Abstract
Maltracking of the patella associated with TKA is usually the result of several factors coming together in the same patient. Causes of maltracking include residual valgus limb alignment, valgus placement of the femoral component, patella alta, poor prosthetic geometry, internal rotation of the femoral or tibial component, excessive patellar thickness, asymmetric patellar preparation, failure to perform a lateral release when indicated, capsular dehiscence, and dynamic instability.
Prior to wound closure after implantation of total knee arthroplasty, patellar tracking should be evaluated to assess the potential need for lateral release. The incidence of lateral release in the past was quite high in some series.
Most experienced surgeons will report a lateral release rate less than 5% for varus knees. It is usually higher for valgus knees because they are often associated with patella alta and preoperative subluxation. The classic intraoperative test for patellar tracking has been referred to as the “rule of no thumb” In this test, first suggested by Fred Ewald, the patella is returned to the trochlear groove in extension with the capsule unclosed. The knee is then passively flexed and one assesses whether or not the patella tracks congruently without capsular closure. If it does and the medial facet of the patellar component contacts the medial aspect of the trochlea no lateral release need be considered. If the patella dislocates or tilts, lateral release may be necessary. The test should be repeated with 1 suture closing the capsule at the level of the superior pole. If tracking then becomes congruent without excessive tension on the suture, no release is necessary. If tilting still persists, some surgeons like to assess tracking with the tourniquet deflated so that any binding effect on the quadriceps can be eliminated from the test. A tight PCL can also impart apparent patellar tilt as the femoral component is drawn posteriorly while the tibia (with its tubercle) moves anteriorly.
