ABSTRACT
BACKGROUND:Posterior dislocation after total hip replacement is one of the most common complications that second only to loosen, and can affect the stability of the hip joint seriously. There is controversy on the effect of femoral head diameter and acetabular anteversion on the stability of hip joint in clinical study. OBJECTIVE:To investigate the effect of the femoral head diameter and acetabular anteversion on the stability of hip joint after hip prosthesis replacement. METHODS:The femoral head diameter and acetabular anteversion that affect the posterior instability after hip prosthesis replacement were measured on the cadaveric bone. The acetabular shel was inserted at 0°-20° of anteversion at five degree intervals. The femoral heads with different diameters (28, 32 and 36 mm) were used for experiment, the internal rotation degrees to dislocation caused by hip at 90° flexion and 0° adduction and at 90° flexion and 30° adduction were recorded. RESULTS AND CONCLUSION:When the cup anteversion varied from 0° to 15°, there was an increase in the degree of internal rotation angle that could cause hip dislocation with the increasing of femoral head diameter (P<0.05). When the cup anteversion varied from 15° to 20°, the increasing trend was not significant. With the hip at 90° flexion and 0° adduction, and the cup anteversion varied from 15° to 20°, the stability of 36 mm group was significantly higher than that of the 28 mm and 32 mm groups (P<0.01);the stability of 32 mm group was higher than that of 28 mm group when the acetabular anteversion in 10° or more (P<0.05);there was no significant difference in stability between groups when the anteversion less than 10°. With the hip at 90° flexion and 30° adduction, the stability of 36 mm group was significantly higher than that of the 28 mm and 32 mm groups (P<0.01);the stability of 32 mm group was higher than that of 28 mm group when the acetabular anteversion in 10° or more (P<0.05);there was no significant difference in stability between groups when the anteversion less than 10°. The results indicate that the increasing of acetabular anteversion can reduce the occurrence of dip dislocation, but when it is difficult to choice the acetabular anteversion, large-diameter femoral head is preferred to increase the stability of hip joint.
ABSTRACT
Objective To investigate clinical outcomes and complications of isolated polyethylene liner exchange for revision total hip arthroplasty.Methods From April 1995 to December 2007,80 patients (93 hips) underwent revision total hip arthroplasty during which only polyethylene liner was exchanged with reservation of acetabular cup.There were 41 males and 39 females,aged from 27 to 82 years (average,53.3 years).The duration from the primary THA to the revision surgery ranged from 0.3 to 18.4 years (average,10.9 years).The reasons for liner exchange included:polyethylene wear with osteolysis (78 hips),polyethylene wear without osteolysis (5 hips),polyethylene wear with stem loosening (4 hips),recurrent dislocation (3hips),infection (1 hip),periprosthetic fracture (1 hip) and liner dislodgement (1 hip).Forty-seven liners were fixed into the old cup using cement,and 46 were fixed with the original locking mechanism.Sixty cross-linked polyethylene liners and 33 conventional polyethylene liners were used.Results All patients were followed up for 5 to 15 years (average,7 years).The average Harris hip score improved from preoperative 86.0±16.9 to 89.4±11.6 at final follow-up.Complications included dislocation (10 hips),infection (2 hips),periprosthetic fracture (1 hip) and liner dislodgement (1 hip).Ten hips underwent rerevision due to different reasons:cup exchange (5 hips),conventional polyethylene wear (2 hips),infection (2 hips) and liner dislodgement (1 hip).Using component loosening as the end point,the 10-year survival rate was 100％ in the cement fixation group and 84.8％ in the original locking group.Using rerevision as the end point,the 10-year survival rate was 90.4％ in the cement fixation group and 65.0％ in the original locking group.Conclusion Liner exchange either with cement or original locking mechanism is a safe and successful method.Highly cross-linked polyethylene has a higher wear resistance,which can reduce incidence of osteolysis and improve survival rate of prosthesis.