position under three conditions: (1) attempting to break the fall by using an arm; (2) falling with the body relaxed; and (3) falling with the body tensed. Subjects fell from a kneeling position onto a force platform array covered with foam padding and impact force data were recorded. The ground reaction force-time curve was generally bimodal due to sequential impacts of the hip and shoulder. Impact forces at the hip and shoulder were 12 and 16% less for the slap condition (p < 0.05) than for the tensed condition. The impact forces for the relaxed and tensed conditions were not significantly different, although impact forces tended to be less in the relaxed condition. We concluded that active responses reduce the impact forces experienced at the hip and shoulder in falls to the side. Decreased effectiveness of protective responses, due to increases in reaction time and decreases in strength with age, may help explain why so many hip fractures occur in the elderly but so few occur in younger people.

Accidental Falls↗
PubMed1999

Patellar tendon graft position after anterior cruciate ligament reconstruction. Interobserver variability on lateral radiographs.

We compared the reliability and validity of graft position measurements made by 4 orthopedic surgeons on intraoperative radiographs obtained using fluoroscopic control and postoperative radiographs obtained from the same 17 patients 6 weeks after ACL reconstruction. Measurements from postoperative radiographs varied significantly more than those from intraoperative radiographs. There was little agreement between the postoperative and intraoperative measurements of the tibial and femoral graft position. We conclude that postoperative radiographs are not a sufficient tool for assessing graft placement after ACL reconstruction using patellar tendon autografts. In order to consider graft position in follow-up studies and to compare results from various surgeons, we suggest intraoperative fluoroscopy to produce radiographs for accurate and reliable measurements.

Adolescent↗
PubMed1999

A new technique for removing noncemented acetabular components in revision total hip arthroplasty.

Removal of noncemented acetabular components during revision surgery can be a time-consuming technical challenge, resulting in exacerbation of defects and compromised bone stock. These factors are deleterious to reconstructive efforts and can compromise clinical results. A technique is described that can accomplish timely removal of noncemented acetabular components. The advantages of this technique include no further weakening of the remaining structural supports, minimal bone loss, avoidance of intrapelvic perforations, and reduction in operative time.

Acetabulum↗
PubMed1998

Computer assistance in arthroscopic anterior cruciate ligament reconstruction.

Accurate placement of the graft is considered one of the most important factors in anterior cruciate ligament surgery. However, reconstruction with contemporary guiding systems still can result in unacceptable graft placement variability. To improve the reproducibility of graft placement, intraoperative visual feedback was added to the arthroscopic technique. First, fluoroscopic visualization was added to evaluate guidewire placement before tunnel drilling. Second, computer graphic overlays were added to the fluoroscopic view. Three groups of patients were treated: 29 patients with arthroscopy, 53 patients with fluoroscopy added, and 50 patients with computer overlays added. Graft placement variability was reduced significantly with fluoroscopic visualization. Computer overlays resulted in additional significant reductions in graft placement variability. Simple visual enhancements seem to be useful in improving the accuracy of arthroscopic anterior cruciate ligament reconstruction.

Anterior Cruciate Ligament↗
PubMed1998

Wear patterns on tibial plateaus from varus and valgus osteoarthritic knees.

The size and location of articular cartilage wear was assessed on 106 varus and 37 valgus osteoarthritic tibial plateaus resected during total knee arthroplasty. Anterior cruciate ligament integrity was assessed intraoperatively, and calibrated digital images were used to measure the wear patterns. Complete anterior cruciate ligament deficiency was seen in 25% of the varus and 24% of the valgus knees. Wear patterns on anterior cruciate ligament intact and attenuated varus tibial plateaus occurred in the middle to anterior aspect of the medial plateau. Anterior cruciate ligament deficient varus plateaus had significantly larger wear areas located more posterior on the medial plateau. In contrast, anterior cruciate ligament intact and deficient valgus tibial plateaus had wear located posterior to the center of the lateral plateau. Anterior cruciate ligament integrity is a discrete feature of advanced osteoarthritis that strongly influences the articular wear patterns. The anterior cruciate ligament deficient wear patterns show a wear mechanism that is consistent with the posterior femoral subluxation and posterior tibiofemoral contact observed after acute anterior cruciate ligament rupture. These observations provide insight into the altered knee mechanics that exist in osteoarthritic knees and the resulting mechanical factors that contribute to degenerative changes.

Aged↗
PubMed1997

In vivo kinematics of cruciate-retaining and -substituting knee arthroplasties.

A fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during a step-up activity. Three groups of knee arthroplasty subjects with excellent clinical outcomes and similar ranges of motion were evaluated. Each group received different prosthetic components and surgical treatments of the posterior cruciate ligament (PCL). Group 1 had relatively flat articular surfaces with retention of the bony insertion of the PCL, group 2 had similar articular geometry but recessed the PCL without retaining the bony insertion, and group 3 had prostheses with greater sagittal conformity and post/cam substitution of the sacrificed PCL. Although none of the knees exhibited normal knee kinematics, the ranges of axial rotation and condylar translation for group 1 were similar to ranges previously reported for normal and anterior cruciate-deficient knees. Axial rotations and condylar translations decreased when the PCL was surgically recessed or substituted. The smallest kinematic ranges were observed in group 3. The results indicate that both prosthetic component selection and surgical technique have a significant effect on prosthetic knee kinematics during functional activities.

Aged↗
PubMed1997

Wear analysis of a retrieved hip implant with titanium nitride coating.

There is increasing interest in using surface modification technology to improve the wear properties of titanium alloy and limit articular surface wear of metal and polyethylene components. This report details the in vivo wear performance of titanium nitride coating on a retrieved hip implant obtained postmortem from a low demand patient 1 year after total hip arthroplasty. Analysis of the well-functioning implant revealed that wear debris can originate from a titanium nitride coated femoral head, as delaminated surface asperities, and manifest as adhesive wear on the articular surface. The wear observed on this implant indicates that rigorous testing and evaluation of titanium nitride coating technology should be conducted prior to widespread use on total joint implants.

Acetabulum↗
PubMed1996

Accurate measurement of three-dimensional knee replacement kinematics using single-plane fluoroscopy.

A simple extension of a previously reported object recognition technique has been used to implement a six-degree-of-freedom position/orientation estimator for the measurement of knee replacement motion from two-dimensional (2-D) fluoroscopic images. Computer modeling studies and controlled mechanical tests were performed to assess the accuracy of the technique. The results indicate that knee rotations can be measured with an accuracy of approximately one degree and that sagittal plane translations can be measured with an accuracy of approximately 0.5 mm. The measurement technique is uniquely well suited for performing dynamic kinematic measurements on individuals with knee replacements, and for performing comparative studies among subjects with different designs of knee replacements.

Computer Simulation↗
PubMed1995

Hitting a baseball: a biomechanical description.

A tremendous amount of time and energy has been dedicated to the development of conditioning programs, mechanics drills, and rehabilitation protocols for the throwing athlete. In comparison, a significantly smaller amount has been spent on the needs of the hitting athlete. Before these needs can be addressed, an understanding of mechanics and the demands placed on the body during the swing must be developed. This study uses three-dimensional kinematic and kinetic data to define and quantify biomechanics during the baseball swing. The results show that a hitter starts the swing with a weight shift toward the rear foot and the generation of trunk coil. As the hitter strides forward, force applied by the front foot equal to 123% of body weight promotes segment acceleration around the axis of the trunk. The hip segment rotates to a maximum speed of 714 degrees/sec followed by a maximum shoulder segment velocity of 937 degrees/sec. The product of this kinetic link is a maximum linear bat velocity of 31 m/sec. By quantifying the hitting motion, a more educated approach can be made in developing rehabilitation, strength, and conditioning programs for the hitting athlete.

Adult↗