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Basic science / Classifications and tables

Useful Tables

Basic scienceClassifications and tablesthinKbox SBA
Type Location Related Disease
1 Bone; Skin; Annulus; Tendon; Ligament Osteogenesis Imperfecta (AD, AR, AR, AD); Ehlers Danlos (AD), Dupuytren's Contracture (AD)
2 Hyaline Cartilage; Nucleus Pulposus
3 Granulation Tissue; Skin ( Callus, scar) Dupuytren's Contracture (AD)
4 Basement membrane
5 Interstitial tissue; IVD; Articular Cartilage Classic Ehlers Danlos (AD)
6 Intervertebral Disc; (Specific to IVD); Articular Cartilage
7 Basement membrane
8 Basement membrane
9 Articular cartilage; Epiphyseal Cartilage MED (AD)
10 Mineralising cartilage; (calcified zone)
11 Articular Cartilage Acts as an adhesive
12 Tendon

Changes in Articular Cartilage with Ageing

Feature Ageing OA
1. Water content Decreases Increases
2. Collagen content Decreases Decreases
3. Collagen concentration Decreases Increases (Decrease in PG)
4. Chondroitin: Keratin ratio Decreases Increases
5. Proteoglycan degradation Decreases Increases
6. Proteoglycan content Decreases Decreases
7. Chondrocyte number Decreases No change
8. Synthetic activity Decreases Increases
9. Chondrocyte Size Increases No change
10. Stiffness (young's modulus) Increases Decreases (high water content)

Energy Expenditure and level of Amputation

Amputation Level Energy Expenditure
Long Trans Tibial 10%
Trans Tibial 25%
Short Trans Tibial 40%
Trans femoral 65%
Hip Disarticulation 100%
Bilateral Trans Tibial 41%
Bilateral Trans Femoral 200%
Wheelchair 5%

Young's Modulus for various Orthopaedic Materials
Material Young's Modulus
Ceramic 250
CoCr 225
Stainless Steel 200
Titanium 100
Cortical Bone 20
PMMA 2
Polyethylene 1.5
Cancellous Bone 1
Tendon 0.1
Cartilage 0.02

Genes & Inheritance patterns in Orthopaedic Disease

Condition Gene Mutation Inheritance Pattern
Chondrosarcoma Telomerase/RB Genes
Multiple Hereditary Exostosis; (Osteochondromatosis) EXT 1 & EXT 2
Neurofibromatosis Type 2 Chromosome 22
Osteosarcoma RB Gene / p53
Coxa Vara AD
Charcot Marie Tooth PMP 22 (Chrom 17) AD
Achondroplasia FGFR 3 AD; 80% new mutations
Cleidocradial Dysplasia CBFA AD
Ehlers-Danlos Syndrome COL5A AD
Facioscapulohumeral Dystrophy AD
Kniest Syndrome COL2A1 AD
Marfan syndrome Fibrillin Gene; (C15q21) AD
Multiple Epiphyseal Dysplasia COL9A1 AD
Neurofibromatosis Type 1 Neurofibromin (Ch 17) AD
Pseudo-Achondroplasia COMP (Ch 19) AD
Spondyloepiphyseal Dysplasia COL2A1 AD; Tarda type; X linked Recessive
Tarsal Coalition AD
Gaucher disease Beta glucocerebrosidase AR
Dejerine-Sottas disease (HSMN 3) AR
Friedreich's ataxia FRATAXIN protein AR
Diastrophic Dysplasia SLC26A2 gene AR
Mucopolysaccharidoses e.g. Morquio AR
Sickle Cell Disease HBSS gene (Ch 6) AR
Spinal Muscular Atrophy AR
Familial Vitamin D dependant Rickets Alpha 1 hydroxylase problem; Vit D resistance AR
Osteogenesis Imperfecta COL1A1, COL1A2 Type 1 & 4 AD; Type 2 & 3 AR
Hypophosphataemic Vit D resistant Rickets PEX X Linked Dominant
Beckers Muscular Dystrophy Reduced Dystrophin X Linked Recessive
Duchenne Muscular Dystrophy Absent Dystrophin protein X Linked Recessive

Layers of the Posterolateral Corner of the Knee

Layer Contents
Superficial Biceps Femoris; ITB
Common Peroneal Nerve
Middle Patellofemoral Ligament; Patella retinaculum
Deep Superficial Lateral Collateral; Fabellofibular Ligament
Lateral Geniculate Artery
Deep Deep Popliteus tendon; Arcuate Ligament; Coronary Ligament; Popliteofibular ligament; Lateral Capsule

Medial layers of knee

Layer Contents
Layer 1 Patella Retinacular fascia; Sartorius & Sartorius Fascia
Semitendinosus
Layer 2 Superficial Medial Collateral; POL
Layer 3 Semimembranosus (5 insertions); Medial Capsule; Deep MCL

Gait

Prerequisites of Gait
Stable Stance
Adequate Step Length
Foot Clearance
Energy Conservation
Pre-positioning of Foot

Determinants of Gait
Pelvic Tilt
Pelvic Lateral bend
Pelvic rotation
Knee flexion
Ankle Motion

Gait Definitions

Step Heel strike to the heel strike of the opposite foot
Stride Heel strike to the next heel strike of the same foot
Cadence Steps per unit time
Velocity Stride length/Stride time

Rockers of Gait

1st Rocker Eccentric contraction of Dorsiflexors
2nd Rocker Eccentric contraction of Plantarflexors
3rd Rocker Concentric Contraction of Plantarflexors

Nerve Injury Classification

Seddon Pathology Prognosis Sunderland Equivalent
Neuropraxia Axon in continuity; No Wallerian Degeneration; Epineurium intact; Segmental Demyelination Good 1
Axonotmesis Wallerian Degeneration distal to lesion; Epineurium disrupted; Variable perineurial damage; Endoneurium intact Good 2-4
Neurotmesis Wallerian degeneration distal to lesion Epi, peri & Endoneurium disrupted Poor; (No tube for growth) 5

Sensitivities & Specificities for diagnosis of Periprosthetic Infection
Test Sensitivity Specificity
Combined CRP & ESR (>15 & >30) 99% 95%
PET Scan 98% 98%
Triple phase Bone Scan 99% 95%
Frozen Section 85% 95%
Joint aspiration & Culture (⇑ by multiple aspirations) 70% 95%
Gram Stain 25% 95%
PCR (too sensitive – contaminants = false positive) >99% 80%

Types of Joint

Type Subtype Examples
Fibrous SUTURES Between skull bones
SYNDESMOSIS Ankle syndesmosis
Cartilaginous Primary SYNCHONDROSIS Physis; Epiphysis
Cartilaginous Secondary SYMPHISIS Pelvic Bones; IVD
Synovial (Diarthrodial) HINGE Ulnohumeral; IPJs; Ankle; Knee
Synovial (Diarthrodial) SADDLE Thumb CMCJ
Synovial (Diarthrodial) CONDYLOID MCPJ; Wrist
Synovial (Diarthrodial) ROTATORY PRUJ
Synovial (Diarthrodial) BALL & SOCKET Hip; Shoulder
Synovial (Diarthrodial) SLIDING Carpal; Tarsal

X Ray Features of Rickets
Hazy Physis
Widened Physis
Metaphyseal cupping
Metaphyseal Flaring
Looser's zones
Coxa Vara
Tibial Varus
Small ossific nuclei
Coarse Trabecullae
Thickened cortices

Clinical Features of Rickets
Coxa Vara
Varus Tibia
Rachitic Rosary
Short Stature
Frontal Bossing
Waddling Gait
Harrisons Sulcus
Dental Disease
Codfish Spine -- central depressed vertebrae
Kyphosis -- cat back

Newtons Laws

1st Law The sum of forces acting on a body at rest must be equal
2nd Law Acceleration is directly proportional to the force applied (F=MA)
3rd Law Every action has a reaction of equal magnitude and opposite direction

Assumptions of a free body diagram

J Joints are frictionless hinges
O Only compressive forces act on joints
I Internal forces are all equal
N No antagonistic muscle action
B Bones are rigid rods
M Muscle pull is in one direction only
W Weight is at the centre of the body mass

Tumors and location

Tumour Location Features
Osteoid Osteoma Posterior Apex & convexity of curve; Curve resolves with resection
Osteoblastoma Posterior Painful; Adults
ABC Posterior May spread anterior; May be within a malignant tumour
Osteochondroma Posterior Snapping Scapula syndrome
Fibrous Dysplasia Body 50% with polyostotic have FB in spine
Haemangioma Body Jail house Vertebrae
Eosinophilic Granuloma Body Vertebra Plana
Giant cell Tumour Body May undergo malignant change
Myeloma Body Lytic, multiple lesions
Cordoma Body Sacrum, Radiosensitive
Lymphoma Body Ivory vertebra

Osteosarcoma Subtypes

Type Location Features
Intramedullary (classic) MD junction; Around knee 80%; High grade; Metaphysis-diaphysis junction; Classic type features
Parosteal Distal femur; Proximal; Humerus 15%; Low grade; On Bone surface; Mainly osteoid -- like osteochondroma
Periosteal Tibia; Femur; Diaphysis Very rare; Low grade; Bone surface; Chondroid and osteoid features
Telangiectatic Around knee Highly grade; Poor prognosis; Lytic; May mimic ABC
Post Radiotherapy Anywhere High grade; Mean occurrence 17 years post Rx; Poor prognosis
Pagets Femur; Pelvis; Humerus High grade; Mainly in polyostotic chronic disease

Poor Prognostic Indicators of Osteosarcoma
High LDH levels
High Alkaline phosphotase
Expression of p Glycoprotein
Absence of Antishock protein 90
Pelvic location
Pathologic fracture at presentation
<90% tumour necrosis after neo-adjuvant chemo
Vascular invasion
Recurrence/incomplete margins
Metastases at presentation (bone worse than lung)

Chondrosarcoma Subtypes

Type Location Features
Intramedullary (classic) Pelvis; Shoulder; Prox; Femur; Hand Mean age 45; Telomerase/RT genes; Slow growing large mass; Prognosis correlates to grade; Not radio- chemo sensitive
Dedifferentiated Same Low grade CS on Spindle cell Tumour (OS); Worst prognosis (10% at 5 y ears); Rx for both lesions
Clear Cell Epip hysis Mimics Chondrobla stoma; Low grade, lytic
Mesenchymal Same Very rare; Younger patients; Bad prognosis

Typical Histologic or Radiologic Features of Tumours

Tumour Feature
Adamantinoma or GCT Soap Bubble Appearance
Chondroblastoma Chicken wire calcification
Chondrosarcoma Featureless a ppearance; Large binuclear cells
Chordoma Phylsaliferous cells
Eosinophilic Granuloma Birbeck granules (raquet shaped)
Ewings Sarcoma Round blue cells
Fibrosarcoma Herring Bone Pattern Spindle cells
Fibrous Dysplasia Ground Glass appearance; Chinese letter /Alphabet soup appearance
Lymphoma Small round B cells (CD20 positive)
Malignant Fibrous Histiocytoma Storiform appearance; No spindle cells
Osteosarcoma Pleomorphic Spindle cells
Plasma cells Clock face pattern
Rhabdomyosarcoma Raquet shaped cells
Synovial Sarcoma Biphasic pattern

Mean surface roughness of orthopaedic materials

Polished Exeter stem 0.01
Ceramic head 0.02
Metal head 0.025
Polyethylene cup 2.0
Articular cartilage 3.0

Co-efficients of friction of articulations

Native Knee 0.005
Native hip 0.01
Metal on poly 0.02
Metal on metal 0.8

Summary of types of Lubrication

Boundary Single molecular thickness boundary between surfaces; Predominant in prosthetic joints; Lift off phase of gait
Fluid Film Predominates in Native Joints; Also in MoM articulations; Preferred
Hydrodynamic High speed low load; More in prosthetic joints; Higher loads lead to contact of surfaces
Elastohydrodynamic Predominant in native articular cartilage; Reliant on deformation of articular cartilage; Increased SA, viscosity and decreased shear rate
Squeeze Film Rapid loading builds pressure in lubricating fluid; Enables fluid to resist load better; Initial contact in gait
Weeping Compression elutes further fluid from articular surface
Boosted Under constant load water is pressurised into cartilage; This leaves a more viscous hylaronic rich fluid

Lubrication during the Gait cycle

Gait Cycle Phase Predominant type of Lubrication
Initial contact Squeeze Film
Stance Elastohydrodynamic
Lift off Boundary & Elastohydrodynamic
Swing Hydrodynamic
Prolonged Stance Boundary, boosted

Conditions affecting various parts of the Physis & Epiphysis

#### Zone #### Disease
Epiphysis MED; SED; Trevors
Reserve Pseudoachondroplasia; Gauchers
Proliferative Achondroplasia; Gigantism
Hypertrophic; Maturation & Degenerative SUFE; Trauma; Enchondroma; Mucopollysacharidoses
Hypertrophic; Zone of Provisional Clacification Rickets; Osteomalacia
Metaphysis Renal SUFE; Scurvy; Osteomyelitis; Osteogenesis Imperfecta

Statistical Terminology

Term Definition
Sensitivity Ability of a test to correctly identify those with the disease - TP/TP+FN
Specificity Ability of a test to correctly identify those without the disease - TN/TN+FP
PPV How often a positive test result is truly positive - TP/TP+FP
NPV How often a negative test result truly is negative - TN/TN+FN
Accuracy With repetition who often a test is correct - TP+TN/TP +FP+TN+FN
Reliability With repetition how often a test will produce the same result; Inter & Intra -observer
Odds Ratio Likelihood the positive finding will occur more often in the treatment group rather than the control group
Validity Degree to which a test or study correctly measures what its meant to be measuring
P revalence The number of people with a disease within an at risk population at any given time point -- a snapshot
Incidence The number of new diagnoses of a disease within an at risk population per year
P value The probability that the finding was purely by chance
Type 1 Error Rejecting the null hypothesis in correctly (5% acceptable)
Type 2 Error Accepting the null hypothesis in correctly (20% acceptable)
Power 1-Type 2 error
Power Analysis Tells us how many participants are needed to have no more than a type 2-error rate of 0.2 (20%) (pre or post hoc)
Normal Distribution A distribution in which the mean, mode and median are the same
Non-Parametric A distribution in which the mode and median must be used to describe the central tendancy, not the mean
Power Analysis Tells us how many participants are needed to have no more than a type 2-error rate of 0.2 (20%) (pre or post hoc)
Standard Deviation Describes the deviation away from the mean for a parametric distribution
Confidence Interval Describes the spread away from the mean for a non-parametric distribution; The range of values in which there is a 95% chance the true result lies
Inte rquartile Range Describes the spread from the mean for a non-parametric distribution; Just another method to confidence intervals (confidence intervals p referred)

Statistical Tests

Test Use
Student T Test Parametric; 2 variables
ANOVA Parametric; Multiple variables
Chi Squared Non-Parametric; For 2 discrete variables; e.g. to show that the number of females and number of males with or without SUFE is different
Yates Correction Correction to Chi Squared when sample size <30
Fisher's exact test Replaces Chi-squared when sample size <5
Mann Whitney U Non-Parametric For discrete data; e.g. to show the difference between the PS angle measurement in men and women
Kruskal l-Wallace Non-Parametric; Multiple variables; Continuous Data

Trauma Severity Scores

AIS Score Injury
1 Minor
2 Moderate
3 Serious
4 Severe
5 Critical
6 Unsurvivable
Body Region Injury description AIS Square of top 3
Head & Neck Cerebral contusion 3 9
Face No injury
Chest Flail chest 4 16
Abdomen Liver Laceration 4 16
Extremity Femur Fracture 3
External No Injury 0
Total ISS score 41

ISS >25 = severe injury ISS >40 = life threatening

Muscle Layers of the Foot

Layer 1; (most plantar) ABDm; ABDh; FDB
Layer 2 Lumbricals; FHL; FDL; Quadratus Plantae
Layer 3 ADDh; FHB; FDM
Layer 4; (deepest) Dorsal Interossei x4; Plantar Interossei x3; Peroneus Longus; Tibialis Posterior
Dorsal EDB; EHB (only rarely present)

Types of Pelvic Osteotomy

Type Description Notes
Salter Volume neutral; Hinges on sciatic notch and pubic symphisis Triradiate can be open
Ganz Volume neutral; Multiplanar osteotomy close to acetabulum; Allows large correction Triradiate must be closed
Pemberton Volume Reducing; Iliac wing to triradiate held open with bone; Hinges on triradiate
Dega Volume reducing; Iliac wing to just before sciatic notch
Chiari Volume Increasing - Salvage; Osteotomies around acetabulum and medialisation; Creates a lateral shelf to increase coverage Fibrocartilage forms beneath shelf; Salvage
Shelf Volume Increasing -- Salvage; Bone grafting lateral to acetabulum; Creates a shelf Salvage

Stabilisers of the Elbow

Primary Static Secondary Static Secondary Dynamic
Ulna collateral of LCL; (varus & posterolateral) Radial Head; Primary stabilizer if coronoid/MCL fractured /torn(v algus & AP) Anconeus
Anterior band of MCL(valgus) Brachialis
Coronoid Process Flexor & Extensor masses

MRC Muscle Power

Grade Clinical Findings
0 No Movement
1 Flicker of movement
2 Active movement with gravity eliminated
3 Active movement against gravity
4 Active movement against some resistance
5 Normal power

Small Fragment Set

Screw Type Cortical Cortical Cancellous Locking Locking
Thread diameter 2.7 3.5 4.0 2.7 3.5
Drill 2.0 2.5 2.5 2.0 2.8
Tap 2.7 3.5 4.0 Self tap Self tap

Large Fragment Set

Screw Type Cortical Cortical Cancellous Locking Locking
Thread diameter 4.5 5.5 6.5 4.0 5.0
Drill 3.2 4.0 3.2 3.2 4.3
Tap 4.5 5.5 6.5 Self tap Self tap

Shoulder Imaging

View Description Use
True AP Beam at 45 degree to body or; Arm externally rotated GHJ pathology; General screening
Axilliary Lateral Arm abducted 90 deg; Beam shot cranially through axilla Dislocations; Humeral head shape
Trauma Axilliary Arm abducted 20 deg Same -- slightly inferior quality
Valpeau Axilliary Beam directed caudally through shoulder Allows sling to be left on; Inferior quality
Trans-scapula Shot in plane of scapula spine Dislocation
Supraspinatus outlet In plane of scapula with 10 degree caudal tilt Acromium morphology
Westpoint Prone with arm of table at 90 degrees.; Beam shot 25 deg caudally and medially Glenoid rim fractures
Stryker notch Supine with hand on hed; Beam shot 10 degree cephalic Hill Sachs lesion
Zanca AP with 10 degree caudal tilt ACJ
Serendipity 45 degree cephalic SCJ
Garth Apical Oblique Seated with arm in IR; Beam 45 deg caudal and lateral Shoulder instability; Hill Sach, Glenoid rim

Positions for Arthrodesis of Joints

Joint Position
Hip Flexion 30; Adduction 5; ER 10
Knee Flexion 0- 10; Valgus 5; ER 10 (Charnley recommended full extension -- cosmetic)
Ankle Flexion 0; Valgus 5; ER 10; Slight posterior dis placement of talus (reduces stress on knee)
1st MTPJ Valgus 10, neutral rotation; Dorsiflexion -- toe just of floor in plantigrade foot position
Subtalar Joint Valgus 10; Flexion 0 (neutral)
Shoulder Flexion 30; Abduction 30; IR 30 (IR is most important determinant of function)
Elbow Flexion 70-90; (More better for personal hygiene, less better for other use); (If bilateral one should be more flexed than the other)
Wrist Ulna deviation 5; Extension 5(some extension better for grip -- too much limits pronation/supination)
Thumb CMCJ Abduction 30; Extension 30; Pronation 15
Thumb MCPJ Flexion 25
Finger MCPJ [Flexion 45 (Index with supination 10 degrees -- pinch grip)
Finger PIPJ Index & Middle -- Flexion 20 with supination( pinch); Ring & Little -- Flexion 40 (grip)
Finger DIPJ Index & Middle] -- straight; Ring & Little -- straight stops catching, 5 deg flex ion aids grip

Ligamentous Stability of Shoulder

Ligament Restrains against
SGHL ER in Adduction
MGHL Anterior translation in mid range of Abduction
Anterior IGHL Anterior translation in 90 deg Abduction & ER
Posterior IGHL Posterior Translation in 90 deg Abduction & IR

Orthopaedic Pharmacology

Medication Mode of Action
Paracetamol Weak COX inhibition; Central action (poorly understood)
NSAIDs Inhibit cyclo- oxegenase enzyme -- prevent PG formation; COX1 non s elective, COX2 selective
Opiates Mimic endogenus opioids; Centrally via G proteins on mu receptors
Steroids Direct inhibition of T Lymphocytes and Macrophages (immunosupressive); Prevent transcription of gene which codes for COX2 enzyme ( anti-inflammatory)
Local Anaesthetics Inhibit action potential formation by blocking Na channels pH dependent
Warfarin Affects Factors 2, 7, 9, 10 (Vit K dependent); Prevents carboxylation of glutamine residues; Renders these factors useless; Also de- activates Protein C and protein S
Heparin Forms a complex with Ant ithrombin 3; Primarily directly inhibits Thrombin (factor 2a) and Factor
10a; Also affects all active factors in intrinsic pathway 12a, 11a, 9a
LMWH Also forms a complex with Ant ithrombin 3; But, se lectively affects Factor 10a only
Fondaparinaux Selective factor 10a inhibitor
Rivaroxiban Selective factor 10a inhibitor
Dabigatran Direct THROMBIN (factor 2a) inhibitor
Aspirin Binds irreversibly with COX1 enzyme; Inhibits PG production; Prevents platelet aggregation and prevents platelet secretion of Thromboxane A2 (prothrombotic agent)
Bisphosphonates Stabilise HA crystals; Directly inhibit Osteoclasts -- prevent ruffled border formation; Cause apoptosis of osteoclasts; Nitrogen Containing; malevonate pathway: farnesyl synhthesis; Non -nitrogen containing; form toxic ATP anologue - apoptosis
Strontium Anabolic and Catabolic effect on bone; Increase formation and decrease r esorption
Methotrexate Non biologic DMARD; Inhibits purine metabolism (azothioprine similar)
Entanercept Biologic DMARD -- TNF inhibitor
Infliximab Biologic DMARD -- TNF inhibitor
Penicillamine Biologic DMARD -- Reduces T Lymphocytes
Anakinara Biologic DMARD -- Interleukin 1a ntagonist

Differential Diagnosis of Intoeing

Condition Features
Metatarsus Adductus Packaging issue -- benign; Due to stronger inverters and plantar flexors; Measured by thigh foot axis; Resolves spontaneously by WB age
Internal Tibial Torsion Normal; Measured by inter-malleolar axis; Resolves by age 2-4 years (30 degrees ER)
Anteversion of the femoral neck Normal variant; Resolves by age 5 -- 8 to 20 deg anteversion
Club Foot Pathologic
Cerebral Palsy Pathologic

Differential Diagnosis of Torticollis

Cause Features
Muscular Most common; SCM spasm and contracture (Intrauterine Compartment syndrome); Head tilted towards the contracture, neck away; Plagiocephaly, facial asymetry
Acute Idiopathic Wakes up with it; No SCM contracture or mass
Congenital Look for low hair line, webbed neck etc.
Neurogenic No SCM contracture; Nerve tumour
Occular Due to visual problem
Atlanto-Axial; Rotatory Instability Traumatic; Syndromic (Morquio's, Down's etc.); Infective -- Griesel's

Causes of Paediatric Genu Valgum, Genu Varum

Genu Varum Genu Valgum
Blount's Disease Fibula Hemimelia -- Hypoplastic LFC
Rickets (all types) Morquio Syndrome
Achondroplasia MED
Tibial Hemimelia Cozen's fracture
Osteogenesis I mperfecta Hypophos phataemic Rickets sometimes
Multiple hereditry Osteochond romatosis; Infection; Trauma

Perthes Disease - Catteral's Head at Risk Signs
Sign
Gage's Sign: triangular lucency from lateral aspect of physis
Lateral Head Subluxation
Calcification lateral to the head
Horizontal physis

Perthes Stages

Stage Features
Initial Sclerosis -- normal head shape
Fragmentation Fragmented head usually lateral aspect epiphysis; This is the time where treatment can affect outcome most
Re-Ossification Head resorption
Re- Modelling Head attempts to remodel into normal shape

Acceptable C Spine Radiographic Measurements

Measurement Value
ADI (C1/2) Normal = 3mm (adult) 5mm (child); 3-5mm = Transverse ligament torn (adult); >5mm = Transverse, apical & alar ligaments torn (adult); 3.5 mm change on Flexion/extension = Instability; >9mm in RA is an indication for surgery; (In RA 4-9mm may not be an indication for surgery if neurologically normal)
PADI (SAC) (C1/2) <14mm indicates stenosis; (<14mm best prognostic indicator for successful surgery); <10mm indicates absoloute stenosis
Ranawat Index <14mm indicates Basilar invagination -- indication for surgery
Subaxial Instability Up to 4mm or 40% displacement of vertebrae is acceptable
Fl exion-; Extension views >11 degree Cobb angle change indicates instability
Powers Ratio <1 is normal (more may indicate Atlanto-occipital dissociation)
Torg Ratio 0.8 or less indicates stenotic spine
Lateral Mass widening >7mm indicates TL disruption of C2 (on PEG view)
Schwischuks; line Interspinous processes of C1-3 intersect within 2mm; Allows C2/3 or C3/4 pseudosubluxation up to 4mm or 40%
Pre-vertebral; Soft Tissue; Swelling >7mm at C3 abnormal (adult); >20mm at C6 abnormal (adult); >5mm at C3 abnormal (child) - may be false positively increased if child crying -- retropharangeal swel ling); >16mm at C6 abnormal (child)

Incidence of Concurrent Spinal Trauma in C-spine Fractures

Level Risk
C1 50%
C2 30%
C3 20%

Composition of Orthopaedic Metals

Metal Composition
Stainless Steel 316L 60% Iron; 20% Chromium; 16% Nickel; 3% Molybdenum; 0.03% Carbon; L = low carbon: improves heat resistance
Titanium AL-6 V-4 90% Titanium; 6% Aluminium; 4% Vanadium; <1% other
Cobalt Chrome 60% Cobalt; 25% Chromium; 5% M olybdenum; 10 % other

Types of Nerve Fibre

Fibre Type Example Myelination Diameter Velocity
Aα Motor; large diameter Myelinated 20 100
Aβ Organised sensory ( hair) Myelinated 10 50
Aδ Pain & Temperature Myelinated 5 25
B Auto nomic Pre- Gangl ionic Myelinated 5 10
C Autonomic Postganglionic; Cutaneous slow pain Unmyelinated 1 2

Modic Changes in Degenerative Disc Disease

Type T1 T2 Relevance
Modic 1 Dark Bright Associated with pain and inflammation; End plate fissuring; Histology -- vascular granulation; (25%)
Modic 2 Bright Bright Trabecular fissuring; Fatty infiltration of vertebra; Correlates with chronic stable back pain; Most common type (70%)
Modic 3 Dark Dark Rare to see; Sclerotic vertebra and end plates

Waddell's Non-Organic Signs
Sign
Over reaction
Hysteria
Simulation
Non-dermatomal pain
Pain and numbness simultaneously
Pain on light touch
Distraction pain reduction

Cell Cycle

Phase Features
Interphase Encompasses the whole cycle except Mitosis; G1, S and G2 are all part of interphase
G0 When a cell has left the cell cycle i.e. not dividing; Neurons are permanently in G0
G1 Growth phase; Controlled by p53 gene; Cells are increasing in size; Being redied for synthesis
S DNA Synthetic phase; Chromosomes divide into chromatids; Still all contained in one nucleus
G2 Growth phase 2; Again the cell grows post synthesis; Readies itself for mitosis
M Mitosis -- cell division (not part of interphase); Chromatids are separated into different nuclei; Cell divided (cytokinesis); This is the shortest phase

Dorsal Wrist Compartments

1st APL, EPB
2nd ECRL, ECRB
3rd EPL
4th EDC, EIP,PIN
5th EDM
6th ECU

Structures Exiting the Sciatic Foraminae (11 in total)

Greater Lesser
Above Piriformis Superior Gemellius
Superior Gluteal Nerve Obturator Externus
Superior Gluteal Artery Inferior Gemellius
Below Piriformis Quadratus Femoris
Inferior Gluteal Nerve
Inferior Gluteal artery
Pudendal Nerve
Pudendal Artery (internal)
Sciatic Nerve
Nerve to Obturator Internus
Posterior Femoral Cutaneous Nerve
Nerve to Quadratus Femoris
Don' forget Piriformis

Facet Orientation in Spine

Vertebrae Coronal Plane Sagittal Plane
Cervical 0 45
Thoracic 20 55
Lumbar 50 90

Pedicle Sizes

T4 smallest in whole spine

L1 smallest in lumbar spine

T1 largest in Thoracic spine

Anatomic differences between vertebrae

Vertebra Features
Cervical Foramina transversarium (C7's is empty); Bifid spinous processes (not C7); Facets 0 degree in coronal, 45 degree sagittal plane
Thoracic Costal facets on all vertebral bodies; Costal facets on T1-9 transverse processes; Facet orientation 20 coronal 55 sagittal
Lumbar Mamilliary processes; Taller anteriorly -- provide lordosis; Shorter wider pedicles; Facet orientation 50 coronal, 90 sagittal

Wiberg Patella types

Type Features
Type 1 Medial and Lateral Facets equal -- ridge central
Type 2 Medial Facet smaller -- ridge medialised (most common)
Type 3 Medial facet tiny & far medialised rendering ridge almost absent

Types of Prosthetic Knee Articulation

Type Features
Polycentric (4 Bar Linkage) Allows varied COR during gait; COR Anterior during flexion/sitting; COR Posterior during stance for stability; Bilateral amputees; Transfemoral; Through Knee
Hydraulic/Pneumatic Knee Heavier; Provides most fluid gait pattern; Varied resistance during flexion; Good for young high demand patients
Constant Friction Basic hinge that uses a pad/screw to dampen flexion; Stance control not great; Common in children
Variable Friction; (cadence control) Varied resistance with multiple pads; Poor durability
Stance Phase Control; (safety knee) Knee freezes in extension (frictional jamming); Provides extra stability in extension for stable stance; Good for elderly or those at risk of falling
Manual Locking Knee Knee can be physically locked in extension; For very weak, unstable patients

Factors that negatively influence healing of an amputation stump
Albumin <3.5 g/dL
Lymphocyte count <1500mm3
Low Serum Transferratin
ABPI <0.45
Transcutaneous Oxygen Sats <20mmHg (>40 is a positive predictor)
Hb <10g/dL

Ideal Amputation Levels

Region Level
Forearm Junction proximal 2/3 and distal 1/3
Humerus Middle 1/3
Trans Tibial 8cm per meter of height (usually around 15 cm below TT)
TransFemoral Middle 1/3

Common Parts of Prosthesis

Part Features
Socket Interface between residuum and prosthesis
Suspension Method of attachment to the residuum
Struts Restore length; Connect to the terminal device
Articulations Replace joint function as necessary
Terminal Device Most distal part; Passive (cosmetic) or active (functional); Active are controlled by cables, struts, or myoelectric

Types of Hypersensitivity Reaction (Remember EMG Tests)

Type Immunoglobulin Examples
1 IgE Atopy & allergy; Immediate hypersensitivity; Asthma
2 IgM Antibody related -- cytotoxic ITP, Graves disease etc.
3 IgG Immune complex mediated; e.g SLE & Rheumatoid arthritis
4 T cells Delayed hypersensitivity; Mantoux test; Contact dermatitis

Complement

Inate form of immunity that 'complements' other forms of immunity. Main role is enhancing macrophage function, chemotaxis and cytokine co-ordination.

Radiation

Angioplasty -­‐upto 57mSv │ 15-­‐20years
Bone Scan--T99m -­‐3mSv │ 1year
CT Neck -­‐0.6mSv │ 2months
CT Pelvis-­‐abdo │ -­‐10mSv │ 3years
CXR -­‐0.1mSv │ 10 days background
DEXA scan -­‐0.001mSv │ <1day
Limb X-­‐ray │ -­‐0.001mSv │ <1day
PET Scan -­‐14mSV │ 4years
Spine X-­‐ray │ -­‐1.5mSv │ 6months

Differences between Tendon & Ligament

Feature Ligament Tendon
Elastin Content Greater Less
Strength Weaker Stronger
Collagen; Arrangement Layered; Each layer has parallel fibres Longitudinal
Insertion Direct Indirect or Direct
Function Stabilise j oints Place muscle at optimal distance; Act as a spring -- store energy
Blood Supply Via insertion site; Uniform Via Para tenon (vascular); Via single Vinculae & diffusion ( avascular); Musculotendinous junction; Insertion site

Composition of Ligaments and Tendons

Component Features
Cells; 20% Fibrob lasts Predominate
Tenocytes Some present after healing of tendon/ligament
Matrix 80% Collagen 90% 90% Type 1; Type 3 during proliferative phase of healing; <1% other types
Proteoglycans Negatively charged at tract water -- create gelatinous matrix
Elastin Aids ability to recoil -- more in ligaments
Other Proteins MMP's, glycoprotein's etc.

Stem Failure

Mode XR features Cause
1a PIVOT Stem subsidence Inadequate bonding
(Stem in cement) Lucency zone 1 & 7; Cement fracture zone 4 Inadequate cement
1b P IVOT; (cement in bone) Subsidence; Circumferential lucency Inadequate pressurization; Removal of all cancellous bone
2 Mid -- Stem Pivot Lucency zone 1, 2, 5, 6; Cement fracture at midstem; Stem in varus Poor fixation proximal & distal
3 Calcar Pivot Lucency zones 4,5,6; Windscreen wipering stem; Sclerosis at stem tip Poor distal fixation
4 Canti lever Bending Lucency 1, 2,6,7; Stem fracture Poor proximal fixation

Evolution of Cementing Technique

1****st****Generation 2****nd****Generation (1975) 3****rd****Generation (1982)
Finger Packing Cement Gun -- retrograde Porosity reduction (vacuum mix)
Sharp edged stem Pulse lavage Pressurisation (interdigitation)
Canal brushed & dryed Stem centraliser (mantle defects)
Cement Restrictor Rough Stem Finish

Composition of Bone Cement (1:2) (as per Biomet website)

Liquid (1 Part) Powder (2 Parts)
Monomer -MMA Polymer - PMMA
Accelerator -- N-Dimethyl-p-toludine Initiator -- Di-benzoyl Peroxide
Inhibitor -- Hydroquinone Barium Sulphate
Dye (chlorophyll) Antibiotics

Phases of Cement Setting

Phase Features
Mixing Phase Performed homogenously in a vacuum to reduce porosity
Waiting (Dough phase) From mixing until cement is no longer doughy Viscosity increases; Too low a viscosity will allow blood to mix into cement
Working Phase The time during which cement can be manipulated; Difference between doughy and setting times
Hardening Phase Cement completely hardens; Influenced by temperature of stem, cement, theatre
Setting Time From mixing until cement has reached half its maximal heat

Cementing

  • Radiographic analysis
  • Barrack and Harris grading system
  • grade A
  • complete filling of medullary canal
  • "white-out" of cement-bone interface
  • grade B
  • slight radiolucency of cement-bone interface
  • grade C
  • radiolucencies > 50% of bone-cement interface or incomplete cement mantles
  • grade D
  • gross radiolucencies and/or failure of cement to surround tip of stem

Order of Soft tissue releases in TKR

Deformity Releases
Varus Osteophytes; Medial capsule & deep MCL; PM corner & Semimembranosus; PCL; Sequential release of superficial MCL at Pes Anserinus
Valgus Osteophytes; Lateral capsule from tibia; ITB if tight in extension, Popliteus if tight in flexion; LCL from femur; Pie crust posterolateral capsule
Flexion Posterior condyle osteophytes & capsule; Sequential PCL release; Pie crust posterior capsule; Increase tibial slope; Downsize femur

Patella Radiographic Measurements

Measurement Method Values
Height Lateral XR in 30 deg flexion; Blumensats line; Insall-Salvetti; Patella tendon:Patella length[Balckburn-Peel]; Distal pole patella to joint line: Patella articular surface Distal pole lies at B line; <0.8 = Baja; >1.2 = Alta; <0.8 = Baja; >1.0 = Alta
Tilt Merchant; CT mid-axial cuts Between patella edges and horizontal line >10 = significantly abnormal; <7= normal
TTTG Distance CT mid-axial cuts <10 = normal; 10-20 = borderline abnormal; >20 = significantly abnormal

Useful Formulas & Equations

Name Equation Clinical relevance
Law of wear V=SL/H Volumetric wear can be reduced by decreasing head size, decreasing load or increasing hardness of the bearings
Radial Clearance Cup r - Head r Increased clearance articulations have a longer bedding in period; Mid-polar contact achieved with 90400um Radial clearance
Fracture Energy E=1/2MV² Fracture energy more influenced by velocity than mass
Bending Rigidity BR = SMI x Young's BR is a product of the material and its spacial distribution around the neutral axis of the plate
2nd moment of inertia of a plate SMI = W x T³ SMI influenced more by thickness (to the power 3 for a plate) than width therefore BR more influenced by thickness
2nd moment inertia of a cylinder SMI = 0.25 x 3.14 x r⁴ Bending rigidity of a tube is increased to the 4th power
Torsional Rigidity TR = PMI x Young's Polar moment of inertia reflects torsional rigidity
Polar Moment of Inertia PMI = 0.5 x 3.14 x r⁴ Torsional rigidity of a tube is increased to the 4th power but more influenced by increase in size than bending rigidity (x0.5)
PMI of a hollow tube PMI=0.5x3.1 4(rₒ-rᵢ)⁴ Difference between radii of outer and inner part of nail
Newtons law of viscosity Viscosity = Shear stress /Shear rate; V is proportional to change in shear rate Synovial fluid is a non-newtonian fluid; Disobeys this law; Displays Thixotropy and pseudoplasticity

Corrosion

Type of Corrosion

Features Details
Uniform Attack Most common form of corrosion
Affects the whole surface of the implant
Occurs when a metal is in an electrolyte solution -- e.g. human body
Galvanic Corrosion Two dissimilar metals create an electrochemical gradient between them
Effectively a small battery
As ions are exchanged
Typical with Stainless Steel, especially when coupled with Titanium
Crevice Corrosion Cracks in the metal destabilise the passivity layer
The base of the cracks lacks oxygen therefore can't self passivate
Corrosion occurs at these defects
Pitting Corrosion Similar process to crevice corrosion
More insidious and localised
Crevice more widespread
Fretting Corrosion Actually a combination of wear and corrosion
Two non-articulating areas abrade each other
Micromotion abrades the passive layer and wear debris are generated
Head neck junction in large diameter MoM THR
Intergranular Corrosion Galvanic gradient occurs between grains in the metal ultrastructure
Caused by the presence of impurities trapped in manufacturing process
Occurs at the grain boundaries
Leeching (Intragranular Corrosion) Effectively intra-granular corrosion
Galvanic corrosion within, not between metal grains
Inclusion Corrosion Iatrogenic corrosion
Galvanic corrosion occurs because of accidentally retained metal fragments
E.g., screw driver tip
Stress Corrosion Repeated stress in one area disrupts the passive layer
Common in cyclically loaded stainless steel

Bone Healing

Primary Bone Healing

Features Details
Contact Healing Minimal activity at areas in direct contact
Mesenchymal cells differentiate to osteoblasts
Lay down lamellar bone in small gaps, woven bone in large gaps
Gap Healing Cutting Cones: Osteoclast-headed cutting cones tunnel across the fracture
Neo-vascularisation and osteoblasts migrate in their wake
Osteoblasts form Harversian canals which take 1-2 years
Remodeling Osteoblasts form Harversian canals which takes 1-2 years

Secondary Bone Healing

Features Details
Haematoma Hours
Clot formation
Platelet degradation -- PDGF released
Activates clotting cascade & complement system
Activates chemotactic factors (TNFa, TGFb, IL-1 & 6)
Attract PMN's and activate BMPs
Inter-fragmentary strain is 100%
Inflammation 1 week
BMPs cause angiogenesis and are osteoinductive
PMN's attract macrophages, fibroblasts, and osteoclasts
Macrophages phagocytose necrotic bone and debris
Osteoclasts resorb bone ends
Fibroblasts lay down granulation tissue (type 3 collagen)
Inter-fragmentary strain reduced to 15%
Soft Callus 1-4 weeks
Chondroblasts proliferate and lay down Type 2 cartilage
Forms bridging endosteal callus
Strain further reduced to 2-5%
Hard Callus 4-16 weeks
Chondroclasts resorb cartilage
Osteoblasts lay down type 1 collagen
At endosteal surface replacing cartilage (endochondral)
At periosteal surface (intra-membranous)
Collagen mineralized to form woven bone (hard callus)
Fracture stable
Strain <1%
Remodeling Years
Woven bone remodeled according to Wolff's Law to give stress-oriented mature lamellar bone

Composition of Articular Cartilage

Component Amount Features
Cells Chondrocytes 2% Maintain and produce Matrix
Extracellular Matrix Water 80% wet weight Permits deformation and nutrition by movement in and out of cartilage
Collagen 70%; 90% type 2; 10% 6, 10, 11 Responsible for tensile strength; 6 – binds chondrocytes to matrix; – calcified zone; – Acts as a binder of the lattice
Proteoglycans 20% Responsible for tensile strength; Negatively charged therefore attract water
Other; Proteins 10% Matrix Mettaloproteinases; Elastin; Glycoproteins

Changes to Articular Cartilage with Age and Osteoarthritis

Parameter Ageing OA
Water content Decreases Increases
Synthetic activity Decreases Increases
Collagen content Decreases Decreases (concentration increases)
Proteoglycan content Decreases Decreases
Chondrocyte Size Increases
Chondrocyte number Decreases
Chondroitin: Keratin ratio Decreases Increases
Stiffness (young's) Increases Decreases (high water content)

Diagnostic Criteria For RA (American college of Rheumatologists)
1. 3 or more joints swollen for >6 weeks
2. Morning Stiffness for 1 hour per day for >6 weeks
3. Hand or Wrist involvement for >6 weeks
4. Symmetric polyarthropathy
5. Rheumatoid nodules
6. Rheumatoid factor positive
7. Radiographic features typical of RA

Biologic Changes after Nerve Injury

Region Changes
Proximal Axon atrophies but doesn't die
Cell body changes
Migrates to periphery of cell
Starts producing regenerative proteins
Cell volume Increases
Chromatolysis -- degeneration of Nissl bodies
Distal Wallerian degeneration occurs
De-myelination
Axon is phagocytosed
Endoneurium collapses but intact (unless neurotmesis)
Schwann cells proliferate
Proximal axon forms growth cones -- sprouts on each fibre
Schwann cells form columns (bands of bunger) - direct re-growth
Motor End Plate <3 months: More end plates are generated -- seek out nerve supply
3-6 months: Begins to degenerate
12-18 months: Muscle spindles and sensory organs regenerate
End plate dies: Unable to be re-innervated

Pathologic Process of Osteoarthritis

Stage Features
Stage 1 Mechanical disruption of the collagen network
Increased water content
Stage 2 Alters balance of cartilage metabolism -- catabolic processes dominate
Products of catabolism are released into synovial fluid
(Chondroitin & keratan sulphate, collagen & PGs fragments)
Stage 3 Incites an inflammatory response
PMNs, Macrophages, IL-1 and MMPs accumulate
Stage 4 These mediators degrade the cartilage matrix, disrupt collagen further and alter chondrocyte function
Stage 5 Histology shows Fibrillated, eburnated, sclerotic shiny cartilage with loss of chondrocytes, collagen and PGs

Related FRCS revision notes

ClassificationsIntervertebral discCartilageKnee MeniscusSpine biomechanicsBone formation

Linked from

← Classifications and tables← Classifications← Intervertebral disc← Osteoarthritis classifications

Written/reviewed by Kishore Puthezhath

Professor of Orthopaedics and Consultant Paediatric Orthopaedic Surgeon

FRCS (Tr & Orth) revision resource

Reviewed: September 2026

Core revision references: Miller's Review of Orthopaedics; Campbell's Operative Orthopaedics; Orthobullets. Current specialty guidelines are linked within individual notes where applicable.