Strains and micromotions of press-fit femoral stem prostheses.

Average femoral geometry was determined from sections of 25 human femurs. A 'stem design program' was used to determine the largest femoral stem that could be introduced into the canal. The stem was fine tuned by observations of fit in Plexiglass models of the 25 femurs. This stem was called the 'Exact-Fit'. Type 1 stem was formed by grinding the anterior and posterior faces flat. Type 2 stem was formed by additionally grinding the medial and lateral faces flat. Four fresh femurs were used for the experiments. Strain gages were located on the proximal medial area and level with the distal lateral tip. Displacement transducers were mounted proximally to measure stem-bone micromotion. Vertical and anterior-posterior forces were applied to the femoral head and normal strain data obtained. The stems were then inserted in sequence and the strains and micromotions were measured. After the uncemented stems had been tested, a smaller size of 'exact-fit' stem was cemented and the tests repeated. The strains with the uncemented stems were closer to normal than with the cemented stems. For example, compressive calcar strains averaged 56% of normal uncemented compared with 30% cemented for the different loadings. The micromotion was higher uncemented, but was still at a low level. The 'exact-fit' stem gave less resultant micromotion than the type 1 and type 2 stems. The high variation of the strain results was attributed to variations in stem-bone contact and fit. The study provided information of direct application to press-fit stems in hip replacement surgery.

[1]  P. D. Wilson,et al.  A ten-year follow-up study of our first one hundred consecutive Charnley total hip replacements. , 1981, The Journal of bone and joint surgery. American volume.

[2]  P S Walker,et al.  Design of intramedullary femoral stems using computer graphics. , 1985, Engineering in medicine.

[3]  P. D. Wilson,et al.  Long-term results of revision total hip replacement. A follow-up report. , 1985, The Journal of bone and joint surgery. American volume.

[4]  C. Engh,et al.  Hip arthroplasty with a Moore prosthesis with porous coating. A five-year study. , 1983, Clinical orthopaedics and related research.

[5]  K. Markolf,et al.  The effect of calcar contact on femoral component micromovement. A mechanical study. , 1980, The Journal of bone and joint surgery. American volume.

[6]  D R Pedersen,et al.  A measurement of proximal femur strain with total hip arthroplasty. , 1980, Journal of Biomechanical Engineering.

[7]  P. Ring,et al.  Osteolytic changes in the upper femoral shaft following porous-coated hip replacement. , 1985, The Journal of bone and joint surgery. British volume.

[8]  Ring Pa.  Five to fourteen year interim results of uncemented total hip arthroplasty. , 1978 .

[9]  W H Harris,et al.  Proximal strain distribution in the loaded femur. An in vitro comparison of the distributions in the intact femur and after insertion of different hip-replacement femoral components. , 1978, The Journal of bone and joint surgery. American volume.

[10]  C. M. Evarts,et al.  Prosthetic replacement in femoral neck fractures. , 1980, Clinical orthopaedics and related research.

[11]  H P Chandler,et al.  Total hip replacement in patients younger than thirty years old. A five-year follow-up study. , 1981, The Journal of bone and joint surgery. American volume.

[12]  Ring Pa,et al.  Ring UPM total hip arthroplasty. , 1983 .

[13]  H. Amstutz,et al.  "Modes of failure" of cemented stem-type femoral components: a radiographic analysis of loosening. , 1979, Clinical orthopaedics and related research.

[14]  J CHARNLEY,et al.  THE ELIMINATION OF SLIP BETWEEN PROSTHESIS AND FEMUR. , 1965, The Journal of bone and joint surgery. British volume.

[15]  J. G. Andrews,et al.  A biomechanical investigation of the human hip. , 1978, Journal of biomechanics.

[16]  J. P. Paul.  Approaches to design - Force actions transmitted by joints in the human body , 1976, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[17]  P. D. Wilson,et al.  Results of revision total hip replacement. , 1984, The Hip.

[18]  P S Walker,et al.  Adaptive changes in the femur after implantation of an Austin Moore prosthesis. , 1984, The Journal of bone and joint surgery. American volume.

[19]  L. Lanyon,et al.  In vivo strain measurements from bone and prosthesis following total hip replacement. An experimental study in sheep. , 1981, The Journal of bone and joint surgery. American volume.

[20]  R. N. Stauffer.  Ten-year follow-up study of total hip replacement. , 1982, The Journal of bone and joint surgery. American volume.

[21]  E Y Chao,et al.  A survey of finite element analysis in orthopedic biomechanics: the first decade. , 1983, Journal of biomechanics.