Successful cemented femoral arthroplasties reveal very often stiffened bone structures

Background: PMMA bone cements represent one of the oldest biomaterials used in general and orthopedic surgery since 1938. The use and application still raise questions with respect to osseointegration and long-lasting behavior in combination with artificial implants. Objectives: The study focuses on the following questions: Why do some implants last for many years and others do not, can bone embedded in bone cement survive, will heat gener- ated by the exothermic reaction yield a necrosis of the bony trabeculae, can the once obstructed medullary canal be remodeled for full revascularization, can preserved cancellous bone stiffened by bone cement carry the load and finally, is the so-called cemented-press-fit really an improvement as indicated? Purpose: The purpose of the study is to define the necessities for the long-lasting success of cemented components by scientifically answering the stated questions. Material and Methods: Twelve human specimens were selected. Long-lasting results between two and 20 years, an average of 8.2 years, were gathered from four female and eight male patients who died from causes other than arthroplasty. Inclusion criteria were the intact cement-to-bone transition without radiolucent line, and full-load bearing, with the exception of one amputee for comparison and the pain-free wearing until death. The well-preserved specimens were processed and fixated with a buffered Karnovsky solution cut into a series of sections using a special saw which thus guaranteed the preservation of the soft tissue together with metal and plastic, as well as bone cement. Documentation included the new HIIFL microscope, embedding in cross-linked polymers, and thinly ground cross-sec- tions documented in transmitted and polarized light, as well as freeze-dried and sputtered with gold for the scanning electron microscopy. Documentation was carried out with the PSEM 500 and Rollei Flex, as well as Leitz Orthoplan and Ploemopak. Results: The standardized cemented components revealed similar histo-pathological find- ings. All specimens presented enlarged areas with preserved cancellous bone, partly stiffened with bone cement. All specimens showed vital bone, signs of fracture healing and new bone formations immediately on or beside the bone cement. Furthermore, in all specimens, the medullary cavity was rebuilt by a complicated remodeling process resulting in a secondarily built medullary canal. It was obvious that heat necrosis plays no role in long-lasting symbiosis and it was proven that cancellous bone stiffened by bone cement can carry the load. The unloaded implantation revealed extreme bone atrophy in addition to stable implantation, recognizable by the lack of any fibrous encapsulation and the support by trabeculae oriented perpendicularly towards the implant. The cemented press-fit anchorage showed aggressive granulomata penetrating the interface and destroying the osseointegration. Conclusion: Preserved cancellous bone stiffened by bone cement can carry the load, heat necrosis plays no role, and bone cement is biocompatible and stable for 20 years and cer- tainly longer. It will be destroyed mechanically, however, by a press-fit implant anchoring directly with the bone which characterizes the principle of a mill and results in the finest bone-cement debris, a self-destroying system