Biomechanics

Effect of Lumbar Fusion and Pelvic Fixation Rigidity on Hip Joint Stress

A Finite Element Analysis

Kozaki, Takuhei MD, PhD^a,b; Lundberg, Hannah J. PhD^a; Mell, Steven P. PhD^a; Samartzis, Dino PhD^a; Kawakami, Mamoru MD, PhD^c; Yamada, Hiroshi MD, PhD^b; Inoue, Nozomu MD, PhD^a; An, Howard S. MD^a

Author Information

^aDepartment of Orthopedic Surgery, Rush University Medical Center, Orthopedic Building, Suite 204, 1611 W. Harrison Street, Chicago, IL, 60612, USA

^bDepartment of Orthopaedic Surgery, Wakayama Medical University, 811-1 Kimiidera, Wakayama City, Japan

^cDepartment of Orthopaedic Surgery, Saiseikai Wakayama Hospital, 12bancho45 Wakayama City, Japan

Declarations: Funding: Not applicated.

Ethics approval This study was approved by an Institutional Review Board of Wakayama Medical University (No. 2511).

Consent to participate and for publication The patient was obtained informed consent to participant and publication of this study.

Conflict of interest: None of the authors have any potential conflicts of interest.

Address correspondence and reprint requests to Takuhei Kozaki, MD, PhD, Department of Orthopaedic Surgery, Wakayama Medical University, 811-1 Kimiidera, Wakayama City, Wakayama 641-8510, Japan; E-mail: [email protected]

Spine ():10.1097/BRS.0000000000004791, August 2, 2023. | DOI: 10.1097/BRS.0000000000004791

Abstract

Study Design.

This study compared hip stress among different types of lumbopelvic fusion based on finite element (FE) analysis.

Objective.

We believe that the number and placement of S2 AI screws, and whether the screws loosen likely influence hip joint stress in the finite element model.

Summary of Background Data.

Spinopelvic fixation hs been shown to increase the risk of progression for hip joint osteoarthritis. The biomechanical mechanism is not well understood. We hypothesize that the rigid pelvic fixation may induce stress at adjacent joints.

Methods.

A three-dimensional nonlinear FE model was constructed from the L4 vertebra to the femoral bone. From the intact model, we made four fusion models, each with different lower vertebrae instrumentation: 1) L4-S1 fusion; 2) L4-S2 AI screw fixation; 3) L4-S2 AI screw fixation with S2 AI screw loosening; and 4) L4-S1 and dual AI screw fixation (DSIF). A compressive load of 400 N was applied vertically to the L4 vertebra, followed by an additional 10 Nm bending moment about different axes to simulate either flexion, extension, left lateral bending, or right axial rotation. The distal femoral bone was completely restrained. von Mises stress and angular motion were analyzed across the hip joints within each fusion construct model.

Results.

Hip joint cartilage stress, and range of motion increased for all postures as pelvic fixation became more rigid. The DSIF model increased stress and angular motion at the hip joint more than SIF model. Our results suggest that more rigid fixation of the pelvis induces additional stress on the hip joint, which may precipitate or accelerate adjacent joint disease.

Conclusion.

Dual sacral AI fixation led to the highest stress, while loosening of S2 AI decreased stress on the hip joint. This study illustrates that more rigid fixation among lumbosacral fusion constructs increases biomechanical stress on the hip joints.

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Effect of Lumbar Fusion and Pelvic Fixation Rigidity on Hip Joint Stress

A Finite Element Analysis