انواع پروتز لگن (قطعه استم فمورال) – همراه با شرح ویژگی ها و نتایج بالینی

General description

Femoral stem prosthesis is one of the main components of the total hip replacement (THR) which would be inserted through the proximal third femur bone to be articulated with the acetabular prosthesis. Femoral stem could be divided in different sections or portions as neck, metaphyseal, and diaphyseal. The neck portion is dedicating the femoral neck of the femur bone, while the metaphyseal and diaphyseal portions are designed to be anatomically matched with the anatomy of the proximal third bone at the trochanter and diaphyseal sections of the femur bone at the proximal third. The design of the femoral stem in frontal plane would be managed with extended width at the proximal portion and narrowed gradually to the distal portion to be replaceable through the intramedullary canal of the diaphysis bone. The extended width portion would be at the trochanter zone (Fig. 3.1). The basic principles of the femoral stem designing are similar among the all orthopedic implant manufacturers, however specific features and benefits design conceptions might be implemented to enhance its effectiveness in long-term implantation. a

  Function

The function of the femoral stem is to establish the mechanical column for replacement of the femoral head. It acts as the load-bearing element against of bending and compressive stresses which is created at the articulation surface. The femoral stem would be integrated with the proximal third zone of the femur bone. Its mechanical fitness with the diaphyseal portion and metaphyseal zones and biological integrity with the metaphyseal zone would establish the stable functionality in long-term implantation.

       Possible failures

The femoral stem might be failed in the various forms and different types of reasons. Other than conventional failures that might be occurred in all internal implantation (e.g. infection, delayed wound healing, soft tissue disease, nerve diseases, etc.), there would be other specific failures that might be occurred due to the ineffective interactions between the bone and femoral stem prosthesis. As following, such failures are described.

Subsidence

Fracture

Loosening

Peri-prosthetic bone fracture

Cortical Hypertrophy

Allergy

   Variants

Femoral stem prosthesis is designed in different types with specific features and benefits. The highlighted design parameters in the Table 2 might be modelled differently to enhance the effectiveness of the prosthesis function and performance in various types of bone and injury conditions at the proximal third of the femur bone. The main variants of the femoral stem prosthesis are highlighted as following and further details, description, features, advantages, disadvantages along with their illustrations are provided in Tables 3 to 9.

Ultra-short femoral stem

Short length femoral stem

Biopolar femoral prosthesis

Collared femoral stem

Double tapered femoral stem

Triple tapered femoral stem

Porous coated femoral stem