Level III, retrospective comparative series.

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Background: Surgical treatment for metastatic pathological femur fractures is associated with high mortality. Correct estimation of prognosis helps in determining the palliative value of surgical treatment and informs surgical decision. This study evaluates the risk factors for mortality in these patients who were surgically treated. Methods: This is a retrospective study of 112 patients with surgical treatment of metastatic pathological femur fractures. Risk factors evaluated included age, ASA status, Charlson comorbidity index, preoperative serum albumin and haemoglobin, primary tumour site, presence of visceral metastases, presence of spinal metastases, time from diagnosis of cancer to occurrence of pathological fracture, type of surgical procedure performed, lesion and whether treatment was received for an actual or impending fracture. A Cox regression model was used to determine if these factors were independent significant factors for survival. Results: Mortality at 2 years after surgical treatment of metastatic femoral fractures was 86%. Cox regression analysis of risk factors revealed that preoperative serum albumin and type primary tumour were independent risk factors for mortality. Presence of visceral metastases was strongly correlated to serum albumin levels. Conclusion: Preoperative serum albumin level and primary tumour site are independent risk factors of survival in patients treated for pathological femur fractures. Serum albumin level may be used as a prognostic tool to guide treatment in this cohort of patients with high mortality rates.

Introduction: Periprosthetic fractures are a devastating complication following total knee arthroplasty. Little is known about the effect of mechanical factors on the incidence of periprosthetic fractures. The aim of this study was to examine the correlation between pre-operative mechanical factors, like side of surgery, coronal alignment and pre-operative range of motion and intra-operative factors, and the incidence of a periprosthetic fracture, following primary total knee arthroplasty (TKA). Materials and Methods: Forty-two patients with periprosthetic fractures (PPF) after primary TKA were identified from our hospital arthroplasty registry. These patients were matched two-to-one for gender and age at primary knee arthroplasty to 84 patients without PPF. The incidence of periprosthetic fracture with regards to laterality, coronal alignment and pre-operative range of motion was analysed. Intra-operative factors like implant type, patellar resurfacing and notching were also analysed using logistic regression. Results: Coronal alignment, pre-operative range of motion and patella resurfacing were not significant predictors of periprosthetic fractures. Anterior femoral notching was found to be significantly higher in the fracture group with an odds ratio of 17. Left sided surgery was also significantly higher in the periprosthetic fracture group. Conclusion: Periprosthetic fractures are 17 times more likely to occur in a knee with anterior femoral notching. Preoperative factors like coronal alignment and poor preoperative range of motion do not seem to increase the risk of periprosthetic fractures after TKA.

The proximal humerus is the most common site of occurrence of primary bone tumors in the upper limb. Endoprosthetic replacement is deemed as the preferred reconstructive option following primary resection of bone tumors. However, it has been also associated with complications such as stress shielding and aseptic loosening compromising prosthetic survival. Our objective was to conduct a finite element (FE) study to investigate the effect of varying endoprosthesis length on bone stresses as well as to quantify the extent of stress shielding across the bone length (BL) in a humerus‐prosthesis assembly for proximal humeral replacement after tumor excision thereby allowing us to identify the optimal implant length with best biomechanical performance. FE models of the intact humerus and humerus‐prosthesis assemblies were established where they were loaded at the elbow joint under torsion with the glenohumeral joint fixed to represent twisting. After dividing the bone into individual slices consisting of 5% BL, the maximum cortical and cancellous principal, von Mises and shear bone stresses were calculated. To measure the level of stress shielding, the percentage stress change from the intact state was evaluated across each slice. Similar stress patterns were observed between the intact state and shorter endoprosthesis compared to the longer endoprostheses. Our findings illustrated the possibility of stress shielding occurring under torsional forces with its effect increasing with implant lengthening. To conclude, we believe that using a shorter prosthesis may substantially diminish the risk of potential implant failure due to stress shielding.

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To analyse bone stresses in humerus-megaprosthesis construct in response to axial loading under varying implant lengths in proximal humeral replacement following tumour excision.CT scans of 10 cadaveric humeri were processed in 3D Slicer to obtain three-dimensional (3D) models of the cortical and cancellous bone. Megaprostheses of varying body lengths (L) were modelled in FreeCAD to obtain the 3D geometry. Four FE models: group A consisting of intact bone; groups B (L=40mm), C (L=100mm) and D (L=120mm) comprising of humerus-megaprosthesis constructs were created. Isotropic linear elastic behaviour was assigned for all materials. A tensile load of 200N was applied to the elbow joint surface with the glenohumeral joint fixed with fully bonded contact interfaces. Static analysis was performed in Abaqus. The bone was divided at every 5% bone length beginning distally. Statistical analysis was performed on maximum von Mises stresses in cortical and cancellous bone across each slice using one-way ANOVA (0-45% bone length) and paired t-tests (45-70% bone length). To quantify extent of stress shielding, average percentage change in stress from intact bone was also computed.Maximum stress was seen to occur distally and anteriorly above the coronoid fossa. Results indicated statistically significant differences between intact state and shorter megaprostheses relative to longer megaprostheses and proximally between intact and implanted bones. Varying levels of stress shielding were recorded across multiple slices for all megaprosthesis lengths. The degree of stress shielding increased with implant lengthening being 2-4 times in C and D compared to B.Axial loading of the humerus can occur with direct loading on outstretched upper limbs or indirectly through the elbow. Resultant stress shielding effect predicted in longer megaprosthesis models may become clinically relevant in repetitive axial loading during activities of daily living. It is recommended to use shorter megaprosthesis to prevent failure.