Influence of clearance on the time-dependent performance of the hip following hemiarthroplasty: a finite element study with biphasic acetabular cartilage properties

Abstract

Hip hemiarthroplasty is a common treatment for femoral neck fracture. However, the acetabular cartilage may degenerate after hemiarthroplasty leading to postoperative failure and the need for revision surgery. The clearance between the acetabular cartilage and head of the prosthesis is one of the potential reasons for this failure. In this study, the influence of joint clearance on the biomechanical function of a generic hip model in hemiarthroplasty was investigated using biphasic numerical simulation. Both a prolonged loading period of 4000 s and dynamic gait load of 10 cycles were considered. It was found that a larger clearance led to a higher stress level, a faster reduction in load supported by the fluid and a faster cartilage consolidation process. Additionally, the mechanical performance of the acetabular cartilage in the natural model was similar to that in the hemiarthroplasty model with no clearance but different from the hemiarthroplasty models with clearances of 0.5mm and larger. The results demonstrated that a larger clearance in hip hemiarthroplasty is more harmful to the acetabular cartilage and prosthesis heads with more available dimensions (i.e. smaller increments in diameter) could be manufactured for surgeons to achieve a lower clearance, and reduced contact stress in hemiarthroplasty surgeries.

Keywords: Articular cartilage; Biphasic; Contact mechanics; Finite element; Hemiarthroplasty; Hip.

Fig. 1

The three dimensional hip model in hemiarthroplasty (a) and the metal heads with four different dimensions articulating against with the acetabular cartilage (b–e) (C: clearance).

Fig. 2

Contour of the contact stress (MPa) of the acetabular cartilage of the natural hip model and the hip models in hemiarthroplasty with different head dimensions at 0.6 s and 4000 s in the static loading case (lateral and posterior refer to the orientation of the pelvis during standing).

Fig. 3

Results over 4000 s period for the natural hip model and the hip models in hemiarthroplasty with different head dimensions in the static loading case.

Fig. 4

Contour of fluid flux on the acetabular cartilage for the hemiarthroplasty model with 0 and 2 mm radial clearances respectively at the instantaneous period in the static loading case. The directions of fluid flux were exhibited by grey vectors.

Fig. 5

Results of the natural hip model and the hip model in hemiarthroplasty with different head dimensions over 10 cycles of gait, along with the contours of contact stress at mid-swing during the 1st cycle.