Unidentified HAND complications after ICU due to COVID-19 infection

A woman, born in 1950, has been infected with Covid-19 early 2020 during the first wave in The Netherlands. Her situation began to get worse and was eventually admitted to the ICU, where she has stayed for 14 days in a coma being tubed to the ventilator. After those 14 days she had woken up with a rather unusual problem. Apparently the nurse at ICU had found a rare hand/arm condition at both sides. The ICU nurse told her she had to use force to extend her fingers, so her hands could be opened up.

It’s a sort of spasms of the m. flexor digitorum. Her phalanges 3-5 are constantly in a flexed position. There is nothing significant found in her thumb and index finger. She is not able to actively extend her fingers. However, when passively extending the fingers 3-5, she is able to extend them (almost) fully to the normal ROM.

The condition gives her no pain at rest. There is hypertonia in the m. flexor digitorum and m. biceps brachii in the distal region. There is also palpable pain in those regions. She does not experience paresthesias or other sensations. No signs of Dupuytren as well. Her right hand is dominant.

She wears a brace during the night, but when removed after the night’s rest her hand will return into ‘the spasm’ position within five minutes.

Tests with the handheld dynamometer have given the following results:

• Tests in 0 degrees flexion elbow (fully extended):
  Left = 20 kilogram-force
  Right = 18 kilogram-force

• Tests in 90 degrees flexion elbow:
  Left = 14 kilogram-force
  Right = 12 kilogram-force

She has visited a neurologist, rheumatologist, physiatrist, and a hand surgeon and they all couldn’t give a suitable diagnosis. Specific examinations done by these physicians are unknown.

She has also had surgery for CTS in her left hand in 2018. There were no complications afterwards.

I suspect the condition is a heavy entrapment of the n. ulnaris in the subcubital tunnel, due to the prone position during ventilation at the ICU. Does anyone recognize this clinical entity and is anyone able to help me with the diagnosis? And what possible treatment could be successful to treat this unfamiliar physical disorder?