Tarsal Coalition: This condition is characterized by an abnormal connection between two or more of the tarsal bones in the foot, which can be congenital or acquired. The presence of a coalition between the calcaneus, cuboid, and navicular bones, as seen on the x-ray, strongly supports this diagnosis. Tarsal coalition can lead to limited mobility and degenerative changes, which are also mentioned in the findings.

Degenerative Arthritis: The mention of mild to moderate degenerative changes suggests that degenerative arthritis could be a contributing factor to the patient's symptoms. This condition can occur independently or as a result of the altered biomechanics caused by the tarsal coalition.
Overuse Injury: Given the degenerative changes, it's possible that the patient has experienced overuse or repetitive stress injuries, which could exacerbate symptoms and contribute to the degenerative process.

Infection (Osteomyelitis): Although less likely, infection of the bone (osteomyelitis) could present with degenerative changes and needs to be considered, especially if there are symptoms such as pain, redness, or swelling that are out of proportion to the expected findings from a tarsal coalition or degenerative arthritis.
Tumor: Bone tumors, whether benign or malignant, could cause changes visible on an x-ray and must be ruled out, particularly if the patient's symptoms are worsening or if there are atypical findings on the x-ray.

Neuropathic Arthropathy: This is a rare condition that can cause degenerative changes, often in the context of a neuropathy (nerve damage). It's less likely but could be considered if other diagnoses are ruled out and there's a history suggestive of neuropathy.
Congenital or Acquired Bone Dysplasias: Certain rare bone dysplasias could potentially cause abnormal connections between bones or degenerative changes. These would be considered if the patient has a relevant family history or other systemic symptoms.