Diagnostic Analgesia 2021/22 - BEVA 2009 PDF

Diagnostic analgesia MOD 2021/22 Dr Peter Milner Senior Lecturer Equine Orthopaedics BEVA 2009 Learning outcomes • To describe the indications and contraindications for the use of diagnostic analgesia in the horse • To synthesise a plan for investigating a lame horse • To describe the approaches...

Diagnostic analgesia MOD 2021/22 Dr Peter Milner Senior Lecturer Equine Orthopaedics BEVA 2009 Learning outcomes • To describe the indications and contraindications for the use of diagnostic analgesia in the horse • To synthesise a plan for investigating a lame horse • To describe the approaches to diagnostic analgesia of the equine digit and recognise limitations based on current research Introduction • Integral part of the lameness examination • Pre-requisite knowledge of anatomy – Correct placement of local anaesthetic – Correct interpretation of result V good book! What you need for diagnostic anaesthesia • • • • • Lame horse Good handler Good technique Logical step-wise approach Ability to recognise improvement • Understand structures desensitised • Plenty of time! Local anaesthetics • Used surgically and diagnostically for last 150 years • Act by blocking sodium channels and preventing depolarisation • Mepivicaine and bupivicaine commonly used in equine diagnostics – Differ in length of onset/effect • Mepivicaine: 1-2min onset/45-60min duration • Bupivicaine: 4-5 min onset/1-2hr duration Contra-indications for the use of diagnostic anaesthesia • Suspect fracture • Cellulitis • Uncooperative horse Complications of diagnostic anaesthesia • Broken needles – Small needles – Bent needles – Horse moving • Severe lameness after block – “Flare” – Synovial sepsis Reasons for poor response to local anaesthesia • Severe pain – e.g. P3 fractures and subsolar abscessation • Poor technique/inadequate volume – Review technique or re-block on a separate occasion • Subchondral bone pain – Bone pain modelling may not be desensitised by intraarticular anaesthesia • Pain originating more proximal – e.g. neck pain • Neurological/ mechanical – Lameness/gait abnormality may not significantly improve – Perform neurological exam Diagnostic analgesia - options • Forelimb – Perineural • • • • Palmar digital nerve block Abaxial sesamoid nerve block Low 4-point nerve block High 4-point; subcarpal; lateral palmar nerve block • Median/ulnar • (Cutaneous antebrachial) – Synovial • DIPJ; NB; PIPJ; DFTS; MCPJ; carpal joints; carpal sheath; elbow; shoulder; bicipital bursa • Others – Thoracolumbar spine; sacroiliac; local infiltration • Hindlimb – Perineural • • • • (Plantar digital nerve block) Abaxial sesamoid nerve block Low 6-point nerve block High 6-point; subtarsal; deep branch lateral plantar nerve block • Tibial/peroneal – Synovial • DIPJ; NB; PIPJ; DFTS; MTPJ; tarsal joints; calcaneal bursa; tarsal sheath; stifle; hip; Palmar digital analgesia Site: just proximal to collateral cartilage, abaxial to edge of DDFT Technique: limb non‐ weightbearing; • palpate neurovascular bundle with thumb; place needle angled distal and over bundle • Needle: 23/25G 5/8” • Volume: 1.5‐2ml Structures desensitised by PDNB Traditional view • Localises lameness to palmar aspect of the foot (Adams 1974) In reality... • Navicular bone; navicular bursa; collateral suspensory ligaments; distal sesamoidean impar ligament; distal deep digital flexor tendon and tendon sheath; insertion of superficial digital flexor tendon; digital cushion; palmar third of lamellar corium and corium of sole; palmar processes of the pedal bone; collateral cartilages; +/- collateral ligaments of DIP joint; palmar pouch of DIP joint; • +/- PIP joint analgesia (Schumacher et al., 2004) Abaxial sesamoid nerve block Site: immediately palmar to neurovascular bundle at the abaxial surface of the base of the PSB Technique: • limb non‐weightbearing; • palpate neurovascular bundle with thumb; needle inserted distal and parallel to bundle • Needle: 23/25G 5/8” • Volume: 2ml Structures desensitised by ASNB – it’s not just the foot! • As for PDNB but rest of digit • Rest of P3/P2 and palmar P1 • Collateral ligaments of the DIP and PIP joints; DIP and PIP joints • Distal sesamoidean ligaments • Lamellar corium and coronary band • Distal digital extensor tendons • Dorsal extension branch of the suspensory ligament). Note: may partially desensitise fetlock joint if too high - proximal diffusion of contrast in ~20% of cases (Nagy et al 2009) Distal interphalangeal joint Site: • Dorsal approach • Technique: weight‐bearing; midline; • palpate depression just proximal to coronary band (1‐2cm) on dorsal aspect of pastern; • insert needle vertically through skin and extensor tendon • (can also be done via dorsolateral or dorsal inclined approach) • Needle: 20G 1.5” • Volume: 6ml Anaesthesia of the DIPJ Structures desensitised • DIP joint • +/– Collateral ligaments of DIP joint • Navicular bone/bursa • Toe region of sole (not heel) Navicular bursa Site: palmar approach • between bulb of heels; • horizontal, midline through DDFT Technique: weight‐bearing or in a navicular Hickmans block • skin bleb; use radiographic control (+ contrast) • Needle: 18G spinal • Volume: 2‐4ml Schumacher et al., 2003. Diagnostic analgesia of the equine digit. Equine Veterinary Education 25: 408-421 Other relevant references