Metatarsophalangeal Arthrocentesis Technique

Updated: Nov 03, 2020
  • Author: Jefferson R Roberts, MD; Chief Editor: Erik D Schraga, MD  more...
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Aspiration of Metatarsophalangeal Joint

Identify and mark the metatarsophalangeal (MTP) joint line. Distract the affected toe with one hand by applying gentle passive flexion while extending the toe. Insert the needle perpendicularly and into the joint space. [3, 5] Avoid extensor tendons. [8, 6]

A study by Manadan et al found that fluoroscopy-guided arthrocentesis of the first MTP joint, as well as of the radiocarpal joint, was more accurate than traditional palpation-guided joint aspiration. [9] Ultrasonographic guidance has also yielded good results, [10, 11]  though not all authors have found it to be clearly superior to the traditional landmark-based approach. [12]


Analysis of Joint Aspirate

On aspiration, the viscosity, color, and turbidity of the fluid can offer important clues to the diagnosis when inflammation is present. For example, turbidity tends to increase with inflammation. Also, normal synovial fluid should be able to form a string as a result of its high viscosity; however, this is not a very specific sign, in that septic synovial fluid may also be highly viscous. Blood within the fluid may reflect hemarthrosis when seen in large amounts or a traumatic arthrocentesis when less abundant. [2]

Formal fluid analysis of any joint aspirate should include, but is not limited to, the following:

  • Cell count with differential
  • Gram stain and culture
  • Microscopic crystal analysis (with polarized light microscopy)

Typically, white blood cell (WBC) counts higher than 50,000/μL are associated with infectious etiologies. In some cases, however, crystal arthropathies have been known to lead to similarly high counts. When evaluating a sample for crystals, it is important to note that gout’s monosodium urate crystals are needle-shaped and negatively birefringent when viewed with polarized light, whereas pseudogout’s crystals are positively birefringent and rhomboid in shape. [2]

Inflammatory and noninflammatory arthritis are often delineated by a cell count higher than 2000/μL. Inflammatory fluids can often be seen in rheumatoid arthritis and crystal arthropathy. The prototypical noninflammatory arthritis is osteoarthritis; however, crystal arthropathy can have cell counts lower than 2000/μL. Cell counts of approximately 200/μL are often considered normal.