Osteomyelitis: Given that the patient had surgical debridement 30 days ago and the wound is not healing, osteomyelitis (bone infection) is a strong consideration. MRSA can infect bone, and the proximity of the wound to bone, along with the failure of the wound to heal after debridement, makes this a likely diagnosis.

Residual or Recurrent MRSA Infection: Despite surgical debridement, there could be residual infection in the soft tissues that has not been fully eradicated, or the patient could have been re-infected.
Poor Wound Care or Inadequate Antibiotic Therapy: If the wound care has been suboptimal or if the antibiotic regimen was not appropriate for the MRSA strain, this could lead to non-healing.
Vascular Insufficiency: Although the patient is not diabetic, vascular insufficiency could still be a factor, especially if the patient has other risk factors such as smoking or hypertension.

Deep Vein Thrombosis (DVT) or Arterial Insufficiency: These conditions could severely impair wound healing and have significant morbidity and mortality if not addressed promptly.
Squamous Cell Carcinoma or Marjolin’s Ulcer: Chronic wounds can rarely transform into squamous cell carcinoma, a condition known as Marjolin’s ulcer. Although rare, this is a critical diagnosis not to miss due to its implications for treatment and prognosis.
HIV or Other Immunosuppressive Conditions: An underlying immunosuppressive condition could significantly impair the body’s ability to heal wounds and fight off infections like MRSA.

Ehlers-Danlos Syndrome or Other Connective Tissue Disorders: These conditions can affect tissue integrity and healing.
Sickle Cell Disease: Although more commonly associated with other complications, sickle cell disease can affect wound healing due to chronic ischemia and other factors.
Factitious Disorder (Munchausen Syndrome): In rare cases, non-healing wounds can be self-inflicted or exacerbated by the patient, often for attention or other psychological reasons.