Notas / Notes - Active Congress.......

JUEVES / THURSDAY
142
to be detrimental. High patellofemoral loads are also thought
to contribute to cartilage deterioration over time.
Recent prospective, randomized studies favor patellar resurfacing
over retaining the native patella, reporting increased
reoperation rates for patellar problems and increased anterior
knee pain in subjects in which the patella has not been resurfaced.
These studies also document the reoperation rates to
convert unresurfaced to resurfaced patellae exceeding those
for complications after patellar resurfacing. In addition, the
incidence of residual patellofemoral pain after secondary resurfacing
is substantially higher than when patellofemoral
resurfacing is done primarily. Therefore, one cannot be assured
of an equivalent result (as compared with primary resu-rfacing)
with secondary patellar resurfacing if substantial patellofemoral
pain occurs following TKA without initial patellar resurfacing.
Most studies of subjects in which bilateral TKA has been performed
with the patella resurfaced in one TKA and nonresurfaced
in the other have demonstrated patients prefer the TKA
with the resurfaced patella. Lastly, studies which have analyzed
intraoperative cartilage condition at the time of TKA have found
a poor correlation between intraoperative cartilage condition
and postoperative patellar pain and function, supporting the
concept that it is difficult to determine who will do well clinically
without patellar resurfacing based on intraoperative findings.
Patient selection criteria are critical in the decision-making
process. Patellofemoral complications, the greatest argument
against resurfacing, have been diminished with improved surgical
techniques and implant design. Surgical techniques for
patellar resurfacing that emphasize a patellar resection that
reproduces equal facet thickness, native patellar height and
central patellar tracking, while respecting vascular principles,
have produced complication rates which range from 0% to
4%. This is superior to a 10-29% patellofemoral pain incidence
demonstrated in review of the literature of series without patellar
resurfacing. If resurfacing is chosen, adherence to proper
surgical technique principles is imperative as outlined below.
I. SURGICAL TECHNIQUE GOALS
A. Preserve the Patellar Tendon
B. Duplicate Patellar Thickness
C. Assure Patellar Symmetry
D. Assure Patellar Tracking
E. Preserve Patellar Vascularity
II. PRESERVE THE PATELLAR TENDON
A. Release Infrapatellar Adhesions
B. Release Patellofemoral Ligament
C. Extend Capsulotomy
D. Externally Rotate Tibia
E. Secure (Clamp) Tendon Insertion
III. DUPLICATE PATELLAR THICKNESS
A. Measure Patellar Thickness
1. Highly Variable (Average 20-25 mm)
B. Measure Patellar Component Thickness
1. Usually 8.5-11 mm
C. Remove What You’re Replacing
IV. ASSURE PATELLAR SYMMETRY
A. Normal Anatomy
1. Medial Thicker Than Lateral Facet
B. Minimal Lateral Facet Resection
1. Typically Flush With Subchondral Bone
C. Measure Symmetry Post-Resection
D. Don’t Over-resect To Obtain Flat Surface
1. Asymmetric Patella ≥ Instability
2. Lateral Defect ≥ Drill & Fill (PMMA)
V. ASSURE PATELLAR TRACKING
A. Surgical Approach
1. Superior Tracking with Mid-Vastus/Subvastus
B. Proper Component Positioning
1. Femoral - Avoid Medial Shift / Internal
Rotation / Excessive
Valgus / Femoral Component Flexion
a. Transepicondylar Axis: Place Parallel To
b. Anteroposterior Axis: Place Perpendicular To
2. Tibial - Avoid Medial Shift / Internal Rotation
3. Patella - Avoid Lateral Shift
a. Median Crest (High Point) Is 5.42 mm
(Average) Medial To Midpoint Of Patella
(Hofmann, et al, J. Arthroplasty, 1997)
b. Predrill Median Crest - Marker Of Median Crest
c. Position Highpoint of Dome Over Median Crest
C. Lateral Retinacular Release / VMO Imbrication If
Subluxation
D. Assessment
1. No Thumb Technique
2. Assess After Tourniquet Release
a. Tourniquet Creates Tenodesis Effect
VI. PRESERVE PATELLAR VASCULARITY
A. Maintain the Fat Pad
B. Preserve the Superolateral Geniculate Artery
1. If Lateral Release Required
C. Avoid Large Central Lug Component
1. Disrupts Midpatellar Intraosseus Blood Supply
VII. PATELLOFEMORAL PROSTHETIC DESIGN
A. Patellar Component
1. Dome / Modified Dome Shape – More Forgiving
2. Three Small Peripheral Fixation Lugs
a. Less Stress Raiser / Reduced Fracture Risk
B. Femoral Component
1. Anatomic Trochlear Groove
a. Assists Patellar Capture / Reduced Shear
Stresses (Colwell)
2. Extended Trochlear Groove
a. Maximizes Contact Area in Deep Flexion
REFERENCES
1. Boyd Jr AD, Ewald FC, Thomas WH, Poss R, Sledge CB:
Long-term complications after total knee arthroplasty with
or without resurfacing of the patella. J Bone Joint Surg
75A: 674-681, 1993.