Plant Thorn Arthritis (Plant Thorn Synovitis)

Pathology photo showing multinucleated giant cell granulomatous reaction (triangle point), synovial hyperplasia, fibrosis, and adjacent foreign vegetable matter (arrow with thorn fragments) with hematoxylin and eosin stain (H&E stain). Kindly provided by Xiaohui (Sheila) Zhao, MD, PhD, of the Department of Pathology and Laboratory Medicine, University of California, Irvine Medical Center.

Plant thorn arthritis is a noninfectious inflammation of a joint as a result of a thorn puncturing the joint and leaving residual plant matter lodged within the joint. The plant thorn fragments cause a localized inflammation reaction in the joint lining tissue that leads to swelling, stiffness, loss of range of motion, and pain. The joint lining tissue is called the synovium. Inflammation of this tissue is medically referred to as synovitis. Plant thorn arthritis is also called plant thorn synovitis.

The plants that commonly cause plant thorn arthritis are those that produce thorns. These plants include palm trees, roses, black-thorn shrubs, cacti, bougainvillea, yucca, pyracantha, plum trees, and mesquite trees. Exposure to these plants is the greatest risk factor for plant thorn arthritis.

Risk factors for plant thorn arthritis include:

• Gardening, especially without gloves
• Exposure to thorn-bearing plants, including:
  • Palm trees
  • Roses
  • Black-thorn shrubs
  • Cacti
  • Bougainvillea
  • Yucca
  • Pyracantha
  • Plum trees
  • Mesquite trees

Plant thorn arthritis causes the involved joint to be:

• swollen,
• slightly reddish,
• stiff, and
• painful.

The joint loses its full range of motion and is often tender.

These symptoms may be noticed only many days after the initial thorn puncture. It is not uncommon for the person affected by plant thorn arthritis to remove the thorn immediately after the puncture and then develop the arthritis many days or weeks later and not even recall that the joint had been punctured previously. This is because the original thorn has left behind small fragments of thorn vegetable matter that gradually cause the inflammation of plant thorn arthritis.

This form of single joint arthritis (monoarthritis) then becomes chronic until appropriately treated.

Plant thorn arthritis is suspected in a patient who presents with a single joint that is inflamed after it has been punctured by a plant thorn. This is true even if the patient recalls removing the thorn, as described above because the thorn can leave behind tiny fragments of thorn matter that lead to the chronic inflammation of plant thorn arthritis.

Removal of joint fluid (joint aspiration) is performed to rule out bacterial or fungal infection of the joint.

Ultimately, the diagnosis of plant thorn arthritis requires either detection of a piece of thorn within the joint by radiology testing or surgical removal of the thorn fragments and identification of the fragments microscopically in the laboratory. Sometimes tiny pieces of thorns can be visualized using magnetic resonance imaging (MRI scanning), high-resolution computerized tomography (HR-CAT scanning), or ultrasound imaging. Often, however, the residual thorn fragments are too small to be seen with these methods and are detected only when identified in tissue that is surgically removed from the joint.

The affected joint lining tissue (synovium) is examined in the pathology department using microscopes. The tissue forms a characteristic reaction, called a granulomatous reaction, within the synovium (granulomatous synovitis). The microscopic thorn fragments are easily identified using a polarized light microscope as they appear brilliantly shiny (birefringent) to the examining pathologist.

Pathology photo showing thorn material (blue and yellow birefringent material) visualized under polarized light microscopy. Kindly provided by Xiaohui (Sheila) Zhao, MD, PhD, of Department of Pathology and Laboratory Medicine, University of California, Irvine Medical Center.

Plant thorn arthritis requires operative intervention. Doctors who perform operative treatments include orthopedic surgeons and plastic surgeons.

Plant thorn arthritis typically affects only a single joint -- the joint that was pierced by the plant thorn. The most common joints affected by plant thorn arthritis are those that can be exposed to being stabbed by falling into or brushing up against plants with thorns. Joints that are commonly affected by plant thorn synovitis include the small joints of the hands (metacarpophalangeal joints, proximal interphalangeal joints), feet, elbows, knees, and ankles.

It is important to recognize that puncturing a joint with foreign material, such as a plant thorn, can lead to bacterial infection (septic arthritis) or fungal infection (fungal arthritis) of the joint. This possibility can be excluded by removing joint fluid and culturing the fluid in the laboratory. While plant thorn arthritis is technically noninfectious, these two forms of infectious arthritis can occur from plant thorn puncture of a joint, with or without true plant thorn arthritis. These forms of arthritis require urgent antibiotic treatment.

For plant thorn arthritis, anti-inflammatory medications may quiet some of the inflammation. However, chronic arthritis eventually develops even long after the plant thorn injury because of the thorn fragments remaining in the joint. This arthritis persists until the fragments are removed with a surgical operation. Without surgical resection of the plant fragments, joint inflammation persists and permanent joint destruction can occur. There is no specific medication or home remedy for plant thorn arthritis.

The surgical operation that can cure plant thorn arthritis is called a synovectomy with joint lavage (joint washout cleaning). During a synovectomy, the surgeon will remove the affected and surrounding joint lining tissue (synovium) to be certain that microscopic joint fragments within the joint and its lining are eliminated from the body.

With permission, these are intraoperative photos of the author's right third metacarpophalangeal joint exposing inflamed joint lining tissue (synovium) from which a 1 mm thorn tip from the common palm tree Phoenix roebelenii was surgically resected. Kindly provided by Gabriel Trainer, MD, and Neil Jones, MD, orthopedic hand surgery, University of California, Irvine Medical Center.

With permission, photos of joint lining tissue (yellowish synovium) resected from author's right third metacarpophalangeal joint after thorn puncture with 1 mm thorn tip (dark dot on thorn-covered with joint lining tissue) from the common palm tree Phoenix roebelenii. Surgical resection of the inflamed tissue (synovitis), as well as all thorn fragments, is the key to curing plant thorn arthritis (plant thorn synovitis). Kindly provided by Gabriel Trainer, MD, and Neil Jones, MD, orthopedic hand surgery, University of California, Irvine Medical Center.

Once a synovectomy for plant thorn arthritis has been performed, the joint tends to heal well without residual problems. The sooner the synovectomy is performed, the better the outcome as chronic joint inflammation can risk damage to the cartilage of the joint. Physical therapy rehabilitation exercises can be helpful to restore normal joint function.

Plant thorn arthritis can be prevented by avoiding exposure to the thorns of plants. It can help to wear protective clothing, gloves, etc., as well as be cautious when near or working with thorny plants.