Standard image-free navigation systems have proven to improve the accuracy of components placement and reduce the proportion of outliers for lower limb mechanical axis in total knee arthroplasty (TKA). However, their disadvantages include a longer duration of surgery and pin-tract related complications. More recently, pinless navigation has been developed to address these shortcomings. This study aims to investigate the effectiveness of a new pinless navigation system (Zimmer® iAssist™ Knee) in TKA. Power analysis was performed. To detect a significant difference in the proportion of outliers for lower limb mechanical axis at a power of 0.80, a sample size of 50 patients would be required. Between May 2013 and April 2014, 50 patients diagnosed with osteoarthritis of the knee were divided into two surgical technique arms: 1) iAssist™; 2) conventional TKA. One Adult Reconstruction surgeon performed all the surgeries. The patients were prospectively followed up and postoperative long leg radiographs were taken at one month post-surgery. Two reviewers blinded to the surgical method performed the measurements on radiographic films. Five radiographic measurements were measured: 1) Hip-Knee-Ankle Angle (HKA); 2) Coronal Femoral-Component Angle (CFA); 3) Coronal Tibia-Component Angle (CTA); 4) Sagittal Femoral-Component Angle (SFA); and 5) Sagittal Tibia-Component Angle (STA), The Mann-Whitney U test was used to compare the two groups for quantitative variables while the Fisher's exact test was used for categorical variables.Introduction
Methods
Interest in minimal-incision total knee arthroplasty (TKA) has increased in recent years. The advantages of minimally invasive techniques (MIS) used for TKA are faster functional recovery, shorter hospital stay and better early knee range of motion. It is known that the long-term outcome after TKA is related to component position and ligament balance. The smaller incision in MIS might be associated with increased risk of malalignment of components due to limited visualisation. Malalignment of implants in TKA has been associated with implant failure and poor long-term functional results. There is a lack of evidence in the literature that MIS can achieve the same results as the standard TKR approach in terms of component alignment precision. Seventy patients scheduled for a primary TKA were prospectively evaluated postoperatively with coronal and sagittal radiographic long limb films. Mini-midvastus approach was used for all TKA. There were no complications and the radiographic evaluation found no implant or limb malalignment, or signs of early loosening. We did not observe wound healing problems, fractures or implant notching. The mini-midvastus approach can reproduces the same accuracy in component positioning as the standard medial parapatellar approach. A precise operation technique and adequate visualisation of anatomical landmarks during implantation are the key points of success in mini-midvastus approach.
