Congenital Malformations of the First Sternal Rib

[Diagnostic imaging of the equine cervical spine - Part one: Radiography - A review of the literature on findings and their clinical significance]

A number of indications exist that necessitate radiologic examination of the equine cervical spine. Different neurologic and pain-associated clinical signs within the scope of lameness or poor performance may be associated to pathologies of the cervical spine. Moreover, the number of requests for radiographic examinations of the cervical spine, for example as part of the pre-purchase examination, has increased significantly in recent years. However, the interpretation of radiographs represents a challenge, particularly in the case of clinically sound horses, as it often necessitates the resolution of a prognostic question. At present, a number of radiologic findings of the equine cervical spine lack clear clinical significance, as some findings (e. g. osteochondrosis dissecans [OCD] of the facet joints) also occur in clinically healthy horses. In acute neurologic cases, such as spinal ataxia, radiographic examination of the cervical spine is the imaging procedure of choice. The subjective and objective assessment of radiographs frequently leads to a diagnosis of cervical static myelopathy. Acute trauma, fractures or degenerative processes, may be distinguished from this entity. This literature review presents a summary of the current state of knowledge regarding the interpretation and clinical relevance of radiological findings of the equine cervical spine.

Congenital variants of the ventral laminae of the sixth and seventh cervical vertebrae are not associated with clinical signs or other radiological abnormalities of the cervicothoracic region in Warmblood horses

BACKGROUND

There is controversy about the clinical relevance of congenital variants of the ventral laminae of the sixth (C6) and seventh (C7) cervical vertebrae and their relationship with other radiological abnormalities.

OBJECTIVES

To document the prevalence of congenital variants of C6 and C7 and that of other radiological abnormalities from C6 to the second thoracic vertebra (T2).

STUDY DESIGN

Cross-sectional.

METHODS

The study included Warmblood horses ≥3 years of age undergoing clinical assessment at two referral institutions: 127 control horses and 96 cases (neurologic, neck pain or stiffness, or neck-related forelimb lameness). All horses underwent a standardised orthopaedic and neurologic examination. Lateral-lateral and lateral 45°-55° ventral-lateral dorsal (left to right and right to left) radiographic views of C5 to T2 were acquired and assessed blinded to the horse's clinical category using a predetermined grading system.

RESULTS

The ventral profile of C7 was abnormal in 54 horses (24.2%). Cases were less likely to have congenital variants than control horses, p = 0.0002, relative risk (RR): 0.63 (95% confidence intervals [CIs]: 0.4, 1.0). There was no association between the presence of a congenital variant of C7 and the presence of modelling of the articular processes (APs) of C6-C7, C7-T1 or T1-T2. Cases were more likely to have severe modelling of the APs at C6-C7, p = 0.01, RR: 1.94, CI: 1.1, 3.5 and C7-T1, p = 0.04, RR: 1.97, CI: 1.2, 3.2 compared with control horses.

MAIN LIMITATIONS

Radiographs were read by one assessor independently at each institution.

CONCLUSIONS

There was no association between the presence of congenital variants of C7 and any other radiological findings. Congenital variants occurred less frequently in cases compared with control horses. There was no association between the presence or absence of a congenital variant and the type of case.

Radiological abnormalities of the cervicothoracic vertebrae in Warmblood horses with primary neck-related clinical signs versus controls

Radiological observations at the cervicothoracic junction in horses with or without related clinical signs have not been comprehensively described. The aim was to evaluate the seventh cervical (C7) to second thoracic (T2) vertebrae in horses with neck-related clinical signs (neck pain and/or stiffness, neck-related forelimb lameness, or general proprioceptive [spinal] ataxia) and control horses. This prospective analytical cross-sectional study included 127 control horses and 96 cases, examined using standardized clinical and radiological protocols. Univariable logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI) to identify factors associated with radiological abnormalities. Severe modeling of the articular processes at C7-T1 was more likely in cases compared with controls, OR, 4.25; CI, 1.04-17.36; P = .04. Cases were more likely to have spondylolisthesis at C7-T1 than controls, OR, 3.61; CI, 1.75-7.44; P < .001. There was a lack of uniformity of disc space width at C6-C7, despite normal alignment of the vertebrae, in five (5.2%) cases and no control horses. Discospondylosis was seen in 9 (9.4%) horses at C7-T1 and 10 of 64 (15.6%) at T1-T2. The sagittal ratio for T1 was smaller for horses with neck-related forelimb lameness (P < .0002), neck pain/ stiffness (P = .04), or neurological cases (P < .001) than controls. The prevalence of radiological abnormalities at C7-T1 and T1-T2 highlights the importance of careful evaluation of the cervicothoracic junction in horses with neck-related signs.

Increased incidences of cervical ribs in deer indicate extinction risk

Mammals as a rule have seven cervical vertebrae, a number which remains remarkably conserved. Occasional deviations of this number are usually due to the presence of cervical ribs on the seventh vertebra, indicating a homeotic transformation from a cervical rib-less vertebra into a thoracic rib-bearing vertebra. These transformations are often associated with major congenital abnormalities or pediatric cancers (pleiotropic effects) that are, at least in humans, strongly selected against. Based on data from Late Pleistocene mammoths (Mammuthus primigenius) and woolly rhinoceroses (Coelodonta antiquitatis) from the North Sea, we hypothesized that high incidences of cervical ribs in declining populations are due to inbreeding and/or adverse conditions impacting early pregnancies. In this study, we investigated the incidence of cervical ribs in an extinct Late Pleistocene megaherbivore, giant deer (Megaloceros giganteus) from Ireland and in the extant highly inbred Père David deer (Elaphurus davidianus) and in twenty other extant species. We show that the incidence of cervical ribs is exceptionally high in both the Irish giant deer and the Père David deer and much higher than in extant outbred deer. Our data support the hypothesis that inbreeding and genetic drift increase the frequencies of maladaptive alleles in populations at risk of extinction. The high incidence of cervical ribs indicates a vulnerable condition, which may have contributed to the extinction of megaherbivore species in the Late Pleistocene. We argue that cervical rib frequency may be a good proxy for extinction risk in inbred populations.

Equine intervertebral disc disease with dorsal protrusion and spinal cord compression: A computed tomography, myelography, MRI, and histopathologic case study

A 3-year-old American Saddlebred gelding presented for progressive tetraparesis, ataxia, and cervical hyperaesthesia. Radiographic myelography identified spinal cord compression at C6-7 in neutral, extended, and flexed positions and at C4-5 in the flexed position. CT myelography and postmortem MRI identified severe vertebral canal stenosis/compression at C6-7. MRI further identified severe intervertebral disc herniation at C6-7 with intramedullary changes. Disc protrusion was confirmed macroscopically at postmortem. Lesions consistent with compressive myelopathy were confirmed microscopically at C6-7. This is the first report of equine disc protrusion and myelocompression confirmed by multiple advanced imaging modalities and postmortem examination.

Characterization and Association of the Missing Ventral Tubercle(s) from the Sixth Cervical Vertebra and Transpositions on the Ventral Surface of the Seventh Cervical Vertebra in Modern Equus ferus caballus

In recent years, equine complex vertebral malformation (ECVM) has been of concern in the equine community, with studies identifying numerous associative morphological variations. Here, we examine the morphological association between C6 and C7 for dependency in ECVM cases, where the partially absent ventral process of C6 transposes on the ventral surface of C7. A C6 ventral process presents two tubercles, one cranial (CrVT) and one caudal (CVT). In this study, the C6 osseous specimens (n = 85) demonstrated a partial or completely absent CVT (aCVT) graded 1-4 that often extended cranially creating a partially absent cranial ventral tubercle (aCrVT) graded 1-3. In the 85 C6 osseous specimens examined, the corresponding C7s demonstrated either a complete or incomplete transposition of the ventral process from C6 in 44/85, with 30/44 replicating a transverse foramen. A strong statistical dependency existed between C6 grade 4 aCVTs and grades 1-3 aCrVTs and C7 transpositions with replicated transverse foramen. Sidedness was also demonstrated, where a left sided absent C6 associated with transposition on the left ventral surface of C7. This likewise applied to right sidedness and most bilateral cases. These findings might benefit practitioners when radiographing the extent of the ECVM configuration in patients presenting caudal cervical pain.

Historic Horse Family Displaying Malformations of the Cervicothoracic Junction and Their Connection to Modern German Warmblood Horses

Malformations of the equine cervicothoracic junction affect the C6 and C7 cervical vertebrae, the T1 thoracic vertebra and in variable extent the first and second sternal ribs. To date, the clinical impact of this malformation, its prevalence and mode of inheritance in equine populations are not yet determined. We examined five skeletons for signs of malformation of the cervicothoracic junction, including three skeletons from widely used Thoroughbred stallions affected with the malformation and two skeletons serving as a comparison. The three affected historical horses were the Thoroughbred stallions Der Loewe XX, Birkhahn XX and their common great grandsire Dark Ronald XX. Malformations of C6 and C7 showed a large variation between the three stallions, as Dark Ronald XX, Der Loewe XX and Birkhahn XX were affected uni-laterally at C6 and C7, uni-laterally at C6 and bi-laterally at C6 and C7, respectively, with varying grades. In order to evaluate whether or not these malformations are incidental, we took a random sample of 20 living German Warmblood horses, which are distant descendants of these stallions. This sample consisted of ten controls and ten horses with malformations of C6/C7. Blood proportions of the historical sires in the modern Warmblood horses ranged from 0.10 to 6.25%. The contribution to inbreeding in each individual horse of our selected horse group by those sires was expressed as a percentage of the total inbreeding coefficient and ranged from 0.01 to 17.96%, demonstrating their influence on the modern Warmblood. In the present study, we were able to describe the variability of the malformation of C6/C7 within a horse family including historic and modern horses. Additionally, we detected variations appearing in connection with malformations of the cervicothoracic junction that have not been described in the literature yet. This is the first time that the malformations of C6 and C7 have been described within a familial context, providing hints on inheritance in Thoroughbreds and Warmbloods. It is worthwhile to carry out further studies in a larger setting to gain more comprehensive insights into the inheritance of the malformation and the role of important ancestors.

Breaking the constraint on the number of cervical vertebrae in mammals: On homeotic transformations in lorises and pottos

Mammals almost always have seven cervical vertebrae. The strong evolutionary constraint on changes in this number has been broken in sloths and manatees. We have proposed that the extremely low activity and metabolic rates of these species relax the stabilizing selection against changes in the cervical count. Our hypothesis is that strong stabilizing selection in other mammals is largely indirect and due to associated pleiotropic effects, including juvenile cancers. Additional direct selection can occur due to biomechanical problems (thoracic outlet syndrome). Low metabolic and activity rates are thought to diminish these direct and indirect effects. To test this hypothesis within the primates, we have compared the number of cervical vertebrae of three lorisid species with particularly low activity and metabolic rates with those of more active primate species, including with their phylogenetically closest active relatives, the galagids (bushbabies). In support of our hypothesis, we found that 37.6% of the lorisid specimens had an abnormal cervical count, which is a higher percentage than in the other nine primate families, in which the incidence varied from zero to 2.2%. We conclude that our data support the importance of internal selection in constraining evolvability and of a relaxed stabilizing selection for increasing evolvability. Additionally, we discuss that there is no support for a role of the muscularized diaphragm in the evolutionary constraint.

A systematic review of clinical signs associated with degenerative conditions and morphological variations of the equine caudal neck

Conditions of the equine caudal neck (C5-C7) are thought to be associated with various clinical signs. However, little investigation has been undertaken to isolate clinical indicators associated with specific conditions of the equine caudal cervical spine. This systematic review aimed to evaluate associations of clinical signs with anatomical malformation of caudal cervical vertebrae, spinal cord compression of the caudal cervical spine, and arthropathy of the caudal cervical articular process joints (APJs). A literature search was carried out using Google Scholar in accordance with PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines. Studies were selected for inclusion in this systematic review according to a set of inclusion criteria, resulting in a small group of eligible studies (n=12) that addressed clinical signs associated with caudal cervical spine conditions in horses. The results of the included studies indicate that there are grounds for further investigation of clinical presentations of specific conditions of the equine caudal neck such as anatomical variations, myelopathy, and alteration to the APJs.

Radiographic findings and anatomical variations of the caudal cervical area in horses with neck pain and ataxia: case-control study on 116 horses

BACKGROUND

Abnormalities of the ventral lamina of the sixth cervical vertebra (AVL-C6) are thought to exert abnormal stress on the articular process joints (APJs) of the cervicothoracic junction. The aim of the study was to investigate the association between AVL-C6 and radiographic findings in the caudal cervical area and between clinical signs of neck pain and ataxia and radiographic findings.

METHODS

Medical records of horses subjected to cervical radiography were reviewed. Horses were classified into those with neck pain (group C), those with ataxia (group A) and healthy horses (group H). Presence of AVL-C6 and increased size, dysplasia, remodelling, fragmentation and osteochondral fragment at the APJs (C5-T1) were recorded. Univariable logistic regression analysis was performed to identify the associations between explanatory and dependent variables. Variables with P<0.2 were included in the multivariable analysis.

RESULTS

One hundred and sixteen horses were included (44 in group C, 29 in group A, 66 in group H); 24 of 116 horses had radiographic AVL-C6. Age, AVL-C6 and overall/C6-C7 increase in size remained in the final models.

CONCLUSIONS

The presence of AVL-C6 and moderate/severe increase in size of the caudal cervical APJs increase the odds of showing neck pain and, if severe, ataxia.

A Radiographic Technique for Assessment of Morphologic Variations of the Equine Caudal Cervical Spine

Equine Caudal Cervical Morphologic Variation (ECCMV) is a congenital malformation of the caudal cervical spine distinct from the more commonly recognized Cervical Vertebral Stenotic Myelopathy (CVSM). The most common presentation of ECCMV is recognized on the sixth cervical vertebra (C6). In "normal" presentations, the transverse processes on the left and right sides have a caudal lamina projecting ventrally below the caudal vertebral body in a heel shape. With ECCMV, variations occur to the structure of the caudal ventral lamina on one or both sides of C6 and may include the seventh cervical (C7) and first thoracic (T1) vertebrae and ribs, in varying configurations. Whereas the prevalence of ECCMV is not known, it has been recognized for many years and has been reported to occur with relatively high frequency within multiple populations of domesticated horses. To date, there is no documented link between the occurrence of ECCMV and clinical signs. However, based on retrospective studies, multiple authors have recognized the potential impact on performance that this condition may have. Establishing a reliable radiographic protocol for the consistent diagnosis of ECCMV would allow quantitative, scientific evaluation of the problem and support clinicians working in this field. We present a radiographic technique, which has been illustrated by diagnosis of ECCMV in three horses and confirmation of the diagnoses in two cases via postmortem examination.

Caudal cervical vertebral morphological variation is not associated with clinical signs in Warmblood horses

BACKGROUND

Variation in equine caudal cervical spine morphology at C6 and C7 has high prevalence in Warmblood horses and is suspected to be associated with pain in a large mixed-breed group of horses. At present no data exist on the relationship between radiographic phenotype and clinical presentation in Warmblood horses in a case-control study.

OBJECTIVES

To establish the frequency of radiographically visible morphologic variation in a large group of Warmblood horses with clinical signs and compare this with a group without clinical signs. We hypothesised that occurrence of morphologic variation in the case group would not differ from the control group, indicating there is no association between clinical signs and morphologic variation.

STUDY DESIGN

Retrospective case-control.

METHODS

Radiographic presence or absence of morphologic variation of cervical vertebrae C6 and C7 was recorded in case (n = 245) and control horses (n = 132). Case and control groups were compared by univariable Pearson's Chi-square and multivariable logistic regression for measurement variables age, sex, breed, degenerative joint disease and morphologic variation at C6 and C7. Odds ratio and confidence intervals were obtained. A P≤0.05 was considered statistically significant.

RESULTS

Morphologic variation at C6 and C7 (n = 108/377 = 28.6%; Cases 58/245 = 23.7%; Control 50/132 = 38%) was less frequent in horses with clinical signs in univariable testing (OR 0.48, 95% CI 0.3-0.8, P = 0.001). Age, sex, breed and degenerative joint disease were not retained in the final multivariable logistic regression step whereas morphologic variation remained significantly less present in horses with clinical signs.

MAIN LIMITATIONS

Possible demographic differences between equine clinics.

CONCLUSIONS

Morphologic variation in the caudal cervical spine was detected more frequently in horses without clinical signs. Therefore, radiographic presence of such variation does not necessarily implicate the presence of clinical signs.