Advances in Surgical Treatment of Osteochondritis Dissecans of the Knee

Osteochondritis dissections of the knee is a challenging condition to treat in both skeletally-immature and mature individuals. Guiding treatment principles are the improvement of both the biology and stability of the lesion. Advances in both imaging and arthroscopic assessment have aided surgeons in the treatment of these aspects of osteochondritis lesions. However, level of evidence for best treatment remains low overall. Both arthroscopic and open techniques may be utilized to treat these lesions. Subchondral drilling, injection of bone marrow aspirate concentrate, and debridement with retro-articular or open bone grafting have all been described as methods of biologic augmentation. Bioabsorbable and metallic implants traversing the progeny and parent aspects of the lesion, as well as surface compressive suture fixation may be appropriate techniques for augmenting lesion stability. These techniques are further described with recognition that further study regarding indications and outcomes remains ongoing.

Introduction

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. 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. The femoral trochlea and patella may also be affected 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. ^, Delayed healing despite appropriate nonoperative management, and lesion instability remain the primary indications for operative intervention. ^, 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.

Indications for Surgical Management of OCD Lesions

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. ^, ^, ^, ^, 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 stabilization. ^, ^, 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.

Surgical Techniques for OCD Management

Selection of surgical technique for the treatment of osteochondritis dissecans of the knee Is largely dependent upon stability of the lesion. ^, 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 ( Fig. 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 ( Fig. 2 ). When 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. ^, ^, ^, 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. 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. ^, 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. Surgical techniques biologic augmentation and stabilization for the above salvageable lesions will be further discussed.

Drilling of Symptomatic Stable OCD Lesions with Biologic Augmentation

Both trans-articular and retro-articular drilling techniques to provide bone marrow and biologic response between the parent and progeny bone have been well described. Results of these techniques are generally good, particularly in younger patients and small- to moderate-size lesions. Standard practice entails use of a 0.045 K-wire at 2-3 mm intervals, with a 0.062 wire often utilized for a retro-articular approach. With increasing lesion size, particularly greater than 20 mm in the major diameter, and with patients approaching skeletal maturity, resultant osseous formation in the progeny may be diminished. To improve results in lesions with characteristics that may be less favorable for healing, augmentation of drilling with bone marrow aspirate concentrate injection or the addition of retro-articular bone graft has been described.

Augmentation With Bone Marrow Aspirate Concentrate (BMAC) for OCD Lesions

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 environment. ^, 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.

Bone marrow aspirate concentrate may then be delivered into the lesion via a trans-articular or retro-articular approach ( Fig. 2 ).

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 2 to 3 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 nonweight bearing for 6 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 3 mm intervals, retro-articular cancellous autograft may be added. ^, A small incision over the Ipsilateral anterior iliac crest is used for manual curettage and cancellous bone harvest. Alternatively, a 6 mm autograft osteochondral harvester or a commercially-available cylindrical tap-harvester on a cordless drill may be employed. Three to 5 mL of cancellous bone, or a 6-mm core may be harvested for retro-articular bone grafting.

A 2.4 mm 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 7 mm 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 ( Fig. 3 ).

Postoperatively, 6 weeks of nonweight 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.

Advanced Techniques and Augmentation with Internal Fixation of Unstable OCD Lesions

Stabilization and compression of OCD lesions is indicated when signs of instability exist. 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. 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. These implants have all been used in settings of both ossified and unossified progeny lesions. Suture bridge fixation is another described method for providing stability and compression that may offer advantages in certain situations. ^, Choice of fixation method is dependent upon surgical assessment of the lesion, and evidence for best techniques is evolving.

Open and Arthroscopic Lesion Fixation With Screws

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. 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. ^, 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 1 mm below the depth of the deep margin of the articular cartilage. When ossified progeny is not present, screws should be placed a minimum of 4 mm 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 10 mm 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 ( Fig. 4 ).