Introduction. Tendinopathies are debilitating and painful conditions. They are believed to result from repetitive overuse, which can create micro-damage that accumulates over time, and initiates a catabolic cell response. The aetiology of tendinopathy remains poorly understood, therefore the ideal treatment remains unclear. However, current data support the use of eccentric exercise as an effective treatment. In a previous study, we have shown that eccentric loading generates perturbations in the tendon at 10Hz, which is not present during other less effective loading regimes. Consequently, we hypothesis that 10Hz loading initiates an increased anabolic response in tenocytes, that can promote tendon repair. Materials and Methods. Human tenocytes from healthy hamstring tendons and tendinopathic Achilles tendons were derived by collagenase digest and outgrowth respectively. Tenocytes were seeded into 3D collagen gels. The gels were fixed in custom-made chambers and placed in an incubator for 24hrs whilst gene expression stabilised. After 24hrs, cyclic uniaxial strain at 1% ± 1% was applied to the cells, at either 1Hz (n=4) or 10Hz (n=4) using a Bose loading system. After 15 minutes of cyclic strain, the samples were maintained in chambers under 1% static strain for 24 hrs after which gene expression was characterised using RT-PCR. Results. In healthy cells, data showed an increase in expression of all analysed genes after loading (MMP1, MMP2, MMP13, COL1A1, COL3A1, COL5A1, ADAMTS5, IL6, IL8 and TIMP3). Furthermore, the increase in gene expression was larger in the higher frequency loading group, across all genes. Tendinopathic cells showed a more varied response, with upregulation of MMP1, MMP13, COL3A1, ADAMTS5, IL6 and IL8, and downregulation of COL1A1 and COL5A1. Once again, all changes were more pronounced in the higher frequency loading group. Discussion. These preliminary data suggest increased matrix turnover as a result of loading, particularly with high frequency loading in healthy tenocytes, whilst the profile of tendinopathic cells, may indicate an early healing response, where collagen type III is preferentially unregulated relative to types I and V. High frequency loading elicited a more pronounced cellular response, perhaps correlating with the improved repair seen with eccentric loading in vivo

Background. While total shoulder arthroplasty (TSA) is a generally successful procedure, glenoid loosening remains a common complication. Though the occurrence of loosening was related to patient-specific factors, biomechanical factors related to implant features may also affect the fixation of the glenoid component, in particular increased glenohumeral mismatch that could result in eccentric loads and translations. In this study, a novel test setup was used to quantify glenohumeral pressures for different motion patterns after TSA. Methods. Six cadaveric human shoulders were implanted with total shoulder replacements (Exactech, Inc., USA) and subjected to cyclic internal-external, flexion-extension and abduction-adduction rotations in a passive motion testing apparatus. The system was coupled to a pressure sensor system (Tekscan, Inc., USA) to acquire joint loads and to a Zebris system (Zebris Medical, GmbH, Germany) to measure joint kinematics. The specimens were subjected to a total of 2160 cycles and peak pressures were compared for each motion pattern. Results. It was shown that during abduction the contact area between the humeral head and the glenoid component shifts from a posterior to an anterior position, while also moving inferiorly. For internal-external rotation a mean peak pressure of 8.37 ± 0.22 MPa was registered, while for flexion-extension a pressure of 9.37 ± 0.38 MPa and for abduction-adduction a pressure of 9.88 ± 0.07 MPa were obtained. Conclusion. This study showed how glenohumeral pressures after TSA vary during simulated internal-external, flexion-extension and abduction-adduction rotations in a cyclic testing setup. It showed that peak loads are mainly obtained in abduction, and that these occurred mainly near the anterior part of the glenoid. Future steps involve implantation of other type of anatomical glenoid components to obtain different levels of glenohumeral mismatch and relating the 3D measurements of motion patterns to contact pressures

The direction of wear in the acetabular socket has implications for the amount of debris that is generated during movement, for the magnitude of eccentric loading and for the incidence of impingement of the neck. We observed the direction of penetration with respect to a global co-ordinate system in 84 acetabular components retrieved at reoperation. The mean direction of wear relative to the open face of the sockets was found to be 37° with a range from 0° to 87°. For those values determined using the inclination of the socket on the prerevision radiograph, the mean direction of penetration in the coronal plane had a lateral, rather than a medial, component. The mean angle was 84° (SD 17°) with respect to the horizontal. The angle of penetration was found to correlate significantly with the depth, in that the lateral component became larger as the wear progressed. There was also a significant correlation between the rate of penetration and the direction of wear. Despite the theoretical advantage of penetration in the superolateral direction, i.e., along the margin of the socket, in reducing the probability of impingement of the neck, no significant correlation was seen between the angle of penetration and the period of use in vivo. This may suggest that impingement of the femoral neck on the rim of the socket may not be the dominant factor in loosening of the socket but can still be important in a few cases

The treatment of fractures of the proximal tibia is complex and makes great demands on the implants used. Our study aimed to identify what levels of primary stability could be achieved with various forms of osteosynthesis in the treatment of diaphyseal fractures of the proximal tibia. Pairs of human tibiae were investigated. An unstable fracture was simulated by creating a defect at the metaphyseal-diaphyseal junction. Six implants were tested in a uniaxial testing device (Instron) using the quasi-static and displacement-controlled modes and the force-displacement curve was recorded. The movements of each fragment and of the implant were recorded video-optically (MacReflex, Qualysis). Axial deviations were evaluated at 300 N.

The results show that the nailing systems tolerated the highest forces. The lowest axial deviations in varus and valgus were also found for the nailing systems; the highest axial deviations were recorded for the buttress plate and the less invasive stabilising system (LISS). In terms of rotational displacement the LISS was better than the buttress plate.

In summary, it was found that higher loads were better tolerated by centrally placed load carriers than by eccentrically placed ones. In the case of the latter, it appears advantageous to use additive procedures for medial buttressing in the early phase.