Current Considerations In Performing Transmetatarsal Amputations

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Author(s): 
Adam R. Johnson, DPM, and Lee C. Rogers, DPM

Emphasizing The Importance Of Adequate Vascular Assessment And Appropriate Referrals

There are other predictors of wound healing that can assist in determining which patients are most likely to heal a TMA. Vascular studies are the most important and the workup should include Doppler examination of the foot itself to determine which, if any, arteries are viable to guide incision and flap planning.10

   If severe vascular disease exists and the previous vascular tests are inconclusive, one may pursue transcutaneous oxygen (TcO2) studies and angiogram studies.11,12 A TcO2 reading of 30 mmHg or higher has been associated with a 90 percent chance of healing, readings between 20 to 29 mmHg predict a 70 percent chance of healing and readings of less than 20 mmHg suggest a 50 percent rate of healing.12 It should be noted, however, that transcutaneous oxygen studies in the face of infection may lead to a falsely elevated tissue perfusion reading. Accordingly, one should exercise caution in using these studies.13

   If vascular studies show results that are incompatible for healing, a referral for limb revascularization is indicated. Many institutions have interventional radiologists and vascular surgeons who can open occluded and stenosed arteries, and place stents while performing angiograms. One may also consider further intervention by the way of vascular bypass to restore vascular flow to the distal extremity and assist with healing and preservation of the extremity. In limbs without stents in place, intermittent pneumatic compression may be another means to temporarily treat critical ischemia.14

   Failing to address vascularity prior to performing a non-urgent TMA can negatively impact outcome and require a more proximal amputation.

Other Keys To Facilitate Healing

Finally, researchers have cited serum album, a simple measure of nutrition, at levels of >3.0 gm/dL and immunocompetence, measured by a total lymphocyte count of >1,500, as required thresholds for healing an amputation.11,15,16

   In order to help achieve the goals of a high quality of life and decreasing mortality, one needs to ensure the salvaged limb is functional and resistant to excessive tissue breakdown. This requires that the remaining foot be plantigrade in nature with concurrent balancing of the foot and addressing ankle equinus at the time of amputation.

Addressing The Impact Of Peripheral Neuropathy

Peripheral neuropathy affects all three divisions of the peripheral nervous system including the sensory, autonomic and motor divisions. The cumulative effects of diabetes mellitus on the peripheral nervous system lead to an insensate, xerotic and biomechanically unbalanced foot, which is more prone to tissue breakdown.17 The loss of protective sensation to the feet leads to an increased risk of ulceration.18 Advanced glycation end products produced in uncontrolled diabetes mellitus lead to decreased joint mobility by way of tendinopathy and loss of elasticity due to alterations in collagen fibers.19 The rigid foot often has increased peak plantar pressure, which also correlates with increases the risk for plantar ulceration.

   While sensory loss due to most peripheral neuropathies is non-reversible at this time, one can modify pressure with offloading by accommodative orthotic devices or surgical modification.17,18,20-25

What The Literature Reveals About Adjunctive Surgical Procedures

Traditionally, the tendo-Achilles lengthening has been a successful procedure for relieving ankle equinus and associated abnormal forefoot pressures.26-28 However, recent literature suggests that performing gastrocnemius recession for the equinus can be an alternative option.29

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