56 y/o F with severe left hip pain following a ground level fall.
Minimally displaced intertrochanteric fracture of the left femur.
The term “hip fracture” generally refers to a proximal femur fracture, usually involving the femoral neck. However, injuries involving the innominate bone or adjacent musculature may result in a similar clinical presentation. Fracture lines should be hypointense on both T1 and T2 weighted images. In an acute fracture, there should be high signal (indicative of marrow edema) surrounding the fracture on fluid sensitive sequences. Sometimes hypointense fracture lines may be more difficult to appreciate on fluid sensitive sequences relative to their appearance on T1 weighted images.
Muscular injuries can be diagnosed by increased signal on fluid sensitive sequences. Muscular injuries may result in edema, hemorrhage +/- hematoma formation, or frank muscle tear. Edema is seen as non-geographic areas of T1 low and T2 high signal intensity. A hematoma is seen as a defined area of signal abnormality. The signal abnormality associated with a hematoma can have varying signal intensities on both T1 and T2 weight images, dependent on the evolving state of hemoglobin. Muscular tears tend to occur near the myotendinous junction. A complete muscular tear will manifest as total disruption of the muscle with muscular retraction and associated blood/edema. A partial tear is seen as high signal without complete transection of the muscle (see the findings in our case).
Elderly patients are generally fragile and fractures can be present in patients with atypical symptoms, such as several weeks of pain or instability. A history of recent trauma may not be readily recalled. This does not preclude a patient from having a fracture. Conversely, some patients may present with symptoms concerning for a fracture but may ultimately be found to have an alternative explanation for their pain. For example, this 81 y/o F was found to have an iliopsoas abscess. Please see Figure 4b in this AJR article for further description. Some patients may simply be having an exacerbation of chronic hip arthritis or may be suffering from osteonecrosis. Please see Figure 7 in this Radiographics article for a helpful example of how to assess for osteonecrosis vs. a subchondral insufficiency fracture.
Low force hip fractures are serious injuries with a mortality rate of up to 10% for elderly patients who suffer a hip fracture following a ground level fall, and the mortality rate is increased when diagnosis/surgical management is delayed. Delayed diagnosis/treatment can result in displacement of a previously non-displaced fracture and mandate a more complex surgical repair. Unfortunately, these are common injuries and “ground level fall” is a common reason for emergency department visits. Roughly 1/3 of the population over 65 years old, and >50% of the population over 80 years old, suffer a fall every year.
Radiographs should be the initial evaluation for a suspected hip fracture. However, the reported false negative rates of radiography range from 2-10%. In one study of 179 patients with post-traumatic hip pain and an inability to ambulate, 40% of patients with negative radiographs were found to have an occult fracture following subsequent CT or MRI. Clearly, hip fractures can be difficult or impossible to detect on a radiograph. Lateral impact fractures can be missed on radiographs due to subtlety of cortical disruption at the head/neck junction, and the “sclerotic lateral cortical impaction triangle” may be your best clue for detection (please see Figure 12 in this Radiographics article).
MRI remains the “gold standard” for the detection of hip fractures and has been traditionally recommended for all symptomatic patients with negative radiographs. Due to continued advances in CT technology, similar sensitivity rates have been reported for CT and MRI and some authors even advocate for CT as the first line imaging modality for the detection of radiographically occult fractures given its lower cost and greater availability. Still, MRI will likely continue to be the “gold standard” and has been shown to detect fractures in a small percentage of cases where CT is negative (as we have seen in this case).
Orthopedic surgery consultation for consideration of surgical fixation. Femoral head/neck fractures will generally be managed surgically, while non-displaced obturator ring fractures or isolated soft tissue injuries may be managed conservatively.
1. Sheehan SE, Shyu JY, Weaver MJ, Sodickson AD, Khurana B. Proximal Femoral Fractures: What the Orthopedic Surgeon Wants to Know. RadioGraphics. 2015 Jul 17;35(5):1563–84.
2. Dominguez S, Liu P, Roberts C, Mandell M, Richman PB. Prevalence of Traumatic Hip and Pelvic Fractures in Patients with Suspected Hip Fracture and Negative Initial Standard Radiographs—A Study of Emergency Department Patients. Academic Emergency Medicine. 2005;12(4):366–9.
3. Rehman H, Clement RGE, Perks F, White TO. Imaging of occult hip fractures: CT or MRI? Injury. 2016 Jun 1;47(6):1297–301.
4. Pfortmueller CA, Kunz M, Lindner G, Zisakis A, Puig S, Exadaktylos AK. Fall-Related Emergency Department Admission: Fall Environment and Settings and Related Injury Patterns in 6357 Patients with Special Emphasis on the Elderly [Internet]. Vol. 2014, The Scientific World Journal. Hindawi; 2014 [cited 2020 Nov 2]. p. e256519. Available from: https://www.hindawi.com/journals/tswj/2014/256519/
5. Lubovsky O, Liebergall M, Mattan Y, Weil Y, Mosheiff R. Early diagnosis of occult hip fractures: MRI versus CT scan. Injury. 2005 Jun 1;36(6):788–92.
6. Oka M, Monu JUV. Prevalence and Patterns of Occult Hip Fractures and Mimics Revealed by MRI. American Journal of Roentgenology. 2004 Feb 1;182(2):283–8.
7. Gill SK, Smith J, Fox R, Chesser TJS. Investigation of Occult Hip Fractures: The Use of CT and MRI [Internet]. Vol. 2013, The Scientific World Journal. Hindawi; 2013 [cited 2020 Nov 2]. p. e830319. Available from:https://www.hindawi.com/journals/tswj/2013/830319/
8. Hakkarinen DK, Banh KV, Hendey GW. Magnetic Resonance Imaging Identifies Occult Hip Fractures Missed by 64-slice Computed Tomography. The Journal of Emergency Medicine. 2012 Aug 1;43(2):303–7.
9. Bush CH. The magnetic resonance imaging of musculoskeletal hemorrhage. Skeletal Radiol. 2000 Jan 1;29(1):1–9.
10. Rubio M, Rodriguez M, Patnaik S, Wang P. Spontaneous Iliopsoas Tendon Tear. Geriatr Orthop Surg Rehabil. 2016 Mar;7(1):30–2.