Experimental reaming of the proximal femur and acrylic cement implantation: vascular and histologic effects.

The technique of microangiography and correlated histology was used, in experiments on the proximal femora of mature mongrel dogs, to study the effects of simple medullary reaming and of reaming followed by insertion of acrylic cement. The hip joints were not disturbed. A segment of Steinmann pin, representing the stem of a hip prosthesis, was inserted into the cement as it was polymerizing. The most significant results, after reaming alone, were devascularization and apparent necrosis of large areas of the cortex of the subtrochanteric femoral diaphysis. Full recovery was observed in 6 months. However, when acrylic cement was introduced following the reaming, extensive necrosis of the inner layers of the diaphyseal cortex was still present after a year, when the observations were terminated. The presence of necrosis of bone was judged by the lack of visible osteocytes in the lacunae. After the devascularization caused by filling the diaphyseal medulla with acrylic cement, the apparently necrotic cortex was revitalized without osteoclasia. That is in contrast to the results in another study in which osteoclasia and osteoneogenesis were required to restore cortex with empty cell lacunae. This raises the question of dormant osteonecrosis in contrast to total osteonecrosis. These studies show, in thin histologic preparations, acrylic bone cement in situ in the tissues. A fibrous membrane was found at the cement-bone interface in most areas. It was thicker in the diaphysis than in the metaphysis. The physiologic effects of acrylic cement implantation are considered to be likely factors in the loosening which is observed clinically when the femoral components of hip prostheses are under protracted stress.