Biomedical subjects

Frederick W Werner

Publications and source records attributed to Frederick W Werner.

At least 19 recordsLinked to original sources

PubMed2007

Severity of scapholunate instability is related to joint anatomy and congruency.

PURPOSE: To determine whether the bony architecture of the distal radius and proximal scaphoid have a role in stabilizing the scaphoid, and to determine whether a relationship between the bony geometry measurements and the amount of wrist constraint could be determined. METHODS: Eight cadaver wrists were tested in a wrist joint motion simulator. The level of scapholunate instability after sectioning the scapholunate interosseous, radioscaphocapitate, and the scaphotrapezium ligaments was determined and related to radiographic measurements of volar tilt, lateral tilt (ulnar tilt of the radioscaphoid fossa), the depth of the radioscaphoid fossa, and 6 radii of curvature measurements of the proximal scaphoid and distal radius. The force to dorsally dislocate the scaphoid out of the radioscaphoid fossa was computed. RESULTS: The radioscaphoid fossa and scaphoid curvatures were larger in those wrists that did not show gross instability after ligamentous sectioning in the wrist simulator. Similarly, those wrists with a deeper radioscaphoid fossa and greater volar tilt were also more stable. The force required to dislocate these wrists was greater than in those wrists that showed gross carpal instability. CONCLUSIONS: This study suggests that the bony anatomy of the radius and scaphoid have a role in stabilizing the carpus after ligament injury. The effect of ligament sectioning on producing carpal instability may be moderated by the bone geometry of the radiocarpal joint. This may explain why some people may have a tear of the scapholunate interosseous ligament but not present with clinical symptoms.

Biomechanical Phenomena↗

PubMed2006

The hysteresis effect in carpal kinematics.

PURPOSE: Carpal bones show hysteresis that is dependent on the direction of wrist motion during a continuous active loading protocol. We describe an accurate methodology for analyzing the hysteresis effect and we apply this model to analyze the effect of sequential ligament sectioning on scapholunate instability. METHODS: In 8 fresh cadaver forearms scaphoid, lunate, and third metacarpal motions were recorded while each wrist was moved in continuous cycles of active motion in flexion-extension and radioulnar deviation. Motions were analyzed for the intact state and after sequential sectioning of the scapholunate interosseous, scaphotrapezium, and radioscaphocapitate ligaments. Carpal motion was curve-fitted with respect to the third metacarpal motion using optimization criteria. The area between the 2 curves that represents opposite directions of wrist motion was measured to give the total hysteresis area. Repeated-measures analysis of variance was used to determine significance. RESULTS: In the flexion-extension trials the scaphoid and lunate total hysteresis area was significantly greater than the intact state only after all 3 ligaments were sectioned. In the radioulnar deviation trials the scaphoid total hysteresis area was significantly greater than the intact after just scapholunate interosseous ligament sectioning; however, the lunate total hysteresis area decreased with additional sequential sectionings in 4 of the 8 specimens as compared with the intact state. These 4 specimens started with a significantly greater intact total hysteresis area than the other 4 specimens. CONCLUSIONS: The computation of the total hysteresis area from the hysteresis effect was found to be a sensitive technique to determine the subtle onset of abnormal carpal motion. By using this technique in a ligament sectioning study significant increases in the total hysteresis area were seen after just scapholunate interosseous ligament sectioning during wrist radioulnar deviation. This subtle change may signify the onset of dynamic scapholunate instability. The total hysteresis area of the lunate in a subset of lax specimens did not increase after ligament sectioning. This divergent behavior may explain why some patients with scapholunate instability do not develop dorsal intercalated segmental instability.

Aged↗

PubMed2005

A biomechanical study on flexible intramedullary nails used to treat pediatric femoral fractures.

Flexible intramedullary nails have been indicated to treat femoral fractures in pediatric patients. The purpose of this study was to examine the stability of simulated transverse fractures after retrograde intramedullary flexible nail fixation. Various nail diameter combinations were tested using composite femurs in bending, torsion, and a combined axial/bending test where a vertical compressive force was applied to the femoral head. The cross-sectional percent area fill of the nails within the femurs was also determined. In 4 point bending, the greatest repair stiffness was 12% of the intact stiffness. In torsion, the greatest stiffness was 1% of the intact stiffness for either internal or external rotation. The greatest repair stiffness was 80% of the intact stiffness for a compressive load applied to the femoral head. Nail combinations with single nail diameters greater than 40% of the mid-shaft canal width, as measured from an AP radiograph, prevented the fracture from being reduced and left a posterior gap. Flexible intramedullary nails may be of value in the treatment of pediatric femoral fractures, but care must be taken to insert nails that are correctly sized for the canal and to protect the healing fracture from high torsional and bending loads.

Biomechanical Phenomena↗

PubMed2005

The effect of valgus/varus malalignment on load distribution in total knee replacements.

Valgus or varus malpositioning of the tibial component of a total knee implant may cause increased propensity for loosening or implant wear and eventually may lead to revision surgery. The aim of this study was to determine the effect of valgus/varus malalignment on tibio-femoral mechanics during surgical trial reduction and simulated gait loading. In seven cadaver legs, posterior cruciate sparing total knee replacements were implanted and tibial inserts representing a neutral alignment and 3 degrees and 5 degrees varus and valgus alignments were sequentially inserted. Each knee with each insert was loaded in a manner representative of a trial reduction performed during knee surgery and loaded in a physiological knee simulator. Simulated gait performed on the simulator demonstrated that internal/external and adduction/abduction rotations showed statistical changes with some of the angled inserts at different points in the walking cycle. Neither medial/lateral nor anterior/posterior translations changed statistically during simulated walking. The pressure distribution and total load in the medial and lateral compartments of the tibial component changed significantly with as little as a 3 degrees variation in angulation when loaded in a manner representative of a trial reduction or with a knee simulator. These results support the need for precise surgical reconstruction of the mechanical axis of the knee and proper alignment of the tibial component. These results further demonstrate that tibial contact pressures measured during a trial reduction method may be predictive of contact mechanics at the higher loading seen in the knee simulator.

Arthroplasty, Replacement, Knee↗

PubMed2005

ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion--Part II: shoulder, elbow, wrist and hand.

In this communication, the Standardization and Terminology Committee (STC) of the International Society of Biomechanics proposes a definition of a joint coordinate system (JCS) for the shoulder, elbow, wrist, and hand. For each joint, a standard for the local axis system in each articulating segment or bone is generated. These axes then standardize the JCS. The STC is publishing these recommendations so as to encourage their use, to stimulate feedback and discussion, and to facilitate further revisions. Adopting these standards will lead to better communication among researchers and clinicians.

Anthropometry↗

PubMed2005

Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: Part II.

PURPOSE: This study is a continuation of our previous investigation of the ligaments stabilizing the scaphoid and lunate. We evaluated the effects of sectioning the scapholunate interosseous ligament, radioscaphocapitate ligament, and scaphotrapezial ligament in 3 sequences. METHODS: Three sets of 8 cadaver forearms were placed in a wrist simulator and moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the 3 ligaments were sectioned in various sequences and after the wrist was moved through 1,000 cycles of motion. RESULTS: Sectioning only the scaphotrapezium ligament (ST) or the radioscaphocapitate ligament (RSC) resulted in minimal angular changes to the motion of the scaphoid and lunate. Sectioning of the scapholunate interosseous ligament (SLIL) or 1,000 cycles of repetitive wrist motion after ligament sectioning altered scaphoid and lunate kinematics. CONCLUSIONS: Based on these findings it was concluded that the SLIL is the primary stabilizer and the RSC and ST are secondary stabilizers of the scapholunate articulation. Repetitive motion after ligament injury probably results in further carpal instability.

Adult↗

PubMed2005

Changes in patterns of scaphoid and lunate motion during functional arcs of wrist motion induced by ligament division.

PURPOSE: To determine the in vitro motion of the scaphoid and lunate during wrist circumduction and wrist dart-throw motions and to see how these motions change after the ligamentous stabilizers of the scaphoid and lunate are sectioned in a manner simulating scapholunate instability. METHODS: Twenty-one fresh-frozen cadaver forearms were moved through a dart-throw motion and a circumduction motion using a wrist joint simulator. Scaphoid and lunate motion were measured with the wrist ligaments intact and after sectioning of the scapholunate interosseous ligament, the scaphotrapezium ligament, and the radioscaphocapitate ligament. RESULTS: In the intact wrist the scaphoid and lunate moved more during circumduction than during the dart-throw motion. With ligamentous sectioning the scaphoid flexed more and the lunate extended more during both the circumduction and dart-throw motions. During the circumduction motion both before and after sectioning the global motion of the scaphoid was greater than that of the lunate. After sectioning the scaphoid motion increased and the lunate motion decreased. CONCLUSIONS: The scaphoid and lunate motions were observed to change remarkably after ligamentous sectioning. The observed changes in carpal motion correlate with the clinical observation that after ligamentous injury arthritic changes occur in the radioscaphoid joint and not in the radiolunate joint. Analysis of the injured wrist in positions that combine flexion-extension and radial-ulnar deviation may allow noninvasive diagnosis of specific wrist ligament injuries.

Adult↗

PubMed2004

Three-dimensional modeling and animation of two carpal bones: a technique.

The objectives of this study were to (a). create 3D reconstructions of two carpal bones from single CT data sets and animate these bones with experimental in vitro motion data collected during dynamic loading of the wrist joint, (b). develop a technique to calculate the minimum interbone distance between the two carpal bones, and (c). validate the interbone distance calculation process. This method utilized commercial software to create the animations and an in-house program to interface with three-dimensional CAD software to calculate the minimum distance between the irregular geometries of the bones. This interbone minimum distance provides quantitative information regarding the motion of the bones studied and may help to understand and quantify the effects of ligamentous injury.

Carpal Bones↗

PubMed2004

Scaphoid and lunate motion during a wrist dart throw motion.

PURPOSE: The primary purpose of this study was to measure the in vitro scaphoid and lunate motion during 9 different variations of a wrist dart throw motion. Another goal was to determine the specific dart throw motion that minimized scaphoid and lunate motion. METHODS: Scaphoid and lunate motion were recorded in 7 cadaver forearms during various combinations of wrist dart throw motions caused by a wrist joint motion simulator. RESULTS: During wrist flexion and extension the scaphoid and lunate motions follow the wrist motion. During wrist radial and ulnar deviation the scaphoid and lunate correspondingly flex and extend. During intermediate motions the scaphoid and lunate move as little as 26% of the total third metacarpal motion and do not necessarily follow a planar motion. CONCLUSIONS: These findings suggest that there may be a dart throw motion during which there may be minimal scaphoid and lunate motion. If a subject's wrist motion could be clinically restricted to this dart throw motion, early hand mobility might be possible after surgery on the scaphoid and lunate.

Aged↗

PubMed2004

Arthroscopic resection of arthrosis of the proximal hamate: a clinical and biomechanical study.

PURPOSE: The purpose of this study was to present a series of patients with arthrosis of the proximal hamate treated by arthroscopic resection. To further investigate this condition a biomechanical study also was undertaken to document the effect this proximal hamate resection has on carpal loading. METHODS: Between 1991 and 2001 there were 23 patients who had arthroscopic proximal hamate resection for the treatment of proximal hamate arthrosis. Twenty-one patients were available for final follow-up evaluation (average, 4.7 y). Patients were evaluated by using a modified wrist score that examined pain relief, patient satisfaction, range of motion, and grip strength. Six cadaver wrists had resection of the proximal hamate. Loads across the carpal and midcarpal joints were documented with pressure-sensitive film before and after proximal hamate resection. RESULTS: Ninety-five percent of the patients had a type II lunate. Twenty-one of 23 wrists had lunotriquetral tears confirmed on arthroscopic examination. Follow-up evaluation revealed 14 excellent, 4 good, 1 fair, and 2 poor results. Biomechanical studies revealed that resection of 2.4 mm of the proximal hamate unloads the hamatolunate articulation without changing the load at the triquetrohamate joint. CONCLUSIONS: Arthrosis of the proximal pole of the hamate seems to be associated closely with tears of the lunotriquetral joint and may be part of the spectrum of ulnar-sided wrist degeneration. Arthroscopic resection of the proximal pole of the hamate appears to be a useful treatment in patients with symptomatic hamate arthrosis, even in those patients with lunotriquetral laxity.

Adult↗

PubMed2004

A biomechanical modeling of injury, repair, and rehabilitation of ulnar collateral ligament injuries of the thumb.

PURPOSE: The use of early active motion protocols after repair of the thumb ulnar collateral ligament (UCL) theoretically could avoid the complications of postoperative immobilization and improve ligament healing. The goals of this study were as follows: (1) to develop an accurate model of acute UCL rupture, (2) to determine the strain pattern in the UCL during constrained active thumb motion in intact and repaired thumbs, and (3) to determine the load to failure and strain of the UCL during rupture in forced abduction. METHODS: Sixteen fresh-frozen adult cadaver thumbs were mounted in a testing apparatus designed for testing the strain in the UCL during constrained active motion and abduction load to failure. Strain data for the UCL during motion were measured. Specimens were tested to failure using an MTS machine. Dynamic strain data were acquired throughout the loading cycle. Repair of the torn ligament was performed with a suture anchor technique. Strain and load-to-failure measurements then were repeated in the repaired specimens. Differences in the strain values and failure forces between the intact and repaired specimens then were compared. RESULTS: A reliable model of a UCL rupture was created. Strains in the UCL were similar during active motion in both intact and repaired specimens. A significant decrease in maximum load to failure was noted in repaired specimens but failure reliably occurred at strains 3 times greater than expected with active motion. CONCLUSIONS: A controlled active motion therapy protocol after suture anchor repair of a ruptured UCL of the thumb is safe from a biomechanical point of view.

Adult↗

PubMed2004

The safety of pumpkin carving tools.

BACKGROUND: Even with optimal treatment, injuries from pumpkin carving accidents may leave people with compromised hand function. Pumpkin carving tools may reduce the incidence and/or magnitude of these injuries. However, evidence that they are safer is required before these knives can be recommended. METHODS: Two pumpkin carving knives were compared to a serrated and a plain kitchen knife. The forces required to cut and pierce a pumpkin were determined and then applied by a servo-hydraulic machine to each knife placed against cadaver hands in a manner designed to either lacerate Zone 2 of the finger (six tests for each knife) or to puncture the hand. Inspection and dissection determined the extent of injury. RESULTS: The pumpkin knives produced some injuries, however, they were fewer and less severe than those caused by the kitchen knives. CONCLUSIONS: Tools designed specifically for pumpkin carving may indeed be safer. Use of these products, and increased overall awareness of the risks of pumpkin carving in general, which clinicians could help promote, might reduce the frequency and severity of pumpkin carving injuries.

Cooking and Eating Utensils↗

PubMed2004

Biomechanical study of pins in cementing of contained proximal tibia defect.

Defects from curettage for giant cell tumors of bone frequently have been reconstructed with bone cement with or without reinforcement pins. The biomechanical basis for the addition of reinforcement pins was examined using a model of a contained defect in the proximal tibia. Fifty-four cadaveric proximal tibia in matched pairs were divided into five test groups: intact tibia, medial metaphyseal contained defect, defect reconstructed with cement alone, defect reconstructed with cement and pins inserted within the medullary canal, and defect reconstructed with cement and pins inserted through the cortex. Specimens were tested to failure during one cycle of compressive loading. Defect specimens were significantly weaker and less stiff than intact specimens, establishing the validity of the model-contained defects. For the reconstructions, there was no statistically significant difference in load to failure, stiffness, energy to failure, or displacement for the polymethylmethacrylate treatment alone when compared with matched specimen receiving polymethylmethacrylate and pins treatment. Similarly, there was no statistical difference in biomechanical properties in comparing matched specimens treated with polymethylmethacrylate alone or polymethylmethacrylate/pins (cortex). For contained defects of the proximal tibia that are typical after curettage for giant cell tumor, there appears to be no biomechanical advantage to use of reinforcement pins in the cement.

Biomechanical Phenomena↗

PubMed2004

Contained femoral defects: biomechanical analysis of pin augmentation in cement.

Although in the proximal tibia the need for pin augmentation of cemented giant cell tumor defects depends on whether the defect is contained, there is controversy regarding the role for pins in the distal femur. The current study investigated whether Steinmann pin augmentation offers biomechanical advantages in cement reconstruction of contained defects of the lateral femoral condyle. Twelve pairs of human femurs were used. They were tested either with the bone intact, with a standardized contained defect in the lateral condyle, with a defect repaired with cement alone, and with a defect repaired with pins in the cement. Intact specimens had significantly higher load to failure than specimens with a defect. In the repaired specimens there were no significant differences in stiffness, peak load to failure, and energy to failure between the specimens repaired with just cement or augmented with pins. This study did not show any significant biomechanical advantage of this configuration of Steinmann pin reinforcement in cement for contained defects of the lateral femoral condyle.

Biomechanical Phenomena↗

PubMed2003

Capsuloligamentous restraints to dorsal and palmar carpal translation.

PURPOSE: The purpose of this study was to determine biomechanically the relative contributions of the dorsal and palmar capsuloligamentous structures to dorsal and palmar carpal stability. METHODS: Seven fresh-frozen cadaver specimens were tested using a testing machine (MTS, Eden Prairie, MN) with low loads applied perpendicular to the axis of the radial diaphysis. We determined the loads required to achieve dorsal and palmar translation of the carpus on the radius as palmar and dorsal ligaments and capsule were sectioned sequentially. The relative contributions of the dorsal and palmar capsuloligamentous structures to dorsal and palmar stability were determined. RESULTS: The palmar structures provided a statistically significantly greater restraint (61%) to dorsal translation of the carpus than did the dorsal structures (2%). The palmar structures also provided a statistically greater restraint (48%) to palmar translation of the carpus than did the dorsal structures (6%). CONCLUSIONS: The palmar capsuloligamentous structures provided greater restraint to both dorsal and palmar translation of the carpus. We suggest that surgeons consider repair or reconstruction of traumatic injuries to these structures.

Aged↗

PubMed2003

Wide excision of the distal ulna: biomechanical testing of a salvage procedure.

PURPOSE: To study changes in the relationship of the distal radius and ulna after progressive resection of the distal ulna. METHOD: Six-degree-of-freedom motion sensors were used to determine relative motion and a displacement transducer was used to determine strain changes in the interosseous membrane (IOM). These were applied in cadaveric specimens loaded to simulate wrist motion and axial compressive forces. RESULTS: Strain in the IOM decreased with increasing resection of the distal ulna. The distance between the radius and ulna decreased with increasing resection up to 20% of ulna length. CONCLUSIONS: The decreased strain in the IOM and stabilization of the distance between the radius and ulna at 20% resection level provides biomechanical support for the satisfactory clinical results seen after wide ulnar resection. Wide excision of the distal ulna may be a viable salvage alternative to creation of a one-bone forearm.

Biomechanical Phenomena↗

PubMed2002

The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics.

The role of the dorsal radiocarpal wrist ligament has been the subject of several investigations. Several biomechanical studies have used sensors inserted dorsally into the wrist joint to evaluate its pressure distribution. The purpose of this study was to evaluate whether a dorsal capsulotomy that sections the dorsal radiocarpal ligament or insertion of a flexible pressure sensor alters scaphoid or lunate kinematics. Eight cadaver upper extremities were instrumented with motion sensors and placed in a wrist joint simulator. Each arm was moved through continual cycles of wrist flexion/extension and radial/ulnar deviation. Motion data were obtained in the intact state, after a capsulotomy, and after insertion of the sensor. We found that either a dorsal capsulotomy sectioning the dorsal radiocarpal ligament or insertion of the pressure sensor alters scaphoid and lunate kinematics during dynamic wrist motion. This study supports the clinical belief that this dorsal wrist ligament should be spared during surgical approaches to the carpus.

Aged↗

PubMed2002

Radiologic evaluation of the ulnar styloid.

The ulnar styloid (US) architecture was examined radiologically and directly by dissection in 13 cadaver wrists to examine a potential relationship between US shape and US abutment syndrome and to determine an optimal radiographic view that could be used to detect US fractures. A higher incidence of US abutment syndrome in the radially deviated US type was observed by dissection. Radiographs taken at varying shoulder abduction angles suggested that the base of the US and ulnar head are not round. To best evaluate the fovea and the US for possible US fractures, radiographs should be taken with the glenohumeral joint abducted 45 degrees, the elbow flexed 90 degrees, the forearm in neutral rotation, and the x-ray beam directed through the wrist perpendicular to the floor.

Dissection↗