- Email: [email protected]
Quantifying Pelvic Motion During Total Hip Arthroplasty Using a New Surgical Navigation Device
The Journal of Arthroplasty xxx (2017) 1e5
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Quantifying Pelvic Motion During Total Hip Arthroplasty Using a New Surgical Navigation Device Ran Schwarzkopf, MD, MSc a, Jeffrey M. Muir, MSc, DC, MSc (Clin Epi) b, Wayne G. Paprosky, MD, FACS c, Scott Seymour, MD d, Michael B. Cross, MD e, Jonathan M. Vigdorchik, MD a, * a
Department of Orthopaedic Surgery, NYU Langone Medical CentereHospital for Joint Diseases, New York, New York Department of Clinical Research, Intellijoint Surgical, Inc, Waterloo, Ontario, Canada Department of Orthopedics, Central DuPage Hospital, Winfield, Illinois d Department of Orthopedics, MacNeal Hospital, Berwyn, Illinois e Department of Orthopedic Surgery, Hospital for Special Surgery, New York, New York b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 January 2017 Received in revised form 21 March 2017 Accepted 24 April 2017 Available online xxx
Background: Accurate cup positioning is one of the most challenging aspects of total hip arthroplasty (THA). Undetected movement of the patient during THA surgery can lead to inaccuracies in cup anteversion and inclination, increasing the potential for dislocation and revision surgery. Investigations into the magnitude of patient motion during THA are not well represented in the literature. Methods: We analyzed intraoperative pelvic motion using a novel navigation device used to assist surgeons with cup position, leg length, and offset during THA. This device uses an integrated accelerometer to measure motion in 2 orthogonal degrees of freedom. We reviewed the data from 99 cases completed between February and September 2016. Results: The mean amount of pitch recorded per patient was 2.7 (standard deviation, 2.2; range, 0.1 9.9 ), whereas mean roll per patient was 7.3 (standard deviation, 5.5; range, 0.3 -31.3 ). Twenty-one percent (21 of 99) of patients demonstrated pitch of >4 . Sixty-nine percent (68 of 99) of patients demonstrated >4 of roll, and 25% (25 of 99) of patients demonstrated roll of 10 . Conclusion: Our findings indicate that while the majority of intraoperative motion is <4 , many patients experience significant roll, with a large proportion rolling >10 . This degree of movement has implications for acetabular cup position, as failure to compensate for this motion can result in placement of the cup outside the planned safe zone, thus, increasing the potential for dislocation. Further study is warranted to determine the effect of this motion on cup position, leg length, and offset. © 2017 Elsevier Inc. All rights reserved.
Keywords: total hip arthroplasty pelvic movement cup position navigation surgical
Accurate acetabular cup placement is one of the most challenging aspects of total hip arthroplasty (THA). Improper placement of the acetabular component can increase the likelihood of dislocation and revision surgery [1e4]. To minimize these risks,
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2017.04.046. * Reprint requests: Jonathan M. Vigdorchik, MD, Department of Orthopaedic Surgery, NYU Langone Medical CentereHospital for Joint Diseases, 301 East 17th Street, New York, NY 10003. http://dx.doi.org/10.1016/j.arth.2017.04.046 0883-5403/© 2017 Elsevier Inc. All rights reserved.
surgeons position the acetabular cup component within a supposed functional “safe zone” of 40 ± 10 of inclination and 15 ± 10 of anteversion [5], first proposed by Lewinnek et al [6]. This range is thought to be associated with a lower likelihood of instability and dislocation; however, there is growing debate regarding its true association with lower dislocation rates [7,8]. Although others have suggested alternate ranges (eg, 40 ± 10 abduction/30 ± 10 anteversion [9] or 30 abduction/20 anteversion [10]), the Lewinnek zone continues to be the benchmark. Placement of the acetabular component within this safe zone, however, is particularly challenging, given the potential movement of the pelvis that occurs intraoperatively during THA [11e15]. Changes in pelvic tilt, rotation, and obliquity directly affect anteversion and inclination [16e19]. One study reported that for every 1 increase in pelvic obliquity, anteversion changed
2
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
by 0.4 , and for every degree increased pelvic tilt, anteversion was altered by 0.8 [18]. Another study reported a linear relationship between pelvic tilt and anteversion, with every 1 increase in posterior pelvic tilt associated with a 0.74 change in anteversion [17]. Inclination changed in a nonlinear fashion, with each 1 increase in tilt initially altering inclination by 0.29 . The magnitude of change grew more dramatic as pelvic tilt increased, with 15 of posterior tilt associated with a change of 0.47 of inclination [17]. Surgeons attempt to orient the patient on the operating table in a neutral position before surgery. When positioned laterally, a neutral patient position implies that the patient's sagittal plane is coplanar with the operating table (which is coplanar with the floor), whereas the patient's longitudinal axis is in line with the long dimension of the operating table (Fig. 1). Patient positioners are utilized during the procedure to maintain the patient in this position. Surgeons generally assume that the pelvis remains in this neutral position throughout the procedure, despite the movement and manipulation of the leg and hip joint that occurs during THA. In traditional hip arthroplasty, there is no method of determining if the pelvis remains in the same position throughout the procedure, including the time of implantation of the acetabular component [11]. Significant movement can occur between the initial patient positioning and acetabular component trialing and implantation. Such movement can result in errors in placement of the acetabular components, errors which, if not accounted for or corrected for, can increase the likelihood of components being placed outside the safe zone, leading to increased wear, edge loading, impingement, and dislocation [17,18]. The purpose of this study was to record the magnitude and direction of patient movement during THA surgery. Simple and reliable methods for monitoring and/or compensating for changes in patient position during surgery have not been developed to date, with previous studies using specialized equipment to monitor movement [11,12,14,20]. These devices, however, while providing some useful data, are cumbersome and could interfere with the normal surgical workflow. We used a novel navigation device that uses infrared optical technology and integrated inertial sensors to make intraoperative measurements during THA procedures. Although predominantly used to assist surgeons with component placement by monitoring cup position, leg length, and offset parameters, the device is also able to measure the 2-dimensional motion (or “tilt”) of the pelvis (relative to gravity) and record the magnitude and direction of movements during surgery. Our hypothesis was that significant pelvic motion would be recorded during THA between patient positioning and final implant placement.
Methods Study Design This study was a retrospective review of navigation system data from THA procedures performed at one of 7 sites using the navigation tool. A total of 11 orthopedic surgeons contributed case data for this study. All procedures were performed via the posterior approach with surgeons utilizing their choice of patient positioner and retractor. Data Eligibility Data were eligible for inclusion in this study if the patient underwent a THA procedure between February and September 2016 at one of the participating facilities (4 in New York City, 2 in Chicago, and 1 in upstate New York). Only navigation system data were reviewed; no patient identifiers or demographic data were included in the analysis. Procedures where the navigation tool was used were eligible for inclusion in the study. Data were excluded from procedures where the navigation tool was removed before measurements being taken with either trial components or final implants in place or cases where there was instability in the navigation system's pelvic platform such that accurate measurements were not obtainable from the navigation tool. Intellijoint HIP Navigation Tool The Intellijoint HIP (Intellijoint Surgical, Inc, Waterloo, ON, Canada) navigation tool is a miniature surgical tool that uses infrared optical technology and integrated microelectronics, including inertial sensors, to measure cup implant angle, leg length, offset, and center of rotation to assist surgeons with component placement during THA. The device has been described in detail previously [21]. In brief, with the patient in the lateral decubitus position, a pelvic platform is fixed to the ipsilateral iliac crest via 2 surgical pins. A camera is magnetically secured to the pelvic platform while a tracker is magnetically attached to a femoral platform fixed to the greater trochanter or to a cup impactor, to measure changes in leg length and offset, as well as native acetabular orientation and cup position (Fig. 2). The camera captures motion and position data from the tracker to calculate center of rotation, length leg, and offset for both the native hip and the artificial joint. The attachment of the camera to the pelvic platform creates a fixed system, such that the camera and the pelvis are rigidly coupled (ie, any movement of the pelvis will also move the camera). Pelvic Motion Calculations
Fig. 1. Neutral positioning of the patient in the lateral position. The patient's sagittal plane, A, is coplanar with the operating table. The patient's frontal plane, B, is oriented along the long axis of the table.
The navigation system camera, in addition to its optical components, contains integrated inertial sensors (in particular, a 3-axis accelerometer). The inertial sensing system is configured to measure motion and orientation in 2 orthogonal degrees of freedom (ie, similar to a 2-axis bubble level). Movement is recorded by the navigation system at specific steps during the surgical procedure. Immediately after patient positioning (before hip exposure), the camera is installed on the patient's iliac crest and an initial measurement is recorded to register the horizontal plane, which coincides with the patient's sagittal plane. In addition, the patient's frontal plane is registered and the frontal and sagittal planes are combined to form the patient registration (ie, the spatial relationship between the camera and the patient's anatomy). Later in the procedure (after surgical exposure, hip dislocation, and femoral head resection but
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
3
Statistical Analysis Alpha was set a priori at 0.05 for all statistical comparisons. Means were compared using Student t tests or 1-way analysis of variance where applicable. All mean values are presented as mean (standard deviation, range). MATLAB (MathWorks Inc, Natick, MA) was used to analyze exported measurement data for the cases included in this study to determine the magnitude and direction of patient movement. Results
Fig. 2. The navigation tool in use. The camera, A, in its sterile drape, is attached to the pelvic platform, B, via 2 screws. The tracker, C, is magnetically attached to the femoral platform. The camera captures movements of the tracker when registering the native orientation of the acetabulum or trialing implant components and relays the information to a workstation for review by the surgeon. An accelerometer in the camera measures movement of the pelvis during surgery.
immediately before cup implantation), the system allows a surgeon to define an acetabular reference plane, at which time another measurement is recorded. The system software exports measurement data for each case, including the initial and preimplantation orientations, and the patient registration. From these data, the change in pelvic position may be computed by comparing the patient's initial position on the operating table with the position at the time of cup implantation (recorded during the acetabular reference plane measurement). The patient registration is used to represent the camera-based movement measurements with respect to the pelvis. As a result, the angular movement of the pelvis from incision to the cup implantation step may be quantified for a given case. Patient movement is expressed as both pitch (rotation in the coronal plane about an anteroposterior [AP] axis) and roll (rotation in a transverse plane about a cephalad-caudal axis; Fig. 3). Positive pitch represents rotation about the AP axis that results in obliquity, causing the operating side hemipelvis to move cephalad, increasing abduction angle. Positive roll is rotation about the longitudinal axis that moves the patient toward the prone position. Negative pitch reflects caudal movement of the operative hemipelvis; negative roll represents movement toward a supine position.
Fig. 3. Axes of rotation used in this study. The navigation tool measures pelvic motion during total hip arthroplasty (THA) in 2 planes. Pitch is measured as rotation in the coronal plane about an anteroposterior axis. Roll is measured as rotation in a transverse plane about a cephalad-caudal axis.
From a total of 104 eligible cases, movement data from 99 procedures were included in this study. Of the 99 procedures included in this study, 92 (93%) were primary THAs, while 7 (7%) were revision procedures. Five (5) cases were excluded owing to an inability to achieve adequate bony fixation of either the pelvic (n ¼ 4) or femoral platform (n ¼ 1), resulting in the device being removed before measurements being recorded. Pitch The mean amount of intraoperative pitch recorded per patient was 2.7 (SD, 2.2), with a range of between 0.1 and 9.9 . A pitch of >4 was recorded in 21 of 99 (21%) patients. Roll The mean amount of roll per patient was 7.3 (SD, 5.5), ranging from 0.3 to 31.3 . Over 4 of roll was observed in 68 of 99 (69%) patients, with roll in excess of 6 observed in 53 of 99 (54%) patients and roll 10 recorded in 25 of 99 (25%) patients (Fig. 4). Discussion Examinations of the degree of change in patient position during THA and its implications are not well documented in the literature. There have been few investigations into the pelvic motion that occurs as a result of patient position shift during THA. The studies available report the use of various extraneous devices to monitor and quantify patient motion [11,12,14,20]. Although under-represented in the literature, the importance of characterizing intraoperative motion is significant, as it relates to the difficulty in accurately implanting the acetabular cup component as well as the impact of undetected pelvic movement on cup position. As surgeons generally position the cup component relative to the patient's initial, neutral position, failing to account for intraoperative movement can result in cup placement out of or close to the limits of the Lewinnek safe zone [6], which may increase the likelihood of dislocation and revision surgery [22e24]. To investigate patient movement during THA, we used a novel navigation tool to quantify intraoperative pelvic motion during THA and found that a substantial proportion of patients moved to such a degree as to result in potential placement of the cup outside the planned safe zone. Previous studies examining the degree to which the pelvis moves during THA have used specially designed devices to measure movement intraoperatively. Asayama et al [12] used a digital compass and a 3-dimensional direction indicator to create a pelvic tilt goniometer to evaluate the degree of movement during 30 consecutive lateral-approach THA procedures and found that the pelvis tilted forward during surgery, with a mean of 14.57 of anterior tilt in the horizontal plane, movement that was noted in all 30 patients in the cohort. Smaller movements, with a mean of 0.47 of adduction-abduction and 3.0 of AP inclination, were also noted.
4
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
Fig. 4. Histogram summarizing the proportion of patients exhibiting pitch (blue) and roll (green) motion during THA.
These same authors used their pelvic tilt goniometer device to compare the pelvic motion in the translateral approach with that of the posterolateral approach in a cohort of 100 THA procedures [14]. They noted similar degrees of internal rotation (14.25 ) in the posterolateral approach but less rotation in the translateral approach (1.75 ). In both cases, they noted that the internal rotation was associated largely with the use of Hohmann retractors placed at the anterior rim of the acetabulum. Grammatopoulos et al [11] used a photogrammetric technique to evaluate pelvic motion in 67 THA procedures and found that the pelvis moved a mean of 9 during the procedure. They also noted difficulties in intraoperator reliability, with statistically significant differences in pelvic positioning and movement noted between surgeons. They concluded that inconsistencies in patient setup and movement during surgery accounted for the majority of the variability in acetabular component orientation. Our study found maximum degrees of pitch and roll (9.9 and 31.3 ) similar to that of Asayama et al [12] and Ezoe et al [14] (9 of pitch and 31 of roll in both studies). Our study identified a number of other important findings as well. Primarily, we observed that more than 1 in 3 patients (35%) roll more than 8 during surgery, with 1 in 4 patients (25.3%) moving over 10 . Movement, especially roll, to this degree can have a significant impact on cup orientation. When using conventional guides, failure to compensate for movement of this degree could result in placement of the cup outside the safe limits for anteversion, thus, increasing the risk of dislocation [22,24]. Manual methods of managing leg length changes and cup position cannot monitor this type of patient movement, and traditional navigation does not adequately compensate for changes in pelvic position, with changes in pelvic tilt known to render traditional navigation measurements inaccurate [25]. As such, the inability to properly monitor and compensate for intraoperative movement has the potential to increase both cup malpositioning and complication rates by increasing the potential for instability and dislocation [25e28]. We found that the navigation tool was effective at identifying intraoperative pelvic motion in over 95% of cases. Importantly, because the device is fixed to the iliac crest during
surgery, cup position values provided intraoperatively are true values relative to the current position of the pelvis and not to gravity or the initial neutral position of the patient. Further study is required to determine the specific relationship between pelvic movement and final cup position. Our study is limited somewhat by its retrospective nature, which may limit the strength with which the conclusions can be extrapolated. Although data on patient movement are recorded actively during THA, the retrospective nature of this study limits our ability to analyze the data beyond providing a value for the maximum magnitude of movement. Future studies will prospectively collect data examining the relationship between patient movement, types of positioners, and body mass index and correlate to final cup position. Although surgeons do rely on conventional guides for placement of the acetabular component, they also rely on anatomic landmarks that move with the pelvic motion during THA. In future studies, we will also correlate movement with milestones and/or specific tasks performed during THA to determine the movement associated with each step in the THA procedure. Conclusion Intraoperative motion during THA is common and has the potential to cause inaccuracies in component positioning, errors that can ultimately lead to instability and potential dislocation of the artificial hip joint. We used a novel navigation tool to quantify patient movement during THA and found that 1 in 4 patients roll over 10 , movement that significantly impacts the ability of the surgeon to accurately place the acetabular cup in the planned safe zone and, thus, increases the risk of impingement, edge loading, and dislocation. Monitoring and correcting for this intraoperative motion has the potential to improve cup placement accuracy and decrease the related complications. Further study is needed to determine the effect of patient motion on parameters such as cup position, leg length, and offset and the effect of factors such as patient body mass index, age, gender, retractor type, and surgical positioner on intraoperative motion.
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
Acknowledgments The authors thank Drs Patrick Meere, Bedros Bakirtzian, Vladimir Tress, Morteza Meftah, and Ivan Madrid for contributing data and for editing the article. References [1] Hassan DM, Johnston GH, Dust WN, Watson G, Dolovich AT. Accuracy of intraoperative assessment of acetabular prosthesis placement. J Arthroplasty 1998;13:80e4. [2] Kennedy JG, Rogers WB, Soffe KE, Sullivan RJ, Griffen DG, Sheehan LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty 1998;13:530e4. [3] Woo RY, Morrey BF. Dislocations after total hip arthroplasty. J Bone Joint Surg Am 1982;64:1295e306. [4] Jorgensen CC, Kjaersgaard-Andersen P, Solgaard S, Kehlet H. Hip dislocations after 2,734 elective unilateral fast-track total hip arthroplasties: incidence, circumstances and predisposing factors. Arch Orthop Trauma Surg 2014;134: 1615e22. [5] Meftah M, Yadav A, Wong AC, Ranawat AS, Ranawat CS. A novel method for accurate and reproducible functional cup positioning in total hip arthroplasty. J Arthroplasty 2013;28:1200e5. [6] Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217e20. [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;474:386e91. [8] Esposito CI, Gladnick BP, Lee YY, Lyman S, Wright TM, Mayman DJ, et al. Cup position alone does not predict risk of dislocation after hip arthroplasty. J Arthroplasty 2015;30:109e13. [9] McCollum DE, Gray WJ. Dislocation after total hip arthroplasty. Causes and prevention. Clin Orthop Relat Res 1990;261:159e70. [10] Harris WH. Advances in surgical technique for total hip replacement: without and with osteotomy of the greater trochanter. Clin Orthop Relat Res 1980: 188e204. [11] Grammatopoulos G, Pandit HG, da Assuncao R, Taylor A, McLardy-Smith P, De Smet KA, et al. Pelvic position and movement during hip replacement. Bone Joint J 2014;96-B:876e83. [12] Asayama I, Akiyoshi Y, Naito M, Ezoe M. Intraoperative pelvic motion in total hip arthroplasty. J Arthroplasty 2004;19:992e7.
5
[13] Blondel B, Parratte S, Tropiano P, Pauly V, Aubaniac JM, Argenson JN. Pelvic tilt measurement before and after total hip arthroplasty. Orthop Traumatol Surg Res 2009;95:568e72. [14] Ezoe M, Naito M, Asayama I, Ishiko T, Fujisawa M. Pelvic motion during total hip arthroplasty with translateral and posterolateral approaches. J Orthop Sci 2005;10:167e72. [15] Murphy WS, Klingenstein G, Murphy SB, Zheng G. Pelvic tilt is minimally changed by total hip arthroplasty. Clin Orthop Relat Res 2013;471:417e21. [16] Zhou X, Wang Q, Zhang X, Chen Y, Shen H, Jiang Y. Effect of pelvic obliquity on the orientation of the acetabular component in total hip arthroplasty. J Arthroplasty 2012;27:299e304. [17] Maratt JD, Esposito CI, McLawhorn AS, Jerabek SA, Padgett DE, Mayman DJ. Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter? J Arthroplasty 2015;30:387e91. [18] van Bosse HJ, Lee D, Henderson ER, Sala DA, Feldman DS. Pelvic positioning creates error in CT acetabular measurements. Clin Orthop Relat Res 2011;469: 1683e91. [19] Ranawat CS, Ranawat AS, Lipman JD, White PB, Meftah M. Effect of spinal deformity on pelvic orientation from standing to sitting position. J Arthroplasty 2016;31:1222e7. [20] Digioia AM, Jaramaz B, Plakseychuk AY, Moody JEJ, Nikou C, Labarca RS, et al. Comparison of a mechanical acetabular alignment guide with computer placement of the socket. J Arthroplasty 2002;17:359e64. [21] Paprosky WG, Muir JM. Intellijoint HIP: a 3D mini-optical navigation tool for improving intraoperative accuracy during total hip arthroplasty. Med Devices 2016;9:401e8. [22] Bozic KJ, Kurtz SM, Lau E, Ong K, Vail TP, Berry DJ. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am 2009;91:128e33. [23] Havelin LI, Engesaeter LB, Espehaug B, Furnes O, Lie SA, Vollset SE. The Norwegian Arthroplasty Register: 11 years and 73,000 arthroplasties. Acta Orthop Scand 2000;71:337e53. 24 Canadian Institute for Health Information. Hip and Knee Replacements in Canada: Canadian Joint Replacement Registry 2015 Annual Report. Ottawa, ON: CIHI; 2015 [25] Lembeck B, Mueller O, Reize P, Wuelker N. Pelvic tilt makes acetabular cup navigation inaccurate. Acta Orthop 2005;76:517e23. [26] Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stockl B. Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component. J Bone Joint Surg Br 2005;87:762e9. [27] Morrey BF. Instability after total hip arthroplasty. Orthop Clin North Am 1992;23:237e48. [28] Lakshmanan P, Ahmed SMY, Woodnutt DJ. A calibrated patient positioning device for total hip arthroplasty. Eur J Orthop Surg Traumatol 2008;18:173e4.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Quantifying Pelvic Motion During Total Hip Arthroplasty Using a New Surgical Navigation Device Ran Schwarzkopf, MD, MSc a, Jeffrey M. Muir, MSc, DC, MSc (Clin Epi) b, Wayne G. Paprosky, MD, FACS c, Scott Seymour, MD d, Michael B. Cross, MD e, Jonathan M. Vigdorchik, MD a, * a
Department of Orthopaedic Surgery, NYU Langone Medical CentereHospital for Joint Diseases, New York, New York Department of Clinical Research, Intellijoint Surgical, Inc, Waterloo, Ontario, Canada Department of Orthopedics, Central DuPage Hospital, Winfield, Illinois d Department of Orthopedics, MacNeal Hospital, Berwyn, Illinois e Department of Orthopedic Surgery, Hospital for Special Surgery, New York, New York b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 January 2017 Received in revised form 21 March 2017 Accepted 24 April 2017 Available online xxx
Background: Accurate cup positioning is one of the most challenging aspects of total hip arthroplasty (THA). Undetected movement of the patient during THA surgery can lead to inaccuracies in cup anteversion and inclination, increasing the potential for dislocation and revision surgery. Investigations into the magnitude of patient motion during THA are not well represented in the literature. Methods: We analyzed intraoperative pelvic motion using a novel navigation device used to assist surgeons with cup position, leg length, and offset during THA. This device uses an integrated accelerometer to measure motion in 2 orthogonal degrees of freedom. We reviewed the data from 99 cases completed between February and September 2016. Results: The mean amount of pitch recorded per patient was 2.7 (standard deviation, 2.2; range, 0.1 9.9 ), whereas mean roll per patient was 7.3 (standard deviation, 5.5; range, 0.3 -31.3 ). Twenty-one percent (21 of 99) of patients demonstrated pitch of >4 . Sixty-nine percent (68 of 99) of patients demonstrated >4 of roll, and 25% (25 of 99) of patients demonstrated roll of 10 . Conclusion: Our findings indicate that while the majority of intraoperative motion is <4 , many patients experience significant roll, with a large proportion rolling >10 . This degree of movement has implications for acetabular cup position, as failure to compensate for this motion can result in placement of the cup outside the planned safe zone, thus, increasing the potential for dislocation. Further study is warranted to determine the effect of this motion on cup position, leg length, and offset. © 2017 Elsevier Inc. All rights reserved.
Keywords: total hip arthroplasty pelvic movement cup position navigation surgical
Accurate acetabular cup placement is one of the most challenging aspects of total hip arthroplasty (THA). Improper placement of the acetabular component can increase the likelihood of dislocation and revision surgery [1e4]. To minimize these risks,
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2017.04.046. * Reprint requests: Jonathan M. Vigdorchik, MD, Department of Orthopaedic Surgery, NYU Langone Medical CentereHospital for Joint Diseases, 301 East 17th Street, New York, NY 10003. http://dx.doi.org/10.1016/j.arth.2017.04.046 0883-5403/© 2017 Elsevier Inc. All rights reserved.
surgeons position the acetabular cup component within a supposed functional “safe zone” of 40 ± 10 of inclination and 15 ± 10 of anteversion [5], first proposed by Lewinnek et al [6]. This range is thought to be associated with a lower likelihood of instability and dislocation; however, there is growing debate regarding its true association with lower dislocation rates [7,8]. Although others have suggested alternate ranges (eg, 40 ± 10 abduction/30 ± 10 anteversion [9] or 30 abduction/20 anteversion [10]), the Lewinnek zone continues to be the benchmark. Placement of the acetabular component within this safe zone, however, is particularly challenging, given the potential movement of the pelvis that occurs intraoperatively during THA [11e15]. Changes in pelvic tilt, rotation, and obliquity directly affect anteversion and inclination [16e19]. One study reported that for every 1 increase in pelvic obliquity, anteversion changed
2
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
by 0.4 , and for every degree increased pelvic tilt, anteversion was altered by 0.8 [18]. Another study reported a linear relationship between pelvic tilt and anteversion, with every 1 increase in posterior pelvic tilt associated with a 0.74 change in anteversion [17]. Inclination changed in a nonlinear fashion, with each 1 increase in tilt initially altering inclination by 0.29 . The magnitude of change grew more dramatic as pelvic tilt increased, with 15 of posterior tilt associated with a change of 0.47 of inclination [17]. Surgeons attempt to orient the patient on the operating table in a neutral position before surgery. When positioned laterally, a neutral patient position implies that the patient's sagittal plane is coplanar with the operating table (which is coplanar with the floor), whereas the patient's longitudinal axis is in line with the long dimension of the operating table (Fig. 1). Patient positioners are utilized during the procedure to maintain the patient in this position. Surgeons generally assume that the pelvis remains in this neutral position throughout the procedure, despite the movement and manipulation of the leg and hip joint that occurs during THA. In traditional hip arthroplasty, there is no method of determining if the pelvis remains in the same position throughout the procedure, including the time of implantation of the acetabular component [11]. Significant movement can occur between the initial patient positioning and acetabular component trialing and implantation. Such movement can result in errors in placement of the acetabular components, errors which, if not accounted for or corrected for, can increase the likelihood of components being placed outside the safe zone, leading to increased wear, edge loading, impingement, and dislocation [17,18]. The purpose of this study was to record the magnitude and direction of patient movement during THA surgery. Simple and reliable methods for monitoring and/or compensating for changes in patient position during surgery have not been developed to date, with previous studies using specialized equipment to monitor movement [11,12,14,20]. These devices, however, while providing some useful data, are cumbersome and could interfere with the normal surgical workflow. We used a novel navigation device that uses infrared optical technology and integrated inertial sensors to make intraoperative measurements during THA procedures. Although predominantly used to assist surgeons with component placement by monitoring cup position, leg length, and offset parameters, the device is also able to measure the 2-dimensional motion (or “tilt”) of the pelvis (relative to gravity) and record the magnitude and direction of movements during surgery. Our hypothesis was that significant pelvic motion would be recorded during THA between patient positioning and final implant placement.
Methods Study Design This study was a retrospective review of navigation system data from THA procedures performed at one of 7 sites using the navigation tool. A total of 11 orthopedic surgeons contributed case data for this study. All procedures were performed via the posterior approach with surgeons utilizing their choice of patient positioner and retractor. Data Eligibility Data were eligible for inclusion in this study if the patient underwent a THA procedure between February and September 2016 at one of the participating facilities (4 in New York City, 2 in Chicago, and 1 in upstate New York). Only navigation system data were reviewed; no patient identifiers or demographic data were included in the analysis. Procedures where the navigation tool was used were eligible for inclusion in the study. Data were excluded from procedures where the navigation tool was removed before measurements being taken with either trial components or final implants in place or cases where there was instability in the navigation system's pelvic platform such that accurate measurements were not obtainable from the navigation tool. Intellijoint HIP Navigation Tool The Intellijoint HIP (Intellijoint Surgical, Inc, Waterloo, ON, Canada) navigation tool is a miniature surgical tool that uses infrared optical technology and integrated microelectronics, including inertial sensors, to measure cup implant angle, leg length, offset, and center of rotation to assist surgeons with component placement during THA. The device has been described in detail previously [21]. In brief, with the patient in the lateral decubitus position, a pelvic platform is fixed to the ipsilateral iliac crest via 2 surgical pins. A camera is magnetically secured to the pelvic platform while a tracker is magnetically attached to a femoral platform fixed to the greater trochanter or to a cup impactor, to measure changes in leg length and offset, as well as native acetabular orientation and cup position (Fig. 2). The camera captures motion and position data from the tracker to calculate center of rotation, length leg, and offset for both the native hip and the artificial joint. The attachment of the camera to the pelvic platform creates a fixed system, such that the camera and the pelvis are rigidly coupled (ie, any movement of the pelvis will also move the camera). Pelvic Motion Calculations
Fig. 1. Neutral positioning of the patient in the lateral position. The patient's sagittal plane, A, is coplanar with the operating table. The patient's frontal plane, B, is oriented along the long axis of the table.
The navigation system camera, in addition to its optical components, contains integrated inertial sensors (in particular, a 3-axis accelerometer). The inertial sensing system is configured to measure motion and orientation in 2 orthogonal degrees of freedom (ie, similar to a 2-axis bubble level). Movement is recorded by the navigation system at specific steps during the surgical procedure. Immediately after patient positioning (before hip exposure), the camera is installed on the patient's iliac crest and an initial measurement is recorded to register the horizontal plane, which coincides with the patient's sagittal plane. In addition, the patient's frontal plane is registered and the frontal and sagittal planes are combined to form the patient registration (ie, the spatial relationship between the camera and the patient's anatomy). Later in the procedure (after surgical exposure, hip dislocation, and femoral head resection but
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
3
Statistical Analysis Alpha was set a priori at 0.05 for all statistical comparisons. Means were compared using Student t tests or 1-way analysis of variance where applicable. All mean values are presented as mean (standard deviation, range). MATLAB (MathWorks Inc, Natick, MA) was used to analyze exported measurement data for the cases included in this study to determine the magnitude and direction of patient movement. Results
Fig. 2. The navigation tool in use. The camera, A, in its sterile drape, is attached to the pelvic platform, B, via 2 screws. The tracker, C, is magnetically attached to the femoral platform. The camera captures movements of the tracker when registering the native orientation of the acetabulum or trialing implant components and relays the information to a workstation for review by the surgeon. An accelerometer in the camera measures movement of the pelvis during surgery.
immediately before cup implantation), the system allows a surgeon to define an acetabular reference plane, at which time another measurement is recorded. The system software exports measurement data for each case, including the initial and preimplantation orientations, and the patient registration. From these data, the change in pelvic position may be computed by comparing the patient's initial position on the operating table with the position at the time of cup implantation (recorded during the acetabular reference plane measurement). The patient registration is used to represent the camera-based movement measurements with respect to the pelvis. As a result, the angular movement of the pelvis from incision to the cup implantation step may be quantified for a given case. Patient movement is expressed as both pitch (rotation in the coronal plane about an anteroposterior [AP] axis) and roll (rotation in a transverse plane about a cephalad-caudal axis; Fig. 3). Positive pitch represents rotation about the AP axis that results in obliquity, causing the operating side hemipelvis to move cephalad, increasing abduction angle. Positive roll is rotation about the longitudinal axis that moves the patient toward the prone position. Negative pitch reflects caudal movement of the operative hemipelvis; negative roll represents movement toward a supine position.
Fig. 3. Axes of rotation used in this study. The navigation tool measures pelvic motion during total hip arthroplasty (THA) in 2 planes. Pitch is measured as rotation in the coronal plane about an anteroposterior axis. Roll is measured as rotation in a transverse plane about a cephalad-caudal axis.
From a total of 104 eligible cases, movement data from 99 procedures were included in this study. Of the 99 procedures included in this study, 92 (93%) were primary THAs, while 7 (7%) were revision procedures. Five (5) cases were excluded owing to an inability to achieve adequate bony fixation of either the pelvic (n ¼ 4) or femoral platform (n ¼ 1), resulting in the device being removed before measurements being recorded. Pitch The mean amount of intraoperative pitch recorded per patient was 2.7 (SD, 2.2), with a range of between 0.1 and 9.9 . A pitch of >4 was recorded in 21 of 99 (21%) patients. Roll The mean amount of roll per patient was 7.3 (SD, 5.5), ranging from 0.3 to 31.3 . Over 4 of roll was observed in 68 of 99 (69%) patients, with roll in excess of 6 observed in 53 of 99 (54%) patients and roll 10 recorded in 25 of 99 (25%) patients (Fig. 4). Discussion Examinations of the degree of change in patient position during THA and its implications are not well documented in the literature. There have been few investigations into the pelvic motion that occurs as a result of patient position shift during THA. The studies available report the use of various extraneous devices to monitor and quantify patient motion [11,12,14,20]. Although under-represented in the literature, the importance of characterizing intraoperative motion is significant, as it relates to the difficulty in accurately implanting the acetabular cup component as well as the impact of undetected pelvic movement on cup position. As surgeons generally position the cup component relative to the patient's initial, neutral position, failing to account for intraoperative movement can result in cup placement out of or close to the limits of the Lewinnek safe zone [6], which may increase the likelihood of dislocation and revision surgery [22e24]. To investigate patient movement during THA, we used a novel navigation tool to quantify intraoperative pelvic motion during THA and found that a substantial proportion of patients moved to such a degree as to result in potential placement of the cup outside the planned safe zone. Previous studies examining the degree to which the pelvis moves during THA have used specially designed devices to measure movement intraoperatively. Asayama et al [12] used a digital compass and a 3-dimensional direction indicator to create a pelvic tilt goniometer to evaluate the degree of movement during 30 consecutive lateral-approach THA procedures and found that the pelvis tilted forward during surgery, with a mean of 14.57 of anterior tilt in the horizontal plane, movement that was noted in all 30 patients in the cohort. Smaller movements, with a mean of 0.47 of adduction-abduction and 3.0 of AP inclination, were also noted.
4
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
Fig. 4. Histogram summarizing the proportion of patients exhibiting pitch (blue) and roll (green) motion during THA.
These same authors used their pelvic tilt goniometer device to compare the pelvic motion in the translateral approach with that of the posterolateral approach in a cohort of 100 THA procedures [14]. They noted similar degrees of internal rotation (14.25 ) in the posterolateral approach but less rotation in the translateral approach (1.75 ). In both cases, they noted that the internal rotation was associated largely with the use of Hohmann retractors placed at the anterior rim of the acetabulum. Grammatopoulos et al [11] used a photogrammetric technique to evaluate pelvic motion in 67 THA procedures and found that the pelvis moved a mean of 9 during the procedure. They also noted difficulties in intraoperator reliability, with statistically significant differences in pelvic positioning and movement noted between surgeons. They concluded that inconsistencies in patient setup and movement during surgery accounted for the majority of the variability in acetabular component orientation. Our study found maximum degrees of pitch and roll (9.9 and 31.3 ) similar to that of Asayama et al [12] and Ezoe et al [14] (9 of pitch and 31 of roll in both studies). Our study identified a number of other important findings as well. Primarily, we observed that more than 1 in 3 patients (35%) roll more than 8 during surgery, with 1 in 4 patients (25.3%) moving over 10 . Movement, especially roll, to this degree can have a significant impact on cup orientation. When using conventional guides, failure to compensate for movement of this degree could result in placement of the cup outside the safe limits for anteversion, thus, increasing the risk of dislocation [22,24]. Manual methods of managing leg length changes and cup position cannot monitor this type of patient movement, and traditional navigation does not adequately compensate for changes in pelvic position, with changes in pelvic tilt known to render traditional navigation measurements inaccurate [25]. As such, the inability to properly monitor and compensate for intraoperative movement has the potential to increase both cup malpositioning and complication rates by increasing the potential for instability and dislocation [25e28]. We found that the navigation tool was effective at identifying intraoperative pelvic motion in over 95% of cases. Importantly, because the device is fixed to the iliac crest during
surgery, cup position values provided intraoperatively are true values relative to the current position of the pelvis and not to gravity or the initial neutral position of the patient. Further study is required to determine the specific relationship between pelvic movement and final cup position. Our study is limited somewhat by its retrospective nature, which may limit the strength with which the conclusions can be extrapolated. Although data on patient movement are recorded actively during THA, the retrospective nature of this study limits our ability to analyze the data beyond providing a value for the maximum magnitude of movement. Future studies will prospectively collect data examining the relationship between patient movement, types of positioners, and body mass index and correlate to final cup position. Although surgeons do rely on conventional guides for placement of the acetabular component, they also rely on anatomic landmarks that move with the pelvic motion during THA. In future studies, we will also correlate movement with milestones and/or specific tasks performed during THA to determine the movement associated with each step in the THA procedure. Conclusion Intraoperative motion during THA is common and has the potential to cause inaccuracies in component positioning, errors that can ultimately lead to instability and potential dislocation of the artificial hip joint. We used a novel navigation tool to quantify patient movement during THA and found that 1 in 4 patients roll over 10 , movement that significantly impacts the ability of the surgeon to accurately place the acetabular cup in the planned safe zone and, thus, increases the risk of impingement, edge loading, and dislocation. Monitoring and correcting for this intraoperative motion has the potential to improve cup placement accuracy and decrease the related complications. Further study is needed to determine the effect of patient motion on parameters such as cup position, leg length, and offset and the effect of factors such as patient body mass index, age, gender, retractor type, and surgical positioner on intraoperative motion.
R. Schwarzkopf et al. / The Journal of Arthroplasty xxx (2017) 1e5
Acknowledgments The authors thank Drs Patrick Meere, Bedros Bakirtzian, Vladimir Tress, Morteza Meftah, and Ivan Madrid for contributing data and for editing the article. References [1] Hassan DM, Johnston GH, Dust WN, Watson G, Dolovich AT. Accuracy of intraoperative assessment of acetabular prosthesis placement. J Arthroplasty 1998;13:80e4. [2] Kennedy JG, Rogers WB, Soffe KE, Sullivan RJ, Griffen DG, Sheehan LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty 1998;13:530e4. [3] Woo RY, Morrey BF. Dislocations after total hip arthroplasty. J Bone Joint Surg Am 1982;64:1295e306. [4] Jorgensen CC, Kjaersgaard-Andersen P, Solgaard S, Kehlet H. Hip dislocations after 2,734 elective unilateral fast-track total hip arthroplasties: incidence, circumstances and predisposing factors. Arch Orthop Trauma Surg 2014;134: 1615e22. [5] Meftah M, Yadav A, Wong AC, Ranawat AS, Ranawat CS. A novel method for accurate and reproducible functional cup positioning in total hip arthroplasty. J Arthroplasty 2013;28:1200e5. [6] Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217e20. [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;474:386e91. [8] Esposito CI, Gladnick BP, Lee YY, Lyman S, Wright TM, Mayman DJ, et al. Cup position alone does not predict risk of dislocation after hip arthroplasty. J Arthroplasty 2015;30:109e13. [9] McCollum DE, Gray WJ. Dislocation after total hip arthroplasty. Causes and prevention. Clin Orthop Relat Res 1990;261:159e70. [10] Harris WH. Advances in surgical technique for total hip replacement: without and with osteotomy of the greater trochanter. Clin Orthop Relat Res 1980: 188e204. [11] Grammatopoulos G, Pandit HG, da Assuncao R, Taylor A, McLardy-Smith P, De Smet KA, et al. Pelvic position and movement during hip replacement. Bone Joint J 2014;96-B:876e83. [12] Asayama I, Akiyoshi Y, Naito M, Ezoe M. Intraoperative pelvic motion in total hip arthroplasty. J Arthroplasty 2004;19:992e7.
5
[13] Blondel B, Parratte S, Tropiano P, Pauly V, Aubaniac JM, Argenson JN. Pelvic tilt measurement before and after total hip arthroplasty. Orthop Traumatol Surg Res 2009;95:568e72. [14] Ezoe M, Naito M, Asayama I, Ishiko T, Fujisawa M. Pelvic motion during total hip arthroplasty with translateral and posterolateral approaches. J Orthop Sci 2005;10:167e72. [15] Murphy WS, Klingenstein G, Murphy SB, Zheng G. Pelvic tilt is minimally changed by total hip arthroplasty. Clin Orthop Relat Res 2013;471:417e21. [16] Zhou X, Wang Q, Zhang X, Chen Y, Shen H, Jiang Y. Effect of pelvic obliquity on the orientation of the acetabular component in total hip arthroplasty. J Arthroplasty 2012;27:299e304. [17] Maratt JD, Esposito CI, McLawhorn AS, Jerabek SA, Padgett DE, Mayman DJ. Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter? J Arthroplasty 2015;30:387e91. [18] van Bosse HJ, Lee D, Henderson ER, Sala DA, Feldman DS. Pelvic positioning creates error in CT acetabular measurements. Clin Orthop Relat Res 2011;469: 1683e91. [19] Ranawat CS, Ranawat AS, Lipman JD, White PB, Meftah M. Effect of spinal deformity on pelvic orientation from standing to sitting position. J Arthroplasty 2016;31:1222e7. [20] Digioia AM, Jaramaz B, Plakseychuk AY, Moody JEJ, Nikou C, Labarca RS, et al. Comparison of a mechanical acetabular alignment guide with computer placement of the socket. J Arthroplasty 2002;17:359e64. [21] Paprosky WG, Muir JM. Intellijoint HIP: a 3D mini-optical navigation tool for improving intraoperative accuracy during total hip arthroplasty. Med Devices 2016;9:401e8. [22] Bozic KJ, Kurtz SM, Lau E, Ong K, Vail TP, Berry DJ. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am 2009;91:128e33. [23] Havelin LI, Engesaeter LB, Espehaug B, Furnes O, Lie SA, Vollset SE. The Norwegian Arthroplasty Register: 11 years and 73,000 arthroplasties. Acta Orthop Scand 2000;71:337e53. 24 Canadian Institute for Health Information. Hip and Knee Replacements in Canada: Canadian Joint Replacement Registry 2015 Annual Report. Ottawa, ON: CIHI; 2015 [25] Lembeck B, Mueller O, Reize P, Wuelker N. Pelvic tilt makes acetabular cup navigation inaccurate. Acta Orthop 2005;76:517e23. [26] Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stockl B. Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component. J Bone Joint Surg Br 2005;87:762e9. [27] Morrey BF. Instability after total hip arthroplasty. Orthop Clin North Am 1992;23:237e48. [28] Lakshmanan P, Ahmed SMY, Woodnutt DJ. A calibrated patient positioning device for total hip arthroplasty. Eur J Orthop Surg Traumatol 2008;18:173e4.