Risk of stem undersizing with direct anterior approach for total hip arthroplasty

The direct anterior approach (DAA) for total hip arthroplasty (THA) is claimed to be as effective but less invasive than the conventional posterior approach (PA). However, the higher risk of femoral fracture and soft tissue damage cannot be underestimated. The present authors believe that the difficult femoral exposure and the surgeon's knowledge of possible complications related to femoral preparation may result in a higher rate of undersized stems when compared to PA, even when a short femoral component is employed to minimise these risks.

A retrospective study was performed to compare the effective adherence of surgical sizing to preoperative planning in a series of 112 short stem THAs, of which 59 were implanted through PA and 53 through DAA without intraoperative imaging, by a single surgeon skilled in both techniques.

the frequency of stems smaller than expected was 3-times higher with DAA than with PA (54.72% vs 16.95%, p<0.001), while the frequency of stems at least 2 sizes smaller than expected was more than 6-times higher with DAA than with PA (24.53% vs 3.39%, p = 0.001). Conversely, no differences of size discrepancy distribution were found for cups and prosthetic heads. Postoperative x-rays confirmed an inferior mean canal fill in the DAA group, but excluded a different incidence of frontal malalignment between the groups.

The technical difficulty of femoral preparation and the surgeon's knowledge of possible related complications might lead to implant undersized stems more frequently through DAA than through PA, especially if intraoperative imaging controls are not used.