Sudden knee pain in an underweight, older woman: obturator hernia

Abstract

In December, 2012, a 92-year-old woman with a body-mass index of 14·2 kg/m2 presented to our emergency department with a 2 day history of sudden onset right knee pain and 1 day of nausea and vomiting. She had no history of abdominal surgery and had given birth to fi ve children by normal vaginal delivery. 2 days before her visit she had been diagnosed with degenerative osteoarthritis of the knee by an orthopaedic surgeon on the basis of radiographs; however, on presentation to our department there was no swelling or tenderness of the knee joint. During examination, she often fl exed the right knee to relieve the pain. She had abdominal distension and tenderness to deep palpation, but no signs of peritoneal irritation and no abdominal mass. Rectal examination revealed a small extraluminal mass on the right side. An abdominal radiograph showed small-bowel obstruction. Axial CT of the abdomen and pelvis showed a fl uid-fi lled mass between the pectineus and external obturator muscles (appendix). Both coronal and sagittal images showed the small intestine herniating into the right obturator canal (fi gure). The incarcerated bowel loop had prominent wall enhancement consistent with early vascular compromise. The patient immediately underwent a laparoscopy, which showed a loop of the mid ileum in the right obturator foramen. We reduced the aff ected bowel loop with gentle traction, restoring viability and rendering bowel resection unnecessary. We repaired a fi ngertip-sized defect caused by the obturator hernia with a mesh plug. The patient recovered well, and at follow-up 1 year later she had no indication of recurrence and no further knee pain. Obturator hernia is rare, and remains a diagnostic and therapeutic challenge. The usual presentation of obturator hernia is acute small-bowel obstruction with strangulation, frequently necessitating emergency bowel resection. Because of laxity of the pelvic fl oor associated with a wide obturator canal, old age, previous pregnancy, emaciation, and raised intra-abdominal pressure, obturator hernia occurs almost exclusively in multiparous, underweight, older women. Because the sigmoid colon acts as an anatomical barrier, obturator hernia presents less frequently on the left side. About a third of patients have recurrent bowel obstruction followed by spontaneous remission. A palpable groin mass in the medial thigh is uncommon, because obturator hernia is concealed beneath the pectineus. A hernia is sometimes palpable on rectal or vaginal examination. Occasionally, obturator herniae produce pathognomonic signs because of compression of the obturator nerve, such as the HowshipRomberg sign (pain of the medial thigh, which is exacerbated by extension, abduction, and inward rotation, and relieved by fl exion), and the Hannington-Kiff sign (absent thigh adductor refl ex). However, severe abdominal symptoms can mask obturator neuropathy, causing these defi nitive signs to be mistaken for degenerative arthralgia in older women. In the era of CT, multiplanar reformations have greatly aided the early and correct diagnosis of obturator hernia. Immediate surgical exploration based on an accurate diagnosis is crucial. Many possible surgical approaches exist for repairing obturator herniae, although the choice depends on individual circumstances. Laparoscopic techniques provide a minimally invasive option, and laparoscopy can clarify the best course of action in bowel incarceration and ambiguous cases. Because frail older women are poor candidates for surgery, delays in diagnosis cause high rates of morbidity and mortality, so the timing of CT during the symptomatic period is of paramount importance. Awareness of this disease process with its characteristic presentation is crucial. Heightened clinical suspicion in an underweight older woman should steer clinicians toward timely CT, prompting surgical intervention without delay.