Prothèse totale de genou Hermès™ conservant les deux ligaments croisés : comparaison avec la version postérostabilisée au recul de huit ans

Les buts de l’étude étaient de connaître les résultats cliniques, fonctionnels et radiologiques des prothèses totales de genou conservant les deux ligaments croisés (PTG 2C) à plateau fixe Hermès™ au recul de huit ans et de trouver les facteurs qui influencent le résultat par rapport à la même prothèse postérostabilisée. Les résultats d’une série continue de 41 PTG 2C posées entre 1991 et 1994 avec l’aide d’un distracteur extra-articulaire ont été analysés au recul d’un et de huit ans en se fondant sur les scores IKS et l’évolution radiologique. Les résultats ont été comparés à ceux d’une série continue de 35 PTG postérostabilisées (PS) Hermès™ posées sans distracteur pendant la même période. Pour les deux séries, les caractéristiques des patients et des genoux à opérer, le mode de fixation des implants et les réaxations frontales postopératoires étaient semblables. Les genoux porteurs de PTG 2C restaient douloureux (36,7) et peu mobiles (106°) mais le score fonction était bon (80,8). Quatre implants tibiaux s’étaient descellés et six modifications de la fémoropatellaire étaient apparues. Les genoux porteurs de PTG PS étaient presque indolores et plus mobiles (113,8), avec un moins bon score fonction (72,9). Les descellements tibiaux étaient en même nombre alors que les modifications fémoropatellaires des PTG PS étaient moins nombreuses. Les moins bons résultats cliniques et les modifications radiologiques de la fémoropatellaire plus fréquents des PTG 2C s’expliquaient par une mauvaise utilisation du distracteur. Les PTG 2C ne sont pas plus exposées aux descellements prothétiques que les PTG PS. Mais, pour obtenir des genoux plus mobiles et indolores, leur pose demande une grande précision opératoire.

Purpose of the study

The purpose of this study was to determine the functional, clinical and radiographic results obtained with total knee arthroplasty (TKA) preserving both cruciate ligaments using the Hermès™ prosthesis with a fixed plateau. Mid-term results at eight years mean follow-up were compared with the outcome achieved at the same follow-up with posterior-stabilized (PS) Hermès™ TKA with a fixed bearing.

Material and methods

The results of a continuous series of 41 TKA with bicruciate preservation implanted between 1991 and 1994 with and extra-articular distractor were analyzed at one and eight years follow-up using the IKS scores and radiographic findings. A change in the medial femoral and tibial angles greater than 2° was considered to indicate implant loosening. Results were compared with those of a continuous series of TKA with PS knees implanted during the same period without a distractor and with independent bone cuts. The patients and operated knees were not different between the two groups: femoral and tibial implants were cemented in the large majority of knees with press-fit metal-backed patellar implants and comparable postoperative alignment (179°).

Results

The knees with the TKA bicruciate preservation were painful (37.6%) and exhibited limited mobility (106°) from the first postoperative year, but the function score was good (80.8 points). Four tibial implants exhibited varus displacement greater than 2° (mean 6.5°) and six femoropatellar changes were noted (five with lateral displacement of the patella on a non-cemented patellar implant). The knees with a posterior-stabilized TKA were almost all pain-free (44.3 points) and exhibited better range of motion (113.8°). Among the PS designs, there was the same number of tibial loosenings which were favored, as for the bicruciate preservation TKA, by excessive frontal laxity in extension at one year. Femoropatellar modifications appeared to be less common with the posterior PS knees (one event). There was no measurable polyethylene wear.

Discussion

The good clinical and radiological results obtained by Cloutier, who used the same distractor for the same TKA implants with bicruciate preservation, suggest that the less favourable clinical results and the radiographic modifications of the patellofemoral component, which were more frequent in our bicruciate preserved implants, can be explained by an inadequate use of the distractor. By creating greater ligament tension (which we attempted to achieve), the independent bone cuts do not allow perfect respect of the dynamics of the cruciate ligaments compromising the frontal femoropatellar mechanics.

Conclusion

The risk of prosthetic loosening is not greater with TKA bicruciate sparing designs than with PS knees when the postoperative frontal laxity and the frontal realignment are satisfactory. They enabled better function but greater operative precision is required to achieve pain-free knees with a good range of motion.