Divergent Pins Research Articles

Biomechanical Analysis of Lateral Humeral Condyle Fracture Pinning

The purpose of this study was to determine the optimum pin configuration and the number of pins needed to stabilize the Milch type II lateral humeral condyle fractures in a pediatric bone model. Forty synthetic pediatric humeri were sectioned through the lateral distal humerus to simulate a Milch type II lateral condyle fracture. Each fracture was stabilized with 0.062-in K-wires in 1 of 5 configurations: 2 convergent pins, 2 parallel pins, 2 divergent 30-degree pins, 2 divergent 60-degree pins, and 3 divergent pins (n=8/group). Models were tested in extension, flexion, varus, and valgus by applying a translational force through the distal fragment at 0.5 mm/sec oscillating between 5 N and 50 N for 10 cycles. For internal and external rotation, constructs were tested at 0.5 degree/sec between ±1 Nm more than 10 cycles. The maximum force and torque values were also recorded. For bending loads, stiffness was calculated between 0.5 and 5 mm of displacement, whereas torsional stiffness was calculated between 1 degree and 10 degrees of rotation. Data for stiffness were analyzed with a 1-way analysis of variance and a 2-sample t test (P<0.05). Among 2-pin configurations, divergent (60 degrees) pins provided statistically greater stability than less divergent pins in torsional loading, and greater stability than parallel pins in valgus loading. Three divergent pins had statistically greater stability than all the 2-pin configurations in valgus and torsional loading, and tended to provide more secure fixation in varus loading. For 2-pin constructs, maximizing pin divergence at the fracture site provided greater stability in torsional loading and valgus loading. The addition of a third pin in a divergent orientation increases stability compared with 2-pin constructs in valgus, internal, and external rotation loading. Bicortical pins placed with maximum divergence and spread at the fracture site maximizes stability for 2-pin constructs in Milch type II lateral condyle fractures. If the stability of the fracture is questionable after 2 pins are inserted, the addition of a divergent third pin enhances the stability.

Biomechanical Analysis of Supracondylar Humerus Fracture Pinning for Slightly Malreduced Fractures

The most common position of malreduced type III supracondylar humerus (SCH) fractures is internal rotation and medial collapse of the distal fragment. The purpose of this study was to determine the effect of SCH fracture rotational deformity on stability with various pin configurations. Specifically, is the biomechanical stability lost when an SCH fracture is pinned in slight malreduction (compared with anatomical pinning) improved by adding a third pin? Sixty-four synthetic humeri were sectioned in the mid-olecranon fossa to simulate an SCH fracture. Specimens were randomized to an anatomically reduced group or a group with 20 degrees of distal fragment internal rotation (n = 32 per group). Each was randomized to one of 4 pin configurations: 2 laterally divergent pins, 2 crossed pins, 3 laterally divergent pins, or 2 lateral with 1 medial pin (n = 8 per group). All fractures were stabilized with 1.6 mm (0.062 in) Kirschner wires. Models were tested in extension, varus, and valgus for 10 cycles between 5 N and 50 N. Internal and external rotations were tested between +/-1 Nm. Data for fragment stiffness (newtons per millimeter or newton millimeters per degree) were analyzed with a 2-way analysis of variance (p < 0.05). Internally rotated fractures were significantly less stable than the anatomically reduced group for external rotation, internal rotation, and varus loading regardless of pin configuration. Within the malreduced group, 3-pin configurations were more stable than 2-pin configurations in internal rotation, varus, and extension loading. Two lateral divergent pins were similar to 2 crossed pins, except in extension, where 2 lateral pins had greater stiffness. Construct stiffness for malreduced specimens after pinning was less than those pinned with an anatomical reduction when loaded in varus, internal rotation, and external rotation. For simulated fractures with residual internal rotation, the addition of a third Kirschner wire compared with an anatomically reduced 2-crossed-pin configuration resulted in increased stiffness of the model for all loading directions. Consider a 3-pin pattern, either 3 laterally divergent pins or 2 lateral pins and 1 medial pin, for SCH fractures when a less than complete anatomical reduction is obtained.

Biomechanical Analysis of Pinning Techniques for Pediatric Supracondylar Humerus Fractures

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. 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. 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. 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.

Displaced pediatric supracondylar humerus fractures: biomechanical analysis of percutaneous pinning techniques.

Supracondylar humerus fractures are a common childhood occurrence. Displaced fractures are typically treated with closed reduction and percutaneous pinning. Controversy continues over the appropriateness of various pinning techniques. The most common include crossed or lateral pins. A biomechanical comparison of crossed pins, "parallel" lateral pins, and "divergent" lateral pins was performed using a pediatric synthetic bone model. Mechanical testing of each pin configuration was performed in extension, varus, valgus, internal rotation, and external rotation. The divergent configuration provided statistically greater stability than parallel pins under varus and valgus loading. Divergent pins had similar stability compared with crossed pins in extension, varus, and valgus testing. In axial rotation testing, crossed pins were more stable. If the surgeon feels confident in the ability of lateral pins to provide satisfactory fracture stability, divergent lateral pins provide greater stability than parallel lateral pins while avoiding ulnar nerve injury (associated with crossed pins).

Displaced Pediatric Supracondylar Humerus Fractures: Biomechanical Analysis of Percutaneous Pinning Techniques

Supracondylar humerus fractures are a common childhood occurrence. Displaced fractures are typically treated with closed reduction and percutaneous pinning. Controversy continues over the appropriateness of various pinning techniques. The most common include crossed or lateral pins. A biomechanical comparison of crossed pins, “parallel” lateral pins, and “divergent” lateral pins was performed using a pediatric synthetic bone model. Mechanical testing of each pin configuration was performed in extension, varus, valgus, internal rotation, and external rotation. The divergent configuration provided statistically greater stability than parallel pins under varus and valgus loading. Divergent pins had similar stability compared with crossed pins in extension, varus, and valgus testing. In axial rotation testing, crossed pins were more stable. If the surgeon feels confident in the ability of lateral pins to provide satisfactory fracture stability, divergent lateral pins provide greater stability than parallel lateral pins while avoiding ulnar nerve injury (associated with crossed pins).

In vitro comparison of the standard short limb cast and three configurations of short limb transfixation casts in equine forelimbs

Summary Axial stability of equine oblique proximal phalangeal osteotomies with application of the standard short limb cast or 1 of 3 configurations of transfixation casts was determined in vitro. Transfixation cast methods included use of parallel pins, divergent pins, or parallel pins incorporating a metal walking bar. Displacement at the osteotomy was recorded for each limb at 4,448 N. Standard short limb casts provided significantly (P = 0.0002) less axial stability than did any form of transfixation cast. Significant differences were not found between the 3 transfixation casts.

In vitro comparison of the effect of parallel and divergent transfixation pins on breaking strength of equine third metacarpal bones

Summary Breaking strength (torque at failure) of equine third metacarpal bones, with transfixation pins placed parallel in the frontal plane and 30° divergent from the frontal plane, was determined in vitro. Two transfixation pins were placed through the distal metaphysis, using a jig designed to drill the holes in the assigned configuration. Paired metacarpal bones II through IV from 12 horses were tested in torsion. The torsional moment of the force applied through the transfixation pins at failure was compared for each limb. Metacarpal bones with divergent pins were significantly (P = 0.030) stronger, compared with those with parallel pins. Metacarpal bones with parallel pins failed with longitudinal oblique fractures through a proximal bone-pin interface, whereas those with divergent pins failed with more comminuted fractures through multiple bone-pin interfaces.

Biomechanical Comparison of Three Repair Methods for Proximal Femoral Physeal Fractures in Shear and Tension

SummaryProximal femoral physeal fractures were created in femora harvested from 64 immature dogs and repaired with one of three repair techniques. Techniques used included a single lag screw placed distal to the trochanter, three divergent pins from below the trochanter, and two screws placed from the articular surface of the femoral head. The re-paired fractures were tested in tension and shear for strength and stiffness. The strength and stiffness were recorded by a hydraulic testing machine and the mode of failure was determined by visual inspection. Fractures repaired with a single lag screw and with the two screws were significantly stronger in tension than those repaired with multiple pins. Significant differences were not found between the repair techniques for shear strength or stiffness in neither tension nor shear. The modes of failure differed between the repair techniques.Three techniques of proximal femoral physeal fracture repair; a single screw from below the greater trochanter, three divergent pins, and two screws placed from the articular sur-face, were tested in tension and shear. Fractures, created on in vitro femora, repaired with a single lag screw and the two screws, were significantly stronger in tension than those repaired with multiple pins. Significant differences were not found between the repair techniques for shear strength or stiffness in neither tension nor shear.

L'ostéosynthèse par la technique des broches « en palmiersdes fractures du col chirurgical de l'humérus

Presented in 1974, this technique consists of internal fixation of the humeral neck by means of three divergent K-wires. These are introduced through a proximal entry point located on the lateral aspect of the humeral diaphysis at the lower end of the "V" shaped insertion of the deltoid which is one of the three subcutaneous areas of this bone. The two principles of this technique are: anchorage of the epiphysis by three divergent pins driven into the cancellous bone of the head and introduction of the pins from a very proximal point that allows easy access across the fracture without the disadvantages of nerve and joint proximity, as in other techniques involving other pins through the olecranon fossa (April), or medial epicondyle or lateral (Vichard). Moreover, this technique is quite different from the Hackethal technique by nails introduced through the olecranon fossa. An oblique hole is drilled at the selected point, and three 2 mm K-wires, after bending their ends are introduced into the medullary canal. After reduction of the fracture, they are driven into the cancellous humeral head bone. By turning the handle, the pins are made to diverge. Exceptionally, operative reduction is necessary by a separate axillary approach. X-ray control or the use of an image intensifier permits one to see if a K-wire is too long and to pull it out somewhat. No cast, no operation splinting, is used. Active and passive mobilization is possible the next day so the functional results are excellent in most cases. Pin removal is possible after 3 weeks in children and 5 in adults. The indications are all the upper extremity humeral fractures, and especially in children (epiphyseal fractures); in adults and aged people, except comminuted fractures.

The dry wear of steels II. Interpretation and special features

The pattern of wear outlined in part I is interpreted in the light of further experiments which reveal that the change from severe wear to mild is governed by the hardness and state of oxidation of the surfaces. At light loads (&lt; T 1) severe wear is inhibited by the combined effects of strain hardening and oxidation. At higher loads (&gt; T 2) mild wear recurs primarily as a consequence of a change of phase induced by frictional heating. The hardness accompanying the phase change is great enough, initially, to suppress severe wear without the intervention of an oxide film. At loads immediately above T 2, however, the hardness tends to fall if rubbing is prolonged and oxidation is again essential to preserve the mild wear state. Sustained phase-hardening does not occur until a higher load, roughly coinciding with the T 3 transition, is attained and this finding has an important bearing on the influence of inert atmospheres. The onset of permanent hardening is not responsible for the divergent pin and ring wear rates at T 3, though the phenomena may be linked by the magnitude of the temperatures required to cause phase-hardening; the T 3 transition and the trend at higher loads have been identified as special effects associated with the thermal asymmetry of the rubbing system.