Optimal positioning in TKR and THR:

Tools and techniquesEdward T Davis

The Royal Orthopaedic Hospital, Birmingham, UK

Dudley Group of Hospitals, Dudley, UK

Knee arthroplasty

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!

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!

What navigation can do.

• Measure distances (and tension)

• Prevent anterior femoral notching.• Correct resection levels.• Gap balance

(flexion/extension gaps).

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.

What navigation can do.

• Gap Balanced– Femoral component is positioned parallel to the

resected proximal tibia with each collateral ligament equally tensioned.

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).

Gap Balanced

What navigation can do

• Provide real time verification of what you have done.

• Teach you how to do a knee replacement well.

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!

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 cost

• Or can it!

Patient specific guides

• Strong drivers– Reduce 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 .

Patient specific guides

• Evidence lacking.• Probably reduce outliers compared to standard

technique but not as good as navigation.• Can’t dynamically balance ligaments.

Patient specific guides

Compound errors– Long leg alignment (if from standard films)– Segmentation– Fit on bone (osteophytes), tibia most challenging–Movement of pins used to hold cutting block.– Saw deflection

• No ability to validate cuts.

Optimal stem & cup placement in THR

Edward T DavisThe Royal Orthopaedic Hospital, Birmingham,

UKDudley Group of Hospitals, Dudley, UK

Is component orientation important?

YES

Metal on metal has taught us a lot!

• Consequences of incorrect orientation apparent much earlier than with metal on poly.

• Important in other bearings– Dislocation

• Metal on poly– Increased wear rates– Liner fracture in highly cross linked

• Ceramic on ceramic– Squeaking– Liner fracture.

Are we as good as we think we are?

No

• 1952 THR’s/SR• Acceptable position defined as 30-45 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.

Standard Total number of surgeries

Acceptable position

Bosker et al. 40+/- 1015+/- 10

200 70.5%

Reize et al. 40+/- 1015+/- 10

85 41%

Saxler et al. 40+/- 1015+/- 10

105 25.7%

Leichtle et al. 45+/-520+/-5

950 65.5%

Callanan et al. 30-4515+/-10

1952 47%

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.

Mean error -0.4 degrees Standard Deviation 2.3 degrees98 within +/- 5 degrees (outliers -6 and -8 degrees)

62% acceptable

99% acceptable(outlier 46 degrees)

Component orientation

• Acetabular Component– The “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 Sign– Male ß+b~20° to 30° – Female ß+b~45°

• Widmer paper– Cup anteversion + 0.7 x Stem antetorsion = 37.3

K.-H. Widmer , B. Zurfluh.Compliant positioning of total hip components for optimal range of motion. Journal of Orthopaedic Research 22 (2004) 815-821.

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).

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!

•Clinical study.–Prospective cohort study.–50 Navigated THR’s performed by ETD.–Post operative CT scans for component orientation.–2 patients excluded.

Inclination Anteversion

Mean Error (degrees) -1.1 0.9

Standard Deviation 3.1 4.3Min Value -6.9 -7.8Max Value 5.7 8.2

The new lateral position registration techniqueNo need for APP registration!

Miniaturized navigation system for computer aided surgery SCHKOMMODAU E, COIGNY F, FINDEISEN C, HIRSCHMANN M, BALLWEG C, JÜRGENS P, THORANAGHATTE R, KNOBEL B

“ 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.”

What do I want?

• Accurate placement.• Able to workout complex algorithms – i.e ROM, ligament balancing.

• No line of site issues.• No pins.• Reduce inventory. • Fast.• Cheap!

Combination of navigation technologies