Charnelys friction arthroplasty in orthopaedics 10 marks pg answer with flow chart and images

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A detailed medical flowchart for Charnley's Low Friction Arthroplasty (LFA) of the hip. The flowchart should show: 1) Definition box at top: "Charnley's Low Friction Arthroplasty (LFA) - Total Hip Replacement". 2) Three main principle boxes: Small femoral head (22.25mm), UHMWPE acetabular socket, PMMA bone cement fixation. 3) Indications branch: Primary OA, Rheumatoid Arthritis, Ankylosing Spondylitis, AVN, Failed previous surgery. 4) Contraindications branch: Active infection, Young active patients, Poor bone stock. 5) Surgical steps flowchart: Patient positioning → Approach (Posterior/Lateral) → Greater trochanter osteotomy → Femoral head excision → Acetabular preparation & cup insertion with cement → Femoral canal preparation → Stem insertion with cement → Reduction → Trochanter reattachment. 6) Complications box: Dislocation, Loosening, Infection, DVT, Nerve injury, PE wear/osteolysis. 7) Results box at bottom: 90% survival at 10 years. Clean white background, medical blue and green color scheme, clear arrows connecting each step.

Here is a complete 10-mark answer on Charnley's Low Friction Arthroplasty (LFA):

Charnley's Low Friction Arthroplasty (LFA) of the Hip

Introduction

Sir John Charnley introduced Low Friction Arthroplasty (LFA) at the Centre for Hip Surgery, Wrightington, England, in the early 1960s. It is the prototype and gold standard of total hip replacement (THR). The fundamental principle is to reduce frictional torque at the bearing surface so that forces transmitted to the bone-cement interface are minimized, thereby protecting fixation and prolonging implant survival.

Principle of Low Friction

Charnley's concept: Frictional torque = friction coefficient × load × radius of femoral head

To minimize frictional torque, three design innovations were combined:

Component	Charnley's Choice	Rationale
Femoral head	Small (22.225 mm diameter)	Reduces lever arm, minimizes torque
Acetabular socket	Ultra-High Molecular Weight Polyethylene (UHMWPE)	Very low friction coefficient (~0.02) vs. cartilage (0.002)
Fixation	PMMA bone cement (acrylic)	Secure interface load transfer

The articulation is metal-on-polyethylene (MoP). The stainless steel femoral prosthesis has a small, highly polished spherical head. This results in a coefficient of friction of approximately 0.02 - far lower than metal-on-metal or Teflon (his early failed attempt).

Components

1. Femoral Component

Forged stainless steel (later cobalt-chrome alloys)
Small polished spherical head: 22.225 mm (originally tried 41 mm then reduced)
Straight stem cemented into femoral canal with PMMA
Later designs: smooth polished slip-taper stems (designed to slightly subside in cement, compressing it into bone)

2. Acetabular Component

All-polyethylene cup (UHMWPE)
Cemented into reamed acetabulum
Flanged designs improve cement pressurization
Cup positioned at 45° abduction (Lewinnek safe zone: 40-50° abduction, 5-25° anteversion)

3. Bone Cement (PMMA)

Polymethylmethacrylate
Acts as a grout - fills trabecular spaces for microinterlock
Does NOT chemically bond to bone or metal - purely mechanical
Strongest in compression, weakest in tension (hence cemented cups fail more than stems)

Hip joint with arthritic changes and the low friction concept

The Charnley concept: small femoral head within a deep UHMWPE socket - reduces the frictional torque at the bearing surface

Indications

Primary indications:
- Osteoarthritis (most common) - Kellgren-Lawrence Grade 3 and 4
- Rheumatoid arthritis
- Ankylosing spondylitis
- Avascular necrosis of femoral head
- Failed previous hip surgery / hemiarthroplasty
- Post-traumatic arthritis
- Neglected congenital dislocation of hip
- Protrusio acetabuli
General criteria:
- Debilitating pain affecting activities of daily living
- Pain not controlled by conservative measures
- Patient medically fit for surgery
- No active infection anywhere in body

Contraindications

Active infection (local or systemic)
Young, very active patients (cement fatigue risk)
Neuropathic joint (Charcot arthropathy)
Insufficient bone stock
Neurological disorders with spasticity
Patient unable to comply with postoperative restrictions

Surgical Technique

Patient Position: Lateral decubitus (for posterior/posterolateral) or supine (for anterior approach)

Approaches (Table):

Approach	Interval	Risk	Pros
Posterior (Southern)	Gluteus maximus split + external rotator tenotomies	Sciatic nerve	Extensible, quick
Lateral (Hardinge)	Gluteus medius split	Superior gluteal nerve/artery	Good stability
Anterolateral (Watson-Jones)	TFL and gluteus medius	SGA branch	Stable
Anterior (Smith-Petersen)	Sartorius/TFL + rectus/gluteus medius	LFCN, ascending LCFA	No dislocation

Charnley's Original Technique used the lateral approach with greater trochanter osteotomy:

Greater trochanter detachment (osteotomy) for wide exposure
Hip dislocation and femoral head excision at neck
Acetabular reaming to hemispherical shape
Cement pressurization into acetabular cancellous bone
UHMWPE cup insertion at 40-45° abduction, 10-15° anteversion
Femoral canal preparation (broaching)
Cement gun insertion of PMMA into femoral canal
Stem introduction - press-fit, then cement hardens
22.225 mm head reduction into cup
Greater trochanter reattachment with wires/cables
Wound closure in layers

Flowchart

Cemented Femoral Stem Design

Comparison of composite beam (left) vs smooth polished slip-taper stem (right)

FIG: Composite beam stem (left) is bonded to cement; the smooth polished Charnley-type stem (right) is designed to slightly subside, compressing the cement-bone interface and reducing shear force - the original Charnley principle

Cement fixation key points:

Microinterlock with endosteal bone trabecular spaces
Cement fatigues with cyclic loading starting at stress points
A mantle defect (where prosthesis touches bone) = area of high stress concentration
Cemented stems fail at a lower rate than cups because stems experience primarily compressive forces, while cups experience shear/tension

Biomechanical Basis - Joint Reaction Force Reduction

Charnley also advocated medializing the acetabulum (placing cup at the true acetabulum) and using a small femoral head to:

Reduce the joint reaction force (JRF)
Minimize wear and mechanical loosening
Protect the bone-cement interface

Dorr Classification (Guides Stem Selection)

Dorr classification of proximal femoral morphology

Type A ("champagne flute") - young males, thick cortices. Type B - intermediate. Type C ("stovepipe") - elderly females, osteoporosis - best treated with cemented stem (as per Charnley)

Complications

Early:

Dislocation (most common - especially posterior approach, ~2-3%)
Wound infection / deep periprosthetic infection
DVT / Pulmonary embolism
Nerve injury (sciatic > femoral)
Vascular injury
Periprosthetic fracture

Late:

Aseptic loosening - most common late complication
- Cement-bone interface failure
- Osteolysis from polyethylene wear particles
PE wear and osteolysis: Submicron PE particles phagocytized by macrophages → RANKL-mediated osteoclast activation → bone resorption. Volumetric wear = π × r² × w
Heterotopic ossification (Brooker classification)
Trochanteric non-union (specific to original technique)
Periprosthetic fracture (Vancouver classification)
Leg length discrepancy

Results

Charnley's original series: 90%+ survivorship at 10 years, 80%+ at 20 years
Long-term results published by Wroblewski (Wrightington series): Charnley LFA 25-year survivorship approaching 75-80%
The low-friction principle remains the foundation of all modern THA designs
Modern improvements: highly cross-linked PE (HCLPE), cementless fixation, modular heads, ceramic bearings - all build on Charnley's framework

Summary Points for Exam

Feature	Detail
Introduced	Sir John Charnley, 1960s, Wrightington
Femoral head size	22.225 mm stainless steel
Socket material	UHMWPE (ultra-high MW polyethylene)
Fixation	PMMA bone cement
Friction coefficient	~0.02
Approach	Lateral with GT osteotomy (original)
Key principle	Low frictional torque = protect cement-bone interface
10-year survival	~90%

Sources: Miller's Review of Orthopaedics 9th Edition, Section 5 THA, pp. 380-414; Campbell's Operative Orthopaedics 15th Ed 2026; Wroblewski (2009) - principle of low frictional torque

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