FOREFOOT:

Nerves are blocked at four sites.

1) Dorsal metacarpal nerve (branch of the radial nerve). Blocking this nerve removes sensation from the dorsal surface of the foot. This nerve is found on the dorsal surface of the metacarpal bone, medial to the medial digital extensor tendon. (J4.128.w1)

• Palpate the nerve on the dorsomedial aspect of the metacarpus at the junction of the proximal and medial thirds of this bone (J4.128.w1); at about the middle of the metatarsus, medial to the extensor tendon. (B205.12.w12)
• Injected at this point (the nerve divides near the middle of the metacarpus). (J4.128.w1)
• The dorsal metacarpal vein, medial to the nerve, should be avoided. (J4.128.w1)

2) Abaxial dorsal nerve (dorsal branch of the ulnar nerve) and abaxial volar nerve (palmar branch of the ulnar nerve) of the fourth digit.  

• The abaxial dorsal nerve is the branch of the ulnar nerve (dorsal branch of the ulnar nerve). It is found in a groove between the intraosseous tendon and the metacarpal bone and it continues over the lateral surface of the fetlock. The abaxial volar nerve, a branch of the medial nerve, is found medial to the flexor tendons. At the middle of the metacarpus it divides into three volar digital nerves and part of a fourth nerve. The lateral branch of the median nerve joins the volar branch of the ulnar nerve to form the abaxial volar nerve of the fourth digit. (J4.128.w1)
• The needle is inserted 1 inch (2.5 cm) above the fetlock joint on the lateral side, between the suspensory ligament and the flexor tendons, in order to anaesthetise both nerves. (J4.128.w1)
• Insert the needle on the lateral aspect of the limb, about 5 cm (2 inches) above the fetlock in the groove between the metacarpal bone and the suspensory ligament. (B205.12.w12)

3) The two axial volar digital nerves. These are branches of the median nerve which lies in a groove at the bifurcation of the flexor tendons. (J4.128.w1) 

• Both nerves can be blocked by an injection 1/2 to one inch (1.25 to 3.5 cm) proximal to the dewclaws on the volar midline (J4.128.w1); inject in the midline just above the fetlock. (B205.12.w12)
• Palpate with the fingers to locate the groove formed by the bifurcation of the tendon. Inject beneath the skin and deep fascia. (J4.128.w1)
• Alternatively inject in the midline just below the dewclaws, just after the nerve branches emerge from below the fibrous plate of the dewclaws. (B205.12.w12)

4) The axial volar nerve of the third digit, a branch of the medial nerve (medial branch of the medial nerve). This is found in a groove between the suspensory ligament and the flexor tendons and crosses the fetlock just behind the medial digital vein. (J4.128.w1)

• Insert the needle one inch (2.5 cm) proximal to the fetlock joint in the groove formed by the suspensory ligament and the flexor tendons. (J4.128.w1)
  • Inject on the medial side of the limb about 5 cm (two inches) above the fetlock. (B205.12.w12)
    • Injecting further proximal is not practical since the nerve is deep to the artery and vein. (B205.12.w12)

HINDFOOT:

A) To desensitise the foot below the fetlock: (B205.12.w12)

Inject about 5 ml of local anaesthetic solution at each site. (B205.12.w12)

1) Superficial peroneal nerve. This nerve is found just beneath the skin on the dorsal surface of the metatarsal bone and continuing distally over the extensor tendons. It divides at the middle of the metatarsus into medial and lateral branches, the axial dorsal nerves of the third and fourth digits. The lateral branch sometimes originates more proximally at the hock and then progresses parallel to the remainder of the nerve, lateral to the dorsal metatarsal vein. (J4.128.w1)

• Insert a 1/2 inch (1.25 cm) needle at the junction of the proximal and middle thirds of the metatarsus on the dorsal surface. (J4.128.w1)
• Inject about 5 ml of 2% lidocaine. (B205.12.w12)

2) Deep peroneal nerve. This nerve is found in the groove on the dorsal surface of the metatarsal bone, covered by the extensor tendons and deep fascia. (J4.128.w1)

• Insert a 1inch (2.5 cm) 22 gauge needle from the lateral side medially to its full length to pass beneath the extensor tendons. (J4.128.w1, B205.12.w12)
• Deposit local anaesthetic solution as the needle is withdrawn. (J4.128.w1)
  • Avoid the dorsal metatarsal artery which lies in the groove with the nerve. (J4.128.w1)
• Inject about 5 ml of 2% lidocaine. (B205.12.w12)

The combined effect of these two injections is to remove sensation from the dorsal aspect of the hindfoot. (J4.128.w1)

3) Lateral plantar metataral nerve, This is the lateral branch of the tibial nerve, is found on the lateral surface of the metatarsus, between the suspensory ligament and the flexor tendons. It continues distally as the abaxial nerve of the fourth digit. (J4.128.w1)

• Insert a needle at the middle of the metatarsus on the lateral side between the suspensory ligament and the flexor tendons, to beneath the superficial fascia covering the nerve, (J4.128.w1) about 5 cm proximal to the fetlock joint. (B205.12.w12)
  • Inject about 5 ml of 2% lidocaine. (B205.12.w12)

4) Medial plantar metatarsal nerve. This is the medial branch of the tibial nerve and is found on the medial surface of the metatasus, between the suspensory ligament and the flexor tendons. The nerve divides distally to form the abaxial plantar nerve of the third digit and the two axial plantar digital nerves. (J4.128.w1)

• At the middle of the metatarsus on the medial side insert a 1/2 inch needle medially between the suspensory ligament and the flexor tendons, deep to the superficial fascia. (J4.128.w1)
  • Inject about 5 ml of 2% lidocaine. (B205.12.w12)

B) Alternative hindlimb block above the hock, providing analgesia below the hock: (B205.12.w12)

1) Fibular (peroneal) nerve:

• Palpate the bony prominence of the caudal edge of the lateral condyle of the tibia. The nerve runs immediately behind the caudal edge of this bone and over the fibula and may be palpable against the bone. (B121.20.w20)
• Insert an 18 or 20 gauge 2.5 cm needle through the skin and through the aponeurotic sheet of biceps femoris until the point of the needle just touches the caudal edge of the lateral condyle of the tibia. (B205.12.w12)
• Inject 20 ml of 2% lidocaine hydrochloride. (B205.12.w12)
• Analgesia develops after 20 minutes. (B205.12.w12)

2) Tibial nerve (on the medial aspect of the limb, just in front of the gastrocnemius tendon).

• Grasp the gastrocnemius (Achilles) tendon between the thumb and index finger of one hand about 10-12 cm above the summit of calcaneous. (B205.12.w12)
• Insert a 2.5 cm needle just below the thumb until the point of the needle can be felt by the index finger, just below the skin on the other side of the tendon. (B205.12.w12)
• Inject 15-20 ml local anaesthetic solution. (B205.12.w12)
• Inject an additional 5 ml on the medial side of the leg to block a small cutaneous nerve at this site. (B205.12.w12)
• Analgesia develops after 15 minutes. (B205.12.w12)

• For surgical treatment of interdigital fibromata, claw amputation etc. (J4.128.w1)

• The animal is able to walk as soon as surgery is completed. (J4.128.w1)
• Local analgesia generally results in fewer complications than does general anaesthesia in cattle. (J4.128.w1)
• Hyaluronidase may be combined with the local anaesthetic solution. (J4.128.w1)
• The technique for blockage of the hind limb by injecting above the hock has the advantages that: 
  • Only two injections are required; (B121.20.w20)
  • Injections are made into soft tissues at a convenient level, therefore making them easier to perform, with thin needles and with minimal restraint of the animal; (B121.20.w20)
  • The position of the nerves may be readily determined by palpation of definite landmarks; (B121.20.w20)
  • The leg continues to bear weight in an almost normal manner; (B121.20.w20)
  • There are no complications associated with injection into diseased tissues lower on the limb. (B121.20.w20)

General notes for local anaesthesia:

• The analgesic technique chosen should be decided based on the procedure to be undertaken, the facilities available and the skills of the practitioner. (J215.7.w1)
• Standard aseptic techniques should be practiced when performing local analgesia, including surgical preparation of the skin, and sterile injection techniques. (J215.7.w1)
• Aspiration to check for blood should be carried out prior to injection, to avoid inadvertent intravenous injection. (J215.7.w1)
• Epinephrine (adrenaline) at 1 part per 200,000 or norepinephrine at 1 part per 100,000 may be added to the local anaesthesia solution to decrease the absorption of the agents and prolong their action. These vasopressors should not be used for analgesia of appendages such as the tail, teats or toes as they may produce sufficient circulatory compromise of the appendage to result in tissue necrosis and sloughing. (J215.7.w1)
• Hyaluronidase may be added to local anaesthetic solutions to increase tissue permeability and thus decrease the time to onset of analgesia and reduce the volume of local anaesthetic solution required; it will also reduce the duration of analgesia. However it is questionable whether it is needed other than with procaine hydrochloride solution, since other local anaesthetic agents, such as lidocaine, penetrate tissues adequately. If used, then 150 turbidity reducing units (TRUs) of hyaluronidase may be added per 25 mL of 2% lidocaine. Combining both adrenaline and hyaluronidase with local anaesthetic solution may both increase initial spread and onset while also reducing uptake and therefore prolonging anaesthesia. Note: Use of hyaluronidase is NOT a substitute for accurate placement of local anaesthetic solution, since the tissue fascial planes will still act as barriers. (B342.16.w16)

• Incorrect placement of injections will result in the nerves not being blocked. 
• The skin over the limb below the carpus/tarsus is tense and subcutaneous tissue is fibrous, therefore it is not easy to palpate and precisely locate the nerves. (B205.12.w12)

• Local anaesthetic solution: 2% lidocaine. 
• Syringe.
• Needles.
  • A 1/2 inch 22 gauge needle is ideal for most of the injections as this penetrates to the required depth.  (J4.128.w1)
  • A 18 or 20 gauge 2.5cm needle is recommended for blocking the hindlimb nerves above the hock. (B205.12.w12)

• Knowledge of regional anatomy, including the positions of the nerves, is required for appropriate placement of injections. 
• Procedure should only be undertaken by an individual with appropriate clinical training and practical experience; this would usually be a veterinarian or someone with advanced veterinary technician training.

• Inexpensive. 

• Analgesia, either by this technique, another local anaesthetic technique, or through general anaesthesia of the patient, should be employed whenever a painful procedure, such as surgical intervention, is to be carried out.
• In some countries there may be legislation restricting the use of this type of technique to licensed veterinarians. For example in the UK: "The Veterinary Surgeons Act 1966 (Section 19) provides, subject to a number of exceptions, that only registered members of the Royal College of Veterinary Surgeons may practice veterinary surgery." (see: LCofC1 - RCVS Guide to Professional Conduct 2000 - Treatment of Animals by Non-Veterinary Surgeons).