Diagnosis of palmar 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 ⅓ to ½ 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 ⅓ 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

o 1 cm above coronary band

o 1.5 cm lateral to midline

o Needle inserted at 90º angle to bottom of foot

• Dorsal

o Through the common digital extensor

o Needle angled just distal to horizontal

• Lateral (palmar pouch)

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

o 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

o 1 cm proximal to the annular ligament

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

o Direct needle slightly distal

• Base of sesamoid

o Axial to the midbody of the sesamoid

o Leg flexed 225º

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

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

• Pastern region

o 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:

o Use 6 ml of anesthetic

o 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

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

o 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

o Inject using distal palmar approach with radiographic guidance

o 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

o DDFT

o Distal sesamoidean ligaments

o SDFT

o Palmar annular ligament of the fetlock

o Digital annular ligament

• Recommendations:

o Anesthesia is specific

o Use as described

• Diagnostic imaging

o Radiographic exam

• Views:

• Lateral

• DP navicular

• DP P3

• Skyline navicular

• Optional:

o DP oblique P3

• Radiographic grading of navicular changes* (Dyson SJ: Diagnosis and Management of Lameness in the Horse; pp 293)

• 0: Excellent

o Good corticomedullary demarcation

o Fine trabecular pattern

o Flexor cortex of uniform thickness

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

o R and L symmetrical

• 1: Good

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

• 2: Fair

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

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

o Fewer than 8 synovial invaginations of variable size

o Mild enthesiophyte formation along proximal border

o Navicular bones asymmetrical

• 3: Poor

o Medullary sclerosis

o Thickening of dorsal and flexor cortices

o Lucent zones along the proximal border of the bone

o Large enthesiophytes formation on proximal border

o Discrete mineralization within a collaeral ligament

o Radiopaque fragment on the distal border

• 4: Bad

o Large cyst-like lesion within medulla

o Lucent region in the flexor cortex

o 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

• Nuclear scintigraphy of foot

o Both pool (soft tissue) and bone phases

o Views

• Dorsal

• Lateral

• Solar

o Value in diagnosis of palmar foot lameness

• Dyson SJ (EVJ 2002 34(2):164-170)

• Cases

o 15 normal grand prix horses

o 53 horses with primary foot pain

o 21 horses with foot pain and another cause of lameness

o 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

o Recovery

• High cost:

o Purchase

o Installation

o Maintenance

o Anesthesia

• High field strength

o Higher resolution

o Faster

o Larger field

o Less motion artifacts

o More images/series

o More detail

o Subtle lesions can be identified

o 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

o Good anatomic detail

o Less tissue contrast

• T2-weighted

o Highlights fluid and sensitive to anatomic change

o Less anatomic definition

• STIR

o Fat-suppressing

o Detect fluid in soft tissue and bone

• Sectioning

• Transverse

• Sagittal

• Dorsal

• Tissue characteristics

• Bone

o Cortical bone– black

• Protons tightly bound and little signal

o Medullary bone- hyperintense

• 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