Validation of a preoperative formula to estimate postoperative pelvic sagittal alignment and mobility before performing total hip arthroplasty for patients with hip osteoarthritis
Arthroplasty volume 5, Article number: 13 (2023)
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.
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.
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).
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.
In total hip arthroplasty (THA), the optimal positioning of the acetabular cup is mandatory to prevent dislocation. In 1978, Lewinnek et al. reported that the acetabular component and cup should be implanted within the “safe zone”, with a cup inclination angle of 40° ± 10° and an anteversion of 15° ± 10° . However, recent studies have reported that dislocation could occur even if the cup was positioned in the Lewinnek safe zone [2,3,4]. Abdel et al. reported that 58 % of dislocated THAs had a cup implanted within the Lewinnek safe zone .
Recent research has found that changes in the pelvic alignment consequently changed the cup angle, resulting in posture- and time-dependent alternations in spinopelvic alignment. The posture-dependent change is that the spinopelvic alignment differs between the supine, standing, and sitting positions [6,7,8,9,10,11]. In particular, the sagittal alignment of the pelvis changed about 20° from supine to standing position . The time-dependent change is that the spinopelvic alignment changes after THA [13, 14]. The pelvic inclination in the supine and standing positions is significantly more posterior at 1 year after THA compared with that before THA, and the standing pelvic inclination became significantly more posterior over a 10-year period of time .
There is a growing interest in the preoperative evaluation of spinopelvic mobility using the sitting position . In general, the pelvis tilts posteriorly from the standing to the sitting position in which the distance between acetabular and femoral side increases, which avoids impingement . However, it was reported that certain patients, even if they had not undergone previous spinal fusion surgery, had a decreased posterior tilt during postural changes from standing to sitting, potentially increasing the risk of anterior impingement . Furthermore, pelvic mobility, assessed as the change in sacral slope (SS) between the standing and sitting positions, varies widely among patients, and there existed an individual variation in the ΔSS after THA [17, 18].
Although it is important to consider the 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. Therefore, it is unclear whether pelvic alignment and mobility can be predicted using preoperative factors. The purpose of this study was to investigate the pelvic alignment and mobility before and after THA, and to develop a predictive formula by using preoperative factors to calculate the postoperative sagittal alignment and mobility.
Materials and methods
After obtaining institutional review board approval, we retrospectively reviewed the medical records of all 498 patients who had undergone primary THA at our university hospital from May 2013 to December 2017.
The study flowchart is shown in Fig. 1. The exclusion criteria were previous hip surgeries, including THA, osteotomy, and osteosynthesis on the ipsilateral side (osteotomy, n = 9; osteosynthesis, n = 6) or THA on the contralateral side (n = 86); idiopathic osteonecrosis of the femoral head (n = 50); trauma (n = 56); previous spine surgery (n = 8); ankylosing spondylitis (n = 3); rheumatoid arthritis (n = 4); bilateral surgery on the same day (n = 4); neurological or musculoskeletal disorders or diseases that might adversely affect pelvic alignment (Parkinson's disease, n = 1); operative complications such as fracture, nerve palsy, and postoperative implant loosening (femoral fracture, n = 1; femoral nerve palsy, n = 1; cup loosening, n = 1); new vertebral compression fracture during follow-up (n = 0); limitations of ordinary activity or work after THA because of moderate or severe hip pain graded in terms of the modified Harris hip score (n = 1); post-spinal tuberculosis (n = 1); unclear images (n = 5); insufficient images (n = 51); and loss to follow-up (n = 38). After eliminating patients who met the exclusion criteria, the study cohort comprised 170 patients (34 men, 136 women) with hip osteoarthritis who had undergone primary THA. These 170 patients were randomly assigned into a prediction model analysis group (n = 85) and an external validation group (n = 85).
All operations were performed via the direct anterior approach, with the patient in the supine position on a standard table with fluoroscopic control . A cementless stem was used in all cases, including the Accolade TMZF or Accolade II (Stryker Orthopaedics, Mahwah, NJ, USA) in 153 hips, Taperloc Complete Microplasty system (Zimmer Biomet, Warsaw, IN, USA) in five, meta-diaphyseal anchoring calcar-guided short-stemmed Optimys (Mathys Ltd., Bettlach, Switzerland) in eight, TwinSys femoral stem (Mathys Ltd.) in two, and Modulus System (Lima Corporate San Daniele Del Friuli, Udine, Italy) in two. A cementless cup was used in 166 patients; the Trident cup (Stryker Orthopaedics) was used in 157 hips (modular dual mobility cup in 54 hips), G7 cup and G7 dual mobility system (Zimmer Biomet) were used in five, and a Kerboull-type acetabular reinforcement device with X3 Rim Fit (Stryker Orthopaedics) was used in four. Postoperatively, all patients followed the same rehabilitation protocol and walking exercise with full weight-bearing began on postoperative day 1.
Sagittal spinopelvic alignment was assessed on standing lateral radiographs of the full spine, including the pelvis and femoral heads . The radiographs were obtained on a vertical film, with a fixed distance (200 cm) between the subject and the radiographic source. Radiographic data were collected in accordance with a strict protocol. Each subject was instructed to adopt a comfortable standing position, with the fingers resting on the clavicles. This position has been described as reproducible and reliable [21, 22]. Computerized picture archiving and communication system technology (SYNAPSE; Fuji Film, Tokyo, Japan) was used.
The following sagittal radiographic variables were measured (Fig. 2).
▪ Thoracic kyphosis angle (TK): the angle between lines drawn along the inferior endplate of T12 and the superior endplate of T4. Lordosis was expressed as a negative value, while kyphosis was presented as a positive value.
▪ Lumbar lordosis angle (LL): the angle between lines drawn along the superior endplates of L1 and S1. Lordosis was expressed as a positive value, while kyphosis was given as a negative value.
▪ Pelvic tilt (PT): the angle between the vertical plane and the line joining the middle of the upper endplate of S1 with the bicoxofemoral axis. PT is a positional parameter.
▪ Pelvic incidence: the angle between the line perpendicular to the middle of the superior endplate of S1 and the line joining this point to the bicoxofemoral axis. Pelvic incidence is a morphological parameter that is not affected by posture or pelvic position [12, 23, 24].
▪ SS: the angle between the horizontal plane and the upper endplate of S1. SS is a positional parameter that varies in accordance with pelvic position.
Spine and contralateral hip disease
The following spine and contralateral hip diseases were evaluated.
▪ Spondylolisthesis: a slip of > 5 mm between two adjacent vertebrae on the lateral radiograph .
▪ Vertebral compression fracture: the presence of wedge, biconcave, or compression deformities .
▪ Lumbar scoliosis: the Cobb angle of > 10°.
The parameters were measured a few days before THA (preoperative period) and more than 3 months after surgery (postoperative period), when the patients had achieved normal gait and kinematics .
The Mann-Whitney U test was used to compare continuous variables between two groups, while the Chi-squared test was used to compare dichotomous variables. Before conducting the multivariate analysis, Spearman's rank correlation coefficient was calculated to evaluate the relationships between variables.
In the prediction model analysis group, multiple regression analysis was performed using the stepwise method, with each postoperative factor (postoperative SS in standing, postoperative SS in sitting, and postoperative ΔSS) as the dependent variable and each preoperative factor as the independent variable. This was used to develop predictive formulas that were applied to the external validation group. The predicted values in the external validation group were compared with the actual postoperative values of each parameter in the same group. Data were statistically analyzed using IBM SPSS Statistics for Macintosh, version 22.0 (IBM Corp., Armonk, NY, USA).
Multiple linear regression analysis
The Spearman rank correlation analysis revealed strong relationships between preoperative SS in standing and preoperative LL in standing, preoperative SS in sitting and preoperative LL in sitting, and preoperative TK in standing and preoperative TK in sitting (r > 8). Thus, preoperative LL in standing, preoperative LL in sitting, and preoperative TK in sitting were excluded from the multivariate analysis.
The dependent variables were the postoperative SS in standing, SS in sitting, and ΔSS. The independent variables were BMI, age, sex, pelvic incidence, preoperative SS in standing, preoperative SS in sitting, preoperative TK in standing, and the presence or absence of spondylolisthesis, vertebral compression fracture, lumbar scoliosis, and osteoarthritis in the contralateral hip. These parameters were employed to develop the following equations to predict each postoperative parameter (Table 3).
Postoperative SS in standing = 14.836 + preoperative SS in standing × 0.764 + preoperative SS in sitting × 0.123 – age × 0.154 (R2 = 0.810).
Postoperative SS in sitting = -0.703 + preoperative SS in standing × 0.335 + preoperative SS in sitting × 0.612 – the presence of contralateral hip osteoarthritis × 4.729 (R2 = 0.672).
Postoperative ΔSS = 6.253 + preoperative SS in standing × 0.439 − preoperative SS in sitting × 0.491 + the presence of contralateral hip osteoarthritis × 5.639 – the presence of scoliosis × 4.548 (R2 = 0.423).
The values of predicted and postoperative parameters were very close with no significant difference. The SS in standing (33.87 vs. 34.23, P = 0.834), the SS in sitting (18.86 vs. 19.51, P = 0.228), and ΔSS (15.38 vs. 14.72, P = 0.619) (Table 4).
The match rates within the targeted error ranges between the predicted and measured postoperative values are shown in Table 5.
Dislocation after THA sometimes occurs even if the acetabular cup is implanted in the optimal position [2,3,4,5, 31, 32]. This is thought to result from the cup alignment alterations with postural changes from sitting to standing and over time after THA. Moreover, the ΔSS after THA (as a measure of pelvic mobility) varies widely between individuals . Therefore, there is a need to predict postoperative spinopelvic alignment and mobility after THA. In the present study, we created formulas to predict the postoperative spinopelvic parameters and revealed that the predicted values calculated using preoperative parameters were close to the postoperative values.
We believe that it is important to evaluate not only preoperative pelvic mobility using spinopelvic parameters in standing and sitting positions but also the spinal alignment and condition of the contralateral hip before THA, and to predict the postoperative pelvic mobility using these parameters. The present results showed that pelvic mobility significantly decreased after THA. In the prediction formula, the ΔSS of patients with hip osteoarthritis on the contralateral side increased after THA. This might be caused by decreased hip motion and increased pelvic motion due to pain and/or stiffness of the contralateral hip. Similar findings have been reported previously, and it is believed that patients restricted their hip motion because of pain and stiffness and compensated for this by increasing their pelvic motion before THA. After THA, these hip limitations are improved and the compensatory pelvic motion decreases [6, 17]. In addition, the ΔSS of patients with scoliosis reportedly decreased after THA because patients with scoliosis had minimal spinal motion, sacroiliac joint degeneration, and remaining low pelvic mobility after THA . These previous findings support the present results. In a similar study, Watanabe et al. reported that lower pelvic mobility and lumbar alignment were preoperative factors for low postoperative mobility .
Upon predicting the postoperative alignment and mobility before THA, the cup positioning and implant selection should be considered. In particular, it is important to identify patients with flexed or extended pelvic alignment in standing positions with low pelvic mobility. Patients with flexed pelvic alignment with low pelvic mobility (e.g., after spinal fusion) may be at increased risk of anterior hip impingement in the sitting position and posterior dislocation. Therefore, the placement of the cup in low anteversion should be avoided [33, 34]. In contrast, patients with extended pelvic alignment with low pelvic mobility might be at increased risk of posterior hip impingement in the standing position and anterior dislocation. Hence, placement of the cup in high anteversion should be avoided. In both cases, a dual mobility cup or a large femoral head might be suitable [33, 34].
Although the present study created predictive formulas with a certain degree of validity, more accurate predictive formulas should be established in the future because the R2 values in the formulas to predict the postoperative SS in sitting and ΔSS were not sufficiently high compared with the formula to predict the postoperative SS in standing. This suggests that the prediction of the SS in a sitting position is affected by further unidentified parameters. There are two reasons for the relatively lower R2 values for the SS in sitting and ΔSS. First, although the patients placed their fingers on their clavicles in both the sitting and standing positions, the sitting posture might have varied widely among individuals. We assume that the sitting posture might be influenced by pain in the contralateral hip and spinal disease. Second, the present study used standard radiography rather than the EOS system. The visualization of the spinopelvic bones in the sitting position was relatively difficult compared with the standing position. Further understanding of the sitting position and better image evaluation are needed in future research [11, 35].
The present study has several limitations. First, the follow-up period ranged from 3 to 24 months. It may be too early to evaluate hip function at 3 months after THA, as the functional component of the Harris hip score tends to plateau at 12 weeks after THA via the direct anterior approach . However, Ishida et al. reported that the PT changed most markedly within the first 3 months and then continued changing slowly until 1 year after THA . Therefore, although further long-term studies are also needed, we believe that our follow-up period was appropriate. Second, we did not assess hip pain or range of motion. As the disease progresses and hip osteoarthritis becomes more severe, worsening of the contracture reportedly further impairs the ability of the pelvis to rotate posteriorly . Third, we did not evaluate the patients’ spinal symptoms, which might influence the pelvic parameters. Although spinal symptoms are considered to exert only a small influence on pelvic parameters, further research is needed to verify this. Lastly, the exclusion criteria in this study were too strict, thereby the result is limited to specific patients. However, variations in patients’ conditions may or may not influence spinopelvic alignment and mobility. We aimed to analyze general patients without those variations. Further extended analysis with various patients must be performed in the future.
The present study showed that pelvic alignment and mobility after THA can be predicted using preoperative factors for patients with hip osteoarthritis. However, a model with higher accuracy is needed. It is important to use a predictive formula to estimate the postoperative condition before performing THA.
Availability of data and materials
Data are available within the article.
Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978;60(2):217–20.
Danoff JR, Bobman JT, Cunn G, Murtaugh T, Gorroochurn P, Geller JA, et al. Redefining the acetabular component safe zone for posterior approach total hip arthroplasty. J Arthroplasty. 2016;31(2):506–11.
Reina N, Putman S, Desmarchelier R, Sari Ali E, Chiron P, Ollivier M, et al. Can a target zone safer than Lewinnek’s safe zone be defined to prevent instability of total hip arthroplasties? Case-control study of 56 dislocated THA and 93 matched controls. Orthop Traumatol Surg Res. 2017;103(5):657–61.
Seagrave KG, Troelsen A, Malchau H, Husted H, Gromov K. Acetabular cup position and risk of dislocation in primary total hip arthroplasty. Acta Orthop. 2017;88(1):10–7.
Abdel MP, von Roth P, Jennings MT, Hanssen AD, Pagnano MW. What safe zone? The vast majority of dislocated THAs are within the lewinnek safe zone for acetabular component position. Clin Orthop Relat Res. 2016;474(2):386–91.
Berliner JL, Esposito CI, Miller TT, Padgett DE, Mayman DJ, Jerabek SA. What preoperative factors predict postoperative sitting pelvic position one year following total hip arthroplasty? Bone Joint J. 2018;100-B(10):1289–96.
Lum ZC, Coury JG, Cohen JL, Dorr LD. The Current Knowledge on Spinopelvic Mobility. J Arthroplasty. 2018;33(1):291–6.
Kim Y, Pour AE, Lazennec JY. How do global sagittal alignment and posture change after total hip arthroplasty? Int Orthop. 2020;44(2):267–73.
Stephens A, Munir S, Shah S, Walter WL. The kinematic relationship between sitting and standing posture and pelvic inclination and its significance to cup positioning in total hip arthroplasty. Int Orthop. 2015;39(3):383–8.
Tamura S, Takao M, Sakai T, Nishii T, Sugano N. Spinal factors influencing change in pelvic sagittal inclination from supine position to standing position in patients before total hip arthroplasty. J Arthroplasty. 2014;29(12):2294–7.
Lazennec JY, Rousseau MA, Rangel A, Gorin M, Belicourt C, Brusson A, et al. Pelvis and total hip arthroplasty acetabular component orientations in sitting and standing positions: measurements reproductibility with EOS imaging system versus conventional radiographies. Orthop Traumatol Surg Res. 2011;97(4):373–80.
Ochi H, Baba T, Homma Y, Matsumoto M, Nojiri H, Kaneko K. Importance of the spinopelvic factors on the pelvic inclination from standing to sitting before total hip arthroplasty. Eur Spine J. 2016;25(11):3699–706.
Tamura S, Nishihara S, Takao M, Sakai T, Miki H, Sugano N. Does pelvic sagittal inclination in the supine and standing positions change over 10 years of follow-up after total hip arthroplasty? J Arthroplasty. 2017;32(3):877–82.
Taki N, Mitsugi N, Mochida Y, Akamatsu Y, Saito T. Change in pelvic tilt angle 2 to 4 years after total hip arthroplasty. J Arthroplasty. 2012;27(6):940–4.
Ransone M, Fehring K, Fehring T. Standardization of lateral pelvic radiograph is necessary to predict spinopelvic mobility accurately. Bone Joint J. 2020;102-B(7_Supple_B):41–6.
Wyatt MC, Kunutsor SK, Beswick AD, Whitehouse MR, Kieser DC. Outcomes following primary total hip arthroplasty with pre-existing spinal fusion surgery. Bone Joint J. 2020;102-B(6):664–70.
Homma Y, Ishii S, Yanagisawa N, Ochi H, Baba T, Nojiri H, et al. Pelvic mobility before and after total hip arthroplasty. Int Orthop. 2020;44(11):2267–74.
Watanabe S, Choe H, Kobayashi N, Ike H, Kobayashi D, Inaba Y. Prediction of pelvic mobility using whole-spinal and pelvic alignment in standing and sitting position in total hip arthroplasty patients. J Orthop Surg (Hong Kong). 2021;29(2):23094990211019099.
Kobayashi H, Homma Y, Baba T, Ochi H, Matsumoto M, Yuasa T, et al. Surgeons changing the approach for total hip arthroplasty from posterior to direct anterior with fluoroscopy should consider potential excessive cup anteversion and flexion implantation of the stem in their early experience. Int Orthop. 2016;40(9):1813–9.
Jean L. Influence of age and sagittal balance of the spine on the value of the pelvic incidence. Eur Spine J. 2014;23(7):1394–9.
Aota Y, Saito T, Uesugi M, Ishida K, Shinoda K, Mizuma K. Does the fists-on-clavicles position represent a functional standing position? Spine (Phila Pa 1976). 2009;34(8):808–12.
Marks M, Stanford C, Newton P. Which lateral radiographic positioning technique provides the most reliable and functional representation of a patient's sagittal balance? Spine (Phila Pa 1976). 2009;34(9):949–54.
Boulay C, Tardieu C, Hecquet J, Benaim C, Mouilleseaux B, Marty C, et al. Sagittal alignment of spine and pelvis regulated by pelvic incidence: standard values and prediction of lordosis. Eur Spine J. 2006;15(4):415–22.
Roussouly P, Pinheiro-Franco JL. Biomechanical analysis of the spino-pelvic organization and adaptation in pathology. Eur Spine J. 2011;20(Suppl 5):609–18.
Rousseau MA, Lazennec JY, Boyer P, Mora N, Gorin M, Catonne Y. Optimization of total hip arthroplasty implantation: is the anterior pelvic plane concept valid? J Arthroplasty. 2009;24(1):22–6.
Hong JY, Suh SW, Modi HN, Hur CY, Song HR, Park JH. The prevalence and radiological findings in 1347 elderly patients with scoliosis. J Bone Joint Surg Br. 2010;92(7):980–3.
Eastell R, Cedel SL, Wahner HW, Riggs BL, Melton LJ 3rd. Classification of vertebral fractures. J Bone Miner Res. 1991;6(3):207–15.
Valera M, Ibanez N, Sancho R, Tey M. Reliability of Tonnis classification in early hip arthritis: a useless reference for hip-preserving surgery. Arch Orthop Trauma Surg. 2016;136(1):27–33.
Tonnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am. 1999;81(12):1747–70.
Radcliff KE, Orozco F, Molby N, Delasotta L, Chen E, Post Z, et al. Change in spinal alignment after total hip arthroplasty. Orthop Surg. 2013;5(4):261–5.
Heckmann N, McKnight B, Stefl M, Trasolini NA, Ike H, Dorr LD. Late dislocation following total hip arthroplasty: spinopelvic imbalance as a causative factor. J Bone Joint Surg Am. 2018;100(21):1845–53.
Buckland AJ, Puvanesarajah V, Vigdorchik J, Schwarzkopf R, Jain A, Klineberg EO, et al. Dislocation of a primary total hip arthroplasty is more common in patients with a lumbar spinal fusion. Bone Joint J. 2017;99-B(5):585–91.
Stefl M, Lundergan W, Heckmann N, McKnight B, Ike H, Murgai R, et al. Spinopelvic mobility and acetabular component position for total hip arthroplasty. Bone Joint J. 2017;99-B(1 Supple A):37–45.
Ike H, Dorr LD, Trasolini N, Stefl M, McKnight B, Heckmann N. Spine-pelvis-hip relationship in the functioning of a total hip replacement. J Bone Joint Surg Am. 2018;100(18):1606–15.
Bittersohl B, Freitas J, Zaps D, Schmitz MR, Bomar JD, Muhamad AR, et al. EOS imaging of the human pelvis: reliability, validity, and controlled comparison with radiography. J Bone Joint Surg Am. 2013;95(9):e58.
Barrett WP, Turner SE, Leopold JP. Prospective randomized study of direct anterior vs postero-lateral approach for total hip arthroplasty. J Arthroplasty. 2013;28(9):1634–8.
Ishida T, Inaba Y, Kobayashi N, Iwamoto N, Yukizawa Y, Choe H, et al. Changes in pelvic tilt following total hip arthroplasty. J Orthop Sci. 2011;16(6):682–8.
We thank to Dr. Hidetoshi Nojiri and Dr. Takatoshi Okuda for their valuable advice.
Ethics approval and consent to participate
This study was approved by the institutional Ethical Review Board.
Consent for publication
All authors of this paper have read and approved the final version submitted.
We declare the authors have no conflict of interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Tanabe, H., Homma, Y., Yanagisawa, N. et al. Validation of a preoperative formula to estimate postoperative pelvic sagittal alignment and mobility before performing total hip arthroplasty for patients with hip osteoarthritis. Arthroplasty 5, 13 (2023). https://doi.org/10.1186/s42836-023-00171-w