Numerical analysis of the effects of padded pelvic belts as a treatment for sacroiliac joint dysfunction

Abstract

Background: Pain related to the sacroiliac joint (SIJ) accounts for low back pain in 15%-30% of patients. One of the most common treatment options is the use of pelvic belts. Various types of pelvic belts exist; however, the mechanisms underlying treatment and their effectiveness remain unclear to date.

Objective: To analyze stress distribution in the pelvis when a pelvic rubber belt or a padded pelvic belt is applied, to assess the effectiveness of treatment from a numerical biomechanical perspective.

Methods: The pressure distribution at the pelvic belts was measured using a device and subsequently modeled with the finite element method of a pelvis with soft tissues. The stress environment when wearing a pelvic belt in a double-leg stance was simulated.

Results: With the application of pelvic belts, the innominate bone rotated outward, which was termed an out-flare. This caused the SIJ to compress and cause reduction in sacrotuberous, sacrospinous, interosseous, and posterior sacroiliac ligament loading. Padded pelvic belts decreased the SIJ displacement to a greater extent than in pelvic rubber belts.

Conclusion: Pelvic belts aid in compressing the SIJ and reduce its mobility.

Keywords: Finite element analysis; low back pain; numerical analysis; pelvic belt; sacroiliac joint dysfunction.

Fig. 1.

Finite element model of the pelvis including soft tissue, displayed on whole model (left) and hidden the soft tissue (Right) with anterior views. The scale bar: 100 mm. S: superior, L: left.

Fig. 2.

The positions and names of the pelvic ligaments modelled in this study, in a meshed pelvis model with anterior (left) and posterior (right) views. The ligaments are the anterior longitudinal ligament (LLA), anterior sacroiliac ligament (ASL), iliolumbar ligament (IL), inguinal ligament (INL), long posterior sacroiliac ligament (LPSL), obturator membrane (MO), posterior longitudinal ligament (LLP), posterior sacroiliac ligament (PSL), pubic ligament (PL), interosseous sacroiliac ligament (ISL), sacrospinous ligament (SS) and sacrotuberous ligament (ST). The scale bar: 60 mm. S: superior, L: left, R: right.

Fig. 3.

(a) Sample of the pelvic rubber belt and (b) padded pelvic belt used in this study.

Fig. 4.

Scheme of pressure measurement in this study. (Left) A pressure measuring device was placed on a body and the pelvic belts were wrapped on the device. Blue: a pressure measuring device. Orange: pelvic belt. (Right top) Pressure distribution on the pelvic belts and (right bottom) straightly opened results.

Fig. 5.

Pelvic belt types and related pressure measurements in-vivo in a setup on the volunteer (left row), and pressure distribution on the pelvic belts (right row). Black areas indicate the anterior superior iliac spines as reference marks.

Fig. 6.

(a) The red arrows indicate the places and directions the pressures are applied (trimetric view), and (b) the orange arrows indicate where the loads are applied (anterior view). The scale bar: 60 mm. S: superior, L: left, A: anterior.

Fig. 7.

(a) Horizontal displacement of the innominate bones shown from an anterior (1st line) and posterior (2nd line) view. The positive directions are the directions that the arrows point to, to right on the models. The scale bar: 100 mm. S: superior, L: left, R: right. (b) Scheme of pelvic deformation. The innominate bone was rotated outward by using pelvic belts.

Fig. 8.

(a) Minimum principal stress distribution of right (1st line) and left (2nd line) sacroiliac joint cartilage shown from left and right, respectively. The red area shows the tensile area, and the tensile area decreased by pelvic belts. The scale bar: 40 mm. S: superior, A: anterior, P: posterior. (b) The comparison of mean minimum principal stress rates for the control condition. Right and left mean right and left sacroiliac joints, respectively.

Fig. 9.

(a) Resultant displacement distribution of right (1st line) and left (2nd line) sacroiliac joint cartilage shown from left and right, respectively. The very low displacement area (blue area) increased with pelvic belts. The scale bar: 40 mm. (b) The comparison of mean resultant displacement rates for the control. Right and left mean right and left sacroiliac joints, respectively.

Fig. 10.

The comparison of ligament loading rates on anterior sacroiliac joint (ASL), sacrotuberous ligament (ST), sacrospinous ligament (SS), posterior sacroiliac ligament (PSL) and interosseous sacroiliac ligament (ISL) for the control. The left and right graphs are the results on the right and left sides of ligaments, respectively.

Fig. 11.

Minimum principal strain distribution of soft tissue (1st and 3rd lines) and pelvis (2nd and 4th lines). The top and bottom two lines are shown from posterior and right views, respectively. The gray lines indicate the level of the anterior superior iliac spines. The scale bar: 100 mm. S: superior, R: right, A: anterior.