Assessment of pelvic tilt in anteroposterior radiographs by means of tilt ratios

Accuracy of intraoperative approximation of pelvic tilt using preoperative standing radiographs

Background

Anterior approach surgeons who utilize intraoperative fluoroscopy often try to match a preoperative radiograph as a reference for intraoperative cup position. Every degree of inaccuracy in tilt leads to a roughly 0.7° change in anteversion. This study aimed to determine how closely pelvic tilt (PT) is approximated intraoperatively when compared to preoperative anteroposterior (AP) radiographs.

Methods

This was a retrospective review of 193 primary THA's done by 2 surgeons at an academic tertiary referral center between September 2021-January 2023. There were 24 patients excluded for distorted anatomy, post-traumatic arthritis, insufficient x-rays, or a sacroiliac joint that could not be visualized on film. Data collected included age and BMI. PT was calculated using the formula, Tilt = -(ln((B/A) x (1/0.483)))/0.051. Value A is the distance from the base of the SI joint to the superior margin of the obturator foramen; value B is the height of the obturator foramen.

Results

Mean preoperative PT was 0.2° versus intraoperative PT was 3.4° (p < 0.001). Mean absolute difference was 6.5°. 48% of patients (n = 81) had an absolute difference less than 5°, 31% (n = 52) between 5° and 10°, 14% (n = 24) between 10° and 15°, and 7% (n = 12) greater than 15°. There was no correlation between BMI or age and PT discrepancy.

Conclusion

Of the patients, 21% had a discrepancy of 10° or greater between their preoperative radiographs and intraoperative fluoroscopic images. Surgeons should be aware of potential errors in cup positioning and be particularly diligent in high-risk cases.

Evaluating pelvic tilt using the pelvic antero-posterior radiographs: A novel method

Pelvic tilt (PT) is an important parameter for orthopedic surgeries involving hip and spine, typically determined from sagittal pelvic radiographs. However, various challenges can compromise the feasibility of measurement from sagittal imaging, including obscured landmarks, anatomical variations, hardware interference, and limited medical resources. Addressing these challenges and with the aim of reducing radiation exposure to patients, our study developed a novel method to estimate PT from antero-posterior (AP) radiographs, using vertical distances from the pelvic outlet and obturator foramen. We correlated these measurements with PT, defined both anatomically (anterior pelvic plane, PTa) and mechanically (centers of femoral heads and sacral plate, PTm). The study explored creating linear, exponential, and multivariate regression models based on twelve 3D CT-derived pelvic models (six men, six women), simulating AP radiograph projections with controlled PTs. We then validated these models against 105 pairs of patient stereoradiographs. Statistical analysis revealed that combined exponential-linear models yielded the most accurate results, with Pearson correlation coefficients of 0.75 for PTa and 0.77 for PTm, and mean absolute errors of 3.7° ± 2.6° for PTa and 4.5° ± 3.4° for PTm, showing excellent measurement reliability (all ICCs > 0.9) without significant gender discrepancies. In conclusion, this study presents a validated, simple, and accessible method for estimating PT using AP radiograph parameters, supported by the Supporting Information S1: Excel Tool, showing great potential for clinical application in hip and spine procedures.

Automated assessment of pelvic radiographs using deep learning: A reliable diagnostic tool for pelvic malalignment

Pelvic malalignment leads to general imbalance and adversely affects leg length. Timely and accurate diagnosis of pelvic alignment in patients is crucial to prevent additional complications arising from delayed treatment. Currently, doctors typically assess pelvic alignment either manually or through radiography. This study aimed to develop and assess the validity of a deep learning-based system for automatically measuring 10 radiographic parameters necessary for diagnosing pelvic displacement using standing anteroposterior pelvic X-rays. Between March 2016 and June 2021, pelvic radiographs from 1215 patients were collected. After applying specific selection criteria, 550 pelvic radiographs were chosen for analysis. These data were utilized to develop a deep learning-based system capable of automatically measuring radiographic parameters relevant to pelvic displacement diagnosis. The system's diagnostic accuracy was evaluated by comparing automatically measured values with those assessed by a clinician using 200 radiographs selected from the initial 550. The results indicated that the system exhibited high reliability, accuracy, and reproducibility, with a Pearson correlation coefficient of ≥0.9, an intra-class correlation coefficient of ≥0.9, a mean absolute error of ≤1 cm, mean square error of ≤1 cm, and root mean square error of ≤1 cm. Moreover, the system's measurement time for a single radiograph was found to be 18 to 20 times faster than that required by a clinician for manual inspection. In conclusion, our proposed deep learning-based system effectively utilizes standing anteroposterior pelvic radiographs to precisely and consistently measure radiographic parameters essential for diagnosing pelvic displacement.

Evaluating Pelvic Tilt Using the Pelvic Antero-Posterior Projection Images: A Systematic Review

BACKGROUND

Pelvic tilt (PT) is a routinely evaluated parameter in hip and spine surgeries, and is usually measured on a sagittal pelvic radiograph. This may not always be feasible due to limitations such as landmark visibility, pelvic anomaly, and hardware presence. Tremendous efforts have been dedicated to using pelvic antero-posterior (AP) radiographs for assessing sagittal PT. Thus, this systematic review aimed to collect these methods and evaluate their performances.

METHODS

Two independent reviewers searched the PubMed, Ovid, Cochrane, and Web of Science databases in June 2023 with backward reference trailing (Google Scholar archive). There were 30 studies recruited. Risk of bias was assessed using the prediction model risk of bias assessment tool. The relevant data were tabulated in a standardized form for evaluating either the absolute PT or relative PT. Disagreement was resolved by discussing with the senior author.

RESULTS

There were 19 parameters from pelvic AP projection images involved, with 4 studies which used artificial intelligence, eyeball, or statistical shape method not involving a specific parameter. In comparing the PT values from pelvic sagittal images with those extrapolated from antero-posterior projection images, the highest correlation coefficient was found to be 0.91. The mean absolute difference (error) was 2.6°, with a maximum error reaching 10.9°. Most studies supported the feasibility of using AP parameters to calculate changes in PT.

CONCLUSIONS

No individual AP parameter was found to precisely estimate absolute PT. However, relative PT can be derived by evaluating serial AP radiographs of a patient in varying postures, employing any AP parameters.

Concurrent Learning Approach for Estimation of Pelvic Tilt from Anterior-Posterior Radiograph

Accurate and reliable estimation of the pelvic tilt is one of the essential pre-planning factors for total hip arthroplasty to prevent common post-operative complications such as implant impingement and dislocation. Inspired by the latest advances in deep learning-based systems, our focus in this paper has been to present an innovative and accurate method for estimating the functional pelvic tilt (PT) from a standing anterior-posterior (AP) radiography image. We introduce an encoder-decoder-style network based on a concurrent learning approach called VGG-UNET (VGG embedded in U-NET), where a deep fully convolutional network known as VGG is embedded at the encoder part of an image segmentation network, i.e., U-NET. In the bottleneck of the VGG-UNET, in addition to the decoder path, we use another path utilizing light-weight convolutional and fully connected layers to combine all extracted feature maps from the final convolution layer of VGG and thus regress PT. In the test phase, we exclude the decoder path and consider only a single target task i.e., PT estimation. The absolute errors obtained using VGG-UNET, VGG, and Mask R-CNN are 3.04 ± 2.49, 3.92 ± 2.92, and 4.97 ± 3.87, respectively. It is observed that the VGG-UNET leads to a more accurate prediction with a lower standard deviation (STD). Our experimental results demonstrate that the proposed multi-task network leads to a significantly improved performance compared to the best-reported results based on cascaded networks.

The influence of lumbo-sacral transitional vertebrae in developmental dysplasia of the hip: a matched pair analysis

Lumbo-sacral transitional vertebrae (LSTV) are the most common congenital alteration of the lumbo-sacral junction and known to significantly influence pelvic anatomy. However, the influence of LSTV on dysplasia of the hip (DDH) and the surgical treatment by periacetabular osteotomy (PAO) remains unknown. We retrospectively examined standardized standing anterior-posterior pelvic radiographs of 170 patients in 185 PAO procedures. Radiographs were examined for LSTV, lateral-central-edge-angle (LCEA), Tönnis-angle (TA), femoral-head-extrusion index (FHEI), and anterior-wall-index (AWI) and posterior-wall-index (PWI). Patients with LSTV were compared to an age- and sex-matched control group. Patient-reported outcome measurements (PROMs) were evaluated pre- and in the mean 63.0 months (range 47-81 months) postoperatively. 43 patients (25.3%) had LSTV. Patients with LSTV had significantly greater PWI (p = 0.025) compared to the matched control group. No significant differences were seen in AWI (p = 0.374), LCEA (p = 0.664), TA (p = 0.667), and FHEI (p = 0.886). Between the two groups, no significant differences were detected in pre- or postoperative PROMs. Due to the increased dorsal femoral head coverage in patients with LSTV and DDH compared to patients with sole DDH, a more pronounced ventral tilting might be performed in those patients with prominent posterior wall sign to avoid anterior undercoverage, which is a significant predictor for premature conversion to hip arthroplasty after PAO. However, anterior overcoverage or acetabular retroversion must be avoided due to the risk of femoroacetabular impingement. Patients with LSTV reported similar functional outcomes and activity after PAO as the control group. Therefore, even for patients with concomitant LSTV, which are frequent with one-fourth in our cohort, PAO is an efficient treatment option to improve clinical symptoms caused by DDH.

Change in functional biomechanics following a targeted exercise intervention in patients with acetabular retroversion and femoroacetabular impingement syndrome

BACKGROUND

Acetabular retroversion is a form of hip dysplasia that may cause femoroacetabular impingement syndrome (FAIS), leading to pain and restricted hip range of motion. An exercise intervention aiming at altering pelvis tilt and related functional biomechanics may be a useful first-line intervention for patients who are not eligible for surgical repositioning.

RESEARCH QUESTION

Does squat and gait biomechanics change following an 8-week targeted exercise program in individuals with symptomatic acetabular retroversion and FAIS?

METHODS

This prospective intervention study used participants as their own controls. Examinations were conducted at three time-points: T1 baseline; T2 following an 8-week control period; T3 after 8 weeks' intervention. At each time-point, three-dimensional motion analysis of a deep squat and level gait was performed, and pain intensity was recorded using a numerical rating scale (NRS 0-10). The intervention consisted of a home-exercise program to improve core stability and pelvic movement. Differences in waveforms between time-points across pelvis and lower-limb biomechanics were evaluated using statistical parametric mapping. Delta (Δ, differences between T1-T2 and T2-T3) was used to evaluate changes in spatiotemporal gait parameters and pain.

RESULTS

Nineteen patients (18 females), mean age 22.6 (SD 4.5) years, BMI (kg/m2) 23.0 (SD 4.1), were included. Changes (Δ T1-T2 vs. Δ T2-T3) in squat biomechanics were observed as: (i) decreased anterior pelvic tilt, (ii) deeper vertical pelvis position, and (iii) increased knee flexion angle. Contrary, no significant changes in gait biomechanics, Δ walking speed, Δ step length, or NRS for pain were found.

SIGNIFICANCE

Following a targeted exercise intervention, participants were able to squat deeper, potentially allowing better hip function. The deepened squat position was accompanied by increased knee flexion and reduced anterior pelvic tilt. Gait biomechanics and patient-reported pain remained unchanged post-intervention. These findings are important for future design of exercise interventions targeting pelvic tilt in symptomatic individuals.

Exercise in patients with acetabular retroversion and excessive anterior pelvic tilt: A feasibility and intervention study

BACKGROUND

Acetabular retroversion is associated with femoroacetabular impingement syndrome (FAIS). Anterior pelvic tilt enhances risk of FAIS.

OBJECTIVES

To investigate feasibility and change in patient-reported symptoms of a home-based exercise intervention in patients with acetabular retroversion and excessive anterior pelvic tilt, in comparison with a prior control period.

DESIGN

Prospective intervention study.

METHODS

Patients (18-40 years) not eligible for surgery, with radiographic signs of acetabular retroversion and excessive anterior pelvic tilt were recruited. An 8-week control period was followed by an 8-week training period. The home-based intervention consisted of education and exercises for core stability, muscle strengthening and stretching for reducing anterior pelvic tilt. Feasibility assessments were dropout (≤10%), adherence (≥75% of sessions), exercise-related pain, and adverse events. Primary outcome was change in the Copenhagen Hip and Groin Outcome Score (HAGOS) pain-subscale. Pelvic tilt was measured by EOS scanning.

RESULTS

Forty-two patients (93% female, mean age 22.2 ± 4.2 years) were included. Dropout rate was 7% and satisfactory adherence was demonstrated by 85%. Exercise-related pain and adverse events were acceptable. Between-period mean change score for HAGOS-PAIN was 5.2 points (95% CI: -0.3-10.6) and -1.6° (95% CI: -3.9-0.7) of anterior pelvic tilt. Patients responding positively (≥10 points) (n = 10, 26%), had pre-exercise moderate pain (HAGOS-PAIN 47.5-70 points).

CONCLUSIONS

Current exercise intervention was feasible. However, we found no clinically relevant changes in self-reported hip-related pain or anterior pelvic tilt. Post hoc responder analysis revealed that patients with moderate pain at baseline might benefit from this exercise.

Change of Pelvic Sagittal Tilt after Total Hip Arthroplasty in Patients with Bilateral Crowe Type IV Developmental Dysplasia of the Hip

Objective

To explore and analyze the change of pelvic sagittal tilt (PST) after total hip arthroplasty (THA) in patients with bilateral Crowe type IV developmental dysplasia of the hip (DDH).

Methods

The study retrospectively evaluated 43 patients with bilateral Crowe type IV DDH undergoing THA from January 2008 to June 2019 who were followed up for 12 months postoperatively. Four parameters, including the ratio between the height and width of the obturator foramina(H/W ratio), the vertical distance between the upper edge of the symphysis and the middle of the sacrococcygeal joint (SSc distance), the vertical distance between the upper edge of the symphysis and the line connecting bilateral hip centers (SC distance) and the vertical distance between the upper edge of the symphysis and the line connecting the bilateral lower ends of the sacroiliac joints (SSi distance), which could indirectly reflect the change of PST, were observed and measured by radiographs. The change of each parameter before operation, immediately after operation, and in 3, 6 and 12 months postoperatively was compared and analyzed.

Results

Compared with the value before operation, the H/W ratio immediately after operation and in 3, 6 and 12 months postoperatively were 0.61 ± 0.12 (t = 0.893, P = 0.377), 0.61 ± 0.11 (t = 1.622, P = 0.112), 0.67 ± 0.10 (t = 5.995, P < 0.001) and 0.76 ± 0.12 (t = −9.313, P < 0.001), respectively, and the SSc, SC and SSi distance in 6 months postoperatively were 30.12 ± 7.06 mm (t = 3.506, P = 0.002), 42.8 ± 7.7 mm (t = 5.843, P < 0.001), 129.3 ± 12.6 mm (t = 5.888, P < 0.001), respectively, and in 12 months postoperatively were 27.24 ± 7.68 mm (t = 6.510, P < 0.001), 36.1 ± 9.1 mm (t = 9.230, P < 0.001), 118.9 ± 14.9 mm (t = 8.940, P < 0.001), respectively. The radiographs obtained in 6 and 12 months postoperatively demonstrated a significantly increased H/W ratio and decreased SSc, SC and SSi distance. At the last follow‐up, the clinical evaluations significantly improved in all patients and there were no revisions.

Conclusion

The significant change of pelvic sagittal posterior tilt in patients with bilateral Crowe type IV DDH might be a significant phenomenon after THA, which could occur in 6 months postoperatively.

Total Hip Replacement Influences Spinopelvic Mobility: A Prospective Observational Study

BACKGROUND

Abnormal spinopelvic mobility is identified as a contributing element of total hip arthroplasty (THA) instability. Preoperative identification of THA patients at risk is still a remaining challenge. We therefore conducted this study to (1) evaluate if preoperative and postoperative spinopelvic mobility differs, (2) determine the interactions between the elements of the spinopelvic complex, and (3) identify preoperative parameters for predicting spinopelvic mobility.

METHODS

A prospective observational study assessing 197 THA patients was conducted with biplanar stereoradiography in standing and relaxed sitting positions preoperatively and postoperatively. Two independent investigators determined spinopelvic mobility based on 2 different classifications (Δ sacral slope [SS] and Δ pelvic tilt [PT]; Δ from standing to sitting; Δ < 10° stiff, Δ ≥ 10°-30° normal, Δ > 30° hypermobile). Multiple regression analysis and receiver operating characteristic analysis were used to identify predictors for postoperative spinopelvic mobility.

RESULTS

Spinopelvic mobility significantly increased after THA based on ΔPT (Pre/Post: 18.5°/22.8°; P < .000) and ΔSS (Pre/Post 17.9°/22.4°; P < .000). A distinct shift in the ratio from stiff (Pre/Post: 24%/9.7%) to hypermobile (Pre/Post: 10.2%/22.1%) mobility postoperatively was observed. Receiver operating characteristic analysis predicted postoperative stiffness using preoperative PT_Standing ≥ 13.0° with a sensitivity of 90% and a specificity of 51% and hypermobility with preoperative SS_Standing ≥ 35.2° with a sensitivity of 81% and a specificity of 34%. Age at surgery, preoperative PT_Standing, and pelvic incidence were independent predictors of spinopelvic mobility (R² = 0.24).

CONCLUSION

Definition of preoperative stiffness should be interpreted with caution by arthroplasty surgeons as mobility itself is influenced by THA. For the first time thresholds for standing preoperative parameters for predicting postoperative spinopelvic mobility could be provided. For preoperative standing only lateral assessment could serve as a screening tool for spinopelvic mobility.

[Lumbo-pelvino-acetabular alignment-basics and clinical consequences]

The spinal shape and the pelvic ante-/retroversion of an individual are determined by its innate, genetically fixed lumbosacral angulation. This can be measured with little effort in the lateral standing radiograph of the patient. In spinal surgery, there are a lot of original papers on the topic. In hip surgery, however, the individual pelvic version and its consequences for the acetabular orientation have not received the same attention so far.This review focuses on previous data on the relationship between lumbosacral angulation and pelvic ante-/retroversion. Four anatomically definable pelvic types can be distinguished; three of those have to be considered as facultatively pathogenetic. Clinical consequences arise for the clinical pictures of spondylolisthesis, non-specific lower back pain, acetabular retroversion and developmental dysplasia of the hip, as well as for acetabular cup positioning in total hip arthroplasty.

Increased anterior pelvic tilt in patients with acetabular retroversion compared to the general population: A radiographic and prevalence study

INTRODUCTION

The prevalence of acetabular retroversion is sparsely investigated. It may be associated with increased anterior pelvic tilt. The purpose of this study was to investigate whether patients with symptomatic and radiographically verified acetabular retroversion demonstrated increased anterior pelvic tilt compared to a control group, and furthermore to evaluate the prevalence of acetabular retroversion in the general population.

METHODS

Anteroposterior pelvic radiographs in standing position of 111 patients with acetabular retroversion prior to anteverting periacetabular osteotomy (PAO) and 132 matched controls from the general Danish population were assessed. Pelvic tilt was assessed by the sacrococcygeal joint-symphysis distance and pelvic-tilt-ratio. Acetabular retroversion was defined as positive cross-over sign and posterior wall sign. Prior to assessments, interrater reliability analysis was performed. Measurements were agreed by two independent assessors. A nonparametric regression model was used to test between-group differences in median pelvic tilt. The prevalence was calculated as the ratio of subjects and hips with acetabular retroversion, respectively.

RESULTS

The patient group had significantly larger median anterior pelvic tilt of 14.3 mm in sacrococcygeal joint-symphysis distance and -0.08 in pelvic-tilt-ratio, compared to controls. The prevalence of subjects in the general population with either unilateral or bilateral acetabular retroversion was 24% and 18% for all hips.

CONCLUSION

Our data demonstrated that patients with symptomatic acetabular retroversion have increased anterior pelvic tilt compared to the general population. Radiographic sign of acetabular retroversion was highly prevalent in the general population.

IMPLICATION FOR PRACTICE

Increased anterior pelvic tilt should be considered when diagnosing and treating patients with hip pain, as symptoms may be related to the functional position of the pelvis and not necessarily solely come from the radiographic verified acetabular retroversion.

Clinical Measures of Pelvic Tilt in Physical Therapy

Pelvic tilt refers to the spatial position or motion of the pelvis about a frontal horizontal axis on the rest of the body in the sagittal plane. It is relevant for several musculoskeletal conditions commonly seen in physical therapist practice, particularly conditions affecting the hip and groin. Despite the relevance of pelvic tilt identified in biomechanical studies, and the historical precedence for assessing pelvic tilt, there is a lack of clarity regarding the utility of clinical measures that are practical in a rehabilitation setting. There are several options available to assess pelvic tilt which are discussed in detail in this commentary. All of these options come with potential benefits and considerable limitations. The purpose of this commentary is to provide an overview of the relevance of understanding pelvic tilt in the pathology and rehabilitation of conditions affecting the hip joint, with a focus applying evidence towards identifying clinical measures that may be useful in the rehabilitation setting and considerations that are needed with these measures.

LEVEL OF EVIDENCE

5.

Correlation between the lateral and anteroposterior sacral ratios in anorectal malformations

BACKGROUND

The sacral ratio has been used as a tool for evaluating sacral development in patients with anorectal malformations. Sacral ratios can be calculated by obtaining sacral radiographs in the anteroposterior (AP) and lateral planes.

OBJECTIVE

The objective of the study was to determine the correlation and agreement in sacral ratio calculations.

MATERIALS AND METHODS

In this single institution retrospective cohort study, we reviewed medical charts of all pediatric anorectal malformation patients treated between March 2014 and September 2018 who had both AP and lateral images of their sacrum. All sacral ratios were measured by three radiologists. Pearson's correlation coefficients and corresponding 95% confidence intervals (CIs) were used to assess the correlation between the AP and lateral radiographs. A weighted Kappa statistic was used to measure the agreement between how the AP and lateral sacral ratios categorized observations into risk groups.

RESULTS

Our initial cohort consisted of 646 observations from patients with anorectal malformations who had radiographs obtained in both AP and lateral planes. We excluded all observations (n=76) where the radiographs were deemed to be inadequate or not appropriately centered to measure sacral ratio. For a given pair of measurements, the mean lateral sacral ratio was 0.07 units greater than the AP plane (95% CI 0.06-0.09, paired t-test P-value <0.0001). AP and lateral images had a moderate positive correlation (Pearson's r=0.76, 95% CI 0.73-0.79, P<0.0001) and moderate agreement in risk categorization (unweighted kappa = 0.60, P<0.0001). AP and lateral readings conducted by all three radiologists had excellent inter-rater reliability with intraclass correlations for AP and lateral sacral ratios of 0.88 and 0.84, respectively.

CONCLUSION

Even though the AP and lateral sacral ratios had moderate positive correlation, the mean sacral ratio determined by images in the lateral plane was 0.07 units greater than the AP plane. AP and lateral sacral ratios concluded different risk categories relatively often. Future studies are needed to determine whether AP or lateral sacral ratios correlate better with continence in patients with anorectal malformations.

Progression of pelvic retroversion is a critical factor for clinical outcome after Opening-wedge high tibial osteotomy among elderly patients

Purpose

To evaluate the clinical outcome after opening-wedge high tibial osteotomy (OWHTO) and to determine the critical factors for a poor clinical outcome after OWHTO in patients aged over 65 years.

Methods

Our retrospective analysis was based on the data from 233 patients who underwent OWHTO for medial compartment knee OA at our institution between January 2013 and December 2018, and 88 patients (36 men and 52 women) over 65 years of age were included in this study. Radiographic parameters of weight-bearing line ratio (WBLR) and pelvic inclination (PI); the knee function, range of motion (ROM) and extension; and clinical outcome with Lysholm score were obtained preoperatively and postoperatively at the final follow-up visit. To evaluate the critical factors for the clinical outcome, univariate regression analysis was used to identify the relationship between postoperative and improved Lysholm score and pre-and post-operative essential factors. To reveal the factor having a greater impact on the clinical outcome, a p < 0.05 in univariate factors was entered into a multivariate regression analysis.

Results

The preoperative WBLR was significantly changed, and Lysholm score improved from 59.5 to 81.5 (p < 0.0001), whereas the PI, knee extension and ROM were not changed after OWHTO. Regarding the essential factors affecting clinical outcome after OWHTO, age and delta PI were negative, whereas preoperative WBLR, postoperative ROM, especially extension, had a positive effect (p < 0.05). Furthermore, only delta PI had affected the improvement of clinical outcome with OWHTO (p < 0.01), and postoperative knee extension was negatively correlated with the progression of pelvic retroversion (p < 0.01).

Conclusion

Age at surgery and progression of pelvic retroversion were the critical factors for poor postoperative clinical outcomes after OWHTO. Care should be taken for the progression of pelvic retroversion after OWHTO because it deteriorates the clinical outcome by inducing the knee flexion contracture as the compensatory mechanism for the balance of sagittal alignment.

Can a simple iPad app improve C-arm based component position in anterior THA?

INTRODUCTION

Correct acetabular component positioning improves hip biomechanics, impingement free range of motion and may lead to a reduced risk of postoperative dislocation. The C-arm is a simple and cost-effective tool for THA in a supine position, however, evaluation of the images can be challenging due to parallax. The current study aimed to investigate whether a software app-based measurement technique can control acetabular component position and leg length in anterior THA.

MATERIALS AND METHODS

Ninety-three patients with end-stage osteoarthritis aged 65.2 ± 9.6 years (range 30-86 years) were included in this prospective study. All patients underwent direct anterior THA using a Hana orthopedic surgery table. C-arm imaging and an iPad software app were used to determine intraoperative acetabular anteversion, inclination and leg length discrepancy. The app provides a measuring tool that is applied to intraoperative c-arm images. The intraoperative measurements were compared to the measurements of standard postoperative AP-pelvis radiographs.

RESULTS

Intraoperative software app-based anteversion measurements averaged 20.5° (range 16.0° to 24.0°) compared to 20.9° (range 14.7° to 25.6°) postoperatively. Mean intraoperative inclination was 40.5° (range 35° to 48°) compared to postoperative 40.7° (range 35° to 49°). Mean intraoperative leg length discrepancy was 0.9 mm (range - 4-5 mm) compared to postoperative 0.6 mm (range - 5-6 mm). A strong Pearson's correlation was observed between the intraoperative and postoperative measurements for anteversion (r = .701; P < .0001), inclination (r = .816; P < .0001) and leg length discrepancy (r = .542; P < .0001).

CONCLUSIONS

The software app used in the current study allowed for a simple and accurate measurement of intraoperative cup position and leg length in direct anterior THA.

Axial pelvic tilt in direct anterior Total hip Arthroplasty using a traction table

BACKGROUND

Direct anterior approach total hip arthroplasty may be undertaken on a traction table, but the effects that patient positioning can have on axial pelvic tilt (aPT) are unknown. The aim of this study was to assess the degree of error from patient positioning on the traction table during anterior minimally-invasive surgery (AMIS) THA.

METHODS

Patients were included who underwent direct anterior THA via the AMIS technique at a single institution between 11/2018 and 03/2019. Axial pelvic tilt was measured (a) in the supine position on the operating table, and (b) after positioning on the traction table, by the same consultant surgeon in all cases.

RESULTS

In the above-mentioned study period, 50 patients (F: 32; M: 18) with an average age of 60.6 ± 13.6 (range: 26.5 to 88.3) years, and an average BMI of 27.2 ± 5.0 (range: 17.9 to 41.5) kg/m² met the inclusion criteria. When measured in supine position, the average aPT was - 0.2 ± 1.7 (range: - 5.6 to 3.8) degrees. After positioning on the traction table, the average aPT was - 3.5 ± 2.1 (- 8.5 to 1.6) degrees (p < 0.001). In patients with an aPT of more than 5 degrees, the caput-collum-diaphyseal (CCD) angle was significantly lower (125 ± 11° vs. 134 ± 8°, p = 0.007).

CONCLUSION

This study raises awareness for the potential risk of aPT during positioning of the patient on the traction table, commonly used during direct anterior THA via the AMIS technique.

Automatic Characterization of Pelvic and Sacral Measures from 200 Subjects

BACKGROUND

An understanding of pelvic and acetabular morphology and orientation is required for accurate surgical reconstruction of the hip and spine, as well for component placement in a total hip arthroplasty. Our objectives were to develop an automated system for measuring pelvic and sacral orientations utilizing computed tomographic (CT) scans and to characterize these measures across 200 asymptomatic subjects.

METHODS

An automated feature recognition algorithm was created to identify acetabular and pelvic orientation across 200 scans generated for non-musculoskeletal conditions. Three-dimensional models were generated from CT data to serve as inputs to the algorithm. Acetabular orientation was defined by comparing a plane fit to the acetabular rim with the anterior pelvic plane. Pelvic inclination, pelvic tilt, and sacral slope were defined as the angles between landmarks identified across the pelvis: pubic tubercles, acetabular center, left and right anterior superior iliac spines, and sacral plate.

RESULTS

The mean sacral slope was 36.49°, the mean pelvic tilt was 15.60°, and the mean pelvic incidence was 52.05°. The mean sacropubic angle was 32.48° and the mean pelvic-Lewinnek angle was 8.93°. Significant differences between male and female subjects were observed in the sacral slope (mean difference, 4.72°; p < 0.05), pelvic tilt α (mean difference, 4.17°; p < 0.05), pelvic tilt γ (mean difference, 3.06°; p < 0.05), and the pelvic-Lewinnek angle (mean difference, 1.76°; p < 0.05). The comparison of acetabular orientation measures with those in a prior study of the same cohort yielded intraclass correlation coefficients (ICCs) all above 0.97. The validation of sacral orientation via manual measurement also yielded ICC values all at or above 0.97.

CONCLUSIONS

Our algorithm showed a high degree of consistency in acetabular orientation measures with respect to a prior study of the same cohort. The measures of pelvic orientation were found to be accurate and reliable when compared with manual measurements of the same data set. All measurements of pelvic orientation were consistent with the means reported in the literature.

CLINICAL RELEVANCE

An accurate and reproducible, automated technique for determining pelvic and acetabular orientation provides a way to characterize these measures as an aid in clinical diagnosis and preoperative planning.

The Impact of Spinopelvic Mobility on Arthroplasty: Implications for Hip and Spine Surgeons

Spinopelvic mobility represents the complex interaction of hip, pelvis, and spine. Understanding this interaction is relevant for both arthroplasty and spine surgeons, as a predicted increasing number of patients will suffer from hip and spinal pathologies simultaneously. We conducted a comprehensive literature review, defined the nomenclature, summarized the various classifications of spinopelvic mobility, and outlined the corresponding treatment algorithms. In addition, we developed a step-by-step workup for spinopelvic mobility and total hip arthroplasty (THA). Normal spinopelvic mobility changes from standing to sitting; the hip flexes, and the posterior pelvic tilt increases with a concomitant increase in acetabular anteversion and decreasing lumbar lordosis. Most classifications are based on a division of spinopelvic mobility based on ΔSS (sacral slope) into stiff, normal, and hypermobile, and a categorization of the sagittal spinal balance regarding pelvic incidence (PI) and lumbar lordosis (LL) mismatch (PI–LL = ± 10° balanced versus PI–LL > 10° unbalanced) and corresponding adjustment of the acetabular component implantation. When performing THA, patients with suspected pathologic spinopelvic mobility should be identified by medical history and examination, and a radiological evaluation (a.p. pelvis standing and lateral femur to L1 or C7 (if EOS (EOS imaging, Paris, France) is available), respectively, for standing and sitting radiographs) of spinopelvic parameters should be conducted in order to classify the patient and determine the appropriate treatment strategy. Spine surgeons, before planned spinal fusion in the presence of osteoarthritis of the hip, should consider a hip flexion contracture and inform the patient of an increased risk of complications with existing or planned THA.

Can measurements from an anteroposterior radiograph predict pelvic sagittal inclination?

Pelvic sagittal inclination (PSI) is often evaluated in patients with hip pathology using lateral radiographs. However, it would be useful if PSI could be predicted from an anteroposterior radiograph since this film is ubiquitous in the evaluation of hip pathology. Herein, computer-modeling was applied to predict PSI from radiographic measurements assessed in the anteroposterior plane. Three-dimensional surface models of the pelvis, femur, and sacrum were reconstructed from computed tomography images of 50 women with hip dysplasia. This study cohort was selected as changes in PSI alter femoral head coverage, which is relevant to the diagnosis and treatment of hip dysplasia, a known cause of hip osteoarthritis. Five radiographic parameters commonly used to independently estimate PSI were evaluated after bone surfaces were projected to an anteroposterior plane, including the symphysis to sacrococcygeal joint distance (S-S distance), the pelvic foramen aspect ratio (PF ratio), the distance between the symphysis and a line connecting the femoral head centers (S-H distance), the sacro-femoral-pubic angle (SFP angle), and the pelvic vertical ratio (PVR). Regression models determined the ability of these parameters to predict PSI from -20° to 20° at 1° increment. All five parameters showed a strong correlation with the PSI (all r > 0.9). From the regression models, PSI was estimated with a median (maximum) absolute error of 3.6° (18.4°), 3.8° (17.7°), 5.2° (17.9°), 5.8° (28.8°), and 3.2° (23.5°) for the S-S distance, PF ratio, S-H distance, SFP angle, and PVR, respectively. The regression model for S-S distance had a mean slope of 2.18 that ranged from 1.98 to 2.41 when the sacrococcygeal joint was located superior to the symphysis. Results indicated that substantial errors occur when estimating the actual value of PSI from an anteroposterior radiograph. However, the change in PSI could be estimated from the S-S distance, which may aid surgeons to successfully increase head coverage through periacetabular osteotomy and to locate the acetabular cup in a functional position for total hip arthroplasty.

[Discrepancy between radiographic and true cup position after total hip arthroplasty : Are we interpreting our radiographic quality indicators correctly? Video article]

BACKGROUND

After total hip arthroplasty (THA), objective postoperative quality control is done via X‑rays by as component position assessment. The cup position is defined by its version and inclination. However, there is a discrepancy between radiographically measured and true (anatomic) cup position, which may lead to misinterpretation.

METHODS

To visualize the discrepancy between true and radiographically measured cup position, in this video, a cup holder was used to set the angular cup version and inclination. Hereby, the cup position (anteversion and inclination) can be characterized in its radiographic and anatomic definition in greater detail. The viewer of this video should receive an impression as to when radiographically measured cup angles must be considered with caution.

RESULTS

In a simultaneous X‑ray and image sequence, this video shows decreased radiographic inclination measurement with increasing anterior rotation of the cup exceeding 20° of anteversion, yet with unchanged true inclination on the cup holder. Isolated consideration of the radiographic angles of anteversion and inclination may cause misinterpretation of true cup position. In pectoral illustration we show that variations in cup version and inclination may remain undetected when considering isolated the radiographic cup parameters.

CONCLUSION

True cup position in its anatomical definition can be calculated from the radiographically measured position. For this purpose, both cup parameters (radiographic anteversion and radiographic inclination) have to be taken into account.

Structural risk factors for low-energy acetabular fractures

In this study, we aimed to clarify proximal femur and acetabular structural risk factors associated with low-energy acetabular fractures in the elderly using three-dimensional (3D) computed tomography (CT). Pelvic bones and femurs were segmented and modeled in 3D from abdominopelvic CT images of 121 acetabular fracture patients (mean age 72 ± 12 years, range 50-98 years, 31 females and 90 males) and 121 age-gender matched controls with no fracture. A set of geometric parameters of the proximal femur and the acetabulum was measured. An independent-samples t-test or a Mann-Whitney U test was used for statistical analyses. The fractured side was used for proximal femur geometry, while the contralateral side was used for acetabular geometry. The neck shaft angle (NSA) was significantly smaller (mean 122.1° [95% CI 121.1°-123.2°] vs. 124.6° [123.6°-125.6°], p = 0.001) and the femoral neck axis length (FNALb) was significantly longer (78.1 mm [77.0-79.2 mm] vs. 76.0 mm [74.8-77.2 mm], p = 0.026) in the fracture group than in the controls when genders were combined. The NSA was significantly smaller both for females (120.2° [117.8°-122.6°] vs. 124.7° [122.5°-127.0°], p = 0.007) and for males (122.7° [121.5°-123.8°] vs. 124.6° [123.4°-125.7°], p = 0.006) in the fracture group. However, only males showed a significantly longer FNALb (80.0 mm [78.9-81.1 mm] vs. 77.8 mm [76.6-79.0 mm], p = 0.025). No statistically significant associations of acetabular geometry with fractures were found. However, the mean values of the acetabular angle of Sharp (34°), the lateral center-edge angle (40°), the anterior center-edge angle (62°), and the posterior center-edge angle (105°) indicated possible over-coverage. In conclusion, our findings suggest that proximal femur geometry is associated with low-energy acetabular fractures. Especially elderly subjects with an NSA smaller than normal have an increased risk of acetabular fractures.

Changes in acetabular orientation during total hip arthroplasty

AIMS

The aims of this study were to determine the change in pelvic sagittal alignment before, during, and after total hip arthroplasty (THA) undertaken with the patient in the lateral decubitus position, and to determine the impact of these changes on acetabular component position.

PATIENTS AND METHODS

We retrospectively compared the radiological pelvic ratio among 91 patients undergoing THA. In total, 41 patients (46%) were female. The mean age was 61.6 years (sd 10.7) and the mean body mass index (BMI) was 20.0 kg/m² (sd 5.5). Anteroposterior radiographs were obtained: in the standing position preoperatively and at six weeks postoperatively; in the lateral decubitus position after trial reduction intraoperatively; and in the supine position in the post-anaesthesia care unit. Pelvic ratio was defined as the ratio between the vertical distance from the inferior aspect of the sacroiliac (SI) joints to the superior pubic symphysis and the horizontal distance between the inferior aspect of the SI joints. Changes in the apparent component position based on changes in pelvic ratio were determined, with a change of > 5° considered clinically significant. Analyses were performed using Wilcoxon's signed-rank test, with p < 0.05 considered significant.

RESULTS

Intraoperatively, in the lateral decubitus position, the pelvic ratio increased (anterior tilt) in 69.4% of cases, did not change significantly in 20.4%, and decreased (posterior tilt) in 10.2% of cases. When six-week postoperative radiographs were compared with preoperative radiographs, the pelvic ratio decreased in 44.9% of cases, did not change significantly in 42.3%, and increased in 12.8% of cases. This change in alignment correlated with a change in acetabular component version of > 5° in 79.6% of cases intraoperatively and 57.7% of cases at six weeks postoperatively.

CONCLUSION

Changes in pelvic sagittal pelvic position occur throughout THA that, if unaccounted for, introduce errors in acetabular component placement. The use of intraoperative imaging may help the appropriate placement of the acetabular component. Cite this article: Bone Joint J 2019;101-B(6 Supple B):45-50.

"Simple mechanical devices did not improve pelvis positioning in AP pelvis radiographs for reliable assessment of the acetabular orientation"

BACKGROUND

The aim of this study was to develop two simple positioning devices for anteroposterior pelvis radiographs and to evaluate their effect on accuracy of the radiographs for assessment of the acetabular orientation compared with non-instrumented positioning.

METHODS

The superior anterior iliac spines and the pubic symphysis were used as anatomical landmarks to obtain a horizontal orientation of the pelvis according to the anterior pelvic plane. Anteroposterior pelvis radiographs were taken of 11 human cadaveric pelvic bones with each of the positioning devices and without any device. Defined measurements were carried out to objectify the tilt and rotation of the pelvis and to assess the cross-over sign as well as the presence of the ischial spine sign. Computed tomography scans were performed as a standard of reference. Bland-Altman-Plots were used to compare the continuous measurement values and Cohen's Kappa was applied for the categorical data. Intra- and inter-observer reliability was determined by the intraclass correlation coefficient and Cohen's Kappa.

RESULTS

The mean values of the measurements showed a high variability. A low correlation of the measurement values was found between the radiographs of the different positioning methods and the computed tomography scans. The intra- and inter-observer reliability was good (Cohen's Kappa 0.78 and 0.69; intraclass correlation coefficient 0.99 and 0.98).

CONCLUSION

The use of positioning devices did not lead to more accurate anteroposterior pelvis radiographs compared to non-instrumented positioning. Simple positioning devices do not provide standardized anteroposterior pelvis radiographs for reliable assessment of the acetabular orientation.