Yan Hirotaka, Sato Kotaro, Takahashi Gaku, Mimata Yoshikuni, Murakami Kenya, Doita Minoru
Department of Orthopaedic Surgery, Iwate Medical University, Iwate, Japan.
Department of Orthopaedic Surgery, Iwate Medical University, Iwate, Japan.
J Hand Surg Am. 2023 Oct;48(10):1062.e1-1062.e6. doi: 10.1016/j.jhsa.2022.02.022. Epub 2022 Aug 13.
The load axis of the carpals is located on the volar side of the normal distal radius. A volar lunate facet fracture (VLFF) is exposed to volar-shearing stress, which can cause volar displacement of the carpus. A previous biomechanical study reported that the load at the scaphoid fossa was located more dorsally and the pressure at the lunate fossa decreased in a dorsally-angulated model. However, the distal radius load distribution for various volar tilts remains unclear. We speculate that if the volar tilt decreases, the load distribution moves dorsally and decreases the stress on the VLFF. Therefore, we analyzed a dorsally-angulated distal radius model to evaluate changes in the load distribution using finite element analysis.
A 3-dimensional finite element wrist model was developed using computed tomography images. The ligaments were modeled as tension-only spring elements. We considered the intact wrist model for a volar tilt of 15° and created 5 additional models for volar tilts of 10°, 5°, 0°, -5°, and -10°.
As the dorsal angulation increased, the stress distribution moved from volar to dorsal and from the lunate fossa toward the scaphoid fossa. The maximum stress on the volar lunate facet was reduced as volar tilt decreased. The maximum stress was higher on the lunate fossa for volar tilts from 15° to 5°. In contrast, the maximum stress was higher on the scaphoid fossa for volar tilts of ≤0°.
Load transmission moved from volar to dorsal and from the lunate fossa to the scaphoid fossa when the volar tilt decreased. Therefore, a decrease in the volar tilt would reduce the load on the VLFF.
This study provides surgeons accurate knowledge regarding load distribution of the distal radius for various volar tilts that could be helpful in treating patients with VLFFs.
腕骨的负荷轴位于正常桡骨远端的掌侧。掌侧月骨小面骨折（VLFF）承受掌侧剪切力，可导致腕骨掌侧移位。先前的一项生物力学研究报告称，在背侧成角模型中，舟骨窝处的负荷位置更靠背侧，月骨窝处的压力降低。然而，不同掌侧倾斜度下桡骨远端的负荷分布仍不清楚。我们推测，如果掌侧倾斜度减小，负荷分布会向背侧移动，并降低VLFF上的应力。因此，我们分析了一个背侧成角的桡骨远端模型，以使用有限元分析评估负荷分布的变化。
使用计算机断层扫描图像建立三维有限元腕关节模型。韧带被建模为仅受拉的弹簧元件。我们考虑了掌侧倾斜度为15°的完整腕关节模型，并创建了另外5个掌侧倾斜度分别为10°、5°、0°、-5°和-10°的模型。
随着背侧成角增加，应力分布从掌侧移向背侧，从月骨窝向舟骨窝移动。随着掌侧倾斜度减小，掌侧月骨小面上的最大应力降低。掌侧倾斜度从15°到5°时，月骨窝处的最大应力较高。相比之下，掌侧倾斜度≤0°时，舟骨窝处的最大应力较高。
当掌侧倾斜度减小时，负荷传递从掌侧移向背侧，从月骨窝移向舟骨窝。因此，掌侧倾斜度减小会降低VLFF上的负荷。
本研究为外科医生提供了关于不同掌侧倾斜度下桡骨远端负荷分布的准确知识，这可能有助于治疗VLFF患者。
