- Discussion:
- stress shielding is the redistribution of load (and consequently stress on
the bone) that occurs when the femoral head is replaced by the femoral
component of a total hip replacement;
- stress on proximal 10 cm of femoral cortex is reduced, because much of the
load bypasses this region and is carried in the metal stem to the
isthmus of the femur;
- w/ extensively porous coated stems, upto 25-30% of femurs will demonstrate
some stress shielding;
- as noted by Bugbee et al 19997, significant stress shielding was present in
23% of 207 hips at 2 years (using the anatomic medullary locking hip);
- X-rays:
- atrophy of the proximal femur is substantially greater w/ stiff
cementless femoral components than w/ cemented components.
- for most pts this incr degree of local disuse osteoporosis has not
yet had clinical consequences, but there are examples of severe
disuse osteoporosis in which much or all of proximal femoral
cortex has been completely resorbed;
- stress shielding of prox femur is more pronounced when a stem of
large diameter has been used;
- almost all femurs demonstrating moderate or severe proximal
resorption involves stems of 13.5 mm or greater;
- amount of stress shielding that is acceptable in clinical setting
is difficult to determine;
- fortunately a point of equilibrium is reached and bone loss
does not appear to progress after a period of 2 years;
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Long term clinical consequences of stress shielding after total hip arthroplasty
without cement.
WD Bugbee MD, WJ Culpepper, CA Engh.
JBJS Vol 79-A, No 7. July 1997. p 1007.
Porous-coated hip replacement. The factors governing bone ingrowth,
stress shielding, and clinical results.
