The German Arthroplasty registry (EPRD) has shown that different prosthesis systems have different rates of secondary patellar resurfacing: four years after implantation, the posterior-stabilized (PS) Vega prosthesis has a 3.2% risk of secondary patellar resurfacing compared to the cruciate-retaining (CR) Columbus prosthesis at 1.0% (both Aesculap AG, Tuttlingen, Germany). We hypothesized that PS implants have increased retropatellar pressure and a decreased retropatellar contact area compared to a CR design, which may lead to an increased likelihood of secondary patellar resurfacing. Eight fresh frozen specimens (cohort 1) were tested with an established knee rig. In addition, a possible influence of the registry-based patient collective (cohort 2) was investigated. No significant differences were found in patient data–cohort 2-(sex, age). A generally lower number of PS system cases is noteworthy. No significant increased patella pressure could be detected with the PS design, but a lower contact area was observed (cohort 1). Lower quadriceps force (100°–130° flexion), increased anterior movement of the tibia (rollback), greater external tilt of the patella, and increasing facet pressure in the Vega PS design indicate a multifactorial cause for a higher rate of secondary resurfacing which was found in the EPRD patient cohort and might be related to the PS’ principle function.

Wear is an important factor in the long-term success of total knee arthroplasty (TKA). Therefore, wear testing methods have become standard in implant research and development. In the EU, these are based on two simulation concepts, which are defined in standards ISO 14243-1 and 14243-3, differentiated by the control mode—force-controlled or displacement-controlled. The aim of this study was to compare the mechanical stresses within the different ISO concepts using a finite element model (the newest displacement-controlled norm from 2014 compared with force-controlled). The in silico model showed strong correlation with the experimental data (r > 0.8). The adapted force-controlled ISO showed higher mechanical stress during the gait cycle, which also might lead to higher wear rates (14243-1 (2009): 11.15 MPa, 10.15 MPa and 9.16 MPa). The displacement-controlled ISO led to higher mechanical stress because of the constraint at the end of the stance phase (14243-3: 20.59 MPa and 17.19 MPa). Future studies should analyse different inlay designs within the same ISO standards to guarantee comparability.

The response of soft tissue to loading can be obtained by strain assessment. Typically, strain can be measured using electrical resistance with strain gauges (SG), or optical sensors based on the digital image correlation (DIC), among others. These sensor systems are already established in other areas of technology. However, sensors have a limited range of applications in medical technology due to various challenges in handling human soft materials. The aim of this study was to compare directly attached foil-type SG and 3D-DIC to determine the strain of axially loaded human ligament structures. Therefore, the medial (MCL) and lateral (LCL) collateral ligaments of 18 human knee joints underwent cyclic displacement-controlled loading at a rate of 20 mm/min in two test trials. In the first trial, strain was recorded with the 3D-DIC system and the reference strain of the testing machine. In the second trial, strain was additionally measured with a directly attached SG. The results of the strain measurement with the 3D-DIC system did not differ significantly from the reference strain in the first trial. The strains assessed in the second trial between reference and SG, as well as between reference and 3D-DIC showed significant differences. This suggests that using an optical system based on the DIC with a given unrestricted view is an effective method to measure the superficial strain of human ligaments. In contrast, directly attached SGs provide only qualitative comparable results. Therefore, their scope on human ligaments is limited to the evaluation of changes under different conditions.

Introduction Worldwide more and more primary knee replacements are being performed. Kinematic alignment (KA) as one of many methods of surgical alignment has been shown to have a significant impact on kinematics and function. The aim of the present study was to compare KA and mechanical alignment (MA) with regard to femorotibial kinematics. Materials and methods Eight fresh frozen human specimens were tested on a knee rig during active knee flexion from 30 to 130°. Within the same specimen a medial stabilized (MS) implant design was used first with KA and then with MA. Results The femorotibial kinematics showed more internal rotation of the tibia in KA compared to MA. At the same time, there was a larger medial rotation point in KA. Both alignment methods showed femoral rollback over the knee bend. Conclusion Relating to an increased internal rotation and a more precise medial pivot point, it can be concluded that KA combined with a MS implant design may partially support the reproduction of physiological knee joint mechanics.

Background. Gait and balance disorders in patients with idiopathic Parkinson’s disease (PD) lead to major mobility limitations. To counteract this, physical therapy such as gait, balance, or resistance training is applied. Integrative training methods, which combine these elements, could be particularly effective. Objective. The objective of this study is to evaluate and compare the effects of two integrative interventions on gait and balance of patients with PD. Methods. Twenty-six patients with PD received either resistance training in combination with gait training (gait resistance training, GRT) or resistance training in combination with balance training (stability resistance training, SRT) for six weeks. Gait and balance outcome parameters were assessed before, immediately after, and six weeks after the interventions. The primary outcome parameters were the functional reach test to evaluate balance and stride length to evaluate gait. Secondary outcomes included further gait analysis parameters, knee extension strength, the timed up and go test, and the six-minute walk test. Results. The functional reach test results were significantly better after the intervention in both groups. Stride length increased significantly only in the GRT group. Several further gait parameters and the six-minute walk test improved in the GRT group, and the increase in gait speed was significantly higher than in the SRT group. The SRT group performed better after the intervention regarding the timed up and go test and knee extension strength, the latter being significantly more improved than in the SRT group. At six-week follow-up, the improvement in functional reach was maintained in the SRT group. Conclusions. Integrative therapies, combining gait or balance training with resistance training, have specific positive effects in PD rehabilitation. More pronounced effects on gait parameters are achieved by GRT, while SRT has more impact on balance. Thus, the combination of both training methods might be particularly efficient in improving the mobility of PD patients.