[Long term results of a series of cementless total hip prostheses on patients of less than 50 years old].

UNLABELLED

Since 1974, we have more than 20 years experience with cementless rehabitable total hip arthroplasty.The purpose of this work is a long term study of development of this type of fixation about a personal series of 83 hips which benefitted from this type of arthroplasty before 50 years old between 1974 and 1980.

MATERIAL AND METHODS

The implants used are among the oldest. On the acetabular side, we used the BG spiked acetabular component (Fig. 1), containing 4 teeth for primary fixation, 3 equatorial armatures and a surface treatment. This metal back in two sizes 50 and 54 mm, initially permitted the insertion of a polyethylen insert of an interior diameter of 32 mm with a peripheric thickness of 5.5 mm; since 1979, the insert had a 22.2 mm diameter, assuring 10 mm minimal thickness of. The femoral implant (Fig. 2) for 62 hips was the Huchet prothesis, then in 16 cases, the minimadreporic prothesis composed of a morse cone and a head of 22.2, the Huchet prothesis was one-piece femoral implant.The dominant etiology was coxarthrosis (56 cases) of which 50 % had major dysplasis. The average age at the time of the intervention was 41 years old (18-50 years), the follow-up of this series is 17 years, and 8 months (15-21 years). Resumption of former activities was the rule.Results of the rehabitable pro thesis up to 12.31.1995: Of the 83 cases, the outcome of 55 of them (66.3%) is known : 49 (59%) were examined for this study; the evolution has been documented; 28 (33.7%) were uncontactable, 6 patients (7.3%) were deceased between 8 and 9 years following the operation, without having had the hip revised.Among the 49 protheses which were evaluated, 22 (44.9%) have not been revised to date. Clinically, the function is normal and there are no radiological signs of attrition of the insert or mobilisation of implants. There are 10 Huchet Protheses and 12 minimadreporic protheses in this group. The average age at the time of the intervention was 42 years old (30-50 years old), the follow-up was 16 years and 7 months (15-19 years) (Fig. 3a-d).27 hips (51%) needed to be revised, but the causes of reoperationn include different reasons tied to the failure of biological fixation but particularly to errors in the initial concept of the Huchet prothesis.Reoperation linked to the failure of the biological fixation: Out of 7 acetabular implant reoperations, one was carried out systematically on a cup which was perfectly bone-integrated during the changing of a femoral component, 3 were necessary due to perforation (attrition of the insert). Only 3 acetabular implants (6.1%) required reoperation for symptomatic loosening.Four femoral implants (8.6%) have been taken out because of failure of biological fixation between 2 and 11 years follow-up. Finally, for one patient the persistance of the incapacitating crural pain which lasted for more than one year led to the removal of the femoral stem, nevertheless perfectly integrated.Reoperation linked to the concept of the Huchet prothesis: These were undertaken in two sets of circumstances.Changing only the polyethylene insert was only called for in the Huchet prosthesis and concerned 18 hips (36.7%); the delay to reoperation varied from 11 to 18 years with an average of 14 years delay. Changing of the insert had a simple short post-operative outcome and functional recuperation was between 6 and 8 weeks (Fig. 4a-c).Removal for perforative attrition of polyethylene insert causing metal-to-metal wear between head and metal back. Five Huchet prostheses are included in this group, with an average delay to reoperation of 16 years and 3 months (14-19 years).

COMMENTS

This retrospective study with a 66.3 % rate of re-examination permits three types of comments.The principal cause of revision (23 cases), is linked to polyethylene attrition and is only found in the group with Huchet prosthesis. More than the quality of the polyethylene used at this time, it is its thickness in contact with a 32 mm head which led to the complete removal of the prosthesis in 10.2% of the cases.The second comment argues for the modularisation of the femoral implant. The presence of a stem with a cone and a removable head would have avoided the removal of 5 perfectly bone-integrated femoral implants. Certainly, the literature demonstrates the risk of corrosion generated by the morse cone but it is up to the manufacturers to improve their procedures.Finally, the third comment concerns the current state of the long term of the biological fixation by rehabilitation with surface treatment. With 17 years 8 months follow-up (15-21 years), 81.6% of components are still fixed, the real failure of the bony ingrowth of 10.2% is comparable to the rate of failure in long term follow-up of totally cemented prothesis found in young subjects.

CONCLUSION

With more than 20 years follow-up for the older cases, the concept of the biological fixation of an implant by bony ingrowth using surface treatment seems to be very reliable.The experience of this long term study argues for the thickness of polyethylene to be at least 10 mm for all metal back acetabular component and the future of this kind of implant seems to lie in modularisation made possible by the morse cone which would allow the replacement of the bearing surfaces.