Joint injection and regional anesthesia (Proceedings)

Perineural Techniques

Palmar Digital Block

The palmar digital nerves are blocked by injecting up to 2 ml of anesthetic over the nerves, along the edge of the DDFT. Much discussion has taken place regarding the proximal to distal level that the injection should occur. The PDN can be blocked anywhere from the proximal margin of the collateral cartilage to the mid pastern region. Some believe that it is important to anesthetize the nerves near the proximal margin of the collateral cartilage because blocking the PDN as far distally as possible will decrease the likelihood of anesthetizing the dorsal branches of the palmar digital nerve. The relevance may be limited because studies have shown the dorsal branches are unlikely to contribute much more than sensory innervation to the dorsal aspect of the coronary band and dorsal lamina of the foot.

Performing a PDN at the mid to upper portion of the pastern may result in anesthesia of the pastern joint. Because of this, the preferred location is to block the nerves as distal as possible at the level of the collateral cartilages. The old concept that a PDN blocks the caudal ⅓ of the foot is not accurate. It has been shown that anesthesia of the palmar digital nerves just proximal to the bulbs of the heel alleviated lameness caused by endotoxin-induced pain in the DIP joint, indicating that the palmar digital nerves innervate most, if not all of the DIP joint. This report corroborated an anatomical study that demonstrated that the dorsal branches of the palmar digital nerves do not innervate the DIP joint.

Pastern Ring Block

Some clinicians prefer to do a pastern ring block. This will include the dorsal branches so it will desensitize the entire foot. It is often done in place of a PDN because a ring block after a negative response to a palmar digital nerve block is unlikely to result in a positive response. This is likely because the dorsal branches of the palmar digital nerves contribute little to sensation within the foot. The palmar digital nerve block will already have anesthetized the majority of the foot, with the exception of the dorsal portion of the coronary band and the dorsal lamina of the foot.

This block is performed by doing a midpastern PDN and placing approximately 1 ml of local anesthetic on each side of the extensor tendon.

Abaxial Sesamoid Block

An abaxial sesamoid nerve block desensitizes the foot, pastern, middle phalanx and associated soft tissues, the distal and palmar aspects of the proximal phalanx, and possibly, the palmar portion of the metacarpophalangeal joint including the sesamoid bones. Performing the nerve block at the base of the proximal sesamoid bones decreases the likelihood of partially desensitizing the metacarpophalangeal joint. Using a small volume of local anesthetic solution (i.e., < 2 ml) and directing the needle distally, rather than proximally, also decreases the likelihood of partial analgesia of the metacarpophalangeal joint. Some clinicians prefer to use a basi-sesamoid block to decrease the likelihood of blocking the fetlock joint, however the volume and needle placement are probably as important.

Low 4-Point

A low4-point blocks the medial and lateral palmar nerves and the medial and lateral palmar metacarpal nerves blocked proximal to the button of the splint. All 4 nerves must be blocked to completely desensitize the fetlock region.

The block can be done with the horse standing or by holding the leg. My preference is to do it holding the leg between my knees so there is no tension on the flexor tendons and skin. A one inch needle can be inserted dorsal to the DDFT across the limb to the subcutaneous space medially. You can inject 2 ml at that location, withdraw to the subcutaneous space laterally and inject another 2 ml. At that point, leaving the needle in the skin, but withdrawing and tenting the skin, you can direct the needle to the axial aspect of the distal lateral splint bone. The needle is then removed and inserted palmar to the medial splint bone just above the level of the button and angled between the splint and suspensory to block the medial metacarpal nerve.

It is possible to enter the palmar pouches of the fetlock if the block is done too distally. The injections should be maintained above the buttons of the splint bones. This block will completely desensitize the fetlock.

High 4-Point

The same 4 nerves are blocked as with the low 4-point block, but the block is performed in the proximal metacarpal region. The nerves are blocked in pairs from the ipsilateral side of the limb. The needle is inserted dorsal to the flexor tendons and 2 ml injected subcutaneously to block the palmar nerve then the needle directed to the axial surface of the splint bone, to the back of the cannon bone, slightly withdrawn, and another 2 ml injected to desensitize the metacarpal nerve. This is repeated both on the medial and lateral aspects of the limb.

High 2-Point

The high4-point can be reduced to blocking 2 nerves when the lateral palmar nerve is blocked before it branches forming the medial and lateral palmar metacarpal nerves; the medial palmar nerve is blocked separately. This is done proximal, near the carpometacarpal joint and carpal canal so we scrub well prior to this block.

The lateral palmar nerve is blocked just distal to the accessory carpal bone. This is before it divides to form the medial and lateral palmar metacarpal nerves. The injection is less likely to enter the palmar outsourcings of the carpometacarpal joint at this level, but it may block the carpal canal. One advantage of this technique is that it does not put as much fluid volume in the region which may interfere with subsequent ultrasound of the proximal suspensory ligament.

The leg is held in flexion. A 1 inch needle is inserted from the lateral aspect nearly to the hub in the connective tissue just below the accessory carpal bone. 3-5 ml is injected. Then 2 ml are injected to block the medial palmar as for the high 4-point.

With either the high 2-point or high 4-point, in order to remove sensation to the dorsal distal limb, 2 ml needs to be deposited on both sides of the common digital extensor tendon. A partial ring block may also be used.

With these blocks, one needs to remember that the carpometacarpal joint has palmar extensions that can be entered particularly with the high 4-point. This would block the carpometacarpal and the middle carpal joints. This possibility also dictates an increased level of aseptic technique over that routinely done for perineural injections. And as noted, the high 2-point block can result in analgesia of the carpal canal.

Blocking the palmar metacarpal nerves may provide analgesia to the proximal suspensory ligament, more so with greater volumes that diffuse around the suspensory or distal check ligament. Similarly, blocking the middle carpal joint may desensitize by diffusion the ligaments after 5-10 minutes.

The inferior check ligament and the proximal suspensory ligament can be blocked with direct infusion around the ligaments. It is important to perform a low4-point first because diffusion may block the palmar metacarpal or palmar nerves distally. These blocks are best done with the leg flexed to remove tension and allow for mobility of the needle. As before, it may be wise to perform an ultrasound examination prior to doing these blocks.

The rear limbs are blocked similar to the forelimbs with few exceptions. I prefer to hold all of my rear limb blocks, other than the peroneal/tibial, holding the leg across my thighs. This allows me to better control the horse.

On the rear limb to obtain analgesia dorsally, there are dorsal nerve branches on both sides of the extensor tendon that need to be blocked to desensitize the skin dorsally. Slipping a needle completely under the extensor tendon and injecting while withdrawing will provide denervation of the skin dorsally if required for a wound repair.

The rear limb proximal suspensory ligament can be blocked by blocking the deep branch of the lateral plantar nerve. This nerve runs in the fascia on the medial aspect of the proximal lateral splint bone. I palpate the proximal aspect of the lateral splint bone and insert a needle at that level, about 1 cm plantar to the splint bone at about a 45 degree angle towards the center of the cannon bone. A 1 inch needle to the hub and inject 2-3 ml at that site and another 2-3 ml as you withdraw will bock the proximal suspensory. Alternatively, both plantar metatarsal nerves can be injected axial to the splint bones as proximal as possible. There is a small chance of inject into a plantar out pouching of the tarsometatarsal joint.

When total confusion ensues and you just want to block everything from the carpus or tarsus down, median, ulnar and musculocutaneous or peroneal and tibial blocks can be done. While a grade 2/5 or greater lameness will likely show improvement, the change in gait associated with the blocks can make assessment of outcome more challenging.

Median, Ulnar, and Medial Cutaneous Antebrachial Nerves

The median nerve lies on the caudal aspect of the proximal radius with the median artery and veins. A 1 ½ inch 20 ga needle is inserted on the medial aspect of the radius between the caudal surface of the radius and the origin of the flexor carpi radialis muscle pushing upwards near the insertion of the pectoral muscles, which extend down the medial surface of the forearm. The nerve lies fairly superficially directly along the caudal surface of the bone. If the needle is kept very close to the bone by walking it along, the more caudal vessels will be avoided. If you hit the vessels, you're close. Inject about 10 ml in the region. The ulnar nerve lies between the flexor carpi ulnaris and the ulnaris lateralis under a facial plane. A distinct groove can be palpated between these 2 muscles about 10 cm proximal to the accessory carpal bone. A 20 ga 1.5 inch needed is inserted and 10 mls injected. If skin sensation needs to be blocked the medial cutaneous antebrachial nerve is blocked subcutaneous around the cephalic veins in the mid forearm with 3-5 mls.

Tibial and Peroneal Nerves

The tibial nerve is blocked about 10 cm above the point of the hock between the Achilles tendon and the deep flexor tendon. A 1.5 inch, 18 gauge needle is inserted between these 2 tendons on the medial side of the leg and 15 to 20 ml of local anesthetic is injected in the area, including some subcutaneously under the skin. The superficial and deep personal nerves are blocked at approximately the same level between the long and lateral digital extensor muscles. A 2 inch, 18 gauge needle (spinal needle) is placed in the palpable division between the 2 muscle bellies at their distal end, closer to the tendon muscle junction. The needle is inserted to almost its full depth and 15 ml of local anesthetic is injected deep in the leg. The needle is retracted to a depth of about 2.5 cm and another 10 ml of local anesthetic is injected in the more superficial fascia as the needle is slowly retracted. After these 2 nerves are blocked the horse should not have skin sensation over the block.

Arthrocentesis Techniques

I prefer to not clip most of the areas for injection unless the area is particularly dirty. The exception to that is for some of the more proximal sites such as the hip and shoulder I may clip or shave a small site about 1 inch square when I palpate my landmarks, so that I can move immediately to the correct site when it is prepped.

There was no significant difference in the number of CFU's obtained between joints clipped and given a 5 minute Betadine scrub with a brush followed by a single alcohol wipe and those prepared similarly without clipping. (Hague 1997)

Needles – stifle, shoulder, hip, elbow: 18 gauge spinal needle, 3 ½" for all but the hip which requires a minimum 6" long needle. Spinal needle – stylette keeps needle from becoming plugged and needle has a short bevel which is less likely to score cartilage.

Coxofemoral Joint

Requires a long (6-8") needle that is inserted in the notch between the cranial and caudal parts of the greater trochanter. The needle is directed medial, slightly cranially, and slightly downward until it contacts bone. Fluid is aspirated to confirm arthrocentesis. Inject 30 ml of anesthetic into the joint.

Palpation can be difficult in heavy muscled horses. On a line from the tuber coxae to the tuber ischii, the site will be close to ⅔ of the total distance behind the tuber coxae.

The skin is thick in this area. You can use a larger needle as a stylet to pass the longer needle through. To redirect, you need to withdraw to just below the skin surface. A small volume of local anesthetic SQ can be helpful

Stifle Joint

The articulations are the femoropatella and femorotibial. The three synovial joint capsules are the medial and lateral femorotibial and the femoropatellar. The femoropatellar joint capsule frequently communicates with the medial femorotibial capsule. However, to ensure complete intrasynovial anesthesia of the stifle, each of the three synovial capsules should be injected separately. With practice the three injections can be accomplished from the one injection site by directing the needle to into the various capsules.

Lateral Femorotibial

Can be injected from between the middle and lateral or middle and medial patellar ligaments, about 1 inch above tibial tuberosity, angled slightly down towards lateral collateral ligament (spinal needle).

Between the lateral patellar ligament and long digital extensor muscle tendon with a 1.5 inch needle

Medial Femortibial

Can be injected from between the middle and lateral or middle and medial patellar ligaments, about 1 inch above tibial tuberosity, angled slightly down toward medial collateral ligament.

Traditional medial femorotibial injection site is between the middle patellar ligament and the medial collateral ligament. I prefer to do this from the opposite side of the horse. The 1-1.5 inch needle is placed just proximal to the palpable meniscus and only needs to be advanced 1 inch or less.

Femoropatellar

To enter the femoropatellar pouch the same injection site as described above can be used with the needle directed dorsally toward the patella.

Alternatively the injection site can be moved a half to one inch dorsally toward the patella and the needle directed in a horizontal plane into the femoropatellar pouch. Need to use 18 gauge 3 ½" needle and inject 20 ml of local anesthetic per synovial pouch.

A newer technique has been described for the femoropatellar joint. From the lateral aspect of the limb the 1.5 inch needle is just caudal to the lateral patellar tendon about 5 cm proximal to the lateral condyle of the tibia and is inserted perpendicular to the long axis of the femur. The needle is inserted to bone the withdrawn slightly to be within the lateral outpouching of the joint.

All 3 sites can be accessed using a spinal needle placed between the lateral and middle patellar ligaments, 1 inch above the tibial tuberosity. The needle is directed into each joint the withdrawn into the SQ region and advance into the next location. This is facilitated by a SQ bleb of local anesthesia and an extension set on the needle to it is easier to manipulate.

Tarsal Joints

Four synovial sacs – tarsocrural, proximal intertarsal, distal intertarsal and tarsometatarsal. The first 2 (top 2) communicate in mature horses but often are separate in foals. The distal intertarsal and tarsometatarsal joints communicate in some horses (8-38% depending on the study).

Sites for Injection

Tarsocrural/Proximal Intertarsal – just distal and dorsal to the medial malleolus of the tibia. Plantar to the cranial br of the medial saphenous vein. 1" 20 ga needle.

OR

From the lateral aspect, palpate lateral trochlear ridge of the talus. The talus forms a convex curve going distally then makes an abrupt concave turn back proximally the forms a pencil sized notch that is clearly palpable. You can direct a 1" needle into this notch and slightly proximal with minimal risk of contacting articular cartilage

Distal Intertarsal Joints – 1" 22 G needle. Inject in the notch between the central tarsal bone and the 3rd tarsal bone and the combined 1st and 2nd tarsal bones. Often injection occurs through the cunean tendon.

Tarsometatarsal Joint – lateral plantar surface between the 4th tarsal bone and 4th metatarsal bone. Pass needle in sagittal plane in a dorso-distal direction.

*Note that a high pressure injection of more than 10 ml of local anesthetic into the "easy to hit" tarsometatarsal joint in an attempt to "blow through" into the distal intertarsal joint will force anesthetic into the 2nd joint in 24% of horses. This leaves 76% of horses where this will not occur. Therefore, to ensure correct anesthesia of the distal intertarsal joint the joint must be injected separately. (Sack WO, Orsini PG, J Am Vet Med Assoc 1981;179:355-359).

Tarsometatarsal anesthesia may block the high suspensory.

Shoulder

Identify the point of the shoulder which is the anterior portion of the lateral humeral tuberosity. The point of injection is between the anterior and posterior portions of the lateral tuberosity. This is just cranial to the tendon of the infraspinatus muscle. The needle needs to be directed caudally so as to pass over the head of the humerus into the joint. Inject 30 ml of local anesthetic into the joint.

If you palpate the spine of the scapula the infraspinatus tendon is just caudal to this. The tendon can be found and the needle inserted just cranial to the tendon in the "divet" over the joint space.

Elbow

The elbow can be injected just cranial to the lateral collateral ligament about ⅔ of the way distal between the lateral humeral condyle and the lateral tuberosity of the radius. The needle only needs to be advanced about 1 inch.

There is a bursa of the ulnaris lateralis at the level of the elbow joint. The bursa communicates with the joint in about 50% of the horses. It has been described as an injection site, but is unreliable.

The elbow can be injected from the caudal lateral aspect. The site is 1 cm proximal to a line drawn from the lateral supracondylar crest to the point of the elbow, ⅓ of the way caudally. The needle is directed into the olecranon fossa 45 degrees from vertical. Can be from 4 to 7.5 cm depth.

Carpus

There are three major articulations, the antebrachiocarpal joint, the middle carpal joint, and the carpometacarpal joint. The middle carpal joint and the carpometacarpal joint communicate. Therefore, to achieve intrasynovial anesthesia of the carpus, two injections need to be made.

Dorsal Injection Sites – 1" 20 ga needle

Middle carpal joint. Flexed 50%, the needle is inserted into the depression formed by the distal border of the radiocarpal bone and proximal border of the third carpal bone medial to the extensor carpi radialis tendon, directed caudolateral.

Radiocarpal joint. Nearly full flexion, needle inserted into proximal palpable depression between distal border of radius and proximal border of radiocarpal bone medial to extensor carpi radialis tendon, directed caudolateral.

Lateral Injection Sites – This approach can be made with the horse standing on the limb to be injected. Injections are made with a 20 gauge 1" needle. The antebrachiocarpal joint is entered in the depression between the radius, accessory carpal bone and ulnaris lateralis tendon just at the top edge of the accessory carpal bone. The needle is inserted horizontally and slightly cranial to the hub. Synovial fluid should be obtained. The site of centesis for the midcarpal joint is located in the depression between the distal palmar aspect of the 4th carpal bone and the proximal end of the 4th metacarpal bone approximately 2.5 cm distal to the 1st injection site. Insert the 1" needle halfway to the hub to enter the joint.

Assume if you block the intercarpal joint you have blocked the high suspensory.

Fetlock

Lateral palmar approach. The pouch is located between the palmar distal aspect of the cannon bone, the cranial aspect of the suspensory branch, just proximal to the lateral sesamoid bone. You can squeeze medially to distend the lateral pouch in some horses. The needle is inserted into the pouch slightly downward and only requires ½ inch or less penetration.

Arthrocentesis though the lateral collateral sesamoidean ligament can provide synovial samples with minimal blood contamination and is preferred injection technique by some people. The limb is held flexed and the needle passed through the collateral ligament. There is a palpable depression between the palmar/plantar aspect of the distal cannon bone and the lateral sesamoid bone.

The fetlock can be injected dorsally by inserting a needle toward the midline, lateral to the edge of the common digital extensor tendon just proximal to the dorsoproximal aspect of the proximal phalanx. This approach is harder to obtain synovial fluid, can cause iatrogenic damage to the cartilage and some veterinarians think this is a more sensitive area to the horse.

Pastern

The pastern can be approached dorsally, similar to the fetlock. You find the distal lateral and medial eminences of P1 and go ½ cm proximal to this line just lateral to the extensor tendon and insert the needle slightly distal and medially into the joint.

A newer technique has been described that is done with the limb flexed. The limb is held flexed and a 20 ga 1 inch needle is directed perpendicular to the long axis of the limb into the V shaped depression formed by the palmar margin of P1 dorsally, the distal eminence of P1 distally, and the lateral branch of the SDF tendon palmarly.

Coffin Joint

The dorsal approach is done standing just medial or lateral to the extensor tendon. Some people choose to go through the tendon. About 1 cm dorsal to the coronary band, you can palpate a depression in some horses. The needle is inserted at 120 degrees to the hoof wall, which sets you not quite perpendicular to the ground in most horses. This site will bleed in most cases following injection.

I prefer to inject the coffin joint by inserting a small gauge (23) needle just above the coronary band, parallel to the ground straight into the proximal-dorsal pouch.l

The lateral approach is preferred by some. The leg can be flexed or loaded. A depression just proximal to the lateral collateral cartilage on the lateral surface P2 is identified. The needle is inserted at a 45 degree angle to the ground towards the opposite hoof wall. It will be 1 to 1.5 inches deep and placement is identified by ease of injection. In 8/12 horses they injected only the coffin joint, in 2/12 the coffin joint and navicular bursae, 1/12 into tendon sheath and 1/12 SQ (Mercado 1998).

Blocking or treating the coffin joint may have similar effects in the navicular bursa due to nerve fibers in the impar ligament or diffusion across the impar ligament.

References and Suggested Reading

Hague BA, Honnas CM, Simpson RB, et al. Evaluation of skin bacterial flora before and after aseptic preparation of clipped and nonclipped arthrocentesis sites in horses.Vet Surg 1997; 26(2): 121-5.

Hogan PM, Honnas CM, Carter GK. Arthrocentesis and joint injection techniques in horses: Articulations of the upper limb. Vet Med 1997;92:70-74.

Hogan PM, Honnas CM, Carter GK. Arthrocentesis and joint injection techniques in horses: Articulations of the lower limb. Vet Med 1996;12:1111-1118.

Moyer WA. Guide to Equine Joint Injection. Veterinary Learning Systems, Trenton NJ, 1986.