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Item type:Publication, Access status: with files , Fluted stem designs enhance surgical precision and primary stability in cementless revision hip arthroplasty – a cadaver study(Elsevier, 2026-01); ; ; ; Background: Cortical contact of the stem is a key determinant for primary stability in cementless revision hip arthroplasty. This matched-pair cadaveric study evaluated whether implant designs that increase cortical contact improve primary fixation of cementless revision stems Methods: Ten paired femora received either a tapered monoblock RECLAIM™ stem with advanced spline (RAS) geometry or an identically sized prototype solid stem. Axial seating and rotation were recorded using dynamic image correlation during implantation. Specimens were cyclically loaded up to 200 % body weight, after which torque-to-failure was measured Findings: Both designs showed mean micromotion <50 μm during cyclic loading, consistently favourable for osseointegration. However, solid stems rotated more during implantation than RAS stems (3.6 ± 5.0° vs. 0.5 ± 0.6°, p = 0.088). The cortical contact area of the solid stems was 43.6 % larger than RAS stems (p < 0.001) without an impact on superior fixation: Axial subsidence and rotation during cyclic loading did not differ significantly between the designs but two solid-stem specimens fractured under high loading. Torque-to-failure of the RAS stems was 38.7 ± 7.5 nm, exceeding that of solid stems by 24.3 % (p = 0.032) Interpretation: These findings suggest that maximising circumferential contact by implant design alone cannot compensate for irregularities of the femoral canal. Whereas solid stems wedge firmly only at the cost of positioning accuracy and increased fracture risk, the thin splines of the RAS design engage the cortex progressively, guide the implant to the planned depth, and augment torsional resistance without excessive press-fit. Tapered stems with cortex-indenting splines improve primary stability in cementless revision hip arthroplasty more effectively than increasing contact area alone.Publicationtype: Journal Article21 22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , How does the collar in cementless hip stems work? Comparison of the strain distribution in the cortex of the proximal femur(Elsevier, 2025-12-01); ; ; ; Background: Collared cementless hip stems have demonstrated a reduced incidence of periprosthetic femoral fractures compared to collarless counterparts. Many fractures occur during implantation, when collarless stems are seated to achieve press-fit, causing critical tensile strains in the femur. Collared stems can limit excessive seating and subsidence through calcar-collar contact. This study aimed to explain the clinically observed smaller fracture rates with collared stems by comparing strain distributions during implantation and loading between collared and collarless stems. It was hypothesized that collared stems distribute applied forces through both the collar and stem, increasing compressive axial and shear strains, allowing higher load tolerance. Methods: Seven collared and seven collarless stems were implanted with constant velocity (0.1 mm/s) in porcine femurs until failure. Two human cadaveric femurs were tested as proof of concept. Shear, axial compressive and tangential tensile strains were compared alongside fracture patterns, subsidence and forces. Findings: Collared stems in porcine femurs resisted approximately twice as much force until failure occurred (collared: 4187 N, collarless: 1980 N; p < 0.001), with similar tangential tensile strains (1 % to 1.4 % p = 0.805) and subsidence of 1.6 mm for collarless and 1.1 mm for collared stems at different failure forces (p = 0.288). Axial compressive strain was heavily increased by 1147 % with collared stems (collared: 1.2 %, collarless: 0.1 %; p = 0.026). Human femurs exhibited similar trends. Interpretation: During loading, the collar prevents periprosthetic femoral fractures by increasing axial compressive strains instead of causing critical excessive tangential tensile strains (hoop strains) that can result in fractures.Publicationtype: Journal Article42 18 - 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: without files , Quantification of mechanical properties in long-term in vivo used silicone catheter lines according to DIN 10555-3(2023-07); 25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Which length should the neck segment of modular revision stems have?Background: Fractures of modular revision stems at the taper junction are rare but severe clinical problems. The purpose of this study was the estimation of taper loading to identify configurations which are less prone to failure. Methods: A parametrical analytical 3-D model was developed to determine the influence of neck segment length, offset and anteversion on the loading at the modular taper junction between neck segment and stem. Published in-vivo hip joint forces were used to simulate different activities. Findings: No unique ideal neck segment length can be specified due to the differences in loading magnitude and direction between activities. The best neck segment length for walking is longer than for high loading activities as stair climbing and jogging. A medium length between 70 mm and 90 mm appears to be a good compromise. A shorter offset (37 mm vs. 47 mm) reduces the stress by about 25% for walking and jogging. Retroverted implantation by 5° increases the loading whereas an anteverted implantation by 5° reduces it. A high offset (47 mm) combined with a short neck segment length (50 mm) reaches about 80% of the taper yield strength for jogging (taper diameter 13 mm). Interpretation: Simplified 2-D modelling falsely predicts no bending at the taper junction for a long neck segment, whereas the 3-D model shows substantial stress load along the whole stem length. Stem tapers of short as well as very long neck segments are higher risk for failure. Neck segment length should lie in the range between 70 mm and 90 mm.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Biomechanics applied to incisional hernia repair – Considering the critical and the gained resistance towards impacts related to pressureBackground: Incisional hernia repair is burdened with recurrence, pain and disability. The repair is usually carried out with a textile mesh fixed between the layers of the abdominal wall. Methods: We developed a bench test with low cyclic loading. The test uses dynamic intermittent strain resembling coughs. We applied preoperative computed tomography of the abdomen at rest and during Valsalva's maneuver to the individual patient to analyze tissue elasticity. Findings: The mesh, its placements and overlap, the type and distribution of fixation elements, the elasticity of the tissue of the individual and the closure of the abdominal defect–all aspects influence the reconstruction necessary. Each influence can be attributed to a relative numerical quantity which can be summed up into a characterizing value. The elasticity of the tissues within the abdominal wall of the individual patient can be assessed with low-dose computed tomography of the abdomen with Valsalva's maneuver. We established a procedure to integrate the results into a surgical concept. We demonstrate potential computer algorithms using non-rigid b-spline registration and artificial intelligence to further improve the evaluation process. Interpretation: The bench test yields relative values for the characterization of hernia, mesh and fixation. It can be applied to patient care using established procedures. The clinical application in the first ninety-six patients shows no recurrences and reduced pain levels after one year. The concept has been spread to other surgical groups with the same results in another fifty patients. Future efforts will make the abdominal wall reconstruction more predictable.Publicationtype: Journal ArticleScopus© Citations 19 82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The influence of broach design on bone friction and osseodensification in total hip arthroplastyThe process of cavity preparation by broaching has an impact on the primary stability of uncemented hip stems and on the periprosthetic fracture risk. Osseodensifying broaches may increase primary stability, but have the potential to raise cortex strains and facilitate fracture. The aim of this study was to determine the influence of broach design on the forces acting during broaching, on the microstructure of the broached bone bed and the amount and depth of osseodensification. Methods: Broach models representing compaction, blunt extraction and sharp extraction broaches, were used for quasi-static simulation of femoral cavity preparation on bovine trabecular bone cuboids. Broaching forces were measured and micro-computed tomography scans performed prior and after testing. Friction coefficients during broaching, bone densification parameters and size of the debris particles pushed into the bone were determined. Findings: Friction coefficients during sharp extraction exceeded those during compaction and blunt extraction broaching (by 38% and 37%, P < .001). Total bone densification was enhanced for compaction and blunt extraction compared to sharp extraction broaching (increase of 121% and 117%, P = .005), resulting from higher densification depths for compaction (P = .001) and higher maximum densification for blunt extraction broaching (P = .008), with the latter producing fewer large particles than compaction broaching (P = .005). Interpretation: Higher friction coefficients indicate a decreased periprosthetic fracture risk with sharp extraction broaches for equal implantation forces. The blunt extraction and compaction designs investigated densified the bone to a similar extent. Blunt extraction broaching may support better osseointegration due to smaller bone debris particles.Publicationtype: Journal Article157 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adapter sleeves are essential for ceramic heads in hip revision surgery(2020-01); ; Background: Removing a head during isolated acetabular revision surgery can cause damage to the stem taper surface from extraction tool contact. Implanting a ceramic head on the damaged stem taper might elevate the fracture risk, which can be mitigated with the use of titanium adapter sleeves. The aim of this study was to investigate whether the improved fracture strength of modern generation ceramic heads allows the direct implantation on damaged stem tapers without an adapter sleeve. Methods: Finite element models of taper junctions with and without adapter sleeve were generated. Different stem taper damages were modelled to investigate the influence on the ceramic head fracture load under axial compression. Findings: Heads without adapter sleeves exhibited slightly higher or equal fracture strengths compared with sleeved heads for most scenarios. However, a small metal elevation on the stem taper caused a drastic decrease of the fracture strength if no adapter sleeve was used (−96%). The sleeved head was not influenced by the metal elevation damage. Interpretation: Adapter sleeves are essential to ensure patient safety and prosthesis longevity whenever implanting ceramic heads on used stem tapers.Publicationtype: Journal Article129 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Deformation of acetabular press-fit cups: influence of design and surgical factorsBackground: Deformation of acetabular cups when press-fitted into an undersized cavity is inevitable due to the inhomogeneous stiffness of acetabular bone. Thinner cups or screw holes might increase the risk of high cup deformation. The aim of this study was to examine the influence of cup design and liner assembly on the deformation response during cup implantation. Methods: Acetabular cups with different designs were implanted into polyurethane foam models simulating the anatomical situation with nominal press-fits of 1mm and without nominal press-fits (line-to-line). Deformations were determined using a tactile coordinate measuring machine. A 3D laser scanner was used to determine the contact conditions at the cup-cavity interface. Polyethylene and ceramic liners were assembled to the implanted cups and the influence of the insertion on the deformation response evaluated. Fixation strength of the cups was determined by push-out testing. Findings: Cup deformation increased with smaller wall thickness (P < 0.037) and screw holes (P < 0.001). Insertion of ceramic liners reduced the deformation (P < 0.001), whereas polyethylene liners adapted to the deformation of the implanted cups (P > 0.999). Thin-walled cups exhibited a higher fixation strength for similar implantation forces (P = 0.011). Interpretation: Thin-walled cups achieved higher fixation strengths and might be more bone-preserving. However, in combination with screw holes and high press-fit levels, wall thickness should be considered carefully to avoid excessive cup deformations leading to potential complications during liner assembly. Line-to-line insertion of thin-walled cups should be accompanied with a rough surface coating to minimize the loss of fixation strength due to the low press-fit fixation.Publicationtype: Journal ArticleScopus© Citations 9 556 598 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Impact of stem taper damage on the fracture strength of ceramic heads with adapter sleeves(2019-03-20); ; Using a new ceramic head with a titanium adapter sleeve offers the possibility of maintaining a well fixed stem when conducting cup revision of a total hip arthroplasty. The aim of this study is to test the impact of stem taper damage on the fracture strength of sleeved ceramic heads.Publicationtype: Journal Article212