Finite Element Model of Patient-Specific Flanged Acetabular Components Highlights Biomechanical Effects of Bone Density and Cortical Shell Thickness.

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with severe acetabular defects. We previously developed and published a finite element model that investigated the impact of hip joint center lateralization on construct biomechanics during gait conditions. This model consisted of a patient-specific implant designed to address a superior-medial defect created in a standard pelvic geometry.

Hip joint center lateralization minimally affects the biomechanics of patient-specific flanged acetabular components: A computational model.

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with large acetabular defects. Previous clinical studies from our institution showed that these implants tend to lateralize the acetabular center of rotation. However, the clinical impact of lateralization on implant survivorship is debated.

A novel computational workflow to holistically assess total knee arthroplasty biomechanics identifies subject-specific effects of joint mechanics on implant fixation.

Computational studies of total knee arthroplasty (TKA) often focus on either joint mechanics (kinematics and forces) or implant fixation mechanics. However, such disconnect between joint and fixation mechanics hinders our understanding of overall TKA biomechanical function by preventing identification of key relationships between these two levels of TKA mechanics. We developed a computational workflow to holistically assess TKA biomechanics by integrating musculoskeletal and finite element (FE) models.

An Anterior Spike Decreases Bone-Implant Micromotion in Cementless Tibial Baseplates for Total Knee Arthroplasty: A Biomechanical Study.

Background: Cementless tibial baseplates in total knee arthroplasty include fixation features (eg, pegs, spikes, and keels) to ensure sufficient primary bone-implant stability. While the design of these features plays a fundamental role in biologic fixation, the effectiveness of anterior spikes in reducing bone-implant micromotion remains unclear. Therefore, we asked: Can an anterior spike reduce the bone-implant micromotion of cementless tibial implants?

Methods: We performed computational finite element analyses on 13 tibiae using the computed tomography scans of patients scheduled for primary total knee arthroplasty.

Undersizing the Tibial Baseplate in Cementless Total Knee Arthroplasty has Only a Small Impact on Bone-Implant Interaction: A Finite Element Biomechanical Study.

Background: The tibial component in total knee arthroplasty (TKA) is often chosen to maximize coverage of the tibial cut, which can result in excessive internal rotation of the component. Optimal rotational alignment may require a smaller baseplate with suboptimal coverage that could threaten fixation. We asked: "does undersizing the tibial component of a cementless TKA to gain external rotation increase the risk of bone failure?"

Methods: We developed computational finite element (FE) analysis models from the computed tomography (CT) scans of 12 patients scheduled for primary TKA.

Do Metaphyseal Cones and Stems Provide Any Biomechanical Advantage for Moderate Contained Tibial Defects in Revision TKA? A Finite-Element Analysis Based on a Cadaver Model.

Background: Satisfactory management of bone defects is important to achieve an adequate reconstruction in revision TKA. Metaphyseal cones to address such defects in the proximal tibia are increasingly being used; however, the biomechanical superiority of cones over traditional techniques like fully cementing the implant into the defect has not yet been demonstrated. Moreover, although long stems are often used to bypass the defects, the biomechanical efficacy of long stems compared with short, cemented stems when combined with metaphyseal cones remains unclear.

Treatment of Recurrent Dislocation after Total Hip Arthroplasty Using Advanced Imaging and Three-Dimensional Modeling Techniques: A Case Series.

Background: Surgical treatment options for addressing recurrent dislocation after total hip arthroplasty (THA) vary. Identifying impingement mechanisms in an unstable THA may be beneficial in determining appropriate treatment.

Questions/purposes: We sought to assess the effectiveness of developing pre-operative plans for treating hip instability after THA.

Biplanar Low-Dose Radiography Is Accurate for Measuring Combined Anteversion After Total Hip Arthroplasty.

Background: Acetabular component position alone has not been predictive of stability after total hip arthroplasty (THA). Combined anteversion of the acetabulum and femur has the potential of being more predictive of stability. Unfortunately, femoral component position is difficult to measure on plain radiographs.

The Use of Three-Dimensional Printing for Complex Scaphoid Fractures.

Scaphoid fractures are one of the most common fractures treated by hand surgeons. The complex anatomy and size of the scaphoid bone can make the reduction and fixation of these fractures technically challenging. Careful preoperative planning is required to ensure stable fixation is achieved.

Mechanical performance of cementless total knee replacements: It is not all about the maximum loads.

Finite element (FE) models are frequently used to assess mechanical interactions between orthopedic implants and surrounding bone. However, FE studies are often limited by the small number of bones that are modeled; the use of normal bones that do not reflect the altered bone density distributions that result from osteoarthritis (OA); and the application of simplified load cases usually based on peak forces and without consideration of tibiofemoral kinematics. To overcome these limitations, we undertook an integrated approach to determine the most critical scenario for the interaction between an uncemented tibial component and surrounding proximal tibial bone.

Variable Bone Density of Scaphoid: Importance of Subchondral Screw Placement.

 Ideal internal fixation of the scaphoid relies on adequate bone stock for screw purchase; so, knowledge of regional bone density of the scaphoid is crucial.  The purpose of this study was to evaluate regional variations in scaphoid bone density.  Three-dimensional CT models of fractured scaphoids were created and sectioned into proximal/distal segments and then into quadrants (volar/dorsal/radial/ulnar).

Fixed-bearing medial unicompartmental knee arthroplasty restores neither the medial pivoting behavior nor the ligament forces of the intact knee in passive flexion.

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces.

Effect of Screw Perpendicularity on Compression in Scaphoid Waist Fractures.

 Central and perpendicular (PERP) screw orientations have each been described for scaphoid fracture fixation. It is unclear, however, which orientation produces greater compression.  This study compares compression in scaphoid waist fractures with screw fixation in both PERP and pole-to-pole (PTP) configurations.

A Comparison Between Chinese and Caucasian 3-Dimensional Bony Morphometry in Presimulated and Postsimulated Osteotomy for Total Knee Arthroplasty.

Background: The bone morphologies of intact knees were measured and compared between Chinese and Caucasian populations. However, to assess if distinct designs of implants are necessary for the Chinese population owing to different morphologies and sizes, the knee measurements after osteotomy performed in total knee arthroplasty were evaluated.

Methods: Thirty-seven Caucasian and 50 Chinese patients' knees were examined using computed tomography scans.

Retrieval and radiographic analysis of the Contour antiprotrusio cage.

Introduction: Acetabular reconstruction in the setting of severe bone loss or pelvic discontinuity remains a challenging problem. Multiple methods of treatment have been described including antiprotrusio cages (APCs). The objective of this study is to combine biomechanical analysis of retrieved APCs with radiographic and clinical data to determine which factors influence or predict APC failure.

One Stage Bilateral Total Hip Arthroplasty in Siblings with Larsen Syndrome.

Background: Larsen syndrome is a rare genetic disorder caused by congenital weakness of the connective tissues. It can present with a variety of musculoskeletal and cardiovascular abnormalities. The current report describes two siblings with Larsen Syndrome who presented with severe bilateral hip arthritis and underwent one stage bilateral total hip arthroplasty (THA).

The ACL Graft Has Different Cross-sectional Dimensions Compared With the Native ACL: Implications for Graft Impingement.

Background: Impingement of anterior cruciate ligament (ACL) grafts against the femoral notch and the posterior cruciate ligament (PCL) is thought to be influenced primarily by tunnel position and graft orientation. Recent data have implied that the native ACL is ribbon-shaped.

Purpose: To evaluate the 3-dimensional shape and cross-sectional area of the native ACL versus the ACL graft and to compare the degree of impingement against the femoral notch and PCL.

MRI of Polyethylene Tibial Inserts in Total Knee Arthroplasty: Normal and Abnormal Appearances.

Objective: The purpose of this study was to describe the normal and abnormal MRI appearances of polyethylene tibial inserts. Subjects who underwent MRI before revision total knee arthroplasty were identified. The polyethylene tibial insert's shape was categorized on MRI, and the presence of abnormalities was noted.

Scaphoid Proximal Pole Fracture Following Headless Screw Fixation.

Background Headless screw fixation of scaphoid fractures and nonunions yields predictably excellent outcomes with a relatively low complication profile. However, intramedullary implants affect the load to failure and stress distribution within bone and may be implicated in subsequent fracture. Case Description We describe a posttraumatic fracture pattern of the scaphoid proximal pole originating at the previous headless screw insertion site in three young male patients with healed scaphoid nonunions.

Effect of Spinal Deformity on Pelvic Orientation from Standing to Sitting Position.

Background: The effect of fixed spinal deformities on a functional pelvis from standing to sitting is not fully understood. We aimed to assess the change in preoperative sagittal pelvic tilt angle (SPTA) from standing to sitting in patients undergoing total hip arthroplasty, comparing flexible and fixed spinal deformities.

Methods: Between July 2011 and October 2011, 68 consecutive unilateral total hip arthroplasties were implanted in 68 patients with a mean age of 71 ± 6 years.

Frontal plane stability following UKA in a biomechanical study.

Introduction: Function and kinematics following unicondylar knee arthroplasty (UKA) have been reported to be close to the native knee. Gait, stair climbing and activities of daily living expose the knee joint to a combination of varus and valgus moments. Replacement of the medial compartment via UKA is likely to change the physiologic knee stability and its ability to respond to varus and valgus moments.

Accuracy of Individualized Custom Tibial Cutting Guides in UKA.

Background: Component malposition is one of the major reasons for early failure of unicompartmental knee arthroplasty (UKA).

Questions/purposes: It was investigated how reproducibly patient-specific instrumentation (PSI) achieved preoperatively planned placement of the tibial component in UKA specifically assessing coronal alignment, slope and flexion of the components and axial rotation.

Patients And Methods: Based on computer tomography models of ten cadaver legs, PSI jigs were generated to guide cuts perpendicular to the tibial axis in the coronal and sagittal planes and in neutral axial rotation.