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© 2004 The Journal of Bone and Joint Surgery, Inc. Posterior Slope of the Tibial Implant and the Outcome of Unicompartmental Knee Arthroplasty
1 University Paris XII, Hôpital Henri Mondor, 94010 Creteil, France
Investigation performed at Hôpital Henri Mondor, Creteil,
France
Background: Laboratory studies have suggested that the sagittal displacements permitted by a knee replacement are influenced by the posterior slope of the tibial implant. The effect of the posterior slope of the tibial implant on the outcome of unicompartmental arthroplasty is not well known. The purpose of the present study was to assess the effect of the posterior slope on the long-term outcome of unicompartmental arthroplasty in knees with intact and deficient anterior cruciate ligaments. Methods: We retrospectively reviewed the results of ninety-nine unicompartmental arthroplasties after a mean duration of follow-up of sixteen years. At the time of the arthroplasty, the anterior cruciate ligament was considered to be normal in fifty knees, damaged in thirty-one, and absent in eighteen. At the most recent follow-up, we measured the posterior tibial slope and the anterior tibial translation on standing lateral radiographs. The anteroposterior stability of seventy-seven knees that had not been revised by the time of the most recent follow-up was evaluated clinically.
Results: In the group of seventy-seven knees that had not been
revised by the time of the most recent follow-up, there was a significant
linear relationship between anterior tibial translation (mean, 3.7 mm) and
posterior tibial slope (mean, 4.3°) (p < 0.01). The mean posterior
slope of the tibial implant was significantly less in the group of
seventy-seven knees without loosening of the implant than it was in the group
of seventeen knees with loosening of the implant (p < 0.05). Five ruptures
of the anterior cruciate ligament occurred in knees in which the ligament had
been considered to be normal at the time of implantation; the posterior tibial
slope in these five knees was Conclusions: These findings suggest that >7° of posterior slope of the tibial implant should be avoided, particularly if the anterior cruciate ligament is absent at the time of implantation. An intact anterior cruciate ligament, even when partly degenerated, was associated with the maintenance of normal anteroposterior stability of the knee for an average of sixteen years following unicompartmental knee arthroplasty. Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.
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13°. Clinical evaluation revealed normal
or nearly normal anteroposterior stability at the time of the most recent
follow-up in all sixty-six unrevised knees in which the anterior cruciate
ligament had been present at the time of implantation. Of the eighteen knees
in which the anterior cruciate ligament had been absent at the time of the
arthroplasty, eleven still had the implant in situ at the time of the most
recent follow-up; the mean posterior tibial slope in these eleven knees was
<5°. Seven knees in which the anterior cruciate ligament had been
absent at the time of the arthroplasty were revised. In these knees, the
tibial prosthesis was implanted with a posterior slope of >8°. 
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