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Anatomical Hip Range of Motion After Implantation During Total Hip Arthroplasty With a Large Change in Pelvic Inclination
The Journal of Arthroplasty Vol. 27 No. 9 2012
Anatomical Hip Range of Motion After Implantation During Total Hip Arthroplasty With a Large Change in Pelvic Inclination Hidenobu Miki, MD, PhD,* Takayuki Kyo, MD,* and Nobuhiko Sugano, MD, PhDy
Abstract: The supine functional pelvic plane is the recommended reference pelvic plane for acetabular cup planning in navigation-assisted total hip arthroplasty. However, it is unclear whether it can be used in patients with a large preoperative positional change in pelvic inclination (PC) from the supine to the standing position because it is unknown whether these patients have a different hip range of motion (ROM). We measured the anatomical hip ROM after implantation by computed tomography–based navigation in 91 patients and found it to be similar between those with a small PC (b10°) and those with a large PC (≥10°). There was no significant correlation between ROM and preoperative PC. The supine functional pelvic plane is adequate for cup planning whether the PC is small or large. Keywords: total hip arthroplasty, functional pelvic plane, pelvic inclination, positional change, acetabular cup orientation, preoperative planning. © 2012 Elsevier Inc. All rights reserved.
Proper acetabular cup orientation is essential in total hip arthroplasty (THA) to avoid edge loading and prosthesis impingement, which may lead to serious complications, such as dislocation, mechanical loosening, wear or breakage of the polyethylene liner, metallosis or metal ion release from metal-on-metal bearings, and squeaking or breakage of ceramic-on-ceramic bearings [1-8]. Cup orientation is set relative to a pelvic coordinate system for preoperative three-dimensional (3D) planning. The coordinate system is generally constructed from a reference pelvic plane, which is determined by picking a number of reference points on the surface of a 3D pelvic model in preoperative planning software. Historically, the anterior pelvic plane (APP) was initially used as a reference, and it was defined by 3 reference points: the left anterior superior iliac spine (LASI), the right anterior superior iliac spine (RASI), and the
From the *Department of Orthopedic Surgery, Osaka National Hospital, Osaka, Japan; and yDepartment of Orthopedic Surgery, Medical School of Osaka University, Osaka, Japan. Supplementary material available at www.arthroplastyjournal.org. Submitted February 19, 2011; accepted March 1, 2012. The authors received a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science in support of the study reported here. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2012.03.002. Reprint requests: Hidenobu Miki, MD, PhD, Department of Orthopedic Surgery, Osaka National Hospital, 2-1-14 Hoenzaka, Chu-o-ku, Osaka 540-0006, Japan. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2709-0011$36.00/0 doi:10.1016/j.arth.2012.03.002
midpoint of the left pubic tubercle (LPT) and the right pubic tubercle (RPT). The pelvic coordinate system based on APP is constructed as follows: the x-axis is parallel to the line including the RASI and LASI, the y-axis is perpendicular to the APP, and the z-axis is perpendicular to the x- and y-axes (Fig. 1). Although the APP was considered to be superimposable on the horizontal plane in the supine position and on the vertical plane in the standing position, it has been shown that there is a large degree of interpatient variation in the APP [9-11]. The functional pelvic plane (FPP) in either the supine or standing position (the supine FPP and the standing FPP, respectively) is normally used as the reference pelvic plane [11-13]. Each is created by rotating the APP around the x-axis of the pelvis by the pelvic inclination in the supine position or the standing position (PIsup or PIstand, respectively) measured by preoperative computed tomography (CT) or radiography (Fig. 1). Although the standing FPP corresponds to the position of the pelvis in most daily activities, the current recommendation for acetabular cup orientation is based on previous data using the supine FPP. Several clinical reports have concluded that surgeons should avoid steep cup inclination in supine anteroposterior (AP) radiography to prevent edge loading [1,4,7,8]. Furthermore, simulation studies have been performed since the late 1990s to calculate optimal cup orientation for avoiding prosthesis impingement within the intended hip range of motion (ROM) [14-16]. The results of these studies vary according to intended hip and prosthesis ROM. Although the actual postoperative anatomical hip ROM for
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1642 The Journal of Arthroplasty Vol. 27 No. 9 October 2012
Fig. 1. Definitions of pelvic coordinate systems based on the APP, FPP, and the standing FPP.
individual patients cannot be estimated accurately, the potential anatomical maximum hip ROM has recently been measured precisely by 3D motion analysis and by CT-based navigation systems both in healthy persons and in patients undergoing THA [17,18], and these data have been used as a reference for the desired hip ROM [19-21]. The anatomical hip ROM is defined as relative angles between the pelvis and the femoral coordinate system. In these studies, the APP or the supine FPP was used as the reference plane for the pelvic coordinate system, but the standing FPP was not determined. Although an inclination of 40° to 45° and anteversion based on combined anteversion theory have recently been recommended for cup orientation in THA with a conventional femoral head size, the concept of combined anteversion was also proposed in a similar simulation study to avoid prosthesis impingement within the desired hip ROM defined using the supine FPP [20]. In addition to the advantages of using the supine FPP already mentioned, some authors have recommended using the supine FPP as the reference plane for preoperative planning of cup orientation, as the supine pelvic tilt angle is a reasonable approximation of the standing pelvic tilt angle because the change in pelvic inclination between supine and standing positions (positional change of pelvic inclination [PC]) is small in most cases (within 10° in 83%-90% of cases) [11,12]. However, it remains unclear whether the current recommendation for cup orientation based on the supine FPP can be similarly applied when there is a large PC because it is unclear whether the maximum anatomical hip ROM defined using the supine FPP in
patients with a large PC is comparable with that in patients with a small PC. Therefore, we measured preoperative PC using a 2-dimensional–3D matching technique and performed THA using a CT-based navigation system. During surgery, we determined the intraoperative maximum anatomical hip ROM by using the navigation system as a measurement tool. Then, we compared the intraoperative maximum anatomical hip ROM defined using the supine FPP in patients with a large PC (≥10°) with that in patients with a small PC (b10°). In addition, we investigated the relationship between the preoperative PC and the intraoperative anatomical hip ROM.
Materials and Methods Patients Primary THA was performed in 91 patients (84 women and 7 men) in our hospital using a CT-based navigation system (Stryker CT-Hip System 1.0; Stryker-Leibinger, Freiburg, Germany) between April 2009 and September 2010. We performed computer-assisted hip surgeries, including THA, with the approval of our institute's institutional review board. Informed consent was obtained from all patients. Cementless stems (Centpillar; Stryker Orthopaedics, Cork, Ireland) and metal cups with a metal head (Adept; Finsbury Orthopaedics, London, United Kingdom) were implanted in all cases. Indications for surgery were end-stage hip osteoarthritis (OA) due to dysplasia (n = 85) and avascular necrosis of the femoral head (n = 6). According to Crowe's classification, 76 patients had grade 1 dysplasia, 10 had grade 2, and 5 had grade 3. The average age of patients at
Anatomic Hip ROM After Implantation During THA Miki et al
the time of surgery was 64 years (range, 34-85 years). To date, no patients have experienced any postoperative complications, with the average postoperative duration being 24 months (range, 15-32 months). Preoperative Positional Change of Pelvic Inclination Preoperative PC was determined by using the radiography–CT model matching method reported previously (Fig. 2) [12]. We took AP radiographs of the pelvis in the supine and standing positions before surgery. The vertical diameter of the pelvic foramen (A) divided by the maximum horizontal diameter of the pelvic foramen (B) (A:B ratio) was calculated on AP radiographs of the pelvis in both the supine and standing positions. A was defined as the distance between the line connecting the inferior bilateral margins of the sacroiliac joint and the superior margin of the pubic symphysis, and B was defined as the maximum horizontal diameter of the pelvic foramen. In the planning module of this navigation system, the pelvic coordinate system, based on the APP, was first created on the 3D pelvic model. The AP view of the 3D pelvic model was shown by projecting it onto the x-z plane of the pelvic coordinate system. The vertical diameter of the pelvic foramen (A′) and the maximum horizontal diameter of the pelvic foramen (B′) for the AP view of the pelvic model were defined, and we rotated the pelvic model around the x-axis of the pelvis until the A′:B′ ratio matched the A:B ratio measured on the AP radiograph in the supine and
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standing positions. The rotating angles around the x-axis were defined as the PIsup and PIstand. Therefore, PC from the supine to the standing position (PCsup-stand) was defined as PIsup − PIstand (positive values of PCsup-stand indicated an anterior change). The absolute value of PCsup-stand was defined as PC. Preoperative Planning Although imageless navigation used only the APP as the pelvic reference plane, CT-based navigation can also reference the supine FPP defined in preoperative planning. We completed preoperative planning using the planning module of the CT-based navigation system. In preparation for planning, CT was performed from the pelvis to the knee joint, and the results were transferred into the planning module. Reference points were used to define the coordinate systems of the pelvis and bilateral femurs (Fig. 3; available online at www.arthroplastyjournal.org): the RASI, LASI, RPT, and LPT; the distal-most points of the ischium (right ischium [RIS] and left ischium [LIS]), the midpoint of the pubic symphysis (PUB) and sacral midpoint (SACR) for the pelvic frame; and the center of the femoral head, pyriform fossa (FOS), the posterior-most point of the proximal femur (PF), the medial and lateral posterior condyles (MFC and LFC, respectively), and the knee center (KC) for the femoral frame. The APP was defined using the RASI, the LASI, and the midpoint of the RPT and LPT. The x-axis was parallel
Fig. 2. Model matching method using radiography and CT to measure preoperative pelvic inclinations in the supine and standing positions. 2D indicates 2-dimensional.
1644 The Journal of Arthroplasty Vol. 27 No. 9 October 2012 to the line including the RASI and LASI, the y-axis was perpendicular to the APP, and the z-axis was perpendicular to the x- and y-axes. To adjust pelvic obliquity and rotation, the coordinate system was rotated locally around the y-axis until the x-axis was parallel to a line through the projected points of the RIS and LIS on the x-z plane and around the z-axis until the y-axis was parallel to a line through the projected points of the PUB and SACR on the x-y plane. It was then rotated locally around the x-axis by the PIsup, measured as already described. As a result, the pelvic coordinate system based on the supine FPP was built on the pelvic model. For the femur, the y-axis was perpendicular to the retrocondylar plane (RCP), which included points PF, MFC, and LFC. The z-axis was a line through FOS′ and KC′, the projected points of FOS and KC, respectively, on the RCP. The x-axis was perpendicular to the y- and z-axes. Stem and cup orientation was then planned using a 3D template relative to the pelvic and femoral coordinate systems. Radiographic inclination for the acetabular cup was set at 40°, with cup anteversion adjusted according to the stem anteversion angle; radiographic cup anteversion was set at 20°, 15°, or 10° if stem anteversion was found to be 10° to 15°, 15° to 50°, or 50° to 60°, respectively. This cup target was calculated by a commonly used collision detection technique for 3D objects using computer-aided design models of the Centpillar stem and Adept cup to avoid prosthesis impingement at the required hip ROM (120° flexion, 40° extension, 40° external rotation, and 40° internal rotation at 90° flexion) [22].
examination of intraoperative anatomical hip ROM, the rotation matrix is measured by the navigation system in the operating room. During the operation, the femoral and pelvic trackers are rigidly fixed to the pelvis and femur (Fig. 5). The navigation system can measure the 3D positions of these trackers by using an optical 3D sensor in the camera. In the pelvis, although the navigation camera shows the rotation matrix of the pelvic tracker coordinate system in the camera coordinate system (Pc), it does not recognize the pelvis at this point (Fig. 6). Therefore, it requires registration of the pelvic position within the tracker coordinate system. The coordinates of the surface points on the real pelvis in the pelvic tracker coordinate system are picked up by a navigation pointer. These coordinates of the real pelvic surface and the surface of the pelvic model, defined by the coordinate system based on the supine FPP in preoperative planning, are matched by the computer in the navigation system, and then, the rotation matrix of the pelvic coordinate system into the pelvic tracker coordinate system (Pt) is determined. In the femur, the navigation camera shows the rotation matrix of the femoral tracker coordinate system into the camera coordinate system (Fc). After registration of the femoral position to the femoral tracker is similarly performed, the rotation matrix of the femoral coordinate system into the femoral tracker coordinate system (Ft) is determined. After registration is complete, the rotation matrix (R) of the femoral coordinate system into the pelvic coordinate system (Fig. 7) is determined by the following formula:
Measurement of Intraoperative Anatomical Hip ROM Using a CT-Based Navigation System We used a CT-based navigation system to measure intraoperative anatomical ROM, as described elsewhere [18]. The anatomical hip ROM was defined as the relative angle between the pelvis and the femoral coordinate system, which is not physical hip ROM between the thigh and trunk axis or the surgical table. The neutral position of the anatomical hip ROM was defined as the position in which the x-, y-, and z-axes of the femoral coordinate system, which is based on the RCP, are parallel to the x-, y-, and z-axes, respectively, of the pelvic coordinate system, which is based on the supine FPP (Fig. 4). An anatomical hip ROM in a hip position is expressed as rotation angles into the local femoral coordinate system from the neutral position. The first rotation (θ) is performed around the x-axis, which means flexion or extension. The second (φ) and third (ψ) rotations are around the y-axis and z-axis, which means abduction or adduction and external or internal rotation, respectively. The angles (θ, φ, and ψ) can be mathematically calculated when the rotation matrix (R) of the femoral coordinate system into the pelvic coordinate system is known (Fig. 4). Therefore, in
R = ðPc PtÞ − 1 × ðFc × FtÞ Then, the CT-based navigation system can determine the intraoperative anatomical hip ROM in real time during surgery. Therefore, accuracy of measurement of the anatomical ROM depends on registration accuracy without loosening of the tracker. The accuracy of registration has been found to be 0.9° of bias with 0.3° of the root mean square in the pelvis and 0.6° of bias with 0.3° of the root mean square in the femur [23]. We checked for loosening of both pelvic and femoral trackers after measuring anatomical ROM in the operating room, and the trackers proved to be stable in all cases. The limits of agreement (0.6°-1.5° for the pelvis and 0°-1.2° for the femur) indicated that the angular error of anatomical ROM measured by the system would be within 3°. Computed Tomography–Based Navigation Surgery All surgeries were performed with the patient in the lateral position, using the navigation system and a posterolateral approach via a 10-cm incision, which included complete resection of the joint capsule. Before making the skin incision, we attached a pelvic tracker percutaneously to the ipsilateral ilium with an external
Anatomic Hip ROM After Implantation During THA Miki et al
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Fig. 4. Definitions of anatomical hip ROM.
fixation device (Hoffman II; Stryker-Leibinger) using 2 Apex half pins (Stryker Osteosynthesis, Selzach, Switzerland). After the hip joint was dislocated, a femoral tracker was fixed rigidly to the greater trochanter using a triangular plate with 3 screws. Registration of the femur was completed by surface matching. The verification point for the femur, which was used to check intraoperative loosening of the femoral tracker, was marked on the greater trochanter. Femoral preparation and rasping were then performed. Subsequently, registration of the pelvis was also performed by surface matching, and the verification point for the pelvis was marked on the posterosuperior portion of the acetabular rim. After reaming, implantation of the acetabular cup was performed under navigation-system guidance. Final anteversion and inclination of the cup were recorded
Fig. 5. Overview of the CT-based navigation system.
by a tracker fixed on the cup inserter. Implantation of the stem was performed, and final anteversion and the valgus angle were recorded by a tracker fixed on the stem inserter. Finally, leg length was adjusted by changing the neck length of the femoral head. After implantation and repositioning, the real-time intraoperative hip position was shown on the navigation monitor. We recorded the maximum angles of hip flexion, extension, abduction, external rotation, and internal rotation at 90° flexion. Using these measurements, we aimed to approximate the standard position with regard to the directions of movement from the intended position while viewing the navigation monitor; for example, the optimal angles for abduction and internal rotation were 0° at maximum flexion and 0° of abduction and 90° of flexion on maximum internal rotation at 90° flexion. Although gentle retraction of the skin and soft tissue prevented interference with the pelvic and the femoral trackers during the measurement process, the stability of the trackers was checked by touching the verification points marked on the pelvis and the femur with the pointer after the measurement had been obtained. When the tip of the pointer was displaced more than 2 mm from the registered point on the navigation computer, the reference trackers were considered to have loosened. Both pelvic and femoral trackers proved stable in all cases after the measurement of anatomical ROM. Skin closure was performed after suturing of the short rotators to the greater trochanter. Patients were allowed to engage in full weight bearing at 24 hours after surgery and were discharged from the hospital 2 to 4 weeks later. All patients received standard rehabilitation care.
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Fig. 6. Intraoperative registration of the pelvic coordinate system based on the supine FPP.
Measurement of Implant Orientation We used the value of the final intraoperative record obtained by navigation as the implant orientation instead of the measurement from postoperative CT. The Adept cup is a thick monoblock cup made of cobalt-
chrome alloy. It was difficult to measure postoperative orientation by the standard method using 3D templates on multiplanar reconstruction images from postoperative CT because of strong halation on the images. Moreover, it was also difficult to obtain correct
Fig. 7. Intraoperative measurement of anatomical hip ROM.
Anatomic Hip ROM After Implantation During THA Miki et al
measurements of cup orientation relative to the defined pelvic coordinate system by AP hip radiography. However, the accuracy of CT-based navigation, which was defined as the intraoperative final record of implant orientation minus the postoperative implant orientation measured on postoperative CT, has already been documented [24-26]. Navigation accuracy was −0.8° ± 4.1° (range, −6° to 8°) for cup anteversion, 0.4° ± 2.5° (range, −6° to 5°) for cup abduction, −0.6° ± 4.8° (range, −11° to 10°) for stem anteversion, and −0.2° ± 1.8° (range, −4° to 3°) for stem valgus. The mean absolute value of navigation accuracy was 2.4° to 3.0° (SD, 2.0°2.6°) for abduction and 2.0° to 3.3° (SD, 1.4°-2.3°) for anteversion. Therefore, we used the navigation system as a measurement tool because it has a known accuracy. Individual Safety Margin Up to Prosthesis Impingement Estimated From the Implant Orientation The individual estimated prosthesis ROMs for flexion, extension, external rotation, and internal rotation at 90° flexion were calculated by the collision-detection technique for 3D objects using computer-aided design models of the Adept cup and the Centpillar stem with the same sizes and orientations as in the intraoperative records [22]; therefore, the safety margin for impingement was calculated for those movements from the following formula: estimated prosthesis ROM − maximum intraoperative anatomic hip ROM
Statistics The unpaired t test, simple regression analysis, and 1-factor analysis of variance were performed using StatView software (version 5.0; SAS Institute, Cary, NC). In all analyses, P b .05 was taken to indicate statistical significance.
Results The results for 91 cases are shown in Table 1 as means ± SD (range): PCsup-stand was −7° ± 6° (range, −21° to 5°); PIsup and PIstand were 4° ± 8° (range, −18° to 26°) and −3° ± 11° (range, −32° to 22°), respectively. Strong correlations were found between PIsup and PIstand (R = 0.88) and between PIstand and PCsup-stand (R = 0.75); however, only a weak correlation was found between PIsup and PCsup-stand (R = 0.35). The measured intraoperative anatomical maximum hip ROMs were 93° ± 12° (range, 60°-120°) in flexion, 15° ± 10° (range, −13° to 36°) in extension, 9° ± 13° (range, −25° to 43°) in external rotation, 51° ± 8° (range, 35°-70°) in internal rotation at 90° flexion, and 33° ± 9° (range, 9°-55°) in abduction. The safety margins with regard to prosthesis impingement were 57° ± 13° in flexion, 57° ± 15° in extension, 94° ± 30° in external rotation, and 34° ± 14° in internal rotation at 90° flexion. The mean safety margin for internal rotation at 90° flexion was signifi-
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Table 1. Results for 91 Cases Parameter
Mean ± SD
Preoperative factors −7 ± 6 PCsup-stand (°) 4±8 PIsup (°) −3 ± 11 PIstand (°) Age (y) 64 ± 11 Height (cm) 152 ± 8 Weight (kg) 57 ± 12 24 ± 4 BMI (kg/m2) Intraoperative anatomical hip ROM Max Flex (°) 93 ± 12 Max Ext (°) 15 ± 10 Max ER (°) 9 ± 13 Max IR at 90° Flex (°) 51 ± 8 Max Abd (°) 33 ± 9 Safety margin up to prosthesis impingement Flex (°) 57 ± 13 Ext (°) 57 ± 15 ER (°) 94 ± 30 IR at 90° Flex (°) 34 ± 14
Range −21 to 5 −18 to 26 −32 to 22 34-85 135-178 34-99 16-38 60-120 −13 to 36 −25 to 43 35-70 9-55 28-90 26-98 39-195 4-64
Abbreviations: Abd, abduction; BMI, body mass index; ER, external rotation; Ext, extension; Flex, flexion; IR, internal rotation; Max, maximum. The mean safe margin of internal rotation at 90° flexion was significantly smaller than the mean safe margin for other measurements, as determined by 1-factor analysis of variance (P b .01).
cantly less than those for the other measurements (1-factor analysis of variance, P b .01). There was a PC of greater than 5° in 58 cases (64%), greater than 10° in 27 cases (30%), greater than 15° in 6 cases (7%), and greater than 20° in 2 cases (2%) (Fig. 8). In all cases with a PC of greater than 5°, there was a posterior change in pelvic inclination from the supine to standing position. Of the preoperative factors considered (age, height, weight, body mass index), only age showed a weak correlation with PCsup-stand (R = −0.32). The results of simple regression analyses between maximum ROM and various factors are shown in Table 2. The PCsup-stand was not correlated with ROM in any direction. However, PIsup and PIstand showed moderate negative correlations with maximum flexion (R = −0.36 and −0.37, respectively) and with external rotation (R = −0.44 and −0.44, respectively). With regard to maximum ROM and hip position other than the measured direction, there were moderate correlations only between maximum abduction and hip position of flexion and external rotation at the measurement of abduction (R = 0.46 and −0.35, respectively). Therefore, the results for maximum abduction could be affected by hip position at the time of measurement. We compared intraoperative maximum ROM for 32 patients with a large PC (≥10°) and 59 patients with a small PC (b10°) (Table 3; available online at www. arthroplastyjournal.org). The large PC subgroup had only posterior PCs. The mean PCsup-stand in the large PC subgroup (−13° ± 3°) was significantly smaller than that
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Fig. 8. Histogram of preoperative positional change in pelvic tilt from supine to standing position.
in the small PC subgroup (−4° ± 3°) (P b .0001). Mean PIsup and PIstand in the large PC subgroup (0° ± 6° and −13° ± 8°, respectively) were significantly smaller than those in the small PC subgroup (7° ± 7° and 2° ± 8°, respectively) (P b .0001). The mean age in the large PC subgroup (69 ± 11 years) was significantly higher than that in the small PC subgroup (62 ± 9 years). There were no significant differences between the 2 subgroups with regard to height, weight, body mass index, implant orientation, or hip position other than the measurement direction at determination of intraoperative ROM, except for external rotation under maximum extension. For intraoperative anatomical hip ROM, the mean maximum flexion and external rotation of the large PC subgroup (97° ± 11° and 15° ± 11°, respectively) were significantly larger than those for the small PC
subgroup (90° ± 12° and 6° ± 13°, respectively); the respective P values were less than .01 and less than .005. However, maximum values for maximum flexion and extension, external rotation at 0° flexion, and internal rotation at 90° flexion, and abduction were 117°, 36°, 43°, 67°, and 55°, respectively, in the large PC subgroup and 120°, 32°, 43°, 70°, and 53°, respectively, in the small PC subgroup. There were no significant differences between the 2 subgroups in maximum values for intraoperative maximum ROM.
Discussion Although other studies have indicated that large PCs (N10°) are rare (7%-10%), 30% of patients in our study exhibited a PC with pelvic inclination of greater than 10° [11,12]. This difference might have been
Table 2. Simple Regression Analyses (R Values) of Preoperative Factors Factor Age Height Weight BMI PIsup PIstand PCsup-stand Hip position other than the measured direction Flexion Abduction External rotation Implant orientation Radiographic cup inclination Radiographic cup anteversion Stem anteversion
Flexion
−0.36 −0.37
Extension
External Rotation
Internal Rotation at 90° Flexion
Abduction
−0.44 −0.44
0.46 −0.35
−0.52
0.67
Anatomic Hip ROM After Implantation During THA Miki et al
influenced by average patient age, as we found that PCsup-stand was significantly correlated with age. The average age of patients in 1 report [12] was 56 years, which was lower than in 64 of our 91 patients. Unfortunately, patient age was not recorded in the other report on this issue [11]. Thus, the proportion of patients with a large PC may not always be small, owing to patient selection. Therefore, it is very important to take suitable acetabular cup orientation into consideration in patients with a large PC. It is not necessary for surgeons to change preoperative planning with regard to implant orientation, even in patients with a large preoperative PC, when the supine FPP is used as the reference pelvic plane. In our study, PCsup-stand was not correlated with intraoperative maximum ROM, and intraoperative maximum ROM values were not significantly different between the large PC and small PC subgroups for any direction of movement. However, we also found that the average maximum flexion and external rotation were greater in the large PC subgroup than those in the small PC subgroup. These findings suggest that complications related to impingement, such as posterior or anterior dislocation, will occur more frequently in patients with a large PC when an implant with insufficient prosthesis ROM is used or in whom the components are placed in an incorrect orientation. With regard to patient selection, PCsup-stand ranged from −21° to 5° in our study population. To our knowledge, there has been only 1 previous report regarding the range of PCsup-stand, which was found to be between −18° and 21° in relatively young patients [12]. Therefore, although it was difficult to assess whether our patients were representative of all patients undergoing THA, our series included a sufficient number of patient with a large posterior PC but an insufficient number with a large anterior PC. Intraoperative passive hip ROM can be affected by type of anesthesia used, surgical approach, spatial prosthesis position, and implant design. However, 1 limitation of our study is that those factors may create variations between intraoperative and postoperative hip ROM. Our hip ROM measurements were obtained while patients were under general anesthesia and may, therefore, differ from those obtained from conscious patients because of differences in the level of muscle activation. Although the passive muscle length–tension curve was shown to be the same in the 2 states, the corresponding active curves are different [27]. Thus, active and passive ROM may not be very different theoretically, although the force needed to arrive at the end point of ROM may vary between the 2 states. However, over time, postoperative hip ROM may be higher than the results that we obtained, although the 2 measurements may be similar for a short time after the operation. Intraoperative hip ROM in our study was measured immediately
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after implantation. Because intraoperative ROM in flexion, extension, and external rotation had a large safety margin up to implant impingement, this could increase because of postoperative adaptation of muscles and tendons with increased patient activity [28]. It is difficult to clarify the limitations of our study, as it would be necessary to perform a similar study measuring postoperative hip ROM accurately using a highgrade methodology, such as patient-specific motion analysis [29]. In conclusion, our findings indicate that the current recommendations for cup orientation could be similarly applicable in patients with a large posterior change of pelvic inclination from the supine to the standing position when the FPP in the supine position is used as the reference pelvic plane in navigation-assisted THA.
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1650 The Journal of Arthroplasty Vol. 27 No. 9 October 2012 12. Nishihara S, Sugano N, Nishii T, et al. Measurements of pelvic flexion angle using three-dimensional computed tomography. Clin Orthop Relat Res 2003;411:140. 13. Eckman K, Hafez MA, Ed F, et al. Accuracy of pelvic flexion measurements from lateral radiographs. Clin Orthop Relat Res 2006;451:154. 14. D'Lima DD, Urquhart AG, Buehler KO, et al. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios. J Bone Joint Surg Am 2000;82:315. 15. Jerosch J, Filler TJ, Peuker ET. The cartilage of the tibiofibular joint: a source for autologous osteochondral grafts without damaging weight-bearing joint surfaces. Arch Orthop Trauma Surg 2002;122:217. 16. Seki M, Yuasa N, Ohkuni K. Analysis of optimal range of socket orientations in total hip arthroplasty with use of computer-aided design simulation. J Orthop Res 1998; 16:513. 17. Nadzadi ME, Pedersen DR, Yack HJ, et al. Kinematics, kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation. J Biomech 2003;36:577. 18. Miki H, Yamanashi W, Nishii T, et al. Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 2007; 22:946. 19. Widmer KH, Majewski M. The impact of the CCD-angle on range of motion and cup positioning in total hip arthroplasty. Clin Biomech 2005;20:723. 20. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res 2004;22:815. 21. Yoshimine F. The influence of the oscillation angle and the neck anteversion of the prosthesis on the cup safe-zone
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that fulfills the criteria for range of motion in total hip replacements. The required oscillation angle for an acceptable cup safe-zone. J Biomech 2005;38:125. Gottschalk S, Lin MC, Manocha D. 1996. OBBTree: a hierarchical structure for rapid interference detection. SIGGRAPH '96 Proceedings of the 23rd Annual Conference on Computer Graphics and Interactive Techniques. New York: ACM Press; 1996; p. 171. Sugano N, Sasama T, Sato Y, et al. Accuracy evaluation of surface-based registration methods in a computer navigation system for hip surgery performed through a posterolateral approach. Comput Aided Surg 2001;6:195. Kitada M, Nakamura N, Iwana D, et al. Evaluation of the accuracy of computed tomography–based navigation for femoral stem orientation and leg length discrepancy. J Arthroplasty 2011;26:674. Hananouchi T, Takao M, Nishii T, et al. Comparison of navigation accuracy in THA between the minianterior and -posterior approaches. Int J Med Robot 2009;5:20. Kalteis T, Handel M, Bäthis H, et al. Imageless navigation for insertion of the acetabular component in total hip arthroplasty: is it as accurate as CT-based navigation? J Bone Joint Surg Br 2006;88:163. Zajac FE. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng 1989;17:359. Woolson ST, Maloney WJ, Schurman DJ. Time-related improvement in the range of motion of the hip after total replacement. J Bone Joint Surg Am 1985;67:1251. Hagio K, Sugano N, Nishii T, et al. A novel system of fourdimensional motion analysis after total hip arthroplasty. J Orthop Res 2004;22:665.
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1650.e1
Fig. 3. The pelvic and femoral coordinate systems in the CT-based navigation system. FOS′ indicates projected point of the pyriform fossa; KC′, projected point of the knee center.
Table 3. Maximum Intraoperative ROM: Large PC Group Versus Small PC Group Large PC Parameter Mean ± SD No. of cases 32 Preoperative factors −13 ± 3 PCsup-stand (°) 0±6 PIsup (°) −13 ± 8 PIstand (°) Age 69 ± 11 Height 150 ± 7 Weight 58 ± 13 BMI 26 ± 5 Implant orientation Radiographic cup inclination (°) 39 ± 2 Radiographic cup anteversion (°) 16 ± 3 Stem anteversion (°) 29 ± 8 Intraoperative anatomical hip ROM Max Flex (°) 97 ± 11 Max Ext (°) 18 ± 10 Max ER (°) 15 ± 11 Max IR at 90° Flex (°) 49 ± 7 Max Abd (°) 35 ± 8 Hip position other than the measured direction Abd at Max Flex (°) 1±4 ER at Max Flex (°) −13 ± 9 Abd at Max Ext (°) 5±4 ER at Max Ext (°) −4 ± 10 Flex at Max Ext (°) −1 ± 5 Abd at Max ER (°) 3±4 Flex at Max IR at 90° Flex (°) 86 ± 6 Abd at Max IR at 90° Flex (°) 2±3 Flex at Max Abd (°) 7±7 ER at Max Abd (°) −9 ± 14 Abbreviation: NS, nonsignificant.
Small PC Range 59
Mean ± SD
−21 to −10 −18 to 15 −32 to 3 40-85 137-163 37-99 18-38
−4 ± 3 7±7 2±8 62 ± 9 154 ± 8 56 ± 10 24 ± 3
Range
t Test Results
−9 to 5 −10 to 26 −14 to 22 34-85 135-178 34-93 16-35
P b .0001 P b .0001 P b .0001 P b .005 NS NS NS
36-42 9-23 11-47
39 ± 2 15 ± 3 32 ± 12
35-42 9-20 12-59
NS NS NS
64-117 −4 to 36 −7 to 43 35-67 19-55
90 ± 12 14 ± 9 6 ± 13 52 ± 8 32 ± 10
60-120 −13 to 32 −25 to 43 36-70 9-53
P b .01 NS P b .005 NS NS
−8 to 8 −39 to 10 −5 to 13 −21 to 20 −12 to 13 −8 to 11 59 to 93 −2 to 11 −5 to 22 −37 to 16
0±4 −16 ± 10 5±5 −11 ± 8 1±8 3±5 83 ± 8 1±4 8±9 −14 ± 15
−12 to 7 −32 to 16 −5 to 20 −29 to 7 −21 to 49 −6 to 15 55-93 −10 to 13 −13 to 38 −46 to 10
NS NS NS P b .005 NS NS NS NS NS NS
Anatomical Hip Range of Motion After Implantation During Total Hip Arthroplasty With a Large Change in Pelvic Inclination Hidenobu Miki, MD, PhD,* Takayuki Kyo, MD,* and Nobuhiko Sugano, MD, PhDy
Abstract: The supine functional pelvic plane is the recommended reference pelvic plane for acetabular cup planning in navigation-assisted total hip arthroplasty. However, it is unclear whether it can be used in patients with a large preoperative positional change in pelvic inclination (PC) from the supine to the standing position because it is unknown whether these patients have a different hip range of motion (ROM). We measured the anatomical hip ROM after implantation by computed tomography–based navigation in 91 patients and found it to be similar between those with a small PC (b10°) and those with a large PC (≥10°). There was no significant correlation between ROM and preoperative PC. The supine functional pelvic plane is adequate for cup planning whether the PC is small or large. Keywords: total hip arthroplasty, functional pelvic plane, pelvic inclination, positional change, acetabular cup orientation, preoperative planning. © 2012 Elsevier Inc. All rights reserved.
Proper acetabular cup orientation is essential in total hip arthroplasty (THA) to avoid edge loading and prosthesis impingement, which may lead to serious complications, such as dislocation, mechanical loosening, wear or breakage of the polyethylene liner, metallosis or metal ion release from metal-on-metal bearings, and squeaking or breakage of ceramic-on-ceramic bearings [1-8]. Cup orientation is set relative to a pelvic coordinate system for preoperative three-dimensional (3D) planning. The coordinate system is generally constructed from a reference pelvic plane, which is determined by picking a number of reference points on the surface of a 3D pelvic model in preoperative planning software. Historically, the anterior pelvic plane (APP) was initially used as a reference, and it was defined by 3 reference points: the left anterior superior iliac spine (LASI), the right anterior superior iliac spine (RASI), and the
From the *Department of Orthopedic Surgery, Osaka National Hospital, Osaka, Japan; and yDepartment of Orthopedic Surgery, Medical School of Osaka University, Osaka, Japan. Supplementary material available at www.arthroplastyjournal.org. Submitted February 19, 2011; accepted March 1, 2012. The authors received a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science in support of the study reported here. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2012.03.002. Reprint requests: Hidenobu Miki, MD, PhD, Department of Orthopedic Surgery, Osaka National Hospital, 2-1-14 Hoenzaka, Chu-o-ku, Osaka 540-0006, Japan. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2709-0011$36.00/0 doi:10.1016/j.arth.2012.03.002
midpoint of the left pubic tubercle (LPT) and the right pubic tubercle (RPT). The pelvic coordinate system based on APP is constructed as follows: the x-axis is parallel to the line including the RASI and LASI, the y-axis is perpendicular to the APP, and the z-axis is perpendicular to the x- and y-axes (Fig. 1). Although the APP was considered to be superimposable on the horizontal plane in the supine position and on the vertical plane in the standing position, it has been shown that there is a large degree of interpatient variation in the APP [9-11]. The functional pelvic plane (FPP) in either the supine or standing position (the supine FPP and the standing FPP, respectively) is normally used as the reference pelvic plane [11-13]. Each is created by rotating the APP around the x-axis of the pelvis by the pelvic inclination in the supine position or the standing position (PIsup or PIstand, respectively) measured by preoperative computed tomography (CT) or radiography (Fig. 1). Although the standing FPP corresponds to the position of the pelvis in most daily activities, the current recommendation for acetabular cup orientation is based on previous data using the supine FPP. Several clinical reports have concluded that surgeons should avoid steep cup inclination in supine anteroposterior (AP) radiography to prevent edge loading [1,4,7,8]. Furthermore, simulation studies have been performed since the late 1990s to calculate optimal cup orientation for avoiding prosthesis impingement within the intended hip range of motion (ROM) [14-16]. The results of these studies vary according to intended hip and prosthesis ROM. Although the actual postoperative anatomical hip ROM for
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1642 The Journal of Arthroplasty Vol. 27 No. 9 October 2012
Fig. 1. Definitions of pelvic coordinate systems based on the APP, FPP, and the standing FPP.
individual patients cannot be estimated accurately, the potential anatomical maximum hip ROM has recently been measured precisely by 3D motion analysis and by CT-based navigation systems both in healthy persons and in patients undergoing THA [17,18], and these data have been used as a reference for the desired hip ROM [19-21]. The anatomical hip ROM is defined as relative angles between the pelvis and the femoral coordinate system. In these studies, the APP or the supine FPP was used as the reference plane for the pelvic coordinate system, but the standing FPP was not determined. Although an inclination of 40° to 45° and anteversion based on combined anteversion theory have recently been recommended for cup orientation in THA with a conventional femoral head size, the concept of combined anteversion was also proposed in a similar simulation study to avoid prosthesis impingement within the desired hip ROM defined using the supine FPP [20]. In addition to the advantages of using the supine FPP already mentioned, some authors have recommended using the supine FPP as the reference plane for preoperative planning of cup orientation, as the supine pelvic tilt angle is a reasonable approximation of the standing pelvic tilt angle because the change in pelvic inclination between supine and standing positions (positional change of pelvic inclination [PC]) is small in most cases (within 10° in 83%-90% of cases) [11,12]. However, it remains unclear whether the current recommendation for cup orientation based on the supine FPP can be similarly applied when there is a large PC because it is unclear whether the maximum anatomical hip ROM defined using the supine FPP in
patients with a large PC is comparable with that in patients with a small PC. Therefore, we measured preoperative PC using a 2-dimensional–3D matching technique and performed THA using a CT-based navigation system. During surgery, we determined the intraoperative maximum anatomical hip ROM by using the navigation system as a measurement tool. Then, we compared the intraoperative maximum anatomical hip ROM defined using the supine FPP in patients with a large PC (≥10°) with that in patients with a small PC (b10°). In addition, we investigated the relationship between the preoperative PC and the intraoperative anatomical hip ROM.
Materials and Methods Patients Primary THA was performed in 91 patients (84 women and 7 men) in our hospital using a CT-based navigation system (Stryker CT-Hip System 1.0; Stryker-Leibinger, Freiburg, Germany) between April 2009 and September 2010. We performed computer-assisted hip surgeries, including THA, with the approval of our institute's institutional review board. Informed consent was obtained from all patients. Cementless stems (Centpillar; Stryker Orthopaedics, Cork, Ireland) and metal cups with a metal head (Adept; Finsbury Orthopaedics, London, United Kingdom) were implanted in all cases. Indications for surgery were end-stage hip osteoarthritis (OA) due to dysplasia (n = 85) and avascular necrosis of the femoral head (n = 6). According to Crowe's classification, 76 patients had grade 1 dysplasia, 10 had grade 2, and 5 had grade 3. The average age of patients at
Anatomic Hip ROM After Implantation During THA Miki et al
the time of surgery was 64 years (range, 34-85 years). To date, no patients have experienced any postoperative complications, with the average postoperative duration being 24 months (range, 15-32 months). Preoperative Positional Change of Pelvic Inclination Preoperative PC was determined by using the radiography–CT model matching method reported previously (Fig. 2) [12]. We took AP radiographs of the pelvis in the supine and standing positions before surgery. The vertical diameter of the pelvic foramen (A) divided by the maximum horizontal diameter of the pelvic foramen (B) (A:B ratio) was calculated on AP radiographs of the pelvis in both the supine and standing positions. A was defined as the distance between the line connecting the inferior bilateral margins of the sacroiliac joint and the superior margin of the pubic symphysis, and B was defined as the maximum horizontal diameter of the pelvic foramen. In the planning module of this navigation system, the pelvic coordinate system, based on the APP, was first created on the 3D pelvic model. The AP view of the 3D pelvic model was shown by projecting it onto the x-z plane of the pelvic coordinate system. The vertical diameter of the pelvic foramen (A′) and the maximum horizontal diameter of the pelvic foramen (B′) for the AP view of the pelvic model were defined, and we rotated the pelvic model around the x-axis of the pelvis until the A′:B′ ratio matched the A:B ratio measured on the AP radiograph in the supine and
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standing positions. The rotating angles around the x-axis were defined as the PIsup and PIstand. Therefore, PC from the supine to the standing position (PCsup-stand) was defined as PIsup − PIstand (positive values of PCsup-stand indicated an anterior change). The absolute value of PCsup-stand was defined as PC. Preoperative Planning Although imageless navigation used only the APP as the pelvic reference plane, CT-based navigation can also reference the supine FPP defined in preoperative planning. We completed preoperative planning using the planning module of the CT-based navigation system. In preparation for planning, CT was performed from the pelvis to the knee joint, and the results were transferred into the planning module. Reference points were used to define the coordinate systems of the pelvis and bilateral femurs (Fig. 3; available online at www.arthroplastyjournal.org): the RASI, LASI, RPT, and LPT; the distal-most points of the ischium (right ischium [RIS] and left ischium [LIS]), the midpoint of the pubic symphysis (PUB) and sacral midpoint (SACR) for the pelvic frame; and the center of the femoral head, pyriform fossa (FOS), the posterior-most point of the proximal femur (PF), the medial and lateral posterior condyles (MFC and LFC, respectively), and the knee center (KC) for the femoral frame. The APP was defined using the RASI, the LASI, and the midpoint of the RPT and LPT. The x-axis was parallel
Fig. 2. Model matching method using radiography and CT to measure preoperative pelvic inclinations in the supine and standing positions. 2D indicates 2-dimensional.
1644 The Journal of Arthroplasty Vol. 27 No. 9 October 2012 to the line including the RASI and LASI, the y-axis was perpendicular to the APP, and the z-axis was perpendicular to the x- and y-axes. To adjust pelvic obliquity and rotation, the coordinate system was rotated locally around the y-axis until the x-axis was parallel to a line through the projected points of the RIS and LIS on the x-z plane and around the z-axis until the y-axis was parallel to a line through the projected points of the PUB and SACR on the x-y plane. It was then rotated locally around the x-axis by the PIsup, measured as already described. As a result, the pelvic coordinate system based on the supine FPP was built on the pelvic model. For the femur, the y-axis was perpendicular to the retrocondylar plane (RCP), which included points PF, MFC, and LFC. The z-axis was a line through FOS′ and KC′, the projected points of FOS and KC, respectively, on the RCP. The x-axis was perpendicular to the y- and z-axes. Stem and cup orientation was then planned using a 3D template relative to the pelvic and femoral coordinate systems. Radiographic inclination for the acetabular cup was set at 40°, with cup anteversion adjusted according to the stem anteversion angle; radiographic cup anteversion was set at 20°, 15°, or 10° if stem anteversion was found to be 10° to 15°, 15° to 50°, or 50° to 60°, respectively. This cup target was calculated by a commonly used collision detection technique for 3D objects using computer-aided design models of the Centpillar stem and Adept cup to avoid prosthesis impingement at the required hip ROM (120° flexion, 40° extension, 40° external rotation, and 40° internal rotation at 90° flexion) [22].
examination of intraoperative anatomical hip ROM, the rotation matrix is measured by the navigation system in the operating room. During the operation, the femoral and pelvic trackers are rigidly fixed to the pelvis and femur (Fig. 5). The navigation system can measure the 3D positions of these trackers by using an optical 3D sensor in the camera. In the pelvis, although the navigation camera shows the rotation matrix of the pelvic tracker coordinate system in the camera coordinate system (Pc), it does not recognize the pelvis at this point (Fig. 6). Therefore, it requires registration of the pelvic position within the tracker coordinate system. The coordinates of the surface points on the real pelvis in the pelvic tracker coordinate system are picked up by a navigation pointer. These coordinates of the real pelvic surface and the surface of the pelvic model, defined by the coordinate system based on the supine FPP in preoperative planning, are matched by the computer in the navigation system, and then, the rotation matrix of the pelvic coordinate system into the pelvic tracker coordinate system (Pt) is determined. In the femur, the navigation camera shows the rotation matrix of the femoral tracker coordinate system into the camera coordinate system (Fc). After registration of the femoral position to the femoral tracker is similarly performed, the rotation matrix of the femoral coordinate system into the femoral tracker coordinate system (Ft) is determined. After registration is complete, the rotation matrix (R) of the femoral coordinate system into the pelvic coordinate system (Fig. 7) is determined by the following formula:
Measurement of Intraoperative Anatomical Hip ROM Using a CT-Based Navigation System We used a CT-based navigation system to measure intraoperative anatomical ROM, as described elsewhere [18]. The anatomical hip ROM was defined as the relative angle between the pelvis and the femoral coordinate system, which is not physical hip ROM between the thigh and trunk axis or the surgical table. The neutral position of the anatomical hip ROM was defined as the position in which the x-, y-, and z-axes of the femoral coordinate system, which is based on the RCP, are parallel to the x-, y-, and z-axes, respectively, of the pelvic coordinate system, which is based on the supine FPP (Fig. 4). An anatomical hip ROM in a hip position is expressed as rotation angles into the local femoral coordinate system from the neutral position. The first rotation (θ) is performed around the x-axis, which means flexion or extension. The second (φ) and third (ψ) rotations are around the y-axis and z-axis, which means abduction or adduction and external or internal rotation, respectively. The angles (θ, φ, and ψ) can be mathematically calculated when the rotation matrix (R) of the femoral coordinate system into the pelvic coordinate system is known (Fig. 4). Therefore, in
R = ðPc PtÞ − 1 × ðFc × FtÞ Then, the CT-based navigation system can determine the intraoperative anatomical hip ROM in real time during surgery. Therefore, accuracy of measurement of the anatomical ROM depends on registration accuracy without loosening of the tracker. The accuracy of registration has been found to be 0.9° of bias with 0.3° of the root mean square in the pelvis and 0.6° of bias with 0.3° of the root mean square in the femur [23]. We checked for loosening of both pelvic and femoral trackers after measuring anatomical ROM in the operating room, and the trackers proved to be stable in all cases. The limits of agreement (0.6°-1.5° for the pelvis and 0°-1.2° for the femur) indicated that the angular error of anatomical ROM measured by the system would be within 3°. Computed Tomography–Based Navigation Surgery All surgeries were performed with the patient in the lateral position, using the navigation system and a posterolateral approach via a 10-cm incision, which included complete resection of the joint capsule. Before making the skin incision, we attached a pelvic tracker percutaneously to the ipsilateral ilium with an external
Anatomic Hip ROM After Implantation During THA Miki et al
1645
Fig. 4. Definitions of anatomical hip ROM.
fixation device (Hoffman II; Stryker-Leibinger) using 2 Apex half pins (Stryker Osteosynthesis, Selzach, Switzerland). After the hip joint was dislocated, a femoral tracker was fixed rigidly to the greater trochanter using a triangular plate with 3 screws. Registration of the femur was completed by surface matching. The verification point for the femur, which was used to check intraoperative loosening of the femoral tracker, was marked on the greater trochanter. Femoral preparation and rasping were then performed. Subsequently, registration of the pelvis was also performed by surface matching, and the verification point for the pelvis was marked on the posterosuperior portion of the acetabular rim. After reaming, implantation of the acetabular cup was performed under navigation-system guidance. Final anteversion and inclination of the cup were recorded
Fig. 5. Overview of the CT-based navigation system.
by a tracker fixed on the cup inserter. Implantation of the stem was performed, and final anteversion and the valgus angle were recorded by a tracker fixed on the stem inserter. Finally, leg length was adjusted by changing the neck length of the femoral head. After implantation and repositioning, the real-time intraoperative hip position was shown on the navigation monitor. We recorded the maximum angles of hip flexion, extension, abduction, external rotation, and internal rotation at 90° flexion. Using these measurements, we aimed to approximate the standard position with regard to the directions of movement from the intended position while viewing the navigation monitor; for example, the optimal angles for abduction and internal rotation were 0° at maximum flexion and 0° of abduction and 90° of flexion on maximum internal rotation at 90° flexion. Although gentle retraction of the skin and soft tissue prevented interference with the pelvic and the femoral trackers during the measurement process, the stability of the trackers was checked by touching the verification points marked on the pelvis and the femur with the pointer after the measurement had been obtained. When the tip of the pointer was displaced more than 2 mm from the registered point on the navigation computer, the reference trackers were considered to have loosened. Both pelvic and femoral trackers proved stable in all cases after the measurement of anatomical ROM. Skin closure was performed after suturing of the short rotators to the greater trochanter. Patients were allowed to engage in full weight bearing at 24 hours after surgery and were discharged from the hospital 2 to 4 weeks later. All patients received standard rehabilitation care.
1646 The Journal of Arthroplasty Vol. 27 No. 9 October 2012
Fig. 6. Intraoperative registration of the pelvic coordinate system based on the supine FPP.
Measurement of Implant Orientation We used the value of the final intraoperative record obtained by navigation as the implant orientation instead of the measurement from postoperative CT. The Adept cup is a thick monoblock cup made of cobalt-
chrome alloy. It was difficult to measure postoperative orientation by the standard method using 3D templates on multiplanar reconstruction images from postoperative CT because of strong halation on the images. Moreover, it was also difficult to obtain correct
Fig. 7. Intraoperative measurement of anatomical hip ROM.
Anatomic Hip ROM After Implantation During THA Miki et al
measurements of cup orientation relative to the defined pelvic coordinate system by AP hip radiography. However, the accuracy of CT-based navigation, which was defined as the intraoperative final record of implant orientation minus the postoperative implant orientation measured on postoperative CT, has already been documented [24-26]. Navigation accuracy was −0.8° ± 4.1° (range, −6° to 8°) for cup anteversion, 0.4° ± 2.5° (range, −6° to 5°) for cup abduction, −0.6° ± 4.8° (range, −11° to 10°) for stem anteversion, and −0.2° ± 1.8° (range, −4° to 3°) for stem valgus. The mean absolute value of navigation accuracy was 2.4° to 3.0° (SD, 2.0°2.6°) for abduction and 2.0° to 3.3° (SD, 1.4°-2.3°) for anteversion. Therefore, we used the navigation system as a measurement tool because it has a known accuracy. Individual Safety Margin Up to Prosthesis Impingement Estimated From the Implant Orientation The individual estimated prosthesis ROMs for flexion, extension, external rotation, and internal rotation at 90° flexion were calculated by the collision-detection technique for 3D objects using computer-aided design models of the Adept cup and the Centpillar stem with the same sizes and orientations as in the intraoperative records [22]; therefore, the safety margin for impingement was calculated for those movements from the following formula: estimated prosthesis ROM − maximum intraoperative anatomic hip ROM
Statistics The unpaired t test, simple regression analysis, and 1-factor analysis of variance were performed using StatView software (version 5.0; SAS Institute, Cary, NC). In all analyses, P b .05 was taken to indicate statistical significance.
Results The results for 91 cases are shown in Table 1 as means ± SD (range): PCsup-stand was −7° ± 6° (range, −21° to 5°); PIsup and PIstand were 4° ± 8° (range, −18° to 26°) and −3° ± 11° (range, −32° to 22°), respectively. Strong correlations were found between PIsup and PIstand (R = 0.88) and between PIstand and PCsup-stand (R = 0.75); however, only a weak correlation was found between PIsup and PCsup-stand (R = 0.35). The measured intraoperative anatomical maximum hip ROMs were 93° ± 12° (range, 60°-120°) in flexion, 15° ± 10° (range, −13° to 36°) in extension, 9° ± 13° (range, −25° to 43°) in external rotation, 51° ± 8° (range, 35°-70°) in internal rotation at 90° flexion, and 33° ± 9° (range, 9°-55°) in abduction. The safety margins with regard to prosthesis impingement were 57° ± 13° in flexion, 57° ± 15° in extension, 94° ± 30° in external rotation, and 34° ± 14° in internal rotation at 90° flexion. The mean safety margin for internal rotation at 90° flexion was signifi-
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Table 1. Results for 91 Cases Parameter
Mean ± SD
Preoperative factors −7 ± 6 PCsup-stand (°) 4±8 PIsup (°) −3 ± 11 PIstand (°) Age (y) 64 ± 11 Height (cm) 152 ± 8 Weight (kg) 57 ± 12 24 ± 4 BMI (kg/m2) Intraoperative anatomical hip ROM Max Flex (°) 93 ± 12 Max Ext (°) 15 ± 10 Max ER (°) 9 ± 13 Max IR at 90° Flex (°) 51 ± 8 Max Abd (°) 33 ± 9 Safety margin up to prosthesis impingement Flex (°) 57 ± 13 Ext (°) 57 ± 15 ER (°) 94 ± 30 IR at 90° Flex (°) 34 ± 14
Range −21 to 5 −18 to 26 −32 to 22 34-85 135-178 34-99 16-38 60-120 −13 to 36 −25 to 43 35-70 9-55 28-90 26-98 39-195 4-64
Abbreviations: Abd, abduction; BMI, body mass index; ER, external rotation; Ext, extension; Flex, flexion; IR, internal rotation; Max, maximum. The mean safe margin of internal rotation at 90° flexion was significantly smaller than the mean safe margin for other measurements, as determined by 1-factor analysis of variance (P b .01).
cantly less than those for the other measurements (1-factor analysis of variance, P b .01). There was a PC of greater than 5° in 58 cases (64%), greater than 10° in 27 cases (30%), greater than 15° in 6 cases (7%), and greater than 20° in 2 cases (2%) (Fig. 8). In all cases with a PC of greater than 5°, there was a posterior change in pelvic inclination from the supine to standing position. Of the preoperative factors considered (age, height, weight, body mass index), only age showed a weak correlation with PCsup-stand (R = −0.32). The results of simple regression analyses between maximum ROM and various factors are shown in Table 2. The PCsup-stand was not correlated with ROM in any direction. However, PIsup and PIstand showed moderate negative correlations with maximum flexion (R = −0.36 and −0.37, respectively) and with external rotation (R = −0.44 and −0.44, respectively). With regard to maximum ROM and hip position other than the measured direction, there were moderate correlations only between maximum abduction and hip position of flexion and external rotation at the measurement of abduction (R = 0.46 and −0.35, respectively). Therefore, the results for maximum abduction could be affected by hip position at the time of measurement. We compared intraoperative maximum ROM for 32 patients with a large PC (≥10°) and 59 patients with a small PC (b10°) (Table 3; available online at www. arthroplastyjournal.org). The large PC subgroup had only posterior PCs. The mean PCsup-stand in the large PC subgroup (−13° ± 3°) was significantly smaller than that
1648 The Journal of Arthroplasty Vol. 27 No. 9 October 2012
Fig. 8. Histogram of preoperative positional change in pelvic tilt from supine to standing position.
in the small PC subgroup (−4° ± 3°) (P b .0001). Mean PIsup and PIstand in the large PC subgroup (0° ± 6° and −13° ± 8°, respectively) were significantly smaller than those in the small PC subgroup (7° ± 7° and 2° ± 8°, respectively) (P b .0001). The mean age in the large PC subgroup (69 ± 11 years) was significantly higher than that in the small PC subgroup (62 ± 9 years). There were no significant differences between the 2 subgroups with regard to height, weight, body mass index, implant orientation, or hip position other than the measurement direction at determination of intraoperative ROM, except for external rotation under maximum extension. For intraoperative anatomical hip ROM, the mean maximum flexion and external rotation of the large PC subgroup (97° ± 11° and 15° ± 11°, respectively) were significantly larger than those for the small PC
subgroup (90° ± 12° and 6° ± 13°, respectively); the respective P values were less than .01 and less than .005. However, maximum values for maximum flexion and extension, external rotation at 0° flexion, and internal rotation at 90° flexion, and abduction were 117°, 36°, 43°, 67°, and 55°, respectively, in the large PC subgroup and 120°, 32°, 43°, 70°, and 53°, respectively, in the small PC subgroup. There were no significant differences between the 2 subgroups in maximum values for intraoperative maximum ROM.
Discussion Although other studies have indicated that large PCs (N10°) are rare (7%-10%), 30% of patients in our study exhibited a PC with pelvic inclination of greater than 10° [11,12]. This difference might have been
Table 2. Simple Regression Analyses (R Values) of Preoperative Factors Factor Age Height Weight BMI PIsup PIstand PCsup-stand Hip position other than the measured direction Flexion Abduction External rotation Implant orientation Radiographic cup inclination Radiographic cup anteversion Stem anteversion
Flexion
−0.36 −0.37
Extension
External Rotation
Internal Rotation at 90° Flexion
Abduction
−0.44 −0.44
0.46 −0.35
−0.52
0.67
Anatomic Hip ROM After Implantation During THA Miki et al
influenced by average patient age, as we found that PCsup-stand was significantly correlated with age. The average age of patients in 1 report [12] was 56 years, which was lower than in 64 of our 91 patients. Unfortunately, patient age was not recorded in the other report on this issue [11]. Thus, the proportion of patients with a large PC may not always be small, owing to patient selection. Therefore, it is very important to take suitable acetabular cup orientation into consideration in patients with a large PC. It is not necessary for surgeons to change preoperative planning with regard to implant orientation, even in patients with a large preoperative PC, when the supine FPP is used as the reference pelvic plane. In our study, PCsup-stand was not correlated with intraoperative maximum ROM, and intraoperative maximum ROM values were not significantly different between the large PC and small PC subgroups for any direction of movement. However, we also found that the average maximum flexion and external rotation were greater in the large PC subgroup than those in the small PC subgroup. These findings suggest that complications related to impingement, such as posterior or anterior dislocation, will occur more frequently in patients with a large PC when an implant with insufficient prosthesis ROM is used or in whom the components are placed in an incorrect orientation. With regard to patient selection, PCsup-stand ranged from −21° to 5° in our study population. To our knowledge, there has been only 1 previous report regarding the range of PCsup-stand, which was found to be between −18° and 21° in relatively young patients [12]. Therefore, although it was difficult to assess whether our patients were representative of all patients undergoing THA, our series included a sufficient number of patient with a large posterior PC but an insufficient number with a large anterior PC. Intraoperative passive hip ROM can be affected by type of anesthesia used, surgical approach, spatial prosthesis position, and implant design. However, 1 limitation of our study is that those factors may create variations between intraoperative and postoperative hip ROM. Our hip ROM measurements were obtained while patients were under general anesthesia and may, therefore, differ from those obtained from conscious patients because of differences in the level of muscle activation. Although the passive muscle length–tension curve was shown to be the same in the 2 states, the corresponding active curves are different [27]. Thus, active and passive ROM may not be very different theoretically, although the force needed to arrive at the end point of ROM may vary between the 2 states. However, over time, postoperative hip ROM may be higher than the results that we obtained, although the 2 measurements may be similar for a short time after the operation. Intraoperative hip ROM in our study was measured immediately
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after implantation. Because intraoperative ROM in flexion, extension, and external rotation had a large safety margin up to implant impingement, this could increase because of postoperative adaptation of muscles and tendons with increased patient activity [28]. It is difficult to clarify the limitations of our study, as it would be necessary to perform a similar study measuring postoperative hip ROM accurately using a highgrade methodology, such as patient-specific motion analysis [29]. In conclusion, our findings indicate that the current recommendations for cup orientation could be similarly applicable in patients with a large posterior change of pelvic inclination from the supine to the standing position when the FPP in the supine position is used as the reference pelvic plane in navigation-assisted THA.
References 1. Chen PY, Wu CT, Hou CH, Hou SM. Loosening of total hip arthroplasty with a prosthesis employing a skirted femoral head. J Formos Med Assoc 2005;104:370. 2. Shon WY, Baldini T, Peterson MG, et al. Impingement in total hip arthroplasty a study of retrieved acetabular components. J Arthroplasty 2005;20:427. 3. Barrack RL. Dislocation after total hip arthroplasty: implant design and orientation. J Am Acad Orthop Surg 2003;11:89. 4. Gambera D, Carta S, Crainz E, et al. Metallosis due to impingement between the socket and the femoral head in a total hip prosthesis. A case report. Acta Biomed 2002; 73:85. 5. Iida H, Kaneda E, Takada H, et al. Metallosis due to impingement between the socket and the femoral neck in a metal-on-metal bearing total hip prosthesis. A case report. J Bone Joint Surg Am 1999;81:400. 6. Bader R, Steinhauser E, Zimmermann S, et al. Differences between the wear couples metal-on-polyethylene and ceramic-on-ceramic in the stability against dislocation of total hip replacement. J Mater Sci Mater Med 2004; 15:711. 7. Grammatopoulos G, Pandit H, Glyn-Jones S, et al. Optimal acetabular orientation for hip resurfacing. J Bone Joint Surg Br 2010;92:1072. 8. De Haan R, Pattyn C, Gill HS, et al. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br 2008;90:1291. 9. Gilliam J, Brunt D, MacMillan M, et al. Relationship of the pelvic angle to the sacral angle: measurement of clinical reliability and validity. J Orthop Sports Phys Ther 1994;20:193. 10. Lembeck B, Mueller O, Reize P, Wuelker N. Pelvic tilt makes acetabular cup navigation inaccurate. Acta Orthop 2005;76:517. 11. Babisch JW, Layher F, Amiot LP. The rationale for tiltadjusted acetabular cup navigation. J Bone Joint Surg Am 2008;90:357.
1650 The Journal of Arthroplasty Vol. 27 No. 9 October 2012 12. Nishihara S, Sugano N, Nishii T, et al. Measurements of pelvic flexion angle using three-dimensional computed tomography. Clin Orthop Relat Res 2003;411:140. 13. Eckman K, Hafez MA, Ed F, et al. Accuracy of pelvic flexion measurements from lateral radiographs. Clin Orthop Relat Res 2006;451:154. 14. D'Lima DD, Urquhart AG, Buehler KO, et al. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios. J Bone Joint Surg Am 2000;82:315. 15. Jerosch J, Filler TJ, Peuker ET. The cartilage of the tibiofibular joint: a source for autologous osteochondral grafts without damaging weight-bearing joint surfaces. Arch Orthop Trauma Surg 2002;122:217. 16. Seki M, Yuasa N, Ohkuni K. Analysis of optimal range of socket orientations in total hip arthroplasty with use of computer-aided design simulation. J Orthop Res 1998; 16:513. 17. Nadzadi ME, Pedersen DR, Yack HJ, et al. Kinematics, kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation. J Biomech 2003;36:577. 18. Miki H, Yamanashi W, Nishii T, et al. Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 2007; 22:946. 19. Widmer KH, Majewski M. The impact of the CCD-angle on range of motion and cup positioning in total hip arthroplasty. Clin Biomech 2005;20:723. 20. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res 2004;22:815. 21. Yoshimine F. The influence of the oscillation angle and the neck anteversion of the prosthesis on the cup safe-zone
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that fulfills the criteria for range of motion in total hip replacements. The required oscillation angle for an acceptable cup safe-zone. J Biomech 2005;38:125. Gottschalk S, Lin MC, Manocha D. 1996. OBBTree: a hierarchical structure for rapid interference detection. SIGGRAPH '96 Proceedings of the 23rd Annual Conference on Computer Graphics and Interactive Techniques. New York: ACM Press; 1996; p. 171. Sugano N, Sasama T, Sato Y, et al. Accuracy evaluation of surface-based registration methods in a computer navigation system for hip surgery performed through a posterolateral approach. Comput Aided Surg 2001;6:195. Kitada M, Nakamura N, Iwana D, et al. Evaluation of the accuracy of computed tomography–based navigation for femoral stem orientation and leg length discrepancy. J Arthroplasty 2011;26:674. Hananouchi T, Takao M, Nishii T, et al. Comparison of navigation accuracy in THA between the minianterior and -posterior approaches. Int J Med Robot 2009;5:20. Kalteis T, Handel M, Bäthis H, et al. Imageless navigation for insertion of the acetabular component in total hip arthroplasty: is it as accurate as CT-based navigation? J Bone Joint Surg Br 2006;88:163. Zajac FE. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng 1989;17:359. Woolson ST, Maloney WJ, Schurman DJ. Time-related improvement in the range of motion of the hip after total replacement. J Bone Joint Surg Am 1985;67:1251. Hagio K, Sugano N, Nishii T, et al. A novel system of fourdimensional motion analysis after total hip arthroplasty. J Orthop Res 2004;22:665.
Anatomic Hip ROM After Implantation During THA Miki et al
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Fig. 3. The pelvic and femoral coordinate systems in the CT-based navigation system. FOS′ indicates projected point of the pyriform fossa; KC′, projected point of the knee center.
Table 3. Maximum Intraoperative ROM: Large PC Group Versus Small PC Group Large PC Parameter Mean ± SD No. of cases 32 Preoperative factors −13 ± 3 PCsup-stand (°) 0±6 PIsup (°) −13 ± 8 PIstand (°) Age 69 ± 11 Height 150 ± 7 Weight 58 ± 13 BMI 26 ± 5 Implant orientation Radiographic cup inclination (°) 39 ± 2 Radiographic cup anteversion (°) 16 ± 3 Stem anteversion (°) 29 ± 8 Intraoperative anatomical hip ROM Max Flex (°) 97 ± 11 Max Ext (°) 18 ± 10 Max ER (°) 15 ± 11 Max IR at 90° Flex (°) 49 ± 7 Max Abd (°) 35 ± 8 Hip position other than the measured direction Abd at Max Flex (°) 1±4 ER at Max Flex (°) −13 ± 9 Abd at Max Ext (°) 5±4 ER at Max Ext (°) −4 ± 10 Flex at Max Ext (°) −1 ± 5 Abd at Max ER (°) 3±4 Flex at Max IR at 90° Flex (°) 86 ± 6 Abd at Max IR at 90° Flex (°) 2±3 Flex at Max Abd (°) 7±7 ER at Max Abd (°) −9 ± 14 Abbreviation: NS, nonsignificant.
Small PC Range 59
Mean ± SD
−21 to −10 −18 to 15 −32 to 3 40-85 137-163 37-99 18-38
−4 ± 3 7±7 2±8 62 ± 9 154 ± 8 56 ± 10 24 ± 3
Range
t Test Results
−9 to 5 −10 to 26 −14 to 22 34-85 135-178 34-93 16-35
P b .0001 P b .0001 P b .0001 P b .005 NS NS NS
36-42 9-23 11-47
39 ± 2 15 ± 3 32 ± 12
35-42 9-20 12-59
NS NS NS
64-117 −4 to 36 −7 to 43 35-67 19-55
90 ± 12 14 ± 9 6 ± 13 52 ± 8 32 ± 10
60-120 −13 to 32 −25 to 43 36-70 9-53
P b .01 NS P b .005 NS NS
−8 to 8 −39 to 10 −5 to 13 −21 to 20 −12 to 13 −8 to 11 59 to 93 −2 to 11 −5 to 22 −37 to 16
0±4 −16 ± 10 5±5 −11 ± 8 1±8 3±5 83 ± 8 1±4 8±9 −14 ± 15
−12 to 7 −32 to 16 −5 to 20 −29 to 7 −21 to 49 −6 to 15 55-93 −10 to 13 −13 to 38 −46 to 10
NS NS NS P b .005 NS NS NS NS NS NS