The incidence of clinically significant missed injuries following polytrauma varies from 15 to 22.3%.1 This is directly influenced by patient, staff and investigations. During the management of a polytrauma patient head injury, Glasgow Coma Scale (GCS) < 8, inadequate clinical assessment and poor interpretation of imaging are recognised factors that augment the likelihood of missing a fracture .2-4 The delay in diagnosis of a fracture is further compromised following admission to the intensive care unit (ICU) where clinical assessment is restricted due to the lack of localising signs and communication. In these circumstances scintigraphy helps detect occult fractures early and provides a window of opportunity to intervene promptly.
The intention of this study was to characterize the role of bone scan in polytrauma and also highlight the advantages and drawback of scintigraphy in detecting occult fractures. I
endeavour to advocate its use as an adjunct to tertiary survey and minimise the associated morbidity.
MATERIALS AND METHODS
We reviewed the literature published in English during the last 30 years in regard to scintigraphy in trauma. We combed medline, embase, Cochrane library and google.
Scintigraphic changes tend to manifest early while radiological changes lag behind. Bone scan is primarily indicated in polytrauma patients in ICU with a GCS <8 and when localizing signs are difficult to establish. The optimum period to conduct a bone scan following trauma is 13 to 20 days. A negative scan signifies the absence of a fracture.
Occult fractures of the ipsilateral limb are the commonest missed fractures.
A bone scan preformed early in a polytrauma patient will contribute towards a high false positive result due to traumatic synovitis and ‘bone bruising’. The age of the patient and the site of the fracture will also influence the sensitivity due to the rate of callus formation. Prolonged immobilization will cause increased uptake of uninjured bone and further compromise the result.
In the initial encounter of a polytrauma patient clinical assessment coupled with plain radiographs tend to be the mainstay of investigation to detect fractures. The incidence of undiagnosed injuries during primary and secondary survey is reported to be 1.3 to 39%. Among this group the median percentage of muscular skeletal injuries is 69.2%. This figure is depended on patient factors, staff experience & interpretation of investigations.1
Following polytrauma a GCS < 8, head injury and the presence of splints makes diagnosing fractures a dilemma due to poor localising signs. The inadequate clinical assessment coupled with poor interpretation of imaging increases the likelihood of a fracture remaining undetected. Diagnosing a fracture becomes a challenge if the patient requires admission to ICU. Consequently occult fractures remain undetected until mobilisation is initiated or communication is resumed. In this situation bone scan is a valuable tool utilized to diagnosed fractures and curb associated morbidity.
The retrospective studies focused on missed injuries in polytrauma patients attribute the failure to identify injuries to poor clinical routine, inadequate assessment, insufficient emphasis on subtle signs and symptoms, multi organ involvement and low GCS. They also emphasized the likelihood of missing an injury being increased if the subsequent injury is present on the ipsilateral immobilized limb. In addition poor quality mobile radiographs, misinterpretation of imaging and admission to the wrong unit also contributed towards delay in diagnosis of a fracture.2, 5-11
Bauer12 in 1968 defined the basic principles of radio nucleotide imaging and its applications in orthopaedics. Fractures were identified on bone scan prior to radiographic evidence. On sustaining a fracture the patho-physiological processes act as a beacon for the radio pharmaceutical agents which localize and persist during the healing and remodelling stage.
Following a fracture a periosteal reaction is initiated within 48 hours. Thickening of the periosteum is brought about due to inflammation, angiogenesis and bridging callus formation. The periosteal reaction can be visualised within hours of injury, but is not reliable. The osteoclastic and osteoblastic changes integral to the healing process ensure that preferential uptake of the 99m-technetium bone seeking agent occurs within days.
Bone seeking radio pharmaceuticals are selectively taken up and concentrated at sites of fractures
producing a characteristic hot spot within 3-5 days after injury. In the elderly and debilitated a delay of 7 to10 days is encountered due to compromised bone quality and slow rate of callus formation. In children the augmented osteoblastic activity allows early detection of the fracture. A fracture involving the growth plate results in low uptake due to reduced metabolic activity and growth arrest. Occult Fractures in infants & toddlers will show a generalized increased uptake and pinhole views will be required in this instance.
Martin13 postulated that scan changes following a fracture are confined to three phases. The acute phase persists for 2 to 4 weeks after injury. This is characterised by diffused uptake in which a distinct fracture line is found on delayed images. Following his study of 204 patients he advocated that fractures in 95% of patients can be detected in 24 hours and 100% within 1 week. The sub acute phase was characterised by a well defined linear abnormality at the site of fracture lasting for 8 to 12 weeks. The healing phase commences with gradual normalization of bone uptake and continues up to 3 years. The time for return to normality is influenced by type of bone, age & immobility.
Several studies have reinforced the importance of scintigraphy in localising occult fractures in polytrauma patients. Spitz14 recognised additional fractures in 50% of the 162 polytrauma cases and perpetuated the value of this investigation in detecting fractures. Following a whole body scan Heinrich10 drew our attention to 19 occult fractures in 48 patients presenting with a history of polytrauma and 6 were clinically significant. In 119 cases with forearm fractures a subsequent injury was identified in 9 patients on bone scan by Goldburg.15 Sobus16 focused on 82 children with traumatic head & spinal injury and highlighted the dilemma encountered in recognising fractures in this group. The difficulties were overcome by proceeding with a bone scan which revealed 28 occult fractures. A prospective study was conducted in 1993 at the Royal Hobart Hospital for a period of 7 months. It involved 14 polytrauma patients who were subjected to a bone scan within 2 weeks of injury to identify occult fractures. Following the bone scan undiagnosed fractures were found in all of the 14 patients. It was also noted that the majority of the undetected fractures were present on the primarily affected limb.17
Extensive studies have been generated promoting scintigraphy in detecting scaphoid fractures on clinical suspicion alone with no radiological evidence. This propagated the notion of bone scan being a superior predictor of scaphoid fractures than x rays with an early positive result at 10 days following trauma. Bone scans at day 4 had 100% sensitivity for scaphoid fractures with 92% specificity. A negative scan obtained after 72 hours of presentation ruled out a fracture.18-23
Rolfe24 explored the role of bone scans in carpal injury. He ruled that bone scan had 100% sen
sitivity and 91% specificity following 99 patients undergoing bone scanning after a carpal injury. He found that a fracture can be excluded confidently if the bone scan was negative. He acknowledged that imaging patients within 48 hours might be misleading due to traumatic synovitis.
Positive bone scans in the face of normal plain radiographs may not always correspond to fractures. Disruption of the periosteal attachment and formation of a sub periosteal haematoma leads to an increased uptake throughout the whole body scan. Tracers also tend to accumulate focally in injured soft tissue and ligamentous avulsions which can be deceptive. The disruption of normal blood flow and irregular metabolic processes found around the area of bone trauma lead to abnormal uptake referred to as ‘bone bruising’. This can be demonstrated by a three phase bone scan. Following prolonged immobilization of a patient increased uptake is expected in the vicinity of the uninjured bone. This phenomenon will mask the fracture site and may persist for 3 months.
1369 patients presenting with a fracture were included in the study by Spitz14 to determine the lesion:normal bone ratio which would help dispel the confusion of differentiating a fracture from bone bruising. He postulated that a value greater than 1:1 allowed delineation of a fracture from a soft tissue lesion with reactive hyperaemia. The start, extent and intensity of uptake of the radiological agent were influenced by the site of the fracture. The fractures proximal to the joint were demonstrated in the first few days, while that of the diaphyses of long bones & axial skeleton were revealed after 10-12 days. This was attributed to the variation in production of callus at different sites. He revealed a positive scan rate increased with time in polytrauma patients and the highest yield of occult fractures was detected in 13-20 days.
The technical difficulties encountered include transferring patients to the nuclear department, maintaining close monitoring, the duration of the test and the restlessness encountered among agitated head injury patients. A radiation dose of 4.4mSv and cost associated with the investigation has to be considered. The affinity of the radiological agents towards areas of increased osteoblastic activity or hyperaemia following bone trauma and also the predisposition to areas of infection, neoplasm and arthritis compromises the result.
A tertiary trauma survey has helped reduce the risk of missing a fracture and curb morbidity.25, 26 In conjunction with the tertiary survey bone scan is an ideal tool to curtail the probability of missing a fracture in polytrauma patients.
Scintigraphy plays a role in polytrauma patients as it can detect fractures long before radiographic changes have manifested. It can identify fractures at sites inaccessible to X- ray and also provide the opportunity to localize subtle lesions by delayed images. It has the capability of imaging the entire skeleton and identifies multiple sites of involvement.
Used in conjunction with careful history taking, thorough clinical examination and appropriate radiographic interpretation, bone scanning holds great promise in diagnosing occult fractures that remain undetected until mobilisation is initiated or communication is resumed in ICU patients. As an adjunct and not a substitute to tertiary survey in polytrauma patients, bone scintigraphy will help reduce morbidity perpetuated by undiagnosed fractures.
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