Computer assisted navigation in orthopaedics and trauma surgery

ARTHROPLASTY

Computer assisted navigation in orthopaedics and trauma surgery

a variety of orthopaedic procedures such as hip and knee arthroplasty, sports injuries, trauma, and spinal and bone tumour surgery.6,7

Computer assisted navigation e the basics Computer assisted navigation involves the integration of computer technology for preoperative planning and guidance or performing surgical procedures. Computer assisted navigation systems can be active, with the use of robotic surgeons, or passive where the surgeon is in total control but computer software aids in the positioning of instruments and implants relative to the patient’s anatomy. The concept is often compared to that of the global positioning system (GPS) in cars. A procedure-specific digital map is created with which surgical instruments can interact in real time, to mm accuracy. There are currently three methods of obtaining sufficiently accurate imaging to allow the positioning of instruments to be tracked intraoperatively, which classifies computer assisted navigation systems into CT based, fluoroscopy based and imageless.  CT based imaging (more common in neurosurgical and spinal surgery) e CT scans of the operative site are obtained preoperatively and used to create 3 dimensional (3D) images. The data is matched with the patient’s anatomy after tracking markers, visible to the computer, are fixed to the patient. A pointing device, also visible to the computer, is then used to identify predetermined landmarks  Intraoperative fluoroscopy based imaging (more common in trauma surgery) e Modified fluoroscopy with the help of computer software helps to create an anatomical map. Multiple fluoroscopic images can be acquired and processed by computer software to provide real time multiplanar images without the need for extensive fluoroscopy exposure. The software superimposes the position of surgical instruments and the path of an implant onto real time imaging, allowing the surgeon to modify implant trajectory without the need for further fluoroscopy. 3-D fluoroscopy is an evolution of this technique and consists of a mobile C-arm unit, modified to incorporate a motorized rotational movement that is linked to a computer to provide multiplanar 3-D images of bony structures.  Image free e Computer software has an anatomical model, built up from a database of stored CT scans, for the procedure to be performed. The computer model is then augmented by ‘surface registration’ whereby a pointing device held by the surgeon, and visible to the computer, marks out predetermined areas of the patient’s anatomy. This system avoids radiation exposure to the patient and surgical team. Registration is the process by which the computer identifies bones and joints and logs their positions in space. All of the above techniques require registration before surgery can begin. This is an extremely important step, which is done by the careful and accurate placement of tracking markers identifiable by the computer system onto predetermined anatomical landmarks (Figure 1). While computer assisted navigation has the potential to help surgeons perform procedures more accurately, individuals need a clear understanding of the goals, applications, and limitations

Rohit Rambani Mathew Varghese

Abstract Computer assisted navigation was initially introduced into neurosurgical practice, and then orthopaedic spinal surgery, in the 1990’s. It has gained momentum in recent years, finding applications in multiple branches of orthopaedic surgery including hip and knee arthroplasty, sports injuries, trauma, spinal surgery and bone tumour surgery. The technology provides the surgeon with real-time information regarding the position of surgical instruments and implants in relation to the skeleton and has the potential to improve surgical accuracy and outcome. Computer assisted navigation systems can be active, employing robotic surgeons, or passive where the surgeon remains in total control but computer software aids in the procedure. Computer assisted navigation has the potential to help surgeons perform procedures more accurately, with a view to improving outcome. This article reviews the multiple applications, limitations, and advantages of computer assisted navigation in orthopaedics in the operating theatre and beyond.

Keywords computer; navigation; orthopaedic applications

Introduction Computer assisted navigation was first utilized in neurosurgical practice, aiding preoperative planning using CT, with the aim of increasing intraoperative accuracy. Initial applications were limited to needle biopsies and tumour resection, but provided insight into the potential for wider application of the technologies.1e4 The goal of computer assisted navigation was to improve understanding of the surgical field and thereby improve surgical accuracy and it entered orthopaedic clinical practice in the 1990’s, helping to improve the accuracy of pedicle screw insertion5 in spinal surgery. Over the years that followed improvements in imaging techniques and computing technologies have made computer assisted navigation more user-friendly, leading to the development of applications in mainstream orthopaedics. It was, however, the use of the navigation in hip and knee arthroplasty that made industry and clinicians really take note. With wider acceptance, computer assisted navigation can be a useful tool in

Rohit Rambani MBBS MS Ortho FRCS (Tr & Orth) Senior Knee Fellow, Leeds Teaching Hospital NHS Trust, Leeds, UK. Conflicts of interest: none. Mathew Varghese FRCS (Tr & Orth) Specialist Registrar, Leeds Teaching Hospital NHS Trust, Leeds, UK. Conflicts of interest: none.

ORTHOPAEDICS AND TRAUMA 28:1

50

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

Figure 1 Screen print of the soft tissue balancing in total knee arthroplasty using navigation.

malalignment >2e3 was less likely in the navigated TKA group. Other findings of note included an increased operating time of 23%. Many other studies report on the benefits of computer assisted navigation in terms of mechanical alignment but how this translates into improved clinical outcome has yet to be shown.16,17 The absence of long-term evidence on outcome and survivorship, and the increased costs associated with navigated TKA, are likely to limit the uptake of the technology for now. Multicenter randomized controlled trials with long-term follow up comparing navigated TKA with conventional TKA are needed to show the true clinical benefit.18

of these systems before embracing them into their clinical practice.

Navigation in total knee arthroplasty The first evidence from navigation assisted total knee arthroplasty (TKA) was published in 1997.8 There is a well-recognized relationship between accuracy and outcome in knee arthroplasty, and the potential for technology to improve implant positioning and mechanical alignment was a key-driving factor for computer assisted navigation in TKA. Component alignment in TKAs, within 3 of the mechanical axis, is crucial in order to achieve the best long-term implant survival. Studies have shown that conventional intramedullary or extra-medullary jigs fail to restore the alignment within 3 in 10%e38% of TKAs, even when performed by experienced surgeons.9,10 Navigation has been shown to improve the precision of surgical technique and implant alignment.11e13 Other advantages include accurate restoration of the mechanical axis, dynamic and accurate assessment of the deformity, improved gap balancing and a decreased incidence of fat embolism due to the avoidance of intramedullary instrumentation (Figure 2). Disadvantages, which currently also apply to most applications of computer assisted navigation, include the learning curve associated with embracing a new technology, prolonged surgical time, set up and maintenance costs and the lack of long-term evidence on clinical outcome.14 Revision TKA can involve dealing with significant bone loss, making referencing for implant position and alignment challenging with conventional techniques. Computer assisted navigation can be particularly helpful in such cases, as the system allows the mechanical axis to be checked at all stages and helps to fine-tune the orientation of the revision prosthesis in the sagittal and coronal planes.14 The literature remains clouded, however, regarding the benefits of computer-assisted navigation which are not yet proved. The meta-analysis by Bauwens et al.15 compared navigated TKA with conventional TKA and showed no difference in alignment to the mechanical axis between the two groups, although

ORTHOPAEDICS AND TRAUMA 28:1

Navigation in total hip arthroplasty Computer assisted navigation systems in total hip arthroplasty (THA) are available as active (robotic) and passive (surgeon navigated) forms, the latter being more commonly used. The correct positioning of the implants in THA is vital for optimum long-term survivorship and functional outcome, and is guided by preoperative imaging and templating, intraoperative assessment of the patients anatomy and mechanical alignment jigs. Mechanical alignment jigs are known to have limitations in terms of accurate implant placement.19 The patient’s position on the operating table is also a key factor in determining correct implant placement but can be variable. Poor positioning of the acetabular component has been shown to result in higher rates of asymmetric polyethylene wear, pelvic osteolysis and implant migration.20 The majority of surgeons aim to position the acetabular component in the “safe zone” described by Lewinnek et al.21 for optimal outcome. The correct restoration of leg length is also essential to avoid potential pain, stiffness and early implant failure.22 Navigation assisted THA has gained in popularity recently, as surgeons seek to improve the positioning of implants. The recent meta-analysis by Gandhi et al. concluded that navigation in hip arthroplasty improves the precision of acetabular cup placement over freehand alignment by decreasing the number of outliers

51

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

High tibial osteotomy High tibial osteotomy (HTO) was introduced in the 1950s for the management of uni-compartmental knee arthritis with varus malalignment in young active patients.28,29 HTO is a realignment procedure that redistributes the weight from the diseased medial compartment to the more normal lateral compartment, reducing symptoms and disease progression. When the mechanical axis passes through the centre of the knee in the normal situation, 67% of the load passes through the medial compartment during single leg stance. Moving the mechanical axis to 6 of valgus alters the compartment loading to 40% medial and 60% lateral.30,31 Clinical outcome following HTO is related to the accuracy of the desired correction. The accuracy of conventional techniques has been questioned, as 20% of patients do not achieve the planned mechanical axis correction. The factors contributing to variability include poor preoperative planning, incorrectly executed osteotomies and poor intraoperative control of the mechanical axis with traditional methods.32 The real time intraoperative information regarding the axes around the knee provided by computer assisted navigation can aid the surgeon and reduce the risk of coronal plane valgus under-correction and sagittal plane posterior tibial slope over-correction.33

Figure 2 Screen print showing the registration of the distal femoral condyles during computer assisted total knee arthroplasty

from the desired alignment.23 There are only limited studies regarding navigation and femoral component positioning, though the authors suggest that the technology has a favourable effect with improved implant alignment and accurate restoration of leg length, which will hopefully have a positive effect on clinical outcome.24,25 The technology does not significantly increase complication rates, nor does it lower blood loss since the increased number of steps involved in the procedure results in increased operating times26,27 (Figure 3). Computer assisted navigation in THA does provide a method to improve implant alignment but once again multi-centre randomized controlled trials with long-term follow up are required to show the true clinical benefit.

Anterior Cruciate Ligament reconstruction Over 100 years have passed since the first Anterior Cruciate Ligament (ACL) reconstruction and it is now one of the most commonly performed orthopaedic operations. Revision rates of 10%e40% have been quoted, and 70%e80% of the complications are attributed to malpositioning of the tunnels34 leading to instability, poor function and higher revision rates. Computer

Figure 3 Acetabular cup placement in computer navigated total hip arthroplasty

ORTHOPAEDICS AND TRAUMA 28:1

52

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

despite experienced surgical hands.41,42 Computer assisted navigation has a wide range of spinal applications including decompression, instrumentation and minimally invasive surgery. In the lumbar spine, navigation has been well documented to improve the accuracy of instrumentation and has resulted in a 5fold decrease in the number of misplaced screws.5,43 Disc replacement surgery has also benefited from the intraoperative use of navigation to aid accurate implantation, which has a positive effect on survivorship. The use of 3-D fluoroscopy-based navigation in the thoracic spine allows the surgeon to assess the path of screw placement intraoperatively and correct if required44 (Figure 4). Instrumentation in the cervical spine has become increasingly popular with improving techniques. The use of pedicle screws has improved biomechanical stability and allows for shorter instrumentation. C1/2 transarticular screws, as well as transpedicular screws in the cervical spine and cervico-thoracic junction, can be inserted safely and accurately using computer assisted navigation and this has reduced the rate of neurovascular complications and incorrect screw placement.45,46

assisted navigation can be used in ACL reconstruction as an aid to tibial and femoral tunnel placement in order to restore optimum knee kinematics. Many studies support improved tunnel placement with Navigation but no consensus currently exist in terms of improved function.35 Further long-term, prospective studies comparing functional outcomes in navigated ACL versus conventional reconstructions are required to evaluate the true benefit of this technology.

Fracture treatment Pelvis The unstable pelvic fracture is technically challenging to treat surgically due to the close proximity of neurovascular structures and relatively narrow safe corridors for implant placement. Optimum treatment for posterior ligamentous and osseous ring injuries is considered to be iliosacral screw insertion. The percutaneous approach limits blood loss and morbidity but can be difficult, even with the use of fluoroscopy. The use of navigation to assist percutaneous screw fixation can improve accuracy of placement and reduce the radiation time and dose for the procedure.36

Bone tumour surgery

Femur The use of fluoroscopy-based navigation has been used for cannulated screw insertion in the treatment of femoral neck fractures. Navigation improved screw parallelism and reduced the number of drilling attempts.37 Conventionally treated femoral shaft fractures, treated by intramedullary nailing, can be complicated by malrotation and leg length discrepancy, which may lead to poor clinical outcome. Navigation systems can use 2-D information derived from the uninjured femur to aid restoration of natural leg length, rotational alignment and reduction of the fracture, in the injured limb. Navigation can also reduce the risk of pronounced malrotation, which may be more useful in cases with significant comminution at the fracture site.38 Imageless systems are available for distal locking screw insertion for intramedullary nails, which may reduce operating time and radiation exposure. There are some early studies suggesting a future role of navigation in LISS (Less Invasive Stabilization System, Synthes, Paoli, PA, USA) plate application to improve accuracy and reduce the radiation exposure.39

Bone tumour surgeons are taking on increasingly challenging cases as a result of the evolution of enhanced diagnostic techniques and the increasing availability of limb-preserving approaches and implants. The resection of intra-epiphyseal tumours close to the joint surface requires accuracy, especially when a good fit is needed for custom implant reconstruction. Likewise, resection in difficult anatomic regions, such as tumours of the pelvis, requires careful preoperative planning and intraoperative accuracy. Early studies suggest that navigation can offer real time radiological information regarding the distance from the tumour edge to the resection margin. Consequently, navigation can increase the accuracy of osteotomies and at the same time minimize unnecessary resection, preserve maximum function and achieve good oncological and functional results.47,48

Proposed advantages of computer assisted navigation There is good evidence that computer assisted navigation has the potential to improve the information provided to the surgeon and enable the surgeon to more accurately perform a variety surgical procedures.10,19,23 In some settings navigation has the potential to make a good surgeon even better. Computer navigation systems themselves do not emit radiation. Once the images are captured by the navigation system and stored, they provide continuous intraoperative guidance without the need for further radiation exposure to the patient or surgeon. Thus in certain procedures, navigation may reduce fluoroscopy time and radiation exposure over conventional methods.

Shoulder Complex proximal humerus fractures requiring hemiarthroplasty pose a challenge to surgeons. The severity of the injury and loss of normal bony landmarks can make implant positioning a challenge. Misaligned implants can result in poor joint kinematics and function, increased glenoid wear and secondary arthritis. Methods have been developed using navigation systems to reference off the uninjured shoulder to provide reference information that can used to template and instrument the injured shoulder, resulting in a more anatomical shoulder replacement.40

Limitations with computer assisted navigation Studies have shown that navigation assisted procedures increase the operating time compared to conventional methods in both the trauma and elective setting, in addition to adding theatre set up time before knife-to-skin has taken place.49 With any newly introduced technology or technique the surgeon and team have

Spinal surgery Computer assisted surgery was developed in the early 1990s to assist in pedicle screw insertion in the lumbar spine. The aim was to improve the accuracy of instrumentation over conventional techniques, which report up to 40% misplacement rates

ORTHOPAEDICS AND TRAUMA 28:1

53

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

Figure 4 Three-dimensional view of pedicle screw fixation-using navigation.

“warming up” before a procedure. By programming the patient’s own imaging data into simulation software, rehearsal of the procedure can become patient-specific (Figure 5). A key challenge is to integrate simulation within existing curricular structures in training programmes to ensure that practice takes place within a robust educational framework. Simulation is costly in terms of equipment and teaching facilities and it is not feasible to provide a full range of settings in every medical centre. The establishment of simulation centres at key sites can enable trainees and established surgeons to participate in regular practice and reinforce their clinical training and skills while ensuring patients do not experience avoidable harm. Mapping the dynamic association between the virtual reality centre, the simulated operating suite, and the real environment should become a priority for researchers and healthcare professionals. Up to now, simulation training has mainly been done using saw bones and navigation software. Various centres are working to produce products that would be able to provide computer assisted simulation training using virtual patients and haptic feedback.52

to go through a learning curve. There is an initial increased operating time of around 30 min in navigated TKA over conventional TKA, which reduces to around 10 min after 30 implantations.50 This increased procedure time has implications to the patient, who may need a longer anaesthetic, and to hospital productivity, which may be a significant obstacle to many centres embracing the technology. Navigation systems rely on accurate information provided by image capture, as discussed earlier. Certain systems will require specific theatre set up and equipment to achieve this; for example, a fully radiolucent carbon fibre table with 3-D fluoroscopic image capture. Complex trauma patients may require specific positioning or may have an external fixator in situ, which may limit or interfere with image capture. Navigation assistance may improve on accuracy over conventional non-navigated procedures, but it is still subject to error. There may be misplacement of the tracking marker by the surgeon, or the tracking marker may move or loosen slightly due to osteoporotic bone, both of which will introduce error into the system and thus into the procedure being performed.14 Set up and running costs can be considerable. Until we know how improved implant positioning and fracture reduction, offered with navigation, translates into improved outcome resulting in lower overall costs, the financial burden could be too high for certain centres to entertain.

The future An area of growing interest is patient-specific surgery, where patient-specific instrumentation is created with the aim of improving the accuracy of the surgery for the individual’s needs. In the case of TKA, preoperative imaging (CT or MRI) combined with computer software helps preoperative planning and predicts intraoperative bone resections, component sizes, and alignment.

Training Navigation may have a role to play in the training of surgeons, both junior and established. Studies have shown that established surgeons with experience of computer assisted navigation can show improved freehand accuracy when performing the same procedure without navigation.51 Simulation should be regarded as an adjunct rather than an alternative to clinical experience: simulation could be used for

ORTHOPAEDICS AND TRAUMA 28:1

Summary There is no doubt that computer assisted navigation can improve the information provided to the surgeon in order to more

54

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

Figure 5 DHS guide wire placement using navigation.

accurately perform a variety surgical procedures. In some settings, navigation has the potential to make a good surgeon even better. The quote from Lars Leskell, the inventor of the Gamma Knife, “A fool with a tool is still a fool” is especially apt regarding computer assisted navigation surgery. It remains vital that the surgeon, when using navigation technology, must still be able to perform the procedure well in the conventional way. The technology has come a long way since its inception but is still in relative infancy. It is still evolving and branching into new areas, such as patient-specific surgery. Computer assisted surgical training is another expanding area of interest. The majority of studies suggest that navigation can bring improved accuracy to procedures, but the lack of long-term evidence on clinical outcome through multi-centre RCTs is likely to limit widespread use of navigation technology for the present.A

5

6

7

8

9 10

REFERENCES 1 Apuzzo ML, Sabshin JK. Computed tomographic guidance stereotaxis in the management of intracranial mass lesions. Neurosurgery 1983; 12: 277e85. 2 Barnett GH, Kormos DW, Steiner CP, Weisenberger J. Use of a frameless, armless stereotactic wand for brain tumor localization with two-dimensional and three-dimensional neuroimaging. Neurosurgery 1993; 33: 674e8. 3 Tan KK, Grzeszczuk R, Levin DN, et al. A frameless stereotactic approach to neurosurgical planning based on retrospective patientimage registration. Technical note. J Neurosurg 1993; 79: 296e303. 4 Watanabe E, Watanabe T, Manaka S, Mayanagi Y, Takakura K. Three-dimensional digitizer (neuronavigator): new equipment for

ORTHOPAEDICS AND TRAUMA 28:1

11

12

13

55

computed tomography-guided stereotaxic surgery. Surg Neurol 1987; 27: 543e7. Merloz P, Tonetti J, Pittet L, Coulomb M, Lavallee S, Sautot P. Pedicle screw placement using image guided techniques. Clin Orthop Rel Res 1998; 354: 39e48. Edwards TB, Gartsman GM, O’Connor DP, Sarin VK. Safety and utility of computer-aided shoulder arthroplasty. J Shoulder Elbow Surg 2008; 17: 503e8. So TY, Lam YL, Mak KL. Computer-assisted navigation in bone tumor surgery: seamless workflow model and evolution of technique. Clin Orthop Rel Res 2010; 468: 2985e91. Krackow KA, Bayers-Thering M, Phillips MJ, Bayers-Thering M, Mihalko WM. A new technique for determining proper mechanical axis alignment during total knee arthroplasty: progress toward computer-assisted TKA. Orthopedics 1999; 22: 698e702. Dattani R, Patnaik S, Kantak A, Tselentakis G. Navigation knee replacement. Int Orthop 2009; 33: 7e10. Longstaff LM, Sloan K, Stamp N, Scaddan M, Beaver R. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 2009; 24: 570e8. Blakeney WG, Khan RJ, Wall SJ. Computer-assisted techniques versus conventional guides for component alignment in total knee arthroplasty: a randomized controlled trial. J Bone Joint Surg Am 2011; 93: 1377e84. Mahaluxmivala J, Bankes MJ, Nicolai P, Aldam CH, Allen PW. The effect of surgeon experience on component positioning in 673 Press Fit Condylar posterior cruciate-sacrificing total knee arthroplasties. J Arthroplasty 2001; 16: 635e40. Mihalko WM, Boyle J, Clark LD, Krackow KA. The variability of intramedullary alignment of the femoral component during total knee arthroplasty. J Arthroplasty 2005; 20: 25e8.

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

14 Bae DK, Song SJ. Computer assisted navigation in knee arthroplasty. Clin Orthop Surg 2011; 3: 259e67. 15 Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007; 89: 261e9. 16 The use of image-free computer-assisted systems in total knee replacement surgeriesda final report, 2007. http://www.mcgill. ca/tau. 17 Parratte S, Pagnano MW, Trousdale RT, Berry DJ. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am 2010; 92: 2143e9. 18 Dong H, Buxton M. Early assessment of the likely cost-effectiveness of a new technology: a Markov model with probabilistic sensitivity analysis of computer-assisted total knee replacement. Int J Technol Assess Health Care 2006; 22: 191e202. 19 Kelley TC, Swank ML. Role of navigation in total hip arthroplasty. J Bone Joint Surg Am 2009; 91(suppl 1): 153e8. 20 Kennedy JG, Rogers WB, Soffe KE, Sullivan RJ, Griffen DG, Sheehan LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty 1998; 13: 530e4. 21 Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978; 60: 217e20. 22 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-A: 2310e7. 23 Gandhi R, Marchie A, Farrokhyar F, Mahomed N. Computer navigation in total hip replacement: a meta-analysis. Int Orthop 2009; 33: 593e7. 24 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). 25 Lazovic D, Zigan R. Navigation of short-stem implants. Orthopedics 2006; 29(suppl 10): S125e9. 26 Kalteis T, Handel M, Bathis 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: 163e7. 27 Sugano N, Nishii T, Miki H, Yoshikawa H, Sato Y, Tamura S. Mid-term results of cementless total hip replacement using a ceramic-onceramic bearing with and without computer navigation. J Bone Joint Surg Br 2007; 89: 455e60. 28 Jackson JP, Waugh W. Tibial osteotomy for osteoarthritis of the knee. J Bone Joint Surg Br 1961; 43-B: 746e51. 29 Pearle AD, Goleski P, Musahl V, Kendoff D. Reliability of image-free navigation to monitor lower-limb alignment. J Bone Joint Surg Am 2009; 91(suppl 1): 90e4. 30 Amendola A, Panarella L. High tibial osteotomy for the treatment of unicompartmental arthritis of the knee. Orthop Clin North Am 2005; 36: 497e504. 31 Paley DHJ. Principles of deformity correction. Berlin London: Springer, 2002. 32 Song EK, Seon JK, Park SJ, Seo HY. Navigated open wedge high tibial osteotomy. Sports Med Arthrosc 2008; 16: 84e90.

ORTHOPAEDICS AND TRAUMA 28:1

33 Akamatsu Y, Mitsugi N, Mochida Y, et al. Navigated opening wedge high tibial osteotomy improves intraoperative correction angle compared with conventional method. Knee Surg Sports Traumatol Arthrosc 2012; 20: 586e93. 34 Wright RW, Gill CS, Chen L, et al. Outcome of revision anterior cruciate ligament reconstruction: a systematic review. J Bone Joint Surg Am 2012; 94: 531e6. 35 Picard F, DiGioia AM, Moody J, et al. Accuracy in tunnel placement for ACL reconstruction. Comparison of traditional arthroscopic and computer-assisted navigation techniques. Comput Aided Surg 2001; 6: 279e89. 36 Zwingmann J, Konrad G, Mehlhorn AT, Sudkamp NP, Oberst M. Percutaneous iliosacral screw insertion: malpositioning and revision rate of screws with regards to application technique (navigated vs. Conventional). J Trauma 2010; 69: 1501e6. 37 Liebergall M, Ben-David D, Weil Y, Peyser A, Mosheiff R. Computerized navigation for the internal fixation of femoral neck fractures. J Bone Joint Surg Am 2006; 88: 1748e54. 38 Wilharm A, Gras F, Rausch S, et al. Navigation in femoral-shaft fracturesefrom lab tests to clinical routine. Injury 2011; 42: 1346e52. 39 Al-Ahaideb A, Quinn A, Smith E, Yach J, Ellis R, Pichora D. Computer assisted LISS plate placement: an in vitro study. Comput Aided Surg 2009; 14: 123e6. 40 Bicknell RT, DeLude JA, Kedgley AE, et al. Early experience with computer-assisted shoulder hemiarthroplasty for fractures of the proximal humerus: development of a novel technique and an in vitro comparison with traditional methods. J Shoulder Elbow Surg 2007; 16(suppl 3): S117e25. 41 Amiot LP, Labelle H, DeGuise JA, Sati M, Brodeur P, Rivard CH. Computer-assisted pedicle screw fixation. A feasibility study. Spine 1995; 20: 1208e12. 42 Lavallee S, Sautot P, Troccaz J, Cinquin P, Merloz P. Computer-assisted spine surgery: a technique for accurate transpedicular screw fixation using CT data and a 3-D optical localizer. J Image Guid Surg 1995; 1: 65e73. 43 Tjardes T, Shafizadeh S, Rixen D, et al. Image-guided spine surgery: state of the art and future directions. Eur Spine J 2010; 19: 25e45. 44 Allam Y, Silbermann J, Riese F, Greiner-Perth R. Computer tomography assessment of pedicle screw placement in thoracic spine: comparison between free hand and a generic 3D-based navigation techniques. Eur Spine J 2013; 22: 648e53. 45 Richter M, Mattes T, Cakir B. Computer-assisted posterior instrumentation of the cervical and cervico-thoracic spine. Eur Spine J 2004; 13: 50e9. 46 Weidner A, Wahler M, Chiu ST, Ullrich CG. Modification of C1-C2 transarticular screw fixation by image-guided surgery. Spine 2000; 25: 2668e73. discussion 2674. 47 Cho HS, Kang HG, Kim HS, Han I. Computer-assisted sacral tumor resection. A case report. J Bone Joint Surg Am 2008; 90: 1561e6. 48 Cho HS, Oh JH, Han I, Kim HS. Joint-preserving limb salvage surgery under navigation guidance. J Surg Oncol 2009; 100: 227e32. 49 Chong KW, Wong MK, Rikhraj IS, Howe TS. The use of computer navigation in performing minimally invasive surgery for intertrochanteric hip fractures e the experience in Singapore. Injury 2006; 37: 755e62.

56

Ó 2014 Elsevier Ltd. All rights reserved.

ARTHROPLASTY

50 Jenny JY, Miehlke RK, Giurea A. Learning curve in navigated total knee replacement. A multi-centre study comparing experienced and beginner centres. Knee 2008; 15: 80e4. 51 Leenders T, Vandevelde D, Mahieu G, Nuyts R. Reduction in variability of acetabular cup abduction using computer assisted

ORTHOPAEDICS AND TRAUMA 28:1

surgery: a prospective and randomized study. Comput Aided Surg 2002; 7: 99e106. 52 Rambani R, Viant W, Ward J, Mohsen A. Computer-assisted orthopedic training system for fracture fixation. J Surg Edu 2013; 70: 304e8.

57

Ó 2014 Elsevier Ltd. All rights reserved.