1) Used of a saddle this was formerly the raised parts at the front and back.
The following quotation is part of a deposition which describes how a poor boy was tied on a horse and transported from Dewsbury to Huddersfield: 1689 his heade ... hunge below the sadle crutch on the farr side, and some parte of his face did, by the movinge of the horse, knocke against the sadle crutch . ‘Cruck’ was an alternative dialect spelling: 1731 a saddle and a cruckpanel, Austerfield.
2) A cross in Middle English, an alternative spelling of crouch used in that sense.
In the example quoted here an image on an indenture of 1524 was thought by a witness to portray an abbot, because thyr apperid the overend of a crutch for his face, Kirkby Malzeard.