Comparison Between Pointer-based and Ultrasound-based Navigation Technique in THA Using a Minimally Invasive Approach

Abstract

The use of navigation techniques in primary total hip arthroplasty improves the position of endoprosthetic components, especially cup positioning. An intraoperative registration of the anterior pelvic plane is necessary to define the anteversion and inclination angles on the acetabular side. This study compares the accuracy of manual pointer palpation to ultrasound registration in navigation to determine pelvic plane registration in 60 cases of minimally invasive surgical technique. Findings show more accurate postoperative radiographic anteversion with ultrasound navigation, although both manual pointer palpation and ultrasound registration techniques show a very small standard deviation in anteversion, inclination, and leg length difference. In conclusion, we recommend navigation as a very reliable tool for the positioning of implants.

Arthroplasty of the hip joint is one of the most successful surgical measures in orthopedics. Preconditions for these good results are high-quality implants and soft tissue management, which enable precise implant positioning.

Long-term results of modern hip prosthesis are excellent, with approximately 95% survival rate after 10 years.^1-4 Since the definition of the so-called ”safe zone” of Lewinnek was established, the planned final implant positioning can be determined.⁵ Especially in terms of minimal invasive operative techniques with smaller skin incisions, soft tissue preserving approaches, and a decreased field of view, the incidence of malpositioning and the failure rate in endoprosthetic replacement are increasing.⁶ The navigation ensures improved implant positioning^7,8 and therefore could compensate for the disadvantage of reduced visibility of landmarks associated with minimally invasive techniques. Ultrasound-based navigation is particularly advantageous,⁹ because pelvic landmarks can be registered more easily than with pointer-based hip navigation.

Figure 1: Intraoperative picture of pointer-based pelvic navigation; the reference point at the iliac crest is identical in both methods.

The goal of this study was to compare ultrasound-based vs pointer-based navigation in minimally invasive primary hip replacement.

Material and Methods

Sixty patients were evaluated in this study. All patients were implanted with the same navigated cementless hip endoprosthesis (Plasmacup with polyethylene-inlay, ceramic head, and Excia stem; B. Braun Aesculap AG, Tuttlingen, Germany) using minimally invasive operating technique (anterolateral approach in supine position). Furthermore, the same surgeon performed the procedure in all patients. The navigation system used in all cases was the OrthoPilot with the software THAplus (B. Braun Aesculap AG).

Hip navigation was pointer based for group A and ultrasound based for group B (control group).

Pointer-based stem navigation was used in all patients (Figures 1, 2).

Figure 2: Intraoperative picture of ultrasound-based pelvic navigation, showing the uncovered iliac crests at both sides and the symphysis.

According to Lewinnek,⁵ the aim for cup inclination was 40° to 45°. In case of cup anteversion, the antetorsion of the stem is important. Because of our preference for torsion position of the femoral components of 0°, the aim was a cup anteversion of 20° to 30°. The sum of both components (anteversion of cup plus antetorsion of stem) should equal 20° to 30°.¹⁰ Regarding leg length, balance with the opposite leg was attempted in all cases. Considering the absolute measured value of the displayed radiographs, a slight lengthening of the operated leg often occurs in comparison to the preoperative arthritic condition. Therefore, the comparison of leg length pre- and postoperatively as well as the comparison to the opposite leg was evaluated.

Evaluation of the implant positions in each case was based on standardized radiograph examinations (hip overview and lateral hip recordings) performed preoperatively and 2 weeks postoperatively.

The following is a comparison of radiograph results with data saved from the OrthoPilot.

The basis for this investigation was the acceptance of all patients. Only patients who provided written authorization for the use of their health records were enrolled in the study.

The aim of these investigations was the evaluation of the cup position (inclination and anteversion) as well as the determination of the leg length. In addition, the investigation sought to record intraoperative and postoperative complications.

Results

Both groups were similarly matched for age, sex, body mass index (BMI), and criteria of American Society of Anesthesiologists (ASA) (Table 1). In the ultrasound-based group (group 2), the operation lasted slightly longer (5.2 min; P < .05). Intraoperative blood loss was equivalent between both groups (362 vs 375 mL; P =.08).

Evaluation of the cup position showed no difference for mean value in inclination and anterversion. The comparison of deviation showed a slightly smaller deviation in anteversion in group B (Table 2). There was no difference in deviation with regard to cup inclination.

Evaluation of leg length discrepancy showed no difference between the groups (Table 3). There were no differences in complications between the two groups. There was no hip dislocation or implant dislocation in either group.

Discussion

An important result of this study is that we could evaluate whether navigation enables precise cup positioning and implantation depth of the stem. The deviation of the implant positioning is considerably smaller than that reported in studies without navigation. Even experienced surgeons noticed deviations of the cup inclination of 26° to 64°.⁸ Cup anteversion seems to present a sharper distinction. In these cases, deviations of 9° to 53° were reported.⁸ These indications are confirmed in the meta-analysis of Gandhi et al.⁷ In the evaluation of the navigated cup positioning, this group discovered outliers of 10.7% from the interval recommended by Lewinnek⁵ in comparison with 41.8% outliers in nonnavigated cup positioning. This difference was highly significant (P < .001). Medium- to long-term malpositioning of the cup results in greater wear and cup loosening.¹¹ Therefore, the longevity and long-term result of a hip prosthesis significantly depend on the cup position. In this study, we could demonstrate that the ultrasound-based navigation enables minimization of the deviation of the anteversion of the cup. The reason for this seems to be the more precise display of the osseous landmarks, which depends less on the soft tissue over them than that in the case of pointer-based navigation. This result is an advantage of ultrasound-based navigation. A slightly longer operating time has to be taken into consideration. Furthermore, the operating cover has to be modified (the contralateral iliac crest stays uncovered). This procedure requires extra time.

The position of the stem influences significantly both the complication rate as well as the long-term result. In this study, we found only a maximum 2-mm lengthening on the unilateral side in all navigated hip replacements compared with the contralateral leg. The advantage of stem navigation is intraoperative measurement of leg length, which seems to be very helpful and reasonable.¹² Only small differences, such as 5° abduction or adduction of the leg, can affect leg length difference up to 8 mm,¹³ so a misinterpretation may occur in clinical testing. Additionally, a higher range of malpositioning or malrotation can result without the use of navigation, and the rate of loosening and shorter survival rate of implants should be discussed in this context.¹⁴

We found that navigation of the cup and stem is helpful to achieve the best implant position. However, surgeons must define the correct position further.

Conclusion

Navigation is a secure and recommended system for optimizing implant positioning with no increase in complications. It offers an advantage in cases of smaller field of visibility of the operating situs as in minimally invasive approaches because the risk of malpositioning is higher. In minimally invasive approaches, we could demonstrate that both ultrasound-based and pointer-based hip navigation are approaches that produce lower rates of malpositioning as described.¹⁵ Additionally, ultrasound-based navigation provides higher precision of positioning in anteversion of the cup. The navigation is recommended for primary hip replacement as additional support in implant positioning.

References

1. Aldinger PR, Thomsen M, Mau H, Ewerbeck V, Breusch SJ. Cementless Spotorno tapered titanium stems: excellent 10-15-year survival in 141 young patients. Acta Orthop Scand. 2003; 74(3):253-8.
2. Reigstad O, Siewers P, Røkkum M, Espehaug B. Excellent long-term survival of an uncemented press-fit stem and screw cup in young patients: follow-up of 75 hips for 15-18 years. Acta Orthop. 2008; 79(2):194-202.
3. Siebold R, Scheller G, Schreiner U, Jani L. Long-term results with the cement-free Spotorno CLS shaft. Orthopade. 2001; 30(5):317-22.
4. Swedish National Hip Arthroplasty Register; Johan Kärrholm, Göran Garellick, Peter Herberts. Annual Report 2006. http://www.jru.orthop.gu.se/
5. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR.Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978; 60(2):217-220.
6. Laffosse JM, Chiron P, Molinier F, Bensafi H, Puget J. Prospective and comparative study of the anterolateral mini-invasive approach versus minimally invasive posterior approach for primary total hip replacement. Early results. Int Orthop. 2007; 31(5):597-603. Epub 2006 Oct 12.
7. Gandhi R, Marchie A, Farrokhyar F, Mahomed N.Computer navigation in total hip replacement: a meta-analysis. Int Orthop. 2008 Apr 3. [Epub ahead of print]
8. Haaker RG, Tiedjen K, Ottersbach A, Rubenthaler F, Stockheim M, Stiehl JB.Comparison of conventional versus computer-navigated acetabular component insertion. J Arthroplasty. 2007; 22(2):151-159.
9. Kiefer H, Othman A: Ultrasound vs pointer palpation based method in THA navigation: a comparative study. Orthopedics. 2007; 30(10 suppl):S153-S156.
10. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res. 2004; 22(4):815-821.
11. Garcia-Rey E, Garcia-Cimbrelo E: Long-term results of uncemented acetabular cups with an ACS polyethylene liner: a 14-16-year follow-up study. Int Orthop. 2007; 31(2):205-210.
12. Ecker TM, Tannast M, Murphy SB: Computed tomography-based surgical navigation for hip arthroplasty. Clin Orthop Relat Res. 2007;(465):100-105.
13. Sarin VK, Pratt WR, Bradley GW. Accurate femur repositioning is critical during intraoperative total hip arthroplasty length and offset assessment. J Arthroplasty. 2005; 20(7):887-891.
14. Heller MO, Kassi JP, Perka C, Duda GN. Cementless stem fixation and primary stability under physiological-like loads in vitro. Biomed Tech (Berl). 2005; 50(12):394-399.
15. Kalteis T, Handel M, Bäthis H, Perlick L, Tingart M, 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(2):163-16s7.

Authors

Drs. Hasart, Perka and Tohtz are from the Orthopaedic Department, Charité, in Berlin, Germany.

Drs. Hasart, Perka, and Tohtz are speakers for B. Braun Aesculap.

Correspondence should be addressed to: Olaf Hasart, MD, Orthopaedic Department, Charité, Charitéplatz 1, 10117 Berlin, Germany.