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The mechanical properties of the scapholunate ligament have been previously examined in small sample sizes, with ultimate load and occasionally stiffness reported. The present study examined 16 scapholunate ligaments in uniaxial extension at two rates and determined stiffness, ultimate load, and stress relaxation properties. Mean stiffness values of 66.4 ± 28.6 N/mm at an elongation rate of 50 mm/min and 94.5 ± 44.4 N/mm at an elongation rate of 100 mm/min were found. Relaxation behavior, determined by the percent load remaining after 100 s, was found to be 68.1 ± 12%. Mean ligament ultimate loads were 357 ± 110 N ( n =8). In eight specimens, failure occurred in bone. Positive correlations were observed between bone mineral density of the hand and ligament stiffness, ligament ultimate load, and bone ultimate load. No correlation was observed between bone mineral density and ligament load relaxation behavior. The results provide a comprehensive understanding of scapholunate ligament biomechanics and demonstrate a relationship between bone and ligament properties.

The purpose of this study was to measure the structural stiffness (load/displacement response) and elastic modulus (stress-strain response) of the glenoid labrum at different locations throughout the tissue. It was intended that the results of this work would serve to define the properties of the labrum. This in turn may permit a better understanding of labral function and of the mechanics of injury or degeneration and may ultimately contribute to improving the design of future labral reconstruction procedures. In addition, these data may allow incorporation of labral properties into a glenoid arthroplasty component. The testing procedure consisted of rapid compression of the labrum using a flat indentor. Stiffness and modulus results demonstrated differences between the superior and inferior portions of the labrum. The elastic moduli findings for the labrum were 0.18 +/- 0.17, 0.11 +/- 0.16, and 0.23 +/- 0.20 MPa for the inferior anterior, inferior, and inferior posterior sections, respectively. The superior anterior, superior, and superior posterior sections were respectively 0.19 +/- 0.09, 0. 32 +/- 0.22, and 0.41 +/- 0.32 MPa. These results are similar to those of knee menisci. The modulus findings for the substrate cartilage were 1.92 +/- 0.78, 1.99 +/- 0.70, and 2.00 +/- 1.33 MPa for the inferior anterior, inferior, and inferior posterior sections, respectively. The superior anterior, superior, and superior posterior sections were respectively 1.60 +/- 0.79, 1.29 +/- 0.75, and 1.42 +/- 0.54 MPa, which are comparable to previous cartilage findings.

Three-dimensional analysis of joint motion in vivo provides a tool for assessing the extent to which pathological conditions such as rheumatoid arthritis affect function. Kinematic analyses using conventional six-degree-of-freedom characterizations are strongly coordinate-system depen dent and require careful interpretation. An alternative method, examining the motion in configuration space, permits identification of the number of degrees of freedom used to perform the motion. Radial-ulnar deviation movements of the wrist joint were tracked optoelectronically in a group of twenty-eight volunteers with rheumatoid arthritis, and an age- and gender-matched group of control subjects. Normal wrists demonstrated highly repeatable one-dimensional configuration spaces for five cycles of hand movement. Wrists affected by rheumatoid arthritis displayed more disorganized and two-dimensional configuration spaces. Two parameters from the configuration space trajectories were defined to quantify the range of motion (ROM) and amount of inconsistency or ‘jitter’ in the movement. Plots of jitter against ROM for the population of fifty-six subjects showed strong separation of the case and control groups, with rheumatoid wrists displaying lower ROM and higher jitter. These indices provide a simple means of quantifying differences between rheumatoid and normal wrists with minimal coordinate-system dependence.

Computer assisted surgical interventions and research in joint kinematics rely heavily on the accurate registration of three-dimensional bone surface models reconstructed from various imaging technologies. Anomalous results were seen in a kinematic study of carpal bones using a principal axes alignment approach for the registration. The study was repeated using an iterative closest point algorithm, which is more accurate, but also more demanding to apply. The principal axes method showed errors between 0.35 mm and 0.49 mm for the scaphoid, and between 0.40 mm and 1.22 mm for the pisiform. The iterative closest point method produced errors of less than 0.4 mm. These results show that while the principal axes method approached the accuracy of the iterative closest point algorithm in asymmetrical bones, there were more pronounced errors in bones with some symmetry. Principal axes registration for carpal bones should be avoided.

This paper describes an experimental method for determining the minimum number of degrees of freedom of a human joint. Application of this technique to the wrist suggests that the normal, intact wrist joint uses only two degrees of freedom to move in a plane that is not aligned with the anatomic planes. The technique may be useful in identifying emerging joint pathologies and in simplifying kinematic models of joint function.

A refinement to a previously described three-dimensional reconstruction algorithm based on point identification in calibrated non-orthogonal radiograms (stereo-pairs) is described. The modification involves a computation of the focal point magnitude of the point in three dimensions, analogous to focusing in two dimensions, as well as the most likely location of the target point in 3-space; the focal point magnitude may be thought of as the precision of the point identification. Multiple observer studies of the same stereopair can be used to estimate three-dimensional reconstruction accuracy by providing an average location and a mean distance from average. Both measures are useful parameters for initial selection of bone landmark references and for error propagation studies.

Purpose To establish the accuracy, precision, and clinical feasibility of a novel technique of computer-assisted distal radius osteotomy for the correction of symptomatic distal radius malunion. Methods Six patients underwent a computer-assisted distal radius osteotomy and were followed-up for an average of 25 months. Objective radiographic measurements and functional outcomes, as measured by clinical examination including grip strength and range of motion, and Disability of the Arm, Shoulder and Hand (DASH) questionnaires, were used. Results The mean radiographic parameters included an increase of radial inclination to 21° from 12° (normal, 23°). Dorsal and volar tilt (malunion) were corrected to 9° from −30° and 21°, respectively (normal, 10°). Ulnar variance was corrected to 1.9 mm from 7.5 mm (normal, +1.5 mm). Normal is defined as the average of the contralateral limb radiographs. The mean clinical outcome measures at an average of 25 months included a DASH global score of 14, a DASH individual item average score of 1.6, and an average affected side grip strength of 79% when compared with the unaffected side. Conclusions The results of the computer-assisted technique were comparable with published results of traditional non-computer-assisted opening wedge osteotomy techniques. This technique allows a surgeon to accurately and precisely recognize and correct 3-dimensional deformities of the distal radius including axial malalignment (supination). The technique has the added benefit of reducing radiation exposure to the patient and surgical team because fluoroscopy is not used during the procedure. Additional benefits of the computer-assisted technique include the ability to perform multiple surgical simulations to optimize the alignment plan, and it serves as an excellent teaching tool for less-experienced surgeons.

A three-dimensional developmental finite element model has been created to analyze load transmission pathways in the constrained carpus during static compressive loading. The bone geometry was extracted from an in vivo computed tomography scan using a combination of commercial and proprietary software. The complete geometry, including bone, cartilage, and ligament tissues, was compiled using a commercial finite element program. This model extends the state of biomechanical modeling by being the first to incorporate all eight carpal bones of the wrist and the related soft tissues in three dimensions. The model results indicate that cartilage material modulus and unconstrained carpal rotation have substantial impacts on the articular contact patterns and pressures.

An integrated noninvasive blood pressure simulator for evaluating both oscillometric and auscultatory noninvasive blood pressure monitors has been designed. This integrated simulator features simple but novel approaches to simulating oscillometric pulses and Korotkoff vibrations with potentially high controllability. It provides for emulation of a wide range of microphone placement configurations, use of the electrocardiogram, and simulation of cuff-arm compliance for different cuff sizes. >

Introduces the use of a chromatic triad of hue (H), saturation (S) and light intensity value (V) to uniquely and immediately identify the photoelastic fringe value of all points in a camera's field of view. Digital video images are obtained through a reflective white-light polariscope and converted to H,S,V. A multivariate approach is used, and some filtering of the data is required. The system is suitable for both static and dynamic loads.

We investigated the dependence of 20 radiographic carpal measurements (carpal indices) on rotational positioning errors in posteroanterior and lateral radiographs. The measurements were made from "true perspective" digitally reconstructed radiographs created from computed tomography data. Most posteroanterior indices were not affected by rotation. Carpal height, carpal height ratio, revised carpal height ratio, capitate-radius distance, and carpal ulnar translocation were particularly robust. Lateral-view indices involving the scaphoid were the most sensitive to simulated malpositioning: radioscaphoid, scapholunate, and scaphocapitate angles were reduced from 58 degrees, 48 degrees, and 56 degrees at true lateral to 30 degrees, 24 degrees, and 34 degrees, respectively, at 20 degrees external rotation. Observers were unable to estimate the degree of malpositioning accurately in either view. Our results support use of the "scaphopisocapitate" criterion for assessing correct positioning in lateral plain radiographs.

A protocol for analysing three-dimensional metacarpophalangeal (MCP) joint motion in vivo using two markers on the proximal phalanx is described. The analysis uses an assumption that the rotation of the phalanx about its own long axis is zero. In an experimental study 24 volunteers had surface markers applied to the dorsal surfaces of their hands and index and long finger proximal phalanges, with three-dimensional marker positions recorded in two hand and finger postures in an incomplete box design using a test-retest protocol. Kinematic parameters from the optoelectronic system were compared with those obtained from three-dimensional reconstruction of bone landmarks and of the marker positions identified on stereoradiographs. Pronation/supination angles obtained from bone landmarks showed high test-retest variability, reflecting the difficulty in obtaining reliable pronation/supination data in small bones without the use of implanted markers. Changes in MCP joint extension and deviation angles determined using two surface markers agree with those obtained from bone landmarks. The results indicate a reproducible protocol for tracking MCP joint motion using only two phalangeal markers, suggesting that the ‘no-rotation assumption’ can be applied without affecting measures of extension and deviation motion in the normal joint.

Fixation-based surgery is a new technique for achieving difficult corrections in some orthopedic procedures. The method is premised on using a fixation device, such as a fracture-fixation plate, during the alignment and distration phases of an open-wedge osteotomy. The basic idea is similar to assembly of manufactured components: pilot holes are drilled in the bone fragments, the fixation plate is attached to one fragment and, when the fragment is moved, the alignment has been achieved when the pilot holes in one fragment line up with predetermined through holes in the fixation plate.

The in vitro mechanical properties of 14 wrist extensor tendons salvaged at surgery from patients with inflammatory (rheumatoid) arthritis and noninflammatory arthrosis were measured in uniaxial tension and compared. The rheumatoid tendons had higher extensibility at low stresses, lower stiffness in the linear portion of the stress-strain curve, greater rates of stress relaxation, and lower ultimate strengths than did the nonrheumatoid tendons. Differences in tangent modulus, stress remaining at 100 seconds, and ultimate tensile strength were significant at the 95% confidence level. In vivo, mechanically, impaired tendons may play an important role in destabilization of the wrist in patients with rheumatoid arthritis.

OBJECTIVE: A study was undertaken to determine the experimental accuracy of a non-invasive optoelectonic 3-dimensional tracking system in assessing wrist joint motion. DESIGN: This was an in vivo experimental study involving volunteer subjects performing prescribed wrist motions. BACKGROUND: Current clinical practice does not include routine kinematic analysis for evaluating arthritic disease state, although motion disorders are common. METHODS: Surface markers were applied to 24 subjects assigned two hand postures in a test-retest factorial design for the expected range of motion. The marker positions were measured optoelectronically and using calibrated stereoradiography, to determine the positions of the surface markers and of key bone landmarks. Alignment and motion were compared for the three measurement techniques. Standard kinematic analyses were performed to extract Euler angles and equivalent screw displacement axes for paired postures. RESULTS: The three measurement techniques were highly correlated for wrist flexion-extension. Uncertainties were less than 6 degrees, similar to uncertainties from bone landmark identification errors when implanted markers cannot be used. Measures of motion exhibited higher correlations than those for alignment. Equivalent screw displacement axis orientations had poor intraclass correlations, reflecting sensitivity to coordinate system definitions. CONCLUSIONS: For motion analysis in the wrist in vivo, a non-invasive optoelectronic measurement system is as accurate as stereoradiographic analysis of bone segments.

Characterization of the motion of the hand and wrist requires reference to the underlying bones which, for three-dimensional analyses, are assumed to be rigid bodies. Stereoradiogrammetric techniques involving the identification of prominent bone landmarks have been used as the standard against which surface markers used for in vivo testing have been evaluated. The precision and accuracy with which the 3D positions of bone landmarks in the hand and wrist could be determined was evaluated in a small inter-observer and inter-cadaver study and compared to the precision and accuracy with which implanted lead markers could be located. A subset of landmarks suitable for evaluating wrist and metacarpal-phalangeal joint motion was identified; the mean precison for identifying these points was better than 1.1 mm in all hand positions with a mean inter-observer accuracy of 2.3 mm. These values show that the average uncertainty in locating bone landmarks is at best roughly twice that for implanted markers.

Oscillometric blood pressures are derived from the amplitude envelope of oscillometric pulses generated in an occlusive cuff during cuff inflation or deflation; one factor which will affect the characteristics of these pulses is the size of the cuff bladder. Because limiting values are stipulated in recommendations and standards for bladder sizes, there is a wide variety of acceptable cuff sizes for any particular application. An experimental and theoretical study was undertaken to show the dependence of oscillometric blood pressures on bladder size. Actual cuff-arm compliance data were obtained from two subjects for two cuffs of different bladder size. Theoretical analysis was then applied to the data to predict the effects of different bladder sizes on the characteristics of the pulses. The results show that cuff-arm compliance and bladder size interact to affect the pulse amplitude and hence oscillometric blood pressure determination. These results suggest that blood pressures obtained using the oscillometric method may vary depending on cuff size, and in particular that replacement cuffs for oscillometric non-invasive blood pressure monitors should be chosen carefully.

A method and apparatus for quantitative measurement of the alignment and motion of the joints of the hand in three dimensions has been developed using stereoradiogrammetric principles. Alignment in planes of flexion-extension and radial-ulnar deviation can be determined to within 2.5 degrees; rotation about the long axis of the metacarpals or phalanges is more difficult to determine, and can be measured to within 7 degrees. Stereo views subtending angles in the range of 40 degrees were found to optimize the total system accuracy.

Modelling joint motion in three dimensions is often based on techniques taken from classical dynamics, each analysis resulting in a set of six parameters describing the relative motion betwen two body segments. The literature on joint kinematics has been difficult to compare due to use of different anatomical landmarks, axis nomenclature, and analytical methods. It is here shown that with care in sequence definition, the three alignment-based systems (Euler, Cardan, floating axis) give identical results for angular parameters. While the equivalent screw displacement axis system can be related simply to the other methods only if the functional axis of motion is aligned with a coordinate axis, the basic matrix for relating rigid body positions before and after a motion can always be reconstructed. Therefore the changes in alignment angles may be obtained from screw displacement parameters, permitting the results of different analyses to be compared. Translation parameters are most difficult to interpret in any system. Examples of the way in which simple planar motions are characterized by the various analytical methods are given.

The mechanical compliances of a number of support systems, including beds in general clinical use and mattresses specifically designed to help prevent pressure sores, were determined from indentation tests using flat, circular punches of 5, 10, 15, 20 and 40 cm dia. The Scimedics Polyflotation foam mattress was found to be more compliant (less stiff) overall than either of the two Dunlopillo foam mattresses conforming to NHS contract specifications. Mattresses of T38 Temper Foam displayed such a degree of time-dependance as to render them unsuitable for general clinical use. A horsehair mattress and an interior-sprung mattress were both more compliant than any of the foams with indentors 15–40 cm dia. An Aquatherapy Aqua-Pedic water mattress was found to have mechanical characteristics no better than the horsehair or interior-sprung mattresses except with the largest indentor. The use of waterproofing covers on foam and hair mattresses resulted in decreases in support system compliance which were extreme at small punch sizes.

Interruption of the breathing gas to a ventilated anaesthetized patient due to accidental disconnection or anaesthesia system malfunction may have serious consequences if not detected quickly. A series of tests which covers the range of foreseeable mechanical problems was developed and used to test the performance of three breathing gas interruption monitors, two commercially available and one developed at Vancouver General Hospital. The tests were designed to evaluate the performance of monitors as installed on anaesthesia systems under a variety of failure conditions, including endotracheal tube disconnection with and without occlusion of the opening, kinks in the inspiratory and fresh gas hoses, disconnection of the fresh gas hose, leaks in the breathing circuit, excessive high or low pressure in the scavenging circuit, continuing high breathing circuit pressure, and kinks in the circuit pressure sensing hose. Ability to detect both significant changes in ventilation variables and faults existing at initiation of ventilation were also tested over a representative range of ventilator and patient variables using circle, coaxial and paediatric circuits. Only complete endotracheal tube disconnections with no obstruction of the opening were reliably detected by all three monitors. A commercial monitor with a single fixed-threshold alarm level also detected fresh gas interruptions in circle and adult coaxial circuits, but failed to alarm in response to any other fault condition. A monitor with selectable pressure thresholds and high, low, and continuing pressure limits detected just under half of the fault conditions. A microprocessor-based monitor developed at Vancouver General Hospital detected and correctly identified roughly 80 per cent of the faults. The series of tests forms the basis for a Canadian Standards Association Preliminary Standard (Z168.10) and will allow hospitals to test the performance of breathing gas interruption monitors in use in their institutions. Comments on the test series are solicited.