Muscular Variation Flashcards
What is the 1st muscle/nerve law?
Migration:
- Nerve regarded as indicator of the route the muscle mass migrated along
- eg. Diaphragm
What is the 2nd muscle/nerve law?
Fusion:
- When muscle is supplied by 2 different nerves
- Fusion of 2 masses; each with own innervation
- eg. External oblique supply upper and lower
What is the 3rd muscle/nerve law?
Separation:
- Two different muscle masses supplied by same nerve
- Derived from a single mass
- eg. SCM and trapezius
What is the reference for the muscle/nerve laws?
Shinohara, 1996
What variant of palmaris longus did John Wood describe in the 1880s?
A ‘new’ muscle which flexed 3rd metacarpal:
- Flexor carpi radialis seu profundus
- Arose from radius below FDP
- Inserts into 3rd metacarpal OR 2nd metacarpal and trapezium/palmar fascia
What other variations were noted in the patient that John Wood studied in the 1880s?
Flexor carpi radialis also attached to 4th metacarpal
Extra extensor to middle finger
2x extensor digiti minimi plus slip to ring finger
Slip of fibularis brevis to little toe
What was the hypothesis proposed by Smith et al., (2009) regarding the vastus medialis?
Is it:
- One single muscle
OR
- Vastus medialis obliquus (distally) and vastus medialis longus (proximally)
What participants were used in the study by Smith et al., (2009)?
699 healthy knees
591 knees with patellofemoral dysfunction
What do most of the knees in the Smith et al., (2009) study show?
Substantial variation in fibre alignment from proximal to distal
What variation was seen in a small proportion of both groups in the Smith et al., (2009) study?
A fibrofascial plane dividing the two ‘muscles’ of vastus medialis
What number of nerve branches were seen in both cohorts in the Smith et al., (2009) study?
1 or 2
What did Smith et al., (2009) conclude needs more studying?
Patellar instability
Anterior knee pain
Before 1977, what was the consensus on how muscles formed?
Somites gave rise to body wall muscles
Local cells in limbs formed limb muscles
What did Christ et al., (1977) suggest result in limb muscle formation?
Muscle forming cells left somites and migrated into limb buds
Underwent transition to mesenchyme
What do we now know all trunk muscles develop from?
Somites (dorsal dermomyotome)
What are hypaxial muscles?
Muscles ventral to horizontal septum of vertebrae:
- Diaphragm
- Abdominal muscles
- All limb muscles
What are epaxial muscles?
Muscles dorsal to horizontal septum of vertebrae:
- Erector spinae
- Transversospinalis
- Splenius
- Suboccipital muscles
From where do hypaxial and epaxial muscles form?
All hypaxial muscles form from lateral 1/3 of somite
The remainder of the somite forms the epaxial muscles
Hypaxial muscles must translocate to their final destination. Precursors for what muscles extend into the lateral plate mesoderm?
Pre-vertebral muscles
Intercostal muscles
Abdominal muscles
Hypaxial muscles must translocate to their final destination. Where do limb muscles translocation from?
Ventrolateral lip of dermomyotome
Where do limb muscle precursors translocate to and what do they transition to?
Transition to mesenchmye
Precursors migrate to limbs
What is the final step in the simplified view of development?
Cells move directly from origin to destination:
- Not true for some muscles
Why was the in-out mechanism propsed?
Some muscles originate on body wall and insert into limbs (eg. pec major):
- How do they form?
- Why do some cells remain in trunk and others move into limbs
What is the in-out mechanism?
- Myogenic cells from somites migrate as individual cells to limb buds
- A cohort of MyoD-expressing cells migrate back to trunk
What does the in-out mechanism imply muscle development relies on?
Limb development
What are references for the in-out mechanism?
Valasek et al., (2005)
Evans, (2006)
What models are used to investigate the in-out mechanism?
Mammalian and avian models
Perineal and pectoral girdle muscles
What pectoral muscles attach to the axial skeleton but the main muscle bulk lies outwith limb?
Pectoralis major
Latissimus dorsi
How do pectoral muscles form?
- Precursors start by migrating to forelimb (upper limb bud)
- Some cells stay in limb bud = Insertion sites
- Many MyoD-differentiated cells move back to trunk = Main muscle bulk
How does the nerve supply to pectoral muscles form?
From brachial plexus:
- Initially extend into limb bud
- Then extend onto body wall
Regarding the pectoral region, what muscle formation is seen in mutant mice?
Superficial muscles don't form Deeper muscles do form: - Serratus anterior - Supraspinatus Muscle formation without migration for some muscles between trunk and limbs
What is Poland’s syndrome?
Absence of pectoralis major and serratus anterior
Syndactyly
What variations were noted on the left side of the cadaver in a case study by Mosconi and Kamath, (2003)?
Sternal portion of sternocostal head of pec. major absent
Rest of pec. major well developed
Normal pec. minor
What variations were noted on the right side of the cadaver in a case study by Mosconi and Kamath, (2003)?
Entire pec. major absent Muscles infiltrated by connective tissue and fat: - Pec. minor - Deltoid - Coracobrachialis
What variations were noted on both sides of the cadaver in a case study by Mosconi and Kamath, (2003)? What does this suggest?
Lateral pectoral nerves absent
Medial pectoral nerves present
Suggests developmental failure of embryonic muscles:
- Rather than secondary to polio or Poland’s syndrome
What is the development of pec. major and minor?
Develop from a muscle mass during 5th month in utero
How does pec major develop?
Attaches to clavicle
Then fans out to attach to:
- Ribs
- Sternum
What is the textbook anatomy of flexor digitorum superficialis?
Origins: - Medial epicondyle - Radius Insertion = Middle phalanx of digits 2-5 Innervated by median nerve
Where do most flexor digitorum superficialis anomalies arise?
To ring and little fingers
How does flexor digitorum superficialis develop?
As a single mass (palm or forearm) and develops
OR
As dual origin with palmar mass migrating to join mass in forearm
Regarding the flexor digitorum superficialis, what variation did Kobayashi et al., (2003) note?
Mass in center of flexor retinaculum inserts into middle phalanx of little finger - Split tendon
Normal little finger slip of antebrachial FDS absent
What is extensor digitorum brevis manus?
A muscle mass:
- From dorsal wrist carpals
- Inserts into extensor hood of index/middle finger
What is extensor digitorum brevis manus also called?
Extensor indicis brevis
Extensor medii brevis
What is extensor digitorum brevis manus usually innervated by?
Posterior interosseous nerve (radial nerve branch)
What is the prevalence of extensor digitorum brevis manus according to Rodriguez-Niedenfuhr et al., (2002)?
Seen in 162 hands out of 8111 (2%)
What is extensor digitorum brevis manus associated with?
Absence of extensor indicis
What might the extensor digitorum brevis manus be a derivative of?
Interosseous muscles (Wood, 1864) Dorsal forearm (Kaneff, 1970)
What might extensor digitorum brevis manus be a homologue of?
Extensor digitorum brevis in the foot
What does the innervation to extensor digitorum brevis manus suggest?
It’s a forearm derivative
What can extensor digitorum brevis manus be mistaken for?
Ganglia
Extensor synovitis
Tendon sheath cyst
Soft tumour
How can extensor digitorum brevis manus be differentiated from a ganglion?
EDBM prominent during wrist/digit extension
Ganglion prominent during wrist/digit flexion
What is sternalis?
Anterior thoracic muscle that lies superficial to:
- Sternum
- Sternocostal fascicles of pectoralis major
Is sternalis usually unilateral or bilateral?
Often bilateral:
- May have >1 on each side
Regarding sternalis, what did the case study by Arraez-Aybar et al., (2003) show?
Sternalis in left hemithorax of 70 male cadaver:
- 13cm long
- 7cm wide
- 0.5cm thick
Innervated by branch of left 4th intercostal nerve
What does Turner, (1867) suggest is the origin of sternalis?
Pectoralis cutaneous muscle of lower animals
What does Barlow, (1934) suggest is the origin of sternalis?
Remains of panniculus carnosis:
- Playtsma in humans
What does Clemente, (1985) suggest is the origin of sternalis?
Misplaced pectoralis minor
What does Saddler, (1995) suggest is the origin of sternalis?
Longitudinal column from ventral tips of hypomere:
- Portion of myotome that forms muscles of body wall
What is the innervation to sternalis?
55% from internal and external thoracic nerves
43% from intercostal nerves
2% from both
What issues can sternalis cause
ECG alterations
Mistaken for herniated pectoral muscles
Mistaken for soft tissue mass - Mammography
What is the textbook structure of plantaris?
Originates from lateral condyle of femur above lateral head of gastrocnemius
Long tendon joints tendocalcaneus
Plantarflexes ankle
Regarding plantaris, what did Freeman et al., (2008) find?
Studied 46 knees:
- 26 conformed to standard definitions
- 6 had absent plantaris
- 14 had variations
What variations of plantaris did Freeman et al., (2008) find?
9 with interdigitations with lateral head of gastrocnemius
5 showed a strong fibrous extension to patella
What do the plantaris variations found by Freeman et al., (2008) suggest?
Plantaris assists with lateral head of gastrocnemius
It is involved with patellofemoral dynamics
What is the prevalence of an axillary arch?
7-8%
What is the course of the axillary arch?
Runs from anterior border of latissimus dorsi to posterior layer of pectoralis major tendon
What variations of axillary arch exist?
Can run to coracoid process
Can arise from serratus anterior
Where does the axillary arch pass through and over?
All pass through axilla
Often pass over axillary NVB
What is the prevalence of pectoralis quartis?
11-16%
Where does pectoralis quartis arise?
From costochondral junction of 5th-6th rib
OR
Lateral margin of pectoralis major
Where does pectoralis quartis extend along and insert?
Extends along lateral margin of pectoralis major
Inserts:
- Deep layer of pectoralis major tendon
- May insert into axillary arch
Where does pectoralis quartis course in relation to the axillary NVB?
Passes over axillary NVB
What is the prevalence of chondroepitrochlearis?
0.5% (Flaherty et al., 1999)
Most studies say it is rarer
What is the course of chondroepitrochlearis?
Long muscular band from: - Costal cartilages OR - Aponeurosis of external oblique Insertions: - Distal humerus - Medial epicondyle of humerus
What structure does chondroepitrochlearis cross?
Axilla
How can anomalous muscular structures impact surgery?
Obscures view
Prevents access
Mistaken for other structures
What techniques are often affected more by anomalous structures?
Laparoscopic
Why are muscular anomalies often a ‘surprise’ during surgery?
Not seen on:
- Plain x-ray
- Angiogram
May be very small on CT
What did Natsis et al., (2010) study?
Anomalous muscles which affect axillary lymph clearance
What variations did Natsis et al., (2010) note in a 107 cadaver study?
8 cadavers (7.48%) affected by variations:
- Axillary arch in 5
- Pectoralis quartis in 3
- 1 with both
1 cadaver:
- Almost completely absent pec major on one side
- Both pec minors absent
What was the conclusion of the Natsis et al., (2010) study?
Anomalies obscure surgical field of view
What can additional slips of muscle/tendon impede? What can an accessory head of FPL compress?
Normal passage of nerves and blood vessels
AHFPL can entrap anterior interosseous nerve
What are the origins of the accessory head of flexor pollicis longus referred to as Gantzer’s muscle?
Coronoid process
OR
Medial epicondyle
What percentage of accessory head of FPL cases are Gantzer’s muscle?
50-60%
What is the prevalence of accessory head of FPL?
5.3-75%
What is the relation of the anterior interosseous nerve (which supplies FHL) to an accessory head of FPL in an Indian population? (Reference?)
AIN anterior to AHFPL = 13.4% AIN lateral to AHFPL = 65.8% AIN posterior to AHFPL = 8.1% AIN posterolateral to AHFPL = 12.8% (Mahakkanukrah et al., 2004)
What is the function of FPL?
Stabilises thumb in precision movement
What can anterior interosseous nerve entrapment result in?
Neuralgic amyotrophy neuritis
Where does the ulnar nerve run in relation to the carpal tunnel?
Above it
What does the ulnar nerve run within to enter the hand?
Guyon’s/Ulnar canal
What fibrous arch did Bozkurt et al., (2005) note was an additional structure in Guyon’s canal? What originated from this arch?
Fibrous arch from hook of hamate to pisiform in 21/37 upper limbs:
- In 13 of these, flexor digiti minimi originated from arch
What addition muscles were noted in the study by Bozkurt et al., (2005)? How many ran through Guyon’s canal?
6 additional muscles:
- 5 accessory abductor digiti minimi
- 1 accessory flexor digiti minimi
4 passed through Guyon’s canal
How can the axillary arch cause neurovascular compression?
If it passes through axillary NVB
Telisky and Olinger, (2011) describe a variant case of axillary arch. What unique attachments did this axillary arch display?
Unique attachments to latissimus dorsi:
- Medial fibres of arch in same direction as LD (typical for axillary arch)
- Unique fibres at lateral edge of arch which curled laterally and inserted onto LD tendon
What did the unique course of the axillary arch in the case study by Telisky and Olinger, (2011) affect anatomically?
‘Cradled’ axillary NVB:
- Compression of NVB
- Reduced space in axilla
What were the dimensions of the axillary arch in the case study by Telisky and Olinger, (2011)?
- 5cm long
- 5cm wide
- 5cm thick
After interviewing relatives, what did Telisky and Olinger, (2011) discover the unique attachments of the axillary arch in their case had caused?
Numbness and tingling in left arm for most of life
No vascular issues in left arm
No issues with right arm:
- Variation only seen on left side
What is the summary of findings in the Provyn et al., (2011)?
Mean age 21.3 years
20 (out of 239 subjects) had axillary arch:
- 12 unilateral
- 8 bilateral
Following echo doppler of axillary vessels of normal and axillary arch cohorts, what effects on axillary artery blood flow were noted between the groups by Provyn et al., (2011)?
No difference in blood flow
Following echo doppler of axillary vessels of normal and axillary arch cohorts, what effects on axillary artery circulation velocity were noted between the groups by Provyn et al., (2011)?
Varied significantly with arm at:
- 90 degrees abduction
- 120 abduction
Following echo doppler of axillary vessels of normal and axillary arch cohorts, what effects on axillary artery vessel diameter were noted between the groups by Provyn et al., (2011)?
Varied significantly with arm at:
- 90 degrees abduction and exorotation
- 120 abduction
Following echo doppler of axillary vessels of normal and axillary arch cohorts, what effects on the axillary vien were noted between the groups by Provyn et al., (2011)?
No significant differences
