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Molecular dynamics simulations were used to investigate the effect of epitaxial ordering of the fluid molecules on the microscopic dynamic contact angle. The simulations were performed in a Couette-flow-like geometry where two immiscible fluids were confined between two parallel walls moving in opposite directions. The extent of ordering was varied by changing the number density of the wall particles. As the ordering becomes more evident, the change in the dynamic contact angle tends to be more sensitive to the increase in the relative velocity of the contact line to the wall. Stress components around the contact line is evaluated in order to examine the stress balance among the hydrodynamic stresses (viscous stress and pressure), the deviation of Young's stress from the static equilibrium condition, and the fluid-wall shear stress induced by the relative motion between them. It is shown that the magnitude of the shear stress on the fluid-wall surface is the primary contribution to the sensitivity of the dynamic contact angle and that the sensitivity is intensified by the fluid ordering near the wall surface.

RESUMEN

BACKGROUND: We retrospectively reviewed 137 consecutive total hip arthroplasties performed with AML-A stems and Tri-Lock cups to see whether design modifications made to these components would achieve durable biological fixation in the Japanese population in whom developmental dysplasia of the hip (DDH) is relatively common. Patients from our initial clinical series using these components are available for more than 10 years' follow-up. METHODS: Between April 1988 and June 1994, we performed 137 total hip arthroplasties using the AML-A prosthesis for the patients with osteoarthritis of the hip joint. We excluded 26 hips with less than 10 years' follow-up and five hips from patients who died before the 10-year follow-up. The mean follow-up for the 105 remaining THAs is 155.2 months (range 120-237 months). The average age of these patients at the time of surgery was 53.1 years (range 22-81 years). RESULTS: In total, 17 THAs required component revisions. In seven cases, the first revision was limited to a liner exchange for polyethylene wear or osteolysis. Another seven hips underwent revision surgery for recurrent dislocation. Three cups have been revised owing to aseptic loosening. Because of the high incidence of wear-related revisions, Kaplan-Meier survivorship at the 15-year follow-up, using acetabular component revision for any reason as an endpoint, was 75.0% (95% CI 69.4%-83.8%). In contrast, no revision of the femoral stem was performed. Severe stress shielding occurred in 12 hips. Thigh pain was mild, however, and all of the femoral stems remained stable. CONCLUSIONS: Despite revisions for wear-related complications, the fixation achieved with these porous-coated components remained durable throughout the 15-year follow-up. Acetabular osteolysis has been associated with cup reoperation, but femoral stress shielding has never resulted in stem loosening.

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We reviewed the results of 35 operations performed on 29 patients with osteonecrosis of the femoral head in which a pedicle iliac bone was utilized. The average age was 35 years (17-62). There were 28 patients of stage 2 and 7 of stage 3; there were 17 type C-1 hips and 18 type C-2 hips. The pedicle bone was inserted in the anterolateral direction of the femoral head. The average follow-up period was 8 years and 7 months. Collapse of the femoral head occurred in 19 hip joints. Although 16 of 28 stage 2 hips showed collapse, all 7 stage 3 hips resulted in collapse. Thirteen of 17 hips did not show collapse in patients with type C-1 necrosis, whereas 15 of 18 hips developed collapse in patients with type C-2 necrosis. When the bone graft was inserted in the anterolateral direction of the femoral head, incidence of collapse was reduced. These results indicate that deep circumflex iliac pedicle bone graft may be indicated for stage 2 type C-1 necrosis, and that the penetration of the graft into the anterolateral aspect of the lesion is essential for the procedure to succeed.

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We report two cases of fatigue subcapital fracture of the femur after the removal of the hip plate used for fixation in transtrochanteric rotational osteotomy for osteonecrosis. Two patients, a 42-year-old man and a 43-year-old man, underwent transtrochanteric rotational osteotomy, and bony union was achieved in both patients. However, fatigue subcapital fracture of the femur occurred in both patients 15 months after the removal of the hip plate. Transtrochanteric rotational osteotomy greatly changes the trabecular bone structure in the proximal femur, thus affecting the strength of the femoral neck. Therefore, for the trabecular bone to be remodeled and for the proximal femur to achieve sufficient strength, a sufficient period is necessary after complete bony union has occurred in the transtrochanteric lesion, before removal of the plate.

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