Synoviocentesis

There may be more than one reported method to access a joint or tendon sheath. In this chapter, only one method is presented (the one preferred by the authors). Also there is a trend among practitioners to use smaller gauge needles (than recommended in this chapter) for centesis of some joints. This is personal preference and should be considered. Use of a smaller gauge needle may facilitate synoviocentesis of some fractious horses, and may cause less synovial hemorrhage. These needles are more likely to break, however, if the horse moves during synoviocentesis.

Synoviocentesis

Indications

• To collect synovial fluid for cytological analysis or bacteriological culture
• To administer local anesthetic solution as part of a lameness examination or to administer medication such as a corticosteroid or sodium hyaluronate
• To administer a polyionic fluid or radiocontrast material to check for communication of a joint or tendon sheath with a nearby wound

Materials

• Hair clippers are optional. Traditionally, the site of centesis is clipped prior to needle puncture, but a recent study and experience of some practitioners indicate that clipping is not necessary, if the area is properly scrubbed. Some owners may be more satisfied if the hair is left unclipped.
• An antiseptic soap, such as povidine-iodine or chlorhexidine
• 70% isopropyl alcohol
• Sterile, surgical gloves
• At least two sterile, disposable needles A 20-ga (0.90 mm) needle is commonly used to administer drugs. The needle used to draw medication from a bottle should not be used for joint injection. A new needle should be used for each injection.
• To lessen the likelihood of sepsis, a new, unused bottle of drug should be used for joint injection.
• A lip twitch
• A sedative (best avoided if synoviocentesis is part of a lameness examination) If application of a lip twitch or lip chain does not provide sufficient restraint for synoviocentesis as part of a lameness examination, the horse can be sedated with xylazine HCL or detomidine often without interfering significantly with assessment of gait. The degree to which sedation may interfere with assessment of gait, however, may depend upon the severity of lameness and the skill of the clinician performing the lameness examination.
• Fluid for cytological examination is collected in EDTA tubes. Fluid for bacterial culture can be collected in a capped, air-free syringe for immediate delivery to the laboratory, or if a delay in submission is anticipated, synovial fluid can be collected into Port-A-Cul tubes or vials.
• For intrasynovial analgesia, mepivacaine is the local anesthetic solution most commonly administered because it is relatively non-irritating to tissues. The analgesic effect of mepivacaine lasts about 2 hours. Lidocaine is irritating to tissue and produces analgesia for only 30 to 40 minutes.

Materials

• A sedative
• Stocks are useful.
• Local anesthetic solution
• A #10 and a #22 scalpel blade
• Sterile surgical gloves

Procedure

• The site of needle placement is scrubbed for at least 5 minutes and then rinsed with alcohol.
• For some joints, multiple sites for needle placement have been described. In this text, the examples illustrated are the sites preferred by the authors.
• Not all horses respond in the same way to different methods of restraint, but for most horses, application of a lip twitch provides adequate restraint. The twitch works best when applied immediately prior to needle placement. When a joint is injected with the horse’s limb on the ground, the contralateral limb can be lifted off the ground to enhance the safety of the procedure for the clinician. Clinicians should be aware, however, that some horses might buckle in the knee of the weight-bearing limb and fall when the needle is introduced.
• Synovial fluid is usually more easily collected as it drips from the needle than by aspiration with a syringe. An alternative technique to aspirate synovial fluid involves inserting one end of a blood collection needle into the joint, inserting the other end of the needle into a blood collection tube, and allowing the tube to fill (Fig. 24.1).
• If a sufficient quantity of synovial fluid cannot be collected for bacterial culture, aspirating the joint after infusing it with physiological saline solution usually allows enough fluid to be collected for culture.

Figure 24.1. Synovial fluid can be collected by inserting one end of a blood collection needle into the joint, inserting the other end of the needle into a blood collection tube and allowing the tube to fill.

Interpretation

• Normal synovial fluid is pale yellow and clear. The amount of fluid collected varies, but more fluid can usually be obtained from diseased joints.
• Red blood cells are not a normal constituent of synovial fluid, but blood frequently contaminates synovial fluid during synoviocentesis. Streaks of blood within the sample usually indicate contamination at the time of collection. Dark yellow to amber samples may indicate chronic traumatic arthritis. Marked increase in the number of red blood cells may also indicate sepsis.
• Clotting of the sample indicates severe inflammation of the joint or tendon sheath. Synovial fluid from healthy tendon sheaths and joints or joints affected by degenerative disease does not clot.
• Protein concentration is normally < 2.0 g/dL.
• Cell count is normally less than 600 nucleated cells/uL, most of which are small lymphocytes and monocytes.
• Indications of sepsis are:

• A predominance of segmented neutrophils (often > than 30,000 cells/µL)
• Degenerate neutrophils (In contrast to morphology of neutrophils found in other infected body fluids, however, neutrophils in septic synovial fluid often appear healthy and have little or no degenerative changes.)
• Fluid that clots
• A turbulent fluid
• A protein concentration > 4 gm/dL
• Culture of bacterial colonies. At least one-fourth of samples of septic synovial fluid yield no bacterial growth.

Complications

• Iatrogenic sepsis is an unlikely complication of synoviocentesis, as long as the procedure is performed using sterile technique. Some clinicians routinely administer an antibiotic during synoviocentesis, but we consider this practice usually to be unnecessary, even when an immunosupressive drug, such as a corticosteroid is administered intra-synovially. However, because infection occasionally occurs after intra-synovial administration of polysulphated glycosaminoglycan, we suggest that 150 to 200 mg of amikacin be administered along with this drug.
• Blood contamination of a sample of synovial fluid is common, because the synovial membrane is very vascular.
• Hemarthrosis. Some horses display signs of acute pain following arthrocentesis, possibly because of hemorrhage into the joint during the procedure. Lameness caused by hemarthrosis usually resolves within 24 hours.

Arthrocentesis

Techniques

For some joints, multiple techniques for arthrocentesis have been described. In this section, we describe the techniques that we believe are most easily performed. The optimal amount of local anesthetic agent required for optimal analgesia of each joint has not been established, and volumes stated are only suggestions.

Distal Interphalangeal (Coffin) Joint

Lateral, palmar and dorsal approaches for arthrocentesis have been described for this joint. Using the lateral or palmar approach, however, the navicular bursa or the digital flexor tendon sheath can occasionally be penetrated. We prefer a dorsal approach where the needle enters the dorsal pouch of the distal interphalangeal (DIP) joint. The clinician should be aware that the following technique might be more dangerous to perform than techniques in which the foot can be held off the ground.

Materials

• 20-ga, 1 inch (0.90 x 25 mm) sterile, disposable needles
• 5 to 6 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• Arthrocentesis is performed with the limb bearing weight.
• For some horses, the procedure may be more safely performed by lifting the contralateral limb; however some horses, with the contralateral limb held, may fall to their knees when the needle is inserted. Application of a lip twitch is indicated for this procedure.
• The needle is inserted through the coronary band parallel or slightly oblique to the bearing surface at the dorsal midline (Fig. 24.2). Because the dorsal pouch of the DIP joint extends proximally for several centimeters, the joint is fairly easily accessed using the dorsal parallel approach (Fig. 24.3). (Although some anatomical drawings of the foot show the extensor process of the distal phalanx to extend above the coronary band, the extensor process lies below the coronary band.) Firm digital pressure for several seconds at this site before the needle is inserted may decrease pain and reaction from the horse. Some horses react violently to insertion of the needle by thrusting the limb upwards. To safely perform the procedure, the clinician and person holding the horse should anticipate this reaction and position themselves accordingly.
• Some clinicians, using the dorsal approach, insert the needle through a site on the midline one cm dorsal to coronary band, perpendicular to the bearing surface. This technique is more difficult to perform than the one just described.
• Fluid may drip from the needle, but correct placement of the needle is also indicated by easy injection of drug; the syringe may refill when pressure is removed from the plunger after injection.

Figure 24.2. To place a needle into the coffin joint, the needle is inserted through the coronary band at the dorsal midline, parallel to the bearing surface.

Figure 24.3. Because the dorsal pouch of the DIP joint extends proximally for several centimeters, the joint is easily accessed using the dorsal parallel approach. Six mL of radiocontrast solution were administered into this DIP joint.

Interpretation

• Analgesia of the DIP joint, using 5 or 6 mL of local anesthetic solution, also causes analgesia of the navicular apparatus, the toe region of the sole, and, probably, a portion of the third phalanx.
  Administration of a larger volume of local anesthetic solution (i.e., 10 mL) causes analgesia of the heel region of the sole.
• The gait should be evaluated 10 minutes after analgesia of the DIP joint. If evaluation of gait is delayed, diffusion of local anesthetic solution may result in desensitization of the heel region of the sole.

Proximal Interphalangeal (Pastern) Joint

We prefer the palmar/plantar approach to the pastern joint because the landmarks for needle placement are obvious, because synovial fluid is often obtained to verify proper needle placement, and because the foot is held, making the procedure safer than a dorsal approach where the needle is inserted with the limb bearing weight.

Materials

• 20-ga, 1 inch (0.90 x 25 mm) sterile, disposable needles
• 4 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb held.
• The needle is inserted perpendicular to the long axis of the pastern, close to the palmar border of the first phalanx, just proximal to the easily palpable transverse bony prominence on the proximopalmar aspect of the middle phalanx. The needle is inserted through skin with the joints of the lower limb in extension and then these joints are flexed and the needle is advanced into the proximal interphalangeal (PIP) joint (Fig. 24.4). Because the palmar pouch of the (PIP) joint extends proximally for several centimeters the joint is fairly easily accessed using the palmar/plantar approach (Fig. 24.5).
• Synovial fluid may drip from the needle.

Figure 24.4. For arthrocentesis of the proximal interphalangeal joint, a needle is inserted perpendicular to the long axis of the pastern, close to the caudal border of the first phalanx, just proximal to the transverse bony prominence on the proximopalmar aspect of the middle phalanx (arrow).

Figure 24.5. Because the palmar pouch of the PIP joint extends proximally for several centimeters this joint is fairly easily accessed using the palmar/plantar approach. Four mL of radiocontrast solution were administered into this PIP joint.

Metacarpophalangeal (Fetlock) Joint

Arthrocentesis of the fetlock joint performed using a lateropalmar approach in which the needle is inserted through the lateral collateral sesamoidian ligament is less likely to cause hemarthosis and subcutaneous inflammation than arthrocentesis through the proximal palmar pouch. This technique can be performed solo, but having the limb held in a flexed position by an assistant is helpful.

Materials

• 20-ga, 1.5 inch (0.90 x 38 mm) sterile, disposable needle
• 5 to 10mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is best performed from the lateral side with an assistant flexing the joint.
• A needle is inserted through the lateral collateral sesamoidian ligament between the articular surfaces of the distal metacarpus/tarsus and the lateral proximal sesamoid bone (Fig. 24.6). The ligament is the distal border of a depression formed, when the fetlock is flexed, by the palmar surface of the third metacarpus/metatarsus and the dorsal surface of the lateral, proximal sesamoid bone.
• Synovial fluid is usually observed to drip from the needle.

Figure 24.6. For arthrocentesis of the metacarpo(metatarso)phalangeal joint, a needle is inserted through the lateral collateral sesamoidian ligament. The ligament is the distal border of a depression formed, when the fetlock is flexed, by the palmar surface of the third metacarpus/metatarsus and the dorsal surface of the lateral, proximal sesamoid bone.

Carpal Joints

The carpus consists of 3 principal joints: radiocarpal (antebrachiocarpal), intercarpal (middle carpal or midcarpal), and carpometacarpal. The carpometacarpal joint communicates with the intercarpal joint so accessing the small carpometacarpal joint directly is unnecessary. The radiocarpal and intercarpal joints can be accessed from either a dorsal or a palmarolateral approach. The palmarolateral approach is more difficult but can be performed with the limb bearing weight.

Intercarpal (Middle or Midcarpal) Joint

Materials

• 20-ga, 1.0 inch (0.90 x 25 mm) sterile, disposable needles
• 10 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the carpus flexed. Some clinicians prefer an assistant to hold the limb, but one person can, usually without difficulty, lift the limb and insert a needle while maintaining sterility.
• The joint can be accessed medial or lateral to the tendon of the extensor carpi radialis muscle, but for ease, the lateral side is usually chosen. The joint, when flexed, is easily identified by a depression on either side of the tendon (Fig. 24.7).
• The needle should be inserted no further than 0.5 inch (12.6 mm) and slightly proximal to avoid damaging articular cartilage.
• Care should be taken to insert the needle at the center of the depression to avoid the tendon sheathes of the extensor carpi radialis and common digital extensor muscles.

Figure 24.7. For arthrocentesis of the radiocarpal or intercarpal joint, a needle is inserted medial or lateral to the tendon of the extensor carpi radialis muscle. The joints, when flexed, are easily identified as depressions on either side of the tendon. The higher needle has been placed in the radiocarpal joint and the lower needle has been placed in the intercarpal joint.

Radiocarpal Carpal (Antebrachiocarpal) Joint

Materials

• 20-ga, 1.0 inch (0.90 x 25 mm) sterile, disposable needles
• 10 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the carpus flexed. Some clinicians prefer an assistant to hold the limb, but one person can usually, without difficulty, lift the limb and insert a needle in a sterile manner.
• The joint can be accessed medial or lateral to the tendon of the extensor carpi radialis muscle. The joint, when flexed, is easily identified as a depression on either side of the tendon (Fig. 24.7). Because the depression on the lateral side is smaller and, thus, slightly less accessible, the medial side is sometimes chosen for arthrocentesis.
• Care should be taken to avoid penetrating the tendon sheathes of the extensor carpi radialis and common digital extensor muscles.

Humororadial, Humoroulnar, and Radioulnar (Elbow) Joint(s)

Because disease of the elbow joint is uncommon, arthrocentesis of this joint is seldom performed. Several approaches are described, but the authors are more familiar with the craniolateral approach.

Materials

• 20-ga, 1.5 inch (0.90 x 38 mm) sterile, disposable needles
• 10 to 15 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb bearing weight.
• Landmarks for injection are the lateral humeral epicondyle, the lateral tuberosity of the radius, and the lateral collateral ligament connecting these structures.
• The needle is inserted caudomedially at the cranial edge of the lateral, collateral ligament, two thirds of the distance from the humeral epicondyle to the lateral tuberosity of the radius (Fig. 24.8). Because periarticular administration of local anesthetic agent near the elbow joint can anesthetize motor nerves, some clinicians prefer to inject a relatively short-acting, local anesthetic solution (e.g., lidocaine), to avoid prolonged paralysis of the limb, if this complication occurs. Alternatively, saline can be injected and then aspirated to determine if the needle is placed correctly, before local anesthetic solution is administered.

Figure 24.8. For arthrocentesis of the radiohumeral joint, a needle is inserted craniomedially at the caudal edge (or caudomedially at the cranial edge) of the lateral, collateral ligament, two-thirds of the distance from the humeral epicondyle (upper arrow) to the lateral tuberosity of the radius (lower arrow).

Scapulohumeral (Shoulder) Joint

Because, for some horses, the shoulder joint communicates with the bicipital bursa, intra-articular administration of local anesthetic solution might anesthetize both structures.

Materials

• 18-or 20-ga, 3.5-inch (1.2 or 0.9 x 8.89-cm) sterile, disposable spinal needle
• 20 to 30 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb bearing weight.
• The needle should be inserted in the palpable notch between the cranial and caudal prominences of the lateral tuberosity of the humerus (Fig. 24.9).
• The needle is directed horizontally caudomedially at a 45° angle to the body.
• To penetrate the joint, the needle may need to be inserted 2 or more inches (5 cm).
• A distinct "pop" may be felt as the needle penetrates the fibrous joint capsule.
• For this joint, ease of injection is not a reliable indicator of correct placement of the needle, and joint fluid often fails to flow from the needle. Because periarticular administration of local anesthetic agent near the shoulder joint can anesthetize motor nerves, some clinicians prefer to inject a relatively short-acting, local anesthetic solution (e.g., lidocaine), to avoid prolonged paralysis of the limb, if this complication occurs. Alternatively, saline can be injected and then aspirated to determine if the needle is placed correctly, before local anesthetic solution is administered.

Figure 24.9. For arthrocentesis of the scapulohumeral joint a needle is inserted in the palpable notch between the cranial and caudal prominences of the lateral tuberosity of the humerus (arrows).

Tarsal (Hock) Joints

The tarsus is composed of four principal joints, the tarsocrural, proximal intertarsal, distal intertarsal, and tarsometatarsal joints. The tarsocrural and proximal intertarsal joints probably communicate in all horses. The distal intertarsal and tarsometatarsal joints directly communicate in some horses, and rarely, the proximal intertarsal joint may directly communicate with the distal intertarsal, and tarsometatarsal joints. Centesis of the distal intertarsal joint for the purpose of administering local anesthetic solution or a corticosteroid for diagnosis and treatment of disease of this joint may not be necessary. After administration of mepivacaine HCL or methylprednisolone acetate in the tarsometatarsal joint, there likely is a therapeutic concentration of these drugs in the distal intertarsal joint whether or not there is direct communication of these joints.

Tarsometatarsal Joint

Materials

• 20-ga, 1 or 1.5-inch needle (0.9 x 25 or 38-mm) sterile, disposable needles (some clinicians prefer a smaller gauge needle)
• 4 to 5 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is usually performed with the horse bearing weight on the limb. Some clinicians prefer to access the joint with the limb flexed.
• Using firm digital pressure, a small depression is palpable just proximal to the head of the fourth splint bone.
• The needle is inserted in a dorsomedial direction (Fig. 24.10).
• Fluid often drips from the needle.

Figure 24.10. For arthrocentesis of the tarsometatarsal joint, a needle is inserted in a dorsomedial and slightly distal direction at a small depression palpable just proximal to the head of the lateral splint bone.

Distal Intertarsal Joint

Materials

• 23 or 25-ga, 1-inch (0.6 or 0.5 x 25-mm) sterile, disposable needle
• 4 to 5 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• This procedure is performed with the horse bearing weight on the limb, with the clinician positioned on the contralateral side of the horse.
• The site of centesis is found by identifying the easily palpable medial eminence of the talus. Below and caudal to this eminence is a less discernible medial eminence of the central tarsal bone. Between, and distal to these eminences, is the site for needle insertion (Fig. 24.11). The needle is inserted perpendicular to the long axis of the limb, on the medial side of the tarsus in a palpable depression between the second, third, and central tarsal bones (Fig. 24.12). The needle should be inserted as proximal as possible in this space to avoid entering the tarsometatarsal joint. The site may be difficult to find, especially if the joint has severe degenerative disease.
• Successful insertion of the needle into the joint can be ascertained by easy administration of drug without subcutaneous swelling, and aspiration of drug.

Figure 24.11. The site of centesis of the distal intertarsal joint is found by identifying the easily palpable medial eminence of the talus (A). Below and caudal to this eminence is a less discernible medial eminence of the central tarsal bone (B). Between, and distal to these eminences, is the site for needle insertion (arrow).

Figure 24.12. For arthrocentesis of the distal intertarsal joint, a needle is inserted perpendicular to the long axis of the limb, on the medial side of the tarsus, in a palpable depression located midway between the dorsal and plantar surfaces of the tarsus and midway between and distal to palpable eminences (arrows) on the talus and central tarsal bones.

Tarsocrural (Tibiotarsal) and Proximal Intertarsal Joints

The tarsocrural joint, which usually directly communicates with the proximal intertarsal joint, is the largest joint in the hock. The joint can be accessed easily via the dorsal pouch or medioplantar or lateroplantar pouches. Penetration of the medial branch of the saphenous vein (which is usually readily visible) should be avoided during centesis of the dorsal pouch.

Materials

• 20-ga, 1 or 1.5-inch (0.90 x 25 or 38-mm) sterile, disposable needle
• 10 to 20 mL local anesthetic solution, if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the horse bearing weight on the limb.
• The dorsal pouch is usually palpable just distal to the medial maleolus of the tibia.
• The needle is inserted just medial or lateral to the saphenous vein, 2 cm distal to the medial maleolus (Fig. 24.13).
• Synovial fluid usually flows from the hub of the needle.

Figure 24.13. The tarsocural joint can be accessed easily via the dorsal pouch. Penetration of the medial branch of the saphenous vein (red line) should be avoided during centesis of the dorsal pouch.

Stifle

The stifle is composed of three compartments, the femoropatellar joint pouch, and the medial and lateral femorotibial joint pouches. The femoropatellar joint pouch and the medial femorotibial joint pouch directly communicate in about 65% of horses, but the lateral femorotibial joint pouch seldom directly communicates with the medial compartment or with the femoropatellar joint. To rule out the stifle as a site of disease causing lameness, local anesthetic solution should be administered into each pouch. If the compartments are to be anesthetized sequentially, we prefer to first anesthetize the femoropatellar joint and then the medial compartment of the femorotibial joint.

Femoropatellar Joint Pouch

Materials

• 20-ga, 1.5-inch (0.9 x 38-mm) sterile, disposable needle [For extremely large horses a 20-ga., 3.5-inch (8.89 cm) spinal needle may be needed.]
• 30 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb bearing weight.
• The needle is inserted caudoproximally, midway between the tibial tuberosity and the patella, between the middle and lateral patellar ligaments or between the middle and medial patellar ligaments (Fig. 24.14).
• Unless the joint is distended, fluid usually is not retrieved.

Figure 24.14. For arthrocentesis of the femoropatellar joint (A), the needle is inserted caudoproximally, midway between the tibial tuberosity and the patella, between the middle and medial patellar ligaments (or between the middle and lateral patellar ligaments). For arthrocentesis of the medial femorotibial joint (B), the needle is inserted perpendicular to the long axis of the limb, between the medial patellar and medial collateral ligaments, just dorsal to the proximal edge of the tibia. For arthrocentesis of the lateral femorotibial joint (C), the needle is inserted just dorsal to the proximal edge of the tibia perpendicular to the long axis of the limb caudal to the lateral patellar ligament.

Medial Femorotibial Joint Pouch

Materials

• 20-ga, 1.5-inch (0.9 x 38-mm) sterile, disposable needle
• 20 to 30 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb bearing weight.
• The needle is inserted perpendicular to the long axis of the limb, between the medial patellar and medial collateral ligaments just dorsal to the proximal edge of the tibia (Fig. 24.14).
• Synovial fluid is usually retrieved to indicate proper needle placement.

Lateral Femorotibial Joint Pouch

Materials

• 20-ga, 1.5-inch (0.9 x 38-mm) sterile, disposable needle
• 20 to 30 ml local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the horse bearing weight on the limb.
• The needle is inserted just dorsal to the proximal edge of the tibia perpendicular to the long axis of the limb just caudal to the lateral patellar ligament (Fig. 24.14).
• Synovial fluid is usually retrieved, indicating proper placement of the needle.

Coxofemoral (Hip) Joint

The hip joint is difficult to enter, and with improper needle placement, the sciatic nerve can be damaged.

Materials

• 25-ga (0.5-mm) needle and several mLs local anesthetic solution to inject subcutaneously at the site of needle placement (optional)
• 18-ga, 6-inch (1.2-mm x 15-cm) spinal needle. A longer needle is necessary to reach the joint in heavily muscled horses.
• 20 to 30 mL local anesthetic solution if intra-articular analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb bearing weight.
• The site of needle placement is the middle of the shelf of the anterior trochanter major. This site is difficult to palpate in most horses. It can be found by first identifying the more easily palpated posterior trochanter major. The anterior trochanter major is found about 2.5 inches (5 cm) ventral and cranial to this eminence.
• Local anesthetic solution is administered subcutaneously.
• The needle is inserted just dorsal to the middle of the shelf of the anterior trochanter major (Fig. 24.15). The needle is directed horizontal to the ground in a slightly cranial direction (Fig. 24.16).
• The joint is entered after inserting nearly the entire shaft of the needle.
• Synovial fluid can occasionally be aspirated. Aspiration of local anesthetic solution after administration indicates proper needle placement.

Figure 24.15. For arthrocentesis of the coxofemoral joint, an 18-ga, 6-inch (1.2 x 15-cm) spinal needle is inserted horizontal to the ground in a slightly cranial direction, just dorsal to the middle of the shelf of the anterior trochanter major.

Figure 24.16. For arthrocentesis of the coxofemoral joint, the needle is directed slightly cranially in a horizontal plane.

Centesis of the Navicular Bursa

Five different techniques for centesis of the navicular bursa have been described. The following technique was shown to be the most accurate.

Materials

• 25-ga (0.5-mm) needle and 0.5 - 1 mL local anesthetic solution to inject subcutaneously at the site of needle placement
• 20-ga, 3.5-inch (1.1 x 8.89-cm) spinal needle
• 2 to 3 mL local anesthetic solution if intra-bursal analgesia is required
• Sterile surgical gloves
• Lip twitch
• Sedation (optional)
• Hickman block (optional) to stabilize the foot in a flexed position
• 0.5 - 1 mL sterile, water-soluble, radiocontrast material (optional)
• Radiographic equipment (optional)

Technique

• The skin between the bulbs of the heel, immediately above the coronary band, is desensitized with 0.5 to 1 mL of local anesthetic solution.
• The foot is marked halfway between the most dorsal and the most palmar aspect of the coronary band and 1cm distal to the coronary band. This spot marks the site of the long axis of the navicular bone.
• The spinal needle is advanced toward the bisecting point between the sagittal plane of the foot and the long axis of the navicular bone (i.e., angled and advanced sagittally toward the mark on the hoof wall) (Fig. 24.17).
• The spinal needle is advanced until the tip of the needle contacts bone and the stylet is removed for administration of drug. The tip of the needle is determined to be within the navicular bursa by low resistance to injection and the ability to aspirate the injected contents of the syringe.
• To verify centesis of the bursa, 0.5 - 1 mL sterile, water-soluble radiocontrast solution can be administered along with the drug. On a laterally projected radiograph taken immediately after administration of contrast solution, the bursa appears as a comma shaped structure surrounding the caudal portion of the navicular bone (Fig. 24.18).

Figure 24.17. For centesis of the navicular bursa, the spinal needle is angled and advanced sagittally toward a mark on the hoof wall halfway between the most dorsal and the most palmar aspect of the coronary band and 1cm distal to the coronary band.

Figure 24.18. To verify centesis of the navicular bursa, 0.5 - 1 mL sterile, water-soluble radiocontrast solution can be administered along with the drug. On a laterally projected radiograph taken immediately after administration of contrast solution, the bursa appears as a comma shaped structure (arrow) surrounding the caudal portion of the navicular bone.

Centesis of the Digital Flexor Tendon Sheath

Centesis of the pouches (Fig. 24.19) of the deep digital flexor tendon sheath is difficult when the sheath is not distended with synovial fluid. An approach through the palmar annular ligament of the fetlock (palmar axial sesamoidean approach) was found to be reliable for consistent synoviocentesis of the digital flexor tendon sheath. The palmar axial sesamoidean approach is less likely to result in synovial hemorrhage than other approaches.

Figure 24.19. Pouches of the deep digital flexor tendon sheath are shown in this diagram.

Materials

• 20-ga, 1.5 inch (0.90 x 38 mm) sterile, disposable needle
• 10 to 15 mL local anesthetic solution if intra-synovial analgesia is required
• Sterile surgical gloves
• Lip twitch

Technique

• The procedure is performed with the limb flexed.
• The needle placed through the skin at the level of the midbody of the lateral proximal sesamoid bone, through the palmar annular ligament, 3 mm axial to the palpable palmar border of the lateral proximal sesamoid bone and immediately palmar to the palmar digital neurovascular bundle (Fig. 24.20).
• The needle is inserted in a transverse plane and advanced at an angle to the sagittal plane, aiming toward the central intersesamoidean region to a depth of 1.5 to 2.0 cm.

Figure 24.20. For centesis of the deep digital flexor tendon sheath, the needle is inserted in a transverse plane and advanced at an angle to the sagittal plane, aiming toward the central intersesamoidean region to a depth of 1.5 to 2.0 cm. In this cross section through the proximal sesamoid bones, A = flexor tendons, B = proximal sesamoid bones, C = metacarpus / metatarsus and D = extensor tendon.

Centesis of a Cervical Facet Joint

Centesis of a cervical facet joint is performed in horses with signs of neck pain, and radiographic, ultrasonographic or scintigraphic evidence of disease of a facet joint. Centesis is usually performed for administration of local anesthetic solution or a corticosteroid. Lesions are most commonly found in the joints of facets joining cervical vertebrae 5 & 6 and 6 & 7. Different approaches to these joints are described, but all techniques rely on ultrasonic guidance.

Materials

• Ultrasonographic equipment with a 5 or 7.5 MHz sector or linear transducer
• 25-ga (0.5-mm) needle and local anesthetic solution
• A sedative such as xylazine or detomidine
• A 20 or 18-ga, 3.5-in (0.90 or 1.2-mm, 8.89-cm), spinal needle
• Because the procedure is usually performed for horses suspected to have arthritis of facet joints, intra-articular medication such as a corticosteroid may be administered.

Technique

• The site of cervical facet arthropathy is identified using diagnostic imaging.
• For the average sized horse, the width of a cervical vertebra is the width of a hand palm (Fig. 24.21). The approximate site of centesis is found by placing hand over hand from the poll along the cervical spine, each hand covering the width of a cervical vertebra. The transverse processes of the cervical vertebrae are palpable and the facet joint is located above the caudal extent (dorsal tubercule) of the transverse process (Fig. 24.22).
• The region of the site of centesis is surgically prepared.
• The joint between two adjacent articular facets is identified ultrasonographically in the center of the imaging field, using a probe that has been surgically scrubbed or placed in a sterile surgical glove filled with coupling gel. The skin should be liberally soaked with isopropyl alcohol to achieve acoustic coupling.
• With the ultrasound probe in place, the site of centesis just above the probe is again surgically prepared and local anesthetic solution is administered subcutaneously.
• The spinal needle is inserted just dorsal to the ultrasound probe and advanced at an angle (about 30-45°) that will aim it at the approximate site of the joint (Fig. 24.23). The joint space can be widened if the horse's neck is flexed away from the site of centesis.
• Using ultrasonic guidance, the needle is directed into (or at least close to) the joint space (Fig. 24.24) and drug is injected.
• Joint fluid can often be aspirated if the needle is placed correctly. If the needle is within the joint, drug cannot be visualized ultrasonographically as it is administered.

Figure 24.21. For the average sized horse, the width of a cervical vertebra is the width of a hand palm. The approximate site of centesis is found by placing hand over hand from the poll along the cervical spine, each hand covering the width of a cervical vertebra.

Figure 24.22. The transverse processes (arrows) of the cervical vertebrae are palpable and the facet joint is located above the caudal extent (dorsal tubercle) of the transverse process. A 20 ga needle has been inserted into the vertebral joint C5-6.

Figure 24.23. For centesis of a cervical facet joint, a 20-ga, 3.5-in (0.9-mm, 8.89-cm), spinal needle is inserted and advanced at an angle that will aim it at the approximate site of the joint which is identified using ultrasonography.

Figure 24.24. Using ultrasonic guidance, the needle is directed into (or at least close to) the cervical facet joint space (middle arrow) and drug is injected. Other arrows are pointed at the facets.

Complications

The needle cannot be placed in some joints with advanced arthropathy. Periarticular administration of corticosteroid, however, may be beneficial.

Centesis of the Temporomandibular (TM) Joint

The TM joint in the horse has rarely been mentioned as problematic, however, with recent advancements in equine dentistry and geriatric medicine we are finding that the TM joint may develop the same diseases, as do other joints in the horse. Centesis of the TM joint is made through a caudodorsal approach.

Materials

• 20-ga, 1.5 inch (0.90 x 38 mm) sterile disposable needles
• 5 mL local anesthetic solution if intra-articular analgesia is required
• Sedative
• Sterile gloves
• Lip twitch
• An assistant facilitates the procedure by controlling the position of the head as well as manipulating the mandible in order to palpate the joint.

Technique

• The procedure is performed on a sedated horse.
• The lateral margin of the mandibular condyle is identified approximately midway on a line between the lateral canthus of the eye and the base of the ear (Fig. 24.25). Its location can be confirmed by palpation while manipulating the mandible from side to side.
• Locate a soft depression 1 - 2 cm dorsal and 1 cm caudal to the condyle.
• The needle is inserted in this soft depression in a rostral ventral direction to a depth of approximately 1 inch (25 mm) (Fig. 24.26).
• Fluid may fill the needle hub. If the needle hits bone, the needle should be partially withdrawn and directed more ventrally. If the needle is directed too far ventrally, it may become embedded in the articular disc and should be partially withdrawn.

Figure 24.25. The lateral margin of the mandibular condyle is identified on a line approximately midway between the lateral canthus of the eye and the base of the ear.

Figure 24.26. For centesis of the temporomandibular joint, a 20-ga, 1.5 in needle is inserted in a rostral ventral direction to a depth of approximately 1 inch in a soft depression 1 - 2 cm dorsal and 1 cm caudal to the mandibular condyle.

Suggested Readings

de Mercado RV, Stover SM. Comparison of six techniques for a lateral approach to the coffin joint. In: Proceedings of the 44th Annual Proceedings American Association of Equine Practitioners, December 6-9, 1998, Baltimore, MD 178-179. - Available from www.ivis.org -

Grisel GR, Grant BD, Rantanen NW. Arthrocentesis of the equine cervical facets. In: Proceedings of the 42nd Annual Proceedings American Association of Equine Practitioners, December 8-11, 1996, Denver, CO. 197-198.

Hassel DM, Stover SM, Yarbrough TB, Drake CM, Taylor KT. Palmar-plantar axial sesamoidean approach to the digital flexor tendon sheath in horses, J Am Vet Med Assoc 217:1343, 2000.

Lewis RD. Techniques for arthrocentesis of equine shoulder, elbow stifle and hip joints. In: Proceedings of the 42nd Annual Proceedings American Association of Equine Practitioners, December 8-11, 1996, Denver, CO. 55-63.

May KA, Moll HD, Howard RD, Pleasant RS, Gregg JM. Arthroscopic anatomy of the equine temporomandibular joint. Veterinary Surgery 30:564-571, 2001. - PubMed -

Misheff M, Stover SM. Comparison of two techniques for arthrocentesis of the equine metacarpophalangeal joint. Equine Vet J 23:273-276, 1991. - PubMed -

Moyer W, Carter GK. Techniques to facilitate intra-articular injection of equine joints. In: Proceedings of the 42nd Annual Proceedings American Association of Equine Practitioners, December 8-11, 1996, Denver, CO. 48-54.

Schramme MC, Boswell JC, Hamhoughias K, Toulson K, Viitanen M. An in vitro study to compare 5 different techniques for injection of the navicular bursa in the horse. Equine Vet J 32:263, 2000. - PubMed -

Schumacher John, Schramme MC, Schumacher Jim, DeGraves F, Smith RKW, Coker M. A review of recent studies concerning diagnostic analgesia of the equine forefoot. In: Proceedings of the 49th Annual Proceedings American Association of Equine Practitioners, November 21-25, 2003, New Orleans, LA. 312-316.  - Available from www.ivis.org -