الفهرس 
History of Total Hip ReplacementOnly 14 pages are availabe for public view
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Abstract
The outcomes of cemented femoral stems in young patients have been less favorable. Cement provides a static mechanical interlock, which may degrade with time. Cementless fixation provides a dynamic biological fixation, which is cyclically renewed. This seems to offer the potential for more durable fixation, particularly in the younger patient. Early cementless implants obtained reproducible fixation distally. However this was associated with thigh pain and the distal offloading pre-disposed to proximal stress shielding with proximal stress protection osteopenia.
Many factors may affect bone remodeling after THA. These include patient-related factors such as sex, age, underlying disease and quality of bone before the hip replacement, and also prosthesis-related factors such as the influence of the size and stiffness of the implant and the extent of the porous coating. However, the main determinant of bone mass redistribution seems to be stress shielding. Periprosthetic bone resorption in the proximal femur after uncemented THA appears to result from stress shielding and distal transfer of loads to the diaphysis. A proximal-loading device with extended metaphyseal geometry (lateral flare) preserves bone mass and increases periprosthetic bone stock.
Young candidates for THA don’t need only better functional abilities, but also long survivorship of the implant. This is the motivation for the development of short stem via preserving the bone stock, improving the load transfer to simulate the normal and to decrease the stress shielding.
The pre-requisites for short stem include the following: normal shape of the proximal femur, good bone stock and preoperative templating.
Bone resorption in the proximal femur is commonly seen after uncemented THA and is evident with DEXA Scan, however, the results of DEXA in short stem are quite different with increase bone density especially in zones 2 and 4.
The advantages of short stems over conventional stems are the following: more physiological load transfer, bone preservation, no stress shielding, more femoral flexibility, no thigh pain and easy revision.