HIGH VIRULENCE AND POLYMICROBIAL ARTHROPLASTY LATE INFECTIONS: MICROBIOLOGICAL AND ORTHOPAEDIC RESULTS

Abstract

Introduction: Papers about high-virulence infections are not usual, results contradictory, and orthopaedic outcomes not described.

Purpose: to compare infectious and orthopaedic results after late arthroplasty infections by single vs. polymicrobial isolates, low vs. high-virulence, and Gram-positive vs. Gram-negative organisms, when treated by exchange surgery plus long cycles of combined oral antibiotics.

Patients and Methods: A late arthroplasty infection was diagnosed in 68 consecutive patients (48 female) of 72.2(+/−10.2) years (37 hips/31 knees).

Cultures were polymicrobial in 22 cases and by Gram-positive in 55 (80.9%). Highly-resistant organisms: methicillin-resistant Staphylococcus (36 patients) and ESBL-producing Enterobacteriaceae (2 patients). “Problematic-treatment”: Enterococcus (6 patients), Pseudomonas (3 patients), non-fermenting Gram-negative (2), moulds (1).

Oral antibiotic selection: according to bacterial sensitivity, biofilm and intracellular effectiveness. Protocolized surgery: two-stage exchange. Average follow-up: 4.7+/−2.7 years (1–11).

Healing of infection is diagnosed if absence of clinical, serological and radiological signs of infection during the whole follow-up. Orthopaedic outcome is evaluated by HHS for hips and by KSCRS for knees.

Results: Surgery was not possible in 7 infections (rejected by patients), and reimplantation in 17 additional cases (patients died shortly after first surgery, rejected 2nd surgery, or was contraindicated because of medical reasons).

Healing of infection: 59/68 patients (86.8%), 32/37 hips (86.5%) and 27/31 knees (87.1%). Infection not healed: 7/68 cases (10.3%) (4/37 hips, 3/31 knees) (5 by highly-resistant and 1 by “problematic-treatment” bacteria). There are no differences between hips and knees (p=0.55).

Orthopaedic Results: HHS averages 80.5+/−16.2 (81+/−16 in healed infection, 56+/−23.5 in persistent infection). KSCRS averages 77.2/58.1 +/− 19.8/24.5 in healed infections, 32.6/0+/−25.8/0 in persistent infections. Infective and orthopaedic results present a strong statistical correlation in hips (p=0.016) and knees (p=0.0001).

Statistically significant differences are not found when comparing subgroups according to Gram stain (p=0.43), multiple vs single bacteria (p=0.47 infective, p=0.71 orthopaedic), highly-resistant bacteria (p=0.2 infective, p=0.1/0.5 orthopaedic), or “problematic-treatment” (p=0.68).

Conclusions:

1. A strong statistical correlation appears between infective and orthopedic results after late arthroplasty infections.

2. With the number of cases presented significant differences in infective or in orthopaedic results are not found when comparing single vs. polymicrobial, gram-negative vs. gram-positive, high vs. low antimicrobial resistance and “problematic-treatment” infections.