The Biomechanics of Ambulation After Partial Foot Amputation


Table of Contents


Surgical Aspects

Figure 1. Direct weight bearing on a transmetatarsal residuum.
Condie DN, Stills ML. 16-B Partial-Foot Amputations: Prosthetic and Orthotic Management. In: Bowker JH, Michael JW, eds. Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles, 2nd edition, Rosemont, IL:AAOS, 2002. Image downloaded from the O & P Virtual Library, www.oandplibrary.org; Accessed January 2008.

The decision to proceed with a partial foot amputation arises emergently as a result of infection, ischemia, trauma, or some combination thereof. Amputations and disarticulations within the foot offer the advantage of direct weight bearing, which is especially important to older individuals (Figure 1).

Because most PFA procedures are done for diabetic and/or dysvascular persons, who are at considerable risk of a contra-lateral amputation within five years, preservation of a partial foot is vital to the maintenance of independent ambulation if the amputation of the second limb must be at the transtibial level or higher. On the other hand, a partial foot ablation for younger trauma victims may not be acceptable because of the loss of load-bearing capacity and stability, especially at the more proximal levels. The loss of this load-bearing capacity makes the restoration of effective running gait difficult or impossible with currently available prostheses and orthoses.

Until the latter half of the 20th century, partial foot amputations and disarticulations were done almost exclusively for trauma sustained in battle or industrial accidents. Prior to that, the accepted treatment was major lower limb amputation. The rationale at that time was to amputate at a level where primary healing could safely be anticipated. More often than not, the transfemoral level amputation was chosen. Because failure of primary healing posed a very real danger of death during that era, the emphasis was on survival rather than functional rehabilitation.

Figure 2. Amputation being performed in a hospital tent, Gettysburg, July 1863.
National Park Service's National Register of Historic Places, “Teaching with Historic Places (TwHP) Program”. Accessed November 2007 http://www.free.ed.gov/.

With convergent advances in fields such as tissue oxygenation analysis, vascular and amputation surgical techniques, antibiotic therapy, and wound healing, the surgeon now has the opportunity to consider the foot, rather than the tibia or femur, as the level of choice for amputation in selected cases of trauma, ischemia, or diabetic infection, with or without peripheral vascular disease.1

Advantages of PFA:

  • Weight Bearing with Proprioceptive Feedback - With at least the hindfoot remaining, a person can continue to bear weight directly on the residual foot with proprioceptive feedback along normal neural pathways. This is in contrast to a patient with a transtibial (TT) level amputation. Transtibial patients must interpret feedback from previously non-weight bearing tissue of the tibial section.
  • Nearly Normal Gait - Walking function following single ray (toe and metatarsal) amputation or amputation of all toes at the metatarsophalangeal (MTP) joints can nearly mimic that of normal gait.
  • Greater Independence - In elderly or debilitated patients, retention of even the hindfoot can preserve far greater independence in both transfer activities and ambulation without a prosthesis compared to either a transtibial or transfemoral amputation, which require a prosthesis for bilateral weight bearing.
  • Body Image - Partial foot amputations and disarticulations result in the least alteration of body image, often requiring only shoe modifications or a limited orthosis, prosthesis, or "prosthosis."

Disadvantages of PFA:

  • Impairment of Walking - In the case of midtarsal (Chopart) disarticulation, walking function is significantly impaired.
  • Limited Barefoot Walking - Barefoot walking after ablation, at any foot level proximal to the metatarsal heads, is markedly impaired because the load-bearing capacity, stability, and dynamic function of the foot are reduced.2
  • Limitations for Complex Activities - Restoration of more complex activities important to younger patients, such as running, remains problematic.

Indications for PFA:

  1. Infection with tissue necrosis in diabetic patients.
    • The typical pathway that leads to an amputation for a diabetic patient involves the combination of sensory neuropathy and ill-fitting shoe wear. Because of the loss of protective sensation, the skin over any bony prominence (or under minor trauma) can develop an ulcer that eventually penetrates the bones and joints beneath. This penetrating ulceration is followed by infective (wet) gangrene. (Figure 3)
      Figure 3. Wet gangrene.
      Photo courtesy of Ronald A. Sage, DPM, Loyola University, Hines VA Hospital, Maywood, Illinois.
  2. Ischemia may also be an indication for PFA. Ischemia can be due to a variety of conditions: Cigarette smoking can be an aggravating factor in all of these conditions.
  3. Trauma, such as:
    • moving machinery, for example, lawn mowers or motor vehicle accidents (MVAs);
    • crush injuries, with or without fractures;
    • degloving injuries (Figure 4) that remove a significant portion of weight-bearing skin; or
      Figure 4. Lower limb of a man following complete degloving of foot and ankle by gear box on a construction crane. Unwarranted attempt at salvage of totally insensate, contracted foot with split skin graft.
      Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.
    • lacerations that devitalize the forefoot.
    • thermal injuries which include frostbite or burns. Thermal burns are less common and often associated with diabetic sensory neuropathy or electrical injury.
  4. Rarely, a congenital abnormality of the foot requires surgical correction to allow fitting of a shoe.

Contra-indications to PFA:

  1. If the patient wishes to return to activities involving running, a transtibial amputation may be preferable.
  2. The patient exhibits strong behavioral overtones such as:
    1. nicotine addiction; and/or
    2. poor plasma glucose control.
  3. The patient has nutritional deficiencies.
  4. Level of tissue oxygen perfusion.
    • If transcutaneous oxygen measurements are less than 30 mmHg, consultation with a vascular surgeon is indicated.
    • Arterial flow can often be improved with vessel recanalization or bypass, or compensated for by postoperative hyperbaric oxygen therapy, allowing a distal amputation to be performed.
GENERAL CONSIDERATIONS FOR SURGICAL TECHNIQUES

If the criteria for level selection and wound healing are met, no amputation level in the foot need be excluded on the basis of etiology alone. However, the procedure must be done proximal to a malignant tumor, an irreparably damaged body part, or gangrenous tissue. The bony level selected must match the skin available for coverage in both length and quality. A lack of skin in relation to bone, therefore, requires further shortening of bone to a level where this criterion can be met.3 This will ensure both closure without tension and placement of scar tissue away from areas of direct weight bearing and shear forces. When this principle is ignored in an attempt to save length at any cost, the result for the patient can be prolonged morbidity and excessive delay in returning to maximum functional status (Figures 5 and 6).

Figure 5. A: Lateral view. B: Plantar view. Foot of a 17-year-old boy who sustained partial forefoot amputation at age 9 years in a motorcycle accident. Unwarranted attempt to salvage residual forefoot with split-skin grafts resulted in stiff, painful foot with frequent ulcerations.
A B
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.
Figure 6. Plantar view of right foot of 28-year-old man who was severely scalded at 14 months of age. Residuum healed with scar and split-skin graft. Note scar and painful ulcers. He eventually had a transtibial amputation, followed by return to full-time work.
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

To absorb the shear and pressure forces generated during gait, the soft-tissue envelope must be mobile. Although muscle tissue is an integral part of the soft-tissue envelope in more proximal amputations, it is not available at most distal levels. In the foot, ideal flaps are formed from plantar skin, subcutaneous tissue, and investing fascia. This multi-layer soft tissue construct will provide mobility over the underlying bone, minimizing the adherence of skin to bone. Conversely, coverage with split-skin grafts should be avoided on the distal, lateral, and plantar surfaces of the residuum.4 (Figure 7) Nonetheless, split-skin grafts placed on well-granulated dorsal bony surfaces can last indefinitely with reasonable care. Proper contouring of bone ends will prevent damage to the soft-tissue envelope from within wherever it is compressed between bone and the prosthesis, orthosis, or shoe.

Figure 7. Bilateral Chopart disarticulations following frostbite closed distally with split-skin grafts. Note large ulceration distal end of left residuum resulting from shear forces from flexible AFO with distal filler.
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

Salvage of a useful portion of the foot whenever possible is strongly indicated in diabetic and/or dysvascular persons. Statistically, they are at considerable risk of amputation of the opposite leg within five years.5 Therefore, preservation of a partial foot at the first operation is vital to the maintenance of independent ambulation, especially since the amputation of the second limb might be at the transtibial level or higher. Longitudinal (ray), rather than transverse, amputation should be the goal whenever technically and functionally feasible. By only narrowing the foot, rather than shortening it, loss of load bearing capacity and stability are minimized, and postoperative shoe fitting is simplified.

Postoperative casting is recommended for all but minor partial foot procedures to support and protect the wound. Edema-producing foot dependency is discouraged, and weight bearing is not allowed until the wound is solidly healed. To prevent equinus contracture of the ankle joint in foot ablations proximal to the MTP joints, postoperative casting in slight dorsiflexion for 3 to 4 weeks is recommended. By thus encouraging atrophy of the more massive ankle plantar flexors, immobilization may result in a more muscle-balanced residual foot. All casts should be changed weekly for wound inspection.

SPECIFIC LEVELS OF AMPUTATIONS & DISARTICULATIONS

I. TOE DISARTICULATIONS

A. Interphalangeal (IP) Joint of the Great Toe

Figure 8. Interphalangeal disarticulation of great toe for infective (wet) gangrene in a diabetic patient
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

The remaining proximal phalanx will aid with balance and may result in a better gait than after disarticulation at the metatarsal phalangeal joint. (Figure 8) The clinical assumption is that this is due to preservation of a useful toe lever length, the flexor hallucis brevis complex, including the sesamoids and, therefore, the windlass mechanism.

When a more radical resection of the proximal phalanx is required, Wagner6 recommends leaving just its base. This keeps both the sesamoids and the plantar fat pad beneath the metatarsal head, although the windlass mechanism is lost because the activating toe lever is gone.

B. Metatarsal Phalangeal (MTP) Joint of the Great Toe

After division of the flexor hallucis brevis insertions on the proximal phalanx, the sesamoid bones will retract just proximal to the metatarsal head and may produce troublesome bony prominences. For this reason, the sesamoids should be excised and the crista removed with a rongeur if it is prominent. (Figure 9)

Figure 9.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

C. Disarticulation of 2nd Toe MTP Joint

Disarticulation of the second toe at the MTP joint may result in a hallux valgus (bunion) deformity due to the removal of lateral support for the great toe. (Figure 10)

Figure 10. Figure 11.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

The skin over the bony prominence of the first metatarsal head may then ulcerate, especially in an insensate foot. To avoid this possibility, it is often better to perform a second ray amputation, dividing the metatarsal through its proximal metaphysis. Then, the first and third metatarsals will usually approximate each other, narrowing the foot, resulting in a good cosmetic and functional outcome. (Figure 11)

D. MTP Joint of Toes 3 or 4

If toes three or four alone are disarticulated, the adjacent ones will tend to close the gap and restore a good contour to the distal forefoot for shoe fitting. (Figure 12)

Figure 12.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.
Figure 13
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

However, leaving a lesser toe isolated by removing toes on either side will increase its susceptibility to injury. (Figure 13) This is particularly problematic for the insensate foot. The exposed toe is constantly exposed to minor trauma. In the case shown, the patient will be better served by partial removal of the isolated toe.

E. All Five Toes

Occasionally, removal of all five toes is indicated because of ischemic gangrene due to occlusion of the end arteries. (Figure 14) In this case, disarticulation of all five toes with primary coverage of the metatarsal heads is feasible, provided that the dorsal and plantar incisions are both made as far distally as possible in the web spaces. This technique preserves the forefoot lever length.

Figure 14.
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

FUNCTIONAL CONSIDERATIONS AFTER TOE DISARTICULATIONS

Walking function after great toe disarticulation at the MTP joint may be altered because of loss of the first ray's role in the final transfer of weight during late stance phase, in addition to a possible decrease in foot stability medially due to loss of the windlass mechanism. This effect of great toe loss was studied by Mann et al.7 in ten patients (average age, 23 years) who had undergone pollicization of the great toe for loss of a thumb. They found a shift in the endpoint of progression of the moving center of plantar pressure during stance from the second metatarsal head to the third. In this group, clinical complaints after an average of three years were minimal, except for difficulty in making rapid movements requiring intact medial foot stability and great toe flexion during active sports.

Following MTP disarticulation of all five toes, forefoot stability and barefoot gait clinically appear to be better than after transmetatarsal amputation, presumably because of retention of the load-bearing capacity of the metatarsal heads.

II. RAY AMPUTATIONS

First Ray Amputation Second Ray Amputation Fifth Ray Amputation

During a ray amputation, the toe and a variable portion of its metatarsal are excised.

A. First Ray

Figure 15.
Photo courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

The first ray is important for balance and forward progression. Therefore, the metatarsal shaft should be left as long as possible to aid in effective elevation of the medial arch by a custom molded insert. An insufficient length of metatarsal shaft remaining will be ineffective for orthotic support of the medial column and could result in a planovalgus position of the foot secondary to loss of the medial column support. (Figure 15)

The usual indication for a first ray amputation is an ulcer beneath the first metatarsal head that has penetrated the MTP joint capsule. Often, only a portion of the head need be removed with the great toe to eradicate the infection, leaving all uninfected portions of the head and shaft. The metatarsal bone should be beveled on the distal-plantar aspect to avoid an area of high pressure during latter stance phase.

B. Single Amputations of Rays 2, 3 or 4

Single ray amputations of rays two, three or four will only moderately affect the width of the forefoot. Resection is best carried out through the proximal metaphysis just distal to the intersection of the base of the involved ray with those of the adjacent metatarsals, leaving the tarsometatarsal joints intact. (Figure 16a-c)

Figure 16a-c.
a = the square of Second Ray Amputation b = Fourth Ray Amputation c = x-ray
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

C. 5th Ray Amputation

The shaft should be transected obliquely with an inferolateral-facing facet, leaving the uninvolved half to three-quarters of the shaft to preserve forefoot width and retain the insertion of the peroneus brevis. (Figure 17)

Figure 17.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

D. Multiple Ray Amputations

Removal of two or more medial rays is a poor choice, both functionally and cosmetically, as is removal of two or more central rays. (Figure 18) If two or more lateral rays must be excised, the metatarsals should be divided obliquely, with each affected one being cut somewhat longer as one progresses toward the first ray. (Figure 19)

Figure 18
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.
Figure 19
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

If all but the first ray are involved, it can be left as the only complete one. With appropriate pedorthic fitting, this procedure is preferable to a transmetatarsal amputation.6,8,9 (Figure 20)

Figure 20
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

FUNCTIONAL CONSIDERATIONS AFTER RAY AMPUTATIONS

An intact medial column is essential to proper foot balance during both stance and forward progression. With single lesser ray amputations, only the width of the forefoot is reduced, preserving adequate rollover function, overall foot balance during terminal stance, and acceptable cosmetic appearance. Removal of several lateral rays, performed conservatively, can retain both rollover function and full foot length in a shoe.

III TRANSMETATARSAL AMPUTATION

A transmetatarsal amputation should be considered when two or more medial rays must be amputated. It is important to save as much metatarsal shaft length as can be covered by healthy plantar skin in order to provide maximum surface area on the foot for secure suspension of a shoe. Plantar and dorsal transverse skin incisions are made at the base of the toes to assist in obtaining this goal and to assure distal coverage of the metatarsal shafts with durable skin. Avoid using fragile split-skin grafts distally and plantarly. Residual dorsal defects, however, can be easily managed with split-skin grafts with good assurance that they will not break down later, provided proper footwear is consistently used. (Figure 21)

Figure 21 A. Medial view. B. Dorsal view of ideal transmetatarsal amputation. Note position of distal plantar flap, overall length of residual forefoot, maintenance of medial arch, and absence of equinus deformity.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.
Figure 22. A. Radiograph of transmetatarsal amputation showing the angular cut of the metatarsals to parallel the “toe break”. B. Schematic representation of the beveling of the metatarsal shafts for same procedure.
Radiograph courtesy of CSUDH O & P Program. Schematic image downloaded from The Amputation Surgery Center, www.ampsurg.org/index.html; Accessed January 2008.

Once again, to help preserve length, the metatarsal cuts should begin medially, if possible within the cancellous bone of the first metatarsal head. The 15-degree transverse angle that parallels the MTP joints and "toe break" of the shoe should be reproduced to assist forward progression. Plantar beveling of the metatarsal shafts will help reduce distal plantar pressures during late stance. (Figure 22)

Application of a well-padded short leg cast, in slight dorsiflexion, on the operating table will prevent postoperative equinus deformity. If no passive dorsiflexion is present before surgery, a percutaneous fractional Achilles tendon lengthening is indicated to reduce distal pressures under the metatarsal shafts. If "drop foot" is secondary to nerve trauma, transfer of a posterior muscle-tendon unit may be added for its tenodesis effect, with an ankle-foot orthosis (AFO) fitted after wound healing.

FUNCTIONAL CONSIDERATIONS AFTER TRANSMETATARSAL AMPUTATION

Figure 23
Courtesy of CSUDH O & P Program.

Barefoot walking after transmetatarsal amputation is impaired because of loss of the weight-bearing metatarsal heads and elimination of forefoot pronation and supination during gait.2 A rigid rocker bottom (RRB) shoe may help reduce distal pressure and shear from a flexible-soled shoe wrapping around the end of the residual foot. (Figure 23)

Although these forces may be just a matter of discomfort to a traumatic amputee, for a person with an insensate or dysvascular residuum, they may cause ulceration, resulting in re-amputation to a more proximal level. A foot orthosis (FO) with a distal filler will maintain the shape of the toe box. (Figure 24) Some patients (i.e., those unconcerned with cosmesis) may choose a custom-made short shoe, however, this fitting will result in an asymmetrical "drop-off" gait due to the shortened forefoot lever arm. Consequently, this "drop-off" gait will add undo stress to the contra-lateral limb.

A more rigid forefoot plate may be required to support the patient's body weight. These options include adding a carbon fiber plate to a FO, an inframalleolar prosthesis or an ankle-foot orthosis (AFO) made from plastic or laminate. These devices are appropriate for a Chopart level amputation as well.(Figure 25)


Figure 24. A custom foot orthosis with a distal toe filler.
Courtesy of CSUDH O & P Program.
Figure 25. An example of the addition of a carbon fiber plate to a FO.
Courtesy of CSUDH O & P Program.

Another option for a short transmetatarsal amputation is an ankle-foot orthosis (AFO). The AFO may have a toe filler incorporated into the distal foot plate. A variation of the AFO for this amputation level may include an anterior shell to provide improved stability and balance. The AFO may or may not have an attached carbon fiber foot plate.

Figure 26. A. Example of an AFO with a toe filler. B. Example of a laminated floor reaction AFO with an attached carbon fiber foot plate.
a b
(Photo A from: Condie DN, Stills ML. 16-B Partial-Foot Amputations: Prosthetic and Orthotic Management. In: Bowker JH, Michael JW, eds. Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles, 2nd edition, Rosemont, IL:AAOS, 2002. Image downloaded from the O & P Virtual Library, www.oandplibrary.org; Accessed January 2008. Photo B courtesy of Ossur North America, www.ossur.com. )

IV TARSOMETATARSAL (LISFRANC) DISARTICULATION

This procedure, first described by Lisfranc in 1815,10 is often used for instances of trauma and selected cases of foot tumor, but is also applicable for infection. The first, third, and fourth metatarsals are disarticulated, whereas the "keystone" base of the second metatarsal should be left in place to help preserve the proximal transverse arch.

A portion of the fifth metatarsal base is also retained to preserve the insertion of the peroneus brevis tendon. To help maintain a balanced residual foot, in addition to the peroneus brevis, the insertions of the peroneus longus and anterior tibial tendons are preserved.

With a significant loss of forefoot lever length, the massive triceps surae muscles can easily overpower the relatively weaker dorsiflexors, leading to equinus contracture.

This deformity can be avoided through a primary percutaneous fractional Achilles tendon lengthening, followed by application of a cast with the foot in a plantigrade or slightly dorsiflexed position for three weeks. In lieu of an Achilles tendon lengthening, a cast immobilization of the residual foot in dorsiflexion for three to four weeks will hasten atrophy of the triceps surae. The goal is to maintain active plantar and dorsiflexion of the ankle and active inversion and eversion of the foot. (Figure 27)

Figure 27.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

FUNCTIONAL CONSIDERATION AFTER LISFRANC AMPUTATION

This level represents a major loss of forefoot length, with a corresponding decrease in barefoot walking function. In many instances, it is necessary to provide an intimately fitting prosthesis or orthosis that extends well onto the shin. However, in some cases, sufficient suspension surface may be available to allow fitting of an inframalleolar device.

V MIDTARSAL (CHOPART) DISARTICULATION

This disarticulation occurs through the talonavicular and calcaneocuboid joints. As with the Lisfranc level, it is most useful in trauma and selected cases of foot tumor. It is rarely applicable to extensive diabetic foot infections because of the proximity of infection to the heel pad.

Removal of the sharp anteroinferior corner of the calcaneus is also recommended. If the bone is not properly contoured and equinus deformity occurs, this corner is apt to cause pain during stance and gait because some of the distal surface becomes weight bearing.

Figure 28.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

At the time of disarticulation, all ankle dorsiflexors are divided. Without restoration of dorsiflexor function and weakening of the plantar flexors, severe equinus deformity from myostatic contracture of the unopposed triceps surae is inevitable. Weight bearing in equinus becomes painful as it shifts from the heel pad to the distal talus and calcaneus.

Active dorsiflexion can be restored to this extremely short residual foot by attachment of the anterior tibial tendon to the talus, either through a drill hole in the talar head or with sutures or staples to a groove in the distal aspect of the head.11 (Figure 28) To further restore relative balance between dorsiflexors and plantar flexors, the author has found it effective to remove 2 to 3 cm of the Achilles tendon, rather than lengthen it. This is done through a separate longitudinal incision, leaving the sheath of the tendon in place to allow rapid reconstitution of the tendon at its new length.

Marquardt13 suggests that anterior tibial tendon transfer to the talus alone is insufficient because the transferred muscle elevates only the talus, while the continued plantar flexion force on the calcaneus by the triceps surae produces separation and instability of the subtalar joint over time. He has developed a tenomyoplastic operation that restores some dorsiflexion power to both bones13 by attaching the anterior tibial and extensor hallucis longus tendons to the talar head and the long toe extensor tendons to the calcaneus.

Figure 29.
Courtesy of John H. Bowker, MD, Professor Emeritus in the Department of Orthopaedics, Miller School of Medicine, University of Miami, Florida.

Post-operatively, a cast should be applied with the hindfoot in slight dorsiflexion for about six weeks to prevent equinus contracture and to allow secure healing of the transferred tendon to talus. (Figure 29) Alternatively, Baumgartner12 recommends postoperative external fixation of Chopart disarticulations to prevent equinus deformity.

If weight bearing becomes painful because of severe equinus, Baumgartner12 recommends Z-lengthening of the Achilles tendon with wedge resection and arthrodesis of the subtalar joint, with transfer of the anterior tibial tendon to the lateral border of the residuum. The heel pad again becomes plantigrade, and the vertical clearance for a prosthetic foot is increased by 1 to 2 cm.12

Because a prosthesis for this level blocks both ankle and subtalar motion without necessarily preventing deformity, some authors have recommended arthrodesis of both the subtalar and ankle joints after a Chopart disarticulation. The advantages cited are prevention of equinus deformity by ankle fusion and prevention of progressive talocalcaneal instability by subtalar fusion14,15.

FUNCTIONAL CONSIDERATION OF CHOPART DISARTICULATION

Preservation of full leg length and a stable heel pad allows the Chopart patient to walk with direct end bearing for short distances without a prosthesis. However, this short residuum has no inherent rollover function. An intimately fitted rigid ankle prosthesis or orthosis, as well as a shoe with a rigid rocker bottom, are commonly provided solutions.

DISCUSSION

Despite the direct weight bearing, proprioceptive, and cosmetic advantages of PFAs and disarticulations, their full potential has yet to be realized because:

  1. In some surgical and prosthetic circles, these procedures have a reputation for poor wound healing.
  2. Post-operative development of equinus contracture is common, followed by painful gait, which can occur if proper muscle balance has not been restored to the residual foot.
  3. Later development of ulcers as a result of equinus contracture can also occur.
  4. Failure can also result from the desire to "save foot length at any cost" on the part of the surgeon and patient.

Postoperative wound healing problems can be traced to:

  1. Failure to select patients for these procedures who have adequate tissue oxygen perfusion.
  2. Failure to select patients for these procedures who have sufficient mobile durable skin for wound closure without tension.
  3. Failure to detect and remove contaminated tissues. For example, all amputations done for trauma or infection should be considered 'contaminated' with the wound left open until it is healthy enough to safely close.

Development of postoperative equinus contractures can result from failure to immobilize the ankle in maximum dorsiflexion until the wound is soundly healed. If the residuum remains in a plantarflexed angle afterward, ambulation will cause pressures to shift to other areas increasing the likelihood of ulcerations.

From a surgical perspective, certain basic criteria must be met to ensure the greatest functional benefit from each level of amputation. These basic surgical criteria include:

  1. maintenance of adequate bone length;
  2. proper contouring of bony elements where they interface with skin; and
  3. wound closure without tension accompanied by well-perfused, proportionate, mobile, and durable soft tissue.

Preservation or restoration of ankle motion is another major goal to allow comfortable end bearing on a plantigrade heel pad.

At the Lisfranc level, good surgical technique will leave the foot dorsiflexors and everters in place. However, after Chopart disarticulation, ankle dorsiflexion function must be restored by the transfer of dorsiflexor muscle-tendon units to the hindfoot.

Necessary post-op management includes:

  1. All partial foot ablations proximal to the metatarsal heads should be totally enclosed in a well-padded cast on the operation table to protect the wound, control edema, and prevent equinus contracture.
  2. Foot dependency is avoided.
  3. Weekly cast changes will suffice because there is no need for daily wound inspection. However, if infection occurs, there will be systemic signs or unexpected drainage, at which point the cast is promptly removed and the wound evaluated.
  4. Patient compliance. This includes:
    1. avoidance of weight bearing until the wound is sound enough for suture removal,
    2. maintenance of adequate nutrition,
    3. avoidance of vasoconstrictors, such as nicotine and caffeine,
    4. good control of plasma glucose levels by diabetics,
    5. minimal walking,
    6. keeping the foot elevated whenever the patient is not walking to reduce the negative effect of edema on wound healing.
Patient with Chopart level amputation using a laminated, floor reaction AFO with carbon graphite foot plate.
Courtesy of Ossur North America, www.ossur.com.

At the current stage of prosthetic design, partial foot amputations and disarticulations may not equally meet the needs of all patient populations. For example, older individuals who may have poor balance or vision, find that secure end-bearing ambulation is a distinct advantage. Many long term diabetic persons have the same impairments because of insensate feet and retinopathy. Dysvascular amputees typically walk at one slow pace because of generalized cardiovascular disease. These groups, as well as sedentary adults and children with traumatic amputations or congenital foot deficiencies, do quite well overall with the devices currently available.

Younger adults with ablations for trauma can often benefit from in-depth counseling prior to a definitive procedure. They should meet with the surgeon, their prospective prosthetist, and one or more trained peer counselors matched for possible levels of amputation, their pre-trauma activity level, age, and gender. If these individuals/patients wish to return to sports that require extensive running, they may be more satisfied with a long transtibial amputation or Syme ankle disarticulation than a partial foot ablation, given the difficulty of restoring running gait with currently available devices.

CONCLUSIONS

With convergent advances in wound healing, tissue oxygenation evaluation, and antibiotic therapy, as well as improvements in vascular and amputation surgery techniques, today's surgeons have the opportunity to consider the foot, rather than the tibia or femur, as the site of election for amputations resulting from a variety of traumatic, ischemic, or infectious conditions.

Advantages of PFAs include:

  1. Direct weight bearing with proprioceptive feedback along normal neural pathways.
  2. Retention of the hindfoot alone can provide for greater independence without a prosthesis than higher levels, such as transtibial or transfemoral amputations, which require prostheses for walking. This is especially important for elderly patients who often have significant cardiopulmonary comorbidities, poor balance, and possible contralateral amputation.
  3. In addition, amputation levels within the foot result in the least alteration of body image, often requiring only shoe modifications or a limited orthosis or prosthesis for the more distal levels.

Disadvantages of PFAs include:

  1. Variable loss of load-bearing capacity, stability, and dynamic function of the foot when the metatarsal heads have been removed. Barefoot walking is severely compromised.
  2. The loss of surface area available may become problematic for secure suspension of a lower aspect prosthesis that would allow ankle motion in Lisfranc and Chopart disarticulations.
  3. Younger patients, who participate in running sports, may find a transtibial amputation or Syme ankle disarticulation more functional for these more complex activities due to the previously stated disadvantages.

With additional research and development by the prosthetic and orthotic professions, it is anticipated that these limb-sparing procedures can become more applicable to all age groups and levels of activity.

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