A Novel Modified Adjunct Procedure for Patients With Diabetic Foot Infection and Chronic Limb-Threatening Ischemia
Patients with chronic lower extremity wounds complicated by peripheral arterial disease (PAD) and diabetes face a high risk of delayed wound healing and potential limb loss despite traditional management. Chronic limb-threatening ischemia (CLTI) is the end-stage of PAD with development of severe soft tissue deformity in the majority of patients and a 60% mortality rate within 5 years of diagnosis.1 Of the >200 million people affected by PAD globally, more than 11% progress to CLTI.2-3 Twenty-five percent of patients in the US are not eligible for revascularization, which results in approximately 60,650 major limb amputations annually.1 Patients with no-option critical limb-threatening ischemia (CLTI) also experience notably worse quality of life and mortality risk at levels similar to terminal cancer.1
The Tibial Cortex Transverse Transport system (TTT) is an innovative technique that uses the tension stress effect through cortical distraction to promote distal angiogenesis and stimulate soft tissue recovery in no-option limb preservation. The technique was developed to enhance wound healing and has shown effectiveness in management of chronic diabetic foot ulcers (DFUs) and CLTI treated by orthopedic surgeons primarily in China.4 At our institution, we currently have the highest volume center in the US using a modified TTT technique, the Fixator Assisted Soft Tissue Repair (FASTR™) as an adjunct procedure for improving microvascular circulation affected by diabetes and CLTI to assist in soft tissue repair.
The Tension Stress Effect Focused to Angiogenesis
The Ilizarov tension stress effect is a longstanding method of genesis and growth of soft tissue and bone with gradual tension of a planned osteotomy site.4 Surgeons commonly apply this technique to cases of limb lengthening through lateral distraction of a digit or limb with a distraction engine stabilized by an external fixator device.4-6 The metabolic tissue activation results in a number of physiologic responses:7
• mechanical stimuli via the gradual mechanical distraction of bone and surrounding soft tissues promotes growth factor release and angiogenesis
• microenvironmental changes alter demands for oxygen and nutrients to the site of stress
• the increased demand for oxygen in the area of hypoxia stimulates production of VEGF
• osteoblastic activity in bone regeneration promotes a cellular response with recruitment of pro-angiogenic factors and neovascularization
• matrix remodeling of the extracellular matrix promotes scaffold formation for ingrowth of new blood vessels
• finally, enhancement of blood flow to the osteotomy site supports the metabolic needs for repair of distal soft tissue defects
It is our contention and current experience that the tension-stress effect is not solely a local response and that the FASTR approach promotes healing to remote sites.
Harnessing the Tension Stress Effect for the Dysvascular Limb
Current indications support TTT’s use in severe diabetic foot infections (Wagner III+) with at least one vessel runoff with the goal of regenerating tissue, rebuilding local microcirculation of small vessels in the medullary cavity and ultimately restoring vascular and oxygen supply through continuous cortical distraction. The surgeon creates an initial unicortical osteotomy window at the proximal tibia. Two half pins are inserted into the cortical osteotomy window and secured to a distraction engine stabilized by an external fixation device. A latency period of approximately 5-7 days allows for initial healing of the osteotomy site prior to initiating a gradual distraction and restoration of the window at 1 mm per day (0.25 mm four times a day) over a course of weeks. This induces a biologic response with controlled tension that stimulates a biologic cascade. As osteogenesis develops in the bone gap, soft tissues adapt and regenerate to include muscle, nerve, and blood vessels. The mechanical stimuli of cortical distraction is thought to promote growth factor expression, angiogenesis, and migration of bone marrow stem cells, resulting in the reformation of distal collateral circulation. The external fixation device is then removed after completing a consolidation phase.
The TTT in Current Literature
Current literature supports use of the TTT in patients with severe chronic foot ulcers, revealing improvement in ankle-brachial index (ABI), healing time, and limb salvage rates.8-20 Pin site infection and fracture at the corticotomy site are the most commonly reported complications with a bone window around 7 cm x 1.5 cm.8-20
A systematic review and meta-analysis by Hu and colleagues in 2022 analyzed 7 studies with a total of 818 TTT participants using a monorail distraction device.14 Pooled healing rates and limb salvage rates were high, at 96% and 98% respectively. Mean pooled healing was 15.03 months. The study also noted improvements in ABI by a mean of 0.23 and skin temperature by a mean of 1.56°C, consistent with the findings of studies
performed after publication. The most common complications included fracture at the corticotomy site and pin site infection.14
Liu and team retrospectively reviewed 98 patients who underwent a TTT at a medical facility in Beijing, China for management of distal foot gangrene.19 The study noted a healing rate of 95.83% over an average of 53.18 ± 20.18 days. At 3 months after TTT application, the patients had significant improvement in ABI and ulcer classification (P<0.05). Three patients underwent digital amputations and 3 patients developed pin site infections without osteomyelitis.19
Chang and coworkers demonstrated a 100% healing rate without amputation with a mean time of 25.8 ± 7.8 days in 13 patients who underwent a TTT.10 This study found improvements in skin temperature to the dorsal aspect of the affected foot by 2.6°C and ABI by 0.2 at 3 months postoperatively. Additionally, they appreciated increased collateral circulation on a 2 month postoperative computed tomography angiogram (CTA) compared to preoperative imaging. The authors report a single case of pin site infection.10
The FASTR System
The traditional TTT method uses 2 half pins and a monorail with 2 cortical windows. We have worked to develop a modified TTT, the FASTR, to improve the stability of the structure at the corticotomy site and lower extremity. We have successfully applied this technique following the same basic principles of half pins with a distraction device with a few adjustments, including adding a circular external fixator frame for stability of the corticotomy site with the option of offloading with a foot plate. We are also working to modify the intraoperative techniques for better efficiency and efficacy. We have progressed from open incisions to a percutaneous procedure with a corticotomy site of 5 cm x 2 cm.
Surgical Pearl: The corticotomy window should always be made in the proximal tibia in the zone of vascularity.
Neglecting to do so, in our experience, increases both risk of failure at the corticotomy site and of providing sufficient stimuli to achieve angiogenesis.
FASTR Surgical Technique
The surgeon confirms the planned placement of the distraction engine at the medial face of the tibia, approximately 3 cm distal to tibial tubercle, accounting for adding the proximal ring and the location of the fibular neck. The surgeon performs straightforward soft tissue dissection down to the periosteum, then introducing half pins within the planned osteotomy site prior to the corticotomy cuts to improve stability. The corticotomy then takes place with a sagittal saw to form a 5 cm x 2 cm unicortical bone window (Figure 1A-1D).
Alternatively, the surgeon may opt to perform the procedure percutaneously, which allows for minimal tissue handling. The half pins are secured percutaneously followed by creation of unicortical burr holes in a 5 cm x 2 cm formation that are then connected with a small osteotome via a minimally invasive technique to form the bone window (Figure series 2).
Surgical Pearl: Make sure to have the proximal external fixator ring in place prior to half pin placement to avoid difficulty maneuvering the ring over the pins.
Closure of the surgical wound then takes place around the pins. The engine attaches to the 2 half pins and secures to the external fixator rings. The rings are then secured to the limb with the standard Ilizarov method via wire placement, with confirmation of ring placement to the engine and leg. The surgeon then tests the engine when satisfied with the final construct (Figures 3A-D).
Postoperative Protocol Pointers
Most patients remain non-weight-bearing, as there is commonly an associated wound requiring offloading. However, patients have been able to fully weight-bear with our construct if indicated. The patients follow a distraction protocol with a latency period, distraction, restoration, and consolidation prior to FASTR device removal. The engine is left in place during a latency period of 5 to 7 days. The patient then initiates lateral cortical distraction with 1 mm per day (¼ turn every 6 hours) for 2 weeks followed by restoration for 1 mm per day for an additional 2 weeks. After a 2 week consolidation period, FASTR frame removal takes place in the OR and the patient is placed in a high tide CAM walker or a total contact cast based on wound care needs.
Current Outcome Observations
Our case series has reviewed patient demographics, perioperative vascular evaluations, surgical interventions, and outcomes.
Since 2023, we have performed a total of 15 FASTR procedures in patients with severe recalcitrant foot ulcers and critical limb threatening ischemia. Our patients range from 28 to 92 years of age. Nine of the 15 patients underwent a lower extremity vascular intervention prior to deciding to proceed with the FASTR procedure due to persistent peripheral ischemia. The majority of our patients had additional severe cardiac and renal comorbidities.
Our longest follow-up period is 16 months. Overall, we have had one patient go on to an above-knee amputation (AKA) of the affected extremity. This patient was lost to follow-up due to social circumstances immediately after completion of the FASTR procedure and an adjunct complex myofascial adipocutaneous flap to a heel deficit. He developed an infection requiring early removal of the external fixator and underwent a subsequent AKA after transfer to a tertiary center for concurrent cardiac concerns. Remaining postop complications have included one Checketts-Otterburn Grade V pin tract infection involving a foot pin, 3 cases of secondary gangrene to the digits or forefoot, locally managed with debridement, isolated amputation, or transmetatarsal amputation (TMA), one incomplete tibial fracture healed with immobilization, and one tibial insufficiency fracture. In this case, the patient fell from his wheelchair during a cardiac event and fractured the tibia at the site of the corticotomy 2 months after external fixator removal. The fracture has been managed with open reduction and internal fixation with placement of an antibiotic rod, followed by a keystone advancement flap for coverage over the anterior tibia and a final tibial nail exchange. We did observe one death from unrelated causes. To date, 8 of our patients have achieved full epithelialization of their original wounds and 6 show advanced wound healing. Of the 5 patients that received perioperative angiograms by the same vascular surgeon, improved vascular reconstitution was demonstrated on 4 of the repeat angiograms.
Cases From the Series
A 46-year-old male initially presented with a severe diabetic foot infection (DFI) and calcaneal osteomyelitis. After 5 months of hospitalizations and surgeries including a partial calcanectomy and rotational flap, the wound appeared healthy, but epithelialization stalled. The patient underwent the FASTR procedure. He did experience a distal embolic event requiring amputations of digits 2 and 3 with monorail fixation performed during removal of the FASTR external fixator. At 2 months, his wound had contracted and the team placed a split-thickness skin graft (STSG). At 3 months, the wound had completely engrafted (Figures 4A-D).
Another patient was a 28-year-old female with a DFI who presented after 3 months of surgical and medical management of a nonhealing TMA site. She underwent a revisional TMA with application of the FASTR external fixator. At one month status-post application, her wound had signs of granulation and wound contraction. At 5 months, the patient’s wound had advanced considerably and the patient received a STSG the following month. Her original wound had fully epithelialized at 8 months. A fixed equinus deformity did result in a small area of soft tissue breakdown without signs of infection at the TMA site once the patient was fully ambulating at 10 months, but we expect complete recovery with standard surgical management (Figures 5A-D online).
Ongoing Considerations
The FASTR is a promising approach for limb salvage in patients with diabetes and CLTI with complex wounds. While there have been some complications, short-term results are encouraging, demonstrated by improved soft tissue recovery and neovascularization. There has been one case of limb loss in total within our no-option CLTI cohort. Our findings to date have been consistent with current literature. We do require continued follow-up and larger cohorts to validate these results. As our cohort increases, we will continue to improve upon objective methods of evaluating tissue response and rate of healing in addition to the order and timing of distraction and restoration in our current distraction protocol (2 weeks distraction and 2 weeks restoration versus one week alternating for 4 weeks). Additionally, use of the technique could be considered for soft tissue repair in patients with less severe lower extremity wounds given the encouraging low morbidity rates and successful outcomes in a high-risk population.
Dr. Theodoulou is an Assistant Professor of Surgery at Harvard Medical School. He is the Division Chief of Foot and Ankle Surgery at Cambridge Health Alliance.
Dr. Guo is a second-year podiatric surgery resident at Cambridge Health Alliance in Cambridge, MA.
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