Introduction

The discoid meniscus is a congenital anatomical variant characterized by an alteration in the shape (width and thickness), stability, and structure of the meniscus^1,2. It usually occurs in the lateral meniscus, and its incidence is difficult to determine due to the large number of asymptomatic cases. In the USA, an incidence of 3-5% has been calculated; however, in Asian populations, it is described as up to 17%^3,4.

The discoid meniscus is susceptible to injuries even with low-energy mechanisms. In some cases, it is necessary to resect a large part of the meniscus, given the complexity and extension of the tears, leaving a meniscus that lacks a normal function⁵. It is known that the long-term results of a total or subtotal meniscectomy are poor since they are associated with early development of osteoarthritis of the knee. In children, substantial meniscal loss is of more concern than in adults because they need a functional knee for a longer lifespan, and early degenerative joint changes should be limited. Discoid meniscus, being a congenital condition, can lead to meniscectomy surgery at a younger age than patients without discoid meniscus, and thus can lead to early osteoarthritis. This is particularly relevant in the lateral compartment since it is more vulnerable to the meniscal deficit than the medial compartment^6,7.

Allogeneic meniscal transplants have been used in the last decades for the treatment of post-meniscectomy syndrome, with good functional results in the short and medium term^8-10. However, most of the series reported in literature, in which the results are indistinctly achieved in patients with and without a history of discoid meniscus, are heterogeneous. Conversely, also due to the younger age of patients treated with total or subtotal meniscectomy for complex discoid meniscus tears, and to a different meniscal anatomy, the results in these patients could be impaired. For these reasons, it is relevant to know the clinical course of a patient who presented a total/subtotal meniscectomy due to a torn discoid meniscus and who underwent MAT.

There are two main fixation methods used to fix a MAT: suture-only fixation (soft tissue) and bone-plugs fixation. The first one consists of fixing a completely soft tissue graft only using sutures through the body and meniscal horns, while the meniscal roots are fixed using a transtibial suture technique. In the bone-plug technique, the graft is prepared with a bone plug attached to each root, securing a bone-to-bone fixation in the meniscal roots, the rest of the meniscus being fixed with sutures. Also, there is a keyhole technique, which is a subgroup of bone plugs: a 10-mm wide and high bone bridge is prepared from the anterior to the posterior root of the meniscus.

To date, the literature is scarce on reports evaluating MATs in the setting of discoid meniscus patients, especially in the long term; moreover, there is no systematic review that analyzes the functional and imaging results of MATs in the discoid meniscus population. Therefore, the purpose of the present study was to perform a systematic review of clinical and radiological outcomes of MATs in patients with discoid meniscus.

The hypothesis is that MAT is a valid option for the treatment of post-meniscectomy syndrome after total/subtotal meniscectomy in the setting of discoid meniscus.

Materials and Methods

A literature review of the MEDLINE, EMBASE, and Cochrane databases was performed from the date of inception to June 2023 for studies that assessed clinical and MRI-related outcomes in patients with discoid meniscus who underwent MAT. Search terms used were “meniscal allograft transplantation” OR “meniscus transplantation” OR “meniscus allograft” OR “meniscal allograft” AND “discoid meniscus”. The study quality was assessed using the modified Coleman Methodology Score (mCMS) for all studies (Table 1). Inclusion criteria in this review were: studies that reported clinical or MRI-related outcomes of MAsT in the discoid meniscus, studies that reported clinical or MRI-related outcomes of MATs in young population in which patients with discoid meniscus could be analyzed separately, and clinical reports of any level of evidence. Exclusion criteria included: non-English language articles, nonhuman studies, review or surgical technique articles, editorials, and conference abstracts. Two authors (AG and ME) independently screened titles and abstracts of the searched articles and selected all relevant literature for a full-text review. We used a predefined data extraction electronic form as follows: first author, year of publication, study design, sample size (patients/knees), gender, medial or lateral discoid meniscus, mean age at the time of MAT, time between first surgery and MAT, allograft type and storage method mean follow up, values of Lysholm, Tegner activity scale and subjective IKDC scores, healing and extrusion assessed in MRI at final follow up. The outcomes were defined as follows: (1) Clinical outcomes at final follow-up: Lysholm, Tegner activity scale, and subjective IKDC scores and (2) MRI-related outcomes at final follow-up: allograft healing (percentage of MATs healed) and extrusion (percentage of MATs with extrusion >3 mm).

Due to the low level of evidence of the included studies and to the heterogenous data available, it was not possible to perform further quantitative analysis of the abstracted data.

Table 1. Description of articles included in the study, including data on number of cases, age at the time of MAT, surgical technique, associated procedures, sizing method, graft type, and mCMS (modified Coleman Methodology Score).

ND: not determined.

Results

The database search identified a total of 19 studies (Figure 1) whose abstracts were screened and selected according to predefined inclusion and exclusion criteria. After duplicates were removed, a total of 12 studies were included for the final analysis^11-19. No studies in this review were randomized or controlled. Two studies were case series with 14 and 16 knees, respectively, a study reported outcomes for 3 knees, two studies for 2 knees, and 4 were singular case reports.

Figure 1. Flowchart of the inclusion process.

Demographic Data

A total of 116 MATs in 115 patients were included, with a mean final follow-up of 52.8±51.7 months (range 19-180, Table 1). Gender was reported in all cases, with 54 males (47%) and 61 females (53%). Lateral discoid meniscus was present in 113 of the 116 knees (97.4%), while medial discoid meniscus was only present in 3 knees (2.6%). The mean age at MAT was 22.7±8.2 years, while the mean time between the first meniscectomy and MAT was reported in 10 of the 12 studies and was 53.4±18.0 months (range 5.5-9.6 y). The associated procedures were reported in 9 of the 12 studies and were present in 21 of the 116 MATs (18.1%), including osteotomies (6 tot), cartilage procedures (4 osteochondral autograft techniques for osteochondritis dissecans, 1 osteochondral allograft, 6 microfractures, 1 chondroplasty), 2 posterolateral corner reconstructions, 1 anterior cruciate ligament reconstruction. Regarding the meniscal graft features, the size determination was reported in 113 of the 116 MATs (97.4%), in 38 cases were described by X-ray, and in 83 cases by MRI. The type of MAT was reported in 52 cases, being fresh frozen in 48 of the cases and cryopreserved in 4 patients. The selected technique was reported in 112/116 MATs: the keyhole procedure was used in 33 cases, the bone plug in 11 knees, the modified bone-plug technique in 37 cases, the bone bridge technique in 22 knees, and the trans-tibial tunnel for the posterior horn and soft tissue fixation for the remaining meniscus in two cases.

Clinical Outcomes

Regarding clinical outcomes, 6 of the 12 studies^{12,13,18,20,21} reviewed (107 MATs) found a statistically significant difference between the outcomes analyzed in the pre-operative and final follow-up. Overall, 10 studies^12-15,17-22 (114 MATs) reported the Lysholm score, and at the final follow-up, the mean was 83.2±9.8 (range 62-97). 8 studies^{12,14,15,17-22} (99 MATs) reported the Tegner activity scale being 5.4±1.5 (range 4-8) at the final follow-up. Regarding subjective IKDC score, it was reported by 6 studies^{12,15,18-20,22} (101 MATs); at the final follow-up, the mean subjective IKDC score was 78.2±7.2. In one study¹⁴ that included 2 patients with discoid meniscus, it was reported the pedi-IKDC that was 70.5 (Table 2).

Table 2. Clinical and MRI outcomes described in the studies included in the systematic review.

ND: not determined; *: significant statistical differences.

In a total of 114 MATs studied, there are 5 cases of re-operations (4.39%): 1 partial meniscectomy for MAT injury, 1 stem cell treatment, 1 total meniscectomy of meniscus graft for recurrent synovitis with chronic swelling and effusion, 1 arthrolysis, 2 repairs with suture. In addition, unspecified conservative treatment was performed in only one case.

MRI-related Outcomes

Of the 12 studies, 5 of them^13-15,17,19 (including 21 MATs, 18.4%) reported the healing of the graft in MRI at final follow-up which was complete in all cases. Regarding to extrusion, it was reported in others 6 studies^13-15,17-19 (including 37 MATs, 32.5%) and only 2 patients (1.8%) presented a graft extrusion bigger than 3 mm.

Discussion

The main finding of this systematic review was that MAT is a safe and successful procedure to treat patients with meniscal deficiency due to discoid meniscus, presenting good clinical and MRI-related outcomes.

In the past decades, the treatment of discoid meniscus consisted of total or subtotal meniscectomy, but degenerative changes have developed with time^23-25. Räber et al²⁶ reviewed 17 total meniscectomies in 14 patients with discoid meniscus. At a mean of 19.8 years (range, 12.5-26.0 years), 10 of 17 knees had clinical and radiological signs of osteoarthritis. Currently, the treatment of choice is arthroscopic saucerization with preservation of the meniscal rim. A recent systematic review²⁷ that included 422 discoid lateral menisci treated surgically reported good clinical results and a low rate of moderate/advanced degenerative changes with long-term follow-up. However, Kim et al²⁸, in the largest series on discoid meniscus, showed a statistical difference in the radiological changes over 5 years of follow-up between patients treated with total and partial meniscectomies. For this reason, patients who previously have undergone total or subtotal meniscectomy for discoid meniscus may be candidates for MAT. The indications of MATs in this population are, in fact, the same as in the general population, that is, patients with meniscal deficit secondary to total or subtotal meniscectomies, and that present pain in the affected compartment of the knee without signs of advanced joint degeneration. The role of prophylactic MAT in the acute setting of discoid meniscus lesions is still debated, and no strong evidence is available on MAT chondroprotection. Therefore, considering the possible morbidity of MAT, especially in young patients with open physis, MAT should be reserved for symptomatic patients after meniscal removal.

During the preoperative study and planning, it is important to know the skeletal maturity of these patients, since the surgical technique of the MAT must respect the physis, if it is still open¹⁴. On the other hand, it is important to recognize and treat other factors that may be present in these patients, such as instability, the state of the cartilage, and the axis of the lower extremities.

A relevant point when performing a MAT is the size match of the graft. Although different methods have been described to measure the size of the graft, there is no method that is clearly superior to the others. Pollard et al²⁹ described the size measurement in the AP and lateral X-ray and is one of the most used. Approximately in half of the cases reviewed^{11,15,16,19-22} in this work, the measurement was done by X-ray and in the other half by MRI.

In a recent cadaveric study by Rohde et al³⁰, the authors described the typical meniscal widths along the rim, indicating that all axial widths increase with age, and medial and lateral menisci varied at linearly proportional rates. Therefore, age and stage of development are important considerations for surgeons in selecting appropriate MAT in pediatric patients with discoid menisci.

Despite the lack of high-quality evidence, MAT can be considered as a chondroprotective procedure in young people with meniscal deficiency^31,32. At short and intermediate follow-up, clinical results are demonstrated³³ to be good to excellent in terms of pain and function levels. In fact, in a recent pilot randomized controlled trial³⁴, the authors demonstrated that MATs provided superior patient-reported outcomes than personalized physiotherapy. Smith et al³³, in a systematic review evaluating clinical outcomes of 1,374 MATs in the general population, showed an average Lysholm score of 81.3 points, a subjective IKDC of 70 points, and Tegner activity score of 4.7 points at a mean final follow-up of 5.1 years. However, it is not clear if MATs have the same results in patients with a history of discoid meniscus. In this regard, Yoon et al¹⁸ reviewed retrospectively a series of 36 patients who underwent MATs with a previous meniscectomy, comparing the clinical results of 16 with discoid meniscus vs. 20 with nondiscoid meniscus. They did not report significant differences in the Lysholm, VAS, and subjective IKDC scales; they only observed a small decrease in the postoperative range of motion in patients with discoid meniscus (132.8±15.7 vs. 140.0±6.6, p<.05). Similarly, no differences in terms of extrusion at the MRI evaluation were observed between groups.

With the available data obtained from this review, the clinical outcomes of patients who underwent MAT in the setting of the discoid meniscus can be considered similar to the reported series of MAT in the general population. The pooled clinical outcomes obtained in the present systematic review (Lysholm 83.2±9.8, subjective IKDC 78.2±7.2, Tegner activity 5.4±1.5), are comparable to those reported by Smith et al³³ for general population (Lysholm 81.3, subjective IKDC 70, Tegner 4.7). Only a slight difference can be noted in the Tegner score, with higher values in patients with discoid meniscus. However, this finding could be influenced by the younger age of patients with discoid meniscus, which are, therefore, more likely to be involved in sports activities. In fact, the average age at surgery of MATs performed in the general population has been reported³⁵ to be 33.7 years, with a range between 19.8 and 48 years, while the mean age at surgery of MAT for discoid meniscus reported in this systematic review was 22.7±8.2 years, ranging between 11 and 35.8 years.

Limitations

The present study had several limitations, which were mostly inherent to the systematic review study design and the quality of the data of the included studies. The inclusion of studies with lower levels of evidence with respect to the RCT reduced the global level of evidence of the systematic review; however, we wanted to have the most comprehensive view on this specific topic, and we believe that this compromise was necessary. The modified Coleman methodology score highlighted shortcomings in the quality of the studies, especially regarding the type of study, sample size, and description of postoperative rehabilitation. Moreover, the heterogeneity in patient characteristics and surgical technique did not allow a sophisticated statistical analysis. In addition, a second look and a pre- or postoperative MRI check were not performed in all studies. Finally, the relatively short follow-up in some of the included studies leaves concerns regarding the effectiveness of the MATs.

Conclusions

This systematic review showed that MAT is an effective and safe procedure to treat patients with pain and functional limitation after total or subtotal meniscectomy for a torn discoid meniscus. Good clinical and MRI-related outcomes can be expected at short and intermediate follow-up.

Conflict of Interest

Nothing to declare.

Funding

None.

ORCID ID

Anna Pagano: 0009-0001-3402-7530

Maximiliano Espinosa: 0000-0003-3155-4009

Giacomo Dal Fabbro: 0000-0002-8258-6425

Piero Agostinone: 0000-0002-5024-6944

Gian Andrea Lucidi: 0000-0003-3065-9212

Alberto Grassi: 0000-0003-4236-1798

Stefano Zaffagnini: 0000-0002-2941-1407

Data Availability

Data are available from the corresponding author.

Ethics Approval

Not applicable.

Informed Consent

Not applicable.

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