Musculocutaneous Growth and Injury Flashcards by Ross Tulloch

At what age do the growth plates of bones fuse?

13/14

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What are the characteristics of cortical bone?

Diaphysis
Resists bending and torsion
Laid down circumferentially
Less biologically active

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What are the characteristics of cancellous bone?

Metaphysis
Resists/absorbs shock
Site of longitudinal growth
Very biologically active

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What is a fracture?

A break in the structural continuity of a bone, can be a break, crack, split, crumbling or buckle

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What are the causes of a bone to fail?

High energy transfer in normal bone
Repetitive stress in normal bone
Low energy transfer in abnormal bone

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What are the stages of healing after a fracture?

Inflammation
Soft callus
Hard callus
Bone remodelling

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Describe the inflammation stage of healing of a fracture

The first stage is inflammation, which begins immediately after the fracture. Haematoma and fibrin clots are formed within the break, which recruit platelets, neutrophils, monocytes and macrophages. By products of cell death (lysosomal enzymes) are also present within the break. Fibroblasts, mesenchymal cells and osteoprogenitor cells are all also recruited to the break. Angiogenesis also occurs to restore blood supply and muscle contraction takes place to try and stiffen up broken limbs. This stage can be helped along with NSAIDs and surgery.

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Describe the soft callus stage of healing of a fracture

The second stage of a fracture is soft callus. It begins when the pain and swelling subsides and lasts until the bony fragments are united by cartilage or fibrous tissue. This gives the fracture some stability, with an increased vascularity and angulation can still occur. This stage can be helped along with replacement of cartilage (demineralised bone matrix), or jumping straight to bone with a bone graft or substitute.

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Describe the hard callus stage of healing of a fracture

The third stage is hard callus. This process involves conversion of cartilage to woven bone and occurs in a typical long bone fracture. The bone becomes increasingly rigid during this stage.

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Describe the bone remodelling stage of healing of a fracture

The fourth stage is bone remodelling. This involves conversion of woven bone to lamellar bone. The medullary canal is reconstituted and the bone begins to respond to loading characteristics.

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How is instability of a fracture expressed?

Expressed as magnitude of strain (% change of initial dimension)

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What happens when strain on a fracture is too low and too high?

If strain is too low then mechanical induction of tissue differentiation fails
If strain is too high then the healing process does not progress to bone formation

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What are the possible causes of delayed union?

High energy injury
Instability
Infection
Steroids
Immunosuppression
Smoking (fractures take 50% longer to heal if smoking actively during fracture healing)
Warfarin
NSAIDs
Ciprofloxacin

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How can delayed healing be fixed?

Different fixation
Dynamization
Bone grafting

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What is a peripheral nerve?

Peripheral nerves are the part of a spinal nerve distal to the nerve root

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What lines a peripheral nerve?

Schwann cells form a thin cytoplasmic tube around nerve

Larger fibres insulated by a myelin sheath

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How are axons organised to form a nerve?

Axons are bundle together to form fascicles, which are coated with perineurium and bound together to form a nerve which is covered with epineurium

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What are the different kinds of peripheral nerve injury?

Can be compression or trauma
Compression injuries can occur at different levels
Trauma injuries can be direct or indirect and can be further classified as neurapraxia, axonotmesis or neurotmesis

What are the characteristics of a neurapraxia?

Neurapraxia refers to a nerve that is damaged but is still in continuity. The nerve can be stretched or bruised and can result in reversible conduction block, local ischaemia and demyelination. The prognosis of these injuries is generally good, with recovery occurring within weeks or months.

What are the characteristics of an axonotmesis?

Axonotmesis refers to injuries in which the endoneurium is still intact but the axons themselves are disrupted. These can occur due to stretch, crush or direct blow. Wallerian degeneration follows these injuries and the prognosis of these injuries is fairly good as the tube is still intact for the axons to regrow down.

What are the characteristics of a neurotmesis?

Neurotmesis is an injury in which the nerve is completely severed. Neurotmesis injuries will not recover spontaneously but will repair by direct suturing or a graft. This is because the endoneural tubes are disrupted so there is a high chance of miswiring during regeneration. The prognosis of these injuries is generally quite poor.

What are the characteristics of an open nerve injury?

Open injuries are usually associate with nerve division. These can be treated with early surgery. The distal portion of the nerve shows Wallerian degeneration for 2-3weeks after the injury.

What are the characteristics of a closed nerve injury?

Closed injuries are associated with nerves in continuity, such as in neuropraxis or axonotmesis. Spontaneous recovery is possible but surgery is required if there are still symptoms after three months.

What are the possible symptoms of a nerve injury?

Dysaesthesia (including numbness or pins and needles)
Muscle weakness/paresis
Paralysis
Wasting
Dry skin
Diminished or absent reflexes

How do nerve injuries heal?

Healing of nerve injuries is very slow, starting with initial death of axons distal to the site of injury. This is known as Wallerian degeneration which is followed by degradation of the myelin sheath. Proximal axonal budding occurs after about four days. Regeneration occurs at around 1mm/day and pain is the first modality to return

What does the prognosis of a nerve injury depend on?

- Whether nerve is pure (sensory OR motor) or mixed (sensory AND motor) - How distal the lesion is (proximal worse) - Tinel’s sign can monitor recovery

How can nerve injuries be repaired?

Nerve repair can be done with either direct repair or nerve grafting. Nerve grafting can be helpful in cases where there is nerve loss and late repair.

Describe the surgical timing in cases of peripheral nerve injuries?

- Immediate surgery within three days for clean and sharp injuries - Early surgery within three weeks for blunt/contusion injuries - Delayed surgery, performed three months after injury for closed injuries

Describe the structural organisation of a tendon

Collagen bundles are covered by endotenon, which are bundled to form fascicles. These are covered by paratenon and these are bundled together to form a tendon, which is covered in epitenon

What physiological changes occur within a tendon when it is immobile?

Water content is reduced Glycosaminoglycan concentration reduced Glycoasminoglycan strength reduced

Describe a degeneration tendon injury

Intrasubstance mucoid degeneration, can be painful, swollen, tender or asymptomatic. Can also be a precursor to rupture. Achilles tendon is an example

Describe an inflammation tendon injury

Examples include de Quervain’s stenosing tenovaginitis, in which the tendons of the EPB and APL passing through the common tendon sheath at the wrist become inflamed and result in swelling, tenderness, hotness, redness and a positive Finklestein’s test

Describe an enthesiopathy

Inflammation at insertion of tendon into bone

Describe a traction apophysis

Examples include Osgood Schlatter’s disease in which the insertion of the patellar tendon into the anterior tibial tuberosity becomes inflamed, commonly in active adolescent boys

Describe an avulsion

Can be with or without a bone fragment, there is a failure in the tendon insertion that is caused by a load exceeding failure strength while the muscle is contracting. This can be the cause of Mallet finger. Treatment is conservative (limited application, retractive tendon) or operative (reattachment of tendon through bone, fixation of bone fragment)

Describe an intrasubstance rupture

occurs when the load exceeds failure strength. Achilles Tendon rupture is example, which feels like a punch in the back of the leg. Treated either conservatively where ends can be opposed or where healing will occur with a splint or cast, or operatively, which has a high risk of re-rupture

Describe a tendon laceration

Most common in finger flexors and M>F, also common in young adults. Repair is surgical and early

What is a ligament?

Dense bands of connective tissue than run from bone to bone

What is the function of a ligament?

To provide joint stability through the range of movement of a joint

What are the component parts of a ligament?

- Collagen fibres - Fibroblasts for communication - Sensory fibres- proprioception, stretch and sensory - Vessels - Crimping to allow stretch

When does a ligament rupture occur?

When the force exceeds the strength of the ligament, this can be expected or unexpected

Describe the healing process of a ligament rupture

* Haemorrhage- blood clot which is reabsorbed, replaced with a heavy cellular infiltrate and is followed by a hypertrophic vascular response * Proliferative phase- production of scar tissue/disorganised collagenous connective tissue * Remodelling- matrix becomes more ligament like, major differences in composition and architecture persist

Describe the treatment of a ligament rupture

Conservative treatment can be done when the rupture is partial and there is no instability Operative treatment is required when the rupture is instable and when it is preferable to the patient

How does Achille's tendon rupture present on examination?

Positive Simmond's test | Palpable tender gap