There was only one intraoperative technical complication related to the robotic system, in which the senior surgeon judged the cup placement guidance by the robotic system to be outside the safe zone based on the intraoperative bony landmarks, the transverse acetabular ligament, and the patient’s lateral position. He repositioned the cup using the conventional technique, and the postoperative measurements of that cup were within the safe zones of Lewinnek et al. and Callanan et al. There were no intraoperative technical complications in the conventional THA group.
Acetabular cup positioning in THA is critical to ensure stability of the prosthetic hip and longevity of the implant. Component malposition has been associated in numerous reports of complications, including impingement, dislocation, accelerated wear, and revision surgery [1, 4-6, 11, 21, 25, 26, 28, 29, 33, 38, 40]. Some studies have offered recommended cup orientation ranges, most suggesting 30° to 50° inclination [5, 25, 26, 38] and 0° to 30° anteversion [5, 23, 26, 38]. The safe zone established by Lewinnek et al.  is the most widely used range of acceptable angles with inclination of 30° to 50° and anteversion of 5° to 25°, and was used in our study to compare our results with the most common safe zone reported in previous publications. Callanan et al. suggested a modified safe zone with inclination of 30° to 45° and anteversion of 5° to 25° . They suggested a lower upper limit of inclination (45° instead of 50° suggested by Lewinnek et al.) based on the study by Leslie et al.  that showed increased wear and edge loading in THAs with a hard-on-hard bearing surface with an abduction angle greater than 45°. We used the safe zone suggested by Callanan et al. because several reports have suggested that steeper cups increase polyethylene and metal wear, and in our opinion, reducing the inclination safe zone to 30° to 45° would accommodate evidence in the literature [8, 25, 38]. We therefore sought to determine the proportion of cups placed in the safe zones using robotic THA and conventional THA, and we compared acetabular component accuracy between the two systems.
The major limitation of our study was the lack of clinical data at short- or long-term. The system adds expense, and we will not know whether that expense is justified until studies show improvements that patients can perceive, such as reduced dislocation rates or a lower likelihood of revision. The robotic system was a capital expenditure by the hospital, and its cost is unknown to us. However, there was no additional cost to the patients or patients’ insurance companies. All our radiographic measurements were done on the coronal plane of the pelvis as described by Murray  and were compared with the safe zone described by Lewinnek et al. . However, Lewinnek et al. defined the safe zone for cup placement with measurements done on the anterior pelvic plane of the pelvis and not the coronal plane. Despite this limitation, their safe zone has been widely used even in the radiographic coronal plane [7, 13, 17, 18]. Combined anteversion (cup anteversion + stem anteversion) has been described as being critical for stability in THA with the optimal range of 25° to 45° being the accepted safe zone . We used different types of acetabular components in each group because of introduction of the robotic system to our practice and the compatibility of this system with certain implant types. Our small sample of patients in each group (50 in each) added to the limitations of this study. Another limitation was that we assessed acetabular cup position without taking into account femoral anteversion. Femoral component anteversion measurement is possible on CT scans that involve the hip and the knee simultaneously, which would add radiation and cost to the patients. The dose of radiation from the CT scan per patient in this study was 60 mGy, and was consistent and standardized throughout all the cases. The senior surgeon (BGD) is an experienced high-volume consultant for the robotic company, and results in this study may not apply to lower-volume or less-experienced surgeons. Use of the robotic technology needs to be validated in future multiple-surgeon independent series. Finally, some selection bias might have been part of patient selection, especially after introduction of the robot.
The use of robotic-assisted THA provided good accuracy and reproducibility in placing the cup in the safe zones in our patients. Similar studies comparing computer-assisted THA with conventional THA have shown greater accuracy in cup placement in the safe zone. Hohmann et al.  compared imageless navigation with manual implantation of acetabular cups using the direct lateral approach, and measured cup angles postoperatively on CT scans. Of cups in the navigation group, 76.7% (23/30) were placed in the safe zone of Lewinnek et al. compared with 20% (6/30) using the manual technique (p = 0.01) . Parratte and Argenson  compared cup positioning using imageless computer-assisted navigation with freehand cup placement, using the supine anterolateral approach. Computer navigation provided greater accuracy in placing the cup in the safe zone of Lewinnek et al. with 20% (6/30) outliers compared with 57% (17/30) outliers in the freehand group (p = 0.002) . Kalteis et al.  compared conventional alignment guides with imageless navigation in cup placement using the supine anterolateral approach. Eleven of 22 cups in the conventional group were placed outside the safe zone of Lewinnek et al. compared with three of 23 in the navigation group (p = 0.003) .
Callanan et al. reported on acetabular cup positioning performed by several experienced surgeons during a 5-year period . Using the conventional THA technique, they reported 47% of cups were in their modified safe zone . Our results were superior using the conventional (62%) and robotic techniques (92%) in placing the cup in their modified safe zone. Determining the 3-D position of the pelvis intraoperatively is challenging [7, 13, 14, 16, 27]. Pelvic tilt, obesity, and hip flexion contracture play a significant role in judging the position of the pelvis and subsequently placement of the cup [5, 13, 14, 41]. Alignment jigs and bony and soft tissue landmarks have been used for intraoperative orientation with varying degrees of accuracy and reproducibility [2, 3, 10, 14, 20, 32]. The introduction of computer-assisted surgery for THA has provided a useful tool for orthopaedic surgeons to improve accuracy in placing the cup in the safe zone and to prevent long-term adverse outcomes. Despite the improved accuracy using navigation, additional cost, operating room time, and duration of surgery have limited widespread acceptance of computer-assisted systems [7, 18].
Robotic-assisted THA was consistent in placing the acetabular cup in the safe zones of Lewinnek et al. and Callanan et al. with minimal intraoperative technical complications. However, whether the radiographic improvements we observed will translate into clinical benefits for patients, such as reductions in component impingement, acetabular wear, and prosthetic dislocations, or in terms of improved longevity, remains unproven. Further studies are needed to investigate the short- and long-term clinical outcomes, possible long-term complications, and cost-effectiveness of robotic-assisted THA.
We thank Zachary Finley BA, Ryan Baise BS, Jennifer C. Stone MA, and Anthony P. Trenga BA for assistance with data collection and analysis and literature review.
1. Ali Khan, MA., Brakenbury, PH. and Reynolds, IS. Dislocation following total hip replacement. J Bone Joint Surg Br.
1981; 63: 214-218.
2. Archbold, HA., Mockford, B., Molloy, D., McConway, J., Ogonda, L. and Beverland, D. The transverse acetabular ligament: an aid to orientation of the acetabular component during primary total hip replacement: a preliminary study of 1000 cases investigating postoperative stability. J Bone Joint Surg Br.
2006; 88: 883-886. 10.1302/0301-620X.88B7.17577
3. Beverland, D. The transverse acetabular ligament: optimizing version. Orthopedics.
2010; 33: 631.
4. Biedermann, R., Tonin, A., Krismer, M., Rachbauer, F., Eibl, G. and 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: 762-769. 10.1302/0301-620X.87B6.14745
5. Callanan, MC., Jarrett, B., Bragdon, CR., Zurakowski, D., Rubash, HE., Freiberg, AA. and Malchau, H. The John Charnley Award: risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res.
2011;469:319-329. 3018230. 10.1007/s11999-010-1487-1.
6. Haan, R., Pattyn, C., Gill, HS., Murray, DW., Campbell, PA. and Smet, K. 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: 1291-1297. 10.1302/0301-620X.90B10.20533
7. Digioia, AM, 3rd, Jaramaz, B., Plakseychuk, AY., Moody, JE, Jr, Nikou, C., Labarca, RS., Levison, TJ. and Picard, F. Comparison of a mechanical acetabular alignment guide with computer placement of the socket. J Arthroplasty.
2002; 17: 359-364. 10.1054/arth.2002.30411
8. Dorr, LD. Acetabular cup position: the imperative of getting it right. Orthopedics.
2008; 31: 898-899. 10.3928/01477447-20080901-10
9. Dorr, LD., Malik, A., Dastane, M. and Wan, Z. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res.
2009;467:119-127. 2600986. 10.1007/s11999-008-0598-4.
10. Epstein, NJ., Woolson, ST. and Giori, NJ. Acetabular component positioning using the transverse acetabular ligament: can you find it and does it help? Clin Orthop Relat Res.
2011;469:412-416. 3018210. 10.1007/s11999-010-1523-1.
11. Gallo, J., Havranek, V. and Zapletalova, J. Risk factors for accelerated polyethylene wear and osteolysis in ABG I total hip arthroplasty. Int Orthop.
2010;34:19-26. 2899268. 10.1007/s00264-009-0731-3.
12. Ha, YC., Yoo, JJ., Lee, YK., Kim, JY. and Koo, KH. Acetabular component positioning using anatomic landmarks of the acetabulum. Clin Orthop Relat Res.
2012;470:3515-3523. 3492628. 10.1007/s11999-012-2460-y.
13. Haaker, RG., Tiedjen, K., Ottersbach, A., Rubenthaler, F., Stockheim, M. and Stiehl, JB. Comparison of conventional versus computer-navigated acetabular component insertion. J Arthroplasty.
2007; 22: 151-159. 10.1016/j.arth.2005.10.018
14. Hassan, DM., Johnston, GH., Dust, WN., Watson, G. and Dolovich, AT. Accuracy of intraoperative assessment of acetabular prosthesis placement. J Arthroplasty.
1998; 13: 80-84. 10.1016/S0883-5403(98)90079-1
15. Hohmann, E., Bryant, A. and Tetsworth, K. A comparison between imageless navigated and manual freehand technique acetabular cup placement in total hip arthroplasty. J Arthroplasty.
2011; 26: 1078-1082. 10.1016/j.arth.2010.11.009
16. Jaramaz, B., DiGioia, AM, 3rd, Blackwell, M. and Nikou, C. Computer assisted measurement of cup placement in total hip replacement. Clin Orthop Relat Res.
1998; 354: 70-81. 10.1097/00003086-199809000-00010
17. Jolles, BM., Genoud, P. and Hoffmeyer, P. Computer-assisted cup placement techniques in total hip arthroplasty improve accuracy of placement. Clin Orthop Relat Res.
2004; 426: 174-179. 10.1097/01.blo.0000141903.08075.83
18. Kalteis, T., Handel, M., Bathis, H., Perlick, L., Tingart, M. and Grifka, J. 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: 163-167. 10.1302/0301-620X.88B2.17163
19. Kalteis, T., Handel, M., Herold, T., Perlick, L., Baethis, H. and Grifka, J. Greater accuracy in positioning of the acetabular cup by using an image-free navigation system. Int Orthop.
2005;29:272-276. 3456647. 10.1007/s00264-005-0671-5.
20. Kalteis, T., Sendtner, E., Beverland, D., Archbold, PA., Hube, R., Schuster, T., Renkawitz, T. and Grifka, J. The role of the transverse acetabular ligament for acetabular component orientation in total hip replacement: an analysis of acetabular component position and range of movement using navigation software. J Bone Joint Surg Br.
2011; 93: 1021-1026. 10.1302/0301-620X.93B8.25720
21. Kennedy, JG., Rogers, WB., Soffe, KE., Sullivan, RJ., Griffen, DG. and Sheehan, LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty.
1998; 13: 530-534. 10.1016/S0883-5403(98)90052-3
22. Kumar, PG., Kirmani, SJ., Humberg, H., Kavarthapu, V. and Li, P. Reproducibility and accuracy of templating uncemented THA with digital radiographic and digital TraumaCad templating software. Orthopedics.
2009; 32: 815.
23. Kummer, FJ., Shah, S., Iyer, S. and DiCesare, PE. The effect of acetabular cup orientations on limiting hip rotation. J Arthroplasty.
1999; 14: 509-513. 10.1016/S0883-5403(99)90110-9
24. Leenders, T., Vandevelde, D., Mahieu, G. and Nuyts, R. Reduction in variability of acetabular cup abduction using computer assisted surgery: a prospective and randomized study. Comput Aided Surg.
2002; 7: 99-106. 10.3109/10929080209146021
25. Leslie, IJ., Williams, S., Isaac, G., Ingham, E. and Fisher, J. High cup angle and microseparation increase the wear of hip surface replacements. Clin Orthop Relat Res.
2009;467:2259-2265. 2866926. 10.1007/s11999-009-0830-x.
26. Lewinnek, GE., Lewis, JL., Tarr, R., Compere, CL. and Zimmerman, JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am.
1978; 60: 217-220.
27. McCollum, DE. and Gray, WJ. Dislocation after total hip arthroplasty: causes and prevention. Clin Orthop Relat Res.
1990; 261: 159-170.
28. Morrey, BF. Difficult complications after hip joint replacement: dislocation. Clin Orthop Relat Res.
1997; 344: 179-187.
29. Murphy, SB. and Ecker, TM. Evaluation of a new leg length measurement algorithm in hip arthroplasty. Clin Orthop Relat Res.
2007; 463: 85-89.
30. Murray, DW. The definition and measurement of acetabular orientation. J Bone Joint Surg Br.
1993; 75: 228-232.
31. Parratte, S. and Argenson, JN. Validation and usefulness of a computer-assisted cup-positioning system in total hip arthroplasty: a prospective, randomized, controlled study. J Bone Joint Surg Am.
2007; 89: 494-499. 10.2106/JBJS.F.00529
32. Saxler, G., Marx, A., Vandevelde, D., Langlotz, U., Tannast, M., Wiese, M., Michaelis, U., Kemper, G., Grutzner, PA., Steffen, R., Knoch, M., Holland-Letz, T. and Bernsmann, K. The accuracy of free-hand cup positioning: a CT based measurement of cup placement in 105 total hip arthroplasties. Int Orthop.
33. Shon, WY., Baldini, T., Peterson, MG., Wright, TM. and Salvati, EA. Impingement in total hip arthroplasty a study of retrieved acetabular components. J Arthroplasty.
2005; 20: 427-435. 10.1016/j.arth.2004.09.058
34. Siebenrock, KA., Kalbermatten, DF. and Ganz, R. Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers. Clin Orthop Relat Res.
2003; 407: 241-248. 10.1097/00003086-200302000-00033
35. Steinberg, EL., Shasha, N., Menahem, A. and Dekel, S. Preoperative planning of total hip replacement using the TraumaCad system. Arch Orthop Trauma Surg.
2010; 130: 1429-1432. 10.1007/s00402-010-1046-y
36. Wan, Z., Malik, A., Jaramaz, B., Chao, L. and Dorr, LD. Imaging and navigation measurement of acetabular component position in THA. Clin Orthop Relat Res.
2009;467:32-42. 2600979. 10.1007/s11999-008-0597-5.
37. Westacott, DJ., McArthur, J., King, RJ. and Foguet, P. Assessment of cup orientation in hip resurfacing: a comparison of TraumaCad and computed tomography. J Orthop Surg Res.
2013;8:8. 3637092. 10.1186/1749-799X-8-8.
38. Widmer, KH. and Zurfluh, B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res.
2004; 22: 815-821. 10.1016/j.orthres.2003.11.001
39. Woo, RY. and Morrey, BF. Dislocations after total hip arthroplasty. J Bone Joint Surg Am.
1982; 64: 1295-1306.
40. Yamaguchi, M., Akisue, T., Bauer, TW. and Hashimoto, Y. The spatial location of impingement in total hip arthroplasty. J Arthroplasty.
2000; 15: 305-313. 10.1016/S0883-5403(00)90601-6
41. Ybinger, T., Kumpan, W., Hoffart, HE., Muschalik, B., Bullmann, W. and Zweymuller, K. Accuracy of navigation-assisted acetabular component positioning studied by computed tomography measurements: methods and results. J Arthroplasty.
2007; 22: 812-817. 10.1016/j.arth.2006.10.001