Description

Overall the success rate of TKR is very high with high patient satisfaction and outcomes. Survivorship depends on patient selection and surgical techniques. Femoral and tibial component mal-alignment might lead to early failure.

Although recent studies have questioned the significance of overall postoperative mechanical alignment on survivorship, most studies still demonstrate alignment to be a crucial factor in the clinical success of TKA [1]. Ritter et al [2], in a review of 6070 TKAs, noted the risk of aseptic failure to significantly increase with a tibial component orientation less than 90° relatives to the tibial axis and a femoral component orientation greater than 8° of valgus relative to the femoral axis (failure rate, 8.7%).

Berend et al [3], in a review of 3152 TKAs, demonstrated that a tibial varus alignment of greater than 3° increased the odds of implant failure and medial bone collapse by roughly 17 times.

The most commonly used methods of component alignment in TKA are an extramedullary (EM) alignment guide for the tibial resection and an intramedullary (IM) alignment guide for the distal femoral resection. Unfortunately, these "conventional" methods have demonstrated a limited degree of accuracy for both overall mechanical alignment and individual component Method to create an even more accurate resection includes the use computer-assisted navigation technique. In a meta-analysis of 29 studies comparing computer assisted surgical (CAS) to conventional techniques in TKA (Mason et al). The authors found that only 68.2% of TKAs in the conventional group achieved an overall mechanical axis within 3° of neutral (vs 91.0% in the CAS group), 65.9% achieved a femoral varus/valgus alignment within 2° of perpendicular to the femoral mechanical axis (vs 90.4% in the CAS group) and 79.7% achieved a tibial varus/valgus alignment within 2° of perpendicular to the tibial mechanical axis (vs 95.2% in the CAS group).

However, despite these advantages, concerns regarding increased capital costs, operative times, extra pin sites, and the learning curve associated with the use of CAS techniques have continued to limit its widespread acceptance.

Another factor that might have limited its usage is that so far no study has shown the accuracy with CAS can directly lead to a longer survivorship of the implant or a better functional outcome. However, the most surgeon still believes a correct align knee will yield a better function and outcome.

This shed the light to a new navigation device. Iorio et.al [4]The KneeAlign 2 system (OrthAlign Inc, Aliso Viejo, California) is an accelerometer-based, portable navigation device for TKA that attempts to combine the alignment accuracy of large-console CAS systems, with the ease of use and convenience of conventional alignment methods. It is used to perform the proximal tibial and distal femoral resections in TKA. It does not require the use of a large console for registration and alignment feedback and is compatible with any TKA system. It consists of a disposable display console (2 × 4 × 2 inches in size) and a reference sensor, both of which are used for the tibial and femoral resections The KneeAlign 2 is the second version of the KneeAlign originally developed to perform only the proximal tibia resection in TKA. The KneeAlign 2 required the additional design of a femoral jig and cutting block and allows for the use of the same display console to perform both the proximal tibia and distal femur resections. The display console and reference sensor each contains triaxial accelerometers that communicate wirelessly with one another. The surgical technique for using the KneeAlign 2 to perform the tibial resection is the same as previously described Briefly, the tibial jig has 2 primary components (a fixed component and a mobile component) connected by a proximal articulation .The fixed component, with the attached reference sensor, is first pinned to the tibia. The purpose of the fixed component is to account for the movement of the tibia during cutting block alignment.