MetaMet: Bone Cutter Versus Bone Saw for Ray Amputation

Toe amputation is a commonly performed operation for infection and/or ischaemia (tissue death due to lack of blood flow). However, a large number of patients having this surgery ultimately require further amputation due to poor wound healing, new infections and/or new ulcers. Research to date has focused on patient-related factors associated with poor wound healing (e.g. diabetes, lack of blood flow, poor kidney function). However, there is no research looking at the technical surgical aspects of the procedure, specifically how the toe bone is cut.

For this feasibility study, we will recruit forty patients whom a consultant vascular surgeon has decided requires amputation of one-to-two adjacent toes. The participants will be randomised by a computer model into one of the two metatarsal transection methods (bone cutters or bone saw) and the rest of the procedure will be carried out in the standard fashion. Patients and assessors will be blinded to which transection method is chosen.

Patients will undergo a post-operative foot x-ray to assess for bone fragments within 48 hours of surgery and another at six months to assess for bone healing. Patients will be asked to rate their pain in the post-operative period using the verbal rating score. Patients will be followed after discharge from hospital by their public health nurse, as is standard practice, with regular follow-up in the surgical outpatients to assess wound progress. Patients will be asked to rate their quality of life at six weeks and six months post-operatively. These assessments will be coordinated with their routine post-operative follow-up clinic appointments, so as not to inconvenience patients with supernumerary visits.

Toe amputation is a common minor vascular procedure and is increasingly performed in the context of irretrievable diabetic foot infection, with and without concurrent ischaemia. Approximately 422 million people worldwide have diabetes mellitus and peripheral arterial disease (PAD) affects approximately 200 million people(1). The intersection between diabetes, neuro-ischaemic foot ulceration and lower limb amputations is well established(2). Recently published data from the United States reported overall rates of lower limb amputations in diabetic patients rose between 2000 and 2015, in part due to a 62% increase in the rate of minor (foot and toe) amputations(3). It is estimated that 6% of Irish adults are diabetic; from this, we can extrapolate the burden of managing diabetic foot complications(4). Resource utilisation notwithstanding, the financial costs of managing diabetic foot complications are estimated to outstrip some cancers(5). As the prevalence of diabetes mellitus rises amongst an ageing Irish population, the importance of achieving durable functional outcomes after partial foot amputation is paramount.

Re-ulceration, re-infection, re-amputation and hospital re-admission after partial foot amputation for digital gangrene is well documented in the literature in both diabetic and PAD cohorts(6). Across the literature, rates of re-amputation at five years post-index surgery for diabetic foot complications range from 45-65% (6, 7). A recent study by Collins et al reported that, out of 146 Irish patients undergoing minor amputations, 43% (n=63) required further ipsilateral amputation, 21 (14.4%) of which were trans-tibial or trans-femoral(8). Chronic kidney disease, diabetes with or without poor gylcaemic control, peripheral neuropathy, peripheral arterial disease, ongoing tobacco smoking, obesity (BMI \>30), concurrent sepsis at the time of index operation have all been identified as independent risk factors for amputation failure and the need for revision(9-11). While numerous studies have investigated patient-dependent factors predictive of amputation failure, there is a dearth of evidence examining the impact of surgical technique on this commonly performed procedure.

An exhaustive search of the literature surrounding surgical technique and outcomes after ray amputation yielded several papers on the benefits of various soft tissue flaps for covering wound defects but just one detailing a particular methods of bone transection. However, Moodley et al focused on the use of a Gigli saw, which is beyond the scope of this feasibility study(12). There have been no randomised controlled trials evaluating the impact of metatarsal transection method on outcomes after ray amputation, specifically whether a manual bone cutter or an electric/oscillating/pneumatic bone saw were used. We hypothesise that utilising a manual bone cutter is more subject to inter-user variability, as it depends on the physical strength of the operating surgeon; improperly applied forces are liable to fracture the remaining bone, leaving small comminuted fragments that may become necrotic and act as a nidus for further infection within the wound bed. Furthermore, using an oscillating microsaw has the advantage of providing a clean bony transection regardless of the physical strength of the operator, however it may cause more damage to the surrounding connective tissues and disturb microvascular periosteal supply, which could also lead to osteonecrosis. We propose a pilot randomised controlled trial to test the feasibility and to generate sufficient data to permit sample size calculation for a trial designed to evaluate the outcomes after ray amputation using either a bone cutter or a bone saw.

Eligibility Criteria:
Inclusion Criteria:

* Consenting patients, aged 18 and over, undergoing transmetatarsal amputation of one-to-two adjacent toes

Exclusion Criteria:

* Significant peripheral arterial disease, as defined by ABPI \<0.4 or digital pressures of \<50mmHg, not undergoing concurrent revascularisation;
* Patients undergoing amputation of three of more adjacent toes
* Patients unfit for surgery;
* Patients unable to provide informed consent