Purpose: Implantation of a unicompartmental knee pros-thesis (UKP) via a short incisiosn was proposed to improve rapid postoperative recovery. But it is known that long-term survival is highly dependent on implantation quality. The purpose of this study was to evaluate the influence of implantation quality assessed radiographically and that of rapid recovery after unicompartmental arthroplasty using the conventional or minimally invasive approach.

Material and methods: A continuous series of the first 25 cases of UKP implanted using the minimally invasive approach (group 1) was compared with a homogeneous group of matched knees in a series of 145 UKP implanted with the same approach as used for total knee arthroplasty (group 2). The groups were comparable for age, gender, weight, and height. The same medial cemented UKP with a metallic tibial base plate was implanted in both groups. Postoperative radiographic measures included the overall mechanical axis, the femoral and tibial implantation orientations, and the posterior tibial slope.

Results: There was no significantly different between groups 1 and 2 for mechanical axis (3.6° and 4.7° respectively), tibial implantation angle (87° and 88°), or posterior tibial slope (2.6° and 2°). The femoral implantation angle was also comparable (2.3° and 2.9°) with the exception of one knee (9°) in group 1. Hospital stay, use of crutches and resumed activity were significantly shorter in group 1. Blood loss (222 and 244 ml respectively), postoperative pain (visual analogue scale), and full flexion at one year were comparable between the groups.

Discussion: The basic difference between the two approaches is the absence of patellar eversion and rupture of the extensor system with the minimally invasive method. This probably explains the more rapid recovery of function and activity in this group. The one case of significant femoral deviation noted in this group points out the need for greater care in positioning the specific guides for the short incision approach. To evaluate the long-term results of UKP implanted with the minimally invasive approach, the same criteria for patient selection and prosthetic implantation should be used.