11/13/24, 7\:32 PM Guide | Hip x-ray interpretation

Hip x-ray interpretation

Table of contents

Introduction

Hip X-rays are a frequently requested radiological investigation and the ability to interpret them is a key clinical skill. It should
be noted that projectional radiography has limitations and other imaging modalities such as MRI and CT should be considered
if further evaluation is required.
Some salient points to remember when interpreting any radiological scan include\:
Apply a systematic approach to interpretation
Consider abnormalities in the broader clinical context of the speci
For the purpose of this article, we will concentrate on a systematic approach to interpreting hip X-rays with an antero-posterior
(AP) view, which is the commonest and most likely to be presented to you in an exam situation.

Con

Begin by con
Patient details (name, date of birth, unique identi
Date and time the radiograph was taken
Anatomical site (e.g. left hip)
If previous radiographs are available, these should also be reviewed to provide a point of reference.

Views

There are two standard projections produced when a hip X-ray is performed\:
Antero-posterior (AP) view
Lateral view (a.k.a.
'frog leg view')

Antero-posterior view

The AP view obtains a view of the whole pelvis, usually from the femoral shaft to above the ilium. The patient is either standing
or supine, and usually, have both legs internally rotated so as not to obscure the femoral neck length.

Lateral view

The lateral view has the patient lying supine in a frog-leg position; the patient’s knees are
externally rotated. This view is often used in paediatric patients for pathologies such as slipped upper femoral epiphysis (SUFE)
and developmental dysplasia of the hip (DDH).

Interpretation

It is important to apply a systematic approach to the interpretation of any X-ray; a commonly used approach with
musculoskeletal imaging is ABCS\:
Adequacy/alignment
Bones
Cartilage (and joint spaces)
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Soft tissue

Adequacy and alignment

Adequacy
femoral shaft.
Ensure the appropriate anatomy is visible within the borders of the image\: usually above iliac crests to one-third down the
Alignment
Ensure that the coccyx tip and pubic symphysis are in the midline.
Figure 1. Normal female pelvis & hip joints (yellow=pelvic brim, red=obturator foramen) [1]
Follow-up imaging
Not all hip fractures are visible on initial X-ray and follow-up cross-sectional imaging may be required if there is
ongoing clinical concern.

Bones

General approach
Assess the following characteristics of both the femur and visible pelvis\:
Cortical outline\: identifying any bony fragments or fractures
Bony texture\: including trabecular lines of the femur that may indicate joint disruption
Symmetry\: absence of symmetry can allow identi
Femur
Inspect all visible elements of the femur including\:
Proximal femur
Femoral head
The neck of the femur (NOF)
Greater and lesser trochanters
Trace Shenton’s line (Figure 3)\:
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Shenton’s line runs anatomically along the medial edge of the femoral neck and the inferior edge of the superior pubic
ramus (Figure 3).
Interruption of Shenton's line may suggest a neck of femur (NOF) fracture in adults or DDH in children.
It is important to note that loss of contour of Shenton’s line does not always mean there is an underlying fracture (and so an
intact Shenton’s line does not always rule out a NOF fracture), and thus should be used with caution when interpreting pelvic X-
rays.
Figure 3. Shenton’s line [2]
Intracapsular vs extracapsular fractures
It is important to understand the di
management and prognosis di
Intracapsular fractures
Intracapsular fractures are located at the neck of the femur (NOF)\:
Sub-capital (just distal to femoral head - Figure 5)
Transcervical (mid-femoral neck)
Basicervical (distal femoral neck at the NOF base)
This fracture type disrupts the joint capsule and therefore potentially the blood supply to the femoral head (branches of
the profunda femoris, most importantly the lateral circum
This means there is a higher chance of avascular necrosis (AVN) as well as fracture non-union/poor healing.
Remember that AVN is not just limited to NOF fractures, highlighting the importance of clinical context (e.g. long-term
steroid use can result in spontaneous avascular necrosis).
Extracapsular fractures
Extracapsular fractures do not involve the neck of the femur and are located below the intertrochanteric line\:
Intertrochanteric (fracture runs between the lesser/greater trochanters)
Subtrochanteric (fracture is distal to the trochanters)
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Figure 4. Classi
Pelvic bones
Assess the pelvic bones including the\:
Ischium
Ilium
Pubis (including pubic rami)
Sacrum (including sacral foramina)
Trace the borders of the 3 pelvic rings (Figure 6)\:
Pelvic brim
Obturator foramina (x2)
Comment on the continuity of the borders of these rings; remember, the rings are unlikely to be broken in only one place.
Pubic rami fractures are sometimes diagnosed in elderly patients who have fallen and present with non-speci
and/or di
7).
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Figure 6. Normal female pelvis & hip joints (yellow=pelvic brim, red=obturator foramen) [1]
Bony metastases
Bony metastases are most commonly found in areas of bone with a rich blood supply such as the pelvis, vertebrae,
proximal femur, proximal humerus and skull. Bony metastases can promote local bone formation, resulting in sclerotic
areas on X-ray (i.e. increased opacity) as well as bone resorption, resulting in lytic areas on X-ray (i.e. decreased opacity).
Figure 8. Bony metastases in the pelvis appearing as sclerotic lesions [6]

Cartilaginous joints

Acetabular joint
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Assess the characteristics of the acetabular joint including\:
Location of the femoral head in relation to the acetabulum (e.g. dislocation)
Joint space (typically 3-5mm)
Osteoarthritis
Osteoarthritis commonly a
including\:
Reduced joint space
Osteophytes (small bony outgrowths)
Subchondral sclerosis (sclerotic changes at the joint margin)
Subchondral cysts (
Pubic symphysis
Assess the joint space of the pubis symphysis which di
~10 mm at 3 years
~6 mm at 20 years
~3 mm at 50 years
During pregnancy, the joint space can increase by up to 3mm as a result of hormones such as relaxin to assist with childbirth.
Pubic diastasis
Pubic diastasis involves separation of the pubic symphysis without associated fracture. Typical clinical features include
pain in the symphyseal region aggravated by weight-bearing/walking and a waddling gait. A joint space of greater than
10mm is considered diagnostic in adults.
Sacroiliac joint
Assess the characteristics of each sacroiliac joint including\:
Joint space (should be 2-4mm in healthy individuals)
Joint end-plates (should appear smooth/regular)
Sacroiliitis
Sacroiliitis involves in
pain. The condition is typically associated with ankylosing spondylitis.
X-ray has low diagnostic sensitivity, but potential radiographic features include\:
Sclerosis of the endplates particularly on the iliac side
Irregular joint end plates
Widening of joint spaces
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Figure 9. Sacroiliitis visible on a pelvic X-ray [7]

Soft tissue & other

Inspect the soft tissue surrounding the bones and joints for\:
E
Periosteal reaction\: nonspeci
Calci
Foreign bodies (e.g. total hip replacement)

Summary

When interpreting a hip X-ray, remember the following key points\:
Begin by con
anatomical site (e.g. left hip).
Compare the images to previous radiographs where possible to provide additional context.
Assess the adequacy of the radiograph (above iliac crests to one-third down the femoral shaft).
Assess the alignment of the radiograph (e.g. location of the tip of the coccyx and pubic symphysis).
Inspect the femur and bones of the pelvis (ischium, ilium, pubis, sacrum) for abnormalities including interruptions to the
cortical outline, changes to the bony texture or asymmetry.
Inspect the acetabular joint for abnormalities including displacement of the femoral head or loss of joint space.
Inspect the joint space of the pubic symphysis for widening (e.g. pubic diastasis).
Inspect the sacroiliac joints for loss of joint space and changes to joint-end plates (e.g. sacroiliitis).
Inspect the soft tissues that surround the hip joint for abnormalities such as e
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