Knuckling refers to flexion of the fetlock joint caused by damage to spinal cord, nerves, muscle or tendons. There may be partial flexion where the soles of the hooves are bearing weight, or extreme flexion where the front of the pastern is bearing weight.
Many injuries or conditions may cause knuckling. In the live export process the main cause of knuckling in the hindleg is injury to the spinal cord, the sciatic nerve and its branches, or the gastrocnemius muscle or tendon. Knuckling in the forelegs is from injury to the radial nerve.
Spinal cord injury may occur from being ridden by or riding other animals, or pulling and twisting the head or neck when it is stuck under a pen rail or over a gate chain. These animals stand weakly on the front and hind limbs with both hind fetlocks knuckling equally. The tail may have reduced muscle tone or be flaccid, and anal reflex may be absent.
Cattle with mild calving paralysis knuckle bilaterally in the hind limbs as a result of compression injury to nerves in the pelvic canal suffered during parturition. A pelvic fracture may cause similar signs.
In animals recumbent for a long time on hard or uneven surfaces, compression injury to a branch of the sciatic nerve (the peroneal nerve) as it crosses the lateral stifle can cause knuckling. Sometimes both hind limbs are affected, and this resembles calving paresis.
Unilateral knuckling in a hind leg may also be the result of injection site paresis affecting the sciatic nerve. Injection site paresis is where needle puncture or irritant injections in the gluteal region or caudal thigh result in injury to the sciatic nerve and branches. The risk is greater in animals with small muscle mass (young or very thin animals), and in any animal where large volumes of irritant medications or long large gauge needles, are injected intramuscularly.
Knuckling in the forelimb is usually from injury to the radial nerve but can be due to rupture of or severe trauma to the extensor tendon or its associated musculature. With these injuries, the elbow is dropped, the fetlock is hyperflexed, and the limb appears unable to bear weight. Radial nerve injury is seen in animals that have been stuck in lateral recumbency for long periods, following blunt trauma to the shoulder area (striking a gate), or following avulsion injury such as from struggling to free a stuck front leg.
A severely dropped hock in conjunction with knuckling indicates rupture of the gastrocnemius muscle or tendon (Achilles tendon).
Note that knuckling may also be caused by systemic diseases such as rabies, Aspergillus clavatus poisoning, cerebral babesiosi and Histophilus somni meningitis.
Provide rest and confinement and administer non-steroidal anti-inflammatory drugs (flunixin meglumine, ketoprofen, meloxicam, or tolfenamic acid). Recovery from nerve damage may take weeks or months, and may not occur at all. Bandage or splint fetlocks in the extended position to assist standing and walking, and to protect the anterior pastern. Provide non-slip flooring. Treat any underlying conditions leading to the injuries causing knuckling.
Injections into the neck and subcutis are preferred if manufacturers' directions allow. Roll downer animals from side to side every few hours to reduce compression damage to limb muscles and nerves.