Camelidae and Cervidae Congenital Musculoskeletal Defects – NAVLE Study Guide

Overview and Clinical Importance

Congenital musculoskeletal defects are abnormalities of the bones, joints, muscles, and connective tissues present at birth. These conditions are particularly significant in South American camelids (SACs) including llamas and alpacas, where they occur more commonly than in other domestic livestock species. The relatively narrow genetic diversity in North American camelid populations, stemming from limited original stock importation, contributes to the higher prevalence of inherited defects.

In cervids (deer), congenital musculoskeletal abnormalities are less frequently documented in clinical literature, partly due to reduced survival of affected fawns in wild populations. However, understanding these conditions is important for wildlife rehabilitation, zoological medicine, and farmed deer operations.

Etiology of Congenital Defects

The causes of congenital defects in camelids and cervids are multifactorial. Understanding the etiology is essential for prevention and client counseling regarding breeding decisions.

Angular Limb Deformities (ALD)

Angular limb deformities are the MOST COMMON musculoskeletal congenital defects in both camelids and cervids. They represent deviation of the limb in the frontal plane, either laterally (valgus) or medially (varus).

Definition and Terminology

• Valgus: Lateral (outward) deviation of the limb distal to the affected joint ("knock-kneed")
• Varus: Medial (inward) deviation of the limb distal to the affected joint ("bow-legged")
• Naming convention: Named for the joint where deviation originates plus direction (e.g., "carpal valgus" = outward deviation at the carpus)

Prevalence in Study Populations

Etiology of Angular Limb Deformities

Congenital ALD is most often associated with prematurity. Premature neonates have joint instability due to immaturity of ligaments and muscle-tendon units, leading to altered weight bearing and eccentric loading of physes.

Acquired ALD is multifactorial and may include: hypovitaminosis D, micro/macromineral imbalances (copper, calcium, phosphorus), trauma, genetics, or secondary to other musculoskeletal defects.

Key mechanism: Physes respond to biomechanical loading by changing growth rates. Asymmetric loading causes one side of the bone to grow faster than the other, resulting in angular deviation.

Clinical Presentation and Diagnosis

Clinical Signs:

• Visible deviation of limb(s) from normal alignment
• Most commonly affects forelimbs bilaterally
• Carpal valgus is the most frequently observed deformity
• May be hidden by fiber in llamas/alpacas until shearing or close examination
• Mean age at presentation: 6.2 months (range 2.5-11 months) in llamas

Diagnostic Approach:

• Physical examination: Shear or wet down fiber to visualize limb contour
• Radiography: Essential for determining origin of defect, angle of deviation, physeal status, and soft tissue involvement
• Blood chemistry: Evaluate calcium, phosphorus, vitamin D levels to rule out rickets

Treatment Options

Prognosis and Outcome

• 74% of surgically treated limbs achieve full straightening
• Deviations greater than 19° have decreased success rates
• Animals less than 4 months at surgery have higher failure rates
• Hypophosphatemia at surgery is associated with poorer outcomes
• A hereditary component has been proposed; affected animals should not be bred

Arthrogryposis

Arthrogryposis ("curved joint") refers to congenital, non-progressive joint contractures affecting two or more body areas. It represents a clinical syndrome rather than a single disease, with over 300 different conditions potentially causing the phenotype.

Clinical Features

• Multiple rigid joints with severe limitation of range of motion
• May affect forelimbs, hindlimbs, or both
• Often accompanied by muscular malformations/hypoplasia
• Can occur with polydactyly in camelids
• Crias are often unable to stand or nurse

Etiology

• Reduced fetal movement during development
• Neurological abnormalities affecting motor neurons
• Muscle development abnormalities
• Connective tissue disorders
• Intrauterine crowding or malpositioning
• Teratogenic agents (plant toxins, viruses)

Diagnosis and Treatment

Diagnosis:

• Clinical examination reveals multiple rigid joints
• Radiographs to evaluate bone and joint structures
• Differentiate from simple tendon contracture

Treatment:

• Mild cases: Physical therapy, splinting, serial casting
• Moderate cases: Soft tissue release surgery
• Severe cases: Often euthanasia is warranted due to poor quality of life
• Prognosis depends on severity and number of joints affected

Polydactyly and Syndactyly

Polydactyly

Polydactyly (additional digits) is relatively common in domestic camelids, with reports in dromedary camels, llamas, alpacas, and even wild guanacos. It is presumed to be caused by an autosomal dominant gene in alpacas.

Clinical Features:

• One to three accessory digits on one or all limbs
• Extra digit usually located medially
• May or may not bear weight
• Can occur in combination with arthrogryposis
• Prevalence greater than 3.6% reported in some studies

Treatment:

• Surgical excision of extra metacarpus/metatarsus and digit
• Success depends on severity and involvement of carpus/tarsus
• Not life-threatening; breeding recommendations should consider hereditary nature

Syndactyly

Syndactyly (fused digits) also occurs in camelids and is thought to be hereditary. Affected animals have partial or complete fusion of the two digits, which may involve soft tissue only or include bone fusion.

Neither polydactyly nor syndactyly is typically life-threatening, but affected animals should be excluded from breeding programs due to the hereditary component.

Flexural Limb Deformities

Flexural deformities affect the sagittal plane and primarily involve soft tissues (tendons, ligaments), resulting in joint hyperflexion ("contracted tendons") or hyperextension (laxity).

Tendon Laxity (Hyperextension)

Clinical Features:

• Prevalence: 12.3% in European SAC survey
• Excessive dorsal flexion of fetlock
• Animal may "knuckle over" or walk on dorsal surface of pastern
• Often associated with prematurity or poor development

Treatment:

• Mild cases often self-correct with controlled exercise
• Moderate cases: Splinting for 7-14 days
• Protection of soft tissue structures is essential

Tendon Contracture (Hyperflexion)

Clinical Features:

• Functional shortening of flexor tendon unit
• Excessive palmar/plantar flexion of joint
• May prevent normal standing and nursing

Treatment:

• Physical therapy and stretching
• Splinting or casting
• Oxytetracycline (causes tendon relaxation)
• Severe cases may require surgical tendon transection

Vertebral and Spinal Defects

Types of Vertebral Abnormalities

Cervical Ribs in Cervids

Recent research has identified cervical ribs (ribs on the normally rib-less seventh cervical vertebra) as a significant marker of inbreeding and extinction risk in deer populations. High incidences have been found in:

• Late Pleistocene giant deer (Megaloceros giganteus) before extinction
• Highly inbred Père David deer (Elaphurus davidianus)
• These cervical ribs are associated with other skeletal abnormalities including vertebral fusions, abnormally shaped bones, and marked asymmetry

Craniofacial Defects

Maxillofacial Dysgenesis (Wry Face)

Maxillofacial dysgenesis (wry face or wry nose) is characterized by lateral deviation of the maxilla ranging from slight (less than 5°) to severe (greater than 60°). The mandible may or may not have similar deviation (campylognathia).

Clinical Features:

• Variable degrees of facial asymmetry
• May be associated with choanal atresia
• Severe cases cause occlusion of nares
• Malocclusion of incisors and dental pad

Prognosis:

• Mild cases may be cosmetic only
• Severe cases usually require euthanasia due to inability to breathe/nurse

Brachygnathism and Prognathism

• Brachygnathism: Mandibular or maxillary shortening ("parrot mouth" when mandible is short)
• Prognathism: Mandibular or maxillary elongation ("monkey mouth" when mandible is long)
• Both reported as hereditary in camelids
• Also documented in white-tailed deer
• Breeding affected animals should be discouraged

Cervid-Specific Congenital Defects

Congenital defects are rarely documented in wild cervids due to reduced survival of affected fawns. However, several conditions have been reported:

Memory Aids for NAVLE

"CAMELID DEFECTS = C.A.M.E.L.I.D."

• Choanal atresia (most common overall)
• Angular limb deformity (most common MSK)
• Maxillofacial dysgenesis (wry face)
• Extra digits (polydactyly)
• Locked joints (arthrogryposis)
• Inbreeding = increased risk
• Don't breed affected animals!

"VALGUS vs VARUS"

• VaLgus = L for Lateral (limb goes outward = "knock-kneed")
• VaRus = R goes to center (medial) (limb goes inward = "bow-legged")

"ALD Surgery Timeline"

• Birth to 2 weeks: Splinting if joint laxity
• Less than 3 months: Periosteal stripping + ulnar ostectomy
• Greater than 3 months: Transphyseal bridging
• Closed physes: Wedge ostectomy