DFUs, Wagner Grade 3, and Osteomyelitis: Is it only skin deep?

mdavis107
Sep 11, 2023
3 min read

Updated: Jul 23

When it comes to diabetic foot ulcers (DFUs), depth matters more than many realize. According to Booker (2020) with Palmetto GBA, a Wagner Grade 3 wound is defined as a “deep ulcer with cellulitis or abscess formation, often with osteomyelitis.” But what does "deep" really mean?

Surprisingly, not very deep at all.

Dr. Poonawalla (2008) noted that the epidermis—the outermost layer of skin—is only as thick as a piece of paper. Beneath it, the dermis averages just 1 to 4 millimeters thick, about the width of two stacked quarters. Beyond the dermis lies the subcutaneous tissue, positioned just above the deep fascia (Smith, 2019).

Understanding this anatomy is critical: when a DFU extends even a few millimeters beyond the dermis, it enters a zone where infections can more easily reach the bone—and that's where osteomyelitis becomes a serious concern.

Visual comparison of a deep diabetic foot ulcer and corresponding X-ray with a yellow probe indicating bone involvement, highlighting Wagner Grade 3 osteomyelitis.

Osteomyelitis and Wagner Grade 3 DFUs: A Dangerous Link

In a comprehensive review, Giurato et al. (2017) revealed that approximately 60% of diabetic foot ulcers are complicated by infection—and in over two-thirds of cases, infection is the leading cause of major amputations. Wagner Grade 3 and deeper wounds are particularly vulnerable to underlying bone infections like osteomyelitis.

Their findings included:

Ulcer Size and Depth Matter: Deep ulcers greater than 3 mm are significantly more likely to be associated with underlying osteomyelitis compared to superficial wounds (82% vs 33%).
Probe-to-Bone Test (PTB): Although clinical signs like ulcer size and depth are suggestive, additional tools can help raise suspicion. One clinical tool sometimes used is the PTB—where a sterile blunt probe is used to gently explore the wound. If bone is encountered, the test is considered positive and may increase suspicion of osteomyelitis in diabetic foot wounds.

However, it’s important to note that Medicare and most payers do not accept the PTB test alone as a definitive diagnostic tool. A confirmed diagnosis of osteomyelitis typically requires advanced imaging (such as X-ray, MRI, or bone scans) or bone biopsy with culture to satisfy documentation and reimbursement requirements.

In short: if a diabetic patient presents with an infected, deep ulcer, clinicians should maintain a high suspicion for underlying bone infection.

Why Early Detection and Aggressive Treatment Matter

Patients with DFUs complicated by osteomyelitis face a much higher risk of amputation compared to those with superficial infections. Early recognition, thorough evaluation, and a proactive treatment plan can mean the difference between limb salvage and irreversible loss.

Wound care specialists, podiatrists, and interdisciplinary teams must work together to promptly identify these risks and initiate appropriate interventions—ranging from targeted antibiotic therapy to advanced wound care techniques such as hyperbaric oxygen therapy (HBOT).

At the intersection of chronic wounds and limb salvage, early diagnosis and proactive treatment of osteomyelitis in Wagner Grade 3 DFUs can change the trajectory for patients.