1 Introduction

The importance of the menisci in optimal knee health and function is well established, providing a critical role in knee joint stability, load transmission and shock absorption, joint lubrication, proprioception and cartilage nutrition.^1–5 There is a risk of long-term joint degeneration as a result of meniscal resection,⁶ with improved outcomes with repair versus meniscectomy in the context of symptomatic meniscal tears.^7,8 Therefore, there has been a growing trend towards meniscal preservation surgery for symptomatic meniscal tears.⁹

After isolated meniscal repair, studies have generally reported good clinical outcomes and return to sport (RTS) rates.^10–12 While many of these studies have explored outcomes in adults, outcomes in paediatric patients are less reported. While a systematic review published in 2019 reported improved clinical outcomes and a low failure rate after meniscal repair in a paediatric and adolescent population,¹³ with 52 % of meniscal repairs undertaken concomitantly with anterior cruciate ligament reconstruction (ACLR), it has been reported that failure rates are higher in children and adolescents, compared with adults, in long-term studies reporting on meniscal repair outcomes.¹² It should be noted that most of these included studies are retrospective in nature, only report on patient-reported outcome measures (PROMs) with no relevant objective measures of lower limb strength or function, employ PROMs that were designed for an adult (and not paediatric) population in the context of paediatric studies, and fail to report actual RTS rates.

This prospective study sought to evaluate clinical, functional and MRI-based outcomes in paediatric patients undergoing meniscal repair either in isolation, or concomitant with ACLR. It was hypothesized that: 1) a significant improvement in PROMs and objective strength and hop outcomes would be observed following surgery, 2) satisfactory MRI-based meniscal healing would be observed, 3) a low reinjury rate (<10 %) would be observed within 24 months of surgery, and 4) no differences would be observed between paediatric patients undergoing isolated meniscal repair versus repair concomitant with ACLR.

2 Methods

2.1

2.1 Patients

Between September 2020 and September 2022, 32 paediatric patients (mean age 13.8 years, SD 2.2, range 9–16) underwent primary meniscal repair, either in isolation (n = 14) or concomitant with ACLR (n = 18), under one of four paediatric orthopaedic surgeons (PA, RL, DM, CM) (Fig. 1). Patients were referred for study invitation, recruitment and subsequent pre-operative clinical review if they were deemed likely candidates for meniscal repair surgery, based on clinical history and orthopaedic examination, as well as Magnetic Resonance Imaging (MRI). Further study inclusion criteria included 8–16 years of age and scheduled for primary meniscal repair surgery, including the anticipation of multiple meniscal repairs, or meniscal repair concomitant with ACLR. Patients were excluded if they did not want to participate and/or were unwilling to complete the ethics-approved consent documentation, or if the child was classified as morbidly obese (body mass index >40). This study was approved by the hospital Human Research Ethics Committee (HREC), and registered with the Australian New Zealand Clinical Trials Registry.

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Fig. 1 Flowchart demonstrating recruitment and evaluation over the pre- and post-operative period.

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3 RESULTS

3.5

3.5 MRI-based outcomes

Both intra-observer (rho = 0.935, p < 0.0001) and inter-observer (rho = 0.916, p < 0.0001) reliability assessment indicated strong correlations. Of the cohort recruited, 25 patients attended post-operative MRI review (Table 5). Of these, 68 % demonstrated complete or near-full healing, with 32 % demonstrating mild or moderate healing (Table 5). Figures 2 and 3demonstrate MR images for two patients recruited within the study, with corresponding scores and scoring rationale.

Table 5 MRI-based outcome measures for the cohort that underwent post-operative imaging review (n = 25).

MRI Criteria	n (%)
1 = complete healing - original tear signal had reduced by at least one grade over at least 95 % of the tear	8 (32 %)
2 = near-full healing - original tear signal had reduced by at least one grade over 75–95 % of the tear	9 (36 %)
3 = moderate healing - original tear signal had reduced by at least one grade over 50–75 % of the tear	4 (16 %)
4 = mild healing - original tear signal had reduced by at least one grade over 25–50 % of the tear	4 (16 %)
5 = no healing - original tear signal remained in at least 75 % of the tear	0 (0 %)

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Fig. 2 Sagittal T2 fat saturated images prior to surgery (1A, 1B and 1C) show a peripheral tear at the posterior horn of the medial meniscus with vertical fluid signal indicated by the solid white arrows. The post-operative images (2A, 2B and 2C) show a mixture of high intermediate and low intermediate signal at the tear site (dashed white arrows). The signal had reduced by at least one grade over at least 95 % of the tear so was graded as complete healing by both readers.

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Fig. 3 Sequential sagittal T2 fat saturated images from before (1A-E) and after (2A-E) surgery showing a tear at the posterior horn of the lateral meniscus. The solid white arrows in 1D and 1E show areas of fluid signal which have not changed significantly when compared with 2D and 2E. The dashed arrow in 1A shows an area of high intermediate T2 signal which has not changed when compared with 2A. Fluid signal indicated by arrowheads in 1B and 1C has improved to low intermediate signal in 2B and 2C. This case was scored as mild healing by one reader and moderate healing by the other, on consensus scored as mild healing.

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4 Discussion

Subjective and physical performance test scores improved following meniscal repair, either in isolation or concomitant with ACLR, with s sound ability to return to pre-injury activity levels by 24 months. While those undergoing isolated meniscal repair (versus repair concomitant with ACLR) demonstrated improved hop test LSIs at 6 months, strength and hop test LSIs were similar at 12 and 24 months, with mean performance test LSIs ≥90 % by 12 months.

All PROMs significantly improved over time, as did the LSIs for quadriceps strength and hop measures, supporting the first hypothesis. Prior studies have reported improvement in PROMs, with the most common PROMs employed including the IKDC, Lysholm, KOOS and Tegner.^24–29 Of interest, these studies were retrospective, only employing PROMs to investigate outcome at a final endpoint without serial PROMs completion to document change over time, and all employed adult versions of these PROMs. The current study employed the pedi-IKDC and KOOS-Child, PROMs that have been developed specifically for a paediatric population. Nonetheless, Gabr et al.²⁴ reported a retrospective review of 59 paediatric patients (6–16 years), of which six underwent concomitant ACLR, followed to a mean 53 (range 26–140) months after isolated meniscal repair. They reported mean IKDC, Lysholm and Tegner scores of 88, 94 and 7, respectively. Lucas et al.²⁵ published a retrospective review of outcomes in 17 patients that underwent isolated meniscal repair at a mean follow-up of 22.3 (range 3.5–46) months, with a mean age at surgery of 14 (range 9–18) years. They reported significant pre-to post-operative improvements in Lysholm (55.9–85.4) and Tegner scores (3.9–7.1), with good outcomes reported in 12 (70 %) patients. Schmitt et al.²⁶ reported outcomes in 19 paediatric patients (31 % with concomitant ACL tears) after meniscal repair. Patients had a mean age of 14.8 (range 9.1–16.3) years and were followed up at a mean 6.1 (range 3–9) years. Good mean post-operative Lysholm (95.7), IKDC (90.7) and Tegner (7.6) scores were reported. Krych et al.²⁷ reported outcomes at a mean 5.8 years (range, 2.5 months to 13.8 years) after isolated meniscal repair in 44 patients with a mean age of 15.8 (range 9.9–18.7) years. At final follow-up mean IKDC and Tegner scores were 89.4 and 8, respectively. A follow up review of 32 patients within this cohort published by Hagmeijer et al.²⁸ at a mean follow-up of 17.6 (range, 13.1–25.9) years, reported mean IKDC and Tegner scores of 92.3 and 6.5, respectively. Finally, Tagliero et al.²⁹ reported a mean 16.6-year follow-up in paediatric and adolescent patients that underwent meniscal repair, with or without ACLR. Overall, 47 (of an eligible 99) patients with a mean age of 16 years were included, with significant pre-to post-operative mean improvements observed for the IKDC (47.9–87.7) and Tegner (1.9–6.3) scores.

The current study reported post-operative improvements in quadriceps strength and hop test symmetry, with mean LSIs >90 % at 12 and 24 months. To our knowledge, the assessment of lower limb strength and hop capacity has not been reported in paediatric patients after meniscal repair. Research in an adult ACLR population has shown an increased re-rupture risk if patients are unable to meet ≥90 % LSIs during physical tests,^30,31 including strength and hop capacity. Regardless, the importance of a sound recovery of strength and functional capacity in a cohort eager to return to sporting activities may be obvious, both to improve their sporting performance though also mitigate the future risk of re-injury.

In the current study and, at a post-operative timeframe of 6–9 months, 68 % demonstrated complete or near-full healing on MRI, partially supporting the second hypothesis. Limited studies have reported on MRI assessment after meniscal repair in paediatric patients.^25,26 Unfortunately, comparison to existing studies is difficult given the varied timeframes that post-operative MRI may be employed. Furthermore, the authors acknowledge the difficulty in interpreting the degree of meniscal healing on MRI, albeit high intra- and inter-observer reliability of scoring was demonstrated in the current study. Schmitt et al.²⁶ reported outcomes in 15 of the 17 available paediatric patients that underwent meniscal repair at a mean 6 years post-surgery, reporting that all 15 cases demonstrated healing. Lucas et al.²⁵ reported on post-operative MRI outcome in 10 of 19 paediatric patients that underwent meniscal repair a mean follow-up of 22 months, and reported that five were normal, three showed a persistent grade 3 tear, one persistent grade 2 tear and one a persistent grade 1 tear.

Of the 32 patients that underwent surgery in the current study, two experienced re-injury (one isolated meniscal repair patients, and one ACL re-tear) over the 24-month period. While a longer-term assessment pathway may be required to ascertain the true incidence of re-injury in this cohort, the 6.3 % knee re-injury rate, though only 3.1 % meniscal re-injury rate, was in support of the third hypothesis. Gabr et al.²⁴ reported a 17 % re-operation rate (two repairs and nine meniscectomies) in 59 patients followed to a mean 53 (range 26–140) months after isolated meniscal repair. Schmitt et al.²⁶ reported a meniscal survival rate of 89.5 % in 19 paediatric patients (31 % with concomitant ACL tears) after meniscal repair followed up at a mean 6.1 (range 3–9) years. Tagliero et al.²⁹ reported that 28 % of 47 paediatric and adolescent patients that underwent meniscal repair failed. In patients under 18 years of age undergoing isolated meniscal repair, Krych et al.²⁷ reported a 38 % re-operation rate at a mean 17 (range, 3–61) months, including two repairs and 15 meniscectomies. No further failures in this cohort were observed at a mean follow-up of 17.6 (range, 13.1–25.9) years.²⁸

Numerous reviews have been published on the outcomes of meniscal repair. Firstly, a systematic review on return-to-play and rehabilitation protocols published by Fried et al.,¹⁰ in patients after isolated meniscal repair with a mean weighted age of 31.5 years followed up over a mean of 49 (range 3–204) months, reported a 71–100 % return-to-play rate, with 54–93 % returning to the same (or greater) activity level. A recent systematic review of long-term results reported by Petersen et al.¹² in patients after meniscal repair, with and without ACLR, included 12 retrospective case series with a mean follow-up that ranged from 10 to 20.6 years and patients mean ages that ranged from 16.1 to 35.1 years. Favourable PROMs were reported across studies, with failure rates ranging from 5 to 48 %, with failure rates higher in studies that examined children and adolescents. A systematic review published by Eberbach et al.¹¹ that spanned paediatric, adolescent and adult populations, reported comparable pre-injury and post-operative Tegner scores following isolated meniscal repair, with an 89 % return to pre-injury sport level. A significant improvement in both the IKDC and Lysholm scores were reported, along with a pooled failure rate of 21 % was reported, with a mean patient follow up in studies of 58 (range 18–247) months. Finally, a systematic review published by Liechti et al.¹³ on outcomes after meniscal repair in paediatric patients, with or without concomitant ACLR. A mean age of 15.1 (range, 4–18) years was documented, with a mean follow up of 51.6 (range, 22.3–96) months, of which 158 (52 %) of the included 301 meniscal repairs underwent concomitant ACLR. The post-operative range of Lysholm and Tegner scores across studies was 85.4–96.3 and 6.2–8, respectively. Of the included 301 meniscal repairs, 52 failures (17.3 %) were reported to occur at a mean time of 16.6 months post-surgery, of which 50 underwent re-operation (nine revision meniscal repairs and 41 meniscectomies).

No differences were observed in PROMs between patients that underwent isolated meniscal repair or repair concomitant with ACLR. Furthermore, while hop-test LSIs differed between groups for the THD (6 months), TCHD (6 months) and MHD (6 and 12 months), likely due to a more accelerated rehabilitation that may be permitted with meniscal repair in isolation, no other strength or hop differences were seen. This was in partial support of the fourth hypothesis.

An investigation of physical performance outcomes in patients after meniscal repair performed with or without ACLR is yet to be reported, let alone in a paediatric cohort. While not in paediatric patients, a systematic review by Totlis et al.³² reported a 90 % RTS rate and high post-operative activity level following meniscal repair, which was not significantly affected in the presence of concomitant ACLR. A more recent study undertaken by Gabr et al.³³ reported inferior 2-year clinical scores in those undergoing meniscal repair concomitant with ACLR, versus isolated ACLR, though there were no differences between groups at 5 years post-surgery. Of interest, some studies have reported that meniscal healing may be better when performed with concomitant ACLR,^34,35 largely due to the rich biologic environment created at the time of surgery. However, a study undertaken by Kahan et al.³⁶ employing a large national database in the US reported no difference in rates of secondary knee surgery between those undergoing meniscal repair with or without concomitant ACLR. The numbers in the current study did not permit a comparison across different tear types.

We acknowledge several limitations with the current study. Despite the prospective nature of the study, robust clinical review including MRI though also the assessment of lower limb strength and lower limb hop capacity that has not been reported previously, along with the good patient retention over the 24-month period, we appreciate it was a relatively small sample size. However, while this was limited by the flow and frequency of patients presenting and progressing toward surgery, the numbers reported were adequate for the priori sample size calculation and do not differ significantly from previously reported studies reporting outcomes after paediatric meniscal repair.^24–29 However, it is likely the study was underpowered for some secondary outcomes. Secondly, this study presented outcomes across an array of meniscal tear types, as typically presenting in clinical practice. Furthermore, while surgery was performed by one of four paediatric orthopaedic surgeons, the collaborative nature of the study ensured that treatment strategies were comparable and similar repair techniques were chosen for each tear type. Nonetheless, as mentioned earlier, a more comprehensive evaluation of outcome based on tear type is not attainable with the small patient cohort available. Thirdly, post-operative MRI was employed and, despite the high intra- and inter-observer reliability observed in the scoring tool employed, we acknowledge the difficulty in interpreting the degree of meniscal healing on MRI. Furthermore, both 1.5 T or 3 T clinical scanners were employed, based on accessibility at the imaging centers utilized. No second-look arthroscopy was undertaken in this case series, albeit this provides ethical barriers, particularly when patients have a good early outcome and remain asymptomatic.

5 Conclusion

Despite 68 % of patients demonstrating complete or near-complete healing, albeit 100 % showing some level of meniscal healing, the current study demonstrated a low re-injury rate out to 24 months post-surgery and improvement in subjective and physical performance test scores following meniscal repair (with mean performance test LSIs ≥90 % by 12 months), either in isolation or concomitant with ACLR. Furthermore, s high rate of RTS was observed. While those undergoing isolated meniscal repair (versus repair concomitant with ACLR) demonstrated improved hop test LSIs at 6 months, outcomes were generally similar by 12 months.

Consent to participate

Informed and written consent was obtained from all participants (and their parents) included in the study.

Author contributions

The following authors have conceived and designed the study (JE; DM; RL; PA), supervised the conduct of the study (JE; EG; DM; RL; CM; PA), analyzed the data (JE; EG; MM; PC), wrote the initial drafts (JE; EG; MM; PC; DM), critically revised the manuscript (JE; EG; MM; PC; DM; RL; CM; PA) and ensure the accuracy of the data and analysis (JE; EG; MM; PC; DM; RL; CM; PA). I confirm that all authors have seen and agree with the contents of the manuscript and agree that work has not been submitted or published elsewhere in whole or part.

Ethics approval statement

Ethics approval was obtained from the Child and Adolescent Health Service (CAHS) Human Research Ethics Committee, Government of Western Australia (RGS000000326).

Data availability statement

Data has not been made publicly available, though data generated during the current study can be made available from the corresponding author on reasonable request.

Funding statement

This study was supported by an independent funding grant provided by Johnson & Johnson (DPS-JMP-2018-065).