ABSTRACT
PURPOSE: The purpose of this study was to analyze the relative micromotions between the straight and the curved stems during the immediate postoperative stage of noncemented total hip replacement which load simulating the single leg stance and stair climbing. MATERIALS AND METHODS: The authors developed 3-dimensional numerical finite element models implanted with the straight stem, which was composed of a total of 1,170 elements of 8 nodes, and which had a curved stem composed of a total of 885 elements of 8 nodes, and then analyzed the relative micromotions of the straight and curved stems. RESULTS: In the single leg stance, the curved stem was more stable especially in terms of its rotational stability. Rotational displacement accounted for over 90% of the total micromotion in both types of stem and this was highest for the proximal medial portion of the stem, but markedly less distally. Stair climbing produced more micromotion than the single leg stance regardless of the stem configuration. CONCLUSION: It is recommended that surgeons do not allow patient weight bearing until bony ingrowth has been achieved. In the future more attention should be placed upon increasing the initial rotational stability of the two types of femoral stem to prevent loosening by excessive micromotion.
Subject(s)
Humans , Arthroplasty, Replacement, Hip , Leg , Weight-BearingABSTRACT
PURPOSE: This study was undertaken to compare the initial micromotion and stress shielding of a "fit and fill" stem to a "proximal fitting and distal tapered" stem in the early postoperative period using the load simulating single leg stance and stair climbing. MATERIALS AND METHODS: Using the data from 3-D human CT scan, authors developed two types of 3-dimensional finite element total hip replacement model of proximal femur, which were inserted with a "fit and fill" stem and a "proximal fitting and distal tapered" stem. The constructions of stems were based on the OmnifitTM stem (about 13,000 element & 20,000 nodes). We compared micromotion, maximal principal stress and strain energy of each stems. RESULTS: The results indicate that micromotion in a fit and fill stem were slightly lower than that of a tapered stem, especially in stair climbing over that in the single leg stance. The maximum principal stress on the cortex of femur was slightly higher in a tapered stem in the case of single leg stance, and 2 times higher in the case of stair climbing. Strain energy also was much higher in a tapered stem in both single leg stance and stair climbing gait. CONCLUSION: These findings indicate that a tapered stem design could provide more favorable biomechanical benefits rather than a fit & fill stem after cementless total hip replacement.