Hiroshi Inui et al investigate what bearing navigation software has on clinical outcomes
Background
Total knee arthroplasty (TKA) has become one of the most successful surgical procedures in orthopaedic surgery.1,2 The success of this procedure depends on many factors, including surgical techniques and the design and material of the components.
With regard to surgical techniques, implant positioning and soft tissue balancing are very important. Malpositioning of any component can lead to an increased risk of loosening, instability, and pain.3,4
Restoration of the tibiofemoral angle to within 3° of neutral during TKA is thought to be associated with better outcome.4-7 The accurate rotational alignment of femoral and tibial components is also considered important.3,8,9
Computer-assisted navigation systems are designed to increase the accuracy of implantation, and have become much more accepted and prevalent in recent years.
Several studies, including a meta-analysis study have demonstrated superior alignment of the components in the coronal plane in navigated compared with conventional implanted TKA, with fewer outliers outside a range of 3° varus or valgus.7,10,11
Some studies have noted an improvement in the accuracy of rotational alignment using navigation systems.12,13 However, it is still not clear whether navigation can improve rotational alignment consistently.14,15
Recently, several software and adapted instrument advancements have been made to further improve the accuracy of total knee component positioning. One recent study demonstrated that advancements in navigation software improved the accuracy of overall mechanical alignment and several individual component positioning variables; however rotational alignment was not evaluated in that study.16
Although consistent and accurate rotational positioning is desirable, it remains to be elucidated whether currently available navigation software improves rotational accuracy of placement of components.
Version 2.0 of the Stryker image-free navigation system was first implemented in our institute in January 2007. It was updated to version 3.1 in July 2007 and version 4.0 in January 2009. Molli et al demonstrated several advancements of the 3.1 system over the 2.0 system, which led to more accurate implant positioning.16 Several advancements of the 4.0 system have also been noted.
Therefore, we hypothesised that this recent navigation system update would improve alignment in TKA and reduce operating time. We evaluated several outcome measurements including overall alignment, individual component positioning, knee score, range of motion, and operating time.
Methods
This study was approved by the institutional review boards of the University of Tokyo (No.2674). All patients provided written informed consent.
Of a total of 109 consecutive primary TKA procedures performed in 93 patients between December 2007 and March 2009, 46 consecutive knees in 33 patients were replaced using the Stryker 3.1 image-free computer navigation system (Stryker Orthopedics, Mahwah, NJ, USA) between December 2007 and December 2008.
Sixty-three consecutive knees in 60 patients were replaced using the updated Stryker 4.0 image-free navigation system between January 2008 and March 2009. Thirty-three knees in 30 patients of the Stryker 3.1 group and 49 knees in 48 patients of the Stryker 4.0 group met the inclusion criteria: no major previous orthopaedic surgeries (i.e. arthroplasty, open reduction-internal fixation procedures, osteotomy), satisfactory full-length standing anteroposterior (AP) and lateral radiographs after operation, complete data entry, and adequate follow up of minimum 1 year.
Preoperative variables were recorded including age, sex, body mass index, preope