PubMed Health⌕ Search

Biomedical subjects

Keikhosrow Firoozbakhsh

Publications and source records attributed to Keikhosrow Firoozbakhsh.

11 recordsLinked to original sources
PubMed2006

Measurement of rotation of the first metacarpal during opposition using computed tomography.

PURPOSE: Opposition is an important movement of the hand and rotation of the first metacarpal is the essential component. There is no agreement on the exact magnitude of rotation of the first metacarpal during opposition. This study used computed tomography to describe rotation measurement of the first metacarpal in the hands of a group of healthy individuals. METHODS: The rotation of the first metacarpal was measured with reference to the fixed unit of the hand. Computed tomographic images were taken of the hands of 10 healthy individuals with the thumb in retroposition, resting position, and opposition to the index, middle, ring, and small fingers. On each image a tangential line was drawn along the dorsal margin of the second and third metacarpals. A second line was drawn through the head of the first metacarpal at the level of the sesamoids. The angle between the 2 lines was measured as the angle of rotation of the first metacarpal in different thumb positions. RESULTS: The mean angle of rotation of the first metacarpal in retroposition was 54 degrees+/-10 degrees with reference to the fixed unit of the hand. In the resting position the angle of rotation of the first metacarpal changed to 74 degrees+/-10 degrees. In the position of opposition to the index, middle, ring, and small fingers the angle of rotation of the first metacarpal increased to 100 degrees+/-7 degrees , 103 degrees+/-6 degrees, 105 degrees+/-6 degrees, and 110 degrees+/-7 degrees, respectively. CONCLUSIONS: The first metacarpal rotates 56 degrees when it moves from retroposition to the position of opposition to the small finger.

Adult↗
PubMed2006

Biomechanic comparison of 3 tendon transfers for supination of the forearm.

PURPOSE: Flexion-pronation of the hand and the forearm is a common deformity when the upper extremity is affected by cerebral palsy. Solutions used to improve the pronation deformity and increase supination include transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis, pronator teres rerouting, and brachioradialis rerouting. The purpose of this study was to compare the biomechanic efficacy of these 3 tendon transfers in simulated supination in cadaveric forearms. METHODS: Ten fresh-frozen adult cadaveric above-elbow upper extremities were used. In each specimen the 3 tendon transfers were performed sequentially in random order and were loaded in increments of 4 N (1 lb) to a maximum of 36 N (8 lb). Measurements were recorded from the starting point of 90 degrees of pronation. Statistical analysis of the data included the Student t test with the Bonferoni correction. RESULTS: For all transfers, supination increased in a nonlinear manner as the load was increased in a nonlinear manner. For the flexor carpi ulnaris transfer, the forearm reached its neutral position at a load of 9 N (2 lb). The forearm continued to rotate to up to 84 degrees of supination with 36 N (8 lb) of load. With the brachioradialis transfer, the forearm reached its neutral position at 13 N (3 lb) of load and continued to rotate to up to 33 degrees of supination with 36 N of load. With the pronator teres transfer, the forearm never reached the neutral position. Under a maximum load of 36 N, only 55 degrees of rotation from full pronation was obtained. CONCLUSIONS: Transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis proved to be the most effective transfer for producing supination in cadavers. The brachioradialis transfer was second best. The pronator teres rerouting was the least effective transfer in effecting simulated supination in this experiment.

Adult↗
PubMed2006

Extensor hallucis capsularis: frequency and identification on MRI.

BACKGROUND: The extensor hallucis capsularis (EHC) is the most common name given to the accessory tendon sporadically seen medial to the extensor hallucis longus (EHL). We performed cadaver dissections and MRI evaluation to determine the frequency of its occurrence, the pattern of its origin and insertion, and its potential suitability as tendon graft. METHODS: The EHC was examined by dissection in 81 cadaver feet. Physical parameters pertaining to EHC size and location were recorded. MRI was performed on six cadaver legs to determine if the EHC can be identified radiographically. MRI images were evaluated independently by a foot and ankle specialist and a radiologist. RESULTS: The EHC was present in 71 (88%) of the specimens. It originated from the EHL tendon or muscle in 93% and inserted into the first metatarsophalangeal joint capsule in 99% of cases. All EHC tendons were less than or equal to 4 mm in width; only 16% were more than 2 mm wide. Correct prediction of the presence or absence of EHC by MRI varied according to EHC width: two of two in tendons more than 2 mm, five of eight in tendons 1 to 2 mm, and zero of two in tendons 1 mm or less. CONCLUSION: Up to 14% of the population may have an EHC tendon suitable for grafting in reconstructive surgeries, particularly surgeries related to hallux dysfunction. MRI may have a role in the preoperative identification of the EHC.

Cadaver↗
PubMed2005

Dynamic effects of joint-leveling procedure on pressure at the distal radioulnar joint.

PURPOSE: Wrist joint-leveling procedures for decompression of the radiocarpal and ulnocarpal joints are accompanied by the risk for subsequent disorders of the adjacent distal radioulnar joint (DRUJ). This study evaluated the dynamic change of the pressure pattern at the DRUJ after joint-leveling procedures. METHODS: Thirteen fresh-frozen adult cadaveric upper extremities were used. A segment of the radius was excised at its midshaft to allow lengthening and shortening via a mini external fixator attachment. Dynamic pressure sensors were inserted into the DRUJ and the ulnocarpal joint. Axial loads were applied to the extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris for a total of 89 N with or without 30 N of radioulnar loading. The dynamic pressure distribution for full range of forearm rotation was recorded from 6 mm of radial shortening to 6 mm of radial lengthening in increments of 1 mm. RESULTS: The peak pressures at the DRUJ before the joint-leveling procedures averaged 3.3 MPa without radioulnar loading and 5.0 MPa with radioulnar loading. The peak pressures with axial and radioulnar loading increased 85% at 6 mm of lengthening and only 8% at 6 mm of shortening. The peak pressures at the DRUJ for radial lengthening of 4 mm or more were significantly greater than that of the original length. Pressure at the ulnocarpal joint increased in proportion to the amount of radial shortening and decreased with radial lengthening. CONCLUSIONS: Radial lengthening but not radial shortening significantly increases the peak pressure at the DRUJ.

Adult↗
PubMed2004

Smart intramedullary rod for correction of pediatric bone deformity: a preliminary study.

We were interested in determining if a smart intramedullary rod made of nitinol shape-memory alloy is capable of correcting deformed immature long bones. Because of limitations in our study design the process was reversed in that we examined the smart rod's ability to create a deformity rather than to correct one. Smart rods of different lengths and diameters were heat-treated to resume a radius of curvature of 30 to 110 mm. The low and high temperature phases of the smart rods were set, respectively, at 0 degrees C to 4 degrees C and 36 degrees C to 38 degrees C. The preshaped smart intramedullary rods were implanted in the cooled martensite phase in the medullary canal of the tibia in eight rabbits, where they restored their austenite form, causing a continuous bending force. On a weekly basis anteroposterior and lateral radiographs of the surgically treated tibia and the contralateral tibia were obtained for comparison. Rabbits were euthanized 6 weeks after surgery and computed tomography scans of both tibias were used for image analysis. Smart rods with a larger radius of curvature showed only minimal signs of remodeling; however, rods with a radius of curvature of 50 and 70 mm generated enough force history to create bone remodeling and deformation. The amount of bone deformation was highly magnified when unicortical corticotomy on the tension side was done. Based on this preliminary study the technology of the smart intramedullary rod may provide a valuable alternative method to correct pediatric skeletal deformities.

Alloys↗
PubMed2002

Flexor tendon repair using shape memory alloy suture: a biomechanical evaluation.

The purpose of the current study was to test in vitro a new shape memory alloy suture for flexor tendon repair. Forty fresh-frozen human anatomic flexor superficialis and profundus tendons were divided and repaired via the cruciate four-strand technique using one of two suture materials (the shape memory alloy suture and the 4-0 Ethibond suture). The forces required to cause a 1, 2, and 3 mm gap, ultimate load to failure, and repair stiffness were compared. Twenty specimens of each suture material also were tensile tested for load to failure, tensile strength, and elongation at failure. The shape memory alloy suture had a significantly higher mean resistance force to 1, 2, and 3 mm gap formation than the 4-0 Ethibond suture (47 N versus 31 N, 51 N versus 36 N, and 57 N versus 41 N, respectively). The shape memory alloy suture repair was 40% stronger than the 4-0 Ethibond suture (61.9 +/- 8.8 N versus 44.3 +/- 10.6 N). Repair with the shape memory alloy suture was significantly stiffer than repair with the 4-0 Ethibond suture (8.1 +/- 1.0 N/mm versus 6.1 +/- 0.9 N/mm). The load to failure and tensile strength of the shape memory alloy suture were significantly higher than that of the 4-0 Ethibond suture. The values of elongation for the two materials were not significantly different. The results of the current study suggest that the shape memory alloy suture may be superior to the 4-0 Ethibond suture in resisting gap formation in the range of forces generated in the early rehabilitation protocol and may be the future material of choice for tendon repairs.

Alloys↗
PubMed2002

A study of ulnar collateral ligament of the thumb metacarpophalangeal joint.

The current study examined the biomechanical properties of intact and repaired ulnar collateral ligaments of the metacarpophalangeal joint of the thumb to determine a safe rehabilitation protocol after repair. In the first part of the study mechanical properties of the ligament were examined and the induced stress and strain were determined during simulated pinch and grip. In the second part of the study the strength and limitations of ulnar collateral ligament repair using a mini-Mitek bone suture anchor was determined. The biomechanical study was done on 16 fresh-frozen thumbs from male cadavers. Failure load, maximum stress, and Young's modulus of intact ulnar collateral ligament were 294.3 +/- 28.2 N, 11.4 +/- 1.2 MPa, and 37.3 +/- 5.1 MPa, respectively. There was no significant correlation between the low grip force and the ligament strain. There was, however, a significant correlation between the pinch force and the ligament strain. The failure load and joint rigidity of intact ulnar collateral ligaments were significantly higher (3.1 and 2.3 times, respectively) than the mini-Mitek repaired ligaments. The current study suggests that pinch activity during the rehabilitative process after repair or reattachment of the ulnar collateral ligament should be eliminated. Repaired ligaments with mini-Mitek bone suture anchors may be able to do a moderate range of motion during postoperative rehabilitation; however, additional in vivo studies are necessary before any clinical recommendation is made.

Aged↗
PubMed2002

Application of computer-generated stereolithography and interpositioning template in acetabular fractures: a report of eight cases.

To determine the effectiveness of stereolithography modeling technologies in the surgical treatment of complex acetabular fractures, five patients with a complex fracture of the acetabulum and three patients with posterior wall fractures were considered in this study. The patients were surgically treated using an interposition template for accurate positioning of the fixation plate and screw trajectories. Intraoperative fluoroscopy confirmed precise plate placement and that all screw trajectories missed the hip joint. Fluoroscopy was only needed for confirmation of fracture reduction and for confirmation of screw location. Application of a life-size stereolithographic model of the pelvis and an interpositioning template along with the computer model of the reversed nonfractured contralateral hemipelvis provides an effective means for preoperative planning and accurate fixation of acetabular fractures. Further studies with this type of preplanning equipment may show a decrease in operative time and morbidity, decrease in radiation exposure, and improvement in accuracy of plate and screw placement.

Acetabulum↗
PubMedDate not supplied

Biomechanical analysis of pinning techniques for pediatric supracondylar humerus fractures.

BACKGROUND: Closed reduction and percutaneous pin fixation is the recommended treatment of displaced (Gartland types 2 and 3) supracondylar humerus fractures. The need for a medial pin for maximal stability remains controversial. The purpose of this study was to develop a model of supracondylar humerus fractures simulating medial column comminution and to evaluate the torsional stability of various pin configurations recommended in the current literature. METHODS: Transverse cuts were made in synthetic humeri with a wedge taken from the medial aspect of the proximal fracture fragment in one half of the specimens to simulate medial column comminution. Each fracture was then reduced and fixed with 1 of 4 pin configurations using 0.062 in K-wires. The fixed specimens were then subjected to a torsional load producing internal rotation of the distal fragment. Rotation in degrees and the corresponding torque was recorded for statistical analysis. RESULTS: Specimens with the medial wedge removed demonstrated less torsional stability than their identically fixed counterparts with the intact medial column. In specimens with the intact medial column, the greatest torsional stability was achieved with the 2 lateral divergent and medial cross pin configuration followed by 3 lateral pins, then standard crossed pins with 2 lateral divergent pins demonstrating the least torsional stability. For the medial comminution group the 2 lateral, 1 medial pin construct again had the greatest torsional stability and 2 lateral pins the least. The standard crossed pin and 3 lateral pin constructs were not significantly different in the presence of medial comminution. CONCLUSIONS: In a synthetic humerus model of supracondylar humerus fractures, medial comminution was shown to reduce torsional stability significantly in all pin configurations. There was no statistical difference in torsional stability between 3 lateral pins and standard crossed pins in specimens with medial comminution.

Biomechanical Phenomena↗
PubMedDate not supplied

Thumb amputations from team roping.

BACKGROUND: Thumb injuries during team roping have elements of both avulsion and crush, resulting in a poor prognosis for replantation success. PURPOSE: To review 19 cases of thumb amputation from team roping at our institution since 1983. STUDY DESIGN: Retrospective cohort study. METHODS: Cases were included in the study only if a microvascular repair of artery and vein was needed for the thumb to survive. Vein grafts were used to span the damaged vessel segment. Of the 19 thumb amputation cases, 15 attempts were made to replant the thumb. In the remaining four cases, patients had bone shortening and primary closure. The force of injury was calculated based on mechanism. RESULTS: Of the 15 attempts at replantation, only 5 (33%) were successful, despite meticulous technique. One patient subsequently had an emergency toe-to-thumb transfer after an unsuccessful replant, and the remaining nine underwent amputation. Nine of the 10 patients with failed replants had poor flow intraoperatively. In the group of patients younger than 15, the success was 3 of 5 (60%) and in the group 15 years or older the success was 2 of 10 attempts (20%.) Follow-up was available in 13 of the 15 cases of replanted thumbs. CONCLUSIONS: All patients were subjectively satisfied with their results, and all patients with successful replants and seven patients with no thumb returned to rodeo. Biomechanical analysis showed a huge amount of force and pressure, several times larger than that of ring avulsion injury, results when a steer pulls on the thumb.

Adolescent↗