Biomedical subjects

A F Tencer

Publications and source records attributed to A F Tencer.

At least 55 records · Page 3Linked to original sources

PubMed1995

Comparison of residual stability in thoracolumbar spine fractures using neutral zone measurements.

Because treatment algorithms for spinal injuries depend largely on the clinical assessment of stability after injury, this study both quantified and compared the mechanical stability after three different patterns of injury in the thoracolumbar spine. We created compression fractures, burst fractures, and flexion-distraction injuries in 26 thoracolumbar specimens from human cadavers in order to compare residual stability as a function of type of injury. Spinal stability was evaluated using measurements of the boundaries of the neutral zone, which provide a measure of spinal laxity in various directions of motion. An increase after injury was indicative of greater spinal laxity and hence reduced residual stability. Geometric characteristics (or parameters) of the neutral zone boundaries were used for statistical comparison between the types of injury. Of the three groups, burst fractures retained the least residual stability and compression fractures, the greatest. The angular ranges of motion in the neutral zone for burst fractures demonstrated increases (compared with average values for intact specimens) of 154% in flexion-extension, 134% in lateral bending, and 108% in torsion after injury. The results for flexion-distraction injuries were similar to those for burst fractures in flexion-extension (126%) and torsion (62%); however, more residual stability was retained in lateral bending than was seen for burst fractures (48%). Compression fractures retained the most residual stability, with increases in motion of 40% in flexion-extension, 56% in lateral bending, and 3% in torsion. These findings may be useful in determining the necessity for surgical stabilization of the spine and selection of the appropriate system of fixation.

Biomechanical Phenomena↗

PubMed1995

The scapholunate allograft: a biomechanical feasibility study.

The feasibility of a new method for reconstruction of the isolated scapholunate ligament tear with a scapholunate allograft was studied biomechanically using a fresh cadaver upper extremity model. Seven specimens were first tested intact for wrist range of motion, contact characteristics of the radiocarpal articulation, and relative motion of the scaphoid with respect to the lunate. Then a segment consisting of the radial third of the lunate, the adjoining scapholunate interosseus ligament, and the proximal pole of the scaphoid was resected. This segment was matched to a donor allograft of similar size and geometry, which was then placed into the recipient carpus and secured with one central transverse Kirschner wire and two shorter interfragmentary Kirschner wires placed into the lunate and scaphoid. The allografted specimen was subjected to the same tests as the intact wrist. Results showed that there were no significant differences in wrist range of motion, radiocarpal articular surface contact area and pressure, and relative flexion-extension rotation between the scaphoid and lunate during passive radioulnar deviation between the intact and allografted wrists.

Biomechanical Phenomena↗

PubMed1995

A comparison of malreduction after plate and intramedullary nail fixation of forearm fractures.

A study was performed to compare the degree of malreduction after intramedullary nail and plate fixation of the forearm and to determine if the degree of malreduction was clinically significant. Eight matched pairs of forearms, including the wrist and elbow joints, were harvested from cadaver upper extremities. The forearms were put through a full range of motion, and physiological loads were applied to simulate those during normal use. Standardized anteroposterior and lateral radiographs of each forearm were obtained with the specimen intact, and after an osteotomy and internal fixation of one bone, both bones, and with gap at the osteotomy sites. In each forearm pair, plating was randomly performed in one specimen and intramedullary nailing was performed in the matching contralateral specimen. Forearm architecture was assessed by quantification of the magnitude and location of maximum radial bow and radial angulation. In this study, plate fixation was superior to nail stabilization in restoration of the normal radial architecture. Plating did not change any of the radiographic indices (magnitude and location of maximum radial bow and radial angulation) at any stage of testing. None of the radiographic indices was changed by nailing of only one of the forearm bones. The magnitude of maximum radial bow and the radial angulation were changed by nailing both forearm bones after osteotomy and both forearm bones with a gap (p < 0.05). Despite this, both techniques were well within the limits of what is radiographically acceptable for reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Nails↗

PubMed1995

A biomechanical comparison of two methods of fixation of fractures of the forearm.

In this study two different types of forearm internal fracture fixations were compared: limited-contact dynamic compression (DC) plates and fluted intramedullary (IM) rods. Eight matched pairs of intact forearms, consisting of the distal part of the humerus, elbow joint, radius, ulna, interosseus membrane, wrist joint, and metacarpals, were randomly separated into two groups. Each was placed into a custom-designed apparatus and subjected to medial bending, supination, pronation, axial compression, and distraction loading. Loads were applied by a materials testing system, and angular displacements were measured by inclinometers. The procedure consisted of first testing specimens intact, then retesting after osteotomizing and fixing the radius with either a plate or rod in half of the group and retesting after osteotomizing and fixing the ulna in the other half. Testing was continued by osteotomizing and remaining intact bone to create a two-bone fracture, fixing them, and retesting after creating a 5-mm gap at the osteotomy sites. These tests showed that the intact ulna contributes more to forearm stability in bending and torsion than does the radius. Therefore, if the radius is fractured but the ulna remains intact, IM rodding will produce constructs with greater stiffnesses, particularly in torsion, than if the ulna is fractured and the radius is intact. In the case of a two-bone fracture, implantation of rods will result in a construct with significantly less stiffness in torsion, as well as distraction and compression (in the case of a fracture gap), than if the fractures were plated.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMed1995

Stiffness of screw fixation and role of cortical hinge in the first metatarsal base osteotomy.

The authors investigated various factors that affect stiffness of screw fixation in the oblique first metatarsal osteotomy. One screw versus two screw fixation with intact medial cortical hinge, and two screw fixation without hinge were tested on the same metatarsal specimen. Mechanical properties of the fixation patterns were measured on a materials testing apparatus. Each metatarsal was tested at below failure threshold for stiffness within the elastic range of the specimen. Load versus displacement curves and fixation stiffness values were generated for axial loading, valgus torque, and plantar-to-dorsal cantilever bending. Osteotomies with an intact hinge demonstrated superior stiffness in most parameters as compared to osteotomies without a hinge. Two screw fixation with intact hinge showed significantly increased axial stiffness as compared to one screw fixation. There was no statistical difference between one and two screws in cantilever bending and torsional stiffness with an intact hinge. The major stabilizing factor of the first metatarsal base osteotomy is the medial cortical hinge.

Adult↗

PubMed1995

Contact characteristics of the subtalar joint after a simulated calcaneus fracture.

A simple calcaneus fracture consisting of two parts was modeled in nine fresh cadaver hindfoot specimens to assess changes in subtalar joint contact characteristics with increasing plantar depression of the posterolateral fracture component. To perform the experiment, rods were placed in the tibial and fibular shafts of each specimen, which was mounted in a frame in neutral stance. A pneumatic cylinder was used to deliver a vertical compressive load through the rods into the foot while permitting free motion of the foot in the horizontal plane. Sealed packets of pressure-sensitive film were inserted into the anterior-middle and posterior facets of the talocalcaneal articulation, and a 700-N load was applied. After testing of the intact foot, a primary fracture line was created using a microoscillating saw. The osteotomized posterolateral component was anatomically reduced and fixed, the film inserted, and the load reapplied. The test was repeated after the posterolateral fragment was displaced 2, 5, and 10 mm in a plantar direction. The resulting pressure prints were scanned along with pressure/color density calibration strips using a flat-bed scanner, and an image analysis system was used to determine contact areas within specified pressure intervals. The contact area (> 0.5 MPa) of the posterior facet was significantly decreased with 2, 5, and 10 mm displacements of the posterolateral calcaneus fracture component. The ratio of high-pressure area (< 5.0 MPa) to contact area in the posterior facet was significantly increased only with displacements of 5 and 10 mm. There were no significant changes in any contact parameters in the anterior-middle facet.(ABSTRACT TRUNCATED AT 250 WORDS)

Ankle Joint↗

PubMed1995

The acetabular T-type fracture. A biomechanical evaluation of internal fixation.

The purpose of this study was to evaluate the stability of different types of internal fixation requiring anterior, posterior, or combined surgical approaches for the T-type acetabular fracture. Eight specimens were loaded 25 times in a cyclic manner to 150 N for each type of fixation construct evaluated. The model attempted to range the hip through an arc of motion anticipated in the limited activities expected after surgery. Strain gauges were placed on the 3 fracture planes of the T-type fracture. These gauges measured displacements. Internal fixation consisted of a single anterior column plate, compared with a single posterior column plate, compared with simultaneous placement of both anterior column and posterior column plates. The differences in displacements measured between the 3 types of fixation at each of the 3 fracture sites were not statistically significant. In evaluating motion at the anterior fracture line, the anterior plate made the largest contribution to stability, although this result was not statistically significant. The posterior plate similarly contributed most to posterior fracture stability, although again not statistically significant. Each of the 3 fixations controlled the inferior fracture line motions in a comparable manner.

Acetabulum↗

PubMed1995

Anterior versus posterior provisional fixation in the unstable pelvis. A biomechanical comparison.

Pelvic ring injuries with associated hemorrhage often require provisional fixation to achieve tamponade. Biomechanics information regarding these provisional fixators is unknown. Six fresh-frozen cadaveric pelvic specimens were physiologically loaded, first intact and then after each of the following modifications: disrupted--unilateral superior and inferior rami osteotomies, ipsilateral anterior and posterior sacroiliac joint, and sacrospinous and sacrotuberous ligament disruption; disrupted and with placement of a Ganz pelvic resuscitation clamp; and disrupted and with placement of a simple anterior 2-bar external fixator. This injury resulted in significant motion at the disrupted rami and the injured sacroiliac joint, compared with the intact pelvic specimen. Motions at the superior ramus and injured sacroiliac joints were significantly (p < 0.05) greater than the intact specimen, with both the external fixator and the Ganz clamp. Motions at the superior ramus and injured sacroiliac joints were not significantly (p < 0.05) different when comparing the Ganz clamp to the external fixator. However, the anterior external fixator decreased motion to a greater degree at the disrupted rami, whereas the Ganz clamp decreased motion to a greater degree at the disrupted sacroiliac joint.

Aged↗

PubMed1994

Geometric changes in the cervical spinal canal during impact.

SUMMARY OF BACKGROUND DATA: Although the extent of injury after cervical spine fracture can be visualized by imaging, the deformations that occur in the spinal canal during injury are unknown. STUDY DESIGN: This study compared spinal canal occlusion and axial length changes occurring during a simulated compressive burst fracture with the residual deformations after the injury. METHODS: Canal occlusion was measured from changes in pressure in a flexible tube with fluid flowing through it, placed in the canal space after removal of the cord in cadaver specimens. To measure canal axial length, cables were fixed in C1 and led through the foramen transversarium from C2-T1, then out through the base, where they were connected to the core rods of linearly variable differential transformers (LVDT). Axial compressive burst fractures were created in each of ten cadaveric cervical spine specimens using a drop-weight, while force, distraction, and occlusion were monitored throughout the injury event. Pre- and post-injury radiographs and computed tomography scans compared transient and post-injury spinal canal geometry changes. RESULTS: In all cases, severe compressive injuries were produced. Three had an extension component in addition to compression of the vertebra and retropulsion of bone into the canal. The mean post-injury axial height loss measured from radiographs was only 35% of that measured transiently (3.1 mm post-injury, compared with 8.9 mm measured transiently), indicating significant recovery of axial height after impact. Post-injury and transient height loss were not significantly correlated (r2 = 0.230, P = 0.16) demonstrating that it is not a good measure of the extent of injury. Similarly, mean post injury canal area was 139% of the minimum area measured during impact, indicating recovery of canal space, and post-injury and transient values were not significantly correlated (r2 = 0.272, P = 0.12). Mean post-injury midsagittal diameter was 269% of the minimum transient diameter and showed a weak but significant correlation (r2 = 0.481, P = 0.03). CONCLUSIONS: Two potential spinal cord injury-causing mechanisms in axial bursting injuries of the cervical spine are occlusion and shortening of the canal. Post-injury radiographic measurements significantly underestimate the actual transient injury that occurs during impact.

Biomechanical Phenomena↗

PubMed1994

Tensions in the palmar ligaments of the wrist. I. The normal wrist.

We developed a method for measurement of the in situ tensions in the ligaments of the palmar side of the wrist in cadaver specimens. The technique is based on deflecting the ligaments transversely (i.e., perpendicular to their longitudinal axis) using an instrumented probe. Based on measurement of the load required to deflect the ligament, magnitude of the transverse deflection, and axial length of the ligament, the axial tension in the ligament can be determined without otherwise disturbing it. The tensions in 8 palmar ligaments in 10 functional positions of the wrist in each of 5 fresh cadaver specimens were assessed. The position of the wrist was monitored, but the specimen was not loaded. We concluded that (1) the palmar ligaments are in tension, even with the wrist in neutral position and unloaded; (2) the following ligaments act as passive stabilizers: in neutral the triquetrocapitate and distal part of the radioscaphocapitate, in radial deviation the radiolunate, in ulnar deviation the ulnolunate, in pronation the proximal part of the radioscaphocapitate, in supination the ulnolunate, and in extension the ulnolunate, radiolunate, and radioscaphocapitate; (3) in any position some ligaments are in a state of greater tension than others. The radiolunate, ulnolunate, radioscaphocapitate had the greatest tension; and the lunotriquetral, trapeziocapitate, and scaphocapitate had the least.

Aged↗

PubMed1994

A biomechanical comparison of four methods of fixation of the trapeziometacarpal joint.

Four methods of internal fixation for trapeziometacarpal arthrodesis were evaluated for biomechanical stability under axial compression, torsion, and cantilever bending in either flexion-extension or radial-ulnar deviation. The techniques tested included crossed Kirschner wires, cerclage wiring, cup and cone with a single oblique Kirschner wire, and a tension band technique that has not previously been reported. Results reported included stiffness (load/deformation) of the construct and toggle (displacement without load applied, after cyclic loading). The tension band and cerclage techniques provided greater construct stiffnesses in axial loading than crossed Kirschner wire or cup-and-cone fixation, and toggle was significantly lower than for specimens fixed by the cup-and-cone technique. In torsion the tension band technique produced fixation that was significantly stiffer than cup-and-cone fixation. In cantilever bending the differences between fixation systems were not significant, except between cerclage and cup-and-cone techniques in flexion-extension. On the basis of our results in a biomechanical model, the tension band technique offers superior fixation in torsion, the cerclage technique in flexion-extension, and both in axial loading.

Arthrodesis↗

PubMed1994

Biomechanical effects of internal fixation of the distal tibiofibular syndesmotic joint: comparison of two fixation techniques.

This biomechanical study compares two methods of internal fixation of the tibiofibular syndesmosis used in Weber type C malleolar fractures of the ankle. The transverse syndesmotic 3.5-mm screw was compared with two 1.5-mm Kirschner wires introduced obliquely across the distal tibiofibular syndesmosis. The influence of implants on distal tibiofibular joint motion and contact characteristics of the intact ankle joint were determined. Up to 1.25 mm of lateral displacement and 2 degrees of external rotation of the lateral malleolus during uninjured ankle dorsiflexion was recorded. Both techniques stabilized the injured syndesmotic joint and limited its normal motion during flexion and extension of the ankle. Pressure distribution displaced laterally in internally stabilized ankles compared with intact specimens, regardless of the type of fixation used. Therefore, both techniques alter joint biomechanics equivalently compared with the intact ankle.

Ankle Injuries↗

PubMed1994

Contact characteristics of the ankle joint. Part 1. The normal joint.

The contact characteristics of ankle joints in 18 fresh cadaver specimens were studied by using pressure-sensitive film to provide baseline information for subsequent studies of various pathologic ankle conditions. Specimens, consisting of the distal half of the tibia and fibula and the intact ankle and foot, were mounted in a materials testing system on a loading frame that allowed positioning in neutral, and 20 degrees of plantarflexion and dorsiflexion. An 800 N load (1 body weight) was axially applied to the specimens through the tibia with 10% of the total load distributed through the fibula. Transducers made of pressure-sensitive film were used to make a contact print and were scanned along with calibration strips to form a digital image. The image was analyzed quantitatively to determine total contact area, mean contact pressure, ratio of contact to plafond areas, and high pressure zone centroid location as a function of sagittal plane foot position in the normal ankle joint. The results demonstrated significant changes in ankle joint contact characteristics with different foot positions.

Ankle Joint↗

PubMed1994

1994 William J. Stickel Gold Award. Contact characteristics of the ankle joint. Part 2. The effects of talar dome cartilage defects.

Variations in ankle joint contact characteristics caused by articular defects of the talar dome were investigated in 14 fresh-frozen cadaver specimens using pressure-sensitive film. Intact ankle and foot specimens were mounted in a materials tester on a loading frame which allowed positioning in neutral, and 20 degrees of dorsiflexion and plantarflexion. Joint contact prints were recorded while an 800 N load was axially applied through the leg. Specimens were randomly placed into two lesion groups: either anterolateral or posteromedial. During testing, each specimen had four concentrically placed lesions on the talar dome, graduated in size. Following removal, the film transducers were digitized along with pressure calibration prints. The images were analyzed quantitatively to determine contact areas, mean contact pressures, ratio of to contact plafond areas, and high pressure centroid position as a function of lesion size and location. The results demonstrated significant changes in contact characteristics for larger lesions (> or = 7.5 x 15 mm) (P < 0.05). These findings suggest that determining the size of a lesion may assist in predicting the long-term outcome of ankles with cartilage defects.

Ankle Injuries↗

PubMed1994

Biomechanical evaluation of methods of internal fixation of the distal humerus.

The best results following fractures of the distal humerus are provided by anatomic reduction and rigid internal fixation. Plates of two designs placed in five different fixation configurations were used to determine the construct that would maximize rigidity of fixation of the distal humerus. Using a cadaver distal humerus osteotomy, with and then without cortical contact, motion of the distal fragment was measured with respect to the proximal fragment in axial and torsional loading, anterior to posterior and posterior to anterior bending, and lateral to medial and medial to lateral bending. With cortical contact, two plates when placed medial and lateral or at 90 degrees to each other provided equivalent rigidity. However, with a cortical gap, the combination of a specially designed anatomic lateral buttress "J" plate and a medial reconstruction plate gave the greatest rigidity (ANOVA, p < 0.05). Two-plate constructs do not require placement at 90 degrees to obtain sufficient rigidity, but do require placement on separate bony pillars and different surfaces.

Biomechanical Phenomena↗

PubMed1994

Internal fixation of the unstable anterior pelvic ring: a biomechanical comparison of standard plating techniques and the retrograde medullary superior pubic ramus screw.

The purpose of this study was to evaluate pubic ramus fracture fixation. This biomechanical evaluation compared standard plating techniques with retrograde medullary screw fixation of a superior pubic ramus fracture in a pelvic fracture model. Six fresh-frozen, cadaveric pelvic specimens with a mean age of 79 years were harvested. These specimens were physiologically loaded according to the following modifications and instrumentations: (a) intact; (b) an APC-II unstable pelvic injury, specifically, unilateral superior and inferior rami osteotomies combined with ipsilateral anterior sacroiliac (SI) joint, sacrospinous, and sacrotuberous ligamentous disruptions, without fixation; (c) disrupted as in (b) but fixed anteriorly with a 10-hole 3.5-mm reconstruction plate contoured to the superior ramus and secured with four 3.5-mm cortical screws; (d) disrupted as in (b) but fixed anteriorly with a 10-hole 3.5-mm reconstruction plate contoured to the superior ramus and secured with six 3.5-mm cortical screws; (e) disrupted as in (b) but fixed anteriorly with a 4.5-mm retrograde medullary superior pubic ramus cortical screw 80 mm long (medial to the hip joint); and (f) disrupted as in (b) but fixed anteriorly with a 4.5-mm retrograde medullary superior pubic ramus cortical screw 130 mm long that was extraarticular and engaged the lateral iliac cortex cephalad to the ipsilateral hip joint. The posterior disruptions of the pelvic ring were not fixed. The APC-II injury created in this study resulted in significant (p < 0.05) motion at the disrupted rami and the injured SI joint, compared with the intact pelvic specimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1994

Box plate fixation of the symphysis pubis: biomechanical evaluation of a new technique.

The purpose of this study was to compare common techniques of pubic symphyseal fixation with a new method, the "box plate," for fractures of the pelvis where the bone is osteopenic. This symphyseal fixation construct consists of two, two-hole, 4.5-mm narrow dynamic compression plates (DCP) oriented parallel to one another. One plate is recessed within the symphysis, and the other is located on the pubic tubercles. The plates are interlocked using two 6.5-mm fully threaded screws, forming a box-like construct. To determine the mechanical properties of this construct, five fresh, cadaveric pelvic specimens with a mean age of 75 years were harvested. The femora of each specimen were potted into containers and fixed to the base of a materials testing machine. The pelvis was constrained from rotating about the hip joints by anterior and posterior restraints. A vertical compressive load was applied through the lumbar spine. Force to a magnitude of 1,000 N was applied through three cycles. Gapping motions at the symphysis pubis (SP) and the sacroiliac (SI) joints, and flexion-extension of the sacrum with respect to the ilia were measured under the following conditions: (a) intact, (b) SP ligament, unilateral anterior SI ligaments, and ipsilateral sacrospinous and sacrotuberous ligaments disrupted (anteroposterior compression type II injury), and these injuries fixed using (c) a 4.5-mm narrow two-hole DC plate placed on the superior SP held by two cancellous bone screws, (d) the DC plate well as a single 7.0-mm cannulated cancellouoffliosacral lag screw across the injured SI joint, (e) the DC plate and a five-hole 3.5-mm reconstruction plate on the anterior SP, (f) a 3.5-mm, four-hole, DC plate on the superior SP using four fully threaded screws, and (g) the box plate symphyseal construct described above. All fixations reduced SP joint gapping compared to the disrupted joint. However, all but the box plate still allowed significantly greater motion than the intact SP joint. No fixation significantly reduced SI joint gapping or sacral flexion compared to the injured state.

Aged↗

PubMed1994

Biomechanical simulation of the anteroposterior compression injury of the pelvis. An understanding of instability and fixation.

Seven fresh cadaveric pelvic specimens were biomechanically analyzed. Testing was first performed on intact pelves and then after progressive disruption of the (1) symphysis pubis, (2) unilateral anterior and interosseous sacroiliac ligaments and capsule, (3) ipsilateral sacrospinous and sacrotuberous ligaments; and fixation with a 4.5-mm narrow dynamic compression plate at the symphysis pubis, or a 4.5-mm narrow dynamic compression plate at the anterior sacroiliac joint with and without the symphysis pubis plate, or a 7.0-mm sacroiliac lag screw anchored into the S1 vertebral body with and without the symphysis pubis plate. Symphyseal gapping occurred after isolated symphysis pubis disruption. With additional disruption of the unilateral sacroiliac joint ligaments, symphysis pubis displacement was unaffected; however, the injured sacroiliac joint gap displacement, and sacroiliac joint flexion angulation on both intact and injured sides increased as compared to the specimen in the intact state. Further disruption of the ipsilateral sacrotuberous and sacrospinous ligament complex produced little additional motion at either symphysis pubis or sacroiliac joints. Plate fixation of the symphysis pubis alone reduced symphysis pubis motion, but not sacroiliac motion. Use of sacroiliac fixation alone without a symphysis pubis plate did not affect symphysis pubis motion. The symphysis pubis plate is the key to stabilizing symphysis pubis motion, and similarly, sacroiliac joint fixation is required to control sacroiliac joint motion. Both single iliosacral screws and plates produced equivalent decreases in sacroiliac joint motion.

Biomechanical Phenomena↗