Calcium oxalate crystals can be a challenge to manage sometimes. Also the formulations on glucosamines can vary. I would recommend that a urine sample be submitted while on the glucosamine. 4-6 hours post medicating might be helpful.
Another option for joint heath would be fish oil supplementation. Omega 3 fatty acids, specifically EPA (eicosapentanoic acid) will help reduce joint inflammation.
Also adding in an NSAID can also help. Previcox, Metacam, etc...
Hope this helps.
Christopher A. Lee, D.V.M., C.V.L.S.
Promoting surgical options and pet comfort through the use of lasers.