Emerg Radiol (2015) 22:211–214 DOI 10.1007/s10140-014-1286-1
CASE REPORT
Aseptic hip pneumarthrosis following modular total hip arthroplasty: a potential mimic of hip infection Yoav Morag & Corrie M. Yablon & Alexander E. Weber & Catherine Brandon & David J. Blaha
Received: 4 October 2014 / Accepted: 18 November 2014 / Published online: 10 December 2014 # American Society of Emergency Radiology 2014
Abstract Pneumarthrosis following total hip arthroplasty accompanied by acute hip symptoms is a potentially ominous finding suggesting infection with gas-forming bacteria, a medical emergency. We describe a case of a 61-year-old male presenting to the Emergency Department 43 months following a titanium/titanium (Ti/Ti) modular neck-stem total hip arthroplasty (MTHA) (Wright Medical Systems, Arlington, Tennessee) with acute presentation of hip symptoms and joint gas on radiographs proven to be aseptic hip pneumarthrosis. We review the imaging features of aseptic hip pneumarthrosis following MTHA which have not been elaborated on previously and suggest a less aggressive workup in select cases. We believe emergency radiologists should be aware of this unusual complication as it may mimic a septic hip which may entail an unnecessarily aggressive workup.
associated with complications such as fretting and wear [2, 3]. Pneumarthrosis following joint replacement often raises concern for a gas-forming joint infection, a dreaded postsurgical complication. We present a case of a patient with a MTHA implanted with a titanium/titanium modular neck-stem interface who presented to the Emergency Department with acute groin pain and aseptic pneumarthrosis 1 year after contralateral aseptic hip pneumarthrosis following MTHA (described in a prior study) [4]. Herein, we review the presentation of this complication, discuss the differential diagnosis of joint gas, and suggest a workup.
Keywords Modular . Arthroplasty . Hip . Pneumarthrosis . Complication
A 61-year-old male (BMI 31) 43 months status post left MTHA (size 5 Profemur Z stem, short varus femoral neck, Conserve Plus 52 mm +0 head, Wright Medical Systems, Arlington, Tennessee) presented to the Emergency Department with 3 days of acute severe left groin pain following a treadmill workout. Initial pain was severe, and the patient could not bear weight but had significantly improved pain following 2 days of NSAIDs. The symptoms were not accompanied by fever or chills or mechanical complaints such as creaking or clunking. On physical examination, there was a stable gait with preserved strength and preserved range of motion of the hip, without accompanying tenderness in the groin or greater trochanter. Radiographs at presentation depicted a large collection of gas in the hip joint (Fig. 2). The patient had a 1 year prior history of contralateral right hip aseptic pneumarthrosis following MTHA with a similar presentation for which he had undergone a revision [4]. A presumptive diagnosis of aseptic pneumarthrosis and pain of
Introduction The utilization of a modular femoral neck in total hip arthroplasty (MTHA) enables the separation of the crucial step of distal femoral component fixation from other aspects of the procedure, such as offset and leg length (Fig. 1) [1, 2]. However, modular components may be Y. Morag (*) : C. M. Yablon : C. Brandon Department of Radiology, Division of Musculoskeletal Radiology, University of Michigan Health System, 2910F Taubman Center, SPC 5326, 1500 East Medical Center Drive, Ann Arbor, MI 48109, USA e-mail:
[email protected] A. E. Weber : D. J. Blaha Department of Orthopedics, University of Michigan Health System, Ann Arbor, MI, USA
Case report
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Discussion
Fig. 1 Modular neck total hip arthroplasty illustration
muscular origin was made based on the patient’s history and clinical findings. The patient was discharged with a recommendation for a follow-up appointment given the concern for left hip component corrosion. Radiographic follow-up 6 months later revealed no evidence of pneumarthrosis. The patient was followed up for 19 months without evidence of infection with ESR and CRP within normal range on two occasions. While blood metal ions were found to be elevated (chromium 6.5 ng/ml, cobalt 9.3 ng/ml), hip function was preserved without pain on weight-bearing or complaints of mechanical creaking.
Fig. 2 a, b Sixty-one-year-old male with pneumarthrosis (arrows) involving the left hip including a small distal gas pocket (arrowhead) as seen on radiographs
Pneumarthrosis typically presents as a consequence of vacuum phenomenon in native joints and intervertebral discs [5], but to our knowledge, vacuum phenomenon has not been described in prosthetic joints. When gas is identified in a prosthetic joint, a recent intervention causing the incidental introduction of air, penetrating trauma, or a spontaneous fistulas to gas containing hollow viscus should be excluded [6–9]. Pneumarthrosis may also occur in the context of prosthetic joint infections. Early prosthetic infections (occurring 0– 24 months postoperatively) may be acquired during surgery while late infections (occurring greater than 24 months postoperatively) are typically secondary to hematogenous spread arising from other infected sites [10]. Gas formation in the context of soft tissue infection is typically associated with Escherichia coli and anaerobes. Anaerobic joint infections are uncommon, accounting for approximately 1 % of all cases of bacterial joint infections, and these often occur in immunocompromised patients [11, 12]. Gas-forming clostridial infections may occur following open traumatic injuries or contaminated surgical wounds which or may be associated with significant comorbidities such as malignancy [13, 14]. Radiographically apparent joint gas in the context of infection is considered rare and may be absent even in the presence of an anaerobic joint infection [12, 15]. On imaging, gas is described dissecting into adjacent extra-capsular tissues and occasionally extending into bone [15–22]. Our patient presented with atraumatic acute groin pain following THA with a titanium/titanium modular neck-stem interface relatively late after the index surgery (43 months) without accompanying signs or symptoms of infection. A review of the imaging studies of previously described cases of MTHA aseptic pneumarthrosis [4] was undertaken; initial radiographs in all cases depicted a large amount of intra-
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Fig. 3 a, b Sixty-one-year-old male status post left total hip arthroplasty on presentation to Emergency Department with a large amount of intra-articular gas (arrows) and large gas-fluid levels as seen on CT
articular gas. CT studies available in two cases (Fig. 3) depicted gas distribution in a non-dependent fashion without evidence of gas loculation or of intra-osseous gas. There was CT evidence of gas dissecting in an extra-capsular fashion (Fig. 4) with accompanying gas-fluid levels (Fig. 3). There was no evidence of subcutaneous emphysema. In the current case, as well as in prior cases presenting at our center, there was no evidence of intra-articular loculation of gas. Significant distention of the joint with gas may occur and is not a concerning finding. There was no evidence of subcutaneous emphysema, a finding which has been described in the context of gas-forming joint infections [13, 23, 24]. Pneumarthrosis may be accompanied by joint fluid as demonstrated by joint aspiration or visualized on CT, where it presented as large gas-fluid levels in prior cases. The clinical presentation in this case did not suggest an infection, and there was no evidence of infection during 19 months of follow-up. While the concern for component corrosion was raised, the patient indicated a preference for continued observation.
The proposed mechanism of aseptic gas formation following MTHA is cyclic motion between the prosthetic titanium alloy neck and stem due to component mismatch resulting in progressive oxidation and release of diatomic hydrogen, which then may become entrapped in the distal crevice between the components. Abrupt release of the accumulated hydrogen into the hip joint following movement and/or progressive corrosion or component fracture may result in acute hip pain. Thus, pneumarthrosis is an indicator of crevice corrosion and may be an early indicator of other complications such as difficult stem removal, component fracture, and effects of metallosis [4]. From a diagnostic perspective, the acute presentation and presence of gas mimic the rare acute hip joint infection caused by a gas-forming organism. However, systemic signs or symptoms expected from a gasforming infection are absent and these patients are immunologically competent. The radiographic presentation with accumulation of large gas pockets without subcutaneous emphysema or intra-osseous extension was similar in all cases encountered at our center. Extra-capsular dissection of gas may occur. Based on our experience with aseptic pneumarthrosis in patients with a modular Ti/Ti neck-stem prosthesis, we have adopted the following diagnostic algorithm: history, physical examination, and radiographs are obtained. An infection workup including CBC, ESR, and CRP is performed based on the clinical concern. When imaging shows the presence of large non-dependent gas pockets, without concerning clinical findings, then aseptic pneumarthrosis is considered. Imageguided joint aspiration should be pursued if there are concerning clinical findings. Follow-up radiographs should depict spontaneous resorption of gas. Findings to the contrary with persistent symptoms should raise the possibility of infection.
Fig. 4 Sixty-one-year-old male with dissecting extra-capsular gas (arrow) from left hip pneumarthrosis as seen on CT
Conflict of interest The authors declare that they have no conflict of interest.
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