Anterior cruciate ligament injury has been shown to be caused by the forces which act on the ligament. These forces can result from hyperextension of the tibia or the internal rotation of tibia. The anatomical parameters of the knee joint (i.e., notch width index, anterior cruciate ligament width and length) have no role in the cause of an injury.

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.

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 < 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.

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.

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