Clarence L. Nicodemus

High-speed, three-dimensional kinematic analysis of the normal wrist.

Carpal kinematics during a wrist flexion/extension motion using high-speed videodata acquisition was investigated. A cadaver forearm was stabilized, allowing unconstrained excursion of the wrist for passive range of motion (ROM). The extensor and flexor pairs of the wrist were looped together and a 1-lb weight was attached to each pair, simulating synergistic muscle tension. Capitate/radius and third metacarpal/radius angles were calculated to determine which measurement would be best for determining global wrist angle. The average difference in capitate/radius and third metacarpal/radius angles at each respective flexion/extension wrist angle for all wrists was 1.1 degrees +/- 1.6 degrees (the maximum difference was 4 degrees). Hence, the capitate-third metacarpal joint can be considered rigid. Capitate/lunate motion as described by capitate-radius Euler angles ranged from -16.9 to 23.5 with total capitate/lunate motion of 40.5 (35%) in the 114 degrees total global wrist ROM measured. Radius/lunate motion as described by lunate-radius angle ranged from -8.2 to 48.4 with total radius/lunate motion of 56.5 (49%) in the 114 degrees total global wrist ROM measured. During global wrist motion, the radiolunate joint contributes more motion in flexion than the capitolunate joint and the capitolunate joint contributes more motion in extension than the radiolunate joint. The instantaneous screw axes (ISAs) were calculated for each third metacarpal position with respect to the radius. The average distance difference between ISAs for the 4 wrists tested was -1.23 +/- 14.97 pixels. The maximum distance was 56.51 pixels and the minimum was -24.09 pixels. This new combination of motion analysis and 3-dimensional reconstructions of computed tomography images affords a high-speed, dynamic analysis of kinematics. It shows that during wrist flexion/extension, normal carpal kinematics does not have an ISA fixed in or limited to the capitate. In addition, the ISA data provide evidence that translational motion is a real and measurable component of normal carpal motion. These findings alter the understanding of carpal kinematics obtained from the results of previous studies which suggested that the center of rotation was fixed in the capitate.

Correlation of bone equivalent mineral density to pull-out resistance of triangulated pedicle screw construct

Thirty single-pedicle and triangulated pedicle screws were subjected to pull-out tests until complete dislodgment was achieved. Peak load, displacement curves, angle of triangulation, and equivalent mineral density were recorded. Dual pedicle screw triangulation produced a 154.4% increase in peak pull-out strength compared with that of the single pedicle screw. Salvage triangulation (replacing failed screws with a triangulation construct) produced a 127.4% increase in peak strength over that of the single screw. Positive correlation was found between individual screw peak strength, bone mineral density, and displacement at peak load. Primary and salvage triangulation produced higher resistance to pull-out than a single pedicle screw, which reflects the potential, beneficial effect of using this technique. Triangulation, therefore, can be used as primary (prophylactic) technique to enhance pedicular screw pull-out during forceful vertebral manipulation.

Plaster of Paris as an Osteoconductive Material for Interbody Vertebral Fusion in Mature Sheep

Study Design. In adult female sheep, histologic and biomechanical criteria were used to determine whether the osteoconductive performance of plaster of paris would promote the incorporation of the tubular titanium mesh implants used for interbody vertebral fusions. Objectives. To compare the osteogenicity of plaster of paris with that of autogenous iliac crest bone and bone marrow 6 months after they were loaded into tubular titanium mesh cages and implanted as L3–L5 bridges after L4 corpectomies. Summary of Background Data. One of the aims of surgery for vertebral pathology is to stabilize the spine by interbody fusions. The morbidity associated with the use of iliac crest autograft bone for fusion grafts prompted trials using plaster of paris as an osteoconductive substrate. Methods. The total volume of bone that invested the L3–L5 mesh cages after 6 months was quantitated by computed tomography scans. All specimens subsequently were cut into fusion mass segments for biomechanical testing in flexion, extension, compression, and torsion, and then embedded in plastic for sectioning and histomorphometry to determine the trabecular bone volume within the titanium mesh. Results. In each experimental model, implants of plaster of paris were the osteoconductive equal of autogenous iliac crest bone/marrow preparations. The volumes of bone formed around and within the titanium mesh were identical, and the tissues were biomechanically indistinguishable. A partial mechanism was determined by modifying the system for midshaft femoral defects. Conclusions. In the sheep, a tubular titanium mesh packed with plaster of paris forms an osteoconductive conduit to achieve a biomechanically stable interbody lumbar vertebral fusion.

Reliability of static standing balance in nondisabled children: comparison of two methods of measurement

Static standing balance is commonly measured with research laboratory systems (LabSys) or clinical systems (ClinSys). The purposes of this study were to (1) assess the reliability of two systems designed to measure static standing balance in nondisabled children, (2) compare the findings derived from the two systems of measurement, and (3) examine the relationship between anthropometric measures and postural sway. Twenty-five nondisabled children (12 male, 13 female) ages 1 year 11 months to 12 years 2 months (mean = 6 years 4 months; SD = 4 years 3 months) participated in the study. Each child stood on the LabSys and the ClinSys for three consecutive 10 second measurement periods. Intraclass correlation coefficients (ICC (2, 1)) for the three trials on each system were 0.62 (LabSys) and 0.63 (ClinSys). The level of agreement between the two systems was 0.61 (ICC (2, 1)). Younger children exhibited more variability and less agreement between measurement trials using the ClinSys. However, older children demonstrated more similar sway indices when comparing the two systems of measurement. Two-way analysis of variance indicated that there were significant differences between sway indices measured by the two systems (p < 0.01) and between the youngest children (aged 2-4 years) and all other children (p < 0.01). In addition, agreement among trials for the two systems was different depending on the age group measured. Correlation coefficients for sway index and age, height, weight, and foot length ranged from -0.52 to -0.64 for the LabSys (p < 0.01) and -0.62 to -0.73 for the Clin-Sys (p < 0.01). Stepwise multiple regression analysis indicated that height was the most significant predictor of sway when measured by the ClinSys (R2 = 0.536, p < 0.01) whereas age was the most significant predictor when sway was measured using the LabSys (R2 = 0.403, p < 0.01). The results suggest that the degree of postural sway and the reliability of the measurement itself are influenced by the age of the child and the measurement system employed.

Location and geometric description of carpal bones in CT images

The carpal regions of ten cadaver extremities were imaged by CT. The images were combined into a 3-dimensional model of the carpus using a technique based on a dynamic programming algorithm to find an optimal estimate of the location of the bone boundaries in the CT images. The resulting set of surface points on each bone was used to compute volumes and principal and antipodal axes for the bones. A spatial coordinate system was established based on the positions of the centroids of three bones in the distal carpal row. The angular orientations of all carpal bones were determined with respect to this system. The principal axes for the same bone among ten wrist specimens proved to be more widely dispersed than the antipodal axes for the same bones. The antipodal axes also correspond more closely to an intuitive notion of the “longest axis” of the bones. We conclude that the antipodal axis is a more reliable and useful measure of bone orientation than the principal axis.

Torsional injury resulting in disc degeneration: I. An in vivo rabbit model

Torsional injuries may be a precursor to intervertebral disc degeneration, but published rabbit models indicate a latent time of 6 months. We describe a rabbit model in which instability and disc degeneration appear within 3 months. Sixty-five male New Zealand rabbits underwent presurgical irradiation to inhibit heterotopic bone formation. Control animals then underwent either a soft-tissue release or facetectomy and capsulotomy, whereas experimental animals received surgery and an acute 30 degrees torsional lumbar injury. Capsulotomy, as well as facetectomy without torsion, failed to effect disc degeneration. However, the rabbits that received torsion exhibited clear indications of degenerative disc changes (thinning, increased PLA2 levels, and decreased nucleus pulposus volume) within 60-90 days. The observations associate disc degeneration with a destabilizing acute torsional injury.

Audit of autotransfusion in spine surgery

Summary.A prospective evaluation has been undertaken of 382 patients undergoing reconstructive spine surgery during a thirty-six month period. Acute normovolaemic haemodilution and haemapheresis for blood component sequestration was used in 80 patients in the operating theatre. An average of two units each of freshly collected autologous red cells and fresh plasma together with a therapeutic dose of a plateletpheresis product were prepared for each patient prior to surgical incision. The same supplies and equipment were subsequently used for conventional blood salvage and autotransfusion. The other 302 patients received salvaged blood only. Of the total blood transfused, autologous red cells comprised 87% of sequestration and 49% of autotransfusion-only patients. Each group received the same total perioperative red blood cell support. The cost for one red cell equivalent by intraoperative autologous transfusion was competitive with that of providing one unit of cross-matched allogeneic red cells. As compared with salvage alone, sequestration combined with salvage was even more cost effective and decreased reliance on allogenic products and preoperative autologous blood donations. The rate of transfusing autologous blood products was markedly increased.Résumé.Cette étude prospective rapporte 382 patients qui ont subi une chirurgie réconstructive de la colonne durant une période de 36 mois. Quatre-vingt (80) patients ont subi une hémodilution normovolèmique et une sequestration de produits sanguins sous anesthesie générale dans la salle d’opération. Une moyenne de deux unités de globules rouges autologues, de plasma frais et une unité de plaquettephérése thérapeutique ont été préparées avant l’intervention chirugicale. L’équipement utilisé pour la sequestration des produits sanguins a été ensuite utilisé pour une auto-transfusion conventionelle. Les autres 302 patients ont reçu seulement une auto-transfusion. De toutes les unités transfusees le sang autologue etait de 87% dans le groupe sequestré et 49% dans le groupe seulement autotransfusé. Chaque groupe a reçu le même total de globules rouges comme support de base pendant l’operation. Le coût de récuperation des globules rouges était comparable au coût d’une unite de globules rouges allogéniques. Le coût de la sequestration et de l’autotransfusion comparéà celui de l’autotransfusion seule a demontré une diminution du coût des produits sanguins allogéniques et de celui de l’obtention préopératoire de sang autologue. Les produits sanguins autologues s’avérent done aussi rentables.

A note on the determination of angular velocities in human motion studies.

Often the study of sports activities involves a reduction of film data to determine displacements, rotations, velocities and accelerations. Many researchers use the change in position of the projection of a body segment onto a plane of interest (usually the film plane) to determine the component of angular velocity in the plane. This techanical note illustrates that the determination of angular velocity components in this manner leads to erroneous values except in some special cases.

The efficacy of dynamic external fixation for treatment of distal radius fractures using 3D kinematic analysis

The purpose of this study was to investigate the kinematics of external fixation devices used for distal radius fractures. Dynamic external fixator devices that are placed across the wrist joint facilitate fracture healing by allowing force transmission across the fracture site and articular cartilage repair by allowing wrist motion. If external fixation devices are to be used dynamically, then their actual effect on wrist kinematics should be determined. Unfortunately, there has been no agreement among authors regarding normal carpal kinematics. This study investigated several parameters, global wrist flexion/extension, angles between carpal bones, and the instantaneous screw axis (ISA), in an attempt to quantify normal kinematics and the kinematics of wrists with external fixators attached. The results of this study show that the center of rotation of the wrist is not limited to the proximal head of the capitate as previously suggested. It also shows that the global range of motion of the wrist is limited with the application of any of the dynamic external fixators tested. Finally, the intercarpal bone joint angles are altered with the application of an external fixator. The radial-lunate joint has an increased range of motion with an external fixator attached in order to compensate for the constraints imposed by the external fixator.

Kinematic Geometry of the Wrist: Preliminary Report

This research significantly advances the state of the art in our ability to visualize the dynamic kinematics of the wrist. Beginning 150 years ago, investigations into the kinematics of the wrist were anatomical descriptions5,6,8,10,20,21 with observations made by the eye and including the earliest use of the x-ray after its discovery in 1895. It was not until much later that McConail12 began to apply basic mechanical laws to the curiosities and movement of the wrist and its complex of eight carpal bones. Motion studies began with cineradiography1,26 and moved parallel with technological development of optical and electronic methods of measuring minute distances accurately while the joint is moving. Use of LED path generation on photographic plates was used in conjunction with both cineradiographic and cinematographic (movie film)26 methods in an attempt to improve and automate the laborious and error prone requirement of hand digitizing data. With the introduction of the spark gap, or sonic digitizer, 3-D positional data could be taken automatically from moving joint components.3,4,27 Experimental error associated with the sonic digitizing equipment, its dependency on acoustic related environmental conditions (temperature, humidity, air movement) and the physical size of the spark gap apparatus itself still left much to be desired. Because of these concerns, recent investigators have attempted to return to basic approaches (manual analysis of biplanar radiographs) to increase precision even at the expense of fewer data points and increase in digitization error.7,9,14