Anterior hip dislocation is much less common than a posterior hip dislocation. It constitutes only 5-18% of all hip dislocations.
While the posterior dislocation is often associated with fractures, the anterior dislocation is mostly an isolated injury 1.
It can be classified into superior and inferior subtypes.
Radiographic signs of anterior hip dislocation are the lesser trochanter being more visible due to external rotation. The hip is abducted, and the femur head is usually inferior to the acetabulum. Shenton's line is also broken.
Whereas inferior anterior hip dislocation is easily recognized on an anteroposterior radiograph of the pelvis, the radiographic appearance of superior anterior hip dislocation is less straightforward, often leading to an initial misdiagnosis of posterior hip dislocation. Two radiologic findings may help to distinguish these two from each other:
- lesser trochanter more visible in anterior dislocation due to external rotation
- femoral head will appear larger than the contralateral hip on account of geometric magnification
- 1. Greenspan A. Skelettradiologie. Urban & Fischer. (2003) ISBN:3437230603. Read it at Google Books - Find it at Amazon
- 2. Erb RE, Steele JR, Nance EP et-al. Traumatic anterior dislocation of the hip: spectrum of plain film and CT findings. AJR Am J Roentgenol. 1995;165 (5): 1215-9. AJR Am J Roentgenol (abstract) - Pubmed citation