Complications of the patellofemoral articulation are the most frequent cause of early problems and revision after total knee arthroplasty (TKA).1,9,22,29 Complications include patellar fracture (3-21%),1,9,21,34 fixation peg failure (< 1%),13,14maltracking(< 1-20%),24,29impingement(< 1- 20%),1 and component loosening (< 1-5%).9 Some surgeons do not recommend resurfacing the patella because of the high risk of complications.32,33
Patella maltracking, subluxation, and dislocation are serious problems after TKA, causing weakness, instability, and unusual noises. In general, patella maltracking is a sign of technical error.26 These technical problems may be related to malrotation or malalignment of the femoral component, or too large of a component in the anteroposterior (AP) dimension.5,10,25,27,28 Malrotation of the tibial component, especially with fixed-bearing prostheses, may also predispose to maltracking or premature, excessive polyethylene wear.2,15 Maltracking may be related to the amount of patella resection or patella component position and thickness.8
Many studies describe techniques for determining the correct rotation of the femoral component in TKA.4,6,25,27,31 However, few have investigated methods to determine neutral or optimal tibial component rotation.2,15 The amount of patella resection and prosthesis replacement and positioning have received relatively little attention.21
We determined the incidence of lateral retinacular release and patella complications using a new posterior- stabilized total knee arthroplasty and a specific protocol for the patellofemoral articulation.
MATERIALS AND METHODS
We retrospectively reviewed 255 consecutive cemented posterior-stabilized knee arthroplasties performed in 192 patients from May 1998 to December 2003. The data had been prospectively collected from operative reports, preoperative and postoperative knee scores, and postoperative patella complications. During the time span of the study, the senior author (PFL) also performed 16 primary constrained condylar knee arthroplasties in 14 patients who had severe medial collateral ligament insufficiency. Of the 192 patients (255 knees), eight patients (11 knees) died before 2 years postoperatively and 13 patients (17 knees) were lost to followup. Thus, there were 171 patients (227 knees) with followup of 2 to 7 years (mean, 3.7 years). There were 115 unilateral procedures and 88 one-stage bilateral procedures (44 patients). There were 24 staged bilateral procedures (12 patients). There were 124 women (167 knees) and 47 men (59 knees). The mean patient age was 71 years (range, 46-88 years), the mean weight was 82.3 kg (range, 41.4-117.3 kg), and the mean height was 165 cm (range, 147-200 cm). The preoperative diagnosis was osteoarthritis (OA) in 199 knees (87%; 149 patients), rheumatoid arthritis (RA) in 15 knees (nine patients), osteonecrosis in five knees (5 patients), and various other diagnoses in eight knees (eight patients). The size of the patella component was 32 mm in 47 knees (37 patients), 35 mm in 123 knees (90 patients), 38 mm in 48 knees (39 patients), and 41 mm in nine knees (six patients). One patient who had bilateral procedures has a 32-mm patella in one knee and a 35-mm patella in the other knee. The preoperative knee alignment was varus in 144 knees (63%) (113 patients), excessive valgus in 45 knees (20%; 38 patients), and neutral (2°-7°) in 38 knees (17%; 31 patients).
The TKAs were performed under tourniquet control (100 mmHg above highest systolic pressure) with an Insall-type anterior approach to the knee.17 The components included an anatomic femoral component with deepened patella trochlea, a modular symmetric tibial component, and an offset dome allpolyethylene patella component with three pegs for fixation (NexGen® Legacy PS, Zimmer, Warsaw, IN). Femoral component rotation was established using a perpendicular to the midtrochlear line (Whiteside's lines).4 Intramedullary instrumentation was used for the distal femoral bone resections. The proper size of the femoral component in the AP dimension was determined by preoperative templating and corroborated by an AP sizing guide instrument. A smaller femoral component was selected if the distal femur was between sizes to avoid overstuffing. Fixed anatomic landmarks (tibial crest and medial ⅓ of the tibial tubercle) were used to determine tibial component rotation. The symmetric tibial component resulted in 1 to 2 mm of posterolateral tibial overhang. The techniques for patella resection and preparation have been described previously.21,22 Using a patella cutting clamp, the patella resection was asymmetric: thinner laterally, through the subchondral bone of the lateral facet, and thicker medially. The thickness of the patella before and after the TKA was checked with a caliper with the goal of reproducing the thickness within 2 mm. The component was aligned with the medial edge of the resected patella, and the resultant uncovered 2 to 3 mm of lateral patella was smoothed with a small rongeur. With all trial components in place, patella tracking was checked throughout full range of motion (ROM) with one towel clip placed at the superior pole of the patella and the tourniquet inflated. A lateral retinacular release from inside the knee, sparing the superior lateral geniculate vessels, was performed in for medial lift-off (tilt) of the patella or subluxation. No patella component dislocated during the trial ROM. The medial structures were closed in extension using nonabsorbable sutures. Physical therapy with a continuous passive motion machine using a previously described protocol20 was started 1 day after surgery.
A clinical research nurse (ESS) evaluated the patients' knees preoperatively and postoperatively using the Hospital for Special Surgery knee score19 and the Knee Society rating system.18 The presence or absence of soft tissue or bony crepitus of the patellofemoral articulation was evaluated with the patient sitting and rated as none, mild, or severe.21 Radiographic analysis was performed by both authors and included sequential standing antero- posterior radiographs, supine lateral radiographs, and tangential radiographs of the patella. The radiographic scoring system of the Knee Society12 was used to determine the overall alignment of the knee, the presence of radiolucent lines in zones adjacent to the cement mantle, and migration of the components. The alignment of the femoral and tibial components in the sagittal plane was not measured. Lateral and tangential views of the patella were evaluated for maltracking, fracture, radiolucent lines, and component loosening.21
The axial patellofemoral position was defined as central (< 5° tilted), medial tilt (> 5° tilted with the medial side depressed), or lateral tilt (> 5° tilted with the lateral side depressed) as described by Bindelglass and Vince.7
A lateral retinacular release was performed in 15 knees (14 patients) of the 227 knees (6.2%). Of the 21 patients (28 knees) who died before 2 years or were lost to followup, two knees (two patients) had a lateral retinacular release. Of the 15 knees (14 patients) that had a lateral retinacular release and 2 years followup, there was a mean preoperative valgus deformity of 15.2° (range, 10°-25°) in 13 knees (12 patients). The other two knees each had a pre- operative varus deformity of 5°.
There were no reoperations for loosening or patellofem- oral problems. One patient had an acute infection at 6 weeks, which was treated by débridement, liner exchange, and suppressive antibiotic therapy. One patient had intramedullary rod fixation of a supracondylar femoral fracture 18 months postoperatively. This patient also had asymptomatic patella fragmentation. Radiographic evaluation of the patella showed no dislocated or subluxated components. Six knees had slight (5°) lateral tilt on the tangential radiograph. One knee had a symptomatic fracture of the patella treated by immobilization for 6 weeks without sequelae. Two knees (two patients) had asymptomatic patella fragmentation-osteonecrosis and apparent loosening of the patella component at 2 and 4 years, respectively. One of these two knees had a lateral retinacular release. Radiolucent lines were seen in one zone in 27 patellas, in two zones in two patellas, and in three zones in four patellas. The two knees with fragmentation and loose patella components had radiolucent lines in all six patellar zones.
The mean Knee Society pain score improved from 55 points preoperatively (range, 15-78 points) to 95 points postoperatively (range, 21-100 points). The mean Knee Society function score improved from 42 points preoperatively (range, 0-90 points) to 59 points postoperatively (range, 0-100 points). The mean postoperative HSS knee score was 87.3 points (range, 41-98), with 159 knees (122 patients) rated as excellent, 61 (51 patients) as good, six (six patients) as fair, and one as poor. One hundred sixty- seven patients (221 knees) stated they were satisfied with the outcome of the knee, and (five) patients (six knees) were dissatisfied with the outcome. One patient who had bilateral procedures is dissatisfied with both knees, and another patient who had bilateral procedures is satisfied with one knee and dissatisfied with the other knee. The mean preoperative flexion was 110° (range, 70°-135°) and the mean postoperative flexion was 113° (range, 70°- 135°). The mean preoperative flexion contracture was 5° (range, 0°-40°) and the mean postoperative flexion contracture was 1° (range, 0°-15°). There was no palpable patellofemoral crepitus in 224 knees (169 patients) and mild asymptomatic soft tissue crepitus in three knees (three patients). One patient who had bilateral procedures had no crepitus in one knee and mild crepitus in the other knee.
Complications related to the patellofemoral articulation are the most frequent early complications after total knee arthroplasty. These complications may be related to the design of the implant or the surgical techniques of the arthroplasty. In a previous study of the Insall-Burstein II posterior-stabilized knee arthroplasty by the author, there was a high incidence of lateral retinacular release and patellofemoral complications.21 A modification of this pros- thesis with an anatomic femoral component, deep troch- lear groove and off-set dome patella component (NexGen Legacy PS) was introduced with the goal of improving patellofemoral mechanics and lowering complication rates.
The limitations of this study are its retrospective nature, relatively short-term followup and lack of a control group. We suspect most patellar problems would occur within the minimum followup time of two years, so the incidence would not likely substantially increase over time. Because we lacked controls, we cannot say whether our approach results in fewer problems than alternative approaches. We did, however, have a relatively large single-surgeon cohort and in the absence of reoperations believe the low incidence of major problems comparable to other approaches.
The senior author (PFL) has previously described a protocol for preparation of the patella in posterior-stabilized knee arthroplasty and these techniques were utilized with this new prosthesis.21,22 Using this specific protocol, we observed low rates of lateral retinacular release and patella complications. There were no reoperations for the patellofemoral articulation at a mean followup of 3.7 years (range, 2-7 years).
Several techniques have been described to establish proper femoral and tibial component rotation in TKA to avoid patellofemoral problems. Alignment of the femoral component using Whiteside's lines4 or the transepicondylar axis6,25,27 prevents internal rotation better than the posterior condylar axis or resection of the posterior condyles parallel to the proximal tibial resection.31 We recommend using Whiteside's lines because the lateral epicondyle cannot be reliably palpated. Several methods have been described to achieve proper tibial component rotation.15,26 Fixed anatomic landmarks have frequently been used, including the tibial crest-medial ⅓ tibial tubercle, transverse axis of the tibial plateau, transmalleolar axis, or the axis of the second ray of the foot. Akagi et al2 recommended alignment of the tibial component perpendicular to the transepicondylar axis based on CT scans of 57 normal knees. Huddleston et al15 recommended a variable rotation of the tibial component with alignment to the femoral component rotation and extension. Optimal rotation of the tibial component may be specific for the constraint and design of the implant system used. In a study of 109 rotating platform knees, Huddleston et al15 determined 95% of knees had a proper rotation within 5° of the medial ⅓ tibial tubercle. However, in six knees (5%) the neutral point for tibial component rotation was greater than or equal to 10° from the anatomic axis. We did not notice a problem with tibiofemoral rotational malalignment or patella tracking problems using a fixed anatomic alignment point. However, the mean 3.7-year followup may have been too short to determine complications.
The use of intraoperative lateral retinacular release of the patella to avoid patella maltracking has varied from 6% to 40%.3,11,16,21,23,30 It may be dependent on whether the tourniquet is inflated,16 or if the no-touch technique is used3,21,23 rather than the towel-clip technique used in our study during trial range of motion. In a study of 118 posterior-stabilized knees, Larson et al21 reported lateral retinacular releases were performed in 33% of knees when the no-touch technique was used to check patella tracking. In addition, preoperative anatomic and patient factors may contribute to the need for lateral retinacular release. These include excessive preoperative valgus deformity, severe patellofemoral arthritis, or a subluxated patella and a knee with poor preoperative ROM.26,29 In these circumstances, an intraoperative lateral release may be necessary despite optimal rotation of the components.
We believe patella maltracking is an avoidable problem in TKA using a posterior-stabilized prosthesis. The surgeon should pay close attention to proper femoral and tibial component rotation and avoid internal rotation. Determining patella thickness before and after resection and medial positioning of the component also may be important in preventing patella maltracking. We recommend a lateral retinacular release for intraoperative tilt or subluxation if component rotation and alignment is satisfactory. We found a low incidence of lateral retinacular release and patella problems with fixed-bearing, posterior-stabilized knee prostheses.
The authors thank Cheryl Cooper for manuscript preparation.
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