T
he medial meniscus (MM) posterior root (PR) has been increasingly recognized to act synergis-tically with the meniscus for the purposes of joint stabi-lization, shock absorption, articular lubrication, and possibly proprioception [1,2]. Due to the intrinsic insufficiency of mobility during knee flexion, the MMPR is prone to injury [3,4]. An MM posterior root tear (PRT) commonly results in altered femorotibial loading, displacement of menisci, and degenerative changes in the knee [5,6]. Pullout repair has been reported to result in favorable clinical outcomes and is recommended for the treatment of MMPRT [7-9]. However, the healing status of the repaired MMPR assessed via direct viewing at second-look arthroscopy differs significantly among studies [10-12].Histological analysis is an increasingly popular methodological option for scrutinizing the anatomical
and pathological features of articular structures, and precise quantitative structural information on MMPR insertion has been obtained by histological analyses [13-15]. However, there are no published reports of histological analysis of the healing status of MMPR fol-lowing a pullout repair.
In this case report, we describe the first histological evaluation of repaired tissue after an MMPR repair, and provide both the histological and arthroscopic findings for comparison.
Case Presentation
This case report was approved by the institutional review board of Okayama University (approval #1857), and informed consent for publication was obtained from the patient. A 65-year-old man accidentally fell and injured his left knee while walking down stairs. An
CopyrightⒸ 2021 by Okayama University Medical School.
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Case Report
Histological Analysis of Repaired Tissue after Pullout Repair of a
Medial Meniscus Posterior Root Tear
Haowei Xue, Takayuki Furumatsu
＊, Yuki Okazaki, Takaaki Hiranaka,
Keisuke Kintaka, Ximing Zhang, Aki Yoshida, and Toshifumi Ozaki
Department of Orthopaedic Surgery, Okayama University Graduate School of Medicine,Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan
A 65-year-old man presented with a left medial meniscus (MM) posterior root tear (PRT). Unicompartmental knee arthroplasty was performed 12 months after transtibial pullout repair of the MMPRT. Repaired MM pos-terior root tissue was subjected to histological analysis. Immunostaining and picrosirius red staining showed sufficient deposition of type I collagen, and hematoxylin-eosin staining using a polarized microscope showed well-aligned fiber orientation in the repaired tissue. The repaired posterior root (post-transtibial pullout repair) showed mature and well-aligned ligament-like tissue. Preserving the MM posterior root remnant to mimic the original posterior root tissue might be useful when performing pullout repair.
Key words: medial meniscus, posterior root tear, unicompartmental knee arthroplasty, histological analysis, case
report
Received August 17, 2020 ; accepted November 11, 2020.
＊Corresponding author. Phone : +81-86-235-7273; Fax : +81-86-223-9727
MMPRT was identified via magnetic resonance imaging (MRI) (Figs.1,2) [16]. Ten weeks after the injury, a primary arthroscopic examination and a transtibial pullout repair of the MMPRT were performed sequen-tially (Fig.3A,B). Satisfactory clinical outcomes were achieved postoperatively. However, 10 months after the primary surgery (i.e., the MMPR repair), the patient severely twisted his left knee again and presented to our institution complaining of pain when walking or lying in bed. MRI indicated articular cartilage degeneration of the medial compartment, while continuity of the repaired meniscal root was observed in both the coronal and sagittal planes (Figs.1C,D,2B). Two months later (1 year after the primary surgery), a second-look arthroscopy and unicompartmental knee arthroplasty were performed simultaneously.
Arthroscopy. Primary arthroscopic examination and transtibial pullout repair of the MMPR using FasT-Fix-dependent modified Mason-Allen sutures (F-MMA) were performed as described previously [17]. Standard anteromedial and anterolateral portals were created, a LaPrade type 2C MMPRT was confirmed, and the MMPR remnant was preserved (Fig.3A) [18]. After initially applying 20-N tension to the sutures at 45° knee flexion, tibial fixation was performed using a double- spike plate and screw (Meira, Aichi, Japan) (Fig.3B).
A second-look arthroscopy was performed 1 year
Preoperative MRI
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Postoperative MRIC
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P re op er at iv e M R I P os to pe ra tiv e M R IFig. 2 Sagittal magnetic resonance imaging (MRI) of the present case with pullout repair of medial meniscus posterior root tear. A, Preoperative MRI showing the ghost sign (white arrowhead); B, Postoperative MRI showing continuity of the posterior root (gray arrowheads).
Fig. 1 Coronal magnetic resonance imaging (MRI) of the present case with pullout repair of a media meniscus posterior root tear. A ,B, Preoperative MRI showing mild medial meniscus extrusion, the giraffe neck sign (dotted area), and the cleft sign (white arrowhead) ; C ,D, Postoperative MRI showing progression of the medial meniscus extrusion (white arrow) and conti-nuity of the posterior root (gray arrowheads).
after the primary surgery. The suture bar of the FasT-Fix suture was found to have fallen off, and severe car-tilage degeneration was observed in the medial tibial plateau (Fig.3C). The continuity of the repaired MMPR was confirmed by probing (Fig.3D).
Unicompartmental knee arthroplasty. Unicom-partmental knee arthroplasty was performed using the Persona® Partial Knee system (Zimmer Biomet, Warsaw, IN, USA) after a second-look arthroscopy and removal of the double-spike plate. Proximal tibial resection was performed using a System 6 sagittal saw (#6208-000-000; Stryker, Kalamazoo, MI, USA), taking particular care to avoid damage to the repaired MMPR. A sagittal cut was made just medial to the apex of the medial tibial spine without damaging the tibial insertions of the ante-rior cruciate ligament. The horizontal cut was made 4 mm from the articular surface, with a tibial slope of 7°. A distal femoral resection was performed using a 10-mm cutting guide. An 8-mm insert was used to achieve a satisfactory flexion–extension balance.
Histological and immunohistochemical analyses.
The obtained MM with repaired tissue (Fig.4A) was fixed in 10% formalin solution and then decalcified in 20% ethylenediaminetetraacetic acid (EDTA) solution (Dojindo, Osaka, Japan). Coronal sections (6 mm thick) containing the posterior horn and repaired tissue were sequentially assessed using safranin-O staining, as previously described [13,14]. For the immunohisto-chemical assessment, after treatment with 0.1%
pro-teinase K (for 20 min at room temperature; Sigma, St. Louis, MO, USA), type I and III collagen depositions were investigated using a rabbit anti-type I collagen antibody (1 : 100; Abcam, Cambridge, MA, USA) and a mouse anti-type III collagen antibody (1 : 100; Abcam), respectively. Picrosirius red staining (0.1%; Abcam) was then performed to simultaneously deter-mine the distribution of collagen types I, II, and III with the use of a polarized microscope. Finally, the fiber arrangement of the repaired tissue was clarified using hematoxylin and eosin (H&E) staining (Abcam).
Repaired tissue that was significantly different from the in situ posterior horn of the MM was identified through histological staining (Fig.4B). The immunos-taining results indicated that the repaired MMPR pre-sented a ligament-like structure. In the superficial layer, immunohistochemical staining of the repaired tissue indicated a much greater amount of type I collagen deposition compared to type III collagen deposition (Fig.4C,D). Picrosirius red staining showed predomi-nant type I collagen deposition in the repaired tissue (Fig.4E). The H&E staining showed that the fiber ori-entation in the repaired tissue was considerably well arranged (Fig.4F). Similar results were observed in the deeper layer, in addition to angiogenesis (Fig.5).
Discussion
The most important findings of this case study were
Primary surgery (pullout repair)
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B
Second-look arthroscopy (UKA)
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D
Fig. 3 Arthroscopic findings of the present case with pullout repair of medial meniscus posterior root tear (MMPRT). A, The complete MMPRT was identified (white arrowhead); B, The MMPRT pullout repair was performed using the FasT-Fix dependent modified Mason-Allen suture technique; C, Severe cartilage degeneration (black arrowheads) and dropout of the suture bar (white arrow) were observed; D, Continuity of the repaired meniscus (gray arrowheads) is shown.
the abundant deposition of type I collagen and good fiber orientation following MMPR pullout repair, revealed by histological analysis of the repaired tissue.
Although the efficacy of MMPR pullout repair has been extensively confirmed in radiological and arthroscopic studies [9,10,12], this study is the first to investigate
B
D
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MM PH Repaired tissueC
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E
F
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C-F PH Repaired tissue Fig. 5Fig. 4 Macroscopic and histological findings of the obtained medial meniscus (MM). A, Top view of the obtained MM sample during the unicompartmental knee arthroplasty (black line: cut slice); B, Coronal section of the safranin-O-stained posterior horn (PH) and repaired tissue; C, Immunostaining using anti-type I collagen autibody (inlet, negative control); D, Immunostaining using anti-type III collagen autibody; E, Picrosirius red staining in polarized microscopy; F, Hematoxylin-eosin staining in polarized microscopy. Bars, 200 µm.
Fig. 5 Histological findings of the deeper layer of the repaired tissue shown in Figure 4B. Angiogenesis was observed (arrowheads). A, Immunostaining using anti-type I collagen auti-body; B, Immunostaining using anti-type III col-lagen autibody; C, Picrosirius red staining in polarized microscopy; D, Hematoxylin-eosin stain-ing. Bars, 100 µm.
the healing status of repaired tissue after an MMPR pullout repair through histological analyses.
Ligaments and tendons show a delayed healing pro-cess due to their hypocellular and hypovascular nature [19]. The healing process is composed of 3 overlapping stages: the inflammation stage, the proliferation or repair stage, and the remodeling stage [20]. In the repair stage, the number of cells increases with the recruitment of collagen-generating fibroblasts for the generation of extracellular matrix and the establishment of the fibrous network [21]. During the subsequent remodeling stage, the fibroblasts and fibers become aligned in the direction of mechanical stress, and the cell number decreases [22]. In the present case, the results of histological analyses showed considerably well-aligned cells and fibrous bundles, implying that the healing status of the repaired MMPR was in the remod-eling stage.
As the most abundant solid component of the extra-cellular matrix, type I collagen constitutes the main tensile component of the ligament and the ligament-like meniscal root [23]. In healthy ligaments, type I colla-gen polymerizes into thick, uniform bundles, and pathological changes reduce the number of fiber bun-dles and disrupt the normal arrangement [24]. An investigation of the cellular characteristics indicates that type I collagen is expressed in normal meniscal root cells [25]. In the present case, the thick bundles of fibrous tissue and the predominant deposition of type I collagen identified in the repaired tissue indicated that the repaired tissue possessed histological similarity to meniscal roots. Because it has been shown that fibro-blasts are extensively recruited and a significant amount of type I collagen is secreted during the remodeling stage [26], the healing status in the present case was deemed to be favorable.
It has been reported that type III collagen is physio-logically co-distributed with type I collagen and is implicated in the healing process of ligaments [27]. The gene expression of type III collagen is upregulated in the early repair stage and down-regulated in remodeling stage processes [28,29]. These studies emphasized the importance of type III collagen for the successful heal-ing of ligaments. However, the over-expression of type III collagen has been shown to be related to scar tissue formation and impaired tensile-bearing ability of healed ligaments [30]. The minimal deposition of type III col-lagen that we observed in the present case indicates that
the healing process of the repaired MMPR was in the remodeling stage and that sufficient tensile-bearing ability might be obtained.
In a previous study investigating structural and com-positional characteristics of meniscal root, tie- fibers were observed originating from the epiligament in the slice of the ligament furthest from the meniscus body, and the blood vessels were surrounded by tie- fibers and oriented along the root [31]. The authors concluded that the root may continue into the outer portion of the meniscus, where it subsequently blends with the more fibrocartilage-like inner portions of the tissue [31]. Similarly, we observed angiogenesis in the deeper layer of the repaired tissue in our patient, although tie-fibers were not identified; this may have been due to the difference in the direction of sample sectioning between these studies.
The biomechanical characteristics of the repaired MMPR have been reported to be significantly inferior to those of the normal MMPR, even at 1 year postopera-tively [30]. A biomechanical study investigating the ultimate failure load of native meniscal roots using cadaveric specimens noted an average failure load of the native MMPR of approximately 500 N [32]. Undoubtedly, the inclusion of mechanical assessments in the protocol of the present study would have contributed to the eval-uation of the repaired MMPR from another perspective. This case had a short-term follow-up, and biomechani-cal properties were not evaluated. The function of the meniscus may not have been sufficiently reconstructed, even with root repair, and the reaction surrounding the suture was not analyzed. Further investigations with long-term follow-ups are needed.
Conclusion
This is the first report of the histological presenta-tion of repaired tissue following the repair of an MMPR. Good fiber arrangement and abundant type I collagen deposition were observed in the repaired tissue. Preserving the root remnant may be useful to enhance biological healing when an MMPR repair is performed.
Acknowledgments. H.X. would like to thank the China Scholarship Council for scholarship support (CSC No. 201909210014). X.Z. would like to thank the Otsuka Toshimi Scholarship Foundation for scholarship sup-port (19-385, 20-89). We would like to thank Editage (www.editage.jp) for English language editing.
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