Reply to letter to editor: patient-specific instruments in total knee arthroplasty.

Abstract

The authors thank you for sharing your thoughts and questions on our study entitled “Patient-specific instruments in total knee arthroplasty”. In your letter [1] you are convinced that patient-specific instruments (PSI) may offer advantages in total knee arthroplasty (TKA) such as decreased operative time, bleeding and faster recovery. Hamilton et al. [2] found that total surgical time was over 4 minutes shorter for patients in the PSI group (57.4 minutes vs. 61.8 minutes). Stronach et al. [3] found a mean surgical time of 59.1 minutes for TKA performed with the standard technique and 59.2 minutes with PSI. Chareancholvanich et al. [4] reported shorter operative times with PSI and concluded the 5.1 minutes saved were not clinically relevant. Nunley et al. [5] found that TKA performed with PSI and traditional instrumentation had similar tourniquet times (61.0 versus 56.2 minutes), similar time in operating room (125.1 versus 137.2) and similar incision to closure time (89.6 versus 93.4). However, in your letter you noted our typing error. In our study [6] we stated that in the coronal plane the mean deviation of the extra-medullary (EM) tibial guides from the ideal alignment (0°) was 0.7° ± 0.39 and of the VISIONAIRE was 129° ± 1.55 (P = 0.22). As previously published [7], the deviation of VISIONAIRE was 1.29°, not 129°. In your letter you suggest that CT-based custom jigs were able to reproduce the posterior slope. We are in agreement with you, that the problem of not being able to reproduce an ideal alignment in the sagittal plane of the tibia may be inherent to the MRI-based jig of Visionaire. In fact, only a MRI imaging with a lateral view extending 8 cm below the joint line is acquired pre-operatively. However, Koch et al. [8] radiographically analysed CT-based custom jigs. They found that for the tibial slope, out of 301 cases, a total of 37 cases (12.3 %) of outliers >3° were found. There are limitations in this study including some lack of precision while measuring axes and component position on conventional X-rays and the lack of a control group either conventional or computer-assisted surgery (CAS) TKA. We believe that the current PSI seem is not able to result in the same degree of accuracy as the CAS system, while comparing well with standard manual techniques with respect to component positioning and overall lower axis, in particular in the sagittal plane. Therefore, even if PSI appears as a promising technology, the accuracy could still be improved, possibly leading to greater reliability.