Large Animal Musculoskeletal Diagnostics Flashcards
describe the common anesthetic drugs and material required to carry out diagnostic anesthesia
drugs: lidocaine (shortest duration), mepivicaine (carbocaine), and bupivicaine (marcaine) (longest duration) are commonly used
perineural: good thorough scrub with a surgical scrub (chlorhexidine or betadine) with an alcohol rinse
intrasynovial: clip usually, routine 5-6 minute surgical scrub with an alcohol rinse, sterile surgical gloves, be mindful of sterile field!
what is the mechanism of action of all diagnostic anesthetics?
voltage-gated Na+ channel blockers- prevent influx of Na into nerve cells required for creation of action potential (to create sensation)
what are the 4 options for diagnostic anesthesia?
perineural, intrasynovial, intrathecal, intrabursal
describe the palmar digital nerve block; including nerves, palpation, technique, any precautions, and region of anesthesia
nerves: medial and lateral palmar/plantar digital nerves
palpate: neurovascular bundle at level of collateral cartilage on either side of DDFT
technique: non weight bearing,
1. introduce 25G 5/8” needle (small needle) DOWNWARD, staying in SQ space
2. deposit 1-2ml lidocaine or CARBOCAINE medial and lateral
caution! be aware of angle and depth of penetration bc you can enter the tendon sheath if too deep = bad news bears
region of anesthesia: back 1/3 of the hoof and the entire sole
(entire sole, navicular apparatus, DIP, soft tissues of heel, distal DDFT)
describe the abaxial nerve block; including nerves, palpation, technique, any precautions, and region of anesthesia
nerves: medial and lateral palmar/plantar digital nerves
palpate: neurovascular bundle along the abaxial border of the proximal sesamoid bones
technique: can perform wt bear or non wt bear
1. introduce 25G, 5/8” (small) needle just palmar/plantar to palpable NV bundle, directing needle downward and staying in SQ space
2. deposit 1-2ml lidocaine or CARBOCAINE medial and lateral
caution! be aware of angle and depth bc can penetrate the tendon sheath if too deep
region of anesthesia: everything from palmar digital PLUS PIP, portions of the distal sesamoidean ligaments, DDFT and insertion of SDFT, and collateral ligaments
-nerves, technique, and caution are same as palmar digital! just blocking the nerves in a different location to block more structures than the PD block (only perform after the PD block)
describe the low 4 point (low palmar) nerve block; including nerves, palpation, technique, any precautions, and region of anesthesia
nerves: medial and lateral palmar/plantar nerves AND medial and lateral palmar/plantar metacarpal/metatarsal nerves
technique for palmar/plantar nerves: weight bearing,
1. palpate space between suspensory branch and DDFT, 3-4 cm proximal to distal MC/MT II and IV (splint bone buttons)
2. introduce a 25G 5/8” or 22G 1” needles perpendicular to skin, between DDFT and suspensory branch
3. deposit 2ml SQ just dorsal to DDFT, medial and lateral
technique for palmar/plantar metacarpal/metatarsal nerves: can perform wt bear or non wt bear
1. nerves enter SQ space at distal end of buttons
2. introduce 25G 5/8” needle between MC/MT III ad distal MC/MT II and IV- IMPORTANT to reduce risk of entering fetlock
3. deposit 2ml SQ medial and lateral
region of anesthesia: the fetlock and all structures distal to it plus the SDFT and DDFT in this region as well as the distal aspect of the branches of the suspensory apparatus
describe the high 4 point (high palmar) nerve block; including nerves, palpation, technique, any precautions, and region of anesthesia
nerves: medial and lateral palmar/plantar nerves and medial and lateral palmar/plantar metacarpal/metatarsal nerves
technique for palmar nerves: can perform wt bear (preferred) or non wt bear
1. palpate dorsal surface of DDFT under fascial layer slightly (3-4cm) below the carpometacarpal joint
2. introduce 25G 5/8” needle perpendicular to skin, deep to fascia just dorsal to DDFT
3. deposit 3-5ml medial and lateral
technique for palmar metacarpal nerves: non weight bearing
1. palpate the nerves just between the palmar surface of MCIII and the axial surface of MC/MT II and IV, aiming for injection point slightly below (3-4cm) the carpometacarpal joint)
2. introduce a 20-22G 1.5” (big daddy) needle along axial border of splint bone until contact with MCIII
3. withdraw slightly and deposit 3-5ml medial and lateral
region of anesthesia: the entire limb distal to the point of blocking, including flexor tendons, suspensory ligament, splint bones, and associated interosseous ligaments
what is the downside of the high 4 point (high palmar) nerve block? what is used instead?
depositing a lot of anesthetic and blocking a giant region = hard to interpret results so use lateral palmar and DBLPN nerve blocks instead
describe the lateral palmar nerve block; including nerves, palpation, technique, any precautions, and region of anesthesia, and an advantage over high 4 point block
nerves: lateral palmar nerve at the level of the accessory carpal bone; blocks nerve proximal to the branch of the palmar metacarpal nerves; can block wt bear or non wt bear
Wheat block/lateral approach technique:
1. palpate accessory carpal ligament 2cm distal to lateral accessory carpal bone
2. introduce 25G 5/8” needle through fascia at palmar border or ligament midway between the ligament’s insertion on distal accessory carpal bone and proximal MC IV; avoid deep penetration to reduce risk of entering carpal canal
3. deposit 3-5ml of anesthetic
Castro block/medial approach technique:
1. palpate mid palmar border or the accessory carpal bone
2. introduce 25G 5/8” needle into distal 1/3 of groove in mediolateral direction until contact with bone
3. withdraw 2-3mm and deposit 1.5-2ml
(this technique reduces risk of injection of carpal canal)
region of anesthesia: loss of sensation from areas supplied by the palmar metacarpal nerves and the lateral palmar nerve
advantage: smaller volume of anesthetic; works well for diagnosing suspensory disease in front limb
describe the deep branch of the lateral plantar nerve block (DBLPN)
background: sterile prep recommended bc common to enter tarsometatarsal joint or tarsal sheath; limb MUST be held off the ground with fetlock in extension; support fetlock in a seated lap to allow manipulation with both hands
technique:
1. palpate head of MT4 at tarsometatarsal joint space
2. push/pull flexor tendons medially with one hand
3. use other hand to introduce 22G 1” needle 15mm distal to tarsometatarsal joint space, perpendicular to the skin, between the axial margin or MT4 and flexor tendons to a depth of approximately 3/4 to 1inch
4. very important that the needle follows the axial surface ot MT4 perpendicular to the proximal canon bone
5. if the needle deflects medially, reposition the point of insertion medially
6. deposit 3-4ml
region of anesthesia: origin of hind suspensory and also blocks portions of the distal hock and plantar aspect of fetlock joint
describe the intrasynovial distal interphalangeal (coffin) joint block
- sterile technique, weight bearing, usually will clip
technique for dorsal approach:
1. introduce 20G 1/2” needle 1cm proximal to coronary band o midline, perpendicular or slight palmar angle to grund
2. will usually obtain joint fluid
3. inject 5-6ml, should flow easy
4. important to evaluate lameness at 5 minute intervals out to 20-30 min
interpretation: increase in volume injected will result in desensitization fo additional structures so be careful
region of anesthesia:
DIPJ!! plus is inject more volume can also anesthetize navicular bursa, toe region of sole, navicular apparatus, possibly DDFT/impar ligaments
describe the intrabursal- navicular bursa anesthesia
sterile technique: non weight bearing, use a hickman block or hoof stand, and guide using radiograph or ultrasound BEFORE inject; palmar heel and palmar lateral approaches are most common
technique:
aiming mark (mark with a sharpie or thumb tack) is mid way between dorsal and palmar coronary band, 1cm distal and perpendicular to the coronary band (location of navicular bone)
performing a SQ block at the entry site and appropriate restraint will reduce the risk of an adverse reaction
will rarely obtain joint fluid
important to eval lameness at 5 minute intervals out to 20-30 min
region of anesthesia:
navicular bursa, toe region of sole, navicular apparatus, DDFT/impar insertional tendinopathy, can help differentiate DIPJ pain
