Fracture of a ceramic component in total hip
replacement is a rare but potentially catastrophic complication.
The incidence is likely to increase as the use of ceramics becomes
more widespread. We describe such a case, which illustrates how
inadequate initial management will lead to further morbidity and
require additional surgery. We present the case as a warning that
fracture of a ceramic component should be revised to another ceramic-on-ceramic
articulation in order to minimise the risk of further catastrophic
wear.
Wear testing of THR has chaperoned generations of improved UHMWPE bearings into wide clinical use. However, previous in vitro testing failed to screen many metal-on-metal hips which failed. This talk tours hip wear testing and associated standards, giving an assortment of THR wear test results from the author's laboratory as examples. Two international hip wear-simulator standards are used: ISO-14242-1 (anatomic configuration) and ISO-14242-3 (orbital-bearing). Both prescribe 5 million (MC) force-motion cycles involving cross-shear synchronized with compression simulating walking gate of ideally aligned THRs. ISO-14242-1 imposes flexion (flex), abduction-adduction (ad-ab) and internal-external (IE) rotations independently and simultaneously. An orbital-bearing simulator more simply rotates either a tilted femoral head or acetabular component, switching from flexion-dominated to ad-ab-dominated phases in each cycle with some IE. In the latter, the acetabular component is typically placed below the femoral head to accentuate abrasive conditions, trapping third-body-wear debris. Wear is measured (ISO-14242-2) gravimetrically (or volumetrically in some hard-on-hard bearings). Wear-rate ranges from negligible to >80mg/MC beyond what causes osteolysis. This mode-1 adhesive wear can therefore “discriminate” to screen hip designs-materials in average conditions. Stair-climbing, sitting, squatting and other activities may cause THR edge-loading and even impingement with smaller head-to-neck ratios or coverage angle, naturally worse in metal-on metal hips. Deformation of thin acetabular components during surgical impaction may cause elevated friction or metal-metal contact, shedding more
Summary. Five year migration results of 49 large-head metal-metal (MoM) total hip arthroplasties show good implant stability and no association between implant migration and