Gelatinase/type IV collagenases in the loosening of total hip replacement endoprostheses.

Gelatinase/Type IV collagenases, namely, 72 kDa matrix metalloproteinase (MMP)-2 type and 92 kDa MMP-9 type, were analyzed to evaluate the role of extracellular matrix degradation in 17 cases of loosening of total hip endoprostheses. Zymographic and densitometric analyses revealed elevated production of MMP-2 and induction of MMP-9 in tissue extracts from both the interface tissues between bone and implants and the pseudocapsular tissues around the loose endoprostheses when compared with those of 8 control noninflammatory knee synovial tissues. The level of MMP-9 was higher in the interface tissues than in the pseudocapsular tissues. MMP-9 activity was not detected in the control samples. Although differences in the type of prosthetic fixation (cemented versus cementless) or the type of alloy (cobalt-chromium-molybdenum versus titanium-aluminum-vanadium) existed, they shared a similar potential to stimulate tissues to produce MMP-2 and MMP-9. These findings suggest a role for MMP-2 and MMP-9 type gelatinase/Type IV collagenases in the degradation of extracellular matrix of periprosthetic tissues, where they may cause weakening of the connective tissue bed and the loosening of total hip replacement endoprostheses. The pseudocapsular tissues could contribute to the loosening via the production and release of matrix metalloproteinases into the synovial fluid. Alternatively, induction of matrix metalloproteinases in such tissues may reflect remodeling of the pseudocapsular connective tissues.