Quantitative ROI differences for assessment of occult intertrochanteric extension of greater trochanteric fractures on pelvis CT.

Purpose: To determine if difference in Hounsfield Units (HU) of the medullary bone between the injured and non-injured femurs in patients with greater trochanteric fractures is associated with occult intertrochanteric (IT) extension.

Methods: Retrospective review was performed of 81 patients (age range 54-102, 54 females and 27 males) who underwent CT and subsequent MRI after identification of a greater trochanteric fracture without evidence of IT extension on radiography and/or CT. Hounsfield units of the injured and non-injured femurs on CT were recorded at the level of the base of the greater trochanter centrally (ROI1) and the level of the upper border of the lesser trochanter posteromedially (ROI2). The difference between the injured and non-injured femur for each ROI1 and ROI2 were calculated. Absence or presence, and if present, extent of IT extension was assessed on MRI. Analysis was performed to determine if there is correlation of difference in density with presence, and extent of occult IT fractures.

Results: 81 cases met inclusion criteria, 14 (17%) had no IT extension, 11 (14%) had less than 50% IT extension and 56 (69%) had 50% or greater IT extension. There was statistical significance between presence and absence of IT extension between the injured and non-injured femur for ROI1 (HU) no IT extension median (IQR): 18.8(4-40), ROI1 (HU) present IT extension median (IQR): 65.5(46-90) p < .0001, and for ROI2 no IT extension median (IQR): 3(-8-25.5) and ROI2 present IT extension 51(40.5-76), p < .0001. There was statistical significance of the extent of IT extension: ROI1 less than 50% IT extension median (IQR): 37.5(27.5-57), ROI1 50% or greater IT extension median (IQR): 72.3(53.5-91.3), p < .0001, and for ROI2 less than 50% IT extension median (IQR): 17.5(8-49), and ROI2 50% or greater IT extension median (IQR): 55.8(45.3-81.5), p < .0001. A threshold ROI2 difference of 50 HU resulted in specificity of 92% and sensitivity 60.7% of for IT extension 50% or greater.

Conclusion: Patients presenting with greater trochanteric fractures, an asymmetric increased density measured by ROI differences within the medullary space of the IT region between the injured and non-injured femur is associated with occult IT extension.