A Plantar Ulcer With a Falsely Reassuring ABI
Mr. R is 58, with type 2 diabetes for 16 years, HbA1c 10.4%, on insulin. He presents with a 2.2 × 1.8 cm full-thickness ulcer on the plantar aspect of the right first metatarsal head; it has been present 5 weeks. The wound bed is granulating with a rim of callus, moderate serous drainage, no purulence, and surrounding erythema limited to 1 cm. A sterile probe reaches bone. Pedal pulses are 1+ and the foot is warm; there is no visible necrosis. ABI is 1.25 on the right. He lives alone, drives a school bus, and says he "can't stay off it." He has not had an eye or foot exam in 2 years. Current medications include lisinopril, atorvastatin, and gabapentin.
1. The ABI is 1.25 and the wound is granulating. Does that rule out peripheral arterial disease, and what does the probe-to-bone finding add? State your next 48-hour actions.
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The ABI is not reassuring - it is uninterpretable. After 16 years of diabetes, medial arterial calcification makes the tibial vessels non-compressible, so an ABI above roughly 1.3 (and arguably 1.25) can mask genuine ischemia. I would not use it to predict healing or to clear him for debridement. Ask for a toe-brachial index or transcutaneous oximetry instead.
Probe-to-bone is a high-value finding. In a diabetic foot, a sterile probe that contacts bone carries a high positive predictive value for osteomyelitis, especially in an ulcer present longer than 2 weeks - his is 5 weeks. I treat bone involvement as the working diagnosis until excluded.
Next 48 hours:
- Urgent referral to foot-and-ankle surgery or infectious disease for plain films now and MRI if available; bone biopsy with culture is definitive.
- CBC, CRP, ESR, and a metabolic panel.
- Deep tissue culture, not a superficial swab; if he is systemically well and bone culture is planned, avoid starting antibiotics first, because they sterilize cultures and delay diagnosis.
- Continue local care and immediate offloading; no sharp debridement of a plantar wound until perfusion is known.
- Document the reasoning and tell him plainly that the ulcer has reached the bone.
2. He cannot use a total contact cast today but must be offloaded. Which device do you choose, and what makes your choice defensible?
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Total contact casting is the benchmark for a plantar neuropathic ulcer at the metatarsal head, but it is contraindicated with suspected deep infection or osteomyelitis, ischemia, heavy exudate, or inability to keep follow-up. He has at least two of those, so a cast today would be the wrong therapy applied skillfully.
A removable knee-high cast walker with its insole, combined with a strict limited-weight-bearing order on that foot and a walking aid, is the defensible compromise: it offloads the metatarsal head, accommodates dressings and daily inspection, and can be removed for skin checks.
Its weakness is adherence - removable devices heal more slowly largely because patients take them off, and he has already told us he will not stay off it. So I would:
- Name the adherence problem out loud and build the plan with him rather than for him.
- Plan to convert to an irremovable option (an "instant" cast over the walker) once infection is excluded and perfusion is known.
- Add crutches or a knee scooter.
- Schedule weekly visits with callus debridement.
Felt padding, a postoperative shoe, or an over-the-counter insert alone are inadequate for a 5-week forefoot ulcer.
3. How do the HbA1c and the gabapentin shape your teaching, and how do you handle his job?
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An HbA1c of 10.4% means the wound is bathed in a milieu that impairs collagen synthesis, leukocyte function, and microvascular flow. Glycemic control is a wound-care intervention here, not a background issue: coordinate with his diabetes team for an individualized target, and tell him to expect slower healing and higher infection risk until it improves.
Gabapentin tells me he has neuropathic pain and probable loss of protective sensation. He will not feel the pressure that caused this ulcer or the friction from a new device, so he needs daily inspection with a mirror, a callus plan, and a clear statement that absence of pain does not mean absence of injury.
His job: driving is non-weight-bearing, so work itself is not the barrier - walking and standing between the bus and the depot are. Arrange temporary accessible parking, discuss modified duty with occupational health, and keep the walker on for every step. Also close the prevention gaps: dilated eye exam, a complete foot exam at every visit, and a note that he has gone 2 years without either.