Patellar tracking should be judged with the tourniquet deflated because an inflated tourniquet has been shown to effect patellar tracking. 35 If gross maltracking occurs after patellar resurfacing, the orientation of the tibial and femoral components should be reassessed. Internal rotation of the tibial and femoral components, in particular, should be avoided. Patellar tracking should be judged before final insertion of the components so that the orientation of the components can be altered if necessary. If the components are judged to be in an optimal or acceptable position and maltracking occurs with the tourniquet deflated with the rule of no thumb, lateral release should be done. 21 It generally is considered desirable to preserve the superior lateral geniculate artery, although it has been difficult to prove that sacrificing the vessel, in itself, leads to specific complications such as avascular necrosis or fracture. Care also should be taken not to incise the vastus lateralis tendon because this may lead to quadriceps tendon rupture or weakness. If slight maltracking persists after lateral release, medial imbrication should be done to additionally improve patellar tracking. 45
The majority of patellofemoral complications can be directly or indirectly attributed to errors in surgical technique. 45,48 With proper alignment and rotation of the components and soft tissue balancing of the extensor mechanism, the incidence of complications relating to the patella should be very low. The two major areas of improvements in additionally decreasing the incidence of patellofemoral complications relate to more reproducible surgical technique and improvements in component design. Bindelglass and Dorr 10 concluded that surgical technique was of greater importance than specific design factors, specifically the presence of an asymmetric component, a raised lateral flange, or an angled trochlear groove. Harwin 24 also reported that a symmetrical dome patellar component and a symmetrical femoral component were compatible with a very low patellar femoral complication rate, in agreement with that Bindelglass and Dorr. The surgical technique probably is more important than certain design details of the femoral component in minimizing the incidence of patellofemoral complications. A persistent problem with surgical technique is the variability of component alignment that is obtained with currently available alignment guides. Eckhoff et al 19 compared four different methods of determining tibial component rotation, for instance, and found a range of 20° from 2° internal rotation to 19° external rotation. A similar study evaluated the alignment and rotation of the femoral component. Olcott and Scott 40 evaluated four commonly used methods of determining component rotation and determined that asymmetry of the flexion gap occurred in 10% to 30% of patients depending on the anatomic landmarks used to determine femoral component rotation.
Early femoral component designs were characterized by a shallow flat trochlear groove, which resulted in a relatively high incidence of patellar subluxation and dislocation. A priority in early cruciate-retaining components was minimal bone resection that resulted in a shallow groove. A gait study by Andriacchi et al 2 subsequently showed that a deeper groove was associated with more normal function particularly in stair climbing. More recent designs have incorporated a separate intercondylar bone cut to allow adequate depth of resection to more closely replicate the normal anatomic trochlear groove. 42 Despite these design changes, patellofemoral kinematics still has not been reproduced completely. 16,50 The other design consideration is the distal extent of the trochlear groove. Earlier designs did not provide support for the patellar component other than two small areas of point contact beyond 90° flexion. By extending the metal surface of the trochlea farther distally, higher contact areas and lower contact stresses can be maintained beyond 90° flexion (Fig 6). This design feature has been incorporated into some recent designs. There is some evidence that this design feature particularly is advantageous when the patellar is left unresurfaced. 37
The issue of the design of the trochlear groove also has been addressed recently with some posterior-stabilized components. Patellar clunk is thought to be largely a design-related complication that virtually is restricted to total knee replacements done with posteriorstabilized components. 17 With these designs, there often is a sharp transition from the trochlear groove to the anterosuperior edge of the intercondylar notch of the femoral component. 46 The combination of a shallow patellar groove, a prominent intercondylar notch, and a small patellar component is thought to contribute to the development of fibrous nodule leading to patellar clunk syndrome 33 (Fig 4). Design modifications that are thought to decrease the risk of this complication include a deeper patellar groove, more distal extent of the trochlear groove, a smoother transition to the anterior edge of the intercondylar notch, and using a larger patellar component. 33 A surgical technique factor that also may diminish the incidence of the formation of fibrous nodule is excision of synovium of the undersurface of the quadriceps tendon particularly superior to the patellar component. By incorporating some of these design and technique considerations, the incidence of patellar clunk and other patellofemoral complications has been reduced dramatically. 33
Whether to resurface the patella remains among the most controversial topics in total knee arthroplasty. The practice varies widely among the options of routine resurfacing, selective resurfacing, and not resurfacing. 30,43 Clinical studies reporting the results of knee replacement with and without patellar resurfacing have yielded widely variable results. Among the first widely quoted studies of total knee replacement with an unresurfaced patellar was that by Picetti et al 44 who reported a 29% incidence of anterior knee pain without patellar resurfacing. There was no control group, however, and the component used was the Total Condylar knee replacement, which is radically different than current designs. Subsequently, a study by Boyd et al 12 compared a total knee replacement with and without patellar resurfacing and reported a much higher incidence of anterior knee pain with unresurfaced patellas. However, this study included patients with inflammatory arthritis. When the analysis was restricted to patients with osteoarthritis, the complication rate was comparable between the two groups with 6% of patients who did not have resurfacing experiencing complications compared with 4% among patients who had resurfacing. Again, this was an older design component that does not meet current design standards as described previously.
The results of many studies may be, to some degree, design specific. Studies by Schroeder Boersch et al 47 using the Duracon Knee (Howmedica, Rutherford, NJ) and Kajino et al 28 using the Kajino-Shoji Knee (Biomet, Warsaw, IN) reported that their patients in whom the patella was resurfaced were able to climb stairs better than patients in whom the patella was not resurfaced. Studies by Ishinishi et al 27 with the PFC Knee (Johnson & Johnson, Raynham, MA), Braakman et al 13 with the Miller-Galante Knee (Zimmer), and Abraham et al 1 with the Variable Axis Knee (Howmedica) reported no difference in functional results between patients with and without patellar resurfacing. Some studies have compared bilateral knee replacements in which one side was resurfaced and the contralateral knee was not resurfaced. Using the LCS Knee replacement (DePuy, Inc, Warsaw, IN) Keblish et al 29 reported no difference in clinical results between the two sides. Enis et al 20 reported on patients with bilateral knee replacements with and without patellar resurfacing using the Townley Knee (DePuy) and found that the patients had a preference for the resurfaced side.
There have been a limited number of prospective randomized studies addressing the decision of whether to resurface the patella. Barrack et al 5 reported the results of a prospective randomized, double-blind study using the Miller-Galante II total knee replacement (Zimmer) and found no difference in knee score or patient satisfaction; however, 10% of patients without resurfacing subsequently underwent resurfacing. 5 Among the patients who had bilateral knee replacements with one side resurfaced and the other side not resurfaced, the knee scores were equivalent and patients expressed no preference for one side over the other. A minimum 5-year followup report of this same group of patients continued to show no significant difference between the groups. The incidence of anterior knee pain had increased in both groups, but more in the patients who had resurfacing. 6 Bourne et al 11 did a similar study using the AMK total knee replacement (DePuy) and reported less pain and higher flexion in patients who did not have resurfacing. Four percent of the patients without resurfacing, however, subsequently required patellar resurfacing. Feller et al 23 reported better stair climbing ability in patients with unresurfaced knees using the PCA component (Howmedica).
Because of the highly variable reports in the literature of the results of total replacement with and without patellar resurfacing, the indications remain controversial. There is a consensus to do patellar resurfacing in cases of primary patellofemoral arthritis in older patients (Fig 7), when a severely deformed patella is present that does not track normally and in patients with inflammatory arthritis. Patellar resurfacing should be avoided when there is a small osteopenic patella present in which case resurfacing may carry with it a high risk of patellar fracture or component loosening. There is also a preference on the part of many surgeons to avoid patella resurfacing in young active patients who have normal or near normal appearing articular cartilage. Recently, computer-assisted decision analysis was applied to the issue of resurfacing of the patella in total knee arthroplasty. 51 This is a technique that is based on probability theory and Bayesian logic that uses computer software and metaanalysis of the available literature. Using this methodology, not resurfacing the patella became the procedure of choice if the probability of postoperative anterior knee pain with an unresurfaced patella decreased below 14%, if the probability of having pain with a resurfaced patella increased above 8%, or if the use of patellar implant failure decreased below 80% of the use of a perfect health state. Several studies reported an incidence of postoperative anterior knee pain below 14% with unresurfaced patellas and an incidence of anterior knee pain above 8% with resurfaced patellas. 4,11,32,33 Surgeons can use these guidelines and the results of their practice to determine whether patellar resurfacing is indicated in their patients.
Among patients with degenerative osteoarthritis there is support in the literature for resurfacing or not resurfacing the patella. 5,6,11,29 If the patella is not resurfaced, it is important to choose a femoral component that is compatible with a native patella. Design features that seem to be favorable include a deep congruent trochlear groove that extends distally to maintain contact beyond 90° flexion. Using such an implant, Kulkarni et al 32 reported excellent results with or without patellar resurfacing. The incidence of anterior knee pain was 7% (seven of 96 patients) compared with 10% in the group that did not have resurfacing (12 of 115 patients); however, only one patient in each group had pain severe enough to require medication. 32 This indicates that at least with some designs, patellar resurfacing may not be necessary. If the patella is not resurfaced, patients also should be informed that subsequent resurfacing may be necessary. If the patella is resurfaced routinely, it is incumbent on the surgeon to maintain a very low complication rate because several series without patellar resurfacing have achieved success in more than 90% of patients. 4–6 The final decision on whether to resurface the patella rests with the surgeon based on his level of training, experience, and intraoperative judgement of the status of the patellofemoral articulation. With optimal surgical technique and implant design, excellent results are obtainable in the majority of knee replacements with or without resurfacing of the patella.
In gaining an understanding of the causes of patellofemoral problems, a more clear understanding of the optimal technique and design of knee arthroplasty has emerged. It has become clear that the patella is a reflection of the overall success of the knee arthroplasty procedure. The occurrence of a patellar complication, such as maltracking or anterior knee pain usually indicates an underlying problem in surgical technique, component design, or both (Table 1). This explains why isolated patellar resurfacing is associated with a high rate of complications and persistent symptoms, 9 why resurfacing a previously unresurfaced symptomatic patella is associated with persistent or recurrent symptoms, 6,32 and why even doing patellectomy after patellar fragmentation can fail to relieve symptoms (Fig 5). Conversely, normal patellar tracking and absence of any peripatellar symptoms is a strong indication of a successful arthroplasty procedure. The patella is like the canary in the mineshaft. In the early days of coal mining in Appalachia, canaries were placed in coal mines to detect low oxygen content and the presence of methane gas. 52 A somnolent canary indicated an underlying problem in the mine just as a patellar problem often is a reflection of a suboptimal total knee replacement. In the process of understanding and minimizing patellofemoral symptoms and complications after knee arthroplasty, a better understanding of the optimal total knee technique and design has been attained.
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O. Sahap Atik, MD, Guest Editor