The LX90 series mount uses a single-bolt to connect the base-plate to the tripod head, and needs an adapter plate to fit onto the three-hole wedges - I'm not sure which type the LX50 series has.
You can buy the adapter at Bintel:
http://www.bintel.com.au/Mounts---Tr...oductview.aspx - but I'm not sure whether you can fit a three-hole wedge onto an LX-90 tripod (which has only a single bolt top-plate).