Postoperative infections after excision of neurogenic heterotopic ossifications at the hip: Risk factors and causative organisms

Abstract

Background: Neurogenic heterotopic ossification (NHO) is usually treated by surgical excision. Postoperative infection (POI) is a possible complication, whose epidemiology, causative organisms, and risk factors are poorly known. We therefore conducted a case-control study to (1) identify the risk factors for POI after surgical excision of NHO at the hip, (2) determine the frequency of POI, (3) and identify the causative organisms.

Hypothesis: Risk factors for POI after NHO excision at the hip can be identified.

Material and methods: In this retrospective case-control study, the BANKHO database for patients with NHO at our centre was used to identify risk factors by comparing patients with and without POI after NHO excision at the hip. To this end, odds ratios (ORs) with their 95% confidence intervals (95%CIs) were computed for each main criterion. Postoperative follow-up was at least 6 months.

Results: Between 1993 and 2013, 411 hip NHO excisions were performed. Among them, 42 (10%) were followed by POI. The American Society of Anesthesiologists (ASA) score was I in 2/42 (5%) patients with vs. 74/369 (20%) patients without POI, II in 30/42 (71%) patients with vs. 258/369 (70%) patients without POI, and III in 10/42 (24%) patients with vs. 37/369 (10%) patients without POI (P<0.01). Mean age was 31±11 years (range, 17-79years) in the group with POI and 39±14 years (range, 15-77years) in the group without POI (P<0.01). The NHO was related to spinal cord injury in 26/42 (62%) patients with POI compared to 92/369 (25%) patients without POI (P<0.01). ORs indicated a significant risk increase in patients with an ASA score of III (2.84; 95%CI, 1.28-6.31), age younger than 30 years (1.85; 95%CI, 1.03-3.32), and spinal cord injury as the cause of NHO (4.89; 95%CI, 2.67-8.98). The predominant organisms were staphylococci (skin flora) in the patients with spinal cord injury and bacteria commonly found in intensive care units in the other patients.

Discussion: A higher ASA score, younger age, and spinal cord injury as the cause of NHO at the hip are risk factors for POI. The proportion of patients with POI after hip NHO excision was 10%, in accordance with previous reports. POI was more common among patients with spinal cord injury (22% vs. 5% in the other patients). Neither changes in prophylactic antibiotic therapy regimens nor the institution of a detailed skin preparation protocol affected the frequency of POI. Skin pH alterations may deserve to be investigated with the goal of diminishing the risk of POI, most notably in spinal cord injury patients.

Level of evidence: III, case-control study.

Keywords: Head injury; Hip; Neurogenic heterotopic ossification; Postoperative infection; Spinal cord injury; Stroke.