A Case of Septic Arthritis of the Shoulder Joint That Developed after Suprascapular Nerve Block

Septic arthritis of the shoulder is uncommon in the immunocompetent patient with no previous risk factors for joint infection. We treated an immunocompetent patient who developed septic arthritis of the shoulder after suprascapular nerve block for pain due to rotator cuff tear. An 80-year-old man with no underlying disease visited a nearby orthopedics clinic with complaint of left shoulder joint pain. Left suprascapular nerve block was performed, but the pain gradually aggravated. On the day after the block, he had a fever of 39˚C and came to our department. On examination, enlargement and tenderness were present at the injection site. Cellulitis at the site was suspected. He was admitted and administration of a cephem antibiotic was started. Pain subsequently decreased. Magnetic resonance imaging (MRI) performed 4 days after hospitalization showed massive effusion close to the injection site. The effusion spread into the joint cavity through the tear site of the supraspinatus. Septic arthritis of the shoulder was strongly suspected, open irrigation and debridement were performed 11 days after hospitalization. After surgery, pain immediately improved. In


Introduction
Septic arthritis of the shoulder is relatively rare (approximately 3% of all joint infection) [1] but is a serious and difficult-to-cure disease in which joint function may be damaged without early treatment [2] [3] [4]. The disease normally develops in elderly people with underlying disease after antecedent infection or a minor invasion such as arthrocentesis [1] [2] [5]. Leslie et al. reported that in patients with septic arthritis of the shoulder, hematogenous causes were responsible for 56% of cases, intra-articular procedures for 11%, and steroid injection for 33% [2]. In contrast, there have been no reports of cases that developed after suprascapular nerve block. Here, we report a case of septic arthritis of the shoulder that suspected to develop after suprascapular nerve block in an elderly man with no underlying disease. We also include a discussion of the literature.

Case Presentation
The patient was an 80-year-old man with a major complaint of left shoulder joint pain. He had no specific medical history. He had become aware of left shoulder joint pain several years ago, but the pain resolved spontaneously at that time. In August 2018, left shoulder joint pain redeveloped without any trauma.
Since the pain did not resolve in several days, he visited a nearby orthopedics clinic, where left suprascapular nerve block was performed for the pain. We confirmed later that 5 ml of 1% xylocaine was injected using a 21-gauge needle after sterilization with povidone-iodine. Subsequently, the left shoulder joint pain gradually aggravated. On the day after the block, he had a fever of 39˚C and came to our department.
At the first visit, body temperature was 38.7˚C, blood pressure was 138/97 mmHg, pulse rate was 80/min, and the patient was lucid. Enlargement and tenderness were present at the injection site for left suprascapular nerve block, but enlargement of the left shoulder joint was mild ( Figure 1). The pain was severe, as shown by a visual analogue scale (VAS) of 10/10 points, and both autokinetic and passive movement of the left shoulder joint was difficult. The Japanese Orthopedic Association (JOA) Score, the University of California at Los Angeles (UCLA) score, and the Constant Shoulder Score were 20/100, 4/35, and 8/100 points, respectively.
The white blood cell (WBC) count was 14,140/μl, the C-reactive protein    The liquid shown as low intensity on T1-weighted images (c) and as high intensity on STIR images (d) spread from the tear site of the supraspinatus into the joint cavity and then to the synovial bursa located anterior to the shoulder joint.
In blood sampling 9 days after hospitalization, WBC had decreased to 5690/μl, but CRP was 12.7 mg/dl, suggesting insufficient improvement. Open irrigation and debridement were performed 11 days after hospitalization. Based on the clinical and imaging findings, the extra-articular injection site for suprascapular nerve block was thought to be the main infected lesion, and thus surgery was performed with open approach. After incision of the supraspinatus and infraspinatus, cloudy serous pus and necrotic tissues were confirmed (Figure 4), which were removed as much as possible and the site was thoroughly cleansed with saline. The amount of pus was small, and the infection had been improved to a certain extent by the antibiotic. After partial incision of the joint capsule, a small amount of pus leaked from the joint cavity ( Figure 4). A Teflon I.V. Catheter was injected at the site and irrigation was performed using 2 liters of saline. All samples of tissues from the supraspinatus and infraspinatus, serous liquid, and joint fluid collected during surgery were negative in bacterial culture.
After surgery, pain immediately improved (VAS 1/10 points) and CRP normalized to 0.3 mg/dl at 4 weeks after surgery with continuous administration of the cephem antibiotic ( Figure 5). At 3.5 months after onset, pain was almost resolved and the shoulder joint could be flexed for 130˚, abducted for 110˚, externally ro-

Discussion
Septic arthritis develops mainly in the knees and hip joints (61% -79%), which carry the load of the lower extremities, but is rare in shoulder joints (approx. 3%) [1]. However, the rate of septic arthritis of the shoulder has increased to 10% -15% of all types of arthritis in recent years due to increased use of arthroscopy and advanced aging [5]. In many cases, septic arthritis of the shoulder develops in patients with chronic underlying diseases, such as diabetes, blood disorder, renal failure, malignant tumor, malnutrition, and rheumatoid arthritis; after administration of immunosuppressive drugs, such as long-term administration of steroids; or after a minor invasion, such as arthrocentesis and antecedent infection. Some cases with infection after surgery for rotator cuff injury have been described in relatively young patients with no underlying disease, and hematogenous infection in infants has also been reported [2] [4] [6]. However, to the best of our knowledge, there has been no previous report of septic arthritis that developed after suprascapular nerve block.   An epidemiological study based on medical checkups in Japan found rotator cuff tear in approx. 25%, 45% and 50% of persons in their 60s, 70s and 80s, respectively [12]. The incidence of rotator cuff tear as a complication of septic arthritis of the shoulder is high: Klinger et al. [9], Jeon et al. [11], and Yamagata et al. [10] reported rotator cuff tear in 14 of 23 patients (approx. 61%, av- Our case received suprascapular nerve block at a nearby hospital, and we confirmed later that 5 ml of 1% xylocaine was injected using a 21-gauge needle after sterilization with povidone-iodine. The rates of septic arthritis after joint injection and arthroscopic surgery are 4 and 14 per 10,000 cases, respectively [13]. No previous reports have suggested septic arthritis after suprascapular nerve block, which indicates the rarity of this condition. Since our case had no underlying disease, it is possible that the technique for suprascapular nerve block in the nearby hospital might have been inappropriate, or the injection agent might have been contaminated.

Conclusion
We experienced the case of septic arthritis of the shoulder developed with the patient who had rotator cuff tear after left suprascapular nerve block. This case suggests the possibility that patients with rotator cuff tear may easily develop septic arthritis because extra-articular infection may spread into the joint cavity through the site of tear.

Consent
The patient gave informed consent to submit this case study for publication.