Meniscal Augmentation and Replacement (Menaflex, Actifit, and NUsurface)

  • Aad Alfons Maria Dhollander
  • Vincenzo Condello
  • Vincenzo Madonna
  • Marco Bonomo
  • Peter Verdonk


In the last decades, the surgical treatment of meniscal injury or damage has shifted from a total meniscectomy to a partial meniscectomy or repair. Rather than a removal of meniscal tissue, the goal of novel surgical techniques is to preserve as much functional meniscal tissue as possible. Recently, attempts have been made to promote meniscal healing, as well as the replacement of damaged menisci with allografts, scaffolds, meniscal implants, or substitutes. This chapter will focus on meniscal augmentation and on three types of meniscal replacement devices. These substitutes are the biological Menaflex™ or collagen meniscal implant (CMI), the biomimetic Actifit™ meniscal scaffold, and the nonbiological NUsurface® meniscal substitute.


Meniscus Menaflex™ CMI Actifit™ NUsurface™ Scaffold Meniscus Augmentation Meniscus implant Meniscus substitute 

Meniscal Augmentation

Current knowledge indicates that meniscus repair is the preferred choice for the treatment of patients with a meniscus lesion. However, there are still conditions in which this is not feasible, for example, lesions located in the inner third of the meniscus, an area with limited vascular supply and healing potential [1]. Repair of degenerative tears of the meniscus is jeopardized because of the tear pattern, the tissue quality, and the typically older patient profile with which they are associated. Therefore, this type of meniscal tears is usually an indication for meniscectomy. Moreover, in the ideal situation, when tears seem to have the appropriate physical and biological characteristics for repair, there still remains a failure rate of up to 30% [2]. For this reason, the consideration of augmentation techniques in order to enhance meniscus repair is of interest for both surgeons and scientists [3]. The goal of these strategies is to overcome the inherent limitations of meniscal healing by promoting chemotaxis, cellular proliferation, and matrix production. Early augmentation strategies were based on mechanical stimuli used to enhance healing by creating vascular access and stimulating cells, cytokines, and bone marrow cells in the proximity of the repair site. These techniques have been applied clinically over the years with varying clinical outcomes [2]. In the literature, the use of an exogenous fibrin clot, growth factors and cells from different origin have also been described to improve meniscal repair [4].

More recently, three clinical studies were published discussing augmentation approaches to enhance meniscus repair. Jang et al. published an arthroscopic technique that adds an autologous fibrin clot to inside-out sutures [5]. This technique had a success rate of 95% (39 of 41 patients). The study included 41 meniscus tears (19 radial tears, 12 longitudinal tears in the red–white zone, 7 transverse tears, and 3 oblique tears). Ra et al. also reported on the efficacy of inside-out meniscus sutures in combination with a fibrin clot used to treat radial meniscus tears [6]. Lysholm scores improved from 65 ± 6 to 94 ± 3 and the International Knee Documentation Committee subjective knee scores from 57 ± 7 to 92 ± 3, at a mean of 30 ± 4 months postoperatively. Complete healing of the meniscus lesion was shown in six of seven cases by second-look arthroscopy. Data from both studies mentioned showed a benefit to using fibrin clot in meniscus surgery [5, 6]. The delivery mechanism described by Jang et al. may provide a user-friendly technique for application in a daily clinical setting [5].

Vangsness et al. published on a randomized double-blind controlled study investigating the safety of intra-articular injection of human mesenchymal stem cells (MSCs) into the knee. The purpose of this study was to investigate the ability of MSCs to promote meniscus regeneration after partial meniscectomy and to evaluate the effects of MSCs on osteoarthritic changes in the knee [7]. At 7 institutions, 55 patients underwent an arthroscopic partial medial meniscectomy. Between 7 and 10 days after meniscectomy, patients were given a single superolateral knee injection. They were randomized and allocated to one of the three treatment groups: group 1, in which patients received an injection of 50 ± 106 allogeneic MSCs; group 2, in which patients were injected with 150 ± 106 allogeneic MSCs; and group 3, which served as a control group, in which patients received sodium hyaluronate (hyaluronic acid/hyaluronan). Over a period of 2 years, safety, meniscus regeneration, overall condition of the knee joint, and clinical outcomes of the patients were assessed. Also sequential magnetic resonance imaging (MRI) was performed. No ectopic tissue formation or clinically important safety issues were identified. There was significantly increased meniscus volume (defined a priori as a 15% threshold) shown by quantitative MRI in 24% of patients in group 1 and in 6% of patients in group 2 at 12 months after meniscectomy (P = 0.022). No patients in the control group met the 15% threshold for increased meniscus volume. Patients with osteoarthritic changes who received MSCs experienced a significant reduction in pain compared with those who received the control vehicle, based on visual analog scale assessments [7].

Meniscal Replacement

Collagen Meniscal Implant (CMI)


First described in 1992, the Menaflex collagen meniscus implant, also called CMI, is a tissue engineering product [8]. CMI was developed for the treatment of irreparable meniscal tears or previous partial meniscectomy. The goal of the implant is to enhance regeneration of meniscal-like tissue and secondarily to prevent degenerative joint changes in the knee. CMI is composed of a three-dimensional type I collagen network originated from bovine Achilles tendon and enriched with glycosaminoglycans (GAGs), including chondroitin sulfate and hyaluronic acid, with the purpose of stimulating cellular ingrowth. It is processed chemically and physically to remove molecular antigens and non-collagenous materials. The shape is similar to the human meniscus, and the used materials are biocompatible (Fig. 28.1) [8].
Fig. 28.1

Collagen meniscus implant (CMI). The semicircular shape and triangular section like a normal meniscus are evident

In vitro studies demonstrated that fibroblasts were able to migrate inside the scaffold. This phenomenon stimulated the proliferation of cells and the production of extracellular matrix [8]. In animal studies, CMI was shown to be biocompatible, and resorption times ranged from 9 to 12 months [8]. These data were confirmed by clinical feasibility studies, which showed the formation of a meniscal-like structure without any cartilage damage and immunologic reaction [9, 10]. In the clinical setting, the variables may be schematically divided into two groups: biological factors , such as age of the patient, degree of joint degeneration, etc., and mechanical factors, such as the size of the lesion, any limb malalignment, and knee instability that represent relative contraindications to the CMI if not corrected before and/or at the time of surgery. The results at medium- and long-term follow-up are promising if correct indications are respected and patients are compliant with the rehabilitation program [11].


Indications :

  • Age less than 55 years

  • Pain after partial meniscectomy

Contraindications :

  • Osteoarthritis (> grade III)

  • Pain after total meniscectomy

  • Allergy to implant material

  • Ligamentous instability

  • Malalignment

  • Infections

  • Rheumatoid diseases

Surgical Technique

CMI is implanted arthroscopically through conventional anterolateral and anteromedial portals. Only the irreparably damaged tissue is removed after a detailed arthroscopic evaluation of the knee joint. The aim is to obtain healthy tissue in the red–red or red–white zones of the periphery of the segmental defect. After debridement, the meniscal defect is measured using a dedicated sizing device, and the CMI is sized and trimmed to fill the defect. In order to augment a “healing response” by potentially enhancing cellular invasion of the implant, trephination of the remnant and perimeniscal synovial abrasion of the adjacent capsule are performed. CMI is then introduced through an arthroscopic cannula. For visualization purposes, a “piecrust” partial release of the MCL may be necessary, which is achieved by trephination of the ligament with a spinal needle. The scaffold is fixated to the meniscal remnant using 2–0 nonabsorbable sutures with a standard all-inside, inside-out, or outside-in technique. Vertical mattress sutures are used for the body of the implant, and horizontal mattress sutures are used to secure the CMI to the posterior horn root and the remaining body of the meniscus, anterior to the segmental defect. The implant stability is tested with a probe after suturing (Figs. 28.2, 28.3, and 28.4).
Fig. 28.2

Collagen meniscal implant (CMI) surgical technique. a Irreparable meniscal lesion. b Debridement of the lesion. c Measurement of the meniscal defect using a dedicated rod. d, e CMI is introduced in an arthroscopic cannula. f Scaffold sutured to the meniscal stump

Fig. 28.3

Final arthroscopic view of CMI after implantation: (*) implant, (<) residual native meniscus, (◄) femoral condyle, and (◄◄) nonabsorbable suture

Fig. 28.4

Appearance of the implant at 6 months: (*) implant, (<) residual native meniscus, (◄) femoral condyle, and (◄◄) nonabsorbable suture


In rest, the knee is kept in extension in a brace for 6 weeks. The patient is immediately allowed to perform continuous passive motion 3–4 times daily: flexion should not exceed 60° for 4 weeks and 90° until the seventh week. During the first 6 weeks, weight-bearing is not allowed, and patients walk using crutches. Partial weight-bearing is allowed 6 weeks after the operation and full weight-bearing 2–3 weeks thereafter. Return to unrestricted sport activities is usually allowed at 6 months.



Actifit™ is a biodegradable, synthetic acellular scaffold composed of two components, a polyester (poly-ε(epsilon)-caprolactone = soft segments) and polyurethane (= stiff segments) (Fig. 28.5). Compared to CMI, Actifit™ by Orteq Bioengineering Ltd. (London, UK) has easier handling and better early biomechanical properties. Preclinical studies in dogs have shown complete infiltration of the porous structure after 3 months and complete integration with the peripheral capsule after 6 months [12]. The Actifit™ is available in two configurations: medial and lateral. In a clinical series consisted of 52 Actifit scaffold implantations, Verdonk et al. reported statistically significant improvement of all clinical outcome scores used in the study (VAS pain, IKDC, Lysholm, and KOOS) at 6 months after surgery. Furthermore the degree of clinical improvement continued, remaining statistically significant as compared with baseline, at 24 months follow-up visit [13]. Tissue ingrowth was demonstrated on MRI in 81,4% (35 of 43) of patients at 3 months after implantation. The same authors showed integration of scaffold during second-look arthroscopy in 97,7% (43 of 44) of patients and meniscus-like tissue ingrowth in all (44) biopsy specimens taken during the second-look arthroscopy at 12 months after implantation [14]. Recently, it was shown that Actifit™ can improve knee joint function and significantly reduce pain in patients with segmental meniscus deficiency up to 5 years after implantation. A 5-year follow-up reported stable cartilage status in the index compartment in only 46.7% of patients, calling into question the chondroprotective ability of the implant. In addition, a relatively high failure rate was noticed. Long-term and randomized controlled studies are mandatory to confirm the initial results and the reliability of this procedure [15].
Fig. 28.5

Actifit™ meniscus implant: available in two configurations, medial and lateral. It is a biodegradable, synthetic acellular scaffold composed by a polyester (poly-ε(epsilon)-caprolactone = soft segments) and polyurethane (= stiff segments)


Indications :

  • Irreparable medial or lateral meniscal tear or partial meniscus loss, with intact rim. Most importantly, the synthetic meniscus substitute is not intended for the treatment of total or subtotal meniscus defects. Ideally, the defect length should be limited to 5–6 cm.

  • Skeletally mature male or female patients.

  • Age 16–50 years.

  • Stable knee joint or knee joint stabilization procedure within 12 weeks of index procedure.

  • International Cartilage Repair Society (ICRS) classification ≤ 3.

Contraindications :

  • Total meniscus loss or unstable segmental rim defect (including posterior root lesions)

  • Multiple areas of partial meniscus loss that could not be treated by a single scaffold

  • Any significant malalignment (varus or valgus)

  • Presence of cartilage defects ICRS classification > 3

  • BMI ≥ 35

  • Infections

  • Rheumatoid diseases

Surgical Technique

A standard arthroscopic surgery procedure and standard equipment are used to place the Actifit® meniscal scaffold in the patient’s knee. Cartilage status and integrity of the meniscal rim and both the anterior and posterior horns should be checked prior to implantation. In the case of a tight medial compartment, the outside-in puncture method (several passes with a spinal needle from outside-in) or the inside-out piecrusting release technique can be used to distend the medial collateral ligament. In this way, the surgeon can adequately visualize both the femoral and the tibial cartilage status and create an adequate working space for the meniscal replacement procedure. In the first stage, the damaged meniscus should be prepared for implantation. This includes surgical debridement and removal of all pathological tissue, in order to ensure that the resulting defect site extends into the vascularized red-on-red or red-on-white zone of the damaged portion of the meniscus. Defects located away from the synovial border have limited healing potential and therefore should be excluded from this type of surgery. The meniscal rim may be punctured in order to create vascular access channels to stimulate a healing response. Gentle rasping of the synovial lining may further enhance meniscal integration and tissue ingrowth. With use of the specially designed meniscal ruler and meniscal ruler guide, the meniscal defect is measured along the curvature of its inner edge. Actifit® is then measured and, using a scalpel, cut to fit in such a place and manner that sterility is maintained at all times. Oversizing of the length by 10% is advised (3 mm for defects <3 cm and 5 mm for defects ≥3 cm), to allow for shrinkage of the scaffold caused by suturing of the spongelike material and to ensure a snug optimal fit into the prepared defect. The anterior side of the scaffold should be cut at an oblique angle of 30–45°, in order to achieve a perfect fit with the native meniscus at the anterior junction (Fig. 28.6). An enlargement of the portal used for insertion of the device may be requested (the size of the little finger is usually sufficient) to allow for a smooth entry of the scaffold.
Fig. 28.6

The Actifit® meniscal scaffold is tailored on surgical field using a scalpel for a perfect fit to the meniscus defect

Fixation of Actifit® is achieved by suturing the scaffold to the native meniscus tissue and should start with a horizontal all-inside suture from the posterior edge of the scaffold to the native meniscus. Suturing should be secure; however, attention must be paid not to over tighten sutures, as this may alter and indent the surface of the scaffold. The distances between the sutures should be kept to approximately 0.5 cm. Each suture should be placed at one-third to one-half of the scaffold’s height, as determined from the lower surface of the scaffold.

After suturing, the scaffold may be further trimmed and fine-tuned intra-articularly using a basket punch if necessary. Once the scaffold is securely fixed, its stability is tested using the probe and moving the knee through a range of motion (0–90°).

A bone marrow aspirate can be performed from the notch area and directly applied on the dry scaffold after implantation to stimulate a healing response (Fig. 28.7).
Fig. 28.7

Macroscopic aspect of the Actifit® scaffold 1 year after implantation showing full incorporation and integration to the rim and horns


All patients are requested to undergo a conservative rehabilitation program comparable to that of a meniscal allograft, in order to protect the newly formed fragile tissue and to provide an optimum healing environment. The usual rehabilitation period consists of 16–24 weeks. The patient is non-weight-bearing for the first 3 weeks. Partial weight-bearing was permitted from week 4 onwards, with a gradual increase in loading up to 100% load at 9 weeks postimplantation. The progressive weight-bearing is initiated in stages, increasing by 10 kg per week for patients weighing ≤60 kg and by 15 kg per week for patients weighing >60 kg to ≤90 kg. Full weight-bearing with an unloader brace is allowed from week 9 onwards and without the use of the unloader brace from week 14 onwards. Range-of-motion exercises are gradually initiated but limited to 90° of flexion in the first 6 weeks. Gradual return to sports was generally commenced as of 6 months at the discretion of the responsible orthopedic surgeon ; however, contact sports were only permitted after 9 months.



A non-anchored, self-centered, medial meniscus implant (NUsurface® Meniscus Implant, Active Implants LLC, TN, USA; Fig. 28.8) has been developed as a bridge treatment for middle-aged patients [16], suffering from joint pain associated with loss of meniscal function. This concept of a medial meniscus implant with a reliable biomechanical performance differs from the previous products as it does not require fixation, or attachment, and since it is not designed to allow ingrowth of native tissue. The shape and morphology of the implant are based on an extensive MRI study that included the geometrical analysis of more than 100 knee scans and differs from previous interpositional devices by its unique lateral “bridge” which runs along the tibial spine and femoral notch to restrict excessive motion and dislocation [17, 18, 19]. Biomechanical optimization of the material properties of the implant was based on in vitro measurements of contact pressure under the implant in cadaver knees and computational finite element (FE) analyses and mixed-mode wear simulations [20]. The last preclinical stage was a sheep study in which an extensive quantitative cartilage evaluation was conducted microscopically, postimplantation [21]. The material properties of the device were tailored to provide it with an optimal pressure distribution capacity, to reduce cartilage loads and, thus, to relieve pain [22]. This concept distinguishes it from other interpositional devices because it is able to conform moderately under load, without risking its integrity.
Fig. 28.8

The NUsurface®: a medial meniscus implant made of polycarbonate-urethane (PCU), reinforced circumferentially with ultrahigh molecular weight polyethylene (UHMWPE) fibers (Dyneema® Purity, DSM)

A first-in-man series has been conducted starting in May 2008. Inclusion criteria were those mentioned in the following section but included patients with grade 4 cartilage degenerative disease according to Outerbridge classification. The second major difference versus the inclusion criteria listed below was that in this original series, no attention had been directed to the posterior root status of the involved meniscus. These two changes were made as a result of some clinical failures (unpublished data). Based on these data, a prospective, multicenter, nonrandomized, open-label study was started in Europe and Israel.

Between 2011 and 2013, 128 patients in Europe and Israel were enrolled in the single-arm, multicenter trial (MCT) of the NUsurface® Meniscus Implant. Key findings of this MCT included clear and significant clinical improvement based on KOOS, VAS, IKDC, and EQ-5D at every time point out to 2 years post-op. MRIs taken over this 2-year period provide some preliminary evidence that the NUsurface® maintained the condition of the cartilage adjacent to the implant in the majority of patients. During the study it was determined that a failure mode had been identified for the implant that could be addressed by implementing some manufacturing improvements that doubled the fatigue strength compared to the first generation of the device. Some patients were revised from the first-generation implant to the newer version, and the experience from these cases revealed that the device can be removed and replaced without any damage to the cartilage of the knee and that prior to removal of a device, any particle debris generated during normal use of the device is well tolerated and does not cause acute synovitis.

Currently, two FDA clinical studies are ongoing in the USA, including patients from the EU and Israel: a prospective, multicenter, randomized controlled clinical trial (VENUS: Verification of the Effectiveness of the NUsurface® System ) and a prospective, multicenter study (SUN: Safety Utilizing NUsurface® ). The device used in these two studies is over twice as strong as the first-generation device implanted in the first-in-man and RCT trials.


Indications :

  • Degenerative and/or torn medial meniscus and/or previous meniscectomy confirmed by diagnostic MRI

  • Pain score of 75 or less on the KOOS pain scale, with 100 being normal

  • Neutral alignment ± 5° of the mechanical axis

  • Age between 35 and 75 years at the time of the planned surgery

Contraindications :

  • Grade IV articular cartilage loss (Outerbridge grading system) on the medial tibial plateau or femoral condyle that could contact the NUsurface® implant

  • Lateral compartment pain with lateral articular cartilage damage greater than grade II (OB) and/or lateral meniscus tear(s)

  • Varus or valgus knee deformity > 5°

  • Laxity level of more than II according to the ICRS score, secondary to previous injury of the ACL and/or PCL and/or LCL and/or MCL

  • Patellar instability or non-anatomically positioned patella

  • Patellar compartment pain and/or patellar articular cartilage damage greater than Grade II Outerbridge

  • Need for a tibial osteotomy at the time of surgery

  • ACL reconstruction performed < 9 months before implanting the NUsurface® device

  • Previously implanted prosthetic meniscus or ligament or knee implant made of plastic

  • Knee flexion contracture > 10°

  • Unable to flex the knee to 90°

  • Leg length discrepancy causing a noticeable limp

  • Previous major knee condyle surgery

  • Knee joint inflammatory disease including Sjogren’s syndrome

  • Morbidly obesity with a BMI > 35

Surgical Technique

Standard arthroscopic anterolateral and anteromedial portals are established. In the first stage, the remaining meniscus tissue is debrided to a stable meniscus rim. The continuity of the meniscus rim and horns is checked, the stability of the cruciate ligaments is documented, and the cartilage degeneration is evaluated. Subsequently, a longitudinal skin incision is made along the medial side of the patella with the knee flexed at 90°, approximately 5–7 cm long, starting from the apex of the patella down to the medial tibial metaphysis (Fig. 28.9). After the capsular incision, some synovial tissue and fat pad can be removed to improve visualization of the medial side of the joint from the capsule to the notch area.
Fig. 28.9

The skin incision is made on the medial side of the patella, approximately 5–7 cm long

Preoperatively, it is possible to determine the appropriate size of the implant using a template superimposed on a standardized X-ray of the knee, which measures the dimension of the medial compartment in the anteroposterior and medial–lateral directions. Seven implant sizes are available from size 30–90. Each step in size represents an increase of ~4% in all dimensions. For each implant size, a correlative trial device of the same dimension, with a circumferential radio-opaque line for intraoperative fluoroscopic positioning control, is available (Fig. 28.10).
Fig. 28.10

Intraoperative fluoroscopic anteroposterior view of the trial

The optimal position for the device insertion is around 30° of knee flexion in valgus stress. The device is clamped by a dedicated inserter that holds it along the anterior border (Fig. 28.11). After the NUsurface® is placed into the medial compartment, several cyclic flexion–extension movements are performed to center the device. The inspection should focus on medial side overhang; a few millimeters of medial extrusion are well tolerated by the medial capsular-ligament structures. Avoiding lateral impingement in the notch area is an important key point to allow a smooth sliding movement. For this reason, a limited posterior notchplasty is performed over the medial femoral condyle in order to facilitate the sliding of the device. Special attention should be given to the “roof” of the notch, to prevent impingement with the superior surface of the device under weight-bearing. The NUsurface® trial position can easily be controlled by fluoroscopy: this allows not only to confirm the static position but also the displacement in flexion and extension and to compare different sizes. After trial insertion, tracking and impingement of the device can be controlled by inserting the scope through the anterolateral portal during flexion–extension cycles. The insertion of the definitive implant is performed using the same technique as with the trial insertion. Capsular closure is performed in the standard fashion, while evaluating for possible anterior impingement in full extension. A drain may be used for the first night.
Fig. 28.11

Dedicated instruments to insert and out the NUsurface®


The knee is placed in a brace, locked in full extension for the first week. From the first day post-op, partial weight-bearing and quadriceps isometric exercises are allowed. Full weight-bearing as tolerated, hydrotherapy, and exercises in closed kinetic chain are started in the second week. Open kinetic chain exercises are allowed after 6 weeks. Proprioceptive exercises are encouraged, since lack of proprioception seems to be one of the main complaints of the patients during the first 2–3 months after implantation.

General Conclusion

Meniscus augmentation and replacement still represent an unresolved problem in orthopedics. There appears to be significant potential for augmentation strategies in meniscus surgery to enhance options for repair. However, there is still a lack of clinical studies being reported in this regard. There is a strong need for improved translational activities and infrastructure to link the large amounts of in vitro and preclinical biological data to clinical application [3].

Meniscal substitutes based on synthetic or natural polymers have been described [11, 12, 13, 14, 15]. Most of these implants are based on biodegradable materials, which form temporary scaffolds that degrade in the body over time and are replaced gradually by newly formed tissue. Potential shortcomings of this approach include the lack of durability, associated with most biodegradable materials under in vivo knee loading conditions, as well as the variability in the individual patient’s biological response to the implant, limited age of the target population, and the quality of the tissue formed [11, 12, 13, 14, 15].

Currently, conservative care (e.g., knee bracing, activity modification, and injections), and even primary, secondary, or multiple meniscectomies, represents the mainstream treatment for a ±50-year-old patient with symptoms from meniscal functional deficiency. At a later age, e.g., older than 65 years, clinicians often choose arthroplasty. Traditional unicompartmental knee arthroplasty (UKA) is still popular but requires significant bone resection and subsequent modification of the patient’s activity. Total knee arthroplasty (TKA) is a reliable procedure, but it is not usually recommended for younger patients, less than 55 years of age, who might require subsequent revision surgery.

The treatment gap noted above may now have treatment options which are in the investigational stage. Further research and development may eventually extend these biological options to more challenging meniscal lesions, in order to truly regenerate meniscal tissue with biological and biomechanical properties close to native meniscus.


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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Aad Alfons Maria Dhollander
    • 1
  • Vincenzo Condello
    • 2
  • Vincenzo Madonna
    • 2
  • Marco Bonomo
    • 2
  • Peter Verdonk
    • 3
    • 4
  1. 1.Department of Orthopedic Surgery and TraumatologyAZ KLINABrasschaatBelgium
  2. 2.Department of Orthopedics and TraumatologySacro Cuore-Don Calabria HospitalNegrar (Verona)Italy
  3. 3.Antwerp Orthopedic Center, Monica HospitalsAntwerpBelgium
  4. 4.Department of Orthopedic Surgery, Antwerp University HospitalAntwerpBelgium

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