In this report we present our long-term developmental and clinical results with both highly cross-linked and extensively cross-linked polyethylene materials. Beginning in 1970s, we performed wear screening studies on UHMWPE (GUR412) sterilized by gamma- irradiation in air (range 0 to 10, 000 kGy) . From these scientific studies the 1, 000 kGy dose (100 Mrad) appeared optimal, and so we began clinical use in 1971, and that continued into 1978. The radiographic wear-rates in patients with 1, 000 kGy sockets, assessed by radiography, appeared 6-fold reduced compared to our standard UHMWPE sockets. Note also that we had not used any post-sterilization heat treatment for these pioneering extensively crosslinked polyethylene sockets. With clinical use now over 30 years, it was also clear that there was no adverse oxidation created by any free radicals present in our extensively cross-linked polyethylene sockets. With these encouraging clinical results, we further studied laboratory wear results with the modern UHMWPE resins, using the irradiation doses 1, 000, 5, 000, 10, 000 and 15, 000kGy and with both saline and serum lubricants in hip simulators. These more recent studies demonstrated that the wear in extensively cross-linked polyethylene sockets was undetectable, less even than the measurement errors in the simulator techniques. It was unfortunate that the physical properties of such extensively cross-linked polyethylene sockets did not meet the current ISO and ASTM standards. Thus, despite the excellent wear performance of these materials, we decided to investigate also the properties of the 60 kGy irradiated UHMWPE. The polyethylene sheet (GUR 1050) was first irradiated with 35 kGy under N2 and then heat treated to remove free radicals. The socket liners were then machined to shape and resterilized with 25 kGy under N2 gas. The mechanical and tribological properties were then measured for this moderately cross-linked polyethylene material. Our clinical studies are still very short and so much longer follow-up will be required for these moderately cross-linked polyethylene sockets. With continuing clinical success with moderately cross-linked, highly cross-linked and extensively cross-linked polyethylene sockets, it may be necessary to reconsider the criteria for ISO and ASTM standards.

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The objective of this study was to compare the wear mode of polyethylene (PE) cups run in a hip simulator to retrieved PE cups, and to evaluate the efficacy of the PE wear model.
Fifteen PE cups were tested in vitro: 3 at each of the irradiation doses 0, 2, 5, 50, 100 and 150 Mrad (in a 9 channel hip simulator, 6.2 million cycle duration, physiological load profile by Paul, 2000N maximum load at 1Hz using 30% bovine serum) .
Five retrieved PE cups were examined: there were three SOM cups (Mizuho Medical Instrument Co., COP alloy 28 mm head), of which one, given 0 Mrad, was retrieved after 8 years of clinical use, and two of which, given 100 Mrad, were retrieved after 15 years of clinical use. The other two were T28 PE 2.5 Mrad cups (Zimmer) : one after 18 years, and one after 13 years of clinical use. The cups were examined using a SEM (Philip XL30 FEG) for wear-scar locations and PE wear-topography.
Original machine marks were observed in the weight-bearing areas of the extensively cross-linked (ECL) in-vitro PE. No machine marks were observed for the 0 and 2.5 Mrad in-vitro cups and retrieved cups. The formation of more nodules and fibrils in the 0 Mrad cups, compared to the ECL cups (in-vitro and retrieved), was striking. The frequency of occurrence and length of the fibrils and nodules were dependent on the dose of gamma irradiation. More ripples were formed in the 2.5 Mrad and higher cups, compared to the non-irradiated cups (in-vitro and retrieved) . The in-vitro cups formed more ripples than the retrieved cups. In general, the SEM features for in-vitro Mrad cups appeared similar to those of the retrieved Mrad cups.
The in-vitro Mrad cups accurately reflected the conditions of the artificial joint in the living body. Therefore, comparisons of retrieved PE cups with simulator PE cups appeared to be a very powerful research tool. SEM observation demonstrated far less wear damage in the ECL cups than in the non-ECL PE. Thus the ECL PE cups appeared to be a significant improvement over conventional non-irradiated PE cups, in terms of wear resistance.

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PE cups with 0, 2.5, 50, 100 and 150 Mrad radiation treatments were run in a hip simulator, and we examined the cup surfaces for micro-wear phenomena and analysed the corresponding wear debris. In general, the size and frequency of the PE surface fibrils and the size of the retrieved PE debris decreased with increasing radiation dose. The PE fibrillar sizes and geometrical shape-factors on the cup surfaces correlated well with radiation dose. However, the trends for debris size and shape-factors as related to radiation dose were weak. Thus, the morphology of the PE-fibrils on the cup surfaces was more sensitive to variations in radiation dose than the actual wear debris produced in simulator tests.

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Osteoprotegerin (OPG) is a key regulator of osteoclastogenesis. We investigated the presence of OPG and bone-resorbing cytokines, the potential of osteoclastic differentiation in joint fluid from failed total hip arthroplasty (THA), and the inhibitory effect of OPG on osteoclast formation in vitro induced by the joint fluid. This study aimed to clarify one important step in the cascade of periprosthetic osteolysis in the process of implant loosening. OPG levels in joint fluid in 20 cases of failed THA were significantly lower than in 15 cases of osteoarthritis (OA) (p<0.001) . The levels of bone-resorbing cytokines and interleukins (IL) -1β and IL-6 were significantly higher in failed THA joints than in OA fluid (p<0.001 and p=0.001, respectively) . Marked osteoclast formation was observed in the presence of failed THA joint fluid in the mouse coculture system, when compared to OA fluid (p<0.001) . The addition of 100 ng/ml OPG to the mouse coculture system completely inhibited osteoclast formation in the presence of failed THA joint fluid (p<0.001) . The data suggested that low levels of OPG combined with higher IL-1β and IL-6 levels represent the potential of osteoclast differentiation and activation in failed THA joint fluid. Inhibition of osteoclastogenesis in vitro by OPG suggests that a low level of OPG with elevated bone resorbing cytokines contributes to periprosthetic osteolysis via osteolytic joint fluid, thus leading to THA prosthesis loosening.

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Objective: Postoperative infection is one of the most difficult-to-treat complications after total knee arthroplasty (TKA) . Various measures are taken to prevent it, but none is effective enough, and the prognosis in infection after TKA is generally poor. In the present study, we evaluated the effects of the use of a tourniquet on the onset of early postoperative infection.
Methods: Findings obtained from patients who underwent primary TKA in this facility between April 1988 and September 1999 using a tourniquet (tourniquet group; 159 joints) were compared to those obtained from patients who underwent primary TKA between October 1999 and March 2001 without using a tourniquet (non-tourniquet group; 92 joints) . Follow-up observations were conducted for 2 to 20 months in both groups.
Results: The total volume of bleeding was obviously greater in the non-tourniquet group (803.5±433.0 ml) than in the tourniquet group (458.2 ±326.8ml) . Postoperative infection occurred in 3 patients in the tourniquet group, but none in the non-tourniquet group.
Conclusions: Hypoxia in the wounded areas caused by the use of a tourniquet results in the suppression of vascularization and fibroblast activity and a reduction in macrophage activity. This is expected to result in a delay in wound healing and the impairment of the infection defense system. The non-use of a tourniquet may contribute to the prevention of early postoperative infection.

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The clinical results of reconstruction of ruptured extensor tendons in rheumatoid hands were investigated from September 2000 to May 2001. Surgical treatment was done for ruptured extensor tendons in 32 digits of 12 patients with rheumatoid arthritis. We started fitting dynamic splints at the third postoperative day, and started active exercise.
Ranges of active flexion and extension of MP joints, and the ROM of wrist joints were examined.
A postoperative program using dynamic splints was superior to casting, in terms of improved MP joints flexion and maintaining wrist ROM, despite the remaining deficient extension of MP joints.

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Recently, many knee joint ganglia have been diagnosed by MRI. However, there are no reports of the natural course of knee joint ganglia. We encountered two cases in which the knee joint ganglion shrank or disappeared.
Case 1. A two-year-old boy was brought to our clinic with a complaint of bilateral knee snapping. Left knee snapping disappeared at the age of three. MRI was performed on the right knee at the age of four. There were normal menisci, with a ganglion between the tibia and popliteal muscle. Right knee snapping was gone at the age of five, and follow-up MRI demonstrated shrinking of the ganglion.
Case 2. A twenty-nine-year old woman consulted our clinic with a complaint of right knee pain and maximal-flexion disturbance. MRI was performed three months after the first consultation. There were normal menisci, and a ganglion around the posterior cruciate ligament. She was scheduled for arthroscopic examinations. However, her complaint disappeared one month after MRI examination. Follow-up MRI demonstrated disappearance of the ganglion.
Many kinds of therapy have been reported for knee joint ganglia. Some reports proposed total ganglion resection by arthrotomy, but there was a report of recurrent knee joint ganglion after arthroscopic treatment. Although we describe two cases of spontaneously disappearing or shrinking knee joint ganglia, the rate of disappearance of each knee joint ganglion is unknown. We propose avoiding arthrotomy and observing the ganglion for a few months in patients without severe complaint caused by the knee joint ganglion.

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Pyogenic sacroiliitis is relatively rare in childhood. We report two cases: Case 1, a girl aged 12 years 6 months, who visited our hospital with a high fever (40.3°C) and right coxalgia. Case 2, a girl aged 11 years 7 months, presenting with a fever (39°C) and left buttock pain. Although no abnormalities were observed in the initial radiographs in either case, magnetic resonance imaging (MRI) indicated changes in the sacroiliac joint. Subsequent bone scintigraphy was valuable in localizing the sites. Laboratory examinations showed CRP levels of 6.4 mg/dl and 13.6mg/dl respectively. Blood-cultures indicated Staphylococcus aureus in both cases. After treatment with intravenous antibiotic, and about two or three weeks rest, the patients were able to walk unaided, without pain, and there has been no recurrence of infection.
Because clinical findings in pyogenic sacroiliitis may generally resemble a herniated intervertebral disc, septic spondylitis, or coxatitis, diagnosis is generally difficult in early stages. However, MRI and bone scintigraphy proved very useful.

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