Rib Fracture in a Pilot after Centrifuge Training:

항공우주의학회지 제26권 제1호

□ Case Report □

21

Rib Fracture in a Pilot after Centrifuge Training:

Evaluated by Ultrasonography

Kyung Han Ro, M.D.

, Dong Jun Choi, M.D.

1Aeromedical Squadron of the 1st Flighter Wing, Republic of Korea Air Force, Gwangju,

2Department of Nursing, Gwang Yang Health College, Gwangyang, Korea

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Rib fracture is the most common injury resulting from blunt chest trauma. We report a case of rib fracture in operational pilot after the human centrifuge training up to 8 G. The fracture was initially missed on plain radiographs, but diagnosed by the ultrasonography (US) in aeromedical squadron. The case highlights that physicians must be aware that rib fractures can occur even to healthy experienced pilots with the centrifuge training and must set the period of grounding to take time for proper treatment and avoid high-G aircraft flight.

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Key words: Rib fracture, Ultrasonography, Centrifuge training

Received: February 4, 2016, Accepted: February 19, 2016

Correspondence: Kyung Han Ro, Aeromedical Squadron of the 1st Flighter Wing, Republic of Korea Air Force, PO Box 305-6, Dosan-dong, Gwangsan-gu, Gwangju 62451, Korea Tel: 82-62-940-1177, Fax: 82-62-945-1306 E-mail: [email protected]

I. INTRODUCTION

Fracture of rib is the most common (25%) injury resulting from blunt chest trauma [1]. It is usually revealed on radiographs, conventionally documented with a posteroanterior chest radio- graph, followed by an oblique rib view if clinically indicated [2].

But recent study shows up to 50% of rib fractures may be missed at radiography [3]. Previous studies have shown diagnostic ultra- sonography is more sensitive than radiography for the detection of acute rib fractures [4]. An immediate diagnosis would allow proper treatment and could avoid such pulmonary complications [5].

Early in their careers, as part of their training to become fighter pilots, pilots undergo centrifuge training in order to learn effective anti-G straining maneuvers (AGSM) and to test their G tolerance, which is extremely important for the high-performance jet aircrafts (HPJA) in use today. It is a combination of sustained muscle tensing and cyclical Valsalva maneuvers performed every 3 s. The latter increases the intrathoracic pressure, the effect of which is transmitted to the heart and great vessels. This raises systemic

arterial blood pressure and maintains the cerebral blood flow of a pilot in a high G environment [6]. There have been few reports of traumatic injuries sustained during human centrifuge runs in scientific journals. In this case report, we present a case of rib fracture after human centrifuge training which was diagnosed by US, but undetectable by digital radiography.

The patient discussed in the following case gave verbal consent to educational usage of radiologic images and clinical data.

II. CASE REPORT

A 31-year-old operational KF-16 pilot with 700-odd hours on

type came to the clinic. Since he was scheduled to be an instructor

pilot of T-50, he was exposed to refresher centrifuge training 4

days ago. The pilot had undergone previous centrifuge training (up

to ＋9 Gz) several times in the Aerospace Medical Training Center

on human centrifuge (Authentic Tactical Flight Simulator-400

(Environmental Tectonics Corporation, Southhamptom, Pa)) with

no problems. In this centrifuge training profiles included a gradual

onset run (GOR, onset of 0.2 Gz×s

) up to 1.4 Gz and short-

term expose with Gz level from 1.4 Gz to 8 Gz at onset rate of

6 Gz×s

(rapid onset run, ROR). He completed the profile

successfully without any medical problems or symptoms, but he

started to feel pain on left chest wall with time. And 4 days later,

he came to our aeromedical squadron for severe pain of getting

worse.

22 Kyung Han Ro, Dong Jun Choi

Fig. 1. Diagnositc US　in the longitudinal plane demonstrates de- pressed anterior cortex of the rib (arrow）and surrounding hema- toma (asterisk).

His symptoms included pain with breathing (especially forced expiration), coughing, and forward or left-side bending of trunk.

He has no previous chest trauma, or excessive exercise history, except centrifuge training. Vital signs were normal. On physical examination, pain and tenderness covered lower lateral margin of left pectoralis major muscle. And the pain was severely aggravated when he was trying to sit up from lying down. Radiography of the chest and left ribs were ordered for confirmation of the fractures and exclusion of a pneumothorax. The images were inter- preted as negative for fracture and there were no other compli- cating factors, such as pneumothorax. US of the left anterior chest wall was performed for evaluation of the muscle injury and to rule out rib fracture. He was examined with a GE Logiq P5 (GE healthcare, Milwaukee, WI) ultrasound system using a high fre- quency linear transducer (11 L) operating at 12 MHz utilizing a standardized rib protocol. The most painful area with focal rib tenderness and the adjacent asymptomatic ribs were examined in detail with transducer aligned in the longitudinal and transverse planes along its entire extent. US examination in the longitudinal plane revealed cortical discontinuity of the left fourth anterolateral ribs approximately 2.5 cm lateral to the costochondral junction.

Overlying hematoma was evident at fracture site (Fig. 1).

The pilot was scheduled a period of ground training for a month, thus he was treated with oral analgesic, muscle relaxants, starting with NSAIDs. Over the following 3 weeks, the patient experienced disturbed sleep and continuation of his presenting symptoms.

However, there were concurrent gradual improvements. After 4

weeks, pain started to subside, and on the 5th week, the pilot was able to return to his flying duties with T-50.

III. Discussion

The present report describes the diagnosis of rib fracture after human centrifuge training by US in aeromedical squadron. To date, there have been cases of injuries sustained as a result of centrifuge training, but little has been actually reported in scien- tific literature. Gan et al. has reported a case series of six cases of pneumomediastinum in pilot trainees attributed to their ab initio human centrifuge training. They performed a retrospective review of the human centrifuge training database in the Republic of Singapore Air Force, carried out for the period 1995~2006, but there were no cases of pneumomediastinum in operational pilots from refresher centrifuge training [6]. Low et al. reported on a case of vertebral compression fracture during centrifuge training.

He was subsequently diagnosed to have osteopenia with a bone mineral density. After treatment, the pilot has returned to flying duties, albeit in a transport platform [7]. To our knowledge, this is the first instance of such rib fracture to operational pilot after refresher human centrifuge training reported in a scientific journal.

Rib fractures are the most common anatomic deformity resulting from blunt trauma but are rarely life threatening. Whereas blunt trauma to the chest is the most common cause of injury in rib fractures, less common causes include stress from severe or pro- longed coughing and overuse stress in certain sports such as rowing, baseball (pitching), and golf [8]. The pilot in this report was in normal range of regular medical check-up involving body mass index and laboratory finding. He has no previous trauma or overuse stress in exercise, furthermore he had successfully accom- plished his human centrifuge training up to ＋9 Gz before. But, even though he was a healthy experienced operational pilot, the increased intrathoracic pressure during the AGSM might have caused rib fracture. Further study should be required to find out more specific relationship between the AGSM and rib fracture, such as positioning during the centrifuge training or inducible cut- off value of G to cause rib fracture.

Improvement and maintenance of physical fitness and health

require commitment to a physically active lifestyle that may include

exercise and sports. In recent study, Keith et al. surveyed the rates

and proportion of all injuries caused by exercise- and sports-related

(ESR) activities among United States military personnel using a

web-based survey conducted by the Human Resources Strategic

Assessment Program of the Defense Manpower Data Center, and

52% of all injuries were ESR injuries [9]. At the 1st Fighter Wing

Rib Fracture in a Pilot after Centrifuge Training: Evaluated by Ultrasonography 23

of ROKAF, advanced pilot training utilizing high-G aircraft is conducted by 250 pilots who are on duty as instructor and student pilot. Most of them answered that they would play soccer game at least once a week to maintain fitness and consolidate unity.

Regardless of this case, we have diagnosed three cases of rib frac- ture resulting from direct trauma during soccer game. And all of these cases were missed by radiography. Clinically, rib fractures are usually suspected based on the patient’s history and pain, which is accentuated with inspiration, cough, and localized palpation [10]. Early recognition of rib fractures is of clinical importance for the prompt initiation of appropriate treatment. Accurate and quick diagnosis of such rib fractures in the air base may positively in- fluence patient outcomes and reduce time and effort to perform further evaluation like computer tomography at military hospital.

When a normal rib is scanned along its long axis, the anterior cortex appears as a smooth, continuous echogenic line. This line is usually continuous, although a narrow discontinuity without a step may be seen at the costochondral junction in healthy patients.

The costal cartilage appears relatively hypoechoic compared with the osseous rib. A fracture appears as a gap, step or displacement of the cortex of the rib. The fracture may be associated with a localized hematoma, effusion, or soft tissue swelling [11]. In this case, it was somewhat challenging to diagnosis as rib fracture, because we could not find obvious breakage point or cortical offset, while our US image showed some disruption and depressed cortical line like compression fracture. But, we carefully examined focal tenderness area and observed cortical discontinuity with localized surrounding hematoma. The obvious reason of our report showed depressed cortical line on US is unknown yet. We made two supposition about this. First, rib fracture of this case is caused by non-traumatic event, while most of the rib fractures are generally occurred by thoracic trauma, fall, or direct crash. So, the appearance of US examination of this case might be different from the trauma cases of rib fractures. Second, the pilot was wearing an anti-G suit which is a flight suit worn by aviators who are subject to high levels of acceleration force. The human centrifuge training of Korea Aerospace Medical Training Center allows the pilots to wear anti-G suit above 7 G training. The pressure from the strap of the anti-G suit against force to expansion of thoracic cavity during AGSM might be the cause of thoracic injury. As mentioned above, the pilot in this case have already undergone successful high-G centrifuge training several times, thus further study with more cases is required. However, to avoid the possibility of worsening the injury during fighter flight maneuvers, we recommend to set the grounding period for high-G aircraft pilots immediately after diagnosis of rib fracture.

US can visualize the costal cartilage, as well as the osseous part of the rib and includes lack of interference from respiratory motion, which is a limitation of magnetic resonance imaging. It is advan- tageous as a non-invasive imaging technique due to rapid examina- tion and the portability of the device. It also avoids ionizing radia- tion, unlike radiography, computerized tomography, or bone scinti- graphy. US examines each rib parallel to its long axis unlike com- puterized tomography [12]. Furthermore, the imaging of a rib fracture with US is not a complicated procedure and can also be performed by trained and experienced clinicians. And every aero- medical squadron of ROKAF Fighter Wings have portable ultra- sound system. Since expedite and accurate diagnosis would allow proper treatment and help manage the flight schedule of the Fighter Wing more effectively without spending time costs to further eva- luation, we therefore recommend the use of US in these patients.

In conclusion, the present report appears to be the first to describe a case of rib fracture in operational pilot after the human centrifuge training. The fracture was initially missed on plain radiographs, but was diagnosed by the US in aeromedical squa- dron. The case highlights that physicians must be aware that rib fractures can occur even in healthy experienced pilots with the centrifuge training and should set the period of grounding to take time for proper treatment and avoid high-G aircraft flight.

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