PM R 9 (2017) 998-1005www.pmrjournal.org

Original Research

Sonographically Guided Knee Meniscus Injections: Feasibility,Techniques, and Validation

Michael R. Baria, MD/MBA, Jacob L. Sellon, MD, Dan Lueders, MD, Jay Smith, MD

Abstract

Background: There is a growing interest in the use of biologic agents such as platelet-rich plasma and mesenchymal stem/stromalcells to treat musculoskeletal injuries, including meniscal tears. Although previous research has documented the role of diag-nostic ultrasound to evaluate meniscal tears, sonographically guided (SG) techniques to specifically deliver therapeutic agentsinto the meniscus have not been described.Objective: To describe and validate SG injection techniques for the body and posterior horn of the medial and lateral meniscus.Design: Prospective, cadaveric laboratory investigation.Setting: Academic institution procedural skills laboratory.Subjects: Five unenbalmed cadaveric knee-ankle-foot specimens from 5 donors (3 female and 2 male) ages 33-92 years (mean age74 years) with body mass indices of 21.1-32.4 kg/m2 (mean 24.1 kg/m2).Methods: A single, experienced operator completed SG injections into the bodies and posterior horns of the medial and lateralmenisci of 5 unenbalmed cadaveric knees using colored latex and a 22-gauge, 38-mm needle. After injection, coinvestigatorsdissected each specimen to assess latex distribution within the menisci and identify injury to intra-articular and periarticularstructures.Main Outcome Measures: Latex location within the target region of meniscus (accurate/inaccurate), and iatrogenic injury to “atrisk” intra- and periarticular structures (present/absent).Results: Seventeen of 20 injections were accurate. Two of 3 inaccurate injections infiltrated the posterior horn of the medialmeniscus instead of the targeted meniscal body. One inaccurate lateral meniscus injection did not contain latex despite sono-graphically accurate needle placement. No specimen exhibited injury to regional neurovascular structures or intra-articularhyaline cartilage.Conclusions: SG meniscus injections are feasible and can accurately and safely deliver injectates such as regenerative agents intobodies and posterior horns of the medial and lateral menisci. The role of SG intrameniscal injections in the treatment of patientswith degenerative and traumatic meniscal disorders warrants further exploration.Level of Evidence: Not applicable.

Introduction

Knee meniscal injuries are very common, maysignificantly impact function, and predispose the kneeto accelerated osteoarthritis [1]. The body and posteriorhorn of the meniscus are particularly susceptible toacute injury and chronic degeneration [2]. Symptomaticmeniscal tears may be treated with activity modifica-tion, modalities, bracing, therapeutic exercise, intra-articular injections and, when clinically indicated,surgical debridement or repair [3].

In recent years, there has been increased interest inthe use of biologic agents (eg, platelet-rich plasma,

1934-1482/$ - see front matter ª 2017 by the American Academy of Physihttp://dx.doi.org/10.1016/j.pmrj.2016.12.012

bone marrow aspirate concentrate, and mesenchymalstem/stromal cells [MSCs]) to treat patients sufferingfrom a variety of musculoskeletal disorders, includingtendinosis, osteoarthritis, and meniscal tears [4,5].Vangsness et al [6] found that a single, postoperativeintra-articular injection of culture expanded, alloge-neic, bone marrow�derived MSCs was well tolerated,improved pain, and promoted meniscal regeneration inpatients after arthroscopic debridement of degenera-tive meniscal tears. Multiple authors also have reportedtherapeutic benefits from direct placement of biologicagents (eg, fibrin clots, stem cell-scaffold combinations)into the meniscus as an adjunct to arthroscopic surgery

cal Medicine and Rehabilitation

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[7,8]. Although intra-articular injections of cultureexpanded, autologous, bone marrow�derived MSCs alsomay improve symptoms and possibly promote meniscalregeneration in the context of nonoperative treatmentprograms for degenerative meniscal tears [9], thefeasibility of percutaneous intrameniscal delivery ofbiologic agents has not been explored previously.

The ability of high-resolution ultrasound (US) toimage the meniscus has been well-established [10-12];however, the feasibility of using sonographic guidance(SG) to specifically deliver needles/injectates into thebodies and posterior horns of the medial and lateralmenisci has not been evaluated formally. Consequently,the primary purpose of this investigation was to deter-mine the feasibility of SG intrameniscal injections; morespecifically, to determine the safety and accuracy of SGbody and posterior horn intrameniscal injections byusing an unembalmed cadaveric model. We hypothe-sized that SG could be used to accurately and safelyplace a standard 22-gauge needle into the bodies andposterior horns of the medial and lateral menisci. Clin-ically, the results of this investigation would provide afoundation for the clinical implementation of SG intra-meniscal injections in appropriately selected patients.

Methods

General Design

A single, experienced operator (the correspondingauthor) injected 0.5-1.0 mL of colored latex dye (Ward’sBiological Science, Rochester, NY) into the bodies andposterior horns of both the medial and lateral menisci in5 unembalmed, cadaveric knee-ankle-foot specimensusing direct SG and a 22-gauge, 38-mm needle. At thetime of the investigation, the operator had more than 12years of experience in diagnostic and interventionalmusculoskeletal US, including SG knee injections. Allspecimens were obtained from the Department ofAnatomy’s Foundation Bequest Program and were freefrom deformity, signs of trauma, and postsurgicalchange. Study coinvestigators dissected each specimento determine the accuracy of intrameniscal latex in-jection as well as the presence or absence of iatrogenicinjury to the regional neurovascular structures andintra-articular hyaline cartilage. This investigation wasapproved by the Bio-Specimens Subcommittee of theInstitutional Review Board at the authors’ institution(Institutional Review Board no. 14-005967).

Equipment

All imaging and injections were completed with aPhilips iU22 ultrasound machine and a 12-5 MHz lineararray transducer (Philips Ultrasound Systems, Bothell,WA). All injections were completed with standard22-gauge, 38-mm stainless-steel needles.

Injection Procedure

Each specimen was placed in a side-lying positionwith the target side of the knee facing the ceiling. Tooptimize sonographic visualization and meniscal access,the knee was flexed to 30-60� and a gravity-inducedvalgus or varus stress was imparted on the joint byplacing a small, rolled-up towel under the dependentside of the knee [11]. The transducer was then placed inan anatomical coronal plane across the joint, perpen-dicular to the long axis (LAX) of the meniscus, yielding ashort-axis view (or cross-section) of the meniscus.Thereafter, the regional “at-risk” structures wereidentified sonographically and their locations weremarked with an indelible ink markerdthe saphenousnerve medially and the common fibular nerve laterally.

The medial and lateral meniscal body injections wereconducted via a similar technique. After identificationof the regional “at-risk” structures, the meniscal bodywas reidentified in the coronal plane (short-axismeniscal view). For the medial meniscal body, a 22-gauge, 38-mm stainless-steel needle was thenadvanced with a SG, out-of-plane, anterior-to-posteriorapproach. During the first 3 injections, the needle entrypoint and trajectory were chosen primarily based onavoiding the saphenous nerve. However, after thedocumentation of 2 inaccurate injections placed intothe posterior horn (as described in the Results section),the medial meniscal body injection technique wasmodified to use the medial collateral ligament (MCL) asa consistent landmark. For these subsequent injections,the transducer was placed in the coronal plane justanterior to the MCL to facilitate consistent needle andlatex placement into the body of the medial meniscususing the out-of-plane approach. Once the needle tipwas visualized within the meniscal body, the transducerwas rotated 90� into the anatomical axial plane, yieldingan LAX view of the meniscus and an in-plane view of theneedle (Figure 1). The needle was advanced to theinnermost/deepest portion of the meniscal body usingdirect SG and an in-plane approach. After final needleplacement, the operator injected 0.5-1.0 mL of coloredlatex dye into the meniscus as the needle was with-drawn. The lateral meniscal body was injected via asimilar technique, with the transducer placed in ananatomical coronal plane at the level of popliteussulcus.

To inject the posterior horns of the menisci, themeniscal body initially was identified as described pre-viously. Thereafter, the transducer was translated pos-teriorly over the region of the posterior horn. However,in contrast to the meniscal body injection technique,before needle entry the transducer was rotated toprovide a LAX view of the posterior horn. Pilot in-vestigations had indicated that visualizing the posteriorhorn in its LAX throughout the procedure facilitatedidentification and maintenance of the necessary

Figure 1. (A) Setup for a SG out-of-plane right medial meniscus body injection showing probe and needle position in an unembalmed cadavericspecimen. (B) Short-axis view of the medial meniscus body (hollow yellow arrow) demonstrating a medial meniscus body injection with a 22-gaugestainless-steel needle. The needle (solid yellow arrow) is initially positioned using an out-of-plane approach, entering anterior to the MCL(asterisks) and advanced posteriorly. (C) Setup for medial meniscus body injection after probe rotation into a long-axis view of the medialmeniscus and in-plane view of the needle. (D) Long-axis view of the medial meniscus body (hollow yellow arrow) and an in-plane view of theneedle (solid yellow arrows). ANT ¼ anterior; FEM ¼ femur; IA ¼ intra-articular space; MCL ¼ medial collateral ligament; POST ¼ posterior; SQ ¼subcutaneous tissue; TIB ¼ tibia.

1000 Sonographically Guided Knee Meniscus Injections

trajectory to place the needle into the deeper portionsof the posterior horn. After sonographic visualization ofthe posterior horn, a 22-gauge, 38-mm stainless-steelneedle was advanced using an in-plane, anterior-to-posterior approach. The needle tip was advanced to thedeepest visible aspect of the posterior horn (Figure 2)and 0.5-1.0 mL of latex dye was injected as the needlewas withdrawn.

After each injection, coinvestigators dissected thespecimen to determine injection accuracy and assess for

Figure 2. (A) Setup for a SG in-plane right lateral meniscus posterior hocadaveric specimen. (B) LAX view of the lateral meniscus posterior horn (hsteel needle (solid yellow arrows). Needle is advanced in an anterolateraligament (anisotropic). ALAT ¼ anterolateral; PMED ¼ posteromedial; SQ ¼

iatrogenic injury to the regional “at-risk” structures.Accuracy was scored as either “accurate” (a clear trackof latex dye within the targeted meniscus region) or“inaccurate” (no clear track seen within the targetedmeniscus region). Qualitative observations included thequality of latex spread within the target region, thepresence of latex overflow into adjacent regions, andthe presence of iatrogenic injury to the regional “at-risk” structures including the saphenous nerve, commonfibular nerve, lateral inferior geniculate artery, and

rn injection, showing probe and needle position in an unembalmedollow yellow arrow) demonstrating injection with a 22-gauge stainlessl to posteromedial direction. Asterisk indicates the posterior cruciatesubcutaneous tissue; TIB ¼ tibia.

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intra-articular hyaline cartilage. All outcomes weregraded by a consensus of 2 coinvestigators. Results weresummarized with descriptive statistics.

Figure 3. Superior view of the medial meniscus demonstrating anaccurately placed latex trail in the posterior horn (PH); however, themeniscal body injection (B) was placed too far posteriorly and there-fore was considered inaccurate. The injection technique was subse-quently modified to prevent this “overshoot” by placing the transducerjust anterior to the MCL (solid yellow arrow, see text for explanation).Top ¼ posterior; Bottom ¼ anterior; Left ¼medial/superficial; Right ¼lateral/deep.

Results

A total of 20 SG intrameniscal injections were per-formed in 5 unembalmed cadaveric knees from 5 donors(3 male, 2 female) ages 33-92 years (mean 74 years) andbody mass indices of 21.1-32.4 kg/m2 (mean 24.1 kg/m2). Sonographic visualization of the meniscal body andposterior horn, saphenous nerve, and common fibularnerve was satisfactory in all specimens. Not unexpect-edly, sonographic visualization of the lateral inferiorgeniculate artery was not possible in all specimensbecause of the absence of pulsatile blood flow. Needlevisualization was excellent in all specimens and 2 gen-eral injection flow patterns were observed: (1) highresistance flow, in which latex distribution was morediscrete and limited to the needle track, and (2) lowresistance flow, in which the latex distribution was moreirregular and extended into the meniscus beyond theneedle track. Although formal sonographic assessmentof meniscal status was not performed as part of thisinvestigation, the former flow pattern was more com-mon in normal menisci, whereas the latter was observedin association with degenerative changes and/ormeniscal clefts potentially representing tears.

Injection accuracy is presented in Table 1. Seventeenof 20 injections were accurate. Two of the 3 inaccurateinjections were medial meniscal body injections inwhich the latex was placed more posteriorly thandesireddin the region of the posterior horn (Figure 3).This was determined to result from initial placement ofthe transducer just superficial to the MCL. With thistransducer placement, during the out-of-plane needleapproach the needle had a tendency to pass too farposteriorly (ie, out of the region of the body and intothe region of the posterior horn) by the time it reachedits target depth. This technical limitation was resolvedby placing the transducer anterior to the MCL duringsubsequent meniscal body injections. The third

Table 1Injection accuracy

Meniscus RegionAccurate(n)

Inaccurate(n) Observation

Medial meniscusbody

3 2 Latex posterior totarget e inposterior horn

Medial meniscusposterior horn

5 0

Lateral meniscusbody

4 1 No latex deposition

Lateral meniscusposterior horn

5 0

Total 17 (85%) 3 (15%)

inaccurate injection was a lateral meniscus body in-jection in which no latex was seen in the meniscus. Nospecimens demonstrated evidence of iatrogenic injuryto the saphenous nerve, common fibular nerve, lateralinferior geniculate artery, or intra-articular hyalinecartilage.

Discussion

The most important finding of this investigation wasthat SG intrameniscal injections are feasible and cansafely place injectates into the bodies and posteriorhorns of the medial and lateral menisci with acceptableaccuracy. Consequently, the current results provide afoundation for consideration of SG intrameniscalinjections in clinically appropriate populations.

Improving pain and function in patients with symp-tomatic degenerative or traumatic meniscal tears con-tinues to challenge clinicians. Although surgicalintervention is clearly indicated in selected cases, sur-gery is not without consequences. For example, Rooset al [13] demonstrated that when compared with age-matched controls with healthy knees, patients treatedwith total meniscectomy had a relative risk of 14.0 fordeveloping advanced radiographic findings of osteoar-thritis and a 2-fold increased risk of developing clinicallysignificant knee pain at a mean of 21 years postsurgery.These and similar findings have fostered the philosophyof meniscal preservation when managing symptomaticmeniscal disorders. For example, multiple studies haveemphasized the clinical and biomechanical benefits ofpartial versus total meniscectomy [14,15].

1002 Sonographically Guided Knee Meniscus Injections

Even partial meniscectomy, however, is not withoutconsequence. A prospective, randomized trial by Hedeet al [16] demonstrated that only 62% of patientstreated with partial meniscectomy had an excellentoutcome at a median 7.8 years’ follow-up, which wasnot statistically significantly different from the 52%excellent outcome in the total meniscectomy group.Consequently, as the evidence in support of meniscalpreservation has accumulated, a variety of meniscalrepair techniques have evolved to avoid or minimize theextent of meniscal resection. Many of these techniqueshave been augmented successfully by intraoperativebiologic treatments such as fibrin clot application,trephination, meniscocapsular abrasion, and morerecently application of cell-based therapies and scaf-folds [7,8]. The primary goal of these adjunctive bio-logic treatments is to facilitate healing and preserve orperhaps regenerate the meniscus.

Although the intraoperative application of biologicagents in the treatment of meniscal tears is wellestablished, the use of biologic agents as an adjunct tononoperative meniscus tear treatment has been limitedto a few select case reports [9]. One potential expla-nation for this discrepancy is the inability to preciselydeliver the desired biologic agent into the meniscus inthe absence of direct intraoperative visualization. Asdemonstrated in the current study, high-resolution UScan fill this void by facilitating precise and accurateneedle placement into the bodies and posterior horns ofthe medial and lateral menisci, the most common re-gions associated with acute and chronic symptomaticmeniscal tears [2]. Consequently, the role of SG intra-meniscal injections can now be explored via futureresearch and collective clinical experience.

There are several limitations and technical factorsthat warrant further discussion in the context of thecurrent study. First, clinicians should exercise appro-priate caution when extrapolating the results of thiscadaveric investigation to clinical scenarios. Althoughthe current study documents the feasibility of SGmeniscal injections, we are unable to comment on theclinical efficacy of intrameniscal injections with respectto specific therapeutic agents or the role of intra- versusextrameniscal injections in specific clinical circum-stances. With respect to safety, we did not directlyvisualize the lateral inferior geniculate artery due tolack of Doppler flow. Although this artery can be easilyvisualized on US and therefore avoided when performingSG lateral meniscal injections, the current study designprecludes definitive statements pertaining to the safetyof SG injections with respect to the perimeniscalvasculature.

Second, we used a 22-gauge, 38-mm stainless-steelneedle to accommodate the viscosity of the latex. Werecognize that some therapeutic agents may havehigher or lower viscosities that will influence the choiceof needle gauge and the propensity for injectate spread

from the target site postinjection. A low-viscosityinjectable can be delivered via a small-gauge needle,thus minimizing inadvertent tissue trauma; however,the therapeutic agent may have a tendency to migratefrom the target site. In comparison, a greater viscosityagent may more likely remain at the target site butwould require a larger gauge needle and potentiallyincur additional risk of inadvertent tissue trauma. Inaddition to the needle gauge, we acknowledge the po-tential differences in viscosity between latex used inthis study and that of various biologic agents used inclinical practice. That said, the purpose of this studywas to validate injection technique. We used latexbecause of previous experience using this model incadaveric studies. The advantages of latex for the studyinclude ease of use and the ability to define a clear in-jection deposit on dissection. We recognize that theviscosity of latex may not be the same as biologic agentsused in practice. There is no standard viscosity forvarious biologics because they may vary between pa-tients and among different preparations. Therefore, it isimpractical to test the flow characteristics of the “bi-ologics” in the presented model. This limitation doesnot limit the applicability of the described injectiontechnique. Operators will need to consider all thesefactors during any clinical application of SG meniscalinjections.

Third, we reported 3 inaccurate injections, 2 ofwhich resulted from technical factors that were miti-gated by procedural changes as previously described(ie, placing the transducer anterior to rather than su-perficial to the MCL for the medial meniscus body in-jection). The reason for the third inaccurate injectionremains indeterminate but may have resulted from thehigh latex viscosity. In the setting of normal menisci,which was the case with respect to the specimen inquestion, the latex injection required high injectionpressure due to the densely packed meniscal fibers.Although the latex was “injected” as the needle waswithdrawn, the flow of latex into the needle track couldnot be directly sonographically visualized in all cases.The use of small injection volumes and the compress-ibility of the latex solution further limited the ability tounequivocally confirm the actual delivery of intra-meniscal latex during the injection. Consequently, wehypothesize that despite accurate needle placement asevidenced by the anatomically identified needle track,it is probable that no latex was in fact injected into thelateral meniscus in this case. We also recognize the lesslikely possibility that some latex was initially injectedinto the meniscus but subsequently flowed back out ofthe needle track as the result of high intrameniscalpressures. In either case, the lack of latex within themeniscus does not reflect a limitation of the SG intra-meniscal injection since the needle was in fact placedaccurately. Furthermore, from a clinical perspective,operators should not encounter these technical

Figure 5. Superior view of the lateral meniscus body. Similar toFigure 4, the meniscus has been incised parallel to its long axis and thesuperior aspect of the meniscus body reflected to reveal the accuratemeniscal body injection (solid yellow arrow). In comparison withFigure 4, this meniscus was grossly normal and the latex spread wastherefore restricted to the needle track. Note also the staining fromthe accurately placed posterior horn (PH) injection in this specimen(hollow yellow arrows). Left ¼ deep/medial; Right ¼ superficial/lateral; Top ¼ posterior; Bottom ¼ anterior; AH ¼ anterior horn;B ¼ body.

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challenges when injecting menisci affected by acute orchronic tears, where low pressure distribution of theinjectate is likely to be observed (Figure 4 versusFigures 5, 6, and 7).

Fourth, from our dissections it is clear that SG can beused to deliver injectates across the full width of themeniscus, including the innermost portion of the body(the white-white zone) and the root of the posteriorhorn (Figures 6 and 8, respectively). Therefore, SGintrameniscal injections could be considered to accu-rately deliver biologics to the avascular regions of themeniscus with poor spontaneous healing potential [17].

Fifth, the lateral meniscus was technically moredifficult to inject than the medial meniscus because ofits greater mobility. Specifically, as the needle wasbeing placed into and advanced through the lateralmeniscus, the meniscus often moved considerably.Meniscal degeneration or tearing may accentuate thisphenomenon. Identifying mitigation strategies for thisundesirable movement will require further investigationand experience.

Sixth, as exhibited in several of our specimens,injectate flow beyond the confines of the meniscus ispossible and perhaps in some cases expected (Figures 4and 7). Although the clinical significance of extra-meniscal extension remains unknown and probably isdependent on the specific clinical scenario, extra-meniscal extension can be minimized by precise needleplacement and control facilitated by (1) practice incadaveric specimens when available, (2) confirmation ofneedle tip position in 2 orthogonal planes, (3) avoidanceof needle passage beyond the sonographically identifiedlimits of the meniscus, (4) control of injection volume,

Figure 4. Superior view of medial meniscus posterior horn (PH). ThePH has been incised longitudinally and the superior half reflected toreveal the full injection pathway. Note the distribution of latex withinthe PH. This meniscus exhibited structural changes consistent withdegenerative meniscal tearing. Consequently, the latex spreadthroughout the region of degeneration. Left ¼ superficial/medial;Right ¼ deep/lateral; Top ¼ anterior; Bottom ¼ posterior; AH ¼anterior horn; B ¼ body.

and (5) the use of identifiable anatomical landmarksduring the setup and execution of the procedure.

With respect to the latter recommendation, theanterior aspect of the MCL and the popliteal sulcusproved to be reliable landmarks for transducer place-ment and needle entry during medial and lateral bodyinjections, respectively, whereas the posterior cruciateligament (PCL) also can be used to facilitate identifi-cation of the posterior horns of the menisci and ifdesired, the posterior roots [18]. The PCL initially isidentified in an anatomical oblique sagittal plane and

Figure 6. Cross-sectional view of the lateral meniscus posterior hornshowing an accurate injection pathway. The specimen has beendissected to specifically demonstrate the posterior root (PR) of thelateral meniscus. The body and anterior horn have been resected toproduce a meniscal cross section at the junction of body and posteriorhorn (asterisk), and a portion of the inner third (ie, white-white zone)of the posterior horn has been removed to demonstrate the injectiontrack. Similar to the specimen in Figure 5, this meniscus was grosslynormal, thus limiting latex flow to within the confines of the needletrack (compare with Figure 4). Left ¼ deep/medial; Right ¼ superfi-cial/lateral; Top ¼ cranial; Bottom ¼ caudal.

Figure 7. Inferior view of the medial meniscus showing accurate latexdeposition into both the body (B) and posterior horn (PH) regions.Similar to the specimen in Figure 4, this specimen exhibited degen-erative changes in the body and posterior horns. The distribution oflatex within the middle and inner thirds of the meniscus reflectaccurate needle placement into these regions as described in theMethods. Note the extension of latex outside of the confines of themeniscus, which was observed in several specimens (See text for dis-cussion). Left ¼ superficial/medial; Right ¼ deep/lateral; Top ¼anterior; Bottom ¼ posterior; AH ¼ anterior horn.

1004 Sonographically Guided Knee Meniscus Injections

the transducer is then translated medially or laterally tothe side of interest. The posterior horn of the meniscusis the first soft-tissue, intra-articular structure seen inthe tibiofemoral joint after translating medially orlaterally off of the PCL. Once the posterior horn isidentified, the transducer is rotated 90� into theanatomical axial plane, yielding a LAX view of the pos-terior horn.

Seventh, all injections in the current investigationwere performed by a single experienced operator.Although the techniques described herein have beeneasily taught to less-experienced operators, interoper-ator reliability was not investigated formally in thisstudy. Finally, it is unknown whether there is any

Figure 8. Cross-sectional view of medial meniscus body showinginjectate deposition into middle (ie, red-white zone) and inner thirds(ie, white-white zone) of the meniscus. Top ¼ superior; Bottom ¼inferior; Left ¼ lateral/deep; Right¼ medial/superficial; R ¼ red-redzone; W ¼ white-white zone.

clinically relevant iatrogenic injury associated with thistechnique. Meniscal trephination using an 18-gaugeneedle is a well-described, long-accepted operativetechnique to facilitate meniscal healing, and the tech-nique described in this study is similar in principle [19].Given that primum non nocere remains a guiding prin-ciple, this technique should be applied targeting onlydamaged tissue and using SG so as to minimize theextent of normal tissue traversed.

Conclusions

SG intrameniscal injections are technically feasibleand should be considered when clinically indicated.Further research and clinical experience is necessary toclarify the role of SG intrameniscal injections to reducepain, improve function, and preserve or regenerate themeniscus in patients with symptomatic acute or chronicdegenerative meniscal tears.

Acknowledgments

We thank the staff of the Mayo Clinic Procedural SkillsLaboratory and the noble generosity of the whole-bodydonors, whose altruistic gift made this study possible.

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Disclosure

M.R.B. The Ohio State University Sports Medicine Center & Department ofPhysical Medicine and Rehabilitation, Columbus, OHDisclosure: nothing to disclose

J.L.S. Department of Physical Medicine and Rehabilitation, Mayo Clinic,Rochester, MNDisclosure: nothing to disclose

D.L. Department of Physical Medicine and Rehabilitation, University of Michigan,Ann Arbor, MIDisclosure: nothing to disclose

J.S. Department of Physical Medicine and Rehabilitation, Mayo Clinic, W14 MayoBuilding, 200 1st St, SW, Rochester, MN 55905. Address correspondence to: J.S.;e-mail: smith.jay@mayo.eduDisclosures outside this publication: license agreement, stock, and sales roy-alties, Tenex Health Inc; license agreement, stock, and Chief Medical Officer,Sonex Health, LLC; other, Section Editor, Journal of Ultrasound in Medicine

Funded by Mayo Clinic Institutional Funds.

Submitted for publication August 23, 2016; accepted December 23, 2016.