Shown ceramic cup and asked to talk.what are the different bearing surfaces. Your choice in different age groups in THR

Metal on Polyethylene

Advantages

1. Tried and tested articulation with widely published evidence-base

2. Cheap

3. Easy to manufacture

Disadvantages

1. Polyethylene induced osteolysis (manufacturing process encouraging cross-linking to combat this problem with polyethylene)

Ceramic on Ceramic

Advantages

2. Biocompatibility; Biostability

Disadvantages

1. Brittle – concerns regarding fracture but with improved manufacturing process (increased purity, density, improvement in size and distribution of grains, accurate Morse taper) fracture rate in region of 0.02%

2. Squeaking (high pitched audible sound during hip movements) – often asymptomatic; multifactorial including component malpositioning, edge loading, impingement, third-body particles

3. Striped wear – impingement of the partially distracted head on rim of socket during gait

*(2) & (3) also reported in Metal on Metal articulations

Metal on Metal

Advantages

1. High wear resistance – High Young’s modulus of elasticity (Cobalt Chromium 210GPa); Fracture toughness; Hard

2. Self-polish – surface scratches may be substantially polished out during subsequent activity

Disadvantages

1. Metal ions – uncertainty regarding long-term biologic effects therefore caution regarding teratogenicity

2. Metallosis, Aseptic Lymphocytic Vasculitis Associated Lesions (ALVAR), Pseudotumours – believed to be due to wear debris (smaller and higher in numbers relative to Metal on Polyethylene articulation) and hypersensitivity.

3. Run-in wear – initial transitional elevation of wear which stabilises

Walter WL, Yeung E, Esposito C. A review of squeaking hips. J Am Acad Orthop Surg. 2010; 18(6): 319-26

Haddad FS, Thakrar RR, Hart AJ, Skinner JA, Nargol AV, Nolan JF, Gill HS, Murray DW, Blom AW, Case CP. Metal-on-metal bearings: the evidence so far. J Bone Joint Surg Br. 2011;93(5):572-9

Clinical picture of bone cement.properties and factors affecting it

Properties

1. Acts as a space filling grout aiding load transfer

2. Viscoelastic – strong in compression, weak in shear

3. Young’s modulus of elasticity – 2.2GPa

Components

1. Monomer (liquid) – methylmethacrylate, toludene (accelerator) and hydroquinone (inhibitor)

2. Polymer (powder) – polymethylmethacrelate (PMMA), benzoyl peroxide (initiator), barium dioxide (radio-opacifier); chlorophyll (colouring agent)

1. Vaccum mix

2. Pulse lavage and brushing

3. Centraliser

4. Retrograde insertion with use of vent

5. Pressurisation

Polymerisation – exothermic reaction

1. Dough time –time from beginning of mixing to when cement is no longer sticking (2-3 min)

2. Setting time – time from beginning of mixing to point where surface temperature is half maximum (8-12 min)

3. Working time – Difference between dough time and setting time

Variables affecting polymerisation times

1. Environmental temperature – increase in temperature shortens dough and setting times

2. Humidity – increase in humidity increases setting time

3. Mixing technique – increase in frequency of beating and duration of mixing shortens dough and setting times

Variables affecting mechanical properties of cement

Beyond control of surgeon

1. Environmental temperature – increase in temperature decreases compressive strength

2. Equilibirum moisture content – cement absorption of fluid over time reduces strength

3. Strain Rate – stronger at high strain rates (viscoelastic)

1. Radio-opaque fillers – reduces strength by upto 5%

2. Antibiotics – up to 1 gram of antibiotic to 40 grams of polymer leads to no more than 4% reduction in strength; thorough mixing to avoid localised areas of weakness.

3. Mixing technique – frequency of beating and duration of mixing govern monomer loss from evaporation and porosity

4. Cement insertion – laminations harder to obliterate with increasing viscosity; pressurisation to reduce lamination and porosity

Partially under control of surgeon

1. Blood and tissue debris – reduces strength in unpredictable manner

2. Local stress risers secondary to implant design – cement is brittle

3. Constraint – viscoelastic nature of cement (creep) may be significant in unconstrained models

4. Cement mantle thickness – optimum thickness not known; ‘French paradox’

Complications

1. Hypotension

2. Fat embolism

3. Thermal necrosis of bone

4. Third body wear from retained loose fragments

5. Cement mantle defect

Lee AJ, Ling RS, Vangala SS. Some clinically relevant variables affecting the mechanical behaviour of bone cement. Arch Orthop Trauma Surg. 1978;92(1):1-18

Clinical picture of bone graft

Definition – material that assists with bone healing through its osteoconductive, osteoinductive and/or osteogenic properties.

Properties

1. Osteoconduction – process by which graft acts as three dimensional scaffold for ingrowth of capillaries and osteoprogenitor cells from recipient host bed. Examples – Calcium phosphate, Synthetic polymers.

2. Osteoinduction – process supporting differentiation of mesenchymal stem cells into osteoprogenitor cells capable of forming new bone. Examples – Bone Morphogenetic Proteins (BMP), Transforming growth factor-β, Platelet-derived growth factor.

3. Osteogenic – use of naturally occurring materials that induce or support formation of bone. Examples – autologous bone marrow graft, autologous/allogenic bone grafts

Classification

Type

1. Cortical- structural integrity

2. Cancellous- more porous compared to cortical therefore more rapid revascularisation

3. Corticocancellous

Vascularity

2. Non-vascularised graft

Source

1. Autograft – same person

2. Allograft – same species (Isograft – twins)

3. Xenograft – different species

4. Synthetic

Preservation

1. Fresh – unprocessed; immunogenic

2. Fresh frozen – unprocessed stored at -70°C for minimum of 180 days; least impact on strength and preservation of immunogenicity and growth factors

3. Freeze dried – processed to remove soft tissues and washed to deplete cell and marrow content followed by freeze drying; least immunogenic but lowest likelihood of disease transmission as irradiated

Screening

Syphilis Ab

HBsAg

Anti-HCV

Anti-HIV

Anti-HBc

HCV-PCR

HIV-PCR

HBV-PCR

Nuclear medicine imaging that detects distribution of an injected radio-labelled tracer on image projections sensitive to gamma ray emissions. The process involves injection of a radio-labelled tracer followed by gamma camera recording of photoemissions.

Radiolabelled tracers

1. Technetium- 99m – affinity for osteoblasts; t_1/2 6 hours

2. Gallium-67 – affinity for inflammatory proteins; t_1/2 3.2 days

3. Indium-111 – autologous leucocytes obtained and labelled with Indium-111 then re-injected; t_1/2 2.8 days

Triple phase bone scintigraphy

1. Nuclear angiogram (flow phase) – images immediately post-injection; demonstrates arterial flow and areas of hyperperfusion

2. Blood pool phase – images 5 minutes post-injection; demonstrates relative vascularity where areas of inflammation result in ‘pooling’ of blood due to stagnant flow in dilated capillaries (soft tissues and bone)

3. Static phase – images 3 hours post-injection; demonstrates bone activity

Limitations

1. High sensitivity but low specificity for increased bone activity

2. Two dimensional imaging – poor localisation of small lesions; alternative is single photon emission computer tomography (SPECT) imaging

Indications

1. Metastatic disease

2. Primary bone tumours

3. Trauma – stress fractures, occult fractures

4. Infection

5. Arthritis

6. Complex Regional Pain Syndrome

Hsu W, Hearty TM. Radionuclide imaging in the diagnosis and management of orthopaedic disease. J Am Acad Orthop Surg. 2012;20(3):151-9

Talk about calcium metabolism. What is rickets?

Calcium (plasma concentration 2.2 – 2.6mmol/L)

• 99% of body calcium stored in bone
  
• <1% in plasma: bound to albumin or free

Hypercalcaemia

Presentation

‘Bones, stones, groans and moans’

Causes

• Malignancy
  
• Hyperparathryoidism

Hypocalcaemia

Presentation

Neuromuscular irritability (Trosseau’s sign, Chvostek’s sign)

Causes

• Hypoparathyroidism
  
• Thyroidectomy

Vitamin D

Sources:

Minor – Dietary (eggs, liver, fish) Vitamin D absorbed in jejunum (Vitamin D deficiency – malabsorption syndromes)

Pathway:

1. Hydroxylation in liver – Vitamin D to 25-hydroxycholecalciferol (Vitamin D deficiency – cirrhosis)

2. Further hydroxylation in kidneys – 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol (Vitamin D deficiency – chronic renal failure)

Actions:

1,25-dihydroxycholecalciferol (active metabolite)

• Increase calcium and phosphate absorption from gastrointestinal tract
  
• Increase osteoclastic resorption of bone

Enhances secretion – Increased parathyroid hormone (PTH) levels

Inhibits secretion – Decreased PTH levels, increased serum calcium and/or phosphate levels

Effect:

• Increase in serum calcium levels
  
• Increase in serum phosphate levels

Parathyroid hormone (PTH)

Source:

• Enhances secretion – decreased serum calcium and/or phosphate
  
• Inhibits secretion – increased serum calcium or 1,25-dihydroxycholecalciferol

Actions:

• Increases renal hydroxylation of 25-hydroxycholecalciferol
  
• Increases resorption of calcium and decreases resorption of phosphate in kidneys
  
• Increases osteoclastic resorption of bone

Effect:

• Increase in serum calcium levels
  
• Decrease in serum phosphate levels

Calcitonin

Souce:

Parafollicular C cells of thyroid gland

• Enhances secretion – increased serum calcium levels
  
• Inhibits secretion – decreased serum calcium levels

Actions:

• Decreases calcium absorption from gastrointestinal tract
  
• Decreases calcium resorption in kidneys
  
• Decreases osteoclastic resorption of bone

Effect:

Pathology

Vitamin D-dependent rickets/Osteomalacia

Vitamin D-resistent rickets (X-linked dominant hypophosphatemic rickets)

Hyperparathyroidism

Hypoparathyroidism

Renal osteodystrophy

Articular cartilage

• Aneural; Avascular; Alymphatic
  
• Cells embedded in extra-cellular matrix’

Composition

Structure

1. Superficial zone – thinnest; collagen fibres parallel to articular surface (tensile and shear strength); high water content; low PG content

2. Transitional zone

3. Deep zone – collagen fibres perpendicular to articular surface (resist compression); low water content; high PG content TIDEMARK – histologically visible border between deep zone and calcified zone

4. Calcified zone – low metabolic activity; Type X collagen

Cartilage healing

• Ability for cartilage defects to heal based on whether injury is deep to tidemark – i.e. involves subchondral vascular bone marrow resulting in release of mesenchymal progenitor cells into defect
  
• Fibrocartilage healing – biomechanically and structurally inferior to hyaline cartilage

Factors associated with cartilage repair

Surgical options for cartilage defects

Microfracture

Multiple controlled ‘microfractures’ to ensure release of mesenchymal progenitor cells from subchondral vasculature.

Steadman JR, Briggs KK, Rodrigo JJ, Kocher MS, Gill TJ, Rodkey WG. Outcomes of microfracture for traumatic chondral defects of the knee: average 11-year follow-up. Arthroscopy 2003;19(5):477-84

Mosaicplasty

Multiple cylindrical osteochondral plugs harvested from non-weightbearing area and plugged into prepared chondral defects to create a ‘mosaic’ pattern.

Hangody L, Vásárhelyi G, Hangody LR, Sükösd Z, Tibay G, Bartha L, Bodó G. Autologous osteochondral grafting – technique and long-term results. Injury. 2008;39 Suppl 1:S32-9

Autologous chondrocyte implantation (ACI)

Two stage procedure in which cartilage is harvested arthroscopically and grown in vitro, followed by implantation of chondrocytes into cartilage defect with an open procedure.

Peterson L, Vasiliadis HS, Brittberg M, Lindahl A. Autologous chondrocyte implantation: a long-term follow-up. Am J Sports Med. 2010;38(6):1117-24

Gait cycle – events occurring when one foot makes contact with the walking surface and ends when the same foot makes contact again

Step length – linear distance between one heel strike to heel strike of other foot

Stride length – linear distance between one heel strike to next heel strike of same foot; Stride length = 2 x step length

Stance phase (60%)

1. Initial contact

2. Loading response

3. Mid-stance

4. Terminal stance

5. Pre-swing

Swing phase (40%)

1. Initial swing

2. Mid-swing

3. Terminal swing

*Double stance – 10% of gait cycle

Perry J. Gait analysis: normal and pathological function. Thorofare (NJ): SLACK; 1992.

Gage – Pre-requisites of gait based on Perry’s work

1. Stability in stance – stable when extremity weight-bearing on ground

2. Clearance in swing

4. Foot clearance in swing

5. Energy conservation (Gage) – ambulation must be energy efficient to ensure gait is functional

Gage JR: The treatment of gait problems in cerebral palsy.London, Mac Keith Press; 2004.

Saunders – Determinants of normal walking

1. Pelvic tilt

2. Pelvic rotation

3. Pelvic lateral displacement

4. Knee mechanisms

5. Knee flexion in stance phase

6. Foot and ankle mechanisms

Loss or compromise of two or more determinants produces uncompensated and inefficient gait.

Saunders JBDM, Inman VT, Eberhart HD: The major determinants in normal and pathological gait. J Bone JointSurg. Am 1953, 35A:543-728.

Perry – ‘3 Rockers’

1^st rocker (heel rocker) – controlled plantarflexion to lower foot to walking surface during loading response.

2^nd rocker (ankle rocker) – controlled tibial advancement and increasing dorsiflexion between mid and late stance during which the body advances over stationary foot.

3^rd rocker (toe rocker) – propulsion with rapid ankle plantarflexion during pre-swing.

Perry J. Kinesiology of lower extremity bracing. Clin Orthop Relat Res 1974;102:18e31.

1. Clinical assessment including video analysis

2. Instrumented Gait Analysis (IGA) – Sagittal; Coronal; Transverse

3. Dynamic electromyography (D-EMG)

4. Plantar pressure analysis

Cerebral Palsy

Stiff knee gait

• Throughout gait cycle – knee held in extension

Jump knee gait

• Initial contact – increase hip and knee flexion with slight dorsiflexion
  
• Loading response and mid-stance – rapid knee extension and ankle plantarflexion

Crouch gait

• Throughout gait cycle – increase hip and knee flexion with excessive dorsiflexion

True equinus

• Calf spasticity or fixed ankle equinus contracture

Apparent equinus

• Increased hip and knee flexion throughout stance phase with relatively normal ankle motion
  
• Initial contact is with forefoot as a result of the flexed hip and knee

Shown clinical picture of diathermy

Diathermy (Greek diathrough;therme:heat) – cutting and coagulation of body tissue with a high frequency current

• High frequency alternating current
  
• Current between two electrodes in contact with the body heats all tissues between them
  
• Cutting mode – continuous current; Coagulation mode – pulsed current (50 – 100 s^-1)

Monopolar diathermy

• Current established between active electrode (diathermy instrument) and Indifferent electrode (electrical plate/pad)
  
• Heating effect inversely proportional to area of contact with electrodes
  
  
  
  • Active electrode small – heating concentrated at diathermy instrument
    
  • Indifferent electrode large – minimal heating effect

Bipolar diathermy

Risks

Implantable cardioverter defibrillators (ICDs)/Pacemakers

• Risk of electrical interference leading to inhibition of pacemaker output, temporary increase in pacing or loss of programme settings
  
• ICD pre-cautions when using diathermy
  
  
  
  • Programme to ‘monitor only mode
    
  • Magnet over ICD
    
  • Deactivate (use of external defibrillator)
    
  • Post-operative ICD check
  
  
• Favour bipolar mode but if monopolar mode is used:
  
  
  
  • Use in short bursts
    
  • Ensure current pathway remote from ICD (importance of position of return electrode)

Smoke plume – vapour containing particles released during electrosurgery on body tissue

• Chemical by-products; Carbonised tissue; Blood particles; Viral DNA particles; Infectious viruses and bacteria
  
• Use of smoke evacuators with ultra-low penetrating air filters and high filtration face masks

Explosion

• Anaesthetic gases
  
• Bowel gases
  
• Ignition of skin preparations

What is orthosis? parts of BK prosthesis

Prosthesis

Externally applied device used to replace wholly, or in part, an absent or deficient limb segment.

Indications for Amputation

• Peripheral vascular disease
  
• Trauma
  
• Tumours
  
• Infection
  
• Congenital abnormalities

Pre-operative assessment

• Multi-disciplinary approach
  
• Case-by-case approach
  
• Amputation level

Components of Prosthesis

1. Socket- connection between residual limb and prosthesis. e.g. ischial tuberosity-bearing, patella tendon-bearing

2. Suspension – attachment of prosthesis to residual limb. e.g. bands/belts, sleeves, suction

3. Articulation – non-articulating (e.g. solid-ankle/cushioned heel) or articulating (e.g. stance-phase control or swing-phase control)

4. Shank – link between socket and terminal device to restore limb length

5. Terminal device – non-energy storing or energy storing

Externally device applied used to modify the structural and functional characteristics of the neuromuscular and skeletal system.

International Organisation for Standardisation (ISO)

Nomenclature established in 1989 and endorsed by the American Association of Orthopaedic Surgeons (AAOS) and International Society for Prosthetics and Orthotics (ISPO) in 1992.

Nomenclature

Upper Limb – Shoulder (S), Elbow (E), Wrist (W), Hand (H), Finger (F)

Lower Limb – Hip (H), Knee (K), Ankle (A), Foot (F)

Spine – Cervical (C), Thoracic (T), Lumbar (L), Sacro-iliac (S)

Indications

Upper Limb

• Trauma – tendon, nerve, joint injuries; burns
  
• Post-surgery
  
• Painful conditions – arthritis
  
• Deformities – neuromuscular problems

Static; Dynamic; Combined (Functional)

Lower Limb

Spinal

• Trauma – fractures
  
• Post-surgery
  
• Deformity
  
• Intervertebral disc pathology

Ground Reaction Ankle Foot Orthosis (GRAFO)

• Accentuates knee extension at mid-stance (Indications – weak quadriceps)
  
• Compensate for weak/absent gastrocnemius or soleus (Indications – weak plantarflexors)

Elements

• Full toe plate; Rigid ankle in neutral; Rigid anterior tibial shell

Principles

International Organization for Standardization. ISO 8549-1: Prosthetics and orthotics-vocabulary, Part 1: General terms for external limb prostheses and external orthoses. Geneva: International Organization for Standardization, 1989:1-6.

International Organization for Standardization. ISO 8549-3: Prosthetics and orthotics-Vocabulary, Part 3: Terms relating to external orthoses. Geneva: International Organization for Standardization, 1989:1-5.

Bowker JH, Michael JW (eds.) Atlas of Limb Prosthetics- Surgical, Prosthetic and Rehabilitation Principles. St. Louis: American Academy of Orthopaedic Surgeons and C.V. Mosby Co. :1992.

Magnetic resonance (MR) imaging employs a stationary magnetic field and application of an external radiofrequency pulse to create an image based on the response of hydrogen proton molecules in the studied tissue.

Mechanism

• Magnetic field results in parallel alignment of hydrogen protons within studied tissue(s)
  
• Radiofrequency pulse results in energy absorption by hydrogen protons leading to
  
  
  
  • Change in direction and precession of protons
    
  • Above changes dependent on direction of applied radiofrequency pulse with respect to stationary magnet
  
  
• Cessation of radiofrequency pulse results in reverting of alignment of protons back to direction before radiofrequency pulse and loss of coherence of precession. There is a time-dependent release of energy from the protons that was previously absorbed.
  
• Electronic image produced based on capturing patterns of energy release from protons

Terminology

T1 (Spin-lattice or longitudinal relaxation time)