Biomedical subjects

D R Pichora

Publications and source records attributed to D R Pichora.

At least 19 recordsLinked to original sources

PubMed2005

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.

Bone Wires↗

PubMed2001

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.

Humans↗

PubMed2001

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.

Biomarkers↗

PubMed2001

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.

Accidental Falls↗

PubMed2000

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.

Arthroplasty, Replacement↗

PubMed2000

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.

Activities of Daily Living↗

PubMed1999

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.

Aged↗

PubMed1998

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.

Arthritis, Rheumatoid↗

PubMed1998

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.

Adolescent↗

PubMed1996

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.

Animals↗

PubMed1996

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.

Journal Article↗

PubMed1996

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.

Diagnosis, Differential↗

PubMed1996

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.

Arm↗

PubMed1994

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.

Animals↗

PubMed1993

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.

Bone and Bones↗

PubMed1993

A kinematic technique for describing wrist joint motion: analysis of configuration space plots.

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.

Biomechanical Phenomena↗

PubMed1992

Rationalization of kinematic descriptors for three-dimensional hand and finger motion.

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 between 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.

Biomechanical Phenomena↗

PubMed1992

Strain-gauge evaluation of lunate unloading procedures.

A biomechanical study was undertaken to determine which procedure(s) most effectively relieve load from the lunate. Strain gauges were mounted on the lunates of 20 preserved cadaveric limbs. Three types of procedures were performed: scaphotrapeziotrapezoid arthrodesis, capitohamate arthrodesis, and ulnar lengthening. Load testing was performed both before and after the simulated fusions and ulnar lengthenings. Ulnar lengthening of 3 mm was the most effective method of lunate strain reduction. Capitohamate arthrodesis decreased compressive strain but increased shear strain. Scaphotrapeziotrapezoid fusion significantly increased both compressive and shear strain in the lunate. Of the three procedures that were tested, ulnar lengthening to create a neutral variance is the most reliable means of unloading the lunate.

Analysis of Variance↗