Monolateral pin-to-bar-clamp fixators are commonly used to stabilize acute extremity injuries. Certain rules regarding frame geometry have been established that affect construct stability. The influence of sagittal pin angulation on construct stiffness and strength has not been investigated. The purpose of this biomechanical study was to demonstrate the effect of a pin angulation in the monolateral fixator using a composite cylinder model. Three groups of composite cylinder models with a fracture gap were loaded with different mounting variants of monolateral pin-to-bar-clamp fixators. In the first group, the pins were set parallel to each other and perpendicular to the specimen. In the second group, both pins were set convergent each in an angle of 15° to the specimen. In the third group, the pins were set each 15° divergent. The strength of the constructions was tested using a mechanical testing machine. This was followed by a cyclic loading test to produce pin loosening. A pull-out test was then performed to evaluate the strength of each construct at the pin–bone interface. Initial stiffness analyses showed that the converging configuration was the stiffest, while the diverging configuration was the least stiff. The parallel mounting showed an intermediate stiffness. There was a significantly higher resistance to pull-out force in the diverging pin configuration compared to the converging pin configuration. There was no significant difference in the pull-out strength of the parallel pins compared to the angled pin pairs. Convergent mounting of pin pairs increases the stiffness of a monolateral fixator, whereas a divergent mounting weakens it. Regarding the strength of the pin–bone interface, the divergent pin configuration appears to provide greater resistance to pull-out force than the convergent one. The results of this pilot study should be important for the doctrine of fixator mounting as well as for fixator component design.

The aim of this study was to determine if a negative pressure wound therapy (NPWT) system can facilitate wound healing and withstand mechanical stress owing to the high range of motion of the knee joint in total knee arthroplasty. The benefits of NPWT include aiding wound granulation and a reduction in wound edema and secretion; our goal is to investigate its benefits in primary wound closure. Within an eight-day duration of treatment, we compared standard wound dressing (gauze and compression) with the disposable NPWT system (PICO)^TM. A total of 79 patients were recruited in a controlled, randomized, prospective, single-institution clinical trial. A total of 40 patients were allocated to the study group and 39 to the control group. In terms of blood loss and infection parameters, there was no significant difference between both groups. In the NPWT group, we determined a significant reduction in wound edema but none in wound secretion. While the NPWT dressings survived the mechanical effects of movement during postoperative physiotherapy, conventional compressive dressings were often renewed. Even though the risk factors that could lead to delayed wound healing were reduced in the test group, we could not identify any significant difference pertaining to delayed wound healing that required surgical treatment.