In the UK between January 2019 to December 2020, over 3000 below knee amputations (BKA) were performed and the national ratio of above knee amputations (AKA): BKA was 0.98.1 Higher levels of amputation result in greater difficulty with transfers, increased energy expenditure for ambulation and lower rates of ambulation with a prosthesis. 2 Failure of an amputation to heal however can result in prolonged hospital admission, multiple debridements and ultimately may result in revision to a higher level along with a delay in commencing rehabilitation. The aim of this study was to determine factors associated with wound healing in patients who underwent BKA.

This was a single-centre retrospective case series of all BKAs carried out over a 3-year period between 01/05/2018-26/05/2021. Patients who had amputations for indications other than peripheral vascular disease (e.g. trauma, malignancy) were excluded. Data were collated on patient characteristics, laboratory results, imaging findings and the requirement for revision surgery at any point. The primary outcome was the requirement for revision at any point during follow up (last follow up was in October 2021). Analyses were carried out on a per-patient basis (in patients undergoing bilateral BKA only the first operation was considered). Univariate logistic regression analyses were performed with the requirement for revision as the outcome. We planned to do multivariable logistic regression involving the variables that were significant in univariate analyses. Fisher's exact test was used to compare proportions involving categorical data. Significance was set at 0.05.

252 consecutive patients were identified for analysis (male 78.1%; female 21.9%). The average age was 69.1 years at the time of surgery. The distribution of American Society of Anesthesiologists (ASA) category was as follows: I 0% II 2.7% III 63.9% IV 33.3 V 0%. Operations were performed under general anaesthesia in 49.2%, spinal anaesthesia in 45.6%, regional block in 2.7% or local anaesthetic with sedation in 2.3%. All BKAs were carried out using a posterior flap technique. The majority of patients had significant comorbidities - diabetes mellitus (DM) 67.4%, hypertension 66.6%, ischaemic heart disease (IHD) 42.4% and chronic kidney disease (CKD) 36.1%. 82.5% (208/252) of patients had imaging (CT angiogram or arterial duplex) prior to amputation. Significant inflow disease was defined as a stenosis or occlusion of aorta, iliac or common femoral artery (CFA). 85.3% of limbs healed successfully and 37/252 limbs required revision during the study: 27 to Above Knee, 6 to Through Knee and 4 revised at Below Knee level. Significant inflow disease significantly influenced the requirement for revision (OR 4.4375 (95% CI 2.0465 - 9.6221) P=0.0002). 17/49 patients with significant inflow disease on imaging required a revision 17/159 patients without significant inflow disease on imaging required a revision p=0.003. No significant association was found between the need for revision and patient factors including DM, hypertension, IHD, CKD, or pre-operative blood results including haemoglobin, white cell count, C-reactive protein, albumin or HbA1c.

Healing following BKA is difficult to predict. To our knowledge, this is the largest recorded case series of BKAs that included data on PVD severity. Our overall healing rate was 85.3%. The only significant predictor for the requirement for revision was the presence of inflow disease. Despite this, in patients with significant inflow disease 65% of BKAs healed. We recommend individualised decision making regarding the level of amputation and believe BKA is suitable for a selected sub-group of patients even with inflow disease

1) Waton S, Johal A, Birmpili P, Li Q, Cromwell D, O'Neill R, Williams R, Pherwani A. National Vascular Registry: 2021 Annual Report. London: The Royal College of Surgeons of England, November 2021. 2) Chopra A, Azarbal AF, Jung E, Abraham CZ, Liem TK, Landry GJ, et al. Ambulation and functional outcome after major lower extremity amputation. Journal of Vascular Surgery. 2018 May;67(5):1521-9.