Poor soft tissue balance in total knee arthroplasty (TKA) is one of the most primary causes of dissatisfaction and reduced joint longevity, which are associated with postoperative instability and early implant failure. 1. Therefore, surgical techniques, including mechanical instruments and 3-D guided navigation systems, in TKA aim to achieve optimum soft tissue balancing in the knee to improve postoperative outcome. 2. Patella-in-Place balancing (PIPB) is a novel technique which aims to restore native collateral ligament behaviour by preserving the original state without any release. Moreover, reduction of the joint laxity compensates for the loss of the visco-elastic properties of the cartilage and meniscus. Following its clinical success, we aimed to evaluate the impact of the PIPB technique on collateral ligament strain and laxity behaviour, with the hypothesis that PIPB would restore strains in the collateral ligaments. 3. . Eight fresh-frozen cadaveric legs were obtained (KU Leuven, Belgium, H019 2015-11-04) and CT images were acquired while rigid marker frames were affixed into the femur, and tibia for testing. After carefully removing the soft tissues around the knee joint, while preserving the joint capsule, ligaments, and tendons, digital extensometers (MTS, Minnesota, USA) were attached along the length of the superficial medial collateral ligament (MCL) and lateral collateral ligament (LCL). A handheld digital dynamometer (Mark-10, Copiague, USA) was used to apply an abduction or adduction moment of 10 Nm at fixed knee flexion angles of 0°, 30°, 60° and 90°. A motion capture system (Vicon Motion Systems, UK) was used to record the trajectories of the rigid marker frames while synchronized strain data was collected for MCL/LCL. All motion protocols were applied following TKA was performed using PIPB with a cruciate retaining implant (Stryker Triathlon, MI, USA). Furthermore, tibiofemoral kinematics were calculated. 4. and combined with the strain data. Postoperative tibial varus/valgus stresses and collateral ligament strains were compared to the native condition using the Wilcoxon Signed-Rank Test (p<0.05). Postoperative tibial valgus laxity was lower than the native condition for all flexion angles. Moreover, tibial valgus of TKA was significantly different than the native condition, except for 0° (p=0.32). Although, tibial varus laxity of TKA was lower than the native at all angles, significant difference was only found at 0° (p=0.03) and 90° (p=0.02). No significant differences were observed in postoperative collateral ligament strains, as compared to the native condition, for all flexion angles, except for MCL strain at 30° (p=0.02) and 60° (p=0.01). Results from this experimental study supported our hypotheses, barring MCL strain in mid-flexion, which might be associated with the implant design. Restored collateral ligament strains with reduced joint laxity, demonstrated by the PIPB technique in TKA in vitro, could potentially restore natural joint kinematics, thereby improving patient outcomes. In conclusion, to further prove the success of PIPB, further biomechanical studies are required to evaluate the success rate of PIPB technique in different implant designs

Locking plates have led to important changes in bone fracture management, allowing flexible biological fracture fixation based on the principle of an internal fixator. The technique of locking plate fixation differs fundamentally from conventional plating and has its indications and limitations. Most of the typical locking plate failure patterns are related to basic technical errors, such as under-sizing of the implant, too short working length, and imperfect application of locking screws. After analysis of the fracture morphology and intrinsic stability following fracture reduction, a meticulous preoperative planning is mandatory under consideration of the principles of the internal fixator technique to avoid technical errors and inaccuracies leading to early implant failure

Summary. Biomechanically, a 2° screw deviation from the nominal axis in the PFLCP leads to significantly earlier implant failure. Screw deviation relies on a technical error on insertion, but in our opinion cannot be controlled intraoperatively with the existing instrumentation devices. Background. Several cases of clinical failure have been reported for the Proximal Femoral Locking Compression Plate (PFLCP). The current study was designed to investigate the failure mode and to explore biomechanically the underlying mechanism. Specifically, the study sought to determine if the observed failure was due to technical error on insertion or due to implant design. Methods. To exclude patient and fracture type related factors, an abstract foam block model simulating an unstable pertrochanteric fracture was created for three study groups with six specimens each (n=6). Group 1 was properly instrumented according to the manufacturer's guidelines. In Group 2 and 3, the first or second screw was placed in a posterior or anterior off-axis orientation by 2° measured in the transversal plane, respectively. Each construct was tested cyclically until failure using a test setup and protocol simulating complex axial and torsional loading. Radiographs were taken prior to and after the tests. Force, number of cycles and failure mode were compared. Results. The 2° screw deviation from the nominal axis led to significantly earlier construct failure in Group 2 and 3. The failure mode consisted of loosening of the off-axis screw due to disengagement with the plate, resulting in loss of construct stiffness and varus collapse of the fracture. Conclusions. In our biomechanical test setup, a screw deviation of only 2° from the nominal axis consistently led to the failure mode observed clinically. In our opinion, screw deviation mostly relies on technical error on insertion. But, proper screw insertion may be difficult or impossible with the existing instrumentation devices, especially as it cannot be controlled or guaranteed intraoperatively