How metal augments, polyethylene thickness and stem length affect tibial baseplate load transfer in revision total knee arthroplasty.

BACKGROUND: It is unclear howmetal augments,polyethylene (PE) liner thickness, and length of cemented stemcontribute to load transferwhen reconstructing uncontained tibial metaphyseal bone loss of Anderson Orthopedic Research Institute (AORI) Type II defects during revision total knee arthroplasty (rTKA).The aimof this study is to understand the impact of these three variableson load transfer through the tibial baseplate. For a fixed defect depth, we hypothesized that there is a particular combination of liner and augment thickness and stem length that minimizes bone stress, reducing the risk of aseptic loosening. METHODS: We conducted a finite element analysis (FEA) to model stresses at the bone-cement interface with different iterations of metal augments, PE liner thicknesses andfully-cemented stems lengths. RESULTS: For a 20 mm tibial defect, constructs with thicker metal augments and thinner polyethylene liners were superior. Constructswith a fully cemented stem further reduced bone stress on the tibial plateau. Bone stress was lowest when a 100 mm fully-cemented stem was used, while stems between 30 mm - 80 mm produced similar results. CONCLUSIONS: When addressing a tibial bone defect of AORI Type II in rTKA, our FEA model demonstrates that surgeons should opt to use the thickest metal augments in combination with afully-cemented stem with an added length of at least 30 mm, which allows for surgical flexibility together with the most stable construct.Our study is notably limited by lack of modeling of knee joint moments, which are important when considering micromotion, bone-implant interface and stem effectiveness.

Finite Element Evaluation of the Femoral Neck System as Prophylactic Fixation to Prevent Contralateral Hip Fractures.

Introduction: Hip fractures cause significant morbidity and mortality for geriatric patients, and incidence is increasing as the population ages. Following a primary hip fracture, up to 20% may suffer a contralateral hip fracture within 5 years despite fracture risk reduction measures, including fall prevention and osteoporosis pharmacologic treatment. The aim of this study is to assess whether insertion of the Femoral Neck System (Depuy Synthes, West Chester, PA) into the contralateral proximal femur may strengthen the bone and decrease the incidence of contralateral hip fractures. Materials and Methods: ScanIP, an image processing software was used to produce 3-dimensional models of a cadaver femur with the implanted device. Models were meshed and exported to Abaqus for finite element analysis to evaluate the device's ability to reduce stress in the proximal femur. Results were analyzed for element-wise volume and von-Mises stresses. Results: The implant reduced peak stress and bone failure at all levels of bone quality. Specifically in osteoporotic bone, the implant decreased peak stress by 27%, proximal femur trabecular bone failure by 5% and cortical bone failure by 100% in the femoral neck. Conclusions: Our results from computer generated finite element analyses indicate that the Femoral Neck System may strengthen an osteoporotic proximal femur in the event of a lateral fall. Further investigation with expanded finite element analysis and cadaveric biomechanical studies are needed to validate these results.

An open-access plug-in program for 3D modelling distinct material properties of cortical and trabecular bone.

BACKGROUND: Finite element modelling the material behavior of bone in-silico is a powerful tool to predict the best suited surgical treatment for individual patients. RESULTS: We demonstrate the development and use of a pre-processing plug-in program with a 3D modelling image processing software suite (Synopsys Simpleware, ScanIP) to assist with identifying, isolating, and defining cortical and trabecular bone material properties from patient specific computed tomography scans. The workflow starts by calibrating grayscale values of each constituent element with a phantom - a standardized object with defined densities. Using an established power law equation, we convert the apparent density value per voxel to a Young's Modulus. The resulting "calibrated" scan can be used for modeling and in-silico experimentation with Finite Element Analysis. CONCLUSIONS: This process allows for the creation of realistic and personalized simulations to inform a surgeon's decision-making. We have made this plug-in program open and accessible as a supplemental file.

Atypical knee pain.

The patient found it hard to climb stairs-and to complete a particular task when getting dressed. Difficulty with that task provided a useful diagnostic clue.

Biomechanical restoration of metastatic cancer-induced peri-acetabular bone defects by ablation-osteoplasty-reinforcement-internal fixation technique (AORIF): To screw or not to screw?

BACKGROUND: Minimally invasive percutaneous polymethyl methacrylate cement augmentation procedures offer numerous clinical advantages for patients with periacetabular osteolytic metastatic bone defects in contrast to open reconstructive procedures that are associated with many complications. Several techniques, such as Ablation-Osteoplasty-Reinforcement-Internal Fixation (AORIF), cementoplasty alone, and screw fixation alone are currently used. There is no consensus on optimal skeletal reinforcement of diseased bones. The purpose of this study was to determine the most effective technique of percutaneous acetabular augmentation for joint preservation, with respect to resilience on cyclic loading and fracture pattern at maximal load to failure. METHODS: Five cohorts of hemipelvis composite bones with uniform periacetabular defects and various types of reinforcement techniques were utilized to simulate osteolytic metastasis in the weight bearing dome of the acetabulum. Five groups of hemipelves underwent finite element analysis and biomechanical testing for load to failure, energy absorption to failure, stress relaxation on cyclic loading, and fracture locations. RESULTS: The combination of screws and bone cement augmentation demonstrated significant higher energy absorption than the cement or screw only groups (p < 0.05), and better protection of acetabulum from displaced intraarticular fractures than the screws alone oror cement only groups (p < 0.05). Resilience to cyclic loading was higheest in the screw with cement fixation group than the screw only repair (p < 0.01), though not the cement fixation only group. INTERPRETATION: These data support the hypothesis that cementoplasty combined with screw augmentation such as the AORIF technique provides the best protection of acetabulum from massive metastatic cancer-induced acetabular fractures compared to augmentation with screws or cement alone.

Finite Element Analysis of Cannulated Screws as Prophylactic Intervention of Hip Fractures.

INTRODUCTION: The frequency of hip fractures, a major cause of morbidity and mortality for geriatric patients, is expected to increase exponentially in the next few decades. The aim of this study is to assess the ability of stainless-steel cannulated screws to reduce the risk of a femoral neck fracture, if placed prophylactically prior to a fall. MATERIALS AND METHODS: We created finite element models from computed tomography (CT) scan-based 3D models of a geriatric patient through 3D-image processing and model generation software. We used linear finite element simulations to analyze the effect of cannulated screws in the proximal femur in single-leg stance and lateral fall, which were processed for peak von Mises stresses and element failure. FINDINGS: Prophylactically placed cannulated screws significantly reduced failure in an osteoporotic proximal femur undergoing lateral fall. Three implanted screws in an inverted triangle formation decreased proximal femoral trabecular failure by 21% and cortical failure by 5%. This reduction in failure was achieved with a 55% decrease in femoral neck failure and 14% in lateral cortex failure. CONCLUSION: Our results indicate that cannulated hip screws in an inverted triangle formation may strengthen an osteoporotic proximal femur in the event of a lateral fall. Mechanical testing on cadaveric or composite models is required to validate these results.

Effect of General Anesthesia on Preoperative Hip Range of Motion in Patients Undergoing Hip Arthroscopy.

The purpose of this study was to investigate the effect of general anesthesia on preoperative passive hip range of motion (ROM) in patients undergoing hip arthroscopy for various indications. A total of 260 consecutive patients undergoing hip arthroscopy were included in this study. Passive hip ROM was evaluated bilaterally in the clinic and subsequently under general anesthesia immediately preoperatively. Demographic variables, including age, height, weight, and clinical diagnosis, were recorded for all patients. Hips with pincer-type femoroacetabular impingement (FAI) and hips with acetabular dysplasia showed a mean increase of 4° and 6°, respectively, in hip external rotation at 90° of hip flexion (ER-90) with induction of anesthesia (P=.018 and P=.021, respectively). In contrast, a statistically significant reduction in hip abduction (2°) and hip flexion (4°) was observed following induction of anesthesia in healthy contralateral hips of patients presenting with unilateral hip pathology (P=.01 and P<.001, respectively). Hip ROM does not change to a clinically significant extent with induction of general anesthesia. Small increases in external rotation in patients with FAI or acetabular dysplasia are within the standard error for ROM measurements. [Orthopedics. 2016; 39(6):e1165-e1169.].

Sacroiliac Joint Treatment Personalized to Individual Patient Anatomy Using 3-Dimensional Navigation.

During the past 10 years, the sacroiliac (SI) joint has evolved from being barely recognized as a source of pain, to being a joint treated only nonsurgically or with great surgical morbidity, to currently being a joint treated with minimally invasive techniques that are personalized to the individual patient. The complex 3-dimensional anatomy of the SI joint and lack of parallel to traditional imaging planes requires a thorough understanding of the structures within and around the SI joint that may be at risk of injury. Thus, the SI joint is ideally suited for intraoperative 3-dimensional imaging and surgical navigation when being treated minimally invasively.

Patient-Controlled Transdermal Fentanyl Versus Intravenous Morphine Pump After Spine Surgery.

Patient-controlled analgesia (PCA) is regularly used to manage pain following major surgery. The fentanyl hydrochloride iontophoretic transdermal system (ITS) was developed to overcome some of the limitations of intravenous (IV) PCA. The small, self-adhesive, needle-free disposable system is applied to the skin on the upper arm or chest and is controlled by patients clicking a button on the device. The authors identified patients who were underwent spinal surgery from 2 prior multicenter, randomized studies and analyzed their data. Of the 1296 patients in the original trials, 170 underwent spine surgery procedures: 90 were randomized to the fentanyl ITS (40 mcg/activation) and 80 to IV PCA morphine (1 mg/dose). More patients treated with the fentanyl ITS rated their method of pain control as "excellent" across all time points, but differences did not reach statistical significance. However, investigators' ratings of "excellent" satisfaction with study treatment were significantly higher for the fentanyl ITS. Discontinuation rates and overall adverse event rates were similar between groups. The only significant difference was that patients treated with the fentanyl ITS had a higher rate of application site reactions than infusion site reactions in the IV PCA morphine group; the reactions were typically mild-to-moderate erythema that resolved shortly after removal of the fentanyl ITS device and did not require further treatment. Ratings of satisfaction with pain control method were consistently higher for the fentanyl ITS than the IV PCA morphine. The 2 groups had a similar safety profile. These results suggest that the fentanyl ITS appears to be a safe, efficacious alternative to IV PCA in spine surgery patients.

Measurement of lateral acetabular coverage: a comparison between CT and plain radiography.

UNLABELLED: We prospectively evaluated the degree of absolute agreement between measurements of lateral center-edge angle (LCEA) on plain radiography (XR) and computed tomography (CT) in a consecutive cohort of 205 patients (410 hips) undergoing hip arthroscopy. Preoperative measurements of the LCEA were performed bilaterally utilizing standardized anteroposterior radiographs and coronal reformatted CT scans. Demographic variables including age, gender, height, weight, BMI and clinical diagnosis were recorded for all patients. Overall, measured values of the LCEA were 2.1° larger on CT compared with XR (32.9° versus 30.8°, P < 0.001). Subgroup analysis revealed the highest mean difference in hips with acetabular dysplasia and concomitant cam-type femoroacetabular impingement (FAI) [mean difference (CT-XR) 5.5°, 95% confidence interval (CI) 3.7°-7.3°, P = 0.011], followed by hips with isolated acetabular dysplasia (mean difference [CT-XR] 4.9°, 95% CI 2.7°-7.0°, P < 0.001). In contrast, 119 (29.0%) of the hips demonstrated larger measurements of the LCEA on 25 XR relative to CT. Of these hips, 20 (16.8%) had pincer-FAI and 25 had cam-FAI (21.0%), representing a significantly higher proportion compared with all other clinical subgroups (P = 0.045 and 0.036, respectively). Our study demonstrates measured values of the LCEA are consistently inflated on CT relative to XR for a wide variety of hip pathologies, highlighting the need for standardization and validation of CT-based measurements to improve the quality of clinical decision making. LEVEL OF EVIDENCE: Diagnostic Level II.