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

Extending the intermedullary nail will not reduce the potential risk of femoral head varus in PFNA patients biomechanically: a clinical review and corresponding numerical simulation

Femoral head varus is an important complication in intertrochanteric fracture patients treated with proximal femoral nail anti-rotation (PFNA) fixation. Theoretically, extending the length of the intramedullary nail could optimize fixation stability by lengthening the force arm. However, whether extending the nail length can optimize patient prognosis is unclear. In this study, a review of imaging data from intertrochanteric fracture patients with PFNA fixation was performed, and the length of the intramedullary nail in the femoral trunk and the distance between the lesser trochanter and the distal locking screw were measured. The femoral neck varus status was judged at the 6-month follow-up. The correlation coefficients between nail length and femoral neck varus angle were computed, and linear regression analysis was used to determine whether a change in nail length was an independent risk factor for femoral neck varus. Moreover, the biomechanical effects of different nail lengths on PFNA fixation stability and local stress distribution have also been verified by numerical mechanical simulations. Clinical review revealed that changes in nail length were not significantly correlated with femoral head varus and were also not an independent risk factor for this complication. In addition, only slight biomechanical changes can be observed in the numerical simulation results. Therefore, commonly used intramedullary nails should be able to meet the needs of PFNA-fixed patients, and additional procedures for longer nail insertion may be unnecessary.

Interimplant femoral fracture: analysis of risk factors

Interimplant fractures present a significant challenge for orthopedic surgeons. Despite a noticeable rise in these cases in recent years, our understanding of this specific fracture type remains limited. This study aims to analyze and identify the primary risk factors associated with interimplant femoral fractures. We conducted a retrospective analysis involving 20 patients with interimplant femoral fracture (case group) and 18 patients who had both proximal and distal femoral implants but did not experience interimplant fractures (control group). Our analysis focused on demographic factors (age, sex, BMI) and radiographic parameters (implant types, gap between implants, cortical thickness, femoral canal area) to identify potential risk factors. In the case group, all patients were females, whereas in the control group, 16 patients were female and 2 were males. The mean age in the case group was 88 [Formula: see text] 9 years and in the control group was 87 [Formula: see text] 12 years. None of the demographic differences reached statistical significance. The mean cortical thickness in the case group was 6 [Formula: see text] 2.25 mm, whereas in the control group, it was 9 [Formula: see text] 1.75 mm (p-value < 0.001). The median gap between the proximal and distal tips of the implants measured 194 [Formula: see text] 126 mm in the case group and 66 [Formula: see text] 78 mm in the control group (p-value < 0.001). Additionally, the mean femoral canal area was 284 [Formula: see text] 102 mm2 in the case group and 227 [Formula: see text] 26 mm2 in the control group (p-value < 0.010). Our data indicate that a small cortical thickness, a wide femoral canal area, and having a hip arthroplasty despite a gap between the implants exceeding 110 mm are factors that elevate the risk of interimplant femoral fracture. Notably, osteoporosis therapy emerges as a protective factor against these fractures.

Addressing osteoporosis treatment after hemiarthroplasty for a femoral neck fracture: impact on survival rates after a subsequent periprosthetic femoral fracture - a multicenter (TRON group) retrospective study

This study investigated the impact of osteoporosis treatment on the prognosis of patients with periprosthetic femoral fracture (PPF) following femoral neck fracture (FNF). Our results suggested an association between osteoporosis treatment and potentially improved survival prognosis in patients who underwent surgery for PPF. These results imply that osteoporosis treatment may have a beneficial effect on patient outcomes.

PURPOSE

This study aimed to investigate the effect of osteoporosis treatment on the prognosis of periprosthetic femoral fracture (PPF) patients after femoral neck fracture.

METHODS

A multicenter retrospective study named as TRON was conducted. The study population included 156 PPF patients who had undergone hemiarthroplasty for femoral neck fracture between January 2010 and December 2019. Patients were divided based on whether they had received osteoporosis treatment before PPF injury. A log-rank test was used to compare survival rates. We conducted a Cox proportional hazards analysis to identify factors associated with the survival rate after PFF injury.

RESULTS

Twenty-seven of the 156 patients had received osteoporosis treatment prior to PPF injury. The 1-year and 2-year overall survival rates after PPF were 80.9% and 75.3%, respectively. The log-rank test revealed that the 1-year survival rate with and without osteoporosis treatment was 89.5% and 78.1%, respectively (P=0.012). In the Cox proportional hazards analysis, age, BMI, presence or absence of surgery, and presence or absence of osteoporosis treatment showed independent associations with the survival rate after PFF injury. The hazard ratio for the presence of osteoporosis treatment was 0.22 (95% confidence interval 0.07-0.75, P=0.015).

CONCLUSION

The findings of this study suggest an association between osteoporosis treatment and potentially improved survival prognosis in patients who underwent surgery for PPF. These results imply that osteoporosis treatment may have a beneficial effect on patient outcomes. It is important to consider that osteoporosis treatment could be significant not only in preventing secondary fractures but also in potentially improving prognosis in the rare event of PPF.

Ultrasonic Interferometric Procedure for Quantifying the Bone-Implant Interface

The loosening of an artificial joint is a frequent and critical complication in orthopedics and trauma surgery. Due to a lack of accuracy, conventional diagnostic methods such as projection radiography cannot reliably diagnose loosening in its early stages or detect whether it is associated with the formation of a biofilm at the bone-implant interface. In this work, we present a non-invasive ultrasound-based interferometric measurement procedure for quantifying the thickness of the layer between bone and prosthesis as a correlate to loosening. In principle, it also allows for the material characterization of the interface. A well-known analytical model for the superposition of sound waves reflected in a three-layer system was combined with a new method in data processing to be suitable for medical application at the bone-implant interface. By non-linear fitting of the theoretical prediction of the model to the actual shape of the reflected sound waves in the frequency domain, the thickness of the interlayer can be determined and predictions about its physical properties are possible. With respect to determining the layer's thickness, the presented approach was successfully applied to idealized test systems and a bone-implant system in the range of approx. 200 µm to 2 mm. After further optimization and adaptation, as well as further experimental tests, the procedure offers great potential to significantly improve the diagnosis of prosthesis loosening at an early stage and may also be applicable to detecting the formation of a biofilm.

[Translated article] Comparative clinical and biomechanical study of different types of osteosynthesis in the treatment of distal femur fractures

INTRODUCTION AND OBJECTIVES

Distal femoral fractures represent a problem due to their high number of complications. The aim was to compare the results, complications and stability achieved with retrograde intramedullary nailing and the angular stable plate in the treatment of distal femoral diaphyseal fractures.

MATERIAL AND METHOD

A clinical and experimental biomechanical study was carried out using finite elements. The results of the simulations allowed us to obtain the main results related to the stability of osteosynthesis. For clinical follow-up data, frequencies were used for qualitative variables, and Fisher's exact test and χ2 test were used to evaluate the significance of the different factors, with the condition of P<.05.

RESULTS

In the biomechanical study, the retrograde intramedullar nails demonstrated superiority, obtaining lower values in terms of global displacement, maximum tension, torsion resistance, and bending resistance. In the clinical study, the rate of consolidation of the plates was lower than nails (77% vs. 96%, P=.02). The factor that most influenced the healing of fractures treated with plate were the central cortical thickness (P=.019). The factor that most influenced the healing of nail-treated fractures was the difference between the diameter of the medullary canal and the nail.

CONCLUSIONS

Our biomechanical study shows that both osteosynthesis provide sufficient stability, but biomechanically behaves differently. Nails provide greater overall stability being preferable the use of long nails adjusted to the diameter of the canal. Plates form less rigid osteosynthesis, with little resistance to bending.

Comparative clinical and biomechanical study of different types of osteosynthesis in the treatment of distal femur fractures

INTRODUCTION AND OBJECTIVES

Distal femoral fractures represent a problem due to their high number of complications. The aim was to compare the results, complications and stability achieved with retrograde intramedullary nailing and the angular stable plate in the treatment of distal femoral diaphyseal fractures.

MATERIAL AND METHOD

A clinical and experimental biomechanical study was carried out using finite elements. The results of the simulations allowed us to obtain the main results related to the stability of osteosynthesis. For clinical follow-up data, frequencies were used for qualitative variables, and Fisher's exact test and χ2 test were used to evaluate the significance of the different factors, with the condition of P<.05.

RESULTS

In the biomechanical study, the retrograde intramedullar nails demonstrated superiority, obtaining lower values in terms of global displacement, maximum tension, torsion resistance, and bending resistance. In the clinical study, the rate of consolidation of the plates was lower than nails (77% vs. 96%, P=.02). The factor that most influenced the healing of fractures treated with plate were the central cortical thickness (P=.019). The factor that most influenced the healing of nail-treated fractures was the difference between the diameter of the medullary canal and the nail.

CONCLUSIONS

Our biomechanical study shows that both osteosynthesis provide sufficient stability, but biomechanically behaves differently. Nails provide greater overall stability being preferable the use of long nails adjusted to the diameter of the canal. Plates form less rigid osteosynthesis, with little resistance to bending.

Risk of Interprosthetic Femur Fracture Is Associated with Implant Spacing-A Biomechanical Study

BACKGROUND

Ipsilateral revision surgeries of total hip or knee arthroplasties due to periprosthetic fractures or implant loosening are becoming more frequent in aging populations. Implants in revision arthroplasty usually require long anchoring stems. Depending on the residual distance between two adjacent knee and hip implants, we assume that the risk of interprosthetic fractures increases with a reduction in the interprosthetic distance. The aim of the current study was to investigate the maximum strain within the femoral shaft between two ipsilateral implants tips.

METHODS

A simplified physical model consisting of synthetic bone tubes and metallic implant cylinders was constructed and the surface strains were measured using digital image correlation. The strain distribution on the femoral shaft was analyzed in 3-point- and 4-point-bending scenarios. The physical model was transferred to a finite element model to parametrically investigate the effects of the interprosthetic distance and the cortical thickness on maximum strain. Strain patterns for all parametric combinations were compared to the reference strain pattern of the bone without implants.

RESULTS

The presence of an implant reduced principal strain values but resulted in distinct strain peaks at the locations of the implant tips. A reduced interprosthetic distance and thinner cortices resulted in strain peaks of up to 180% compared to the reference. At low cortical thicknesses, the strain peaks increased exponentially with a decrease in the interprosthetic distance. An increasing cortical thickness reduced the peak strains at the implant tips.

CONCLUSIONS

A minimum interprosthetic distance of 10 mm seems to be crucial to avoid the accumulation of strain peaks caused by ipsilateral implant tips. Interprosthetic fracture management is more important in patients with reduced bone quality.

Fracture Risk Assessment Tool Scores and Radiographical Bone Measurements in Total Hip Arthroplasty Patients

BACKGROUND

Osteoporosis is a major risk factor for periprosthetic fractures (PPFx) in total hip arthroplasty (THA) patients but is not routinely screened for in this population. Given the availability of hip x-rays and preoperative screenings, Fracture Risk Assessment Tool (FRAX) scores and radiographic bone measurements are potentially promising, novel risk stratification tools. This study aims to characterize FRAX scores and radiographic bone measurements in THA and PPFx patients.

METHODS

A retrospective chart review for demographic variables and FRAX scores was performed on 250 THA and 40 PPFx patients. Radiographic bone measurements including cortical thicknesses (both antero-posterior [AP] and lateral), canal to calcar ratio, canal flare index, and Dorr classifications were obtained from preoperative x-rays. Correlation between FRAX scores and radiographic bone measurements was investigated with linear regressions. FRAX scores and radiographic bone measurements were compared between the THA and PPFx patients. Multivariate logistic regressions were used to identify factors predicting PPFx.

RESULTS

FRAX scores were significantly correlated with both AP (P < .001) and lateral (P = .007) cortical thicknesses. Compared to THA patients, those with PPFx had significantly higher FRAX scores (P = .003) and lower AP cortical thickness (P = .005). Multivariate logistic regressions demonstrated that FRAX major osteoporotic fracture risk score and AP cortical thickness were independent predictors of PPFx (P = .001 and .024, respectively).

CONCLUSION

Cortical thicknesses are good proxy measurements of osteoporosis-related fracture risk in THA patients. In addition, both major and AP cortical thickness indices are promising tools for identifying patients who are at a high risk of PPFx in the THA population.

Interprosthetic Femur Fractures: A Review Article

➢

The prevalence of interprosthetic femur fractures (IFFs) is rising with the aging population and increased prevalence of total joint arthroplasty.

➢

IFFs have high rates of complications and high associated morbidity and mortality.

➢

The main treatment methods available for IFFs include plate fixation, intramedullary nailing, combined plate fixation and intramedullary nailing, and revision arthroplasty including partial and total femur replacement.

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There have been several proposed classification systems and at least 1 proposed treatment algorithm for IFFs; however, there is no consensus.

➢

Whichever treatment option is chosen, goals of surgery should include preservation of blood supply, restoration of length, alignment, rotation, and sufficient stabilization to allow for early mobilization.

Interimplant femoral fractures

The number of hip or knee arthroplasties, and internal fixations of the proximal and distal femur, is increasing in proportion to the growing and ageing population, whose life expectancy is lengthening. Thus, fractures of the femur between proximal and distal implants, although rare, are becoming more frequent. Women over the age of 70, with fragile bones and whose ends of the two implants are close to each other ("kissing implants") are particularly vulnerable to them. Reliable and reproducible fracture classifications exist when it comes to 2 prostheses, but they are less well established in the presence of one, or even two, non-prosthetic implants. Their treatment is difficult and must consider the possibility of fracture consolidation while ensuring or restoring the stability and role of the implants. Whether it is the main element of treatment or a complement to prosthesis revision, locked plating forms the basis of the treatment but it must be rigorous, considering that failures are mainly the result of technical errors. Other more invasive treatments (total femoral arthroplasty, cortical sleeves) are offered more rarely if consolidation appears compromised.

Periprosthetic femoral fracture type and location are influenced by the presence of an ipsilateral knee arthroplasty implant: A case-control study of 84 interprosthetic femoral fractures

BACKGROUND

This multicentre case-control study compares Vancouver Classification System (VCS) grade and Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) fracture type in interprosthetic femoral fractures (IPFFs) between primary total hip arthroplasty (THA) and ipsilateral total knee arthroplasty (TKA) to periprosthetic femoral fracture (PFF) without ipsilateral TKA.

METHODS

Data were collected following institutional approval. Eighty-four IPFFs were assessed for VCS grade and AO/OTA type. Each IPFF case (84) was matched to five PFF controls (360) by age, gender and stem fixation philosophy (SMD<0.1). VCS grade and AO/OTA type were compared between the IPFF and PFF groups using weighted proportions and medians.

RESULTS

Median (IQR) age of IPFF patients was 81.75 (76.57-85.33) years and 61 (72.6%) were female. The commonest VCS grade was B1 (34, 40.5%). The commonest AO/OTA type was spiral (51.8% of VCS B fractures; 50.0% of VCS C fractures). A greater proportion of fractures occurred distal to the stem in IPFF patients versus PFF patients (33.3% versus 18.2%, p = 0.003). VCS grade was significantly different between groups (p = 0.015). For VCS C fractures, twice as many AO/OTA transverse and wedge fractures occurred in the IPFF group compared to the PFF group (25.0% versus 12.6% and 7.1% versus 3.3%, respectively) although the overall difference was not statistically significant (p = 0.407).

CONCLUSION

The presence of an ipsilateral TKA affects the location of PFF with more fractures occurring distal to the stem. A greater proportion of bending type fractures occurred when an ipsilateral TKA was present. These unstable fractures often require more complex surgery.

Computational analysis of the effects of interprosthetic distance on normal and reduced cortical thickness femur models

Distal femoral fractures associated with the femoral stem in a well-fixed hip arthroplasty pose a risk of an interprosthetic fracture, the treatment of which is known as difficult. To effectively prevent and treat IP fractures, biomechanical effects must be demonstrated. We defined eight variations of the interprosthetic distance ranging from 48 mm overlap to 128 mm gap. Femoral geometries with normal and reduced cortical thickness were modeled to evaluate the effects of cortical thickness. In addition to the intact model, a total of 16 finite element models were analyzed under physiological boundary conditions. Maximum and minimum principal strains on the lateral and medial cortex surfaces were always found to be greater in models with reduced cortical thickness than in normal femurs. The model with 48 mm overlapping interprosthetic distance produced the least peak strain and the model with 16 mm interprosthetic gap produced the greatest strain with both normal and reduced cortical thickness. The screw holes produced local strain concentrations and increased the peak strains on the cortex surfaces, especially close to the stem tip. Statistically, a significant correlation (R² = 0.9483) was found between strain shielding and interprosthetic distance. Axial stiffness, interfragmentary shear motion, and maximum von-Mises stress on the distal plate showed a high correlation with the interprosthetic distance. It was concluded that the overlapping structures are superior to other fixations we analyzed in that they offer better mechanical stability and eliminates the local strain concentrations.

Outcomes of operatively treated interprosthetic femoral fractures

AIMS

The prevalence of ipsilateral total hip arthroplasty (THA) and total knee arthroplasty (TKA) is rising in concert with life expectancy, putting more patients at risk for interprosthetic femur fractures (IPFFs). Our study aimed to assess treatment methodologies, implant survivorship, and IPFF clinical outcomes.

METHODS

A total of 76 patients treated for an IPFF from February 1985 to April 2018 were reviewed. Prior to fracture, at the hip/knee sites respectively, 46 femora had primary/primary, 21 had revision/primary, three had primary/revision, and six had revision/revision components. Mean age and BMI were 74 years (33 to 99) and 30 kg/m² (21 to 46), respectively. Mean follow-up after fracture treatment was seven years (2 to 24).

RESULTS

Overall, 59 fractures were classified as Vancouver C (Unified Classification System (UCS) D), 17 were Vancouver B (UCS B). In total, 57 patients (75%) were treated with open reduction and internal fixation (ORIF); three developed nonunion, three developed periprosthetic joint infection, and two developed aseptic loosening. In all, 18 patients (24%) underwent revision arthroplasty including 13 revision THAs, four distal femoral arthroplasties (DFAs), and one revision TKA: of these, one patient developed aseptic loosening and two developed nonunion. Survivorship free from any reoperation was 82% (95% confidence interval (CI) 66.9% to 90.6%) and 77% (95% CI 49.4% to 90.7%) in the ORIF and revision groups at two years, respectively. ORIF patients who went on to union tended to have stemmed knee components and greater mean interprosthetic distance (IPD = 189 mm (SD 73.6) vs 163 mm (SD 36.7); p = 0.546) than nonunited fractures. Patients who went on to nonunion in the revision arthroplasty group had higher medullary diameter: cortical width ratio (2.5 (SD 1.7) vs 1.3 (SD 0.3); p = 0.008) and lower IPD (36 mm (SD 30.6) vs 214 mm (SD 32.1); p < 0.001). At latest follow-up, 95% of patients (n = 72) were ambulatory.

CONCLUSION

Interprosthetic femur fractures are technically and biologically challenging cases. Individualized approaches to internal fixation versus revision arthroplasty led to an 81% (95% CI 68.3% to 88.6%) survivorship free from reoperation at two years with 95% of patients ambulatory. Continued improvements in management are warranted. Cite this article: Bone Joint J 2021;103-B(7 Supple B):122-128.

A pilot agreement study of a new classification system for Peri-implant femoral fractures

BACKGROUND

Peri-implant fractures occur in association with an implant, used to treat a previous injury that is still attached to the bone. We recently published a proposal for a classification system for peri-implant femoral fractures [Videla-Cés, Injury,2019].

AIM

To assess the agreement of our classification system for peri-implant femoral fractures among a group of future users of said classification system.

METHODS

A prospective, multicentre, international agreement pilot study was conducted among a group of independent traumatologists/orthopaedic surgeons (evaluators): senior (a minimum of 10 years' experience) and junior (in fourth or fifth training year). A set of 30 radiographs of peri-implant femoral fractures were selected (stratified into 3 levels of difficulty: low, medium and high). Each evaluator interpreted the radiographs on 2 different occasions separated by a period of one month and in a different order each time. The level of difficulty was masked from the evaluators and they had one week to classify the radiographs each time. Logistic regression and Cohen's kappa coefficient (κ) and its 95% confidence interval (95%CI) were used to assess the accuracy and agreement, both intra- and inter-evaluator. Between senior and junior surgeons was performed an exploratory analysis.

RESULTS

35 traumatologists/orthopaedic surgeons (17 senior and 18 junior) from 16 tertiary hospitals from 4 countries acted as evaluators. The accuracy, percentage of correct classifications (2 digits and 3 letters), in the first and second evaluation was: 56% (95%CI: 53-59%) and 55% (95%CI: 51-57%), respectively. (insert space) Negligible differences were found between junior and senior evaluators (first evaluation, OR: 1.46, 95%CI: 0.82-2.61, p-value: 0.199; second evaluation, OR: 1.06, 95%CI: 0.56-2.00, p-value: 0.860). (insert space) Both medium and low radiograph difficulty were associated with a lower probability of an incorrect classification compared with those of high difficulty (first evaluation, OR: 7.60, 95%CI: 5.24-11.05, p-value: <0.001; OR: 14.15, 95%CI: 9.12-21.96, p-value: <0.001, respectively; second evaluation, OR: 7.11, 95%CI: 4.88-10.38, p-value: <0.001, OR: 15.28, 95%CI: 9.77-23.89, p-value: <0.001). (insert space) The kappa for intra-observer agreement between the first and second evaluation was: 0.66, 95%CI: 0.63, 0.69. The kappa for inter-observer agreement considering all 30 radiographs was: 0.40, 95%CI: 0.40, 0.41 in the first evaluation and 0.39, 95%CI: 0.39, 0.40 in the second evaluation.

CONCLUSION

The proposed classification for peri-implant femoral fractures may be useful and user-friendly. Future studies are needed to assess the how clinically useful this classification system may be (the third phase in the validation process).

Research Update on Stress Riser Fractures

Stress fractures are fatigue-induced fractures which are caused by repetitive force, often from overuse. They are well-established and frequently encountered in the field of orthopedics. Stress fractures occur in the bone because of low-bone strength and high chronic mechanical stress placed on the bone. Stress riser fractures are also stress fractures that occur because of the presence of cortical defects (holes), changes in stiffness, sharp corners, and cracks (fracture lines). Periprosthetic or peri-implant fractures are good examples of stress riser fractures that occur in regions where stress forces are higher than those in the surrounding material. Most stress riser fractures are related to technical errors (iatrogenic causes) and are difficult to manage. It is possible and more effective to prevent the creation of stress riser fractures through better surgical techniques. The proper terminology for stress fractures, stress riser fractures, periprosthetic fractures, peri-implant fractures, interprosthetic fractures, and interimplant fractures is discussed. This review of the current state of knowledge, diagnosis, treatment, and prevention of stress riser fractures is based on clinical evidence and recent literature.

Comparative Biomechanical In Vitro Study of Different Modular Total Knee Arthroplasty Revision Stems With Bone Defects

BACKGROUND

The aim of this study is to investigate the effects of different stem lengths and types including cones on primary stability in revision total knee arthroplasty with different femoral bone defects and fixation methods in order to maximize bone preservation. It is hypothesized that longer stems provide little additional mechanical stability.

METHODS

Thirty-five human femurs were investigated. A distal bone defect, Anderson Orthopedic Research Institute classification (s. 33) type-F2a, was created in group 1-3 and type-F3 in group 4-6. A cemented, rotating hinge femoral component was combined with different stems (100 and 160 mm total or hybrid cemented cones, or a 100-mm custom-made anatomical cone stem). The femora were loaded according to in vivo loading during gait. Relative movements were measured to investigate primary stability. Pull-out testing was used to obtain a parameter for the primary stability of the construct.

RESULTS

Relative movements were small and similar in all groups (<40 μm). For small defect, the pull-out forces of cemented long (4583 N) and short stems (4650 N) were similar and about twice as high as those of uncemented stems (2221 N). For large defects, short cemented stems with cones showed the highest pull-out forces (5500 N). Long uncemented stems (3324 N) and anatomical cone stems (3990 N) showed similar pull-out forces.

CONCLUSION

All tested stems showed small relative movements. Long cemented stems show no advantages to short cemented stems in small bone defects. The use of cones or an anatomical cone stem with hybrid cementation seems to offer good stability even for larger bone defects. The use of a short cemented stem (with or without cone) may be a suitable choice with a high potential for bone preservation in total knee arthroplasty revision with respective bone defects.

[Periprosthetic fractures: basics, classification and treatment principles]

Periprosthetic fractures (PPFx) are becoming an increasingly important topic in orthopedics and trauma surgery due to the rising number of endoprosthetic joint replacements. The recently published unified classification system (UCS) has replaced numerous historical classification systems and can be applied to all PPFx regardless of the bone or joint involved. The treatment of PPFx requires individual therapeutic concepts taking patient-dependent and patient-independent factors into consideration. The conservative treatment of PPFx is only justified in exceptional situations. In contrast, the choice between operative treatment and deciding between osteosynthesis or revision arthroplasty is particularly based on the assessment of the implant stability. In order to achieve fracture consolidation and also a good functional outcome, knowledge of the basic biomechanical principles of operative (osteosynthesis or endoprosthesis) treatment of periprosthetic fractures is necessary.

Management of periprosthetic fractures of knee arthroplasty with revision surgery

Objective

As periprosthetic knee fractures are becoming common with the increase in incidence of primary and revision total knee arthroplasty, their management and treatment have become important. The current study aims to evaluate the revision knee arthroplasty carried out due to the failure of primary treatment of periprosthetic femoral fractures.

Methods

The study was conducted from May 2012 to September 2019 at Orthopedics department of Xinjiang Medical University; out of 21 patients 11 were women and 10 men aged 44 to 80 (mean, 70.76 ± 8.31) years who underwent revision surgery for periprosthetic fractures of 19 distal femur, 1 patellar, and 1 proximal tibial fracture. Nineteen cases had definite trauma history leading to periprosthetic fracture, and 2 cases had fracture during post-operative functional exercise. All patients had revision surgery with extended stems with either constrained or limited condylar knee prosthesis.

Results

The duration of follow-up averaged 4.3 years. The Hospital for Special Surgery (HSS) knee score before fracture averaged 91 + 7.01 points (89-95 points) and 85.5 + 6.18 points (81-90 points) at the last follow-up. The average range of motion of knee joint before fracture was 115.7 [+7.6] (110 [~126]), and 101.3 [+9.8] (85 [~115]) at the last follow-up. There was no significant statistical difference. No complications such as infection, component loosening or nonunion. 2 patients had lower extremity vein thrombosis.

Conclusion

Revision surgery of the knee for the periprosthetic fractures with proper prosthetic selection can attain good outcomes after primary total knee arthroplasty. Reasonable and correct procedure is the main principle for a successful operation. The benefits and applicability of revision TKA is the reconstructive solution for the issues of prosthetic knee fractures, is highly recommended.

Lower reoperation rate with locking plates compared with conventional plates in Vancouver type C periprosthetic femoral fractures: A register study of 639 cases in Sweden

AIM

To investigate demographics and outcomes of Vancouver type C periprosthetic femoral fractures (PPFF) treated with open reduction and internal fixation.

METHODS

Patient data were obtained from medical charts of cases reported to the Swedish Hip Arthroplasty Register and/or from the National Patient Register. Vancouver type C fractures undergoing surgery between 2001 and 2011, in patients who had received their primary THR between 1979 and 2011, were included. Any further reoperation performed between 2001 and 2013 and related to the PPFF constituted the primary outcome.

RESULTS

A total of 632 patients with 639 Vancouver type C fractures were identified. The majority of the patients were women (84%) and they had a fracture distal to a cemented stem (95%). The mean age at the time of fracture was 72 years. Treatment was performed with a locking plate (363 cases), a conventional plate (184 cases), an intramedullary nail (62 cases), or with double plating (30 cases). The overall reoperation rate was 17%, and mortality within one year of the operation was 16%. Locking plates had a significantly lower reoperation rate than conventional plates (p<0.001) and intramedullary nailing (p = 0.005). Interprosthetic femoral fractures did not have a statistically different outcome compared with non-IPFFs.

CONCLUSIONS

The lowest reoperation rate was observed using locking plates in Vancouver type C fractures when compared with conventional plates or intramedullary nailing. The presence of an ipsilateral knee prosthesis did not influence the outcome of the surgical treatment.

Inter-implant fractures: an unmet medical need-a preventive approach proposal

Inter-implant fractures are associated with reduced quality of life and increased 1-year mortality. For that reason, we propose, instead of treating, a novel, preventative surgical approach that involves splinting the inter-implant femoral shaft interval. In patients with a previous femoral implant in whom a second surgery for new material implantation was necessary (including knee or hip arthroplasty, plate or femoral nailing), an overlapping technique using the minimally invasive plate osteosynthesis technique was performed during the second surgery. Nine patients were included, all females with median (range) age of 78 (55-88) years. No surgery-related complications or mortality occurred. Two patients suffered fractures from a casual fall postoperatively with no implant failure or hospital admission required. In conclusion, instead of treating such fractures after they occur, we propose an effective, safe and reproducible preventative surgical approach, not previously reported, which involves internal femoral splinting, a plate and the minimally invasive plate osteosynthesis technique.

Interprosthetic femoral fractures: Morbidity and mortality in a retrospective, multicenter study

INTRODUCTION

Interprosthetic femoral fractures (IFF) are becoming more frequent; however they have not been the subject of many publications and the largest study on this topic includes only 30 cases. The complication rate and clinical outcomes have only been evaluated in small case series. This led us to conduct a retrospective, multicenter, observational study in IFF patients with at least 12 months' follow-up to (1) determine the mortality and morbidity (2) determine the clinical and radiological outcomes and (3) identify elements of the treatment indications.

HYPOTHESIS

The morbidity and mortality rates will be comparable to those in recent studies on this topic.

MATERIALS AND METHODS

The study included 51 patients (49 women, 2 men) with a mean age of 82.8±9.2 years [55-97], a mean Parker score of 4.9±2.4 and a mean Katz score of 4.4±1.4 who had suffered an IFF between 2009 and 2015. According to the SoFCOT modifications of the Vancouver classification, 30 fractures were interprosthetic in the shaft segment where there were no implants (19 double C and 11 type D (corresponding to a type C with less than two diaphysis widths between the extension stems of the hip and knee implants)) while 21 were periprosthetic, with 12 around the THA (11 B1 and 1 B3) and 9 around the TKA (8 B1 and 1 B3). One patient was treated conservatively with an external fixator but died the next day, 2 patients received a new total hip arthroplasty and 47 underwent plate fixation of their fracture (one patient was treated non-operatively because of poor medical condition).

RESULTS

One patient was lost to follow-up, and nine died during the first 6 months. Six early surgical site complications occurred and 13 general ones. Within 1 year of the IFF, there were six mechanical complications, two surgical site infections and two cases of loosening. The mean follow-up was 27.6±17.2 months. The mean time to union was 19.25±8.8 weeks. The mean final Parker score was 3.37±2.6 and the mean Katz score was 2.98±1.8; both were significantly lower than the initial scores. Six patients died between months 12 and 50. The overall mortality at the final review was 31% (16/51) with a median survival of 3.45 years.

DISCUSSION

Our hypothesis was not confirmed because the mortality and morbidity in our study were higher than in other published studies. In the six relevant studies identified, the surgical site infection rate was 12.3%, the major revision rate was 11.6% and the mortality rate was 6.5%. In our study, these values were 24%, 24% and 31%, respectively. These worse results may be explained by the very fragile nature of the studied population and the surgeons not following appropriate technical rules for fracture fixation.

LEVEL OF EVIDENCE

IV, Retrospective study.

Mechanical analysis of femoral stress-riser fractures

BACKGROUND

A stress-riser fracture develops when stress in an object is higher than that in the surrounding material. The aim of this retrospective study was to evaluate all consecutive femoral stress-riser fractures during a period of >10 years and to verify high-risk factors by using mechanical analysis.

METHODS

Forty clinical fractures caused by local stress concentration in the femoral cortical bone were included. Risk factors were analyzed, and Sawbones models were used to verify their effect. One hundred thirty-six models were divided into 6 groups to simulate clinical cases of stress-riser fractures. A dynamic test instrument was used to simulate weight-bearing on the femoral head by continuous application of increasing axial force; the lever arm was applied at a constant speed of 0.1 mm/s until a fracture developed.

RESULTS

Female gender (57.5%), subtrochanteric area (40%), osteoporosis (40%), and technical or surgical errors (50%) were risk factors for stress-riser fractures in clinical analysis. Cortical perforation, tiny cracks, sharp corners, and changes in hardness were the main risk factors in biomechanical aspects. Mechanical analysis identified that these factors contributed to stress-riser fractures (P = 0.000), especially cortical perforations and sharp corners.

CONCLUSION

A cortical perforation (screw hole), tiny crack (fracture line), sharp corner (bone cut), and change in hardness (tip of an implant or cement) can act as a stress riser. Screw holes are the most common and critical contributor to femoral stress-riser fractures.

Proposal for the classification of peri-implant femoral fractures: Retrospective cohort study

Background Peri-implant fractures occur in association with an implant used to treat a previous injury and that is still attached to the bone. Peri-implant fractures are considered to be relatively "new" fractures and they lack any classification system that is accepted in practice. Generally, the fracture classification systems currently used in our clinical practice were not developed or validated using rigorous scientific evaluation methods. Aim To provide data for a proposed classification of peri-implant femoral fractures. Methods This is an international and multicentre study (12 centres) based on a cohort of consecutive peri-implant fractures with the criterion being: a fracture in any segment of the femur in association with previously-used osteosynthesis material, whether a nail, plate or screws. A proposed system for the classification was tested, based on a topographical classification using alphanumeric coding, following a similar nomenclature to that explained in the "Vancouver-Classification-for-Total-Hip-Arthroplasty-Periprosthetic-Fractures", and classified according to whether the implant is a nail, a screw or a plate, and the location of the fracture in relation to the original implant and the affected femoral segment. The study coordinator performed the first classification exercise, which was discussed subsequently for the study coordinator group to reach a consensus. A descriptive analysis of the fractures was produced. The proportion of peri-implant femoral fractures was estimated, and 95% confidence interval (95%CI) was calculated. Results Between January 2013 and December 2016, data on a total of 143 peri-implant femoral fractures were collected. Only 5 (3.5%) fractures had to be discussed to reach a consensus. The most common peri-implant femoral fractures were located at the diaphyseal segment (#32) and associated with nails or plates: 51%, 73/143, 95%CI:43-59%; at the proximal segment (#31): 39%, 56/143, 95%CI:32-47%; and at the distal femoral segment (#33): 10%, 14/143, 95%CI:6-16%. The highest proportion of peri-implant femoral fractures corresponded to #31-AN (trochanteric and neck area) and #32-CNP (diaphysis fractures distant from the implant, often distal and spiral). Conclusion The proposed classification for peri-implant femoral fractures appears to be useful and easy to accomplish. Future studies will be necessary to validate it and demonstrate the effectiveness of its application in clinical practice.

Stable Fixation and Immediate Weight-Bearing After Combined Retrograde Intramedullary Nailing and Open Reduction Internal Fixation of Noncomminuted Distal Interprosthetic Femur Fractures

With an aging population, treatment of interprosthetic femur fractures continues to pose a challenge to the orthopaedic surgeon. Retrograde intramedullary nailing combined with open reduction internal fixation using a tissue-preserving plating technique was used in our series of 9 patients with noncomminuted, distal femur fractures. No interfragmentary screws, cables, cerclage wires, or supplemental bone grafts of any type were used. Each patient initiated weight-bearing as tolerated after operative intervention. Every fracture healed at an average of 20 weeks (range 18-24 weeks). Use of a lateral locking plate combined with a retrograde intramedullary nailing enables immediate postoperative weight-bearing and stable fixation for patients with interprosthetic femur fractures.

Interprosthetic Fractures of the Femur

As the rate of hip and knee arthroplasty procedures increases, so will the rate of interprosthetic fractures. Several factors, including bone quality, bone quantity, and stability of the prosthetic components, play a role in determining the appropriate operative treatment. Patients with stable components should undergo reduction and internal fixation, while patients with loose components should undergo either revision arthroplasty, with or without additional fixation, or conversion to total femur replacement. Despite implant and technique advances, complications remain frequent. [Orthopedics. 2018; 41(1):e1-e7.].

Revision Total Knee Arthroplasty for the Management of Periprosthetic Fractures

Periprosthetic fractures after total knee arthroplasty (TKA) can present reconstructive challenges. Not only is the procedure technically complex, but patients with these fractures may have multiple comorbidities, making them prone to postoperative complications. Early mobilization is particularly beneficial in patients with multiple comorbidities. Certain patient factors and fracture types may make revision TKA the ideal management option. Periprosthetic fractures around the knee implant occur most frequently in the distal femur, followed by the tibia and the patella. Risk factors typically are grouped into patient factors (eg, osteoporosis, obesity) and surgical factors (eg, anterior notching, implant malposition). Surgical options for periprosthetic fractures that involve the distal femur or proximal tibia include reconstruction of the bone stock with augments or metal cones or replacement with an endoprosthesis.

Plate Positioning in Periprosthetic or Interprosthetic Femur Fractures With Stable Implants-A Biomechanical Study

BACKGROUND

Angular stable plate fixation is a widely accepted treatment option for interprosthetic or periprosthetic femoral fractures with stable implants. This biomechanical study tries to establish a safe distance of the plate from the tip of a femoral prosthesis.

METHODS

A total of 38 composite femurs were reamed to an inner diameter of 23 mm to create an osteoporotic bone model. A Weber hip stem was cemented into each and a distal femoral NCB plate applied with the distance to the stem varying from 8 cm apart to 6 cm overlap in 2-cm steps. Each specimen was tested in cyclic axial loading (400 N-1500 N) and then cyclic torsion (0.6 Nm-50 Nm). Peak strain on the femur around the tip of the plate was measured with a 3D image correlation system and averaged over 26 cycles (excluding the first 3 and the last cycles). Finally, each femur was axially loaded to failure.

RESULTS

Strain increased with decreasing overlap or gap. Seven specimens failed early between 2-cm overlap and 2-cm gap. Results were divided into a far group with a distance of >4 cm and a close group of <4 cm. Strain was significantly higher in the close group for axial (P < .001) and torsional (P < .001) loading. Failure load was significantly lower in the close group (P = .002).

CONCLUSION

A minimal gap and/or overlap of at least 6 cm is recommended in osteoporotic bone to avoid stress risers.

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.

Periprosthetic fracture fixation in osteoporotic bone

Fixation techniques of periprosthetic fractures are far from ideal although the number of this entity is rising. The presence of an intramedullary implant generates its own fracture characteristics since stiffness is altered along the bone shaft and certain implant combinations affect load resistance of the bone. Influencing factors are cement fixation of the implant, intramedullary locking and extramedullary or intramedullary localization of the implant and the cortical thickness of the surrounding bone. Cerclage wires are ideally suited to fix radially displaced fragments around an intramedullary implant but they are susceptible to axial and torsional load. Screws should be added if these forces have to be neutralized. Stability of the screw fixation itself can be enhanced by embracement configuration around the intramedullary implant. Poor bone stock quality, often being present in metaphyseal areas limits screw fixation. Cement augmentation is an attractive option in this field to enhance screw purchase.

[Ipsilateral THA after stemmed TKA: Risk of interprosthetic fracture?]

BACKGROUND

There is an increasing number of patients who have undergone stemmed total knee arthroplasty and total hip arthroplasty in the same leg. These patients may be at increased risk of periprosthetic and interprostethic fracture. Etiology and the potential therapy strategies are not well represented in the current literature.

OBJECTIVES

Determination of the risk factors for interprosthetic fractures and possible prevention.

MATERIALS AND METHODS

We performed a review of the literature and additionally a survey among experts (members of the German Association for Arthroplasty [AE]) to investigate the risk and the necessity for a preventive internal fixation.

RESULTS

There are only a few biomechanical studies. The interprosthetic distance seems to have little influence on the fracture risk, but the thickness of the cortex and the cortical area at the diaphysis seems to be important. The value of a bridging osteosynthesis remains uncertain. Ninety experts took part in the survey. The risk of fracture risk was estimated to be only slight to medium. Opinions regarding the necessity of preventive internal fixation were heterogeneous.

CONCLUSIONS

The indication for preventive internal fixation could be derived neither from the literature nor from the survey of experts. The thickness of the cortex and co-morbidities (osteoporosis, tendency to fall, and medication) seem to be more important than the interprosthetic distance.