Clinical and radiographic outcomes of an accelerometer-based system for the tibial resection in total knee arthroplasty.

PURPOSE: The accelerometer-based system is a portable surgical navigation system for TKA that does not require the use of a large computer console for registration and alignment feedback as required in computer-assisted surgery (CAS). The purpose of this prospective study was to determine the accuracy of the accelerometer-based system in the tibial component positioning and also to evaluate clinical outcomes. METHODS: Between December 2011 and July 2012, a total of 53 consecutive patients with primary gonarthrosis were prospectively enrolled for unilateral TKA using a handheld surgical navigation system to perform the tibial resection. Pre-operatively and postoperatively, patients were asked to fill out a visual analogue scale for pain (VAS) and a knee injury and osteoarthritis outcome score (KOOS). Standing antero-posterior (AP) hip-knee-ankle (HKA) and lateral knee-to-ankle radiographs were performed to determine the varus/valgus alignment and the posterior slope of the tibial components relative to the mechanical axis. RESULTS: The mean duration of follow-up was 23 months. Average preoperative VAS was 8.3 ± 0.67, which significantly improved to a mean 1.2 ± 0.57 at final follow up (P < 0.001). All scores significantly increased compared with pre-operative scores, except for the KOOS sport component (P = 0.075) and quality of life (P = 0.19). Intra-operatively, the average reading provided by the system with regard to varus/valgus alignment before performing the tibial resection was 0.55° ± 0.43. The average postoperative radiographic alignment of the tibial component in the coronal plane was 0.65° ± 0.59 of deviation by the ideal alignment (P > 0.05). CONCLUSION: This study demonstrates that the OrthAlign navigation system combines the accuracy of the computer-assisted surgery systems with the ease of use and familiarity of the traditional instruments while avoiding the drawbacks of the CAS technique and disadvantages of conventional IM femoral alignment systems. The system could demonstrate an improvement in the incidence of outliers in final coronal alignment, as compared with a patient-specific cutting guide.

Evaluation of the accuracy of a patient-specific instrumentation by navigation.

PURPOSE: The aim of this study is to evaluate the accuracy of a patient-specific instrumentation (PSI) as assessed by the intraoperative use of knee navigation software during the surgical procedure. METHODS: Fifteen patients with primary gonarthrosis were selected for unilateral total knee arthroplasty. The first three patients were excluded from this study, as they were considered to be a warm up to set-up the procedure. All patients were operated on with a cemented posterior-stabilised prosthesis cruciate ligament-sacrificing by the same surgeon using the patient matched cutting jigs. The size of the implant, level of resection, and alignment in the coronal and sagittal planes were evaluated. An unsatisfactory result was considered an error ≥2° in both planes for each component as a possible error of 4° could result in aggravation. RESULTS: On the coronal plane the mean deviation of the tibial guide from the ideal alignment was 1.2 ± 1.5 (range 0-5°) and in the sagittal plane was 3.8 ± 2.4 (range 0-7.5°). On the coronal plane the mean deviation of the femoral guide from the ideal alignment was 1.2 ± 0.6 and in the sagittal was 3.7 ± 2. CONCLUSION: On the basis of this preliminary experience the PSI system based only on data acquisition with A-P radiograms and RMN cannot be defined as accurate. In cases of the use of the custom made cutting jigs it is recommended to perform an accurate control of the alignment before making the cuts, for any step of the procedure. LEVEL OF EVIDENCE: II.

Are MRI-based, patient matched cutting jigs as accurate as the tibial guides?

PURPOSE: The aim of this study is to evaluate the accuracy of VISIONAIRE (Smith & Nephew Inc., Memphis, TN, USA) Patient Matched cutting tibial jigs in comparison with extramedullary (EM) tibial instrumentation by analysing data as detected by intra-operative use of VectorVision knee navigation software from BrainLAB (Redwood City, CA, USA). METHODS: Twelve patients were selected for unilateral total knee replacement (TKR). They underwent a full-length weight-bearing anteroposterior (AP) radiograph and magnetic resonance imaging (MRI). During surgery, once the EM guides were placed and fixed on the tibia, the orientation in the coronal and sagittal planes was checked by the navigator and then compared with the data obtained by measuring the orientation of VISIONAIRE Patient Matched cutting tibial jigs. An unsatisfactory result was considered an error ≥2° in both coronal and sagittal planes for the tibial component as a possible error of 4° could result. RESULTS: In the coronal plane the mean deviation of the EM tibial guides from the ideal alignment (0°) was 0.7 ± 0.39° and of the VISIONAIRE was 129 ± 1.55° (P = 0.22). In the sagittal plane the mean deviation of the EM tibial guides from 3° of posterior slope was -1.62 ± 1.78° and of the VISIONAIRE was +1.16 ± 4.29° (P < 0.05). Negative values indicate a more posterior slope from the ideal and positive values an anterior slope. CONCLUSIONS: This preliminary study documented only a fair accuracy of the method with a consistent risk of error of more of 3° especially in the sagittal plane. We could speculate that the problem in the sagittal plane was due to the fact that the pre-operative protocol does not include a lateral X-ray projection of the knee and only includes an AP standing X-ray of the straight leg and MRI.