A Guide To Digital Amputations In Patients With Diabetes
Digital amputation has the potential to allow patients with diabetes to resume daily activities with few alterations in gait. Accordingly, these authors discuss proper procedure planning, how to ensure appropriate vascular supply and key surgical pearls.
Most podiatrists who treat patients with diabetes at some point will encounter a patient in need of a partial or complete digital amputation. These patients typically have had exhaustive treatments including various wound therapies, surgical debridements, antibiotics as well as incision and drainage. The indications for digital amputation include osteomyelitis, septic arthritis, gas gangrene, ischemia/gangrene and an advancing soft tissue infection.
In certain patients, an elective partial toe amputation may be advisable. These patients who do not have an active infection may suffer from a rigid hammertoe deformity with a non-healing ulcer on the tip of their toe. In these situations, partial digital amputation would address the hammertoe deformity and the non-healing ulcer at the same time. A candidate for this type of a procedure would be a patient who is elderly, someone who has multiple comorbidities or an individual with minimal mobility who would benefit from a quick and easy procedure with minimal postoperative healing time.
Typically, one can avoid higher level amputations with early digital amputations that allow patients to return to normal activities with minimal disability.
Accordingly, let us take a closer look at the senior author’s approach to digital amputations including appropriate preoperative evaluation, incision planning and pearls in performing various digital procedures.
There are many benefits of more distal amputations in comparison with amputations at a higher level. Distal amputations are more functional and have many physiological benefits such as energy preservation during ambulation.1,2
In a study of eight patients who had undergone partial foot amputations and a cohort of matched non-amputee control patients, Dillon and Barker report that amputations distal to the metatarsophalangeal joint (MPJ) had little impact on the normal pattern of ankle power generation.3 Distal amputations are preferred to proximal amputations as they preserve length and therefore normal biomechanics of the foot. The simple rule of thumb is to save as much length as possible when performing partial foot amputations.
What You Should Know About Lesser Toe Procedures
When performing central toe amputations, it is important to make an effort to leave a segment of the proximal phalanx intact. Leaving a stump of the second, third or fourth toe intact allows the stump to function as a buttress, preventing the adjacent toes from developing a shift in the transverse plane. Amputations of lesser digits generally result in a gait with minimal to no disturbance.
Questions frequently come up as to whether a guillotine amputation of the toe is appropriate. In our facility, we prefer to avoid guillotine amputations and make an effort to plan the incision in order to close the wound primarily or in a delayed primary fashion. In order to perform closure of the amputation site, we often carry out more proximal bone resection to allow tension free closure. Although guillotine amputation of the toe can preserve length, the risk of leaving an open wound to heal via secondary intention does not outweigh the benefit of primary closure when possible.
The preferred incision for a partial toe amputation is a transverse fish-mouth incision, which tends to give the best outcome both cosmetically and functionally.
Pertinent Insights On Performing A Hallux Amputation
The hallux plays an important role in stabilizing the medial aspect of the foot and the extensor hallucis longus (EHL) is one of the most important extrinsic muscles of the foot during the swing phase of gait. Therefore, amputation of the hallux frequently leads to an apropulsive gait.4 The degree of biomechanical dysfunction depends on the level of amputation.
The anatomy of the hallux is different from the lesser toes and deserves a quick review. The base of the proximal phalanx has the insertion of the flexor hallucis brevis, sesamoid complex and plantar fascia, which make up the windlass mechanism. The windlass mechanism provides stability and rigidity to the medial side of the foot, preventing arch collapse and allowing for a propulsive gait.
Accordingly, surgeons should not approach a hallux amputation lightly and should exercise caution, precision and careful incision planning. Total hallux amputation will inevitably lead to extensor tendon contracture with development or exacerbation of lesser hammertoe deformities. The retrograde pressure from the lesser digits leads to prominent metatarsal heads and distal fat pad migration. The transfer of weightbearing becomes very obvious and will frequently lead to adjacent metatarsal head ulcerations.
A study by Mann and colleagues shows the effect of hallux amputation in patients who underwent re-implantation of the hallux in place of a lost thumb. The authors found that the plantar pressure moved from the second metatarsal head to the third.5 This was due to the loss of the flexor hallucis brevis and windlass mechanism causing the load to transfer laterally.
When approaching a hallux amputation, one should make an effort to salvage as much of the base of the proximal phalanx as possible. An ideal situation would be to leave the base of the proximal phalanx intact in order to keep the windlass mechanism intact. Doing so would save the MPJ. Hakim-Zargar and colleagues reported that one should retain 10 mm of the hallux proximal phalangeal base during amputation to preserve the integrity of the flexor hallucis brevis insertion to a physiologic load.6 Resecting the insertion results in decreased flexion strength, retraction of the sesamoids and transfer metatarsalgia. In our experience, one can perform the majority of hallux amputations without resecting the base of the proximal phalanx.
Keys To Ensuring Adequate Vascular Supply
Arterial perfusion is often one of the most important predictors of healing and is also an important factor in planning the level of amputation. Non-invasive arterial studies are the mainstay recommendations prior to any amputation.7 In the senior author’s opinion, predicting the level of amputation and the level of healing depends on several factors.
First, the surgeon must understand that there is no specific pressure or value that is 100 percent predictive of healing. Generally speaking, the toe pressure of >40 mmHg is considered to be consistent with healing. The higher the pressure is above 40 mmHg, the higher the likelihood of healing.8
So does this mean that patients with pressures of 40 mmHg and below will not be able to heal? The simple answer is that some patients will be able to heal and some patients will not. It is our recommendation that anyone with toe pressures of less than 40 mmHg should undergo a vascular workup for a possible revascularization. However, we all see patients who are too frail or too old, and are not candidates for revascularization. It is these patients — whose toe pressures are less than 40 mmHg and who are not candidates for revascularization — whom we need to assess and figure out whether their digital amputation will heal.
In our facility, we look for clinical findings such as evidence of granulation tissue or viability of skin margins. We also examine whether there is advancing necrosis along the skin margins, how long a wound/ulcer has been open and if it has developed gangrenous changes. By getting answers to these questions, we gather evidence for and against healing the proposed digital amputation. We also listen to the digital arteries via the Doppler.9,10 In our experience, if at least two to three of the digital arteries are audible, there is a high likelihood that the amputation site will heal.
Edema is one of the most underemphasized clinical findings and may play a vital role in healing. If the patient has severe edema of the foot and the toes, healing may be hindered. Controlling and minimizing postoperative edema can be the critical factor in determining the success or failure in healing the amputation site.
In summary, arterial evaluation should consist of noninvasive arterial testing along with a clinical evaluation by the surgeon. Relying on toe pressures alone may lead one astray in predicting healing in patients with severe arterial occlusive disease.
What You Should Know About Incision Planning
Incision planning can occur in various ways. It is important to evaluate the extent of viable tissue and ensure that there is adequate coverage. Commonly, we are forced to resect more of the phalanges in order to obtain tension free closure. However, this typically occurs in patients who have osteomyelitis of the distal phalanx or those in whom the dorsal and/or plantar skin has necrosis that extends to the level of the proximal interphalangeal joint. This scenario forces us to resect the non-infected bone in order to get to the viable dorsal and plantar skin of the toe. Surgeons must avoid tension at the incision site to prevent dehiscence.
Incision options include transverse fish-mouth, sagittal fish-mouth or guillotine approaches. We believe that utilizing more of the plantar skin is preferred since the plantar skin is 4 to 5 mm thick, which is two times thicker than the dorsal skin.11 Another common mistake made during amputation surgery is to remove too much viable skin. Our approach is to salvage as much viable dorsal and plantar skin as possible, and then remodel as necessary immediately before closure.
Tips On Post-Op Management
Proper post-op management is essential in patients following digital amputations. Even after an ideal surgical intervention, complications can arise due to less than ideal postoperative conditions.
One should encourage patients to limit their activity for the first three to five days postoperatively. The immediate postoperative period is when hematomas develop. Hematomas may eventually lead to an infection and dehiscence if the patient is up on his or her feet.
Case Study: Addressing A Partial Toe Amputation In A Patient With PAD
An 80-year-old female with a history of peripheral arterial disease (PAD) presented to the clinic with an ischemic ulceration of her left second toe, which she noticed two weeks previously. Her past medical history was significant for coronary artery disease, PAD and hypertension. The examination of her feet revealed non-palpable pedal pulses with a capillary refill time of 10 seconds. The second toe was erythematous without any evidence of an underlying abscess or osteomyelitis.
She received an immediate referral to vascular surgery and underwent a femoral to dorsalis pedis bypass. At the time of the bypass, the distal aspect of the second toe became gangrenous to the level of the distal interphalangeal joint. After a successful bypass graft, the patient had a partial second toe amputation at the level of the midshaft of the proximal phalanx.
We did consider amputation of the entire second toe but whenever possible, we prefer to leave a stump of the toe to act as a buttress and prevent transverse plane deformity of the lesser toes and the hallux.
Infections develop often in diabetic feet with ulcerations. If these infections become refractory to conservative measures, early surgical intervention is important to decrease the need for major amputations. Clinical judgment can generally provide reliable information as to whether surgical intervention will be a successful treatment. If there are any questions about the vascular status, one should order noninvasive vascular studies.
Amputation of lesser toes will generally cause minimal gait disturbance. However, when amputating the hallux, there is a disturbance of weightbearing pressures, which increases the vulnerability of the remaining toes. When amputating the hallux, one must take care to retain 10 mm of the proximal phalangeal base to preserve the integrity of the intrinsic muscle attachments and the windlass mechanism. During skin closure, the lengths of the flaps can vary but tension free closure with a plantar flap is ideal.
When one ensures careful planning, digital amputation is a procedure that can allow patients to return to functional activity with minimal disturbance to their gait.
Dr. Reyzelman is an Associate Professor and the Chairman of the Department of Medicine at the California School of Podiatric Medicine at Samuel Merritt University.
Dr. Kim is a second-year podiatry resident at St. Mary’s Medical Center in San Francisco.
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