hi jules and welcome a sad welcome
a subject close to my heart and val not here at the moment so i will answer: you have a cks? is that correct?
ok - this is what we call in the clumber spaniel world a herniated disc
we do not know if it genetic in the sense that it is carried in the dna or if it about certain lines giving a certain conformity when they are mated together.
imagine the back bone is like a tube of polo mints with the spinal cord going through the middle - and between each one is a cushion - this normally acts like a shock absorber but when a disc starts to herniate then the cushion becomes brittle and can shatter - this then bulges into the spinal column and causes a 'bubble' sometimes if it is mild then the bone will calcify around the injured point and nature will work to protect - sometimes if it has happened suddenly as a result of jumping up or coming downstairs (the 2 most common ways for it to happen) then it can actually sever the spinal cord causing death.
the treatment depends on how bad it is and how long it has been there - for mild disc injuries then the vet will say rest in the hope that the calcifying happens - dogs that have not responded to this or have/ had multiple relapses or are parallised or have weakness of or pain in the limbs will want to do surgery - has your vet done any MRI, myelogram, or CT scans/tests - these must be done to confirm the diagnosis and to locate the site of the problem.
the surgery involves decompression to relieve pressure on the spinal cord caused by the bits of disc that have shattered - the vet does what is called a hemilaminectomy - this creates a cap out of the bone overlying the spinal cord and then removes the bits of bone debris - relieving pressure on the spinal cord - the success rate is about 70% if done soon enough and the nerve damage has not caused any neurological impairment - in breeds that are prone then chest harnesses can cause/aggravate this - which always makes me cross because most are sold to the owners of the dogs that have the problem in the breed first place.
do you know how it happened - what are his lines?
i am sorry for your boy - it is a very painful and can be very very nasty