Accuracy and repeatability of axes for femoral component rotation in total knee arthroplasty: a cadaver study

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Abstract

Background:

This study measured the three bony axes usually used for femoral component rotation in TKA to compare accuracy and repeatability of different measurement techniques.

Methods:

Fresh cadaver limbs (n=8) were used. Three observers (student/fellowship-trainee/consultant) identified the posterior condylar (PCA), anteroposterior (AP) and the transepicondylar (TEA) axes, using a computer navigation system to record measurements. The AP axis was measured before and after being marked with an ink line. The TEA was measured by palpation of the epicondyles both before and after an incision was made in the medial and lateral gutters at the level of the epicondyles, allowing the index finger to be passed behind the gutters. For all axes and each observer the repeatability coefficient (rc) was calculated. The TEA was then identified after dissection of all the soft tissues and was the reference to compare the accuracy of the other palpated axes.

Results:

Identification of the PCA was the most repeatable (rc: 1.1°) followed by the AP after drawing the ink line (4.5°), then the AP before the link line (5.7°), and last the TEA (12.3°) with no improvement after incisions (13.0°). The PCA was within 3° of the reference TEA 71% of the time, the AP axis 62%, and TEA less than 50% of the time.

Conclusions:

This study echoed previous studies in demonstrating that palpating the PCA intraoperatively is highly precise. The line perpendicular to the AP axis most closely paralleled the reference TEA when measured after being identified with an ink line. The palpated TEA was variable irrespective of observer experience.

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