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Biomedical subjects

K Firoozbakhsh

Publications and source records attributed to K Firoozbakhsh.

15 recordsLinked to original sources
PubMed2001

Potential of increased risk of neurovascular injury using proximal interlocking screws of retrograde femoral nails in patients with acetabular fractures.

OBJECTIVES: Neurologic and vascular structures are at risk of iatrogenic injury from proximal interlocking screw insertion after retrograde nailing. This risk may increase in the presence of acetabular fractures because of the displacement of soft tissues resulting from hematoma. The purpose of this study was to establish and compare the relative safe zones (RSZs) for interlocking screw insertion in adults with and without concomitant acetabular fractures. MATERIALS AND METHODS: Thirty pelvic computed tomography scans of patients with acute unilateral acetabular fracture and magnetic resonance imaging scans of five healthy legs were used to evaluate the course of the femoral sheath, neurovascular complex, and the sciatic nerve as they course through the proximal thigh in sixty-five limbs. RESULTS: The anatomy of the neurovascular structures on the fractured side was statistically different from that of the normal side. On the normal side, the RSZ at the lesser trochanteric level was identified from +7 degrees medial to +20 degrees lateral to the sagittal axis (27-degree angle zone) for anteroposterior screw placement. These values for the fractured side, respectively, changed to +1 degrees and +14 degrees (13-degree angle zone), a 52 percent decrease. The RSZ for lateral-medial screw placement was 28 degrees anterior to 39 degrees posterior to the coronal axis (67-degree angle zone) for the normal side, which changed, respectively, to 32 degrees and 41 degrees (73-degree angle zone) for the fractured side. At the level of the lesser trochanter, rotation in the femoral shaft was mimicked only in part (approximately 50 percent) by the neurovascular structures. CONCLUSION: Lateral-medial screw insertion is safer than anteroposterior insertion. Anteroposterior screw insertion becomes even more critical if the acetabulum is fractured. Femoral external rotation after rod insertion, but before screw insertion, will enlarge the safe zones.

Acetabulum↗
PubMed2001

Three-dimensional CT modeling versus traditional radiology techniques in treatment of acetabular fractures.

Recently, the authors have used the computer-generated three-dimensional (3-D) CT moving images for preoperative planning and screw/pin insertion in more than 28 cases involving plate and screw fixation of complex acetabular fractures. The authors also used stereolithography (wax or plastic 3-D model of bony anatomy) to develop a computer-generated "clip on" interpositioning template for accurate placement of plate and screws. Application of these new technologies gives the surgeon precise information about the fracture patterns and provides an effective means for preoperative planning and accurate fixation of acetabular fractures. The accuracy of the 3-D virtual presentation of the anatomy is impressive and was substantiated by phantom studies. Postoperation CT revealed no case of screw penetration in the joint. Among other benefits over conventional surgical technique, the computer-assisted surgery provided decreased operative time and morbidity, decreased radiation exposure, and obviated the need for oblique, inlet and outlet roentgen views of the pelvis for preoperative planning. A case report specifically demonstrates preoperative planning for reconstruction of acetabular fracture.

Acetabulum↗
PubMed2000

Computed tomography image-guided surgery in complex acetabular fractures.

Eleven complex acetabular fractures in 10 patients were treated by open reduction with internal fixation incorporating computed tomography image guided software intraoperatively. Each of the implants placed under image guidance was found to be accurate and without penetration of the pelvis or joint space. The setup time for the system was minimal. Accuracy in the range of 1 mm was found when registration was precise (eight cases) and was in the range of 3.5 mm when registration was only approximate (three cases). Added benefits included reduced intraoperative fluoroscopic time, less need for more extensive dissection, and obviation of additional surgical approaches in some cases. Compared with a series of similar fractures treated before this image guided series, the reduction in operative time was significant. For patients with complex anterior and posterior combined fractures, the average operation times with and without application of three-dimensional imaging technique were, respectively, 5 hours 15 minutes and 6 hours 14 minutes, revealing 16% less operative time for those who had surgery using image guidance. In the single column fracture group, the operation time for those with three-dimensional imaging application, was 2 hours 58 minutes and for those with traditional surgery, 3 hours 42 minutes, indicating 20% less operative time for those with imaging modality. Intraoperative computed tomography guided imagery was found to be an accurate and suitable method for use in the operative treatment of complex acetabular fractures with substantial displacement.

Acetabulum↗
PubMed2000

In vitro biomechanical evaluation of the double loop suture for flexor tendon repair.

Fifty-one fresh frozen human anatomic specimen flexor superficialis and profundus tendons that had been transected completely were repaired using the double loop, the single loop, and the modified Kessler techniques, and the resistances to mechanical distraction at 1, 2, and 3 mm and the ultimate load to failure were compared. The mechanical distraction at 1, 2, and 3 mm created nearly identical gaps at the tendon repair sites. There was no significant difference among the three repair techniques to resisting distraction at 1 and 2 mm. However, the double loop technique presented a mean resistance force of 22.0 N to distraction at 3 mm and 45.8 N in load to failure, which was significantly greater than the single loop (18.8 N at 3 mm distraction and 31.5 N failure load) and the modified Kessler (19.0 N at 3 mm distraction and 26.0 N failure load). This suggests the double loop technique may be superior to the single loop and the modified Kessler techniques in resisting gap in the range of forces generated in the early rehabilitation protocol.

Biomechanical Phenomena↗
PubMed2000

A biomechanical evaluation of internal fixation for ankle arthrodesis comparing two methods of joint surface preparation.

This study compared the biomechanics of two methods of joint preparation for ankle fusion with internal fixation. In the first method, the articular cartilage of the ankle joint was removed leaving the joint contour intact. In the second method, parallel flat saw cuts were used to prepare the joint surface for fusion. The specimens were loaded submaximally in a cyclic repetitive fashion before they were loaded to failure. Increasing joint motion occurred as the number of cycles increased. The difference between the two specimen types was not statistically significant during the repetitive tests or when loaded to failure. These results demonstrate both techniques of joint preparation studied are useful and biomechanically sound.

Adult↗
PubMed1999

Elbow ligament strain under valgus load: a biomechanical study.

This study assessed the importance of the anterior and posterior bundles of the medial collateral ligament in the elbow by measuring in situ strain in response to valgus loads at three positions of forearm rotation throughout a full arc of motion. Strain in the anterior bundle was significantly greater than in the posterior bundle and increased with more flexion. The anterior bundle developed strain at a lower flexion angle (30 degrees) than the posterior bundle (60 degrees). Strain ratio increased with load increase for all flexion angles. Forearm position minimally affected strain. These results indicate that the anterior bundle is important in resisting a valgus load, particularly in mid-flexion, while the importance of the posterior bundle increases as the elbow approaches full flexion.

Adult↗
PubMed1995

Mechanics of retrograde nail versus plate fixation for supracondylar femur fractures.

Two common types of internal fixations for the supracondylar femur fractures--the retrograde intramedullary nail and the 95 degrees sideplate and screw--were mechanically tested in synthetic composite femur bones to determine the quantitative differences in their inherent rigidity. The medial and lateral femoral condyles were separated by a sagittal osteotomy, and a standardized medial segmental shaft defect was created at the distal shaft. The osteotomized specimens were stabilized using one of the two implants and were tested in different modes of loading. The bending stiffness of both constructs were not significantly different in varus compression, medial bending (pure varus), and bending in flexion. The plate and screw implant was three times stiffer in lateral bending (pure valgus) and 1.2 times stiffer in valgus compression than the retrograde supracondylar nail (p < 0.01). The torsional stiffness of the plate and screw implant was significantly higher, 1.6 times that of the nail. Clinically, the most important and common cause of implant failure is varus loadings due to loss of medial cortical contact. Although the retrograde nail was less rigid in other physiologically less critical modes of loading, it had a rigidity comparable to that of the plate in varus loading. Therefore, a supracondylar nail may be considered a mechanically possible alternative to plate fixation.

Biomechanical Phenomena↗
PubMed1995

Determination of in vitro metatarsocuneiform pressure before and after surgical modification of the great toe.

In vitro contact pressures were measured at the first metatarsocuneiform joint in order to determine the effect of resectional arthroplasty and arthrodesis of the metatarsophalangeal joint of the great toe. Eight fresh cadaver feet were loaded with the Instron machine to determine the pressure seen at the first metatarsocuneiform joint. The specimens were subsequently modified by performing either an arthrodesis of the great toe metatarsophalangeal joint or an arthroplasty of this joint by removal of the proximal one third of the proximal phalanx. A second test was then performed. Pressure-sensitive film was analyzed to determine maximum pressure and total transmitted force. No significant pressure change was seen after the arthrodesis. After the resection arthroplasty, there was a significant decrease in both the maximum pressure and the total force measured at the first metatarsocuneiform joint.

Adult↗
PubMed1993

Ulnar translation of the carpus in rheumatoid arthritis: an analysis of five determination methods.

Five x-ray methods of assessing ulnar translation of the carpus were compared to each other. Overall, we found the uncompensated semiquantitative method proposed by Gilula et al. to be the most practical and the best method with a sensitivity index of 82%, a specificity index of 88%, an accuracy of 87%, and an interobserver correlation of 90%. The method, however, decreased in specificity and accuracy when a corrective formula was applied to adjust the ulnometacarpal angle to zero degrees deviation. Our conclusion is that the sensitivity indices are relatively low for all methods, and underdiagnosis may occur. At present the semiquantitated method of Gilula et al. is the most practical, with the highest sensitivity index, and is recommended as a screening tool for assessment of ulnar translation of the carpus.

Adult↗
PubMed1992

Evolution of bone inhomogeneity around a hole in an orthotropic plate of bone: theoretical predictions.

The problem of the evolution of bone inhomogeneity around a hole in a plate of bone with orthotropic symmetry is considered. The internal remodeling theory of Cowin and Hegedus is employed to show the existence of final inhomogeneity following stress concentration. The speed of remodeling around the hole and its variation with respect to distance is investigated. Results indicate that the effect of stress concentration around a hole is slightly less pronounced if bone is considered orthotropic rather than transversely isotropic. The speed of remodeling is found to be unaffected but the amplitude of inhomogeneity with respect to distance drops and disappears slightly faster if bone is considered orthotropic.

Bone Density↗
PubMed1989

The effect of stress concentration on bone remodeling: theoretical predictions.

Theoretical predictions of internal bone remodeling around an elliptical hole are studied. The internal remodeling theory due to Cowin and Hegedus is employed. The bone is modeled as an initially homogeneous adaptive elastic plate with an elliptical hole under a superposed steady compressive load. It is shown that there will exist a final inhomogeneous remodeling distribution around the hole that will disappear away from the hole. The remodeling is such that the compressive stress concentration causes the bone structure to evolve to one of greater density and stiffer elastic coefficients. The speed of remodeling around the hole and its variation with respect to distance is investigated and discussed. It is shown that the rate of bone reinforcement in the area of compressive stress concentration is much higher than the rate of bone resorption in the area of existing tensile stress. Special cases of a circular hole and vertical and horizontal slots are studied and discussed.

Biomechanical Phenomena↗
PubMed1981

An analytical model of Pauwels' functional adaptation mechanism in bone.

In this paper it is argued and partially demonstrated that the features of Pauwels' qualitative theory of functional adaptation of bone tissue are expressed mathematically by the cubic approximation to the theory of internal remodeling presented by Cowin and Hegedus. Complete solutions for the steady stress and steady strain situations in the cubic approximation to the theory of internal remodeling are presented. The cubic remodeling rate equation is shown to correspond closely to the remodeling equation suggested by Kummer for the qualitative theory of Pauwels.

Adaptation, Physiological↗
PubMed1980

Devolution of inhomogeneities in bone structure--predictions of adaptive elasticity theory.

In this paper we consider an initially inhomogeneous adaptive elastic body subjected to a steady homogeneous stress state. The adaptive elastic body, which is a model for living bone tissue, is inhomogeneous in both its anisotropic elastic properties and its density. The principal result of the paper is the determination of the devolution of the initially inhomogeneous body to a homogeneous body under the influence of the steady homogeneous stress state. A cylindrical body that is inhomogeneous along the axis of the cylinder, but homogeneous in each transverse plane of the cylinder, is used as an example. This cylindrical body is loaded by a steady uniform stress directed along the cylindrical axis. The temporal devolution of an inhomogeneity in the initial shape of a sine wave is illustrated. As time progresses the amplitude of the sine wave decreases, rapidly at first and then more slowly. As time becomes very large the sine wave becomes a straight line signifying that the cylinder has become homogeneous.

Biomechanical Phenomena↗
PubMedDate not supplied

Determining flexor-tendon repair techniques via soft computing.

An SC-based multi-objective decision-making method for determining the optimal flexor-tendon repair technique from experimental and clinical survey data, and with variable circumstances, was presented. Results were compared with those from the Taguchi method. Using the Taguchi method results in the need to perform ad-hoc decisions when the outcomes for individual objectives are contradictory to a particular preference or circumstance, whereas the SC-based multi-objective technique provides a rigorous straightforward computational process in which changing preferences and importance of differing objectives are easily accommodated. Also, adding more objectives is straightforward and easily accomplished. The use of fuzzy-set representations of information categories provides insight into their performance throughout the range of their universe of discourse. The ability of the technique to provide a "best" medical decision given a particular physician, hospital, patient, situation, and other criteria was also demonstrated.

Cadaver↗