The Effect of Intramedullary vs Extramedullary Tibial Guides on the Alignment of Lower Extremity and Functional Outcomes Following Total Knee Arthroplasty: A Randomized Clinical Trial

Total knee arthroplasty (TKA) has been known as a definitive treatment for advanced knee osteoarthritis. Both intramedullary (IM) and extramedullary (EM) tibial guides have been used to restore the desired extremity alignment. However, controversy exists regarding the superiority of either technique We aimed to compare the functional outcomes and accuracy of IM and EM tibial guides in providing neutral alignment after TKA. In a randomized, double-blinded clinical trial, we studied 98 patients undergoing primary TKA in two groups of IM and EM. We measured the medial proximal tibial angle (MPTA), varus angle (VA), and joint-line convergence angle with normal ranges of 90°±3°, 0-2°, and 0±3°, respectively, on a three-joint alignment view after three months. We also assessed the functional outcomes at the last follow-up. Finally, we compared these outcomes between the two groups.  Eighty-four patients (IM=42, EM=42) were included in the final analysis (16 males, 68 females, mean age: 63.9±8.6 years, mean follow-up: 13±2.9 months). The mean postoperative (post-op) alignment angles showed no significant difference, although MPTA outliers were significantly more frequent in the EM group (26.2% vs. 9.5% in IM, P=0.04). None of the functional outcomes showed a significant difference between the two groups. However, the mean increase in knee range of motion (ROM) was significantly higher in the knees with VAs within ±3° of neutral than those outside this range (30.8 vs. 27.4, respectively, P=0.039). We conclude that both techniques were not different regarding the mean alignment angles and functional outcomes. However, fewer MPTA outliers can be seen with the IM technique. A post-op mechanical axis within ±3° of neutral can result in a more ROM increase after one year.  Level of evidence: I