Home About Journal AHEAD OF PRINT Current Issue Back Issues Instructions Submission Search Subscribe Blog    

Users Online: 1997 
Print this page  Email this page Small font sizeDefault font sizeIncrease font size 

 Table of Contents    
Year : 2013  |  Volume : 47  |  Issue : 6  |  Page : 585-590
Computer navigation experience in hip resurfacing improves femoral component alignment using a conventional jig

Department of Orthopaedic Surgery, St. Michael's Hospital, University of Toronto, Toronto, ON, Canada

Click here for correspondence address and email

Date of Web Publication19-Nov-2013


Background:The use of computer navigation has been shown to improve the accuracy of femoral component placement compared to conventional instrumentation in hip resurfacing. Whether exposure to computer navigation improves accuracy when the procedure is subsequently performed with conventional instrumentation without navigation has not been explored. We examined whether femoral component alignment utilizing a conventional jig improves following experience with the use of imageless computer navigation for hip resurfacing.
Materials and Methods:Between December 2004 and December 2008, 213 consecutive hip resurfacings were performed by a single surgeon. The first 17 (Cohort 1) and the last 9 (Cohort 2) hip resurfacings were performed using a conventional guidewire alignment jig. In 187 cases, the femoral component was implanted using the imageless computer navigation. Cohorts 1 and 2 were compared for femoral component alignment accuracy.
Results:All components in Cohort 2 achieved the position determined by the preoperative plan. The mean deviation of the stem-shaft angle (SSA) from the preoperatively planned target position was 2.2° in Cohort 2 and 5.6° in Cohort 1 ( P = 0.01). Four implants in Cohort 1 were positioned at least 10° varus compared to the target SSA position and another four were retroverted.
Conclusions: Femoral component placement utilizing conventional instrumentation may be more accurate following experience using imageless computer navigation.

Keywords: Computer navigation, femoral component alignment, hip resurfacing

How to cite this article:
Morison Z, Mehra A, Olsen M, Donnelly M, Schemitsch E. Computer navigation experience in hip resurfacing improves femoral component alignment using a conventional jig. Indian J Orthop 2013;47:585-90

How to cite this URL:
Morison Z, Mehra A, Olsen M, Donnelly M, Schemitsch E. Computer navigation experience in hip resurfacing improves femoral component alignment using a conventional jig. Indian J Orthop [serial online] 2013 [cited 2020 Feb 20];47:585-90. Available from:

   Introduction Top

Hip resurfacing arthroplasty (HRA) is a conservative alternative to total hip arthroplasty in a young and active patient, with the midterm survival reported between 95% and 96%. [1],[2],[3] Clinical outcomes in hip resurfacing have been shown to be dependent on both patient selection and surgical technique. [4],[5],[6],[7],[8] Femoral neck fracture remains a common failure mode in hip resurfacing and mechanical error, while preparing the femoral head has been well established as a risk factor for catastrophic neck fracture. [4],[9],[10],[11],[12],[13],[14],[15],[16]

The use of computer navigation has been shown to improve the accuracy of femoral component placement, thus reducing the likelihood of preparatory error. [17],[18],[19],[20],[21],[22] Compared to conventional instrumentation, imageless computer navigation increases component alignment accuracy and reduces outliers. [23],[24],[25],[26],[27] There is a challenging learning curve associated with hip resurfacing, with many technical errors occurring early within a surgeon's experience. [28] The use of computer navigation has been demonstrated to reduce the length of the initial learning curve and improve the surgeon's ability to perform the procedure safely. [22]

Despite these demonstrated advantages, imageless computer navigation is sparsely used in many surgical centers. The lack of widespread use may be attributed to availability as well as cost of the navigation systems. [27] Considering the predisposition to technical error early on in hip resurfacing, it would be advantageous for the surgeon as a trainee to utilize computer-based methods to optimize the surgical technique and solidify component implantation methodology. Evidence suggests that the use of computer navigation in the operating room may improve the accuracy of freehand component placement in the absence of navigation. [29] Thus, there may be a role for computer navigation as a training device for novice surgeons, particularly in the context of learning challenging orthopedic procedures, to improve component implantation once navigation is discontinued.

The aim of this study was to examine whether femoral component alignment improved with conventional mechanical guidewire jig following experience with using imageless computer navigation in HSA.

   Materials and Methods Top

213 consecutive hip resurfacings were performed by a single surgeon (EHS) between December 2004 and December 2008. We retrospectively compared the first 17 (Cohort 1) and last 9 (Cohort 2) hip resurfacings performed using the conventional lateral pin guidewire alignment jig [Figure 1]. Cohort 1 was the surgeon's initial 17 cases of hip resurfacing, which were performed prior to our center's acquisition of an imageless computer navigation system (VectorVision SR, BrainLAB, Feldkirchen, Germany). After the center acquired the navigation system, the surgeon performed 187 hip resurfacings using the computer navigation. In December 2008, the navigation unit required replacing. In the period pending replacement of the unit, the surgeon performed nine Birmingham Hip Resurfacings (BHRs) using the conventional jig; these nine patients comprise Cohort 2. Thus, the hip resurfacings in Cohort 2 were performed after the surgeon had gained significant experience with using imageless computer navigation [Figure 2].
Figure 1: The Birmingham Hip Resurfacing conventional lateral pin femoral guidewire alignment jig (Smith and Nephew Inc.)

Click here to view
Figure 2: (a) Anteroposterior (AP) and lateral radiographs of a right BHR implanted using a conventional guidewire alignment jig prior to any experience with imageless computer navigation. (b) AP and lateral radiographs of a right BHR implanted using conventional guidewire alignment jig after experience with imageless computer navigation. (c) AP and lateral radiographs of a right BHR implanted using imageless computer navigation

Click here to view

Of the 17 patients comprising Cohort 1, 16 patients had a preoperative diagnosis of osteoarthritis and one patient was diagnosed with avascular necrosis, who, as a result of this diagnosis was excluded from the analysis. The group included 14 males and 2 females. The mean age of the patients was 48.7 years (SD 6.6, range 39-63) with a mean body mass index (BMI) of 30.4 kg/m [2] (SD 3.9, range 23.3-40.4). Cohort 2 included nine patients all of whom were males with a preoperative diagnosis of osteoarthritis. The mean age of this group was 52.6 years (SD 10.8, range 29-71 years) with a mean BMI of 28.5 kg/m [2] (SD 3.0, range 25.1-34.3 kg/m 2 ). The differences in age and BMI between cohorts were not found to be significant (P > 0.203).

All patients received a BHR (Smith and Nephew Inc., Memphis, TN, USA) through a standard posterolateral approach. The 3-month postoperative digital anteroposterior and cross-table lateral X-rays were used for comparison. Images were obtained via a computed radiography system (DirectView CR850/950; Eastman Kodak, Rochester, NY, USA) using a standardized imaging technique and positioning protocol, and were stored on our institutional Picture Archive and Communication Systems server (Sienet MagicStore VE50; Siemens Medical, Erlangen, Germany). An observer (ZM) experienced in using digital radiograph templating software (MagicView 300, Siemens Medical) analyzed the radiographs, and was blinded to all patient data and operative dates. The component positions in both the coronal and sagittal planes were measured. The coronal stem-shaft angle (SSA) was defined as the angle subtended by the diaphyseal axis of the femur and a line drawn from the center of the prosthesis along the component stem toward the lateral cortex of the femur. The sagittal stem-neck angle (SNA) was defined as the angle subtended by the neck and component stem axis.

Measured values for component alignment were compared to the preoperatively planned position determined by the senior surgeon's (EHS) surgical protocol. The preoperative plan in each case positioned the component in 10° of valgus relative to the native neck-shaft angle (NSA) of the femur in the coronal plane and neutral to the neck axis in the sagittal plane. The component was considered neutral in the sagittal plane if the degree of component anteversion or retroversion was within 10° of the native neck version. [4]

Statistical analysis

A two-tail posthoc power analysis was conducted for each alignment variable. Descriptive statistics were calculated using Microsoft Excel (Microsoft Inc., Redmond, WA, USA) to determine differences between the final component placement and the target position. SPSS 16 (SPSS Inc., Chicago, IL, USA) was used to calculate two-sample t-tests for comparison of demographics as well as alignment values between the two cohorts. Statistical power was determined to be 85.2% (α = 0.05, effect size d = 1.02) for the comparison of SSA.

   Results Top

Coronal alignment of the femoral component in Cohort 2 was more accurate than Cohort 1. The difference was statistically significant (P = 0.01). The mean deviation of the SSA from the target alignment was 2.2° (SD 2.2, 95% CI 0.8°-3.7°) in Cohort 2 and 5.6° (SD 4.3, 95% CI 3.6°-7.6°) in Cohort 1 [Figure 3]. The variance of Cohort 2 (4.9°, range 4° varus to 7° valgus) was threefold less than Cohort 1 (17.6°, range 14° varus to 1° valgus). The mean coronal alignment in Cohort 1 erred in varus relative to the planned SSA [Figure 3].

The component version in Cohort 2 was also more accurate than Cohort 1 [Figure 4]. This difference was also statistically significant (P = 0.03). The mean deviation from the target SNA of Cohort 2 had a mean difference of 4.0° (SD 2.2, 95% CI 2.6°-5.4°), while that of Cohort 1 was 7.3° (SD 5.3, 95% CI 4.8°-9.9°). The variance in Cohort 2 (27.7°, range 8.2° retroversion to 3.6° anteversion) was half that of Cohort 1 (4.7°, range 17.2° retroversion to 5.8° anteversion) [Figure 4]. Four implants in Cohort 1 were considered to be retroverted (>10°) [Figure 5].
Figure 3: Box and whisker plot of stem-shaft angle accuracy for the two conventional jig cohorts (negative values denote relative varus and positive values denote relative valgus)

Click here to view
Figure 4: Box and whisker plot of stem-neck angle accuracy of the two conventional jig cohorts (negative values denote retroversion and positive values denote anteversion)

Click here to view
Figure 5: Comparison of the accuracy of implant positioning using a conventional jig between the pre and post navigation cohorts

Click here to view

   Discussion Top

Hip resurfacing provides a viable bone conserving option for a young, active patient with end-stage hip disease. In addition to patient selection, surgical technique contributes greatly to the clinical outcomes of the procedure. [5],[6] In spite of many advances in surgical technique, femoral neck fracture remains a concern with hip resurfacing and continues to be the most common reason for revision. [10] The etiology of femoral neck fracture in hip resurfacing has been studied thoroughly, and although the causes are often multifactorial, the biomechanics of implant alignment play a large role in resurfacing construct strength and resilience. Previous biomechanical studies investigating implant alignment have shown that relative valgus alignment of the femoral component strengthens the proximal femur and may be protective against neck fracture. [4],[11],[14],[30] In addition, studies looking at femoral neck notching have demonstrated that as little as a 2-mm superior femoral neck notch may increase the risk of neck fracture. [9],[11],[30] Despite this knowledge, notching of the femoral neck and femoral components implanted in relative varus are still encountered, particularly during the surgical learning period for this procedure. [7],[28],[31],[32] These adverse events may be attributed to the difficulty of the procedure or the lack of experience of the surgeon.

In this study, we found that the cohort of hip resurfacing patients following experience using computer navigation (Cohort 2) was more accurate and showed less variance in component positioning. The mean SSA for Cohort 2 was 3.4° less than the mean SSA for Cohort 1. This decrease in mean SSA for component positioning results in a decrease of stress across the superior neck, potentially reducing the risk of femoral neck fracture. [12] Further, improved accuracy of positioning in the sagittal plane may theoretically reduce the risk of impingementn [Figure 5].

It has been well documented that computer-assisted surgery by way of imageless navigation functions to curtail femoral implant malalignment in hip resurfacing. [19],[21],[22],[26] However, the cost and availability of current navigation systems make ubiquitous use unrealistic, particularly for those centers that perform only small volumes of hip resurfacings. In order for surgeons new to hip resurfacing to perform optimally using conventional instrumentation, it may be necessary to first train using computer-assisted methods in order to enhance both surgical technique and component insertion protocol. A concern of using computer navigation for training purposes is reliance on the technology with poor retention performance following discontinuation. [33] Thus, this study looked to establish whether femoral component implantation accuracy utilizing a conventional guidewire alignment jig improves following the use of imageless computer navigation in HSA. In this study, Cohort 1 was the senior surgeon's initial experience with hip resurfacing.

A limitation of this study is the inability to account for the learning process that would occur normally after performing a series of hip resurfacings. In a study by Seyler et al., fellowship trained staff surgeons with experience in hip resurfacing (>75 cases) exhibited a greater scatter of insertion angles when using conventional instrumentation than less experienced residents using imageless navigation as a surgical aid. [22] This not only demonstrates the accuracy of computer navigation but also that experience alone may not prevent a greater degree of inaccuracy when using conventional manual instrumentation. A second limitation is that the number of resurfacings performed using a conventional jig is small relative to the number performed using computer navigation. The optimal number of procedures to achieve competency and a higher level of accuracy using conventional guidewire alignment jigs may be smaller than in the current study. Further investigation is required to determine the ideal number of training cases required in order to obtain proficiency using conventional instrumentation in hip resurfacing. Lastly, the lateral pin jig utilized in this study may not be representative of other guidewire alignment devices. The results of this study may not be extrapolated to other conventional guidewire alignment jigs in hip resurfacing.

In this study, all femoral components implanted with a manual jig after acquiring experience using imageless navigation achieved the desired minimum of 10° of valgus relative to the native NSA and all were considered to have neutral SNA angles. This is compared to three implants which were positioned more than 10° varus relative to the target SSA and another four which were considered retroverted in the group performed prior to experience using navigation. The improved use of the manual jig may be attributable to an increased familiarity with the location of the optimal guidewire insertion point. Often the native anatomy of the end-stage hip disease patient is distorted with osteophytes and remodeled bone which can prove problematic when using a manual jig, as alignment and positioning depend largely on a visual assessment of the local anatomy for guidewire placement.

The results from this study show improved accuracy and precision using a conventional guidewire alignment jig after training with computer navigation. This improvement conflicts with the literature on cognitive motor learning which suggests that the form of feedback that computer-assisted surgery provides may actually be detrimental to learning. [34] According to motor learning theory, individuals learn new motor skills by evaluating available feedback to alter future performance. Feedback can either be intrinsic (as a natural consequence of the action) or extrinsic (from an external source such as an instructor or a computer). Computer navigation provides a form of extrinsic feedback, or continuous concurrent feedback, in which continuous visual feedback guides the trainee to the correct position, thus minimizing errors and reinforcing proper technique. It has been hypothesized, however, that concurrent feedback does not contribute to retention of task performance as a result of the learner developing dependence on extrinsic feedback or being distracted from using intrinsic feedback. [34],[35] In contrast, a prospective randomized study by Gofton et al. analyzing the effect of computer navigation on the learning of surgical skills by trainees demonstrated that concurrent feedback during the insertion of the acetabular cup in hip replacement did not compromise the learning process of trainees. [36] This finding is supported by a systematic review by Saithna and Dekker looking at the influence of computer navigation in hip resurfacing training in which they concluded that there exists minimal evidence to support concerns regarding the detrimental impact of computer navigation on trainee learning and subsequent performance in hip resurfacing. [33]

The study demonstrates that femoral component placement utilizing conventional instrumentation may be more accurate following experience using imageless computer navigation. Training or experience using computer navigation may provide the surgeon with appropriate feedback to facilitate adequate motor skill acquisition and spatial awareness that can be transferred in turn to conventional instrumentation. The success of hip resurfacing is particularly sensitive to surgical technique and component alignment; training with computer navigation early in the learning curve may help optimize the subsequent use of conventional hip resurfacing instrumentation. Larger studies are required to provide more robust evidence.

   References Top

1.Khan M, Kuiper JH, Edwards D, Robinson E, Richardson JB. Birmingham hip arthroplasty: Five to eight years of prospective multicenter results. J Arthroplasty 2009;24:1044-50.  Back to cited text no. 1
2.Rahman L, Muirhead-Allwood SK, Alkinj M. What is the midterm survivorship and function after hip resurfacing? Clin Orthop Relat Res 2010;468:3221-7.  Back to cited text no. 2
3.Steffen RT, Pandit HP, Palan J, Beard DJ, Gundle R, McLardy-Smith P, et al. The five-year results of the Birmingham Hip Resurfacing arthroplasty: An independent series. J Bone Joint Surg Br 2008;90:436-41.  Back to cited text no. 3
4.Beaulé PE, Lee JL, Le Duff MJ, Amstutz HC, Ebramzadeh E. Orientation of the femoral component in surface arthroplasty of the hip: A biomechanical and clinical analysis. J Bone Joint Surg Am 2004;86-A:2015-21.  Back to cited text no. 4
5.Amstutz HC, Takamura KM, Le Duff MJ. The effect of patient selection and surgical technique on the results of conserve plus hip resurfacing 3.5- to 14-year followup. Orthop Clin North Am 2011;42:133-42.  Back to cited text no. 5
6.Nunley RM, Della Valle CJ, Barrack RL. Is Patient Selection Important for Hip Resurfacing? Clin Orthop Relat Res 2009;467:56-65.  Back to cited text no. 6
7.Marker DR, Seyler TM, Jinnah RH, Delanois RE, Ulrich SD, Mont MA. Femoral neck fractures after metal-on-metal total hip resurfacing: A prospective cohort study. J Arthroplasty 2007;22:66-71.  Back to cited text no. 7
8.Shimmin AJ, Back D. Femoral neck fractures following Birmingham hip resurfacing: A national review of 50 cases. J Bone Joint Surg Br 2005;87:463-4.  Back to cited text no. 8
9.Anglin C, Masri BA, Tonetti J, Hodgson AJ, Greidanus NV. Hip resurfacing femoral neck fracture influenced by valgus placement. Clin Orthop Relat Res 2007;465:71-9.  Back to cited text no. 9
10.Australian Orthopaedic Association National Joint Replacement Registry, Hip and Knee Arthroplasty Annual Report 2011. 2011.  Back to cited text no. 10
11.Davis ET, Olsen M, Zdero R, Papini M, Waddell JP, Schemitsch EH. A biomechanical and finite element analysis of femoral neck notching during hip resurfacing. J Biomech Eng 2009;131:041002.  Back to cited text no. 11
12.Davis ET, Olsen M, Zdero R, Waddell JP, Schemitsch EH. Femoral neck fracture following hip resurfacing: The effect of alignment of the femoral component. J Bone Joint Surg Br 2008;90:1522-7.  Back to cited text no. 12
13.Olsen M, Davis ET, Whyne CM, Zdero R, Schemitsch EH. The biomechanical consequence of insufficient femoral component lateralization and exposed cancellous bone in hip resurfacing arthroplasty. J Biomech Eng 2010;132:081011.  Back to cited text no. 13
14.Richards C, Giannitsios D, Huk O, Zukor D, Steffen T, Antoniou J. Risk of periprosthetic femoral neck fracture after hip resurfacing arthroplasty: Valgus compared with anatomic alignment. A biomechanical and clinical analysis. J Bone Joint Surg Am 2008;90:96-101.  Back to cited text no. 14
15.Schnurr C, Nessler J, Meyer C, Schild HH, Koebke J, Konig DP. Is a valgus position of the femoral component in hip resurfacing protective against spontaneous fracture of the femoral neck?: A biomechanical study. J Bone Joint Surg Br 2009;91:545-51.  Back to cited text no. 15
16.Vail TP, Glisson RR, Dominguez DE, Kitaoka K, Ottaviano D. Position of hip resurfacing component affects strain and resistance to fracture in the femoral neck. J Bone Joint Surg Am 2008;90:1951-60.  Back to cited text no. 16
17.Bailey C, Gul R, Falworth M, Zadow S, Oakeshott R. Component alignment in hip resurfacing using computer navigation. Clin Orthop Relat Res 2009;467:917-22.  Back to cited text no. 17
18.Olsen M, Davis ET, Waddell JP, Schemitsch EH. Imageless computer navigation for placement of the femoral component in resurfacing arthroplasty of the hip. J Bone Joint Surg Br 2009;91:310-5.  Back to cited text no. 18
19.Romanowski JR, Swank ML. Imageless navigation in hip resurfacing: Avoiding component malposition during the surgeon learning curve. J Bone Joint Surg Am 2008;90:65-70.  Back to cited text no. 19
20.Olsen M, Schemitsch EH. Avoiding short-term femoral neck fracture with imageless computer navigation for hip resurfacing. Clin Orthop Relat Res 2010;469:1621-6.  Back to cited text no. 20
21.Schnurr C, Michael JW, Eysel P, König DP. Imageless navigation of hip resurfacing arthroplasty increases the implant accuracy. Int Orthop 2009;33:365-72.  Back to cited text no. 21
22.Seyler TM, Lai LP, Sprinkle DI, Ward WG, Jinnah RH. Does computer-assisted surgery improve accuracy and decrease the learning curve in hip resurfacing? A radiographic analysis. J Bone Joint Surg Am 2008;90:71-80.  Back to cited text no. 22
23.Davis ET, Gallie P, Macgroarty K, Waddell JP, Schemitsch E. The accuracy of image-free computer navigation in the placement of the femoral component of the birmingham hip resurfacing: A cadaver study. J Bone Joint Surg Br 2007;89:557-60.  Back to cited text no. 23
24.Ganapathi M, Vendittoli PA, Lavigne M, Günther KP. Femoral component positioning in hip resurfacing with and without navigation. Clin Orthop Relat Res 2009;467:1341-7.  Back to cited text no. 24
25.Hart R, Svab P, Filan P. Intraoperative navigation in hip surface arthroplasty: A radiographic comparative analysis study. Arch Orthop Trauma Surg 2008;128:429-34.  Back to cited text no. 25
26.Olsen M, Chiu M, Gamble P, Boyle RA, Tumia N, Schemitsch EH. A comparison of conventional guidewire alignment jigs with imageless computer navigation in hip resurfacing arthroplasty. J Bone Joint Surg Am 2010;92:1834-41.  Back to cited text no. 26
27.Resubal JR, Morgan DA. Computer-assisted vs conventional mechanical jig technique in hip resurfacing arthroplasty. J Arthroplasty 2009;24:341-50.  Back to cited text no. 27
28.Della Valle C, Nunley R, Raterman S, Barrack R. Initial American experience with hip resurfacing following FDA approval. Clin Orthop Relat Res 2009;467:72-8.  Back to cited text no. 28
29.Leenders T, Vandevelde D, Mahieu G, 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.  Back to cited text no. 29
30.Nabavi A, Yeoh K, Shidiac L, Appleyard R, Gillies RM, Turnbull A. Effects of positioning and notching of resurfaced femurs on femoral neck strength: A biomechanical test. J Orthop Surg (Hong Kong) 2009;17:47-50.  Back to cited text no. 30
31.Berend KR, Lombardi AV Jr, Adams JB, Sneller MA. Unsatisfactory surgical learning curve with hip resurfacing. J Bone Joint Surg Am 2011;93 Suppl 2:89-92.  Back to cited text no. 31
32.Nunley RM, Zhu J, Brooks PJ, Engh CA Jr, Raterman SJ, Rogerson JS, et al. The learning curve for adopting hip resurfacing among hip specialists. Clin Orthop Relat Res 2010;468:382-91.  Back to cited text no. 32
33.Saithna A, Dekker AP. The influence of computer navigation on trainee learning in hip resurfacing arthroplasty. Comput Aided Surg 2009;14:117-22.  Back to cited text no. 33
34.Schmidt RA, Wulf G. Continuous concurrent feedback degrades skill learning: Implications for training and simulation. Hum Factors 1997;39:509-25.  Back to cited text no. 34
35.Wierinck E, Puttemans V, Swinnen S, van Steenberghe D. Effect of augmented visual feedback from a virtual reality simulation system on manual dexterity training. Eur J Dent Educ 2005;9:10-6.  Back to cited text no. 35
36.Gofton W, Dubrowski A, Tabloie F, Backstein D. The effect of computer navigation on trainee learning of surgical skills. J Bone Joint Surg Am 2007;89:2819-27.  Back to cited text no. 36

Correspondence Address:
Zachary Morison
Division of Orthopaedic Surgery St. Michael's Hospital, 55 Queen Street East, Suite 800, Toronto, Ontario M5C 1R6
Login to access the Email id

Source of Support: This was a surgeon initiated study and was not funded,, Conflict of Interest: The senior author (EHS) has received institutional support from Smith & Nephew Inc.

DOI: 10.4103/0019-5413.121585

Rights and Permissions


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *
* Registration required (free)  

    Materials and Me...
    Article Figures

 Article Access Statistics
    PDF Downloaded76    
    Comments [Add]    

Recommend this journal