Medial meniscus posterior root repair reduces the extruded meniscus volume during

Medial meniscus posterior root repair reduces the extruded meniscus volume during 1

knee flexion with favorable clinical outcome 2

3

Ximing Zhang¹⁾, Takayuki Furumatsu*¹⁾, Yoshiki Okazaki²⁾, Yuki Okazaki¹⁾, Takaaki 4

Hiranaka¹⁾, Haowei Xue¹⁾, Keisuke Kintaka¹⁾, Takatsugu Yamauchi³⁾, Toshifumi Ozaki¹⁾. 5

6

Affiliations:

7

1) Department of Orthopaedic Surgery, Okayama University Graduate School of Medicine 8

Dentistry and Pharmaceutical Sciences, 2-5-1 Shikatacho, Kitaku, Okayama 700-8558, Japan.

9

2) Department of Orthopaedic Surgery, Chikamori Hospital, 1-1-16 Okawasuji, Kochi 10

780-8522, Japan.

11

3) Division of Radiology, Medical Technology Department, Okayama University Hospital, 12

2-5-1 Shikata-cho, Kitaku, Okayama 700-8558, Japan.

13

Corresponding author: Takayuki Furumatsu 14

Department of Orthopaedic Surgery, Okayama University Hospital, 15

2-5-1 Shikatacho, Kitaku, Okayama 700-8558, Japan 16

Telephone No.: +81 862 237 151 17

Fax No.: +81 862 239 727 18

E-mail address: [email protected] 19

First author: Ximing Zhang, MD 20

Department of Orthopedic Surgery, Okayama University Graduate School, 2-5-1 Shikata-cho, 21

Kitaku, Okayama 700-8558, Japan 22

Tel: +81-86-235-7273, Fax: +81-86-223-9727, 23

E-mail: [email protected] 24

Declarations 25

Funding No funding was received.

26 27

Conflicts of interest The authors report no conflicts of interest.

28 29

Ethics approval 30

This retrospective study was approved by the Institutional Review Board of Okayama 31

University (ID: 1857). All the procedures performed in studies involving human participants 32

were consistent with the ethical standards of the institutional review board and the 1964 33

Helsinki declaration and its later amendments.

34 35

Acknowledgement 36

We would like to thank Editage (http://www.editage.jp) for English language editing.

37 38

Authors’ contribution 39

Takayuki Furumatsu designed the study. Ximing Zhang prepared the manuscript. Ximing 40

Zhang, Yoshiki Okazaki,Yuki Okazaki, and Takaaki Hiranaka contributed to the data 41

collection. Toshifumi Ozaki, Haowei Xue, Keisuke Kintaka, and Takatsugu Yamauchi 42

contributed to the analysis of data. All authors have critically reviewed the manuscript, 43

approved the final version of the manuscript, and agreed to be accountable for all aspects of 44

the work.

45 46

Abstract 47

Purpose: The volume of medial meniscus (MM) extrusion at 10° and 90° knee flexions using 48

three-dimensional (3D) magnetic resonance imaging (MRI) and assessed relevant clinical 49

outcomes at 1-year follow-up were evaluated.

50

Methods: Twenty-four patients who underwent MM posterior root repair were retrospectively 51

reviewed. At 10° and 90° knee flexions, the meniscal extrusion distance and volume were 52

measured using 3D meniscus models constructed by SYNAPSE VINCENT®. The correlation 53

between Knee Injury and Osteoarthritis Outcome Score, Lysholm, International Knee 54

Documentation Committee scores, Tegner activity, and pain visual analog scales and changes 55

in MM extrusion were assessed.

56

Results: No significant differences in the MM medial extrusion were observed between 10°

57

and 90° knee flexions postoperatively. MM posterior extrusion (MMPE) decreased 58

significantly at 10° and 90° knee flexions postoperatively. At 90° knee flexion, the meniscus 59

volume at the intra-tibial surface increased at 3 and 12 months postoperatively. The MM 60

extrusion volume increased slightly at 10° knee flexion; however, the volume decreased 61

significantly at 90° knee flexion postoperatively. The change in MMPE significantly 62

correlated with clinical scores. All 12-month clinical scores were significantly improved 63

compared to preoperative scores.

64

Conclusions: The progression of meniscus posterior extrusion and reduction of its volume at 65

90° knee flexion can be suppressed by MM posterior root repair. Postoperative clinical scores 66

correlated with reductions of the posterior extrusion. Regarding clinical relevance, the 67

dynamic stability of the meniscus can be maintained by MM posterior root repair, which is an 68

effective therapeutic method for improving its clinical status.

69 70

Level of Evidence: Level IV 71

Keywords: Medial meniscus, Posterior root tear, Transtibial pullout repair, Meniscal 72

extrusion, Three-dimensional magnetic resonance imaging 73

74

Introduction 75

Load transfer, concussion absorption, lubrication, and joint stabilization are included as the 76

main functions of the meniscus [21]. Great elasticity and compressive properties are shown by 77

the meniscus, which is composed of tight collagen fibers [24]. High pressure during 78

weight-bearing is resisted by the medial meniscus (MM), which causes the meniscus to slide 79

outward during compression [15]. Complete radial and/or oblique tears near the posterior root 80

attachment are included in MM posterior root tear (MMPRT), which damages the functional 81

meniscus of the ligament and accelerates the degeneration of the knee cartilage [7, 26, 30].

82

The appearance of an MM extrusion (MME) is caused by MMPRT, and an MME ≥3 mm is 83

associated with the degeneration of articular cartilage [4].

84

Good clinical efficacy in treating MMPRT has been achieved by MM posterior root repairs 85

[5]. Several other techniques have been reported to provide favorable clinical outcomes, 86

including modified Mason-Allen suture with FasT-Fix and pull-out repairs using two simple 87

stitches [5]. However, MM posterior root repair could not reduce the MME completely, as 88

suggested by some studies [1, 13]. Magnetic resonance imaging (MRI) is an important 89

method for diagnosing an MME in patients with MMPRT [28]. However, in conventional 90

two-dimensional (2D) MRI, it is difficult to evaluate an MME stereoscopically because it can 91

only be analyzed in coronal and sagittal cross-sections [6, 16]. Calculations of the meniscus 92

volume are possible by three-dimensional (3D) MRI, which provides accurate visualizations, 93

thereby enabling a proper size assessment [17]. The volume of the MME is an important 94

index that reflects the degree of whole meniscal extrusion. MM posterior root repair 95

reportedly decreased the extrusion volume at 3 months postoperatively [6]. However, no mid- 96

or long-term follow-up studies have been conducted to date. Therefore, time-dependent 97

changes in the MME volume (MMEV) after increasing weight-bearing and overall activity 98

remain unclear.

99

This is the first 1-year follow-up study using 3D MRI to evaluate the changes of MMEV 100

and relevant clinical scores after full weight-bearing and exercise. The improvement of 101

postoperative outcome is considered to be related to the dynamic stability of meniscus after 102

surgery, which provided a reference for the rehabilitation plans. It was hypothesized that MM 103

posterior root repair could suppress the progression of MM posterior extrusion (MMPE) and 104

reduce the extrusion volume at a 90° flexion position while improving the clinical scores.

105 106

Materials and methods 107

This study was approved by the Institutional Review Board of Okayama University Graduate 108

School (ID number: 1857). Written informed consent was obtained from all patients. A total 109

of 24 patients who underwent the MM posterior root repair between August 2017 and 110

December 2018 were included. Knee injuries are generally caused by descending (50%), 111

walking (25%), physical exercise (12.5%), and twisting (12.5%). Preoperative radiographs 112

and MRI in all patients confirmed that the femoral-tibial angle was smaller than 180° with a 113

mild cartilage lesion in Outerbridge grade I or II, and all patients needed surgical repair. MRI 114

revealed a ghost sign, radial tear sign, cleft sign, and giraffe neck sign [3]. According to the 115

LaPrade classification, the types of MMPRT determined by intraoperative examination were 116

as follows: type I, partial tear; type II, complete radial tear; type III and type IV, a complete 117

radial tear with a bucket-handle tear and an oblique tear extending into the meniscus root 118

attachment; and type V, root avulsion fracture [10]. Type II and IV tears were repaired using 119

two simple stitches suture or modified Mason-Allen stitch through the tibia [5]. After 120

applying tension from 20 N to 30 N, the tibia was fixed with a bioabsorbable screw or a 121

double-spike plate [5]. In the first 2 weeks after the operation, all patients maintained a 122

non-weight-bearing state. Knee flexion began at 2 weeks postoperatively and progressively 123

increased to 120° knee flexion at 6 weeks postoperatively. Partial weight-bearing with 124

crutches was increased by 20 kg per week. At 6 weeks, the patients progressed to full 125

weight-bearing. MRI was performed 3 and 12 months after the operation. Deep knee flexion 126

was allowed at 3 months postoperatively. Athletic activities were permitted at 6 months 127

postoperatively. The clinical outcomes were evaluated at 3, 6, and 12 months after the surgery 128

using the Knee Injury and Osteoarthritis Outcome Score (KOOS), Lysholm score, Tegner 129

activity scale (TAS), International Knee Documentation Committee (IKDC) score, and visual 130

analog scale (VAS). The KOOS includes pain, symptoms, activities of daily living (ADL), 131

sport and recreation activities (sport/rec), and knee-related quality of life (QOL) outcomes.

132

3D MRI protocol and meniscus reconstruction 133

Patients were examined by open MRI using an Oasis 1.2 Tesla instrument (Hitachi Medical, 134

Chiba, Japan) in a non-weight bearing state. Continuous multi-planar 1-mm-thick images 135

were taken at 10° and 90° knee flexions. In both coronal and sagittal planes, multiplanar 136

images were obtained by a proton density-weighted isotropic resolution fast spin-echo (iso 137

FSE, Hitachi Medical) sequence [17].

138

The MRI images were imported into a 3D image analysis workstation (SYNAPSE 139

VINCENT®). The 3D models of femur, tibia, and fibula were generated semi-automatically 140

through a volume rendering technology, and the bone surface was segmented by an intensity 141

threshold [19]. The 3D meniscus models were extracted and constructed on every slice using 142

a texture tracking technology by a radiologist and two orthopedic doctors with more than 5 143

years of experience in meniscus MRI analysis [27]. The intraclass correlation coefficient 144

(ICC) was used to evaluate reliabilities. Recent research has demonstrated that the size and 145

volume of 3D meniscus models are very similar to those of the real meniscus [17].

146

Measurement methods 147

The 3D-based measurement was performed above the axis parallel to the tibial plateau using a 148

3D model of the meniscus, as described previously [17]. The MME area was created by 149

identifying the contour of the tibial plateau and cutting the inside of the MM through the 150

contour. MM medial extrusion (MMME) was described as the length between the medial tibia 151

edge and the outer MM edge. The MMPE was described as the length from the posterior tibia 152

edge to the MM edge. SYNAPSE VINCENT® was used to automatically calculate the 153

volume of the meniscus through voxel counting. The MM volume (MMV) was defined as the 154

total volume of the MM, and the MMEV was defined as the extruded part volume of the MM.

155

The MMEV ratio was defined as MMEV divided by MMV and multiplied by 100%. The 156

MMV on the intra-tibial surface was defined as the MM residual volume (MMRV). The 157

MMRV ratio was defined as the MMRV divided by MMV, multiplied by 100%. The 3D 158

parameters mentioned above were evaluated among the preoperative stage, 3 months, and 12 159

months postoperative stages with knee flexions at 10° and 90° (Figure 1).

160

Statistical analysis 161

Statistical analyses were performed using SPSS Statistics, version 25.0 (IBM Corp., Armonk, 162

NY, USA). The data are presented as mean ± standard deviation (SD), and values of p <0.05 163

were considered statistically significant. A repeated-measures analysis of variance was used to 164

compare the clinical scores, and Dunnett's multiple comparison test was used to compare the 165

preoperative and postoperative MRI parameters. A Pearson’s correlation analysis was used to 166

compare the clinical scores with the changes in MMME and MMPE. The sample size was 167

estimated to have a minimum statistical power of 80% (α=0.05). A sample size of 20 patients 168

can detect a difference in the design.

169 170

Results 171

3D-MRI parameters 172

The baseline characteristics and demographics of all 24 patients are presented in Table 1.

173

There was no significant difference between patients' knee alignment preoperatively (177.5° ± 174

1.8°) and 1-year postoperatively (177.1° ± 1.7°).

175

At 10° knee flexion, the MMME was smaller at 3 and 12 months postoperative stages than 176

that at the preoperative stage; however, no significant differences were observed. MMPE at 177

12 months postoperative stage decreased significantly compared to that at the preoperative 178

and 3 months postoperative stages. The MMEV and MMEV ratios decreased significantly at 3 179

months postoperatively (Table 2, Figure 2).

180

At 90° knee flexion, the MMME at 3 and 12 months postoperatively was smaller than that 181

at the preoperative stage, although no significant differences were observed. The 182

postoperative MMPE decreased significantly; however, no significant difference was 183

observed between the values at 3 and 12 months. The MMEV and MMEV ratios decreased at 184

3 months (p < 0.01) and 12 months postoperatively (p < 0.01), while the MMRV and MMRV 185

ratios increased at 3 and 12 months postoperatively (p < 0.01) compared to preoperative 186

values (Table 3, Figure 2).

187

Clinical scores 188

All the clinical scores at 12 months postoperative were significantly improved compared to 189

the preoperative scores (Figure 3). Postoperative changes in MMME did not correlate with the 190

clinical scores. Similarly, postoperative changes in MMPE at 10° knee flexion did not 191

correlate with the clinical scores at 12 months postoperatively. However, the changes in 192

MMPE at 90° knee flexion were significantly correlated with 12-month postoperative clinical 193

scores (Table 4).

194

Reliability evaluation 195

The ICCs for intra-observer reliability of MMV and MMEV were 0.92 (95% CI, 0.88–0.95) 196

and 0.93 (95% CI, 0.89–0.96), respectively. The ICCs for intra-observer reliability of MMME 197

and MMPE were 0.90 (95% CI, 0.87–0.94) and 0.92 (95% CI, 0.89–0.95), respectively.

198

The ICCs for inter-observer reliability of MMV and MMEV were 0.95 (95% CI, 0.93–

199

0.97) 200

and 0.96 (95% CI, 0.94–0.98), respectively. The ICCs for inter-observer reliability of MMME 201

and MMPE were 0.92 (95% CI, 0.89–0.96) and 0.93 (95% CI, 0.89–0.96), respectively.

202 203

Discussion 204

The main finding of this study was that MMPE was significantly reduced following MM 205

posterior root repair. At 90° knee flexion, the MMEV and MMEV ratios significantly 206

decreased at 3 and 12 months postoperatively, whereas the MMRV and MMRV ratios 207

significantly increased compared to the preoperative values. These results indicate that MM 208

posterior root repair could reduce the posterior displacement during knee flexion and increase 209

the volume or contact surface area, facilitating the restoration of meniscus functionality. The 210

healing of the meniscal degeneration reached a plateau with an increase in the load and 211

suppression of the MMEV. Notably, all the clinical scores were significantly higher at the 212

12-month postoperative stage than at the preoperative stage.

213

MMPRT prevents the conversion of an axial load into hoop stress by the meniscus. The 214

increased stress makes the MM move outward, leading to cartilage degeneration [22]. Early 215

recognition and treatment could prevent cartilage degeneration and the development of knee 216

osteoarthritis [14]. MME progresses shortly after the onset of MMPRT [4]. MM posterior root 217

repair plays an important role in improving clinical outcome [1, 31] and impedes the 218

advancement of osteoarthritis [8, 9]. Compared with the surgical repair of a meniscus body 219

tear, the MM posterior root repair has achieved good clinical outcomes [29]. The effect of 220

surgical treatment on the posterior root repair is also better than non-surgical treatment [11]. If 221

patients meet the surgical indications for MMPRT repair, MM posterior root repair should be 222

used to treat symptomatic MMPRT immediately following the diagnosis [11]. The ideal 223

postoperative rehabilitation plan is different after MM posterior root repair, and it is difficult 224

to separate the results from rehabilitation programs [23]. Long periods of non-weight-bearing 225

and physiotherapy are also factors responsible for improving clinical outcomes.

226

Additionally, 3D MRI has higher measurement accuracy than 2D MRI, and it can 227

accurately estimate the shape and size of the entire meniscus [17]. In a recent study, MMPE 228

was shown to become larger at 90° knee flexion. However, the change in MMME was not 229

affected by the flexion angle of the knee joint [12]. In another study [18], MMPE was shown 230

to be reduced at 90° knee flexion at 3 months postoperatively, which is consistent with our 231

results. In this study, at the 12-month follow-up, MMPE decreased further and became more 232

significant at 10° knee flexion. In another 1-year follow-up study, the postoperative MMME 233

was higher than that measured preoperatively, and the knee joint cartilage was partially 234

degenerated [9]. However, in this study, although MMME at 12 months postoperatively was 235

slightly higher than that at 3 months postoperatively, it was lower than the preoperative level.

236

This might be due to the increase in postoperative weight-bearing and overall activities, 237

resulting in the laxity of the meniscus and joint capsule [20]. The severity of MME is related 238

to the decrease in the meniscus volume of the medial compartment and the narrowing of the 239

medial joint space [14, 28]. However, the mechanism underlying changes in postoperative 240

MMME remains unclear; therefore, further research is needed. The changes in MMME have 241

limited contributions to the MMEV, and they are not related to the increasing clinical scores.

242

At 10° knee flexion, the values of MMPE are negative and cannot contribute to the actual 243

MMEV. However, the values of MMPE are positive at 90° knee flexion and contribute to the 244

MMEV. The significantly reduced MMPE is notably related to improved clinical scores.

245

Anatomical repair is important for restoring the normal contact pressure of the medial 246

compartment during knee flexion [2]. The appropriate increase in the meniscus volume in the 247

medial compartment could better maintain the functionality of the meniscus [25]. In our study, 248

we observed that the MMEV and MMEV ratios were significantly reduced. Similarly, the 249

MMRV and MMRV ratios were significantly improved at 12 months postoperatively at 90°

250

knee flexion, while no significant difference was observed between the values at 3 and 12 251

months postoperatively. Moreover, these observations highlight that MM pullout repair plays 252

an important role in maintaining the MMV at the intra-tibial surface, as the meniscus volume 253

was increased at both the 3 months and 12 months postoperative stages.

254

This study has several limitations. First, the number of patients included was rather small, 255

and the follow-up period was only 1 year. Second, the SYNAPSE VINCENT® method 256

generated measurement errors due to the discrepancy between the manual segmentation and 257

identification of the meniscus boundary and the actual boundary. Third, MME varied between 258

the unloaded knee and the actual load-bearing knee. Finally, the marginal increase in MMME 259

at the 12-month postoperative stage compared with that at the 3-month postoperative stage is 260

yet to be investigated.

261

Regarding the clinical relevance, the dynamic stability of the MM at the knee flexion 262

position can be maintained by MM posterior root repair. Furthermore, the MM posterior root 263

repair could prevent the progression of MME and reduce MMEV. The procedure is an 264

effective therapeutic method for the treatment of MMPRT and amelioration of MME. In 265

addition, the visualization of the morphological changes of MM is helpful for adjusting 266

rehabilitation plans and clinical outcome evaluations.

267 268

Conclusion 269

MM posterior root repair can suppress the postoperative progression of MMPE associated 270

with the 90° flexion position. Moreover, the MM posterior root repair is effective for 271

inhibiting the progression of MME and reducing MMEV. All postoperative clinical scores 272

were significantly improved than those at the preoperative stage, and they correlated with the 273

changes in MMPE at 90° knee flexion.

274

LIST OF ABBREVIATIONS 275

MM, medial meniscus 276

MME, medial meniscus extrusion 277

MMEV, medial meniscus extrusion volume 278

MMME, medial meniscus medial extrusion 279

MMPE, medial meniscus posterior extrusion 280

MMPRT, medial meniscus posterior root tear 281

MMRV, medial meniscus remaining volume 282

MMV, medial meniscus volume 283

MRI, magnetic resonance imaging 284

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398

Figure legends 399

Fig. 1 Three-dimensional (3D) reconstructed images of an MMPRT knee using SYNAPSE 400

VINCENT ® (Fuji Medical System, Tokyo, Japan) 401

a. Measurement of the 3D model of the meniscus at 10° of knee flexion including the 402

meniscus (cyan area) and extrusion area (purple area). A red reference line intersecting the 403

tibial intercondylar eminences is created. The MMME (black arrow) refers to the distance 404

from the medial edge of the tibia (grey dashed line) to the meniscus (black dashed line). The 405

MMPE (black arrow) refers to the distance from the posterior edge of the tibia (grey dashed 406

line) to the meniscus (black dashed line).

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b. Measurement of the 3D model of the meniscus at 90° of knee flexion including the 408

meniscus (cyan area) and extrusion area (purple area). The volume of the intra-tibial surface 409

area (cyan area) is represented by MMRV. MMPRT medial meniscus posterior root tear;

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MMME medial meniscus medial extrusion; MMPE medial meniscus posterior extrusion;

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MMRV medial meniscus residual volume.

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Fig. 2 The changes of the 3D meniscus morphology of a 55-year-old female patient 414

preoperatively, 3 months postoperatively, and 12 months postoperatively 415

a. At 10° flexion preoperatively, the extruded meniscus (purple area) was located on the 416

medial inside. b. At 90° flexion, preoperatively, the meniscus moved backward, and the 417

purple area concentrated on the posterior side. c. At 10° flexion, 3 months postoperatively, the 418

purple area on the medial side was reduced. d. At 90° flexion, 3 months postoperatively, the 419

purple area and the posterior displacement was decreased, with the cyan area inside the joint 420

also increasing. e. At 10° flexion, 12 months postoperatively, there were only slight changes 421

in the purple area on the medial side. f. At 90° flexion, 12 months postoperatively, the 422

posterior displacement and the purple area continued to decrease, with the cyan area 423

increasing.

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Fig. 3 Time-dependent clinical outcomes 426

Data were analyzed preoperatively, 3 months postoperatively, and 12 months postoperatively.

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All scores significantly increased at 12 months postoperatively. a. KOOS. b. Lysholm score, 428

Tegner activity score, IKDC score, and VAS pain. KOOS Knee Injury and Osteoarthritis 429

Outcome Score, ADL activities of daily living, Sport/Rec sport and recreation function, QOL 430

quality of life, IKDC International Knee Documentation Committee subjective knee 431

evaluation form, VAS visual analogue scale. *p < 0.05; **p < 0.01.

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