Cadaveric Analysis of an Accelerometer Based, Hand-held Navigation System for Distal Femoral Cutting Block Alignment in Total Knee Arthroplasty

PURPOSE: Concerns regarding implant malalignment in TKA still remain, as it has been shown to decrease component survivorship and increase the rate of revision surgery. The most commonly used method for distal femoral cutting block alignment is via an intramedullary (IM) guide, in which a cutting block is fixed to the distal femur at a specific angle relative to the IM rod. Most surgeons set the distal femoral resection angle to the same degree of valgus for all TKAs with a preoperative varus alignment (e.g. 6°), and to a different degree for all TKAs with a preoperative valgus alignment (e.g. 3°); the goal being to obtain a distal femoral resection perpendicular to the femoral mechanical axis. However, this method assumes no variation in the femoral mechanical-anatomical angle between patients, and relies on the assumption that the difference between the femoral mechanical and anatomic axes is approximately 6°. Unfortunately, numerous studies have demonstrated this to be inaccurate, and thus using a fixed resection angle for performing the distal femoral resection commonly fails to achieve a neutral resection. Although numerous studies have demonstrated statistically significant improvements in both overall mechanical alignment and femoral component positioning with CAS techniques, concerns over increased operative times, capital costs, and the associated learning curve have limited its widespread acceptance. The KneeAlign2 TM device (OrthAlign Inc., Aliso Viejo, CA) is an accelerometer based, hand-held surgical navigation system for performing the distal femoral resection in TKA (Figure 1). It does not require the use of a large-console for registration and alignment feedback as with most CAS systems. In addition, it relies on accelerometer-based navigation, versus CT-guided, image based, or imageless navigation technologies. The aim of this cadaveric study was to validate the accuracy of the KneeAlign2 TM system in navigating distal femoral cutting block alignment in TKA. Our hypothesis is that the KneeAlign2 TM system will align the distal femoral cutting block with the same accuracy as a predicate device, the Orthosoft Sesamoid CAS Navigation System (Zimmer Inc., Warsaw, IN).