Orthopedics

Feature Article 

Comparison Between the Attune and PFC Sigma in Total Knee Arthroplasty: No Difference in Patellar Clunk and Crepitus or Anterior Knee Pain

Dexter K. Bateman, MD; Jared S. Preston, MD, MBA; Steven Mennona, MD; Evan Gui, BA; Stephen Kayiaros, MD

Abstract

Patellar crepitus and clunk (PCC) is a known complication in total knee arthroplasty (TKA) and the cause of dissatisfaction. Patellofemoral articulations have reportedly been optimized in newer TKAs. This study compared the incidence of PCC between a historical and modern TKA design. A single-surgeon retrospective review of primary PFC Sigma (DePuy Synthes, Warsaw, Indiana) or Attune TKA (DePuy Synthes) was performed. A total of 114 PFC Sigma and 103 Attune implants were analyzed at a mean 3.2 years follow-up for overall PCC, painful PCC, anterior knee pain (regardless of crepitus), and PCC necessitating revision. Similar rates of overall PCC (14.6% vs 20.2%, P=.803), painful PCC (8.7% vs 6.1%, P=.605), and anterior knee pain (15.5% vs 9.7%, P=.219) were observed in the Attune and PFC Sigma groups, respectively. No clinically significant differences in range of motion, pain, or Knee Society Scores were found between groups. Subgroup analyses of mobile vs fixed bearing PFC Sigma implants demonstrated higher rates of overall PCC (32.4% vs 15.0%, P=.043), painful PCC (20.6% vs 5.0%, P=.016), anterior knee pain (17.6% vs 1.3%, P=.003), and crepitus requiring revision surgery (17.6% vs 1.3%, P=.003) for mobile bearing PFC Sigma implants. No difference was found in the rates of anterior knee pain or PCC between the PFC Sigma and Attune implants. Subgroup analysis suggests that a mobile bearing PFC Sigma implant results in higher PCC. The authors believe the true incidence of anterior knee pain and PCC is underreported in the literature because many outcome measures do not capture these complications. [Orthopedics. 2020;43(6):e508–e514.]

Abstract

Patellar crepitus and clunk (PCC) is a known complication in total knee arthroplasty (TKA) and the cause of dissatisfaction. Patellofemoral articulations have reportedly been optimized in newer TKAs. This study compared the incidence of PCC between a historical and modern TKA design. A single-surgeon retrospective review of primary PFC Sigma (DePuy Synthes, Warsaw, Indiana) or Attune TKA (DePuy Synthes) was performed. A total of 114 PFC Sigma and 103 Attune implants were analyzed at a mean 3.2 years follow-up for overall PCC, painful PCC, anterior knee pain (regardless of crepitus), and PCC necessitating revision. Similar rates of overall PCC (14.6% vs 20.2%, P=.803), painful PCC (8.7% vs 6.1%, P=.605), and anterior knee pain (15.5% vs 9.7%, P=.219) were observed in the Attune and PFC Sigma groups, respectively. No clinically significant differences in range of motion, pain, or Knee Society Scores were found between groups. Subgroup analyses of mobile vs fixed bearing PFC Sigma implants demonstrated higher rates of overall PCC (32.4% vs 15.0%, P=.043), painful PCC (20.6% vs 5.0%, P=.016), anterior knee pain (17.6% vs 1.3%, P=.003), and crepitus requiring revision surgery (17.6% vs 1.3%, P=.003) for mobile bearing PFC Sigma implants. No difference was found in the rates of anterior knee pain or PCC between the PFC Sigma and Attune implants. Subgroup analysis suggests that a mobile bearing PFC Sigma implant results in higher PCC. The authors believe the true incidence of anterior knee pain and PCC is underreported in the literature because many outcome measures do not capture these complications. [Orthopedics. 2020;43(6):e508–e514.]

Demand for total knee arthroplasty (TKA) continues to increase, with a recent projected volume of 1.26 million procedures per year by 2030.1 Posterior stabilized (PS) TKA implants have demonstrated good results, with survivorship greater than 94% at long-term follow-up.2 However, upward of 15% of patients remain unsatisfied postoperatively.3,4 Anterior knee pain, including patellofemoral joint symptoms and patellar clunk and crepitus (PCC), is one cause for dissatisfaction.

The etiology of PCC is thought to be due to fibrosynovial proliferation on the posterior aspect of the distal quadriceps tendon that becomes entrapped in the intercondylar box during knee flexion.5,6 Dennis et al7 noted that patients developed patellar crepitus at a mean interval of 10.9 months after primary TKA. However, prior studies report highly variable rates of PCC, and this complication may occur in up to 33% of PS TKA knees.8–11 Risk factors associated with increased rates of patellar crepitus include decreased patellar component size and thickness, patellar baja, increased posterior femoral condylar offset, use of smaller femoral components and thicker tibial polyethylene inserts, placement of the femoral component in a flexed posture, and anterior placement of the tibial tray.7,12–16 In addition, femoral component and patellofemoral designs have been identified as common factors associated with PCC.8 This has led major manufacturers and physicians to examine and refine modern TKA designs in an effort to improve patient functional outcomes and satisfaction.

Most changes in implant design have focused on modification of the trochlear aspect of the femoral component. Fukunaga et al8 described the transition zone from the trochlear groove to the intercondylar box as the intercondylar box ratio (intercondylar box height vs anteroposterior height of the femoral component). Femoral components with an increased intercondylar box ratio may permit contact between the distal quadriceps tendon and the anterior intercondylar box, leading to soft tissue irritation. Updated component designs with an intercondylar box ratio less than 0.7, in which the trochlear groove extends more distally and posteriorly, may have decreased rates of PCC.8,9,17 Reduction in the intercondylar box width, as well as improved patellar tracking with a deepened trochlear groove, may also reduce PCC.8,17–18

The purpose of this study was to compare the incidence of PCC between 2 different total knee implants from a single manufacturer: Attune (DePuy Synthes, Warsaw, Indiana), an updated design that incorporates the suggested trochlear and intercondylar box changes, vs PFC Sigma (DePuy Synthes), which has a previously reported incidence of patellar crepitus.11,15–20 The authors hypothesized that the patellofemoral design changes of the Attune TKA would result in lower rates of anterior knee pain and PCC. Secondary outcomes included postoperative knee range of motion (ROM), functional outcome scores, complications, and revisions.

Materials and Methods

Following institutional review board approval, a retrospective review of a single surgeon's (S.K.) database was performed to identify all patients who underwent primary PS TKA using either PFC Sigma or Attune implants from August 2012 to July 2016. A minimum of 1 year of follow-up was required for inclusion in this study. Revision surgeries were excluded.

All surgeries were performed by a single, high-volume, fellowship-trained arthroplasty surgeon (S.K.). Patients underwent either spinal or general anesthesia with peripheral nerve blocks. All patients received a periarticular injection. A standard midline incision with a medial parapatellar approach was used. A gap-balancing technique was used, and all components were cemented. A free-hand technique was used to resurface all patellae, and tracking was checked using the “no thumbs” method. Implant selection was at the discretion of the senior author (S.K.), with a general trend toward offering Attune and rotating platform PFC Sigma to younger patients because these implants contained vitamin E–infused highly cross-linked polyethylene (AOX; DePuy Synthes).

Patient demographic information, medical comorbidities, and surgical characteristics were extracted during chart review. Postoperative knee ROM was assessed in clinical follow-up by the senior author. Visual analog scale (VAS) score for pain, Knee Society Scores (KSS),21 complications, and secondary procedures, including manipulation under anesthesia, were recorded. Patients were queried at most recent follow-up or via phone interview for symptoms including PCC (defined as an audible clunk or crepitation during knee ROM) and anterior knee pain. The PCC was subdivided into overall PCC, painful PCC, anterior knee pain (regardless of crepitus), and PCC necessitating revision surgery. Subgroup analysis was performed to investigate the influence of sex, preoperative coronal alignment, and bearing type (mobile vs fixed) on anterior knee symptoms.

Statistical Analysis

Welch's t test was used to compare continuous variables. Fisher's exact test was used to compare categorical data. The alpha level for statistical significance for all tests was set at .05. Analyses were completed using Prism, version 7.0 (GraphPad, La Jolla, California).

Results

A total of 222 patients were identified who met inclusion criteria for the study. There were 98 patients who used Attune implants (Attune group; n=121 knees) and 124 patients who used PFC Sigma implants (PFC Sigma group; n=138 knees). Of these, 16 patients in the Attune group and 22 in the PFC Sigma group were deceased or lost to follow-up after multiple attempts to contact them. Therefore, the final groups consisted of 82 patients (103 knees) in the Attune group and 102 patients (114 knees) in the PFC Sigma group, with an overall mean±SD follow-up of 38.2±4.7 months (Table 1). All patients in the Attune group received fixed bearing components, whereas 34 (29.8%) patients in the Sigma group received mobile bearing components.

Patient Demographic and Surgical Characteristics

Table 1:

Patient Demographic and Surgical Characteristics

Demographics

Body mass index and American Society of Anesthesiologists scores were similar between the 2 cohorts. The Attune TKA group included fewer women (67.1% vs 80.4%, P=.043), who were significantly younger (61.3±7.9 vs 68.4±8.3 years, P<.001) and had shorter follow-up (32.2±10.1 vs 43.6±15.9 months, P<.001) compared with the PFC Sigma group. Preoperative coronal alignment was similar for the 2 groups (P=.345). Subgroup analysis of the PFC Sigma group revealed that the mobile bearing PFC Sigma implant was used in fewer women (47.1% vs 82.5%, P=.002), who were significantly younger (61.3±6.1 vs 70.7±7.6 years, P=.001), had longer follow-up (53.1±12.9 vs 39.7±15.4 months, P<.001), and were more likely to have varus preoperative alignment (91.2% vs 65%, P=.005) compared with the fixed bearing PFC Sigma implant. No radiographic loosening was seen in any group at final follow-up.

Range of Motion

Preoperative mean±SD ROM was similar between groups for flexion (Attune vs PFC Sigma group: 110.6°±10.9° vs 111.3°±11.9°, P=.653) and extension (Attune vs PFC Sigma group: 5.5°±3.4° vs 5.9°±3.7°, P=.415; Figure 1). At final follow-up, flexion and extension improved significantly from baseline for both groups (P<.001). No differences were noted in postoperative knee extension between the 2 groups (Attune vs PFC Sigma group: 0.4°±1.9° vs 0.7°±2.1°, P=.283). A nonsignificant trend toward greater postoperative flexion was observed with the Attune implant (123.9°±12.9° vs 120.7°±11.7°, P=.059).

Range of motion. Pre- and postoperative active knee range of motion for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Figure 1:

Range of motion. Pre- and postoperative active knee range of motion for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Knee Society and Visual Analog Scale Pain Scores

Preoperative mean±SD KSS scores were similar between groups (knee score: 38.7±11.4 vs 39.1±10.8, P=.765; function score: 41.2±11.9 vs 42.7±11.3, P=.332). Mean±SD KSS improved significantly from baseline for each cohort (P<.001; Figure 2). No significant differences in mean±SD KSS scores were observed at final follow-up (knee score: 79.3±8.9 vs 77.8±10.1, P=.221; function score: 95.1±15.7 vs 94.5±14.3, P=.799).

Knee Society Scores. Pre- and postoperative Knee Society Knee and Function scores for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Figure 2:

Knee Society Scores. Pre- and postoperative Knee Society Knee and Function scores for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Both groups experienced significant reduction in mean±SD VAS pain scores (P<.001), with no significant differences between the 2 groups at baseline (5.5±2.3 vs 5.7±2.2, P=.418) or final follow-up (2.5±2.2 vs 2.2±1.8, P=.238; Figure 3).

Visual analog scale (VAS) pain score. Pre- and postoperative Knee Society Knee and Function scores for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Figure 3:

Visual analog scale (VAS) pain score. Pre- and postoperative Knee Society Knee and Function scores for Attune (DePuy Synthes, Warsaw, Indiana) and Sigma TKA (DePuy Synthes). *Significant difference (P<.05).

Anterior Knee Pain and Patellar Clunk and Crepitus

Similar rates of overall PCC, painful PCC, and anterior knee pain (regardless of crepitus) were seen in the Attune and PFC Sigma groups: overall PCC (14.6% vs 20.2%, P=.803), painful PCC (8.7% vs 6.1%, P=.605), and anterior knee pain (15.5% vs 9.7%, P=.219; Table 2). Three (2.9%) patients with Attune implants and 7 (6.1%) with PFC Sigma implants underwent arthroscopic synovectomy for intractable painful PCC (P=.339). Three (2.9%) patients with Attune implants and 1 (0.09%) with a PFC Sigma implant underwent manipulation under anesthesia for arthrofibrosis (P=.348) at an average of 16.3 weeks. Prosthetic joint infection developed in 1 (1.0%) patient with an Attune implant and 2 (1.8%) with PFC Sigma implants (P=1.0), treated with irrigation and debridement (n=2) and 2-stage revision (n=1).

Anterior Knee Outcomes

Table 2:

Anterior Knee Outcomes

Subgroup Analysis

Subgroup analysis for patient sex or preoperative coronal alignment revealed no significant difference in the development of overall PCC, painful PCC, anterior knee pain, or operative PCC for either implant (Table 3). For the Sigma group, mobile bearing components were significantly associated with higher rates of overall PCC (32.4% vs 15.0%, P=.043), painful PCC (20.6% vs 5.0%, P=.016), anterior knee pain (17.6% vs 1.3%, P=.003), and PCC requiring a return trip to the operating room (17.6% vs 1.3%, P=.003).

Subgroup Analyses

Table 3:

Subgroup Analyses

Discussion

Excellent long-term outcomes have been obtained in patients undergoing PS TKA.22 However, patellofemoral symptoms, including PCC and anterior knee pain, can develop in a subset of patients, which has been reported as high as 33%, depending on the implant evaluated.8–10

Patellar clunk, thought to be caused by impingement of fibrous overgrowth at the superior patellar pole, typically describes painful catching of the patella while the knee is extended.5–8,12,16 Patellar crepitus refers to a clicking, popping, grinding, or snapping phenomenon during knee motion that may be audible, experienced by the patient during motion, or solely detected by the examiner.7,9,14–20 Symptoms range from painful to asymptomatic and have been reported using inconsistent terminology in previous literature regarding PS TKA.5–20 Asymptomatic crepitation may not represent a clinically significant complication but still may be associated with higher patient dissatisfaction.10,11,16,23 Recently, the combination of mechanical patellofemoral symptoms has been grouped in PCC.13,20

To address the risk of PCC, the Attune design has features that were incorporated specifically to address patellofemoral symptoms, including a lower intercondylar box height ratio (<0.7) and a thinner and narrower anterior trochlear flange of the femoral component compared with the PFC Sigma design.18 These changes were hypothesized to reduce overall extensor mechanism and retinacular tension, which leads to reduced quadriceps tendon-femoral contact and pressure in the transition region between the trochlea and intercondylar box. Overall, these changes decreased the risk of tendon irritation and subsequent fibrosynovial proliferation on the posterior aspect of the distal quadriceps tendon.17,18

The results of this study do not align with several previously published reports on these particular implants. The authors' reported rates for overall PCC for the Attune and PFC Sigma implants (14.6% vs 20.2%), painful PCC (8.7% vs 6.1%), anterior knee pain (15.5% vs 9.7%), and operative PCC (2.9% vs 6.1%) were similar between implants and much higher than previously reported rates.11,15–20 In a larger cohort of patients using the same implants, Martin et al18 found a significantly lower incidence of crepitus in participants implanted with the Attune vs PFC Sigma designs at 1 year (0.55% vs 6.26%, P<.001) and 2 years (0.83% vs 9.4%, P<.001) postoperatively. When reviewing mobile vs fixed bearing Attune designs, those authors found no difference in PCC incidence.18

Indelli et al19 also examined outcomes between the fixed bearing PFC Sigma and Attune implants. In their retrospective review, they found significantly higher rates of mild anterior knee pain in the PFC Sigma group (9%) vs the Attune group (2%). Severe painful patellofemoral crepitations were also significantly more common in the PFC Sigma vs Attune group (5% vs 1%). Final mean ROM was significantly better for Attune (123° vs 115°) compared with PFC Sigma. No differences in functional outcome scores were reported.19

Ranawat et al11 evaluated the clinical outcomes of the Attune and PFC Sigma implants at 2 years of follow-up in 200 patients using a prospective matched-pair analysis. No significant differences were reported in KSS pain and functional outcomes or overall satisfaction scores. The incidence of anterior knee pain (25.8% vs 12.5%, P=.02) and mechanical crepitation (30.9% vs 17.7%, P=.02) was significantly higher in the PFC Sigma group. The incidence of painful PCC was similar between groups (4.1% vs 1.0%, P=.37).11

Previous investigations have reported mixed results regarding higher rates of PCC in rotating platform PS TKA designs. In a mid- to long-term follow-up of a rotating high-flex (PFC Sigma RP-F; DePuy Synthes) vs fixed bearing PS TKA design (Scorpio NRG; Stryker, Mahwah, New Jersey), Snir et al16 found that patellar clunk developed in 22 (11.7%) knees in the mobile bearing group and in 4 (1.8%) knees in the fixed bearing group (P<.001). A total of 23 (85%) of 26 cases resolved with a single arthroscopic treatment and 2 (7.7%) more cases resolved with a second arthroscopic procedure. In addition, final postoperative ROM for resolved cases of patellar clunk syndrome did not differ significantly from postoperative ROM for TKAs without clunk syndrome.16

In a review of 826 PS TKAs involving 5 designs, Choi et al20 found that the PCC incidence was higher in the PFC Sigma rotating platform (11 of 113 knees, 9.7%) than in the others (7 of 713 knees, 1.0%). Similarly, Ranawat et al23 reported a significantly lower incidence of PCC in the fixed bearing PFC Sigma (1.5%) compared with the rotating platform (12%). Because the femoral component is identical for both articulations, it is reasonable to suggest the bearing type may influence the development of PCC. However, other reports have not found a significant relationship between mobile bearings and PCC, and the impact of the bearing surface has not been fully elucidated.8,11,18,24

Contrary to most previous studies, the current study reported a much higher overall incidence of PCC and anterior knee pain, regardless of implant. The authors hypothesize 2 factors to explain their findings. First, because patients were directly queried in follow-up about anterior knee pain and PCC, this introduced recall bias. Second, popular outcome measures, such as the KSS and Oxford Knee Score, do not adequately capture patellofemoral symptoms. Questions regarding maneuvering stairs or kneeling can allude to patellofemoral complaints, but the value of these functional issues is ultimately lost among the gamut of questioning. Thus, anterior knee pain and PCC may be missed in pure chart review series, leading to an under-reporting of these complications.

Previous retrospective studies have not contacted patients to specifically ask about PCC and have only reported incidences based on chart review18,19 or painful crepitus.20 The overall incidence of anterior knee pain and PCC in the current study is most similar to the values reported by Ranawat et al,11 who used a specific questionnaire to elicit the presence of anterior knee pain and mechanical crepitation. The current authors believe the true incidence of anterior knee pain and PCC to be much higher than is commonly reported in the literature.

The authors note several limitations of the current analysis. First, the study was a small, retrospective review of patients and, therefore, suffers the inherent limitations of retrospective analyses. Second, the limited sample size may be underpowered to demonstrate a true statistical difference in the incidence of anterior knee pain and PCC between groups. However, the findings echo those of Ranawat et al11 in that the true incidence of these complaints is likely higher than many previous reports and is not fully captured by commonly used outcome measures.

The authors did not perform radiographic analysis to evaluate component positioning and its relation to PCC. In addition, there was no randomization protocol to determine implant selection, which was determined solely based on surgeon discretion, introducing the possibility of selection bias. Attune and mobile bearing PFC components were implanted in significantly younger patients, who may experience higher rates of residual knee symptoms compared with older patients, potentially accounting for some aspect of the authors' results.25

Finally, although the follow-up duration for the PFC Sigma group was longer due to chronologically earlier implantation, the authors believe that the follow-up duration of the Attune group was adequate to accurately capture the incidence of PCC. Previous analyses of PS TKAs showed that the mean time for the diagnosis of patellar crepitus was within the first postoperative year.7,20

Conclusion

Despite previously reported data, the current study shows that there was no difference in the rate of anterior knee pain, patellar clunk, or crepitus between the PFC Sigma and Attune implants. However, given the overall higher rate of PCC in both implants, the authors believe there may be confounding variables to consider because many outcome measures do not capture anterior knee pain or PCC. This subgroup analysis suggests the use of mobile bearing articulation in the PFC Sigma PS TKA may result in higher PCC. More research is still needed to clarify whether component design can improve anterior knee pain and PCC, and thus improve outcomes.

References

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  10. Pritchett JW. A comparison of the noise generated from different types of knee prostheses. J Knee Surg. 2013;26(2):101–104. PMID:23288762
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  23. Ranawat AS, Ranawat CS, Slamin JE, Dennis DA. Patellar crepitation in the P.F.C. Sigma total knee system. Orthopedics. 2006;29(9) (suppl):S68–S70. PMID:17002154
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  25. Parvizi J, Nunley RM, Berend KR, et al. High level of residual symptoms in young patients after total knee arthroplasty. Clin Orthop Relat Res. 2014;472(1):133–137. doi:10.1007/s11999-013-3229-7 [CrossRef] PMID:24061845

Patient Demographic and Surgical Characteristics

CharacteristicAttuneaSigmaaPbPc

TotalFixedMobile
TKA, No.1031148034
Sex, male/female, No.27/5532/8214/6618/16.043.002
Follow-up, mean±SD (range), mo32.2±10.1 (12–54)43.6±15.9 (12–68)39.7±15.4 (12–68)53.1±12.9 (15–66)<.001<.001
Age, mean±SD, y61.3±7.968.4±8.370.7±7.661.3±6.1<.001.001
BMI, mean±SD, kg/m231.6±5.430.3±5.030.1±5.130.5±5.2.069.705
ASA score, mean±SD2.2±0.42.4±0.52.4±0.52.3±0.6.001.391
Preoperative alignment, varus/valgus, No.81/2283/3152/2831/3.345.005

Anterior Knee Outcomes

CharacteristicNo.P

AttuneaPFC Sigmaa
Total knee arthroplasty103114
Overall PCC15 (14.6%)23 (20.2%).803
Anterior knee pain16 (15.5%)11 (9.7%).219
Painful PCC9 (8.7%)7 (6.1%).605
Operative crepitus3 (2.9%)7 (6.1%).339

Subgroup Analyses

DesignNo.No. Overall PCCPNo Anterior Knee PainPNo. Painful PCCPNo. Operative PCCP
Attunea
  M485 (10.4%).4025 (10.4%).2783 (6.3%).4911 (2.1%).989
  F5510 (18.2%)11 (20%)6 (10.9%)2 (3.6%)
  Varus8110 (12.4%).30412 (14.8%).7527 (8.6%).9022 (2.5%).523
  Valgus225 (22.7%)4 (18.2%)2 (9.1%)1 (4.5%)
  Fixed10315 (14.6%)16 (15.5%)9 (8.7%)3 (2.9%)
  Mobile00000
PFC Sigmaa
  M325 (15.6%).6053 (9.4%).9892 (6.3%).9912 (6.3%).989
  F8218 (22%)8 (9.8%)5 (6.1%)5 (6.1%)
  Varus8318 (21.7%).60710 (12%).2817 (8.4%).1896 (7.2%).667
  Valgus315 (16.1%)1 (3.2%)0 (0%)1 (3.2%)
  Fixed8012 (15%).0434 (5%).0161 (1.3%).0031 (1.3%).003
  Mobile3411 (32.4%)7 (20.6%)6 (17.6%)6 (17.6%)
Authors

The authors are from the Department of Orthopaedic Surgery (DKB, JSP, SM, EG, SK), Rutgers Robert Wood Johnson Medical School, and University Orthopaedic Associates (SK), New Brunswick, New Jersey.

Dr Bateman, Dr Preston, Dr Mennona, and Mr Gui have no relevant financial relationships to disclose. Dr Kayiaros is an unpaid consultant for DePuy Synthes Orthopaedics.

Correspondence should be addressed to: Dexter K. Bateman, MD, Department of Orthopaedic Surgery, Rutgers Robert Wood Johnson Medical School, 1 RWJ Place, MEB 422A, New Brunswick, NJ 08901 (dexterbateman@gmail.com).

Received: June 24, 2019
Accepted: August 05, 2019
Posted Online: August 20, 2020

10.3928/01477447-20200812-05

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