THE ITALIAN EXPERIENCE IN COMPUTER ASSISTED TOTAL KNEE REPLACEMENT: MINI-INCISION VS MINI-INCISION AND COMPUTER ASSISTED SURGERY TKR

Abstract

Introduction: No comparison between minimally invasive TKR using traditional alignment guides and computer navigation systems has been documented in the literature. The aim of this prospective randomised trial is compare the radiological results of 2 different groups of TKRs performed with a less invasive surgical approach (mini-parapatellar) using either a traditional hand guided technique (MIS) or the assistance of a computer assisted alignment system (MICA).

Materials and Methods: Since 2004 seventy-four patients undergoing TKR with the same implant have been enrolled in the study. Inclusion criteria included a body-mass index less than 30, no major ligamentous laxity, no flexion deformity and no previous open knee surgery.

Patients were randomly assigned to either the traditional or computer-assisted alignment group opening a closed envelope just prior to the skin incision. In the MIS group (37 knees) a minimally invasive approach was performed using an intramedullary femoral guide and an extramedullary tibial guide. In the MICA group (37 knees) the implant was positioned using a CT-free computer assisted alignment system (Vector Vision, version 1.52, BrianLAB, Munich, Germany) using the same minimally invasive surgical approach (mini-parapatellar). The duration of surgery was documented in all cases.

Eight months after surgery each patient had long-leg standing anterior-posterior radiographs and lateral radiographs of the knee. All the radiographs were always taken with a standardized protocol with the same magnification.

The radiographs were assessed by an independent radiologist blinded to the original procedure to determine the frontal femoral component angle (FFC), the frontal tibial component angle (FTC), the hip-knee-ankle angle (HKA) and the sagittal orientation (slope) of both femoral and tibial components. The number and percentage of outliners for each parameter was determined. In addition the percentage of patients from each group with all 5 parameters within the desired range was calculated.

Results: The mean surgical time was 89.4 minutes (range: 75–112) in the MICA group and 75.84 minutes (range: 48–106) in the MIS group. This difference was statistically significant (p< 0.001).

The alignment of the femoral component as determined by the slope was significantly better in the MICA group (p< 0.001). Comparison of the FTC angle showed a statistically better alignment in the MICA group (p< 0.029). There were no statistical significant differences in HKA, FFC angles and in the slope of the tibial component between the 2 groups. All the implants in the MICA group achieved HKA and FTC angles aligned within this range while only 31 implants (83.8%) in the MIS group achieved similar accuracy. These differences in HKA and FTC angles were statistically significant (p=0.025). Thirty-six (97.3%) implants in the MICA group achieved a femoral slope aligned within 3 degrees of the desired position compared with 31 (83.8%) implants in the MIS group. In the MICA group 36 implants (97.3%) achieved a tibial slope aligned within this range while in the MIS group 33 implant (86.5%) achieved a similar result. A FFC angle aligned within 3 degrees of the desired position was achieved in 35 (94.6%) and 32 (86.5%) of the implants in the MICA and MIS groups respectively. These differences in femoral and tibial slope and FFC angle were not statistically significant.

A statistically significant difference (p< 0.001) in the total number of outliners was seen with 158 and 181 in the MICA and MIS groups respectively. The number of implants with all 5 radiological parameters aligned within the desired range was statistically higher in the MICA group (p=0.001). Thirty-three implants (89.2%) in the MICA group and 20 (54.1%) in the MIS group were correctly aligned in all measured parameters.

Discussion: Minimally invasive joint replacement has become increasingly popular driven both by the orthopaedic community and patient expectations. However, malalignment has been identified as a potential problem when performing joint replacement surgery through small incisions. Minimally invasive techniques can make implant positioning more difficult by limiting visualisation of anatomical landmarks. As the matter of fact many theory has been proposed for knew more conservative surgical approaches to the soft tissue such as the mid-vastus or sub-vastus even without any consideration about what already centuries ago biologist had established. At the beginning of the last century Bizozzero already compared muscle to nerve as perpetual tissues which can recover after an injury only with scared.

However recently, after initial enthusiasm, authors have recommended caution when using mini-invasive techniques for total joint replacement.

Computer-assisted surgery has the potential to address the difficulties of correct component positioning and alignment in minimally invasive knee replacement. Recently a prospective randomised study comparing computer navigation assisted minimally invasive TKR to conventional TKR reported a lower incidence of radiological outliners and better pain score in the computer navigation group.

In this prospective randomized the comparison of the radiological results showed statistically significant differences between the 2 groups for component positioning both in the coronal plane and sagittal plane. The desired femoral slope and FTC angle were achieved in significantly more patients in the MICA group than the MIS group. Furthermore the results supported previous studies showing a statistically significant reduction in the number of outliners in the computer-assisted technique. In addition, the number of implants with all parameters aligned within desired values was statistically higher in the MICA group. No complications were seen in either group however the surgical time was statistically longer in the MICA group.

Longer follow-up will be needed to demonstrate any correlation between the lower numbers of outliners and superior clinical outcome and implant survivorship in the computer navigation group.