The spinopelvic alignment is often assessed via the Pelvic Incidence-Lumbar Lordosis (PI-LL) mismatch. Here we describe and validate a simplified method to evaluating the spinopelvic alignment through the L1-Pelvis angle (L1P). This method is set to reduce the operator error and make the on-film measurement more practicable. 126 standing lateral radiographs of patients presenting for Total Hip Arthroplasty were examined. Three operators were recruited to label 6 landmarks. One operator repeated the landmark selection for intra-operator analysis. We compare PI-LL mismatch obtained via the conventional method, and our simplified method where we estimate this mismatch using PI-LL = L1P - 90°. We also assess the method's reliability and repeatability. We found no significant difference (p > 0.05) between the PI-LL mismatch from the conventional method (mean 0.22° ± 13.6) compared to L1P method (mean 0.0° ± 13.1). The overall average normalised root mean square error (NRMSE) for PI-LL mismatch across all operators is 7.53% (mean -3.3° ± 6.0) and 6.5% (mean -2.9° ± 4.9) for the conventional and L1P method, respectively. In relation to intra-operator repeatability, the correlation coefficients are 0.87 for PI, 0.94 for LL, and 0.96 for L1P. NRMSE between the two measurement sets are PI: 9.96%, LL: 5.97%, and L1P: 4.41%. A similar trend is observed in the absolute error between the two sets of measurements. Results indicate an equivalence in PI-LL measurement between the methods. Reproducibility of the measurements and reliability between operators were improved. Using the L1P angle, the classification of the sagittal spinal deformity found in the literature translates to: normal L1P<100°, mild 100°<L1P<110°, and severe L1P>110°. Surgeons adopting our method should expect a small improvement in reliability and repeatability of their measurements, and a significant improvement of the assessment of the mismatch through the visualisation of the angle L1P

Introduction. Hip osteoarthritis (OA) results in reduced hip range of motion and contracture, affecting sitting and standing posture. Spinal pathology such as fusion or deformity may alter the ability to compensate for reduced joint mobility in sitting and standing postures. The effects of postural spinal alignment change between sitting and standing is not well understood. Methods. A retrospective radiographic review was performed at a single academic institution of patients with sitting and standing full-body radiographs between 2012 and 2017. Patients were excluded if they had transitional lumbosacral anatomy, prior spinal fusion or hip prosthesis. Hip OA severity was graded by the Kellgren-Lawrence grades and divided into two groups: low-grade OA (LOA; grade 0–2) and severe OA (SOA; grade 3–4). Spinopelvic parameters (Pelvic Incidence (PI), Pelvic Tilt (PT), Lumbar Lordosis (LL), and PI-LL), Thoracic Kyphosis (TK; T4-T12), Global spinal alignment (SVA and T1-Pelvic Angle; TPA; T10-L2) as well as proximal femoral shaft angle (PFSA: as measured from the vertical), and hip flexion (difference between change in PT and change in PFSA) were also measured. Changes in sit-stand radiographic parameters were compared between the LOA and SOA groups with unpaired t-test. Results. 548 patients were identified with sit-stand radiographs, of which there were 311 patients with LOA & 237 with SOA. After propensity score matching for Age, BMI, and PI, 183 LOA & 183 SOA patients were analyzed. Standing alignment analysis demonstrated that SOA patients had greater SVA (31.1 ± 36.68 vs 21.7 ± 38.83, p=0.02), and lower TK (−36.21 ± 11.98 vs −41.09 ± 11.47, p<0.001). SOA patients had lower PT, greater PI-LL, lower LL, lower T10-L2, and lower TPA (p>0.05). PFSA (9.09 5.19 vs 7.41 4.48, p<0.001) was significantly different compared to LOA while SOA KA was not significantly different compared to LOA. Sitting alignment analysis demonstrated that SOA patients had higher PT (29.69 ± 15.65 vs 23.32 ± 12.12, p<0.001), higher PI-LL (21.64 ±17.86 vs 12.44 ±14.84 p<0.001), lower LL (31.67 ± 16.40 vs 41.58 ± 14.73, p<0.001), lower TK (−33.22 ± 15.76 vs −38.57 ± 13.01, p=0.01), greater TPA (27.91 ± 14.7 vs 22.55 ± 11.38 p=0.01). TK, SVA, and PFSA were not significantly different compared to LOA. SOA and LOA groups demonstrated differences in standing and sitting spinopelvic alignment for all global and regional parameters except PI. When examining the postural changes from standing to sitting, there was less hip ROM in SOA than LOA (71.45 ± 18.55 vs 81.64 ± 12.57, p<0.001). As a result, SOA patients had more change in PT (15.24 ± 16.32 vs 7.28 ± 10.19, p<0.001), PI-LL (20.62 ± 17.25 vs 13.74 ± 11.16, p<0.001), LL (−21.37 ± 15.55 vs −13.09 ± 12.34, p<0.001), and T10-L2 (−4.94 ± 7.45 vs −1.08 ± 5.19, p<0.001) to compensate. SOA had a greater improvement in TPA (15.06 vs 9.59, p<0.001), and less change in PFSA (86.65 vs 88.81, p<0.001) compared to LOA. Conclusions. Spinopelvic compensatory mechanisms are adapted for reduced joint mobility associated with hip OA in standing and sitting

Adverse spinopelvic characteristics (ASC) have been associated with increased dislocation risk following primary total hip arthroplasty (THA). A stiff lumbar spine, a large posterior standing tilt when standing and severe sagittal spinal deformity have been identified as key risk factors for instability. It has been reported that the rate of dislocation in patients with such ASC may be increased and some authors have recommended the use of dual mobility bearings or robotics to reduce instability to within acceptable rates (<2%). The aims of the prospective study were to 1: Describe the true incidence of ASC in patients presenting for a THA 2. Assess whether such characteristics are associated with greater symptoms pre-THA due to the concomitant dual pathology of hip and spine and 3. Describe the early term dislocation rate with the use of ≤36mm bearings. This is an IRB-approved, two-center, multi-surgeon, prospective, consecutive, cohort study of 220 patients undergoing THA through anterolateral- (n=103; 46.8%), direct anterior- (n=104; 27.3%) or posterior- approaches (n=13; 5.9%). The mean age was 63.8±12.0 years (range: 27.7-89.0 years) and the mean BMI 28.0±5.0 kg/m. 2. (range: 19.4-44.4 kg/m. 2. ). There were 44 males (47.8%) and 48 females (52.2%). The mean follow-up was 1.6±0.5 years. Overall, 54% of femoral heads was 32 mm, and 46% was 36mm. All participants underwent lateral spinopelvic radiographs in the standing and deep-flexed seated positions were taken to determine lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic-femoral angle (PFA) and pelvic incidence (PI) in both positions. Spinal stiffness was defined as lumbar flexion <20° when transitioning between the standing and deep-seated position; adverse standing PT was defined as >19° and adverse sagittal lumbar balance was defined as mismatch between standing PI and LL >10°. Pre-operative patient reported outcomes was measured using the Oxford Hip Score (OHS) and EuroQol Five-Dimension questionnaire (EQ-5D). Dislocation rates were prospectively recorded. Non-parametric tests were used, significance was set at p<0.05. The prevalence of PI-LL mismatch was 22.1% (43/195) and 30.4% had increased standing PT (59/194). The prevalence of lumbar stiffness was 3.5% (5/142) and these patients had all three adverse spinopelvic characteristics (5/142; 3.5%). There was no significant difference in the pre-operative OHS between patients with (20.7±7.6) and patients without adverse spinopelvic characteristics (21.6±8.7; p=0.721), nor was there for pre-operative EQ5D (0.651±0.081 vs. 0.563±0.190; p=0.295). Two patients sustained a dislocation (0.9%): One in the lateral (no ASC) and one in the posterior approaches, who also exhibited ASC pre-operatively. Sagittal lumbar imbalance, increased standing spinal tilt and spinal stiffness are not uncommon among patients undergoing THA. The presence of such characteristics is not associated with inferior pre-operative PROMs. However, when all characteristics are present, the risk of instability is increased. Patients with ASC treated with posterior approach THA may benefit from the use of advanced technology due to a high risk of dislocation. The use of such technology with the anterior or lateral approach to improve instability is to date unjustified as the rate of instability is low even amongst patients with ASCs

INTRODUCTION. Standing spinal alignment has been the center of focus recently, particularly in the setting of adult spinal deformity. Humans spend approximately half of their waking life in a seated position. While lumbopelvic sagittal alignment has been shown to adapt from standing to sitting posture, segmental vertebral alignment of the entire spine is not yet fully understood, nor are the effects of DEGEN or DEFORMITY. Segmental spinal alignment between sitting and standing, and the effects of degeneration and deformity were analyzed. METHODS. Segmental spinal alignment and lumbopelvic alignment (pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), PI-LL, sacral slope) were analyzed. Lumbar spines were classified as NORMAL, DEGEN (at least one level of disc height loss >50%, facet arthropathy, or spondylolisthesis), or DEFORMITY (PI-LL mismatch>10°). Exclusion criteria included lumbar fusion/ankylosis, hip arthroplasty, and transitional lumbosacral anatomy. Independent samples t-tests analyzed lumbopelvic and segmental alignment between sitting and standing within groups. ANOVA assessed these differences between spine pathology groups. RESULTS. There were 183 NORMAL, 216 DEGEN and 92 DEFORMITY patients with significant differences in age, gender, and hip OA grades. After propensity matching for these factors, there were 56 patients in each group (age 63±14, 58% female) [Fig. 1]. Significant differences were noted between spinal pathology groups with regard to changes from standing to sitting alignment with regard to NORMAL vs DEGEN vs DEFORMITY groups in PT (13.93° vs −11.98° vs − 7.95°; p=0.024), LL (21.91° vs 17.45° vs 13.23°; p=0.002), PI-LL (−22.32° vs −17.28° vs −13.18°; p<0.001), SVA (−48.99° vs −29.98° vs −32.12°; p=0.002), and TPA(−16.35° vs −12.69° vs −9.64; p=0.001). TK (−2.08° vs −2.78° vs −2.00°, p=0.943) and CL (−3.84° vs −4.14° vs −3.57°, p=0.621) were not significantly different across spinal pathology groups [Fig. 2]. NORMAL patients had overall greater mobility in the lower lumbar spine from standing to sitting compared to DEGEN and DEFORMITY patients. L4-L5 (7.50° vs 5.23° vs 4.74°, p=0.012) and L5-S1 (6.96° vs 5.28° and 3.69°, p=0.027). There were no significant differences in change in alignment from standing to sitting at the upper lumbar levels or lower thoracic levels between the three groups [Fig. 3]. CONCLUSION. The lower lumbar spine provides the greatest sitting to standing change in lumbopelvic alignment in normal patients. Degeneration and deformity of the spine significantly reduces the mobility of the lower lumbar spine and PT. With lumbar spine degeneration and flatback deformity, relatively more alignment change occurs at the upper lumbar spine and thoracolumbar junction

Introduction. Excessive standing posterior pelvic tilt (PT), lumbar spine stiffness, low pelvic Incidence (PI), and severe sagittal spinal deformity (SSD) have been linked to increased dislocation rates. We aimed to compare the prevalence of these 4 parameters in unstable and stable primary Total Hip Arthroplasty (THA) patients. Methods. In this retrospective cohort study, 40 patients with instability following primary THA for osteoarthritis were referred for functional analysis. All patients received lateral X-rays in standing and flexed seated positions to assess functional pelvic tilt and lumbar lordosis (LL). Computed tomography scans were used to measure pelvic incidence and acetabular cup orientation. Literature thresholds for “at risk” spinopelvic parameters were standing pelvic tilt ≤ −10°, lumbar flexion (LL. stand. – LL. seated. ) ≤ 20°, PI ≤ 41°, and sagittal spinal deformity (PI – LL. stand. mismatch) ≥ 10°. The prevalence of each risk factor in the dislocation cohort was calculated and compared to a previously published cohort of 4042 stable THA patients. Results. Median supine cup inclination for the dislocating cohort was 43° (range, 26°- 58°). Median cup anteversion was 23° (range, 7° − 40°) for the dislocating cohort. 65% of the dislocating patients had socket positions within the Lewinnek safe zone (Figure 1). Standing PT (-10° v −1°), lumbar flexion (20° v 45°), and PI-LL mismatch (12° v −1°) were all significantly different (p < 0.001) in the dislocating group compared to the stable THA population (Figure 2). There was no difference in PI between the dislocating group and the stable THA population (58° v 56° respectively, p = 0.33), with the numbers available. 80% of the dislocating patients had one or more of the 3 statistically significant risk factors, compared to only 24% of the stable THA population. Conclusion. Excessive standing posterior pelvic tilt, low lumbar flexion and a severe SSD are highly prevalent in unstable THAs. Pre-op screening for these parameters may reduce the prevalence of dislocation. For any figures or tables, please contact the authors directly