Comparing the locking screw direction of three locking plates for lateral clavicle fractures: a simulation study

Background The locking plate is a useful treatment for lateral clavicle fractures, however, there are limits to the fragment size that can be fixed. The current study aimed to measure the screw angles of three locking plates for lateral clavicle fractures. In addition, to assess the number of screws that can be inserted in different fragment sizes, to elucidate the size limits for locking plate fixation. Methods The following three locking plates were analyzed: the distal clavicle plate [Acumed, LLC, Oregon, the USA], the LCP clavicle plate lateral extension [Depuy Synthes, LLC, PA, the USA], and the HAI clavicle plate [HOMS Engineering, Inc., Nagano, Japan]. We measured the angles between the most medial and lateral locking screws in the coronal plane and between the most anterior and posterior locking screws in the sagittal plane. A computer simulation was used to position the plates as laterally as possible in ten normal three-dimensional clavicle models. Lateral fragment sizes of 10, 15, 20, 25, and 30 mm were simulated in the acromioclavicular joint, and the number of screws that could be inserted in the lateral fragment was assessed. Subsequently, the area covered by the locking screws on the inferior surface of the clavicle was measured. Results The distal clavicle plate had relatively large screw angles (20° in the coronal plane and 32° in the sagittal plane). The LCP clavicle lateral extension had a large angle (38°) in the sagittal plane. However, the maximum angle of the HAI clavicle plate was 13° in either plane. The distal clavicle plate allowed most screws to be inserted in each size of bone fragment. For all locking plates, all screws could be inserted in 25 mm fragments. The screws of distal clavicle plate covered the largest area on the inferior surface of the clavicle. Conclusions Screw angles and the numbers of screws that could be inserted in the lateral fragment differed among products. Other augmented fixation procedures should be considered for fractures with fragment sizes < 25 mm that cannot be fixed with a sufficient number of screws.

Effect of Calcaneus Fracture Gap Without Step-Off on Stress Distribution Across the Subtalar Joint

Background: Subtalar arthritis is a common consequence following calcaneal fracture, and its development is related to the severity of the fracture. Previous calcaneal fracture models have demonstrated altered contact characteristics when a step-off is created in the posterior facet articular surface. Changes in posterior facet contact characteristics have not been previously characterized for calcaneal fracture gap without step-off. Methods: The contact characteristics (peak pressure, area of contact, and centroid of pressure) of the posterior facet of the subtalar joint were determined in 6 cadaveric specimens. After creating a calcaneal fracture to simulate a Sanders type II fracture, the contact characteristics were determined with the posterior facet anatomically reduced followed by an incremental increase in fracture gap displacement of 2, 3, and 5 mm without a step-off of the articular surface. Results: Peak pressure on the medial fragment was significantly less with a 5-mm gap compared to a 2- or 3-mm gap, or reduced. On the lateral fragment, the peak pressure was significantly increased with a 5-mm gap compared to a 2- or 3-mm gap. Contact area significantly changed with increased gap. Conclusion: In this study, there were no significant differences in contact characteristics between a <3-mm gap and an anatomically reduced fracture, conceding the study limitations including limiting axial loading to 50% of donor body weight. Clinical Relevance: A small amount of articular incongruity without a step-off can be tolerated by the subtalar joint, in contrast to articular incongruity with a step-off present.

Determination in regenerating tissues of Dugesia dorotocephala: the influence of nerve cord grafts

Lateral fragments which contained no nerve cord were isolated from the postpharyngeal body section of Dugesia dorotocephala and fused with nerve cord grafts soon after isolation and at daily intervals through 8 days of regeneration. Fragments fused soon after isolation formed ‘headless’ regenerates but had normal body proportions. If the lateral cordless fragment was allowed to regenerate for 1 day or longer before fusion with the nerve cord fragment, the head always developed and the body proportions were normal. Therefore, head structures become determined in the lateral fragment within the first 24 h of regeneration; during this time these tissues can also respond to the head-inhibiting influence of the nerve cord. The competence to form particular structures of the postcerebral body regions must emerge after head-forming competence is lost, that is about 24h after isolation; however, it persists at least through the first 8 days of regeneration. Normal body proportions can be induced by nerve cord grafts throughout the first 8 days of regeneration. Lateral fragments fused at any time after isolation with another fragment containing no nerve cord developed head structures but failed to differentiate tissues of the postcerebral regions. This confirms that the nerve cord is responsible for inhibition of head structures and induction of differentiation of body regions and normal body proportions.