Pullout strength of connected pins in hand surgery: Effect of pin diameter and insertion angle

OBJECTIVE

The purpose of this study was to examine the effect of insertion angles on the pullout strength of connected pins using a synthetic model simulating a hand bone.

MATERIAL AND METHODS

The material consisted of Sawbones® (20 mm×20 mm × 60 mm), fixation pins secured to a connecting rod much like an external fixator, an electric drill (speed 1,290 rpm) and a tensile testing machine. The Sawbones® were drilled with different pin diameters (1.2 mm, 1.5 mm, and 1.8 mm) and insertion angles (100°, 110° and 120°). A vertical displacement of 1 mm/min was applied until the pins were extracted (maximum force).

RESULTS

The pullout strength increased with the insertion angle of the connected pins. It also increased with their diameter. Regardless of the pin diameter, the load-displacement curve during the pullout test had 4 sections (peak 1, ascending slope, peak 2, descending slope) that corresponded to the combined frictional force and contact force between the pins and Sawbones®.

DISCUSSION

Our study findings showed that, theoretically, for wrist or hand fractures treated with connected pins, the larger the diameter and insertion angle, the better the mechanical holding power of the pins.

LEVEL OF EVIDENCE

I, experimental study.

Interaction between Discs large and Pins/LGN/GPSM2: a comparison across species

The orientation of the mitotic spindle determines the direction of cell division, and therefore contributes to tissue shape and cell fate. Interaction between the multifunctional scaffolding protein Discs large (Dlg) and the canonical spindle orienting factor GPSM2 (called Pins in Drosophila and LGN in vertebrates) has been established in bilaterian models, but its function remains unclear. We used a phylogenetic approach to test whether the interaction is obligate in animals, and in particular whether Pins/LGN/GPSM2 evolved in multicellular organisms as a Dlg-binding protein. We show that Dlg diverged in C. elegans and the syncytial sponge Opsacas minuta and propose that this divergence may correspond with differences in spindle orientation requirements between these organisms and the canonical pathways described in bilaterians. We also demonstrate that Pins/LGN/GPSM2 is present in basal animals, but the established Dlg-interaction site cannot be found in either Placozoa or Porifera. Our results suggest that the interaction between Pins/LGN/GPSM2 and Dlg appeared in Cnidaria, and we therefore speculate that it may have evolved to promote accurate division orientation in the nervous system. This work reveals the evolutionary history of the Pins/LGN/GPSM2-Dlg interaction and suggests new possibilities for its importance in spindle orientation during epithelial and neural tissue development.

What Can Pinterest Do for Radiology?

The rapid growth of social media over the last decade soon convinced businesses including medical practices and academic medical centers to enter the social media fray-for profit, education, and expanding access. Launched in 2010, Pinterest (San Francisco, CA, USA) differed from many of the established social media platforms by presenting collection and curation features based on the sharing of images rather than text. Thus, Pinterest allows users to categorize website links using photos, GIFs, and videos, and catalog them for future consideration, saved on a virtual folder or "pinboard." Facebook, Twitter, and LinkedIn are text-heavy social media platforms that do not allow for significant curating activities. Instagram, the other of the two primary photo-oriented social media giants, was launched the same year as Pinterest. Owned by Facebook, Instagram caters to a more personal experience and mostly relies on mobile technology. Because Pinterest users are mainly focused on finding and collecting other users' content, Pinterest is thought to generate website traffic and is more conducive to use on larger screens. It further distinguishes itself by encouraging appreciation/learning over self-promotion and its range of categories exceeds that of other such sites. Some of the more visually oriented medical specialties (i.e., dermatology, plastic surgery, and radiology) have begun to consider what role, if any, the popular site Pinterest, with more than 250 million monthly users, might play in disseminating healthy messages, reaching patients, and contributing to medical education. We investigated how Pinterest could work for our radiology education mission and then decided to establish a presence on the site to ascertain if creating our own board would have any practical benefits.

Where should the pins be placed to decrease the failure rate after fixation of a Mayo IIA olecranon fracture? A biomechanical analysis

BACKGROUND

Clinically, treatment of Mayo IIA olecranon fractures (MIOF) using pins is associated with a high rate of failure. The purpose of our study was to compare the biomechanical stability and strength of four different fracture fixation configurations and to recommend the best method for the clinical treatment of MIOFs.

METHODS

Twenty synthetic ulnar models were created and equally divided into 4 different fracture fixation groups: a double cortical configuration using Kirschner (K) wires; a double cortical configuration using transcortical pins; an intramedullary pin system; and an intramedullary pin system with a 3-mm distance between the eyelet and the proximal end of the olecranon (loose fixation). The stiffness and strength of all specimens were tested under a loading rate of 2 mm/min. Between-group differences were evaluated using an independent t-test, with significance set at P < 0.05.

RESULTS

Stiffness and strength were significantly better for the K-wire than intramedullary group: stiffness, 63.467±14.063 N/mm and 36.243±5.625 N/mm, respectively (P=0.009); and strength, 624.293±148.728 N and 406.486±74.109 N, respectively (P=0.019). There was no difference in stiffness (P=0.370) or strength (P=0.929) between the use of transcortical pins and K-wires. Moreover, a 3-mm prominence of the pin at the olecranon did not have a negative effect on either stiffness (P=0.494) or strength (P=0.391).

CONCLUSIONS

Our biomechanical analysis indicated that using a double cortical pin configuration provided the best stability and strength and, thus, may lower the risk of fracture fixation failure. The use of either K-wires or pins in the double cortical configuration did not influence fixation stability. A loose double cortical configuration might decrease fracture stability, although there differences were not significant.

Loss of the canonical spindle orientation function in the Pins/LGN homolog AGS3

In many cell types, mitotic spindle orientation relies on the canonical "LGN complex" composed of Pins/LGN, Mud/NuMA, and Gα_i subunits. Membrane localization of this complex recruits motor force generators that pull on astral microtubules to orient the spindle. Drosophila Pins shares highly conserved functional domains with its two vertebrate homologs LGN and AGS3. Whereas the role of Pins and LGN in oriented divisions is extensively documented, involvement of AGS3 remains controversial. Here, we show that AGS3 is not required for planar divisions of neural progenitors in the mouse neocortex. AGS3 is not recruited to the cell cortex and does not rescue LGN loss of function. Despite conserved interactions with NuMA and Gα_iin vitro, comparison of LGN and AGS3 functional domains in vivo reveals unexpected differences in the ability of these interactions to mediate spindle orientation functions. Finally, we find that Drosophila Pins is unable to substitute for LGN loss of function in vertebrates, highlighting that species-specific modulations of the interactions between components of the Pins/LGN complex are crucial in vivo for spindle orientation.

Absorbable biologically based internal fixation

Absorbable devices for use in internal fixation have advanced over the years to become reliable and cost-effective alternatives to metallic hardware. In the past, biodegradable fixation involved a laborious implantation process, and induced osteolysis and inflammatory reactions. Modern iterations exhibit increased strength, smoother resorption, and lower rates of reactivity. A newer generation manufactured from silk has emerged that may address existing limitations and provide a greater range of fixation applications.

In-out-in pinning for phalangeal fractures

Although a commonly used technique, percutaneous pinning of phalangeal fractures is tricky because of the difficulties associated with getting the correction pin orientation when entering the medullary canal of one fragment from the outer cortex of the other fragment. This has led us to develop the "in-out-in" pinning technique. The principle consists of entering the medullary canal of one of the fragments directly from the fracture site. The pin is inserted and drilled outward through the outer cortex. The second pin is inserted in the same manner. The fragments are then aligned and the pins pushed forward in the medullary canal of the other fragment.