The high prevalence of pathologic calcium crystals in pre-operative knees

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals are important in the pathogenesis of osteoarthritis (OA) but are under recognized even in end stage disease. We determined the prevalence of these calcium crystals in synovial fluid (SF) of persons undergoing total knee arthroplasty for degenerative arthritis.

SF samples were obtained from 53 knee joints undergoing total arthroplasty for a pre-operative diagnosis of OA. SF were analyzed via compensated light microscopy for CPPD crystals and a semiquantitative radiometric assay for BCP crystals. Fifty pre-operative radiographs were analyzed and graded according to the scale of Kellgren and Lawrence.

Patients had an average age of 70 years at the time of surgery. CPPD and/or BCP crystals were identified in 60% of SF. Overall radiographic scores correlated with mean concentrations of BCP crystals. Higher mean radiographic scores correlated with the presence of calcium-containing crystals of either type in SF Radiographic chondrocalcinosis was identified in only 31% of those with SF CPPD.

Pathologic calcium crystals were present in a majority of SF at the time of total knee arthroplasty. Intraoperative SF analysis could conveniently identify pathologic calcium crystals providing information that may be relevant to the future care of the patient's replaced joint and that of other joints. This information could also potentially aid in predicting the likelihood of the need for contralateral total knee arthroplasty.