Musculoskeletal Growth, Injury and Repair Flashcards
What are the main anatomical components of a long bone?
Diaphysis - haematopoietic tissues Metaphysis - flare at end of shaft Epiphysis - on joint side of physis Physis - growth plate Medullary canal
Why is the diaphysis follow?
To increase diameter and strength but keep the bone light
What centres are particularly important in bone growth?
Ossification centres
What does cortical bone e.g. the diaphysis resist?
Bending and torsion
What are the features of cortical bone?
Laid down circumferentially
Less biologically active
Made up of tubes with blood vessels in the middle
Contains osteocytes
Always remodelling without affecting the whole bone
What does cancellous bone e.g. the metaphysis resist?
Resists/absorbs compression
What are the features of cancellous bone?
Site of longitudinal growth
Very biologically active
What is a fracture?
Any break in the structural continuity of bone
May be a crack, break, split, crumpling or buckle
What is the shorthand sign for a fracture?
#
What energy is needed to cause normal bones to fracture?
High energy transfer - takes a lot of energy in a normal bone to cause a fracture, energy applied in an unexpected way
Or repetitive stress e.g. stress fractures in athletes
What energy is needed to cause abnormal bones to fracture?
Only low energy transfer required to fracture an abnormal bone e.g. a bone with osteoporosis, osteomalacia, metastatic tumour, other bone disorders etc.
The older you get, the less energy it takes to cause a fracture
What is the general biological effect of a fracture?
Mechanical and structural failure of bone
Disruption of blood supply
Regenerative process - no scar, four stages
What is critical for the progression of fracture healing?
Mechanical properties of tissues and there environment
What is involved in stage 1 of the regenerative process following a fracture?
Begins immediately after fracture
Haematoma and fibrin clot form immediately
Platelets, PMNs, neutrophils, monocytes and macrophages produce
Lysosomal enzymes
Fibroblasts
What is the role of mesenchymal and osteoprogenitor cells in the regenerative process following a fracture?
Transformed endothelial cells from the medullary canal and/or periosteum
Osteogenic induction of cells from muscle and soft tissues
How does angiogenesis occur following a fracture?
Oxygen gradient is required in normal bone, this is low in fractures
Macrophages produce angiogenic factors under hypoxic conditions
What can have an effect on stage 1 of the regenerative process?
NSAIDs
Loss of haematoma e.g. surgery or open fractures
Extensive tissue damage and poor blood supply
What is stage 2 of the regenerative process following a fracture?
Soft callus formation
What is involved in stage 2?
Provides some stability of the fracture - fibroblasts produce collagen around the fracture which prevents shortening of the fracture
Angulation can still occur
Continued increase in vascularity
When does stage 2 begin and end?
Begins when pain and swelling subside
Lasts until bony fragments are united by cartilage or fibrous tissue
What can have effects on stage 2?
Replacing cartilage e.g. DMB
Bone graft
Bone substitutes
What are the features of autogenous cancellous bone graft?
Gold standard, best choice for majority of bone graft needs
Osteoconductive or osteoinductive
What are the types of allograft bone grafts?
Cortical Cancellous Fresh Prepared Structural Osteoconductive Non-osteoconductive
What does allograft bone carry a risk of?
Disease transmission from donor to recipient
What is stage 3 of the regenerative process following a fracture?
Hard callus formation
What is involved in stage 3?
Conversion of cartilage to woven bone
Typical long bone fracture - endochondral bone formation and membranous bone formation
Increasing rigidity - secondary bone healing, obvious callus
Although bone is healing it cannot take normal load
What is stage 4 of the regenerative process following a fracture?
Bone remodelling
What is involved in stage 4?
Conversion of woven bone to lamellar bone
Extra bone is removed as far as possible
Medullary canal is reconstructed
Bone responds to loading characteristics
How does strain affect bone healing?
Degree of instability is best expressed as magnitude of strain
If strain is too low, mechanical induction of tissue differentiation fails
If strain is too high, the healing process does not progress to bone formation
What is delayed union?
Failure to heal in the expected time
What are the causes of delayed union?
High energy injury Distraction Instability Infection Steroids Immunosuppression Smoking Warfarin NSAIDs Ciprofloxacin
What is the effect of smoking on union?
50% extension to union
What is non-union?
Failure to heal
What are the causes of non-union?
Failure of calcification of fibrocartilage Usually due to instability Abundant callus formation Pain and tenderness Persistent fracture line Sclerosis
What should be considered in delayed healing?
Alternative management:
- different fixation
- dynamisation
- bone grafting
What are the features of ligaments?
Dense bands of collagenous tissue
Span a joint
Anchored to the bone at either end
Joint stability through a range of motions
Different portions of the ligament are tensioned at different joint positions
What is the structure of ligaments?
Collagen fibres - type 1 Fibroblasts - communication Sensory fibres - proprioception, stretch and sensory Vessels Crimping - allows stretch
What is the difference of percentage of collagen, proteoglycans and water, organisation of collagen fibres and shape of fibroblasts between tendons and ligaments?
Ligaments have
- lower percentage of collagen
- higher percentage of proteoglycans and water
- less organised collagen fibres and rounder fibroblasts
What causes ligament rupture?
When forces applied to the ligament exceed the strength of the ligament - can be complete or incomplete
What needs to be considered in ligament rupture?
Effects on the stability of the joint and proprioception loss
What is involved in the healing of ligaments?
Haemorrhage
Proliferative phase
Remodelling
What are the features of haemorrhage in the healing of a ligament rupture?
Blood clot reabsorbed
Replaced with a heavy cellular infiltrate
Hypertrophic vascular response
What are the features of the proliferative phase of healing of a ligament rupture?
Production of scar tissue
Disorganised collagenous connective tissue
What are the features of remodelling in the healing of a ligament rupture?
Matrix becomes more ligament-like
Major differences in composition, architecture and function persists
What are the treatment options for ligament injury?
Conservative
- partial
- no instability
- poor candidate for surgery
Operative
- instability
- expectation e.g. athletes
- compulsory, multiple e.g. knee dislocation
Where is the motor unit (efferent) located?
Anterior horn cell located in the grey matter of the spinal cord
Motor axon and muscle fibres
Where is the sensory unit located?
Cell bodies in the posterior root ganglia (i.e. outside the spinal cord)
Nerve fibres join to form what?
Anterior (ventral) motor roots
Posterior (dorsal) sensory roots
What combines to form a spinal nerve?
Anterior and posterior roots
How do spinal nerves exit the vertebral column?
Via an intervertebral foramen
What are the features of peripheral nerves?
The part of a spinal nerve distal to the nerve roots
Bundles of nerve fibres
Range in diameter from 0.3-22um
Schwann cells form a thin cytoplasmic tube around them
Larger fibres arranged in a multi-layered insulating membrane myelin sheath
Multiple layers of connective tissue surrounding the axons
What are peripheral nerves composed of?
Highly organised structures comprised of nerve fibres, blood vessels and connective tissue
What are axons coated with?
Endoneurium
What are axons grouped into?
Fascicles
What are fascicles covered with?
Perineurium
What are fascicles grouped into?
Grouped to form the nerve
What is the nerve covered with?
Epineurium
What are the functions of group IA and IB (A-alpha) afferents?
Large motor axons
Muscle stretch
Tension sensory axons
What are the functions of group II (A-beta) afferents?
Touch, pressure, vibration and joint position sensory axons
What are the functions of A-gamma fibres?
Gamma efferent motor axons
What are the functions of group III (A-delta) afferents?
Sharp pain, very light touch and temperature sensation
What are the functions of B fibres?
Sympathetic preganglionic motor axons
What are the functions of group IV (C fibres) afferents?
Dull, aching, burning pain and temperature sensation
How can peripheral nerves be injured?
Compression
Trauma e.g. direct blow, laceration, avulsion
Neurapraxia, axonotmesis, neurotmesis
When might peripheral nerves become compressed?
Entrapment
Carpal tunnel syndrome (median nerve at wrist)
Sciatica (spinal root by intervertebral disc)
Morton’s neuroma (digital nerve in 2nd or 3rd web space of foot
What is neurapraxia?
Temporary loss of sensory and motor function due to blockage of nerve conduction - local ischaemia and demyelination, reversible conduction block
Good prognosis
What is axonotmesis?
Damage to a peripheral nerve where disruption of the axons occurs, but endoneurium, perineurium and epineurium remain intact
Wallerian degeneration follows
What causes axonotmesis?
Nerve stretched (15% elongation disrupts axons), crushed or a direct blow
What causes neurapraxia?
Nerve stretched or bruised
What is the prognosis of axonotmesis?
Fair - sensory recovery often better than motor
Often not returned to normal but returned enough to recognise pain, temperature and sharp and blunt objects
What is neurotmesis?
Complete nerve division - both the nerve and the nerve sheath are disrupted
Endoneural tubes disrupted so high chance of mis-wiring during regeneration
What causes neurotmesis?
Laceration or avulsion
What is the prognosis of neurotmesis?
Poor prognosis
No recovery unless repaired, either by direct suturing or grafting
What are closed nerve injuries associated with?
Nerve injuries in continuity - classically neuropraxia or axonotmesis
When is surgery indicated for closed nerve injuries?
After 3 months if no recovery is identified (clinical, electromyography)
What is the axonal growth rate?
1-3mm/day
Give an example of a closed nerve injury
Brachial plexus injuries
Radial nerve in humeral fracture
What are open nerve injuries usually associated with?
Laceration
Frequently related to nerve division - neurotmetic injuries e.g. knives, glass
How are open nerve injuries treated?
With early surgery
At what point does Wallerian degeneration occur?
2-3 weeks after the injury
What are the sensory clinical features of nerve injury?
Dysaesthesiae
Anaesthesia
Hypo/hyper-aesthetic
Paraesthetic
What are the motor clinical features of nerve injury?
Paresis or paralysis +/- wasting Dry skin (loss of tactile adherence since sudomotor nerve fibres are not stimulating the sweat glands in skin)
What are the reflex clinical features of nerve injury?
Diminished or absent reflexes
What are the features of healing of a nerve injury?
Very slow
Starts with initial death of axons distal to site of injury (Wallerian degeneration), then the degradation of the myelin sheath
Proximal axonal budding after about 4 days
What is the rate of the regeneration process of a nerve injury?
1mm/day
What is the first modality to return in the healing of a nerve injury?
Pain
What does the prognosis for recovery from a nerve injury depend on?
Whether the nerve is pure or mixed, and how distal the lesion is
Prognosis is worse with more proximal lesions
What sign can be used to monitor recovery?
Tinel’s sign - tap over the site of the nerve and parasthesia will be felt as far distally as regeneration has progressed
How can nerve injury be assessed and recovery monitored?
By electrophysiological nerve conduction studies
When is direct repair of a nerve injury indicated?
Laceration
No loss of nerve tissue
What are the methods of direct repair for a nerve injury?
Microscope/Loupes
Bundle repair
Growth factors
When is nerve grafting indicated?
Nerve loss
Late repair - retraction, sural nerve
What is the ‘rule of three’ - surgical timing in traumatic peripheral nerve injury?
Immediate surgery within 3 days for clean and sharp injuries
Early surgery within 3 weeks for blunt/contusion injuries
Delayed surgery, performed 3 months after injury, for closed injuries
What are the examination findings of an UMN lesion?
Decreased strength Increased tone Increased deep tendon reflexes Clonus present Babinski's sign present Atrophy absent
What are the examination findings of a LMN lesion?
Decreased strength Decreased tone Decreased deep tendon reflexes Clonus absent Babinski's sign absent Atrophy present
What is the structure of the muscle/tendon composite unit?
Muscle origin from bone Muscle belly Musculotendinous junction Tendon Tendinous insertion into bone
What is the anatomy of a tendon?
Longitudinal arrangement of cells and fibres, orientated along the line of stress
Fascicles of long, narrow, spiralling collagen bundles
Collagen bundles covered by endotenon
Fascicles covered by paratenon
Tendon covered by epitenon
What is the blood supply to tendons?
Needs to come from outside - rather than running through the middle, this allows tendons to move without damaging blood supply
Viniculum
Fine network of blood vessels in the paratenon
How are tendons connected to the tendon sheath?
By vincula, synovial lining and fluid
What do thickenings of the tendon sheath form?
Strong annular pulleys, where tendons have to move round an angle
What are the functions of tendons?
Flexible and very strong in tension
Movement of the limb in order to enable function
What does immobility cause in tendons?
Immobility reduces water content and glycosaminoglycan concentration and strength
What are the types of tendon injury?
Degeneration Inflammation Enthesiopathy Traction apophysitis Avulsion +/- bone fragment Tear - intrasubstance or musculotendinous Laceration/incision Crush, ischaemia or attrition Nodules
What are the features of degeneration of a tendon?
Intra-substance mucoid degeneration
May be swollen, painful, tender or asymptomatic
Possible precursor to rupture
Rheumatoid arthritis should be considered
What are the features of inflammation of a tendon?
Swollen, tender, hot and red
Positive Finklestein’s test
What are the features of enthesiopathy of a tendon?
Inflammation at insertion to bone
Usually at muscle origin rather than tendon insertion
Common extensor origin
Tennis elbow - classic presentation
What are the features of traction apophysitis?
Insertion of patellar tendon into anterior tibial tuberosity
Common in adolescent active boys
Recurrent load
Bone hypertrophies, inflammation occurs
Painful
No cure or treatment other than reducing activity
What are the features of avulsion +/- bone fragment?
Failure at insertion
Load exceeding failure while muscle contracts
What is the treatment for avulsion?
Conservative
- if you can, get tendon ends to re-join
- limited application
- retraction tendon
Operative
- reattachment of tendon, normally through bone
- fixation bone fragment
What causes intrasubstance rupture?
Tear
Load exceeds failure strength
What is the mechanism of rupture?
53% - pushing off with weight bearing forefoot whilst extending knee joint
17% - unexpected dorsiflexion of ankle
10% - violent dorsiflexion of plantar flexed foot
What are the features of Achilles tendon rupture?
Positive Simmond’s test
Palpable tender gap
What is the treatment of tendon rupture?
Conservative
- where ends can be opposed, mobilise, splint/cast
- where healing will occur
Operative
- high risk of re-rupture
- high activity
- where ends cannot be opposed
Why is there no chance of re-joining finger tendons following laceration?
Tendon end retracts as soon as it is lacerated
What is the treatment of laceration?
Repair surgically and early
