In the name of GOD

Patellofemoral joint in Total Knee Arthroplasty M. Mardani Kivi Guilan University of Medical Sciences

Poursina Hospital

Anatomy Patella is the largest sesamoid bone in the body. Patella has the thickest articular cartilage of any of the joints: Depth of articular cartilage  6-10 mm . Overall thickness of patella  21-25 mm .

Anatomy Thickness of less than 15 mm is relative contraindication for resurfacing patella and a thickness of 18 mm or more usually is considered safe.

Anatomy Patella normally articulate with the distal femur at about 20 degrees of flexion undergoing 7 cm of excursion from extension of full flexion.

Anatomy Patellofemoral contact zones changes with knee flexion

Biomechanics 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.

Biomechanics 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.

Biomechanics Patellofemoral stability Articular surface geometry Soft tissue remains

Biomechanics

Biomechanics 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 8 times body weight for jumping from a small height.

Biomechanics Altered biomechanics at the patellofemoral joint “Anterior Knee Pain”

Patellar resurfacing??? There are three approaches: Relative indications for resurfacing and non-resurfacing Selective resurfacing Selective non-resurfacing

Relative indications for the patellar resurfacing: Older age Ant. Knee pain Inflammatory arthritis obesity female Hx. Of patellar subluxation Intra-op. patellofemoral wear Intra-op. patellar maltracking Non-anatomic trochlea groove on femoral implant

Relative indications for the patellar NON resurfacing 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

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 ending to do well with un- resurfacing patella.

Boyed et al.: retrospective study Patellofemoral complications (Ant. Knee pain) 4% : Patella resurfacing 12% : patella un-resurfacing

Abraham et al.: Prospective study Bilateral arthroplasty no difference in stair-climbing ability or incidence of anterior knee pain.

Barrack et al: randomized prospective study with 10-year follow up No difference in Ant. Knee pain, functional score or revision rates between resurfaced and un-resurfaced groups.

Revisions in resurfaced group Revisions in Non-resurfaced group Patello-femoral problems All reasons No. Knees Min. F/Up (yr) Knee implant used Author 1 2 6 100 6.3 AMK Bourne et al 40 3 PCA modular Feller et al Not specified Schroeder et al 7 93 5 Miller Galante II Barrack et al 9 15 198 wood et al 11 474 PFC Waters 14 (1.5%) 17 (1.8%) 37 (3.9%) 41 (4.3%) 954 (100%) 3.4 (mean) 4 types Totals AMK: Anatomic Modular Knee; PFC: Press Fit Condylar; PCA: Porous Coated Anatomic

All-polyethylene component Metal-backed component Implant designs Inlay design Onlay design All-polyethylene component Metal-backed component

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

Patellar cut

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

“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. Resistance of one or two stitches on the medial side

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

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

Patellofemoral complications Patellofemoral instability Patellar fractures Patellar component loosening (0.6-2.4%) Patellar clunk syndrome Patellar tendon rupture (allo-graft Vs. auto-graft Repair)

Patellofemoral complications Treatment  Arthroscopic debridement of nodule.

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

Patelloplasty Second step 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

Take home massage Ant. Knee pain in TKA is usually due to tibial or femural component malrotation not because of patellofemoral joint DJD.

With Regards