Measurement of carpal bone geometry by computer analysis of three-dimensional CT images

Sex-Specific Size Analysis of Carpal Bones: Implications for Orthopedic Biomedical Device Design and Therapy Planning

Consideration of the individual carpal bone characteristics of the wrist plays a key role in well-functioning biomedical devices and successful surgical procedures. Although geometric differences and individual bone sizes have been analyzed in the literature, detailed morphologic descriptions and correlations covering the entire wrist reported in a clinical context are lacking. This study aimed to perform a comprehensive and automatic analysis of the wrist morphology using the freely available "Open Source Carpal Database" (OSCD). We quantified the size of each of the individual carpal bones and their combination. These sizes were extracted in n = 117 datasets of the wrist of the OSCD in anatomical directions and analyzed using descriptive statics and correlation analysis to investigate the morphological characteristics under sex-specific aspects and to provide regression plots and equations to predict individual carpal bone sizes from the proximal and distal row dimensions. The correlations in the proximal row were higher compared to the distal row. We established comprehensive size correlations and size rations and found that there exist statistical differences between sex, particularly of the scaphoid. The regression plots and equations we provided will assist surgeons in a more accurate preoperative morphological evaluation for therapy planning and may be used for future anatomically inspired orthopedic biomedical device designs.

Radiological measurement of pelvic fractures using a pelvic deformity measurement software program

BACKGROUND

It is difficult for the surgeon to measure pelvic displacement in the closed reduction operation for unstable pelvic fracture. We therefore developed a pelvic deformity measurement software program based on standardized radiographs. The objectives of the present study were to evaluate the inter-observer reliability of the program for measuring specific fracture types on preoperative pelvic films and to assess the validity of the measurement software program by comparing it with a gold standard.

METHODS

Twenty-five patients diagnosed with AO/OTA type B or C pelvic fractures with the unilateral pelvis fractured and dislocated were included in this study. Four separate observers repeatedly determined the translational and rotational patterns and outcomes using the software program and hand measurement, and calculated the displacement using computed tomography (CT) coupled with a three-dimensional (3D) CT model. The validity of the measurement software was calculated by assessing the consistency between the software measurements and the gold standard. Additionally, inter-observer reliability was assessed for the software. The software was also applied in preliminary clinical practice for closed reduction procedures.

RESULTS

The overall inter-observer reliabilities of the software program, CT coupled with 3D reconstruction, and hand measurements were high, with kappa values of 0.956, 0.958, and 0.853, respectively. The software showed validity similar to that of CT coupled with 3D reconstruction (0.939 vs. 0.969), and better than that of hand measurement (0.939 vs. 0.858). A preliminary clinical application demonstrated that the software is effective for guiding closed reduction of pelvic fractures.

CONCLUSIONS

Our newly established pelvic deformity measurement program is a reliable and accurate tool for analyzing pelvic displacement patterns and can be used for guidance of closed reduction and planning of the reduction pathway.

LEVEL OF EVIDENCE

III.

Evaluation of the geometric accuracy of computed tomography and microcomputed tomography of the articular surface of the distal portion of the radius of cats

OBJECTIVE

To evaluate accuracy of articular surfaces determined by use of 2 perpendicular CT orientations, micro-CT, and laser scanning.

SAMPLE

23 cat cadavers.

PROCEDURES

Images of antebrachia were obtained by use of CT (voxel size, 0.6 mm) in longitudinal orientation (CT_LO images) and transverse orientation (CT_TO images) and by use of micro-CT (voxel size, 0.024 mm) in a longitudinal orientation. Images were reconstructed. Craniocaudal and mediolateral length, radius of curvature, and deviation of the articular surface of the distal portion of the radius of 3-D renderings for CT_LO, CT_TO, and micro-CT images were compared with results of 3-D renderings acquired with a laser scanner (resolution, 0.025 mm).

RESULTS

Measurement of CT_LO and CT_TO images overestimated craniocaudal and mediolateral length of the articular surface by 4% to 10%. Measurement of micro-CT images underestimated craniocaudal and mediolateral length by 1%. Measurement of CT_LO and CT_TO images underestimated mediolateral radius of curvature by 15% and overestimated craniocaudal radius of curvature by > 100%; use of micro-CT images underestimated them by 3% and 5%, respectively. Mean ± SD surface deviation was 0.26 ± 0.09 mm for CT_LO images, 0.30 ± 0.28 mm for CT_TO images, and 0.04 ± 0.02 mm for micro-CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Articular surface models derived from CT images had dimensional errors that approximately matched the voxel size. Thus, CT cannot be used to plan conforming arthroplasties in small joints and could lack precision when used to plan the correction of a limb deformity or repair of a fracture.

A computer aided measurement method for unstable pelvic fractures based on standardized radiographs

BACKGROUND

To set up a method for measuring radiographic displacement of unstable pelvic ring fractures based on standardized X-ray images and then test its reliability and validity using a software-based measurement technique.

METHODS

Twenty-five patients that were diagnosed as AO/OTA type B or C pelvic fractures with unilateral pelvis fractured and dislocated were eligible for inclusion by a review of medical records in our clinical centre. Based on the input pelvic preoperative CT data, the standardized X-ray images, including inlet, outlet, and anterior-posterior (AP) radiographs, were simulated using Armira software (Visage Imaging GmbH, Berlin, Germany). After representative anatomic landmarks were marked on the standardized X-ray images, the 2-dimensional (2D) coordinates of these points could be revealed in Digimizer software (Model: Mitutoyo Corp., Tokyo, Japan). Subsequently, we developed a formula that indicated the translational and rotational displacement patterns of the injured hemipelvis. Five separate observers calculated the displacement outcomes using the established formula and determined the rotational patterns using a 3D-CT model based on their overall impression. We performed 3D reconstruction of all the fractured pelvises using Mimics (Materialise, Haasrode, Belgium) and determined the translational and rotational displacement using 3-matic suite. The interobserver reliability of the new method was assessed by comparing the continuous measure and categorical outcomes using intraclass correlation coefficient (ICC) and kappa statistic, respectively.

RESULT

The interobserver reliability of the new method for translational and rotational measurement was high, with both ICCs above 0.9. Rotational outcome assessed by the new method was the same as that concluded by 3-matic software. The agreement for rotational outcome among orthopaedic surgeons based on overall impression was poor (kappa statistic, 0.250 to 0.426). Compared with the 3D reconstruction outcome, the interobserver reliability of the formula method for translational and rotational measures was perfect with both ICCs more than 0.9.

CONCLUSIONS

The new method for measuring displacement using a formula was reliable, and could minimise the measurement errors and maximise the precision of pelvic fracture description. Furthermore, this study was useful for standardising the operative plan and establishing a theoretical basis for robot-assisted pelvic fracture surgery based on 2-D radiographs.

Variation in the femoral bow: a novel high-throughput analysis of 3922 femurs on cross-sectional imaging

OBJECTIVES

To evaluate femoral radius of curvature in a large sample of computed tomography scans to definitively determine the relationship between radius of curvature and femoral length, age, gender, ethnicity, body mass index and cortical thickness.

METHODS

A retrospective review was conducted of the electronic medical records and advanced imaging of 1961 patients who underwent pulmonary embolism protocol computed tomography scans between December 1999 and March 2010. The computed tomography scans were imported from the clinical picture archiving and communication system archive into a research image archive and analysis system. Each scan was processed by an automated system that algorithmically determined bony landmarks, adjusted for body position within the scanner and measured the radius of curvature.

RESULTS

The mean medullary radius of curvature of 3922 femurs was 112 cm (SD = 26 cm). The mean anterior radius of curvature of the femurs was 145 cm (SD = 55 cm). There was a moderately strong positive correlation (0.36-0.39) between femoral length and radius of curvature (P < 0.0001) that was not affected by age, body mass index, cortical thickness, gender, or ethnicity. No significant relationship was found between either gender or ethnicity and radius of curvature independent of femoral length.

CONCLUSIONS

Differences in radius of curvature based on ethnicity and gender exist primarily because of the variation in average height, and therefore femur length, that exists between ethnic groups and genders. These data may prove useful in the design of safer intramedullary implants that accommodate a greater spectrum of anatomic variation.

Measurement of intraarticular wrist joint biomechanics with a force controlled system

Pathologies of the wrist, such as fractures or instabilities, can lead to alterations in joint biomechanics. Accurate treatment of these pathologies is a frequent challenge for the surgeon. For biomechanical investigations, a test-setup that applies physiological loading of the wrist joint is necessary. A force controlled test-bench with agonistic and antagonistic muscle forces was built to move six fresh frozen human upper extremities through flexion and extension of the wrist joint. Tendon forces, range of motion, intraarticular contact area and contact pressure of the lunate and scaphoid facet as well as tendon excursion were investigated and compared with the current literature. During wrist motion the extensors exerted double the force of the flexors. Capsulotomy and sensor insertion decreased the range of motion from 63.4° (SD 14.1) to 45.9° (SD 23.7). The ratio of force transmitted through the radius and ulna was 77:23 and pressure distribution between the scaphoid and lunate facet showed a 70:30 relationship. The obtained data indicate a good agreement with the available literature. Therefore, the force controlled test-bench in combination with intraarticular radiocarpal measurements can be used to investigate the influence of wrist pathologies on joint biomechanics.

The length and position of the long axis of the scaphoid measured by analysis of three-dimensional reconstructions of computed tomography images

We established the maximum length and the position of the long axis of the scaphoid from three-dimensional reconstructions of spiral computed tomography in 30 pairs of wrists. The distance between two points on the three-dimensional scaphoid surface model were calculated using commercially available software and corresponding coordinates of the two points were documented. The mean length was 29.3 (SD 1.6) mm for men and 26.6 (SD 1.8) mm for women. The location of the distal point was at the centre of the scaphoid tuberosity, with the proximal point of the long axis located at the dorsal ridge of the scapholunate facet.

Interobserver reliability of coronoid fracture classification: two-dimensional versus three-dimensional computed tomography

PURPOSE

This study tests the hypothesis that 3-dimensional computed tomography (CT) reconstructions improve interobserver agreement on classification and treatment of coronoid fractures compared with 2-dimensional CT.

METHODS

A total of 29 orthopedic surgeons evaluated 10 coronoid fractures on 2 occasions (first with radiographs and 2-dimensional CT and then with radiographs and 3-dimensional CT), separated by a minimum of 2 weeks. Surgeons classified fractures according to the classifications of Regan and Morrey and of O'Driscoll et al., identified specific characteristics, recommended the most appropriate treatment approach, and made treatment recommendations. The kappa multirater measure (kappa) was calculated to estimate agreement between observers.

RESULTS

Regardless of the imaging modality used, there was fair to moderate agreement for most of the observations. Three-dimensional CT improved interobserver agreement in Regan and Morrey's classsication (kappa(3-dimensional) = 0.51 vs kappa(2-dimensional) = 0.40; p < .001) and O'Driscoll et al.'s classifications (kappa(3-dimensional) = 0.48 vs kappa(2-dimensional) = 0.42; p = .009). There were trends toward better reliability for 3-dimensional reconstruction in recognition of coronoid tip fractures (kappa(3-dimensional) = 0.19, kappa(2-dimensional) = 0.03; p = .268), comminution (kappa(3-dimensional) = 0.41 vs kappa(2-dimensional) = 0.29; p = .133), and impacted fragments (kappa(3-dimensional) = 0.39 vs kappa(2-dimensional) = 0.27; p = .094), and in surgeons' opinions on the need for something other than screws or plate for surgical fixation (kappa(3-dimensional) = 0.31 vs kappa(2-dimensional) = 0.15; p = .138). Interobserver agreement on treatment approach was better with 2-dimensional CT (kappa(3-dimensional) = 0.27, kappa(2-dimensional) = 0.32; p = .015).

CONCLUSIONS

Three-dimensional CT reconstructions improve interobserver agreement with respect to fracture classification compared with 2-dimensional CT.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic III.

Ontogenetic scaling of foot musculoskeletal anatomy in elephants

This study quantifies the shape change in elephant manus and pes anatomy with increasing body mass, using computed tomographic scanning. Most manus and pes bones, and manus tendons, maintain their shape, or become more gracile, through ontogeny. Contrary to this, tendons of the pes become significantly more robust, suggesting functional adaptation to increasingly high loads. Ankle tendon cross-sectional area (CSA) scales the highest in the long digital extensor, proportional to body mass(1.08+/-0.21), significantly greater than the highest-scaling wrist tendon (extensor carpi ulnaris, body mass(0.69+/-0.09)). These patterns of shape change relate to the marked anatomical differences between the pillar-like manus and tripod-like pes, consistent with differences in fore- and hindlimb locomotor function. The cartilaginous predigits (prepollux and prehallux) of the manus and pes also become relatively more robust through ontogeny, and their pattern of shape change does not resemble that seen in any of the 10 metacarpals and metatarsals. Their CSAs scale above isometry proportional to body mass(0.73+/-0.09) and body mass(0.82+/-0.07) respectively. We infer a supportive function for these structures, preventing collapse of the foot pad during locomotion.

Load transmission through the wrist in the extended position

PURPOSE

The wrist is subjected to extremely high compressive loads in the extended position, but pathoanatomy of this region remains unclear. The purpose of this study was to analyze force transmission in the maximum extended position to clarify the pathomechanics of wrist injury.

METHODS

Two sets of computed tomography images of wrist joints were obtained for 7 normal subjects: one set in neutral position and the other set in maximum extension. A three-dimensional rigid body spring model was used to analyze stress distributions through the wrist joint. The wrist joint was constructed from computed tomography images. External force was applied to the 5 metacarpals in neutral position and to the palm in extended position. Force transmissions through the carpus and ligament tension in extended position were compared with those in neutral position, and force distributions were compared in each position.

RESULTS

Force transmission ratio on the scaphoid fossa significantly increased from 52% in neutral to 62% in extension (p< .05), whereas the ratio through the lunate fossa decreased from 42% to 36%. In the midcarpal joint, force to the scaphoid significantly increased from 60% to 69% (p< .05). Force distributions of the radiocarpal joint in the extended position moved on the center of the lunate fossa and interfossal ridge of the scaphoid fossa. The dorsal ridge of the radial articular surface appeared as the new contact area. Tension in 3 palmar intrinsic ligaments and the flexor retinaculum greatly increased in the extended position.

CONCLUSIONS

Force transmission in the extended position shifted radially, concentrating at the scaphoid. We could show how bending force causes scaphoid fracture and concentration of force on the radius surface might cause intra-articular fracture coinciding with the fracture pattern introduced by Melone. The palmar intrinsic ligaments appear key to maintaining the carpal arch in push-up position. Our theoretical analysis could well explain several patterns of wrist injuries.

Modélisation du carpe osseux et biomécanique

Carpal morphology and orientation of carpal bones are usually studied on two-plane radiography. Those measurements depend on the incidence of X-ray and on the expertise of physician. A method that eliminates both should improve the accuracy of those measurements. The digital data from computed tomography scans can be use to describe carpal geometry. We defined biometric and angular parameters allowing the study of carpal morphology and bones orientation. From digital data from computed tomography scans software can obtain bone volume, inertia principal axis and volume of ellipsoid of inertia. Bone centroid location and principal axis orientation can be used to study bones orientation. 3D distances ratio between geometry centroid of carpal bones. The measurements allowed by this methodology are numerous. A study of a more consistent series of normal wrists will allow in the future for each quantitative parameter to define the normal range. A comparative study of normal wrists and pathology wrists should allow defining, for each pathology, the most judicious quantitative parameters.

Carpal kinematics after proximal row carpectomy

PURPOSE

Proximal row carpectomy (PRC) is a clinically useful motion-sparing procedure for the treatment of certain degenerative conditions of the wrist. Clinical outcome studies after PRC have shown that wrist flexion-extension averages approximately 60% of that of the contralateral wrist. The purpose of this study was to determine how the kinematics of the wrist are altered after PRC.

METHODS

Eight fresh-frozen cadaver forearms were scanned with computed tomography before and after PRC. Forearms were scanned in 5 different wrist positions (neutral, extension, flexion, radial deviations, and ulnar deviation). Wrists were positioned dynamically and then held statically in a custom fixture through forces applied to the 4 wrist flexor/extensor tendon groups. Three-dimensional computer models of the radius, lunate, and capitate were generated from the computed tomographic images, and the kinematics of the capitate and lunate were calculated relative to the neutral position. For the intact wrist, the motion of the capitate was calculated relative to both the lunate (midcarpal motion) and the radius (overall wrist motion) and the motion of the lunate was calculated relative to the radius (radiocarpal motion). After PRC, only the movement of the capitate relative to the radius was calculated, which represents radiocapitate and overall wrist motion. All motions were plotted in 3 dimensions for purposes of qualitative visualization.

RESULTS

After PRC, the capitate articulated with the lunate fossa of the radius for all positions in all samples. Overall wrist motion decreased 28%, 30%, 40%, and 12% in flexion, extension, radial deviation, and ulnar deviation, respectively. Motion at the radiocarpal joint after PRC, however, was greater compared with motion at the radiocarpal and midcarpal joints of the intact wrist during flexion and extension. This was not the case in radial deviation because of impingement of the trapezoid on the radial styloid. In radial and ulnar deviation, motion of the capitate head changed from predominantly rotational in the intact wrist (midcarpal joint) to a combination of rotation and translation after PRC (radiocarpal joint).

CONCLUSIONS

Removal of the proximal carpal row decreased normal wrist flexion and extension. Although ulnar deviation was preserved, radial deviation was limited by impingement of the trapezoid on the radial styloid. Radiocapitate range of motion after PRC was greater than capitolunate range of motion in the intact wrists. Compared with previously published requirements, wrist range of motion observed after PRC was sufficient for activities of daily living.

Two and three-dimensional computed tomography for the classification and management of distal humeral fractures. Evaluation of reliability and diagnostic accuracy

BACKGROUND

Complex fractures of the distal part of the humerus can be difficult to characterize on plain radiographs and two-dimensional computed tomography scans. We tested the hypothesis that three-dimensional reconstructions of computed tomography scans improve the reliability and accuracy of fracture characterization, classification, and treatment decisions.

METHODS

Five independent observers evaluated thirty consecutive intra-articular fractures of the distal part of the humerus for the presence of five fracture characteristics: a fracture line in the coronal plane; articular comminution; metaphyseal comminution; the presence of separate, entirely articular fragments; and impaction of the articular surface. Fractures were also classified according to the AO/ASIF Comprehensive Classification of Fractures and the classification system of Mehne and Matta. Two rounds of evaluation were performed and then compared. Initially, a combination of plain radiographs and two-dimensional computed tomography scans (2D) were evaluated, and then, two weeks later, a combination of radiographs, two-dimensional computed tomography scans, and three-dimensional reconstructions of computed tomography scans (3D) were assessed.

RESULTS

Three-dimensional computed tomography improved both the intraobserver and the interobserver reliability of the AO classification system and the Mehne and Matta classification system. Three-dimensional computed tomography reconstructions also improved the intraobserver agreement for all fracture characteristics, from moderate (average kappa [kappa2D] = 0.554) to substantial agreement (kappa3D = 0.793). The addition of three-dimensional images had limited influence on the interobserver reliability and diagnostic characteristics (sensitivity, specificity, and accuracy) for the recognition of specific fracture characteristics. Three-dimensional computed tomography images improved intraobserver agreement (kappa2D = 0.62 compared with kappa3D = 0.75) but not interobserver agreement (kappa2D = 0.24 compared with kappa3D = 0.28) for treatment decisions.

CONCLUSIONS

Three-dimensional reconstructions improve the reliability, but not the accuracy, of fracture classification and characterization. The influence of three-dimensional computed tomography was much more notable for intraobserver comparisons than for interobserver comparisons, suggesting that different observers see different things in the scans-most likely a reflection of the training, knowledge, and experience of the observer with regard to these relatively uncommon and complex injuries.

The influence of three-dimensional computed tomography reconstructions on the characterization and treatment of distal radial fractures

BACKGROUND

Computed tomography identifies important characteristics of distal radial fractures better than plain radiographs do. Our hypothesis was that three-dimensional computed tomography images would further increase the reliability and accuracy of radiographic characterization of distal radial fractures.

METHODS

Four independent observers evaluated radiographic images of thirty intra-articular fractures of the distal part of the radius for the presence of a fracture line in the coronal plane, impacted central articular fragments, the presence of comminution (defined as more than three articular fragments), and the number of fracture fragments. A treatment was selected on the basis of the interpretation of the radiographic studies. Three rounds of evaluation were compared: (1) radiographs and two-dimensional computed tomography, (2) radiographs and three-dimensional computed tomography two weeks later, and (3) all three types of images two weeks after that. This cycle was then repeated to assess intraobserver reliability.

RESULTS

Three-dimensional computed tomography improved the intraobserver agreement, but not the interobserver agreement, regarding the presence of coronal plane fracture lines and central articular fragment depression. Three-dimensional computed tomography improved both the intraobserver and the interobserver agreement regarding the presence of articular comminution. Interobserver agreement increased when three-dimensional computed tomography was used to determine the exact number of articular fracture fragments. The sensitivity and accuracy of identifying specific fracture characteristics (as compared with intraoperative findings) improved when three-dimensional imaging was used in conjunction with two-dimensional imaging as compared with two-dimensional imaging alone. The addition of three-dimensional computed tomography to two-dimensional computed tomography influenced treatment recommendations, resulting in a significantly greater number of decisions for an open approach (p < 0.05) and combined dorsal and volar exposure (p < 0.001).

CONCLUSIONS

Three-dimensional computed tomography improves both the reliability and the accuracy of radiographic characterization of articular fractures of the distal part of the radius and influences treatment decisions. Future studies will be required to determine the impact of these decisions on patient outcome.

Skeletal segments of the human pollical and hallucal rays: comparison and analysis of their intrinsic proportions

Since in humans, the first digital ray has a different functional significance in the hand and in the foot, the comparison of the pollical and hallucal rays seems interesting in order to evaluate the influence of specific evolutionary functional factors and biomechanical constraints. The objective of this study was to provide original and detailed data on the intrinsic proportions of the three segments of the human pollical and hallucal rays (metacarpal or metatarsal bone, proximal phalanx, and distal phalanx) in order to allow a quantitative comparison of their relative development. No similar data evaluated from three-dimensional approaches (volumetric or ponderal) seem to be available in the literature. The material consisted of 77 skeletons of the pollical ray and 77 skeletons of the hallucal ray of normal adult individuals. The ponderal approach was used. The first metapodial represented a mean of 57.17% for the pollical ray and 68.48% for the hallucal ray, whereas the phalanges respectively represented 42.83% and 31.52%. The intrinsic phalangeal proportions were almost identical for the pollex and for the hallux (respectively, 71.76% and 72.88% for the proximal phalanx; and 28.24% and 27.12% for the distal phalanx). Since these intrinsic proportions are the reflection of biological, functional and evolutionary constraints, these data seem of interest for the analysis of the functional significance of these rays, for the characterization of malformative syndromes in clinical practice, for reference in comparative morphology, and for the interpretation of hominid fossil bones.

A morphological study of the scaphoid using a mathematical technique and comparative study of the three-dimensional measurements of the scaphoid

To guide reconstruction of scaphoid non-union, we attempted to create full-scale models of the scaphoid by three-dimensional computed tomography (3D CT) of the healthy side. In this study, we obtained 3D scans of 51 cadaveric hands and studied the difference in morphology between genders and between the left and right sides. The major axis length on a fixed plane and Fourier transformation curve were examined. Ten scaphoid images were also obtained with 3D CT before and after removal from the cadaveric hands. Our findings suggest good correlation between models produced using 3D CT images of the scaphoid alone, and this could serve as an accurate model if the magnification is corrected using the regression line. However, the model using 3D CT images of the intact wrist joint has a large margin of error and its use will not be practical.

The use of medical imaging-based kinematic analysis in the evaluation of wrist function and outcome

The authors developed a 3D CT technique to analyze in vivo variations in carpal bone position based on 3D reconstruction of transverse CT data in 5 wrist positions. The subject groups analyzed consisted of 40 asymptomatic volunteers and 30 patients with various wrist disorders (fractures, instabilities). In 11 anatomic specimens, this kinematic analysis was completed by a radiographic morphologic study and an investigation of capsular ligament anatomy. Clinical applications showed that carpal bone motion in the injured wrist was not significantly different from contralateral, asymptomatic wrist motion. In both wrists of patients with unilateral pathology, however, significant differences were observed as compared with asymptomatic volunteers. Scaphoid motion was bilaterally altered, suggesting the existence of anatomic or kinematic factors predisposing to certain carpal pathologies.

Data representation for joint kinematics simulation of the lower limb within an educational context

Three-dimensional (3D) visualization is becoming increasingly frequent in both qualitative and quantitative biomechanical studies of anatomical structures involving multiple data sources (e.g. morphological data and kinematics data). For many years, this kind of experiment was limited to the use of bi-dimensional images due to a lack of accurate 3D data. However, recent progress in medical imaging and computer graphics has forged new perspectives. Indeed, new techniques allow the development of an interactive interface for the simulation of human motions combining data from both medical imaging (i.e., morphology) and biomechanical studies (i.e., kinematics). Fields of application include medical education, biomechanical research and clinical research. This paper presents an experimental protocol for the development of anatomically realistic joint simulation within a pedagogical context. Results are shown for the lower limb. Extension to other joints is straightforward. This work is part of the Virtual Animation of the Kinematics of the Human project (VAKHUM) (http://www.ulb.ac.be/project/vakhum).

Biomechanics and muscle coordination of human walking. Part I: introduction to concepts, power transfer, dynamics and simulations

Current understanding of how muscles coordinate walking in humans is derived from analyses of body motion, ground reaction force and EMG measurements. This is Part I of a two-part review that emphasizes how muscle-driven dynamics-based simulations assist in the understanding of individual muscle function in walking, especially the causal relationships between muscle force generation and walking kinematics and kinetics. Part I reviews the strengths and limitations of Newton-Euler inverse dynamics and dynamical simulations, including the ability of each to find the contributions of individual muscles to the acceleration/deceleration of the body segments. We caution against using the concept of biarticular muscles transferring power from one joint to another to infer muscle coordination principles because energy flow among segments, even the adjacent segments associated with the joints, cannot be inferred from computation of joint powers and segmental angular velocities alone. Rather, we encourage the use of dynamical simulations to perform muscle-induced segmental acceleration and power analyses. Such analyses have shown that the exchange of segmental energy caused by the forces or accelerations induced by a muscle can be fundamentally invariant to whether the muscle is shortening, lengthening, or neither. How simulation analyses lead to understanding the coordination of seated pedaling, rather than walking, is discussed in this first part because the dynamics of pedaling are much simpler, allowing important concepts to be revealed. We elucidate how energy produced by muscles is delivered to the crank through the synergistic action of other non-energy producing muscles; specifically, that a major function performed by a muscle arises from the instantaneous segmental accelerations and redistribution of segmental energy throughout the body caused by its force generation. Part II reviews how dynamical simulations provide insight into muscle coordination of walking.

Relative weights of the human carpal bones: biological and functional interests

The relative carpal weights (Weight of each of the eight carpal bones/Weight of the complete carpus x 100) were studied in a series of 95 complete human adult carpi (dried bones). The greatest was the capitatum (19.92%; mean rank 1.16) and the smallest the pisiform (4.43%; mean rank 8.00). The scaphoideum and the hamatum presented very near values (17.19 and 15.81%; mean ranks 2.34 and 2.74), as did the lunatum and trapezium (12.56 and 12.52%; mean ranks 4.41 and 4.48), and the triquetrum and trapezoideum (9.21 and 8.36%; mean ranks 6.19 and 6.68). Within the proximal row, a regular radio-ulnar decrease was observed from the scaphoideum (39.58%) to the pisiform (10.20%). Within the distal row, a marked break existed between the trapezoideum (14.77%) and the capitatum (35.19%); the capitato-hamatal element represented 63.11% of the distal row. The distal row (mean 56.61%) was always a little heavier than the proximal row (mean 43.39%), resulting in a mean proximo-distal weight ratio of 0.77. A radio-ulnar decrease in the relative weights was observed from the radial to the ulnar carpal columns. The determination of the relative carpal weights is simple, reproducible, non-invasive, rapid, and inexpensive, and can be considered an interesting and valuable approach to the estimation of the relative carpal volumes. Relative carpal weights reveal the intrinsic proportions of the carpus and are the reflection of biological, functional and evolutionary constraints. Interesting relations appear with carpal growth and ossification, with functional characteristics, and with evolutionary processes.

Kinematics of the wrist with a new dynamic external fixation device

The kinematic properties of a new dynamic external fixator device for treatment of distal radial fractures are described. Using a combination of data obtained from computed tomography scans and high-speed video images, a three-dimensional reconstruction of carpal motion was made. To describe carpal motion, the radiolunate, capitolunate, and scapholunate angles were measured during flexion and extension and during radioulnar deviation. During these types of motion, the device changed normal carpal kinematics to a limited extent although the differences in kinematic pattern with and without the device were small. The results for flexion and extension correspond with data from previously published studies with other dynamic external fixators. However, because the new device (Flexafix) allows flexion and extension and radioulnar deviation, in contrast to other dynamic external fixation devices, with its use normal carpal kinematics can be approached more closely.

Computer simulation of the upper extremities

The development of real-time, interactive, three-dimensional, computer graphic simulation of the musculoskeletal system with emphasis on the upper extremities is described. Developments in image analysis, scientific visualization, and interactive computer methods and the continuous improvement in knowledge of musculoskeletal function have combined to provide an exciting new tool for musculoskeletal research. Interactive simulation also has promising applications in medical education and clinical rehabilitation. Only those developments that fit the specific criteria of realism, real-time response, intuitive interaction, three-dimensional structures, and modeling flexibility are discussed. It is hoped that an improved understanding of this emerging tool and an appreciation for its potential applications will be gained.

Variations in the skeletal morphologic features of the wrist

Increased attention to and interest in the wrist and the field of hand surgery has brought about the discovery, rediscovery, and better description of variations in the skeletal morphologic features of the hand and wrist. In the second through fifth carpometacarpal joints, the fourth carpometacarpal articulation is the area of greatest variability. In the midcarpal joint, the scaphotrapeziotrapezoid and the capitolunate (hamate) articulations are areas of considerable variability in their skeletal morphologic features. New knowledge and awareness of variations in skeletal morphologic features in the carpus offer a better understanding and the opportunity to revisit various injury patterns and/or orthopaedic problems, and normal kinetics and kinematics to assess the effect and any differences that may be related to these different skeletal morphologic features.

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.

Three-dimensional magnetic resonance imaging of the interosseous membrane of forearm: a new method using fuzzy reasoning

We now report newly developed three-dimensional magnetic resonance imaging (3D-MRI) system which is based on semiautomatic tissue extraction from the axial MR images utilizing the fuzzy reasoning calculation method and 3D-image reconstruction with surface rendering. We also studied normal in vivo dynamic changes of the interosseous membrane (IOM) of forearm during rotation using this 3D-MRI. Serial axial MRI of right forearms of five healthy volunteers was obtained in five rotational positions, and extraction and 3D-reconstruction of the radius, ulna, and IOM was made using the system. Extraction results were well with the fuzzy reasoning method. 3D-MRI of the radius and ulna, IOM were reconstructed from these images respectively, and their 3D-shapes were almost identical to the anatomic shape. 3D-MRI showed there were wavy deformities on the IOM in pronation position in the all five subjects and dorsiflexion on the most dorsal portion of the IOM at maximum supination in three forearms. In neutral position, the IOM of all five volunteers was almost flat. From anatomic orientation, these dynamic changes of the IOM mainly occurred at the membranous portion, which is soft, thin, and elastic. Otherwise, the tendinous portion which is a thick and strong complex of 5 to 10 bundles run from proximal one third of the radius to distal one fourth of the ulna, demonstrated minimal dynamic changes on the 3D-MRI. Therefore, the tendinous portion is considered to be taut during rotation to provide stability between the radius and the ulna, while the membranous portion is easy to deform and allowing smooth rotation. Furthermore, because of wide-use, our 3D-MRI system is useful for in vivo analysis of soft tissue kinesiology in normal and abnormal musculoskeletal systems.

Noninvasive technique for measuring in vivo three-dimensional carpal bone kinematics

Our present knowledge of the three-dimensional kinematic behavior of skeletal joints has been largely acquired with cadaveric models and use of invasive monitoring. In the wrist, the small size and complex motion of the carpal bones present a difficult challenge for implanted internal or external marker systems. This paper describes a technique for quantifying the three-dimensional kinematics of the wrist and carpal bones in vivo using noninvasive computed tomographic imaging. An error analysis employing a cadaveric specimen suggests that noninvasive carpal kinematics can be measured with an accuracy within 2 degrees of rotation and 1 mm of translation along a helical axis of motion. The in vivo application of this technique is illustrated with a single normal individual. Potential applications include the quantification of normal wrist motion, analysis of pathomechanics, and evaluation of surgical intervention. The technique is also applicable to other joints and imaging modalities.

In vitro analysis of the accuracy of subtraction radiography and computed tomography scanning for determination of bone graft volume

PURPOSE

This study evaluated the accuracy of digital subtraction radiography (DSR) and three-dimensional computed tomography (3D CT) for determination of bone graft volume in the maxillofacial region.

MATERIALS AND METHODS

Standardized bone defects were made on the top of the alveolar ridge in 10 dry pig mandibles. To resemble the clinical situation, a bone block was harvested from the symphyseal region of the mandible and fixed in the defect. True bone graft volume was determined by the water displacement technique (VOL I) and correlated to direct measurements by calipers (VOL II). The mean gray value of the bone graft as imaged by DSR was correlated to the directly measured thickness. Furthermore, VOL I was correlated to the 3D CT of the bone graft (VOL III) and to the 3D CT with the bone graft fixed in the defect (VOL IV).

RESULTS

There was a strong correlation between VOL I and VOL II (r = .95), whereas there was a poorer correlation between mean gray level in DSR and measured bone thickness (r = .63). A strong correlation was also registered between VOL I and VOL III (r = .97) and VOL I and VOL IV (r = .97).

Volumetry of bone grafts by three-dimensional computed tomographic reconstruction: an animal study in the minipig

OBJECTIVES

To evaluate the accuracy of 3D-CT reconstruction for determination of bone graft volume in an animal model.

MATERIALS AND METHODS

Eight minipigs had bone graft reconstruction of an alveolar ridge defect. The true volume of the graft (VOL I) was determined by Archimedes principle before reconstruction. Following fixation, axial CT-scans (1 mm slice thickness with 50% overlap) were performed and segmented into grafted and residual bone for 3D-reconstruction. Using the volume tool of the 3D program the volume (VOL II) was calculated.

RESULTS

There was a strong correlation between VOL I and VOL II (r = 0.93, P = 0.001). There was a tendency, which was not statistically significant, to overestimate the volume measured by 3D-CT.

CONCLUSION

The volume of a bone graft can be determined by 3D-CT. However, further refinements of the technique are needed to improve the accuracy.

A non-invasive method for studying in vivo carpal kinematics

Seven uninjured and three injured patients were studied using midsagittal computed tomographic (CT) images at 10 degrees increments from full extension to full flexion. Each injured patient had a confirmed scapholunate ligament tear and normal radiographs. CT bony contours were digitized, and incremental motion determined using a specifically designed automated contour-matching algorithm. We expressed wrist motion as a ratio of lunocapitate (midcarpal) motion, and radiolunate (radiocarpal) motion. In normal wrists, motion occurred equally at the midcarpal and radiocarpal joints. In wrists with scapholunate ligament disruption, lunocapitate motion increased significantly throughout the arc of motion.

Can cast immobilization successfully treat scapholunate dissociation associated with distal radius fractures?

During a 3.5-year period, 20 of 424 consecutive patients with fractures of the distal radius presented with evidence of scapholunate dissociation upon x-ray films and traction view fluoroscopy. The sequential changes of x-ray abnormalities of the scapholunate joint were consistently observed over a 1-year period, and wrist functions were evaluated 1 year after injury. The scapholunate gaps were 3.5 +/- 0.5 mm at the time of injury, 3.2 +/- 0.4 mm immediately after closed reduction of the fracture, 3.4 +/- 0.5 mm at the time after removal of fixation, and 3.8 +/- 0.4 mm 1 year after injury. By the modified clinical scoring system of Green and O'Brien, of these 20 patients, none had excellent, 2 had good, 14 had fair, and 4 had poor wrist function 1 year after injury. The wrists with scapholunate dissociation had significantly worse function as compared to a selected subgroup of 228 wrists with no signs of intercarpal ligament disruption. All 20 patients with signs of scapholunate dissociation on x-ray examination at the time of injury had clinical signs in the scapholunate joint and positive x-rays findings of dissociation 1 year later. After 1 year, 8 of the 20 patients underwent surgery for relief of symptoms and to stabilize the joint. Arthrography in the patients with persistent symptoms showed disruption in scapholunate interosseous ligaments. This study indicates that scapholunate dissociation with concomitant fractures of the distal radius cannot be cured by cast immobilization of the fracture. Early operative treatment should be instituted for the concomitant scapholunate dissociation.

Carpal bone anatomy measured by computer analysis of three-dimensional reconstructions of computed tomography images

Using quantitative analysis of three-dimensional reconstructions of computed tomography scan data, a normative database of carpal bone morphology was built. Thirty-five wrists were imaged in a computed tomography scanner. Each slice was processed to determine the bone edges and assembled as a three-dimensional model by stacking. Quantitative measurements of volume, surface area, maximum length, and intercarpal distances were then assessed. A reliable three-dimensional carpal height ratio was calculated by dividing the carpal height (minimum distance between the fourth metacarpal and the radius) by the capitate maximum length. For volume, maximum length, and surface area, the order for the eight carpal bones with respect to size (in descending order) were: capitate, hamate, scaphoid, trapezium, lunate, trapezoid, triquetrum, and pisiform. Male wrists were significantly larger than female wrists. There were no significant differences in the relative dimensions between left and right wrists, or between left and right wrists of matched pairs. This technology offers automated analysis of three-dimensional geometric carpal information and the opportunity to obtain a body of information about normal and abnormal morphology as well as spatial relationships between carpal bones.

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.