- Open Access
Accuracy of image-free navigation in intraoperative leg length change from total hip arthroplasty using evaluations from 2D and 3D measurements
BMC Musculoskeletal Disorders volume 22, Article number: 1021 (2021)
Leg length discrepancy is one of the most common problems after total hip arthroplasty (THA). The aim of this study was to investigate the accuracy of image-free navigation in intraoperative leg length change (LLC) using evaluations from anteroposterior radiographs (2D measurement) and 3D bone models using CT data (3D measurement).
One hundred THAs with cementless cups and stems were performed using an image-free navigation system in our hospital. We evaluated the accuracy of image-free navigation based on LLC from 2D and 3D measurements. Furthermore, we also investigated error in absolute value and correlations between 2D and 3D measurements in LLC.
The accuracy of image-free navigation based on 2D measurement was 94% within 5 mm and 76% within 3 mm. The accuracy of image-free navigation based on 3D measurement was 92% within 5 mm and 81% within 3 mm. The error in absolute value in LLC between 2D and 3D measurements was 1.7 ± 1.4 mm (range, 0 to 6 mm). A strong correlation was observed between 2D and 3D measurements in the LLC.
In the present study, good accuracy of image-free navigation in intraoperative LLC was confirmed for both evaluation methods from 2D and 3D measurements. In addition, the error in absolute value in the LLC between 2D and 3D measurements was very small, and we observed a strong correlation between 2D and 3D measurements. Based on these results, evaluation of LLC from radiographs was considered sufficient if radiographs can be taken accurately.
Leg length discrepancy (LLD) is one of the most common problems after total hip arthroplasty (THA). LLD can be a cause of patient dissatisfaction because of ipsilateral gait disorder, knee pain, back pain and implant failure associated with inferior clinical outcomes [1,2,3,4,5,6]. Several methods have been reported for adjusting and equalizing leg length after THA [3, 7,8,9,10,11,12]. As one of these methods, use of computer navigation in THA has been increasing over the last decade. Many reports have described good accuracy for CT-based navigation and image-free navigation in terms of intraoperative leg length change (LLC) [13,14,15,16,17,18]. However, almost all those reports evaluated LLC using a two-dimensional (2D) measurement based on pre- and postoperative anteroposterior radiographs. In recent years, a three-dimensional (3D) method based on 3D bone models from computed tomography (CT) data has been used for preoperative and postoperative evaluation of total joint arthroplasty. Several reports have described that the evaluation using 3D method was more accurate than using 2D method for implant position and offset [19,20,21]. Therefore, we hypothesized that the 3D measurement could evaluate leg length change more accurate than the 2D measurement. No reports appear to have compared between the 2D and 3D measurements for the accuracy evaluation of image-free navigation. The aim of this study was to investigate the accuracy of image-free navigation in intraoperative LLC using evaluation methods based on 2D and 3D measurements.
Study design and patient selection
This retrospective case series was approved by the ethics committee of our institution (No. H2018–083). From November 2014, our institution performed 118 consecutive primary THAs with cementless cup and stems (Kyocera, Kyoto, Japan) using an image-free navigation system (Brain Lab; KICK Hip application 6.0, Helmstetten, Germany). We recorded preoperative variables, including age, sex, body mass index and primary diagnosis. For assessment of leg length, all included patients underwent pre- and postoperative radiographic and CT examinations. Postoperative radiography and CT examinations were performed at 2 weeks postoperatively. Exclusion criteria were incomplete operation record and inadequate pelvic x-rays and CT data. All preoperative and postoperative evaluations were performed by the author (ST), and all operations were performed by two senior surgeon (AS and MH).
For the THA procedure, we used a posterolateral approach in the lateral decubitus position. KICK Hip application system for THA is a non-image-based system that uses a virtual data model supplemented by intraoperative registration (Fig. 1a). The system required placement of trackers on the pelvis and distal femur (two pins each) before surgery (Fig. 1b). The reference frame used is the anterior pelvic plane, which is obtained by palpating bilateral anterior superior iliac spines (ASISs) with a special tracked palpation pointer registered to the computer. The femoral reference plane is formed by the piriformis fossa, medial and lateral epicondyles and ankle center. The femur position was registered to the software by holding the leg in a neutral extension position. After trial and final reconstructions, the femur is brought to the neutral position stored during leg alignment, so as to match the centers of the crosshairs displayed on the monitor. When these crosshairs are sufficiently aligned (within 5° of stored leg alignment), the active crosshair turns green. Intraoperative LLC was displayed after holding the leg steady for 2–3 s (Fig. 1c). Intraoperative LLC was defined as the amount of change from the leg length measured as the distance between the two trackers in the neutral position. All procedures were performed in accordance with relevant guidelines.
Evaluation methods of leg length change
The anteroposterior pelvic radiograph was performed in the standard manner with the patient supine with lower limbs placed in internal rotation and the big toes touching each other so that the patella was facing forward. Pre- and postoperative LLD on 2D measurement was measured as the distance between the horizontal line connecting both tear drops and the medial apex of the lesser trochanter in neutral position (Fig. 2a). LLC on 2D measurement was defined as the difference between pre- and postoperative LLD on 2D measurement. Helical CT providing images with a 1-mm slice interval from the ASIS to the knee was performed for all cases. Pre- and postoperative LLD on 3D measurement were measured in the functional pelvic plane after repositioning using the 3D-Template system (ZedHip; LEXI Co., Tokyo, Japan), then assessed as the distance from the ASIS to the intercondylar fossa of femur (Fig. 2b). The 3D-Template system was used to match pre- and postoperative CT digital images. LLC on 3D measurement was defined as the difference between pre- and postoperative LLD on 3D measurement. To evaluate the accuracy of image-free navigation based on 2D and 3D measurements, intraoperative LLC were compared with LLC on 2D and 3D measurements. We also investigated the error in absolute value and the correlation between 2D and 3D measurements of LLC.
All statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). Continuous data were analyzed using the nonparametric Wilcoxon signed-rank test and Spearman’s rank correlation coefficient. Values of P < 0.05 were considered significant. The reproducibility of 2D and 3D measurements was confirmed. For intra-observer reliability, each parameter was measured twice, on 20 hips, at an interval ≥ 4 weeks by one orthopedic surgeon (ST). For inter-observer reliability, two orthopedic surgeons (ST and YN) measured each parameter twice, on 20 hips, at an interval ≥ 4 weeks. Intra-class and inter-class correlation coefficient was calculated to analyse the variability between observers. Values of 0.81–1.00 indicated excellent correlation; 0.61–0.80, substantial correlation; 0.41–0.60, moderate correlation; 0.21–0.40, fair correlation; and 0.00–0.20, poor correlation.
One hundred patients with complete data sets were included for analysis. The patient demographics are shown in Table 1. The intra-class and inter-class correlation coefficients for the 2D measurement were 0.98 and 0.92, respectively. The intra-class and inter-class correlation coefficients for the 3D measurement were 0.97 and 0.94, respectively.
Mean intraoperative LLC with image-free navigation was 12.0 ± 7.2 mm (range, −7 to 32 mm). Mean LLC on 2D measurement were 13.2 ± 7.0 mm (range, −3 to 35 mm). Mean LLC on 3D measurement were 12.9 ± 6.5 mm (range, −1 to 34 mm) (Table 2). Intraoperative LLC with image-free navigation was significantly shorter than LLC on 2D and 3D measurements. There was no significance between 2D and 3D measurements of LLC. In terms of the accuracy of image-free navigation based on 2D measurement, agreement with a difference ≤ 5 mm was confirmed in 94 of 100 THAs (94.0%), agreement with a difference ≤ 3 mm was confirmed in 76 of 100 THAs (76.0%). In the accuracy of image-free navigation based on 3D measurement, agreement with a difference ≤ 5 mm was confirmed in 92 of 100 THAs (92.0%), agreement with a difference ≤ 3 mm was confirmed in 81 of 100 THAs (81.0%) (Fig. 3). Errors in absolute value for LLC between 2D and 3D measurements were 1.7 ± 1.4 mm (range, 0 to 6 mm). A strong significant correlation between 2D and 3D measurements of LLC was observed (Fig. 4).
THAs have very high success rates in terms of providing pain relief and improving mobility among patients with advanced osteoarthritis, osteonecrosis, and rheumatoid arthritis. However, these adult reconstructive procedures are also associated with a known potential for major complications, which may lead to litigation [22,23,24]. Although leg length discrepancy must be ≤10 mm for a patient to have good quality of life, an unexpected difference of 10–16 mm can sometimes occur despite careful attention [3, 6, 25]. Accurately assessing the amount of change in intraoperative leg length is considered very important to minimize the unexpected leg length discrepancy.
Good results have been reported for intraoperative LLC using image-free navigation in previous studies [13,14,15]. Moreover, several studies of intraoperative LLC have reported the accuracy of image-free navigation using pin fixing was significantly higher than free-hand, fluoroscopy and image-free navigation with the pinless device [26,27,28]. In the present study, good accuracy of image-free navigation in intraoperative LLC was confirmed on radiographic assessment, as in previous studies. The most important finding of the present study was the observation of the strong significant correlation of LLC between the evaluation of 2D and 3D measurements. Furthermore, no significant difference was observed the accuracy of LLC between the evaluation of 2D and 3D measurements. Based on these results, we were not confirmed the evaluation of 3D measurement was usefulness than that of 2D measurement in the present study.
On the other hand, a leg length error ≥ 10 mm was observed in 4 cases of this study. Ellapparadia et al. reported that 4 patients showed leg length error > 10 mm among these 6 patients with leg length error > 6 mm . As the potential source of assessment errors in intraoperative assessment, loosening of the device has been reported as a factor inducing error . It is thus necessary to keep in mind that some patients still show LLC >10 mm, although we were unable to clarify the causes of error in the present study.
Several limitations to this study must be considered. First, CT scans expose the patient to irradiation. CT scans is the imaging study that can be used for measurement of the hip geometry, preoperative planning and offset evaluation, but it exposes the patients to large radiation dose compared to conventional radiography [29,30,31]. Increased radiation exposure has been related to increased risk of various cancers, indicating the importance to minimize radiation exposure as much as possible [32, 33]. Therefore, a low dose CT have recently used to preoperative planning and postoperative assessment of total hip arthroplasty [34, 35]. However, we indicated that CT scan might not be necessary for the evaluation of leg length in this study. Second, leg length is often susceptible to errors that can be influenced by flexion contracture and variations in pelvic tilt and rotation. Fortunately, patients with severe flexion contracture were not observed in this study. A third limitation was the difference in evaluation methods between radiograph and CT examinations. 2D measurement was assessed as the distance between the horizontal line connecting both tear drops and the medial apex of the lesser trochanter, while 3D measurement was assessed as the distance from the ASIS to the intercondylar fossa of femur. However, we obtained the strong correlation between 2D and 3D measurement. From this result, the difference between 2D and 3D measurement was little affected for the evaluation of LLC.
The accuracy of image-free navigation in leg length change showed good results for evaluations by both anteroposterior pelvic radiographs and 3D bone models using CT data. With regard to leg length change, evaluation using radiographs alone is possible if accurate radiographs can be obtained.
Availability of data and materials
The datasets used and analysed during the current study available from the corresponding author on reasonable request.
Leg length discrepancy
Total hip arthroplasty
Leg length change
Anterior superior iliac spine
Jasty M, Webster W, Harris W. Management of limb length inequality during total hip replacement. Clin Orthop Relat Res. 1996;333:165–71.
Parvizi J, Sharkey PF, Bissett GA, Rothman RH, Hozack WJ. Surgical treatment of limb-length discrepancy following total hip arthroplasty. J Bone Joint Surg Am. 2003;85:2310–7.
Woolson ST, Harris WH. A method of intraoperative limb length measurement in total hip arthroplasty. Clin Orthop Relat Res. 1985;194:207–10.
Woo RY, Morrey BF. Dislocations after total hip arthroplasty. J Bone Joint Surg Am. 1982;64:1295–306.
Abraham WD, Dimon JH 3rd. Leg length discrepancy in total hip arthroplasty. Orthop Clin North Am. 1992;23:201–9.
Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplast. 2004;19(4 Suppl 1):108–10.
Ranawat CS, Rao RR, Rodriguez JA, Bhende HS. Correction of limb-length inequality during total hip arthroplasty. J Arthroplast. 2001;16:715–20.
McGee HM, Scott JH. A simple method of obtaining equal leg length in total hip arthroplasty. Clin Orthop Relat Res. 1985;194:269–70.
Shiramizu K, Naito M, Shitama T, Nakamura Y, Shitama H. L-shaped caliper for limb length measurement during total hip arthroplasty. J Bone Joint Surg (Br). 2004;86:966–9.
Ogawa K, Kabata T, Maeda T, Kajino Y, Tsuchiya H. Accurate leg length measurement in total hip arthroplasty: a comparison of computer navigation and a simple manual measurement device. Clin Orthop Surg. 2014;6:153–8.
Enke O, Levy YD, Bruce WJ. Accuracy of leg length and femoral offset restoration after total hip arthroplasty with the utilisation of an intraoperative calibration gauge. Hip Int. 2020;30(3):296–302.
Grobler G, Nortje M, Dower B, Chivers D. A vertical measurement system to predict the change in leg length in total hip arthroplasty. Arthroplast Today. 2020;6(3):330–7.
Ellapparadja P, Mahajan V, Atiya S, Sankar B, Deep K. Leg length discrepancy in computer navigated total hip arthroplasty - how accurate are we? Hip Int. 2016;26:438–43.
Nishio S, Fukunishi S, Fukui T, Fujihara Y, Yoshiya S. Adjustment of leg length using imageless navigation THA software without a femoral tracker. J Orthop Sci. 2011;16:171–6.
Takeda Y, Fukunishi S, Nishio S, Fujihara Y, Yoshiya S. Accuracy of component orientation and leg length adjustment in total hip arthroplasty using image-free navigation. Open Orthop J. 2017;11:1432–9.
Ecker TM, Tannast M, Murphy SB. Computed tomography-based surgical navigation for hip arthroplasty. Clin Orthop Relat Res. 2007;465:100–5.
Kitada M, Nakamura N, Iwana D, Kakimoto A, Nishii T, Sugano N. Evaluation of the accuracy of computed tomography-based navigation for femoral stem orientation and leg length discrepancy. J Arthroplast. 2011;26(5):674–9.
Rajpaul J, Rasool MN. Leg length correction in computer assisted primary total hip arthroplasty: a collective review of the literature. J Orthop. 2018;15(2):442–6.
Sariali E, Boukhelifa N, Catonne Y, Pascal MH. Comparison of three-dimensional planning-assisted and conventional acetabular cup positioning in total hip arthroplasty: a randomized controlled trial. J Bone Joint Surg Am. 2016;98(2):108–16.
Bayraktar V, Weber M, von Kunow F, Zeman F, Craiovan B, Renkawitz T, et al. Accuracy of measuring acetabular cup position after total hip arthroplasty: comparison between a radiographic planning software and three-dimensional computed tomography. Int Orthop. 2017;41(4):731–8.
Weber M, Merle C, Nawabi DH, Dendorfer S, Grifka J, Renkawitz T. Inaccurate offset restoration in total hip arthroplasty results in reduced range of motion. Sci Rep. 2020;10(1):13208.
Wolf BR, Lu X, Li Y, Callaghan JJ, Cram P. Adverse outcomes in hip arthroplasty: long-term trends. J Bone Joint Surg Am. 2012;94:e103.
Bokshan SL, Ruttiman RJ, DePasse JM, Eltorai AEM, Rubin LE, Palumbo MA, et al. Reported litigation associated with primary hip and knee arthroplasty. J Arthroplast. 2017;32:3573–7.e1.
Zengerink I, Reijman M, Mathijssen NM, Eikens-Jansen MP, Bos PK. Hip arthroplasty malpractice claims in the Netherlands: closed claim study 2000–2012. J Arthroplast. 2016;31:1890–3.e4.
Edeen J, Sharkey PF, Alexander AH. Clinical significance of leg-length inequality after total hip arthroplasty. Am J Orthop (Belle Mead NJ). 1995;24:347–51.
Weber M, Woerner M, Springorum R, Sendtner E, Hapfelmeier A, Grifka J, et al. Fluoroscopy and imageless navigation enable an equivalent reconstruction of leg length and global and femoral offset in THA. Clin Orthop Relat Res. 2014;472(10):3150–8.
Weber M, Thieme M, Kaiser M, Völlner F, Worlicek M, Craiovan B, et al. Accuracy of leg length and offset restoration in femoral Pinless navigation compared to navigation using a fixed pin during Total hip Arthroplasty. Biomed Res Int. 2018;2018:1639840.
Confalonieri N, Manzotti A, Montironi F, Pullen C. Leg length discrepancy, dislocation rate, and offset in total hip replacement using a short modular stem navigation vs conventional freehand. Orthopedics. 2008;31(10 Suppl 1):35–9.
Salem HS, Marchand KB, Ehiorobo JO, Tarazi JM, Matzko CN, Sodhi N, et al. Benefits of CT scanning for the management of hip arthritis and arthroplasty. Surg Technol Int. 2020;36:364–70.
Hassani H, Cherix S, Ek ET, Rüdiger HA. Comparisons of preoperative three-dimensional planning and surgical reconstruction in primary cementless total hip arthroplasty. J Arthroplast. 2014;29(6):1273–7.
Pasquier G, Ducharne G, Ali ES, Giraud F, Mouttet A, Durante E. Total hip arthroplasty offset measurement: is CT scan the most accurate option? Orthop Traumatol Surg Res. 2010;96(4):367–75.
Brenner DJ, Hall EJ. Computed tomography--an increasing source of radiation exposure. N Engl J Med. 2007;357(22):2277–84.
Mathews JD, Forsythe AV, Brady Z, Butler MW, Goergen SK, Byrnes GB, et al. Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ. 2013;346:f2360.
Su AW, Hillen TJ, Eutsler EP, Bedi A, Ross JR, Larson CM, et al. Low-dose computed tomography reduces radiation exposure by 90% compared with traditional computed tomography among patients undergoing hip-preservation surgery. Arthroscopy. 2019;35(5):1385–92.
Huppertz A, Lembcke A, Sariali el-H, Durmus T, Schwenke C, Hamm B, et al. Low dose computed tomography for 3D planning of total hip arthroplasty: evaluation of radiation exposure and image quality. J Comput Assist Tomogr. 2015;39(5):649–56.
This study was not supported by any funding.
Ethics approval and consent to participate
This study was approved by Institutional Review Board at Mie University hospital. All patients provided their informed consent.
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
About this article
Cite this article
Tone, S., Hasegawa, M., Naito, Y. et al. Accuracy of image-free navigation in intraoperative leg length change from total hip arthroplasty using evaluations from 2D and 3D measurements. BMC Musculoskelet Disord 22, 1021 (2021). https://doi.org/10.1186/s12891-021-04906-1
- Image-free navigation
- Leg length change
- Total hip arthroplasty
- 2D measurement
- 3D measurement