Hip joint prosthesis design: effect of stem introducers

Part 2: the influence of prosthesis stem design on remodelling and fracture of the femoral neck

The design features of cemented femoral hip implants …

• 00.71, Revision of hip replacement, acetabular component (includes partial hip revision of acetabular component only and that with exchange of acetabular cup and liner or exchange of femoral head);

Fig 1: Prosthetic fracture of a polished, tapered, collarless femoral stem; a cemented polyethylene cup has been used.

The design features of cemented femoral hip ..

A radical departure, later termed the "Canadian" design, was introduced by McLaurin in 1954 (Fig 21B-2.). This unique approach demonstrated the feasibility of using unlocked hip, knee, and ankle joints that relied on biomechanics to achieve stance-phase stability while permitting flexion at the hip and knee during swing phase.

Design of new generation femoral prostheses using functionally ..

Although the anatomic differences between hip disarticulation and transpelvic (hemipelvectomy) amputations are considerable, prosthetic component selection and alignment for both levels are quite similar. The major differences are in socket design and will therefore be discussed in some detail. A full surgical report identifying muscle reattachments along with postoperative radiographs can be extremely valuable during the initial examination of the amputation site, particularly if any portions of the pelvis have been excised. This information, combined with a thorough physical examination and a precise plaster impression, will influence the ultimate fit and function of the prosthesis.


Comparison of the stability of press-fit hip prosthesis femoral ..

The Exeter™ Universal hip stem (Stryker Inc., Newbury, UK) is a commonly used and well-performing prosthesis in hip arthroplasty. The Australian Orthopaedic Association National Joint Replacement Registry has recorded its use in 91, 601 procedures, which includes 71,849 total hip replacements and 19,752 hip hemiarthroplasties (unipolar, bipolar and trauma stem types), of both the older Exeter type and modern Exeter V40 type. [] The overall revision rate for all stem types is low, at 0.61 revisions/100 observed years.

and shape of the femoral stem of the prosthesis.

A third type that has proved advantageous for this level of amputation is the polycentric (four-bar) knee. Although slightly heavier than the previous two types, this component offers maximum stance-phase stability. Because the stability is inherent in the multilinkage design, it does not erode as the knee mechanism wears during use. In addition, all polycentric mechanisms tend to "shorten" during swing phase, thus adding slightly to the toe clearance at that time. Many of the endoskeletal designs feature a readily adjustable knee extension stop. This permits significant changes to the biomechanical stability of the prosthesis, even in the definitive limb. Because of the powerful stability, good durability, and realignment capabilities of the endoskeletal polycentric mechanisms, they are particularly well suited for the bilateral amputee. Patients with all levels of amputation, up to and including translumbar (hemicorporectomy), have successfully ambulated with these components.

Design Optimization of Cementless Femoral Hip …

For this problem to be addressed, an FE numerical method was developed to predict the progressive failure of a thick laminated composite femoral component for hip arthroplasty. With a laminated composite stem, the designer has the freedom to vary the orientation of each ply and the stacking sequence to achieve beneficial stiffness, stress distribution, component strength, and physiological performance [3,6,17,23-26]. With this in mind, we developed our methodology for designing composite orientation and stacking sequence with the objective to maximize the composite stem fatigue strength in critical regions while minimizing stress shielding effects and keeping the interfacial stresses below user-defined maximum levels. In this paper, we present a numerical method for predicting the progressive failure of a thick laminated composite femoral component. A 3-D global/3-D local technique was developed to capture the overall structural response of this system while also enabling the 3-D ply-level stress state to be determined efficiently and accurately. Different failure criteria and material degradation models were incorporated in this method, giving it the flexibility to simulate a wide range of materials and structures. We also conducted numerical modeling to support the design of experimental test methods for component fatigue testing, which closely simulated in vivo loading conditions. We then conducted parametric studies with the numerical model of an experimental system and compared the results to the damaged behavior of the experimentally determined composite component to assess which parameter set most accurately predicted the actual damage development behavior. Finally, we then applied the best-fitting parameter set to analyze simulated in situ composite femoral components for comparing a variety of implant designs.

Femoral part of a hip joint endoprosthesis. - BRISTOL …

Stress shielding: Stress shielding in femur occurs when some of the loads are taken by prosthesis and shielded from going to the bone (Kuiper, 1993; Paul, 1999). Normally, femur carries its external load by itself where the load is transmitted from the femoral head through the femoral neck to the cortical bone of the proximal femur as shown in . When stiffer stem is introduced into the canal, it shares the load and the carrying capacity with bone. Originally, the load is carried by bone, but it is now carried by implant and bone. As a result, the bone is subjected to reduced stresses and hence stress shielded (Huiskes ., 1992). The upper part of the femur receives fewer loads. The stress shielded area is whiter as shown in . The femur around the distal end of the femoral component is overloaded (darker area as shown in ).