How to Inject the Synovial Cavities of the Digit · a dorsal perpendicular approach to the DIP joint prompted investigation of a palmar approach to the DIP joint.10 The site for injection

How to Inject the Synovial Cavities of the Digit

John Schumacher, DVM, MS, Diplomate ACVIM*; and Ray Wilhite, PhD

Authors’ addresses: Equine Sports Medicine Program (Schumacher) and Department of Anatomyand Physiology (Wilhite), College of Veterinary Medicine, Auburn University, Auburn, AL 36849;e-mail: [email protected]. *Corresponding and presenting author. © 2012 AAEP.

1. Introduction

Arthrocentesis of the equine interphalangeal jointsand synoviocentesis of the digital synovial sheath iscommonly performed for diagnostic analgesia aspart of a lameness examination and to medicatethese structures. The techniques for arthrocente-sis are the same for the forelimb and the hind limb.Restraint is achieved by applying a lip twitch to thehorse. Tranquilization or sedation is rarely usedfor restraint when centesis of these structures ispart of a lameness examination, but in some casestranquilizing or sedating the horse may be neces-sary to increase the safety of the procedure. Ad-ministration of a low dose of xylazine, detomidine, oracepromazine is unlikely to interfere with gait eval-uation1–4 and in some cases may even accentuatelameness. If centesis is performed with the footbearing weight, the contralateral limb can be heldby an assistant. Some horses, however, may buckleat the carpus when the needle is inserted, causinginjury if the carpus strikes the ground.

2. Materials and Methods

Arthrocentesis of the Distal Interphalangeal JointAt least 6 approaches to the distal interphalangeal(DIP) joint have been described: the dorsal perpen-dicular, the dorsal parallel, the dorsal inclined, thedorsolateral, the lateral, and the palmar ap-

proaches. A 20- or 21-gauge, 1- to 1.5-inch (2.54- to3.8-cm) needle is commonly used for arthrocentesisof the DIP joint. A 20-gauge, 3.5-inch (9-cm) spinalneedle is used for the palmar approach. When us-ing a dorsal approach to the DIP joint, the limb canbe held or bearing weight (Fig 1).

Dorsal Perpendicular and Dorsolateral Approaches to theDIP Joint

For the dorsal perpendicular approach, the needle isinserted at the proximal edge of the coronet, approx-imately 0.75 inch (�2 cm) lateral or medial to themidpoint of the coronet (ie, at the edge of the exten-sor tendon) (Fig. 2). The needle is directed distally,perpendicular to the bearing surface of the hoof.5

A slight variation of the dorsal perpendicular ap-proach is the dorsolateral approach, in which theneedle is inserted at the same site and directedbeneath the extensor tendon, aiming for the mid-dle sagittal plane of the foot behind the extensorprocess of the distal phalanx (Fig. 3).5–9 Depth ofpenetration is about 1 inch (2.54 cm). Synovialfluid usually appears in the needle hub, but accu-racy of needle placement can also be determinedby ease of injection. After injection, the syringemay refill when pressure on the plunger isreleased.

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Dorsal Parallel Approach to the DIP JointFor a dorsal parallel approach, the needle is insertedparallel to the bearing surface of the foot through orimmediately proximal to the coronary band (Fig. 4).In the primary author’s experience, firm digitalpressure at the site of arthrocentesis immediatelybefore insertion of the needle may lessen the horse’sreaction to the procedure. The needle can be in-serted on the middle sagittal plane or slightly me-dial or lateral to this plane. The needle passesthrough the digital extensor tendon to enter thedorsal pouch of the DIP joint, which covers most ofthe dorsal aspect of the middle phalanx. Insertingthe needle too far proximal to the coronary band fora parallel approach may result in arthrocentesis of adistodorsal pouch of the proximal interphalangealjoint (Fig. 5). We are unaware of any reports ofcomplication caused by needle puncture of the digi-tal extensor tendon other than a report of mineral-ization in the tendon at the site ofinjection.10 Gandini11 speculated that administra-tion of corticosteroid (with subsequent leakage atthe injection site) may be the cause of this compli-cation. If mineralization of the digital extensortendon is a potential complication of arthrocentesisof the DIP joint, its occurrence probably is insignif-icant. Using a variation of the dorsal parallel ap-proach, the dorsal inclined approach, a needle isinserted perpendicular to the skin surface immedi-ately proximal to the coronary band (Fig. 6). Thisapproach, reported by Kaneps,12 was found to be

more accurate and easier to perform than was thedorsal perpendicular or dorsolateral approaches foraccessing the DIP joint.11

Lateral Approach to the DIP JointThe DIP joint also can be entered using a lateralapproach.13,14 This approach appears to elicit lessreaction than other approaches. The landmark forneedle insertion is a depression in the proximal bor-der of the lateral collateral cartilage palpated nearthe palmar border of the middle phalanx (Fig. 7).A 1-inch (2.54-cm), 20- to 22-gauge needle is insertedthrough the skin, just above the palpable depressionin the proximal edge of the lateral collateral carti-lage. The needle is directed medially at a 45° angledistally and 20° palmar to penetrate the palmarpouch of the DIP joint (Fig. 8). The proximopalmarpouch of the DIP joint is entered, usually at a depthof penetration less than 1 inch (2.54 cm). Using thelateral approach to the DIP joint, the navicularbursa or digital tendon sheath is often inadvertentlyentered if the needle is inserted palmar to the rec-

Fig. 1. When using a dorsal approach to the distal interphalan-geal (DIP) joint, the limb can be held or bearing weight.

Fig. 2. For the dorsal perpendicular approach to the DIP joint,the needle is inserted at the proximal edge of the coronet, approx-imately 0.75 inch (�2 cm) lateral or medial to the midpoint of thecoronet (ie, at the edge of the extensor ligament). The needle isdirected distally, perpendicular to the bearing surface of the hoof.

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ommended site of insertion, particularly if a needlelonger than 1 inch (2.54 cm) is used, or if the proce-dure is performed with the limb held in a flexedposition.13,14 The lateral approach appears to beaccurate for arthrocentesis of the DIP joint onlywhen a needle no longer than 1 inch is inserted withthe horse standing squarely.14

Palmar Approach to the DIP JointA palmar approach to the DIP joint was described byMcIlwraith and Goodman,15 who cited a report ofthe procedure described in a German publication.10

In the German publication, complication of perios-teal reaction at the site of capsular attachment on tothe distal phalanx and hemorrhage associated witha dorsal perpendicular approach to the DIP jointprompted investigation of a palmar approach to theDIP joint.10 The site for injection is a point on thepalmar midline slightly proximal to the deepest in-dentation of the fossa proximal to the bulbs of theheel. A 3.5-inch (9-cm) spinal needle is directeddorsally aiming for a point halfway between thecoronet and the bearing surface of the hoof at the toe

(Fig. 9). The advantages cited for using this tech-nique are less vascularity of periarticular structuresand the large size of the palmar pouch of the DIPjoint. Obvious disadvantages of a palmar approachare that the deep digital flexor tendon must bepenetrated to access the joint and the close prox-

Fig. 3. For a dorsolateral approach to the DIP joint, the needleis inserted at the proximal edge of the coronet, approximately0.75 inch (�2 cm) lateral or medial to the midpoint of the coronet(ie, at the edge of the extensor ligament). The needle is directeddistally beneath the ligament at an angle aiming for the middlesagittal plane of the foot, behind the extensor process of the distalphalanx.

Fig. 4. For a dorsal parallel approach to the DIP joint, theneedle is inserted near or on the midline, parallel to the bearingsurface of the foot through or immediately proximal to the coro-nary band.

Fig. 5. Inserting the needle too far proximal to the coronaryband for a parallel approach to the DIP joint may result inarthrocentesis of a distodorsal pouch (arrow) of the proximalinterphalangeal joint.



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imity of the navicular bursa. We are unaware ofany studies that have examined the accuracy of thisapproach.

The clinician should be aware that administrationof 5 or 6 mL of local anesthetic solution into the DIPjoint desensitizes not only the DIP joint but also thetoe region of the sole and the navicular bone and itssupporting structures.16–18 When a large volume(ie, 10 mL) of local anesthetic solution is adminis-tered into the DIP joint, the palmar portion of thesole is also desensitized.19

Arthrocentesis of the Proximal Interphalangeal JointAt least four approaches to the proximal interpha-langeal (PIP) (pastern) joint have been described.These include a dorsal approach,6,7,20 a dorsolateralapproach,5,8,20 a palmaroproximal approach,21 and alateral approach.22 Synovial fluid is frequently ob-served with the palmaroproximal and lateral ap-proaches21,22 but is observed rarely using the otherapproaches. Three of these four methods for ar-throcentesis of the PIP joint were evaluated for ac-curacy by Poore et al, who found that studentsinexperienced in arthrocentesis of the PIP joint wereonly 32%, 48%, and 36% successful when performingthe dorsal, dorsolateral, and palmaroproximal ap-

Fig. 6. To perform the dorsal inclined approach to the DIP joint,a needle is inserted near or on the midline, perpendicular to theskin surface immediately proximal to the coronary band.

Fig. 7. The landmark for needle insertion for a lateral approachto the DIP joint is a depression in the proximal border of thelateral collateral cartilage palpated near the palmar border of themiddle phalanx.

Fig. 8. For the lateral approach to the DIP joint, a 1-inch (2.54-cm), 20- to 22-gauge needle is inserted through the skin, justabove the palpable depression in the proximal edge of the lateralcollateral cartilage. The needle is directed medially at a 45°angle distally and 20° palmar to penetrate the palmar pouch ofthe DIP joint.



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proaches, respectively.23 The lateral approach wasnot evaluated in this study.

A 20-gauge, 1.5-inch (3.8-cm) needle is used forthe dorsal and dorsolateral approaches, but a 1-inch(2.5-cm) needle is sufficient for the lateral and pal-maroproximal approaches. The palmaroproximalapproach is performed with the limb held, and thelateral approach is performed with the limb bearingweight. The dorsal and dorsolateral approaches tothe PIP joint can be performed with the limb held orbearing weight.

Dorsal Approach to the PIP JointTo perform the dorsal approach to the PIP joint asdescribed by Wheat,7 the needle is inserted on thedorsal midline about 1 cm distal to an imaginaryline drawn between the medil and lateral eminencesfor attachment of the collateral ligaments on thedistal end of the proximal phalanx (Fig. 10) and isdirected obliquely distally and medially. To per-form the dorsal approach to the PIP joint as de-scribed by Stashak,20 the needle is inserted on thedorsal midline one-half inch (1.3 cm) proximal to theimaginary line between the medial and lateral em-inences on the distal end of the proximal phalanxand directed slightly distally and slightly medially(Fig. 10).

Dorsolateral Approach to the PIP JointTo perform the dorsolateral approach as describedby Gabel,6 the PIP joint is entered by placing a

needle at the lateral edge of the common digitalextensor tendon, about one-half inch (1.3 cm) off themiddle sagittal plane of the limb on an imaginaryline drawn between the medial and lateral emi-nences for attachment of the collateral ligaments onthe distal end of the proximal phalanx (Fig. 11).The needle is directed obliquely distally and medi-ally toward the dorsal midline. A variation of thisapproach is to insert the needle about one-halfinch (1.3 cm) below the imaginary line drawn be-tween the medial and lateral eminences for at-tachment of the collateral ligaments on the distalend of the proximal phalanx, one-half inch (1.3cm) from the middle sagittal plane of the limb andto direct the needle medially, parallel to theground (Fig. 11).5

Lateral Approach to the PIP JointTo perform the lateral approach as described byCanonici,22 the PIP joint is entered by inserting theneedle directly through the lateral collateral liga-ment midway between the eminences for the attach-ment of the collateral ligament on the proximal andmiddle phalanges. The needle is directed in aslightly proximal to distal direction (Fig. 12). Sy-novial fluid usually flows from the needle to indicatethat the needle has entered the joint. We are un-aware of studies comparing the efficacy of this ap-proach to the PIP joint with other approaches to the

Fig. 9. The site for injection for the palmar approach to the DIPjoint is a point on the palmar midline slightly proximal to thedeepest indentation of the fossa proximal to the bulbs of theheel. A 3.5-inch (9-cm) spinal needle is directed dorsally, aimingfor a point halfway between the coronet and the bearing surfaceof the hoof at the toe.

Fig. 10. To perform the dorsal approach to the PIP joint asdescribed by Wheat6 (needle A), the needle is inserted on thedorsal midline about 1 cm distal to an imaginary line drawnbetween the medial and lateral eminences for attachment of thecollateral ligaments on the distal end of the proximal phalanx andis directed obliquely distally and medially. To perform the dor-sal approach to the PIP joint as described by Stashak19 (needleB), the needle is inserted on the dorsal midline one-half inch (1.3cm) proximal to the imaginary line between eminences and di-rected slightly distally and slightly medially.



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joint or reports of complications associated withplacing a needle directly through the collateral lig-ament of the joint.

Dorsolateral Approach to the PIP JointTo perform the palmaroproximal approach to thePIP joint as described by Miller et al,21 the needle isinserted into a “V”-shaped depression formed by thepalmar aspect of the proximal phalanx dorsally andthe lateral branch of the superficial flexor tendon asit inserts on the middle phalanx palmarodistally(Fig. 13). The needle is directed distomedially atan angle of 30° from the transverse plane. Thepalmaroproximal approach was found to be ofteninaccurate, with inadvertent injection of the digitalsynovial sheath when attempted by veterinary stu-dents without prior experience.23

Palmarolateral Approach to the PIP JointA palmarolateral approach to the PIP joint was re-ported by Moyer and Carter, who described the siteof needle insertion to be immediately proximal to thetransverse bony prominence on the proximopalmarborder of the middle phalanx.5 The needle is in-serted perpendicular to the sagittal plane close tothe palmar border of the proximal phalanx (Fig. 14).To our knowledge, accuracy of the palmarolateralapproach has not been investigated.

Synoviocentesis of the Digital Synovial SheathThe digital synovial sheath can be entered at any ofthe lateral pouches evident along its length, which isfrom the distal portion of the third metacarpus/metatarsus to the palmar aspect of the proximal halfof the middle phalanx. When the sheath is effused,these pouches are visible in places where the sheathis not encased by annular ligaments (Fig. 15). Evenwhen the sheath is not effused, it often can be en-tered on the palmar aspect of the pastern betweenthe proximal and distal digital annular ligaments,where the deep digital flexor tendon lies close to theskin (Fig. 16). To access the pouch at this location,the point of the needle must remain superficial tothe deep digital flexor tendon. The appearance ofsynovial fluid in the needle hub indicates successfulsynoviocentesis.

A primary indication for synoviocentesis of thedigital synovial sheath is diagnosis of and treatmentfor various traumatic, infectious, and inflammatorydisorders of the sheath.24 In these cases, thesheath is usually effused, thereby simplifying syno-viocentesis. An additional indication for synovio-centesis is diagnostic analgesia, in which case, thesheath is often not effused, thus hampering synovio-centesis. The palmar axial sesamoidean approachto the digital synovial sheath described by Hassel etal was 100% accurate in accessing the sheath whenthe sheath was not distended with synovial fluid.24

Fig. 11. To perform the dorsolateral approach to the PIP joint, aneedle is placed at the lateral edge of the common digital extensortendon, about one-half inch (1.3 cm) from the center of an imag-inary line drawn between the medial and lateral eminences forattachment of the collateral ligaments on the distal end of theproximal phalanx. The needle (A) is directed obliquely distallyand medially toward the dorsal midline. A variation of thisapproach is to insert the needle about one-half inch (1.3 cm) belowthe imaginary line drawn between the medial and lateral emi-nences for attachment of the collateral ligaments, one-half inch(1.3 cm) from the dorsal midline and to direct the needle (B)medially, parallel to the ground.

Fig. 12. To perform the lateral approach to the PIP joint, aneedle is inserted directly through the lateral collateral ligamentmidway between eminences for the attachment of the collateralligament on the proximal and middle phalanges. The needle isdirected in a slightly proximal-distal direction.



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To perform the palmar axial sesamoidean ap-proach to the digital synovial sheath, a 20-gauge,1-inch (2.5-cm) needle is placed at the level of themidbody of the lateral proximal sesamoid bone, 3mm axial to its palpable palmar border and imme-

diately palmar to the palmar digital neurovascularbundle (Fig. 17). The needle is advanced throughthe skin and palmar annular ligament of the fetlockand directed at a 45° angle to the sagittal plane,aiming toward the central intersesamoidean region,

Fig. 13. To perform the palmaroproximal approach to the PIPjoint, the needle is inserted into a “V”-shaped depression formedby the palmar aspect of the proximal phalanx dorsally and thelateral branch of the superficial flexor tendon as it inserts on themiddle phalanx palmarodistally. The needle is directed disto-medially at an angle of 30° from the transverse plane.

Fig. 14. To perform the palmarolateral approach to the PIPjoint, the needle is inserted perpendicular to the sagittal planeclose to the palmar border of the first phalanx proximal to thetransverse boney prominence on the proximopalmar border of themiddle phalanx.

Fig. 15. When the digital synovial sheath is effused, pouches arevisible in places where the sheath is not encased by annularligaments.

Fig. 16. The digital synovial sheath can be entered at any of thepouches evident along its length. Even when the digital syno-vial sheath is not effused, it often can be entered on the palmaraspect of the pastern between the proximal and distal digitalannular ligaments, where the deep digital flexor tendon lies closeto the skin (needle A).



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to a depth of about 0.5 to 0.75 inch (1.3 to 1.9 cm).A possible disadvantage of this approach is that theneedle is likely to penetrate the flexor tendons.24

It is unlikely, in our experience, that penetration ofthe flexor tendons by the needle has any clinicalsignificance.

Figures 4, 7, 10, 13, 15, and 16 are adapted fromMoyer W, Schumacher J, Schumacher J. A Guide toEquine Joint Injections and Regional Anesthesia,courtesy of Dr. Amy Benz, Academic Veterinary So-lutions LLC.

References1. Dyson SJ, Kidd L. Comparison of responses to analgesia of the

navicular bursa and intraarticular analgesia of the distal inter-phalangeal joint in 59 horses. Equine Vet J 1993;25:93–98.

2. Buchner HH, Kubber P, Zohmann E, et al. Sedation andantisedation as tools in equine lameness examina-tion. Equine Vet J Suppl 1999;30:227–230.

3. Ross MW. Movement. In: Ross MW, Dyson SJ, editors.Diagnosis and Management of Lameness in the Horse. StLouis: WB Saunders; 2003:61–73.

4. Furst AE. Diagnostic anaesthesia. In: Auer JA, Stick JA.Equine Surgery. 3rd ed. St Louis: Saunders Elsevier; 2006:901–922.

5. Moyer W, Carter GK. Techniques to facilitate intra-articu-lar injection of equine joints, in Proceedings. Am AssocEquine Pract 1996;42:48–63.

6. Gabel AA. Administration of medicine. In: Bone JF, CatcottEJ, Gabel AA, editors. Equine Medicine and Surgery. Wheaton,IL: American Veterinary Publications, Inc; 1963:93–118.

7. Wheat JD, Jones K. Selected techniques of regional anesthe-sia. Vet Clin North [Am Large Anim Pract] 1981;3:223–246.

8. Riebold TW, Goble, DO, Geiser DR. Large Animal Anesthe-sia, Principals and Techniques. Ames, IA: Iowa State Uni-versity Press; 1982:124.

9. Stashak TS. Examination for lameness. In: Stashak TS,editor. Adams’ Lameness in Horses. 5th ed. Philadel-phia: Lea and Febiger; 2002:113–183.

10. Boening KJ. Komplikationen bei diagnostischen und chir-urgischen Eingriffen am Hufgelink des Pferdes (Complica-tions attending diagnostic and surgical operations on thehoof joint of horse). Der Praktische Tierarzt 1980;10:863–866.

11. Gandini M. Comparison of three dorsal techniques forarthrocentesis of the distal interphalangeal joint in horses.J Am Vet Med Assoc 2007;231:254 –258.

12. Kaneps AJ. Diagnosis of lameness. In: Hinchcliff KW,Kaneps AJ, Geor RJ, editors. Equine Sports Medicine andSurgery. Philadelphia: WB Saunders Co; 2004:143–201.

13. Vazquez R, Stover SM, Taylor KT, et al. Lateral approachfor arthrocentesis of the distal interphalangeal joint inhorses. J Am Vet Med Assoc 1998;212:1413–1418.

14. Vazquez R, Stover SM. Comparison of six techniques for alateral approach to the coffin joint, in Proceedings. Am As-soc Equine Pract 1998;44:178–179.

15. Goodman NL, Baker BK. Lameness diagnosis and treat-ment in the Quarter Horse racehorse. Vet Clin North Am[Equine Pract] 1990;6:85–108.

16. Schebitz H. Podotrochlosis in the horse. Proc Am AssocEquine Pract 1964;10:49–53.

17. Pleasant RS, Moll HD, Ley WB, et al. Intra-articular an-aesthesia of the distal interphalangeal joint alleviates lame-ness associated with the navicular bursa in horses. Vet Surg1997;26:137–140.

18. Schumacher J, Steiger R, Schumacher J, et al. Effects ofanalgesia of the distal interphalangeal joint or palmar digitalnerves on lameness caused by solar pain in horses. Vet Surg2000;29:54–58.

19. Schumacher J, Schumacher J, DeGraves F, et al. A compar-ison of the effects of two volumes of local analgesic solution inthe distal interphalangeal joint of horses with lamenesscaused by solar toe or solar heel pain. Equine Vet J 2001;33:265–268.

20. Stashak TS. Diagnosis of lameness. In: Stashak TS, editor.Adams’ Lameness in Horses. 4th ed. Philadelphia: Lea andFebiger; 1987:100–156.

Fig. 17. To perform the palmar axial sesamoidean approach tothe digital synovial sheath, the fetlock is flexed and a needle isplaced at the level of the midbody of the lateral proximal sesam-oid bone axial to its palpable palmar border and immediatelypalmar to the digital neurovascular bundle. The needle is ad-vanced through the skin and annular ligament of the fetlock anddirected at a 45° angle to the sagittal plane, aiming toward thecentral intersesamoidean region.



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21. Miller SM, Stover SM, Taylor KT, et al. Palmaroproximalapproach for arthrocentesis of the proximal interphalangealjoint in horses. Equine Vet J 1996;28:376–380.

22. Canonici F. Lateral approach for arthrocentesis of the prox-imal interphalangeal joint of the horse. Equine Pract 1997;19:20–23.

23. Poore LAB, Lambert KL, Shaw DJ, et al. Comparison of threemethods of injecting the proximal interphalangeal joint inhorses. Vet Rec 168:302–305-308.

24. Hassel DM, Stover SM, Yarbrough TB, et al. Palmar-plan-tar axial sesamoidian approach to the digital flexor tendonsheath in horses. J Am Vet Med Assoc 2000;217:1343–1347.





Documents

How to Inject the Synovial Cavities of the Digit · a dorsal perpendicular approach to the DIP joint prompted investigation of a palmar approach to the DIP joint.10 The site for injection