Patients suffering from osteoarthritis of the basilar thumb joint often have difficulty maintaining joint stability in the MCP joint during pinch activities. The MCP joint hyperextends instead of staying in a flexed position.

While common in patients with osteoarthritis, MCP Joint Instability can also occur in the following injuries or pathologies:

  • Joint laxity and/or hypermobility, e.g. Ehlers-Danlos Syndrome.
  • Gamekeeper’s thumb: a chronic attritional injury to the MCP joint resulting in instability, marked by pain and weakness.
  • Skier’s thumb: an ulnar collateral ligament strain or rupture and may include an injury to the volar plate of the joint.

Chronic MCP joint instability can be the result of repetitive MCP hyperextension and/or ulnar collateral ligament stresses.

Stability of the thumb MCP joint

Joint stability of the thumb MCP joint is provided by static and dynamic stabilizers.

The static stabilizers include:

  • Proper collateral ligament
  • Accessory collateral ligament
  • Volar plate
  • Dorsal capsule

The dynamic stabilizers include:

  • Extrinsic muscles: extensor pollicis longus, extensor pollicis brevis, and flexor pollicis longus
  • Intrinsic muscles: abductor pollicis brevis, flexor pollicis brevis, and adductor pollicis

Studies have shown that the amount of flexion and extension of the thumb MCP joint tends to vary. Patients with decreased flexion of the MCP joint of the thumb may be more susceptible to sprains and tears of the soft tissues, which play a role in the stability of the joint.

The “Figure of 8” orthosis for MCP joint instability

There are many ways to provide stability to the MCP joint with orthoses. Any orthosis that prevents hyperextension but allows active flexion will benefit the patient. Keep it simple and easy to don and doff without excessive bulk.

Here is an easy to make “Figure of 8” type orthosis from Orficast 3 cm (1”).

“Figure of 8″ orthosis for MCP Joint Instability in Orficast 3 cm (1”)
“Figure of 8″ orthosis for MCP Joint Instability in Orficast 3 cm (1”)

Steps of Fabrication:

  1. Activate a strip of Orficast about 15-20 cm (6-8 inches) long. Pat dry and roll into a tight tubular shape lengthwise.
  2. Starting at the MCP joint of the thumb, make an oval-shaped ring covering the full length of the first metacarpal and the proximal phalanx of the thumb.
  3. Hold the patient’s MCP joint in flexion throughout this process. Pinch the ends of the Orficast together snugly, then stretch the rest of the Orficast under the flexed MCP joint and adhere to the opposite side of the ring. Pinch and cut off the excess material.

Key points for orthotic fabrication for MCP joint instability

  1. Keep the thumb MCP joint in flexion throughout.
  2. Make sure the Orficast is adhered snugly together on both sides of the MCP joint.
  3. You can remove the orthosis carefully and let it harden off or on the patient, but don’t have the patient try to force extension actively against the orthosis while it is still soft.
  4. The sides can be reinforced with a small rolled piece of Orficast.
  5. A strap through the loops and around the wrist can be added if needed.
  6. Sarah Ewald (Occupational Therapist, Hand Therapist and past president of the Swiss IFSHT from Switzerland) also suggests adding an unfolded and trimmed paperclip to reinforce the lateral sides of the orthosis. See her latest article in the IFSSH Ezine, a digital publication at https://www.ifssh.info/pdf/issue-34-may-2019.pdf

MCP joint instability orthoses in Orficast

References

Ewald, S. Improving thumb MCP joint stability with a simple lightweight splint. https://www.ifssh.info/pdf/issue-34-may-2019.pdf

Ford, M., McKee, P., & Szilagyi, M. (2004). A hybrid thermoplastic and neoprene thumb metacarpophalangeal joint orthosis. Journal of Hand Therapy17(1), 64-68.

Heyman, P. (1997). Injuries to the ulnar collateral ligament of the thumb metacarpophalangeal joint. JAAOS-Journal of the American Academy of Orthopaedic Surgeons5(4), 224-229.

Shaw, S. J., & Morris, M. A. (1992). The range of motion of the metacarpo-phalangeal joint of the thumb and its relationship to injury. Journal of Hand Surgery17(2), 164-166.