Journal of Clinical Medicine

Brief Report Intraosseous Bioplasty for a Subchondral Cyst in the Lateral of

Anish G.R. Potty 1,2,3, Ashim Gupta 1,4,5,6 , Hugo C. Rodriguez 1,2 , Ian W. Stone 2 and Nicola Maffulli 7,8,9,*

1 South Texas Orthopaedic Research Institute, Laredo, TX 78045, USA; [email protected] (A.G.R.P.); [email protected] (A.G.); [email protected] (H.C.R.) 2 School of Osteopathic Medicine, University of the Incarnate Word, San Antonio, TX 78209, USA; [email protected] 3 Laredo Sports Medicine Clinic, Laredo, TX 78041, USA 4 Department of Psychology, Illinois Wesleyan University, Bloomington, IL 61701, USA 5 Future Biologics, Lawrenceville, GA 30043, USA 6 BioIntegrate, Lawrenceville, GA 30043, USA 7 Department of Musculoskeletal Disorders, School of Medicine and Surgery, University of Salerno, 84084 Fisciano, Italy 8 Barts and the London School of Medicine and Dentistry, Centre for Sports and Exercise Medicine, Queen Mary University of London, London E1 4DG, UK 9 School of Pharmacy and Bioengineering, Keele University Faculty of Medicine, Stoke on Trent ST4 7QB, UK * Correspondence: n.maff[email protected]

 Received: 7 April 2020; Accepted: 4 May 2020; Published: 6 May 2020 

Abstract: Several conditions can lead to the development of a subchondral cyst. The mechanism by which the cysts form, their location, and their severity depend on the underlying pathology, although the exact pathogenesis is not fully elucidated. Treatment options vary according to the location of the cyst, with less invasive procedures such as calcium phosphate cement injection to a joint arthroplasty when there is an extensive cyst in communication with the joint space. If the cyst is circumscribed, an intraosseous bioplasty (IOBP) can be performed. Described in this paper is an IOBP, a minimally invasive technique that preserves the joint and can be applied to most subchondral cysts. In our patient, both the appearance of the cyst at imaging and pain after IOBP greatly improved with the combined use of decompression and grafting. In those patients in whom conservative management fails to ameliorate symptoms, IOBP should be considered.

Keywords: intraosseous bioplasty; subchondral cysts; marrow edema; orthobiologics; autologous bone marrow; platelet rich plasma; demineralized bone

1. Introduction Subchondral cysts (SC) are common in several conditions including osteoarthritis (OA), rheumatoid arthritis (RA), osteonecrosis, and calcium pyrophosphate deposition (CPD) disease [1–4]. These conditions lead to the development of bone marrow lesions, which are strong predictors of SC development [5]. These cysts are often benign and incidentally found on radiography, with 80% of patients reporting no symptoms unless a fracture occurs [6]. While the location of the cyst does not influence symptoms, pain is associated with the volume of the cystic component [7]. In OA of the hip, SC occur on the pressure segment of the along with the loss of articular space. In contrast, in RA, SC are initially noted at the osteo-chondral junction and may affect the entire femoral head. In osteonecrosis, the cysts develop in the necrotic segment of the femoral head, whereas in CPD disease, they resemble those in the OA but are larger, and more numerous and widespread [1,3].

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The etiology of SC is still not well understood. Two theories—the “synovial intrusion theory” and the “bony contusion theory”—attempted to explain the formation of SC [1,8]. The former suggested that a SC could be secondary to the pathology of the synovium extending into the bone from the resemblance of synovial fluid to the cystic fluid, abnormal articular cartilage over the cyst, and dislocated pieces of hyaline cartilage within the cyst [9]. This is supported by the frequent communication between joint cavities and SC; however, this communication is not present in all SC. The “bony contusion theory” explained this absence of communication: the impact between opposing bone surfaces that have lost their protective cartilage can lead to microfractures and bone necrosis. The synovial fluid then intrudes the bone when this attempts to heal by osteoclastic resorption of the necrotic bone. This is supported by the lack of communication between the joint cavity and the subchondral cyst, the presence of the metaplastic cartilage, and the osteoclasts in the disrupted bone [10]. Another proposed mechanism of cyst formation is the overloading of specific areas within the bone from the unevenness of the articular surfaces [1,11]. This would increase the intraosseous pressure leading to decreased blood flow and impeding the body0s ability to heal itself [12]. Traditionally, SC have been managed using physical therapy with pharmacological agents such as non-steroidal anti-inflammatory drugs, corticosteroids, and viscosupplementation; intra-cyst calcium phosphate cement injection has also been performed [13,14]. When SC progress, and conservative management fails, surgical options in the knee including high tibial osteotomy, unicondylar knee arthroplasty, and total knee arthroplasty (TKA) can be considered [13,14]. These modalities have several limitations including increased risk of early mechanical complications and early revisions after TKA in young patients [15]. Intraosseous bioplasty (IOBP) is a viable alternative in these young patients in whom joint sparing is desirable. In addition, IOBP can be repeated to try and delay a TKA. IOBP involves the structural decompression of the area of pathology, thus reducing intraosseous pressure, followed by injection of a mixture of concentrated platelet rich plasma (PRP) from autologous bone marrow and demineralized bone to allow bone remodeling to not only stabilize the lesion but to heal it. We describe a patient in whom IOBP was utilized, outlining clinical pearls, and indications and benefits of IOBP.

2. Surgical Technique

2.1. Indications IOBP is indicated in patients with imaging findings of a subchondral cyst. In these patients, the lesions have well defined borders, are easily identified at MRI, and patients report pain, stiffness, decreased range of motion and function. A patient0s age plays a key role in identifying the ideal candidates for this procedure. Patients between 30 and 55 with a high risk of a TKA in the near future are ideal candidates for IOBP. Patients should be compliant with the postoperative protocol of non-weightbearing for at least 3 weeks. In this case, the patient reported pain, stiffness and decreased range of motion and function. Along with the associated MRI findings, there was a high risk of subchondral bone collapse and possible TKA an IOBP. The main contraindication for IOBP is a breach in the articular surface of the bone overlying the lesion. This would lead to extravasation of the PRP-DBM mixture and no physiologic remodeling of the bone, which would lead to further trauma to the joint. Patients with joint space narrowing, osteophytes, full thickness cartilage loss, and underlying bone exposure would prompt to consider other procedures rather than IOBP. Some relative contraindications if there is no articular cartilage breach could include other inflammatory, erosive, and crystal arthropathies. The size of the lesion is also important, as cysts > 2.5 cm in diameter have less optimal results (Table1). J. Clin. Med. 2020, 9, x FOR PEER REVIEW 3 of 10

Table 1. Indications, Contraindications and Relative Contraindications of Intraosseous Bioplasty J. Clin. Med. 2020, 9, 1358 3 of 10 Indications Contraindications Relative Contraindications  A subchondral cyst with well- Table 1. Indications, Contraindications and Relative Contraindications of Intraosseous Bioplasty. defined borders  Breach in the  Symptoms suchIndications as pain, articular Contraindications surface of Relative Contraindications  Inflammatory, erosive stiffnessA and subchondral decreased cyst range with of overlying bone • well-defined borders Breach in the articular and crystal arthropathies motion and function  • Evidence of Grade 4 Inflammatory, erosive Symptoms such as pain, stiffness and surface of overlying bone  • Lesion size > 2.5 cm • and crystal arthropathies  Patientdecreased aged range between of motion 30 and function55 osteoarthritisEvidence of Grade • Lesion size > 2.5 cm  AvoidancePatient aged of betweenTotal Knee 30 and 55 4 osteoarthritis • • Avoidance of Total Knee Arthroplasty Arthroplasty•

2.2.2.2. History History and and Diagnosis Diagnosis TheThe initial initial diagnosis diagnosis begins begins with with thorough thorough history history evaluation evaluation.. In Inthis this case case,, the the patient patient was was a 47 a year47 yearss oldold male male with with a past a past medical medical history history of ofchronic chronic pain pain with with no no previous previous trauma trauma to to the the right right knee. knee. AA physical exam is also paramount paramount,, with with emphasis emphasis on on the the knee. knee. Stress Stress testing testing of of all all the the ligaments, ligaments, withwith assessment of the knee range of motion and muscle strength, should be performed. This This allows allows thethe clinician clinician to to assess assess for for other other intra intra-articular-articular pathology pathology,, including ligament instability instability or or meniscal meniscal traumatrauma that that might might need need to to be be addressed addressed concurrently concurrently during during the the IOBP. IOBP. A 6 6--foot standing standing alignment alignment radiographradiograph for for varus varus or or valgus valgus malalignment malalignment should should be be performed, performed, with with a a view view to to correct correctionion if if necessary.necessary. Additionally, Additionally, MRI MRI evaluation evaluation allows allows precise precise localization localization of the of the lesion lesion and and plan planningning of the of procedurethe procedure accordingly. accordingly. MRI MRI evaluation evaluation in the in the patient patient reported reported in in this this article article evidenced evidenced a a large large multiloculatedmultiloculated cystic areaarea withwith internalinternal septs septs in in the the lateral lateral femoral femoral condyle, condyle, close close to theto the insertion insertion of theof thepopliteal popliteal tendon, tendon, measuring measuring 2.3 2.2.13 × 2.12.0 x cm2.0 (Figurecm (Figure1A,B). 1A A and diagnostic 1B). A diagnostic arthroscopy arthroscopy was planned was to × × plannedevaluate to the evaluate joint space the joint and ensurespace and this ensure was not this compromised. was not compromised.

FigureFigure 1. 1. (A) (RightA) Right knee kneemagnetic magnetic resonance resonance image, fat image,-saturated fat-saturated FSE-IR (fast FSE-IR spin-echo (fast inversion spin-echo- recovery)inversion-recovery).. Coronal plane Coronal shows planea multiloculated shows a multiloculated cystic area (red cystic circle) area in the (red lateral circle) femoral in the condyle lateral withfemoral proximal condyle bone with marrow proximal edema bone. (B) marrow Right knee edema. magnetic (B) Rightresonance knee image, magnetic non resonance-fat-saturated image, T2 weighted.non-fat-saturated Axial plane T2 weighted. image shows Axial the plane cystic image area shows (red thecircle) cystic used area for (red localization circle) used and for planning localization of procedureand planning. of procedure.

2.3.2.3. Patient Patient Setting Setting TheThe patient patient was was brought brought to the to operating the operating room and room was placedand was supine placed followed supine by administration followed by administrationof general anesthesia. of general The anesthesia. right lower The extremity right lower was prepped extremity and was draped prepped in the and routine draped fashion. in the

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Aroutine fluoroscope fashion.with A fluoroscope a sterile drape with was a usedsterile to drape localize was the used cyst. to The localize position the wascyst. maintained The position during was themaintained Intraosseous during Bioplasty. the Intraosseous Bioplasty.

2.4. Diagnostic Arthroscopy StandardStandard antero-lateralantero-lateral and antero-medialantero-medial portals were established, and a routine diagnostic arthroscopy was performed using a 4.0 mmmm 3030°◦ arthroscope. The aforementioned meniscal findingsfindings were confirmedconfirmed andand addressed; thethe articulararticular surfacesurface ofof the femur was inspectedinspected to ensure that surface was not breached (Figure(Figure2 2).).

Figure 2. Arthroscopy appearance appearance of of the l lateralateral compartment of the knee from the antero-lateral antero-lateral portal.portal. T Thehe knee is in the the figure figure-four-four position to allow allow adequate adequate visualization visualization of the the lateral lateral joint joint space. space. The lateral condyle was intact. Crystal deposits are evident in the articular cartilage.cartilage.

2.5. Bone Marrow Harvest and Preparation

The 4.0 mm 30 ◦° arthroscope waswas inserted through the antero-lateralantero-lateral portal that was used during the diagnostic arthroscopyarthroscopy and utilized for direct visualization of the intercondylar notch during the harvesting process. An 8G by 11 cm Jamshidi needle was introduced into the joint space through the antero-medialantero-medial portal. It It was i impactedmpacted into the intercondylar notch usin usingg a hammer to the depth of 0.4 cm.cm. Under the guidance of of l lateralateral knee knee fluoroscopy fluoroscopy w withith 90 90 ◦° knee flexionflexion to provide for precise anatomical location into the medullary canal,canal, thethe arthroscopic fluidfluid was then turned off off and the inner stylus of the needle was removed. Two Two 30 mL syringes pretreated with anticoagulant citrate dextrose solution werewere thenthen placed placed connected connected to to the the needle needle to harvestto harvest 60 mL60 mL of bone of bone marrow marrow aspirate. aspirate. The bone The marrowbone marrow aspirate aspirate was slowly was extractedslowly ex whiletracted rotating while androtating slowly and withdrawing slowly withdrawing the needle the to adequately needle to filladequately the syringe fill the (Figure syringe3). This(Figure location 3). This for location bone marrow for bone harvesting marrow harvesting avoids the avoids need to the make need an to additionalmake an additional incision (traditionallyincision (traditionally this would this be would at the be anterior at the anterior superior superior iliac spine). iliac spine).The 60 The mL 60of bonemL of marrow bone marrow was then wa placeds then placed into the into Arthrex the Arthrex Angel CPRPAngel and CPRP Bone and Marrow Bone Marrow Processing Processing system (Arthrex,system (Arthrex, Inc., Naples, Inc. Naples, FL, USA) Florida and processed USA) and as perprocessed manufacturer’s as per manufacturer’s instructions. After instructions. centrifugation After forcentrifugation a 17 min, the for concentrated a 17 min, the Platelet concentrated Rich Plasma Platelet (PRP) Rich wasPlasma mixed (PRP) with was 5 mL mixed of demineralized with 5 mL of bonedemineralized matrix (DBM) bone untilmatrix the (DBM) consistency until the of a consistency dense paste of was a dense reached. paste This was mixture reached. was This ready mixture to be introducedwas ready to once be theintroduced cyst had once been decompressed.the cyst had been During decompressed. the entire bone During marrow the entire harvest bone process, marrow it is importantharvest process, to utilize it serial is importa fluoroscopynt to utilize and arthroscopic serial fluoroscopy visualization. and arthroscopic This allows proper visualization. visualization This ofallows the location proper ofvisualization the intercondylar of the location harvest andof the ensures intercondylar that there harvest is no breech and ensur in thees articular that there surface is no overbreech the in SC. the articular surface over the SC.

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Figure 3. HarvestHarvest setup setup.. The The knee knee is is flexed flexed over over the the side side of of the the table table and and the Jamshidi needle is impactedimpacted into thethe intercondylarintercondylar notchnotch of of the the femur femur with with a a pretreated pretreated 30 30 mL mL syringe. syringe. The The arthroscope arthroscope is isin in the the anterior-lateral anterior-lateral portal portal for for visualization. visualization.

2.6. Core Core Decompression Decompression While the AngelAngel systemsystem waswas processing processing the the 60 60 mL mL aspirate, aspirate, the the cyst cyst was was decompressed decompressed (Video (Video S1). SWith1). With the aid the of aid fluoroscopy of fluoroscopy and previous and previous MRI images, MRI images, the lesion the at lesion the lateral at the condyle lateral of condyle the femur of wasthe femurlocated was using loc anated 8G using by 11 an cm 8G Jamshidi by 11 cm needle. Jamshidi A 1 cmneedle long. A incision 1 cm long was incision made along was themade distal-lateral along the distalportion-lateral of the portion right femur of the over right the femur lateral over condyle the lateral under condyle fluoroscopic under guidance. fluoroscopic The guidance. iliotibial band The iliotibialand proximal band structures and proximal were retracted structures for were adequate retracted visualization for adequate of the visualizationlateral condyle of of the the lateral femur. condyleA 2.4 mm of guidethe femur. pin was A 2.4 then mm directly guide pin drilled was intothen the directly lesion drilled and used into tothe ream lesion it withand used a low to profile ream it7 mm with reamer a low (Video profile S1). 7 mm The reamerarthroscope (Video was S1) introduced. The arth inroscope the tunnel was to introduced visualize the in wall the of tunnel the cyst to visualizeand assess the whether wall of furtherthe cyst septae and assess needed whether to be broken. further Itseptae is important needed toto ensurebe broken that. It the is wallimportant of the tocyst ensure is removed, that the and wall the of underlying the cyst is boneremoved, is actively and the bleeding. underlying The loculationsbone is actively were thenbleeding. removed The loculationswith the use were of curettes, then removed taking with care the that use the of opposite curettes, bone taking cortex care wasthat notthe opposite compromised bone cortex (Video wa S1).s notThis compromised can be achieved (Video by using S1). serialThis can fluoroscopy be achieved imaging by using as well serial as arthroscopy. fluoroscopy The imaging arthroscope as well was as arthroscopy.used to visually The ensure arthroscope that the was articular used to surface visually of ensure the femur that was the notarticular breached. surface of the femur was not breached. 2.7. PRP Inoculation and Bone Impaction 2.7. PRPAn Open-TipInoculation 8G and by11 Bone cm Impaction delivery cannula was used (Figure4A) to allow direct delivery into the lesionAn and Open maximum-Tip 8G precision by11 cm whiledelivery the PRP-DBMcannula wa mixtures used is(Figure being 4 introduced.A) to allow The direct delivery delivery cannula into thewas lesion placed and directly maximum into the precision lesion underwhile the careful PRP fluoroscopic-DBM mixture guidance is being and introduced. arthroscopy The to delivery ensure cannulathat the oppositewas placed cortex directly was notinto penetrated the lesion andunder that careful the articular fluoroscopic surface guidance remained and intact arthroscopy (Figure5A). to ensureThe mixture that the of 50:50opposite Isovue cortex dye, was demineralized not penetrated bone and matrix, that the and articular PRP in surface the 14 mLremained syringe intact was (Figureloaded on5A). the The delivery mixture cannula of 50:50 (Figure Isovue4A,B) dye, and demineralized delivered under bone direct matrix, observation and PRP with in fluoroscopy. the 14 mL syringeIt can be was helpful loaded to transfer on the the delivery mixture intocannula a smaller (Figure 1 mL 4A syringe and 4 (FigureB) and4 A) delivered using an under adapter direct that observationconnects the with two syringesfluoroscopy. if high It resistancecan be helpful is present. to transfer The stylet the mixture from the into cannula a smaller can also 1 mL be syringe used to (Figurepush the 4A) mixture using against an adapter resistance. that connects Allograft the cancellous two syringes bone wasif high then resistance impacted is into present. the defect The stylet using froma curette, the cannula and the can remaining also be mixtureused to push was thenthe mixture injected against while viewing resistance. the Allograft cyst with cancellous an arthroscope. bone wasReinserting then impacted the stylet into into the the defect cannula using at a this curette, time and would the makeremaining certain mixture that all was of the then mixture injected is while in the viewingcyst. The the arthroscope cyst with an was arthroscope. then used toReinserting ensure that the the stylet injected into materialthe cannula did a nott this extravasate time would into make the certainjoint space. that all A finalof the fluoroscopy mixture is in assessment the cyst. The of the arthroscope lesion was was performed then used (Figure to ensure5B). that the injected material did not extravasate into the joint space. A final fluoroscopy assessment of the lesion was performed (Figure 5B).

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Figure 4. (A) The open-tip cannula is used for the direct approach of Intraosseous Bioplasty. Removal FigureFigure 4. (4.A ()A The) The open-tip open-tip cannula cannula is is used used forfor thethe direct approach approach of of Intraosseous Intraosseous Bioplasty. Bioplasty. Removal Removal of theof thestylet stylet will will show show the the circular circular open open end, end, rather rather than than thethe 3-pin 3-pin side endend delivery delivery used used in in the the of the stylet will show the circular open end, rather than the 3-pin side end delivery used in the indirect indirectindirect approach. approach. 1 mL 1 mL syringe syringe and and 14 14 mL mL syringe syringe filled filled with with 50:5050:50 Isovue dye,dye, DemineralizedDemineralized Bone Bone approach. 1 mL syringe and 14 mL syringe filled with 50:50 Isovue dye, Demineralized Bone Matrix MatrixMatrix (DBM) (DBM) and and Platelet Platelet Rich Rich Plasms Plasms (PRP) (PRP). .( B(B) )The The DBMDBM inin thethe plastic containercontainer will will be be mixed mixed (DBM) and Platelet Rich Plasms (PRP). (B) The DBM in the plastic container will be mixed with the withwith the thePRP PRP from from the the Angle Angle system system in in the the container container andand willwill bebe inserted intointo thethe 11 mL mL or or 14 14 mL mL PRP from the Angle system in the container and will be inserted into the 1 mL or 14 mL syringes seen syringessyringes seen seen in Figurin Figure 4eA. 4A. in Figure4A.

Figure 5. (A) Fluoroscopic image of the open-tip delivery cannula injecting the biologic mixture into FigureFigurethe 5. 5.decompressed ((AA)) Fluoroscopic Fluoroscopic Subchondral image image of of the Cyst the open-tip open-tip (SC) (red delivery delivery circle) cannula cannula with arthroscopicinjecting injecting the the guidance.biologic biologic mixture mixture (B) Final into into thethe fluoroscopic decompressed decompressed image Subchondral Subchondral of the right Cyst knee Cyst (SC) after ( (redSC injection) circle) (red of circle)with the arthroscopicbiologic with arthroscopicmixture guidance. into the guidance. (B SC) Final (red fluoroscopiccircle). (B) Final fluoroscopicimage of the image right knee of the after right injection knee after of the injection biologic of mixturethe biologic into mixture the SC (red into circle). the SC (red circle). 2.8. Postoperative Protocol 2.8.2.8. Postoperative PostoperativePost-operatively, Protocol Protocol the patient was instructed to not to weight bear for 3 weeks, followed by 3 weeksPost-operatively,Post-operatively, of toe touch weightthe the patient patient bearing, was was continuing instructed instructed with to to not 3 not weeks to to weight weightof partial bear bear weight for for 3 weeks, 3bearing, weeks, followed and, followed finally, by by 3 weeks3 weeksprogress of oftoe toe fulltouch touch weight weight weight bearing. bearing, bearing, The continuing patientcontinuing was with with seen 3 3weeks 12 weeks days of of followingpartial partial weight weight the procedure bearing, bearing, and, for and, suturefinally, finally, progressprogressremoval full full. Serial weight weight Anteroposterior bearing. bearing. The The patient (AP) patient and was Lateral was seen seen 12 radiographs days 12 days following followingwere the obtained procedure the at procedure 3 forand suture 6 months for removal. suture at removalSerialfollow Anteroposterior. Serialup appointments Anteroposterior (AP) to andassess (AP) Lateral for andadequate radiographs Lateral progressive radiographs were filling obtained we ofre the obtained at defect 3 and and 6at months 3 compared and 6 at months follow to pre- upat operative radiographs for reference. (Figures 6A–F). An Ossur CTI knee brace was used for all daily followappointments up appointments to assess forto assess adequate for adequate progressive progressive filling of thefilling defect of the and defect compared and compared to pre-operative to pre- activities. The overall goal, that our patient has successfully achieved, was to have ROM to flex the operativeradiographs radiographs for reference. for reference. (Figure6 A–F).(Figures An 6A Ossur–F). CTIAn Ossur knee braceCTI knee was brace used forwas all used daily for activities. all daily activities.The overall The goal, overall that goal, our patientthat our has patient successfully has successfully achieved, achieved, was to havewas to ROM have to ROM flex theto flex knee the to J. Clin. Med. 2020, 9, 1358 7 of 10 J. Clin. Med. 2020, 9, x FOR PEER REVIEW 7 of 10 knee0◦–120 to◦ 0,° have–120°, minimal have minimal or no pain or no with pain 50% with activity, 50% activity, and gradually and gradually experience experience minimal minimal pain 80% pain of 80%the day.of the day.

FigureFigure 6. 6. ((AA)) Anteroposterior Anteroposterior ( (AP)AP) radiograph radiograph of of the the right knee, pre pre-operative.-operative. The The lateral lateral femoral femoral condylecondyle can can be be visualized visualized with with the the area area of of decreased decreased opacity opacity representing representing the the SC SC (red (red circle). circle). The The joint joint spacespace is is well well preserved preserved with with mild mild patellofemoral patellofemoral OA OA with with osteophytes. osteophytes. ( (BB)) Lateral Lateral rad radiographiograph of of the the rightright knee, knee, pre pre-operative.-operative. The The red red circle circle depicts depicts the the same same SC. SC. The The lateral lateral and and medial medial femoral femoral condyles areare outlined outlined in yellow. BothBoth (6AA) andand (6BB) will bebe usedused asas aa baseline baseline for for comparison. comparison. (C (C) AP) AP radiograph radiograph of ofthe the right right knee knee 3 months3 months following following IOBP. IOBP. The The lateral lateral femoral femoral condyle condyle can can be visualizedbe visualized with with signs signs that thatthe areathe area of the of previous the previous SC is fillingSC is (redfilling circle). (red circle). (D) Lateral (D) radiographLateral radiograph of right kneeof right 3 months knee 3 following months followingoperation. operation. The red circleThe red depicts circle the depicts area the of the area SC. of (theE) APSC. radiograph (E) AP radiograph of the right of the knee right6 monthsknee 6 monthsfollowing following IOBP. The IOBP. area Theof the area previous of the SC previous (red circle) SC has (red increased circle) has in opacity increased in comparison in opacity in to comparisonthe previous to image the previous at 3 months. image (F at) Lateral 3 months. radiograph (F) Lateral of theradiograph right knee of sixthe months right knee following six months IOBP. followingThe area of IOBP. the previous The area SC of (red the circle)previous is more SC (red opaque, circle) an is indication more opaque, that there an indication is progressing that fillingthere is of progressingthe previous filling lesion. of This the previous suggest that lesion. the This IOBP suggest has been that successful. the IOBP has been successful.

3.3. Discussio Discussionn IOBPIOBP is is a a viable viable option option to to manage manage SC SC in in selected selected patients patients avoiding avoiding an an open open approach approach [1 [166].]. CalciumCalcium phosp phosphatehate and cement havehave beenbeen used,used, butbut they they are are brittle, brittle, and and their their use use is is usually usually limited limited to tonon-load-bearing non-load-bearing areas areas [17 ]. [1 In7]. IOBP, In IOBP, the combination the combination of decompression of decompression and autologous and autologous bone marrow bone marrowgrafting allows grafting achievement allows achievement of a long-lasting of a long solution-lasting as well solution as naturally as well promoting as naturally regrowth promoting of the regrowthaffected bone of the [18 – affected22]. In this bone way, [18 the–22]. structural In this way, integrity the of structural the joint integrity space is maintained, of the joint the space tissue is maintained,where the cyst the has tissue developed where can the be restored cyst has [19 developed], as shown in can the be postoperative restored [1 imaging9], as shown and improved in the postoperativepostoperative symptoms imaging and [21 ]. improved Ultimately, postoperative this procedure symptoms allows to spare [21]. Ultimately, the joint and this delay procedure the need allowsfor major to proceduresspare the joint and and is particularly delay the indicatedneed for major in younger procedures individuals. and is IOBP particularly carries minimalindicated risks in youngerfor adverse individuals. events, as IOBP it employs carries autologous minimal risks bone for marrow adverse graft events, (Table as2 ).it employs autologous bone marrow graft (Table 2).

Table 2. Advantages and Disadvantages of IOBP.

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Table 2. Advantages and Disadvantages of IOBP.

Advantages Disadvantages Minimally invasive Intraoperative time needed to prepare • • Joint preservation, avoiding arthroplasty PRP-DBM solution • Wide choice of revision options Bone marrow harvest is needed, thus might • • Biological solution: physiological remodeling need to have an extra incision site • used for stabilization Unable to perform if overlying bone is breached •

Careful assessment of the cyst and joint cavity should be performed both pre- and intra-operatively, as communication between the two would lead to extravasation of the graft material, and it is a definite contraindication to IOBP. It is imperative to ensure adequate pin placement through fluoroscopy prior to decompressing the cyst. Delivery of the biologic material should be performed under direct visualization under fluoroscopy, as a radio-opaque dye is added to the biologic mixture to ensure proper location of the injection and direct delivery of the PRP-DBM into the lesion. The cancellous bone graft impacted into the defect contains high concentrations of osteoblasts and osteocytes, conferring a high osteogenic capacity. Its large trabecular surface area confers stability and encourages revascularization (Table3). A local hematoma forms: it is rich in inflammatory cells and chemotactic mitogens that recruit mesenchymal stem cells to the defect, leading to neovascularization, osteoid deposition, and ultimately mineralization leading to new bone [22].

Table 3. Pearls and Pitfalls of IOBP.

Pearls Pitfalls Directly visualize the articular surface via arthroscopy to • asses articular surface Harvest bone marrow without making an • additional incision Perform the core decompression during the centrifugation • Failing to do serial fluoroscopy and arthroscopy Use a guide pin during the decompression process • • Breach in the opposite cortex or articular surface Perform a tunnel scope to for direct visualization • • during decompression Impact allograft cancellous bone into the decompressed • lesion to add structural stability and increase revascularization Use a 1 mL syringe or utilize the inner stylet during • PRP Inoculation

In conclusion, IOBP is a minimally invasive procedure which provides a permanent and biologic solution for SC. IOBP gives clinicians a versatile way of utilizing the physiological principles involved in bone remodeling to not only stabilize the lesion but to heal it. This is in accordance with a recently published article where IOBP was used to treat in similar lesion in lateral Tibial plateau [23]. With successful treatment, the pain can be addressed while ensuring that the joint integrity is preserved.

Supplementary Materials: The following are available online at http://www.mdpi.com/2077-0383/9/5/1358/s1, Video S1: Core Decompression. The 2.4 mm guide pin was drilled directly into the lesion and used during the reaming process with a 7 mm reamer. Excess loculations were removed with a series of curettes. Author Contributions: Conceptualization, A.G.R.P. and A.G.; methodology, A.G.R.P.; validation, A.G.R.P., H.C.R. and I.W.S.; formal analysis, A.G., H.C.R. and I.W.S.; investigation, A.G.R.P., A.G. and H.C.R.; resources, A.G.R.P., H.C.R. and I.W.S.; data curation, A.G. and H.C.R.; writing—original draft preparation, A.G., H.C.R., I.W.S.; writing—review and editing, A.G.R.P., A.G., H.C.R., I.W.S. and N.M.; supervision, A.G.R.P., A.G. and N.M.; project administration, A.G. and H.C.R. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. J. Clin. Med. 2020, 9, 1358 9 of 10

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