Femoral cortical thickness influences the pattern of proximal femoral periprosthetic fractures with a cemented stem.

INTRODUCTION: Periprosthetic fractures of the proximal femur place a significant burden on the patients who endure them, as well as the medical health system that supports them. The purpose of this study was to determine whether femoral cortical thickness, as an absolute measurement, is a predictor of periprosthetic fracture pattern. METHOD: A cohort of 102 patients who had sustained a periprosthetic hip fracture were retrospectively identified. This included 58 males and 44 females with a mean age of 79.8 years. The femoral periprosthetic fracture pattern was classified based on the Vancouver classification system. Stem fixation was recorded and femoral cortical thickness measured. Patients were grouped into cemented and cementless stems. The relationship between cortical thickness and periprosthetic fracture pattern was assessed using the primary stem fixation method. Receiver operating characteristic (ROC) curve analysis was used to identify a threshold in the cortical thickness that predicted fracture pattern. Multinomial logistic regression analysis was used to adjust for confounding variables to assess the independent influence of cortical thickness on the risk of sustaining a Vancouver type A, B or C. RESULTS: There were 65 (63.7%) patients in the cemented group and 37 (36.3%) in the cementless group. The pattern of periprosthetic fractures around cemented stems was significantly (p < 0.001) influenced by the femoral cortical thickness, with a thinner cortical thickness associated with a type A fracture pattern. In contrast, no association between femoral cortical thickness and fracture pattern assessment was demonstrated in the cementless group (p = 0.82 Chi square). Comparing the rate of type A fracture patterns between the groups illustrated a significantly decreased risk in the cemented group with a cortical thickness of > 7 mm (odds ratio 0.03, p < 0.001). ROC curve analysis of the cemented group demonstrated a threshold value of 6.3 mm, offering a sensitivity of 83.3% and a specificity of 78.9% in predicting an A type fracture. Using this threshold, patients with a cortical thickness of 6.3 mm or less were significantly more likely to sustain a Vancouver type A fracture (OR 18.9, 95% CI 2.0-166.7, p < 0.001) when compared to patients with a cortical thickness of > 6.3 mm. In contrast, the ROC curve analysis did not find cortical thickness to be a predictor of fracture pattern in the cementless group. When adjusting for confounding variables, multinomial logistic regression demonstrated a cortical thickness of 6.3 mm or less was a significant predictor of a type A fracture (OR 3.28, 95% CI 1.06-10.16, p = 0.04) relative to those sustaining a type B fracture. CONCLUSION: Cortical thickness was found to influence the periprosthetic fracture pattern around cemented femoral stems, but this was not observed with cementless stems. Type A fracture patterns were significantly more likely to occur with a cortical thickness of 6.3 mm or less around cemented stems.

[Periprosthetic Femoral Fractures after Total Hip Replacement: Our Results and Treatment Complications]. / Periprotetické zlomeniny femuru po implantaci aloplastiky kycelního kloubu: nase výsledky a komplikace pri lécení.

PURPOSE OF THE STUDY The study consists of a retroactive evaluation of results of surgical treatment in patients with periprosthetic femoral fracture after total hip replacement and a comparison with results reported in the literature. MATERIAL AND METHODS In the period from 2003 to 2013, a total of 83 patients with periprosthetic femoral fracture after total hip replacement were treated at our clinic, namely 69 women and 14 men. The mean age in the cohort was 74 years (range 47-87). The Vancouver classification was used to grade the fractures. The cohort included 31 patients with type B1 fracture, 25 patients with type B2 fracture, 8 patients with type B3 fracture, and 19 patients with type C fracture. Altogether 80 patients underwent a surgery, 3 patients with non-displaced type B1 fracture were treated conservatively. The mechanism of injury was a simple fall in 75 % of primary endoprostheses and in 56% of revision endoprostheses. The average time to fracture was 7.6 years in primary implant and 3.6 years in revision endoprosthesis. In fractures with a well-fixed stem (type B1 and C) plate osteosynthesis was used. In case of a comminution zone, osteosynthesis was followed by spongioplasty. In patients with a loose stem (type B2 and B3), the fracture was treated with a revision uncemented stem. In two cases a combination of a revision stem and a massive corticocancellous bone graft was used. The evaluation was performed using the Harris Hip Score and the minimum follow-up from the surgery was 3 years. RESULTS In the group of patients with type B1 fracture, 28 patients were treated surgically. An excellent result was achieved in 22 patients (84%), in 4 patients (16%) the result was very good. The remaining 2 patients failed to meet the requirement of the minimum follow-up of 3 years. In the group of patients with type B2 fractures, composed of 25 patients, the femoral component was replaced with a revision uncemented stem with cerclage wires or titanium tapes or cables. Osseointegration of the stem was recorded in 24 patients, one female patient died 4 months after the surgery. An excellent result was achieved in 16 patients (64%), a very good result in 4 patients (16%). The remaining 5 patients (20%) failed to meet the minimum follow-up of 3 years. In 8 patients with type B3 trauma, the reimplant of a revision stem was supplemented by spongioplasty, in 2 cases by solid corticocancellous bone grafts with cerclage. In this group osseointegration occurred in all the cases within 6-9 months. The follow-up was affected by the older age of patients and 6 patients died during the follow-up period. The requirement of a follow-up longer than 3 years was met in 2 patients (25%) only and the result was considered very good. In the group of 19 patients with type C fracture, plate osteosynthesis was performed, which was in 12 cases complemented with spongioplasty. Healing occurred within 6 months in 13 patients (72%), within 9 months in 3 patients (17%) and in 2 patients (11%) reoperation was carried out due to fixation failure. One female patient died 16 days after the surgery. An excellent result was achieved in 15 patients (83%), in the remaining three patients the follow-up was shorter than three years due to their death. DISCUSSION Periprosthetic femoral fractures after total hip replacement is a rare but feared complication. Its incidence ranges from 0.1 to 4%. It occurs most frequently 7 to 8 years after the primary implant and 3 to 4 years after the revision of endoprosthesis implantation. The main risk factor is the loosening of stem of endoprosthesis. Another risk factor is osteoporosis. Age, sex and obesity do not constitute significant risk factors. Stem stability and presence of bone defects are the main criteria in favour of surgical treatment. If the stem remains well fixed, the osteosynthesis is opted for, whereas if the stem is loose, its replacement has to be performed. The management of bone defects is an integral part of femoral reconstruction and restoration of endoprosthesis stability. CONCLUSIONS Surgical treatment of periprosthetic fractures, thanks to the introduction of new implants for osteosynthesis and development of new stems for revision endoprostheses, helps achieve ever better results. Of major importance for choosing the treatment method is correct classification of fracture and stem stability. Poor bone quality is a common feature, therefore a perfect mechanical fixation is necessary. The long-term results are affected primarily by the patient s age. Key words: periprosthetic femoral fractures, surgical treatment, results, complications.

Underneath the cerclage: an ex vivo study on the cerclage-bone interface mechanics.

INTRODUCTION: Cerclages regain interest due to a rising number of periprosthetic fractures. The contact distribution at the circumferential cerclage-bone interface is still unknown. Local interface pressure depends on the amount of contact area. Cortical damage at the interface would provoke cerclage loosening. Therefore, the contact area, the bone pressure along the interface and the cortical resistance underneath loaded cerclages were determined in an ex vivo model. MATERIALS AND METHODS: Human diaphyseal femoral bone was used with differing cross-sectional geometry. Bone contact points of fixed 1.5 mm wire and 1.7 mm cable cerclages were identified from axial radiographs. Pressure distribution at the cerclage-bone interface was recorded with a pressure-measuring film using a distraction setup with two cortical half shells. Bone shells with installed cerclages were separated with up to 400 N force and were subsequently analyzed histologically to detect cortical damage. RESULTS: Both cerclage types exhibited a point contact fixation with non-loaded spanned zones in-between. Cables cover larger contact areas. Both cerclages exhibited an inhomogeneous interface pressure distribution depending on the bone surface geometry. Histology revealed intact cortical bone without cortical affection after loading of both cerclage types. CONCLUSION: Point contact fixation of the cerclages installs non-loaded, spanned zones where the periosteum is not compressed, rendering a strangulation of the blood supply unlikely. Cortical bone withstands static concentric pressure produced by the cerclage. Cortical groove formation is attributed to instability under functional load and not to weakness of the cortex itself.

[Postoperative imaging of the hip]. / Postoperative Bildgebung des Hüftgelenks.

CLINICAL ISSUE: To assess postoperative imaging of the hip joint regarding possible complications, it is indispensable to have in-depth knowledge of commonly used surgical techniques, access routes, and the implanted materials. STANDARD RADIOLOGICAL METHODS: While radiography is used to evaluate the position of foreign material and to rule out periprosthetic fractures that have occurred intraoperatively, follow-up examinations might show signs of material failure, aseptic loosening, prosthesis infections, or the occurrence of heterotopic ossifications. If radiographic findings are ambiguous, computed tomography (CT) may be used to clarify findings, whereas magnetic resonance imaging (MRI) is helpful to identify intra- and periarticular soft tissue pathologies such as surgery-associated cartilage and ligament damage, muscle insufficiency, or metallosis. METHODOLOGICAL INNOVATION AND EVALUATION: To guide clinical decision making in common postoperative complications, various classification systems are available, e.g., for periprosthetic fractures, aseptic loosening, or heterotopic ossification. However, the differentiation between aseptic material loosening and septic endoprosthesis infection remains challenging if based on imaging alone. PRACTICAL RECOMMENDATIONS: The assessment of postoperative hip imaging should be closely linked to the respective surgical technique and the implanted foreign material, whereby different probabilities of specific complications can be derived.

Plate fixation in periprosthetic femur fractures Vancouver type B1-Trochanteric hook plate or subtrochanterical bicortical locking?

INTRODUCTION: Proximal plate fixation in periprosthetic femur fractures can be improved by plate anchorage in the greater trochanter (lateral tension band principle) or bicortical locking screw placement beside the prosthesis stem in an embracement configuration. Both concepts were compared in a biomechanical test using a femoral hook plate (hook) or a locking attachment plate (LAP). METHODS: After bone mineral density (BMD) measurement in the greater trochanter, six pairs of fresh frozen human femora were assigned to two groups and instrumented with cemented hip endoprostheses. A transverse osteotomy was set distal to the tip of the prosthesis, simulating a Vancouver B1 fracture. Each pair was instrumented using a plate tensioner with either hook or LAP construct. Cyclic testing (2Hz) with physiologic profile and monotonically increasing load was performed until catastrophic failure. Plate stiffness was compared in a four-point-bending-test. Paired student's-t-test was used for statistical evaluation (p<0.05). RESULTS: Mean BMD was 250mgHA/ccm±47. The hook construct exhibited a significantly (p=0.015) lower number of cycles and load to failure (26'177cycles±2777; 3'118N±778) correlating significantly with BMD (R2=0.83; p=0.04) compared to the LAP construct (37'423cycles±5'299; 4'242N±1'030) (R2=0.71;p=0.11). BMD was a significant covariate (p=0.01). Plate stiffness was in a comparable range (hook Plate 468N/mm±7; LCP 445N/mm±6). CONCLUSION: Subtrochanterically placed LAP provides an increased fixation strength under repetitive loading compared to hook plate fixation in the greater trochanter. Trochanteric fixation is highly BMD dependent and may be restricted to major greater trochanteric involvement requiring stabilization.

A 42-year-old patient presenting with femoral head migration after hemiarthroplasty performed 22 years earlier: a case report.

INTRODUCTION: Treatment of femoral neck fractures in young adults may require total hip arthroplasty or hip hemiarthroplasty using a bipolar cup. The latter can, however, result in migration of the femoral head and poor long-term results. CASE PRESENTATION: We report a case of femoral head migration after hemiarthroplasty performed for femoral neck fracture that had occurred 22 years earlier, when the patient (a Japanese man) was 20 years old. He experienced peri-prosthetic fracture of the femur, subsequent migration of the prosthesis, and a massive bone defect of the pelvic side acetabular roof. After bone union of the femoral shaft fracture, the patient was referred to our hospital for reconstruction of the acetabular roof. Intra-operatively, we placed two alloimplants of bone from around the transplanted femoral head into the weight-bearing region of the acetabular roof using an impaction bone graft method. We then implanted an acetabular roof reinforcement plate and a cemented polyethylene cup in the position of the original acetabular cup. Eighteen months post-operatively, X-rays showed union of the transplanted bone. CONCLUSIONS: Treatment of femoral neck fractures in young adults is usually accomplished by osteosynthesis, but it may be complicated by femoral head avascular necrosis or by infection or osteomyelitis. In such cases, once an infection has subsided, either hip hemiarthroplasty using a bipolar cup or total hip arthroplasty may be required. However, if the acetabular side articular cartilage is damaged, a bipolar cup should not be used. Total hip arthroplasty should be performed to prevent migration of the implant.

Impaction bone grafting for periprosthetic fractures around a total hip arthroplasty.

The incidence of periprosthetic fractures has been reported to be between 1 and 20.9% and appears to be on the rise. Fractures that occur around the femoral stem, particularly when the stem is loose or there is a loss of bone stock pose a technical challenge. These are rare injuries and there is considerable debate regarding their optimal treatment. Reconstruction with large segment endoprosthetic replacement is an acceptable solution for elderly patients who have limited functional demands and where the prosthesis is expected to outlive the patient. The younger patient poses a much greater challenge, the bone must be reconstituted and the femoral canal geometry must sufficiently restored to allow the stable insertion of a prosthesis. There are very few techniques that exist in this scenario. One such technique is impaction bone grafting and revision to a long smooth tapered cemented stem. This allows the restoration of bone stock and the stable insertion of a prosthesis. The aim of this article is to discuss the theory behind impaction bone grafting, the technical aspects and challenges of this technique, including fracture reduction methods, and to appraise all the literature available on impaction bone grafting for periprosthetic fractures.

Periprosthetic fractures around polished collarless cemented stems: the effect of stem design on fracture pattern.

BACKGROUND: Predictable patterns of periprosthetic fracture have been observed around polished double tapered stems. Finite element studies have suggested that triple-tapered stems cause less cement strain in torsion compared to double-tapered stems. Hence, we hypothesised that the in vitro behaviour of implanted double- and triple-tapered polished stems, like the CPT (Zimmer, Warsaw, USA) or C-Stem (DePuy, Leeds, U.K.) when subjected to pathological torsional loads may cause different patterns of periprosthetic fractures. METHODS: Ten double-tapered stems (CPT) and ten triple-tapered stems (C-Stem) were cemented into synthetic femur bones. A constant axial compression load of 100 N and a torsional pre-load of 0.1 N.m were applied using a biaxial testing machine. The distal femur was then loaded in external rotation at 45 degrees until failure. RESULTS: Seven of the 10 CPT stems fractured at the level of the stem body while fracturing the cement mantle at the same level. In three of ten of the CPT stems and all ten C-Stems, the synthetic bone fractured at the tip of the prosthesis while the cement mantle remained intact. This was significant for the resulting fracture pattern (P=0.001). There was no significant difference between the groups for either torque (P=0.13) or angle at failure (P=0.49). INTERPRETATION: This biomechanical study indicates that the CPT and C-Stem create a different fracture pattern under the same loading condition. The C-Stem (a triple tapered stem) may produce lower strain in torsion to the cement mantle of a cemented THA. However, fractures that do occur may be more difficult to treat than those produced around a stem like the CPT subjected to comparable loading.

Finite element analysis modelling of proximal femoral fractures, including post-fixation periprosthetic fractures.

Biomechanical testing has been a cornerstone for the development of surgical implants used in fracture stabilisation. In a multi-disciplinary collaboration complex at the University of Wales, Swansea, novel computerised clinically relevant models were developed using advanced computational engineering. In-house software (developed initially for commercial aerospace engineering), allowed accurate finite element analysis (FEA) models of the whole femur to be created, including the internal architecture of the bone, by means of linear interpolation of greyscale images from multiaxial CT scans. This allowed for modelling the changing trabecular structure and bone mineral density as seen in progressive osteoporosis. Falls from standing were modelled in a variety of directions (with and without muscle action) using analysis programmes which resulted in fractures consistent with those seen in clinical practice. By meshing implants into these models and repeating the mechanism of injury in simulation, periprosthetic fractures were also recreated. Further development with simulated physiological activities (e.g. walking and rising from sitting) along with attrition in the bone (in the boundary zones where stress concentration occurs) will allow further known modes of failure in implants to be reproduced. Robust simulation of macro and micro-scale events will allow the testing of novel new designs in simulations far more complex than conventional biomechanical testing will allow.

Clostridium perfringens infection complicating periprosthetic fracture fixation about the hip: successful treatment with early aggressive debridement.

Periprosthetic fracture and infection are both challenges following hip arthroplasty. We report the case of an 87 year old female who underwent open reduction and internal fixation of a periprosthetic femoral fracture. Her post-operative course was complicated by infection with Clostridium perfringens. Early aggressive antibiotic treatment and surgical debridement were successful, and allowed retention of the original components.

Morphologic analysis of periprosthetic fractures after hip resurfacing arthroplasty.

BACKGROUND: Periprosthetic fractures have long been recognized as one of the major complications of hip resurfacing arthroplasty. The objective of this study was to develop a systematic and morphologic classification of the fracture mode based on pathogenesis. METHODS: One hundred and seven retrieved specimens consisting of the femoral remnant and the femoral component of a total hip resurfacing arthroplasty that had failed as a result of a periprosthetic fracture were analyzed with regard to the morphologic failure mode. The location of the fracture line was used to differentiate the fractures. The fractures were also classified histopathologically as acute biomechanical, acute postnecrotic, or chronic biomechanical. RESULTS: Fifty-nine percent (sixty-three) of the fractures occurred within the bone inside the femoral component. Fifty-one percent (fifty-five) of the fractures were classified morphologically as acute postnecrotic; 40% (forty-three), as chronic biomechanical; and 8% (nine), as acute biomechanical. Acute biomechanical fractures were found exclusively in the femoral neck and occurred earlier (mean time [and standard deviation] between implantation and revision, 41 +/- 57 days) than acute postnecrotic fractures (mean time between implantation and revision, 149 +/- 168 days; p = 0.002) or chronic biomechanical fractures (mean time between implantation and revision, 179 +/- 165 days; p = 0.001). The latter two fracture types both occurred predominantly in the bone inside the femoral component. CONCLUSIONS: Three distinct fracture modes were characterized morphologically. Osteonecrosis was the most frequent cause of fracture-related failures. We suggest that an intraoperative mechanical injury of the femoral neck such as notching and/or malpositioning of the femoral component might lead to changes in the loading pattern or in the resistance to fracture of the femoral neck and may result in both acute and chronic biomechanical femoral neck fractures. These findings may serve as feedback information for the surgeon and possibly influence future therapeutic strategies.