SPARC and intervertebral disk degenerative disorder: Combination therapies, in which multiple pharmacological agents synergize to ameliorate pain without similar potentiation of adverse reactions, may be useful in improving therapeutic outcome in these patients.The SPARC-null mouse model of low back pain due to disc degeneration was used to assess the effects of opioid (morphine) and α2-adrenergic agonist (clonidine) coadministration on measures of axial and radiating pain.