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

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

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 91:128-33. 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

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

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

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

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)

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

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

IMPACT OF Head size (berry et al. 2005) 30 years follow up of THAs at MAYO hospital, USA HEAD SIZE INCIDENCE 22mm 12% 28mm 07% 32mm 04%

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.

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?

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

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

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

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

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

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

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

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

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

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, 2010. 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.

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

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.

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

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

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

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.

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