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Purpose: The number of patients having hip and knee arthroplasties on the ipsilateral leg is going to rise. In this regard, the prevalence of interprosthetic femoral fractures is going to increase further. The treatment of these fractures is difficult and sometimes it is impossible to perform an osteosynthesis because of worse bone quality. The goal of this study was to investigate the use of an interposition sleeve as an alternative treatment option for interprosthetic fractures with major bone loss., Methods: Six human cadaveric femurs were instrumented using cemented hip- and knee prosthesis. Interprosthetic fractures were induced during a four-point-bending test and then treated using the interposition sleeve. Afterwards the constructs were tested using the four-point-bending test again., Results: Load-to-failure of the construct before fracturing was significantly higher than after treatment with the interposition sleeve (10681 N vs. 5083 N; p = 0.002). The failure mechanism of the femurs with the interposition sleeve was plastic deformation of the hip or knee prosthesis. The interposition sleeve did not fail in any specimen., Conclusion: The interposition sleeve is a valuable treatment option for interprosthetic fractures in situations in which osteosynthesis is impossible or insecure due to major bone defects. However, fracture healing should be preferred whenever possible.

Introduction: Due to the demographic trend, pertrochanteric fractures of the femur will gain increasing importance in the future. Both extra- and intramedullary implants are used with good results in the treatment of these fractures. New, angular stable extramedullary implants promise increased postoperative stability even with unstable fractures. Additional trochanteric plates are intended to prevent secondary impaction, varisation and shortening of the fracture, as well as medialisation of the femoral shaft. The aim of this study was to perform a biomechanical comparison of both procedures regarding their postoperative stability and failure mechanisms., Materials and Methods: Twelve fresh-frozen human femurs were randomized into two groups based on the volumetric bone mineral density (vBMD). Standardized pertrochanteric fractures (AO31-A2.3) were generated and treated either with an angular stable dynamic hip screw (DHS) or an intramedullary nail (nail). Correct implant position and the tip-apex distance (TAD) were controlled postoperatively using X-ray. Specimens were mounted in a servohydraulic testing machine and an axial loading was applied according to a single-leg stance model. Both groups were biomechanically compared with regard to native and postoperative stiffness, survival during cyclic testing, load to failure, and failure mechanisms., Results: TAD, vBMD, and native stiffness were similar for both groups. The stiffness decreased significantly from native to postoperative state in all specimens (p < 0.001). The postoperative stiffness of both groups varied non-significantly (p = 0.275). The failure loads for specimens treated with the nail were significantly higher than for those treated with the DHS (8480.8 ± 1238.9 N vs. 2778.2 ± 196.8 N; p = 0.008)., Conclusions: Extra- and intramedullary osteosynthesis showed comparable results as regards postoperative stiffness and survival during cyclic testing. Since the failure load of the nail was significantly higher in the tested AO31-A2.3 fracture model, we conclude that intramedullary implants should be preferred in these, unstable, fractures.

Purpose: Aseptic loosening of the tibial component remains a major cause for revision surgery in total knee arthroplasty (TKA). A stable initial fixation of the tibial implant has been suggested to reduce micromotion of the implant and could be decisive regarding its long-term performance. Different techniques for applying cement to the tibial surface have been described in the literature, with controversial results. No guidelines in favour of any particular approach are available., Methods: In this study, we compared three commonly used cementing techniques (layered application, stem cementation, cement gun) with surface-only fingerpacking cementation following pulsed lavage (paired human tibiae, four groups, n = 24). Specimens underwent computed tomography scanning for three-dimensional analysis of cement penetration and mechanical testing for assessing interface strength., Results: Bone cement penetration decreased with increasing bone mineral density (BMD) (R (2) = 0.18, p = 0.023), while interface strength increased with BMD (R (2) = 0.56, p < 0.001). No significant effect of cementation techniques on cement penetration (p ≥ 0.069) or interface strength (p = 0.180) was found in any group., Conclusion: Adequate surface preparation using pulsed lavage and copious drying of the tibial surface appears to be of overruling importance, thus limiting the effect of any particular technique applied to improve implant fixation. This study emphasises the fundamental importance of surface preparation and pulsed lavage in TKA.

Purpose: Aseptic loosening of the tibial component remains a limitation to the highly successful procedure of total knee arthroplasty (TKA). Pulsed lavage improves bone cement penetration and interface strength in tibial tray cementation. This study tested whether pressurized cement application with a cement gun can compensate the use of jet lavage for bone surface preparation., Methods: Tibial components were implanted in six pairs of cadaveric tibiae. On one side, pulsed lavage of the tibial bone was combined with finger packing of bone cement; on the other side, syringe lavage and gun cementing was used. Cement penetration into the bone was determined from computed tomography scans, and Interface strength was determined by pull-out testing., Results: Cement penetration was greater (p = 0.004) and interface strength was higher (p = 0.028) in the pulsed lavage group., Conclusion: Pressurization of cement by gun application could not compensate for the omission of pulsed lavage. Thus, pulsed lavage should be considered a crucial factor in TKA to improve implant fixation, which cannot be compensated for by cement application technique.

Purpose: The use of inappropriate cementation techniques has been suggested as an adverse factor for the long-term survival of hip-resurfacing arthroplasty. Inadequate initial fixation, thermal osteonecrosis and interface biological reactions are possible causes of failure. We analysed morphological changes associated with the cementation technique in a large collection of retrieved femoral components., Methods: One hundred and fifty femoral components (mean time to failure of 8.3 months±11.0) obtained at revision surgery were analysed morphometrically and histopathologically. Cement mantle and penetration were quantified in six different regions of interest. Histopathological analysis of the bone-cement interface was performed on undecalcified processed bone tissue., Results: The vast majority of the cases differed substantially from laboratory-based cement-penetration depth recommendations. Fifty-nine cases had a fibrous membrane at the cement-bone interface. This membrane was significantly thicker in cases with osteonecrosis compared to cases viable bone., Conclusions: Our results demonstrate that most failures were cemented inappropriately. We suggest that poor cementation was an important adverse factor; however, the cause of the failures was obviously multifactorial. The thickness of the fibrous membrane at the cement-bone interface differed significantly between cases with osteonecrosis and specimens with viable bone tissue.

Pulsatile lavage is purported to improve radiographic survival in cemented total knee arthroplasty (TKA). Similarly, a potential improvement of fixation strength of the tibial tray has been assumed based on the increased cement penetration. In this study, the influence of pulsed lavage on fixation strength of the tibial component and bone cement penetration was evaluated in six pairs of cadaveric specimens. Following surgical preparation, the tibial surface was irrigated using pulsatile lavage on one side of a pair, while on the other side syringe lavage was applied. All tibial components were implanted using the same cementing technique. Cement penetration and bone mineral density was assessed based on computed tomography data. Fixation strength of the tibial trays was determined by a pull-out test with a material testing machine. Median pull-out forces and cement penetration were significantly (p = 0.031) improved in the pulsed lavage group as compared to the syringe lavage group. Enhanced fixation strength is suggested as being a key to improved survival of the implant. Consequently, pulsatile lavage should be considered as a mandatory preparation step when cementing tibial components in TKA.

Introduction: Failures involving the femoral part in hip resurfacing remain problematic in terms of overall implant survival. In this context, effects of impaction strength on cement mantle morphology and trabecular bone damage have not been studied to date., Materials and Methods: Sixteen paired cadaveric femora that had undergone hard and gently impacted hip resurfacing using a manual packing cementing technique in a previous study, were evaluated morphologically. The earlier study had revealed lower failure loads for hard impacted heads. A central slice of each femoral head underwent microradiography., Results: Overall cement mantle thickness averaged 2.0 mm (range 0-5 mm) in the hard and in the low impact group with no significant difference between groups (p = 0.299). No signs of damage in the bone remnants inside the prosthesis of the fractured proximal femurs were detected in the microradiographic analysis., Conclusion: Cement mantle thickness was not influenced by impaction strength when using a manual packing cementing technique. No trabecular damage underneath the implant was detected despite lower failure loads, confirming the difficulty to identify small trabecular damage in an in vitro study.

Objective: Before the re-introduction of the current generation of total hip resurfacing arthroplasty, component loosening and osteolysis were of great concern to the orthopaedic community. Early, mid- and long-term clinical results are encouraging, but component loosening still exists., Materials and Methods: Macroscopic, contact radiographic and histopathological analyses after undecalcified preparation of bone tissue specimens were performed. To investigate the frequency and morphological patterns of the loosening of the femoral component, we analysed a series of 190 retrieved femoral remnants that were revised for aseptic failures., Results: Thirty-five (18.4%) hips were revised for clinical and/or radiographic loosening of the femoral component. Pseudoarthrosis (n = 17; median in situ time: 16 weeks, interquartile range [IQR]: 9 to 34), collapsed osteonecrosis (n = 5; median in situ time: 79 weeks, IQR: 63 to 97), cement-socket debonding (n = 3; median in situ time: 89 weeks, IQR: 54 to 97) and at later follow-up bone-cement loosening (n = 10; median in situ time: 175 weeks; IQR 112 to 198; p =0.005) were distinct patterns of the femoral remnant-implant loosening. Fibrocartilaginous metaplasia of interface bone trabeculae (n = 38; median in situ time: 61 weeks, IQR: 32 to 138) was strongly associated with femoral component loosening (p = 0.009). Both the trabecular hyperosteoidosis (n = 32; median in situ time: 71 weeks, IQR 50 to 129) and excessive intraosseous lymphocyte infiltration (n = 12; median in situ time: 75 weeks, IQR 51 to 98) at the bone-cement interface correlated strongly with fibrocartilaginous metaplasia (p = 0.001 and p = 0.016 respectively) and all three lesions were associated with the female gender (p = 0.021, p = 0.009, and p = 0.051)., Conclusion: Femoral component loosening at early follow-up was mostly caused by pathological changes of the femoral remnant bone tissue: pseudoarthrosis and collapsed osteonecrosis. Fibrocartilaginous metaplasia was frequently observed in hips with femoral component loosening. The potential role of interface hyperosteoidosis as a precursor lesion of bone-cement loosening and its possible association with delayed type hypersensitivity reaction are discussed.

The aim of the present in vitro study was to evaluate migrational characteristics of cementless primary hip arthroplasty stems in combination with a diameter 50 mm head (hemiarthroplasty) and a diameter 28 mm head in and with a polyethylene cup (total hip arthroplasty) in fresh-frozen human specimens. Two different types (Endo SL, FMT) were implanted into seven pairs of fresh-frozen human femoral specimens. The implanted stems were combined with a diameter 50 mm head (hemiarthroplasty) on one side and with a polyethylene cup and a 28 mm head (total hip arthroplasty) on the other side. Dynamic mechanical loading was applied for 50,000 cycles while recording relative motions between stem and bone stock using a 3-D motion analysis system. The Endo SL stem showed a significantly higher amplitude of relative motion in all translational and rotational components regardless of the head used. In both stem types a strong tendency for higher axial migration with the diameter 50 mm head in comparison to the THA head was found. The lowest axial migration was found in the FMTstem in combination with the small head and a PE cup. The highest axial migration was found in the Endo SL stem combined with the diameter 50 mm head. Our results indicate that the head might play an important role for axial migration of cementless stems.

This study was designed to investigate the relationship between trunk muscle fatigue and associated changes in the electromyographic (EMG) signals during a dynamic iso-inertial test. Eleven subjects performed dynamic trunk flexion/extension movements against 40% maximum voluntary contraction (MVC) torque until exhaustion in a tri-axial trunk dynamometer. EMG parameters in the time and frequency domain were studied by analysing changes of the signal amplitudes and the spectral density (using the zero-crossing-rate and the median frequency). The kinematics of the movement were analysed according to the movement velocities and the deviations from the required movement plane. The flexion and extension velocities decreased from the beginning to the end of the test. Movement deviations from the sagittal plane into the frontal and transverse plane increased with increasing test duration, as did the EMG amplitude. The median frequency during periods with maximum muscle activity decreased, as did the zero-crossing-rate. The increase in amplitude and decrease in median frequency were more pronounced in the trunk flexors than in the trunk extensors. The parameters of median frequency, zero-crossing-rate and amplitude seem to be sensitive identifiers of muscle fatigue during well-controlled dynamic contractions. While the kinematic data did not yield any information on the mechanisms of the fatigue, changes in the EMG parameters demonstrated that the duration of the test was limited by the fatigue of the trunk flexors.