Reverse rhino sign as a radiological sign of low-grade infected reverse shoulder arthroplasty

Low-grade infections following shoulder surgery are difficult to diagnose. Recently, curved-shaped bony spurs, further mentioned "reverse rhino signs" because of its shape, growing inferior on the glenoid were noticed on X-rays of patients with a reverse shoulder arthroplasty (RSA) and a Cutibacterium acnes (C. acnes) infection. This study aimed to determine the sensitivity and specificity of the reverse rhino sign as a radiological marker for detecting low-grade shoulder infections in RSA.

A diagnostic study was performed including patients who underwent revision surgery of an RSA with perioperative cultures taken. Blinded radiographic evaluation was performed by two orthopedic surgeons for presence of rhino signs, humeral osteophytes, and notching. Efficacy measures of the reverse rhino sign for detecting low-grade infections were determined. Furthermore, results were stratified for notching and gender.

Thirty-two revised RSA patients had a low-grade infection and 36 had no infection. Seventeen (53%) patients with infection had a reverse rhino sign present, compared to 6 (17%) in the non-infection group. Sensitivity, specificity, positive and negative predictive value of the reverse rhino sign were, respectively, 53%, 83%, 74%, and 67%. These measures changed to 68%, 77%, 72%, and 74% for patients without notching and to 47%, 100%, 100%, and 8% for males.

In the absence of a reverse rhino sign in RSA patients, a low-grade shoulder infection is unlikely. Hence, the reverse rhino sign can be used to rule in a low-grade shoulder infection, especially in males and in the absence of notching. Low-grade infections should be considered in patients with unexplained persistent shoulder complaints after RSA placement, especially when a rhino sign is present. For these patients, we advise to perform mini-open biopsy for cultures.

Diagnostic level IV.