The position of the bipolar cup reflects the direction of the hip contact force acting on it.
We radiographically measured the bipolar cup position to analyze the direction of joint force acting on the bipolar cup. The abduction angle of the bipolar cup was measured in each radiograph taken immediately and at six 12 weeks and yearly after the operation. Radiographs in patients with weight bearing were also investigated. The results indicated that the abduction angle of the bipolar cup was 24.1 degrees +/- 11.2 degrees immediate postoperatively and was 16.2 degrees +/- 5.1 degrees at 6 weeks, 16.1 degrees +/- 5.1 degrees at 3 months, and 16.2 degrees +/- 5.1 degrees at 1 year. The cup abduction angles with weight bearing were not different from those without weight bearing and were 15.9 degrees +/- 4.9 degrees , 16.2 degrees +/- 4.4 degrees , and 16.1 degrees +/- 4.7 degrees on the supine, double-legged stance, and single-legged stance radiographs, respectively. Because the position of the bipolar cup reflects the direction of loads pivoting on it, the direction of the joint force in the frontal plane acting on the bipolar prosthesis is about 16 degrees to vertical.
Lee
Mel S
MS
Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chang Gung Institute of Technology, Taoyuan, Taiwan.
Chen
Alvin C Y
AC
Kuo
Chung-Hsien
CH
Tai
Ching-Lung
CL
Senan
Vinesh
V
Shih
Chun-Hsiung
CH
D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011859:Radiography; D013314:Stress, Mechanical; D016474:Weight-Bearing