May 30, 2024

SIR JOHN CHARNEY (1911- 1982) is also called the Father of  Total hip arthroplasty

He is an English orthopedics surgeon

Sir John Charney
Sir John Charney

History

In 1954, Sir John Charney introduced Low Friction Arthroplasty (LFA)

LFA consists

  1. Metal femoral stem (have a small head to reduce wear and tear at the bearing surface)
  2. Polyethylene acetabular components
  3. Acryline bone cement

He is also responsible for operative room hygiene with the stress of sepsis

He explained hip biomechanics and introduced concepts such as deepening of the acetabulum and trochanteric osteotomy to alter mechanics favorability

Charnley initially used ‘Teflon cup + Steel femoral components’

However, this system had a failure at 12 months follow-up due to excessive wear

So, the Teflon cup was replaced by initially high molecular weight polyethylene and later Ultra-high molecular weight polyethylene (UHMWPE)

After conversion to UHMWPE, there is a 90% success rate

Sir John Charney searched for a 10% failure rate, which he found to be ‘chemical rejection of cement’ [ Cement disease]

So, he reduced it to 5% after introducing of  clean air enclosure + vacuum mixing and centrifugation

Methyl methacrylate

Postulated to cause cement disease

Localized lysis of bone

Third body wear

Acceleration of the loosening process

Evolution of cementless acetabular components

It is divided into 2 types as per mechanism of action

  1. Devices designed to achieve mechanical fixation to the pelvis, generally via the geometrical shape of the implant, large pegs, and threaded rings
  2. Devices designed to achieve biological fixation to the pelvis with the porous-coated surface to provide bony ingrowth

Evolution of cementing techniques

First-generationSecond generationThird generation
Limited bone bed preparationBone bed preparation (bulb syringe irrigation/drying)Through bone bed preparation (pulsatile lavage)
Unplugged femurDistal cement restrictorThe improved distal cement restrictor
Dougy cement introduced by handCement gunCement gun  
Digital pressurizationFemoral and acetabular cement pressurizationFemoral and acetabular cement pressurization
Hand mixing of cementOpen atmosphere mixing by handVacuum mixing/centrifugation of cement
Evolution of cementing techniques

Bone Cement (Polymethyl methyacrylate)

Polymer of methylmethacrylate a/k/a Plexiglas/ Perspex

Used in hip arthroplasty for fixation of femoral and acetabular components

Uses

  1. Filling bone defect
  2. Enhancing hold of fracture fixation devices in osteoporotic bone
  3. Delivery of the local antibiotics

Space-filling/ Load transferring material

It doesn’t chemically bond to bone or the surface of metal components or polyethylene (acts as a grout)

For fixation of prosthesis joint to bone

Basic components (MMA)

  1. Monomer liquid A in an ampule
  2. Polymer powder in a pack

Polymer between polymer(powder) + monomer (liquid)

Polymerization Reactions

  1. Mixing phase: powder and liquid are mixed to achieve uniform consistency
  2. Waiting phase: mixture increases viscosity and stops sticking to gloves hand
  3. Application phase: ends when cement dough cannot be joined back together again
  4. Setting phase: once the application phase is overàleads to the setting of cement

Vacuum mixing and centrifugation

  • 50% increase in tensile strength
  • Decrease no. of voids in mixture

Cleaning of the bone and pressurization of the cement within the bone cavity prior introduction of implants improves the interdigitation of cement into interstices of the bone surface.

With partially polymerized cement is forced into bone: drop-in B.P.

(that is attributed to uptake of residual monomer, while can cause peripheral vasodilation and fat embolization from bone marrow)

Bone Cement Implantation Syndrome-BCIS

Seldom a problem for a fit patient with OA, but in the case of the elderly it is common

Monomer and marrow fat may enter circulation very rapidly so when cement is compressed and fall in B.P. can be alarming (sometimes fatal), particularly in dehydrated conditions

If the initially preparation/application of cement is not perfect, a fibrous layer is formed between cement/bone interfaces

Thickness depends upon the degree of cement penetration into bone crevices, in this layer and fine granulation tissue and foreign body giant cells can be seen

If there is excessive movement at the cement bone interface or if  polyethylene or metallic wear particle track down into the cement/ bone interface

Aggressive granulomatosis/osteolysis

Loosening with a low-grade infection

BearingAdvantagesDisadvantages
Metal on polyethylene (MOP)Longest track record of bearing surface, Lowest cost, Most modularityHigher wear + osteolysis compared to ceramics, Smaller head size reduces wear rate but the risk of dislocation, Potential for corrosion at modular junctions
Metal on metal (MOM)Lower wear than MOP, Large head size allow for ↑ROM & ↓ dislocationMore expensive than MOPs, ARMD (adverse reaction to metal debris), Particularly concerned in pregnant/renal patients
Ceramics on ceramics (COC)Best properties of all bearing surfaces, Inert particlesExpensive# of linear or/and head due to brittle nature of the material, Squeaking, Less modularity with fewer neck length options
Ceramics on Polyethylene (COP)Potentially better wear profile than MOPs, Avoid risks of ceramics liners fractures, Avoid the risk of squeaksMinimize the risk of corrosion at modular junction↑ cost compared to the metal head, Risk of head fractures
Advantages and disadvantages of different bearing in THR

Metal on metal bearing

In 1938, Philips wiles introduced 1st metal on metal hip replacement

Used stainless steel components that fit into each other precisely

Keneth Mckee used (cobalt-chrome alloy) articulation with cemented acetabulum components and Thompson-type femoral implants

1st Generation MOM (muller) had a Press-fit design

2nd Generation MOM (using cobalt chrome alloy) with Hard cobalt-chrome alloy and thin acetabular components. So, a larger femoral head helps to improve the ROM of the Hip

So-called “Fluid film lubrication” reduced the wear rate

3rd/4th Generation MOMs: Bone conserving surgeries

Use of ‘Co-Cr-Mo’ alloy bearing with high carbon component

Have cementless fixation of acetabular component+cemented femoral components

Advantages of MOM

  1. ↓ Impingement
  2. Improved hip Kinematics
  3. ↓ dislocation

Disadvantages of MOM

Metal wear particles had biological reactions leading to bone lysis i.e. Aseptic, lymphocytic dominated vasculitis associated lesion and lysis (ALVAL)

Metal on polyethylene

Good result but partial wear is seen that leads to osteolysis

The volume of wear in metal on polyethylene depends upon the radius

V=r2w

↑ radius = ↑ wear rate

Wear is ↓ by increasing the cross-linking of polyethylene

Ceramics on polyethylene

Head has better wear characteristics compared to metalheads

Lower wear rates

Initially showed high fracture rates

Ceramics on ceramics

Developed in the 1970s

Has in fracture rate but improvement in mechanical property and introduction of alumina/zirconia

Wear rate is better than metal on polyethylene and metal on polyethylene

See also: Complications of Total Hip Arthroplasty

See also: Total Knee Arthroplasty