Presentation
Acute left hip pain whilst running. Now pain persists and is associated with leg weakness and focal groin pain.
Patient Data
Two separated bone fragments are seen on the left side above above the acetabulum. On the oblique this is nicely demonstrated and represents avulsion of the AIIS apophysis (origin of the rectus femoris straight head supero-laterally) and acetabular rim (origin of the rectus femoris reflected head medially) - arrows.
The abnormalities demonstrated on recent pelvic x-ray are confirmed. There is an avulsion fracture of the straight head rectus femoris from the anterior inferior iliac spine (AIIS) with a gap of perhaps 6mm as well as the reflected head (nicely seen on the sagittal projection as a Y-shape). Soft tissue swelling with fluid in the intervening gap. The tendon remains attached to these separated bony fragments. This would account the two fragments of bone seen on the plain radiograph.
No other specific bone or joint abnormality. No intrinsic hip joint pathology in particular no joint effusion.
Conclusion: The patient has definite avulsion of the straight head of rectus femoris from the anterior inferior iliac spine with a gap of around 6mm. There is also avulsion of the 2nd rectus femoris head (posterior or reflected) from the rim of the acetabulum. This would account for the two bone fragments seen on the plain radiographs. No other intrinsic hip joint abnormality.
Case Discussion
Avulsion of the AIIS at the rectus femoris origin is not uncommon but in this case there is avulsion of both the straight (AIIS) and reflected heads (acetabular rim) causing 2 bone fragments on the radiograph.
This is a very nice example of applied anatomy.