Complex sentence: Normally this muscle is opposed by ulnar innervated muscles that flex the joints, but with an ulnar neuropathy the muscle is relatively unopposed so it pulls the finger up and to the ulnar side.
Split into simpler sentences: Normally this muscle is opposed by ulnar innervated muscles that flex the joints. But with an ulnar neuropathy, the muscle is relatively unopposed so it pulls the finger up and to the ulnar side.