This week we will discuss imaging of joint replacements. Radiography is the the preferred first imaging modality, both in the immediate post-operative period and for any suspected complication. CT, MRI, and nuclear medicine bone scan can also be utilized if radiographs are negative and there is still suspicion for complication.

Today's case is a 70 year-old woman who presented with right hip pain after a fall. AP radiograph of the femur reveals a right femoral neck fracture (1st image). Patient proceeded to undergo right hip hemiarthroplasty. Immediate post-operative radiograph reveals good alignment of both the femoral stem and the femoral head prosthetic. Expected post-surgical soft tissue gas is seen in the soft tissues of the right hip. Left central venous line is in satisfactory position.

Today's case is a 70-year-old woman with bilateral thigh pain. Radiograph of the femurs reveals cortical irregularities of the lateral femurs, the classic location and appearance of bisphosphonate-related stress fracture. This is an atypical location for stress fractures in a patient who is not taking bisphosphonates.

This week we will be discussing imaging of the heel. Let's start with some anatomy! The calcaneus (aka the "heel bone") has a surprisingly intricate anatomy, rendered artistically in this image.

There are 4 articular surfaces, colored green; The anterior process of the calcaneus (a) has 2 facets, one of which articulates with the cuboid (C) and the other with the talus (A). The middle (M) and posterior (P) facets also articulate with the talus.

Other landmarks are the groove for the flexor hallucis longus tendon (Fhl), lateral process (Lp), medial process (Me), peroneus longus groove (Pl), sustentaculum tali (S), sulcus calcanei (SC), posterior tuberosity (T), and trochlear process (Tp).

This annotated image shows some normal features of a lateral calcaneal radiograph.

Compression trabeculae (white lines) and traction trabeculae (black lines) are present, with the "neutral triangle" marking an area with no trabeculae. Boehler's angle is formed by drawing lines connecting the anterior process of the calcaneus to the posterior articular facet and to the calcaneal tuberosity (white angle, normal 25-40 degrees). The Gissane angle is less commonly used. It is formed by the angle from the anterior process to the calcaneal sulcus to the posterior facet (normal values vary but this should be >90 degrees). When abnormal, these angles can be used to assess fracture severity.

Depression fracture of the tibial plateau can be quite subtle on a radiograph. The injury should be suspected by mechanism (axial load on the lower extremity). If in doubt, CT can be obtained.

This patient is an 80 year-old man with elevated PSA. Whole body bone scan demonstrates non-focal uptake in the left tibia. Radiograph reveals thickened cortex and trabecular thickening. Findings are compatible with Paget's disease; a good reminder that just because a patient has prostate cancer doesn't mean everything on their scan is prostate cancer. 

Lucent lesions of bone can be "Brown tumors" of bone, caused by hyperparathyroidism (HPT, either primary or secondary). A patient must have a history of hyperparathyroidism or renal failure (secondary HPT) to consider this diagnosis.

Case:

Bilateral hand radiograph of a young patient with chronic renal failure shows signs of secondary hyperparathyroidism:

--irregular, frayed and ill-defined cortical outline, pronounced at radial aspect of middle phalanges –> subperiosteal bone resorption

--multiple lytic expansile lesions –> brown tumors (arrows)

--osteosclerosis

--accentuated trabecular pattern