Hyperextension injury is severe damage of the ligaments that supports the wrist (or carpus) of the forelimb.

Diagnosis is based on palpation of the limb and x-rays.

Treatment usually involves surgical fusion of the carpal joint.

Most dogs respond well to surgery.

What is it?

• Hyperextension injury is severe damage of the ligaments that supports the wrist (or carpus) of the forelimb
• The result is that the paw sinks down to the ground during weight-bearing as seen in the animation to the right

Pertinent Anatomy

• The carpus is equivalent to the wrist joint in man
• The palmar fibrocartilage is a very strong ligamentous structure on the back side of the wrist that prevents the wrist from extending too much (called hyperextension)

Clinical Signs

• This injury is most common in large breed active dogs, however small breeds can also sustain hyperextension injury
• Lameness
• Swelling of the carpus
• Hyperextension of the carpus

Diagnosis

• Physical examination
  • pain on palpation of the carpus
  • carpus extends beyond normal limits
• Radiographs (x-rays)
  • these are helpful to determine which joint(s) are affected and helps the surgeon decide if the entire carpus must be fused or just two lower joints joints of the carpus

Treatment

• Conservative treatment
  • If the ligament injury is significant, conservative treatment is not effective; typically conservative treatment is not effective
  • conservative treatment includes rest for 3 months and splinting the fore limb for about 2 months; splint changes are done every other week
• Surgical treatment
  • Surgical fusion of the carpal joints is usually required
  • In most cases all three joints of the carpus must be fused, however in some cases only the bottom two joints can be fused
  • Surgical principles
    • Joint must be free of infection
    • All cartilage surfaces of the joint are removed
    • Bone graft harvested from the patient is packed into the joints to stimulate healing
    • Joint is positioned in a functional angle and stabilized with rigid fixation devices such as
      • plates and screws
      • screws
      • pins and wires
      • external skeletal fixator
      • we prefer the use of plates and screws as this results in our best outcomes; we usually use an arthrodesis plate specifically made for this purpose
      • The plates and screws usually are not removed.
      • After the surgery, in most cases, the carpus must be supported with a cast for about 6 to 8 weeks; the soft bandage material beneath the cast is changed every 2 weeks
  • Other indications for surgical arthrodesis of the carpus
    • Debilitating arthritis that is no longer responsive to medications
    • Irreparable fractures
    • Rheumatoid arthritis
    • Limb spare surgery following removal of a part of the radius bone that articulates with the carpus - done to remove bone cancer
• Postop care in our hospital
  • Pain management
  • The limb is supported in a cast or splint during the healing phase which is about 6 weeks
  • The padding of the cast or splint is changed every 2 weeks
  • Limited leash walks for urination/bowel movements until arthrodesis has been confirmed to be healed on radiographs
  • Radiographs are taken 6 to 8 weeks after surgery
  • After the cast has been removed, exercise is gradually increased on a leash over the next 6 weeks; during the first week a 5 minute walk twice daily is permitted; the walks can be increased by 5 minute increments each week until a normal amount of walking has been achieved

Aftercare

• Administration of pain medication
• Exercise limited until bone has healed together
• Cast care
  • check toes daily for signs of swelling or coldness
  • put plastic bag on cast when going outside and remove bag when back indoors
  • watch for signs of problems with the cast
    • cast slips out of position on the limb
    • cast has odor
    • cast has discharge
    • pet is chewing at cast
    • pet stops bearing weight on the limb
    • any of the above problems could indicate serious problems beneath the cast such as pressure sores

Potential Complications

• Anesthetic death is very uncommon with our sophisticated monitoring devices and advanced anesthesia protocols
• Infection is possible but very uncommon
• Cold sensitivity requiring removal of the plate and screws after a year
• Failure of healing, necessitating regrafting of the joints
• Breakage of the plate or screws
• Pressure sores from the cast or splint

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