Spinal factors influencing change in pelvic sagittal inclination from supine position to standing position in patients before total hip arthroplasty

Increased hip flexion angle and protrusion of the anterior acetabular component can predict symptomatic iliopsoas impingement after total hip arthroplasty: a retrospective study

BACKGROUND

Iliopsoas impingement (IPI) is a known complication of total hip arthroplasty (THA). The aim of this study was to identify risk factors and the cut-off cup protrusion length for symptomatic IPI.

METHODS

We retrospectively reviewed 218 hips (46 men, 172 women) of 190 consecutive Japanese patients who underwent primary THA at our institution. Hips with IPI (n = 24) and control hips (n = 194) were compared according to age, body mass index, and clinical scores. We evaluated leg-length discrepancy, global offset, implant alignment angles, pelvic inclination, and anterior cup protrusion on plain radiographs and computed tomography scans.

RESULTS

Symptomatic IPI had an incidence of 11.0% and a predilection for hips with osteonecrosis. Pre- and postoperative hip flexion angles were significantly greater in hips with symptomatic IPI (p = 0.013 and p = 0.006, respectively). Cup protrusion length was significantly greater in hips with IPI (4.7 mm vs. 1.4 mm; p = 0.001). Receiver-operating characteristic curve analysis identified a threshold cup protrusion length of 3.9 mm (sensitivity 0.89, specificity 0.63) for symptomatic IPI. The incidence of symptomatic IPI tended to be lower in patients with greater posterior pelvic sagittal inclination despite the cup protrusion length being greater.

CONCLUSIONS

An increased hip flexion angle and protrusion of the anterior acetabular component predicted symptomatic IPI. The threshold cup protrusion length suggesting mild IPI might be about 3.9 mm and could be useful for identifying candidates for conservative treatment.

Direct Anatomic Registration in Computer-Assisted Total Hip Arthroplasty Improves Accuracy of Acetabular Cup Alignment

Background

Computer-assisted total hip arthroplasty using direct anatomic registration (DAR) with acetabular center axis software is an alternative method to the indirect anterior pelvic plane method. The software maps the center of hip rotation and orientation of the native acetabulum in 3 dimensions. This study aimed to evaluate the accuracy of acetabular cup alignment using DAR navigation combined with a mechanical guide device (MGD).

Methods

This prospective nonrandomized controlled study included 106 patients who underwent primary cementless total hip arthroplasty through the posterolateral approach. Fifty-four patients in the study group underwent DAR combined with MGD, whereas 52 patients underwent MGD only for acetabular cup positioning. Plain radiographs of both hips and computerized tomographic scans were obtained 2 months postoperatively for the evaluation of acetabular cup inclination and anteversion, respectively.

Results

The acetabular cup alignment in the study group was within the Lewinnek safe zone more than that in the control group (81.5% vs 59.6%, P < .05). The study group had a mean inclination angle of 43.88°° (standard deviation [SD] 5.38) and anteversion angle of 12.82° (SD 5.99), whereas the control group had 41.10° (SD 6.79) and 12.82° (SD 9.53), respectively. There were no significant differences in estimated blood loss, length of stay, and Harris hip scores at preoperative and 3 and 6 months postoperatively, except for the operative time, which was longer in the study group (P < .01). There was 1 posterior hip dislocation in each group.

Conclusions

DAR navigation combined with MGD provides better accuracy for acetabular cup positioning within the Lewinnek safe zone compared with the conventional technique.

Validation of a preoperative formula to estimate postoperative pelvic sagittal alignment and mobility before performing total hip arthroplasty for patients with hip osteoarthritis

BACKGROUND

Although it is important to consider pelvic alignment and mobility in the standing and sitting positions before THA, it is not known how to preoperatively predict individual postoperative pelvic alignment and mobility. The purpose of this study was to investigate the pelvic alignment and mobility before and after THA, and to develop a predictive formula using preoperative factors to calculate postoperative sagittal alignment and mobility.

METHODS

One hundred seventy patients were assessed. The 170 patients were randomly divided into a prediction model analysis group (n = 85) and an external validation group (n = 85). In the prediction model analysis group, preoperative spinopelvic parameters were used to develop the predictive formulas to predict the postoperative sacral slope (SS) in standing and sitting positions and ΔSS. These were applied to the external validation group and assessed.

RESULTS

R² in multiple linear regression models for postoperative SS in standing, SS in sitting and ΔSS were 0.810, 0.672, and 0.423, respectively. The values of predicted and postoperative parameters were very close with no significant difference: SS in standing (33.87 vs. 34.23, P = 0.834), SS in sitting (18.86 vs. 19.51, P = 0.228), and ΔSS (15.38 vs. 14.72, P = 0.619).

CONCLUSION

The present study showed that the pelvic alignment and mobility after THA can be predicted using preoperative factors. Although a model with higher accuracy is needed, it is important to use a predictive formula to estimate the postoperative condition before performing THA.

What Changes in Pelvic Sagittal Tilt Occur 20 Years After THA?

BACKGROUND

Cup orientation in THA in the supine, standing, and sitting positions is affected by pelvic sagittal tilt (PT). Patterns of PT shift between these positions may increase the risk of dislocation and edge loading. The PT has also been reported to change during the aging process; however, there is limited research regarding long-term changes in PT and PT shifts after THA.

QUESTIONS/PURPOSES

(1) What changes occur in PT in the supine, standing, and sitting positions during 20 years of follow-up after THA in patients who have not had revision or dislocation? (2) What factors are associated with the differences between preoperative supine PT and postoperative sitting or standing PT (Δ sitting and Δ standing, respectively) 20 years postoperatively?

METHODS

Between January 1998 and December 1999, 101 consecutive patients underwent THA for appropriate indications. AP radiographs of the pelvis in the supine, standing, and sitting positions preoperatively and at 1, 10, and 20 years after THA were longitudinally performed to evaluate changes in PT. Fifty-nine percent (60 of 101) of patients were lost before 20 years of follow-up or had incomplete sets of imaging tests, leaving 41% (41 of 101) eligible for analysis here. There were no patients who had recurrent dislocation or underwent revision arthroplasty in the cohort; therefore, this analysis regarding postoperative changes in PT indicates the natural course of the change in PT during follow-up of THA. PT was measured based on the anterior pelvic plane. PT shifts with positional changes, Δ standing, and Δ sitting during the follow-up period were calculated. Posterior changes and shifts are represented by negative values. To analyze the factors associated with Δ standing and Δ sitting after 20 years, the correlations between these parameters and preoperative factors (including sex, age, pelvic incidence [PI], lumbar lordosis [LL], preoperative PT, and preoperative PT shift) and postoperative factors (including the occurrence of new lumbar vertebral fractures, lumbar spondylolisthesis, contralateral THA performed during follow-up, and PI-LL 20 years after THA) were determined.

RESULTS

Median (IQR) supine and standing PTs changed (moved posteriorly) by -5° (-11° to -2°; p < 0.01) and -10° (-15° to -7°; p < 0.01), respectively. Sitting PT did not change during the 20-year follow-up period. Median (IQR) PT shift from standing to sitting changed from -34° preoperatively (-40° to -28°) to -23° after 20 years (-28° to -20°). There were posterior changes in median (range) Δ standing (median -12° at 20 years [-19° to -7°]); Δ sitting did not change during the follow-up period (median -36° at 20 years [-40° to -29°]). Patients with a large preoperative posterior PT shift from supine to standing demonstrated larger posterior tilt of Δ standing at 20 years. Patients with lumbar vertebral fractures during follow-up demonstrated larger posterior tilt of Δ standing at 20 years.

CONCLUSION

Patients who demonstrate a large preoperative posterior shift from supine to standing deserve special consideration when undergoing THA. In such circumstances, we recommend that the anteversion of the cup not be excessive, given that there is a relatively high risk of further posterior tilt in PT, which may lead to anterior dislocation and edge loading. Further longitudinal study in a larger cohort of patients with complications including postoperative dislocation and revision, as well as older patients, is needed to verify these assumptions on the potential risk for dislocation and edge loading after THA.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Pelvic position, lying on a traction table, during THA by direct anterior approach. Comparison with the standing position and influence on the acetabular cup anteversion

INTRODUCTION

The placement of prostheses for a total hip arthroplasty (THA) is essential to limit complications and optimize functional results. In a recent study of more than 100 THA placed through a direct anterior approach using a traction table, we found that the mean anteversion of the cup was greater (30°) than recommended (20°). To explain this phenomenon, we considered that the anterior pelvic plane (APP), defined by the plane passing through the anterior-superior iliac spines and the pubic symphysis, which serves as a landmark for the placement and calculation of the anteversion of the cup, was not horizontal when the patient was lying on the traction table. This concept has not been evaluated so we conducted a prospective study to: 1) measure the position of the pelvis on a traction table; 2) compare to the standing position, 3) assess its impact on the anteversion of the cup.

HYPOTHESIS

The standing pelvic version is identical to the supine pelvic version on the traction table.

MATERIAL AND METHODS

A prospective 3-month monocentric study was conducted. All patients operated on for a THA by a direct anterior approach, on a traction table, were included. The position of the pelvis was assessed by measuring the tilt of the APP on lateral pelvic X-rays, while on the traction table and while standing. The impact of the position of the pelvis on the positioning of the cup, as well as the anteversion, were measured using the EOS imaging system. The anatomic anteversion of the cup was measured in relation to the APP.

RESULTS

Fifty-eight patients were included (32 women, 26 men) with an average age of 67 years. The tilt of the supine APP was 6°±8.3 [range of -10.5 to 31.0] (indicating a retroverted pelvis on the traction table). The difference between the tilt of the standing and lying APP (within 90°) was not significant (standing was on average 4.5° [range of -11.0 to 27.0] versus lying on the table, was on average 6° [range of -10.5 to 31.0] (p=0.75). A strong correlation was observed between the tilt of the supine APP and the anatomic anteversion of the cup (p<0.001). Thus, the more retroverted the pelvis was on the traction table, the lower the anatomic anteversion of the acetabular cup.

CONCLUSION

The supine pelvis on the traction table is not always horizontal and its position on the traction table is similar to its standing position, within 90 degrees. The analysis of the positioning of the preoperative pelvis appears to be essential in the planning of a THA through direct anterior approach using a traction table.

LEVEL OF EVIDENCE

IV; Prospective Cohort Study.

The Impingement-free, Prosthesis-specific, and Anatomy-adjusted Combined Target Zone for Component Positioning in THA Depends on Design and Implantation Parameters of both Components

BACKGROUND

Lewinnek's recommendation for orienting the cup in THA is criticized because it involves a static assessment of the safe zone and because it does not consider stem geometry. A revised concept of the safe zone should consider those factors, but to our knowledge, this has not been assessed.

QUESTIONS/PURPOSES

(1) To determine the shape, size, and location of target zones for combined cup and stem orientation for a straight stem/hemispheric cup THA to maximize the impingement-free ROM and (2) To determine whether and how these implant positions change as stem anteversion, neck-shaft angle, prosthetic head size and target range of movements are varied.

METHODS

A three-dimensional computer-assisted design model, in which design geometry was expressed in terms of parameters, of a straight stem/hemispheric cup hip prosthesis was designed, its design parameters modified systematically, and each prosthesis model was implanted virtually at predefined component orientations. Functional component orientation referencing to body planes was used: cups were abducted from 20° to 70°, and anteverted from -10° to 40°. Stems were rotated from -10° to 40° anteversion, neck-shaft angles varied from 115° to 143°, and head sizes varied from 28 to 40 mm. Hip movements up to the point of prosthetic impingement were tested, including simple flexion/extension, internal/external rotation, ab/adduction, combinations of these, and activities of daily living that were known to trigger dislocation. For each combination of parameters, the impingement-free combined target zone was determined. Maximizing the size of the combined target zone was the optimization criterion.

RESULTS

The combined target zones for impingement-free cup orientation had polygonal boundaries. Their size and position in the diagram changed with stem anteversion, neck-shaft angle, head size, and target ROM. The largest target zones were at neck-shaft angles from 125° to 127°, at stem anteversions from 10° to 20°, and at radiographic cup anteversions between 17° and 25°. Cup anteversion and stem anteversion were inverse-linearly correlated supporting the combined-anteversion concept. The range of impingement-free cup inclinations depended on head size, stem anteversion, and neck-shaft angle. For a 127°-neck-shaft angle, the lowest cup inclinations that fell within the target zone were 42° for the 28-mm and 35° for the 40-mm head. Cup anteversion and combined version depended on neck-shaft angle. For head size 32-mm cup, anteversion was 6° for a 115° neck-shaft angle and 25° for a 135°-neck-shaft angle, and combined version was 15° and 34° respectively.

CONCLUSIONS

The shape, size, and location of the combined target zones were dependent on design and implantation parameters of both components. Changing the prosthesis design or changing implantation parameters also changed the combined target zone. A maximized combined target zone was found. It is mandatory to consider both components to determine the accurate impingement-free prosthetic ROM in THA.

CLINICAL RELEVANCE

This study accurately defines the hypothetical impingement-free, design-specific component orientation in THA. Transforming it into clinical precision may be the case for navigation and/or robotics, but this is speculative, and as of now, unproven.

Incidence and determinants of anteflexion impairment after rotational acetabular osteotomy

This study aimed to identify the incidence of anteflexion impairment after rotational acetabular osteotomy based on patient-reported outcome measures, and the morphological factors and postoperative bony range of motion associated with anteflexion impairment at 2 years postoperatively. We analyzed 26 patients with developmental dysplasia of the hip who underwent rotational acetabular osteotomy at our institution. Using questionnaires, we defined anteflexion impairment as difficulty in clipping toenails and pulling up and removing socks. Morphological parameters and bony range of motion measured using a postoperative three-dimensional surface model, were compared between the subjects with and without anteflexion impairment. The incidence of anteflexion impairment was 69% at 6 months, 35% at 1 year, and 12% at 2 years after rotational acetabular osteotomy. The mean bony flexion angle was smaller in subjects with impairment than in those without impairment. The mean internal rotation (IR) angle at 90° of flexion was smaller in subjects with impairment than in those without impairment. The incidence of impairment was significantly higher in subjects with both less than or equal to 105° of bony flexion and less than or equal to 20° of IR at 90° of flexion than in the remaining subjects. No significant difference was observed in postoperative femoral head coverage and preoperative morphological parameters including spinal condition between the two groups. To prevent femoroacetabular impingement after rotational acetabular osteotomy, surgeons need to reorient the acetabulum to restore postoperative bony flexion to more than or equal to 105° and/or postoperative IR range of motion to more than or equal to 20° at 90° of flexion.

Reproducibility of pelvic sagittal inclination while acquiring radiographs in supine and standing postures

PURPOSE

Pelvic position on the sagittal plane is usually evaluated with the pelvic sagittal inclination (PSI) angle from a single radiograph. However, the reproducibility of pelvic positioning has not been investigated, and thus, the validity of measuring the PSI from a single film/time point is not understood. Herein, the reproducibility of a patient's pelvic positions in supine and standing postures was analyzed.

METHODS

A total of 34 patients who underwent either a pelvic osteotomy or total hip arthroplasty were enrolled in this study. Preoperative radiographs in both supine and standing postures were acquired twice (first X-ray and second X-ray) within 6 months; preoperative computed tomography (CT) images of the full pelvis were also acquired in a supine posture (preop-CT). To eliminate measurement variability, each PSI was automatically measured from radiographs and CT images through the use of CT segmentation and landmark localization followed by intensity-based 2D-3D registration. The absolute difference of PSI among each image was calculated and the intra-class correlation coefficient (ICC) in each posture was also analyzed.

RESULTS

The median absolute differences of PSI in the supine posture were 1.3° between the first and second X-rays, 1.2° between the first X-ray and preop-CT, and 1.3° between the second X-ray and preop-CT. The median absolute difference of PSI in the standing posture was 1.5°. The ICC was 0.965 (95% CI: 0.939-0.981) in supine and 0.977 (95% CI: 0.954-0.988) during standing.

CONCLUSIONS

Pelvic positions in supine and standing postures are reproducible. Thus, measuring the PSI from a single radiograph is reliable.

The Influence of Pelvic Tilt on the Anteversion Angle of the Acetabular Prosthesis

The concept of the "safe area" of the acetabular prosthesis has a long history and has been recognized by many scholars. It is generally believed that postoperative hip dislocation rate is low, when the acetabular anteversion angle is placed in the range of 15° ± 10°. Despite this, hip dislocation is a common complication after total hip arthroplasty. In recent years, more and more scholars have paid attention to the influence of pelvic tilt on the acetabular anteversion angle. The concept of acetabular anteversion changes as the pelvic tilt changes, and is challenging the traditional acetabular prosthesis "safe area." This study summarized the potential influencing factors of pelvic tilt and discussed the influence of the phenomenon on the anteversion angle of total hip arthroplasty (THA) acetabular prosthesis based on the literature review. We conclude that from the supine position to standing, followed by sitting, the pelvis tends to move backward. Pelvic sagittal activity, lumbar disease (ankylosing spondylitis), lumbar fusion (lumbar fusion, spine-pelvic fusion), and other factors related to the tilt are THA risk factors for postoperative dislocation and revision. With the change of body position, the degree of acetabular anteversion is directly related to the degree of pelvic tilt. The acetabular anteversion varies greatly, which leads to increased hip prosthesis wear and even hip dislocation. The lateral X-ray of the spine and pelvis is recommended in supine, standing, and sitting positions before THA. In addition, the pelvic tilt should be regarded as a reference of the acetabular prosthesis in the preoperative planning of THA.

Posterior Pelvic Tilt From Supine to Standing in Patients With Symptomatic Developmental Dysplasia of the Hip

Pelvic sagittal inclination (PSI) significantly affects the femoral head coverage by the acetabulum in patients with developmental dysplasia of the hip (DDH), while no reports have quantified PSI in DDH patients in the supine and standing positions. Furthermore, little is known about how PSI changes after periacetabular osteotomies. Herein, PSI in the supine and standing positions was quantified in DDH patients preoperatively and postoperatively. Twenty-five patients with DDH who had undergone periacetabular osteotomies were analyzed. The preoperative PSI and the PSI 2 years after surgery were measured in the supine and standing positions using the image registration technique between radiographs and computed tomographic images. The percentage of patients who showed PSI changes of more than 10° from the supine to the standing position was quantified. PSI changed 8.2 ± 5.0° posteriorly from the supine to the standing position during the preoperative period. Posterior pelvic tilt of more than 10° was found in nine cases (36%). Two years after periacetabular osteotomies, the postural PSI change was 7.1 ± 3.9° posteriorly. When the preoperative and postoperative PSI values were compared, PSI in the standing position did not differ (p = 0.20). Similarly, the amount of PSI change from the supine to standing position was not significantly different (p = 0.26). In conclusion, posterior pelvic tilt in the standing position was found preoperatively in symptomatic DDH patients, and it remained for 2 years after periacetabular osteotomies. This postural change in PSI does not seem to influence the outcome of periacetabular osteotomy. However, during preoperative planning, surgeons should recognize that acetabular anteversion or anterior acetabular coverage differs between the supine and standing positions in some patients with DDH. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:578-587, 2020.

Does Acetabular Coverage Vary Between the Supine and Standing Positions in Patients with Hip Dysplasia?

BACKGROUND

Although variation in physiologic pelvic tilt may affect acetabular version and coverage, postural change in pelvic tilt in patients with hip dysplasia who are candidates for hip preservation surgery has not been well characterized, and its clinical importance is unknown.

QUESTIONS/PURPOSES

The aim of this study was to determine (1) postural changes in sagittal pelvic tilt between the supine and standing positions; (2) postural changes in the acetabular orientation and coverage of the femoral head between the supine and standing positions; and (3) patient demographic and morphologic factors associated with sagittal pelvic tilt.

METHODS

Between 2009 and 2016, 102 patients underwent pelvic osteotomy to treat hip dysplasia. All patients had supine and standing AP pelvic radiographs and pelvic CT images taken during their preoperative examination. Ninety-five patients with hip dysplasia (lateral center-edge angle < 20°) younger than 60 years old were included. Patients with advanced osteoarthritis, other hip disease, prior hip or spine surgery, femoral head deformity, or inadequate imaging were excluded. Sixty-five patients (64%) were eligible for participation in this retrospective study. Two board-certified orthopaedic surgeons (TT and MF) investigated sagittal pelvic tilt, spinopelvic parameters, and acetabular version and coverage using pelvic radiographs and CT images. Intra- and interobserver reliabilities, evaluated using the intraclass correlation coefficient (0.90 to 0.98, 0.93 to 0.99, and 0.87 to 0.96, respectively), were excellent. Demographic data (age, gender, and BMI) were collected by medical record review. Sagittal pelvic tilt was quantified as the angle formed by the anterior pelvic plane and a z-axis (anterior pelvic plane angle). Using a 2D-3D matching technique, we measured the change in sagittal pelvic tilt, acetabular version, and three-dimensional coverage between the supine and standing positions. We correlated sagittal pelvic tilt with demographic and CT measurement parameters using Pearson's or Spearman's correlation coefficients.

RESULTS

Although functional pelvic tilt varied widely among individuals, the pelvis of patients with hip dysplasia tilted posteriorly from the supine to the standing position (mean APP angle 8° ± 6° versus 2° ± 7°; mean difference -6°; 95% CI, -7° to -5°; range -17° to 4.1°; p < 0.001; paired t-test).The pelvis tilted more than 5° posteriorly from the supine to the standing position in 39 patients (60%), and the change was greater than 10° in 12 (18%). In the latter subgroup of patients, the mean acetabular anteversion angle increased (22° ± 5° versus 27° ±5°; mean difference 5°; 95% CI, 4°-6°; p < 0.001) and the mean anterosuperior acetabular sector angle notably deceased from the supine to the standing position (91° ± 11° versus 77° ± 14°; mean difference -14°; 95% CI, -17° to -11°; p < 0.001; paired t-test). Postural change in pelvic tilt was not associated with any of the studied demographic or morphologic parameters, including patient age, gender, BMI, and acetabular version and coverage.

CONCLUSIONS

On average, the pelvis tilted posteriorly from the supine to the standing position in patients with hip dysplasia, resulting in increased acetabular version and decreased anterosuperior acetabular coverage in the standing position. Thus, assessment with a supine AP pelvic radiograph may overlook changes in acetabular version and coverage in weightbearing positions. We recommend assessing postural change in sagittal pelvic tilt when diagnosing hip dysplasia and planning hip preservation surgery. Further studies are needed to determine how postural changes in sagittal pelvic tilt affect the biomechanical environment of the hip and the clinical results of acetabular reorientation osteotomy.

LEVEL OF EVIDENCE

Level IV, diagnostic study.

Influence of Spinopelvic Alignment on Pelvic Tilt after Total Hip Arthroplasty

Objective

To evaluate the impact of spinopelvic parameters and hip contracture on change in the pelvic tilt (PT) after Total hip arthroplasty (THA).

Methods

One hundred patients (15 male and 85 female) who underwent THA were included in this prospective study. Radiographic data were obtained preoperatively and 1 year after THA. Radiographic parameters included sagittal anterior pelvic plane (APP), sagittal vertical axis (SVA), sacral slope (SS), pelvic inclination (PI), and lumbar lordosis angle (LL). The APP was defined as the angle between the anterior pelvic plane and the vertical plane. A positive value indicates pelvic retroversion. Postoperative changes in PT were divided into three groups: the PA group (pelvic anteversion, ΔAPP < −5°), the PR group (pelvic retroversion, ΔAPP > 5°), and the PT group (minimal change, ΔAPP ≤ ± 5°). The Kruskal–Wallis test and the Steel–Dwass test were used to compare the preoperative and postoperative spinopelvic parameters among the three groups. The Spearman's rank correlation coefficient was used to evaluate the correlation between ΔAPP and spinopelvic parameters.

Results

Minimal change in pelvic tilt was observed in 59% of patients, while pelvic anteversion was observed in 16% of patients and pelvic retroversion was observed in 25% of patients. There were no significant changes in the spinopelvic parameters, including TK, LL, SVA, LL, SS, and APP after THA. The Femoral angle (FA) was significantly decreased after THA (P < 0.001). Preoperative APP was significantly more retroverted in the PA group than the PR group, and the PT group (6.8 ± 12.2, 0.2 ± 9.9, −8.3 ± 8.3, P < 0.001). Preoperative SS, PI‐LL, and PI were significantly smaller in the PA group than the PT group and the PR group. A significant negative correlation was identified between preoperative APP and ΔAPP (r = −0.418, P < 0.001).

Conclusion

Approximately 60% of the patients did not have any marked change in PT after THA. Preoperative APP was the only predictive factor associated with marked anterior or posterior change in PT.

Trigonometric Algorithm Defining the True Three-Dimensional Acetabular Cup Orientation: Correlation Between Measured and Calculated Cup Orientation Angles

BACKGROUND

Acetabular cup orientation plays a key role in implant stability and the success of total hip arthroplasty. To date, the orientation has been measured with different imaging modalities and definitions, leading to lack of consensus on optimal cup placement. A 3-dimensional (3D) concept involving a trigonometric description enables unambiguous definitions. Our objective was to test the validity and reliability of a 3D trigonometric description of cup orientation.

METHODS

Computed tomographic scans of the pelvis, performed for vascular assessment of 20 patients with 22 primary total hip replacements in situ, were systematically collected. On multiplanar reconstructions, 3 observers independently measured cup orientation retrospectively in terms of coronal inclination, sagittal tilt, and transverse version. The angles measured in 2 planes were used to calculate the angle in the third plane via a trigonometric algorithm. For correlation and reliability analyses, intraobserver and interobserver differences between measured and calculated angles were evaluated with use of the intraclass correlation coefficient (ICC).

RESULTS

Measured and calculated angles had ICCs of 0.953 for coronal inclination, 0.985 for sagittal tilt, and 0.982 for transverse version. Intraobserver and interobserver reliability had ICCs of 0.987 and 0.987, respectively, for coronal inclination; 0.979 and 0.981, respectively, for sagittal tilt; and 0.992 and 0.978, respectively, for transverse version.

CONCLUSIONS

The 3D concept with its trigonometric algorithm is a valid and reliable tool for the measurement of cup orientation.

CLINICAL RELEVANCE

By calculating the transverse version of cups from coronal inclination and sagittal tilt measurements, the trigonometric algorithm enables a 3D definition of cup orientation, regardless of the imaging modality used. In addition, it introduces sagittal tilt that, like pelvic tilt, rotates around the transverse axis.

Effect of Pelvic Tilt and Rotation on Cup Orientation in Both Supine and Standing Positions

BACKGROUND

The purpose of this study is to analyze the effect of pelvic tilt and rotation on radiographic measurement of cup orientation.

METHODS

A total of 68 patients (79 hips) were included in this study. The patients had a computed tomography study and approximately 3 months of postoperative standing anteroposterior pelvic radiographs in both supine and standing positions. We used 2-dimensional (2D)/3-dimensional (3D) matching to measure pelvic tilt and rotation, and cup orientation.

RESULTS

There was a wide range of pelvic tilt between individuals in both supine and standing positions. Supine pelvic tilt was different from standing pelvic tilt (P < .05). There were differences in cup anteversion before and after 2D/3D matching in both supine and standing positions (P < .05). Supine and standing pelvic tilt correlated with differences in cup anteversion before and after 2D/3D matching. When all 79 hips were separated into right and left side, pelvic rotation inversely correlated with the pelvic tilt-adjusted difference in anteversion before and after 2D/3D matching of the right side but directly correlated with that of the left side in both supine and standing positions.

CONCLUSION

This study demonstrated that the measurement of cup anteversion on anteroposterior radiographs is significantly affected by both pelvic tilt and pelvic rotation (depending on the side). Improved understanding of pelvic orientation and improved ability to measure pelvic orientation may eventually allow for desired cup positioning to potentially protect against complications associated with malposition of the cup.

Can Anatomic Measurements of Stem Anteversion Angle Be Considered as the Functional Anteversion Angle?

BACKGROUND

Stem anteversion angle is important in the combined anteversion theory to avoid implant impingement after total hip arthroplasty (THA). However, anatomic measurements of stem anteversion angle may not represent functional anteversion of the femur if the femur undergoes axial rotation. Herein, the femoral rotational angle (FRA) was measured in supine and standing positions before and after THA to evaluate the difference between anatomic and functional measurements.

METHODS

A total of 191 hips (174 patients) treated with THA for osteoarthritis were analyzed in this retrospective, case-controlled study. The FRA was measured as the angle between the posterior condylar line and the line through the bilateral anterior superior iliac spines (positive for external rotation) and was measured preoperatively and postoperatively in supine and standing positions with computed tomography segmentation and landmark localization of the pelvis and the femur followed by intensity-based 2D-3D registration. The number of cases in which the absolute FRA remained <15° in both positions was also calculated.

RESULTS

The average ± standard deviation preoperative FRA was 0.3° ± 8.3° in the supine position and -4.5° ± 8.8° during standing; the postoperative FRA was -3.8° ± 9.0° in supine and -14.3° ± 8.3° during standing. There were 134 cases (70%) in which the preoperative absolute FRA remained <15° in both positions while only 85 hips (45%) remained <15°, postoperatively.

CONCLUSION

Substantial variability was seen in the FRA, especially during the postoperative period. These results suggest that the anatomic stem anteversion angle may not represent the functional anteversion of the femur.

Change in Pelvic Sagittal Inclination From Supine to Standing Position Before Hip Arthroplasty

BACKGROUND

Cup anteversion and inclination are important for avoiding implant impingement and dislocation in total hip arthroplasty. However, functional cup anteversion and cup inclination also change as the pelvic sagittal inclination (PSI) changes. Therefore, PSI in both supine and standing positions was measured in a large cohort in this study.

METHODS

A total of 422 patients (median age, 61; range, 15-87) who underwent total hip arthroplasty were the subjects of this study. There were 83 patients with primary osteoarthritis (OA), 274 patients with developmental dysplasia-derived secondary OA, 48 patients with osteonecrosis, and 17 patients with rapidly destructive coxopathy (RDC). Preoperative PSI in supine and standing positions was measured by automated computed topography segmentation and landmark localization of the pelvis followed by intensity-based 2D-3D registration, and the number of cases in which PSI changed more than 10° posteriorly was calculated. Hip disease, sex, and age were analyzed if they were related to a PSI change of more than 10°.

RESULTS

The median PSI was 5.1° (interquartile range, 0.4°-9.4°) in supine and -1.3° (interquartile range, -6.5° to 4.2°) in standing position. There were 79 cases (19%) in which the PSI changed more than 10° posteriorly from supine to standing. Elder age and patients with primary OA and RDC were revealed to be the related factors.

CONCLUSION

PSI changed more than 10° posteriorly from supine to standing in 19% of cases. Age and diagnosis of primary OA and RDC were the significant factors for the posterior rotation.

The Evolution of Computer-Assisted Total Hip Arthroplasty and Relevant Applications

In total hip arthroplasty (THA), the accurate positioning of implants is the key to achieve a good clinical outcome. Computer-assisted orthopaedic surgery (CAOS) has been developed for more accurate positioning of implants during the THA. There are passive, semi-active, and active systems in CAOS for THA. Navigation is a passive system that only provides information and guidance to the surgeon. There are 3 types of navigation: imageless navigation, computed tomography (CT)-based navigation, and fluoroscopy-based navigation. In imageless navigation system, a new method of registration without the need to register the anterior pelvic plane was introduced. CT-based navigation can be efficiently used for pelvic plane reference, the functional pelvic plane in supine which adjusts anterior pelvic plane sagittal tilt for targeting the cup orientation. Robot-assisted system can be either active or semi-active. The active robotic system performs the preparation for implant positioning as programmed preoperatively. It has been used for only femoral implant cavity preparation. Recently, program for cup positioning was additionally developed. Alternatively, for ease of surgeon acceptance, semi-active robot systems are developed. It was initially applied only for cup positioning. However, with the development of enhanced femoral workflows, this system can now be used to position both cup and stem. Though there have been substantial advancements in computer-assisted THA, its use can still be controversial at present due to the steep learning curve, intraoperative technical issues, high cost and etc. However, in the future, CAOS will certainly enable the surgeon to operate more accurately and lead to improved outcomes in THA as the technology continues to evolve rapidly.

Does Pelvic Sagittal Inclination in the Supine and Standing Positions Change Over 10 Years of Follow-Up After Total Hip Arthroplasty?

BACKGROUND

Functional anteversion and inclination of the cup change as the pelvic sagittal inclination (PSI) changes. The purposes of this study were to investigate the chronological changes of PSI during a 10-year follow-up period after total hip arthroplasty (THA) and to report the characteristics of patients who showed a greater than 10° change in the PSI from the supine to the standing position.

METHODS

The subjects were 70 patients who were followed up for 10 years after THA. PSI values in the supine and standing positions were measured by 2D-3D matching using computed tomography images and pelvic radiographs. PSI values before THA and 1, 5, and 10 years after THA were compared in both the supine and standing positions.

RESULTS

Supine PSI showed less than 5° of change, whereas standing PSI showed a significant decrease with time over the 10-year period. Although 43% of patients with less than 10° of difference in the PSI between the supine and standing positions before THA increased PSI posteriorly (reclining) more than 10° in standing from the supine position at 10 years, no late dislocation was observed.

CONCLUSION

Supine PSI showed no significant change, but standing PSI showed a significant increase posteriorly with time over a 10-year period. However, this PSI change did not reach the level that it caused negative consequences such as late dislocation. The pelvic position in the supine position might still be a good functional reference position of the pelvis for aiming to achieve proper cup alignment at 10 years.

Functional orientation of the acetabular component in ceramic-on-ceramic total hip arthroplasty and its relevance to squeaking

Aims

Long-term clinical outcomes for ceramic-on-ceramic (CoC) bearings are encouraging. However, there is a risk of squeaking. Guidelines for the orientation of the acetabular component are defined from static imaging, but the position of the pelvis and thus the acetabular component during activities associated with edge-loading are likely to be very different from those measured when the patient is supine. We assessed the functional orientation of the acetabular component.

Patients and Methods

A total of 18 patients with reproducible squeaking in their CoC hips during deep flexion were investigated with a control group of 36 non-squeaking CoC hips. The two groups were matched for the type of implant, the orientation of the acetabular component when supine, the size of the femoral head, ligament laxity, maximum hip flexion and body mass index.

Results

The mean functional anteversion of the acetabular component at the point when patients initiated rising from a seated position was significantly less in the squeaking group than in the control group, 8.1° (-10.5° to 36.0°) and 21.1° (-1.9° to 38.4°) respectively (p = 0.002).

Conclusion

The functional orientation of the acetabular component during activities associated with posterior edge-loading are different from those measured when supine due to patient-specific pelvic kinematics. Individuals with a large anterior pelvic tilt during deep flexion might be more susceptible to posterior edge-loading and squeaking as a consequence of a significant decrease in the functional anteversion of the acetabular component. Cite this article: Bone Joint J 2016;98-B:910–16.

Late Anterior Dislocation Due to Posterior Pelvic Tilt in Total Hip Arthroplasty

Background:

Excessive pelvic tilt may be one of the factors leading to instability in total hip arthroplasty (THA), even when the acetabular cup is placed properly. To our knowledge, only a few studies have described late anterior dislocation due to posterior pelvic tilt. We present 3 cases with late anterior dislocations possibly due to posterior pelvic tilt.

Cases Presentations:

Case-1: An 84-years-old woman fell and presented with an anterior dislocation 12-years after THA. Her pelvis had tilted to approximately 30° posteriorly in a supine position. After conservative treatment, she presented with 10 recurrent anterior dislocations. She had thoracolumbar kyphosis due to multiple compression fractures. Revision with anterior placement of an elevated liner and a 32-mm head corrected the dislocation, and no further dislocations occurred.

Case-2: A 78-years-old woman fell and presented with an anterior dislocation 4-years after THA. Her posterior pelvic tilt had increased 23° due to a lumbar compression fracture. Revision by decreasing the cup anteversion was performed, but recurrent posterior dislocations occurred. Owing to her worsened general condition, further treatment was abandoned.

Case-3: A 79-years-old woman twisted her body and presented an anterior dislocation 3-years after THA. After manual reduction and conservative treatment, the dislocation recurred. Her posterior pelvic tilt had increased 16°.

Conclusion:

Although minor trauma triggered the anterior instability in these patients, the underlying pathomechanism existed in the progressive pelvic posterior tilt due to thoracolumbar kyphosis. As longer life expectancy as well as implant survivorship is predicted, attention must be paid to the change of pelvic tilt in elderly patients.

The Validity of Using the Posterior Condylar Line as a Rotational Reference for the Femur

Rotation of the femur is usually measured by the posterior condylar line (PCL). However, the functional position of the PCL has not been studied well. The angles between the PCL and the horizontal body line (HBL) were measured on preoperative computed tomographic (CT) images of 324 hips with osteoarthritis and compared with the CT images taken after hip arthroplasty. The PCL rotated 0.4° (±10.9° SD) internally from the HBL on preoperative CT images and was significantly correlated with femoral anteversion, Kellgren-Lawrence grade, and sex. On postoperative CT images, the PCL rotated 10.1° (interquartile range, 1.7°-15.5°) internally from the HBL. There was individual variance in the position of the PCL, and caution may be needed when using it as a rotational reference.

Hip range of motion during daily activities in patients with posterior pelvic tilt from supine to standing position

In most patients with hip disorders, the anterior pelvic plane (APP) sagittal tilt does not change from supine to standing position. However, in some patients, APP sagittal tilt changes more than 10° posteriorly from supine to standing position. The purpose of this study was to both examine APP sagittal tilt and investigate the hip flexion and extension range of motion (ROM) required during daily activities in these atypical patients. Patient-specific 4-dimensional (4D) motion analysis was performed for 50 hips from 44 patients who had undergone total hip arthroplasty. All patients divided into two categories, such as atypical patients for whom the pelvis tilted more than 10° posteriorly from supine to standing position preoperatively (19 hips from 18 patients) and the remaining typical patients (31 hips from 26 patients). The required hip flexion and extension angles did not differ significantly between atypical patients and typical patients. In conclusion, the hip flexion ROM during deep bending activities and hip extension ROM during extension activities required in those atypical patients with pelvic tilt more than 10° backward from supine to standing position did not shift in the direction of extension.

Risk of edge-loading and prosthesis impingement due to posterior pelvic tilting after total hip arthroplasty

BACKGROUND

Proper implant orientation is essential for avoiding edge-loading and prosthesis impingement in total hip arthroplasty. Although cup orientation is affected by a change in pelvic tilt after surgery, it has been unclear whether surgeons can prevent impingement and edge-loading by proper positioning by taking into account any change in pelvic alignment associated with alteration of hip range of motion.

METHODS

We simulated implant orientation without edge-loading and prosthesis impingement, even with a change in pelvic tilt and associated change in hip range of motion after surgery, by collision detection using implant models created with computer-aided design.

FINDINGS

If posterior pelvic tilting with a corresponding hyperextension change in hip range of motion after surgery remains within 10°, as occurs in 90% of cases, surgeons can avoid edge-loading and impingement by correctly orienting the implant, even when using a conventional prosthesis. However, if a 20° change occurs after surgery, it may be difficult to avoid those risks.

INTERPRETATION

Although edge-loading and impingement can be prevented by performing appropriate surgery in most cases, even when taking into account postoperative changes in pelvic tilt, it may also be important to pay attention to spinal conditions to ensure that pelvic tilting is not extreme because of increasing kyphosis.