[Estimation of femoral version based on broach geometry after femoral-neck osteotomy]

To find out whether it is accurate to estimate femoral version based on femoral broach after femoral neck osteotomy using computed tomography scans.

In 32 total hip arthroplasty (THA), we performed CT scans before and after operation. Four possible levels (lesser trochanter, 5 mm above, 10 mm above and 15 mm above the lesser trochanter) of broach version were calculated based on the preoperative CT scan. Stem versions were measured on the postoperative CT scan. We determined the difference between the preoperative broach version and the postoperative stem version using the Student's t test for paired samples assuming equal variance.

For the operated hips, preoperative hip version differed according to the level of measurement. Our findings showed that the average femoral version was 37.0°±11.0° at the level of the lesser trochanter (section 1), 34.3°±10.6° at 5 mm above the lesser trochanter (section 2), 28.1°±10.9° at 10 mm above the lesser trochanter (section 3), and 22.4°± 13.7° at 15 mm above the lesser trochanter (section 4), and that the average version for the femoral neck (FNV) was 12.9°±13.8°. The postoperative hip version was the stem version (FSV), which we found to be an average of 26.1°±11.0°. The mean femoral version for section 1 and 2 was larger than the mean postoperative stem version (P<0.01); the mean version for sections 3 and 4 did not differ from the mean postoperative stem version (P>0.05). The mean femoral neck version was less than the mean postoperative stem version (P<0.01); the difference was 13.2°±11.1° of the increased anteversion on average for the FSV compared with FNV.

The accuracy of estimated femoral version after arthroplasty depends on broach level. When it is 10 mm above the lesser trochanter, stem version estimation is accurate, but below that level, there is a tendency to overestimate.