Patellofemoral complications after posterior-stabilized total knee arthroplasty: A comparison of 2 different implant designs

The Journal of Arthroplasty Vol. 17 No. 4 2002

Patellofemoral Complications After PosteriorStabilized Total Knee Arthroplasty A Comparison of 2 Different Implant Designs Michael J. Anderson, MD* David L. Becker, MD,* and Travis Kieckbusch, MD†

Abstract: We conducted a retrospective review of 2 consecutive series of posteriorstabilized total knee arthroplasties (TKAs) to evaluate patellofemoral complications, in particular, significant patellofemoral crepitance or patellar clunk syndrome. Twenty posterior-stabilized Axiom PSK (Wright Medical Technology, Arlington, TN) TKAs (group 1) were compared with 20 posterior cruciate–sacrificed Advance medial pivot (Wright Medical Technology, Arlington, TN) TKAs (group 2). The average age in group 1 was 69 years and in group 2 was 70 years. Preoperative valgus alignment in group 1 was 7.5° and in group 2 was 1.3°. Postoperative valgus alignment for the 2 groups was 4.8° and 5.3° valgus. Postoperative patellar tilt for the 2 groups was 0.9° lateral tilt and 8° lateral tilt. Patellofemoral signs of crepitance ⱖ2⫹ and significant box impingement complaints of either snapping or clunking decreased significantly postoperatively from 5 of 20 (25%) in group 1 to 0 of 20 in group 2 (P⫽.0079). Key words: medial pivot, total knee arthroplasty (TKA), patellofemoral complications, posterior stabilized. Copyright 2002, Elsevier Science (USA). All rights reserved.

Significant patellofemoral complications can be a devastating problem with total knee arthroplasty (TKA). Traditionally, posterior-stabilized designs have had greater patellofemoral complications than cruciate-retaining designs because of the intracondylar box, which is needed to accept the tibial post. These complications usually occur early and can be quite disabling, particularly the so-called box impingement or patellar clunk syndrome. This syndrome has been well described with posterior-stabilized knees because the patella impinges in the box when the knee is coming from a flexed position

to an extended position [1]. This mechanical impingement often results in an overgrowth of a fibrous nodule on the superior aspect of the patellar button. This nodule engages the intercondylar notch of the posterior-stabilized design causing painful catching at approximately 30° to 40° of extension [1–3]. The average time to presentation ranges from 5 to 11 months [2]. Most of these patients required reoperation. Treatment of this problem varied from open arthrotomy for resection of the nodule [1] to arthroscopic resection [3,4]. The cause of the problem is multifactorial and may be related to patellar prosthetic placement and design of the femoral component [1,5]. The original posterior-stabilized knee system, the Insall Burstein I, evolved from the total condylar knee system. Despite the longevity of the Insall Burstein system, there have been reported problems, including patellar clunk syndrome [1]. Stern and Insall [6] documented a 12% occurrence of

From the *Blount Orthopaedic Clinic; and †Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin. Submitted December 30, 2000; accepted December 22, 2001. No benefits or funds were received in support of this study. Reprint requests: Michael J. Anderson, MD, Blount Orthopaedic Clinic, 625 East St. Paul Avenue, Milwaukee, WI 53202. Copyright 2002, Elsevier Science (USA). All rights reserved. 0883-5403/02/1704-0024$35.00/0 doi:10.1054/arth.2002.32173

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Patellofemoral Complications After Posterior-Stabilized TKA • Anderson et al.

Fig. 1. Comparison of the Advance medial pivot (left) and the Axiom PSK (right) femoral components (both Wright Medical Technology, Arlington, TN). The view is of the distal aspect of the implants to show the differences in the trochlear region.

patellofemoral problems after posterior-stabilized TKA. Problems ranged from nonspecific anterior knee pain to crepitance and patellar clunk syndrome. Because of these problems, the patellofemoral groove was redesigned into what is known today as the Insall Burstein II system. Although patellofemoral complications were reduced with the Insall Burstein II, patellar clunk and crepitance still are reported to occur in 4% to 14% of TKAs with this design [6,7]. The purpose of this study was to evaluate the clinical and radiographic outcome of 2 groups of consecutive patients who underwent TKAs using 2 different implant designs. The main focus centered on the clinical performance and complications related to the patellofemoral articulation.

Materials and Methods Design Features and Differences Between Groups In group 1, the Axiom PSK (Wright Medical Technology, Arlington, TN) TKA was used. The Axiom PSK is a traditional cam-and-post posterior cruciate–substituting TKA. This design offers anterior and posterior stability with the cam and post. The trochlear groove is shallow and needs to be truncated to allow room in extension for the tibial post. The femoral geometry is the open box design (Fig. 1). In group 2, the Advance medial pivot (Wright Medical Technology, Arlington, TN) TKA was used. The Advance was released in 1998 and was a new type of posterior-stabilized knee design. This design allows for posterior cruciate substitution but does not require removal of a large piece of bone for the femoral housing (ie, the closed box design). A spherical articular geometry is placed on the medial

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side of the tibial articular surface, which provides high resistance to anterior and posterior movements. The lateral side of the joint allows natural anterior and posterior translation of the knee during normal daily activities. This design was determined to be a more biomechanically friendly knee, resulting in the elimination of the large femoral box but still allowing resection of the posterior cruciate ligament. The trochlear groove of this knee system is recessed, which allows the replaced patella to articulate at the same height as the normal patella. The trochlear groove also is extended inferiorly so that the patella is in contact with the trochlea to 100° of flexion. This new design also contains a 3.6° laterally oriented trochlear groove anteriorly, which has been described as the anatomically correct orientation by Eckhoff et al [8]. The lateral trochlear groove also is raised 5 mm above the deepest part of the trochlear groove to resist any lateral pulling of the patella and subsequent dislocation. Patient Selection Criteria In general, the indications for the procedure were disabling knee pain in patients who had failed conservative treatment. Both groups were selected retrospectively as a consecutive series of patients who had anterior and posterior cruciate ligaments sacrificed and patellae that were resurfaced. Clinical Data Between January 1995 and November 1998, 20 Axiom TKAs with resurfaced patella and posterior cruciate substitution were identified. This was a consecutive series of patients and comprised group 1. After the Advance TKA was released, between March 1999 and January 2000, 20 posterior-stabilized Advance TKAs were identified with resurfaced patella and resection of the posterior cruciate ligament. These patients comprised group 2. All procedures were performed or supervised directly by 1 author (M.J.A.). Group 1 consisted of 6 men and 14 women and 10 right and 10 left knees. The average age was 69 years (range, 38 – 89 years). Diagnoses were degenerative disease in 17 and rheumatoid or inflammatory disease in 3. Preoperative alignment was 7.8° of valgus (Fig. 2). Sizes of the femoral implants ranged from 65 to 80 mm. Patellar size ranged from 25 to 35 mm. Group 2 consisted of 9 men and 11 women and 12 right knees and 8 left knees. The average age was 70 years (range, 47– 84 years). Diagnosis was de-

424 The Journal of Arthroplasty Vol. 17 No. 4 June 2002

Fig. 2. (A) Preoperative patient demographics. (B) Preoperative patient age.

generative disease in all knees. Preoperative alignment was 1.5° of varus (Fig. 2). Sizes of the femoral implants ranged from 55 to 75 mm. Patellar size ranged from 32 to 38 mm. Postoperative Evaluation All patients were evaluated in the postoperative period by 1 author (M.J.A.). Patients were questioned about anterior knee pain, a crepitant sensation that they perceived in their knees, or patellar clunk. The examiner then graded the range of motion in the knee and noted any crepitance or clunking. Clunk was graded as either present or absent. Crepitance was graded 1⫹ for mild roughness, 2⫹ for moderate roughness, and 3⫹ for severe crepitance with an audible corresponding crepitation. Radiographic evaluation consisted of the following views: i) anteroposterior standing 16-inch alignment, ii) 45° bent knee lateral, and iii) bilateral Merchant’s view of the patellofemoral joint. All measurements were done by 1 author (M.J.A.). Operative Technique All operative procedures were similar. In all knees; 5° distal femoral intramedullary valgus cuts and neutral intramedullary tibial cuts were made. Rotational alignment of the femoral implant was 3° externally rotated with respect to the posterior femoral condyles, unless there was significant wear posteriorly. In this case, referencing from the transepicondylar axis was done. A patellar-cutting guide was used to re-establish the preoperative thickness of the patella. A lateral release was performed when the intraoperative tracking with the trial implants in place did not track true. If the patellae either started lateral and jumped into the groove or started neutral and jumped out of the groove with the no thumb test, an inside-out lateral retinacular release was performed. All components of all knees were cemented.

Postoperatively, all patients were treated with similar, standardized postoperative knee protocols. A continuous passive motion machine was started on postoperative day 1. Patients were allowed weight bearing as tolerated using either a walker or 2 crutches for 6 weeks after surgery. Active and active-assisted range-of-motion programs were started with the affected knee on postoperative day 1.

Results Clinical Results Follow-up for the 19 unrevised knees in group 1 averaged 24.3 months (range, 2– 60 months). For the 20 knees in group 2 the follow-up averaged 14.7 months (range, 6 –24 months). Significant patellofemoral symptoms in group 1 were found in 5 of 20 knees (25%). One was in a patient with rheumatoid arthritis, the other 4 were knees with degenerative joint disease. Patellofemoral crepitance of 2⫹ was graded in 2 knees; 3⫹ was graded in 2 knees. Two patients suffered from box impingement, with 1 patient requiring revision (see later). This patient also had 3⫹ crepitance. One patient with significant box impingement did not want a revision. In group 2, no significant patellofemoral symptoms were noted. This was a statistically significant difference between the 2 groups (P⫽.0079, based on a chi-squared test). The range of motion was 118° in group 1 and 115° in group 2. (Fig. 3A). There was no significant postoperative range-of-motion difference between the 2 groups (P⫽.43). No patient suffered a patella fracture in either group. There were no postoperative deep infections. Other than the 1 revised patient in group 1, no knee required reoperation. In group 1, 9 lateral releases were performed (Fig. 3B). In group 2, 4 lateral releases were performed. There was a statistically significant decrease in lat-

Patellofemoral Complications After Posterior-Stabilized TKA • Anderson et al.

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Fig. 3. (A) Postoperative range-of-motion comparison between the 2 groups (P⫽.43). (B) Group comparison of lateral release (P⫽.04) and postoperative alignment.

eral release rate in group 2 (P⫽.04; chi-squared test). Radiographic Results The postoperative anatomic alignment for the 2 groups was 4.8° valgus and 5.3° valgus. There was no significant difference between the postoperative alignment (P⫽.58). Patellar tilt averaged 0.9° lateral tilt (range, 15° medial tilt to 12° lateral tilt) for group 1. For group 2, the average was 8.0° (range, 0 –32°). This difference was statistically significant, with greater lateral tilt in group 2 (P⫽.015). There were no signs of progressive radiolucenies around the patellar implants in either group. No component was noted to have migrated, and no implant was considered loose by radiographic criteria. Revisions One patient in group 1 underwent a revision for symptomatic patellar clunk syndrome, despite conservative treatment with physical therapy modalities and injections. The knee was opened, the large fibrous nodule was removed sharply, and a bur was used to smooth and ramp the superior aspect of the patellar button to allow for more uniform exit from the box onto the trochlea of the patellofemoral joint. This patient has not had a recurrence of patellar clunk syndrome to date and now is 3 years postrevision.

Discussion Significant patellofemoral complications, including severe patellofemoral crepitance and patellar box impingement, can be devastating problems after posterior-stabilized TKA. Patients have a significant functional disability with these problems, especially with stair climbing and with flexed knee positions, such as squatting. They also are disabled by the transient instability sensation from crepi-

tance or the catching of the patella as it leaves the box. This study did not focus on mild patellofemoral symptoms or patient patellofemoral complaints without objective findings. This study shows well the improved clinical results with improved biomechanics of the patellofemoral joint in the Advance medial pivot posterior cruciate–sacrificing TKA. This reduction from 25% to 0% of significant patellofemoral complications reinforces the theoretical improvements that were noted in the design features of this knee, in particular, the patellofemoral joint. Biomechanically, removal of the large femoral box allows the trochlear groove to be extended down so that the patella never leaves the trochlea of the femoral implant until deep flexion. The incidence of patellar complaints in group 2 is significantly lower than that reported by other authors for posterior-stabilized TKA designs [1,6,7]. The group 1 design rate of patellofemoral complaints was within the reported range in the literature for a standard open box femoral design posterior-stabilized TKA. Patellar clunk and crepitance results from the open box design and is obligatory in these designs. The average follow-up of group 1 knees was longer. The shorter follow-up for group 2 was due to the later release of the Advance knee system. No patient in either group developed significant patellofemoral symptoms after 6 months in situ. We believe the differences in length of follow-up did not affect the outcomes addressed by this investigation. Although the rates of lateral release decreased significantly between the 2 groups, this may have been related more to preoperative alignment than implant design changes (see under Materials and Methods). The average preoperative alignment for patients requiring lateral release (n ⫽ 9) in group 1 was 14° valgus compared with 2° valgus in group 2 (n ⫽ 4). The patellar tilt angles, although significantly less in the posterior-stabilized Axiom implant (group 1), were lowered artificially by 3 patients who had an

426 The Journal of Arthroplasty Vol. 17 No. 4 June 2002 and patellar crepitance, between 2 different designs of posterior-stabilized TKAs. We found significantly fewer patellofemoral complications, while allowing for substitution of the posterior cruciate ligament in this design without a cam-and-post mechanism.

Acknowledgment We thank Mr. Steven White, Wright Medical Technology, for statistical analysis. Fig. 4. Merchant view of an Axiom PSK with medial patellar tilt.

average medial tilt of 13°. It appeared radiographically (Fig. 4) that the medial side of the patella was dipping into the box. None of these knees developed a significant crepitation or clunking. The limitations of this study are the small number of knees in each group and the difference in preoperative alignment and disease process. We attempted, to keep the groups comparable by strict inclusion criteria (resection of the posterior cruciate ligament and resurfacing of the patellae). This made the group sizes smaller but limited other biases that may have occurred if the groups were larger but not as homogeneous. Despite these limitations, however, these results are encouraging. We hope that other studies will confirm the positive experience that we have seen.

Conclusion This study documents the difference in patellofemoral complications, in particular, patellar clunk

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