CASE OF THE WEEK – “Bone scanning in the detection of occult fractures” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

Bone scanning in the detection of occult fractures

Orthopedic surgeons often use bone scanning to establish a diagnosis, determine the extent of skeletal disease and monitor the results of surgical treatment. Many benign skeletal conditions requiring orthopedic treatment, occult femoral neck fracture for example, produce increased blood flow and osteoblastic activity, resulting in increased uptake of 99mTc-diphosphonate bone scanning agents.

Bone scanning is a sensitive test which can provide information of practical value to orthopedic surgeons.

OCCULT FRACTURES:-THE ADULT PATIENT WITH CONI1NUING PAIN following TRAUMA

For the majority of adult patients who have sustained significant musculoskeletal trauma, history and physical examination followed by appropriate conventional radiographs are sufficient to establish the diagnosis of fracture.

Failure to detect certain types of fractures requiring urgent orthopaedic treatment is, however, remarkably common. Femoral neck and intertrochanteric fractures, scaphoid fractures and Lisfranc fracture dislocations of the mid-foot are three notable examples.

For example, it is rare to image unstable spinal fractures which were not previously demonstrated by conventional radiographs with bone scanning. However, stable vertebral body fractures producing minimal loss of vertebral body height and sacral insufficiency fractures not initially evident on conventional radiographs frequently are first dis covered using bone scanning. Furthermore, certain fractures detected by bone scanning but frequently missed by radiographs may require no specific treatment. Non displaced rib fractures detected scintigraphically are good examples of this type of injury. For many patients, the cause of post-traumatic chest wall pain is evident on bone scans but not on radiographs: intense focal increased uptake involving adjacent aspects of multiple ribs, even when radiographs are normal, establishes the diagnosis of rib fractures.

The patient with an occult femoral neck or inter-trochanteric fracture frequently is an older female with continued hip pain following a fall. The greater prevalence of osteoporosis among women and the progressive loss of bone mineral density within the femoral neck with advancing age are largely responsible for this frequently encountered clinical problem.

Osteoporosis also makes the radiographic diagnosis of an occult non displaced fracture of the femoral neck or inter trochanteric region more difficult. Conventional x-ray tomography and CT have been applied to this imaging problem, with MRI more recently being recommended for use in this situation. MRI excels in detecting extension of the fracture line not only through cortical bone but also through the medullary space with disruption of the medullary fat. At a fracture site running throughthe medullary space, there is a linear band of characteristic MRI signal change. Bone scanning also is of significant value for detecting occult femoral neck and intertrochanteric fractures in this patient population.

Shortly following the time of injury, there will be an increase in perfusion to the fracture site which can be demonstrated during the rapid sequence flow study and blood-pool phases of the so called three-phase bone scan. most fractures of this type in adults under 75 years of age will show increased uptake on a delayed bone scan image obtained as early as 24 hrs following injury. For older osteoporotic patients it is prudent to wait until three or more days following injury before obtaining delayed bone scintigrams, which will definitively establish or exclude the diagnosis of fracture. Once the diagnosis of an occult proximal femur fracture involving either the intertrochanteric region or the femoral neck has been established, the great majority of patients will be treated with internal fixation. Prompt internal fixation with early ambulation and rehabilitation significantly reduces the morbidity and early mortality of this injury, and therefore the early and accurate diagnosis of such fractures is of practical value to the orthopaedic surgeon.

Case

53 years old lady with history of slip in the bathroom now complaining of severe left hip pain and difficulty in walking.

X-ray pelvis: ? Fracture at left femoral neck.

99mTc MDP Bone scan shows linearly increased tracer uptake in left femoral neck suggestive of fracture as shows with arrow.

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Trauma-linear left femoral neck fracture

Scaphoid Fracture

For patients with normal conventional radiographsand continued pain following trauma to the hand or foot, consideration also should be given to an occult fracture. Fractures requiring specific orthopaedic treatment which have escaped radiographic detection may be imaged by bone scanning.

For example, fractures of the scaphoid and lis franc tarso-metatarsal fracture dislocations may require open reduction and internal fixation. Adult patients with these injuries have sustained significant trauma, often including fractures at other sites. Whereas there are radiographic criteria for optimal examination and interpretation with a view toward detecting these injuries, they are frequently missed on conventional radiographs. Conventional x-ray tomography, CT and MRI have all been applied to these injuries.

A frequent recommendation for patients with suspicion of a scaphoid fracture is to obtain radiographs 1-2 week following the injury. Bone scanning also can be profitably applied to the detection of these injuries. Following a fracture of the scaphoid, there will appear a focus of intense increased uptake usually centred in the scaphoid.

Case

28 years old gentleman with history of fall on right out stretched hand. Complaining of pain and swelling in right scaphoidal region.

X-rays of hand- unremarkable

99mTcMDP WHOLE BODY, SPOT & SPECT CT FUSED IMAGES OF THE HAND BONE

BLOOD POOL IMAGES OF HAND

Focal area of abnormal pooling of tracer seen in right wrist region medially (as compared to opposite).

SPOT AND SPECT CT FUSED IMAGES OF HAND

It shows focal area of abnormally increased tracer uptakes in right scaphoidal bone (mid portion approximately and better appreciated in SPECT-CT fused images).

FOCALLY ACTIVE (HOT SPOT) ABNORMALITY SEEN INVOLVING MID PORTION OF THE SCAPHOIDAL BONE OF RIGHT WRIST PERSISTENT WITH FRACTURE.

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IMAGES OF HANDS

Bone scanning in the detection of occult fractures 05 Bone scanning in the detection of occult fractures 06 Bone scanning in the detection of occult fractures 07

Figure 3,4 & 5 BONE SPECT CT FUSED IMAGES OF THE HANDS

RIGHT WRIST-SCAPHOIDAL BONE FRACTURE.

Occult spinal fractures and sacral insufficiency fractures occur in a variety of clinical circumstances. Older osteoporotic individuals are at particular risk for vertebral body fractures. Such fractures may produce only a minimal loss of vertebral body height that is difficult to appreciate on conventional radiographic examinations. Fractures of the sacrum also are notoriously difficult to appreciate radiographically. The osteoporotic sacrum is prone to a characteristic type of insufficiency fracture with fracture lines running vertically through the left and right sides of the sacrum just medial to the sacroiliac joints in addition to a fracture crossing the mid-sacrumtransversely just below the inferior margins of the sacroiliac joints.

Such osteoporotic fractures of the spine and sacrum infrequently require specific orthopaedic treatment. Nonetheless, establishing a cause for pain in these patients whose radiographics show only osteoporosis is a significant diagnostic problem. Treatment is usually directed toward pain relief and medically treatable causes for the underlying osteoporosis. Bone scanning also has a significant role to play in paediatrics for patients with continued unexplained pain following trauma.

The ability to survey the entire skeleton and identify sites of non accidental trauma is a particular strength of bone scanning . Total body radionucide bone scanning also is useful for imaging adults who have suffered extensive trauma. The full extent of injuries produced by motor vehicle accidents, such as sternal and multiple rib fractures, may be over looked initially in patients with multiple sites of skeletal trauma and severe injury to other organs. Impaction of the anterior chest wall on the steering wheel during a motor vehicle accident often produces a horizontal transverse fracture through the mid sternum along with multiple fractures of adjacent anterior ribs lying one above the other.