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M. Mardani KiviM. Mardani KiviGuilan University of Medical Sciences

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The primary function of the patella is to increase the lever arm of the extensor mechanism around the knee, improving the efficiency of quadriceps contraction.

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Extensor lever arm is greatest at 2020 degrees of flexion and the quadriceps force required for knee extension increases significantly in the last 2020 degrees of extension.

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Patella provides 50% increase in knee extension strength compared with that after patellectomy.

Patellofemoral joint sustains some of the greatest contact pressures of all the joints of the body.

Normal walking generates 50% body weight joint reaction forces which increase to 88 times body weight for jumping from a small height.

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Of all the indications for resurfacing, inflammatory arthritisinflammatory arthritis has been the most widely accepted. Most authors have recommended routine resurfacing for all patients with R.AR.A..

Lighter patients tending to do well with un-resurfacing patella.

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Bilateral arthroplasty no difference in stair-climbing ability or incidence of anterior knee pain.

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No difference in Ant. Knee pain, functional score or revision rates between resurfaced and un-resurfaced groups.

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Revisions in Non-resurfaced

group

Revisions in resurfaced

group

AuthorKnee

implant used

Min. F/Up (yr)

No. Knees

All reasons

Patello-femoral

problems

All reasons

Patello-femoral

problemsBourne et

alAMK 6.3 100 6 2 2 1

Feller et alPCA

modular3 40 0 0 2 0

Schroeder et al

Not specified

2 40 2 2 1 1

Barrack et al

Miller Galante II

5 93 7 7 0 0

wood et alMiller

Galante II2 198 15 15 9 9

Waters PFC 2 474 11 11 3 3

Totals 4 types3.4

(mean)954

(100%)41

(4.3%)37 (3.9%)

17 (1.8%)

14 (1.5%)

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AMK: Anatomic Modular Knee; PFC: Press Fit Condylar; PCA: Porous Coated AMK: Anatomic Modular Knee; PFC: Press Fit Condylar; PCA: Porous Coated AnatomicAnatomic

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The prosthetic patella should be medialized to approximate the median eminance of the normal patella.

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“No thumb” test of patellar tracking should be used as a guide of patellar instability (before retinacular closure)

If the patella can be subluxated half of its diameter over the medial femoral condyle, the retinaculum is probably not too tight.

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If there is any abnormality in patellofemoral tracking deflatedeflate the torniquet and examine again 48% (Marson) or 31% (Husted) it will be normal.

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Correction should be toward the reason. if there is not any component mal-positioning lateral release lateral release should be done.

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Treatment Arthroscopic debridement of nodule.

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