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Item type:Publication, Access status: with files , Dynamik der Hüftschaftimplantation(2026); In cementless hip arthroplasty, mallet blows are used to advance the rasp during the preparation of the femoral canal, to implant the prosthesis, and to join the implant components. The strength of the mallet blows is crucial for a stable press fit, while the dynamics of the involved instruments and the interaction with the femur-tissue system are complex and individual. Therefore, the aim of this study is to investigate the influence of patient- and surgical approach-specific characteristics on the dynamic behavior of the femur-tissue system as well as the force transmission of surgical instruments. The experimentally determined parameters of the femur-tissue system of the human bodies examined varied depending on the positioning on the operating table, which in turn depended on the surgical approach. However, for both surgical approaches examined, the values resulted in a relatively low natural frequency (lateral: 6.7 Hz, direct anterior: 9.6 Hz). Consequently, metal-on-metal mallet blows or comparable short impulses from automated surgical impaction tools lead to overcritical excitation. As a result, the implant is inserted into the femur before the bone itself even starts moving. The experimental and numerical analyses revealed a significant attenuation of the mallet force by the impactor. The design of the impactor had a significant influence on the force transmission: lighter impactors transmitted higher peak forces than heavier variants. Even minor design modifications resulted in differences in the transmitted force by a factor of two. Due to the overcritical excitation, it is not necessary to make intraoperative adjustments of the surgical technique to the patient's positioning or to the mass and stiffness of the surrounding soft tissue. However, the utilization of different impactors can lead to considerable deviations in force transmission. Without adequate briefing for orthopedic surgeons, changing the implant system, the associated instruments, or the surgical approach can increase the risk of complications such as periprosthetic fractures or aseptic loosening.Publicationtype: Doctoral Thesis49 36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Design of surgical impaction instruments matters(Elsevier, 2025-11-12); ; ; ; Background: Femoral stem impaction in total hip arthroplasty is commonly performed by mallet blows on a metal impactor attached to the stem. Factors including the surgeon, the impactor, and the patient can influence the impaction. A wide range of impactors, varying in design and thus in mass and stiffness, are available. However, little is known about their influence on the force transmission and, consequently, about the proportion of the mallet force that ultimately reaches the implant. This study aimed to investigate the force transmission through the impactor for different impactor designs, while investigating different patient-specific femur-tissue systems in situ and in silico. Methods: The mallet and impactor forces of 9 consecutive blows on seated femoral stems were measured for 2 different approaches on each of 4 cadavers. The mallet-implant force transmission was calculated using a phenomenological model for 2 different impactor designs. Results: The attenuated force in the impactor achieved approximately 65% to 75% of the corresponding mallet peak force, regardless of cadaver or surgical approach. Measuring the force distant from the tip resulted in an overestimation of the transferred forces. Depending on impactor design just 24% to 47% of the applied mallet peak force reached the implant itself. Conclusions: The force transmission for overcritical mallet blows can be regarded as independent from patient- and approach-specific boundary conditions and primarily dependent on the impactor design. Surgeons must be aware of this relationship and exercise caution when using other or novel instruments to prevent intraoperative complications.Publicationtype: Journal Article28 29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Dynamic response of soft tissue can be disregarded during femoral stem impaction(Elsevier, 2025-04-20); ; ; ; Background: In cementless total hip arthroplasty stems are inserted into the bone by mallet blows. Surgeons are not instructed to adjust the force of their blows to differences among patients especially with regard to weight. Whether this is linked to complications is yet unknown. This study investigated factors that could affect the mechanical behavior of the femur-tissue system. Methods: Four cadavers were subject to two total hip arthroplasties by the same surgeon – one side via a lateral approach and the contralateral side via a direct anterior approach. A mass-spring-damper model was used to replicate the mechanical response of the femur-tissue system of the cadavers and make them comparable. Findings: The mechanical response in terms of mass-spring-damper parameters differed between the approaches (lateral: 16.5 kg, 29.7 N/mm, 467.1 Ns/m; direct anterior: 11.5 kg, 41.7 N/mm, 553.0 Ns/m). Interpretation: Common metal-on-metal mallet blows in surgery are very short and mostly excite high frequencies that are clearly above the natural frequency of the femur-tissue system. Those overcritical force impulses make the stem slide into the femur before the bone can even start moving. Hence, the individual mechanical behavior of the femur-tissue system can be disregarded provided that the force is applied with very short blows. This needs to be considered for any attempt to replace the mallet in the operation theater (e.g. automated surgical impaction tools) or to modify the mallet (e.g. alternative tip material). Furthermore, it may provide guidance on the fixation of femurs in in vitro testing to mimic surgical reality.Publicationtype: Journal Article44 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The force at the implant cannot be assessed by the mallet force - unless supported by a modelThe implantation of uncemented prostheses requires the application of sufficient forces to achieve a press-fit of the implant in the bone. Excessive forces have to be omitted to limit bone damage. Force measurements along the force transmission path between mallet and implant are frequently used to investigate this trade-off. Placing a load cell at a position of interest (PoI), which might be the implant bone interface or the head taper junction, is technically challenging or even impossible so that nearby positions are chosen. Thus, a certain inertia and stiffness remain between the PoI and the sensor, and consequently the measured dynamic forces differ from those at the PoI. This experimental and numerical study aimed to investigate the amount of force reduction along the transmission path while joining femoral heads to stem tapers. Forces were measured in vitro at the tip of the mallet, directly above the polymer tip of the impactor and below the stem taper. Springs and masses were used to represent the responding tissue of a patient. A semi-empirical numerical model of the force transmission path was developed and validated in order to simulate a larger range of responding tissue properties than experimentally possible and to investigate the influence of different surgical instruments. A distinct attenuation was observed since the peak forces at the impactor reached 35% of the applied peak forces and 21% at the stem taper, respectively. The force curves were replicated with a median root mean square error of 3.8% of the corresponding mallet blow for the impactor and 3.6% for the stem. The force measurement position and the used surgical instruments have a strong influence on the measured forces. Consequently, the exact measurement conditions with regard to sensor positioning and used surgical instruments have to be specified and hence only studies with similar setups should be compared to avoid misestimation of the forces at the PoI. The proposed dynamic numerical model is a useful tool to calculate the impact of the chosen or changed mechanical parameters prior to executing experiments and also to extrapolate the effect of changing the applied forces to the resulting forces at the PoI.Publicationtype: Journal Article17 56 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of bone morphology and femur preparation method on the primary stability of hip revision stems(Wiley, 2023-06); ; ; ; Aseptic loosening is one of the major reasons for re-revisions of cementless revision stems. Insufficient primary stability is associated with bone characteristics and the surgical process. This study aimed to investigate how femur morphology and preparation methods influence the primary stability of revision stems. The Femur morphology was described by the upper femoral curvature (UFC) and an individualized Dorr type classification based on the ratio between the canal-to-calcar ratio (CCR*) and the cortical index (CI*) introduced as the cortical-canal shape (CCS). Manual and powered reaming in combination with helical and straight reamers were used to prepare the bone cavity of 10 cadaveric human femur pairs. Forces during stem impaction were recorded (Reclaim, Depuy Synthes). Micromotion at the bone–implant interface during cyclic axial loading and torsional load to failure was determined. The CCS and impaction forces (R2 = 0.817, p < 0.001) or torsional strength (R2 = 0.577, p < 0.001) are inversely related. CCS did not correlate with micromotion during axial loading (R2 = 0.001, p > 0.999), but proximal femoral curvature did (R2 = 0.462, p = 0.015). Powered reaming and straight reamers led to an improved torsional strength (both: p = 0.043). The Individualized Dorr classification CCS and UFC allows a good estimation of the primary stability of revision stems. For severely curved Dorr type-C femurs, an alternative anchorage method should be considered clinically.Publicationtype: Journal ArticleScopus© Citations 3 55 219