Graf_edit.qxp 28/9/07 12:33 Page 40
Navigation & Imaging
registration, in which the anatomical landmarks are registered prior to Navitrackers the accuracy remains very high, even in difficult operating
beginning the operation. The latter operation requires trackers to be conditions (around 97% versus only 37% for spheres).
placed in the bone. These trackers are identified by the navigation
system and monitored throughout the procedure to ensure that Most of the attention in terms of navigation systems in recent years has
relative distances between the anatomical landmarks are maintained. focused on the placement of the acetabular cup in the pelvis.
Alignment of this component within the safe zone, as defined by
In addition to the image-free technology, there have been great Lewinnek et al.,
10
has been improved with the new systems,
11,12
improvements in software and computing power and speed. This reaching 100% accurate placement in later cases.
13
Therefore, the
means that the newer systems are simpler and quicker to use. They can pressing challenge is to ensure that the computers can also control leg
effectively be operated by the surgeon and only one scrub nurse. This length and offset to give the patients the best chance of a quick and
means that while the first-generation systems took at least 30 minutes successful rehabilitation. Specialised applications can specifically control
longer than conventional surgery, the second-generation systems need these factors (ORTHOsoft Universal Hip 2.2 Length & Offset Program,
on average only 10–15 minutes more. ORTHOsoft, Quebec); time will tell whether the results are compelling.
Latest Innovations
The type of tracking used in navigation has also evolved. In the early
The goal of navigated surgery is to
days an electromagnetic system was used to register the trackers, but
give the surgeon complete control
while the benefits of navigation were clear, there were difficulties. The
system requires cables to be run from the trackers to the computer, during the entire operation; without
which can get in the way of the surgeon. The electromagnetic field can
this, it is very easy to make an error
also cause interference with any metallic instruments. Moreover, the
electromagnetic source had to be fixed on the operating table near the
without seeing it.
hip or joint to be replaced, further complicating the arrangement.
Future Developments
The latest advances have led to
There are more changes to come. Hip replacement will almost certainly
continue to use navigation, but the systems used will be different in
improved optical tracking systems.
even 5–10 years’ time. The best tracking compromise currently is the
These use an infrared camera and optical system, but perhaps in the future it will be through wi-fi or
reflective trackers to pinpoint
bluetooth. Trackers themselves will be less aggressive and less invasive –
smaller, and without pins.
anatomical landmarks.
Even further into the future there will be robots that can work
laparoscopically. Such robots have already been used, but they were big,
The latest advances have led to improved optical tracking systems. complex, expensive and difficult to use. If they can be shrunk and made
These use an infrared camera and reflective trackers to pinpoint simpler, there is definitely a future for them, because the remaining
anatomical landmarks. Of course, the ability of the trackers to reflect problem with navigation is the inaccuracy of the surgeon’s hand.
the infrared rays can be compromised by any tissue and fluid
disgorged during the operation. Hip replacements in particular cause Summary
significant blood loss and lots of tissue remnants that could decrease The goal of navigated surgery is to give the surgeon complete control
the visibility and accuracy of the system. during the entire operation; without this, it is very easy to make an
error without seeing it. New developments mean that leg length and
With the first trackers, which were based on reflective sphere offset can be maintained within acceptable limits. In the long run this
technology, this loss of visibility was a real problem. However, newer should lead to more accurate surgery, better-aligned implants that
surface technology and different arrangements of reflectors mean that survive for longer and faster recuperation for patients. Studies to
water or blood can be poured on the trackers and yet the camera is investigate these techniques will take several more years, but there is
still able to see them. Clinical data suggest that with the new no doubt that good progress is already being made. ■
1. White TO, Dougall TW, Arthroplasty of the hip. Leg length is 6. Longjohn D, Dorr LD, Soft tissue balance of the hip, hip-replacement arthroplasties, J Bone Joint Surg Am,
not important, J Bone Joint Surg Br, 2002;84:335–8. J Arthroplasty, 1998;13(1):97–100. 1978;60(2):217–20.
2. Clark CR, Huddleston HD, Schoch EP 3rd, et al., Leg-length 7. Wright JM, Crockett HC, Delgado S, et al., Mini-incision for 11. Kalteis T, Handel M, Bäthis H, et al., Imageless navigation for
discrepancy after total hip arthroplasty, J Am Acad Orthop Surg, total hip arthroplasty: a prospective, controlled investigation insertion of the acetabular component in total hip
2006;14(1):38–45. with 5-year follow-up evaluation, J Arthroplasty, 2004;19: arthroplasty: is it as accurate as CT-based navigation?, J Bone
3. Edeen J, Sharkey PF, Alexander AH, Clinical significance of 538–5. Joint Surg Br, 2006;88(2):163–7.
leg-length inequality after total hip arthroplasty, Am J Orthop, 8. DiGioia AM 3rd, Plakseychuk AY, Levison TJ, Jaramaz B, 12. Nogler M, Kessler O, Prassl A, et al., Reduced variability of
1995;24(4):347–51. Mini-incision technique for total hip arthroplasty with acetabular cup positioning with use of an imageless
4. Hofmann AA, Skrzynski MC, Leg-length inequality and nerve navigation, J Arthroplasty, 2003;18:123–8. navigation system, Clin Orthop Relat Res, 2004;(426):159–63.
palsy in total hip arthroplasty: a lawyer awaits!, Orthopedics, 9. Hube R, Birke A, Hein W, Klima S, CT-based and fluoroscopy- 13. Dorr LD, Hishiki Y, Wan Z, et al., Development of imageless
2000;23:943–4. based navigation for cup implantation in total hip computer navigation for acetabular component position in
5. Maloney WJ, Keeney JA, Leg length discrepancy after total arthroplasty (THA), Surg Technol Int, 2003;11:275–80. total hip replacement, Iowa Orthop J, 2005;25:1–9.
hip arthroplasty, J Arthroplasty, 2004;19(4 Suppl. 1):108–10. 10. Lewinnek GE, Lewis JL, Tarr R, et al., Dislocations after total
40 EUROPEAN MUSCULOSKELETAL REVIEW 2007
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99