Direct anterior approach to total hip arthroplasty using computer navigation.
Abstract: The incorporation of computer navigation in total hip arthroplasty (THA) has been much slower than for total knee arthroplasty (TKA). One reason for this is that a majority of THAs are performed with the patient in the lateral position through a posterior or lateral approach, making the tracker placement and the registration process cumbersome. In the direct anterior approach, the patient is in the supine position, which accommodates pelvic tracker placement and markedly facilitates the registration process. At our institution, we use the direct anterior approach and computer navigation on all of our primary THAs. We hypothesized that computer navigation improves cup placement without increasing operative time.

Materials and Methods: This was a retrospective study comparing a consecutive series of 150 computer navigated THAs to a consecutive series of 150 non-navigated hips. The two groups were similarly matched by age, gender, and body mass index. Postoperative anteroposterior pelvic radiographs and operative times were analyzed.

Results: The navigation group mean cup inclination was 41[degrees] (range, 32[degrees] to 54[degrees]), compared to 36[degrees] (range, 19[degrees] to 52[degrees]) for the non-navigated group. The mean surgical time for the navigation group was 56 minutes (range, 34 to 91 minutes) and 61 minutes (range, 33 to 119 minutes) for the non-navigated group.

Conclusion: The results suggest that computer navigation is easy to incorporate when utilizing a direct anterior approach and in our series shortens the operative time. The accuracy and precision of cup angle placement is comparable to our non-navigated method but appears to be slightly improved with computer navigation. Although more work is needed for progress with this promising technology, we believe that incorporating computer navigation for hip arthroplasties in the supine position is straightforward and of great value.
Article Type: Clinical report
Subject: Hip replacement arthroplasty (Methods)
Hip replacement arthroplasty (Technology application)
Hip replacement arthroplasty (Research)
Medical computer applications (Usage)
Medical computer applications (Research)
Authors: Kreuzer, Stefan
Leffers, Kevin
Pub Date: 01/01/2011
Publication: Name: Bulletin of the NYU Hospital for Joint Diseases Publisher: J. Michael Ryan Publishing Co. Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 J. Michael Ryan Publishing Co. ISSN: 1936-9719
Issue: Date: Jan, 2011 Source Volume: 69 Source Issue: 1
Topic: Event Code: 310 Science & research Computer Subject: Technology application
Product: Product Code: 3573081 Health Computer Systems; 3573080 Health & Education EDP Use NAICS Code: 334111 Electronic Computer Manufacturing
Accession Number: 289216156
Full Text: To the best of this investigator's knowledge, computer navigation for total hip arthroplasty (THA) was first developed in 1992 by William Bargar. (1) The technology has been shown to allow more precise and accurate component placement, (2-4) which theoretically should decrease complications, such as leg-length inequality, dislocation, high rates of polyethylene wear, and associated osteolysis. (5,6) Implant companies provide mechanical guides with their hip arthroplasty systems to assist component placement, but they still lead to wide variability in component placement. (7) These guides do not take into consideration movement of the pelvis during the operation and rely upon the surgeon's eye to account for any changes in pelvic position. Computer navigation tracks the movement of the pelvis intra-operatively and, therefore, allows for appropriate placement of components within the "safe zone." (8)

Though computer navigation has been shown to improve component placement, some investigators remain skeptical about its use, citing cost, complexity, and increased operative time as major drawbacks. (9) The complexity of many systems has decreased with the interfaces becoming simpler and more user friendly. For instance, the Stryker knee navigation system, which we currently use, does not require CT scans, has improved work flow, and is also available in a pin less version. The hip platform has also been streamlined by improving the workflow and allowing the tracker placement on the opposite iliac crest. With regard to operative time the primary author has found that computer navigation is easily incorporated in the direct anterior approach to the hip. We hypothesized that incorporation of computer navigation using the direct anterior approach for THA improves cup placement and does not significantly add to operative time.

Materials and Methods

The direct anterior approach is utilized with the patient in the supine position. A leg-holding device (the arch table extension) that is separate from the operating room table is utilized (Fig. 1). The patient is draped to allow access to the opposite iliac crest so that a fiducial marker can be attached to this side (Fig. 2). The imageless OrthoMap Modular Hip Navigation system (Stryker, Mahwah, New Jersey) was utilized for all navigated cases. After placing the pelvic tracker onto the iliac crest with three pins, the routine registration of the vertical plan, right and left anterior superior iliac spines, and symphysis pubis was completed (Fig. 3). To improve the accuracy of leg length, the primary investigator has developed a new technique whereby a self-centering drill is utilized to make a small dimple in the distal femur that does not perforate the cortex. This allows for a very accurate reference point for leg-length measurement (Fig. 4). Once the osteotomy is completed and the femoral head is removed, the acetabular registration is completed.


A retrospective chart review and radiographic analysis of 300 consecutive primary THAs with the direct anterior approach from April 2008 to July 2010 was conducted using an institutional review board (IRB) approved joint registry database. The primary investigator began using computer navigation in August 2009. The previous 150 primary THAs before this date were compared to the first 150 primary THAs using computer navigation. The demographics of each group were not statistically different with regards to gender (p = 0.6444), age (p = 0.1435), or body mass index (p = 0.4783) (Table 1).

Postoperative radiographs were analyzed by one investigator (KL) for cup angle, using TraumaCad[R] 2.2 software (Voyant Health, Columbia, Maryland). The inferior rims of the obturator foramina were used as reference points when measuring cup angles (Fig. 5). Surgical time was defined as time from skin incision to final reduction. Simple descriptive statistics and Student t-tests were used to analyze the data.



Statistical significance was set at p < 0.05.


The navigation group mean cup inclination was 41[degrees] (range, 32[degrees] to 54[degrees]; SD, 4.1), compared to 36[degrees] (range, 19[degrees] to 52[degrees]; SD, 6.3) for the non-navigated cohort (p < 0.0001). The mean surgical time for the navigation operations was 56 minutes (range, 34 to 91 minutes; SD, 10.7) and 61 minutes (range, 33 to 119 minutes; SD, 15.8) for the non-navigated cohort (p < 0.0001)(Table 2).


Complications associated with THA such as leg length inequality, dislocation, higher rate of polyethylene wear, and its associated osteolysis have some dependence upon component placement. (5,6) Computer navigation has proven to be more accurate and precise at component placement (2-4) and maintaining femoral offset and leg length. (10) Most of these studies proving the accuracy and precision of computer navigation are done using posterior or anterolateral approaches. No studies were found in the literature that analyzed this technology with the direct anterior approach. It is the investigators' belief that the anterior approach is more accommodating to computer navigation, because the patient is in the supine position throughout the entire procedure. When using a posterior or anterolateral approach, a fiducial tracker is attached to the ipsilateral iliac crest for initial registration, and then the patient is moved into the lateral decubitus position, creating issues with draping and sterility, as well as accuracy of registration. Weaknesses of this study include its retrospective nature, absence of clinical data, and lack of long-term follow-up.



The mean cup angle of our navigation cohort was 41[degrees], compared to the conventional cohort mean cup angle of 36[degrees]. Both means are within Lewinnek and colleagues' (8) safe zone of abduction, (40[degrees] abduction [+ or -] 10[degrees]); however, the navigation group had 97% (145/150) of cups within the safe zone, compared to the percentage of the non-navigated group of 87% (131/150). Kalties and coworkers (3) and Najarian and associates (11) both compared their non-navigated techniques to computer navigation and found that computer navigation placed their cups in the safe zone 93% and 96% of the time, respectively, compared to the non-navigated method, which placed the cup in the safe zone 46% and 87% of the time, respectively. The mean surgical time of the navigation group was 5 minutes less than the non-navigated cohort, and this difference was statistically significant. Based on a previous unpublished in-house analysis by the primary investigator (SK) that was presented at the International Society for Technology in Arthroplasty 2010, operative times before the non-navigated cohort were evenly distributed. The slower operative time of the non-navigated cohort was not due to the learning curve of this approach. Kalties and colleagues (3) and Najarian and coworkers (11) also looked at this parameter when comparing the two techniques but had longer operative times with navigation.

To the best of our knowledge, this is the first report of navigated THAs having shorter operative times than conventional methods. This is a preliminary study, and more powerful prospective studies need to be done. However, it does indicate that navigated THAs can be just as fast as conventional THAs with a surgeon who is experienced with navigation technology. The investigators believe the anterior approach accommodates computer navigation better than the posterior or anterolateral approach because the patient is in the supine position throughout the procedure and does not have to be moved once registration is complete. Another possible reason for the shorter operative times found in the navigated group is that there was less time used for finding the appropriate cup position. The navigation allowed this step to be done quicker than the trial and error non-navigated method. In addition, the decision about what neck length to use for proper leg-length determination was facilitated with the information obtained.


Computer navigation in orthopaedics is still in the proof stage. It is accepted that component placement is extremely important for the survival of implants, but the impact of computer navigation on long-term survival remains to be determined. Our results confirm that navigation is precise and accurate and when used by a surgeon with experience can result in shorter operative time. We remain optimistic about this technology and plan on reporting long-term follow up data in the future.

Disclosure Statement

One of the authors has a proprietary interest in one of the materials discussed and is a consultant to Stryker Orthopaedics.


(1.) Kelley TC, Swank ML. Role of navigation in total hip arthroplasty. J Bone Joint Surg Am. 2009 Feb;91 Suppl 1: 153-8.

(2.) Nogler M, Kessler O, Prassl A, et al. Reduced variability of acetabular cup positioning with use of an imageless navigation system. Clin Orthop Relat Res. 2004 Sep; 426: 159-63.

(3.) Kalteis T, Handel M, Herold T, et al. Greater accuracy in positioning of the acetabular cup by using an image-free navigation system. Int Orthop. 2005 Oct; 29(5): 272-6.

(4.) Gandhi R, Marchie A, Farrokhyar F, et al. Computer navigation in total hip replacement: a meta-analysis. Int Orthop. 2009 Jun; 33(3): 593-7.

(5.) Kennedy JG, Rogers WB, Soffe KE, et al. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty. 1998 Aug; 13(5): 530-4.

(6.) Schmalzried TP, Guttmann D, Grecula M, et al. The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis. J Bone Joint Surg Am. 1994 May; 76(5): 677-88.

(7.) DiGioia AM, Jaramaz B, Blackwell M, et al. The Otto Au franc Award. Image guided navigation system to measure intraoperatively acetabular implant alignment. Clin Orthop Relat Res. 1998 Oct; 355: 8-22.

(8.) Lewinnek GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978 Mar; 60(2): 217-20.

(9.) Sikorski JM, Chauhan S. Computer-assisted orthopaedic surgery: do we need CAOS? J Bone Joint Surg Br. 2003 Apr; 85(3): 319-23.

(10.) Renkawitz T, Schuster T, Herold T, et al. Measuring leg length and offset with an imageless navigation system during total hip arthroplasty: is it really accurate? Int J Med Robot. 2009 Jun; 5(2): 192-7.

(11.) Najarian BC, Kilgore JE, Markel DC. Evaluation of component positioning in primary total hip arthroplasty using an imageless navigation device compared with traditional methods. J Arthroplasty. 2009 Jan; 24(1): 15-21.

Stefan Kreuzer, M.D., and Kevin Leffers, M.D., are from the Memorial Bone and Joint Research Foundation, Houston, Texas.

Correspondence: Stefan Kreuzer, M.D., Suite 101, Memorial Bone and Joint Research Foundation, 1140 Business Center Drive, Houston, Texas 77043;
Table 1  Demographics for Operative Series

Demographic       Conventional       Navigation
                  Approach           Approach

Males/Females     67/83              71/79
Age (years)       65.8 (26.1-90.1)   64.3 (36.7-90.2)
Body mass index   28.6 (18.8-43.1)   28.2 (17.5-43)
Diagnosis         143 OA, 5 ON,      134 OA, 11 AVN,
                    1 RA, 1 FX         4 FX, 1 other

OA, osteoarthritis; ON, osteonecrosis; RA, rheumatoid
arthritis; FX, fracture

Table 2 Results for Operative Series

Results                   Conventional    Navigation    P Value
                          Approach        Approach

Cup angle (Degrees)       36 (19-52)      41 (32-54)    < 0.0001
Surgical time (Minutes)   61 (33-119)     56 (34-91)    < 0.0001
Gale Copyright: Copyright 2011 Gale, Cengage Learning. All rights reserved.