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Lateral meniscus extrusion on preoperative MRI and its impact upon mid-term clinical outcomes following mobile-bearing unicompartmental knee arthroplasty
⁎Corresponding author: Takafumi Hiranaka. Takafumi.hiranaka@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
The presence of full-thickness cartilage in the lateral compartment on valgus stress radiography is a criterion for medial mobile-bearing unicompartmental knee arthroplasty (UKA). However, the appropriateness of medial UKA is uncertain when preoperative MRI shows extrusion of the lateral meniscus. We therefore assessed how preoperative MRI-detected lateral meniscus extrusion affects mid-term functional outcomes after mobile-bearing UKA.
We retrospectively reviewed the records of our patients that underwent mobile-bearing medial UKA between January 2017 and December 2019. Crema's classification system was used to assess MRI of the lateral meniscus, categorizing patients as either grade 0 or ≥ grade 1. We preoperatively evaluated patient-reported outcomes using the Oxford knee score and Knee Society functional score, and then again at the latest follow-up. We also measured range of motion pre- and postoperatively. We compared preoperative individual data with outcome data obtained for at least three years.
The lateral meniscus extrusion group included 19 knees, and the remainder included 98 knees. Clinical outcomes were similar between these groups (p > 0.05). No progression of lateral arthritis was observed in either group during the follow-up period.
Excluding UKA as an option for cases with lateral meniscus extrusion findings on preoperative MRI may require reconsideration.
Keywords
Unicompartmental knee arthroplasty
Oxford mobile-bearing UKA
Lateral meniscus extrusion
MRI
1 Introduction
Oxford mobile-bearing unicompartmental knee arthroplasty (UKA) has shown excellent long-term clinical outcomes, characterized by quicker recovery and reduced mortality rates than total knee arthroplasty.1–4 Indications for Oxford UKA include anteromedial osteoarthritis or spontaneous osteonecrosis of the knee with full-thickness cartilage in the lateral compartment, absence of bone loss with grooving to the lateral patellar facet, and functionally normal anterior cruciate and medial collateral ligaments.5 Revision surgery is typically due to progression of osteoarthritis in the lateral compartment and aseptic loosening.6–8 Meanwhile, the preoperative Kellgren-Lawrence grade of the lateral compartment has been reported as a good predictor of postoperative progression of lateral osteoarthritis.9,10 Radiography with valgus stress should be used to determine the state of the lateral compartment.3 In cases with full-thickness lateral compartmental cartilage, lateral osteophytes were reported to have no impact upon long-term functional outcomes or implant survival.11 The clinical relevance of magnetic resonance imaging (MRI) to determine the surgical suitability of medial UKAs has been examined in preoperative MRI studies, but they perhaps overstate anterior cruciate ligament deficiency.10
MRI can also be used to evaluate the lateral meniscus, greatly influencing preoperative decisions for UKA if there is possibility of it affecting the clinical results. The mid-term functional outcomes of patients who received mobile-bearing medial UKA were reportedly not influenced by preoperative MRI-detected lateral meniscal degenerative changes.12,13 However, extrusion of the meniscus can apparently lead to knee osteoarthritis.14,15 Reduction in tibial plateau coverage results in elevated cartilage load bearing.16,17 This study therefore examines if extrusion of the lateral meniscus shown on preoperative MRI affects postoperative clinical outcomes in Oxford mobile-bearing UKAs.
2 Methods
2.1 Subjects and surgical procedures
This study was approved by our ethics committee (2023–29) and performed in accordance with the Declaration of Helsinki. All patients provided informed consent. This study included 117 knees in 93 patients who underwent Oxford mobile-bearing UKA at our hospital between January 2017 and December 2019, and who were followed up for at least three years postoperatively. The same experienced surgeon (T.H.) performed or supervised all procedures. Surgical indications for UKAs were similar to those previously reported. They included substantial pain and loss of function due to anteromedial osteoarthritis and spontaneous osteonecrosis of the knee with full-thickness lateral compartment articular cartilage and functionally normal anterior cruciate ligaments.
2.2 MRI, assessment and evaluation
Patients underwent preoperative 1.5 T MRI (Magnetom Aera, Siemens Medical Systems, Erlangen, Germany) with a knee coil and the leg in neutral flexion. The following sequences were recorded on coronal and sagittal views: proton density turbo spin echo fast suppression (240 × 320; thickness 3 mm; repeat time (TR) 4000 ms; echo time (TE) 12 ms); T1 (288 × 320; thickness 3 mm; TR 469 ms; TE 13 ms); and T2 (320 × 320; thickness 3 mm; TR 5000 ms; TE 97 ms). Two veteran orthopedic surgeons examined the MRI images, both of whom were blinded to the other examiners' MRI interpretations and clinical assessments. Results were discussed and confirmed in the event of non-consensus. Extrusion of the lateral meniscus was investigated using preoperative MRI.18 To determine extrusion of the lateral meniscal body we used coronal images. The edge of the tibial plateau was used as a reference for measuring the meniscal body extrusion, minus osteophytes. Grade 0 indicates no extrusion, grade 1 is the presence of extrusion ≤50 % of the body, and grade 2 indicates the presence of extrusion >50 % of the body (Figs. 1–3). Patients were stratified into either the ‘normal’ group or lateral meniscus extrusion group (grades 1–2) on an individual basis. To assess if postoperative clinical outcomes were affected by extrusion of the lateral meniscus on preoperative MRI, we compared pre- and postoperative data.
2.3 Clinical outcome
Height, weight, and BMI were recorded as patient-specific data. A goniometer was used to measure the knee range of motion (ROM). The Oxford Knee score (OKS), Knee Society score-functional (KSS-F), and ROM were evaluated as measures of clinical outcome preoperatively and more than 3 years postoperatively. In patients who underwent bilateral UKA and had different preoperative lateral meniscus statuses, comparisons of the clinical outcomes were incorporated as part of the lateral meniscus extrusion group.
2.4 Data analyses
The reliability of MRI for determining the grade of lateral meniscal extrusion was determined using Cohen's κ coefficient for categorical variables.19 We documented agreement/disagreement rates, representing the percentage of all interobserver comparisons with agreement/disagreement on a parameter. κ-Values were categorized according to Landis and Koch's classification as follows: 0–0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and 0.80–1.00, excellent agreement.20 We evaluated the rate of agreement or disagreement between the classifications of the normal and lateral meniscal extrusion groups.
All statistical analyses were conducted using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), that has been adapted to include commonly used biostatistical functions.21 Independent samples t-test was used to compare the groups. Fisher's exact test was used to compare the proportion of men between the two groups, p < 0.05 was considered to be statistically significant. The mean and standard deviation (SD) values of OKS, KSS-F, and ROM were utilized for both normal and lateral meniscus extrusion groups. Effect sizes were synthesized as standardized mean differences between the normal and lateral meniscus extrusion groups, correcting for the small sample size when necessary (Hedges' g).22 According to Cohen's guideline, the calculated effect sizes were interpreted as follows: small effect = 0.20, moderate effect = 0.50, and large effect ≥0.80 23.
3 Results
There were 98 knees in the normal group and 19 in the lateral meniscal extrusion group. In the lateral meniscus extrusion group, 18 knees were grade 1 and one knee was grade 2. There was substantial agreement between the two examiners in the classification of the normal and the lateral meniscus extrusion groups, as demonstrated by the κ-coefficient of 0.62. Seven patients who underwent bilateral UKA had lateral meniscus extrusion on one knee and a normal knee on the other side. One patient who underwent bilateral UKA had lateral meniscus extrusions in both knees. Preoperative demographic features and clinical measurements of the patients are shown in Table 1. There were no significant differences between the groups in sex, age, body mass index, preoperative femorotibial angle, OKS, KSS-F, or ROM. A comparison of the final clinical measurements is shown in Table 2. The mean postoperative OKS was not significantly different between the groups: 39.4 (SD 6.4) in the normal group and 36.0 (SD 9.9) in the lateral meniscus extrusion group (p = 0.073). The mean postoperative KSS-F was also not significantly different between the groups: was 80.5 (SD 18.5) in the normal group and 75.3 (SD 18.9) in the lateral meniscus extrusion group (p = 0.290, independent-samples t-test). Similarly, the mean postoperative ROM was not significantly different between the groups: 133.5° (SD 13.4°) in the normal group and 130.0° (SD 16.1°) in the lateral meniscal extrusion group (p = 0.313). The calculated Hedge's g was 0.48 for OKS, 0.28 for KSS-F, and 0.25 for ROM, indicating a small effect size. The presence of lateral meniscus extrusion is suggested to have had a minimal impact on clinical outcomes after UKA compared with the normal group. One knee in the normal group required revision to total knee arthroplasty due to infection within three years of the postoperative follow-up. No progression of lateral arthritis was observed in either group during the follow-up period.
| Normal | Extrusion | P-value | |
| Number (patient/knee), n | 75/98 | 18/19 | N/A |
| Sex (men/women), n | 20/55 | 2/16 | 0.224 |
| Mean age, yrs (SD) | 73.1(7.1) | 69.6(9.7) | 0.082 |
| Mean BMI, kg/m 2 (SD) | 25.6(4.0) | 26.4(2.7) | 0.449 |
| Mean OKS (SD) | 27.0(7.6) | 25.1(5.6) | 0.334 |
| Mean KSS-F (SD) | 61.8(20.5) | 59.2(19.3) | 0.618 |
| Mean ROM (SD) | 133.2(15.9) | 130.3(18.7) | 0.480 |
| Normal | Extrusion | P-value | |
| Mean OKS (SD) | 39.4(6.4) | 36.0(9.9) | 0.073 |
| Mean KSS-F (SD) | 80.5(18.5) | 75.3(18.9) | 0.290 |
| Mean ROM (SD) | 133.5(13.4) | 130.0(16.1) | 0.313 |
4 Discussion
The scores were equivalent preoperatively and at 3 years after UKA, suggesting no difference in clinical outcomes or knee function between the normal and lateral meniscus extrusion groups. Contraindication for UKA based on lateral meniscus extrusion. Meniscus extrusion has been acknowledged as an important pathological condition associated with meniscal dysfunction that leads to accelerated cartilage degeneration and early osteoarthritic changes.14,15 Meniscus extrusion can occur following meniscal tears such as radial and root tears. Risk factors for meniscal extrusion include high body mass index, increasing age, degenerative joint changes, female sex and knee malalignment,.18,24 Most studies on meniscus extrusion have focused on the medial meniscus, but some have recently discussed the impact of lateral meniscus extrusion on knee osteoarthritis.25 In asymptomatic middle-aged and older patients, lateral meniscal extrusion reportedly accelerated joint space loss and increased the risk of progression to the need for total knee arthroplasty within 9 years.25 The impact of lateral meniscal extrusion on postoperative clinical outcomes of UKA is being investigated here for the first time. Generally, anteromedial osteoarthritis of the knee is damaging to the medial compartment, but if left untreated, we suggest that damage can also occur in the lateral compartment due to changes in load bearing and inflammatory cytokine efflux from arthritis.26–28 Cases of lateral meniscus extrusion in anteromedial osteoarthritis of the knee indicate partial lateral compartment damage. However, the clinical outcomes between our normal and lateral meniscus extrusion groups were similar, suggesting the possibility of increasing the proportion of UKA surgical cases.
We found no instances of lateral arthritis progression, a common reason for revision after UKA.6 According to a 10-year survival study, the rate of revision surgery for lateral progression of arthritis was 36 %.29 Another study indicated that preoperative lateral compartmental degeneration predicts lateral progression.10 However, long-term functional outcomes or implant survival are unaffected by the presence of lateral osteophytes.11 Similarly, functional outcome in the mid-term is unaffected by lateral meniscus degeneration and injury.12,13 Progression of osteoarthritis in the lateral compartment may be caused by overcorrected lower-limb alignment.30 Even if the lateral meniscus is degenerated or extruded, progression of lateral osteoarthritis may be prevented if UKA is performed and pre-disease alignment is achieved with accuracy. A 4 % revision rate in one study with 15-year follow-up was said to be due to progression of lateral osteoarthritis.31 Surgeons may be hesitant to perform UKA because of the risk of revision for progression of lateral osteoarthritis, but the risk is not considered to be high. Performance of UKA in eligible patients reduces economic costs and improves knee function compared with total knee arthroplasty.4 We suggest that surgeons should increase the proportion of patients with UKA.
Limitations of this study include the follow-up duration being relatively short, with 3-years of follow-up being the shortest. Among the 52 revision cases in a previous study, 25 were due to lateral arthritis progression, with revisions occurring approximately 7 years post-initial surgery.6 Future investigations should incorporate long-term follow-up to explore the correlation between lateral meniscus extrusion and revision surgery. A second limitation of this study is that the sample size was relatively small. The reduced sensitivity of our study raises concerns regarding the possibility of overlooking clinically relevant effects. Furthermore, only one patient with lateral meniscus extrusion (grade 2 of Crema's classification) was included in this series, so it would be interesting to additionally assess the comparison of grades 0–1 vs. grade 2.
5 Conclusion
Even in cases where preoperative MRI reveals lateral meniscus extrusion, it may not have a discernible impact on clinical outcomes three years after UKA surgery. Exclusion of UKA as an option for cases with lateral meniscus extrusion findings on preoperative MRI may require reconsideration.
Informed consent
Informed consent was obtained from all of the patients.
Ethical statement
This retrospective study was performed in accordance with the Declaration of Helsinki and approved by the ethics coVmmittee of Takatsuki general hospital (Approval number 2023–29).
Author contribution
Yasuhiro Fukai collected the data. wrote first draft of the manuscript with support from Takafumi Hiranaka. Takafumi Hiranaka designed the study, the main conceptual ideas, and the proof outline. collected the data. supervised the project. Motoki Koide, aided in interpreting the result. Takaaki Fujishiro, aided in interpreting the result. Koji Okamoto aided in interpreting the result. All authors discussed the results, revised the draft, and approved the final manuscript.
Funding sources
No specific grant from public, commercial, or nonprofit funding agencies supported this research.
Funding statement
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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