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Conservative Care Considerations For Partial Foot Amputation In Patients With Diabetes

Given the elevated risks of re-ulceration and re-amputation after partial foot amputations, these authors discuss various levels of amputation and which mechanical interventions might be the most optimal methods of decreasing these risks. 

Foot and ankle surgeons often focus much effort on the surgical care of a patient requiring a partial foot amputation. Once the wound is healed, there is a great sense of victorious relief. Healing the postoperative wound is a major milestone to success but our efforts should not end there. Re-amputation and re-ulceration are frequent complications following partial foot amputations. For example, approximately 30 percent of transmetatarsal amputation (TMA) cases will go on to major amputation.1 In a more generalized recent systematic review of partial foot amputations, approximately 20 percent had a re-amputation at one year with this number climbing to 30 percent at three years and nearly 46 percent at five years.2 

Re-ulceration is also common. In a study of metatarsal ray resections, about 26 percent of patients reported an ulceration following an amputation at a mean follow-up of 36 months.3 Similarly, Blume and colleagues reported an approximately 22 percent ulceration recurrence rate following healing of a TMA with a 12 month mean follow-up.

Prior to any amputation, patients with healed ulcerations already have high rates of re-ulceration and this rate worsens after amputation.5 The post-amputation biomechanical changes lead to increased areas of pressure. Not surprisingly, Lavery and colleagues noted increased pressure to the forefoot after first ray amputation.6 The majority of patients requiring a partial first ray amputation likely experience increased pressure to the hallux or first ray to the point of ulceration prior to amputation. Likewise, Garbalosa and coworkers reported increased peak plantar pressures after TMAs.7 

Removing the area of high pressure does not eliminate the force placed throughout the foot but merely displaces the pressure elsewhere. Following amputation, even less total foot surface area is present and the overall force to the foot (approximated by patient body weight) likely does not change. One may achieve an equal transfer of pressure across the remaining foot surgically but conservative measures (i.e diabetic inserts, shoes and bracing) can be beneficial as well. 

Ideally, adequately powered, randomized controlled trials looking at amputation levels and corresponding conservative devices could give us guidance in regard to clear and definitive clinical outcomes (such as re-amputation, major amputation, re-ulceration, etc.). Unfortunately, this type of research is not yet available. Furthermore, even if these trials currently existed, no “cookbook” formula would suffice. Too many variables, even in a single amputation level, exist to recommend a catchall prescription. Preexisting deformities and associated pressures will need accommodation. 

Consider for example a patient who has a preexisting metatarsus adductus with a partial fifth ray amputation. A subsequent TMA for this patient will likely increase pressure to the lateral foot and result in a different presentation than a patient who had a TMA after a failed first ray or central ray amputation, or a patient who had a primary TMA to address an infection that compromised certain tendons. Even more variability seems to exist at the partial ray level or digital level. Researchers have shown that the re-amputation rate after partial hallux amputation is significantly greater in patients with radiographic evidence of hallux limitus.8 

Finally, the foot does not exist in isolation to the rest of the patient. One must consider factors such as contralateral major amputation, functional or aesthetic expectations, contralateral ulceration or deformities, and preexisting stability concerns. 

How Effective Are Custom Inserts And Therapeutic Shoes? 

Several randomized trials demonstrate that therapeutic footwear, mainly in the form of custom inserts and extra-depth shoes, reduce plantar ulcer recurrence in patients (mostly without amputations).9 However, providing footwear does not ensure its use. In at least one randomized trial, Bus and colleagues found that an intention-to-treat analysis failed to yield significant results.10 After limiting the trial to patients wearing the custom-made inserts and shoes at least 80 percent of the time, the study authors noted that custom-made footwear significantly reduced ulcerations.10 Observational studies also suggest that patients who wear the prescribed shoes more frequently have fewer re-ulcerations.11 Unfortunately, non-adherence is more frequent at home where patients exhibit greater walking activity in comparison to being away from home.12 

Furthermore, adherence may improve after motivational interviewing but some authors noted a quick return to baseline adherence.13,14 This makes non-adherence a concerning confounder for other studies on conservative devices. It is not enough for a device to be effective when it is worn. The device should also be inviting enough to foster its use. Accordingly, this reinforces the need for definitive, clinically important outcomes such as re-ulceration or re-amputation versus ancillary findings like reduced peak pressure. In the absence of this data, we will have to evaluate the data we do have and make significant extrapolations and assumptions in order to treat the patient as best we can. 

A Closer Look At Toe Fillers And Rocker Bottom Soles 

Considering the higher risk of ulcer recurrence in patient populations with previous amputations, extra-depth shoes and custom inserts are warranted, at a minimum, for a vast majority of patients with previous minor amputations.15 

One of the most frequent modifications after a partial foot amputation seems to be the addition of toe filler. For lesser toe amputations, a filler is not typically necessary but clinicians should use their best judgement in unusual circumstances (see first photo above). The clinician must be aware that toe fillers on their own, due to the softer nature of the materials and location inside the shoe, can result in additional friction and pressure to the stump site. Thus, stiffening the sole of the shoe should be a consideration by adding a carbon fiber foot plate (see second photo above) and/ or adding a rigid rocker bottom sole to the outside of the shoe. 

In a recent systematic review of neuropathic patients with diabetes, Ahmed and coauthors found strong evidence that rocker soles reduced peak plantar pressure.16 Some state that a rocker bottom sole is the most effective way to offload the forefoot in patients with neuropathy.17 A properly constructed rocker sole is important. Suggested rocker apex is 55 to 60 percent of the shoe length to offload the metatarsal heads and 65 percent to offload the toes with a rocker angle of 20 degrees and a 95 degree longitudinal axis. However, the ideal location does vary across patients and anatomic locations (see third photo above).18,19 

Also bear in mind that the aesthetics of a rocker bottom or potential balance concerns caused by the rocker bottom may deter patient acceptance. Carbon fiber plates are a suggested alternative to other more drastic shoe modifications, even in patients with TMAs.20 Certainly if a pre-ulceration or re-ulceration occurs with a carbon fiber plate, one may consider a rigid rocker bottom shoe even if the patient initially declines it. 

What About AFOs? 

Although some may find adequate reduction of ulceration recurrence with a below ankle mechanical intervention, it might be better to approach those with a first ray amputation similar to how one would treat a patient who has had a TMA. Concerns about preserving ankle motion in these cases may not be as important as previously thought and devices such as an ankle-foot orthosis (AFO) may be a consideration in conjunction with an insole filler. The insole filler remains important in preventing creases and ultimately physical breakdown in shoe wear. It is also helpful in minimizing motion and shear forces on the foot inside the shoe. 

Once the amputation involves the metatarsal heads or more proximal areas, remaining ankle power is marginal.21 Postoperative use of a prosthesis or orthosis, irrespective of whether ankle motion is permitted in the device, does not impact the ankle power.21 

In a study of mainly traumatic amputations, below-ankle mechanical interventions failed to restore the effective foot length whereas above-ankle devices were able to restore this effective foot length.22 There are reports of similar results after mainly traumatic Chopart amputations.23 

Mueller and colleagues compared five different types of therapeutic footwear for patients who had TMAs, and concluded all five reduced plantar pressure better than normal shoes with a toe filler alone.24 In this study, the authors also compared a short- versus full-length shoe, total contact insert, rigid rocker bottom shoe and an AFO. They stated that full-length shoes, total contact inserts and rigid rocker bottom soles provided the best options for post-TMA limbs as they had similarly lower plantar pressure, higher adherence and few skin lesions.24 

Mueller and coworkers conceded that some patients did not like that their ankle did not move with the AFO despite one patient demonstrating improved gait.24 The AFO used in this 1997 study was a posterior rigid plastic-type device, which does inhibit ankle motion and was cumbersome to use. Newer carbon fiber, energy-storing AFO designs can be more acceptable to patients as they offer lighter weight, easier foot entry into shoe wear, allowance of some ankle motion and transfer of foot pressures to the anterior leg (see fourth photo above). 

In a small pilot study of six patients with previous TMAs, Spaulding and colleagues compared a more modern AFO design to shoes and inserts, and found balance effects are individually specific.25 Overall, plantar pressure decreases inside the device failed to meet statistical significance but the sample size was quite small. Most of the patients had similar complaints about the AFO as those noted in the aforementioned study by Mueller and team, but two of the patients preferred the AFO in spite of the added difficulty donning it and the lack of ankle range of motion.24,25 Spaulding and coworkers noted that one patient had significant improvements and made a correlation to a longer timed “up and go” test, which may suggest the AFO may be more beneficial in those with decreased functional mobility.25 Certainly, if the patient has misgivings about the device, it is likely he or she will be less adherent and, in turn, less effective in preventing re-ulcerations and re-amputations. However, as with ulceration healing, wearing a more proximal device such as a non-removable CAM walker is more effective than distal interventions such as a half shoe.26 

In our experience, many patients who have had partial foot amputations seem to appreciate utilizing an AFO in addition to custom inserts and shoes. The selection criteria with AFOs seems to be enhanced when targeting those with poor balance and neuropathy and/or poor proprioception of the involved limb. Subjectively, the AFO appears to be helpful in reducing recurrent ulcerations but generally the device is only one of multiple interventions, and improvements could result from other concomitant treatments. 

Key Recommendations From The Authors 

Based on the research and expert opinions in the literature as well as our own experience, a basic guide may be helpful (see “A Suggested Guide To Amputation Levels And Mechanical Interventions” above) but no one-size-fits-all approach offers definitive results. 

For lesser digital amputation without other major deformities, extra depth shoes with custom inserts likely suffice. For a hallux amputation up to the metatarsophalangeal joint (MPJ), the patient would likely benefit from a rigid rocker sole at approximately 65 percent of shoe length or a carbon fiber insert. A toe filler may also be an option but one should employ clinical judgement. 

Ray amputations may also do well with a rigid rocker sole but at approximately 55 to 60 percent of the shoe length to reduce pressure to the metatarsal heads. In many cases of first partial ray amputations and some fifth ray amputations, toe fillers may be a consideration. Think about adding a carbon fiber plate if the shoe is not sufficiently rigid. At times, a full foot plate carbon AFO may help reduce pressure and possibly add stability in balance-challenged patients open to the use of an AFO. The more proximal the amputation of the first ray, the more likely the full foot plate carbon AFO may be helpful given the increased risk of transfer ulcerations. 

However, when weighing the use of an AFO, one should consider the patient’s expectations and the likelihood that an AFO may be better tolerated in lower demand/ functional status populations or those who experience recurrent ulcerations despite appropriate shoe gear use. One may employ a similar strategy for patients with TMAs and an AFO is very likely to be helpful in Lisfranc amputations. Clinicians may choose a more proximal rocker to correspond to the appropriate offloading level. For Chopart amputations, a below-knee amputation may be preferable but one could consider a clamshell AFO with more tibial control. 

For each amputation level, it is important to take note of what the patient will reasonably wear and not dismiss the patient’s concerns and demand for a certain device. This is particularly important following re-ulceration. Although a failure in adequate offloading and reduction of shear may be to blame, certainly there may also be a failure of the patient to wear the therapeutic footwear/device for most of his or her activity. Increasing from a carbon fiber plate device to an AFO will likely worsen an issue with non-adherence associated with “more” device. A genuine curiosity to the underlying cause of the problem will hopefully limit this oversight. 

Finally, given the sparse data, the authors expect recommendations will change with more available information and some may disagree with those presented. Others have provided expert consensus findings on custom-made footwear but did not include a focus on the partial foot amputation population.18 We encourage readers to review their results as well. 

In Conclusion 

Patients with partial foot amputations have elevated rates of re-amputation and frequent ulcerations. Providing the appropriate therapeutic footwear and/or device appears to reduce these occurrences. Custom inserts and extra-depth shoes also appear to reduce ulcerations, but these recommendations are already well followed by providers. More frequent use of rigid rocker bottom shoes is likely in order for many providers as there is evidence these shoes may also reduce re-ulceration. However, most of the other recommendations are based on extrapolated data, small cohorts of patients, clinical gestalt and expert opinion. Given the impact of adherence on effectiveness, one needs to consider individual preferences on a case by case basis as well. Hopefully, greater interest in this area will result in more studies to provide us with better guidance in the future. 

Dr. Thorud is a Diplomate of the American Board of Podiatric Surgery and a Fellow of the American College of Foot and Ankle Surgeons. He is in private practice in McHenry, Ill. 

Mr. Flanagan is an orthotist who is board-certified by the American Board for Certification in Orthotics, Prosthetics and Pedorthics. He is a Fellow of the American Academy of Orthotists and Prosthetists. Mr. Flanagan is affiliated with Mercy Health System in Illinois and Wisconsin, and O & P Innovations, Inc. in Illinois. 

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By Jakob C. Thorud, DPM, MS, FACFAS and Patrick Flanagan, CO, MBA, FAAOP
References

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