Injury (1992) 23, (8), 535-536 Prinfed in Great Britain 535

Isolated sternal fracture: a benign injury?

M. Jackson and W. S. Walker Department of Cardiothoracic Surgery, Royal Infirmary of Edinburgh, Edinburgh, UK

Since seat belt legislation was infroduced in this counfy in 1983, we have seen an increasing number of patients admitted to our unit for observation following seat belt relafed sternal fracfures. In order fo determine the value of routine admission of patients with isolated sternal frucfure we have reviewed a series of 104 consecutive pafienfs admitted befween February 1983 and Februa y 1990 with this inju y. of fhese, 90 were sustained in road accidents, 79 of which were as a consequence of seat belt use. The average age of fhese patients was 54.5 years (range 11-85 years) with an

average durafion of hospital stay of 2.9 nights. No seriolcs complicafions were observed. These jkdings suggest that there may be no need to admit these pufienfs solely for observafion if fheir initial clinical condifion is safisfacfoy and there are no abnormalifies identified by an anferoposferior chest radiograph and elecfrocardiography.

Introduction

It has been demonstrated that the use of seat belts in motor vehicles greatly reduces the incidence and severity of injuries sustained as a result of a collision (Trinca and Dooley, 1975; Mellbring et al., 1981). Their use, however, does not completely abolish injury, and a typical pattern of related injuries has been identified (Trinca and Dooley, 1975). A common result of their use during an accident is fracture of the sternum. It has been the policy of the cardiothoracic unit in Edinburgh, in common with many units in the UK, for patients with this injury to be admitted for a short period of observation to exclude potentially serious complications, most notably the sequelae of blunt myocardial injury.

Patients and methods

All patients with isolated sternal fractures admitted to the cardiothoracic unit at the Royal Infirmary of Edinburgh from 1 February 1983 to 31 January 1990 were identified. During this period there was a total of 104 patients admitted with this injury. In all except 10 cases, the complete case notes were examined. Data were obtained relating to the age, sex, position in the vehicle at impact and seat belt status. Additionally, results of subsequent investigations including chest radiograph, serial electrocardiograms (ECG) and measurement of cardiac enzyme levels were noted. Details of hospital stay, associated injuries (if any), relevant past medical history and subsequent complications were recorded. In those patients whose full case notes were unavailable, data were obtained from the clinical summary

0 1992 Butterworth-Heinemann Ltd 0020-1383/92/080535-02

made at the time of discharge. Patients with any additional injury, including rib fractures, which would normally require inpatient treatment were excluded.

The unit policy is that these patients are admitted for analgesia, cardiac monitoring, twelve-lead electrocardio- gram (ECG) and, if clinically indicated, serial measurement of cardiac enzymes (normally aspartate transaminase (AST) and lactate dehydrogenase (LDH)).

Results

Of the 104 patients suitable for inclusion, 90 were as a consequence of a road accident. The average age of this group was 54.5 years (range 11-85 years) with 38 male patients. The remainder had sustained the injury as a result of a fall (10 patients) or following assault (three patients). One patient sustained this injury when a window frame was blown in onto her bed. There were no deaths as a result of sternal fracture and none of the patients required reduction or stabilization of the fracture. There were no open fractures. Of the 90 patients involved in car accidents, 79 were definitely wearing seat belts at the time of impact, two were not wearing a restraint and in nine others the status is unknown. The position of the patients in the vehicle at the moment of impact was: 45 drivers (56.9 per cent), 29 front seat passengers (36.7 per cent) and four rear seat passengers (5.1 per cent). The position was unknown in 12 cases. None of the patients developed cardiac arrhythmias which required therapeutic intervention during admission. Serial twelve-lead electrocardiograms were performed in 101 patients. In only nine cases did these demonstrate acute changes. Review of these, with the exception of one case, showed this to consist of transient peaking of the T-wave in the anterior chest leads. The exception to this was a patient with a history of previous inferior myocardial infarction who was noted on admission to be in first degree heart block and to have a 3 mm elevation of the ST segment in leads V2 and V3 compatible with an acute contusional injury of the myocardium. This was associated with a significant rise in cardiac enzyme levels, suggesting a contusional injury had occurred. Of the remaining eight patients with acute ECG changes, three had associated minor and transient rises in cardiac enzymes. In three patients, no record of the results of cardiac enzymes could be found.

In all, cardiac enzymes were measured in 42 patients (54.5 per cent). Of these, 12 were abnormal. In 10 patients the rises noted were borderline; however, in two cases (one of which is discussed above) the rise was significant. The other

536 Injury: the British Journal of Accident Surgery (1992) Vol. 23/No. 8

patient had an initial rise in levels of AST but did not develop any subsequent associated rise in LDH.

On admission, two patients were noted to have ejection systolic murmurs and therefore underwent echocardio- graphy. In both cases this demonstrated normal contractility and normal valve function.

Three patients suffered complications attributable to the sternal fracture and in each case this was a mild chest infection indicated by the production of purulent sputum. In both patients, this was readily treated by a course of oral antibiotics and by physiotherapy.

been interpreted as indicating that contusion may have occurred in contradistinction to the greater rises seen following myocardial infarction (Leslie Hamilton et al., 1984). However, estimations of CK isoenzymes are not available routinely in this unit and have therefore not been performed on our patients. In the clinical situation, contusion has been reported as having caused cardiac arrhythmias and ventricular failure which may be delayed until the 4th day after injury. However, we have not noted any serious arrhythmias requiring treatment or any patients developing cardiac failure.

No formal follow-up arrangements were made for any of these patients after discharge from the cardiothoracic unit, although patients were advised to see their general practi- tioners if any further problems arose. In no case was further hospital treatment necessary.

Discussion

The main aim of this study was to document the clinical natural history of isolated sternal fracture and to validate our policy of inpatient investigation and observation of these patients. Despite the retrospective nature of the study, the absence of major complications suggests that policy to be overly cautious. Although the majority of patients had seat belt related injuries, there seems to be little difference between these fractures and those sustained by other mechanisms.

As a result of our policy to admit isolated sternal fractures arising as a consequence of seat belt use, we have failed to identify any patients who thus may have benefited from their period of observation other than from relief of pain.

In order to document the full extent of myocardial injury following isolated sternal fracture, a prospective study using radionuclide angiography, CK-MB enzyme rises and pos- sibly including the measurement of myocardial antibodies would be required. However, an involved study would be hard to justify in view of the apparently benign nature of this injury.

The low morbidity associated with simple seat belt related sternal fracture suggests that in the absence of other significant injuries, a normal anteroposterior chest radio- graph, no ECG abnormalities and a clinically well patient, hospital admission is not indicated.

Sternal fracture has previously been considered a com- paratively rare occurrence. It has increasingly been recog- nized in the multiply-injured patient (Newman, 1984; Newman and Jones, 1984; Otremski et al., 1990), but until now has not been documented as an isolated injury.

References

Many authors have demonstrated the value of the use of seat belts (Trinca and Dooley, 1975). The fact that obser- vation of isolated sternal fracture would seem to be increasing is testimony to the beneficial effect of seat belts. Damage to the heart resulting in serious threat to life following isolated sternal fracture in the absence of other injuries is extremely rare, particularly following restraint by a seat belt.

Leslie Hamilton J. R., Dearden C. and Rutherford W. H. (1984) Myocardial contusion associated with fracture of the sternum: important features of the seatbelt syndrome. Injury 16, 155.

Mellbring G., Damlin S. and Lindblad B. (1981) The hospital experience of seat belt legislation in the county of Skaraborg. Sweden. Injury 12,506.

Newman R. J. (1984) Chest wall injuries and the seat belt syndrome. Injury 16, 110.

The most frequently occurring effect of sternal fracture is causation of ‘contusion’ and ‘concussion’ of the myocar- dium. Concussion has been defined as a post-injury cardiac arrhythmia occurring without an associated rise in enzyme levels or acute ECG changes. Contusion follows a more severe injury and hence may cause changes in both the ECG and rise in cardiac enzyme levels (Leslie Hamilton et al., 1984). Tests of greater sensitivity may be required, and these are provided by isotopic radionuclide studies. These have shown that the right ventricle is the most frequently injured portion of the heart.

Newman R. J. and Jones I. S. (1984) A prospective study of 413 consecutive car occupants with chest injuries.]. Trauma 24,129.

Otremski I., Wilde B. R., Marsh J. L. et al. (1990) Fracture of the sternum in motor vehicle accidents and its association with mediastinal injury. Injury 21, 83.

Trinca G. W. and Dooley B. J. (1975) The effects of mandatory seatbelt wearing on the mortality and pattern of injury of car occupants involved in motor vehicle crashes in Victoria. Med. J. Amt. 1,675.

Paper accepted 14 April 199~.

Research studying the rises in cardiac enzymes have focused on the muscle-brain (MB) isoenzyme of creatine

Re+ests for reprints should be addressed to: Mr M. Jackson, Depart-

kinase (CK). Moderate rises in serum levels of CK-MB have ment of Orthopaedics, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW, UK.