Biomechanics of THA Dislocation Thomas D. Brown, Ph.D. Mark E. - - PowerPoint PPT Presentation

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Biomechanics of THA Dislocation Thomas D. Brown, Ph.D. Mark E. - - PowerPoint PPT Presentation

Nov 25, 2022 335 likes •600 views

Biomechanics of THA Dislocation Thomas D. Brown, Ph.D. Mark E. Nadzadi M.S. Christopher F. Scifert, Ph.D., Douglas R. Pedersen, Ph.D. John J. Callaghan, M/D. Department of Orthopaedic Surgery University of Iowa Rationale for Study

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SLIDE 1

Biomechanics of THA Dislocation

Thomas D. Brown, Ph.D. Mark E. Nadzadi M.S. Christopher F. Scifert, Ph.D., Douglas R. Pedersen, Ph.D. John J. Callaghan, M/D.

Department of Orthopaedic Surgery University of Iowa

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SLIDE 2

Rationale for Study

  • 250,000 THA’s per year
  • 2nd leading cause of failure
  • 2 - 11% primary cases
  • 4 - 25% revision cases
  • $75M per year (Morrey, 2000)
  • Pain, Incapacitation
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SLIDE 3

Clinical Studies

  • Registries
  • Limited statistical power
  • Conflicting conclusions
  • Malposition of cup
  • Empirical “safe-zone”
  • 30-50° Tilt & 5-25° AV (Lewinnek et al., 1978)
  • Factorial associations, but not actual mechanisms
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SLIDE 4

Experimental

  • Cadaveric studies
  • Limited observation variables
  • Small sample size (statistical power)
  • Mainly ROM studies
  • Need to examine local deformation and

characterize dislocation mechanics

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SLIDE 5

Computational

  • n=1
  • Efficient parametric studies
  • Design
  • Orientation
  • Motion Challenge
  • Local deformation & stress
  • Many outcome measures (ROM, resistance)
  • Historically simplified (model, formulation)
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SLIDE 6

Acetabular Cup:

  • Duraloc 22 - 52mm
  • Ti shell
  • UHMWPE liner

Femoral Component:

  • Endurance stem
  • 22mm modular head
  • CoCr Alloy

DePuy, Inc.

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SLIDE 7

Software

  • PATRAN 8.5 - IGES
  • ABAQUS 5.8
  • Acetabular Cup
  • Bonded between UHMWPE

liner & Ti shell

  • 3920 brick elements
  • Femoral Component
  • ECoCr >> Eliner
  • Rigid Bezier surface
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SLIDE 8

Physical Validation

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

A ngle (deg) Resisting Moment (N-m)

Experim ental Data Finite Elem ent Results

Experiment FEA

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SLIDE 9

Kinematic and Kinetic Input

  • 10 healthy subjects (5 male / 5 female)
  • Age (yrs): 49.7 ± 4.97 (44 - 59)
  • Height (m): 1.71 ± 0.14 (1.50 - 1.96)
  • Mass (kg): 77.3 ± 23.8 (40.9 - 122.7)
  • Optotrak
  • Pelvic reference frame
  • Recessed force plate
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SLIDE 10

7 Maneuvers Tracked

SSN / SSL XLG TIE 46 / 39 cm

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SLIDE 11

STOOP PIVOT ROLL

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SLIDE 12

Kinematic Data

  • Cardan angles
  • Flexion
  • Adduction
  • Endorotation

Kinetic Data

  • 47-muscle inverse dynamics model
  • Temporally varying load vector

10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 Frame Number Cardan Angles (Deg) 1 2 3 4 5 6 7 8 Physiologic Load (BW)

Flexion Adduction Endorotation Joint Load

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SLIDE 13

1 2 3 4 5 6 7 8 9 85 90 95 100 105 110 115 120 125 Flexion Angle (deg) Resisting Moment (Nm)

Impingement Peak Resisting Moment Hooking Subluxation Regime Dislocation

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SLIDE 14

UHMWPE Stresses

Von Mises (MPa) 0.02 1.52 3.02 4.51 6.01 7.51 9.01 10.5 12.0 13.5 15.0 33.6

VMES (MPa) Egress Site Impingement Site

Stable Articulation Incipient Dislocation

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SLIDE 15

Influence Factors

Femoral Component Anteversion Head Size Head/Neck Ratio d θ b

Metal Backing Polyethylene Liner

Leg Cross, Rise-from-Seat, Stooping, Shoe-Tying Pivot, Bed-Rollover

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SLIDE 16

Femoral Anteversion Effect

Average 0.4° more flexion per degree of femoral anteversion

2 4 6 8 10 12 90 95 100 105 110 115 120 125 130 135

Flexion Angle (deg) Resisting Moment (N-m) 0 Anteversion 10 Anteversion 15 Anteversion 20 Anteversion

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SLIDE 17

Anteversion Effect

50° Tilt

2 4 6 8 10 12 75 85 95 105 115 125 135 145 Flexion Angle (deg) Resisting Moment (Nm)

0º 40 10 20 30

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SLIDE 18

Tilt Effect

20° Anteversion

2 4 6 8 10 12 75 85 95 105 115 125 135 145 Flexion Angle (deg) Resisting Moment (Nm)

30º 70 40 50 60

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SLIDE 19

Dislocation Resistance Improvement

Moment R.O.M.

Erectly Seated Leg Crossing

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SLIDE 20

Head Size Variation

(Constant H/N Ratio)

90 97 104 111 118 125 132

Flexion Angle (deg) 22 mm 26 mm 28 mm 32 mm

Impingement

Head/Neck Ratio Variation

(Constant Head Size) 2 4 6 8 10 12 14 90 97 104 111 118 125 132

Flexion Angle (deg) Resisting Moment (N-m) H/N = 1.89 H/N = 2.39 H/N = 2.89

Impingement

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SLIDE 21
  • 20
  • 15
  • 10
  • 5

5 10 15 15 25 35 45 55

  • 8
  • 6
  • 4
  • 2

2 4 6

Moment Range of Motion

d

θ

b

Backing Polyethylene

Change in Resisting Moment (%) Liner Chamfer Angle θ (degrees) Change in R.O.M. (degrees)

Design Trade-Offs

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SLIDE 22

Finite Element Results

Maneuver # of Trials # of Dislocations % of Trials Dislocating Low Sit-to-Stand 47 41 87 Normal Sit-to-Stand 55 33 64 Tie 69 31 45 Leg Cross 64 22 34 Stoop 42 6 14

  • Post. Disloc.

Maneuvers 277 133 48 Pivot 58 23 40 Roll 19 12 63

  • Ant. Disloc.

Maneuvers 77 35 45 Overall Series 353 168 47

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SLIDE 23

Summary (Placement)

  • Femoral Anteversion

– ↑ ROM but not resistance

  • Acetabular Tilt & Anteversion

– ↑ ROM and Resistance …. Posterior Dislocations

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SLIDE 24

Summary (Design)

  • Head Size ↑ Resistance
  • H/N ↑ ROM
  • Acetabular: ROM / Resistance Trade-off

– Inset, Chamfer Angle, Lip Width

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SLIDE 25

Summary (Patient Motions)

  • Posterior vs. Anterior Dislocations

– Similar average risk (48-45%) – Posterior maneuvers more frequent?

  • Wide variability of risk: 14 - 87%
  • Highest risk:

– Rising from low seat (87%)

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SLIDE 26

Acknowledgements

Financial Support

DePuy, Inc. VA Merit Award

Assistance

  • Mr. Jason Wilken
  • Ms. Ruchika Wahi
  • Mr. Mike Squire
  • Ms. Hannah Lundberg