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Proceeding of the Belgian Equine Practitioners Society

28 November 2015 - Leuven, Belgium

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Reprinted in the IVIS website with the permission of BEPS

Belgian Equine Practitioners Society Study Days Nov. 2016 - Leuven, Belgium

9

DIAGNOSTIC ANALGESIA OF THE FOOT: TECHNIQUES &

INTERPRETATIONS

PROF. DR. MICHAEL SCHRAMME, JOHN SCHUMACHER, JIM SCHUMACHER AND WILHITE

ECOLE NATIONALE VETERINAIRE DE LYON ( FRANCE) AUBURN UNIVERSITY, ALABAMA (USA)

UNIVERSITY OF TENNESSEE, KNOXVILLE, TENNESSEE (USA)

Summary

A palmar digital nerve block anaesthetises the entire foot, rather than just its palmar half. To

avoid partially anaesthetising the proximal interphalangeal joint, the palmar digital nerves

should be anaesthetised near or distal to the proximal margin of the collateral cartilages. A

basilar sesamoid nerve block may ameliorate pain within the metacarpo (metatarso)

phalangeal joint. Mepivacaine administered into the distal interphalangeal (DIP) joint

desensitises the DIP joint and the subsynovial palmar digital nerves thereby also anesthetising

the navicular apparatus, the toe region of the sole and the digital portion of the deep digital

flexor tendon (DDFT). Even though analgesia of the DIP joint results in analgesia of the

navicular bursa, analgesia of the navicular bursa does not result in analgesia of the DIP joint.

Analgesia of the DDFT sheath likely desensitises only structures within the sheath and the

DDFT distal to the sheath.

Anaesthesia of the palmar digital nerves (Palmar digital nerve block-PDNB)

The PDNB is sometimes referred to as the “heel block” because clinicians have long believed

that a positive response to anaesthesia of the palmar digital nerves localizes pain to the palmar

third or half of the foot, including the palmar portion of the DIP joint. Easter et al.1 found,

however, that anaesthesia of the palmar digital nerves just proximal to the bulbs of the heel

alleviated lameness caused pain in the DIP joint, indicating that the palmar digital nerves

innervate the entire DIP joint.

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10

The PD nerves should be anaesthetised near or distal to the proximal margin of the collateral

cartilage.2,3 One theoretical advantage of anaesthetizing the palmar digital nerves as far

distally as possible is that anaesthesia of the dorsal branches of the palmar digital nerve is

more likely to be avoided (Beeman 1988). According to results of the study by Sack4 and that

of Easter et al.,1 however, the dorsal branches are unlikely to contribute much more than

sensory innervation to the dorsal aspect of the coronary band and dorsal laminae of the foot.

Recent research suggests the even the dorsal laminae of the foot are desensitised by a PDNB.5

Research indicates, therefore, that a PDNB anaesthetises the entire foot.

A more important reason for depositing local anaesthetic solution as far distally in the pastern

as possible when performing a PDNB is that more proximal deposition of local anaesthetic

solution increases the likelihood of causing analgesia of the pastern joint.6

Ring block

A ring block, performed at the level of a PDNB is unlikely to result in a positive response

after a negative response to a PDNB because the dorsal branches of the palmar digital nerves

contribute little to sensation within the foot.1,4,5 The PDNB will already have anaesthetised the

entire foot. The use of a pastern ring block performed at mid pastern level, however, should

be considered as a better alternative to the basilar sesamoid (basisesamoid) nerve block

(BSNB) or abaxial sesamoid nerve block (ASNB) because these blocks may inadvertently,

partially or entirely desensitise the metacarpo/metatarso phalangeal (MC/MT-P) (fetlock)

joint in addition to the entire foot and pastern, which erroneously localise pain to the foot or

pastern in horses with fetlock pain. A positive response to a ring block performed at mid

pastern level, after a negative response to a PDNB, localizes lameness to the pastern region.

Basilar or Abaxial sesamoid nerve block (BSNB or ASNB)

Bassage and Ross6 distinguish between anaesthesia of the palmar or plantar digital nerves

where local anesthetic is deposited at the base of the proximal sesamoid bones (i.e., a BSNB)

and anaesthesia of the palmar or plantar digital nerves where local anaesthetic solution is

deposited more proximally alongside the proximal sesamoid bones (i.e. an ASNB).

Anaesthesia of the digital nerves and their dorsal branches, at either level, alongside or at the

base of the proximal sesamoid bones, desensitises the foot, the pastern joint, the middle

phalanx and associated soft tissues, and the distal and palmar aspects of the proximal phalanx.



11

Clinicians should be aware that an ASNB or BSNB may ameliorate or abolish pain within the

MC/MT-P joint.2,6 Performing the nerve block at the base of the proximal sesamoid bones

(i.e., a BSNB) decreases the likelihood of partially desensitizing the MC/MT-P joint.2 Using a

small volume of local anaesthetic solution (i.e., <2 mL) may also decrease the likelihood of

partially anaesthetising the MC/MT-P joint.

Analgesia of the distal interphalangeal joint (DIP joint)

Local anaesthetic solution is most easily and accurately administered into the DIP joint using

a dorsal parallel or dorsal inclined approach, where a needle is placed into the dorsal pouch of

the DIP joint on or near midline, through or just proximal to the coronary band.

The effect of local anaesthetic solution in the DIP joint has been reviewed.8 Local anaesthetic

administered into the DIP joint desensitises the DIP joint, the navicular bursa, the navicular

bone, the toe region of the sole and the digital portion of the deep digital flexor tendon

(DDFT) of most horses. When a large volume of mepivacaine HCl (e.g. 10 mL) is

administered, the heel region of the sole may also be desensitised.

Possible explanations for analgesia of the navicular apparatus (i.e., the navicular bone and its

associated ligaments) after local anaesthetic solution is administered into the DIP joint is the

desensitization of the palmar digital nerves where they lie in close proximity to the palmar

pouch of the DIP joint.9 Occasionally, the palmar aspect of the coronary band is desensitised

after anaesthesia of the DIP joint;10 this finding, as well as desensitisation of the solar region

of the toe support the theory that analgesia of the DIP joint causes desensitisation of the

palmar digital nerves. A negative response to intra-articular analgesia of the DIP joint may not

eliminate the navicular bone and its related structures as the source of lameness. In a study of

102 horses with chronic foot pain, Dyson found that 21% of horses failed to respond to intra-

articular analgesia of the DIP joint but improved significantly after intrabursal analgesia of the

navicular bursa.11 A later study showed that some lesions of the DDFT at the level of the

tendon’ s insertion to the distal phalanx may be more effectively desensitised by

administering local anaesthetic solution into the navicular bursa than by analgesia of the DIP

joint.12 Some of the lame horses in Dyson’s study 11 that responded to analgesia of the

navicular bursa, but were unresponsive to analgesia of the DIP joint, may have had lesions of

the insertion of the DDFT rather than disease of the navicular bone and its related structures.



12

Ten mL mepivacaine HCl administered into the DIP joint may desensitise the entire sole, but

a smaller volume of mepivacaine (i.e. <6 mL) is unlikely to desensitise the heel portion of the

sole.10

Analgesia of the navicular bursa

Of the various techniques for inserting a needle into the navicular bursa showed that a method

described by Verschooten et al.13 is the most accurate. The foot can be held or placed in a

Hickman block using this method. A 20-gauge, 8.9-cm (3.5-inch), disposable, spinal needle is

inserted between the bulbs of the heel just proximal to the coronary band, and the needle is

advanced along a sagittal plane aiming for a point Verschooten termed “the navicular

position”. No matter the shape of the foot the navicular position is always in the same

location, 1 cm distal to the coronary band, midway between the dorsal and palmar limits of

the coronary band. The spinal needle is advanced toward the navicular position until the tip of

the needle contacts bone. At this time, a digital lateromedial radiograph can be taken to check

the position of the needle prior to injecting 3 to 4 mL of local anaesthetic solution. Injecting

the bursa can be facilitated by flexing the foot. Another method of determining success of the

procedure is to examine the foot radiographically immediately after injecting the bursa,

provided that 0.5 to 1.0 mL of radiopaque contrast medium was added to the local anaesthetic

solution.

Successful centesis of the bursa can also be determined ultrasonographically. For an

ultrasonographic view of the navicular bone, the frog is trimmed to pliable tissue, and soaked

in warm water for 30 to 120 minutes. The needle is advanced into the navicular bursa by

using Verschooten’s method of centesis13 and the position of the needle tip is determined

using a 7.5 MHz linear probe placed on the frog in a sagittal orientation. The needle is

properly placed when the tip of the needle is seen contacting the flexor surface of the

navicular bone. In the absence of imaging equipment, successful centesis of the bursa can be

assumed if the first 2-3 mLs of local anaesthetic solution is easily administered and then, as

pressure within the bursa increases as one to two more millilitres are administered,

administration becomes more difficult, resulting in refilling of the syringe with local

anaesthetic solution when pressure on the plunger is released. Bursal volume varies from 5

mL to greater than 10 mL depending on the presence of fibrosis of the bursa; the bursa may

rupture when a volume of solution between 6 and 10 mL is administered.



13

A positive response to administration of local anaesthetic solution into the navicular bursa

indicates disease of the navicular bursa, the navicular bone, and/or its supporting ligaments,

solar toe pain,15 or disease of the distal portion of the DDFT.16 Even though analgesia of the

DIP joint results in analgesia of the navicular bursa,9 analgesia of the navicular bursa does not

result in analgesia of the DIP joint.14,15 Analgesia of the navicular bursa may help

todifferentiate pain associated with disease of the DIP joint from pain associated with disease

of the navicular bone and associated structures. Pain arising from the DIP joint can likely be

excluded as a cause of lameness when lameness is attenuated within 10 minutes by analgesia

of the navicular bursa.15

One possible explanation for the observation that analgesia of the DIP joint causes analgesia

of the navicular bursa but analgesia of the navicular bursa does not cause analgesia of the DIP

joint is that the site of direct contact between the palmar pouch of the DIP joint and the

palmar digital nerves is located proximal to the origin of the deep branches that innervate the

DIP joint and the navicular bursa, whereas the site of direct contact between the navicular

bursa and the palmar digital nerves is located distal to these branches.

In addition to experimental findings concerning the effect of analgesia of the navicular bursa,

clinical observations indicate that a positive response to intra-articular analgesia of the DIP

joint and a negative response to intra-bursal analgesia of the navicular bursa indicate pain

within the DIP joint as the cause of lameness.16 This clinical observation is valid if solar toe

pain can be eliminated with hoof testers as a cause of lameness.

The effect of time on interpretation of analgesia of the DIP joint or navicular bursa

Some clinicians have assumed that improvement in lameness observed within 10 minutes

after injecting the DIP joint with local anaesthetic solution indicates that lameness is caused

by pain in the DIP joint alone and that improvement observed more than 10 minutes after

injection is caused by diffusion of local anaesthetic solution into the navicular bursa or around

the nerves providing sensory innervation to the navicular bone and its associated

structures.14,17 This assumption appears to be invalid because a positive response to intra-

articular analgesia of the DIP joint has been observed to occur within 5 to 8 minutes of

injection in a majority of horses with navicular disease or experimentally-induced navicular

bursal pain.9,16



14

Intra- articular and perineural analgesia of the proximal interphalangeal (PIP)

(pastern) joint

Approaches to the PIP joint have been reviewed18 and include dorsal, dorsolateral,

palmaroproximal, and palmarolateral approaches. Synovial fluid is frequently observed with

the palmaroproximal and palmarolateral approaches but is observed rarely using the other

approaches. Three of these approaches for arthrocentesis of the PIP joint were evaluated for

accuracy by Poore, et al.19 who found that students inexperienced in arthrocentesis of the PIP

joint were usually unsuccessful when performing these approaches.

A positive response to intra-articular analgesia of the pastern joint localises pain causing

lameness to that joint. Some horse lame because of in the pastern joint, however, do not

respond positively to intra-articular analgesia of the pastern joint when joint disease involves

subchondral bone.20 Because subchondral bone is innervated by nerves that enter the bone

marrow via the nutrient foramen, anaesthesia of nerves proximal to branches that enter the

nutrient foramen may be necessary to resolve subchondral bone pain and lameness. Because

the pastern joint is innervated by branches of the palmar digital nerves and their dorsal

branches, 4 an ASNB or BSNB nerve block resolves lameness caused by pain in the pastern

joint. Perineural anaesthesia of the palmar digital nerves and their dorsal branches at this

location should also anaesthetize these nerves proximal to the origin of the branches that enter

the nutrient foramen of the proximal phalanx and resolve lameness caused by subchondral

bone pain. Marked improvement in lameness of a horse with disease of the proximal

interphalangeal joint was observed when mepivacaine was infused through holes drilled into

the medullary cavity of both the first and second phalanges of the affected digit (Caldwell and

Schumacher, unpublished dataa).

Intra-articular analgesia of the metacarpo/metatarso phalangeal (MC/MT-P) (fetlock)

joint

Several techniques are described for intra-articular analgesia of the MC/MT-P joint. The

authors prefer the technique described by Misheff and Stover21 during which the limb is

positioned in partial flexion by holding the foot with one hand, while the needle is introduced

through the collateral sesamoidean ligament into the space between the articular surface of the

lateral sesamoid bone and the palmar aspect of the lateral metacarpal condyle. A volume of 7-

10 mL mepivacaine is administered.



15

Although a positive response to intra-articular analgesia of the MC/MT-P joint localises

disease to that joint in most horses, not all lameness associated with an injury of the fetlock

joint resolves with intra-articular analgesia, and not all horses with lameness that improves

with intra-articular analgesia of this joint have disease of this joint. Whereas lameness caused

by intra-articular fragmentation, synovitis, capsulitis, and osteoarthritis improves or resolves

after intra-articular analgesia, lameness caused by injury of the subchondral bone or peri-

articular ligaments does not. Lameness caused by desmitis of the proximal portion of the

straight or an oblique distal sesamoidean ligament can improve after intra-articular analgesia

of the MC/MT-P joint.22

Analgesia of the digital flexor tendon sheath (DFTS)

Synoviocentesis of the DFTS can be performed by placing a 20- to 22-gauge needle into one

of the sheath’s several pouches. Access to these pouches is not difficult when the sheath is

distended with synovial fluid but is often difficult when it is not. A palmar axial sesamoidian

approach through the palmar/plantar annular ligament of the MC/MT-P joint is consistently

reliable for accurate synoviocentesis of the DFTS.23 Using this approach, the MC/MT-P joint

is flexed to a dorsal angle of 225o, the needle is placed through the skin at the level of the

midbody of the lateral proximal sesamoid bone, and then through the palmar annular

ligament, 3 mm axial to the palpable palmar border of the lateral proximal sesamoid bone,

immediately palmar to the palmar digital neurovascular bundle. The needle is inserted in a

transverse plane and advanced at an angle of 45o to the sagittal plane, aiming toward the

central intersesamoidean region, to a depth of 1.5 to 2.0 cm.

A basilar sesamoidian approach to the DFTS24 is likely to result in retrieval of synovial fluid

to verify accuracy. To perform the basilar sesamoidian approach the fetlock joint is held in a

slightly flexed position and the needle is inserted distal to the lateral proximal sesamoid bone

into a palpable depression created by the base of this bone and the lateral border of the

superficial flexor tendon. The needle is advanced at an angle of approximately 45° to the

transverse plane (in a lateromedial direction) and 45° to the dorsal plane (in a distoproximal

direction), to a depth of ≤ 1 cm. Seven-10 mL of local anaesthetic solution provides adequate

desensitization of the DFTS.



16

A study demonstrated that pain induced in the toe and heel regions of the sole, pain associated

with synovitis of the DIP joint, and pain associated with synovitis of the navicular bursa were

not significantly attenuated by intrathecal analgesia of the DFTS.25 It is logical, therefore, to

assume that analgesia of the DFTS desensitises only structures that are contained within or

border on the sheath itself (i.e., the superficial and deep digital flexor tendons, the straight and

oblique distal sesamoidean ligaments, and the annular ligaments of the MC/MT-P and PIP

joints). It has been speculated that analgesia of DFTS may desensitise the portion of the

DDFT that lies within the foot.26 Leakage of local anaesthetic solution at the site of injection

or its diffusion from the DFTS, however, may desensitise skin of the heel region of the foot

from anaesthesia of the PDNs in some horses receiving intrasynovial analgesia of the DFTS

which may result in inadvertent desensitisation of the distal portion of the limb.27 The axial

and basilar sesamoidian approaches are less likely to result in leakage than are other

approaches to the DFTS. Skin sensitivity at the heel bulbs should be tested after intrasynovial

anaesthesia of the DFTS to determine if leakage of local anaesthetic solution at the injection

site has inadvertently anaesthetised a PDN.27

Diagnostic analgesia of the digital portion of the DDFT

An ASNB abolished or improved lameness localized to the foot in all of 46 horses found to

have a substantial abnormality in the digital portion of the DDFT using MRI.28 A PDNB,

analgesia of the DIP joint, or analgesia of the navicular bursa, however, each ameliorated

lameness of only about two-thirds of these horses.

Because lameness caused by disease of the DDFT within the foot may fail to improve

substantially after analgesia of the palmar digital nerves, the DIP joint, or the navicular bursa,

we believe that a portion of the DDFT within the foot and distal to the DFTS receives its

sensory supply from more proximal deep branches of the medial and lateral palmar digital

nerves that enter the DFTS. Improvement of lameness in horses with similar lesions of the

DDFT after intrathecal analgesia of the DFTS has been described.26

Performing intrathecal analgesia of the DFTS on horses with lameness that is unchanged after

anaesthesia of the palmar digital nerves but resolves after an ASNB, may be useful.

Resolution of lameness after intrathecal analgesia of the DFTS justifies suspicion of a lesion

within the digital portion of the DDFT or within structures contained within the DFTS.



17

Anaesthesia of the hind foot compared to the forefoot

Innervation of the distal portion of the pelvic limb differs slightly from that of the thoracic

limb because the medial and lateral dorsal metatarsal nerves, which are branches of the deep

peroneal nerve, provide additional innervation to the digit and third metatarsal bone. In

addition, the medial plantar metatarsal nerve may also continue distally into the coronary

dermis. Because of this additional nerve supply to the distal portion of the pelvic limb, some

clinicians recommend that the dorsal metatarsal nerves, in addition to the plantar metatarsal

nerves, be anaesthetised when performing nerve blocks of the lower portion of the pelvic

limb. The authors and others29 believe, however, that most lameness involving the distal

portion of the pelvic limb can usually be evaluated without anesthetising the dorsal metatarsal

nerves.

Diagnostic analgesia of the collateral ligaments of the DIP joint

Lameness caused by disease of the collateral ligaments of the DIP joint often fails to improve

significantly after analgesia of the DIP joint itself.30 Only 24% of 30 horses with MRI

evidence of collateral ligament disease showed a significant improvement in lameness after

intra-articular analgesia of the DIP joint, and none of the horses improved after intra-bursal

analgesia of the navicular bursa. A PDNB, however, improved lameness significantly in 72%

of these horses, and all became sound after an ASNB. Consequently, when lameness is

abolished by a PDNB but not by analgesia of the DIP joint or navicular bursa, and no

radiographic abnormalities of the foot can be detected, collateral desmitis of the DIP joint

must be considered as a possible cause of lameness, as long as the presence of solar pain can

be eliminated with hoof testers.

Clinical impressions suggest that the degree of improvement in lameness associated with

injury to a collateral ligament after PDNB is determined by the extent of the injury and the

level at which the palmar digital nerve is anaesthetised. The further proximal the level of the

injury within the collateral ligament, the less likely that lameness is affected by analgesia of

the DIP joint or anaesthesia of the palmar digital nerves. This observation suggests that the

branches innervating the proximal aspect and origin of the collateral ligaments arise from the

palmar digital nerves proximal to the site where the palmar digital nerves lie alongside the

palmar pouch of the DIP joint or from the dorsal branches of the palmar digital nerve. A

pastern ring block or ASNB may be required to abolish lameness when osseous remodelling

is present at the origin of the collateral ligament at the level of the middle phalanx.



18

a Caldwell, F.J. and Schumacher, J., 2015, Unpublished data, Auburn University, Auburn AL., USA

References

1. Easter JE, Watkins JP, Stephens SL, et coll. Effects of regional anaesthesia on experimentally induced coffin joint synovitis. Proc. Am. Ass. equine Practnrs. 2000;46:214-216.

2. Wyn-Jones G. Equine Lameness. Oxford, Blackwell Scientific Publications. 1988:1-22pp.

3. Beeman GM. The clinical diagnosis of lameness. Comp. cont. Educ. pract. Vet 1988;10:172-179.

4. Sack WO. Nerve distribution in the metacarpus and front digit of the horse. J. Am. vet med. Ass. 1975;167:298-335.

5. Paz CRF, Magalhães JF, Mendes HMF, et coll. Personal communication, March, 2015. 6. Schumacher J, Livesey L, DeGraves FJ, et coll. Effect of anaesthesia of the palmar digital

nerves on proximal interphalangeal joint pain. Equine vet J. 2004;36:409-414. 7. Bassage LH, Ross MW. Diagnostic analgesia, In: Diagnosis and Management of

Lameness in the Horse. Eds Ross MW and Dyson SJ. St. Louis, Elsevier Science. 2011:100-135.

8. Schumacher J, Schramme M, Schumacher J, et coll. Analgesia of the equine digit. Equine vet. Edu. 2013;25:408-421.

9. Pleasant RS, Moll HD, Ley WB, et coll. Intra-articular anaesthesia of the distal interphalangeal joint alleviates lameness associated with the navicular bursa in horses. Vet Surg. 1997;26:137-140.

10. Schumacher J, Schumacher J, DeGraves F, et coll. A comparison of the effects of two volumes of local analgesic solution in the distal interphalangeal joint of horses with lameness caused by solar toe or solar heel pain. Equine vet J. 2001;33:265-268.

11. Dyson S. Comparison of responses to analgesia of the navicular bursa and intraarticular analgesia of the distal interphalangeal joint in 102 horses. Proc. Am. Ass. equine Practnrs. 1995;41:234-239.

12. Schramme MC, Dyson S, Murray R, et coll. Soft tissue pathology in horses with navicular syndrome – MRI Results. Proceedings of the 1st World Orthopaedic Veterinary Congress, Munich. 2002:177pp.

13. Verschooten F, Desmet P, Peremans K, et coll. Navicular disease in the horse: the effect of controlled intrabursal corticoid injection. Errata. J. Equine vet Sci. 1991;11:8.

14. Dyson SJ. Lameness due to pain associated with the distal interphalangeal joint: 45 cases. Equine vet J. 1991;23:128-135.

15. Schumacher J, Schumacher J, Gillette R, et coll. The effects of local anaesthetic solution in the navicular bursa of horses with lameness caused by distal interphalangeal joint pain. Equine vet J. 2003;35:502-505.

16. Dyson SJ. The puzzle of distal interphalangeal joint pain. Equine vet Edu. 1998; 10:119-125.



19

17. Gough MR. Diagnosis of palmar foot pain in the equine forelimb. In Pract. 1998; 20:358-366.

18. Schumacher J, Wilhite R. How to inject the synovial cavities of the digit, in Proc. Am. Ass. equine Practnrs. 2012;58:430-438.

19. Poore LAB, Lambert KL, Shaw DJ, et coll. Comparison of three methods of injecting the proximal interphalangeal joint in horses. Vet Rec 2011;168:302-305&308.

20. Dyson S. Problems associated with the interpretation of the results of regional and intra-articular anaesthesia in the horse. Vet Rec. 1986;118:419-422.

21. Misheff MM, Stover SM. A comparison of two techniques for arthrocentesis of the equine metacarpophalangeal joint. Equine Vet J. 1991;23:273-276.

22. Sampson SN, Schneider RK, Tucker RL, et coll. Magnetic resonance imaging features of oblique straight distal sesamoidian desmitis in 27 horses. Vet Radiol. Ultrasound 2007;48:303-311.

23. Hassel DM, Stover SM, Yarbrough TB, et coll. Palmar-plantar axial sesamoidean approach to the digital flexor tendon sheath in horses. J. Am. vet med. Ass. 2000; 217:1343-1347.

24. Rocconi RA, Sampson SN. Comparison of basilar and axial sesamoidian approaches for digital flexor tendon sheath synoviocentesis and injection in horses. J. Am. vet med Ass. 2013;243:869-873.

25. Harper J, Schumacher J, DeGraves F, et coll. Effects of analgesia of the digital flexor tendon sheath on pain originating in the sole, distal interphalangeal joint or navicular bursa of horses. Equine vet J. 2007;39:535-539.

26. Schneider RK. Magnetic resonance imaging (MRI). What have we learned? Proceedings of the American College of Veterinary Surgeons Symposium, ACVS, San Diego. 2002:75-76 pp.

27. Jordana M, Martens A, Duchateau L, et coll. Distal limb desensitisation following analgesia of the digital flexor tendon sheath in horses using four different techniques. Equine vet J. 2013;46:488-493.

28. Dyson SJ, Murray RC, Schramme M. et coll. Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis using magnetic resonance imaging. Equine vet J. 2003;5:681-690.

29. Carter GK, Hogan PM. Use of diagnostic nerve blocks in lameness evaluation. Proc. Am. Ass. equine Practnrs. 1996;42:26-32.

30. Dyson S, Murray R. Collateral desmitis of the distal interphalangeal joint in 62 horses (January 2001–December 2003). Proc. Am. Ass. equine Practnrs. 2004;50:248-256.



DISTAL LIMB BLOCKSWhat do they really tell me?

DISTAL LIMB BLOCKSWhat do they really tell me?

Michael SchrammeDrMedVet, certEO, Phd, DipECVS, DipACVS

Professor Equine Surgery

University of Lyon

Accurate diagnosis

Prognosis Treatment

Regional Analgesia

Physical Examination

Diagnostic Imaging

LAMENESS

THE PUZZLE OF DISTAL LIMB LAMENESS

The Best Answers still come from Local Analgesia

Navicular Pain or Palmar Heel Pain?



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Texte tapé à la machine

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Annex (Slides of Prof. Schramme's conference) Diagnostic analgesia of the foot : techniques & interpretations

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48

DIAGNOSIS OF FOOT LAMENESS

DIAGNOSIS OF FOOT LAMENESS

by integrating the differential response to1. Abaxial sesamoid nerve block2. Palmar digital nerve block 3. Coffin joint anesthesia4. Navicular bursa anesthesia5. Digital sheath anesthesia

Is it possible to localise pain in the foot accurately?

Diagnosis of Foot Lameness

• What we have been told… and have believed– Palmar Dig Nerve Block (PDNB)

• Only palmar 1/3 of foot– Including dorsal branches

• Entire foot– DIP joint = DIP joint– Bursa = Bursa

• THE END

Palmar Digital Nerve Block



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• Desensitises coffin joint synovitis!

PDNB

Time Preinjection

Postinjection

15 min 30 min 60 min

Lameness 0/4 3/4 0/4 - -


• The dorsal digital nerves do not innervate the joint capsule of the coffin joint.

Sack 1975

Cutaneous only



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• May desensitize the pastern joint!

PDNB

Time Pre injection

Post injection

1 cm 2 cm 3 cm

Lameness

<0/10>

<7/10>

<5/10>

<4/10*>

<4/10*>


• Deep branches of the PD nerves (3 & 5) to the PIP joint, arise at the level of the joint (Sack 1975).

PDNB



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Palmar Digital Nerve BlockFALSE NEGATIVE RESULTS

“A negative palmar digitalnerve block does not ruleout foot pain!”

Parkes and Dyson 2013

Palmar Digital Nerve BlockMinimizing proximal migration

• Insert close to margin of cartilage of the foot

• Point needle distally

• Use small amount of solution : 1 to 1 ½ mL

• Evaluate in 5-6 minutes

ASNB



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• Delayed onset of analgesia possible due to injection outside the perineural fascia.

= FALSE NEGATIVE

• 2 ml iohexol with needle directed distally

• Diffusion average distance of 16.9 mm (up to 28 mm) proximal to injection site in the first 10 minutes.

• Diffusion increased with time to 36 mm proximal to injection site.

• 12 horses

• Lameness abolished by ASNB in 50%: Proximal

phalanx

Sesamoids

MC3

FALSE POSITIVE



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• 8 horses

• Lameness abolished by ASNB in 86%

• None improved after PDNB.

FALSE POSITIVE

• Lameness improved > 80% or abolished by ASNB:

– 4 suspensory branch desmitis

– 1 sesamoiditis

– 1 metacarpophalangeal OA

– 1 osseous injury distal MC3

• 2/3 of branch injuries block to ASNB

– Dyson 2013

FALSE POSITIVE

PASTERN RING BLOCK (proximal palmar digital nerve block)



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MID-PASTERN RING BLOCK• Less risk of fetlock

desensitisation than ASNB (if similar diffusion distance?)

• Adds to PDNB:

– Collateral ligaments

– Dorsal laminae

– Dorsal coronary band

– PIP joint

– Middle phalanx

– +/- Distal sesamoidean ligaments

INTRA-ARTICULAR ANALGESIA OF THE

COFFIN JOINT

COFFIN JOINT ANALGESIA

• Dorsal approach parallel with the solar surface.



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5 cc results in desensitisation of:

• DIP joint (generally not collateral ligs)

• navicular bone

• navicular bursa

• toe region of the sole

• heel region of the sole, if 10 cc used

• distal DDF tendinitis


What is the mechanism for false positive analgesia? (1)

Diffusion?



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Mechanism of DIP Joint Analgesia (2)

Direct contact

Coffin Joint Analgesia

Heel branches

4 cc 7 cc




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COFFIN JOINT ANALGESIAClinical Interpretation

Coffin joint analgesia with low volume of local anesthetic, may differentiate between palmar heel pain and ‘navicular region pain’,provided careful hoof testing does not reveal solar toe pain.

DIP JOINT ANALGESIA

Are there false negative results?



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• 102 horses with foot pain alleviated by PDNB or ASNB (Dyson 1995)

BURSA + BURSA -

COFFIN + 66% 6%

COFFIN - 21% 9%

ANALGESIA OF THE NAVICULAR BURSA

NAVICULAR BURSA ANALGESIA

• Distal palmar approach to the ‘navicular position’ is the most accurate approach (Verschooten 1991; Schramme 2000).



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3 cc results in desensitisation of:

• navicular bone

• navicular bursa

• navicular ligaments

• toe region of the sole

• distal DDF tendinitis


• No anesthesia of the coffin joint!





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Mechanism of Navicular Bursa Analgesia (1)

Mechanism of Navicular Bursa Analgesia (2)

Coffin joint branch

Coffin

Bursa


• Bursal anesthesia can differentiate coffin joint pain from ‘navicular pain (including DDFT)’.

Navicular

Bursa +Navicular

Bursa -

DIP Joint + navicular paintoe pain

DIP joint pain

DIP Joint - navicular pain heel pain



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• Bursal anesthesia can differentiate coffin joint pain from ‘navicular pain (including DDF pain)’.

Dyson 1995105 horses

Navicular

Bursa +Navicular

Bursa -

DIP Joint + 66% 6%

DIP Joint - 21% 9%

REVIEW OF DIGITAL ANALGESIA

Low 4-point nerve block



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Low 4-point nerve block

• 2 ml iohexol with needle directed distally

• Immediate average proximal extension of 25.8 mm

• Increased after 10-20 min up to 81 mm

• Main contrast patch rarely above mid MC level: unlikely to affect PSD pain?

• 2-4 ml mepivacaine:iohexol with needle directed distally

• Diffusion mean distance of 43 mm (up to 59 mm) proximal to injection site

• Diffusion increased with time to between 15-30 minutes.

• Diffusion was greater with 4 ml than 2 ml.



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• Inadvertent penetration digital flexor tendon sheath: 39%.

• Inadvertent penetration fetlock joint: 44%

= potentially FALSE NEGATIVE

Analgesia of the fetlock joint

Fetlock Joint Analgesia

• More consistent synovial fluid aspiration

• Less haemorrhage

• Better control of limb

• Less risk iatrogenic cartilage damage

Preferred method (Misheff 1991)



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Fetlock Joint AnalgesiaFALSE POSITIVE1. Distal sesamoidean

desmitis: 58% improved

(King 2012)

2. Suspensory branch desmitis: 50% improved

(Gonzalez 2010)

FALSE NEGATIVE1. Subchondral bone pain 25% no change

(Dyson 2006)


• Distal sesamoidean ligament desmitis was the most common diagnosis.

• 58% improved with intra-articular analgesia of the fetlock joint.


• Suspensory branch desmitis comprised 18% of lesions.

• 50% improved or abolished with intra-articular analgesia of the fetlock joint.



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• 12 horses with subchondral bone injury of MC3 or P1.

• 25% did NOT improve with intra-articular analgesia of the fetlock joint.

Analgesia of the digital flexor tendon sheath



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ANALGESIA DIGITAL SHEATHPalmar/plantar Axial Sesamoidean Approach

• Needle is inserted through annular ligament of fetlock w/ limb flexed

• In transverse plane 3 mm axial to palmar/plantar border of proximal sesamoid bone

• Advanced ½ - ¾ in toward center of intersesamoidean region

• Synovial fluid can be aspirated consistently

Hassel et. al. JAVMA 217: 1343, 2000

• An 18-gauge, 3.8-cm needle was directed into the palpable depression at an angle of approximately 45° to the transverse plane and 45° to the dorsal plane, to a depth of 1 cm.

• Number of attempts at correct needle insertion were significantly lower than the axial technique.

• The basilar approach was 6 times more likely to result in synovial fluid aspiration

• An 18-20 gauge, 3.8-cm needle directed into the palpable depression at an angle of approximately 45°to the transverse plane and 45° to the dorsal

plane, to a depth of 1 cm.• The basilar approach was

6 times more likely to result in synovial fluid aspiration



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Analgesia of the Digital Sheath• Effects of analgesia of digital flexor

tendon sheath on pain in sole, coffin joint, or navicular bursa– No effect!– i.e., it does not block the palmar digital

nerve• Improvement of lameness in horses after

intrasynovial analgesia of the digital sheath is likely caused by attenuation of pain within the structures contained within the digital sheath.

Digital Flexor Tendon SheathANALGESIA DDFT?

Digital Flexor Tendon SheathFALSE POSITIVE1. Distal sesamoidean

desmitis: All horses

improved >70%(Sampson 2007)

2. DDF tendinopathy in the foot: Dyson 2013

FALSE NEGATIVE1. DDF tendinopathy

in the foot: Dyson 2013



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False positive Analgesia Digital Sheath through leakage of anesthetic?

Proximal Axial Basilar Distal

False positive Analgesia Digital Sheath?• At 30 minutes, 16% of limbs

had partial or complete desensitisation of the lateral heel bulb.

• Probability of loss of skin sensation was:– 4 x higher for proximal than

axial and base in forelimbs– 3 x higher for proximal than

axial and distal in hindlimbs

CONCLUSIONS



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(+)

NB (+)

Navicular painDDF painToe pain

NB (-)

DIP painDDF painToe pain

(-)

Navicular painDDF insertion painToe pain

NB (+)

Heel painToe painCL pain

NB (-)

PDNB

DIPJ

(+)

ASNB (+)Pastern jointP3Dorsal laminae DDFT painCL painAL DesmitisDigital sheath Fetlock joint

(-)

(+)

Intra-articular pain:SynovitisOsteoarthritisIA fragmentationSCLISL desmitis

(-)

Intrathecal pain:Annular ligament syndromeTenosynovitisDDF tendonitisDistal sesamoidean desmitisISL desmitis

Extra-articular pain:Collateral desmitis‘Sesamoiditis’SL branch desmitisSubchondral bone pain

Digital Sheath (+) Digital Sheath (-)

Intra-articular anesthesia

Low 4-PNB (+)

ASNB (+)Foot PasternFetlock region?

(-)ASNB

Fetlock region pain

FOOT (-)



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Proceeding of the Belgian Equine Practitioners Society … · Proceeding of the Belgian Equine...

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