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50 (); 65-69
doi:
10.1016/j.jor.2023.11.076

Cementless medial pivot design demonstrates equal or better outcomes compared to cementless cruciate-retaining design following total knee arthroplasty

, , , , , , ,
Lifebridge Health, Sinai Hospital of Baltimore, Rubin Institute for Advanced Orthopedics, Baltimore, MD, USA

∗Corresponding author: James Nace. jnace@lifebridgeheath.org

Received: , Accepted: ,
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

Traditional total knee arthroplasty (TKA) designs fail to reproduce physiologic knee kinematics, which can contribute to patient dissatisfaction. In an attempt to restore more normal knee kinematics, the medial pivot (MP) design may improve knee function and stability as well as patient satisfaction. A limited number of studies have compared postoperative outcomes of exclusively cementless Cruciate-Retaining (CR) TKAs to cementless MP TKAs. We aimed to compare: (1) 90-day, 1-year, and 2-year complications and revisions, (2) preoperative and postoperative range of motion (ROM), (3) Knee Injury and Osteoarthritis Outcome (KOOS-JR), and (4) visual analog scale (VAS) pain scores at 3-month, 6-month, 1-year, and 2-years.

A retrospective analysis was performed to identify all patients who had previously undergone a TKA at our institution and compare a cementless CR system to a cementless MP design. Categorical variables, including demographics, comorbidities, and complications utilized Chi-square tests in bivariable analysis. Continuous variables, such as age, were compared using Student's t-tests. Significance was defined as p < 0.05.

Cementless CR and cementless MP cohorts showed low profiles of postoperative complications and favorable patient-reported outcome measures (PROMs). The MP cohort had lower VAS pain at 1-year (1.70 vs. 3.76, p < 0.001) and 2-years (1.43 vs. 2.60, p < 0.001) and higher ROM at 3-months (118 vs. 100, p < 0.001), 6-months (113 vs. 103, p < 0.0001), and 1-year (117 vs. 110, p = 0.02), respectively.

This study is the first comparison of postoperative outcomes between a cementless CR TKA and cementless MP TKA designs. Implant design and fixation type are vital components influencing patient satisfaction after TKA. Pain scores and range of motion favored the cementless MP cohort in comparison to the cementless CR cohort.

1

1 Introduction

Patient satisfaction following total knee arthroplasty (TKA) has ranged from 75% to 92%.1 Patients expect significant pain relief, improved knee mobility, and the ability to resume their occupational and recreational activities.2–4 Several factors, such as prosthesis design, preoperative function, baseline pain levels, fulfillment of expectations, fixation methods, and component alignment have been associated with postoperative dissatisfaction and pain after TKA.5,6

Patient dissatisfaction may be a result of the failure of traditional TKA designs to reproduce physiologic knee kinematics.7,8 One meta-analysis of eight randomized controlled studies comprised of 888 patients found no difference between CR and PS knees, in terms of knee society function score, postoperative knee pain, and other complications at 5-years follow-up.9 The medial pivot (MP) design theoretically produces medial congruency and stability along with some lateral slide to facilitate more normal kinematics.10 The theoretical benefits of the design include improved knee function, stability through a full arc of motion including deep flexion, and improved patient satisfaction.10

Most of the literature has focused on comparisons of postoperative outcomes between PS to MP TKAs.11–14 A limited number of studies have compared postoperative outcomes of CR to MP TKAs. The studies evaluating CR and MP TKAs showed some differences in terms of clinical, radiographic, and functional outcomes between the designs.15,16 However, these studies utilized mostly cemented fixation in each cohort, minimizing the applicability of the findings to modern practice with increasing use of cementless fixation.15,16 Cementless TKA offers an alternative to standard cemented procedures and attempts to achieve a physiological bond between the bone and implant.17 In a prospective, randomized study, Fricka et al. showed similar satisfaction scores, pain, and function at 2-years between 100 patients undergoing cemented TKAs and 100 patients undergoing cementless TKAs.18

To our knowledge, this is the first study to compare short-term outcomes of exclusively cementless CR to MP cementless TKAs. We aimed to compare: (1) complications and revisions at 90-days, 1-year, and 2-years; (2) preoperative and postoperative range of motion (ROM), (3) Knee Injury and Osteoarthritis Outcome (KOOS-JR), and (4) visual analog scale (VAS) pain scores at 3-month, 6-month, 1-year, and 2-years.

2

2 Methods

After obtaining Institutional Review Board approval, a retrospective analyses was performed to identify all patients who had previously undergone a primary total knee arthroplasty (TKA) at our institution with a cementless second-generation medial-pivot system (EVOLUTION, MicroPort Orthopaedics Inc., Arlington, TN, USA) between December 1st, 2019 to March 31, 2021 and the cementless cruciate retaining design (Triathlon Total Knee System, Stryker Orthopaedics, Mahwah, New Jersey) between October 5th, 2017 and December 23rd, 2019.

2.1

2.1 Patient selection

We reviewed a consecutive series of patients at a single institution by a single surgeon who performed total knee arthroplasty with either a medial-pivot design (MP) or a cementless cruciate retaining design (CR) from 2017 to 2021. Selection of patients was chosen based on an exclusive transition to MP that occurred from CR to MP in 2019, which resulted from improved clinical results in the MP group. Exclusion criteria included, severe osteoporosis or chronic steroid use making cementless fixation less than ideal.

2.2

2.2 Variables of interest

Knee Injury and Osteoarthritis Outcome (KOOS-JR), visual analog scores (VAS) scores and range of motion (ROM) measurements were collected preoperatively, and postoperatively at the three-month, six-month, and one-year time points. Dependent variable in this study included: age, sex, laterally, alcohol abuse, tobacco use, aseptic loosening, periprosthetic joint infection, surgical site infection (SSI), aseptic loosening, dislocations, pulmonary embolism (PE), periprosthetic fracture (PPFx) and revisions.

2.3

2.3 Statistical analyses

Pearson chi-square tests were utilized to analyze demographics, comorbidities, and complications in bivariate analysis. Continuous variables, such as age, were compared using Student's t-tests. R Studio (Statistics Department of the University of Auckland, New Zealand) was utilized in all analyses with significance defined as p < 0.05.

2.4

2.4 Patient demographics

A total of 123 (69 medial pivot, 54 cruciate retaining) patients who underwent primary TKA between October 5, 2017, and December 23, 2021 were identified. The mean age was 62 (range, 44 to 82) in the medial pivot group, while it was 64 (range, 43 to 77) in the cruciate-retaining cohort. There was a higher incidence of women (69%) in the cementless medial pivot design and in the cruciate retaining design (66%) cohorts, which represented no significant difference (p = 0.761). There was no difference in tobacco use (37.7 versus 35.2%), HTN (63.7 versus 44.4%), CHF (4.4 versus 1.9%) and CKD (4.3 versus 0.0%) in the cementless medial pivot design cohort than cementless cruciate retaining TKA cohort, respectively (See Table 1).

Table 1 Demographics and baseline characteristics.
Variable Medial Pivot Cementless (n = 69) Cruciate Retaining Cementless (n = 54)
n % n %
Age (years) 62 64
Laterality
Left Knee 32 46.4 28 51.9
Right Knee 37 53.6 26 48.2
Gender 0.761
Women 37 68.5 29 65.9
Men 17 31.5 15 34.1
Race
American Indian or Alaska Native 0 0.0 0 0.0
Asian 3 5.6 0 0.0
Black or African American 33 61.1 21 47.7
White 16 29.6 22 50.0
Native Hawaiian, Other Pacific Islander 1 1.9 0 0.0
Declined To Answer 1 1.9 0 0.0
Multiple 0 0.0 1 2.2
Alcohol Use 31 44.9 33 61.1 0.076
Tobacco Users 26 37.7 19 35.2 0.776
Substance Abuse 7 10.1 9 16.7 0.282
COPD 4 5.8 0 0.0 0.073
CHF 3 4.4 1 1.9 0.443
HTN 44 63.7 24 44.4 0.033
CKD 3 4.3 0 0.0 0.125
ASA Class
1 0 0.0 3 5.5
2 39 56.5 27 50.0
3 29 42.0 24 44.4
4 1 1.5 0 0.0
3

3 Results

3.1

3.1 Patient-Reported Outcomes Measure (PROMS)- visual analog scale (VAS)

Compared to preoperative scores, all visual analog scale (VAS) scores were improved by 3-months and continued to improve at 1- and 2-years in both cohorts. However, patients who received the medial pivot implant reported improved scores compared to those who have the cruciate retaining implants (See Table 2). Specifically, 1-year mean VAS pain scores for the cruciate retaining implant was 3.76 (range, 0 to 10) compared to 1.70 (range, 0 to 10) in patient who received the medial pivot implant, p < 0.001.

Table 2 Outcomes and complications.
Variable Medial Pivot Cementless (n = 69) Cruciate Retaining Cementless (n = 54) p-value
n % n %
90-day Complications
Totals 0 0.0 0 0.0 0.962
PJI 0 0.0 0 0.0
SSI 0 0.0 0 0.0
Aseptic Loosening 0 0.0 0 0.0
Dislocations 0 0.0 0 0.0
PE 0 0.0 0 0.0
PPFx 0 0.0 0 0.0
Revision 0 0.0 0 0.0 0.962
1-year Complications
Totals 0 0.0 0 0.0 0.962
PJI 0 0.0 0 0.0
SSI 0 0.0 0 0.0
Aseptic Loosening 0 0.0 0 0.0
Dislocations 0 0.0 0 0.0
PE 0 0.0 0 0.0
PPFx 0 0.0 0 0.0
Revision 0 0.0 0 0.0 0.962
2-year Complications
Totals 0 1.4 0 1.9 0.962
PJI 1 1.4 0 0.0
SSI 0 0.0 0 0.0
Aseptic Loosening 0 0.0 1 1.9
Dislocations 0 0.0 0 0.0
PE 0 0.0 0 0.0
PPFx 0 0.0 0 0.0
Revision 0 0.0 0 0.0 0.962
3.2

3.2 Range of motion

At the two-year mark, the medial pivot cohort had increased range of motion at 3 months (118 vs. 100, p < 0.001), 6-month (113 vs. 103, p < 0.001), and 1-year (117 vs. 110, p = 0.02) between the MP and CR designs, respectively. (See Table 3).

Table 3 Mean VAS and ROM.
Medial Pivot Cementless Cruciate Retaining Cementless P-value
VAS
Preoperative 6.72 (0–10) 6.50 (0–10) 0.65
Postoperative 7.21 (0–10) 7.43 (0–10) 0.66
3 months 3.16 (0–10) 4.73 (0–10) 0.07
6 months 2.88 (0–10) 4.12 (0–10) 0.03
1 year 1.70 (0–10) 3.76 (0–10) <0.001
2 years 1.43 (0–10) 2.60 (0–10) <0.001
ROM
Preoperative 2 to 113 (0–120) 3 to 116 (0–130) NS
Postoperative 1 to 94 (0–130) 2 to 91 (0–120) NS
3 months 1 to 118 (0–120) 5 to 100 (0–130) 0.04
6 months 2 to 113 (0–130) 5 to 103 (0–130) 0.03
1 year 0 to 117 (0–130) 1 to 110 (0–130) 0.05
2 years 0 to 120 (0–130) 0 to 115 (0–130) NS

Patient-Reported Outcomes Measure (PROMS) – Knee Injury and Osteoarthritis Outcome Score (KOOS-JR):

KOOS-Jr scores in the cruciate retaining cohort demonstrated moderate improvement from preoperative to two-years postoperatively. Specifically, scores preoperatively (mean ± SD: 26 ± 8 points) improved at 3-months (mean ± SD: 43 ± 10 points), 6-months (mean ± SD: 55 ± 11 points), 1-year (mean ± SD: 60 ± 8 points), and at 2-years postoperatively (mean ± SD: 66 ± 12 points) (See Table 4).

Table 4 KOOS-JR scores.
KOOS-JR Pre-op Post-op 3-month 6-month 1-year 2-year
Mean ± SD Range Mean ± SD Range Mean ± SD Range Mean ± SD Range Mean ± SD Range Mean ± SD Range
MP 27 ± 9 0 to 37 30 ± 10 14 to 77 49 ± 11 36 to 77 62 ± 9 38 to 92 69 ± 9 41 to 100 71 ± 10 58 to 100
CR 26 ± 8 0 to 55 30 ± 12 18 to 68 43 ± 10 28 to 75 55 ± 11 32 to 89 60 ± 8 40 to 100 66 ± 12 53 to 100
P-Value 0.85 0.76 0.04 0.04 0.03

However, KOOS-Jr scores in the medial pivot cohort had an increased improvement from preoperative to 3-months postoperative and maintained to be improved at 6 months to two-years postoperatively. Specifically, scores preoperatively (mean ± SD: 27 ± 9 points) improved at 3-months (mean ± SD: 49 ± 11 points), 6-months (mean ± SD: 62 ± 9 points), 1-year (mean ± SD: 69 ± 9 points), and at 2-years postoperatively (mean ± SD: 71 ± 10 points). At 3-month (49 vs. 43, p = 0.04), 6-month (62 vs. 55, p = 0.03), 1-year (69 vs. 60, p = 0.02), and 2-years (71 vs. 66, p = 0.03), MP cohort had better KOOS-Jr in comparison to the CR cohort, respectively (See Table 4).

When evaluating the differences in improvement between the cementless medial pivot and cruciate retaining cohort, there was no significant difference in the changes from preoperative KOOS-JR scores to the 3-month, 6-month, 1-year and 2 –year scores. However, patients in the medial pivot group had higher differences with p-values approaching significance at the 1-year time point (See Table 5).

Table 5 KOOS.
Medial Pivot Cementless Cruciate Retaining Cementless p-value
KOOS
Preoperative 26.79 25.49 0.173
Change from preoperative to Postoperative +3.64 +4.30 0.656
Change from preoperative to 3 months +22.35 +17.79 0.328
Change from preoperative to 6 months +37.17 +29.17 0.103
Change from preoperative to 1 year +41.92 +35.29 0.075
Change from preoperative to 2 year +47.54 +40.02 0.231
3.3

3.3 Postoperative complications between cementless medial pivot and cruciate retaining TKA

Revision rates of the cementless medial pivot design and cruciate retaining design demonstrated no significant differences at the 90-day (0.0 versus 0.0%, p = 0.962), one-year (0.0 versus 0.0%, p = 0.962), and two-years (1.4 versus 1.9%, p = 0.461) time points, respectively. There were one periprosthetic joint infection that was effectively resolved in the MP cohort using the 1.5-stage exchange technique.19 There was also one case of aseptic loosening in the CR cohort that was successfully treated with a revision TKA.

4

4 Discussion

Despite improvements in implant design and longevity, as many as 20% of patients remain unsatisfied by the outcome of their primary TKA.20 Various contributing factors to dissatisfaction include: postoperative function, pain levels, fulfillment of expectations, prosthesis design, fixation methods, and component alignment.5,21 The recent resurgence of the MP design has brought the hope of decreasing patient dissatisfaction and restoring more normal knee kinematics. Cementless designs have garnered more recent attention with promising long-term survival outcomes.22,23 Subsequently, this study highlights the potential benefits of combining both MP and cementless designs. Our principal findings were the cementless CR and cementless MP cohorts showed low profiles of postoperative complications and revisions and improvements in patient-reported outcome measures (PROMs), including ROM, KOOS-JR, and VAS pain scores at minimal 1-year follow up. Pain scores and range of motion favored the cementless MP cohort.

We acknowledge limitations in the study. This is a retrospective study of consecutive patients at a single institution with a single surgeon. There were 10 patients lost to follow-up (5.0%) at 2-year follow-up. The same surgical technique and postoperative pain and rehabilitation protocols were utilized in each cohort. The minimal clinical important difference (MCID) was not considered for ROM, KOOS-JR or VAS pain scores. Kunze et al. determined the patient acceptable symptom state for KOOS-JR at 2-years was 63.7.24 In our study, the KOOS-JR of the CR and MP cohorts were 66 and 71 at 2-years, far surpassing the limit set in the literature showing clinical significance as well as statistical significance. This was the first study to compare postoperative outcomes of exclusively cementless CR to cementless MP TKAs.

Only a few studies have directly compared postoperative outcomes between CR and MP TKA designs. Giustra et al. examined 29 CR TKAs and 35 MP TKAs and found similar Knee Society Score (KSS), ROM, Forgotten Joint Score (FJS), and low complication rates in both cohorts at an average follow-up of 28.9 months. The authors showed a slight trend towards better clinical outcomes with the MP design than the CR design, in terms of KSS, knee (96.7 vs. 93.1, p = 0.34) and function score (93.2 vs. 89.9, p = 0.29) and FJS (59.5 vs. 55.7, p = 0.064), respectively. The authors did not make note of fixation type utilized in the study.16 Utilizing Australian and Norwegian databases, Øhrn et al. examined patients undergoing CR TKA and patients undergoing MP TKA. The authors demonstrated low revision rates in all cohorts, 3% and 2% for CR and 6% and 2% for Norway and Australia, respectively. In Norway, all implants had cemented femoral components, while in Australia, 345 (0.7%) had cementless femoral components.15 This is in comparison to our analysis, which solely used cementless fixation in all 123 cases of primary TKAs.

Previous studies have showed similar findings, in regard to low MP TKA postoperative complication profiles and favorable PROMs. At an average follow-up of five-years, the outcome of 1167 MP TKAs reported an average revision rate due to aseptic loosening of 0.2%, an average survival rate of 98.8%, and an average ROM of 119.1.10,25–28 We found comparable results of an aseptic loosening rate of 0%, a revision rate of 5.8%, and an average ROM of 120 at 2-years follow-up. These studies did not include a control group and were mostly cemented designs.25–28 Only two of the five studies reported on PROMs but did not include KOOS-JR or VAS Pain. The MCID for TKA in the literature for KOOS-Jr ranged from 2.21 to 8.16, which is consistent with our finding of 4.30 from preoperative to postoperative in the MP cohort.23 Danoff et al. showed the MCID for VAS pain for TKA was 1.61, which both cohorts achieved as early as 3-months postoperatively (See Table 3).29 In terms of patient satisfaction, Van Overschelde et al. reported an overall very satisfied/satisfied rate of 94.6% at 2 months with satisfactory KOOS, ROM, pain scores, and radiographic outcomes for a second generation medial-pivot system.30

The favorable PROMs in this study may be attributable to design changes. Ueyama et al. compared the second-generation of the medial pivot design, which was solely utilized in the MP cohort in this study, to the first generation of the same company. The improvements in the second-generation design were marked by a tibial tray change to an asymmetric design, enlarged range of single radius of the femoral component, and decreased overhang of the posterior condyle. Design improvements were shown to provide greater postoperative knee flexion and patient satisfaction at 5-year follow-up.31 These findings are supported by fluoroscopic analyses that demonstrate the stability of the medial condyle during kneeling, pivoting, and squatting that prevents the paradoxical anterior femoral shift of other designs.32 In addition, the morphology of the polyethylene insert offers stability through a full arc of motion in the MP design, which may explain why patients with PS or CR TKAs experience pain and discomfort despite balanced components. Interestingly, one systematic review and meta-analysis comparing 26 studies of 2,369 patients in cementless and 2,654 patients in cemented TKA showed better functional recovery in the cementless group at a mean follow-up of greater than 5-years. The authors reported significantly better Knee Society Function Score (p = 0.0004) and lower manipulation under anesthesia (p = 0.007) in the cementless cohort.33 The combined benefit of both the MP design and cementless fixation type in improving functional outcomes and survival warrants further investigation.

To our knowledge, our study is the first comparison of postoperative outcomes between a cementless CR TKA and a cementless MP TKA designs. The findings show low complication rates and improvements in PROMs between the cohorts. Pain scores and range of motion favored the cementless MP cohort in comparison to the cementless CR cohort. Implant design and fixation type may play a vital role influencing patient satisfaction after TKA. With the resurgence of the MP designs and the increasing popularity of cementless fixation, this paper adds value when deciding on implant choices.

Authors’ contribution

ZC- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.

SB- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.

JD- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.

DH- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Roles/Writing - original draft; and Writing - review & editing.

RM- Writing - review & editing.

RG- Writing - review & editing.

RD- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Visualization; Roles/Writing - original draft; and Writing - review & editing.

JN- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Visualization; Roles/Writing - original draft; and Writing - review & editing.

Use of AI tool- No use of AI tool.

Funding

None.

Data availability

Available in a respository upon request.

Patient consent

Patient consent was not needed for this study.

Ethical approval

IRB exemption due to retrospective nature and public database.

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