Biomedical subjects

W D Lew

Publications and source records attributed to W D Lew.

At least 19 recordsLinked to original sources

PubMed1999

Soft tissue release in total knee arthroplasty. Cadaver study using knees without deformities.

Soft tissue releases are performed to correct fixed deformities in total knee arthroplasty. The goal of this in vitro study was to investigate the relationship between the individual steps in a medial (eight anatomic specimen knees) or lateral (four anatomic specimen knees) soft tissue release sequence, the resulting change in the medial and lateral tibiofemoral gaps, and the change in coronal angulation caused by 10 Nm varus and valgus moments in extension and 90 degrees flexion. An optical encoder was used to measure the coronal angulation. The tibiofemoral gaps were measured with calipers with the knee distracted by a 53-N load. In the medial release sequence, a significant increase in coronal angulation and medial gap occurred after the release of the anteromedial sleeve 8 cm from the medial joint line. In the lateral release sequence, there was a significant increase in the coronal angle and lateral gap after the lateral collateral ligament and popliteus tendon were released from the femur. Release of the posterior cruciate ligament led to a significant increase in angle and gap in medial and lateral release sequences. These results are specific for the particular release sequences studied, with release of the posterior cruciate being the final step in each sequence.

Arthroplasty, Replacement, Knee↗

PubMed1999

Improving the detection of acetabular osteolysis using oblique radiographs.

Visualisation of periacetabular osteolysis by standard anteroposterior (AP) radiographs underestimates the extent of bone loss around a metal-backed acetabular component. We have assessed the effectiveness of standard radiological views in depicting periacetabular osteolysis, and recommend additional projections which make these lesions more visible. This was accomplished using a computerised simulation of radiological views and a radiological analysis of simulated defects placed at regular intervals around the perimeter of a cadaver acetabulum. The AP view alone showed only 38% of the defects over all of the surface of the cup and failed to depict a 3 mm lesion over 83% of the cup. When combined with the AP view, additional 45 degree obturator-oblique and iliac-oblique projections increased the depiction, showing 81% of the defects. The addition of the 60 degree obturator-oblique view further improved the visualisation of posterior defects, increasing the rate of detection to 94%. Based on this analysis, we recommend using at least three radiographic views when assessing the presence and extent of acetabular osteolysis.

Acetabulum↗

PubMed1998

Ligament force and joint motion in the intact ankle: a cadaveric study.

The aims of this study were to measure the forces in the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) and the motion in the tibiotalar and subtalar joints during simulated weight-bearing in eight cadaver ankle specimens. An MTS test machine was used to apply compressive loads to specimens held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. The forces in the ATFL and CFL were measured with buckle transducers. Tibiotalar motion and total ankle joint motion were measured with an instrumented spatial linkage. The specimens were positioned sequentially at 10 degrees dorsiflexion, neutral, and 10 degrees and 20 degrees plantarflexion, and this sequence was repeated at 15 degrees supination, neutral pronation/supination, and 15 degrees pronation. Force and motion measurements were recorded in each of these positions with and without a 375 N compressive load simulating weight-bearing. From 10 degrees dorsiflexion to 20 degrees plantarflexion, all motion occurred in the tibiotalar joint. In contrast, the ratio of subtalar motion to tibiotalar motion was 3:1 for supination-pronation and 4:1 for internal-external rotation. Inverse loading patterns were observed for the ATFL and CFL from plantarflexion to dorsiflexion. Compressive loading did not affect CFL tension, but it magnified the pattern of increasing ATFL tension with plantarflexion. The largest increase in ATFL force was observed in supination and plantarflexion with a compressive load (76 +/- 23 N), whereas CFL tension mainly increased in supination and dorsiflexion with a compressive load (109 +/- 28 N). In conclusion, the results showed that the ATFL acted as a primary restraint in inversion, where injuries typically occur (combined plantarflexion, supination and internal rotation). Also, the subtalar joint was of primary importance for normal supination-pronation and internal-external rotation.

Adult↗

PubMed1997

In vivo forces during remodeling of a two-segment anterior cruciate ligament graft in a goat model.

An existing goat model was used to measure in vivo graft forces during walking, to determine if the forces set at surgery change over time under the same external load and if the forces in the graft during in vivo function can be dictated by the forces set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a composite graft consisting of a bone-patellar tendon-bone autograft and a synthetic augmentation segment. The forces in the graft segments were established intraoperatively by a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force, and in the seven other animals, the augmentation segment was set to carry 90% of the total force. The total graft force was the same in all animals. Graft forces due to anterior tibial loads of 67 N were measured before and after fixation and 6 weeks after surgery with the use of buckle transducers mounted extra-articularly over the anterior tibia. They were also measured during straight, level walking at 6 weeks. The forces changed significantly from just after surgery to 6 weeks later, such that the initially set load-sharing was eliminated by 6 weeks. At 6 weeks, a relatively smooth gait had been achieved, and the maximum total graft force in each animal during walking averaged 35 N and was of similar magnitude to forces generated by the anterior tibial loads of 67 N with the animal anesthetized. After fixation, forces in the tendon graft segments were significantly different between the group with high set forces and that with low set forces. At 6 weeks, when functional joint loads were approaching normal levels, the graft segment forces for the two groups were not significantly different. Load-sharing between tendon and augmentation segment and load in the tendon segment at 6 weeks could not be dictated at surgery.

Animals↗

PubMed1997

Mechanics of the anterior drawer and talar tilt tests. A cadaveric study of lateral ligament injuries of the ankle.

We analyzed the changes in lateral ligament forces during anterior drawer and talar tilt testing and examined ankle joint motion during testing, following an isolated lesion of the anterior talofibular ligament (ATFL) or a combined lesion of the ATFL and calcaneofibular ligament (CFL). 8 cadaver specimens were held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. Ligament forces were measured with buckle transducers, and joint motion was measured with an instrumented spatial linkage. An anterior drawer test was performed using an 80 N anterior translating force, and a talar tilt test was performed using a 5.7 Nm supination torque with intact ligaments, after sectioning of the ATFL, and again after sectioning of the CFL. The tests were repeated at 10 degrees dorsiflexion, neutral, and 10 degrees and 20 degrees plantarflexion. In the intact ankle, the largest increases in ATFL force were observed during testing in plantarflexion, whereas the largest increases in CFL force were observed in dorsiflexion. Isolated ATFL injury caused only small laxity changes, but a pronounced increase in laxity was observed after a combined CFL and ATFL injury.

Adult↗

PubMed1996

Intraoperative force-setting did not improve the mechanical properties of an augmented bone-tendon-bone anterior cruciate ligament graft in a goat model.

It has been hypothesized that load affects the mechanical properties of an anterior cruciate ligament graft while it remodels. The goal of this study was to use an existing goat model to evaluate the effect of intraoperative set force on the postoperative mechanical properties of an autograft that had been augmented with a synthetic segment. The following questions were addressed. Do augmented autografts set with a high force intraoperatively have improved structural and material graft properties and lower anterior-posterior knee laxity at 3 months after surgery, compared with autografts set with a low intraoperative force? How do the structural and material properties of these implanted autografts compare with the mechanical properties of an intact anterior cruciate ligament or an unimplanted control autograft? The anterior cruciate ligament was reconstructed in seven goats with use of a composite graft consisting of a bone-patellar tendon-bone autograft and a synthetic augmentation device. A force-setting technique was used intraoperatively to establish the load-sharing between the autograft and augmentation segments such that the autograft carried either a high (16.5 N in four animals) or low (1.5 N in three animals) level of force, while the total force in the composite graft remained constant. Tensile testing was performed at 3 months after surgery to determine the material and structural properties of the autograft, the intact anterior cruciate ligament from the normal contralateral knee, and a control bone-patellar tendon-bone graft of similar size that was harvested from the contralateral knee at the time of necropsy and had never been implanted in the joint. The structural and material properties of the autografts initially set to high or low loads at surgery were not significantly different after 3 months of implantation. The strength and stiffness of the implanted tendons were an average of 24 and 20% of the strength and stiffness of the normal anterior cruciate ligament and 31 and 62% of the control tendons, respectively. Intraoperative set force in an augmented anterior cruciate ligament graft at the levels chosen in this study did not significantly affect weakening of the autograft at 3 months.

Animals↗

PubMed1994

Method for establishing and measuring in vivo forces in an anterior cruciate ligament composite graft: response to differing levels of load sharing in a goat model.

In order to determine the appropriate load history for optimal remodeling of an anterior cruciate ligament graft, methods for establishing and measuring the graft force due to an external load could be set to a preselected value in in vivo are required. Our objectives with this study were to (a) develop a method in which the graft force due to an external load could be set to a preselected value in a living animal, (b) show that this force could be maintained after fixation, and (c) determine what happens to the forces after the animal has functioned for as long as 2 weeks postoperatively, when differing levels of load sharing between the segments had been set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a bone-patellar tendon-bone graft and a synthetic augmentation device. The forces in the graft segments were established, at the time of surgical fixation, with use of a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force; in the remaining seven animals, the augmentation segment was set to share 90% of the total graft force. Graft forces were measured, with the use of buckle transducers mounted extra-articularly over the anterior tibia, under a 67 N anterior tibial load at 60 degrees of knee flexion before and after fixation and at 2 weeks postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Maintenance of set force in anterior cruciate ligament grafts.

This study was undertaken to determine how accurately total graft force and load-sharing between graft segments could be set and maintained during augmented anterior cruciate ligament (ACL) reconstruction in the goat knee. Special procedures were developed to reduce the effect of tissue creep and to overcome difficulties in the setting of graft force. Five knees from goat cadavers were reconstructed using a bone-tendon-bone graft (PT) and a synthetic augmentation device (LAD). Prescribed levels of total graft force and load-sharing between the autograft and LAD were set under a standardized external joint load. Immediately after fixation, the set force declined an average of 9 and 3% in the LAD and PT, respectively. After three subsequent exercise sequences, the set forces fell from their initial level by an average of 25% for the LAD and 28% for the PT. An analysis of variance did not show the loss of force with exercise to be statistically significant. We conclude from this in vitro study that our method can be used to set forces in an ACL reconstruction with reasonable maintenance of load-sharing but that losses of approximately 30% of total graft force after exercise of the reconstructed joint are to be expected.

Animals↗

PubMed1992

Biomechanical effect of a two-segment anterior cruciate ligament graft with separate femoral attachments and differing levels of prescribed load sharing.

The objective of this study was to analyze the biomechanical effect of varying the level of prescribed load sharing between two segments of an anterior cruciate ligament (ACL) graft, and of separating the femoral attachments of these segments. Total anterior-posterior (AP) laxity was measured using an instrumented spatial linkage. Forces in graft segments were measured using buckle transducers. The two-segment graft was formed using the middle third of the patellar tendon with bone blocks and a synthetic augmentation device. Proximal fixation was obtained using a fixture which allowed changing the individual locations of the femoral attachments of the tendon and augmentation segments. Distal fixation was achieved using a force-setting device which allowed the loads in each segment to be set to prescribed levels. Total graft force, load sharing, and total AP laxity were recorded during the application of 100-N AP tibial loads at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 110 degrees flexion, for various combinations of load sharing set at extension and locations of femoral attachment sites. The load sharing, total graft force, and AP laxity during AP loading at the five test flexion angles were not significantly affected by changing the prescribed level of load sharing set at extension for a given femoral attachment configuration. However, varying the separate hole locations of the graft segments for a given level of load sharing significantly affected load sharing, total graft force, and AP laxity. If the tendon graft was located posteriorly (on the medial surface of the lateral femoral condyle) and the augmentation segment proximally, the augmentation carried a greater portion of the total force in flexion. If the augmentation segment was changed to a more posterosuperior location and the tendon posteroinferior, the tendon carried a higher percentage of the total force in flexion. AP laxity in most reconstruction states was significantly greater than in the normal joint with an intact ACL. The nature of the load sharing between the graft segments under AP tibial load over the flexion range can be controlled by the appropriate choice of the segments' femoral attachment locations.

Analysis of Variance↗

PubMed1990

Factors affecting graft force in surgical reconstruction of the anterior cruciate ligament.

The effect of the maximum unloaded graft length (Lo) and femoral fixation hole location on graft force with the knee under anteriorly directed tibial loads was measured in five fresh cadaver knees with a reconstruction of the anterior cruciate ligament (ACL). The reconstruction was performed using a composite graft consisting of the semitendinosus and gracilis tendons augmented with the Kennedy ligament augmentation device (LAD). Buckle transducers were used to measure ligament and graft forces. The total graft force was adjusted to match the intact ACL at 30 degrees flexion using a force-setting method so that a standardized reference configuration could be repeatedly obtained. The graft force was highly sensitive to Lo, typically changing by 50% with a change in Lo of 3 mm. Variation in femoral hole location of 5 mm anterior, posterior, proximal, and distal to the anatomic position produced changes in graft force, particularly at 60 degrees and 90 degrees flexion; however, these changes were not statistically significant. The effect of femoral hole location varied considerably between knees. This variability makes predicting proper hole placement difficult, and suggests the need to adjust each knee at surgery to account for this variable femoral hole position sensitivity.

Adult↗

PubMed1990

Method for setting total graft force and load sharing in augmented ACL grafts.

The objective of this study was to develop a method for obtaining a controllable and reproducible immediate postoperative mechanical state in a knee with an anterior cruciate ligament (ACL) reconstruction. This method, called the force-setting technique, was demonstrated using a composite graft consisting of the middle third of the patellar tendon with bone blocks (PT) and the ligament augmentation device (LAD). The total graft force was set to match the force in the intact ACL at 30 degrees flexion with the knee under the same standardized external load, while at the same time the load sharing between the biologic and augmentation components was controlled. The total graft force was set to match the ACL force three separate times in each knee, with ratios of load sharing set at the following levels: 50% PT-50% LAD, 25% PT-75% LAD, and 75% PT-25% LAD. ACL, PT, LAD, and collateral forces were measured using buckle transducers, and three-dimensional knee motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to eight specimens at 0 degree, 30 degrees, 60 degrees, and 90 degrees flexion with an intact ACL, an excised ACL, and the three load-sharing reconstruction states. The total graft force could be consistently set to within an average of 2% of the intact ACL force at 30 degrees flexion, and load sharing between the graft segments could be set to within an average of 5.1% of the desired ratio at 30 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Cadaver↗

PubMed1990

Anterolateral rotatory instability of the knee. Cadaver study of extraarticular patellar-tendon transposition.

A cadaver knee-testing system was used to analyze the effect of an extraarticular reconstruction for anterolateral rotatory instability in which the lateral one third of the patellar tendon with a patellar bone block was transposed to the lateral femoral condyle. Ligament and reconstruction tendon 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 knee specimens at 0 degree, 30 degrees, 60 degrees, and 90 degrees of flexion by a pneumatic load apparatus. This was done for each knee with first an intact, then an excised anterior cruciate ligament, and finally the extraarticular reconstruction. Forces in the transposed graft exhibited an isotonic pattern over the flexion range, unlike the intact anterior cruciate ligament, which was more highly loaded in extension than in flexion. The transposition of the patellar tendon led to external rotation of the tibia in both unloaded and anterior load conditions throughout flexion. Collateral ligament forces increased with anterior cruciate ligament excision, with the force in the medial ligament remaining higher than normal with the reconstruction, while the lateral forces became lower than normal.

Biomechanical Phenomena↗

PubMed1989

Knee joint motion and ligament forces before and after ACL reconstruction.

The goal of this in vitro study was to investigate the initial postoperative mechanical state of the knee with various types of anterior cruciate ligament (ACL) reconstructions. An experimental knee testing system was developed for the in vitro measurement of ligament forces and three-dimensional joint motion as external loads were applied to fresh knee specimens. Two groups of knee specimens were tested. In test series #1, two intraarticular reconstructions were performed in each of five specimens using semifree and free patellar tendon grafts with bone blocks. In test series #2, a more carefully controlled intraarticular reconstruction was performed in five specimens using a semifree composite graft consisting of the semitendinosus and gracilis tendons augmented with the Ligament Augmentation Device. Ligament force and joint motion data were collected as anteriorly directed tibial loads were applied to the normal joint, the joint with a cut ACL and the reconstructed joint. These knee joint states were compared on the basis of ACL or graft forces, joint motion and load sharing by the collateral ligaments. The dominate result of the study was that the forces and motions defining the mechanical state of the knee after the ACL reconstructions in both test series were highly variable and abnormal when compared to the normal knee state. The higher level of surgical control series #2 did not decrease this variability. There was a poor correlation between motion of the reconstructed knee relative to normal, and the ACL graft force. There was little consistent difference in force and motion results between the surgical procedures tested.

Humans↗

PubMed1989

Knee mechanics after repair of the anterior cruciate ligament. A cadaver study of ligament augmentation.

An experimental knee-testing system was used to investigate the immediate postoperative mechanical state in knees with nonaugmented and augmented repairs of the anterior cruciate ligament. Ligament, repair tissue, and augmentation forces were measured using buckle transducers, and joint motion was measured using an instrumented spatial linkage during the application of 90 N anteriorly-directed tibial loads to seven fresh knee specimens at 0-90 degrees of flexion. Force and motion data were collected from each knee with an intact and excised anterior cruciate ligament, and after performing (1) a nonaugmented repair and an augmented repair using the Ligament Augmentation Device (3M Company) placed either (2) anatomically through the lateral femoral condyle or (3) in the over-the-top position. The forces in the nonaugmented repair and the repair with the augmentation in the two positions were greater than the forces in the intact anterior cruciate ligament with the knee under the same anterior loads; this difference from normal was not significant with the over-the-top augmentation. With the augmentation anatomically placed, the load sharing did not reduce the force in the repair tissue as compared with the nonaugmented case. The over-the-top augmentation, on the other hand, lowered the repair tissue forces at extension while avoiding high repair tissue forces in flexion. The tibia was consistently in an externally rotated configuration compared with normal in both the unloaded and anterior load states with all three repair procedures.

Biomechanical Phenomena↗

PubMed1988

Description and error evaluation of an in vitro knee joint testing system.

An experimental system for the analysis of knee joint biomechanics is presented. The system provides for the simultaneous recording of ligament forces using buckle transducers and three-dimensional joint motion using an instrumented spatial linkage, as in vitro specimens are subjected to a variety of external loads by a pneumatic loading apparatus with associated force transducers. The system components are described, and results of an evaluation of system errors and accuracy are presented. The experimental setup has been successfully used in the analysis of normal knee ligament mechanics, as well as surgical reconstructions of the anterior cruciate ligament. The system can also be adapted to test other human or animal in vitro joints.

Biomechanical Phenomena↗

PubMed1983

The measurement of form and variation in form: an application of three-dimensional quantitative morphology by finite-element methods.

D'Arcy Thompson developed a method of coordinates which allowed for a geometrical presentation of form and form change. While his grid transformations have received much attention, little work in the geometry of form and form change has occurred since. We present a three-dimensional nonhomogeneous finite-element scaling method which allows for the mathematical and geometrical measurement of form change in addition to the graphical representation of these deformations as D'Arcy Thompson grids. This allows a reconciliation between geometrical and statistical methods for analyzing form. The method involves quantification of the transformation of one form into another in three dimensions without special registration and contains algorithms for obtaining a mean form. The method is applied to an analysis of variation in cranial form among adult male rhesus macaques from the Cayo Santiago skeletal collection. Variation was greatest in the superior-inferior direction, followed by the anterior-posterior and medial-lateral directions. The upper facial region is particularly variable. An analysis of allometry relative to local size variation shows that the larger any particular region is, the relatively greater its height, narrower its width, and shorter its length. An analysis of allometry relative to overall size showed that the upper face is positively allometric, the occipital region is strongly negatively allometric, and the other regions are isometric. After within-group variation is characterized, as described here, between-group studies, such as growth series and phylogenetic series, can be performed.

Animals↗

PubMed1982

A note on the application and evaluation of the buckle transducer for the knee ligament force measurement.

Knee ligament forces were directly measured with buckle transducers. Given a collection of buckle transducers with adequate rigidity and a variety of sizes to accommodate different ligamentous geometries, two potential problems remain when using the buckles 1) impingement of the transducers with bone, producing a false output; 2) ligament shortening due to buckle installation, potentially altering the distribution of ligament forces around the knee. This report describes our current buckle transducer designs and installation procedures, and presents data which demonstrated that the errors due to ligament shortening and bone impingement can be assessed and reduced to acceptable levels.

Humans↗

PubMed1982

The effect of knee-prosthesis geometry on cruciate ligament mechanics during flexion.

UNLABELLED: We used buckle transducers in conjunction with a mathematical model to investigate the mechanics of the cruciate ligaments during flexion of knees containing prostheses with differing component geometries. With normal component placement and both cruciate ligaments intact, the full range of flexion is restricted in a knee with the conforming, single radius-of-curvature geometric prosthesis because of large constraint forces in the posterior cruciate ligament. Ligament incompatibility is avoided with multicurvature designs, as represented by the kinematic prosthesis. Low conformity of components allows anterior-posterior displacements to accompany flexion, which provides for a full range of flexion and allows cruciate ligament forces to approach those of a normal knee. CLINICAL RELEVANCE: This analysis points out that special precautions must be taken to avoid ligament constraint forces (and potential loosening) if an implant with highly conforming components is used when both cruciate ligaments are intact. The information presented here, relating implant geometry to cruciate ligament mechanics, must be considered when choosing an appropriate prosthetic design to ensure ligament compatibility in the presence of one, both, or no cruciate ligaments.

Biomechanical Phenomena↗