Nonextruded Grafts Result in Better Cartilage Quality After Lateral Meniscal Allograft Transplantation: Quantitative 3-T MRI T2 Mapping

Abstract

Background:

Several studies have reported that graft extrusion after meniscal allograft transplantation (MAT) is associated with deterioration of surgical outcomes. However, no study has investigated the effect of graft extrusion on the articular cartilage using objective quantitative methods.

Purpose/Hypothesis:

This study aimed to investigate the influence of graft extrusion on the chondroprotective effect of lateral MAT on knee articular cartilage. We hypothesized that MAT without graft extrusion would result in better cartilage quality than MAT with graft extrusion.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Altogether, 105 patients who underwent isolated lateral MAT were divided into the extrusion and nonextrusion groups based on postoperative 3-month magnetic resonance imaging. Quantitative T2 mapping was performed on pre- and postoperative magnetic resonance imaging at midterm follow-up (mean ± SD, 3.2 ± 0.7 years). The weightbearing area of the femoral and tibial plateau articular cartilage was divided into 6 segments (F1, F2, F3, TP1, TP2, and TP3) from the anterior to posterior direction according to the meniscal coverage area. Each segment was further segmented into superficial and deep layers for zonal analysis. Longitudinal change in cartilage T2 value was compared between the groups. Lysholm scores were used to evaluate clinical function.

Results:

The mean T2 value of the nonextrusion group showed a significant improvement in 14 of 18 segments after lateral MAT, whereas the extrusion group demonstrated no statistically significant change. The biochemical properties of cartilage tissue as judged by quantitative T2 mapping indicated improvement in the nonextrusion group as compared with the extrusion group in the F2, TP2, and TP3 segments overall; the deep layers of the F1, F2, and TP2 segments; and the superficial layer of the TP3 segment (P < .05).

Conclusion:

This study shows that the nonextruded graft results in better cartilage properties of the knee joint after lateral MAT as compared with the extruded graft at midterm follow-up.

Keywords

meniscal allograft transplantation quantitative magnetic resonance imaging T2 mapping articular cartilage cartilage assessment chondroprotective effect meniscal graft extrusion

The native menisci of the knee joint have several important roles in overall knee function, including load transmission, shock absorption, nutrition, joint lubrication, proprioception, and increasing joint congruency.⁴ When the knee joint is loaded, the outward-radiating forces acting on the meniscus create hoop stresses within them, which contribute to chondroprotection by distributing the weightbearing load.⁵ However, if a meniscus is torn or pathologically extruded from the tibial plateau rim, chondroprotective functions become partially or completely impaired.^1,27,40,44

For symptomatic patients with meniscal tear undergoing a total or subtotal meniscectomy, meniscal allograft transplantation (MAT) is a promising treatment option to relieve symptoms. In addition, emerging scientific evidence supports that MAT may delay the progression of osteoarthritis^19,33,42 and provide a chondroprotective effect on the articular cartilage.^31,33,43 However, similar to native meniscal extrusion, the chondroprotective effect of MAT may be subdued if there is graft extrusion. Although previous studies revealed that graft extrusion after MAT was not associated with joint space narrowing at midterm follow-up, a greater decrease in the joint space width was observed at long-term follow-up.^{14,21,24,26,43} Hence, it is assumed that graft extrusion may have attenuated the chondroprotective effect of MAT in the midterm period. Nevertheless, the influence of graft extrusion on the chondroprotective effect has not been elucidated owing to a lack of research studies on the articular cartilage quality.

Quantitative magnetic resonance imaging (MRI) T2 mapping is a sensitive and valid tool that can assess the characteristics of cartilage tissue and provide objective quantitative data.^6,11,34 Increased T2 relaxation times (T2 value) reflect a decreased concentration of proteoglycans, an increase in water content, and a loss of collagen content and network integrity in the cartilage, thereby indicating inflammation in cartilage tissues with poor biochemical characteristics.^2,9 Thus, T2 mapping is being increasingly employed in clinical orthopaedic research to determine cartilage quality and for follow-up in cartilage-preserving procedures.^29,45 However, to date, little is known regarding the change in T2 value of articular cartilage after MAT. The purpose of this study was to investigate the effect of graft extrusion on the chondroprotective effect of lateral MAT through quantitative MRI T2 mapping of knee articular cartilage. We hypothesized that MAT without graft extrusion would improve cartilage quality better than MAT with graft extrusion.

Methods

Study Patients

The study protocol was approved by the Asan Medical Center institutional review board (S2021-1648-0001). Symptomatic patients who (1) underwent subtotal or total lateral meniscectomy, (2) had International Cartilage Regeneration & Joint Preservation Society (ICRS) grade ≤2 cartilage lesion with or without focal grade 3 or 4 lesion, and (3) had well-aligned stable knees were indicated for lateral MAT. All patients who underwent lateral MAT between August 2010 and September 2019 were reviewed retrospectively, and those who underwent quantitative 3-T MRI pre- and postoperatively during midterm follow-up (2.0-5.4 years after index surgery) were included. Some patients were excluded per the exclusion criteria. First, patients who underwent concomitant procedures (eg, osteochondral autologous transplantation, bone marrow stimulation, ligament reconstruction, or realignment osteotomies) were excluded to assess the effect of isolated lateral MAT on articular cartilage. Second, patients were excluded when their MRIs had technical issues (eg, motion artifacts, corrupt spectroscopic data, or misregistration between images)^11,29,32 that limited evaluation of T2 mapping. Finally, patients with a focal full-thickness chondral defect on the region of interest (ROI) of the corresponding image were excluded owing to the inability to draw the ROI curve and perform analysis.

Surgical Technique and Rehabilitation

Lateral MAT was performed by a single surgeon (S.-I. B.) using a keyhole technique with a size-matched fresh-frozen allograft. First, a keyhole tibial slot was made just under the lateral tibial eminence, parallel to the anteroposterior axis of the tibia, corresponding to the position of the native meniscus. To avoid meniscal allograft extrusion, the patellar tendon was retracted sufficiently in the medial direction to expose the ideal entry point. Then, the meniscal allograft was introduced through an anterior mini-arthrotomy. After the bone bridge of the meniscal allograft was secured in an optimal position, arthroscopic repair was performed using the inside-out technique from the posterior horn to the midbody and the outside-in technique for the anterior portions, with PDS 2-0 (Ethicon, Somerville, NJ, USA) and Ethibond 2-0 (Ethicon, Somerville, NJ, USA) sutures.¹⁰ Appropriate peripheral suture tension was determined using arthroscopy.

Rehabilitation began with quadriceps strengthening and straight leg–raising exercises immediately after surgery. Crutch ambulation and toe-touch partial weightbearing were allowed after surgery. Range of motion exercises were commenced with a goal to achieve full extension equal to that in the contralateral side within 1 week, 90° of flexion within 4 weeks, and 120° of flexion at 6 to 8 weeks. The intensity of weightbearing was gradually increased starting 2 weeks after surgery, reaching full intensity at 6 to 8 weeks. Patients were forbidden to engage in high-impact or contact sports and instructed to participate only in light sports and physical activity to avoid damaging the transplanted meniscus.

MRI Protocol

Coronal and sagittal proton density–weighted fast spin echo images were acquired using an Achieva or Ingenia 3-T MRI scanner (Philips Medical System) with a dedicated 16-channel knee coil. Conventional MRI was performed with a repetition time of 2403 to 4805 ms, an echo time of 20 ms, a 512 × 512 pixel matrix, and a slice thickness of 2.5 and 1.5 mm in the coronal and sagittal planes, respectively. After conventional MRI scanning, a sagittal multiecho spin echo T2-weighted sequence was obtained for quantitative T2 mapping with the following parameters: 6 echo times of 13, 26, 39, 52, 65, and 78 ms and a repetition time of 3500 ms; a slice thickness of 3 mm; a field of view of 160 × 160 mm; a pixel matrix of 304 × 304; and a total acquisition time of 7 minutes 56 seconds. The T2 relaxation times (in milliseconds) were obtained from the T2 map reconstructed using a multiecho measurement.

MRI Evaluation of the Meniscal Allograft Subluxation

Meniscal subluxation was assessed at postoperative 3-month MRI, after patients achieved full range of motion and full weightbearing according to the rehabilitation protocol. To measure meniscal allograft extrusion, the coronal image showing the center of the meniscocapsular junction was determined among the serial coronal images running from the anterior to posterior meniscocapsular junction in the lateral compartment³⁵ (Figure 1A). Then, the amount of subluxation and the meniscal width were measured twice by the first author (H.Y.L.) at 2-week intervals using the measurement tool in the picture archiving and communication system at our institute. The average of the 2 measurements was used in the analysis. Ten patients were randomly assessed by 2 other blinded investigators (S.-M.K. and S.-J.L.) for intraclass correlation coefficient (ICC) values. An ICC value of 1 represents perfect reliability and 0 represents unreliability. Intraobserver reliability and interobserver agreement were 0.940 (95% CI, 0.759-0.985; P < .001) and 0.933 (95% CI, 0.731-0.983; P < .001), respectively.

Extrusion was defined as >3-mm subluxation of the meniscus, making the results comparable with those of other published studies on extrusion using the same cutoff value.^3,20,35 In addition, allograft extrusion was measured in relative and absolute terms because of the variation in individual knee sizes. The relative values were defined as the relative percentage of extrusion, measured by dividing the absolute value of allograft extrusion by the entire meniscal width (Figure 1B, 1C).

ROI Analysis of T2 Mapping for Cartilage Assessment

Quantitative T2 mapping was conducted on the sagittal image corresponding to the center of the lateral femoral condyle to represent the weightbearing portion of the articular cartilage and to increase the repeatability coefficient by 1 or multiple investigators (Figure 2A, 2B). Then, to perform an ROI analysis on the articular cartilage, weightbearing areas of the femoral and tibial plateau articular cartilages were divided into 6 segments (F1, F2, F3, TP1, TP2, and TP3, where F stands for femoral and TP stands for tibial plateau) according to the area covered by the meniscus, as described in previous studies.^29,43 F1 and F3 segments represent the area of femoral articular cartilage covered by the anterior and posterior horns of the lateral meniscus, respectively, and the intervening cartilage segment was labeled F2. Likewise, articular cartilage on the tibial plateau was divided into 3 segments, wherein TP1 and TP3 respectively represent the anterior and posterior horns of the lateral meniscus and TP2 is the intervening segment (Figure 2C). T2 maps were analyzed using an advanced cartilage assessment application (IntelliSpace Portal; Philips Healthcare) by least squares regression weighted by the variance of the estimates of the signal intensity.³² T2 maps of the articular cartilage of the knee joint, with a color scale ranging between 1 and 81 ms, were created from the T2 mapping source data. ROI curves for the overall articular cartilage layer, from the subchondral bone to the cartilage surface, were drawn referring to the gray and color T2 map images for each segment. The mean T2 value of the ROI was automatically assessed by the software. Moreover, ROIs were automatically divided by the program into 2 layers of equal thickness (superficial and deep) for the evaluation of the zonal variation of the mean T2 values (Figure 2D). A total of 18 ROIs were assessed. Ten patients were randomly reviewed by the first investigator (H.Y.L.) 2 months after the initial assessment for an ICC value, and 2 other blinded orthopaedic surgeons (S.-M.K. and S.-J.L.) for interobserver reproducibility. Interobserver reliability and interobserver agreement were 0.978 (95% CI, 0.973-0.982; P < .001) and 0.975 (95% CI, 0.966-0.981; P < .001), suggesting almost perfect agreement.

Data Analysis

Because the biochemical composition of cartilage tissues is heterogeneous, reported normative T2 values show wide dispersion in the normal population and even zonal variation in the same person.^2,37,39 Hence, there is no consensus on T2 values in terms of a normal range or a minimal clinically important difference. Therefore, we analyzed absolute and relative change in T2 values to investigate the chondroprotective effect of lateral MAT. On one hand, the absolute change in T2 values was compared in the extrusion and nonextrusion groups by the paired Student t test. On the other hand, the relative change (percentage) in the T2 value of each segment was calculated by dividing the absolute change by the preoperative value for comparison between groups. Based on previously reported T2 values and the descriptive statistics of our data (see Appendix, available in the online version of this article), the change in T2 values was classified into 3 categories according to the degree of relative change: improved (≤−30%), deteriorated (≥30%), and stationary (change between −30% and +30%) (Table 1). Linear-by-linear association was performed to assess the relationship between the cartilage quality improvement and the presence of graft extrusion and for comparing the ICRS grade. Chi-square test was employed to compare sex and side. Student t test was used to compare the age, body mass index, mechanical alignment, meniscal-deficient period, MRI follow-up period, absolute amount of extrusion, relative percentage of extrusion, and preoperative Lysholm score. Statistical analysis was performed using SPSS software (Version 21.0; IBM Corp). P values <.05 were considered statistically significant.

Table 1

Classification of Change in Cartilage Quality According to Relative Changes in T2 Value After MAT^a

Classification	Description
Deteriorated	A ≥30% increase in the post- vs preoperative mean T2 value
Stationary	Change between −30% and +30%
Improved	A ≤−30% decrease in the post- vs preoperative mean T2 value

A lower T2 value indicates better biochemical composition of the cartilage tissue. MAT, meniscal allograft transplantation.

Results

Among patients who underwent isolated lateral MAT, 140 were assessed by pre- and postoperative quantitative MRI T2 mapping. Among them, 17 were excluded because of technical issues in MRIs. Another 18 patients had a focal full-thickness chondral lesion in the ROI and were excluded because the image was inapt for ROI analysis of T2 mapping. Ultimately, 105 patients were included in this study. There were no significant differences in patient characteristics between the groups except for the absolute and relative amounts of extrusion (Tables 2 and 3). Regarding the longitudinal change in cartilage T2 value, the nonextrusion group showed significant improvement in 14 of 18 segments after lateral MAT (Table 4). In contrast, the extrusion group demonstrated no statistically significant change in any of the 18 segments (Table 5). Similarly, the relative change in T2 values revealed statistically significant improvement in the nonextrusion group as compared with the extrusion group in the overall layer of F2, TP2, and TP3 segments; the deep layers of F1, F2, and TP2 segments; and the superficial layer of TP3 segment (P < .05) (Table 6, Figure 3). The Lysholm scores in the nonextrusion and extrusion groups improved after lateral MAT from 67.2 ± 14.9 to 89.1 ± 11.2 (P < .001) and from 64.8 ± 17.7 to 89.6 ± 6.7 (P < .001), respectively. There was no significant difference in the extent of improvement in the Lysholm scores between the groups (P = .410).

Table 2

Characteristics of Patients^a

	Total (N = 105)	Nonextrusion (n = 73)	Extrusion (n = 32)	P Value
Age, y	30.5 ± 10.1	30.0 ± 9.8	31.7 ± 10.9	.435
Sex, male:female	60:45	44:29	16:16	.327
Side, right:left	55:50	39:34	16:16	.746
Body mass index	24.0 ± 4.1	24.2 ± 4.4	23.8 ± 3.4	.633
Mechanical axis, deg	2.0 ± 2.7	2.0 ± 2.7	2.1 ± 2.7	.780
Meniscal-deficient period, y	4.3 ± 4.4	4.6 ± 4.7	3.6 ± 3.4	.295
MRI follow-up period, y	3.2 ± 0.7	3.2 ± 0.7	3.1 ± 0.7	.610
Absolute extrusion at 3 mo, mm	2.1 ± 1.8	1.1 ± 1.3	4.1 ± 1.0	<.001
RPE at 3 mo, %	25.3 ± 23.0	13.6 ± 14.3	52.2 ± 15.1	<.001
Preoperative
Lysholm score	66.5 ± 15.8	67.2 ± 14.9	64.8 ± 17.7	.410
ICRS grade: 0, I, II, III, IV
LFC	3, 31, 50, 5, 16	2, 21, 40, 1, 9	1, 10, 10, 4, 7	.220
LTP	1, 4, 66, 22, 12	0, 2, 49, 17, 5	1, 2, 17, 5, 7	.443

Data are shown as mean ± SD or No. Statistical analyses were performed using the *Linear by linear association or ^†Student t test. Bold indicates statistical significance. ICRS, International Cartilage Regeneration & Joint Preservation Society; LFC, lateral femoral condyle; LTP, lateral tibial plateau; MRI, magnetic resonance imaging; RPE, relative percentage of extrusion.

Table 3

Changes in the Amount of Extrusion Between the Groups^a

Postoperative MRI	Total (N = 105)	Nonextrusion (n = 73)	Extrusion (n = 32)	P Value
At 3 mo	2.1 ± 1.8	1.1 ± 1.3	4.1 ± 1.0	<.001 ^b
At midterm follow-up	2.2 ± 1.6	1.4 ± 1.1	4.0 ± 0.9	<.001 ^b
P value

Data are shown as mean ± SD. MRI, magnetic resonance imaging.

Statistical significance.

Table 4

Changes in Absolute T2 Values of Articular Cartilage in the Nonextrusion Group (Graft Extrusion <3 mm)^a

Segment	Preoperative	Postoperative	P Value
F1
Overall	53.8 ± 19.8	46.8 ± 15.1	.028^b
Deep	50.6 ± 19.2	43.5 ± 15.3	.023^b
Superficial	56.5 ± 20.4	50.6 ± 15.7	.082
F2
Overall	58.1 ± 18.8	49.3 ± 16.2	.004^b
Deep	54.4 ± 18.4	46.6 ± 16.2	.009^b
Superficial	62.4 ± 20.4	52.2 ± 16.8	.002^b
F3
Overall	58.7 ± 19.0	51.3 ± 16.6	.014^b
Deep	56.2 ± 18.2	49.9 ± 16.9	.030^b
Superficial	61.4 ± 20.3	53.1 ± 16.9	.009^b
TP1
Overall	36.8 ± 13.0	33.3 ± 10.7	.063
Deep	31.8 ± 11.8	29.1 ± 9.9	.123
Superficial	42.4 ± 14.4	38.1 ± 11.6	.033^b
TP2
Overall	35.7 ± 11.5	32.2 ± 9.6	.038^b
Deep	30.7 ± 11.4	27.6 ± 9.1	.061
Superficial	40.6 ± 12.6	36.8 ± 10.9	.035^b
TP3
Overall	40.3 ± 13.8	35.0 ± 10.6	.006^b
Deep	36.0 ± 13.0	31.5 ± 10.2	.014^b
Superficial	44.9 ± 14.6	38.3 ± 11.3	.002^b

A lower T2 value indicates better biochemical properties of cartilage tissue. Data are shown as mean ± SD. F, femoral; TP, tibial plateau.

Statistical significance.

Table 5

Changes in Absolute T2 Values of Articular Cartilage in the Extrusion Group (Graft Extrusion ≥3 mm)^a

Segment	Preoperative	Postoperative	P Value
F1
Overall	45.6 ± 5.8	49.5 ± 16.7	.226
Deep	43.4 ± 6.9	45.8 ± 15.6	.430
Superficial	48.1 ± 5.7	52.3 ± 17.3	.197
F2
Overall	51.2 ± 9.8	52.1 ± 17.0	.788
Deep	47.5 ± 9.7	49.4 ± 15.6	.542
Superficial	55.3 ± 10.2	55.0 ± 19.0	.933
F3
Overall	52.3 ± 10.8	54.5 ± 21.6	.592
Deep	49.9 ± 11.8	53.6 ± 22.4	.378
Superficial	55.0 ± 11.0	55.6 ± 21.7	.871
TP1
Overall	33.5 ± 7.6	35.6 ± 14.7	.455
Deep	29.3 ± 6.8	31.6 ± 13.6	.409
Superficial	39.7 ± 10.4	39.7 ± 15.1	.984
TP2
Overall	30.9 ± 5.9	33.5 ± 11.3	.253
Deep	25.9 ± 6.1	29.1 ± 10.2	.145
Superficial	36.3 ± 6.2	38.1 ± 12.7	.475
TP3
Overall	36.0 ± 8.8	36.3 ± 14.7	.889
Deep	32.5 ± 10.3	32.9 ± 13.8	.883
Superficial	39.9 ± 9.4	39.5 ± 16.4	.879

A lower T2 value indicates better biochemical properties of cartilage tissue. Data are shown as mean ± SD. F, femoral; TP, tibial plateau.

Table 6

Degree of Change in Cartilage Quality According to the Relative Change in T2 Values^a

	Total (N = 105)			Nonextrusion (n = 73)			Extrusion (n = 32)
Segment	Deteriorated	Stationary	Improved	Deteriorated	Stationary	Improved	Deteriorated	Stationary	Improved	P Value
F1
Overall	17 (16.2)	70 (66.7)	18 (17.1)	10 (13.7)	47 (64.4)	16 (21.9)	7 (21.9)	23 (71.9)	2 (6.3)	.053
Deep	18 (17.1)	67 (63.8)	20 (19.0)	10 (13.7)	46 (63.0)	17 (23.3)	8 (25.0)	21 (65.6)	3 (9.4)	.049^b
Superficial	19 (18.1)	68 (64.8)	18 (17.1)	13 (17.8)	44 (60.3)	16 (21.9)	6 (18.8)	24 (75.0)	2 (6.3)	.189
F2
Overall	12 (11.4)	75 (71.4)	18 (17.1)	6 (8.2)	51 (69.9)	16 (21.9)	6 (18.8)	24 (75.0)	2 (6.3)	.021^b
Deep	11 (10.5)	76 (72.4)	18 (17.1)	6 (8.2)	50 (68.5)	17 (23.3)	5 (15.6)	26 (81.3)	1 (3.1)	.013^b
Superficial	11 (10.5)	76 (72.4)	18 (17.1)	6 (8.2)	52 (71.2)	15 (20.5)	5 (15.6)	24 (75.0)	3 (9.4)	.094
F3
Overall	15 (14.3)	71 (67.6)	19 (18.1)	9 (12.3)	48 (65.8)	16 (21.9)	6 (18.8)	23 (71.9)	3 (9.4)	.117
Deep	15 (14.3)	72 (68.6)	18 (17.1)	9 (12.3)	49 (67.1)	15 (20.5)	6 (18.8)	23 (71.9)	3 (9.4)	.140
Superficial	14 (13.3)	72 (68.6)	19 (18.1)	8 (11.0)	49 (67.1)	16 (21.9)	6 (18.8)	23 (71.9)	3 (9.4)	.087
TP1
Overall	19 (18.1)	70 (66.7)	16 (15.2)	12 (16.4)	47 (64.4)	14 (19.2)	7 (21.9)	23 (71.9)	2 (6.3)	.135
Deep	21 (20.0)	66 (62.9)	18 (17.1)	14 (19.2)	43 (58.9)	16 (21.9)	7 (21.9)	23 (71.9)	2 (6.3)	.157
Superficial	17 (16.2)	64 (61.0)	24 (22.9)	12 (16.4)	46 (63.0)	15 (20.5)	5 (15.6)	18 (56.3)	9 (28.1)	.526
TP2
Overall	12 (11.4)	78 (74.3)	15 (14.3)	6 (8.2)	53 (72.6)	14 (19.2)	6 (18.8)	25 (78.1)	1 (3.1)	.014^b
Deep	15 (14.3)	74 (70.5)	16 (15.2)	9 (12.3)	49 (67.1)	15 (20.5)	6 (18.8)	25 (78.1)	1 (3.1)	.039^b
Superficial	15 (14.3)	74 (70.5)	16 (15.2)	9 (12.3)	50 (68.5)	14 (19.2)	6 (18.8)	24 (75.0)	2 (6.3)	.095
TP3
Overall	14 (13.3)	72 (68.6)	19 (18.1)	8 (11.0)	48 (65.8)	17 (23.3)	6 (18.8)	24 (75.0)	2 (6.3)	.037^b
Deep	14 (13.3)	67 (63.8)	24 (22.9)	9 (12.3)	44 (60.3)	20 (27.4)	5 (15.6)	23 (71.9)	4 (12.5)	.150
Superficial	15 (14.3)	69 (65.7)	21 (20.0)	9 (12.3)	45 (61.6)	19 (26.0)	6 (18.8)	24 (75.0)	2 (6.3)	.035^b

Values are presented as No. (%). F, femoral; TP, tibial plateau.

Statistical significance.

Discussion

The most important finding of the study is an improvement in the biochemical composition of the knee articular cartilage, as judged by quantitative T2 mapping, in the nonextrusion group after lateral MAT at a mean follow-up of 3.2 years, in contrast to that observed in the extrusion group. The role of MAT in delaying the degeneration of the articular cartilage in the affected compartment, in addition to providing symptom relief, has been suggested in the literature.¹³ Numerous authors have reported a potential chondroprotective effect of MAT based on simple radiographic features, such as the joint space width, Kellgren and Lawrence osteoarthritis grading system, and Fairbank classification.^25,26,42 The chondroprotective effect of MAT was also demonstrated by the findings in conventional MRI. Ha et al⁷ found no further articular cartilage degeneration in 78% of patients with MAT at 2.6 years on conventional MRI. Similarly, Verdonk et al⁴¹ found no progression of articular cartilage degeneration on the femoral condyle and tibial plateau in 47% and 41% of patients, respectively, on conventional MRI after an average follow-up of 12.1 years. In addition to the aforementioned methods of assessment, quantitative T2 mapping can provide objective data to evaluate the chondroprotective effect of MAT. A previous study revealed a strong relationship between quantitative MRI and proteoglycan content in cartilage.¹² The biochemical composition and molecular structure of cartilage can be assessed through its mechanical properties and appearance on imaging.^16,22

However, only a few T2 mapping studies have been conducted on patients undergoing MAT.^29,43 In the present study, the articular cartilage was quantitatively analyzed pre- and postoperatively, which demonstrated the improved biochemical composition of cartilage tissue depending on the portions after lateral MAT without graft extrusion.

Meniscal allograft extrusions after MAT have been frequently reported in previous studies.¹⁵ Although graft extrusion is likely to result in inferior outcomes, the actual effect of graft extrusion remains unclear. Regarding the chondroprotective effect, Ha et al⁷ cited a statistically significant correlation between graft extrusion and joint space narrowing, whereas Lee et al¹⁷ noted no correlation. In a long-term study, Wang et al⁴³ found postoperative cartilage T2 values that were suggestive of early osteoarthritis (>3 mm) in the extrusion subgroup and the meniscectomized subgroup, whereas the T2 values of the nonextrusion subgroup were closer to that of the healthy control group. Nevertheless, this result should be interpreted with caution because the normative T2 value shows great dispersion among healthy individuals.² In this study, the T2 values of the extrusion and nonextrusion groups were compared longitudinally, which revealed a marked difference in outcome between the groups. The results of this study reinforce the importance of avoiding graft extrusion while performing MAT.^13,15,18,46 Meanwhile, similar to those reported previously,²³ the Lysholm scores yielded no significant difference between the groups, suggesting no correlation between the biocomposition of the cartilage tissue and its clinical function.

Although quantitative T2 mapping is a valid tool that provides objective data, the normal range and the minimal clinically important difference in T2 values of the knee joint cartilage, which are critical for differentiating between “healthy” and “diseased,” have not been defined for the following reasons: (1) variations in the demographic features of the populations in different studies, (2) physiological variations in the functional demand among individuals,^8,30 (3) variations in reference values based on the version of MRI scanner or sequence,²⁸ (4) zonal variation in articular cartilage, (5) presence of outliers, (6) studies with small sample sizes, and (7) wide dispersion of normative T2 value, which has no absolute zero value in the measured scale.² Moreover, a clinically significant change in the T2 value has not reached a consensus. Several studies conducted repeated T2 mapping on the cartilage of healthy individuals after running,^36,38 reporting a change of approximately 10% within a short period (<30 minutes). Thus, to overcome the limitation of interpretating the longitudinal change in cartilage T2 value, a classification approach was adopted in this study based on the amount of postoperative change. In terms of this classification system, an improving trend was seen in the T2 values in the nonextrusion group as compared with the extrusion group.

There are some limitations to this study. First, this is a retrospective study with potential selection bias. A T2 mapping study is futile in patients with a high-grade chondral lesion who undergo MAT as a salvage procedure, as drawing an ROI curve is impossible when cartilage thickness is inadequate. Thus, the effect of transplanted meniscus in patients with advanced arthritic change using a T2 mapping method cannot be assessed. Second, the follow-up in this study is relatively short, with a mean duration of 3.2 years. To investigate whether MAT can delay the progression of arthritic change in the long term, studies with a longer follow-up would be helpful. Third, the follow-up period ranged from 2.0 to 5.4 years, leading to heterogeneity in the effect among the study participants. However, the groups did not show significant differences in their characteristic features; thus, the results of the analysis between the groups can be considered reliable. Fourth, the MRI for measuring graft extrusion was performed with the knee in full extension. As the characteristics of the meniscus change during weightbearing and walking, scans undertaken in dynamic loading positions would render further useful information. Finally, contralateral knee MRI scanning could not be performed because of the retrospective study design. This could have been helpful to compare the changes in the contralateral knee as a control group for better interpretation of T2 mapping.

Conclusion

This study shows that the nonextruded graft results in better cartilage properties of the knee joints after lateral MAT as compared with the extruded graft at midterm follow-up.

Supplemental Material

sj-pdf-1-ajs-10.1177_03635465221143373 – Supplemental material for Nonextruded Grafts Result in Better Cartilage Quality After Lateral Meniscal Allograft Transplantation: Quantitative 3-T MRI T2 Mapping

Supplemental material, sj-pdf-1-ajs-10.1177_03635465221143373 for Nonextruded Grafts Result in Better Cartilage Quality After Lateral Meniscal Allograft Transplantation: Quantitative 3-T MRI T2 Mapping by Hyo Yeol Lee, Seong-Il Bin, Jong-Min Kim, Bum-Sik Lee, Seung-Min Kim and Seon-Jong Lee in The American Journal of Sports Medicine

Footnotes

Submitted May 20, 2022; accepted October 27, 2022.

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 iD

Seong-Il Bin

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