Evaluating equine foot lameness (Proceedings)

Anatomy of the palmar foot

• Those structures that can be associated with lameness

     o Hoof

          • Digital cushion

          • Collateral cartilages

          • Frog

          • Heels

          • Sole

     o Synovial structures

          • Coffin Joint

          • Navicular bursa

          • Digital sheath

     o Bone

          • P2

          • P3

          • Navicular

     o Tendons

          • Deep digital flexor

     o Ligaments

          • Impar

          • Suspensory ligament of the navicular

          • Distal digital annular ligament

          • Collateral Ligaments of the distal interphalangeal joint

The foot

• Diagnostics - Localization

     o Peri-neural anesthesia

          • Palmar digital nerve block

          • Dorsal branches

          • Abaxial sesamoid nerve block

     o Intra-synovial

          • Coffin joint

          • Navicular bursa

          • Digital sheath

• Palmar Digital Nerve Block

     o 1.5 – 2 ml of anesthetic

     o Placed over neurovascular bundle

     o Just axial to collateral cartilages

     o Desensitizes 1/3 to 1/2 of the foot

     o Structures blocked: (Stashak TS Adams Lameness in Horses pp 162)

          • Navicular bone

          • Navicular bursa

          • Navicular apparatus

          • Distal sesamoidean ligaments

          • DDFT, SDFT

          • Digital sheath

          • Digital cushion

          • Frog

          • Sole

          • Palmar coffin joint

          • Palmar 1/3 and distal aspect of P3

• Dorsal Branches – Pastern Ring Block

     o 3 to 5 ml anesthetic

     o Just proximal to collateral cartilages

     o Directed dorsally

     o Structures blocked

          • Coffin joint

          • Pastern joint

          • Remainder of P3

          • Remainder of sole

          • P2

• Abaxial-sesamoid Nerve Block

     o 2 – 3 ml anesthetic

     o Placed over neurovascular bundle at base of the proximal sesamoids

     o Structures blocked (in addition to those with PD)

• Coffin joint

          • Pastern joint

          • Palmar fetlock joint (variable)

          • Remainder of P3

          • Remainder of sole

          • P2

• Intra-synovial Anesthesia

     o Coffin Joint

          • 3 Techniques

               - Dorsal-lateral

                    • 1 cm above coronary band

                    • 1.5 cm lateral to midline

                    • Needle inserted at 90º angle to bottom of foot

               - Dorsal

                    • Through the common digital extensor

                    • Needle angled just distal to horizontal

               -Lateral (palmar pouch)

                    • Distal palmar border of the middle phalanx and notch in lateral cartilage

                    • Needle inserted laterally in dorso-medial direction

     o Navicular Bursa

          • 5 techniques (Schramme et al EVJ 2000 32:263)

     o Digital Sheath

          • 3 Techniques

               - Proximo-lateral pouch

                    • 1 cm proximal to the annular ligament

                    • 1 cm palmar to the lateral branch of the suspensory ligament

                    • Direct needle slightly distal

               - Base of sesamoid

                    • Axial to the midbody of the sesamoid

                    • Leg flexed 225º

                    • Needle inserted 3mm axial to the border of the midbody

                    • Directed 45º to the sagittal plane 1.5 – 2 cm

               - Pastern region

                    • Outpouching of sheath between proximal and distal annular ligaments

     o Do these provide specific anesthesia only to these structures?

          • Coffin Joint

               - Palmar pouch is close to digital nerves

               - Anesthetic diffuses to navicular bursa and to a lesser extent the navicular bone (Keegan KG et al AJVR 2006 57:422)

               - Recommendations:

                    • Use 6 ml of anesthetic

                    • Observe after 5 minutes

          • Navicular Bursa

               - Palmar digital nerves are in close proximity to the navicular bursa (Bowker RM et al AAEP Proc 1996: 33-47)

               - Also blocking other palmar structures?

               - Diffusion between DIP joint and bursa

                    • Quite variable (Bowker RM et al JAVMA 1993 203:1708-1714)

                    • Less from bursa to DIP than reverse (Gough MR et al EVJ 2002 34:80-84)

               - Eliminated solar toe pain in one study (Schumacher J et al EVJ 2001 33:386-89)

               - After 20 minutes: improved coffin joint-associated lameness (Schumacher J et al EVJ 2003 35(5) 502-505)

               - If within 20 minutes then more specific for bursa and associated structures

               - Recommendations

                    • Inject using distal palmar approach with radiographic guidance

                    • 3 – 4 ml of anesthetic

               - Observe lameness in 10 minutes

          • Digital Sheath

               - Analgesia is specific for the structures within the digital sheath using the palmar-axial sesamoidean technique (Harper J et al EVJ 2007 39(6):535-539)

               - Blocking structures associated with the sheath

                    • DDFT

                    • Distal sesamoidean ligaments

                    • SDFT

                    • Palmar annular ligament of the fetlock

                    • Digital annular ligament

               - Recommendations:

                    • Anesthesia is specific

                    • Use as described

• Diagnostic Imaging

     o Radiographic Exam

          • Views:

               - Lateral

               - DP navicular

               - DP P3

               - Skyline navicular

               - Optional:

                    • DP oblique P3

                    • Radiographic Grading of Navicular Changes* (Dyson SJ: Diagnosis and Management of Lameness in the Horse; pp 293)

               - 0: Excellent

                    • Good corticomedullary demarcation

                    • Fine trabecular pattern

                    • Flexor cortex of uniform thickness

                    • No synovial invaginations along distal border or fewer than 6 narrow synovial invaginations along distal border

                    • R and L symmetrical

               - 1: Good

                    • As above, but synovial invaginations on distal border are more variable in shape

               - 2: Fair

                    • Slightly poor definition between palmar cortex and medullary cavity due to sclerosis

                    • Crescent-shaped lucent zone in central eminence of flexor cortex

                    • Fewer than 8 synovial invaginations of variable size

                    • Mild enthesiophyte formation along proximal border

                    • Navicular bones asymmetrical

               - 3: Poor

                    • Medullary sclerosis

                    • Thickening of dorsal and flexor cortices

                    • Lucent zones along the proximal border of the bone

                    • Large enthesiophytes formation on proximal border

                    • Discrete mineralization within a collaeral ligament

                    • Radiopaque fragment on the distal border

               - 4: Bad

                    • Large cyst-like lesion within medulla

                    • Lucent region in the flexor cortex

                    • New bone on the flexor cortex

          • Radiographic Findings

               - The more changes the more likely to have clinical disease

               - Poorly correlated with degree of lameness

               - Horses will have navicular–related pain without radiographic signs

     o Nuclear Scintigraphy of Foot

          • Both pool (soft tissue) and bone phases

          • Views

               - Dorsal

               - Lateral

               - Solar

          • Value in Diagnosis of Palmar Foot Lameness

               - Dyson SJ (EVJ 2002 34(2):164-170)

                    • Cases

                    • 15 normal Grand Prix horses

                    • 53 horses with primary foot pain

                    • 21 horses with foot pain and another cause of lameness

                    • 49 with other lameness

                    • Horses with foot pain did not have radiographic changes

                    • P3 and navicular have similar uptake in normal horses in work

               - Significant difference of uptake in navicular bone in horses with foot pain

                    • Except horses with low heel confirmation

               - False positives in region of DDFT insertion

               - Pool phase more sensitive for DDFT lesions

               - Conclusion:

                    • Scintigraphy has moderate value in diagnosis of horse with foot pain

                    • Better if correlated with DIP or NB blocks

     o Ultrasound of the Foot

          • Limited access due to hoof

               - Via frog after careful preparation

               - Between heel bulbs

          • Limited view of structures

               - Small window

     o Magnetic Resonance Imaging

          • Now the "Gold Standard" for the specific diagnosis of foot pathology

          • Gives very good anatomic detail for bone and soft tissue

          • High-field MRI

               - General anesthesia

                    • Recovery

               - High cost:

                    • Purchase

                    • Installation

                    • Maintenance

                    • Anesthesia

               - High field strength

                    • Higher resolution

                    • Faster

                    • Larger field

                    • Less motion artifacts

                    • More images/series

                    • More detail

                    • Subtle lesions can be identified

                    • Image further proximal (carpus and tarsus)

               - Low-field MRI

                    • Lengthy procedure

                    • Motion

                    • Foot is best

                    • Poor resolution compared with recumbent MRI

                    • Sedation rather than GA

                    • Less expensive

                    • Careful optimization can result in diagnostic images

                    • Can improve image quality under GA

                    • Most lameness is in the foot

                    • Following the lesion over time is more financially reasonable

               - Common Sequences

                    • T1-weighted

                    • Good anatomic detail

                    • Less tissue contrast

                    • T2-weighted

                    • Highlights fluid and sensitive to anatomic change

                    • Less anatomic definition

                    • STIR

                    • Fat-suppressing

                    • Detect fluid in soft tissue and bone

                    • - Sectioning

                    • Transverse

                    • Sagittal

                    • Dorsal

               - Tissue Characteristics

                    • Bone

                          o Cortical bone– black

                          o Protons tightly bound and little signal

                          o Medullary bone- hyperintense

                          o Bone marrow

                          o Hyperintense: bruising, edema, hemorrhage, inflammation

                    • Ligament and Tendon

                          o Hypointense

                          o Contour and size

                          o Injury: increase intensity(hemorrhage, edema, cellular infiltrate

                    • Cartilage

                          o Contrast: gadolinium (1:250-1:500 with saline)

                          o Reveal cartilage fissures or defects

               - Clinical Use

                    • Soft tissue and osseous injuries identified in absence of radiographic findings

                          o Navicular bone edema

                          o Adhesions between DDFT and navicular bone

                          o Navicular bursitis

                          o DDFT tendonitis

                          o Impar ligament desmitis

                          o Proximal suspensory of navicular bone desmitis

                          o Distal interphalangeal joint synovitis

                          o Combination of problems

                          o Collateral ligament of the DIP joint desmitis

Putting it all together

• Diagnosis of Palmar Foot Pain

     o Very complex

     o Requires multiple modalities