Presentation

A 31-year-old male presented with acute gonarthritis (arthritis of the knee) of 2 days’ duration. He has no further history; 2 years before, he also had an acute gonarthritis resolved after intra-articular glucocorticoid injection. Family history was negative.

Serology was as follows: rheumatoid factor neg, anti-citrulline peptide neg, borrelia neg.

At puncture, the following was found with polarized light microscopy (Fig. 1).

Fig. 1
figure 1

Polarized light microscopy of punctate: circular spherules lying not all in the same plane with positive birefringence

Full size image

Discussion

The punctate from the arthritic knee consisted only of some leucocytes and many crystals called “Maltese crosses”: liquid lipid crystals with positive birefringence (contrary to talc: negative regarding breaking direction); these are shaped like microspherules of 2–30 μm. They are considered to be a result of marked cell membrane damage and phospholipid release, and not causative of the arthritis [1]. Maltese cross occurs rarely and can be present (often solitary) in acute arthritides of recent onset [1].

There is no monosodium urate (MSU) nor calcium pyrophosphate nor calcium oxalate or other specific crystals.

They should not be misinterpreted: it is clearly quite different from MSU needles or cholesterol plates with characteristic notched corners [2, 3]. Glucocorticoid injection gives abrupt relief, and some may well respond to colchicine or NSAID [1].