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Journal of Pediatric Orthopaedics B:
doi: 10.1097/BPB.0b013e32835368f0
Pelvis, Hip & Femur

Obturator internus pyomyositis: iatrogenic haematogenous spread

Kosuge, Dennis Daisaku; Davis, Benjamin J.

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Author Information

Department of Trauma & Orthopaedic Surgery, Norfolk & Norwich University Hospital, Norwich, UK

Correspondence to Dennis Daisaku Kosuge, BMedSci, BMBS, FRCS (Trauma &Orthopaedics), Department of Trauma & Orthopaedic Surgery, Norfolk & Norwich University Hospital, Colney Lane, Norwich NR4 7UY, UK Tel: +44 160 328 6586; fax: +44 160 328 6522; e-mail: dennis_kosuge@hotmail.com

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Abstract

Obturator internus pyomyositis is a rare disorder that should be on the differential diagnosis in a child who presents with a fever, limp, abdominal or groin pain. We present a case of a 5-year-old girl successfully treated with open drainage following failed medical management. We postulate the source of infection to be secondary to an infected elastic stable intramedullary nail in the forearm that was protruding through the skin.

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Introduction

Obturator internus pyomyositis is a condition that affects children and is often diagnosed late in the child presenting with a fever, limp, abdominal or groin pain, with the more common causes such as an acute abdomen, septic hip or transient synovitis taking precedence in the minds of treating clinicians. We present a case of obturator internus pyomyositis successfully treated with open drainage following failed medical management. The source of infection was likely to be haematogenous spread secondary to an infected elastic stable intramedullary nail (ESIN) in the forearm that was protruding through the skin.

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Case report

A 5-year-old girl presented to a local hospital in the summer with a 2-day history of progressive inability to weight-bear on the left lower limb secondary to pain localizing to the groin and abdomen with no previous history of trauma. This was associated with pyrexia and vomiting. No other joints were symptomatic and no prodromal illness was elicited from the history. She had undergone insertion of ESINs in both left forearm bones for closed diaphyseal fractures 6 weeks before the current presentation. The cast had been removed 4 weeks postoperatively and at that time the ulna nail was noted to be protruding through the skin at the olecranon. The decision was made to leave the nail in place. Medical history was otherwise unremarkable.

On examination, a swinging pyrexia was documented with a maximum temperature of 40.2°C, associated with a tachycardia of 135 beats/min. The abdomen was soft but tenderness was elicited in the suprapubic region more towards the left of the midline. There were no localized changes of note on inspection of the left hip but hip ranges of movement elicited discomfort around the groin. There was a tendency for the left hip to rest in an externally rotated attitude. No neurovascular deficit was noted. The ulna forearm nail was noted to be protruding through the skin at the elbow with surrounding erythema and purulent oozing. No other sources of infection were identified on complete physical examination.

Investigations demonstrated an elevated white blood cell count of 18.6×109/l, a neutrophil count of 13.9×109/l, an erythrocyte sedimentation rate of 55 mm/h and C-reactive protein of 111 mg/l. Blood cultures were negative. Plain radiographs of her pelvis were unremarkable and forearm radiographs showed the protruding nail (Fig. 1). A hip and pelvis MRI scan demonstrated a collection associated with the obturator internus (Fig. 2). No osteomyelitis or hip sepsis was noted.

Fig. 1
Fig. 1
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Fig. 2
Fig. 2
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The patient was commenced on intravenous antibiotics but this failed to resolve her clinical condition within a 48-h period. As a result, the patient was transferred to our tertiary pelvic unit where, given the failure to respond to medical management, the decision was made to drain the abscess. This was performed through the iliac window of the ilioinguinal approach to the pelvis, elevating the iliacus from the inner table of the pelvis until the collection within obturator internus was reached and drained adjacent to the medial wall of the left acetabulum. At the same sitting, the protruding ulna intramedullary nail was removed. Microbiological analysis of the obturator internus abscess grew Staphylococcus aureus and antibiotic therapy was tailored to the sensitivities. Intravenous antibiotics were continued for 72 h, during which the clinical condition of the child improved significantly. Oral antibiotics were continued for a further 2 weeks.

At 6-week follow-up, she had made a full recovery clinically and haematologically.

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Discussion

Pyomyositis is a term used to describe an acute bacterial infection of skeletal muscle presenting as an abscess or as a diffuse myonecrotic process. Occasionally referred to as tropical pyomyositis, it was generally thought to be a disease prevalent in Asia and Africa, where the temperature and humidity are high. However, its occurrence is being increasingly reported in areas of temperate climate, with a predilection for presentation in the summer months 1,2.

The obturator internus muscle is an external rotator of the hip and originates from the medial aspect of the obturator membrane as well as the puboischium, and traverses the lesser sciatic notch to attach onto the medial aspect of the greater trochanter. Obturator internus pyomyositis is extremely rare and is a condition that predominantly affects children. The causative organism of an obturator internus pyomyositis is S. aureus in the majority of cases. Aetiology is unclear but possible mechanisms may include localized trauma with simultaneous transient bacteraemia or spread from adjacent structures such as in pelvic osteomyelitis 3,4. In the majority of cases, there is no obvious cause but cases have been described following minor trauma 2. There have been two cases of obturator internus pyomyositis secondary to skin abrasions but none secondary to an operation 5.

As the obturator internus muscle is closely related to the hip, presentation may mimic that of a septic hip. The current case demonstrates the similarities of presentation with an unwell limping child tending to rest the leg in an externally rotated attitude. An MRI scan will help differentiate the two diagnoses and should be obtained in cases of doubt.

We present the first case of obturator internus pyomyositis that we believe is attributable to recent remote orthopaedic surgery – a protruding infected flexible nail used for stabilization of an ulna shaft fracture, but we acknowledge that the lack of microbiological analysis of the wound or protruding ESIN makes the association between the protruding ESIN and obturator internus pyomyositis speculative. However, we believe that the absence of other sources of infection in a normally healthy child and clinical evidence of infection around the ESIN entry point makes the protruding ESIN highly likely to be the source.

The use of ESIN has markedly increased recently due to its minimally invasive nature and lack of complications. This case highlights the importance of ensuring entry point accuracy as the correct point of insertion of an ulna nail would be just distal to the physis and on the radial border, avoiding the ulna nerve 6. This would ensure that the protruding nail would not be beneath the relatively unprotected skin at the tip of the elbow. The nail has to be left proud to aid with removal at a later date but at the same time it cannot be left too proud so as to cause discomfort or, as in this case, skin breakdown. If nail protrusion is noted, one must consider early removal to prevent complications.

The clinical presentation of an obturator internus pyomyositis resembles that of a septic hip and must be on the differential diagnosis if investigations are not suggestive of the hip joint as a source of infection. Radiation of pain down the thigh may be due to the space-occupying effect of the abscess on the obturator or the sciatic nerve.

Treatment is either with intravenous antibiotics or drainage through percutaneous or open methods 3. In the current case, given that the child remained clinically unwell despite 48 h of maximal medical management and with an obvious source of infection, surgery in the form of removal of the offending intramedullary nail and open drainage of the abscess was performed with a favourable outcome. Because of the rare nature and anatomy of this abscess, should open drainage be required, we recommend referral to an orthopaedic surgeon with a specialist interest in pelvic surgery, given the surgical exposure that is necessary.

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Conclusion

This is a rare case of obturator internus pyomyositis proposed to be secondary to a poorly placed ESIN protruding through the skin. This highlights the importance of ensuring correct insertion of the ESIN. In a child with a fever, limp and groin pain not explained by the more common diagnoses of septic arthritis or transient synovitis, one must exclude obturator internus pyomyositis – best diagnosed by an MRI scan.

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Acknowledgements
Conflicts of interest

There are no conflicts of interest.

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References

1. Gibson RK, Rosenthal SJ, Lukert BP. Pyomyositis: increasing recognition in temperate climates. Am J Med. 1984;77:768–772

2. Viani RM, Bromberg K, Bradley JS. Obturator internus muscle abscess in children: report of seven cases and review. Clin Infect Dis. 1999;28:117–122

3. Orlicek SL, Abramson JS, Woods CR, Givner LB. Obturator internus muscle abscess in children. J Pediatr Orthop. 2001;21:744–748

4. Scillia A, Cox G, Milman E, Kaushik A, Strongwater A. Primary osteomyelitis of the acetabulum resulting in septic arthritis of the hip and obturator internus abscess diagnosed as acute appendicitis. J Pediatr Surg. 2010;45:1707–1710

5. Hakim A, Graven M, Alsaeid K, Ayoub EM. Obturator internus abscess. Pediatr Infect Dis J. 1993;12:166–168

6. Barry M, Paterson JMH. Flexible intramedullary nails for fractures in children. J Bone Joint Surg Br. 2004;86:947–953

Keywords:

complication; elastic stable intramedullary nail; obturator internus; pyomyositis

© 2013 Lippincott Williams & Wilkins, Inc.

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