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M. Mardani Kivi Guilan University of Medical Sciences 2

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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. 7

20 20  Extensor lever arm is greatest at 20 degrees of flexion and the quadriceps force required for knee extension increases significantly in the last 20 degrees of extension. 8

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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. 8  Normal walking generates 50% body weight joint reaction forces which increase to 8 times body weight for jumping from a small height. 11

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There are three approaches: Relative indications for resurfacing and non- resurfacing Selective resurfacingSelective non-resurfacing 13

Older ageAnt. Knee pain Inflammatory arthritis obesityfemale Hx. Of patellar subluxation Intra-op. patellofemoral wear Intra-op. patellar maltracking Non-anatomic trochlea groove on femoral implant 14

Younger age Non-Inflammatory arthritis Thin patients Thin/hypo-plastic patella Intra-op. preserved patellar cartilage Intra-op. congruent patellar tracking Anatomic trochlea groove on femoral implant 15

inflammatory arthritis R.A.  Of all the indications for resurfacing, inflammatory arthritis has been the most widely accepted. Most authors have recommended routine resurfacing for all patients with R.A.  Lighter patients tending to do well with un- resurfacing patella. 16

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 Bilateral arthroplasty  no difference in stair- climbing ability or incidence of anterior knee pain. 18

 No difference in Ant. Knee pain, functional score or revision rates between resurfaced and un-resurfaced groups. 19

Revisions in resurfaced group Revisions in Non- resurfaced group Patello- femoral problems All reasons Patello- femoral problems All reasons No. Knees Min. F/Up (yr) Knee implant used Author AMKBourne et al PCA modular Feller et al Not specified Schroeder et al Miller Galante II Barrack et al Miller Galante II wood et al PFCWaters 14 (1.5%)17 (1.8%)37 (3.9%)41 (4.3%) 954 (100%) 3.4 (mean) 4 typesTotals 20 AMK: Anatomic Modular Knee; PFC: Press Fit Condylar; PCA: Porous Coated Anatomic

Implant designsInlay designOnlay design All-polyethylene component Metal-backed component 21

 The prosthetic patella should be medialized to approximate the median eminance of the normal patella. 22

lateral mal- tracking of the patella Internal rotation of tibial component Q angle Internal rotation of femoral component 23

 “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. 24

deflate  If there is any abnormality in patellofemoral tracking deflate the torniquet and examine again  48% (Marson) or 31% (Husted) it will be normal. 25

lateral release  Correction should be toward the reason. if there is not any component mal-positioning lateral release should be done. 26

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Patellofemoral instabilityPatellar fracturesPatellar component loosening ( %)Patellar clunk syndrome Patellar tendon rupture (allo-graft Vs. auto-graft Repair) 28

Treatment  Arthroscopic debridement of nodule. 29

Removal of osteophytes Smoothing of fibrilated cartilage Drilling of e burnated bone First step 30

Soft tissue release from lateral aspect of patella Division of the patellofemoral ligament Denervation of the patella with electrocautery of the patellar rim Second step 31

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