Ganglion Cyst: Grinding with wrist flexion and extension is highly suggestive of a ganglion cyst, particularly if the grinding is localized to a specific area such as the scapholunate joint. This condition is common and often presents with a palpable mass and pain that worsens with movement.

Scapholunate Ligament Injury: Injuries to the scapholunate ligament can cause grinding or clicking sensations during wrist movement, including flexion and extension. This condition often results from trauma or repetitive strain.
Wrist Tendinitis: Tendinitis of the wrist tendons, such as those involved in flexion or extension, can cause pain and grinding sensations during movement. This is often due to overuse or repetitive strain.
Osteoarthritis of the Wrist: Osteoarthritis can cause grinding or crepitus in the wrist, especially with flexion and extension movements. This condition is more common in older adults and those with a history of wrist trauma.

Infectious Arthritis: Although less common, infectious arthritis of the wrist can present with pain, swelling, and decreased range of motion, including grinding with movement. This condition is a medical emergency requiring prompt diagnosis and treatment.
Gout or Pseudogout: These conditions can cause sudden, severe wrist pain and swelling, and may be associated with grinding sensations during movement. They require specific treatment to prevent long-term damage.

Synovial Chondromatosis: A rare condition characterized by the growth of cartilage in the synovial lining of the joints, which can cause grinding or locking sensations. It typically requires surgical intervention.
Kienbock's Disease: A rare condition involving the collapse of the lunate bone in the wrist, which can cause pain and grinding sensations with wrist movement. It often requires specific treatment to address the underlying bone necrosis.