Head size and Dual Mobility

 

Issues

 

Increasing head size

- increase stability / decrease dislocation

- ? affects ROM

- ? increase volumetric wear

 

Stability

 

Head size affects dislocation because of two variables

 

1.  Primary arc range

- distance head can move before impinging and levering out

- increasing head:neck ratio increases the primary arc range

- affected by cup abduction / anteversion / liner elevation

 

2.  Jump distance

- the distance the head must travel in order to dislocate from the socket

- affected by head size

- also affected by cup abduction / anteversion / liner elevation

 

Evidence

 

Large heads and reduced dislocation

 

Zijlstra et al Acta Orthop 2017

- Dutch Registry of 166,000 hips

- dislocation rates higher with 22 - 28 mm heads compared to 32 mm heads

- 36 mm heads reduced dislocation rates with posterolateral approach

 

Jameson et al JBJS Br 2011

- 250,000 THA England Joint Registry

- significant reduction in dislocation rate with heads > 36 mm

 

Berry et al JBJS Am 2005

- 24,000 THA

- dislocation rates size 22 > 28 > 32 mm heads

 

Large heads and ROM

 

Le Duff et al Bull NYU Hospt Jt Disord 2009

- 35 patients with both a hip resurfacing and conventional THA

- no difference in ROM between two hips

 

Zijlstra et al Int Orthop 2011

- RCT of 28 mm head versus 48 mm head MoM

- increased internal rotation with large heads

 

Wear / Revision rates

 

Australian Joint Registry 2023

 

1. Metal / Ceramic on poly (XLPE)

 

Design

A.  Thinner highly cross linked polyethylene liners allow larger femoral heads 32 - 44 mm

B.  Custom poly acetabulum with metal resurfacing

 

Australian Joint Registry 2023 Metal on XLPE 36,000 THA

 

  < 32 mm heads 32 mm heads > 32 mm heads
3 years 2.4 2.3 2.4
5 years 3.0 2.7 3.0
10 years 4.4 3.9 4.4
15 years 5.9 5.1 5.9

 

Treacy et al Bone Joint Res 2019

- metal-on-highly-crosslinked-polyethylene hip resurfacing

- 88 cases at 1.5 years follow up

 

2. Metal on metal

 

Increased failure rates with heads > 32 mm

MoM less commonly performed as many implants removed from market

 

THR Dislocated Birmingham

Dislocated resurfacing THA

 

2. Ceramic on ceramic

 

CoC largeLarge CoC

 

Monoblock acetabular components with ceramic liners that allow large ceramic heads

 

Kostretzis et al BMC Musculoskeletal Disorders 2022

- report of 5 cases large ceramic head THA with liner dissociation

 

Blakeney et al Bone Joint J 2018

- large ceramic head THA with ceramic monoblock acetabulum

- 225 cases

- 23% incidence of squeaking

 

Australian Joint Registry 2023 Ceramic on ceramic / poly 56,000 THA

 

  < 28 32 36-38 > 40
3 years 3.5 2.0 2.0 2.2
5 years 3.9 2.5 2.5 2.9
10 years 5.0 3.7 3.8 3.8
15 years 5.7   5.9  

 

4.  Dual mobility

 

Dual Mobility

 

Dual mobilityDual mobility

 

Stryker dual mobility

 

Concept

 

Femoral head moves within a poly component, which moves within the fixed acetabulum

- primary motion occurs at the inner bearing

- outer bearing moves in cases of extreme range of motion

 

Results

 

Australian Joint Registry 2023 Revision rates

  Standard acetabulum Dual Mobility
1 year 1.7 2.0
3 years 2.5 2.8
5 years 3.1 3.5
10 years 4.6 5.6

 

De Martino et al Bone Joint J 2017

- systematic review of 59 articles and 18,000 THA

- primary THA: dislocation 0.9%

- revision THA: dislocation 3.0%

 

Dislocated dual mobility

Dislocated dual mobility