Simulation of extension, radial and ulnar deviation of the wrist with a rigid body spring model.

A novel computational model of the wrist that predicts carpal bone motion was developed in order to investigate the complex kinematics of the human wrist. This rigid body spring model (RBSM) of the wrist was built using surface models of the eight carpal bones, the bases of the five metacarpal bones, and the distal parts of the ulna and radius, all obtained from computed tomography (CT) scans of a cadaver upper limb. Elastic contact conditions between the rigid bodies modeled the influence of the cartilage layers, and ligamentous structures were constructed using nonlinear, tension-only spring elements. Motion of the wrist was simulated by applying forces to the tendons of the five main wrist muscles modeled. Three wrist motions were simulated: extension, ulnar deviation and radial deviation. The model was tested and tuned by comparing the simulated displacement and orientation of the carpal bones with previously obtained CT-scans of the same cadaver arm in deviated (45 degrees ulnar and 15 degrees radial), and extended (57 degrees ) wrist positions. Simulation results for the scaphoid, lunate, capitate, hamate and triquetrum are presented here and provide credible prediction of carpal bone movement. These are the first reported results of such a model. They indicate promise that this model will assist in future wrist kinematics investigations. However, further optimization and validation are required to define and guarantee the validity of results.

Validation of a new surgical procedure for percutaneous scaphoid fixation using intra-operative ultrasound.

A new technique for percutaneous fixation of non-displaced scaphoid fractures is described. The technique used pre-operative planning from computed tomography images, registration to intra-operatively acquired three-dimensional ultrasound images, and intra-operative guidance using an optical tracking system. Two stand-alone software applications were developed. The first one was used to determine the surgical plan pre-operatively and the second one was used to guide the surgeon during screw insertion. Laboratory validation of the technique included measurements of the inter-operator and intra-operator variability in the outcome of scaphoid fixation using the proposed procedure, and also included comparison of the performance of this procedure with the conventional percutaneous fixation technique using fluoroscopy. The results showed that the tight accuracy requirements of percutaneous scaphoid fixation were met and that the consistency was superior to the conventional technique.

A navigation system for shoulder arthroscopic surgery.

The general framework and experimental validation of a novel navigation system designed for shoulder arthroscopy are presented. The system was designed to improve the surgeon's perception of the three-dimensional space within the human shoulder. Prior to surgery, a surface model of the shoulder was created from computed tomography images. Intraoperatively, optically tracked arthroscopic instruments were calibrated. The surface model was then registered to the patient using tracked freehand ultrasound images taken from predefined landmark regions on the scapula. Three-dimensional models of the surgical instruments were displayed, in real time, relative to the surface model in a user interface. Laboratory experiments revealed only small registration and calibration errors, with minimal time needed to complete the intraoperative tasks.

Computer-assisted guidewire insertion for hip fracture fixation.

OBJECTIVE: : This study was designed to test in a laboratory setting a novel computer-assisted fluoroscopic technique and a conventional fluoroscopic technique for open reduction and internal fixation (ORIF) of hip fractures. Our hypothesis is that a novel computer-assisted fluoroscopic technique will achieve acceptable guidewire placement in one pass, with decreased fluoroscopic time and with accuracy and precision better than conventional technique. DESIGN: Prospective, randomized trials. SETTING: Laboratory. PARTICIPANTS: Thirty, Sawbone, femur phantoms. INTERVENTION: Dynamic hip screw guidewires were inserted into 15 femur phantoms under fluoroscopic guidance by using computer-assisted fluoroscopic ORIF technique, and 15 femurs were inserted by using a conventional fluoroscopic-assisted ORIF technique. MAIN OUTCOME MEASUREMENTS: Ideal guidewire placement was defined as the center of the femoral head, 5 mm from the apical bone edge on anteroposterior and lateral views. Accuracy was measured as distance to ideal placement, and the number of passes and fluoroscopic time were noted for each trial. RESULTS: The computer-assisted technique achieved an average guidewire placement that was as accurate as the conventional technique in fewer passes, 1.1 +/- 0.2 (mean +/- standard deviation) compared with 2.4 +/- 1.1 (P < 0.0001), respectively, and with fewer fluoroscopic images, 2 +/- 0 compared with 13.5 +/- 3 (P < 0.0002), respectively. Guidewire placement in both groups was within the tip-apex distance defined by Baumgaertner et al. CONCLUSIONS: The computer-assisted technique was significantly more accurate and precise than conventional technique. It also required fewer drill tracks through the femur and exposed the patient and the surgical team to significantly less ionizing radiation.

Fixation-based surgery: a new technique for distal radius osteotomy.

OBJECTIVE: The objective was to develop a fixation-based three-dimensional presurgical planner and an intraoperative guidance system for distal radius osteotomy. Fixation-based surgery is a technique premised on using a fixation device, such as a fracture-fixation plate, during the alignment and distraction phases of an osteotomy. MATERIALS AND METHODS: The planning system and guidance system were coded using OpenGL on UNIX workstations. In vitro tests were performed to compare the reproducibility of the computer-enhanced technique to that of the traditional technique, and an in vivo pilot study was initiated. RESULTS: In vitro, the computer-enhanced technique produced a significant reduction by more than one half in both the maximum error of correction and the standard deviation of the correction error. Preliminary in vivo results on six patients suggest that similar error diminution will occur during regular clinical application of the technique. CONCLUSIONS: Both studies showed that the computer system is simple to use. The planning system allowed the surgeon to perform multiple simulations of the surgical procedure preoperatively, which were used to optimize the plan and identify potential problems during realignment. The use of a fixation-based technique avoided the complexity of attempting to guide the surgeon to realign a bone fragment in six degrees of freedom of correction, and eliminated the use of X-ray fluoroscopy for achieving the alignment.

Three-dimensional metacarpophalangeal joint kinematics using two markers on the phalanx.

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.

Cost factors in Canadian pediatric trauma.

OBJECTIVES: To estimate the costs of Canadian pediatric trauma and identify cost predictors. DESIGN: A chart review. SETTING: A regional trauma centre. STUDY MATERIAL: The charts of all 221 children who suffered traumatic injuries with an Injury Severity Score (ISS) of 4 or more seen over 6 years at a regional trauma centre. MAIN OUTCOME MEASURES: Patient data, injury data, all hospital-based costs, excluding nursing, food and medication costs. RESULTS: Mean (and standard deviation) patient age was 12.8 (5) years. Sixty percent were boys. Motor vehicle accidents (MVAs) accounted for 71% of the injuries, followed by falls (11%). The mean (and SD) total cost of care was Can$7,582 (Can$12,370), and the cost of media was Can$2,666. Total cost correlated directly with age (r = 0.29, p < 0.001) and Injury Severity Score (ISS) (r = 0.34, p < 0.001) and inversely with the Pediatric Trauma Score (PTS) (r = -0.20, p = 0.003). The presence of extremity injuries correlated significantly with total cost (r = 0.22, p = 0.001) and PTS (r = -0.25, p < 0.001) but not with the ISS. Logistic regression analysis identified runk injury, ISS and PTS as the main determinants of survival. CONCLUSIONS: The cost of pediatric trauma in Canada can be predicted from admission data and trauma scores. The cost of extremity injuries is significant and can be predicted by the PTS but not the ISS.

Mechanical testing of shoulder prostheses and recommendations for glenoid design.

Glenoid component loosening generates the greatest concern among surgeons performing total shoulder arthroplasty. Laboratory testing of glenoid prostheses may lead to improved design, subsequently leading to a reduction in the incidence of clinical loosening. The goals of this study were to develop a laboratory test method to address glenoid loosening and to apply this method to a variety of prosthesis designs. With use of a biaxial apparatus, glenoid components were cyclically subjected to superoinferior edge loading, mimicking the off-center rocking-horse phenomenon thought to contribute to glenoid loosening clinically. Before and after the rocking test was performed, compression and distraction of the superior and inferior edges were measured with the humeral head displaced to each edge. Rocking performance could not be predicted from initial measurements, indicating the necessity for dynamic loading to evaluate the likelihood of loosening. A roughened fixation surface for outperformed a smooth fixation surface, a curved backing showed almost half the distraction of a flat backing, and a nonconstrained prosthesis distracted less than a more constrained prosthesis.

In situ compressive properties of the glenoid labrum.

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.

Shoulder prosthesis subluxation: theory and experiment.

The articular shapes of the humeral and glenoid components in total shoulder arthroplasty affect the loading, translation, and contact stresses in the joint, thereby affecting stability, glenoid loosening, and wear. Experiments were conducted to determine the subluxation load and corresponding translation for 6 types of glenoid components. The effects of shape, size, testing direction, compressive load, testing speed, testing medium, bone substitute properties, and repeated subluxations were investigated and compared with theoretical, rigid-body predictions. The subluxation load, varying from 45% to 98% of the axial load for the prostheses tested, is affected by glenoid constraint (i.e., the maximum slope at the glenoid articular rim), the compressive load, the coefficient of friction, and the deformability of the articular edge. Rigid-body theory overestimated the experimental load, which was not surprising given the visible deformations, but provides a framework to highlight the relevant design parameters. The subluxation translation, ranging from 1 to 13 mm for the prostheses tested, is determined by the glenoid length and by the conformity between the humeral and glenoid radii. Experimental translations were greater than rigid-body predictions for the most conforming prostheses and roughly equal for less conforming prostheses. The goals of this study were to characterize the subluxation load and translation of a variety of types of prostheses, to develop the rigid-body basis for these results, to compare the rigid-body and experimental results, and to locate experimentally the glenoid articular rim for further testing.

Glenohumeral contact forces.

Glenohumeral contact forces have only been calculated previously either for simple abduction or for athletic activities. The objective of this study was to determine the glenohumeral contact forces for tasks which are demanding of the shoulder but which would commonly be performed by older people. The functional tasks chosen were using the arms to stand up from and sit down into a chair, walking with a cane, lifting a 5 kg box to shoulder height with both hands, and lifting a 10 kg suitcase. The trunk angles, arm angles and hand loads of six healthy subjects, average age 55 years, were recorded. This information was input into a biomechanical computer model which optimized the muscle force distribution by minimizing the sum of squared muscle stresses subject to constraints on the maximum muscle forces and maintaining the direction of the resultant force within the glenoid fossa. Average contact forces ranged from 1.3 to 2.4 times body weight (930-1720 N), the highest force being for lifting a suitcase. This latter value would be even higher if lifting either a greater load or to a greater height. Thus, contact forces at the shoulder should not be underestimated. This study provides functionally relevant contact forces which can be used for mechanical testing or finite element modelling of shoulder prostheses.

Glenoid cancellous bone strength and modulus.

The objectives of this study were to determine the strength and modulus of glenoid cancellous bone, including regional variations. The motivations were: to select a suitable bone substitute for standardized testing of glenoid prosthesis loosening, to assist in shoulder prosthesis design and to provide input data for finite element analyses. Ten glenoids from eight cadavers (mean age, 81) were tested by in situ indentation. Mean strength ranged from 6.7 to 17 MPa for the ten glenoids, the overall mean being 10.3 MPa. Mean E moduli ranged from 67 to 171 MPa for the individual glenoids, the overall mean being 99 MPa. These values are likely at the lower end of what would be expected for normal bone since strength and modulus decrease with age and the available specimens were older. These values may be appropriate for prosthesis design, however, since mechanical properties are reduced in rheumatoid arthritic bone. Regional trends were very similar for modulus and strength. The strongest region was postero-superior. The central column, correlating with the keel position in many glenoid components, was weaker than both the anterior and posterior regions but deeper. A large drop in strength and modulus below the subchondral layer emphasizes the importance of maintaining this layer during prosthetic replacement.

Trauma patients with multiple extremity injuries: resource utilization and long-term outcome in relation to injury severity scores.

BACKGROUND: Trauma patients with multiple extremity injuries (MEI) make heavy demands on hospital resources and face long-term difficulties in rehabilitation, yet the literature contains little about their treatment as a distinct group. METHODS: In this study, a cohort of 54 patients with MEI, all treated at a Level I trauma center, was compared with a trauma control (TC) group that had major injuries not focused at the extremities (but excluding patients with neurologic sequelae of head or spinal cord injuries). Demographic features, primary measures reflecting utilization of hospital resources, return-to-employment and productivity data, and health-related quality of life scores (Medical Outcomes Study 36-Item Short Form Health Survey [SF-36]) were compared. RESULTS: Although mean Injury Severity Scores (ISS) for the MEI and TC groups were almost identical (16.2 and 17.4, respectively), the patients with MEI had a mean hospital stay almost twice as long (25 vs. 13 days) and had double the resource intensity weight compared with the TC group. After discharge, the trend of the MEI group was to greater long-term disability, based on SF-36 scores, and lower "return to productivity" figures. The ISS did not predict the greater demands on resources made by the MEI group relative to our TC group. Main injury severity scores for the extremities were more predictive than the ISS for length of hospital stay and the SF-36 concepts at the 2-year follow-up evaluation. CONCLUSION: The study emphasizes the need for injury scoring systems that better predict the needs of patients with MEI and that will serve as a basis for equitable funding of trauma centers.

Mechanical properties of wrist extensor tendons are altered by the presence of rheumatoid arthritis.

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.

Validation of a 3D optoelectronic motion analysis system for the wrist joint.

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.

Cubital tunnel syndrome and the painful upper extremity.

Cubital tunnel syndrome is the second-most-common compressive neuropathy. With the increasing prevalence of entrapment neuropathies, the presentation of ulnar nerve compression with a painful upper extremity appears to be more common. Although our knowledge and understanding of this disease are increasing, the principles of management remain constant. We are obliged to reach a timely and appropriate diagnosis to minimize the extent of neurologic injury and institute an appropriate treatment regimen to preserve and restore normal neural function. Although there are many ways to reach these goals, the avoidance of complications is paramount to achieve a reliable and pain-free outcome. Preventing injury to the medial antebrachial cutaneous nerve, complete release of all sites of compression, and avoidance of creating new compressive sites are the keys to this end.

High median nerve entrapments. An obscure cause of upper-extremity pain.

Compression of the median nerve at the wrist is the most common nerve entrapment syndrome but may be over- or misdiagnosed. With high (proximal) median nerve entrapment being uncommon and having an elusive diagnosis, proximal compression may be overlooked as a cause of the painful upper extremity. Recognition and diagnosis of this problem will help ensure timely and effective management of the more common pain syndromes.

Finite element stress analysis of a hybrid fracture fixation plate.

Metal plates are commonly used in the operative treatment of bone fractures. Rigid metal plates stabilize the fracture site, maintain good contact between bone fragments and allow early weight bearing and patient mobility. However, treatment with rigid metal plates can cause localized bone atrophy due to stress-shielding and interference with blood circulation, and the weakened bone can refracture after plate removal. A hybrid bone plate system that combines the torsional and bending rigidity of a metal plate with the axial compliance of a polymer insert has been designed. A three-dimensional, quarter-symmetric finite element model was generated for a canine femur diaphysis plated with this metal/polymer hybrid design. A model with a standard metal fixation plate was also generated for comparison purposes. The stress state in the underlying bone was examined for several loading conditions taken from published in vivo studies. The finite element model was used to study the performance of biodegradable polymer inserts in the plate system. The flexible plate reduced stress-shielding effects at the fracture site when subjected to an axial load. The bending strength of the plate was not compromised by the addition of the polymer inserts. Biodegradable inserts further enhanced the performance of the new plate design, transferring less of the axial load to the plate as the inserts broke down.

Efficacy of direct repair to partial arterial lacerations.

These are differences of opinion as to the best method of reconstituting flow following partial laceration of a small artery. This study was undertaken to determine how narrowing of a small vessel by direct repair affects patency rates. Partial arterial lacerations of varying widths were made in both femoral arteries of 30 Sprague-Dawley rats. The vessels were randomized to groups of longitudinal and transverse partial lacerations. Flow was reestablished in experimental vessels with direct repair (with reduction of vessel cross-sectional area ranging from 22% to 62%). In control vessels, resection and end-to-end repair or resection with vein grafting was performed. Two weeks postoperatively all vessels were explored to confirm patency and calculate flow. Immediately after repair all vessels were patent. At 2 weeks all direct and end-to-end repairs remained patent, while two of seven vein grafts had thrombosed. Immediately following repair there were no significant hemodynamic differences between repair groups. The final flow rate measured distal to the repair site averaged 2.5 mm2KHz for vessels with resection and either end-to-end repair or vein grafting (control group) versus 2 mm2KHz for vessels with direct repair of the laceration (experimental group); however, comparisons for specific groups showed no significant velocity or flow differences between control and experimental vessels. Direct repair of a partial arterial laceration with up to 62% narrowing of cross-sectional area gives patency rates equal to or better than those of alternate methods; however, blood flow rates may be altered distal to such a repair site.

Precision and accuracy of bone landmarks in characterizing hand and wrist position.

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 precision 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.