3 What navigation can do. Measure angles Coronal alignment Plenty of evidence (how much do you need!).Significant reduction of “outliers”.Caution on “gold standard” with which to compare it.When is final alignment taken (cemented knees).Difficult to prove significant functional improvement as only extreme outliers will have increased pain.Longevity of knees so good it will take years to see clinical improvement in survivorship!
4 What navigation can do. Measure angles Sagittal alignment Evidence to show that surgeons are very poor at assessing intra operative fixed flexion deformity.Reduction in patients leaving the table with FFD.Should translate to less post operative FFD and improved function.Relies on the surgeon having faith and willingness to correct!
5 What navigation can do. Measure distances (and tension) Prevent anterior femoral notching.Correct resection levels.Gap balance (flexion/extension gaps).
6 What navigation can do. Measured resection Bone landmarks (femoral epicondyles, posterior femoral condyles, or the anteroposterior axis) are the primary determinants of femoral component rotation.
7 What navigation can do. Gap Balanced Femoral component is positioned parallel to the resected proximal tibia with each collateral ligament equally tensioned.
8 What navigation can do.Navigated Gap balance was what we had been waiting for!Improved outcome from navigation and improved alignment (longevity).Benefit greatest in deformed knees (e.g valgus knees).
11 What navigation can doProvide real time verification of what you have done.Teach you how to do a knee replacement well.
12 What navigation can NOT do Reduce operating time.Increase by 5-10mins.But in complex cases reduces uncertainty and perseveration.Define what the targets should be!You need to know where you want to go before navigation can take you there.We really need basic research to define where knee replacements should be. Now that we can put them there!
17 What navigation can NOT do Give the surgeon hand eye co-ordination skills (but does improve them).Stop the surgeon “cheating” or deviating from plan!Control for differential cement thickness (education).Prevent registration errors.Higher when short distances are defined e.g epicondylar axis.Reduce costOr can it!
18 Patient specific guides Strong driversReduce inventory costs with potential savings to implant companies.Manufacturing costs covered by inventory savings +/- MRI or CT costs.Reduce instruments and therefore cost (similar to navigation).Reduce OR time 10mins.Similar surgeon skills to standard TKR i.e no special hand eye coordination .
19 Patient specific guides Evidence lacking.Probably reduce outliers compared to standard technique but not as good as navigation.Can’t dynamically balance ligaments.
20 Patient specific guides Compound errorsLong leg alignment (if from standard films)SegmentationFit on bone (osteophytes), tibia most challengingMovement of pins used to hold cutting block.Saw deflectionNo ability to validate cuts.
21 Optimal stem & cup placement in THR Edward T DavisThe Royal Orthopaedic Hospital, Birmingham, UKDudley Group of Hospitals, Dudley, UK
23 Metal on metal has taught us a lot! Consequences of incorrect orientation apparent much earlier than with metal on poly.Important in other bearingsDislocationMetal on polyIncreased wear ratesLiner fracture in highly cross linkedCeramic on ceramicSqueakingLiner fracture.Metal-on-metal and ceramic-on-ceramic bearings have wear rates 10 to 30 times as high when acetabular cup angles exceeded 55.
25 1952 THR’s/SRAcceptable position defined as degrees of Inclination and 5-25 degrees of antiversion.Only 47% were in an acceptable position!Even in high volume surgeons (164 THA/yr) only 51% were within the acceptable limits.
26 Total number of surgeries StandardTotal number of surgeriesAcceptable positionBosker et al.40+/- 1015+/- 1020070.5%Reize et al.8541%Saxler et al.10525.7%Leichtle et al.45+/-520+/-595065.5%Callanan et al.30-4515+/-10195247%
27 Can we do better?Retrospective review of first 100 navigated hip replacements and hip resurfacings.Lateral position, posterior approach with a porous press fit acetabular component.Brainlab V5 imageless optical navigation.No requirement for pre-operative imaging.All models and axis constructed using intra operative landmarks.
36 Component orientation Acetabular ComponentThe “safe zone”Is Lewinnek’s paper robust enough?Can one position really fit all?Acetabular position (40/15) the same if femoral neck in 20 degrees of antiversion and if 10 degrees retro-verted?Ranawat SignMale ß+b~20° to 30°Female ß+b~45°Widmer paperCup anteversion x Stem antetorsion = 37.3K.-H. Widmer , B. Zurfluh.Compliant positioning of total hip components for optimal range of motion. Journal of Orthopaedic Research 22 (2004)
37 Component orientation What about acetabular offset.The more medial the more bone on bone impingement.The more lateral the more neck on acetabular component impingement.What about femoral offset?Less offset the more bone on bone impingement.In SR changes neck geometry that impinges on the acetabular component/bone.What about pelvic tilt?Changes “functional” orientation of acetabulum (and femur).
39 If navigation is so good why isn’t it being used in hip arthroplasty? Need for pins to be placed in the bone for tracking.One of the main obstacles is the pelvic plane registration.Line of sight in optical navigation.Takes extra time!
40 The new lateral position registration technique No need for APP registration!Clinical study.Prospective cohort study.50 Navigated THR’s performed by ETD.Post operative CT scans for component orientation.2 patients excluded.InclinationAnteversionMean Error (degrees)-1.10.9Standard Deviation3.14.3Min Value-6.9-7.8Max Value5.78.2
44 “ Although the precision of acetabular cup placement is improved with the CT-based individualized instrument guides, even when utilizing the design of highest accuracy from previous work, accuracy is not improved in comparison to conventional technique.”