Hip

The problem of passing MS Orthopaedics

…with a Rank

Scan this

Time, HOTS and Effect horizon

Rote learning vs HOTS

HOTS and Judgement: Breakdown, Analyse, Combine for new Concepts

Diagnosis?

Hip speaks for itself

What will be your long case?

Hip (>90% probability)

What will be your diagnosis in your hip case?

Osteoartritis (>50% probability)

Should you learn Osteoarthritis Hip?

No-brainer

Why arthritis?

Two clinical signs that cling the diagnosis

  • Painful restriction of all ranges of movements

  • Joint line tenderness

Define Osteoarthritis

It is a mechanically driven but biologically mediated complex degenerative disease of a synovial joint starting at the tangential zone of the articular cartilage.

X Ray findings-LOSS

The classic radiographic features of OA are:

• Loss of joint space.

• Osteophyte formation.

• Subchondral sclerosis.

• Subchondral cysts.

What is osteophyte?

Enlarging bony protrusion due to endochondral ossification of chondrocytes arising from periosteal cells.

  • Attempt to stabilise the joint.

  • Seen at margins of weight bearing areas.

  • Grows in the path of least resistance, guided by synovium.

  • TGF𝛽 and BMP2 are implicated in the pathogenesis

What are subchondral cysts?

Subchondral bone cysts represent micro-fractures of the subchondral trabecular bone at various stages of healing and remodelling with gelatinous replacement of the marrow.

Formation Mechanism:

  1. Bone Microfractures

  2. Synovial Fluid Infiltration

  3. Fibrous Tissue & Bone Remodeling – The cysts may be surrounded by fibrous tissue or undergo sclerosis over time.

Any classification you know?

The Kellgren-Lawrence (KL) Classification is a grading system used to assess the severity of osteoarthritis.

Kellgren-Lawrence Grading System for Osteoarthritis

Grade 1 (Doubtful OA)
- Doudtful osteophytosis.

Grade 2 (Mild OA)
- Definite osteophytosis.

Grade 3 (Moderate OA)
- Definite JSN.

Grade 4 (Severe OA)
- Deformity.

In OA, fluid dry up, right?

Changes to Articular Cartilage with Age and Osteoarthritis

Parameter Ageing Osteoarthritis (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 modulus) Increases Decreases (high water content)

What is the bio-mechanical consequence?

Single buzz word is: Bulk Modulus

The resistance to compressive force is reduced, causing failure of load bearing function.

What can you do for him?

Reduce the JRF through the hip

  • Reduce weight

  • Use walking stick on opposite side

  • Carry weight if necessary on the same side

Hip FBD

Abductor moment = body moment in equilibrium

Fd = w x 5d

F = 5w

*w is generally taken as 5/6 of the body weight as the person is standing on one leg. Weight of one leg is generally taken a 1/6 body weight.

*F is the abductor force of contraction.

JRF

How to reduce JRF in hip?

Carry weight on same side!

F x d + F’ x 2d = w x 5d

F + F’ = 5w

F = 5w - F’

So the abductor force of contraction required is reduced from F to F-2F’

How to reduce JRF in hip?

Carry stick on the opposite side!

Pressing the stick on to the ground will produce an equal and opposite ground reaction force, s.

F x d = w x 5d - s x 10d

F = 5w - 10s

So the abductor force of contraction required is reduced from F to F-10s

Any regenerative treatment options?

  • Hyaluronic acid injection

  • Glucosamine

  • chondroitin sulphate

  • PRP

  • Herbs

Tell me more about the first three

Aggrecan and PG Aggregate

  • Proteoglycan is one of the largest macromolecule in our body: 2 x 1018 Dalton is the mw

  • chondroitin sulphate proteoglycan is called Aggrecan

PG Aggregate

Aggrecans self assemble on HA filament to form a supra molecular structure called PG aggregate.

  • Repels water (Eletrostatic repulsion)

Glucosamine, C SO4, HA

Any other options?

My patient needs a painless, stable and mobile hip

Suppose he want only painless and stable hip, what will you offer?

Arthrodesis

Indications

  • Young unilateral osteoarthritis (OA) patients
  • Heavy manual laborers
  • Preserves bone stock
  • Provides indefinite pain relief
  • Allows an active lifestyle

Prerequisites

  • Normal contralateral hip (C/L)
  • Normal ipsilateral knee (I/L)
  • Normal spine function

Disadvantages

  • Immobile joint
  • Leg Length Discrepancy (LLD)
  • Pain in adjacent joints due to altered biomechanics

Techniques

  • Intra-articular (I/A)
  • Extra-articular (E/A)
  • Combined approach

Fusion Position (FADER)

  • Flexion: 30°
  • Adduction: 5°
  • External Rotation: 5°

Brittain’s Technique

Primary THA

  • History
  • Introduce
  • Permission

Case History of Hip

  • Pain
  • SLID
  • Allergy
  • Medical
  • Social
  • Summary
  • Expectation

Pain-ODP

  • Where is the pain?
  • Does it come down to the thigh or leg?
  • How would you describe the pain?
  • Mild, moderate, or severe?
  • Do you limp while walking?
  • How far can you walk before pain stops you?
  • Do you have trouble walking upstairs?
  • Do you have trouble washing and drying yourself?
  • Do you have trouble putting on socks?
  • Does it affect your work or hobbies?
  • Any other pain?

SLID

  • Has your hip become stiff?
  • Limping since childhood?
  • Symptoms of infection?
  • Discharging wound or scars?

History Continued

  • Allergy
  • Past medical history: DM, hip surgeries, blood thinners, steroids
  • Social: Work, limitations, smoking, alcohol
  • Summary for the patient
  • What are your expectations?

Examination

  • Stand and inspect front, side, and back
  • Walk
  • Trendelenberg test
  • Palpate ASIS, TR, Pulse
  • Thomas test and ROM
  • LLD measurement
  • Special tests
  • Spine/Pulse assessment

Indications

  • Severe disabling pain unresponsive to conservative measures, affecting ADL
  • Medically fit
  • No active infection

Surgical Goals

  • Relieve pain
  • Improve function

Technical Goals

  • Correct limb length
  • Correct offset
  • Restore hip CoR
  • Correct positioning of implant
  • Position primary arc range within the functional range required by the patient

Contraindications

  • Infection
  • Neuropathy
  • Vasculopathy
  • Psychiatric illness
  • Obesity

Complications

  • Common (2-5%): DVT, Dislocation, Aseptic loosening
  • Less common (1-2%): Infection
  • Rare (<1%): LLD, Periprosthetic fracture, PE and death, Sciatic nerve palsy

Implant Fixation & Bearing Surface

  • Most common construct: Cemented MoP, 4.87% revision in 14 years
  • 75 years: All bearing surface combinations (except MoM) perform similarly
  • <55 years: CoP shows better results (<4%) compared to MoP (8-10%)

THA of Choice

  • Cemented Exeter Hip: Long-term performance, ODEP rating A* at 10 years
  • Ceramic Femoral Head with 1st or 2nd gen XLPE
  • <55 years: Discuss uncemented THA option

Cemented THA

  • Immediate solid fixation
  • Proven, durable
  • Low failure rate
  • Meets NICE guidelines
  • Cheaper, easier to revise

Why Not Uncemented?

  • Dorr C femur
  • Elderly
  • Pathological bone
  • Stress shielding, thigh pain
  • Difficult to revise

Cement Fixation

  • Microinterlock with bone
  • Cement fatigues with cyclical loading
  • No remodeling
  • Two interfaces: Cement-Bone, Cement-Implant

Design Principles

  • Composite beam (shape closed) Charnley, Stanmore
  • Taper slip (Force closed) Exeter

Composite Beam

  • Rough surface
  • Collared
  • Rigid stem, no movement
  • Stem acts as rod in 2 tubes
  • Stability by friction

Charnley

  • Matt
  • 22 mm head
  • Cobra flange to resist subsidence
  • Flat back changed to round back for fatigue strength
  • AP flange for cement pressurisation

Charnley stem

Exeter Taper slip

  • Polished
  • Collarless
  • Designed to subside in cement
  • Centraliser void prevent cement fracture
  • Hoop stress generated, producing radial compression

Exeter

Centraliser

  • Helps stem subsidence
  • Seals effective joint space
  • Better cement mantle
  • Reduce cement cracking by decreasing tensile forces

Cement

  • Content, property and uses
  • Generations

Cement Generations

Generation first second third Fourth
Mixing Bowl Bowl Vacuum Vacuum
Gun No Yes Yes Yes
Restricter No Yes Yes Yes
Pulse lavage No No Yes Yes
Pressurisation No No Yes Yes
Centraliser No No No Yes
Mantle No Yes Yes Yes
C quality No No Yes Yes
Stem position No No No Yes

Strength Factors

Uncontrollable Partly Controllable Fully Controllable
Moisture Blood and tissue Antibiotic
Aging Stress raisers Vacuum
Fatigue Pressurisation
Mixing speed
Radioopaque filler

Radiology (Barrack et al. 1992)

  • Grade A: Complete “white out” at bone-cement interface
  • Grade B: Slight radiolucency
  • Grade C: 50-99% radiolucency or defective mantle
  • Grade D: 100% radiolucency or uncovered stem tip

Gruen Zones

  • Diagnose osteolysis and cement fracture

  • 7 femoral zones:

Gruen Modes of Failure

Mode Description
Ia Pistoning: stem within cement
Ib Pistoning: stem within bone
II Medial midstem pivot
III Calcar pivot
IV Bending cantilever (fatigue)

Gruen Failure

Cement Mantle Fracture Causes

  • Stress exceeding endurance limit
    Reduced by:
    • Optimal thickness (2-5mm)
    • Symmetric mantle
    • Homogeneous cement

Achieving Optimal Cement Mantle

  • Avoid stem malalignment
  • Preserve 2-3mm proximal medial cancellous bone
  • Use stem centraliser
  • Improve cement quality
  • Better cementing techniques

Uncemented THA Principle

Dynamic biological fixation with lifelong bond between bone and implant.
Methods:
- Bone ingrowth (porous coating)
- Bone ongrowth (grit-blasted/plasma-sprayed surface)

Ingrowth: Rule of 50

  • Pore size: 50µm
  • Pore depth: 50
  • Porosity: 50%
  • Gap: 50µm
  • Micromotion: 50µm
    • Press fit: 1-2mm larger implant
    • Line to line: require additional fixation initially Scratich/frictional

Stem Sinkage Factors

  • Undersized stem
  • Poor bone stock
  • High BMI

Engh Radiological Criteria

  1. Slight rounding of proximal medial femoral neck
  2. Medial cortical density loss (Level 1)
  3. Cortical resorption extending to Level 2
  4. Severe resorption into diaphysis

Femoral Component Stability

  • Stable: No migration + spot welds
  • Stable fibrous ingrowth: No migration + sclerotic lines
  • Unstable: Progressive subsidence + cortical thickening

Ongrowth

  • Initial press fit
  • Bone grows onto divots
  • Titanium implants
  • Hydroxyapatite coating (50µm)

Ceramic

  • Inorganic material made up of combination of metallic and non metallic elements bonded ionically in high oxidised state

Advantage and Distadvantage

Better lubrication, friction and wear prop Brittle
Hard Catastrophic failure
Low co of friction No plastic deformation
Wettable Squeaking
Biocompatable Less range of size
Bioinert cost
No corrosion
no ion release

Manufacture-Sintering

  • Made in to slurry of ceramic powder and water
  • Pressed mechanically
    • Hot isostatic pressing
  • Grinding and polishing using diamond wheel
  • Stress testing

Generations

  • 1st: 13% fracture
  • 2nd: 5%
  • 3rd: Delta alumina : 0.18%
  • 4th gen Biolax Delta: 0.003%

Biolax Delta

  • Composition
    • Al, Zir, Strontium
  • 1st toughening: Transformational toughening
    • Z particles act like airbags
  • 2nd toughening: Platelet like crystals

Revision

  • Once ceramic, always ceramic
  • Revise all

Liner failure

  • Liner fracture
    • Incomplete sitting
      • Peripheral chipping
      • Morse taper
      • Cup deformation
    • Inaccurate cup position
      • Edge loading: Microseperation
      • Medialised cup
      • Stem subsidence
      • Impingement
    • Head size over 36mm: Positive offset

Stripe line

  • Area of roughness created on cup and head due to repeated subclinical subluxation.
  • Due to increased lever range
  • Reduced by reducing lever range by
    • Better design
    • Positioning and offset

Polyethylene

  • Long chain polymer of ethylene monomer (C2H4)
  • Mol wt: 2-5 x 10(^6)
  • Viscoelastic and undergo strain hardening
  • Used as bearing surface

Wear properties

  • Manufacture
    • Ram bar
    • Direct compression moulding
    • Ca stearate
  • Sterilisation
    • Gamma radiation in presence of air: Chain scission
  • Storage:
    • Long shelf life lead to oxidation
    • Package: air leaking

Highly cross linked PE

  • High dose radiation induce cross linking
  • Better wear property
  • More brittle
  • Hard
  • Stiff
  • Reduced UTS
  • reduced work hardening

2nd Gen XPE

  • Vit E treatment
  • Post production anniling

Modes of failure

  • Aseptic loosening
  • Dislocation
  • Fracture
  • Liner failure
  • Edge loading
  • Squeaking

Complications

HO

  • 43%, 9% high grade brooker
  • Patient factors
    • An Sp
    • Pagets
    • Post trauma
    • DISH
  • Surgical factors
    • Muscle ischemia
    • Lateral approach
    • Bone trauma
    • Bone debris

Classification

HO Prophylaxis

  • Indomethacin 75 mg 6 weeks
  • Single peri op RT 700cGy (4hr before to 72 hrs after)
  • Combined RT and indo

Take home message

Remember: If someone gives you something for free,

you are the product

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