Impingement in Total Hip Replacement: Mechanisms and Consequences

Abstract

The occurrence of total hip impingement, whether or not accompanied by frank dislocation, holds substantial untoward clinical consequences, especially as less-forgiving advanced bearing implant designs come into ever more widespread use. Biomechanical aspects of impingement and dislocation have historically received relatively little scientific attention, although that situation is now rapidly changing. The present article reviews contemporary laboratory and clinical research on the impingement/dislocation phenomena, focusing particularly on how implant design variables, surgical implantation factors and patient activity each act individually and in concert to pose impingement and dislocation challenges. In recent years, several powerful new research methodologies have emerged that have greatly expanded the scope for clinical translation of systematic laboratory study. Transferring the findings from such research into yet better implant designs, and even better surgical procedures, offers encouragement that the clinical impact of this troublesome complication can be further reduced.

Figure 1

3-D Finite element model of total hip dislocation, illustrating the initial relative position of the implant components (left), the acetabular component bearing surface stress during stable articulation (center), and the corresponding stresses just prior to a posterior dislocation event (right). From: Scifert CF, Brown TD, Pedersen DR, Heiner AD, Callaghan JJ: Development and Physical Validation of a Finite Element Model of Total Hip Dislocation. Computer Methods in Biomechanics and Biomedical Engineering,1999;2(2):139–147.

Figure 2

Figure 2a. Trade-off between improvement of peak resisting moment versus range of motion, as a function of component design parameter changes (here illustrated for cup rim chamfer.) Figure 2b. Effects of head size (for constant neck diameter) and of head/neck diameter ratio on impingement/dislocation behavior. From Scifert CF, Brown TD, Pedersen DR, Callaghan JJ: Finite Element Analysis of Factors Influencing Total Hip Dislocation. Clin. Orthop. Rel. Res. 355: 152–162, 1998.

Figure 2

Figure 2a. Trade-off between improvement of peak resisting moment versus range of motion, as a function of component design parameter changes (here illustrated for cup rim chamfer.) Figure 2b. Effects of head size (for constant neck diameter) and of head/neck diameter ratio on impingement/dislocation behavior. From Scifert CF, Brown TD, Pedersen DR, Callaghan JJ: Finite Element Analysis of Factors Influencing Total Hip Dislocation. Clin. Orthop. Rel. Res. 355: 152–162, 1998.

Figure 3

Subject reflective marker array and custom bench for sit-to-stand motion tracking.

Figure 4

Propensity for impingement for THA patients for sit-to-stand motion. The estimated impingement envelope is shown shaded.

Figure 5

Complementary FEA and cadaver model analysis of THA impingement/dislocation. From: Scifert CF, Noble PC, Brown TD, Bartz RL, Kadakia N, Sugano N, Johnston RC, Pedersen DR, Callaghan JJ: Experimental and Computational Simulation of Total Hip Arthroplasty Dislocation. Orthopaedic Clinics of North America. 2001 Oct;32(4):553–567

Figure 6

Effects of acetabular component inclination and anteversion on peak resisting moment and on range of motion to dislocation. From: Nadzadi ME, Pedersen DR, Callaghan JJ, Brown TD: Effects of acetabular component orientation on dislocation propensity for small head size total hip arthroplasty. Clinical Biomechanics. 2002;17(1):32–40.

Figure 7

Representation of sectoral capsule properties in a finite element model of THA impingement/dislocation. From: Stewart KJ, Pedersen DR, Callaghan JJ, Brown TD: Implementing Capsule Representation in a Total Hip Dislocation Finite Element Model. Iowa Orthopaedic Journal. 2004;24:1–8.

Figure 8

Finite element analysis of a constrained-liner THA, showing stress contours at the instant of incipient dislocation (A,B), and the effect of cup opening radius for a 28-mm head diameter. From: Bouchard SM, Stewart KJ, Pedersen DR, Callaghan JJ, Brown TD: Design Factors Influencing Performance of Constrained Acetabular Liners: Finite Element Characterization. Journal of Biomechanics. 2006;39(5):885–893.

Figure 9

Computed stress distributions in the capsule during head subluxation (left) and after frank dislocation (right), for situations of 50% (upper) and 25% (lower) circumferential detachment of the capsule at its insertion on the femur, centered posteriorly.

Figure 10

Four-degree-of-freedom hip loading system. For visual clarity, a loaded THA construct is shown in isolation.

Figure 11

A) Surrogate pelvis mounted in the dislocation simulator. B) Experimentally measured resisting moment versus hip flexion angle, as a function of capsule stiffness attenuation. C) Finite element computations of resisting moment versus flexion angle, as a function of capsule stiffness attenuation.

Figure 12

Dislocation trials for a cadaver hip specimen implanted by a purpose-developed trans-pelvic procedure. (A) Specimen mounted in the loading apparatus, (B) Measured decrement of moment resisting dislocation, as a function of progressive release (centered posteriorly) of the capsule’s femoral attachment, (C) Corresponding FEA simulations.