Clinical introduction

An 83-year-old man with a longstanding incisional hernia presented to the ED with a 48-hour history of vomiting and constipation. His medical history included thrombotic stroke, congestive cardiac failure, hypertension, chronic obstructive pulmonary disease and large bowel resection.

The patient was tachypnoeic. All other observations were stable. Examination revealed a distended abdomen with a hernia protruding beneath a midline laparotomy scar. The superior portion of the hernia was reducible and the edges of the wide defect palpable. However, inferiorly there was a firm, irreducible tender knuckle of tissue. An abdominal radiograph was requested to aid diagnosis (figure 1).

Question

Which signs can be observed in the …