Acromegaly with coarse facies and enlarged hands

A 44-year-old man presents with 5 years of progressive ring and shoe tightening, headaches, excessive sweating, and obstructive sleep apnea. Examination reveals frontal bossing, prominent supraorbital ridges, macroglossia, mandibular prognathism with widened interdental spaces, and the finding marked **B** in the diagram. His blood pressure is 158/94 mmHg and fasting glucose is 168 mg/dL. Laboratory workup shows elevated IGF-1 of 890 ng/mL and failure of growth hormone suppression on the 75 g oral glucose tolerance test. MRI of the sella demonstrates a 1.4 cm pituitary macroadenoma. Which of the following best explains the soft tissue thickening and broadening of the hand marked **B**?