Introduction: Gamma type nails are routinely used for the fixation of intertrochanteric fractures of the proximal femur. QCT at the hip is an advanced method that is increasingly being used to estimate BMD and determine the future fracture risk. Yet, implants cause metal artefacts (MA) in CT images, even at the contralateral side due to the high absorption of metal, which may impair BMD accuracy.
Methods: Three human cadavers were scanned first without and then with an implanted Titanium intertrochanteric Gamma type nail. CT scans were carried out on a GE Lightspeed VCT using two scan protocols: 140 kV, 120 mAs and 120 kV, 170 mAs (kernel Standard, 1.25 mm slice thickness). At higher kV, MA should be smaller because of the lower X-ray absorption. A QRM BDC phantom was used for in-scan BMD calibration. BMD was measured in the contralateral hip using MIAF-Femur.
Results: Table 1 shows BMD differences in mg/cm3 and % between scans with and without the nail in integral, cortical and trabecular BMD (120 kV 170 mAs protocol). Values in the intertrochanter and trochanter were similar. At 140 average differences were reduced for trabecular BMD of the neck (3.4%), all other differences were slightly increased. The difference between native and intertrochanteric Gamma type nail scans were slightly higher than in-vivo precision errors of MIAF-Femur (2.2, 3.2 and 3.9% for neck integral, cortical and trabecular BMD respectively).
|Neck BMD (mg/cm3/%)||Trochanter BMD (mg/cm3/%)|
|Average of abs values||6.6/2.9%||7.7/1.4%||6.1/6.5%||2.5/1.4%||6.4/1.6%||1.2/1.4%|
Conclusion: Artefacts of titanium implants at the contralateral hip are small in the neck and negligible otherwise and it is questionable whether the added use of metal artefact reduction software may further reduce this BMD error.
17 - 20 May 2014
European Calcified Tissue Society