Orthopedics

Materials and Methods

A total of 152 patients with osteoarthritis were treated with TKA between January 2005 and December 2006. Inclusion criteria were patients with primary unilateral TKA and those with degenerative osteoarthritis of the knee that did not respond to nonsurgical treatment. Exclusion criteria were patients with patellar resection, rheumatism and rheumatoid arthritis, a history of patellar fracture, patellar instability treated with extensor reconstruction, high tibial osteotomy, severe valgus and varus deformity (>15°), knee stiffness or flexion contracture, a history of septic arthritis and osteomyelitis, serious medical illness limiting walking ability, and other lower-limb joint disease.

Patients were randomized on the basis of a computer-generated random-allocation sequence and divided into the patelloplasty group (group A; n=76) and the traditional treatment group (group B; n=76). Group A comprised 35 men and 41 women (mean age, 64.2 years; range, 55–76 years), and group B comprised 37 men and 39 women (mean age, 65.1 years; range, 56–78 years). No significant differences existed in clinical data, knee scoring, and radiological results between the 2 groups preoperatively (Table 1).

Table 1: Preoperative Data

According to Kellgren/Lawrence osteoarthritis staging, 23 patients were stage 3 and 53 were stage 4 in group A, and 25 patients were stage 3 and 51 were stage 4 in group B. At last follow-up, 22 patients were stage 3 and 46 were stage 4 in group A, and 20 patients were stage 3 and 44 were stage 4 in group B, with no significant difference (P>.05). Twenty patients were lost to follow-up. Complete follow-up data were available for 132 patients, including 68 in group A and 64 in group B.

All operations were performed by the senior joint physician (Y.S.). A bone cement prosthesis (P.F.C. Sigma; DePuy, Warsaw, Indiana) was applied in all patients.

Surgical Technique

Group A Technique

The medial parapatellar approach with anterior midline incision was used to expose the knee joint, which showed that the patella was groove-shaped at various degrees due to serious degeneration and severe hyperostosis. First, the proliferated osteophytes on the margin were removed up to the normal patella margin. The patella thickness was measured, with the midpoint of the patellar ridge as the reference. The patelloplasty thickness was chosen based on the match of the patella with the femoral prosthesis trochlea. The patellar surface was cut with the electric pendulum saw, and the 2-sided grooves were altered to the smooth-slope shape. The peripheral cartilage surface was removed, and the cartilage in the central part and in the slope section of the patella and the subchondral bone remained to alter the patella into the shape close to that of normal patellar articular without degeneration. The patellar tracking and its match with the prosthesis were checked through knee flexion and extension with the suture method.¹⁰ The ridge height of the patella was reduced to a proper degree to diminish the patellofemoral joint pressure in some patients (Figure).

Figure: Intraoperative photographs of the proliferation of osteophytes around the patella seen intraoperatively, with irregular shape and osteoarthritis grade 4 (A), and electric management around the patella (B). Proliferated osteophytes around the patella were removed to determine the center of the patella (C). With the center of the patella used as the base, part of the cartilage and subchondral bone were removed to make an anatomical shape that had a smooth surface curvature to match well with the prosthesis (D). The smooth articular surface could be seen after the patelloplasty, close to the normal anatomy of the patella (E, F). The patella size and shape matched well with the prosthesis trochlea (G).

Results

No significant differences were observed in clinical data, KSS score, HSS score, and ROM preoperatively in the 2 groups (Table 1). At last follow-up, mean KSS score and functional score were 91.2 points and 73.6 points, respectively, in group A, an increase of 47.4 points and 38.0 points, respectively, compared with preoperative levels. In group B, mean KSS score and functional score were 89.1 points and 61.9 points, respectively, an increase of 44.9 points and 25.7 points, respectively, compared with preoperative levels. A significant difference was found in postoperative KSS scores between the 2 groups (P=.045). Group A obtained higher functional scores than group B (73.6 vs 61.9, respectively). Range of motion improved in both groups postoperatively, with no statistical significance. No significant difference was found in Feller patellar score and Lonner patellofemoral score between the 2 groups.

Despite a higher overall incidence of anterior knee pain in group B, the difference between the 2 groups was not statistically significant. Two (2.9%) patients in group A and 3 (4.6%) patients in group B reported anterior knee pain, with no significant difference. Overall patient satisfaction was 92.6% and 85.9%, respectively, in group A and group B (P=.042). The postoperative scores in the patients with reduced patellar ridge, removal of outer edge of the patella or patellar instability was lower than that in the patients with perioperative patellar stability, with no significant difference (P=.072).

Preoperative radiographs revealed no significant differences in the knee axis between the 2 groups, with a mean introversion of 7.2° in group A and 6.9° in group B. Postoperative radiographic evaluation was based on the standard radiographs taken at final follow-up according to the Knee Society Radiological Evaluation and Scoring System.

Various degrees of valgus existed in group A (3.5°) and group B (3.8°), but the difference was not significant (Table 2). The postoperative patellofemoral joint match was evaluated by 3 senior joint surgical specialists based on postoperative and final follow-up radiographs. Postoperative radiological evaluation demonstrated a mean patellofemoral joint match rate of 95.4% and 89.3%, respectively, in group A and group B, of which 85.1% of patients in group A and 69.6% of patients in group B reached 100% of patellofemoral joint match; this was a significant difference (P=.008). Final follow-up radiographs showed a patellofemoral joint match rate of 94.6% in group A and 89.6% in group B, of which 83.2% of patients in group A and 64.8% of patients in group B reached a perfect match (100%), which was a significant difference (P=.008). Follow-up revealed poorer patellofemoral joint match in 5 patients with anterior knee pain (mean joint match rate, 85.4%) (Table 3).

Table 2: Postoperative Scores

Table 3: Postoperative Knee Pain

No prosthesis loosening or revision occurred during follow-up. Subluxation of the patella occurred in 2 patients, and knee pain while going upstairs or downstairs occurred in 1 patient in both groups. No patellar fracture or patella-related complications were observed during follow-up.

Discussion

With the continuous improvement of prosthetic design and surgical technology, knee replacement has become a relatively mature surgical technique, achieving satisfactory mid- and long-term clinical results. However, treatment of the patella (osteoarthritis) has been a controversial topic. During TKA, the patella was once reserved, and later, the patellar prosthesis was introduced for patella resurfacing. A number of studies have demonstrated that patellar resurfacing could reduce the incidence of anterior knee pain and produce a better clinical outcome than patellar nonresurfacing surgery.^5,9,11 Meanwhile, patellar resurfacing also caused patellar fracture, prosthetic loosening, rupture of extensor mechanism, patellar impingement syndrome, and other complications.¹¹

The fundamental basis of retaining the patella was that the autogenous patella could better meet the physiological and anatomical requirements and avoid complications resulting from patellar resurfacing.¹² However, the experts advocating patellar resurfacing claimed that after TKA, a certain degree of change of the articular surface and mechanical properties and obvious change of the patellar motion characteristics could be seen in comparison with the natural anatomy.^5,9,13 In addition, patellar sliding between the patellar cartilage and the metal could lead to wear of the patella. Over time, the retained patella will continue to deteriorate and wear.^5,9,13 Despite the continuing debate on patellar treatment, a growing number of studies have suggested that patellar resurfacing and nonresurfacing could generate similar overall outcomes; neither possessed a significant advantage over the other.^6,8,14,15 Lygre et al¹⁶ reported that patellar resurfacing did not generate evident clinical effects in post-TKA pain and function after following up 972 patients with osteoarthritis undergoing primary TKA. Postoperative knee joint pain was caused by multiple factors, and selection of the proper approach was key to successful treatment.¹⁷

Regarding treatment of the patella during patellar resurfacing, 1 study attached importance to the removal of marginal patellar osteophytes and the peripheral denervation, reporting that traditional patellar treatment resulted in a high incidence of anterior knee pain.¹⁸ Gupta et al¹⁸ found no obvious differences between the 2 groups after comparing peripheral patellar resections. The femoral trochlea was stable relative to the individual’s anatomy, whereas the patellar groove of the femoral prosthesis was different from the patient’s patella. In the meantime, a certain degree of deformity of the patella and cartilage damage may exist in late-stage knee lesions. After traditional patellar management, the patellofemoral joint lost normal alignment and congruence between the treated patella and the femoral prosthesis trochlea, which may induce postoperative complications. Because of this, we adopted patelloplasty for treatment of the patella. According to the prosthesis trochlea groove, the patella was resurfaced to better match the prosthesis trochlea after treatment of the peripheral margin of the patella. In this way, the incidence of the patella-related complication could be reduced, which contributed to good knee extension and low incidence of anterior knee pain.

Our results suggested that group A obtained better results in KSS score, Feller patellar score, Lonner patellofemoral score, and patient satisfaction, as well as a lower incidence of postoperative anterior knee pain than group B. Postoperative radiographs demonstrated a high degree of congruence in group A, which correlated with the patellar resurfacing based on the prosthesis trochlea and accorded with the clinical outcome. The DePuy P.F.C. Sigma bone cement prosthesis was used because the femoral trochlea was deepened and widened and had the properties of good extension and transition to be able to better adapt to the nonresurfaced patella. With appropriate prosthesis design and accurate surgical technique, desirable postoperative effects and lower incidence of anterior knee pain were achieved in both groups.

Osteophyte proliferation around the patella and the bowl-shaped patella (the original appearance of the patella disappeared) were found in most patients during TKA. In patelloplasty, the removal of the peripheral patellar osteophytes and some articular cartilage, trimming of fibrocartilage, and resection of a small section of lateral patella in some patients could create better adaptation to the anatomical femoral prostheses, optimize patellar tracking, and decrease dot and linear contacts, thereby reducing the incidence of anterior knee ache and postoperative patella wear.

Yercan et al² advocated removal of the lateral patella osteophytes and a section of the lateral patella in TKA to reduce the patellofemoral prosthesis collision. Martens and De Rycke¹⁹ obtained satisfactory results in 90% of 20 patients treated with lateral articular surface resection and release of the lateral patellar retinaculum. McCarroll et al²⁰ performed partial articular surface resection in 57 patients and achieved a satisfactory outcome in patients with III and IV patellar cartilage lesions. In the current study, conventional removal of the lateral patellar osteophytes and transformation of the articular facets from the preoperative bowl shape into the smooth convex shape were conducted. Then, the patellofemoral congruence was tested with the nonthumb method. In some patients, a small section of the lateral patella was resected to modify the patellar tracking and reduce the patellofemoral pressure. Patients with unstable patellas were treated with lateral band release and suture, when attention should be paid to the tension suture at medial incision close.

Patelloplasty reserved the patellar bone mass and the bone strength to the greatest degree, prevented such problems as polyethylene particles caused by the loosening and wear of prostheses, and obtained satisfactory effects even in the second revision operation.^17,21 Postoperatively, the knee joint functions and patellar functions were recovered satisfactorily, with a lower incidence rate of the anterior knee pain. Meanwhile, reservation of patellar receptors in the patelloplasty could improve stability while standing on 1 foot. The high patient satisfaction in group A may be attributed to the reliable curative effects and fewer postoperative complications, and may also result from higher sensitivity of the patients to the knee adjustment because of patellar receptor reservation.

This study has some limitations. Due to the relatively short follow-up in this group of patients, the mid- and long-term results and complications need further verification, despite the satisfactory short-term results revealed during follow-up. The number of patients was limited in this study, only 1 prosthesis model was used, and the same surgeon conducted the operations. Lastly, the study did not analyze the other factors (for instance, Q angle) relating with function recovery of the knee after TKA.

Conclusion

Patelloplasty is better than traditional patellar management at relieving pain, enhancing patient satisfaction, and improving function, indicating that patelloplasty is a proper approach in patellar nonresurfacing in TKA.