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Spinopelvic Relationship and Its Impact on Total Hip Arthroplasty

Open AccessPublished:August 19, 2022DOI:https://doi.org/10.1016/j.artd.2022.07.001

      Abstract

      The dynamic, complex interaction among the spine, pelvis, and hip is often underappreciated, yet understanding it is vital for both arthroplasty and spinal surgeons. There is an increasing incidence of degenerative hip and spinal pathologies as a result of the ageing population. Furthermore, hip pathology can cause spine pathology and vice versa through “hip-spine” and “spine-hip syndrome.” Consequently, total hip arthroplasty (THA) and spinal fusion surgery, which both affect spinopelvic mobility, are also on the rise. Alteration in spinopelvic motion can affect the orientation of the acetabulum and, therefore, implant positioning in THA, leading to complications such as dislocation, impingement, aseptic loosening, and wear of components. This makes it imperative to assess spinopelvic motion and pelvic tilt prior to patients undergoing THA. In this paper, we explore how the surgeon should proceed to reduce risk of component malalignment, as well as the role of navigation systems in acetabular cup positioning.

      Keywords

      Introduction

      Upright posture and bipedal gait put considerable and unique demands on the human body [
      • Been E.
      • Gomez-Olivencia A.
      • Shefi S.
      • Soudack M.
      • Bastir M.
      • Barash A.
      Evolution of spinopelvic alignment in hominins.
      ]. The spine and pelvis work together in “biomechanical concert,” an effect often underappreciated by clinicians [
      • Lum Z.
      • Coury J.
      • Cohen J.
      • Dorr L.
      The current knowledge on spinopelvic mobility.
      ]. When moving from a standing to a sitting position, the pelvis, spine, and hip change their relative position to allow movement of the femur and hip flexion while maintaining the line of gravity close to the acetabulum’s centre. The majority of movement (∼75%) occurs at the hip, but there is also tilting of the pelvis (also known as pelvic tilt [PT]) and flexion of the lumbar spine [
      • Innmann M.
      • Merle C.
      • Gotterbaum T.
      • Ewerbeck V.
      • Beaulé P.E.
      • Grammatopoulos G.
      Can spinopelvic mobility be predicted in patients awaiting total hip arthroplasty? A prospective, diagnostic study of patients with end-stage hip osteoarthritis.
      ]. PT being defined as the rotation of the pelvis around the horizontal axis (coronal plane).
      Both hip and spinal pathologies reduce range of movement, which in turn impacts the movement occurring at the spinopelvic junction. In these cases, the spine and hip do not work in harmony and cause excessive and/or abnormal movement. Due to the altered biomechanics, spine pathology can lead to hip pathology and vice versa. This is termed “spine-hip syndrome” when the spine has the initial pathology, or “hip-spine syndrome” if it is the hip. Either can lead to persistent symptoms and higher complication rates after a surgical intervention to treat them [
      • Salib C.
      • Reina N.
      • Perry K.
      • Tauton M.J.
      • Berry D.J.
      • Abdel M.P.
      Lumbar fusion involving the sacrum increases dislocation risk in primary total hip arthroplasty.
      ,
      • Huang G.
      • Zhao G.
      • Chen K.
      • Wei Y.
      • Wang S.
      • Xia J.
      How much does lumbar fusion change sagittal pelvic tilt in individuals receiving total hip arthroplasty.
      ].
      US data show that 2% of all primary total hip arthroplasty (THA) patients will have had lumbar spinal fusion (LSF) prior to THA [
      • Malkani A.
      • Himschoot K.
      • Ong K.
      • Lau E.
      • Baykal D.
      • Dimar J.
      • et al.
      Does timing of primary total hip arthroplasty prior to or after lumbar spine fusion have an effect on dislocation and revision rates?.
      ]. History of spinal fusion has been identified as the strongest predictor of dislocation in the first 6 months after surgery [
      • Gausden E.
      • Parhar H.
      • Popper J.
      • Sculco P.
      • Rush B.
      Risk factors for early dislocation following primary elective total hip arthroplasty.
      ]. This has been linked to the aforementioned adjustments in movements at the spinopelvic junction causing alterations to PT in these patients. Seventy percent of revision THAs for dislocation and 87.5% of late dislocations can be linked to spinopelvic imbalance [
      • Lum Z.
      • Coury J.
      • Cohen J.
      • Dorr L.
      The current knowledge on spinopelvic mobility.
      ].
      Mechanical complications of THA such as impingement, dislocation, aseptic loosening, and wear result from component malpositioning. Optimal intraoperative component orientation requires a detailed assessment of the spinopelvic relationship, as the true pelvic position cannot accurately be determined intraoperatively by the naked eye. Computer navigation can be helpful yet needs to take into account the functional cup position rather than just the anatomical and intraoperative positions. These systems provide the surgeon with real-time feedback to allow for a more-precise cup position; however, at present, their costs are still unproven [
      • Babisch J.W.
      • Layher F.
      • Amiot L.P.
      The rationale for tilt-adjusted acetabular cup navigation.
      ].
      This paper aims to provide a synopsis of the current understanding of the spinopelvic relationship and its impact on PT with reference to THA, as well as to identify methods to reduce risk of component malalignment.

      What is the impact of changing body position?

      PT changes with body position even in healthy individuals [
      • Lum Z.
      • Coury J.
      • Cohen J.
      • Dorr L.
      The current knowledge on spinopelvic mobility.
      ]. In the standing position, there is an anterior PT. This, when combined with physiological lumbar lordosis, allows the acetabulum to position itself to cover the femoral head, permitting the hip extension needed for mobilizing. However, when transitioning to the sitting position, the pelvis tilts posteriorly (∼20°) anteverting the acetabulum (by 15° to 20°). This transition allows hip flexion without anterior impingement or posterior dislocation, resulting in a more-efficient movement of the femur [
      • Babisch J.W.
      • Layher F.
      • Amiot L.P.
      The rationale for tilt-adjusted acetabular cup navigation.
      ].

      Other factors contributing to PT

      Greater anterior PT and acetabular anteversion have been demonstrated in women than in men [
      • McKeon J.
      • Hertel J.
      Sex differences and representative values for 6 lower extremity alignment measures.
      ,
      • Hertel J.
      • Dorfman J.H.
      • Braham R.A.
      Lower extremity malalignments and anterior cruciate ligament injury history.
      ,
      • Zahn R.K.
      • Grotjohann S.
      • Ramm H.
      • Zachow S.
      • Putzier M.
      • Perka C.
      • et al.
      Pelvic tilt compensates for increased acetabular anteversion.
      ]. With increasing age, posterior PT increases. Ageing is linked to disc dehydration and reduced lumbar lordosis, which in turn causes pelvic retroversion. Hip extension becomes increasingly pronounced, leading to compensatory posterior PT [
      • Sing D.
      • Barry J.
      • Aguilar T.
      • Theologis A.
      • Patterson J.
      • Tay B.
      • et al.
      Prior lumbar spinal arthrodesis increases risk of prosthetic-related complication in total hip arthroplasty.
      ]. Pregnancy leads to an increased anterior PT, particularly during weeks 12-36; postpartum, the pelvis begins to return to prepregnancy configuration, but currently no evidence exists about how long this persists [
      • Morino S.
      • Ishihara M.
      • Umekazi F.
      Pelvic alignment changes during the perinatal period.
      ].

      Impact of hip and spinal pathology on spinopelvic movement and PT

      The Bordeaux classification attempts to classify abnormalities of the spino-hip relationship with 2 terms, “spine-hip syndrome” and “hip-spine syndrome”, depending on the joint where the abnormality originates, hip or spine [
      • Rivière C.
      • Lazic S.
      • Dagneaux L.
      • Van Der Straeten C.
      • Cobb J.
      • Muirhead-Allwood S.
      Spine-hip relations in patients with hip osteoarthritis.
      ].

      Spine-hip syndrome

      When standing, patients with flat backs were more posteriorly tilted than “balanced” patients [
      • Buckland A.J.
      • Ayers E.W.
      • Shimmin A.J.
      • Bare J.V.
      • McMahon S.J.
      • Vigdorchik J.
      Prevalence of sagittal spine deformity among patients undergoing total hip arthroplasty.
      ]. Greater flat-back deformities correlated with a significantly higher anterior PT change when patients change stance. Scoliosis leads to a compensatory alteration in PT, with a posterior PT recorded in the standing position [
      • Guo J.
      • Liu Z.
      • Lv F.
      • Zhu Z.
      • Qian B.
      • Zhang X.
      • et al.
      Pelvic tilt and trunk inclincation: new predicative factors in curve progression during the Milwaukee bracing for adolescent idiopathic scoliosis.
      ]. Lumbar degenerative disease has been linked with a posterior PT while standing but a more-anterior PT when sitting [
      • Esposito C.
      • Miller T.
      • Kim H.
      • Barlow B.
      • Wright T.
      • Padgett D.
      • et al.
      Does degenerative lumbar spine disease influence femoroacetabular flexion in patients undergoing total hip arthroplasty.
      ]. This is a result of an altered sitting mechanism in spinal pathology cases with spinal flexion substituted for hip flexion. Lumbo-sacral fractures may also change the PT, even when healed [
      • Boyoud-Garnier L.
      • Boudissa M.
      • Ruatti S.
      • Kerschbaumer G.
      • Grobost P.
      • Tonetti J.
      Chronic low back pain after lumbosacral fracture due to sagittal and frontal vertebral imbalance.
      ]. Spinopelvic motion has been categorized into 4 different types depending on lumbar spine pathology by Phan et al. [
      • Phan D.
      • Bederman S.
      • Schwarzkopf R.
      The influence of sagittal spinal deformity on anteversion of the acetabular component in total hip arthroplasty.
      ] (Table 1). Flexibility looks at the lumbar spine, whereas balance uses a C7 plumb line [
      • Phan D.
      • Bederman S.
      • Schwarzkopf R.
      The influence of sagittal spinal deformity on anteversion of the acetabular component in total hip arthroplasty.
      ].
      Table 1Phan classification of spinopelvic motion.
      ClassificationFound in
      Balanced and flexibleHealthy population
      Balanced and stiffLumbar degenerative disease, prior LSF
      Unbalanced and flexiblePost-laminectomy, neuromuscular kyphosis
      Unbalanced and stiffLong LSF, ankylosing spondylitis

      Hip-spine syndrome

      Acetabular dysplasia is a common cause of hip-spine syndrome. These patients have an anterior acetabular coverage defect resulting in anterior PT to avoid “edge-loading” [
      • Okuzu Y.
      • Goto K.
      • Okutani Y.
      • Kuroda Y.
      • Kawai T.
      • Matsuda S.
      Hip-spine syndrome: acetabular anteversion angle is associated with anterior pelvic tilt and lumbar hyperlordosis in patients with acetabular dysplasia.
      ,
      • Hozumi A.
      • Kobayashi K.
      • Tsuru N.
      • Miyamoto C.
      • Maeda J.
      • Chiba K.
      • et al.
      Total hip arthroplasty using the S-ROM-A prosthesis for anatomically difficult Asian patients.
      ]. Primary hip osteoarthritis is an important cause of hip-spine syndrome. Osteophytes and capsule contracture lead to reduced hip mobility and flexibility [
      • McKeon J.
      • Hertel J.
      Sex differences and representative values for 6 lower extremity alignment measures.
      ]. This leads to increased lumbar lordosis, a greater role for the spine when transitioning position, and an anterior PT [
      • Tateuchi H.
      Gait- and postural-alignment-related prognostic factors for hip and knee osteoarthritis: toward the prevention of osteoarthritis.
      ]. Hip osteoarthritis has also been shown to lead a substantially greater change in PT when transitioning from standing to walking [
      • Sultan A.
      • Khlopas A.
      • Udo-Inyang I.
      • Chugtai M.
      • Sodhi N.
      • lamaj S.
      • et al.
      Hip osteoarthrtiis patients demonstrated marked dynamic changes and variability in pelvic tilt, obliquity, and rotation: a comparative, gait-analysis study.
      ].

      Impact of THA on PT

      Several studies demonstrate no change between preoperative and postoperative PT [
      • Eilander W.
      • Harris S.J.
      • Jenkus H.E.
      • Cobb J.P.
      • Hogervorst T.
      Functional acetabular component position with supine total hip replacement.
      ,
      • Maratt J.
      • Esposito C.
      • McLawhorn A.
      • Jerabek S.
      • Padgett D.
      • Mayman D.
      Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter?.
      ]. Kanto et al. found that ∼60% of patients had no change at 1 year following THA, with over 81% having <10° change [
      • Kanto M.
      • Maruo K.
      • Tachibana T.
      • Fukunishi S.
      • Nishio S.
      • Takeda Y.
      • et al.
      Influence of spinopelivc alignmnet on pelvic tilt after total hip arthroplasty.
      ]. Pelvic retroversion was more common than anteversion (25% vs 16%, respectively) although this was not statistically significant. Preoperative altered PT was the only predictive factor associated with a marked change in postoperative PT. Anterior PT preoperatively had a significant postoperative posterior PT, and vice versa [
      • Blondel B.
      • Parratte S.
      • Tropiano P.
      • Pauly V.
      • Aubaniac J.
      • Argenson J.
      Pelvic tilt measurements before and after total hip arthroplasty.
      ]. However, this is not always the finding. Ishida et al. observed PT change in patients with pre-existing anterior PT, but not for those with a posterior PT [
      • Ishida T.
      • Inaba Y.
      • Kobayashi N.
      • Iwamoto N.
      • Yukizawa Y.
      • Choe H.
      • et al.
      Changes in pelvic tilt following total hip arthroplasty.
      ]. But postoperative changes were heavily influenced by age, with younger patients having largely posterior changes and older patients tending to have anterior changes [
      • Kanto M.
      • Maruo K.
      • Tachibana T.
      • Fukunishi S.
      • Nishio S.
      • Takeda Y.
      • et al.
      Influence of spinopelivc alignmnet on pelvic tilt after total hip arthroplasty.
      ].
      Taki et al. reported a significant difference in both standing and sitting PT postoperatively at yearly intervals (1-4), with PT changing at all the recorded time sessions [
      • Taki N.
      • Mitsugi N.
      • Mochida Y.
      • Akamatsu Y.
      • Saito T.
      Change in pelvic tilt angle 2 to 4 years after total hip arthroplasty.
      ]. Age, female gender, and alteration in PT prior to operation were found to be the greater contributors to postoperative changes [
      • Ishida T.
      • Inaba Y.
      • Kobayashi N.
      • Iwamoto N.
      • Yukizawa Y.
      • Choe H.
      • et al.
      Changes in pelvic tilt following total hip arthroplasty.
      ].

      Impact of LSF on PT

      Matsumoto et al. assessed PT in patients after lumbar fusion for scoliosis and found that 73% with reduced lumbar lordosis displayed an increased posterior PT [
      • Taki N.
      • Mitsugi N.
      • Mochida Y.
      • Akamatsu Y.
      • Saito T.
      Change in pelvic tilt angle 2 to 4 years after total hip arthroplasty.
      ,
      • Matsumoto H.
      • Nicholas D.
      • Schwab F.
      • Lafage V.
      • Sheha E.
      • Roye D.
      • et al.
      Unintended change of physiological lumbar lordosis and pelvic tilt after posterior spinal instrumentation and fusion for adolescent idiopathic scoliosis: how much is too much.
      ]. Longer spinal fusions and spinopelvic fusions can alter the sacral slope during postural transitioning, with a decrease of 0.9° anteversion for each additional level of spinal fusion. Nam et al. found that patients with a history of lumbar or lumbosacral fusion had a more posterior PT in the standing position but a more anterior PT in the seated position, thereby implying a lack of compensatory PT when shifting position [
      • Matsumoto H.
      • Nicholas D.
      • Schwab F.
      • Lafage V.
      • Sheha E.
      • Roye D.
      • et al.
      Unintended change of physiological lumbar lordosis and pelvic tilt after posterior spinal instrumentation and fusion for adolescent idiopathic scoliosis: how much is too much.
      ].

      Impact of LSF on THA

      Two meta-analyses have been performed looking at THA and LSF outcomes. An et al. found LSF to be a significant risk factor for increased dislocation rates (relative risk 2.03; P < .00001) and need for revision (relative risk 3.36; P = .006) [
      • An V.V.G.
      • Phan K.
      • Sivakumar B.S.
      • Mobbs R.
      • Bruce W.
      Prior lumbar spinal fusion is associated with an increased risk of dislocation and revision in total hip arthroplasty: a meta-analysis.
      ]. Patient-reported outcomes were also worse in these patients. However, a meta-analysis for this could not be performed due to nonhomogeneity [
      • An V.V.G.
      • Phan K.
      • Sivakumar B.S.
      • Mobbs R.
      • Bruce W.
      Prior lumbar spinal fusion is associated with an increased risk of dislocation and revision in total hip arthroplasty: a meta-analysis.
      ]. Wyatt et al. echoed these findings, reporting that patients with LSF have “a substantially and significantly increased risk” of dislocation and revision but also that there was significantly increased risk of aseptic loosening, periprosthetic fracture, joint infections, and other adverse events [
      • Wyatt M.
      • Kunutsor K.
      • Beswick A.
      • Whitehouse M.
      • Kieser D.
      Outcomes following primary total hip arthroplasty with pre-existing spinal fusion surgery.
      ]. This was true in patients with long as well as short spinal fusion [
      • Wyatt M.
      • Kunutsor K.
      • Beswick A.
      • Whitehouse M.
      • Kieser D.
      Outcomes following primary total hip arthroplasty with pre-existing spinal fusion surgery.
      ]. Table 2 provides a summary of the literature.
      Table 2Summary table of the literature comparing outcomes of THA with or without prior LSF.
      StudyDesignNumberOutcomes of THA with prior LSF (comparator group, those without prior LSF)
      Sing et al., 2016 [
      • Sing D.
      • Barry J.
      • Aguilar T.
      • Theologis A.
      • Patterson J.
      • Tay B.
      • et al.
      Prior lumbar spinal arthrodesis increases risk of prosthetic-related complication in total hip arthroplasty.
      ]
      Retrospective cohort598,995LSF led to higher rates of dislocation, revision, loosening, and any prosthetic-related complication within 24 mo (P < .001)
      Barry et al., 2017 [
      • Barry J.
      • Sing D.
      • Vail T.
      • Hansen E.
      Early outcomes of primary total hip arthroplasty after prior lumbar spinal fusion.
      ]
      Retrospective cohort105LSF led to higher rates of complications (31.4% vs 8.6%, P = .008), reoperation (14.3% vs 2.9%, P = .040), and general anaesthesia (54.3% vs 5.7%, P = .0001).

      Long LSF (>3 levels) led to increased postop analgesia consumption (P = .001)
      Perfetti et al., 2017 [
      • Perfetti D.C.
      • Schwarzkopf R.
      • Buckland A.J.
      • Paulino C.
      • Vigdorchik J.
      Prosthetic dislocation and revision after primary total hip arthroplasty in lumbar fusion patients: a propensity score matched-pair analysis.
      ]
      Retrospective case-control934LSF led to higher rates of dislocation (RR = 7.19; P < .001) and revision rates (RR = 4.64; P < .001)
      Diebo et al., 2018 [
      • Diebo B.G.
      • Beyer G.A.
      • Grieco P.W.
      • Liu S.
      • Day L.
      • Abraham R.
      • et al.
      Complications in patients undergoing spinal fusion after THA.
      ]
      Retrospective cohort49,920LSF led to increased hip dislocation (OR = 2.2 [P = .002] [short, 2-3 levels] and 4.4 [P < .001] [long >4 levels]). Increased revision rates (OR = 2.0 [P < .001] [short] and 3.2 [P < .001] [long])
      York et al., 2018 [
      • York P.
      • McGee Jr., A.
      • Dean C.
      • Hellwinkel J.
      • Kleck C.
      • Dayton M.
      • et al.
      The relationship of pelvic incidence to post-operative total hip arthroplasty dislocation in patients with lumbar fusion.
      ]
      Retrospective cohort460LSF led to a higher dislocation risk (RR = 4.77; P ≤ .0001), and dislocators with LSF had higher revision rates (RR = 3.24; P = .003)
      Malkani et al., 2018 [
      • Malkani A.
      • Garber A.
      • Ong K.
      • Dimar J.
      • Baykal D.
      • Glassman S.
      • et al.
      Total hip arthroplasty in patients with previous lumbar fusion surgery: are there more dislocations and revisions?.
      ]
      Retrospective cohort62,387LSF led to more dislocation (prevalence = 7.4% vs 4.8% in control; P < .001). LSF led to 48% higher revision rates.
      Parilla et al., 2019 [
      • Parilla F.W.
      • Shah R.R.
      • Gordon A.C.
      • Mardjetko S.
      • Cipparrone N.
      • Goldstein W.
      • et al.
      Does it matter: total hip arthroplasty or lumbar spinal fusion first? Preoperative sagittal spinopelvic measurements guide patient-specific surgical strategies in patients requiring both.
      ]
      Retrospective cohort292LSF increased dislocation risk (RR = 3.0) and revision (RR = 2.7)
      Buckland et al., 2017 [
      • Buckland A.J.
      • Puvanesarajah V.
      • Vigdorchik J.
      • Schwarzkopf R.
      • Jain A.
      • Klineberg E.O.
      • et al.
      Dislocation of a primary total hip arthroplasty is more common in patients with a lumbar spinal fusion.
      ]
      Retrospective cohort14,747LSF led to higher rates of dislocation: 1 to 2 levels of fusion (OR = 1.93; P < .001), 3 to 7 levels (OR = 2.77, P < .001)
      Gausden et al., 2018 [
      • Gausden E.
      • Parhar H.
      • Popper J.
      • Sculco P.
      • Rush B.
      Risk factors for early dislocation following primary elective total hip arthroplasty.
      ]
      Retrospective cohort207,285LSF was highest independent predictor of dislocation (OR = −2.45; P < .0001)
      Salib et al., 2019 [
      • Salib C.
      • Reina N.
      • Perry K.
      • Tauton M.J.
      • Berry D.J.
      • Abdel M.P.
      Lumbar fusion involving the sacrum increases dislocation risk in primary total hip arthroplasty.
      ]
      Retrospective cohort84LSF with sacrum involvement increased dislocation risk (HR = 4.5; P = .03)
      Furuhashi et al., 2021 [
      • Furuhashi H.
      • Yamato Y.
      • Hoshino H.
      • Shimizu Y.
      • Hasegawa T.
      • Yoshida G.
      • et al.
      Dislocation rate and its risk factors in total hip arthroplasty with concurrent extensive spinal corrective fusion with pelvic fixation for adult spinal deformity.
      ]
      Retrospective cohort23LSF had a dislocation rate of 22%
      Lazennec et al., 2017 [
      • Lazennec J.Y.
      • Clark I.C.
      • Folianis D.
      • Tahar I.
      • Pour A.
      What is the impact of a spinal fusionon acetabular implant orientation in functional standing and sitting position.
      ]
      Retrospective case-control243LSF led to reduced adaptability of the lumbosacral junction with significant alterations to PT
      Eneqvist et al., 2017 [
      • Eneqvist T.
      • Nemes S.
      • Brisby H.
      • Fritzell P.
      • Garellick G.
      • Rolfson O.
      Lumbar surgery prior to total hip arthroplasty is associated with worse patient-reported outcomes.
      ]
      Retrospective case-control997LSF led to worse PROMs at 1 y postop
      Loh et al., 2017 [
      • Loh J.L.M.
      • Jiang L.
      • Chong H.C.
      • Yeo S.J.
      • Ngai N.L.
      Effect of spinal fusion surgery on total hip arthroplasty outcomes: a matched comparison study.
      ]
      Prospective cohort164LSF led to worse PROMs at 6 mo (P = 0 .046) and 2 y (P = .054)
      Grammatopoulos et al., 2019 [
      • Grammatopoulos G.
      • Dhaliwal K.
      • Pradhan R.
      • Parker S.
      • Lynch K.
      • Marshall R.
      • et al.
      Does lumbar arthrodesis compromise outcome of total hip arthroplasty?.
      ]
      Retrospective case-control42LSF led to inferior PROMs (P < .001), more surgery-related complications (loosening, periprosthetic fracture or infection, psoas irritation; P = .013), and dislocation (P = .023)
      HR, hazard risk; LSF, lumbar spinal fusion; OR, odds ratio; PROMs, patient-reported outcomes; PT, pelvic tilt; RR, relative risk.

      How should the surgeon proceed?

      Zhu et al. found that 95% of patients undergoing THA had a degree of anterior or posterior PT, with 16% having >10° tilt [
      • Parratte S.
      • Pagnano M.W.
      • Coleman-Wood K.
      • Kaufman K.
      • Berry D.
      The 2008 frank stinchfield award: variation in postoperative pelvic tilt may confound the accuracy of hip navigation systems.
      ,
      • Zhu J.
      • Wan Z.
      • Dorr L.
      Quantification of pelvic tilt in total hip arthroplasty.
      ]. Data show 18%-25% of patients undergoing THA have spinal pathology for which they have seen a spinal surgeon prior, which as previously described will result in PT changes and increased risk of complications [
      • Zhu J.
      • Wan Z.
      • Dorr L.
      Quantification of pelvic tilt in total hip arthroplasty.
      ]. It is therefore imperative to try to identify modifications that can be performed preoperatively, intraoperatively, and postoperatively to improve complication rates in a sizable number of high-risk patients. In addition, patients should be informed during consenting that existing spinal fusion means they are a high-risk group for dislocation, revision, and complications [
      • Sing D.
      • Barry J.
      • Aguilar T.
      • Theologis A.
      • Patterson J.
      • Tay B.
      • et al.
      Prior lumbar spinal arthrodesis increases risk of prosthetic-related complication in total hip arthroplasty.
      ].

      Preoperative planning and assessment

      Yang et al. and Mancino et al. recommend that prior to THA, all patients must undergo standing, supine, and sitting lateral radiographs of the pelvis and the lumbar spine [
      • Yang G.
      • Li Y.
      • Zhang H.
      The influence of pelvic tilt on the anteversion angle of the acetabular prosthesis.
      ,
      • Mancino F.
      • Cacciola G.
      • Di Matteo V.
      • Perna A.
      • Proietti L.
      • Greenberg A.
      • et al.
      Surgical implications of the hip-spine relationship in total hip arthroplasty.
      ]. The views should ideally include L1 or, at the least, the level of L3, as most of the lumbar motion happens between L3 and L5 [
      • Yang G.
      • Li Y.
      • Zhang H.
      The influence of pelvic tilt on the anteversion angle of the acetabular prosthesis.
      ,
      • Mancino F.
      • Cacciola G.
      • Di Matteo V.
      • Perna A.
      • Proietti L.
      • Greenberg A.
      • et al.
      Surgical implications of the hip-spine relationship in total hip arthroplasty.
      ].
      Most of the radiographic analysis of the hip is undertaken on the “standard” anteroposterior (AP) view radiograph, which has the acetabulum in the coronal plane, [
      • Hertel J.
      • Dorfman J.H.
      • Braham R.A.
      Lower extremity malalignments and anterior cruciate ligament injury history.
      ] as a standing film will more accurately represent the functional pelvis position than supine radiographs [
      • Attenello J.
      • Harpstrike J.
      Implications of spinopelvic mobility on total hip arthroplasty: review of current literature.
      ]. However, safe position in the sagittal plane may be more important in patients with existing spinal fusion. It has therefore been recommended that 3 views of the pelvis should be obtained: lateral standing, sitting, and AP standing [
      • Hertel J.
      • Dorfman J.H.
      • Braham R.A.
      Lower extremity malalignments and anterior cruciate ligament injury history.
      ]. Imaging assessing movement while changing stance preoperatively has also been recommended [
      • Eilander W.
      • Harris S.J.
      • Jenkus H.E.
      • Cobb J.P.
      • Hogervorst T.
      Functional acetabular component position with supine total hip replacement.
      ].

      THA or spinal fusion first?

      Sultan et al. originally argued that the most-troublesome issue should be managed first while monitoring the other [
      • Sultan A.
      • Khlopas A.
      • Udo-Inyang I.
      • Chugtai M.
      • Sodhi N.
      • lamaj S.
      • et al.
      Hip osteoarthrtiis patients demonstrated marked dynamic changes and variability in pelvic tilt, obliquity, and rotation: a comparative, gait-analysis study.
      ]. However, their recommendation makes an exemption in the presence of hip flexion contracture, which may clinically mimic or worsen symptoms of spine deformity. If present, it has been advised to perform THA first, as (1) hip flexion contractures and spinal deformity often improve with THA and (2), for best outcomes with spinal fusion, it is important hip flexion contractures have been dealt with before [
      • Sultan A.
      • Khlopas A.
      • Udo-Inyang I.
      • Chugtai M.
      • Sodhi N.
      • lamaj S.
      • et al.
      Hip osteoarthrtiis patients demonstrated marked dynamic changes and variability in pelvic tilt, obliquity, and rotation: a comparative, gait-analysis study.
      ]. Various authors have reported different outcomes based on the order of surgery, from no significant differences in revision and instability [
      • Malkani A.
      • Garber A.
      • Ong K.
      • Dimar J.
      • Baykal D.
      • Glassman S.
      • et al.
      Total hip arthroplasty in patients with previous lumbar fusion surgery: are there more dislocations and revisions?.
      ,
      • Loh J.L.M.
      • Jiang L.
      • Chong H.C.
      • Yeo S.J.
      • Ngai N.L.
      Effect of spinal fusion surgery on total hip arthroplasty outcomes: a matched comparison study.
      ] to decreased dislocation and revision rates when THA is performed before LSF [
      • Malkani A.
      • Himschoot K.
      • Ong K.
      • Lau E.
      • Baykal D.
      • Dimar J.
      • et al.
      Does timing of primary total hip arthroplasty prior to or after lumbar spine fusion have an effect on dislocation and revision rates?.
      ,
      • Hu J.
      • Qian B.
      • Qiu Y.
      • Wang B.
      • Yu U.
      • Zhu Z.Z.
      • et al.
      Can acetabular orientation be restored by lumbar pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis?.
      ] and to the opposite with prior THA leading to significantly increased rates of dislocation, infection, revision, and postoperative opioid usage [
      • Haffer H.
      • Amini D.
      • Perka C.
      • Pumberger M.
      The impact of spinopelvic mobility on arthroplasty: implications for hip and spine surgeons.
      ]. Unfortunately, all these studies are limited by not evaluating the relevance of timing between operations and by being retrospective case-control studies.
      One specific group has been flagged as benefiting from undergoing spinal fusion first: patients with excessive pelvic retroversion due to their spine pathology, for example, patients with ankylosing spondylitis. Hu et al. found that a spinal osteotomy in these patients led to correction of their acetabular abduction and anteversion, thereby allowing relatively normal acetabular orientation and a hypothetical decrease in risk of dislocation [
      • Hu J.
      • Qian B.
      • Qiu Y.
      • Wang B.
      • Yu U.
      • Zhu Z.Z.
      • et al.
      Can acetabular orientation be restored by lumbar pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis?.
      ,
      • Murray D.
      The definition and measurement of acetabular orientation.
      ]. If LSF is to occur prior to THA, Haffer et al. advise that spine surgeons should be aware of a hip flexion contracture and should warn the patients of an increased risk of complications with existing or planned THA [
      • Haffer H.
      • Amini D.
      • Perka C.
      • Pumberger M.
      The impact of spinopelvic mobility on arthroplasty: implications for hip and spine surgeons.
      ,
      • Lewinnek G.E.
      • Lewis J.L.
      • Tarr R.
      • Compere C.
      • Zimmerman J.
      Dislocations after total hip-replacement arthroplasties.
      ].

      Acetabular cup placement

      The orientation of an acetabulum or an acetabular prosthesis is traditionally described by its inclination and anteversion. Orientation can be assessed anatomically, radiographically, and by direct observation at operation. The angles of inclination and anteversion determined by these 3 methods differ because they have different spatial arrangements. There are therefore 3 distinct definitions of inclination and anteversion.
      In 1993, Murray highlighted the fact that operative anteversion is measured around a transverse axis, anatomical anteversion around a longitudinal axis, and radiographic anteversion around an oblique axis [
      • Murray D.
      The definition and measurement of acetabular orientation.
      ]. The author also developed nomograms to allow conversion of one orientation to the other two. Murray concluded that operative definitions be used to describe the prostheses orientation while anatomical definitions be used for normal/dysplastic acetabula. If the orientation is determined from an AP radiograph, it should be converted to operative orientation before being quoted. Anatomical anteversion is best determined from computed tomography (CT) or magnetic resonance images, as it is measured in the transverse plane [
      • Abdel M.
      • von Roth P.
      • Jennings M.
      • Hanssen A.
      • Pagnano M.
      What safe zone? The vast majority of dislocated THAs are within the lewinnek safe zone for acetabular component position.
      ].
      Lewinnek et al. defined a safe zone to minimize dislocation risk, which comprises an operative cup inclination of 40° ± 10° and operative cup anteversion of 15° ± 10° [
      • Eilander W.
      • Harris S.J.
      • Jenkus H.E.
      • Cobb J.P.
      • Hogervorst T.
      Functional acetabular component position with supine total hip replacement.
      ,
      • Lewinnek G.E.
      • Lewis J.L.
      • Tarr R.
      • Compere C.
      • Zimmerman J.
      Dislocations after total hip-replacement arthroplasties.
      ]. Although considered a useful target, the value of this safe zone has nonetheless been called into question in recent years. In an assessment of 9784 primary THAs performed by high-volume surgeons, Abdel et al. reported that 58% (120 of 206) of those that dislocated were within the Lewinnek “safe zone” [
      • Abdel M.
      • von Roth P.
      • Jennings M.
      • Hanssen A.
      • Pagnano M.
      What safe zone? The vast majority of dislocated THAs are within the lewinnek safe zone for acetabular component position.
      ,
      • Pierrepont J.
      • Hawdon G.
      • Miles B.P.
      • O’Connor B.
      • Baré J.
      • Walter L.R.
      • et al.
      Variation in functional pelvic tilt in patients undergoing total hip arthroplasty.
      ]. This finding is likely due to the multifactorial causes contributing to instability, as well as confusion between anatomic and radiographic cup orientation. In addition, altered PT plays a role. Posterior PT has been shown to increase acetabular component anteversion when standing, which is linked to decreased accuracy of placement within the safe zone from 82% to 64% [
      • Kanto M.
      • Maruo K.
      • Tachibana T.
      • Fukunishi S.
      • Nishio S.
      • Takeda Y.
      • et al.
      Influence of spinopelivc alignmnet on pelvic tilt after total hip arthroplasty.
      ,
      • Stefl M.
      • Lundergan W.
      • Heckmann N.
      • McKnight B.
      • Ike H.
      • Murgai R.
      • et al.
      Spinopelvic mobility and acetabular component position for total hip arthroplasty.
      ,
      • Leslie I.J.
      • Williams S.
      • Isaac G.
      • Ingham E.
      • Fisher J.
      High cup angle and microseparation increase the wear of hip surface replacements.
      ]. Therefore, the cup positioning defined only intraoperatively may not be ideal for all patients. The categorizations of spinopelvic motion proposed by Phan et al. may be of value here to help surgeons (Table 3) [
      • Boyoud-Garnier L.
      • Boudissa M.
      • Ruatti S.
      • Kerschbaumer G.
      • Grobost P.
      • Tonetti J.
      Chronic low back pain after lumbosacral fracture due to sagittal and frontal vertebral imbalance.
      ,
      • Phan D.
      • Bederman S.
      • Schwarzkopf R.
      The influence of sagittal spinal deformity on anteversion of the acetabular component in total hip arthroplasty.
      ].
      Table 3Summary of alterations to Lewinnek safe zone depending on Phan classification.
      ClassificationFound inAlteration to Lewinnek safe zone
      Balanced and flexibleHealthy populationUse as described
      Balanced and stiffLumbar degenerative disease, prior LSFIncrease anteversion (15°-25°)
      Unbalanced and flexiblePostlaminectomy, neuromuscular kyphosisReduced anteversion
      Unbalanced and stiffLong LSF, ankylosing spondylitisReduced anteversion
      Stefl et al. describe a further classification system, with 6 classes: normal, stiff (further subdivided into fixed anterior tilt and fixed posterior tilt; PT is present in both sitting and standing), kyphotic, fused, and hypermobile [
      • Stefl M.
      • Lundergan W.
      • Heckmann N.
      • McKnight B.
      • Ike H.
      • Murgai R.
      • et al.
      Spinopelvic mobility and acetabular component position for total hip arthroplasty.
      ,
      • Romagnoli M.
      • Grassi A.
      • Costa G.G.
      • Lazaro L.
      • Lo Presti M.
      • Zaffagnini S.
      The efficacy of dual-mobility cup in preventing dislocation after total hip arthroplasty: a systematic review and meta-analysis of comparative studies.
      ]. They advise placement as shown in Figure 1.
      Figure thumbnail gr1
      Figure 1Recommendation of cup placement algorithm, based on Stefl et al. [
      • Stefl M.
      • Lundergan W.
      • Heckmann N.
      • McKnight B.
      • Ike H.
      • Murgai R.
      • et al.
      Spinopelvic mobility and acetabular component position for total hip arthroplasty.
      ].
      These classifications can be useful as general categories, but it has been advised that the degree of stiffness and sagittal imbalance should be determined on a case-by-case basis. Increased acetabular inclination is not a “free” solution, as it is a recognized risk factor for accelerated bearing surface wear and linear fractures [
      • Tezuka T.
      • Heckmann N.
      • Bodner R.
      • Dorr L.
      Functional safe zone is superior to the lewinnek safe zone for total hip arthroplasty: why the lewinnek safe zone is not always predictive of stability.
      ]. Additionally, it should be noted that as patients age or if their spine disease progresses, they may transition into a category that may increase the risk of late dislocations. In contrast, THA may increase spinopelvic mobility. Stefl et al. found that 54% of patients undergoing THA had normal spinopelvic mobility preoperative and that this increased to 80% after THA, which has been attributed to intraoperative release of hip flexion contracture [
      • McKeon J.
      • Hertel J.
      Sex differences and representative values for 6 lower extremity alignment measures.
      ,
      • Stefl M.
      • Lundergan W.
      • Heckmann N.
      • McKnight B.
      • Ike H.
      • Murgai R.
      • et al.
      Spinopelvic mobility and acetabular component position for total hip arthroplasty.
      ,
      • Romagnoli M.
      • Grassi A.
      • Costa G.G.
      • Lazaro L.
      • Lo Presti M.
      • Zaffagnini S.
      The efficacy of dual-mobility cup in preventing dislocation after total hip arthroplasty: a systematic review and meta-analysis of comparative studies.
      ].

      Hip component

      Dual-mobility cups have been shown to decrease the risk of instability in high-risk patients, both in primary and revision THA, and it is unsurprising they have been mentioned when thinking about THA in patients with altered PTs [
      • Haffer H.
      • Amini D.
      • Perka C.
      • Pumberger M.
      The impact of spinopelvic mobility on arthroplasty: implications for hip and spine surgeons.
      ,
      • Nessler J.
      • Malkani A.
      • Sachdeva S.
      • Nessler J.
      • Westrich G.
      • Harwin S.
      • et al.
      Use of dual mobility cups in patients undergoing primary total hip arthroplasty with prior lumbar spine fusion.
      ]. Tezuka et al. and Nessler et al. looked at dual-mobility cups in patients with LSF and found reduced dislocation rates [
      • Tezuka T.
      • Heckmann N.
      • Bodner R.
      • Dorr L.
      Functional safe zone is superior to the lewinnek safe zone for total hip arthroplasty: why the lewinnek safe zone is not always predictive of stability.
      ,
      • Nessler J.
      • Malkani A.
      • Sachdeva S.
      • Nessler J.
      • Westrich G.
      • Harwin S.
      • et al.
      Use of dual mobility cups in patients undergoing primary total hip arthroplasty with prior lumbar spine fusion.
      ]. Vigdorchik et al. has proposed a new risk-prediction model based on radiological features to try to identify patients who may benefit most from dual-mobility cups. When using this algorithm, there was a significant decrease in dislocation rates (0.5% vs 3.1%) [
      • Vigdorchik J.
      • Sharma A.
      • Elbuluk A.
      • Carrol K.
      • Mayman D.J.
      • Lieberman J.R.
      High offset stems are protective of dislocation in high-risk total hip arthroplasty.
      ].
      High-offset stems also seem to have a role in patients with spinal pathology. A study looking at 12,365 patients who underwent THA found that high-offset stems were protective for dislocation (P < .0001). While high-offset stems can lead to complications such as bursitis, Vigdorchik et al. did find them to be protective and concluded there was benefit in their usage in patients at high risk to mitigate risk of dislocation [
      • Vigdorchik J.
      • Sharma A.
      • Elbuluk A.
      • Carrol K.
      • Mayman D.J.
      • Lieberman J.R.
      High offset stems are protective of dislocation in high-risk total hip arthroplasty.
      ].

      Role of computer navigation

      The pelvis moves when a person alters their position, and the relative change in PT that occurs as a result cannot be accurately assessed by 1 static 2-dimensional AP radiograph of the pelvis. Two-dimensional radiographic images suffer from “out-of-plane” rotations, including pelvis rotation (1° of pelvic rotation can cause 0.8° change in the measurement of acetabular version), femoral rotation, and/or flexion or hyperextension. CT has been proposed as a solution, but the supine position required for imaging does not provide a realistic evaluation of the patient’s compensation mechanisms during weight-bearing [
      • Xu K.
      • Li Y.
      • Zhang H.
      • Wang C.
      • Xu Y.
      • Li Z.
      Computer navigation in total hip arthroplasty: a meta-analysis of randomized controlled trials.
      ].
      Several computer navigation systems are available that may address the challenge of accounting for dynamic spinopelvic movement during imaging of hips. Computer navigation systems are defined by their shared goal of providing guidance to surgeons on patient anatomy in preoperative planning and intraoperative placement of instruments and implants.
      There is support for the notion that navigation improves cup orientation. A meta-analysis by Xu et al. linked computer navigation systems with improvements to the precision of acetabular cup placement (P < .00001); however, no significant differences were found in cup inclination, anteversion, or in the incidence of postoperative dislocation [
      • Xu K.
      • Li Y.
      • Zhang H.
      • Wang C.
      • Xu Y.
      • Li Z.
      Computer navigation in total hip arthroplasty: a meta-analysis of randomized controlled trials.
      ,
      • Liu Z.
      • Gao Y.
      • Cai L.
      Imageless navigation versus traditional method in total hip arthroplasty: a meta-analysis.
      ]. Meta-analyses by Liu et al. (2015) and Beckmann et al. (2009) noted that navigation enhanced cup placement and minimized outliers [
      • Liu Z.
      • Gao Y.
      • Cai L.
      Imageless navigation versus traditional method in total hip arthroplasty: a meta-analysis.
      ,
      • Beckmann J.
      • Stengel D.
      • Tingart M.
      • Götz J.
      • Grigka J.
      • Lüring C.
      Navigated cup implantation in hip arthroplasty.
      ].
      Navigation systems can incorporate a number of techniques developed to correct for PT to better facilitate cup placement. The “kinematic alignment technique” uses the transverse acetabular ligament as a landmark to adjust cup position and judge the patient’s spine-hip relationship. This allows a restoration of the “native” acetabular anteversion and the hip’s centre rotation [
      • Haimerl M.
      • Schubert M.
      • Wegner M.
      • Kling S.
      Anatomical relationships of human pelvises and their application to registration techniques.
      ]. Babisch et al. developed a nomogram to allow navigation systems that rely on the pelvic anterior plane to convert cup alignment values [
      • Babisch J.W.
      • Layher F.
      • Amiot L.P.
      The rationale for tilt-adjusted acetabular cup navigation.
      ]. At 1-year follow-up, none of the 98 patients who underwent navigation using this tool sustained a dislocation, and on CT imaging, 99% of cup anteversion and 97% of cup abduction values were in the target range [
      • Babisch J.W.
      • Layher F.
      • Amiot L.P.
      The rationale for tilt-adjusted acetabular cup navigation.
      ]. In analyzing CT data for 420 patients, Haimerl et al. found that the interteardrop and interfossa distances were consistent in pelvises of the same gender, as was the relationship between the anterior pelvic plane and other reference planes reliant on acetabular points [
      • Haimerl M.
      • Schubert M.
      • Wegner M.
      • Kling S.
      Anatomical relationships of human pelvises and their application to registration techniques.
      ]. From this, they developed a procedure using intraoperatively available landmarks. Using this tool, they were able to plan THA placement, of which 99% were in the Lewinnek safe zone [
      • Haimerl M.
      • Schubert M.
      • Wegner M.
      • Kling S.
      Anatomical relationships of human pelvises and their application to registration techniques.
      ].
      In addition to PT, navigation systems can address the multifactorial reasons that can contribute to instability and dislocation, which may improve functional alignment. Clinical data suggest that navigation offers a superior means than conventional methods for achieving the goals of reduced leg length discrepancy (P = .004) [
      • Xu K.
      • Li Y.
      • Zhang H.
      • Wang C.
      • Xu Y.
      • Li Z.
      Computer navigation in total hip arthroplasty: a meta-analysis of randomized controlled trials.
      ] and offset [
      • Renkawitz T.
      • Weber T.
      • Dullien S.
      • Woerner M.
      • Dendorfer S.
      • Grifka J.
      • et al.
      Leg length and offset differences above 5mm after total hip arthroplasty are associated with altered gait kinematics.
      ,
      • Innmann M.M.
      • Maier M.W.
      • Streit M.R.
      • Grammatopoulos G.
      • Bruckner T.
      • Gotterbarm T.
      • et al.
      Additive influence of hip offset and leg length reconstruction on postoperative improvement in clinical outcome after total hip arthroplasty.
      ,
      • Jia J.
      • Zhao Q.
      • Lu P.
      • Fan G.
      • Chen H.
      • Chaoqun L.
      • et al.
      Clinical efficacy of OrthoPilot navigation system versus conventional manutal total hip arthroplasty: a systematic review and meta-analysis.
      ,
      • Clavé A.
      • Fazileau F.
      • Cheval D.
      • Williams T.
      • Lefèvre C.
      • Stindel E.
      Comparison of the reliability of leg length and offset data generated by three hip replacement CAOS systems using EOS™ imaging.
      ,
      • Davis E.
      • Schubert M.
      • Wegner M.
      • Haimerl M.
      A new method of registration in navigated hip arthroplasty without the need to register the anterior pelvic plane.
      ].
      Robotic-arm-assisted arthroplasty is a similarly novel technique that has been proposed to aid placement of components. When used by a trained professional, robotic-arm-assisted placement was found to be reliable when using bony landmark (83% of cups placed within targets for inclination and anteversion) or using functional planning (90%), with lower variance reported in the functional group [
      • Hepinstall M.
      • Coden G.
      • Salem H.
      • Naylor B.
      • Matzko C.
      • Mont M.A.
      Consideration of pelvic tilt at the time of preoperative planning improves standing acetabular position after robotic-arm assisted total hip arthroplasty.
      ]. However, Hayashi et al. has found that a posterior PT, as found in patients with spinal pathology, is a predictive factor for inaccurate cup positioning [
      • Hayashi S.
      • Hashimoto S.
      • Kuroda Y.
      • Nakano N.
      • Matsumoto T.
      • Ishida K.
      • et al.
      Accuracy of cup position following robot-assisted total hip arthroplasty may be associated with surgical approach and pelvic tilt.
      ].
      Although increasing in use, navigation systems and robotic-arm-assisted arthroplasty are still infrequently employed in THA, likely primarily due to concerns around their associated costs and increased surgical time [
      • Widmer K.H.
      • Zurfluh B.
      Compliant positioning of total hip components for optimal range of motion.
      ].

      Conclusions

      It is essential to appreciate the relationship between pelvis, spine, and hips, as well as the impact of pathology on the movement occurring at the spinopelvic junction and in turn on PT. This is particularly important to understand when planning THA, as both spinal pathology and surgery will have an effect on PT and complication rates of THA. Fused spines following an operation or stiff spines from pathology can all affect PT, and in patients with these conditions, the placement of components should be considered. The ordering of spinal/hip surgery, precise cup placement, and type of cup used can all help reduce dislocation rates. Moreover, preoperative THA planning that involves assessing PT and acetabular inclination and anteversion becomes imperative to achieve precise acetabular cup placement. This differs significantly between individuals and is dynamic and varying with different positions and activities. The previously described “safe zones” do not take into account this dynamic behaviour; therefore, accurate cup placement cannot be achieved. Careful preoperative planning of the component alignment on an individual patient basis could improve outcomes and revision rates [
      • Hayashi S.
      • Hashimoto S.
      • Kuroda Y.
      • Nakano N.
      • Matsumoto T.
      • Ishida K.
      • et al.
      Accuracy of cup position following robot-assisted total hip arthroplasty may be associated with surgical approach and pelvic tilt.
      ]. Acetabular cup placement is not something that the surgeon can be accurate within a specific range of degrees by themselves. Computer navigation systems and robotic-arm-assisted surgery may aid the surgeon and allow for a more-precise cup position. Ideally, navigation systems should work to address the multifactorial contributors to dislocation and instability, of which spinopelvic factors remain a key but often overlooked element. Postoperative care is also an important element that seems to be forgotten by research with no evidence on success of differing physiotherapy or occupational therapy interventions in at-risk individuals.

      Conflicts of interest

      Prof. Hemant Pandit are paid consultants for Medacta International, DePuy Synthes, Smith and Nephew, Meri Life, Invibio, Zimmer Biomet, and JRI Orthopaedics; both receive research support from Medacta International, Zimmer Biomet, DePuy Synthes, and Invibio; and they receive financial or material support from Kennedy’s Law. Mr Stefan Louette and Miss Alice Wignall declares no potential conflicts of interest.
      For full disclosure statements refer to https://doi.org/10.1016/j.artd.2022.07.001.

      Appendix A. Supplementary Data

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