THA

Cemented cup and femur via posterior approach

Set up

- on side

- charnley supports posterior on sacrum

- anteriorly on ASIS

- patient slightly tilted backwards

- avoids cup retroversion

Posterior Approach

- identify short ER

Goal

Initial press fit

- implant geometry fits the cortical bone in the proximal femur

- good initial mechanical stability

Biological fixation for success

- good press fit

- minimal micromotion

- bony or fibrous tissue ingrowth or ongrowth

Management Summary

Stage 0

Natural history mixed

- depends on size of lesion and diagnosis

- treat if becomes asymptomatic

- may benefit from bisphosphonates

Stage 1 / Normal X-ray, abnormal MRI

Forage: 80% G/E

Bisphosphonates

Stage 2 / Abnormal X-ray with cysts and sclerosis

A:  As for Stage I

Aim

Reproduce the normal anatomical centre of rotation

Restore femoral offset 

Maintain equal leg lengths 

Usually template off normal hip

Template

1. LLD

2. Offset

3. Femoral component

4. Acetabular component

5. Osteotomy / femoral seating

Issues

Templating

Approach

Fixation

Bearing Surface

Head Size

Offset

Indications

Disabling hip pain

Severe functional impairment

Failed non operative management

Not Indicated 

Painless deformity

Wear

The removal of material, with the generation of wear particles under an applied load and in relative motion

Tribology is the study of wear and lubrication

Wear mechanisms

Adhesion

- bonding of the surfaces when pressed together

- may pull away material from the weaker surface

Abrasion

- asperities on the harder surface cut and plough 

Definition

Migration of the femoral head past the medial wall of the acetabulum / ilioischial line 

Centre edge angle > 40^o

Aetiology

Primary 

Otto's Disease

- bilateral in one third

- middle aged females

- pain & decreased ROM early 

- coxa vara & OA common

- ? causally related to osteomalacia

Categories

Decreased tone

- Polio

- Down's syndrome

- spina bifida

Increased tone

- cerbral palsy

- Parkinson's

- CVA

Polio

Rare

- case reports only

Down's Syndrome

Acetabular dysplasia not uncommon in this group

Results

Concept

THR in dysplastic hips has a higher failure rate

- due to anatomic abnormalities

- due to generally younger age

Aim

Restore normal biomechanics and preserve bone stock

Issues

Soft tissues

Indications

Severe LBP 

- most common indication

Ipsilateral knee pain

- less beneficial

Malposition

- especially abduction

Contraindications

Absent abductor mechanism

Flail

Active infection

Insufficient bone stock

Examination

LLD