Stress Shielding in Cemented Hip Implants Assessed From Computed Tomography

Background: Aseptic loosening is the major cause of revisions for hip replacement. This mode of failure is often caused by stress shielding. Stress shielding in the femur occurs when some of the loads are taken by the prosthesis and shielded from going to the bone. There is little information regarding the stress shielding among cemented hip implants. Purpose: The purpose of this study is to investigate the effect of stress shielding on the proximal femur with a femoral prosthesis. Methods: A patient had undergone open reduction and internal fixation (ORIF) due to a comminuted reversed oblique fracture of the right intertrochanteric hip. ORIF had failed and was converted to bipolar hemiarthroplasty. CT scans were performed on both the right and left hips. Housefield units were determined by using the probe tool. By using equations formulated by Carter and Hays, Linde et al., various parameters such as apparent density, Young’s’ modulus and ultimate strength were calculated. The results were compared to that a native hip. Results: The hip with the cemented implant had a significant increase in the apparent density, Young’s modulus and ultimate strength, when compared to the left hip. In addition, it was found that the right hip had a higher strain energy density than that of the left. Interpretation: It has been concluded the most stress shielding occurred in the calcar region of the femur. The instances of stress shielding have been extensively reported for non-cemented or direct bone to implant constructs, this paper reports stress shielding in cemented implants supported by imaging data and biomechanical calculations carried out at the bone-cement-metal interface

Gender-Specific Anterior Cruciate Ligament – Gait Forces

The purpose of this study was to investigate gender-based differences in gait biomechanics and to evaluate those effects on forces generated on the ACL during walking. Estimation of gender-specific ACL forces in the frontal plane can provide a better understanding of the biomechanical patterns underlying higher female injury risk. The present study used a sample from the Fels Longitudinal Study to test the hypothesis that there are significant gender-differences in frontal plane ACL loading during walking. A cross-sectional sample of 178 participants, including 79 males and 99 females was used to evaluate differences in gait kinetics. Females walked at higher cadence with narrower steps (P \u3c 0.05). No difference was observed in the peak flexion force and knee rotation moment between males and females (P = 0.51 and 0.07), respectively. Peak abduction moment was significantly lower among females than in males (P = 0.05). A regression equation was developed which considers a person’s weight and height in addition to forces which could give better estimate of the forces acting on the ligament. The peak force acting on the ACL during walking reaches as high as 0.44 of BW, regardless of gender

Methods to determine the volume of infrapatellar fat pad as an indicator of anterior cruciate ligament tear

Introduction: Anterior knee pain is a common problem which affects adolescents and young adults. The most common mechanism for anterior knee pain arises from combination of compression and shear forces across the patellofemoral joint. The structures that commonly cause anterior knee pain include medial and lateral retinaculum, the patellar subchondral bone, the anterior synovium, joint capsule, patellar tendon, and infrapatellar fat pad. It is important to develop methods to measure volume of infrapatellar fat pad without invasive means. The volume of the fat pad was determined based on 3D image reconstruction using Mimics (a software developed by Materialise), by ellipsoidal methods a mathematical method, and program developed using MATLAB. All three methods had used MRI images to determine its volume. The objective of this study is to determine the accuracy of these new methods. The following hypotheses were tested: (1) increased volume of infrapatellar fat pad among torn ACL, (2) increased body mass index would have larger infrapatellar fat pad, and (3) volumes determined from Mimics, MATLAB, and ellipsoidal model would be accurate. Methods: Our institutional review board approved this retrospective study, which involved a search of patient medical records, and waived the requirement for informed consent because there was no change in patient diagnosis or treatment. The study was an evaluation of all consecutive patients who complained of knee problems undergoing MRI examinations at our institution from 2007 to 2013. Two patient groups were evaluated after a search of surgery records for knee procedures: group 1 consisted of patients who had either a partial tear or complete tear of the ACL based on radiologists’ reading on MRI. Group 2 consisted of patients with an intact ACL on MRI. MRI scans were performed using a 1.5 Tesla General Electric (Milwaukee, Wisconsin) signal MRI Scanner. T1 weighted images in 4-mm thick cuts were evaluated based on the integrity of the image. 3D reconstruction was performed using Mimics (Materialise) software. Results: There is a strong correlation between the volumes determined by ellipsoidal model and MRI. It was determined that the coefficient of determination to be 0.9936. The volume estimated by MATLAB was found to be within a band of ±2 MRI values (27.29 mm3; R2 = 0.4186) and may be considered with high statistical confidence. No significant difference was observed between the two groups (p of 0.99 and 0.26) for ellipsoidal and MATLAB, respectively. Conclusions: Volume determinations using ellipsoidal approximation model had been shown to be comparable to that determined by MRI and MATLAB code within a statistical band of ±2. No statistical significance was observed among methods, with p values of 0.99 and 0.26 for ellipsoidal and MATLAB, respectively. The volume and surface of fat pad in patients with torn ACL are significantly larger than those with intact ACL, p values of 0.01 and 0.04, respectively

Analysis of a Clinically Failed, Mechanically Intact, Reconstructive Compression Plate

A reconstructive orthopedic bone plate was submitted for analysis. Traditional failure analysis methods were used to assess the mode of the plate failure. Metallographic investigation of the plate was carried out in this report. Since limited data was available in the literature and clinical data related to subject demography, date of removal as well as reasons for removal unknown, in depth analysis was not possible. However, the plate was received in in-tact condition with minor biological deposits and scratches, it is speculated that the failure of the plate may have been due to biological/clinical reasons, likely infection, rejecting the device due to lack of union at the fracture site

An unusual case of metastasis to the left side of the heart: a case report

<p>Abstract</p> <p>Introduction</p> <p>Cardiac metastases are found in six to 20% of autopsies of patients with malignant neoplasm. The most common neoplasms that metastasize to the heart are malignant melanoma, lymphoma, and leukemia, but the relative numbers are greater with breast and lung cancers, reflecting the most common incidence of these cancers.</p> <p>Case presentation</p> <p>A 60-year-old Hispanic man presented to our hospital after being transferred from an outside hospital for workup and evaluation of an adrenal mass of the abdomen and pelvis, found on computed tomography. His chief complaint upon admission was altered mental status. Physical examination was unremarkable. He was alert and oriented and had a dry and non-erythematous oropharynx, and bilateral diffuse wheezing on lung examination. Computed tomography of the chest showed multiple hypodense lesions in the left ventricular myocardium, suggestive of metastases. There were also tiny sub-centimeter nodular densities in the right upper and lower lobes. Adrenal glands contained hypodense lesions, which showed characteristic adenocarcinomatous malignant cells.</p> <p>Conclusion</p> <p>Cancers which have metastasized to the heart are found in six to 20% of patients with malignant neoplasms. The right side of the heart is more commonly involved in metastasis. This study is unusual in that a tumor of an unknown primary origin had metastasized to the left side of the heart.</p

Anterior Cruciate Ligament Biomechanics, Computational Modeling of Mechanical Behavior and Injury Risk

Knee joint involves interactions from various structures such as cartilage, bone, muscles, ligaments, tendon, as well as neural control. Anterior cruciate ligament (ACL) tears are one of the most frequent soft tissue injuries of the knee. A torn ACL leaves the joint unstable and at risk for further damage to other soft tissues manifested as pain, dislocation, and osteoarthritis. This injury is quite common in sports such as basketball, soccer and football. Females often tear their ACL 2-8 times more frequently than their male counterparts. An ACL injury can be devastating and significantly increases the athlete\u27s risk for osteoarthritis long term. While many advances have been made in terms of surgical and rehabilitation treatments for ACL injured patients, long term outcome studies show that these patients are at a high risk for developing knee osteoarthritis 10-15 years after ACL injury, regardless of the treatment. Currently, the mechanism of non-contact ACL injury is not well understood. Therefore, the knowledge of the ACL biomechanics is of importance in various clinical scenarios, since it would be instrumental in its understanding of structure and function which are necessary to diagnose and prevent ACL injury. This dissertation further investigates four areas; demographic studies which relate anatomical features to ACL injury, computer aided diagnostic tools which can be used to diagnose a common complication with ACL injury, computational simulations of ACL biomechanics using representative gait data, and finally risk of injury assessments. Magnetic resonance images (MRIs) of 32 patients with ACL tears and 40 patients who did not have ACL tears were evaluated from a physician group practice. Digital measurements of femoral condyle length, femoral notch width, ACL width in the frontal and sagittal plane, and the ACL length in the sagittal plane were taken in both groups. Empirical data correlations were performed and trends identified. Similarly, a sample from the Fels gait data was a larger subset which consists of 178 healthy volunteers, out of which 99 were females and the remaining were males. Finite element (FE) analysis has become an increasingly popular technique in the study of human joint biomechanics, as it allows for detailed analysis of the joint/tissue behavior under complex, clinically relevant loading conditions. A wide variety of modeling techniques have been utilized to model knee joint ligaments. However, the effect of a selected constitutive model to simulate the ligaments on knee kinematics remains unclear. Computational knee joint models were based on patients\u27 medical images. Using a sample from Fels Longitudinal study, loads were determined from the gait profile of healthy volunteers and the stress distributions on the ACL were determined. The anatomical representation of the ligament make it feasible to determine stress distribution across the ligament which in turn provide valuable information about the mechanism of ligament injury. 3D anisotropic hyperelastic model was found to simulate physiological behavior of human knee. Females have significantly greater abduction angles (p \u3c 0.005). Similarly, males have significantly larger adduction angles than the females (p\u3c0.05). In this study, the peak ACL force observed during normal walking was less than ½ BW. A combination of tibial and valgus rotations of the tibia had resulted in a Von Mises stress on the ACL as high as 62 MPa which is indicative of ACL injury. A linear relationship was determined to investigate the relationship between NWI and width of the ACL. This may suggest that NWI plays no significant role in the causes for ACL injury. Sensitivity analysis had shown that there is a linear relationship between the forces applied and risk for ACL injury

Stress Shielding in Cemented Hip Implants Assessed From Computed Tomography

Background: Aseptic loosening is the major cause of revisions for hip replacement. This mode of failure is often caused by stress shielding. Stress shielding in the femur occurs when some of the loads are taken by the prosthesis and shielded from going to the bone. There is little information regarding the stress shielding among cemented hip implants. Purpose: The purpose of this study is to investigate the effect of stress shielding on the proximal femur with a femoral prosthesis. Methods: A patient had undergone open reduction and internal fixation (ORIF) due to a comminuted reversed oblique fracture of the right intertrochanteric hip. ORIF had failed and was converted to bipolar hemiarthroplasty. CT scans were performed on both the right and left hips. Housefield units were determined by using the probe tool. By using equations formulated by Carter and Hays, Linde et al., various parameters such as apparent density, Young’s’ modulus and ultimate strength were calculated. The results were compared to that a native hip. Results: The hip with the cemented implant had a significant increase in the apparent density, Young’s modulus and ultimate strength, when compared to the left hip. In addition, it was found that the right hip had a higher strain energy density than that of the left. Interpretation: It has been concluded the most stress shielding occurred in the calcar region of the femur. The instances of stress shielding have been extensively reported for non-cemented or direct bone to implant constructs, this paper reports stress shielding in cemented implants supported by imaging data and biomechanical calculations carried out at the bone-cement-metal interface

Gender-Specific Anterior Cruciate Ligament – Gait Forces

The purpose of this study was to investigate gender-based differences in gait biomechanics and to evaluate those effects on forces generated on the ACL during walking. Estimation of gender-specific ACL forces in the frontal plane can provide a better understanding of the biomechanical patterns underlying higher female injury risk. The present study used a sample from the Fels Longitudinal Study to test the hypothesis that there are significant gender-differences in frontal plane ACL loading during walking. A cross-sectional sample of 178 participants, including 79 males and 99 females was used to evaluate differences in gait kinetics. Females walked at higher cadence with narrower steps (P \u3c 0.05). No difference was observed in the peak flexion force and knee rotation moment between males and females (P = 0.51 and 0.07), respectively. Peak abduction moment was significantly lower among females than in males (P = 0.05). A regression equation was developed which considers a person’s weight and height in addition to forces which could give better estimate of the forces acting on the ligament. The peak force acting on the ACL during walking reaches as high as 0.44 of BW, regardless of gender

Analysis of a Clinically Failed, Mechanically Intact, Reconstructive Compression Plate

A reconstructive orthopedic bone plate was submitted for analysis. Traditional failure analysis methods were used to assess the mode of the plate failure. Metallographic investigation of the plate was carried out in this report. Since limited data was available in the literature and clinical data related to subject demography, date of removal as well as reasons for removal unknown, in depth analysis was not possible. However, the plate was received in in-tact condition with minor biological deposits and scratches, it is speculated that the failure of the plate may have been due to biological/clinical reasons, likely infection, rejecting the device due to lack of union at the fracture site