[targonrotts]

apart from swimming, low impact exercises such as playing/walking in the sand and on thick grass is fine.
if dog is under 18 months, let him be a pup and play at his speed.
if over 18 months, you can do moderate exercises to help built rear muscles.
you might want to consult with a rehab clinic on what they would suggest for him.
supplement with glucosamine/chondroitin and use fatty acids, vitamin c, and vitamin e.
keep him trim.