Radiographic outcome of limb-based versus knee-based patient specific guides in total knee arthroplasty.

Background: Patient specific guides (PSG's) were developed to improve overall component alignment in total knee arthroplasty (TKA). The aim of this study was to undertake a comparative radiographic study of two commonly used PSG and determine whether the radiographic technique used to construct the PSG had a significant effect on overall alignment.

Methods: This prospective cohort study examined the accuracy of limb-based (n=112) versus knee-based (n=105) MR PSG in restoring the mechanical axis in three planes according to post-operative Perth CT scan protocol.

Results: Limb-based MR and knee-based MR PSG systems both restored overall hip-knee-ankle angle (HKAA), femoral coronal alignment, tibial coronal alignment, femoral sagittal alignment, tibial sagittal alignment and femoral rotation alignment to within 3° of a neutral mechanical axis with similar precision (91.1% vs. 86.7% p=0.30, 97.3% vs. 96.2% p=0.63, 97.3% vs. 97.1% p=0.94, 94.6% vs. 89.4% p=0.16, 90.2% vs. 81.0% p=0.05, 91.1% vs. 86.7% p=0.30, respectively). However, when the secondary outcome measure of alignment within 2° was assessed, limb-based MR PSG restored HKAA, femoral coronal and tibial sagittal alignment with greater precision than knee-based MR PSG (73.2% vs. 64.8% p=0.016, 93.8% vs. 80.8% p=0.004 and 82.1% vs. 62.9% p=0.001, respectively).

Conclusions: The findings of this study recommend the use of limb-based MR PSG for improved precision in the restoration of neutral mechanical alignment over knee-based MR PSG in TKA.

Level Of Evidence: Therapeutic level III.