1. Bearing Surface Choice in Patients at High Risk for Dislocation
Dr (Prof) Raju Vaishya
MS, MCh, FRCS
Sr Consultant & Joint replacement surgeon
Indraprastha Apollo Hospitals
New Delhi

2. Dislocation after total hip arthroplasty
Primary : > 5%
Revision : >21%

3. Present
PRESENT:
The Australian Joint Registry highlights the main causes for revision THA. As is evident by this chart, dislocation and wear are among these main causes.
More specifically in the U.S., hip instability is among the top causes for revision. This was detailed in Bozic, K., Kurtz, S., Lau, E., et al. (2009). The Epidemiology of Revision THA in the United States. JBJS 91:
Additionally, those who have suffered a dislocation have been shown to have a higher risk of subsequent dislocation.
Australian Orthopaedic Association 2007 Report Supplementary. Table S-H10: Diagnosis of Revision Hip Replacement

4. High risk patients for dislocation
* Fracture neck of femur - Neuromuscular conditions - Young patients - Revision THR - Spinal conditions

5. Instability after THA 22.5% of revision THR are done for instability
Can we prevent dislocation? : NO
Factors associated:
A) Patient related
B) Surgery related
C) Implant related

6. PATIENT FACTORS FOR INSTABILITY
Females
Hypermobile
Cognitive dysfunction
Neuromuscular issues
Diagnosis:
- Fx NOF
- Osteonecrosis
- DDH

7. SURGICAL FACTORS FOR INSTABILITY
Surgical Approach (Post > Lateral> Anterior)
Choice of implants (smaller > larger heads, Fixed cups>DM cups)
Surgical procedure (implant position, soft tissue reconstruction)

8. Implant Factors Head diameter Trunnion Head neck ratio
Femoral geometry (Lateral & Anterior offset)
Liner options

9. Choice of implants in patients at high dislocation risk
Large diameter head
Dual mobility cups
Constrained liners

10. IMPACT OF Head size (berry et al. 2005)
30 years follow up of THAs at MAYO hospital, USA
HEAD SIZE INCIDENCE
22mm %
28mm %
32mm %

11. Large Heads and Wear: Simple Formula
Small heads:
Less sliding distance, Less wear
As head gets bigger for given cup size:
Longer sliding distance= more wear
Thickness of articulating material decreases
PRESENT
Smaller heads are known to have less sliding distance, less friction and thus less wear.
Large heads on the other hand have a longer sliding distance and theoretically more wear. There is also the fact that with the use of larger heads, the thickness of poly decreases for given cup size.

12. Big Heads for THA: “All the Rage”
ROM
Stability
Surgeon Security
Cup position
Revision THA
Older & noncompliant patients
What about wear?
PRESENT
Large heads appear to be a solution for these complications. They provide enhanced ROM, stability and surgeon security when compared to non-anatomic (< 36mm) heads.
But do they help to address the issue of wear?

13. Large diameter heads (advantages)
Anatomically similar to native femoral head
Provide greater ROM (before impingement)
Decrease incidence of dislocation
Decrease in poly wear

14. LARGE FEMORAL HEADS (CONCERNS)
Not as effective in reducing dislocation in high risk patient!
Adverse Local Tissue Reaction (ALTR)
Anterior groin pain
- Psoas tendon
- Capsule

15. Past: Introduction of Dual Mobility in 1974
-PAST: The concept of dual mobility is an ingenious combination of the Charnley low friction arthroplasty principle (using a small head) to decrease wear and the McKee-Farrar theory using a large diameter head to enhance stability.
-Professor Bousquet designed the original dual mobility acetabular system in 1976.
-35 years of dual mobility clinical history exist from France and it is used approximately 1/3 of the time on primaries in France.
1976: The Introduction of Dual Mobility

16. Dual MOBILITY CUPS Designed by Bosquet and Rambert (1970)
Combined the concept of :
- LFA of Charnley
- Large head of McKee
* Effectively a bipolar into a fixed acetabular socket

17. Dual mobility cups (Clinical use)
Excellent track record in Europe
Increasing adoption in US
Increasing use in revision THR

18. Dual mobility cups Designer’s initial report: - 16 years follow up
- 437 hips
- 5 dislocations (1.1%)
- No obvious lysis

19. Fracture neck of femur Dislocation rates are 5 times compared to OA
14% dislocation with fixed liners
0% dislocation after DM
(Taraseevicius et al)

20. DM cups in Neuromuscular conditions
Dislocation rate 14% with standard liners
Sanders:
- 10 patients of CP
- No dislocation with DM cups at 3.5 years

21. DM cups in Young patients (<70 years)
Epinette et al:
- 0 dislocation at years

22. Addressing Longevity*
6/11/2018 1:03 AM
Addressing Longevity*
Dual Mobility Articulation
X3 Advanced Bearing Technology
Published Clinical Performance**
FUTURE
MDM addresses longevity through its two points of articulation and compatibility with X3 Advanced Bearing Technology.
Recent clinical data shows a linear wear rate of 0.019mm/yr at 3 years. Additionally an RSA (radiosteriometric analysis) study was conducted by an independent third party. The authors concluded that ‘X3 liners have wear properties superior to those of conventional polyethylene. Measurements between 1 and 2 years’ follow up suggest wear is nearly undetectable, which is encouraging for the future clinical performance of this material’.
*Herrera, L., Lee, R., Longaray, J., et al. (2010). Edge Loading Wear due to Inclination Angle for Three Contemporary Hip Bearings. 56th Annual ORS Meeting. Poster #2259.
**D’Antonio, J., Capello, W., Bierbaum, B., et al. Annealed Highly Cross-linked Polyethylenes: Clinical Performance of First and Second Generation Materials, Podium No: 106. Presented at the 56th Annual Meeting of the Orthopaedic Research Society. March 6-9, New Orleans.
**Campbell, D. G., Field, J. R., Callary, S. A. (2010). Second Generation Highly Crosslinked X3™ Polyetheylene Wear: A Preliminary Radiostereometric Analysis Study. CORR: Published Online 12 February 2010.

23. Concerns about dual mobility
Dislocation (intra prosthetic/true)
Wear (2 bearing surfaces)
Modular version (?source of metal/corrosion)

24. Outcomes of constrained liner
J. T. Williams Jr. Constrained components for the unstable hip following total hip arthroplasty: a literature review. International Orthopaedics (SICOT) (2007) 31:273–277.

25. Mechanisms of failure of constrained liners
Proud cemented liner
Traumatic failure
Shell/liner dissociation
Cup failure
Capturing ring fracture
Liner pullout
Disengagement of reinforcement ring
Impingement

26. Concerns with constrained liner
Effect of increased bony stress risers
Accelerated wear
Component failure
Decreased range of motion

27. Constrained acetabular liners: mechanisms of failure (Yun AG, Padgett D, Pellicci P, Dorr LD, 2005);J Arthroplasty 20 (4):536–541
Four modes of failure:
failure of fixation (most common)
liner dissociation
biomaterial failure
dislocation of the femoral head from
the constrained liner

28. Recommendations for constrained liner
Cemented liners not be left proud
Avoidance of insertion into grossly mal positioned shells
Positioning the liner such that the elevated rim is not likely to impinge
Maximal use of screw fixation in cementless designs
Bracing for all patients for a minimum of 6 weeks post- operatively.

29. Thank You