Hip (horizontal beam lateral view)
The horizontal beam lateral hip radiograph or shoot through hip is in the purest terms the orthogonal view of the neck of the femur to the AP projection .
The projection is used to assess the neck of the femur in profile during the investigation of a suspected neck of femur fracture .
Although technically demanding, it is the most versatile hip radiograph, utilized in trauma bays and general radiography rooms. It requires minimal patient movement on the affected side while providing high-quality diagnostic images that can be replicated both intraoperatively and postoperatively .
- the patient is supine with both arms on the chest, the side in question is closest to the image receptor:
- the image receptor can be an upright detector or a portable detector in an upright stand
- the image receptor is angled approximately 20-45° to match the angle of the neck of femur (observed on the AP pelvis/hip); this is done to prevent elongation or foreshortening of anatomy
- the image receptor should be placed in a landscape orientation superior to the iliac crest, allowing for adequate imaging of the femoral neck
- before progressing to the next step
- place a finger on the anterior superior iliac spine of the affected side, ensure it is projected onto the superior third of the image receptor. This will ensure adequate centering in the superior-inferior aspect of the projection
- elevate the bed/trolley until the central ray is at the level of mid-thigh of the unaffected leg
- the patient's unaffected hip can now be flexed and abducted;
- the flexed leg is placed on a dedicated stand; this is incredibly uncomfortable for the patient; the leg should only be up for a limited amount of time
- axiolateral (inferosuperior) projection
- centering point
- the central ray is angled perpendicular to the long axis of the neck of femur; the image receptor should be adjusted to match this angle
- the technical centering point is 13 cm distal to the neck of femur, anecdotally known as centering at the most superior region of the groin
- anteroposterior 9 cm each direction from the midline
- inferosuperior 12 cm each direction from the centering point
- detector size
- 18 cm x 24 cm
- 80-100 kVp
- 80-320 mAs
- 100 cm
- a grid can be used, although it is not uncommon to utilize an air gap technique to achieve similar results
- patients that lack bone density require a compensating filter over the inferior aspect of the femur to allow even distribution of exposure, whilst patients with increased adipose tissue may not need a filter as the adipose tissue does a sufficient amount
Image technical evaluation
The radiograph has a uniform exposure throughout, evident by the fine bony detail and no areas of overexposure. If the distal femur is overexposed, a filter may be required.
The lesser trochanter can be seen in profile, while the proximal femoral shaft superimposes the greater trochanter.
The femoral neck is central to the image and shows no signs of radiographic foreshortening or elongation.
There is a clear visualization of the articular surface of the acetabulum and the head of the proximal femur.
The opposite leg has been elevated enough that there is no obstructing soft tissue artefact.
An oblique lateral hip is helpful for visualization of the articular surfaces of the femoral head, yet it foreshortens the neck and can result in misdiagnosis .
When performing this technique, it is more common to err on positioning the image receptor too distally, hence missing the hip joint completely. Ensure the edge of the image receptor is superior to the iliac crest to ensure anatomy inclusion.
It is imperative to set the room up before positioning the patient, following the patient positioning steps above sequentially will minimize patient discomfort and maximize the quality of the exam.
Although 18 x 24 cm collimation seems ambitious, it is readily achievable with correct centering and well thought out positioning. Tight collimation is important in this examination as it reduces scatter and improves subject detail.
Do not attempt to move the affected leg to position the patient better, the advantage of using this projection is the lack of movement involved. Any movement of the patient should be done via movement of the trolley and/or mattress.
The patient will be in a significant amount of pain, explain what you are about to do before you start the exam and why you are doing it, maintain the patient's decency and ensure they are comfortable as possible.