:By Rasoul Rahimzadeh

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Navicular Syndrome(Podotrochleosis)

Disease or Syndrome?The term Navicular disease is used in this discussion to denote a chronic progressive syndrome involving the navicular bone, its fibro cartilaginous flexor surface, its ligaments and capsular attachment, the deep digital flexor tendon, and the navicular bursa.Variable response to local analgesia of the medial and lateral palmar digital nerve, the distal interphalangeal joint space and the navicular bursa is noted. This variable response suggests that sensory nerves innervating the synovial membranes of the collatral sesamoidean ligament, the distal sesamoidean ligament, distal sesamoidean impar ligament, and the navicular bone itself play a separate or combined role in mediating pain in navicular disease. Because there is no proven cause or treatment it is better referred to as a syndromeNavicular Syndrome is generalized heel pain due to problems with the navicular boneOther causes of heel pain are often misdiagnosed as Navicular Syndrome Dr2R

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AnatomyThe navicular bone has 1- Flexor1. Two surface 2- Articular 1- Proximal2. Two border 2- Distal 1- Medial3.Two extremities 2- Lateral

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Anatomy It has two separate cartilage- covered articular surface. The larger proximal articular surface forms to the condyles of the middle phalanx.A smaller distal articular surface, associated with the distal navicular border, is essentially a narrow facet that articulates whit the distal phalanx.The distal articular surface of the navicular bone and the articular surface of the distal phalanx are usually parallel but can be convergent.The flexor surface has a prominent central ridge – termed the central eminence.

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AnatomyThe deep digital flexor tendon and adjacent bursa make contact with the fibrocartilage-covered flexor surface.The navicular bone is held in position by three strong ligaments.1- The paired suspensory ligaments originate from the dorsolatral and dorsomedial aspects of the proximal phalanx and attach to the praoximal navicular border and both extremities.2- The distal sesamoidan or impar ligament orginates from projection on the disat navicular border just coudal to the articular surface.

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Weight Bearing

Activates navicular bone

Compression of navicular bone Tension of supporting ligaments

Cartilage degeneration,Especially on flexor surface

Abrasion of flexorTendon by eroded cartilage

Abnormal increaseIn bone density

Navicular Bursitis?

Fracture?

Navicular Syndrome

Weight Bearing

Activates navicular bone

Compression of navicular bone Tension of supporting ligaments

Ligament strain &Inflammation, especially

At bottom

Reduced blood flowTo & from navicular

bone

Cavities (“flasks” or“lollipops”) along lower edge

Loss of boneDensity around

vessels

Increased bloodPressure within navicular

bone

Tearing ofLigament(s)?

New bone Production at

Sides (“canoeing”)Compensation from

Vessels at upper edge

Navicular Syndrome

Three Causes of Navicular1. Concussion or trauma to the Navicular

bonea Thinning and erosion of the cartilageb Degeneration of the Navicular bonec Injuries of the Navicular bone and

surrounding areas.2. Arterial obstruction

* strain and inflammation of the impar ligament can obstruct these blood vessels and reduce blood flow to and from the navicular bone.

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interruption of the blood flow to and from the navicular region has been proposed as contributing factor in the development of navicular syndrome. Thrombosis of navicular arteries within the navicular bone , partial or complete occlusion of digital arteries at the level of the pastern and fetlock, and a reduction in the distal arterial blood supply as a result of atherosclerosis of the vessel, resulting in ischemia were thought to be the cause of navicular syndrome.

3. Changes in the Navicular bursa synovium*Osteoarthrosis (degenerative joint disease)

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Predisposing Factors The syndrome has been shown to have a hereditary predisposition, which is perhaps related to conformation.Factor such as faulty conformation, hoof imbalance, improper or irregular shoeing, and exercise on hard surface.Poor hoof conformation

long toes and low heelsnarrow upright feet

Extreme work on hard surfacesStanding in stalls for extended periods of timeImproper trimming and shoeing

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SymptomsNavicular syndrome is primary a slowly developing, intermittent, bilateral forelimb lameness. It is also occasionally recognized in the hindlimb.In general, Navicular syndrome is most common between 3 and 18 years of age(4 and 15 in adams), with a peak incidence of 9 years of age at presentation.Males have involvement more often than do females, gelding have a greater risk than stallion.Often a unilateral lameness.Usually restricted to the forelimbs.Walking toe to heel.Short choppy strides.Reduced wear of the heel region.

The diagnosis is based on a characteristic gait, localization of

pain to the palmar part of the heel,

identification of radiographic signs of

navicular degeneration ,and elimination of

other causes of lameness.

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PathphysiologyClassically, it has been characterized as navicular fibrocartiliginous degeneration whit secondary tendon fibrillation. Palmar cortex bone erosions can develop later. Other bony changes involving the distal border synovial invagination (enlargement) have also been noted. Abnormalities such as dilated vessels, vascular thrombosis, granulation tissue, and empty synovium-lined invagination have been observed histologically to variable degree. Enthesopathy involving the ligaments of the proximal and distal borders can occur with or without distal border framina changes. Many of the gross and histologic features of navicular syndrome support the concept of degenerative arthrosis. Some evidence shows that chronic passive venous congestion of the foot is related to navicular changes of elevated subchondrial bone pressure and arterial hyperemia.

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PathphysiologyPoor correlation of pathologic and radiographic finding with clinical signs and prognosis has been demonstrated.Horses without radiographic abnormalities may have clinical navicular lameness, and horses with pathologic and radiographic changes may be sound.This paradox is explained in part by the fact that horses have different thresholds, are subjected to wide ranges of physical exercise, and are evaluated in variable stages of disease.Several authors agree that radiographic signs of navicular disease in an otherwise clinically normal horses are significant and may warrant prognosis for future soundness.

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Indication for Radiography1- Assessment of bony changes in Navicular Syndrome.2- The identification of significant bone abnormalities during prepurchase examination.3- The assessment of bone or bursal involvement in wounds or abscesses.4- The evaluation of suspected trauma.5- The collection of information about the morphologic progression or remission of navicular bone abnormalities.

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Radiographic Views

1- Dorsoproximal-Palmarodistal Views.2-Lateromedial View.3- Palmaroproximal-Palmarodistal View.4- Dorsopalmar View.

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45 Degree DP (Dorsal 45 degree proximal-palmaro distal)

Cassette in tunnelCenter on coronary band

Normal Radiographic Appearance

Navicular BoneStandard views

Lateral and 45 degree DP (same as for P3)Horizontal DP (same as for P3)65 degree DP Cone-downSkyline (palmaroproximal palmarodistal oblique)

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Normal Navicular Bone

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Lateral

Flexor surfaceArticular surfaceProximal borderDistal border

Horizontal DP

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Evaluation of proximal navicular border

65 degree Cone-down2 methods (use grid with both)

Center on coronary bandUpright pedal

Cassette verticalHigh coronary

Horse stands on cassette tunnel flat on groundEasier but more distortion

Tightly collimated to reduce scatter and film fogNavicular bone is superimposed on P2

Must not be superimposed on DIJ

Best view for evaluation of distal navicular border

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Skyline (Palmaroproximal palmarodistal oblique)

Cassette in tunnelX-ray beam angled along back of distal pasternFlexor surfaceCorticomedullary distinction

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Roentgen Signs of Navicular Degeneration

Proximal Border and ExtremitiesEnthesophytes (spurs) on the extremities Remodeling.Distal Border ChangesSynovial invaginationsSmall osseous fragmentsFlexor Cortex ChangesCortical erosionsMineralization of deep digital flexor tendon Medullary Cavity ChangesRadiolucent cystsSclerosis

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Roentgen Signs of Navicular Degeneration

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Navicular Degeneration/ DiseaseChanges may be present in sound horsesDistal border

Increased size and number of synovial invaginations

Cyst like lucenciesEntheseophytes

Collateral ligaments (proximal border)Impar ligament (distal border)

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Navicular Degeneration/ DiseaseSclerosis/ decreased CM distinctionFlexor surface erosions

Flattening of sagittal ridgeThinning of flexor surface

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Navicular Syndrome

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MRI will allow us to more rapidly and accurately diagnose foot lameneses and addresshorses individually. Eventually, when data from numerous horses of different breedsand disciplines are available, MRI will provide us with more precise treatment regimesand prognoses for horse with these and other lameneses.

Navicular Bone

FracturesEsp. lateral and medial borders

OsteomyelitisPenetrating wound to navicular bursaLysis/ flexor surface erosions

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Thanks for your

attention