L'étude rapporte les résultats d'une série continue, prospective, multicentrique de 425 prothèses Wallaby I^® conservant le ligament croisé postérieur, posées par le groupe Guepar de 1992 à 1995. Le composant fémoral de cette prothèse présente des condyles asymétriques et divergents pour se rapprocher le plus possible de la cinématique du genou normal. Le plateau tibial en polyéthylène est fixe.

L'âge moyen des patients (70,5 ans), la répartition homme (28,3 %) et femme (71,7 %), l'étiologie (91 % d'arthrose primitive ou secondaire) et la déviation préopératoire des genoux (65,6 % de varus > à 3° et 24 % de valgus > à 4°) étaient identiques à ceux qui sont publiés dans la littérature pour ce type de prothèse.

Vingt-six prothèses ont été suivies moins de 1 an, 84 moins de 5 ans et 315 5 ans ou plus. Parmi les 399 genoux suivis plus de 1 an, il y a eu 4 infections (1 %) dont 3 ont nécessité le changement de prothèse, 3 fractures du fémur toutes post-traumatiques, 2 descellements (1 global et 1 tibial) ayant nécessité une reprise, 1 descellement tibial et 3 descellements rotuliens non-repris. Trois patients présentaient des douleurs antérieures du genou traitées avec succès par 2 resurfaçages secondaires de la rotule et 1 section de l'aileron rotulien externe. Dix-neuf fractures de rotules (4,7 %) (dont 17 découvertes fortuitement) constituaient la complication la plus fréquente, sans retentissement fonctionnel.

Le score moyen IKS genou postopératoire était de 90,5 points et le score moyen IKS fonction de 61,6 points. La mobilité moyenne était de 110,5° ; 72,9 % des genoux étaient axés suivant la classification radiologique IKS, La survie de cette prothèse à 8 ans (suivant Kaplan Meier) était de 97,7 % quelle que soit la raison du changement de prothèse et de 98,5 % en ne prenant comme événement que la reprise pour descellement aseptique. Ces bons résultats corroborent ceux qui sont publiés dans la littérature concernant les prothèses conservant le ligament croisé postérieur à plateau tibial fixe.

Posterior Wallaby I^® is a fixed polyethylene tibial plateau prosthesis enabling preservation of the posterior cruciate ligament (PCL). Its asymmetrical and divergent femoral condyles articulate with also asymmetrical tibial plateaus. The purpose of this prospective study was to analyze outcome of the first 425 Wallaby I^® prosthesis of the Guepar group implanted for first-intention treatment.

These 425 prostheses were implanted from December 1992 to February 1995 by senior and junior surgeons. Mean patient age at implantation was 70.5 years. 91% had primary or secondary osteoarthritis and only 8.9% had inflammatory rheumatoid disease. The mean preoperative IKS score was 25.34 points and the IKS function score was 29.04. 10.35% of knees were aligned normally (mechanical axis between 2° varus and 3° valgus) according to the IKS criteria (Ewald), 24% presented valgus ≥ 4° and 65.6% varus ≥ 3°. All tibial and patellar components (except one) were cemented, 5.8% of the femoral pieces were inserted without cement. All but 11 patellae were resurfaced. Clinical outcome was assessed with the IKS score and radiological outcome with the IKS criteria. The patella was considered to be tilted when the alpha angle was > 5° and dislocated when the AA' distance was > 5 mm. The chi-square test was used for comparison of quantitative variables (significance set at 0.05).

Early postoperative complications were rare: two infections cured with debridement-lavage and antibiotics without removal of the prosthesis, one peronal nerve palsy which regressed partially, ten late unions without clinical consequence (particularly in the inflammatory rheumatoid patients). Twenty-six prostheses were followed less than one year (eight patients died and eighteen were lost to follow-up) and 84 less than five years (27 patients died and 57 lost to follow-up before five years). 315 prostheses were followed for more than five years (5-9 years) with a mean follow-up of 6.3 years. Among the 399 prostheses followed for one year or more, we noted: four infections including three requiring change of the prosthesis (one cured by arthroscopic lavage), two aseptic loosenings which were revised (one global one tibial), one tibial loosening and three patellar loosenings which were not revised, and two femoral ossifications limiting joint motion but improved by arthrolysis and resection of the ossifications. Three patients experienced anterior pain requiring secondary patellar resurfacing in two and section of the lateral patellar wing in one. Ninteen patellar fractures (4.7%) were noted, including 17 with no significant functional impact which were not revised. The mean IKS knee score among prostheses followed for five years was 90.5 points, with mean motion 110.5°. Mean IKS function score was 61.63 points. 72.9% of the knees were aligned, 22.2% in varus and 4.9% in valgus. The mechanical axis of 94.3% of the knees was between 5° varus and 5° valgus. Prosthesis survival at eight years (Kaplan-Meier method) was 97.7% considering all reasons for prosthesis removal and 98.5% for removal for aseptic loosening.

This prospective multicentric study demonstrated that the results obtained with the Wallaby I^® prosthesis are as good as those obtained with other prostheses sparing the PCL and published in the literature. Preservation of the PCL enables better knee stability, correct motion (110.5° in our series) with almost no radiological wear of the tibial polyethylene at eight years. The only worrisome complication is patellar fracture.