Partial foot amputations may not offer a biomechanical advantage over transtibial amputations if the metatarsal heads cannot be retained, and some experts suggest amputation level should be selected based on probability of wound healing instead. But others disagree.
By Cary Groner
In recent decades, as approaches to glycemic control and surgical techniques have improved, patients with diabetic neuropathy and poorly healing foot ulcers have increasingly received more distal partial foot amputations (PFAs) rather than more proximal (e.g., transtibial) procedures. PFAs include toe or ray, transmetatarsal, and Lisfranc procedures, among others. Such amputations have been viewed as less an endpoint of treatment than the beginning of a rehabilitation process that ultimately leads to better function and quality of life.1,2
Researchers and clinicians have begun to call attention to the lack of guidelines regarding amputation levels,3 however, and to express concerns about the overall effects of distal approaches. For example, a paper published this August in the Archives of Physical Medicine & Rehabilitation made the case that clinicians may place too much emphasis on the purported benefits of PFAs while downplaying problems with biomechanics, wound healing, and subsequent reamputation.4
“This is a population of people who are chronically unwell,” said study coauthor Michael Dillon, PhD, BPO(Hons), who is a senior lecturer at the National Centre for Prosthetics and Orthotics at La Trobe University in Melbourne, Australia.
“They have diabetes and vascular disease, and most of them are now facing their first amputation,” he continued. “When you consider that a large proportion of them will be dead in five years, a PFA that will take months to heal, if ever, is a poor outcome, irrespective of how much of the foot is left.”
Dillon pointed out that surgical decisions are sometimes based on the assumption that more distal amputations entail functional benefits not available via, say, transtibial procedures. His research4 suggests that assumption is sometimes false.
“Studies comparing energy expenditure don’t show differences between partial-foot and transtibial amputations,” he said. “We don’t see significant differences in gait and walking speed when comparing people with different levels of PFA, or when comparing PFA to transtibial procedures.”
Grim statistics highlight the importance of optimal clinical decision making, in any case. Roughly 618,000 Americans have some form of PFA—about 40,000 are performed annually in the US—and these procedures are twice as common as transtibial amputations.5,6 Only about half of PFAs heal, however, and two-thirds of these patients end up with a more proximal amputation on the same limb. Worse, up to a third of PFA patients die within a year of amputation, frequently due to the underlying complications of diabetes.5
Clinicians seek practice guidelines that would bolster decisions about which procedures are best for which patients but, unfortunately, there isn’t yet a lot of quality evidence in the literature to support or refute disparate professional opinions.
According to Dillon’s coauthor, Stefania Fatone, PhD, BPO(Hons), an associate professor in physical medicine and rehabilitation at Northwestern University in Chicago, the biomechanical results from various PFAs are often fairly similar: once the metatarsal heads are gone, patients stop using their calf muscles to generate power.4,5
“It’s easy to understand why a Syme’s amputee might not generate power, because there is no foot lever. But even at the transmetatarsal level, where you still have something of a foot lever, it doesn’t function,” she said. “And when you have an ankle joint that’s not producing power, then you have to compensate for that loss somewhere else.”
The result, Dillon explained, is that patients with transmetatarsal amputations—like those with transtibial amputations—typically recruit the hips to do more work during gait.7
LER reported in 2010 that pedorthic management of PFAs can help restore patients’ stability and function using a variety of approaches, including ankle foot orthoses (AFOs) and correct shoe
selection.8 AFOs, for example, can replace the lost lever arm of a transmetatarsal or hallux amputation; they can also be used to decrease plantar pressure on the residual foot, as can custom foot orthoses. Partial foot prostheses ideally protect the residuum and help restore more normal gait; they may also be used with AFOs to transfer stress to more proximal tissue.8
In a 2001 article in Orthotics and Prosthetics for the Foot and Ankle, clinicians outlined a number of orthotic and prosthetic approaches for different PFA procedures.2 For example, in patients with toe amputations, who are likely to retain some propulsive power, prostheses can augment propulsion and reduce pressure transfer to the metatarsal heads. Strategies may include soft inserts with custom toe fillers or inserts used in a shoe with a spring steel shank and a rocker sole.
Compensating for ray resections depends, not surprisingly, on which ray is removed. For example, first-ray amputations transfer pressures to the remaining metatarsals and typically result in excessive pronation, so practitioners protect the medial column with multidensity prostheses and compensate for the loss of toe-off with either a rigid footplate or an exterior shank and rocker sole.
More proximal amputations—e.g., Lisfranc (a tarsometatarsal disarticulation), Chopart (disarticulation through the talonavicular and calcaneocuboid joints), and Syme (in which the residuum ends at the distal base of the tibia)—require prostheses with longer toe plates, generally designed to maximize stability and help unload whatever residual foot may remain.
The debate heats up when it comes to transmetatarsal amputations. Studies have reported a wide range of failure rates for the procedure—from roughly 25% to 75%—suggesting significant challenges when it comes to patient selection, follow-up, and compliance.9 Failure may mean a nonhealing wound, higher amputation, or contralateral amputation; but even with “success,” skin breakdown is common and patients experience significantly decreased weight-bearing stability.10 Of course, stability affects biomechanical function. A 2001 paper in Diabetes Care reported that patients with transmetatarsal amputations had higher impairment scores than those in a control group, whereas those with toe and other midfoot amputations did not.11
When prostheses are used in transmetatarsal amputation patients, they’re typically designed to allow the patient to roll over the end of the shoe, shifting the load away from the end of the residuum. Carbon composite footplates and rocker soles can help with this, though rocker soles require caution because they may increase instability.2
Tissues and issues
In a 2010 article in LER, Dillon reviewed aspects of the effects of PFA on gait biomechanics.5 First, as noted, once the metatarsal heads have been compromised, power generation is negligible regardless of residual foot length. Second, the type of O&P intervention plays an important role in restoring normal distal center of pressure (COP) excursion to those with amputations proximal to the metatarsal heads. Dillon reported studies concluding that, in Chopart amputees using a clamshell prosthesis, and in a Lisfranc patient using a carbon composite AFO, the COP progressed beyond the residuum during late stance, allowing the prosthetic forefoot to bear the peak ground reaction force.12-14
In a related paper published in the Journal of Rehabilitation Research & Development the following year, Dillon and his coauthors noted that effective foot length can be restored when a prosthesis incorporates a fairly stiff forefoot, restricts dorsiflexion, and includes a mechanism whereby forces caused by loading the toe lever can be comfortably distributed to the leg.15
“We learned from our 2007 systematic review16 that design elements in a prosthesis were likely important to improve someone’s walking,” Dillon said. “A forefoot stiff enough to support weight is important, but that’s not the only piece of the puzzle. You also need a large shell on the front of the leg that can comfortably distribute the loading forces, and a way to connect the leg, shell, and foot.”
Dillon and his colleagues used a dorsiflexion stop to limit tibial advancement, displacing load from the prosthetic forefoot to the anterior shell.
“Then, as the leg keeps moving forward over the foot, it takes the foot with it,” he explained. “Redistributing forces that way is at the heart of letting someone actually stand on their prosthetic forefoot.”
The review Dillon mentioned16 was one of several papers published in a 2007 special issue of the Journal of Prosthetics and Orthotics (JPO) investigating the biomechanics of ambulation after partial foot amputation. Dillon et al found a high level of evidence that PFA generally affects temporospatial factors, ground reaction forces, ankle kinetics, and plantar pressures during gait.
They found low to moderate evidence that O&P interventions affect ankle kinematics and moments and may moderate COP progression. Hence, the clamshell prosthesis design evaluated in their 2011 study.15
Another paper from the same issue of JPO noted that “amputations and disarticulations within the foot offer important advantages over more proximal levels, including direct weight bearing with proprioceptive feedback along normal neural pathways.” Disadvantages, however, included a loss of load-bearing capacity, stability, and dynamic function of the foot when the metatarsal heads had been removed.17
Comfort and consultation
Comfort and cosmesis are too often overlooked by clinicians, according to Michael Pinzur, MD, a professor of orthopedic surgery and rehabilitation at Loyola University Medical Center in Maywood, IL.
“If you make a device that’s cumbersome or cosmetically unattractive, patients won’t use it,” he said. “The LEAP [Lower Extremity Assessment Project]18 study showed us that amputees frequently value cosmesis over function. Who’s getting partial foot amputations? Three-hundred-pound diabetes patients who have neuropathy—and you’re going to put them into a clamshell device that’s like wearing galoshes in the summer?”
Pinzer said that a distal amputation is better than more a proximal one, all things being equal. The problem, of course, is that frequently all things aren’t equal, and then the clinician has to weigh a variety of factors. In a recent paper, he outlined a four-step approach to such decisions, including whether limb salvage would outperform amputation and a prosthetic limb.19
“You have to do different things for different people,” he told LER. “What does the patient do for a living? What are his wants, needs, and desires? What is the etiology of her problem? What are you, the clinician, capable of doing?”
Traumatic amputations, for example, may be better suited for PFA than dysvascular amputations, because there will likely be fewer problems with circulation and infection.
Pinzur pointed to a couple of his own PFA cases. In one, an elderly woman could take only about six steps with her prosthesis, but was happy because that was all she needed to cook for herself and stay in her home instead of moving into a nursing home. In another case, a middle-aged tennis enthusiast was dissatisfied because, even though he could walk quickly and well, he couldn’t run, and he’d had to give up his favorite pastime.
“You’re not just treating their foot,” said Pinzur. “You’re treating their whole body, and we have to remember that the patient may perceive treatment success very differently than clinicians do.”
In the August paper, Dillon and Fatone extensively reviewed the PFA literature and reported troubling findings. For example, 30% to 50% of patients with PFAs will have complications including skin breakdown, ulceration, and wound failure.4
And several justifications often cited for PFA over higher amputations don’t appear to be supported by published evidence. First, as noted, a PFA that doesn’t preserve the metatarsal heads results in the same lost ankle power generation as a transtibial amputation. Second, as Dillon mentioned above, gait-related energy expenditure doesn’t appear any better after amputations proximal to the metatarsal heads than after transtibial procedures. Third, quality of life appears comparable in those with PFAs and transtibial amputations. Fourth, the lower mortality supposedly associated with PFAs is likely a result of selection bias.
The authors concluded that a case could be made for choosing amputation level based on the probability of wound healing rather than based on any anticipated functional advantages, and that transtibial amputation might be preferable in many patients who are now given PFAs.
Not everyone agrees, of course.
Jeffrey Johnson, MD, professor of orthopedic surgery and chief of the Foot and Ankle Service at Barnes-Jewish Hospital at Washington University Medical Center in St. Louis, said he and his team generally get good results with transmetatarsal amputations as long as certain clinical considerations are observed.
“In a well-done transmetatarsal amputation, you have to get proper skin coverage; you don’t want a split-thickness graft over the end, and you want to use plantar skin rather than dorsal skin if possible,” he said. “Also, the metatarsals have to be cut in an appropriate cascade. You want a nice arc of curvature, and they have to be beveled appropriately so they don’t have high-pressure areas under the edges.”
Johnson said that given the neuropathy and vascular insufficiency in many of these patients, continued ulceration isn’t surprising and shouldn’t necessarily be considered a treatment failure.
“I don’t think it’s appropriate to just say to everyone with a forefoot ulcer, ‘Look, we can’t solve this problem unless we do a below-knee amputation.’ I would much rather do a transmetatarsal; it’s a smaller operation, it allows them to wear regular footwear, and it doesn’t present them with such a difficult decision,” he said.
If transmetatarsal amputations fail or are inappropriate for a given patient, however, Johnson generally eschews more proximal choices and proceeds straight to a transtibial procedure.
“To ‘balance’ a Lisfranc, you have to weaken the heel cord significantly, by lengthening it and probably taking out a section,” he said, as an example. “In the face of infection, which is often the scenario in which you’re doing this, putting in bone anchors and suture materials can compromise the amputation.”
Johnson also noted that the options for reattaching the severed tendons in such cases aren’t ideal. Without reattachment, the residual foot will drift into equinus, load up the distal end, and become more vulnerable to ulcers, but these problems may occur even if the tendons are reattached.
“The same is true for a Chopart amputation, and I don’t think the Pirigoff or Boyd function any better than a Syme,” he said. (Pirigoff and Boyd procedures are designed to preserve some of the calcaneus.) “You really limit your prosthetic options, and the shorter you make the foot, the smaller the weight-bearing surface area, which leaves it much more prone to breakdown.”
One consequence of the wars in Iraq and Afghanistan, Johnson noted, is that wounded veterans are showing they can function at a high level with transtibial amputations and advanced prostheses, and this is influencing those on the home front.
“Patients are more accepting of a transtibial amputation,” he said. “I have patients with deformities asking, ‘If I have this amputation, can I run like that guy on TV?’ In some patients who are otherwise healthy, that’s absolutely true.”
Risks and rewards
“The highest concern for these individuals is their reamputation risk,” said John Steinberg, DPM, an associate professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, DC. “If we can mechanically balance the remaining portion of their foot and leg, then we greatly decrease their chances of having a recurrent wound and reamputation.”
Most of the surgical balancing Steinberg does is, in fact, for transmetatarsal amputations.
“We commonly do an Achilles lengthening, but we are also doing more soft-tissue balancing at the ankle level—specifically, lengthening the tibialis anterior tendon—and that has helped balance the pressures in patients with a varus foot,” he said.
Steinberg and his team haven’t enthusiastically embraced other lengthening procedures, such as those for the peroneals, but surgery, he emphasized, isn’t the sole determinant of success.
“If you put real attention into shoes, orthotics, and accommodative devices, a midfoot amputation can be lifelong and highly functional,” he said. “We have patients with bilateral TMAs who work full time and live independently. I don’t agree that you should do something more proximal just because they’ve lost propulsion.”
At Steinberg’s clinic, patients follow up after surgery with a prosthetist-orthotist, and are then seen every month or two for the first year, to check for complications such as pressure lesions, contracture, or bony prominences. After that, follow-up visits for evaluation and preventive care occur every six months.
“We never completely discharge those patients,” he said.
The CPO’s view
Dennis Amtower, CPO, sees both sides of the argument. Amtower, director of prosthetics at NOPCO, a clinical division of Boston Brace, told LER that patient selection for surgical procedures is highly inconsistent, in his experience.
“There aren’t established protocols,” he said. “A lot more people are having PFAs, but it isn’t always appropriate. Some patients who are given PFAs should have Syme or transtibial amputations.”
Amtower emphasizes the importance of patient awareness regarding their clinical choices.
“If they understand their condition and lack of sensation, and you can support them properly, they can function with a partial foot prosthesis,” he said.
Amtower has, in fact, designed and licensed a filler prosthesis that integrates with a carbon composite AFO, which often works well for his patients. In contrast to Michael Pinzur, he also reports good results with clamshell designs. But as in surgical approaches, patient selection is critical.
“If you’re working with a guy who smokes and drinks and goes walking in the snow without his shoes…” Amtower said, and let the conclusion speak for itself.
Despite the findings in their recent paper, Dillon and Fatone are cognizant of broader issues.
“Pressure management to avoid ulceration and breakdown of tissue is a big consideration,” Fatone said. “We still have big gaps in our information about how pressure changes when you manipulate different prosthetic design variables.”
“Those issues are more significant than whether we can make someone walk a little more normally,” he said. “We have a reasonable handle on the biomechanics now; there are bigger gaps in determining quality of life at different amputation levels.”
The PFA discussion is part of a larger story about decision making as disease-related amputations increase, Fatone added.
“These are difficult discussions to have with patients, and they’re even harder if your information is hazy,” she said. “We need to do a better job of clarifying that picture, so patients get strong and compelling information upon which to base a very personal decision.”
Cary Groner is a freelance writer in the San Francisco Bay Area.
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