Experimental studies of the biological response to a new bone cement: II Soft tissue reactions in the rat.

The biological response to a new bone cement (London Hospital cement), which contains polyethylmethacrylate/n-butylmethacrylate, has been examined experimentally and compared with polymethylmethacrylate. The cellular reaction was identical when the polymer powders of the cements were inserted subcutaneously in rats, there being a macrophage response to the polymer beads of both materials. Experimental implantation of the two cements into the paraspinal musculature of rats showed that there was less tissue damage adjacent to the new material than to polyethylmethacrylate. There was a significantly smaller macrophage and giant cell reaction in relation to the polyethylmethacrylate/n-butylmethacrylate cement. These differences may be related to the lower heat of polymerisation of the new cement and to its smoother surface contour, as demonstrated by scanning electron microscopy.

Polyethylene wear from retrieved acetabular cups.

Laboratory wear testing of ultra high molecular weight polyethylene from 12 Charnley acetabular cups, removed after periods of up to 17.5 years showed that the large patient-to-patient variations in clinical penetration rate cannot be explained by batch-to-batch variation in the wear resistance of the material. Nor was there any evidence of a time-dependent degradation in wear resistance of the material.

The Pipflex splint for treatment of mallet finger.

A new splint is described for the treatment of mallet finger deformity. The splint is in two separate parts which maintain extension of the DIP joint and flexion of the PIP joint respectively. The results of treatment in 25 patients are presented, and are superior in our hands to those resulting from other methods of splintage. The period of treatment is shorter.

The mechanical properties of cement and loosening of the femoral component of hip replacements.

Mechanical and biomechanical testing of a new bone cement suggests that improved load transfer to the proximal femur could be achieved with the combination of a cement having a lower modulus, a greater ductility and a lower creep resistance than polymethylmethacrylate and a suitably shaped femoral component.

Mechanical and biochemical properties of human articular cartilage from the femoral head after subcapital fracture.

Articular cartilage from the femoral heads of 27 patients having an arthroplasty for subcapital fracture was studied, and its mechanical and chemical properties compared to those of a group of 33 age-matched macroscopically normal autopsy specimens. Water and proteoglycan contents were measured, as were swelling ability, compressive and tensile strength of the cartilage, and the density of the underlying bone. Cartilage from the fracture specimens had a significantly reduced proteoglycan content, as measured by fixed charge density, and increased swelling ability. These results indicate that this group differs from the "normal" population and care should be taken before they are accepted as control material for studies on osteoarthritic cartilage. Another finding was that bone density was much the same in the fracture and the normal group. This casts some doubt upon the concept that patients who sustain subcapital fractures are more osteoporotic than the average for the same age range.

Laboratory development of a method of attaching ceramic femoral heads to metal stems.

A method of attaching ceramic femoral heads to metal stems has been developed and tested in the laboratory. Impact tests, fatigue tests in Ringer's solution at body temperature, and tests of the strength of fixation of head to stem, suggest that the method offers significant advantages over the taper-fit method of attachment.

Mechanical and biochemical properties of human articular cartilage in osteoarthritic femoral heads and in autopsy specimens.

We studied the mechanical and biochemical properties of articular cartilage from 22 osteoarthritic femoral heads obtained at operation and 97 femoral heads obtained at autopsy. Cartilage from the zenith and from the antero-inferior aspect of each head was tested both in tension and in compression. Water content, swelling ability and proteoglycan content were measured, the cartilage was examined histologically and the density of the underlying bone was assessed. Fifty-five of the autopsy specimens were defined as macroscopically normal because they exhibited no progressive fibrillation patterns on staining with Indian ink; but significant changes in water content, bone density and tensile strength related to age were seen in this group. In 20 pairs of femoral heads which were both macroscopically normal, we found, surprisingly, that cartilage from the left and right sides of the same patient was sometimes very different. Compared with the normal autopsy specimens the osteoarthritic specimens had a significantly increased swelling ability, a lower proteoglycan content and impaired mechanical properties, being both weaker in tension and softer in compression. Abnormal autopsy specimens had values intermediate between those of osteoarthritic and normal groups. Results from this abnormal group suggest that there is no primary loss of proteoglycan in early osteoarthritis.

The effect of the surface finish of alumina and stainless steel on the wear rate of UHMW polyethylene.

The effect of the surface finish of medical grade alumina and stainless steel on the wear rate of ultra-high molecular weight (UHMW) polyethylene was studied in a six station pin-on-plate wear screening device using bovine serum as lubricant. The wear rate decreased as the surface finish of alumina improved from 0.10 to 0.015 micron Ra, with no evidence of an increasing wear rate below a particular value of surface finish. Tests with surgical grade stainless steel showed a similar polyethylene wear rate around the 0.025 micron Ra level, but there was evidence of a higher wear rate with stainless steel than with alumina between approx. 0.035 and 0.075 micron Ra.

A comparison of RCH 1000 and Hi-Fax 1900 ultra-high molecular weight polyethylenes.

Hoechst RCH 1000 and Hercules Hi-Fax 1900 ultra-high molecular weight (UHMW) polyethylenes have been compared, for the first time, in tests, including wear, fatigue and creep, relevant to artificial human joints. In none of the tests was the behaviour of the Hercules material inferior to that of RCH 1000, and in the wear and creep tests it was superior.

The laboratory development of a new metacarpophalangeal prosthesis.

The paper describes the design and laboratory testing of a new metacarpophalangeal prosthesis. The novel features of the new design include the joining of pairs of prostheses by common hinge-pins and the inclusion of bearings within the proximal phalanges. The common hinge-pins are designed to prevent the recurrence of ulnar drift by sharing the forces on one finger with a neighbouring joint, and together with the intramedullary bearings to prevent potentially loosening torques from acting on the fixation of the components.

The production and biology of polyethylene wear debris.

Polyethylene in the form of a concave bearing surface at the hip wears very slowly, and clinical and histological evidence suggests that the volume of debris so released is well tolerated. However, significantly greater volumetric wear rates are produced when (1) polyethylene is used as the convex component of a joint and (2) abrasives such as PMMA or bone enter the joint. Further, large quantities of polyethylene debris lead to the replacement of bone at the bone-cement interface by soft tissue. Evidence is presented which strongly suggests that this mechanism can produce joint component loosening.

A second study of tensile fatigue properties of human articular cartilage.

The tensile fatigue properties of the collagen fibre meshwork in normal human articular cartilage were measured by subjecting isolated specimens of post-mortem femoral head cartilage to cyclic tensile stress. The results of the study showed (1) that the collagen fibre meshwork is fatigue prone and (2) that its fatigue strength decreases rapidly with age. Extrapolation of the data to physiologically possible stress levels suggests that tensile fatigue failure of the collagen meshwork could occur in life.