Intraoperative fractures although rare are one of the complications known to occur while performing a total hip arthroplasty (THA). However, due to lower incidence rates there is currently a gap in this area of literature that systematically reviews this important issue of complications associated with THA. Method: We looked into Electronic databases including PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), the archives of meetings of orthopaedic associations and the bibliographies of included articles and asked experts to identify prospective studies, published in any language that evaluated intra-operative fractures occurring during total hip arthroplasty from the year 1950-2020. The screening, data extraction and quality assessment were carried out by two researchers and if there was any discrepancy, a third reviewer was involved. Fourteen studies were identified. The reported range of occurrence of fracture while performing hip replacement surgery was found to be 0.4-7.6%. Major risk factors identified were surgical approaches, Elderly age, less Metaphyseal-Diaphyseal Index score, change in resistance while insertion of the femur implants, inexperienced surgeons, uncemented femoral components, use of monoblock elliptical components, implantation of the acetabular components, patients with ankylosing spondylitis, female gender, uncemented stems in patients with abnormal proximal femoral anatomy and with cortices, different stem designs, heterogeneous fracture patterns and toothed design. Intraoperative fractures during THA were managed with cerclage wire, femoral revision, intramedullary nail and cerclage wires, use of internal fixation plates and screws for management of intra operative femur and acetabular fractures. The main reason for intraoperative fracture was found to be usage of cementless implants but planning and timely recognition of risk factors and evaluating them is important in management of intraoperative fractures. Adequate surgical site exposure is critical especially during dislocation of hip, reaming of acetabulum, impaction of implant and preparing the femoral canal for stem insertion. Eccentric and increased reaming of acetabulum to accommodate a larger cup is to be avoided, especially in females and elderly patients as the acetabulum is thinner. However, this area requires more research in order to obtain more evidence on effectiveness, safety and management of intraoperative fractures during THA

Aims

This study intended to investigate the effect of vericiguat (VIT) on titanium rod osseointegration in aged rats with iron overload, and also explore the role of VIT in osteoblast and osteoclast differentiation.

Abstract. Introduction. The long-term biological success of cementless orthopaedic prostheses is highly dependent on osteointegration. Pre-clinical testing of new cementless implant technology however, requires live animal testing, which has anatomical, loading, ethical and cost challenges. This proof-of-concept study aimed to develop an in vitro model to examine implant osteointegration under known loading/micromotion conditions. Methods. Fresh cancellous bone cylinders (n=8) were harvested from porcine femur and implanted with additive manufactured porous titanium implants (Ø4 × 15 mm). To simulate physiological conditions, n=3 bone cylinders were tested in a bioreactor system with a cyclic 30 µm displacement at 1Hz for 300 cycles every day for 15 days in a total of 21 days culture. The chamber was also perfused with culture medium using a peristaltic pump. Control bone cylinders were cultured under static conditions (n=5). Samples were calcein stained at day 7. Post-testing, bone cylinders were formalin fixed and bony ingrowth was measured via microscopy. Results. Viability of the freshly harvested ex vivo bone cylinders was maintained for up to 28 days. Two samples remain unanalysed due to COVID lockdown, one in each group. Similar to osteointegration seen in live animal models, evidence of bony ingrowth was seen more markedly at the bone-implant interface under dynamic conditions. This was evident by a greater intensity of calcein staining, confirming the deposition of new bone, at the bone-implant interface. In comparison, under static conditions, calcein staining was observed randomly all over the cylinder. Conclusion. This proof-of-concept study demonstrates that implant bony adaptation and ingrowth can be measured in vitro under known cyclic micromotion/loading conditions. This comparatively low cost, low ethical impact, controlled loading laboratory method has potential to accelerate the rate of implant development whilst conforming with the principles of NC3Rs. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objective. To estimate the effect of calcar collar contact on periprosthetic fracture mechanics using a collared fully coated cementless femoral stem. Methods. Three groups of six composite femurs were implanted with a fully coated collared cementless femoral stem. Neck resection was increased between groups (group 1 = normal, group 2 = 3mm additional, group 3 = 6mm additional), to simulate failure to obtain calcar collar contact. Periprosthetic fractures of the femur were simulated using a previously published technique. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. High speed video recording identified if collar to calcar contact (CCC) occurred. Results between trials where calcar contact did and did not occur where compared using Mann-Whitney U tests. Results. Where CCC occurred versus where no CCC occurred, fracture torque was greater (47.33 [41.03 to 50.45] Nm versus 38.26 [33.70 to 43.60] Nm, p= 0.05), Rotational displacement was less (0.29 [0.27 to 0.39] rad versus 0.37 [0.33 to 0.49] rad, p= 0.07), torsional stiffness was greater (151.38 [123.04 to 160.42] rad. Nm-1 versus 96.86 [84.65 to 112.98] rad.Nm-1, p <0.01) and rotational work was similar (5.88 [4.67, 6.90] J versus 5.31 [4.40, 6.56] J, p= 0.6). Conclusions. Resistance to fracture and construct stiffness increased when a collared cementless stem made contact with the femoral calcar prior to fracture. These results demonstrate that calcar-collar contact and not a calcar collar per se, is crucial to maximising the protective effect of a medial calcar collar on the risk of post-operative periprosthetic fractures of the femur. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Abstract. Objective. To estimate the effect of calcar collar separation on the likelihood of calcar collar contact during in vitro periprosthetic fracture. Methods. Three groups of six composite femurs were implanted with a collared cementless femoral stem. Neck resection was increased between groups (group 1 = normal, group 2 = 3mm additional, group 3 = 6mm additional), to simulate failure to obtain calcar collar contact. Prior to each trial, the distances between anterior (ACC) and posterior (PCC) collar and the calcar were measured. Periprosthetic fractures of the femur were simulated using a previously published technique. High speed video recording identified when collar to calcar contact (CCC) occurred. The ACC and PCC were compared between trials where the CCC was and was not achieved. Regression estimated the odds of failing to achieve CCC for a given ACC or PCC. Results. CCC was achieved prior to fracture in all cases in group one, 50% in group two and 0% in group three. The median (range) ACC for those trials where CCC was achieved was 0.40 (0.00, 3.37) mm versus 6.15 (3.06 to 6.88) mm, where CCC was not achieved (p <0.01). The median (range) PCC for those trials where CCC was achieved was 0.85 (0.00 to 3.71) mm versus 5.97 (2.23 to 7.46) mm, where CCC was not achieved (p <0.01). Binomial logistic regression estimated risk of failure to obtain CCC increased 3.8 fold (95% confidence interval 1.6 to 30.2, p <0.05) for each millimetre of PCC. Conclusions. Increased separation between collar and calcar reduced the likelihood of calcar collar contact during a simulated periprosthetic fracture of the femur. Surgeons should aim to achieve a calcar-collar distance of less than 1mm following implantation to ensure calcar collar contact during periprosthetic femoral fracture and to reduce the risk of fracture. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Femoral head collapse due to avascular necrosis (AVN) is a relatively rare occurrence following intertrochanteric fractures; however, with over thirty-thousand intertrochanteric fractures per year in England and Wales alone, and an incidence of up to 1.16%, it is still significant. Often patients are treated with a hip fixation device, such as a sliding hip screw or X-Bolt. This study aimed to investigate the influence of three factors on the likelihood of head collapse: (1) implant type; (2) the size of the femoral head; and (3) the size of the AVN lesion. Finite element (FE) models of an intact femur, and femurs implanted with two common hip fixation designs, the Compression Hip Screw (Smith & Nephew) and the X-Bolt (X-Bolt Orthopaedics), were developed. Experimental validation of the FE models on 4. th. generation Sawbones composite femurs (n=5) found the peak failure loads predicted by the implanted model was accurate to within 14%. Following validation on Sawbones, the material modulus (E) was updated to represent cancellous (E=500MPa) and cortical (E=1GPa) bone, and the influence of implant design, head size, and AVN was examined. Four head sizes were compared: mean male (48.4 mm) and female (42.2 mm) head sizes ± two standard deviations. A conical representation of an AVN lesion with a lower modulus (1MPa) was created, and four different radii were studied. The risk of head collapse was assessed from (1) the critical buckling pressure and (2) the peak failure stress. The likelihood of head collapse was reduced by implantation of either fixation device. Smaller head sizes and greater AVN lesion size increased the risk of femoral head collapse. These results indicate the treatment of intertrochanteric fractures with a hip fixation device does not increase the risk of head collapse; however, patient factors such as small head size and AVN severity significantly increase the risk

Study Aim. Femoral components used in total knee arthroplasty (TKA) are primarily designed on the basis of kinematics and ease of fixation. This study considers the stress-strain environment in the distal femur due to different implant internal geometry variations (based on current industry standards) using finite element (FE) analyses. Both two and three dimensional models are considered for a range of physiological loading scenarios – from full extension to deep flexion. Issues associated with micro-motion at the bone-implant interface are also considered. Materials and methods. Two (plane strain) and three dimensional finite element analyses were conducted to examine implant micro-motions and stability. The simple 2D models were used to examine the influence of anterior-posterior (AP) flange angle on implant stability. AP slopes of 3°, 7° and 11° were considered with contact between bone and implant interfaces being modeled using the standard coulomb friction model. The direction and region of loading was based on loading experienced at full extension, 90° flexion and 135° flexion. Three main model variations were created for the 3D analyses, the first model represented an intact distal femur, the second a primary implanted distal femur and the third a distal femur implanted with a posterior stabilising implant. Further each of the above 3D model sets were divided into two group, the first used a frictional interface between the bone and implant to characterise the behavior of uncemented implants post TKA and the second group assumed 100% osseointegration had already taken place and focused on examining the subsequent stress/strain environment in the femur with respect to different femoral component geometries relative the intact distal femur model. Results and Discussion. Analyses indicate a trend relating the slope of the anterior-posterior (AP) flange to implant loosening at high flexion angles for uncemented components. Once cemented, this becomes less important. Results from the 3D analyses show that the posterior stabilising implant causes stress concentrations which can lead to bicondylar fatigue fracture. All femoral components cause stress shielding in cancellous bone particularly when they are fully bonded. Investigations into implant micromotion show that revision implants with box sections provided more resistance to micromotion than the pegged primary implants. However for the gait cycle tested the maximum recorded micromotion of both implants was well within acceptable levels for osseointegration to occur

We implanted titanium and carbon fibre-reinforced plastic (CFRP) femoral prostheses of the same dimensions into five prosthetic femora. An abductor jig was attached and a 1 kN load applied. This was repeated with five control femora. Digital image correlation was used to give a detailed two-dimensional strain map of the medial cortex of the proximal femur. Both implants caused stress shielding around the calcar. Distally, the titanium implant showed stress shielding, whereas the CFRP prosthesis did not produce a strain pattern which was statistically different from the controls. There was a reduction in strain beyond the tip of both the implants. This investigation indicates that use of the CFRP stem should avoid stress shielding in total hip replacement

Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured. After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem. Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain

Bone surface strains were measured in cadaver femora during loading prior to and after resurfacing of the hip and total hip replacement using an uncemented, tapered femoral component. In vitro loading simulated the single-leg stance phase during walking. Strains were measured on the medial and the lateral sides of the proximal aspect and the mid-diaphysis of the femur. Bone surface strains following femoral resurfacing were similar to those in the native femur, except for proximal shear strains, which were significantly less than those in the native femur. Proximomedial strains following total hip replacement were significantly less than those in the native and the resurfaced femur.

These results are consistent with previous clinical evidence of bone loss after total hip replacement, and provide support for claims of bone preservation after resurfacing arthroplasty of the hip.

Post-mortem retrieval of canine, cemented femoral components was analysed to assess the performance of these implants in the dog as a model for human total hip replacement (THR). Mechanical testing and radiological analysis were performed to determine the stability of the implant and the quality of the cement. Thirty-eight implants from 29 dogs were retrieved after time intervals ranging from 0.67 to 11.67 years. The incidence of aseptic loosening was 63.2%, much higher than in human patients (6% in post-mortem studies). Failure of the femoral implants began with debonding at the cement-metal interface, similar to that in implants in man. The incidence of aseptic loosening was much lower in bilateral than in unilateral implants. Significant differences were observed for three different designs of implant. While the dog remains the animal model of choice for THR, results from this study provide insight into interspecies differences in the performance of implants. For example, the performance of THR in dogs should be compared with that in young rather than in elderly human patients.