Hi Mitch
Thank you for sharing this interesting case. I'm sure other colleagues might have more insights but here are some thoughts. Assuming that other DFU interventions are in place and patient is adherent (offloading, nutrition, other co-factors impeding healing, infection control and blood supply), agree it's a good idea to review effectiveness of debridement procedures. 

Assuming this is a "healable" DFU:
For healable DFUs, guidelines recommend debridement of devitalized tissue and surrounding callus (in looking at the picture, it seems like satellite callus is present?), at intervals dependent of how quickly exudate and devitalized tissue are produced (usually 1-4 week intervals). For non-healable or maintenance wounds, expert opinion suggests against active aggressive debridement. 

Sharp debridement is considered "gold standard" for DFU patients with patients with superficial ulcers, without severe PAD (relative contraindication), who are not on active anticoagulant therapy, and are not surgical candidates. It must be performed by trained, licensed healthcare practitioners, who have this procedure within their scope of practice. Clinicians should stop the sharp wound debridement procedure when significant pain occurs, or when viable tissue and/or bleeding is encountered on the wound bed.

Some experts opt to perform wide debridement for healable but stalled DFUs, thereby removing all surrounding callus and ensuring devitalized tissue is removed from the wound bed until viable tissue is encountered. However, they warn that timing is important (usually cannot be done in the first debridement), and important factors need to be considered prior to the procedure, such as whether the foot is sensate and patient can tolerate pain, which anesthesia will be used (local topical and/or injectable), hemostasis can be done properly (is surgical-grade electrocautery available?), and effective offloading device that accommodates an ulcer that will be larger in size is available. The patient should be forewarned that bleeding is likely and that the wound will appear larger after the procedure, when its full extent is exposed. An example of such a case performed by a colleague is shown here. https://woundreference.com/files/4079.jpg
Of note, overly aggressive debridement that involves excessively wide excisions or removing perfectly healthy neoepithelium and dermis are not desirable and should be avoided

Bedside sharp wound debridement does not have the extra risks associated with general/regional anesthesia and costs of surgical facilities. It is less aggressive than surgical debridement and is fast, but may also be imprecise and may carry the greatest risk of tissue damage of any of the debridement methods.

Some resources:
- Checklist for DFU plan reassessment: https://woundreference.com/app/topic?id=diabetic-foot-ulcer#plan-reassessment
- How to perform conservative sharp wound debridement: https://woundreference.com/app/topic?id=how-to-perform-conservative-sharp-wound-debridement
- Assessing Current Options For Debriding Diabetic Foot Ulcers: https://www.podiatrytoday.com/assessing-current-options-debriding-diabetic-foot-ulcers
- Choosing the Best Debridement Modality to 'Battle' Necrotic Tissue: Pros & Cons: https://www.todayswoundclinic.com/articles/choosing-best-debridement-modality-battle-necrotic-tissue-pros-cons

Astute recommendations by Dr. Song above!

The edge does need to be excised to completely flat margins, some options for this include surgical excision vs application of silver nitrate, as well as many other methods of Debridement. I would ask about offloading as well- what methods are in use? Also, has the patient undergone gastroc lengthening? Was the toe amputation a complete ray amp/was sesamoid excised? The wound edge must be flattened completely for epithelial migration but there is also a reason the callus persists.

I agree wholeheartedly with Samantha and Elaine!! When I looked at your photos, my first reaction was that the ulcer continues to build callus. That means the patient is walking on the DFU. Here is my aphorism for the patient when that happens, "I really want to heal that wound, but I can't care for it any more than you do." The second aphorism is similar, "It really doesn't matter what we put ON the wound, what matters most is what we take OFF the wound." In this case, the problem is neuropathic feet and continued, unrecognized, trauma from repetitive stress of walking.

Callus growth is a dead giveaway that the patient is walking on the foot.

So, I prefer a total contact cast (the old fashioned type ... not the walking boot type ...) OK, I get it .. I'm just old and not too fashioned! Change it several times per week (for the first two weeks or so). Perform a total debridement starting with removing every bit of the callus. I think the surface area of wounded tissue with be 50% larger than what your picture shows. I prefer just an absorptive foam dressing then the the contact cast.

Samantha has given a number of great suggestions. The best way to find out whether the Achilles tendon needs to be lengthened is to have the patient sit with leg straight at the knee, then dorsiflex the foot at the ankle. You should have about 100 degrees of dorsiflexion. The second test is to have the patient sit with the leg crossed and knee at 90 degrees, then repeat the dorsiflexion. Should be a little more than 100 degrees if memory serves. Any less that 100 degrees may need an Achilles lengthening. No rush on this though.

The last problem for metatarsal ulcers like this is that there could be bone at the base of the ulcer. The metatarsal head frequently needs to be derided or removed so that the tissue can heal. This is sometime subtle, but if there is bone at the base, it's got to go!

That's all for now. You have a number of great suggestions!