INTRACAPSULAR PRESSURE AND LOOSENING OF HIP PROSTHESES - PREOPERATIVEMEASUREMENTS IN 18 HIPS

We measured the intracapsular pressure preoperatively in 18 hips (17 p atients) before revision of a total hip arthroplasty because of asepti c loosening. Distension of the joint capsule was measured with sonogra phy in 13 cases. In extension, the mean intracapsular pressure was 26 (0-60) mmHg, in extension and inward rotation it was 159 (24-280) mmHg , in extension and outward rotation it was 30 (3-67) mmHg and in 45 de grees of flexion it was 12 (0-28) mmHg. A mean of 6 (0.5-20) mL of joi nt fluid was aspirated after the pressure measurements. Sonography sho wed increased joint fluid/synovial edema and/or increased capsular thi ckness, as compared to 34 unrevised, radiographically not loose prosth etic hips, and that the capsular distension correlated to intracapsula r pressure during extension and inward rotation. We conclude that the intracapsular pressure usually is elevated in a hip joint with loose p rosthetic components, that the intracapsular pressure varies with the position of the hip and that capsular distension reflects increased in tracapsular pressure. The increased and often very high pressure, vary ing during gait, may pump debris away from the joint along the interfa ces and even by itself cause osteolysis and loosening.