The effects of acetabular component position and hip ball diameter on posterior stability after total hip replacement

Abstract

Objective To study the effects of acetabular component position and hip ball diameter on the posterior stability of the hip joint after total hip replacement.Methods Computer navigation system and synthetic bone model were used to simulate the motion of hip after total hip replacement. The hip was flexed to 90 degree and was adducted 0 and 30 degree as indicated by the computer navigation, after then it was progressively internally rotated until the hip was dislocated. The degree of internal rotation when the hip was dislocation was recorded.Results When the acetabular component abduction was 45 degree and anteversion were 0, 5, 10, 15 degrees, and the hip was flexed to 90 degree and adducted to 0 and 30 degrees, there was significant difference between 28 mm and 36 mm hip balls in the degrees of internal rotation when the hip was dislocated (P0.05). 36 mm diameter hip ball was significantly better in stability. The degree of internal rotation when the hip dislocated was less when the hip was adducted 30 degree compared to 0 degree. The stability was diminished with less acetabular component anteversion. With 0 degree anteversion and the hip adducted to 30 degree, a 28 mm diameter hip ball would lead to dislocation even if the hip was in external rotation. Conclusions The increasing anteversion of acetabular component can increase the stability of total hip replacement. Large hip ball is more stable than small hip ball. However, when anteversion of acetabular component is sufficient, there is no difference in stability between large and small hip balls.

目的探討髖臼杯的前傾位置與球頭大小對全髖關節置換(THA)術后后方穩定性的影響。方法利用計算機導航技術在假骨上模擬THA術后,不同髖臼杯前傾位置和不同球頭大小在屈髖90°、內收0°和內收30°時髖關節內旋到引起脫位的角度進行測量和比較發生后脫位時的角度差異。結果在髖臼杯外展45°、前傾0°、5°、10°、15°時,28mm和36mm球頭在屈髖90°內收0°和30°情況下內旋至脫位的角度有明顯差別(均為P<0.05),36mm球頭可有更大的內旋角度,穩定性優于28mm球頭。但當髖臼杯前傾20°時28mm與36mm球頭內旋至脫位的角度間的差異無統計學意義(P>0.05),內收30°時比內收0°時髖關節內旋至脫位的角度減小。關節穩定性隨髖臼杯前傾減小而下降。髖臼杯前傾0°和髖關節內收30°時,28mm球頭在外旋位時就可發生脫位。結論髖臼杯前傾角度增加可增加THA術后關節的穩定性,大球頭的穩定性優于小球頭,前傾達到某一角度時,大球頭和小球頭間的后方穩定性無差別。