Gout: This is a common condition characterized by sudden, severe attacks of pain, swelling, redness, and tenderness in the joints, often occurring at the base of the big toe. The metatarsal head is a common site for gouty arthritis, which can cause fluid accumulation due to inflammation.

Osteoarthritis: Wear and tear of the joint cartilage can lead to fluid accumulation and swelling in the metatarsal head area.
Trauma or Stress Fracture: Direct injury or repetitive stress on the metatarsal bone can cause fluid accumulation due to inflammation or fracture.
Bursitis: Inflammation of the bursae (fluid-filled sacs) near the metatarsal head can cause fluid accumulation and swelling.
Synovitis: Inflammation of the synovial membrane surrounding the joints can lead to fluid accumulation in the metatarsal head area.

Septic Arthritis: Bacterial infection of the joint can cause severe pain, swelling, and fluid accumulation, and if left untreated, can lead to serious complications, including joint destruction and sepsis.
Osteomyelitis: Bone infection can cause fluid accumulation and swelling in the metatarsal head area, and if not promptly treated, can lead to serious complications, including bone destruction and sepsis.
Tumor: Although rare, a tumor in the metatarsal bone can cause fluid accumulation and swelling, and early diagnosis is crucial for effective treatment.

Rheumatoid Arthritis: Although more common in the hands and feet, rheumatoid arthritis can cause fluid accumulation and swelling in the metatarsal head area.
Psoriatic Arthritis: A type of arthritis associated with psoriasis, which can cause fluid accumulation and swelling in the metatarsal head area.
Charcot Foot: A condition characterized by nerve damage and joint destruction, often associated with diabetes, which can cause fluid accumulation and swelling in the metatarsal head area.