Protrusio acetabulae as a sequel to septic arthritis of the hip with obturator internus pyomyositis

Abstract

Pyomyositis is defined as a pyogenic infection of skeletal muscles principally caused by Staphylococcus aureus. It can present either primarily without any associated soft tissue or bone infection or secondary to any surrounding or distant infection focus. Hip pericapsular pyomyositis is one of the most common types of primary pyomyositis. Although many cases are increasingly being described both in tropical and temperate climates, there is no published study regarding the sequelae of untreated pericapsular pyomyositis around the hip joint. The purpose of this study is to describe the sequelae of unaddressed obturator internus abscesses in four adolescent patients and compare their outcome with patients where obturator abscess was also drained using Vanderbilt medial approach. A retrospective study was done with eight patients divided equally into two groups. All the patients were diagnosed as septic arthritis with pyomyositis of obturator internus. Group 1 includes patients treated in between 2012 and 2014 with only hip arthrotomy through anterior approach. Group 2 includes patients treated after 2014 with anterior hip arthrotomy along with drainage of obturator internus abscess. All patients in group 1 had frequent episodes of pain in the first postoperative year with persistent restriction of hip range of motion. Two patients required re-drainage of the hip joint within the first month of indexed surgery. Final follow-up (average 6 years) X-rays revealed grade 2 protrusio acetabuli in three cases and grade 3 in one case as per the Sotelo-Garza and Charnley classification. In contrast to the group 1, group 2 patients had an excellent outcome with an average Iowa Hip Score of 93 at average follow-up of 4.25 years with near normal range of motion, no radiological deterioration and residual pain. The possibility of pericapsular pyomyositis should always be kept in mind, in older children with acute hip pain. A high index of suspicion is required for its early diagnosis. MRI is the gold standard investigation for confirming diagnosis and planning the preferred early surgical treatment. Safe and effective surgical drainage of obturator internus abscess through a minimally invasive Vanderbilt medial approach may prevent long-term sequelae of chronic pain, protrusio acetabuli and secondary osteoarthritis.