Faut-il systématiquement changer une pièce fémorale monobloc cimentée lors d’une reprise d’arthroplastie totale ? Évaluation prospective

Le but de cette étude était d’évaluer les modifications de rugosité et de sphéricité d’une série prospective et continue de reprises d’arthroplasties totales de hanche dont la pièce fémorale monobloc cimentée a été systématiquement explantée. Vingt-deux patients dont l’âge moyen au moment de l’arthroplastie était de 51,3 ans ont été inclus. Le délai moyen à la reprise était de 14,8 ans (sept à 25 ans). Les causes de reprises étaient un descellement acétabulaire isolé (12), deux ostéolyses périacétabulaires sans descellement, une luxation itérative avec descellement acétabulaire, une infection sans descellement, un descellement bipolaire, et cinq descellements fémoraux isolés. Toutes les pièces fémorales monobloc étaient en acier inoxydable 316 L avec une tête de 22,2 mm de diamètre. Parmi les 22 pièces fémorales, la rugosité du pôle de la tête était anormale pour dix (45,4 %) et 18 têtes fémorales (81,8 %) présentaient des zones à rugosité franchement pathologique en dehors du pôle. La sphéricité était supérieure à 5 μm pour 13 des 22 têtes fémorales. Il n’existait aucun facteur prédictif de telles modifications. La conservation de la pièce fémorale dans les cas où cette attitude pouvait être discutée aurait conduit à garder une tête fémorale dont la rugosité était anormale dans 80 % des cas et dont la sphéricité était anormale dans plus de 90 % des cas. Cette étude indique qu’il est préférable si l’âge physiologique du patient et les comorbidités associées le permettent de systématiquement reprendre une pièce fémorale monobloc cimentée quelle que soit la cause de la reprise.

Purpose of the study

The main reason for revision of Charnley type total hip arthroplasty is socket loosening related to high polyethylene wear and periacetabular osteolysis. In these situations, the monobloc cemented stem is frequently not loosened and it is not clear whether the femoral component can be retained during the revision procedure. The aim of this study was to evaluate surface and sphericity damage to the femoral head of a prospective and consecutive series of revision total hip arthroplasties during which the cemented monobloc femoral component has been systematically revised.

Materials and methods

We performed 22 revisions of both components of Charnley type cemented total hip arthroplasties. In all cases, the 22.2 mm head of the monobloc femoral component was made of 316 L stainless steel. The international standard for such femoral heads includes an average surface roughness (Ra) of 0.05 μm, a total roughness (Rt) value of 0.5 μm and a sphericity of ± 5 μm. The mean age of the patients at the time of the index arthroplasty was 51.3 years. The average time to revision was 14.8 years (seven to 25 years). The reasons for revision included isolated socket loosening (12), extensive periacetabular osteolysis without socket loosening (two), recurrent dislocation associated with socket loosening (one), sepsis without implant loosening (one), loosening of both components (one), and isolated loosening of the femoral component (five). Hence, 15 of the 22 (68.2%) femoral components could theoretically have been retained. The surface roughness of the femoral heads was evaluated using a contact-type profilometer. For each head, the apex and two zones, either macroscopically scratched or with loss of the mirror finish, were analyzed. Moreover, the sphericity of the heads was measured using a spherometer.

Results

The stem explanted after recurrent dislocation was analyzed separately as the femoral head had major scratches. The mean Ra and Rt of the series at the apex was 0.029 and 0.876 μm, respectively. The mean Ra and Rt of the series for the macroscopically damaged areas was 0.05 μm and 1.540 μm, respectively. The mean sphericity of the series was 7.2 μm. Hence among the 22 explanted stems, 10 femoral heads (45.4%) had Ra or Rt apex and 18 (81.8%) Ra or Rt scratched area values beyond ISO standards, respectively. Sphericity was greater than ± 5 mm for 13 of the 22 femoral heads (59.1%). With the numbers available, the age at the time of the index arthroplasty, the BMI, the time and the reason for revision were not significantly associated with the degree of femoral head damage for both roughness and sphericity parameters.

Discussion

Retaining the femoral component during revision of the total hip arthroplasty including a monobloc femoral component is theoretically an interesting alternative. However, femoral head surface damage occurring in vivo would have lead us to retain severely scratched heads in over 80% of the hips, and heads with abnormal roughness and sphericity values in over 90% of the hips. Bases upon our results, we recommend systematically revising the femoral component during revision THA including a monobloc stem, irrespective of the reason for revision.