Are Transmetatarsal Amputations Really Better?

Although in some instances there is an obvious answer to whether transmetatarsal amputations (TMAs) are preferable, we frequently encounter this dilemma. Anyone who has performed a handful of partial first ray amputations knows of the seemingly inevitable complications and frequent re-amputations. In their systematic review, Borkosky and Roukis reported a 19.8 percent rate of reamputation after partial first ray amputation in patients with diabetes.¹ Many claim TMAs provide more predictable results. However, after performing TMAs, those same complications and reamputations begin to surface.^2-4 One has to raise the question: are transmetatarsal amputations really better?

Partial first ray amputations seem to be a gateway drug to the next amputation.⁵ More deformities to the adjacent digits as well as increased pressure to these ipsilateral digits and forefoot occur following partial first ray amputations.^6,7 Not surprisingly, re-ulcerations reportedly occur frequently on the lesser digits and lesser metatarsal heads after these operations.⁸ At first glance, there seems to be ample evidence that partial first ray amputations are just not good enough and are fraught with problems.

However, we may be forgetting the population that we are treating. Even prior to amputation, the five-year mortality rate for patients with new onset ulcerations is near 40 percent.⁹ In patients with major amputations, the five-year mortality rate ranges from 52 to 80 percent.¹⁰ In regard to minor amputations, some have reported a roughly 45 percent five-year mortality rate.¹¹ In essence, these are sick patients with limited life expectancy. Furthermore, reulceration rates are extremely high in patients with healed ulcerations. About 34 percent of patients reulcerate at one year, 61 percent after three years and 70 percent after five years.¹² Re-ulceration rates are even higher in patients with a history of amputation.¹² So if these patients are fortunate enough to live more than five years, it is likely they will eventually ulcerate once again.

Comparing outcomes across studies from TMAs and partial first ray amputations is ill-advised as there is a great deal of heterogeneity in the selected patient populations. This creates bias and impacts the results. However, as a randomized controlled trial is unlikely, we can make some comparisons albeit with caution.

Dalla Paola and colleagues reported that 17 percent of 89 healed partial first ray amputations re-ulcerated and 9 percent required reamputation.⁸ The average length of follow-up was approximately 16 months. Blume and coworkers reported that 22 percent (14/62) of healed TMAs re-ulcerated and 13 percent (8/66) required revisional surgery at a mean follow-up of 12 months.¹³

Certainly, we can take no conclusions from these two selected articles with re-ulceration rates other than that the rates are in the same ballpark as one another. However, even if those with partial first ray amputations have more re-ulcerations, this may not automatically crown TMA the winner.

Not all ulcerations are equivalent. Flexor tenotomies of the lesser digits can often alleviate ulcerations quickly and with few complications.¹⁴ Therefore, the re-ulceration rate after exclusion of the toes may be more of an appropriate comparison. One may consider percutaneous Achilles tendon lengthening after TMAs for ulcerations but recurrence is reportedly high. In one 2008 study, 16 out of 28 patients who had a TMA and a tendo-Achilles lengthening (TAL) had new or recurrent neuropathic ulcers.¹⁵ This ratio is higher than the 10 out of 26 patients who had recurrent ulceration after a combination of TAL and total contact casting in the study by Mueller and colleagues in 2003.¹⁶

Considering The Reamputation Rate After TMA
As I noted earlier, Borkosky and Roukis reported a reamputation rate of 19.8 percent after partial first ray amputations in a systematic review.¹ While this is alarming, alternatives to amputations may not yield improvement and may even be worse.

Dillingham and colleagues found that after one year, 25.3 percent of 889 patients with diabetes with toe amputations had one reamputation and 12.1 percent had two or more reamputations.¹⁷ They also found that 29 percent of 314 patients with diabetes had one reamputation after foot/ankle amputations and 11.1 percent had two or more reamputations.

Izumi and coworkers reported similar results and found no significant differences in rates of ipsilateral re-amputations between minor amputations of the toe, ray or midfoot.¹⁸ However, individually, toe and ray amputations had significantly higher reamputations than major amputations. Conversely, reported contralateral amputations were significantly more frequent three years after major amputations in comparison to toe and ray amputations, and in comparison to ray amputations at five years.

Although this is important information, one must be careful in extrapolating data. This may be the function of there being more existing anatomy to amputate on the ipsilateral side. Additionally, in regard to major amputations increasing the risk of contralateral amputations, the obvious culprit is increased pressure to this foot but one should also consider confounding medical conditions that are likely to be present in those with major amputations. In fact, these confounding medical conditions may be key factors with transmetatarsal reamputation rates. Those with TMAs may have already failed partial first ray amputations.

So what is the reamputation rate after TMA? Our most recent research (an unpublished systematic review of 24 articles) suggests that approximately one-third of those who have a TMA will have a subsequent major amputation.¹⁹ Although this figure at face value may immediately persuade some to avoid TMAs altogether, remember once again that this includes many high-risk patients from multiple studies of various populations. We can make no direct comparison with the study by Borkosky and Roukis.¹ However, this does seem to suggest that reamputation is unlikely to be lower after a TMA and without further studies to demonstrate the predictability of the results of TMAs, skipping the first ray amputation to go on to a TMA may not be the solution.

What these high rates of reamputation might really reflect is our inability to predict which patients will heal and which will ultimately fail. Many studies report TMA healing rates in the 40 to 70 percent range.^13,20-29 Unfortunately, although we use the ankle brachial index (ABI) to help predict healing, the ABI has not proven to be an accurate predictor of minor amputation healing.^26,30-32 Instead, the ABI seems to elicit a gradient of risk rather than any one cutoff value (i.e., the lower the ABI, the less likely to heal). The best predictors of failure seem to be host factors, especially renal failure.^13,29 However, the absence of residual bone infection and a lower glycohemoglobin level may also improve results.^33,34

Deciding On An Appropriate Level Of Amputation
In the absence of convincing medical evidence, we can better make the choice by having a well-informed patient. It is likely that the differences in outcome are somewhat minimal when comparing the partial first ray amputation and TMA.

The more important question may really be one of limb salvage (minor amputation) or major amputation. Is this patient ambulating? If the answer is no, why are heroic measures to save the limb important to the patient? If the answer is yes, then saving a limb that is able to perform these preoperative functions is the goal.

However, there are a couple of concerns if one pursues limb salvage. First, is the patient likely to heal a minor amputation? If the patient is on dialysis with an HbA1c of 15 percent, has marginal ABI and/or toe brachial indices (TBIs) and is older, then serious discussion of the likely failure of limb salvage is necessary. Many times, patients believe they will beat the odds and be the one in “X” percent that heals.

Second, we should consider the physical deconditioning following heroic limb salvage as part of the discussion. Not infrequently, minor amputations require months of non-weightbearing for an amputation site to heal. While this may seem insignificant to a young patient who goes on to heal, one-third of such patients may require major amputation.¹⁹ For an older patient to rehabilitate after major amputation following prolonged non-weightbearing from failed minor amputation(s) may simply be too difficult. Although I am not of the belief that major amputations hasten death in most, certainly a bedridden status does not prolong life. Accordingly, our good intentions to save every limb may come with certain risks.

There is no consensus on what provides the best quality of life but the evidence suggests there is little difference in the quality of life between those with partial foot amputation and those who have had a major amputation.³⁵ Some have even suggested that major amputation in the diabetic population may result in a better quality of life in comparison to those with diabetic ulcerations but no amputation.³⁶ However, discussion with each patient may yield different results in different situations and no sweeping conclusions in terms of quality of life are possible as of yet.

In Conclusion
Partial first ray amputations have generally less than ideal outcomes but this does not necessarily mean TMAs will have better outcomes. Upon closer inspection, TMA outcomes in regard to re-amputation appear to be similarly poor and may even be worse. However, selection bias within the available studies limits any definitive conclusions. Finally, it is much more likely that the driving force of the outcomes is more influenced by the health of the individual than that of the surgeon selecting TMA over a partial first ray amputation.

Dr. Thorud is board-certified by the American Board of Podiatric Medicine, and is an Associate of the American College of Foot and Ankle Surgeons. Dr. Thorud is affiliated with Mercy Health System in Illinois.

References

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