Intra-articular BCP (Basic calcium phosphate (BCP) crystal deposits may be found in synovial joint fluid, synovium, and articular cartilage. Co-occurrence of BCP crystals and osteoarthritis (OA) is well-established.
Most periarticular BCP deposits are asymptomatic and most commonly discovered as an incidental finding on plain film radiography. Plain radiographs should be performed, which is the easiest method to detect calcific material in periarticular tissues. These appear dense, homogenous, with well-defined borders.
In mild-moderate-stage OA of the hip and knee (radiographic Kellgren stages two and three) mineralization of the articular cartilage by BCP, particularly apatite, was strongly associated with OA development.
Basic calcium phosphate (BCP) crystals encompass three different types of calcium crystals: Carbonate-substituted hydroxyapatite, octacalcium phosphate, and Tricalcium phosphate.
Hydroxyapatite (HA) is the most common component of BCP crystals. Prevalence of intra-articular BCP crystal deposition is not clearly established; up to 60% of synovial fluid samples from patients with knee joint OA contain apatite crystals, and in a study of 53 preoperative OA knees, the prevalence of BCP was around 50%.
BCP crystals are usually inert and asymptomatic but can cause several syndromes due to deposition in and around the joints and soft-tissues.
Calcific periarthritis Associated with BCP deposits in tendons and bursae, most commonly around the shoulder (particularly rotator cuff), but can occur around almost any joint. Acute calcific periarthritis presents with sudden onset of severe pain, swelling, tenderness, and restricted motion, with overlying redness and warmth.
At the glenohumeral joint, pain is most prominent at the subacromial region, radiating down the lateral arm. Due to rupture of the calcific deposits into adjacent soft tissues, BCP crystals elicit an intense inflammation in subacromial bursa.
Presents with increasing pain, swelling, functional loss over months to years. Pain is most severe at night and on joint use, with reduced range of motion, and sometimes with joint instability. Marked crepitation is typical, and joint effusion may be massive. Destructive arthritis predominantly affects the shoulder but can also occur in the knees, hips, elbows, and other joints.
Most cases occur spontaneously but can occur after mild trauma or overuse injuries. Damage to the rotator cuff apparatus may lead to partial/complete total tears.
Acute neck pain can occur from calcifications around the odontoid process (“Crowned dens syndrome”, which can be composed of apatite, CPP crystals, or both).
Non-selective COX (Cyclooxygenase) inhibitors like diclofenac, ibuprofen, naproxen may be more effective because BCP crystals induce both COX-1 and COX-2 pathways. These block production of both physiological and inflammatory prostaglandins.
Surgical therapy may be necessary for pain relief and restoration of function, but maybe challenging due to extent of damage and age of the patient. This may involve arthroscopic lavage, arthroplasty, but ultimately joint replacement may be necessary for advanced degenerative disease.
Patients with OA complicated by BCP crystal deposition should be treated as in primary OA. In destructive arthritis/Milwaukee shoulder syndrome, advanced destructive changes are usually present, treatment of symptomatic disease is unsatisfactory. Conservative management with analgesics, NSAIDs, joint aspirations, temporary immobilization may sometimes control symptoms. Self-care like ice packs to reduce inflammation and maintaining a healthy weight with exercise and healthy balanced nutrition is also required with follow-up.