Pelvic Incidence Changes Between Flexion and Extension

Standing versus supine pelvic incidence in adult spinal deformity patients

PURPOSE

Pelvic incidence (PI) is commonly used to determine sagittal alignment. Historically, PI was believed to be a fixed anatomic parameter. However, recent studies have suggested that there is positionally-dependent motion that occurs through the sacroiliac joint (SIJ) resulting in changes in PI.

METHODS

We reviewed 100 consecutive adult spinal deformity (ASD) patients seen at our academic tertiary referral center. Two reviewers measured pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL) on standing radiographs and scout computed tomography scans (CT). Unilateral, bilateral, or absent SIJ vacuum sign (VS) was determined using CTs.

RESULTS

Eighty-six patients (42 M:44 F) were included with an average age of 64.1 years and BMI of 28.8 kg/m2. Standing PI was low (< 50°) in 35 patients (40.7%), average (50°-60°) in 22 (25.6%), and high (> 60°) in 29 (33.7%). Average and high PI patients had significant PI changes of 3.0° (p = 0.037) and 4.6° (p = 0.005), respectively. Bilateral SIJ VS was seen in 68 patients, unilateral VS in 9, and VS was absent in 9. The average change in PI between standing and supine was 2.1° in bilateral SIJ VS patients (p = 0.045), 2.2° in unilateral SIJ VS (p = 0.23), and - 0.1° in patients without SIJ VS (p = 0.93). The average absolute difference in PI between supine and standing was 5.5° ±5.5° (p < 0.001).

CONCLUSION

There is a change in PI from supine to standing. In patients with high PI and bilateral VS on CT, the change from supine to standing is significant, perhaps representing instability of the SIJ.

Sacroiliac pain after total hip arthroplasty: a combined analysis of clinical data and three-dimensional imaging in standing and sitting positions

PURPOSE

Patients frequently complain of low back pain and sacroiliac joint pain (SIP) following total hip arthroplasty (THA). We hypothesized that patients with SIP would display different pelvic incidence (PI) values between standing and relaxed sitting positions, indicative of increased motion in the sacroiliac joints.

METHODS

In this retrospective case-control study, 94 patients who underwent unilateral THA and experienced SIP were compared with 94 control patients without SIP. SIP was confirmed through clinical tests and investigated using biplanar imaging in both standing and sitting positions. The key parameters analyzed included PI, sacral slope (SS), lumbar lordosis (LL), and limb length discrepancy (LLD).

RESULTS

Patients without SIP showed a mean difference in PI of -1.5° (-8°-5°) between standing-to-sitting positions, whereas those with SIP showed a difference of -3.3° (-12°-0°)(P < 0.0001), indicating more motion in the sacroiliac joint during daily activities in the latter group. Patients with SIP showed smaller change in LL between standing-to-sitting positions (mean:6.3°; range:-8°-27°) compared with those without SIP (mean:9.5°; range:-12°-28°)(P = 0.006). No significant differences were noted in functional leg length between patients with (mean:7 mm; range:0-12 mm) and without SIP (mean:7 mm; range:0-11 mm)(P = 0.973).

CONCLUSIONS

This study revealed significant sacroiliac joint motion in patients with SIP post-THA, as indicated by PI changes, increased posterior pelvic tilt, and reduced change in the LL. Contrary to common belief, SIP did not correlate with LLD.

Randomized Trial of Augmented Pelvic Fixation in Patients Undergoing Thoracolumbar Fusion for Adult Spine Deformity: Initial Results from a Multicenter Randomized Trial

BACKGROUND

The optimal configuration for spinopelvic fixation during multilevel spine fusion surgery for adult spine deformity remains unclear. Postoperative sacroiliac (SI) joint pain, S2AI screw loosening and implant breakage could be related to continued motion of the SI joint with use of only a single point of fixation across the SI joint.

METHODS

Prospective, international, multicenter randomized controlled trial of 222 patients with adult spine deformity scheduled for multilevel (4 or more levels) spine fusion surgery with pelvic fixation. Subjects were randomized to sacroalar (S2) iliac (S2AI) screws alone for pelvic fixation or S2AI + triangular titanium implants placed cephalad to S2AI screws. Quad rod techniques were not allowed or used. Baseline spinal deformity measures were read by an independent radiologist. Site-reported perioperative adverse events were reviewed by a clinical events committee. Quality of life questionnaires and other clinical outcomes are in process with planned 2-year follow-up.

RESULTS

One hundred thirteen participants were assigned to S2AI and 109 to S2AI + titanium triangular implants (TTI). 35/222 (16%) of all subjects had a history of SI joint pain or were diagnosed with SI joint pain during preoperative workup. Three-month follow-up was available in all but 4 subjects. TTI placement was successful in 106 of 109 (98%) subjects assigned to TTI. In 2 cases, TTI could not be placed due to anatomical considerations. Three TTI ventral iliac breaches were observed, all of which were managed non-surgically. One TTI subject had a transverse sacral fracture and 1 TTI subject had malposition of the implant requiring removal.

CONCLUSIONS

SI joint pain is common in patients with adult spinal deformity who are candidates for multilevel spine fusion surgery. Concurrent placement of TTI parallel to S2AI screws during multilevel spine fusion surgery is feasible and safe. Further follow-up will help to determine the clinical value of this approach to augment pelvic fixation.

Hip-Spine Syndrome: A Focus on the Pelvic Incidence in Hip Disorders

Since Offierski and MacNab reported a close association between the hip and spine as hip-spine syndrome in 1983, many studies on spinal alignment in hip disorders have been conducted. Notably, the pelvic incidence angle (PI) is the most important parameter and is determined by the anatomical variations in the sacroiliac joint and hip. Studies on the association of the PI with hip disorders can help in understanding the pathophysiology of hip-spine syndrome. A PI increase has been observed during the evolution of bipedal locomotion in humans and in the acquisition of gait during child development. Although the PI is a fixed parameter that is stable and unaffected by posture from adulthood onwards, it has become clear that it increases in the standing position in older people. While it may be associated with a greater risk of developing or progressing to spinal disorders, the association between the PI and hip disorders remains controversial because of the multifactorial nature of hip osteoarthritis (HOA) and the wide range of PIs in HOA (18-96°), making the interpretation of results difficult. However, several hip disorders (i.e., femoroacetabular impingement and rapid destructive coxarthrosis) have been shown to be associated with the PI. Further investigation on this topic is, therefore, warranted.

Relationship Between Sacroiliac Joint-related Pain and Spinopelvic Mobility

STUDY DESIGN

A case-control study.

OBJECTIVE

To evaluate the relationship between sacroiliac joint-related pain (SIJ-RP) and spinopelvic mobility.

SUMMARY OF BACKGROUND DATA

No specific radiological findings are available for the diagnosis of SIJ-RP. A previous study reported that a higher pelvic incidence and sacral slope (SS) values were significantly associated with sacroiliac joint pain. The concept of spinopelvic mobility, which is evaluated by the differences between SS in the standing and sitting positions, has been the focus of hip and spine surgeries in recent years.

MATERIALS AND METHODS

The SIJ-RP group comprised patients diagnosed with SIJ-RP based on physical findings and their response to analgesic injections. No other lumbar or hip joint diseases were observed. The non-SIJ-RP group comprised patients with lower back pain for reasons other than SIJ-RP. Radiographs of the lateral view of the pelvis in the standing and sitting positions were evaluated for all patients. We compared and analyzed the backgrounds, SS in the two positions, and difference in SS between the two positions in both groups.

RESULTS

In total, 245 patients were included in the study, with 49 and 196 patients in the SIJ-RP and non-SIJ-RP groups, respectively. More female patients experienced SIJ-RP than male patients ( P =0.0361). There were significant differences between the groups for SS in standing ( P =0.0076), sitting ( P =0.0005), and those with a difference between sitting and standing of <5° ( P =0.0278) in the univariate analyses. Logistic regression analyses, after adjustment for age and sex, revealed significant differences between the groups with an SS difference <5° ( P =0.0088; 95% confidence interval, 1.280-5.519), with an odds ratio of 2.7.

CONCLUSION

On evaluating spinopelvic mobility, we found that SIJ-RP was related to hypomobility of the sacrum, which could indicate the hypermobility of the sacroiliac joint.

Change in Pelvic Incidence Associated With Sacroiliac Joint Dysfunction: A Case Report

The sacroiliac joint (SIJ) is designed primarily for stability with minute motions. SIJ dysfunction refers to improper movement of the SIJs. Diagnosis and evaluation of SIJ dysfunction are difficult, with use of physical maneuvers and image-guided anesthetic injection. This case report describes a 47-year-old female who experienced right buttock pain and painful limp for approximately 2 months. Standing radiographs revealed inflammatory sclerosis surrounding the right SIJ. Physical examination found tenderness over the right SIJ and positive results in provocation (the distraction, compression, and thigh thrust) tests, compatible with right SIJ dysfunction. Her pain was resolved and gait performance was retrieved following 6-month program of combined thoracolumbar manipulation and rehabilitation exercises. Unexpectedly, change in pelvic incidence (PI) angles was noticed on follow-up radiograph. PI remains more or less fixed throughout adult life since the mobility of the SIJs is considered negligible. The current presentation is designed to explore the significance of PI change. The PI disparity unfolds the possibility of recognizing SIJ dysfunction based on consecutive radiographs.

Pelvic incidence change on the operating table

PURPOSE

While a change in the pelvic incidence (PI) after long spine fusion surgery has been reported, no studies have examined the change in the PI on the operating table. The present study examined the PI-change on the operating table and elucidated the patients' background characteristics associated with this phenomenon.

METHODS

This study included patients who underwent lumbar posterior spine surgery and had radiographs taken in a full-standing position preoperatively and a pelvic lateral radiograph in the prone position in the operative room. The patients with PI-change on the operating table (PICOT; PICOT group) and without PICOT (control group) were compared for their background characteristics and preoperative radiographic parameters.

RESULTS

There were 128 eligible patients (62 males, 66 females) with a mean age (± standard deviation) of 69.9 ± 11.7 (range: 25-93) years old. Sixteen patients (12.5%) showed a decrease in the PI > 10°, which indicated placement in the PICOT group. The preoperative lumbar lordosis (LL) and PI-LL in the PICOT group were significantly worse than those in the control group (LL: 20.8 ± 16.6 vs. 30.6 ± 16.2, p = 0.0251, PI-LL: 33.9 ± 19.0 vs. 17.3 ± 14.8, p < 0.0001). The PICOT group had a higher proportion of patients who underwent fusion surgery than the control group, but the difference was not significant (62.5% vs. 44.6%, p = 0.1799).

CONCLUSION

A decreased PI was observed in some patients who underwent lumbar posterior surgery on the operating table before surgery. Patients with a PI decrease on the operating table had a significantly worse preoperative global alignment than those without such a decrease.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.

Postoperative pelvic incidence (PI) change may impact sagittal spinopelvic alignment (SSA) after instrumented surgical correction of adult spine deformity (ASD)

OBJECTIVES

To study factors causing postoperative change of PI after surgical correction of ASD and to assess the effect of this variability on postoperative PI-LL mismatch.

BACKGROUND

PI is used as an individual constant to define lumbar lordosis (LL) correction goal (PI-LL < 10). Postoperative changes of PI were shown but with opposite vectors. The impact of the PI variability on the postoperative PI-LL has not been studied.

METHODS

The medical and radiographic data analyzed for patients who underwent long posterior instrumented spinal fusion. Inclusion criteria are age, ≥ 20 years old; ASD due to degenerative disk disease (DDD) or scoliosis (DS); ≥ 3 levels fused; and 2-year follow-up or revision. Studied parameters are LL (L1-S1), PI, sacral slope (SS), pelvic tilt (PT), and PI-LL. Measurement error and postoperative changes were defined. Statistical analysis includes ANOVA, correlation, regression, and risk assessment by odds ratio; P ≤ 0.05 considered statistically significant.

RESULTS

Eighty patients were included: mean age, 62.4 years-old (SD, 11.1); female, 63.7%; mean body mass index (BMI), 27.1 (SD, 5.6). Distribution of patients by follow-ups includes preoperative 100%; postoperative (1-3 weeks), 100%; 11-13 months. 90%; 22-26 months, 58%; and revision: 24%. Pre- versus postoperative PI (∆PI) changed both positively and negatively and the absolute value of change|∆PI| exceeded measurement error (P ≤ 0.05) reaching as high as 31°, and progressed with time; R² dropped from 0.73 to 0.45 (P < 0.001); ∆PI depended on disproportional changes of SS and PT, preoperative PI, and change of LL. Obesity, DS, and absence of sacroiliac fixation increased |∆PI|. The risk of LL insufficient correction (PI-LL > 10°) associated with a |∆PI|> 6°, P = 0.05. Sacroiliac fixation diminished PI variability only during the first postoperative year.

CONCLUSION

Preoperative variability and postoperative instability of PI diminish the applicability of the PI-LL < 10° goal to plan correction of LL. An alternative method is offered.

LEVEL OF EVIDENCE

IV.

Change in pelvic incidence between the supine and standing positions in patients with bilateral sacroiliac joint vacuum signs

OBJECTIVE

Pelvic incidence (PI) is a commonly utilized spinopelvic parameter in the evaluation and treatment of patients with spinal deformity and is believed to be a fixed parameter. However, a fixed PI assumes that there is no motion across the sacroiliac (SI) joint, which has been disputed in recent literature. The objective of this study was to determine if patients with SI joint vacuum sign have a change in PI between the supine and standing positions.

METHODS

A retrospective chart review identified patients with a standing radiograph, supine radiograph, and CT scan encompassing the SI joints within a 6-month period. Patients were grouped according to their SI joints having either no vacuum sign, unilateral vacuum sign, or bilateral vacuum sign. PI was measured by two independent reviewers.

RESULTS

Seventy-three patients were identified with an average age of 66 years and a BMI of 30 kg/m2. Patients with bilateral SI joint vacuum sign (n = 27) had an average absolute change in PI of 7.2° (p < 0.0001) between the standing and supine positions compared to patients with unilateral SI joint vacuum sign (n = 20) who had a change of 5.2° (p = 0.0008), and patients without an SI joint vacuum sign (n = 26) who experienced a change of 4.1° (p = 0.74). ANOVA with post hoc Tukey test showed a statistically significant difference in the change in PI between patients with the bilateral SI joint vacuum sign and those without an SI joint vacuum sign (p = 0.023). The intraclass correlation coefficient between the two reviewers was 0.97 for standing PI and 0.96 for supine PI (p < 0.0001).

CONCLUSIONS

Patients with bilateral SI joint vacuum signs had a change in PI between the standing and supine positions, suggesting there may be increasing motion across the SI joint with significant joint degeneration.

Sagittal spinal alignment after total hip arthroplasty for neglected high hip dysplasia: does changing the distorted mechanics of the hip normalize spinal alignment?

PURPOSE

The false acetabulum lies more laterally and posteriorly compared with the true acetabulum. Spatial orientation of the pelvis is significantly altered in patients with neglected high hip dysplasia. There has been no study to investigate how pelvic or sagittal spinal alignment change after true acetabulum gains function with hip arthroplasty. The aim of this study was to investigate the effect of total hip arthroplasty with femoral shortening on spinopelvic parameters in patients with neglected high hip dysplasia.

METHODS

Twenty patients with Crowe type 3 or 4 hip dysplasia, who underwent total hip arthroplasty with femoral shortening in our institution were evaluated preoperatively after completion of rehabilitation and return to their normal daily life. Sagittal alignment (sacral slope, pelvic incidence, global tilt, segmental lordosis, segmental kyphosis, GAP score) and coronal alignment angles (coronal tilt, Cobb angle) of patients were measured by two independent observers.

RESULTS

Twenty patients underwent hip arthroplasty with femoral shortening followed up for a minimum of 12 months. We found higher preoperative global lordosis (68.7 ± 9.7) and sacral slope (52.1 ± 8.8) angles, but the pelvic incidences (57.9 ± 10.1) were in the normal range. No statistically significant difference in any sagittal spinopelvic parameters between pre- and postoperative measurements was detected. GAP scores also did not change significantly (p = 0.231). Coronal plane parameters (Cobb angle, coronal pelvic tilt) were the only parameters in which a statistical change was observed (p = 0.02, p = 0.05, respectively).

CONCLUSION

Lumbar lordosis and sacral slope values are outside standard ranges in patients with neglected dysplasia of the hip. The reconstruction of the distorted mechanics of the hip joint does not normalize sagittal pelvic and spine anatomy however improvements in coronal alignment were observed. Disease specific values of sagittal spinal alignment should be used in the treatment of lumbar degenerative problems in patients with neglected high hip dysplasia.

LEVEL OF EVIDENCE

IV.

Movement of the sacroiliac joint: Anatomy, systematic review, and biomechanical considerations

Several researchers investigated the anatomy and biomechanics of the sacroiliac joint (SIJ) to understand the relationship between lower back pain and the SIJ. Many studies concluded that the SIJ has little movement; however, some studies using spinopelvic parameters mentioned high change in pelvic incidence (PI). In this study, SIJ movement and PI change reported in previous studies were reviewed according to position and posture changes. Literature on SIJ movement was reviewed by searching through the publication databases. In biomechanical studies, the result of the rotational angle in the sagittal plane was mainly investigated to compare with the results of PI change. From the results of SIJ movement studies, the minimum movement of nutation and count-nutation was 0.01°, and maximum movement was 2.27°. From the results of PI change studies with different positions and movements, the highest change was 9°, and the lowest change was 0°. Movement of the SIJ was limited by its anatomical structure; maximum movement of the SIJ was 9° in a previous study. Therefore, SIJ movement should be studied more intensely as biomechanical perspective to understand its movement.