Fiona Stanley Hospital (FSH) is a 783-bed tertiary hospital with a specialised multidisciplinary diabetes foot unit (MDFU). This multidisciplinary team comprises of endocrinologists, vascular surgeons, infectious diseases (ID) physicians, podiatrists, and community liaison nurses. The team manages complex diabetes-related foot complications across both inpatient and outpatient settings. A medical photographer attends all outpatient clinics to document ulcer site, size, and the presence of a healed wound. Outpatient wound care and, if required, parenteral antibiotics are provided by a single ambulatory nursing service.
The current study is a sub-study of the Audit of Multidisciplinary Diabetes Foot Unit services at Fiona Stanley and Fremantle Hospitals. Ethical approval was obtained from South Metropolitan Health Human Research Ethics Committee (RGS0000003204). To compare outcomes for patients hospitalised for diabetes related foot disease over time, two time periods of one year duration were studied in 2015 and 2019. For both the 2015 and 2019 cohorts this included hospitalisations during 52-week periods from the first week of February in each year. Between 2015 and 2019, clinical practice remained consistent, as endocrinology, ID and vascular surgery clinical leads remained the same.
The inclusion criteria for this study were as follows: 1] a diagnosis of diabetes, 2] admission for an infected diabetic foot ulcer and 3] minor amputation performed during admission. A minor amputation was defined as either a trans-phalangeal or trans-metatarsal amputation of single or multiple digits. Patients undergoing more complex surgeries including proximal forefoot amputations, revision of previous amputation sites or major lower extremity amputations were excluded.
In addition to the electronic medical record (EMR), data were also collected from laboratory and radiography databases. Demographics including age, sex, type of diabetes, glycaemic control, smoking history, diagnosis of chronic kidney disease and presence of Charcot neuroarthropathy were recorded. Glycaemic control was assessed with a pre-operative glycated haemoglobin (HbA1C). Smoking history was documented as never smoker or a history of previous/current smoking. Presence of chronic kidney disease (CKD) was judged based on the pre-operative eGFR (estimated glomerular filtration rate), and renal replacement therapy was noted. The history of an amputation was captured in the EMR and confirmed with review of operative notes. The requirement for an angioplasty during admission was also recorded.
Bone specimens were collected intraoperatively. Following bone transection, proximal bone samples were collected using a sterile ‘bone-nibbler’ and sent for culture. Our local standard of practice was for 2-weeks of oral antibiotics following the amputation, unless there was clinical evidence of residual soft tissue infection or involvement of adjacent osteoarticular structures. To define infection severity prior to the amputation, we applied the Infectious Diseases Society of America/International Working Group on the Diabetic Foot infection grading system (IDSA/IWGDF) [9, 10]. Amputations were recorded according to whether the most proximal amputation was trans-phalangeal or trans-metatarsal, whether they involved the first (hallux) or fifth ray, and the number of rays amputated. The microbiological results were obtained from superficial swabs (if collected within one month prior to admission) and proximal bone culture. Culture results were recorded according to bacterial species and if they were culture negative, monomicrobial or polymicrobial (> 1 named organisms reported by the microbiology laboratory).
We defined microbiology results as concordant if a swab and bone specimen were sent to the laboratory and the same organism(s) were isolated. We also considered concordant results if the bone cultures were negative, but an organism was isolated from superficial swabs. Pre-operative and post-operative antibiotic choice and planned duration was recorded. If discordance between swab and bone specimen was noted, the change in antibiotic choice was recorded.
Patient outcomes were assessed from the EMR up until six months post initial amputation. The primary outcome measure was the presence of complete healing by the end of the follow-up period. Secondary outcome measures included death, progression to a major amputation and the need for further surgery. If within this six-month period, a patient required intervention for a new ulceration within the immediate vicinity of the original amputation site, this was deemed contiguous with the original infection. Complete healing was defined as complete closure of the primary wound with no evidence of ulcer relapse within six months of the initial surgery. Further surgery was defined as further surgical intervention to the original amputation site, or a site within the immediate vicinity of the original infection.
Descriptive statistics were used to describe the study cohort using medians and interquartile range (IQR) for continuous variables and percentages for categorical variables. Mann Whitney U testing was performed for bivariate analyses of continuous variables, whilst a Chi-squared test was used for categorical variables. Logistic regression was performed with healing as the dependent variable. A backward stepwise approach was applied where explanatory variables with a P-value < 0.1 were eligible for inclusion and retained in the model if P < 0.05. The most parsimonious model was chosen on the basis of the Akaike Information Criterion. All statistical analyses were performed using R .