Alineación en PTR: Una controversia en evolución aun no resuelta Alignment in TKA: An Unresolved Controversy

The problem At 15 years, the survival of these implants is greater than 96% and at 25 years they exceed 82%1 however, this good survival is obscured by a high percentage of patients, around 20%, who continue with pain and other discomfort nonspecific in the knee over time.2 Dissatisfaction after a Total Knee Arthroplasty (TKA) is a phenomenon well documented in the literature.3 Based on a review of the Swedish Registry, Dunbar et al reported that 17% of patients were dissatisfied with the TKA result.4 Baker et al. re-evaluated data from the National Register of England and Wales: 71% of patients reported improvement in knee symptoms, but only 22% rated the results as “excellent”5. In the search for solutions to improve these results, new assistive technologies for the implant have been proposed (from navigation to robotics). Although this is a multifactorial problem, lately an emphasis has been placed on alignment as a modifiable cause of this problem.6 There is controversy regarding the most appropriate type of alignment in TKA.6 The balanced knee concept has no clear definition and can be achieved in more than one way. There are 2 classic techniques described for this: The measured resection (MR) and the gap balancing of the femur and tibia.7 In MR, anatomical references are used to place the implant. Bone cuts are made regardless of the ligamentous situation and are based on the transepicodyle axis, the anteroposterior femoral axis or Whiteside axis and the posterior axis of the condyles. The surgeon follows the guidelines of the instruments, trying to make the distal and posterior femoral bone resections similar; ligaments later adapt through soft tissue releases. In the gap balancing (GB), distraction systems are used to define the best position of the arthroplasty and subsequently bone cuts and ligamentous releases are adapted to it. But regardless of the technique used, the goal for decades has been the same, to obtain a mechanically aligned knee.8 The classic is still mechanical alignment, but this approach ignores the anatomy of the native joint and the relationship between the origin and insertion of the soft tissues. What’s new: kinematic, functional, anatomical alignment etc. The mechanical alignment looks for a knee that respects the mechanical axis of the lower limb, in which the mechanical axles of the femur and tibia form an angle of 180° between them.8 The problem is that this axis is natively neutral in only a certain percentage of the population, which is why it has been questioned as a parameter to be followed. Constitutional varus has been described in up to 30% of men and 17% of women.9 There is no doubt about the excellent results that have been achieved with mechanically aligned TKA.8 But new studies have generated more interest in a new concept of alignment; kinematic alignment. Two randomized clinical trials and other multicenter studies showed that patients treated with kinematic alignment reported a significantly better difference from mechanical alignment in pain relief, function, flexion, and more normal knee sensation, with implant survival of about 2, 3 and 6 years.10–12 The kinematic alignment seeks to reconstruct the axis of the limb prior to the implantation of the Arthroplasty (pre-arthrosic axis),8 and has 3 objectives7: Restore the native tibiofemoral articular surface, restore the native alignment of the lower limb and restore the native laxity of the knee. Riviere et al defined 5 implant alignment methods13: Mechanical, tight mechanical, anatomical, kinematic, and