Effect of Steel Surface Roughness and Expanded Graphite Condition on Sliding Layer Formation

The aim of the research was to evaluate the influence of the initial roughness of a steel pin cooperating with a graphite ring—dry and wet—on the mechanism of sliding layer formation. A ring–pin friction pair was used for the study, where the rings were made of expanded graphite, while the pins were made of acid-resistant steel. In the first case, the steel pin interacted with a dry graphite ring, and in the second case, the graphite rings were moist. To determine the effect of initial surface roughness, the pins were divided into three roughness groups. To determine changes in surface geometry due to material transfer, the Ra and Rz parameters were measured. This project investigated how the initial roughness value of the steel surface pin cooperating with expanded graphite influences the formation of the sliding layer. Increasing the initial roughness of the steel surface interacting with the graphite contributes to faster layer formation and reduced roughness. The state of the expanded graphite—dry and wet—influences the formation of the sliding layer of graphite—a wet graphite component causes a faster smoothing of the steel surface. The running time of the wear apparatus has an effect on the resulting layer. The highest roughness group is the most favorable from the viewpoint of sliding layer formation.

Complications Related to Implant Fixation of Patellar Fractures: Comparison of Ring Pins versus Bent K-Wires

Patellar fractures are characterized by injuries to the extensor and typically require surgical fixation. Among the methods used for fixation, the most common is the modified AO tension-band wiring technique. However, using this technique, implant migration occurs due to the lack of connections between the K-wires and the tension-band wire, which causes irritation and reduces fracture stability. Recently, new methods for tension-band wiring have been developed in which tension bands lock the K-wires through an attached “ring” to prevent migration. The purpose of this study was to compare the clinical outcomes when either the conventional or novel technique was used for tension-band wiring. This was a retrospective study involving 48 patients who underwent tension-band wiring to correct a patellar fracture. Patients in group 1 (n = 23) were treated between December 2010 and February 2012 using conventional tension-band wiring, while patients in group 2 (n = 25) were treated between March 2012 and May 2014 using the novel ring pin method. Different surgeons performed the operations in the two groups, while all other conditions were consistent. The surgical outcomes were assessed according to the level of implant migration, irritation, and implant removal procedures. All patients in group 2 achieved a union of the patella, while two patients in group 1 did not. These two patients underwent partial patellectomy within 1 year of the initial surgery. Implant migration and removal were significantly more common among patients in group 1 (p = 0.0038 and 0.011, respectively), with the implant removal period being significantly shorter as well (p = 0.005). The novel ring pin method was superior to the conventional method in terms of preventing implant migration, removal, or other secondary operations for the correction of complications.