Clinical and experimental studies on total hip arthroplasty

• In a 12-year follow-up study, a low-friction, metal-on-plastic hip prosthetic system (Charnley) was compared with a high-friction, metal-on-metal prosthetic system (McKeeFarrar) in a consecutive series of 169 patients, mean age 67 at the start. Satisfactory results were reported in 92 percent of the patients. One-third of the prostheses showed radiographic signs of loosening. The cumulative aseptic failure rate was 8 percent for the Charnley prosthesis and 15 percent for the MKF prosthesis. The difference was not statistically significant.The performance of a flexible (Bute!) and a rigid (PCA) cementless femoral component was studied in a prospective, randomized study of 28 matched pairs of patients (mean age 52 years). A high rate of stem loosening was observed for the flexible prosthesis and 4 cases of fatigue breakage occurred within the 3- to 5-year follow-up period. Proximal resorption and distal hypertrophy of the femur were frequently noted on the radiographs for the rigid stem. The scintigraphic activity around stems well fixed to bone became normalized in the calcar region. In contrast, it was about 50 percent increased around the prosthetic tip. For loose prostheses, the bony uptake was more intense and did not show the same time-related decrease. The scintimetric results did not correlate well with the signs of bone remodeling seen on the radiographs. Repeated at different time intervals, bone scintimetry may be informative in the followup of noncemented THA.In a consecutive series of THAs, the straight ITI-I stem (n=65), made of titanium alloy, was compared at a 5-year review with the Lubinus femoral component (n=77), curved and made of cobalt-chrome alloy. The ITH stem showed a high frequency of surrounding radiolucent lines. Six of the stems were considered loose as compared with none of the Lubinus stems. To date, 5 have been revised and 2 more are in need of revision operations, all in the ITH group. Although the initial costs were somewhat reduced with the use of the cheaper ITH prosthesis, the estimated accumulated costs turned out to be higher in the ITH than in the Lubinus group due to the increased need for revisions.In a study of THA performed on patients 80 years and older, good pain relief was achieved but at the cost of increased postoperative complications and hospital expenses as compared with patients around 65 years of age at operation. Functional improvement was not as evident as pain alleviation. The procedure did not result in decreased use of welfare services in the elderly group of patients.An experimental study was performed on 10 rabbits. Hydroxyapatite coated titanium plugs were implanted in both femora of each animal. Five were treated for seven days with an NSAID (diclofenac) and five were used as controls, receiving no treatment. A significantly lower force was required to pull out the implants 3 weeks after surgery in the group treated with diclofenac than in the untreated group. The results indicate that even short-term treatment with NSAIDs might interfere with the process of bony ingrowth and thereby endanger primary fixation of the implant despite the presence of a hydroxyapatite coating.A new cementless prosthesis was designed in titanium alloy in order to integrate the principles ofpressfit and flexibility. In a special test set-up the endurance properties of the stem were determined. Prototypes of the prosthesis were subjected to load cycles of 4,000 N in one ·test and to a more physiologic load pattern in another test. In both tests the prostheses broke after approximately 600,000 cycles without showing any material defects. It was concluded that considerable difftculty exists in constructing an "isoelastic" stem with reasonable safety limits to fatigue failure when using titanium alloy.

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