MINIMALLY INVASIVE IMPLANTATION OF A UNICOMPARTMENTAL KNEE PROSTHESIS USING AN CT-FREE NAVIGATION SYSTEM: A FEASIBILITY STUDY

Abstract

Purpose: Implantation quality is an important prognostic factor for long-term outcome of unicompartmental knee prostheses. Minimally invasive techniques allow more rapid rehabilitation but at the price of potentially diminished implantation quality. Navigation systems have been developed to overcome this problem.

Material and methods: We analysed a preliminary series of 20 patients (group A) whose unicompartmental medial femorotibial prosthesis (Search(r), Aesculap, Tuttlingen, Germany) was implanted with the CT-free Orthopilot(r) system (Aesculap, Tuttlingen, Germany). This system uses intra-operative kinematic and anatomic analysis to define the mechanical axes of the femur and tibia in space. The femoral and tibial cut lines are aligned on these axes. This series was compared with a retrospective historical series (group B) of 60 knees with the same prostheses implanted with the same navigation system but with a conventional approach requiring patellofemoral subluxation. Implantation quality was measured using the following angles: AP mechanical femorotibial angle, orientation of the tibial and femoral prostheses (AP and lateral), vertical level of the prosthetic joint space in relation to the preserved joint space.

Results: The AP mechanical femorotibial angle was in the desired range in 16 knees in group A (80%) and in 48 in group B (80%). The femoral component exhibited optimal position in 18 knees in group A (90%) and in 54 in group B (90%). The tibial component exhibited optimal position in 17 knees in group A (85%) and in 53 in group B (88%). Thirteen prostheses in group A (65%) and 37 in group B (62%) were implanted optimally using the studied criteria. The length of the incision varied from 7 to 10 cm in group A. There was no significant difference.

Discussion: This navigation system allows very precise implantation of the medial unicompartmental knee prosthesis, both with the conventional technique and the minimally invasive technique. Use of the minimally invasive technique does not decrease the radiographic quality of the implantation in comparison with the conventional navigation technique. This technique could become the gold standard for implantation of unicompartmental knee prostheses.