Skeletal Variation Flashcards
How can bone remodelling be described generally?
Bone formation and degradation as an ongoing process throughout life
Where is bone created?
In skeletal tissues that are supposed to ossify
What condition is the formation of bony in tissues that are not normally bony?
Myositis ossificans circumscripta:
- Traumatica
Give examples of studies into formation of bone in non-bony tissues?
Sodl et al., (2008):
- Repeated trauma to quadriceps during college hazing resulted in myositis ossificans circumscripta
Salter, (1999)
How can myositis ossificans circumscripta appear on imaging?
Opacity on x-ray
Oedema on MRI
What type of bone is formed following trauma?
Woven
Give examples of studies that show the difference between bony variation and bony pathology?
Chakraborty and Bhattacharya, (2012):
- Describe brachydactyly of 3rd and 4th digits in right foot
- VARIATION
Singh and Downing, (2005):
- ‘Empty’ toe
- Closed degloving injury displacing 5th toe medially
- NOT variation
How do sternal foramina arise?
Incomplete fusion of multiple ossification centres
What risks do sternal foramina pose?
Risk of injury to deep structures during:
- Bone marrow aspiration
- Acupuncture
Describe the study on sternal foramina by Lloret, (2004)?
Anthropological study
Two holes in sternum:
- One with irregular edged and fracture lines = Gunshot wound
- One with smooth, rounded edges (sternal foramen)
What potential reason do Kumarasamy and Agrawal, (2011) give for a large sternal foramen?
Two failed ossification centres
Os odontoideum is an area of debate as to whether or not its variation or traumatic. What is the reasoning behind both?
Variation:
- Congenital condition representing centrum of pro-atlas or atlas
OR
Trauma:
- Chronic non-united fracture of odontoid
What can os odontoideum result in according to 3 case studies by Limo et al., (2008)?
Flexion-extension may cause ossicle and C1 movement relative to C2:
- Results in atlantoaxial instability
What was measured to quantify the instability in the case studies by Limo et al., (2008)?
Interval between:
- Posterior margin of anterior tubercle of C1
AND
- Anterior margin of base of dens and body of C2
This interval is then compared to neutral
What does the study by Candan et al., (2014) describe?
Traumatic os odontoideum in a 3 year old boy
What do non-metric traits result from?
Genetic factors
Environmental factors
What are non-metric traits?
Traits that are either present or not
Regarding the uses for skeletal variation, what did Eroglu, (2008) use?
Used frequency of metopism to obtain information about gene flow in Anatolian populations
What is metopism?
Presence of a persistent frontal suture = A metopic suture
What did Ajmani et al., (1983) study?
Incidence of metopic suture in adult Nigerian skulls
What did Dodo, (1974) study?
Hyperostotic features more common in AInu than Japanese population
What supernumerary ossicle variations of the skull were described by Hanihara and Ishida, (2001a)?
Ossicle at the lambda
Parietal bone notch
Asterionic bone
Occipitomastoid bone
What hypostotic variations of the skull were described by Hanihara and Ishida, (2001b)?
Tympanic dehiscence Ovale-spinosum confluence Metopism Transverse zygomatic suture vestige Biasteronic suture
What variations in the bony structure of the skull did Seema and Mahajan, (2014) find?
Metopism Multiple Wormian (intrasutral) bones at lambda
What variation do Udupi and Srinivasan, (2011) describe?
Large interparietal bone
What did Karau et al., (2010) investigate?
Prevalence of atlas vertebral bridges in Kenyans:
- Bony outgrowths over V3 segment of vertebral artery
What were the results of the Karau et al., (2010) study?
Complete atlas vertebral bridges more common in females:
Atlas vertebral bridges predispose to vertebrobasilar insufficiency
What did Nambiar et al., (1999) study?
Variation in frontal sinuses for forensic indentification
What is the postcranial axial skeleton formed from?
Somites:
- Mesenchyme = Mesenchymal origin
What part of the somite does connective tissue of the skin form from?
Lateral and superficial dermatome
What part of the somite does muscle form from?
Myotome
What part of the somite does the axial skeleton (including vertebrae and ribs) form from?
Medial and ventral sclerotome
What does sclerotome growth towards midline form?
Vertebral body
What does dorsal sclerotome growth do?
Encloses neural tube
What does ventrolateral sclerotome growth form?
Costal processes
What do the costal processes form in the cervical region?
Fuse with transverse process and vertebral body = Foramen transversarium
What do the costal processes form in the thoracic region?
Ribs
What do the costal processes form in the lumbar region?
Fuse with transverse processes
What do the costal processes form in the sacral region?
Pars lateralis (flat plates)
What genes regulate what the costal processes form in each region?
Hox genes
What study investigated the fates of costal processes depending on location?
Chernoff and Rogers, (2004)
Regarding the cervical prevalence of supernumerary ribs, what are the results of a study by Kurihara et al., (1999)?
Cervical (C7) rib in 0.5% of population
C7 rib more common in females
Regarding the prevalence of cervical supernumerary ribs, what are the results of a study by Viertal et al., (2012)?
Cervical ribs in 2% of population
Twice as common in females
40.3% bilateral
Higher incidence in African American population
How do cervical supernumerary ribs present according to the study by Viertal et al., (2012)?
Often asymptomatic Brachial plexus/Subclavian vessel compression: - Thoracic outlet syndrome - In 8.3% of cervical rib patients Underreported on CT
What are the types of intrathoracic ribs? (Reference?)
Type I = Supernumerary intrathoracic rib arising from:
- Ia = Vertebral body
- Ib = Part of rib close to vertebral body
Type II = Bifid intrathoracic rib
Type III = Rib locally depressed into thoracic cavity
(Kamano et al., 2006)
How do intrathoracic ribs present?
Often asymptomatic
Pain if attached to diaphragmatic pleura
How many cases of intrathoracic rib have been reported?
40 cases in literature since 1947
What might an intrathoracic rib be mistaken for?
A bone tumour
Pleural calcified plaque
Pulmonary vein variant
What is the prevalence of lumbar ribs?
0.04-2.0%
Describe sacral/pelvic ribs
Sacral/Pelvic ribs develop bone (with cortex) in soft tissues adjacent to sacrum which may pseudoarticulate
In what state might sacral or pelvic ribs cause issues?
Pregnancy
What does the Schumacher et al., (1992) study show is linked to rub anomalies?
Rib anomalies associated with malignancy:
- 242 rib anomalies in 218/1000 kids with tumours (21.8%)
- Only 11/200 kids without malignancy had rib anomalies (5.5%)
What are cervical ribs associated with according to the Schumacher et al., (1992) study?
Brain tumours (27.4%) Leukaemia (26.8%)
How did the patient of a Kazanci et al., (2012) study present?
No functional issues
Presented following injury
What was the variation seen in the Kazanci et al., (2012) case study?
Unilateral C6 hyperplasia of lamina
Schisis of spinal process:
- Gap between 2 parts of process
Spinous process 15cm long (when removed)
How could the case seen in the Kazanci et al., (2012) study be differentiated from trauma by imaging?
CT would show:
- No pseudoarthritis
- No ossifying haematoma
MRI would show no ossifying haematoma
What is the average length of the styloid process and where does the tip lie?
2.5cm long
Tip between ECA and ICA
Regarding a styloid process, what did the case study by Kolagi et al., (2010) describe?
8cm long styloid process:
- 5cm bone
- 3cm ossified stylohyoid ligament
What implications can styloid processes longer than 3cm have?
Difficulty swallowing
Carotid artery compression
Foreign body sensation
What features of a long styloid process are important regarding whether or not it will result in signs/symptoms?
Direction
Curvature
What are the epidemiological stats for hyperplasia of the styloid process (Kolagi et al., 2010)?
Prevalence = 4-7%
4x more common in males
75% of cases are bilateral
What are the types of upper limb dysplasias?
Osseous
Musculotendinous
Neuromuscular
What does radial deficiency result in?
Longitudinal deficiency in embryonic limb bun leading to defects of:
- Radius
- Carpals
- Radial rays (especially thumb)
What does ulnar deficiency result in?
Longitudinal deficiency in embryonic limb bun leading to defects of:
- Ulna
- Carpals
What other systems may be affected in radial and ulnar deficiency?
Renal
Cardiac
GI
Regarding radial and ulnar deficiency, what did radiographs in a study by Manske, (1996) show?
Radiograph of ulnar deficiency: - Abnormal radius - Absent carpals Radiograph of radial absence: - Centralised ulna (surgically) = More stable wrist
What ribs are usually affected as shortened midthoracic ribs?
6, 7 or 8
What is the prevalence of shortened midthoracic ribs?
16%
Right side = 8%
Left side = 1%
Bilateral = 7%
What is the reference for shortened midthoracic ribs?
Kurihara et al., (1999)
What is the embryological origin of shortened midthoracic ribs?
Early fusion of epiphyseal centre
What are the clinical issues associated with shortened midthoracic ribs?
There are none
What are the functions of bone?
Protection/Support
Muscle attachment
Movements (joints
What are the surgical implications of bony variation?
Transplantation issues
Implantation of prostheses/Fixation
What variation is described in a case study by Varrichio et al., (2013)?
Obturator nerve running in osseous tunnel from near ischial spine to normal pelvic aspect of the obturator canal
What are the implications of the variation described by Varrichio et al., (2013)?
None in this case
May result in issues if pelvic fracture
What is the prevalence of bifid ribs?
0.15-3.4%
What sort of defect is bifid ribs? What other defects may it be associated with because of this?
Mesenchymal
Other defects:
- Cardiac
- Renal
What are the implications of bifid ribs?
Often asymptomatic
May affect NVB branching and rib counting
What can syntosis (fusion) of ribs result in? (Reference?)
Compression of intercostal NVB
Reduced chest expansion = Respiratory issues
(Gupta et al., 2009)
What does bony absence result in?
Leaves soft tissues vulnerable to damage
How does spina bifida occulta arise?
Incomplete midline dorsal bony fusion
What is a possible clinical implication of spina bifida occulta? (Reference?)
Unprotected spinal cord:
- Dural puncture if given epidural anaesthesia
(Senoglu et al., 2008)
According to a study by Senoglu, (2007), how can a missing posterior arch of the atlas present?
Asymptomatic
Transient neurological symptoms
Bony variation may also result in what issues?
Joint instability
Risk of injury during sport
What variations may result in joint instability and how?
Aplasia = No bone to form joint
Malformations of articular surface
What did Tubbs et al., (2005) study regarding bony variation and joint stability?
Duplication of occipital condyles
What were the findings in the Tubbs et al., (2005) study?
Extra occipital condyles results in craniocervical instability
Additional bony prominences form in an attempt to stabilise
What study disagrees with the Tubbs et al., (2005) study on atlanto-occipital joint stability in the presence of additional condyles?
Kunicki and Ciszek, (2005)
What did Hemamalini, (2014) study?
Atlanto-occipital fusion
What anomalies of the atlanto-occipital joint are major enough to affect movement at the joint according to the Hemamalini, (2014) study?
Assimilation of the atlas
Occipitalisation of the atlas
What can atlanto-occipital fusion affect?
Can alter course of or compress: - Vertebral artery - C1 nerve (As both pass over C1 usually) Cord compression (if affecting foramen magnum) Flexion-extension of head
What bony variations may compress neurovascular structures?
Foramina overgrowth
Bony tunnels
Bony spurs
Apart from a variant bone itself compressing a neurovascular structure, what else may compress nerves/vessels? Examples?
Ligamentous material associated with it
Examples:
- Supracondylar spur of humerus and ligament of Struthers (Krishnamurthy and Lakshmiminarayan, 2013)
- Compression of median nerve by ligament of Struthers (Suranyi, 1983)
What can additional bones be mistaken for?
Avulsion fracture
Disease pathology
What ‘normal’ anatomy may be mistaken for variation?
Accessory ossicles
Sesamoid bones in:
- Hands
- Feet
In a study of 984 feet by Coskun et al., (2009), what did they find?
209 accessory ossicles:
- 10.9% of females
- 10.2% of males
What are the implications of an interphalangeal sesamoid bone according to Davies et al., (2003)?
Painful calluses
Migrations into a dislocated joint
How can bony variation affect dental procedures?
Bony landmarks
Foramina for neurovascular structures inside bone used for anaesthesia
What did the Hasan et al., (2010) study find that may affect dental procedures?
Bilateral absence of mental foramen
What racial differences are seen in the termination of mental canals?
Caucasians = More medial (1st/2nd premolar)
Mongoloid population = 2nd premolar
Black population = 2nd premolar/1st molar
How can variation affect dental implants?
Osteotomy for implant may damage inferior alveolar or mental nerve resulting in altered lip sensation
What are the 4 common forms of the pterion?
Sphenoparietal
Sphenoparietal plus Wormian bone
Frontotemporal
Epipteric
What did Ma et al., (2012) investigate regarding the pterion?
Its relation to the middle meningeal artery
What did Ma et al., (2012) find regarding the thickness of the skull at the pterion?
Not always the thinnest part:
- Midpoint is 4.4mm thick vs thinnest part of squamous temporal bone which is 1.1mm on lateral wall of middle cranial fossa
What did Ma et al., (2012) find regarding the pterion and the middle meningeal artery?
Anterior branch of MMA;
- Overlies pterion in only 2/3
- Is posterior to pterion in 1/3
- Is enclosed by protective bony tunnel in 70%
