Florian Fensky

What is the risk of stress risers for interprosthetic fractures of the femur? A biomechanical analysis

PurposeDue to increasing life expectancy we see a rising number of joint replacements. Along with the proximal prosthesis in the femur, more and more people have a second implant on the distal ipsilateral side. This might be a retrograde nail or a locking plate to treat distal femur fractures or a constrained knee prosthesis in the case of severe arthrosis. All these constructs can lead to fractures between the implants. The goal of this study was to evaluate the risk of stress risers for interprosthetic fractures of the femur.MethodsThirty human cadaveric femurs were divided into five groups: (1) femurs with a prosthesis on the proximal side only, (2) hip prosthesis on the proximal end and a distal femur nail, (3) femurs with both a hip prosthesis and a constrained knee prosthesis, (4) femurs with a hip prosthesis on the proximal side and a 4.5-mm distal femur locking plate; the locking plate was 230 mm in length, with ten holes in the shaft, and (5) femurs with a proximal hip prosthesis and a 4.5-mm distal femur locking plate; the locking plate was 342 mm in length, with 16 holes in the shaft.ResultsFemurs with a hip prosthesis and knee prosthesis showed significantly higher required fracture force compared to femurs with a hip prosthesis and a distal retrograde nail. Femurs with a distal locking plate of either length showed a higher required fracture force than those with the retrograde nail.ConclusionsThe highest risk for a fracture in the femur with an existing hip prosthesis comes with a retrograde nail. A distal locking plate for the treatment of supracondylar fractures leads to a higher required fracture force. The implantation of a constrained knee prosthesis that is not loosened on the ipsilateral side does not increase the risk for a fracture.

Cement augmentation of the proximal femoral nail antirotation for the treatment of osteoporotic pertrochanteric fractures—A biomechanical cadaver study

INTRODUCTION Proximal femoral fractures will gain increasing importance in the future due to the epidemiological development. Osteoporosis is often a limiting factor in the achievement of implant stability. New nailing systems offer the possibility of augmentation of the femoral neck component with cement. The aim of this study was to perform a biomechanical comparison of implant stability in osteoporotic pertrochanteric fractures using the proximal femoral nail antirotation (PFNA, Synthes GmbH, Umkirch, Germany) with cement augmented and non-augmented blades. MATERIALS AND METHODS Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA) in six pairs of fresh-frozen human femurs. Standardised pertrochanteric fractures (AO31-A2.3) were treated with a PFNA. Cement augmentation was performed in six constructs. Axial loading was applied according to a single-leg-stance model using a hydraulic testing machine increasing to 1400N over 10,000 cycles. Biomechanical comparisons between the two groups that were comparable concerning BMD, tip-apex-distance and native stiffness were made with regard to postoperative stiffness, survived cycles, load to failure, failure mechanism and axial displacement. RESULTS The stiffness of all stabilised femurs was significantly lower than for native specimens (native 702.5±159.6N/mm vs. postoperative 275.4±53.8N/mm, p<0.001). Stiffness after instrumentation was significantly greater for the cement augmented group than for the non-augmented group (300.6±46.7N/mm vs. 250.3±51.6N/mm, respectively, p=0.001). Five of the twelve constructs survived cyclic testing. Statistically significant differences of the BMD were detected between survived and failed constructs (0.79±0.17g/cm(2) vs. 0.45±0.12g/cm(2), respectively, p=0.028). The failure loads for specimens surviving 10,000 cycles were 4611.9±2078.9N in the cement augmented group (n=3) and 4516.3N and 3253.5N in the non-augmented group (n=2). Postoperative stiffness was found to be a positive predictor of maximum force to failure (R(2)=0.83, p=0.02). CONCLUSIONS The results of this biomechanical study show that cement augmentation of the PFNA increases the implant stability in osteoporotic pertrochanteric fractures. Further studies are necessary to evaluate this procedure in providing long term clinical results.

Fungal periprosthetic joint infection in total knee arthroplasty: a systematic review.

Fungal periprosthetic joint infection (PJI) is a rare but devastating complication following total knee arthroplasty (TKA). A standardized procedure regarding an accurate treatment of this serious complication of knee arthroplasty is lacking. In this systematic review, we collected data from 36 studies with a total of 45 reported cases of a TKA complicated by a fungal PJI. Subsequently, an analysis focusing on diagnostic, medicaments and surgical procedures in the pre-, intra- and postoperative period was performed. Candida spp. accounts for about 80% (36 out of 45 cases) of fungal PJIs and is therefore the most frequently reported pathogen. A systemic antifungal therapy was administered in all but one patient whereas a local antifungal therapy, e.g. the use of an impregnated spacer, is of inferior relevance. Resection arthroplasty with delayed re-implantation (two-stage revision) was the surgical treatment of choice. However, in 50% of all reported cases the surgical therapy was heterogeneous. The outcome under a combined therapy was moderate with recurrent fungal PJI in 11 patients and subsequent bacterial PJI as a main complication in 5 patients. In summary, this systematic review integrates data from up to date 45 reported cases of a fungal PJI of a TKA. On the basis of the current literature strategies for the treatment of this devastating complication after TKA are discussed.

High incidence of osteochondral lesions after open reduction and internal fixation of displaced ankle fractures: Medium-term follow-up of 100 cases.

BACKGROUND The incidence of osteochondral lesions (OCLs) in association with displaced ankle fractures has only been examined in two previous studies. In both studies magnetic resonance imaging (MRI) was performed prior to open reduction and internal fixation (ORIF). Because MRI may overdiagnose or overestimate the extent of OCLs in an acute trauma setting the aim of this study was to determine the incidence of OCLs after ORIF of displaced ankle fractures using MRI at medium-term follow-up, and to analyse if the severity of fracture or the clinical outcome correlates with the incidence of OCLs. PATIENTS AND METHODS Following institutional review board approval a total of 100 patients (mean age, 41.3 years; range, 17.9-64.3 years) with a displaced ankle fracture who had undergone ORIF according to the AO principles were included in this study. The American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score was used to quantify the clinical outcome and MR images were evaluated for OCLs of the talus and distal tibia after a mean of 34.5 months (range, 17.5-54.1 months). RESULTS OCLs were found in 40.4% of the patients. Logistic regression revealed a significant correlation between the severity of fracture and the incidence of OCLs. Patients with a trimalleolar fracture (p=0.04) or an ankle fracture dislocation (p=0.003) had a significantly higher risk for developing an OCL compared to those with a type B fracture. Logistic regression also demonstrated a significant correlation between the clinical outcome (AOFAS score) and the incidence of OCLs (p=0.01). The risk for developing an OCL increases up to 5.6% when the AOFAS score decreases by one point. CONCLUSION OCLs were frequently found in association with acute ankle fractures at medium-term follow-up, and the severity of fracture was associated with an increased number of OCLs. Considering the disadvantages of MRI including the high cost and limited availability, the results of this study may help to explain why anatomic surgical realignment of displaced ankle fractures may still be associated with poor clinical outcomes.

The role of inter-prosthetic distance, cortical thickness and bone mineral density in the development of inter-prosthetic fractures of the femur

It is becoming increasingly common for a patient to have ipsilateral hip and knee replacements. The inter-prosthetic (IP) distance, the distance between the tips of hip and knee prostheses, has been thought to be associated with an increased risk of IP fracture. Small gap distances are generally assumed to act as stress risers, although there is no real biomechanical evidence to support this. The purpose of this study was to evaluate the influence of IP distance, cortical thickness and bone mineral density on the likelihood of an IP femoral fracture. A total of 18 human femur specimens were randomised into three groups by bone density and cortical thickness. For each group, a defined IP distance of 35 mm, 80 mm or 160 mm was created by choosing the appropriate lengths of component. The maximum fracture strength was determined using a four-point bending test. The fracture force of all three groups was similar (p = 0.498). There was a highly significant correlation between the cortical area and the fracture strength (r = 0.804, p < 0.001), whereas bone density showed no influence. This study suggests that the IP distance has little influence on fracture strength in IP femoral fractures: the thickness of the cortex seems to be the decisive factor.

Anterior iliopsoas impingement due to a malpositioned acetabular component - effective relief by surgical cup reorientation

Background Determining the aetiology of persistent pain following total hip arthroplasty (THA) can be challenging. Impingement of the iliopsoas muscle due to a malpositioned acetabular component after THA might be a potential cause of postoperative groin pain. Methods We retrospectively analysed the data of 12 consecutive patients from our orthopaedic department who underwent cup revision for painful iliopsoas impingement after primary THA. Results Thorough physical examination as well as radiological assessment of the included patients revealed that malpositioning of the acetabular component provoked iliopsoas impingement. The Harris Hip Score and the orientation of the acetabular component before and after surgical revision at an average follow-up of 56 months were analysed. Conclusions We were able to demonstrate that surgical cup revision and reorientation resulted in distinctly improved scores and is a feasible option to effectively treat persistent iliopsoas impingement due to a malpositioned acetabular component following THA.

[Periprosthetic and interimplant femoral fractures: Biomechanical analysis].

ZusammenfassungHintergrundMit steigendem Patientenalter nimmt die Anforderung an die Versorgung von Femurfrakturen zu. Unklar ist, inwieweit die Implantate die femorale Stabilität beeinflussen.MethodeUnterschiedliche Frakturversorgungen nach Implantation eines Hüft- und/oder Kniegelenks wurden biomechanisch an humanen osteoporotischen Femora mit der nativen Situation verglichen.ErgebnisseEine Hüftprothese schwächt das Femur um 33 %. Wird zusätzlich ein retrograder distaler Femurnagel implantiert, sinkt die Bruchlast weiter. Diese instabile Situation kann durch eine winkelstabile Brückenosteosynthese signifikant stabilisiert werden. Die höchste Bruchlast wurde bei implantierter Hüft- und ipsilateraler Knieprothese beobachtet.SchlussfolgerungZusammenfassend lässt sich sagen, dass eine Hüftprothese das Femur signifikant schwächt, wobei zwei einzementierte Prothesen eine stabilere Situation als die eines nativen Femurs erzielen. Die Belastungsstabilität muss bei einliegender Hüftprothese und ipsilateralem Femurnagel in Frage gestellt oder durch eine Brückenosteosynthese gesichert werden. Zur Frakturversorgung einer distalen Femurfraktur bei einliegender Hüftprothese ist die winkelstabile, den Prothesenschaft übergreifende Platte zu favorisieren.AbstractBackgroundThe requirements for treatment of femoral fractures are increasing with the rising age of the patients. The aim of this study was to evaluate femoral stiffness and the fracture risk after inserting different implants and implant combinations.MethodsA total of 48 cadaveric femors were harvested and 8 groups were randomized on the basis of the bone mineral density (BMD). Different osteosyntheses following prosthetic stem implantation (hip and knee prostheses) were performed and compared with native femurs. All specimens were biomechanically tested in a four-point bending until fracture.ResultsThe insertion of a femoral stem decreases the stiffness by approximately 33%. Ipsilateral retrograde nailing reduces the force to failure even more. This instable situation can be stabilized by a lateral locking compression plate. The most stable situation occurred in the presence of two cemented stems.ConclusionTaken together these results clearly indicate that a hip prosthesis significantly weakens the femur, whereas two stems produce the most stable situation at all. The situation of a hip prosthesis and an retrograde nail should be avoided or covered by a bridging-osteosynthesis. In clinical practice an extramedullary fixation technique for distal femoral fractures should be preferred.BACKGROUND The requirements for treatment of femoral fractures are increasing with the rising age of the patients. The aim of this study was to evaluate femoral stiffness and the fracture risk after inserting different implants and implant combinations. METHODS A total of 48 cadaveric femors were harvested and 8 groups were randomized on the basis of the bone mineral density (BMD). Different osteosyntheses following prosthetic stem implantation (hip and knee prostheses) were performed and compared with native femurs. All specimens were biomechanically tested in a four-point bending until fracture. RESULTS The insertion of a femoral stem decreases the stiffness by approximately 33%. Ipsilateral retrograde nailing reduces the force to failure even more. This instable situation can be stabilized by a lateral locking compression plate. The most stable situation occurred in the presence of two cemented stems. CONCLUSION Taken together these results clearly indicate that a hip prosthesis significantly weakens the femur, whereas two stems produce the most stable situation at all. The situation of a hip prosthesis and an retrograde nail should be avoided or covered by a bridging-osteosynthesis. In clinical practice an extramedullary fixation technique for distal femoral fractures should be preferred.

Chondrogenic predifferentiation of human mesenchymal stem cells in collagen type I hydrogels

Abstract Hyaline cartilage displays a limited regenerative potential. Consequently, therapeutic approaches have been developed to treat focal cartilage lesions. Larger-sized lesions are commonly treated by osteochondral grafting/mosaicplasty, autologous chondrocyte implantation (ACI) or matrix-induced chondrocyte implantation (MACI). As an alternative cell source to chondrocytes, multipotent mesenchymal stem cells (MSCs) are regarded a promising option. We therefore investigated the feasibility of predifferentiating human MSCs incorporated in hydrogels clinically applied for MACI (CaReS®). MSC-laden hydrogels were cast and cultured over 10 days in a defined chondrogenic differentiation medium supplemented with TGF-β1. This was followed by an 11-day culture in TGF-β1 free media. After 21 days, considerable contraction of the hydrogels was observed. Histochemistry showed cells of a chondrocyte-like morphology embedded in a proteoglycan-rich extracellular matrix. Real-time polymerase chain reaction (RT-PCR) analysis showed the expression of chondrogenic marker genes, such as collagen type II and aggrecan. In summary, we demonstrate that chondrogenic differentiation of human mesenchymal stem cells embedded in collagen type I hydrogels can be induced under the influence of TGF-β1 over a period of 10 days.

[Percutaneous iliosacral screw fixation for pelvis insufficiency fracture after implantation of a pedestal cup: case report].

Insufficiency fractures of the sacrum are frequently overlooked injuries especially in postmenopausal women with an osteoporotic bone structure and without a history of significant trauma. Plain radiographs are frequently inadequate in showing insufficiency fractures of the sacrum. Regarding this a fracture of a pubic ramus combined with appropriate clinical symptoms should raise the suspicion of a concomitant sacral injury. Therefore, further investigations including a CT scan are necessary.The case of an osteoporotic female patient with bilateral insufficiency fractures of the sacrum and a fracture of the right superior and inferior pubic ramus 5 weeks after primary total hip arthroplasty and implantation of a pedestal cup due to an intraoperative fracture of the right acetabulum is presented. To ensure early mobilization as well as avoidance of further concomitant morbidities a percutaneous iliosacral screw fixation was performed. This approach has been established as an operative treatment for minimally or non-displaced insufficiency fractures of the sacrum.

Periprothetische und interimplantäre Femurfrakturen@@@Periprosthetic and interimplant femoral fractures: Biomechanische Analyse@@@Biomechanical analysis

ZusammenfassungHintergrundMit steigendem Patientenalter nimmt die Anforderung an die Versorgung von Femurfrakturen zu. Unklar ist, inwieweit die Implantate die femorale Stabilität beeinflussen.MethodeUnterschiedliche Frakturversorgungen nach Implantation eines Hüft- und/oder Kniegelenks wurden biomechanisch an humanen osteoporotischen Femora mit der nativen Situation verglichen.ErgebnisseEine Hüftprothese schwächt das Femur um 33 %. Wird zusätzlich ein retrograder distaler Femurnagel implantiert, sinkt die Bruchlast weiter. Diese instabile Situation kann durch eine winkelstabile Brückenosteosynthese signifikant stabilisiert werden. Die höchste Bruchlast wurde bei implantierter Hüft- und ipsilateraler Knieprothese beobachtet.SchlussfolgerungZusammenfassend lässt sich sagen, dass eine Hüftprothese das Femur signifikant schwächt, wobei zwei einzementierte Prothesen eine stabilere Situation als die eines nativen Femurs erzielen. Die Belastungsstabilität muss bei einliegender Hüftprothese und ipsilateralem Femurnagel in Frage gestellt oder durch eine Brückenosteosynthese gesichert werden. Zur Frakturversorgung einer distalen Femurfraktur bei einliegender Hüftprothese ist die winkelstabile, den Prothesenschaft übergreifende Platte zu favorisieren.AbstractBackgroundThe requirements for treatment of femoral fractures are increasing with the rising age of the patients. The aim of this study was to evaluate femoral stiffness and the fracture risk after inserting different implants and implant combinations.MethodsA total of 48 cadaveric femors were harvested and 8 groups were randomized on the basis of the bone mineral density (BMD). Different osteosyntheses following prosthetic stem implantation (hip and knee prostheses) were performed and compared with native femurs. All specimens were biomechanically tested in a four-point bending until fracture.ResultsThe insertion of a femoral stem decreases the stiffness by approximately 33%. Ipsilateral retrograde nailing reduces the force to failure even more. This instable situation can be stabilized by a lateral locking compression plate. The most stable situation occurred in the presence of two cemented stems.ConclusionTaken together these results clearly indicate that a hip prosthesis significantly weakens the femur, whereas two stems produce the most stable situation at all. The situation of a hip prosthesis and an retrograde nail should be avoided or covered by a bridging-osteosynthesis. In clinical practice an extramedullary fixation technique for distal femoral fractures should be preferred.BACKGROUND The requirements for treatment of femoral fractures are increasing with the rising age of the patients. The aim of this study was to evaluate femoral stiffness and the fracture risk after inserting different implants and implant combinations. METHODS A total of 48 cadaveric femors were harvested and 8 groups were randomized on the basis of the bone mineral density (BMD). Different osteosyntheses following prosthetic stem implantation (hip and knee prostheses) were performed and compared with native femurs. All specimens were biomechanically tested in a four-point bending until fracture. RESULTS The insertion of a femoral stem decreases the stiffness by approximately 33%. Ipsilateral retrograde nailing reduces the force to failure even more. This instable situation can be stabilized by a lateral locking compression plate. The most stable situation occurred in the presence of two cemented stems. CONCLUSION Taken together these results clearly indicate that a hip prosthesis significantly weakens the femur, whereas two stems produce the most stable situation at all. The situation of a hip prosthesis and an retrograde nail should be avoided or covered by a bridging-osteosynthesis. In clinical practice an extramedullary fixation technique for distal femoral fractures should be preferred.