Cementless total hip replacement (THR) is rapidly being accepted as the surgery for arthritic diseases of the hip joint. The bone-ingrowth rate in porous-type cementless implants was about 90% over 10 years after surgery, showing that biological fixation of cementless THR was well maintained on both the stem and cup sides. As for the stress shielding of the femur operated using a distal fixation-type stem, severe bone resorption was observed. The severe bone resorption group showed continuous progression for more than 10 years after surgery. Stem loosening directly caused by stress shielding has been considered less likely; however, close attention should be paid to bone resorption-associated disorders including femoral fracture. Cementless cups have several specific problems. It is difficult to decide whether a cup should be placed in the physiological position for the case of acetabular dysplasia by bone grafting or at a relatively higher position without bone grafting. The bone-ingrowth rate was lower in the group with en bloc bone grafting, and the reactive line was frequently noted in the bone-grafted region. Although no data indicated that en bloc bone grafting directly led to poor outcomes, such as loosening, cup placement at a higher site without bone grafting is now selected by most operators. The polyethylene liner in a cementless cup is thinned due to the metal cup thickness; however, it has been suggested that the apparent relation between the cup size and the wear rate was absent as long as a cementless cup is used. Comparative study indicated cementless THR was inferior with regard to the yearly polyethylene wear rate and incidence of osteolysis on both the stem and cup sides. Meta-analysis study on the survival rate between cement and cementless THR reported that cemented THR was slightly superior. It should be considered that specific problems for cementless THR, especially with regard to polyethylene wear, do occur.

The concentration and molecular weight of hyaluronan (HA) in the synovial fluid of the hip joint were determined in 13 patients (aged 62.8 +/- 9.4 years) who had undergone prior total hip arthroplasty(THA), 23 patients (aged 65.0 +/- 8.2 years) with osteoarthritis of the hip joint (OA), and 13 patients (aged 40.2 +/- 2.7 years) with idiopathic osteonecrosis of the femoral head (ION). A sample of synovial fluid was obtained during revision THA because of loosening of the total hip prosthesis for the THA group, and during the first replacement surgery or osteotomy for the OA and ION groups. The concentration of HA in the synovial fluid was 0.64 +/- 0.42 mg/ml in the THA group, 1.07 +/- 0.28 mg/ml in the OA group, and 1.30 +/- 0.56 mg/ml in the ION group. The concentration of HA in the synovial fluid of the THA patients was significantly lower than that of the OA and ION patients (P = 0.0156 vs OA, P = 0.003 vs ION). The molecular weight of HA was 309 +/- 88.3 x 10(4) Da in the THA group, 377 +/- 201 x 10(4) Da in the OA group, and 240 +/- 148 x 10(4) Da in the ION group; these values do not differ significantly (P = 0.259 vs OA, P = 0.174 vs ION). Among the THA patients, there was no relation between the concentration of HA and the age of the patient, length of time since the first operation, or type of prosthesis fixation; there was also no relation between the molecular weight of HA and each of these factors. These results suggest that a pseudosynovial membrane is regenerated after THA, and that it produces HA of the same molecular weight as that in patients with OA and ION, although in smaller quantities.

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Fibrous tissue which regenerated on the acetabular arthroplasty surface was obtained from a 52-year-old woman who underwent total hip replacement after cup arthroplasty. The histological features of this newly formed fibrous tissue and expression of keratan sulfate, which is a characteristic matrix component of articular cartilage, were studied. Microscopic observation revealed that the arthroplasty surface consisted mainly of fibrous tissue which did not show metachromasia with toluidine blue staining, but there were many nodular structures communicating with the bone marrow. Immunostaining for keratan sulfate revealed clear positive staining around the cells of the nodular structures communicating with the bone marrow, while only weakly positive staining was observed in the superficial layer of the loose fibrous tissue. The present study revealed marked formation of articular cartilaginous tissue in areas having good communication with the bone marrow, which indicates that maintenance of this communication may be necessary to improve the outcome of cup arthroplasty.