The Long-term Chondroprotective Effect of Meniscal Allograft Transplant: A 10- to 14-Year Follow-up Study

Abstract

Background:

The long-term chondroprotective effect of meniscal allograft transplant (MAT) and its superiority over meniscectomy have rarely been reported.

Hypothesis:

MAT would reduce osteoarthritis (OA) progression when compared with the meniscus-deficient knee. Graft extrusion distance would strongly affect the chondroprotective effect of the MAT.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A total of 17 knees receiving MAT were followed up as the MAT group. The MAT group was further divided into the nonextrusion subgroup (n = 9) and the extrusion subgroup (n = 8) according to 3-mm extrusion on the magnetic resonance imaging (MRI) coronal section. A further 26 consecutive patients receiving meniscectomy in the same period were followed up as the ME group. The healthy control group consisted of healthy contralateral legs chosen from the MAT and ME groups (n = 27). Joint space width (JSW) narrowing was measured on radiographs. Three-dimensional MRI with a T2 mapping sequence was used to quantitatively analyze cartilage degeneration and meniscal allograft extrusion in 5 directions (0°, 45°, 90°, 135°, and 180°). The cartilage degeneration index (CDI) was calculated according to the size and degree of the chondral lesions on MRI scans. The correlation between the CDI increase and the extrusion distance was analyzed.

Results:

The mean follow-up time was 11.3 years (range, 10-14 years). The MAT group had moderate superiority in chondral protection with less JSW narrowing (0.58 ± 0.66 mm) and CDI increase (1132 ± 1589) compared with the ME group (JSW narrowing: 1.26 ± 1.13 mm, P = .025; CDI increase: 2182 ± 1958, P = .079). The JSW narrowing (0.71 ± 0.80 mm; P = .186) and CDI increase (2004 ± 1965; P = .830) of the extrusion subgroup were close to those of the ME group, demonstrating that a 3-mm extrusion led to complete loss of the meniscal chondroprotective effect. The nonextrusion group had significantly less JSW narrowing (0.48 ± 0.48 mm; P = .042) and CDI increase (358 ± 249; P = .011) than the ME group. The JSW narrowing of the healthy control group was 0.22 ± 0.27 mm. The cartilage T2 values of the extrusion subgroup were similar to those of the ME group, with more OA features, whereas the T2 values of the nonextrusion subgroup were closer to those of the healthy control group. The extrusion distance in the 90° direction (P = .002) and the follow-up time (P = .019) significantly affected the CDI increase in the multivariate regression model. The average extrusion distance in the 45°, 90°, and 135° directions better predicted chondroprotection compared with the other individual directions.

Conclusion:

MAT had moderate advantages in chondroprotection compared with meniscectomy in the long term. Graft extrusion distance strongly affected the chondroprotective effect of MAT. The chondroprotective effect of the nonextruded meniscal allograft was close to that of the native meniscus, whereas the allografts with an extrusion >3 mm completely lost their function after meniscectomy.

Keywords

meniscus allograft transplantation extrusion cartilage meniscectomy

Meniscal tear is a common injury among the sports-active population, with an incidence of 61 cases per 100,000 persons and a prevalence of 12% to 14%.²³ A partial meniscectomy or repair is the first-line therapy for meniscal tears. In the circumstance of a large and complex meniscal tear or chronic tear, subtotal meniscectomy would be the only choice, and the function of the meniscus would be completely lost. Because the role of the meniscus pertains to load distribution and stabilization,²⁴ subtotal meniscectomy would dramatically change the knee biomechanical environment and often cause symptoms. The risk of knee osteoarthritis (OA) is also increased.^29,33

For patients with a symptomatic, meniscus-deficient knee, meniscal allograft transplant (MAT) is an effective intervention to relieve symptoms in the short to midterm.³⁶ However, whether the transplanted meniscus could function as the native meniscus and prevent OA progression remains unknown.^19,32,37 There is some evidence that MAT reduces OA progression.³⁷ In contrast, a large proportion of MAT patients have to undergo knee arthroplasty due to OA progression in the 10 to 15 years after MAT, suggesting that the chondroprotective effect of the meniscus is not completely restored.³ So far, the degree of chondroprotection that MAT will achieve in the long term and its superiority over meniscectomy have rarely been reported.

The purpose of this study was to compare the long-term chondroprotective effect of MAT with that of meniscectomy. The effect of graft extrusion on chondral protection was also analyzed because chondroprotection of the meniscus mainly depends on its coverage of the tibial plateau,^4,40 and meniscal extrusion has been reported to be highly associated with symptomatic knee OA.¹² By using 3-dimensional (3D) magnetic resonance imaging (MRI) and T2 mapping sequence, we thoroughly and quantitatively examined the graft extrusion and cartilage status of the knees in this study. We hypothesized that MAT would reduce OA progression compared with the meniscus-deficient knee but would not be as effective as the native meniscus. The graft extrusion distance would strongly influence the chondroprotective effect of MAT.

Methods

This retrospective study was approved by the ethics committee of our hospital (IRB200506).

Patients

A total of 21 MATs (7 medial and 14 lateral menisci) were performed on 18 patients by the same surgeon (J.K.Y.) between June 2005 and February 2010. A total of 18 MATs (6 medial and 12 lateral menisci) in 17 knees of 15 (83.3%) patients who were available for follow-up were included in this study. Three patients were lost to follow-up: 2 of these patients changed their phone number and address, and 1 patient could not complete the examination because of pregnancy.

The indications for MAT were (1) knee symptoms after meniscectomy, such as persistent pain and swelling; (2) age >18 and <35 years; and (3) chondral lesions of Outerbridge grade ≤II. The contraindications for MAT consisted of (1) generalized degenerative arthritis (Outerbridge grade ≥III); (2) uncorrected ligamentous instability; and (3) axial limb malalignment (>5°).

A diagnostic arthroscopic examination was performed to check the status of the meniscus, ligaments, and cartilage before MAT. Grafts were matched based on anteroposterior (AP) and lateral radiographs³⁰ as well as computed tomography and MRI scans. The lateral meniscus was transplanted with bone plugs, whereas the medial meniscal graft was prepared to be soft tissue only. A total of 2 tibial bone tunnels were drilled for fixation of the anterior and posterior roots. The meniscal graft was introduced through the extended arthroscopic portal. The anterior and posterior roots were pulled into the bone tunnels and tied over a bone bridge on the anteromedial tibial cortex. The meniscal allograft was sutured to the meniscotibial ligament of the residual meniscal rim if present. If the meniscal rim was absent, the graft was sutured to the capsule instead. Concomitant anterior cruciate ligament (ACL) reconstruction was performed in patients with ACL rupture.

Patients who received MAT were further divided into 2 subgroups according to the extrusion distance (<3 mm or ≥3 mm) shown on the MRI coronal section at the final follow-up. The nonextrusion group and extrusion group consisted of 9 and 8 knees, respectively. One patient had both medial and lateral MAT on his left knee at the same time and both grafts did not extrude, so this knee was assigned to the nonextrusion group.

Patients who underwent arthroscopic meniscectomy by the same surgeon between June 2005 and February 2010 were considered candidates for the meniscectomy control group (ME group). The inclusion criteria for the ME group were (1) patients receiving subtotal or total meniscectomy; (2) age between 18 and 35 years; (3) chondral lesions of Outerbridge grade ≤II; (4) limb alignment within 5°; (5) normal or corrected ligament instability; and (6) body mass index (BMI) <28 (based on Asian criteria for obesity). A total of 26 patients were retrospectively identified and included in the ME group. The indications for meniscectomy were large, complex meniscal tears that caused symptoms and were unrepairable. Meniscectomy patients without symptoms or whose symptoms were relieved by nonoperative treatments were not considered for MAT.

The healthy control group consisted of the healthy contralateral leg of patients from both the MAT group and the ME group.² Knees with a history of surgery or trauma or discoid meniscus were excluded, and 27 knees were finally included in the healthy control group.

Radiographic and MRI Evaluation

All patients underwent full-length leg radiographs and 45° flexion weightbearing AP radiographs of both sides preoperatively, 5 years after surgery, and at the final follow-up. The joint space width (JSW) was measured as the shortest distance between the femoral condyle and the tibial plateau in the surgical medial or lateral compartment on the AP plain radiographs. For the healthy control group, the corresponding medial or lateral compartment was measured. The alignment was measured on the full-length leg radiograph. The OA status of the knee was evaluated by Kellgren-Lawrence (KL) grade.

All of the patients underwent MRI of the injured side on a GE 3.0-T magnetic resonance scanner preoperatively and approximately 5 years after the surgery. At the final follow-up, knee MRI scans of both sides were obtained from all of the patients. The MRI sequences included 5 routine MRI sequences with a section thickness of 3.5 mm and special 3D fast spin-echo T1 imaging with variable flip angle (CUBE T1) sequence with a 0.6-mm thickness.

The meniscal extrusion distance was measured on the coronal section. The allograft extrusion was defined as the distance from the outer border of the meniscus to the margin of the tibial plateau cartilage, as previously reported²² (distance a in Figure 1A). The relative percentage of extrusion (RPE) was defined as the percentage of the absolute extrusion distance compared with the entire meniscal width (a/b× 100% in Figure 1A). In addition, the absolute extrusion distance and the relative RPE were measured in 5 radial directions through 3D MRI: anterior 0°, anteromedial/anterolateral 45°, medial/lateral 90°, posteromedial/posterolateral 135°, and posterior 180° (Figure 1B).

The preoperative cartilage status was analyzed according to the surgical documents and the preoperative MRI scans. Postoperative cartilage status was evaluated by routine and 0.6-mm CUBE T1 sequences. The Yulish grade was used to evaluate the lesion stage (grade 0 = normal; grade 1 = normal cartilage contour with abnormal signal; grade 2 = superficial fraying, erosion, or ulceration of <50%; grade 3 = partial-thickness defect of >50% but <100%; grade 4 = full-thickness cartilage loss).⁴² The size and degree of the chondral lesions of all patients were documented and overlapped on an International Cartilage Regeneration & Joint Preservation Society mapping system.⁵ To quantitatively analyze each chondral lesion, we defined the cartilage degeneration index (CDI) as follows:

CDI = \sum_{i = 1}^{4} area of the lesion \times grade of the lesion

The T2 mapping sequence was also used to analyze the cartilage degeneration quantitatively. The T2 mapping consisted of a sagittal, multiecho spin-echo, T2-weighted sequence performed with the following parameters: a repetition time of 1200 milliseconds; 8 echo times of 8, 16, 24, 32, 40, 48, 56, and 64 milliseconds; and a slice thickness of 4 mm. The T2 relaxation time was obtained from T2 mappings reconstructed using a multiecho measurement. The T2 mapping images were created from the T2 mapping source with a color scale ranging from 0 to 72 milliseconds. The T2 value sampling sites were on the central femoral condyle and tibial plateau. The region of interest is shown in Figure 1C.

The signal of the meniscal allograft in the coronal and sagittal sections of the T2-weighted, fast spin-echo sequence was graded on a scale of 0 to 3 according to the criteria of Crues et al⁷ (grade 0 = normal; grade 1 = small focal area of hyperintensity, no extension to the articular surface; grade 2 = linear areas of hyperintensity, no extension to the articular surface; grade 3 = abnormal hyperintensity extending to superior and/or inferior articular surface).

All images were measured twice independently by 2 experienced sports medicine surgeons (D.Y.W. and D.J.). The mean value of these measurements was used for further analysis. Two patients had meniscal graft tears 4 years and 8 years after MAT and received partial meniscectomy and nonoperative treatment, respectively. We considered these meniscal grafts still functional, so they were included in the cartilage analysis. One patient had a meniscal graft tear at 10 years and received MAT revision. The MRI before the revision was used for analysis. The signal of the meniscal allograft of these 3 patients was graded as 3.

Patients’ subjective clinical outcomes, including the visual analog scale (VAS), Lysholm, International Knee Documentation Committee (IKDC), and Tegner scores, were also evaluated.

Data Analysis

Chi-square analysis was used to compare patient sex, side, compartment, and ACL reconstruction between the groups. Mann-Whitney test was used to compared the KL grade. Student t test was used to compare age, follow-up time, JSW, and CDI. P < .05 was considered statistically significant. Multivariate linear regression was performed to analyze the prognostic factors for the CDI increase on the femur and tibia, including age, sex, knee compartment, BMI, alignment, concomitant ACL reconstruction, absolute extrusion distance of the 90° direction, and follow-up time. Univariate linear regression was used to analyze the correlation between the CDI increase and the extrusion distance in different directions (0°, 45°, 90°, 135°, and 180° and an average of 45°, 90°, and 135°). One patient had both medial and lateral MAT on his left knee, and both grafts did not extrude; we analyzed this knee as a single sample.

Results

Patient Characteristics

Patient characteristics are shown in Table 1. The mean follow-up time was 11.3 years (range, 10-14 years).

Table 1

Patients Characteristics for All Groups and Subgroups^a

	ME Group(n = 26)	MAT Group(n = 17)	MAT-E Subgroup(n = 8)	MAT-NE Subgroup(n = 9)	P Value
	ME Group(n = 26)	MAT Group(n = 17)	MAT-E Subgroup(n = 8)	MAT-NE Subgroup(n = 9)	MAT vs ME	MAT-E vs ME	MAT-NE vs ME	MAT-NE vs MAT-E
Age, y	26 ± 5	26 ± 9	27 ± 6	24 ± 9	.776	.698	.470	.455
Sex, male:female, n	19:7	12:5	6:2	6:3	.859	.914	.714	.707
Side, left:right, n	10:16	8:9	2:6	6:3	.576	.486	.143	.086
Compartment medial:lateral, n	7:19	6:11	3:5	3:6	.736	.666	.694	≥.999
Body mass index	24.5 ± 2.7	25.3 ± 7.5	23.8 ± 3.8	26.6 ± 5.4	.429	.710	.262	.259
Malalignment^b	−2.2 ± 1.8	−0.9 ± 2.7	−0.5 ± 2.0	−1.4 ± 1.6	.078	.981	.397	.894
ACL reconstruction, n (%)	9 (35)	7 (41)	3 (38)	4 (44)	.752	≥.999	.698	≥.999
Final follow-up time, y	11.2 ± 0.5	11.4 ± 3.1	12.1 ± 1.9	10.8 ± 0.5	.631	.097	.273	.052

Values are expressed as mean ± SD unless otherwise noted. ACL, anterior cruciate ligament; MAT, meniscal allograft transplant; MAT-E, MAT extrusion subgroup; MAT-NE, MAT nonextrusion subgroup; ME, meniscectomy group; n, number of knees.

Malalignment: varus > 0, valgus < 0.

Superiority of MAT in Chondroprotection

The JSW decreased in all groups during follow-up (Table 2). The mean JSW narrowing in the MAT group was 0.58 ± 0.66 mm, significantly better than the 1.26 ± 1.13 mm of the ME group (P = .025) but worse than the 0.22 ± 0.27 mm of the healthy control group (P = .017) at the final follow-up. The mean KL grade increase in the MAT group was 1.4, lower than that of the ME group (P = .021) but higher than that of the healthy control group with a significant difference (P = .001). MRI also showed that the overall MAT group had moderate superiority in chondral protection with less CDI increase (1132 ± 1589) compared with the ME group (2182 ± 1958; P = .079) (Figure 2).

Table 2

Arthritic Changes on AP Radiographs^a

	ME Group(n = 26)	MAT Group(n = 17)	MAT-E Subgroup(n = 8)	MAT-NE Subgroup(n = 9)	Healthy Control(n = 27)	P Value
	ME Group(n = 26)	MAT Group(n = 17)	MAT-E Subgroup(n = 8)	MAT-NE Subgroup(n = 9)	Healthy Control(n = 27)	MAT vs ME	MAT vs Healthy Control	MAT-E vs ME	MAT-NE vs ME	MAT-E vs MAT-NE
JSW narrowing, mm, mean ± SD	1.26 ± 1.13	0.58 ± 0.66	0.71 ± 0.80	0.48 ± 0.48	0.22 ± 0.27	.025	.017	.186	.042	.503
Preoperation KL grade, n	0: 17 I: 8 II: 1 III: 0 IV: 0	0: 10 I: 6 II: 1 III: 0 IV: 0	0: 5 I: 2 II: 1 III: 0 IV: 0	0: 5 I: 4 II: 0 III: 0 IV: 0	0: 23 I: 4 II: 0 III: 0 IV: 0	.650	.045	.772	.671	.956
Postoperation KL grade, n	0: 0 I: 3 II: 14 III: 7 IV: 2	0: 0 I: 7 II: 6 III: 3 IV: 1	0: 0 I: 2 II: 3 III: 2 IV: 1	0: 0 I: 5 II: 3 III: 1 IV: 0	0: 14 I: 11 II: 2 III: 0 IV: 0	.089	<.001	.826	.016	.404
KL grade increase (range)	1.9 (1-4)	1.4 (0-3)	1.6 (1-3)	1.2 (0-2)	0.4 (0-2)	.021	.001	.329	.009	.187

JSW, joint space width; KL, Kellgren-Lawrence; MAT, meniscal allograft transplant; MAT-E, MAT extrusion subgroup; MAT-NE, MAT nonextrusion subgroup; ME, meniscectomy group. Boldface indicates statistical significance.

According to the extrusion distance of 3 mm at the coronal plane, we further divided the MAT patients into 2 subgroups: the extrusion and nonextrusion subgroups. The mean absolute extrusion distances of the nonextrusion and extrusion subgroups were 1.76 ± 0.79 mm and 4.93 ± 1.74 mm, respectively (P < .001). The RPEs of the nonextrusion and extrusion subgroups were 28.8% ± 14.0% and 61.8% ± 24.3%, respectively (P = .004). The chondroprotective effect of the nonextrusion subgroup was significantly better than that of the extrusion subgroup. The JSW narrowing and the KL grade increase of the extrusion subgroup were close to those of the ME group (P > .05), whereas the nonextrusion group had significantly less JSW narrowing and KL progression than the ME group (P = .042 and .009, respectively). The nonextruded meniscal allograft achieved the best chondroprotection on the tibiofemoral joint among the groups, with the lowest CDI increase (358 ± 249) (Figure 2). The chondroprotection of the extruded meniscal allograft was nearly the same as that achieved by meniscectomy. No significant difference was seen in the CDI increase between the extrusion subgroup (2004 ± 1965) and the meniscectomy group (2182 ± 1958; P = .830), demonstrating that a 3-mm extrusion led to complete loss of meniscal chondroprotective effect (P > .05). At the final follow-up, the ME group had a significantly increased T2 values with great variation, suggesting early OA status. The T2 values of the extrusion subgroup had similar OA features to the ME group, whereas the T2 values of the nonextrusion subgroup were closer to those of the healthy control group (Figure 3).

We used multivariate analysis to analyze the prognostic factors for the CDI increase on the femur and tibia. We found that the extrusion distance in the 90° direction (P = .002) and the follow-up time (P = .019) significantly affected the chondral lesion progression, whereas age (P = .444), sex (P = .100), surgical compartment (P = .899), BMI (P = .660), alignment (P = .747), and concomitant ACL reconstruction (P = .825) were not statistically significant in this cohort.

Chondral Lesion Progression

The chondral lesions progressed slowly during the first 5 years after surgery and sped up from 5 to 10 years after surgery (Figure 4). No significant difference was seen in the CDI between the MAT groups and meniscectomy group at the 5-year follow-up, whereas the difference had become significant at the final follow-up. The nonextrusion subgroup achieved the lowest CDI increase among the groups.

Extrusion Direction and Chondroprotection

We measured the extrusion distance in 5 directions (Figure 1B and Table 3) and used bivariate linear regression to analyze the correlation between the CDI increase and different extrusion directions (Figure 5). We noted a linear relationship between the extrusion distance and the chondral lesion progression. We found that the extrusion distance in the posteromedial/posterolateral 135° direction was more relevant to the CDI increase than that in the medial/lateral 90° direction (R² = 0.654 vs 0.598). The average extrusion distance of the meniscal body (45°, 90°, and 135°) predicted the chondroprotective effect better when compared with the other single directions (R² = 0.708).

Table 3

Extrusion Distance and Relative Percentage of the Extrusion^a

	MAT (n = 17)	MAT-E (n = 8)	MAT-NE (n = 9)	P Value
0°	4.47 ± 2.84	5.76 ± 3.62	3.43 ± 1.28	.092
45°	3.76 ± 1.94	4.83 ± 1.81	2.91 ± 1.58	.0377
90°	3.17 ± 2.05	4.93 ± 1.74	1.76 ± 0.79	<.001
135°	3.89 ± 2.76	5.49 ± 3.01	2.60 ± 1.65	.027
180°	1.63 ± 1.48	1.76 ± 1.50	1.53 ± 1.45	.757
Average of 45°, 90°, and 135°	3.60 ± 2.30	5.08 ± 1.99	2.42 ± 1.48	.003

Values are expressed in percentages as mean ± SD. Boldface indicates statistical significance. MAT, meniscal allograft transplant; MAT-E, MAT extrusion subgroup; MAT-NE, MAT nonextrusion subgroup.

The absolute extrusion distance in 5 directions was measured, and the difference between the 2 subgroups was shown. The extrusion subgroup had a more absolute extrusion distance in the anterior 0°, anteromedial/anterolateral 45°, medial/lateral 90°, posteromedial/posterolateral 135°, and posterior 180° directions.

Clinical Outcomes

A total of 3 MAT patients, 2 patients in the nonextrusion group and 1 patient in the extrusion group, demonstrated symptomatic meniscal allograft tears during the follow-up—namely, 4 years, 8 years, and 10 years (at the final follow-up). These patients received partial meniscectomy, nonoperative treatment, and MAT revision, respectively. There were no differences in the clinical outcomes (including VAS, Lysholm, IKDC, and Tegner scores) among the groups. In total, 7 of 8 allografts in the extrusion subgroup and 4 of 10 allografts in the nonextrusion subgroup had grade 3 signals at the final follow-up.

Discussion

The most important finding of this study is that, overall, MAT had moderate superiority in long-term chondroprotection compared with meniscectomy. Graft extrusion strongly affected the chondroprotective effect of MAT. The chondroprotective effect of the nonextruded meniscal allograft was close to that of the native meniscus, whereas an allograft with >3 mm extrusion completely lost its function, similar to meniscectomy. We noted a linear relationship between the extrusion distance and progression of the chondral lesion. The average extrusion distance of the meniscal body (45°, 90°, and 135°) predicted chondral protection the better, compared with the other single directions.

Although the idea that MAT can improve symptoms in patients who have undergone meniscectomy has been widely recognized, the chondroprotective effect of MAT has remained controversial for years. A systematic review found that patients’ mean joint space loss was 0.032 mm at 4.5 years and further concluded that there was some evidence to support the hypothesis that MAT reduced the progression of OA.³⁷ In this study, we found that MAT provided moderate chondroprotection in the long term but could not halt the progression of OA as well as did the native meniscus. The mean JSW narrowing in the MAT group was 0.58 ± 0.66 mm, significantly better than the 1.26 ± 1.13 mm of the ME group (P = .025) but worse than the 0.22 ± 0.27 mm of the healthy control group (P = .017) at the final follow-up. MRI also showed that the overall MAT group had mild superiority in chondral protection with less CDI increase compared with the ME group. Joint degeneration accelerated during the 5- to 10-year follow-up. The superiority of MAT in regard to chondral protection was more significant in the long term, whereas no difference was seen between MAT and meniscectomy in the midterm assessment.

Meniscal allograft extrusion is common after MAT, with a prevalence of 30% to 80%.²¹ A previous study reported that meniscal extrusion did not progress for 3 to 5 years.¹⁶ In the current study, we also found no significance in extrusion distance during the follow-up. Thus, the extrusion probably happens soon after MAT. In contrast, extrusion of the native meniscus is a phenomenon related to degenerative changes or damage to the articular cartilage or meniscal tissue in the knee joint.¹¹ Given the widespread nature of meniscal and chondral degeneration after MAT in the long term, extrusion of the meniscal graft might exacerbate and further impair its chondroprotective function.

Our results highlight the importance of dealing with allograft extrusion. Theoretically, meniscal allograft extrusion decreases the stress distribution capacity of the meniscus and further impairs its chondroprotective effect. We found that extrusion was a strong factor for predicting the chondroprotective effect of MAT. Both the morphological observation on the 0.6-mm MRI sequences and biochemical analysis on the T2 mapping sequence revealed that extrusion >3 mm led to a complete loss of meniscal chondral protection similar to meniscectomy, whereas the nonextruded meniscal allograft achieved better chondroprotection with less chondral lesion progression during the 10-year follow-up. A multivariate linear regression model was used to control the confounding factors, given that many factors might influence the chondroprotective effect of MAT, including age, preoperational cartilage status, concomitant procedures, and graft extrusion.^{20,22,34,35,38,41} We found that extrusion distance and follow-up time were independent factors influencing the progression of chondral lesions in this cohort. The extrusion distance of the meniscal body had a linear relationship with the CDI increase. The results from our cohort mirror those of previous studies reporting that knee radiographs of patients who had undergone MAT hardly changed during a follow-up time of 2 to 5 years,^13,28,39 but differences between the extrusion and nonextrusion patients showed up in the long term.²² MAT patients with a nonextruded allograft would benefit from this procedure in terms of symptom relief as well as long-term cartilage protection.

Some surgeons hold a positive opinion of prophylactic MAT, given that cartilage will significantly degenerate during the meniscus-deficient period but the degeneration is reduced after MAT.¹⁹ Our results also suggest that MAT had more advantages for chondral protection. One study reported that immediate prophylactic MAT led to more satisfactory subjective results, less joint degeneration, and fewer muscle strength deficits when compared with delayed MAT.¹⁴ However, chondral protection differed between extruded and nonextruded grafts, and only nonextruded grafts offered satisfying chondral protection. The difficulties lie in identifying patients with a high risk of extrusion and finding a robust surgical technique to avoid extrusion. Patients’ risk factors related to meniscal graft extrusion might include cartilage lesions and delayed time from previous meniscectomy to MAT.^1,18 Surgical factors might be associated with the anterior and posterior roots and the meniscotibial ligament, the structures taking part in meniscal fixation onto the tibia.²¹ Several techniques have been reported to improve extrusion, including accurate meniscus root repositioning,¹⁵ fixation of the meniscal graft onto the tibia by transosseous sutures,²⁵ and meniscal centralization techniques.^8,17 In the current study, some of the meniscal allografts were sutured to the meniscotibial ligament of the residual meniscal rim, and we found that this might decrease extrusion. Restoring the function of the meniscotibial ligament might be a promising strategy to solve extrusion, and requires further studies. However, no study has reported the long-term outcomes of these techniques in solving the extrusion. Thus, prophylactic MAT should be undertaken cautiously.

The strengths of this study include the direct, comprehensive examination of cartilage status and direction of meniscal extrusion and the long follow-up time. Traditional radiography is an indirect tool to examine cartilage, and it is especially inaccurate for a comparison between MAT and meniscectomy because the JSW is affected by the meniscal volume and position. As well, plain radiography is insensitive to early changes or focal disease, and the joint space can be affected by changes in the other compartments.³⁷ We used not only conventional MRI sequences but also the 0.6-mm CUBE T1 sequence to precisely analyze morphologic cartilage changes and small lesions. In addition, we used T2 mapping sequences to detect the water content and collagen structure in cartilage and to further increase the sensitivity for detecting early degenerative cartilage changes that precede gross morphologic changes.²⁶ Extrusion was measured in 5 directions to better determine the correlation between extrusion direction and chondral protection. Because the chondral lesions develop slowly after surgery, especially for young patients, a long-term follow-up study would be better to examine the chondroprotection effects of MAT.

There are some limitations of this study. First, this is a retrospective study with a small sample size of 17 MAT procedures. However, the groups did not show significant differences in characteristics, so the comparisons among them were meaningful. We also used a multivariate linear regression model to control for confounding factors. Further studies with large sample sizes are needed to evaluate other factors affecting the prognosis of the chondroprotection. Second, MRI was performed only in the supine position. The status of the meniscus might change in various positions, such as standing and walking. Further studies are needed that examine meniscal extrusion on dynamic loading using weightbearing MRI or ultrasonography.^6,10 Because of the retrospective design, the healthy contralateral side did not have preoperative MRI but only underwent MRI at the final follow-up; thus, we couldn’t track the cartilage changes in the healthy knees, and we used the results of postoperative MRI scans as the cartilage status baseline. Although the contralateral knee is commonly used as the control in many studies,³¹ the healthy contralateral knee might not completely represent the normal status of the population because the gait and loading of the contralateral knee might change after surgery.^9,27

Conclusion

MAT had moderate advantages in chondroprotection compared with meniscectomy in the long term. Graft extrusion strongly influenced the chondroprotective effect of MAT. The chondroprotective effect of the nonextruded meniscal allograft was close to that of the native meniscus, whereas an allograft with an extrusion >3 mm completely lost its chondroprotection, similar to meniscectomy.

Footnotes

Submitted December 5, 2020; accepted July 21, 2021.

One or more of the authors has declared the following potential conflict of interest or source of funding: Funding was received from National Natural Science Foundation of China (grant no. 51920105006 and 81630056). The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iDs

Dong Jiang

Jia-Kuo Yu

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