Osteochondritis dissecans (OCD) is defined as a focal idiopathic alteration of subchondral bone and/or its precursor with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis.1 While lesions may occur in multiple joints, the condylar surfaces of the knee are the most common location for osteochondritis dissecans in the human body.2 The femoral trochlea and patella may also be affected 3 While idiopathic, an influence of repetitive activity in OCD is suspected. Understanding of correlates for healing is evolving, but smaller lesion size and younger age at presentation remain strong predictors for lesion healing 1,4,5,6. Delayed healing despite appropriate non-operative management, and lesion instability remain the primary indications for operative intervention 1,[7], [8], [9], [10]. Operative strategies are tailored dependent upon the stability status and location of the lesion, but improving lesion biology and ensuring stability are the primary goals of treatment to provide an environment for vascularization and ossification of the lesion.

Symptomatic, stable osteochondritis lesions that have failed nonoperative treatment and those that have become unstable, as evidenced by a breach in the articular cartilage on the MRI and/or mechanical symptoms or effusion, are indicated for surgical intervention 1,5,7,8,11 .The goal of surgical intervention is to stimulate revascularization from the parent bone into the progeny fragment and encourage the production of ossified bone within the progeny. Additionally, any evidence of micro-instability or gross instability is an indication for stabilization1,9,10. Through these methods, improved structure of the progeny leads to more normal loading of appropriately supported articular cartilage resulting in decreased bone stress, edema, and pain. In addition to these important near-term symptomatic improvements, structural healing and integrity of the progeny preserves the articular cartilage and prevents osteochondral loss that may lead to osteoarthritis.

Selection of surgical technique for the treatment of osteochondritis dissecans of the knee Is largely dependent upon stability of the lesion 1,12. When the lesion is stable on MRI assessment, without evidence of a breach in the articular surface or fluid signal below the progeny fragment, fine wire drilling in a trans-articular or retro-articular fashion is the treatment of choice and is well described [13], [14], [15], [16], [17], [18],. (Figure 1)

These lesions are often described as either ‘cue ball’ or ‘shadow’ lesions by the Research in Osteochondritis Dissecans of the Knee (ROCK) arthroscopic classification system.(Figure 2) When19 the lesion exhibits signs of micro instability, such as a shift of the progeny on the MRI without gross breach of the articular surface, the lesion may be classified as a ‘locked-door’ lesion that has a visible margin but is not able to be hinged open easily. These lesions are felt to have at least some degree of micro-instability and in situ fixation may be indicated in addition to fine wire drilling 9,10,20,21. Grossly unstable lesions with a definitive breach in the articular surface by MRI, may often be noted to be ‘trapdoor’ lesions that may be hinged open arthroscopically. Due to the advanced degree of fibrous interposition, avascular parent bone and necrotic surface of the progeny, debridement of the parent bed and progeny surface is often indicated to improve the biologic environment for healing. Depending upon lesion location and the type of hinge present, this may be accomplished either by arthroscopic or open techniques[22], [23], [24], [25]. Finally, a more advanced lesion with instability in situ or complete displacement of the progeny with a crater at the parent bone may be salvageable when the progeny articular cartilage is in good condition and the attached bone is of adequate quality. These are often best treated by an open approach with aggressive debridement and, in the case of significant bone loss, bone grafting prior to fixation 21,26. The most advanced lesions with severe comminution or degeneration of the articular cartilage of the progeny bone may not be suitable for salvage and may be indicated for osteochondral replacement strategies [27], [28], [29], [30], [31], [32]. Surgical techniques biologic augmentation and stabilization for the above salvageable lesions will be further discussed.

Bone marrow aspirate concentrate (BMAC) may be injected into the progeny or progeny parent bone interface in conjunction with fine wire drilling to augment the biologic environment33,34. Osteogenic precursors within BMAC may improve the healing response compared with marrow stimulation by fine wire drilling alone. While further research surrounding the efficacy of this technique is needed, it may be utilized in this challenging condition.

Bone marrow aspirate concentrate is harvested from the anterior iliac crest via a limited approach. Commercially available equipment and standard technique is employed [35], [36], [37].

A small- to medium-gauge Jamshidi needle, either under direct visualization and a trans-articular approach, or under fluoroscopic control in a retro-articular fashion is used to deliver the BMAC. The Jamshidi needle may be advanced over a suitable size K-wire centered within the lesion to aid in initial localization with later confirmation of location and depth by fluoroscopic control. The BMAC Is then injected slowly, either in a center location of the progeny and progeny parent interface or may be injected in two to three regions within the lesion. In a trans-articular delivery method, a small amount of bone marrow aspirate concentrate may be noted extravasating from the multiple fine wire drill holes, confirming proper distribution of the BMAC throughout the subchondral lesion. Postoperatively the patient remains non-weight bearing for six weeks, as in standard trans-articular drilling protocols. Augmentation with Retro-articular Bone Grafting for OCD Lesions

Femoral condylar OCD lesions with an intact articular surface but significant fibrous interposition between the parent and progeny, or the presence of large subchondral cysts may present significant challenges to fine wire drilling alone. In such cases, additional biologic osteoinductive and conductive tissue may be desired. Following fine wire drilling at 2 to 3mm intervals, retro-articular cancellous autograft may be added 38,39. A small incision over the Ipsilateral anterior iliac crest is used for manual curettage and cancellous bone harvest. Alternatively, a 6mm autograft osteochondral harvester or a commercially-available cylindrical tap-harvester on a cordless drill may be employed. Three to five mL of cancellous bone, or a 6-mm core may be harvested for retro-articular bone grafting.

A 2.4mm guide pin is positioned within the lesion using multiplanar fluoroscopic control. A radiolucent surgical triangle to position the knee in a flexed position, clear of the contralateral extremity, is useful for stable positioning and access during drilling. Following placement of the 2.4 guide pin, a 6 or 7mm reamer may be used to enter the lesion from the medial or lateral margin of the involved condyle, staying distal to the epiphysis in immature patients. Once the core track is established, curettage and suction debridement may be carried out within the fibrous tissue or cyst deep to the progeny fragment. Following preparation of the lesion, the harvested iliac crest bone graft is introduced into the core tract. Utilizing a half-cannula placed at the aperture of the reamer tract may facilitate introduction of the bone graft with smooth forceps or an arthroscopic grasper. Once the bone graft is within the tunnel, a small surgical tamp is used to compress the bone graft into the lesion with fluoroscopic confirmation of tamp position and graft delivery. (Figure 3)

Postoperatively, six weeks of non-weight bearing is employed as with other techniques involving fine wire drilling of intact lesions. Avoidance of impact activity Is recommended until improved bone within the progeny is visualized on imaging. While anecdotal and case reports are encouraging, indications and improved evidence for utilization of this technique is pending.

Stabilization and compression of OCD lesions is indicated when signs of instability exist 20. Healing requires a stable environment for revascularization of the progeny and progeny bone formation. MRI assessment and arthroscopic assessment suggesting any shift in the progeny position relative to the parent bone is a sign that instability exists 10. Arthroscopic examination with findings of a margin of cartilage that has become divided from the surrounding tissue (such as those represented by locked door or trapdoor lesions), or when the cartilage has minimal changes but the lesion is mobile or ballotable by an arthroscopic probe, are the best standards for evaluating stability. The surgeon may elect to add stabilization and compression in any of these lesions. Metallic or bio-absorbable screws provide both stability and compression. While bioabsorbable pins may add stability, they provide compression to a lesser degree 40. These implants have all been used in settings of both ossified and unossified progeny lesions [41], [42], [43]. Suture bridge fixation is another described method for providing stability and compression that may offer advantages in certain situations 25,[44], [45], [46], [47]. Choice of fixation method is dependent upon surgical assessment of the lesion, and evidence for best techniques is evolving.

Compressive screw fixation, weather metallic or bio absorbable, may be used to treat OCD lesions in situ when micro instability without gross displacement is present 48. These lesions may be represented by a slight shift of the progeny position noted on MRI or when arthroscopic evaluation confirms a discernible cartilage margin, denatured cartilage edge of the lesion (locked door lesion) or when the entirety of the lesion is mobile to ballottement with an arthroscopic probe. The relative benefits and risks of metallic versus bio absorbable screw fixation have been evaluated retrospectively and either may be a reasonable option for the treating surgeon 21,[49], [50], [51], [52], [53]. Metallic screws may offer compression without risk of material related synovitis or implant breakage, but like bio-absorbable screws, may loosen and become prominent causing secondary body wear. Metallic screws may also be indicated for removal when they are at the immediate subchondral margin. Implant loosening or surrounding cartilage degeneration leading to an exposed implant may be risks that are decreased by using screws within progeny lesions that have ossified bone within the progeny, or epiphyseal cartilage within the progeny that is still firm and has not become softened with secondary necrosis.

In situ screw fixation may be used in conjunction with fine wire drilling in either an arthroscopic or open fashion to stabilize and compress lesions exhibiting micro-instability. In this setting, surgeons may often choose to place screws arthroscopically with a headless, cannulated screw system. Following arthroscopic lesion assessment and fine wire drilling, these screws may be placed into the femoral condyle or trochlear surface in a standard arthroscopic position with varying degrees of knee flexion to provide perpendicular access to the lesion. The surgeon may improve visualization by using accessory portals and visualizing the lesion from the opposite side of the knee while using a guide wire to assess the best trajectory of approach to enter the lesion in a perpendicular fashion. In the femoral trochlea or more anterior positions of the femoral condyle, a surgical positioning triangle may improve access and fluoroscopic visualization. In the posterior aspects of the femoral condyle, more flexion is required for proper screw trajectory into the lesion.

When placing cannulated screws arthroscopically, portal and fat pad management is important for both visualization and efficiency of cannulated drilling and screw delivery. In addition to accessory portals for viewing, at times an arthroscopic probe in an accessory portal to retract the fat pad and capsule anteriorly away from the condylar structures may assist with visualization and screw delivery into the knee. In practice, guidewire placement percutaneously with secondary portal creation around the guide wire is often most efficient. Screws may be placed in a trajectory through the patellar tendon at times with minimal risk to the tendon when divided in line with its fibers. In deeper degrees of flexion, care should be taken to avoid division through the anterior horn of the medial or lateral meniscus. Once the guidewire is positioned, drilling may be conducted through the created portal established with a 11 blade around the guidewire pin. Further dilation prior to screw placement may be accomplished with the empty screwdriver to further establish the portal prior to screw placement. In general, a screw depth twice the depth of the progeny depth is recommended for stability. Whether metallic or bioabsorbable, screws should be placed approximately 1mm below the depth of the deep margin of the articular cartilage. When ossified progeny is not present, screws should be placed a minimum of 4mm below the articular surface. Screw depth can be estimated by direct visual inspection by moving the arthroscope below the screw tract and looking through the articular defect at the screw interface, or a guide pin may be used to visually probe and estimate the depth from the articular cartilage to the screw head. Fluoroscopy may be used and is recommended to ensure the screws are positioned at an appropriate depth. Leaving the guidewire in place during these maneuvers can aid in efficiency for fine adjustment. Throughout cannulated screw placement, care must be taken to avoid flexion and extension of the knee following guidewire placement as this may result in binding of the guidewire and potential wire breakage. While there is little evidence guiding the number of screws needed for adequate lesion stabilization and compression, one screw for every 10mm in diameter of the lesion is recommended.

An arthrotomy may be necessary to optimize screw placement for OCD lesions in certain locations. Compressive fixation in the patella may require a moderate-sized para-patellar arthrotomy to evert the patella for appropriate access. Femoral trochlea lesions may be accessed arthroscopically in a shallower degree of knee flexion with translation of the Patella medially or laterally to allow guide wire and screw placement. In some lesions, particularly those that are more central, arthrotomy may be needed for appropriate access. Mid-condylar and posterior condyle lesions, particularly in the lateral femoral condyle where the infrapatellar fat pad and capsule limits access and flexion, may necessitate an infra-patellar arthrotomy. Following screw placement, the surgeon should record the details of knee positioning and screw trajectory within the operative report. Screws may be indicated for removal, and a detailed description of positioning during screw placement will aid in implant removal . (Figure 4)

Unstable OCD lesions may have minimal or fragmented bone within the progeny and be less amenable to screw fixation. The articular cartilage on such lesions may be in excellent condition overall and indicated for salvage, but placement of screws within an all-cartilage progeny, or within a progeny with fragmented bone may provide suboptimal fixation or risk further fragmentation of the lesion. These lesions may be indicated for suture bridge fixation. Suture bridge fixation has been described and larger series have been published recently with excellent results in the treatment of osteochondral and chondral fractures, and with results similar to screw fixation for larger, more challenging osteochondritis dissecans lesions 25,[44], [45], [46], [47].

Suture bridge fixation is accomplished by placing either a sliding suture anchor or a knotless anchor device at the margin of the osteochondral lesion. Sutures then span across the surface of the lesion and are fixed with subsequent knotless suture anchors to create several strands of tensioned bridging suture across the surface, applying compression and stability from a compressive surface effect as opposed to point compression with screws. The suture anchors may be placed in a periarticular position in the trochlea or spanning the articular surface and into the notch. However, placing the anchors approximately 2 to 3mm into the healthy margin surrounding a lesion allows the suture to span the lesion crossing a margin of healthy cartilage and minimizes cavitation of the tensioned suture limb into the margin of the lesion. When anchors are placed through the articular surface, 3mm or smaller resultant defects in the surface fill predictably with fibrocartilage in the post-treatment setting. For acute osteochondral lesions, #1 or #2 vicryl suture has been used successfully and has the advantage of dissolving over three to six weeks. This obviates the need for secondary surgery. However, when used for OCD lesions, longer duration of stability and compression may be required for healing, and1.3mm polyester tape has been utilized in this setting. This requires a secondary surgery for suture removal, similar to removal of metallic screw implants. Protocols for optimal implant type, suture type, suture number, tension force, direction of suture strands, and duration of suture implantation are all under study and require further level of evidence for best recommendations.

Suture bridge fixation may be performed with either open or arthroscopic techniques. Following preparation and final reduction of the lesion, the lesion is provisionally held with a trans-articular .045 K wire. For fixation, 2.9 knotless suture anchors with 1.3-millimeter polyester tape sutures are commonly utilized. In the trochlea, a primary anchor with two to four strands may be placed on the posterior central aspect of the lesion 2 to 5mm from the lesion margin. The strands may then be brought to individual knotless anchors that may be placed in the supra-trochlear, non-articular distal femur. This can result in two to four bridging sutures that are in line with the flexion arc of the knee. These are placed with manual tensioning and a mallet is used to engage the anchor. When the lesion is fixed, the sutures may be examined using an arthroscopic probe to confirm proper tension, the K-wire is removed, and the suture is cut flush with the proximal anchors. (Figure 5)

A similar technique may be used for condylar lesions with the primary anchor with multiple strands positioned most posterior with the individual strands bridging to anchors anterior to the lesion. In these lesions the anterior anchors may also be trans-articular and 2- 5mm from the anterior margin of the lesion. Further study of secondary body wear effects is indicated, but sutures in line with the arc of motion have been used preferentially over transverse sutures and very minimal articular surface changes are noted at arthroscopic suture removal. The post-operative protocol is six weeks of non-weight bearing with early motion followed by six weeks of non-impact exercises. . Advanced imaging is obtained at three months to evaluate healing and planning for arthroscopic suture removal. At this time standard arthroscopic evaluation of the lesion can be carried out and the sutures may be elevated with an arthroscopic probe or freer and an arthroscopic grasper may be used with tension and rotation and the suture can be removed by sliding the suture through the subchondral anchor. At second look arthroscopy a small depression on the progeny lesion from the suture tract is commonly noted. Fissuring or cracking of the cartilage is not commonly seen. Fibrocartilage is often appropriate in appearance at the suture anchor positions and second-body wear on the tibial, meniscal, or patellar surfaces has been noted to be minimal and often grade one in nature - similar to other second look arthroscopies, following non-suture related salvage techniques. (Figure 6)

When performed arthroscopically, this technique often requires creation of accessory portals for both access to the lesion and suture management. The knee may also be positioned in varying degrees of flexion to improve access. Using a commercially-available rigid plastic sleeve that is supplied with a waxed suture implant may serve to identify the position and trajectory of the drill tract prior to anchor placement. Visualization of the anchor within the joint and tension on the suture help to ensure that sutures lie flat on the articular surface prior to final implantation. The lesion is then inspected for stability, and the sutures may be inspected for proper tension. (Figure 7)

Unstable OCD lesions with significant fibrous interposition between the progeny and parent bone may be indicated for debridement and bone grafting prior to fixation 21,23,[54], [55], [56], [57]. Improving the biologic environment for osseous healing and then eventual ossification of the progeny should be paramount when planning surgical treatment. In addition to removing fibrous tissue between the parent and progeny fragment, removing the sclerotic margin of the parent bone to expose healthier bleeding cancellous bone may aid in lesion healing. Additional light superficial debridement on the under surface of the progeny fragment to remove superficial necrotic margins may also be beneficial. The debridement of the lesion and placement of interpositional cancellous autogenous bone may be accomplished either by arthroscopic or open technique. A limited arthrotomy may allow best access for most lesions but select lesions with a hinge in a zone of the trochlear or condyle that is accessible arthroscopically may lend themselves to arthroscopic management 22,58.

The lesion is hinged open on any remaining appropriate cartilage margin. The soft tissue adjacent to the posterior cruciate ligament may serve as a hinge, or the progeny may be removed entirely for optimal access. A combination of motorized chondrotome and curettage to remove fibrous tissue and sclerotic bony margins to expose healthy cancellous bone is recommended. At times, a water-cooled, high-speed burr may be employed within the parent bed. The goal of parent bone debridement is to visualize normal cancellous interstices following the removal of dense sclerotic bone. On the under surface of the progeny, light debridement with a curette or a 15 blade at a right angle to the surface may be indicated. Following gross debridement of each surface, a water-cooled .045 K wire drilling at 2-millimeter intervals may be used to aid in improving surface bleeding and preparation for ingrowth within both the parent and progeny fragment.

Following aggressive debridement back to healthy cancellous bone, there is often a defect remaining between the progeny and parent bone. Cancellous autograft bone may be harvested from the distal femur, proximal tibia or the ipsilateral anterior iliac crest. A commercially-available bone graft harvesting cylinder using a high-speed drill may also allow for bone graft harvest with minimal incision or access required. Harvest may be accomplished through an arthrotomy from the supratrochlear distal femur or from the proximal tibia. Care should be taken to be either proximal or distal to the respective physis if the patient is immature.

Bone graft may be placed within the parent bed with digital compression followed by a tamp. Trialing placement of the progeny back across the lesion to estimate proper filling and restoration of contour may be required. Once appropriate fill of the defect and contour of the progeny fragment is achieved, the progeny is stabilized with a .045 K wire in preparation for either screw or suture bridge fixation. (Figure 8)

In the arthroscopic setting, morselized cancellous autograft may be delivered through a slightly enlarged arthroscopic portal using a modified tuberculin syringe to deliver the bone graft into the parent bed and below the progeny fragment.22 Once the adequate bone graft is delivered a probe and other arthroscopic instruments may be used to temporarily stabilize the progeny in a reduced position and a .045 K wire can be utilized to stabilize the progeny in preparation for either arthroscopic screw or suture bridge final fixation. Following stabilization of the progeny, a motorized chondrotome may be used to evacuate any loose graft material from the joint.