Metatarsophalangeal Arthrocentesis 

Updated: Feb 28, 2019
Author: Jefferson R Roberts, MD; Chief Editor: Erik D Schraga, MD 

Overview

Background

Metatarsophalangeal (MTP) arthrocentesis is a critical diagnostic tool in the setting of acute monoarticular arthritis. Joint aspiration is useful for distinguishing inflammatory from noninflammatory musculoskeletal disorders and is the gold standard for ruling out septic arthritis. It also is an effective therapeutic option for pain relief, injection of medications, or drainage of a septic or inflammatory effusion. When done properly and with aseptic technique, it is a safe and well-tolerated procedure that is associated with a low frequency of adverse events.[1]

The clinician performing the procedure should be familiar with the anatomy of the involved joint in order to avoid puncture of tendons, blood vessels, and nerves. The MTP joint line is located at the base of the metatarsals on the extensor surface of the foot. It can be best appreciated by applying gentle passive flexion while extending the toe.

Indications

Diagnostic indications for MTP arthrocentesis include the following:

  • Evaluation of monoarticular arthritis
  • Evaluation of suspected septic arthritis
  • Evaluation of joint effusion
  • Identification of crystal arthropathy [2, 3]

Therapeutic indications for MTP arthrocentesis include the following:

  • Relief of pain by aspirating effusion or blood
  • Drainage of septic effusion [2, 3]
  • Injection of medications (eg, corticosteroids, antibiotics, anesthetics) [2, 3, 4]

Contraindications

There are no absolute contraindications for MTP arthrocentesis. Relative contraindications include the following[2] :

  • Overlying cellulitis of the joint
  • Skin lesion or dermatitis overlying the joint
  • Known bacteremia
  • Adjacent osteomyelitis
  • Uncontrolled coagulopathy
  • Joint prosthesis

Consider hospitalization if arthrocentesis is performed for the administration of intravenous (IV) antibiotics.

When there is a high probability of a septic joint, the joint should be aspirated regardless of possible overlying cellulitis or the presence of bacteremia or septicemia.

In patients with a joint prosthesis, it is preferable that aspiration be done by or discussed with an orthopedic surgeon.

Technical Considerations

Complication prevention

Proper skin cleansing and the use of aseptic technique minimize the risk of introducing infection into a sterile joint.

Potential damage to cartilage can be minimized by understanding the joint anatomy and by avoiding further advancement of the needle into the joint space, indicated by synovial fluid entering the syringe.[5]

Hemarthroses are typically small and self-limited and require only observation. Hemarthrosis in patients with coagulopathy requires correction of the coagulopathy in consultation with a hematologist.

When arthrocentesis is performed through infected skin for the diagnosis of a potentially septic joint, IV antibiotics should be given immediately following the procedure. The patient should be hospitalized for continuation of antibiotics.

Pain may occur, as with any musculoskeletal procedure.[2]

 

Periprocedural Care

Equipment

Equipment for metatarsophalangeal (MTP) arthrocentesis includes the following:

  • Sterile gloves
  • Gauze pad (4 × 4 in.)
  • Skin preparatory solution
  • Lidocaine 1%
  • Syringe for lidocaine, 5 mL
  • Needle for anesthetic, 27 gauge
  • Syringe for arthrocentesis, 5 or 10 mL
  • Needle for arthrocentesis, 21 gauge
  • Specimen tubes - Purple top for cell count and sterile tubes for Gram stain, culture, and crystal analysis
  • Adhesive bandage [3, 6]
  • Hemostat may be helpful

Patient Preparation

Anesthesia

Local anesthesia may be needed, depending on both the provider’s and patient’s preferences.[7] After consent is obtained and typical skin preparation performed, including identification of the needle insertion site, a 27-gauge needle is used to inject 1-2 mL of local anesthetic (eg, lidocaine 1%) into the subcutaneous tissue.[6]

An alternative to an injectable local anesthetic is a localized spray of topical anesthetic skin refrigerant (eg, ethyl chloride).

Positioning

The patient should be placed either in the sitting or the supine position with the foot supported.[3, 6]

 

Technique

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.

 

Questions & Answers