Arthroscopic Delivery of Cancellous Tibial Autograft for Unstable Osteochondral Lesions in the Adolescent Knee

Abstract

The appropriate surgical technique for the treatment of unstable osteochondral lesions of the knee remains unclear and had been traditionally described with an open arthrotomy. Administration of bone grafting material in the knee may be performed for a variety of pathologic conditions, including unstable osteochondritis dissecans, traumatic osteochondral defects, or subchondral fracture nonunion, or for preparation of residual tunnels during revision anterior cruciate ligament reconstruction. Although various grafting materials have been described in the literature, cancellous autograft remains the gold standard for treatment safety and efficacy. We describe a successful technique for arthroscopic delivery of autogenous bone graft during fixation of unstable osteochondral lesions of the knee. When the indication for grafting is established, cancellous autograft is harvested from the proximal tibia, undergoes morcellation, and is soaked in bone marrow aspirate obtained through the harvest window. The bone graft is then packed into a modified tuberculin syringe. After arthroscopic preparation of the unstable osteochondral fragment and the respective donor surface, the tuberculin syringe is placed through a standard arthroscopy portal and the bone graft is introduced into the defect under direct visualization, followed by an appropriate osteochondral fixation technique.

Osteochondral lesions of the knee may occur as a result of osteochondritis dissecans or trauma. A variety of treatments exist for stable lesions, including activity restrictions, casting, bracing, or arthroscopic drilling. Lesions are considered unstable when the fragment is mobile on examination or when advanced imaging shows evidence of subchondral bone discontinuity or synovial fluid behind the lesion. Unstable lesions are preferably treated with fixation but sometimes require removal of the loose fragment. If the fragment is amenable to fixation, the addition of autologous bone graft has been described as supplementing unstable osteochondral lesions through an arthrotomy to deliver the biologic tissue.^1-4

With advances in arthroscopic techniques for assessing and fixing unstable lesions, a less invasive method of delivering autologous bone graft is desirable. In this technical note, we describe a safe, cost-effective arthroscopic technique to introduce autologous bone graft into an osteochondral lesion of the knee.

Technical Procedure

Evaluation of an adolescent or young adult in whom an osteochondral lesion is suspected includes a detailed history and thorough physical examination. Particular attention is given to a patient's age, mechanical symptoms, or evidence of a knee effusion because these factors may be indicative of an unstable fragment and therefore influence treatment selection. Imaging includes standard radiographic knee images, including a notch view, as well as magnetic resonance imaging. These modalities are used to establish skeletal maturity, the location of injury, and stability of the lesion. Surgical intervention is recommended for any patient with a clinical picture or advanced imaging consistent with an unstable osteochondral lesion.

The operation is performed with the patient under general anesthesia in a supine position. After establishing standard anterolateral and anteromedial arthroscopic portals, the surgeon completes a diagnostic evaluation inspecting the entire knee (Video 1). If a loose body is suspected, the surgeon should identify the free osteochondral fragment and determine whether it is amenable to fixation. In our experience most unstable lesions are typically unstable in situ. Once the lesion is identified on the condylar surface, visualization and probing of the entire lesion are performed to assess regions of instability or the presence of an incompletely displaced lesion, which may be hinged on 1 side (Video 1). An attempt should be made to retain the intact hinge because this will assist with reduction after debridement and grafting of the lesion.

The osteochondral lesion is carefully elevated with an arthroscopic probe or a freer elevator through the standard anterior portal or a second accessory 5-mm anterior portal (Video 1). Typically, there is fibrous tissue deep to the lesion that is debrided with an arthroscopic shaver and manual curettage with standard or ring curettes placed through the anterior portal. A microfracture awl or a drilling technique is used to fenestrate the base of the lesion in multiple points to improve access for blood flow to the debrided base of exposed bone. After this lesion preparation, the defect and lesion reduction are assessed. When a significant subchondral osseous defect is present between the fragment and donor bed, bone graft is indicated for structural support, as well as osteoconductive and inductive properties.

Autologous bone graft harvest is achieved through a 2-cm longitudinal incision with the proximal aspect 1 cm lateral to the maximal prominence of the tibial tuberosity (Video 1). After subcutaneous mobilization, the anterior compartment musculature is released from the periosteal insertion along the lateral margin of the tibial crest and elevated from the anterior cortex for a distance of 2 cm. A 2.0 K-wire is used to drill corner points for a cortical window that is completed by connecting these points with a 0.25-inch osteotome. In the skeletally immature patient, this resultant window is recommended to be at least 2 cm or greater distal to the proximal tibial physis. Before harvest, an 18-gauge needle on a 5-mL syringe is used to obtain bone marrow aspirate from the proximal tibia to mix with the autologous bone graft. A curette is then used to harvest the metaphyseal cancellous bone. In a skeletally immature patient, harvest should not be performed proximal to the cortical window to prevent injury to the proximal tibial physis. The size of the lesion will dictate the amount of bone graft; however, filling the 1-mL tuberculin syringe (Becton Dickinson, Franklin Lakes, NJ) will typically yield an appropriate amount for most defects (Table 1).

Table 1.

Pearls and Pitfalls: Complete List of Helpful Tips and Cautions When Performing Arthroscopic Application of Autologous Bone Graft to Osteochondral Lesion in Knee

Pearls The 1-mL tuberculin syringe with a Luer slip tip allows for easy modification of the tip using a No. 10 blade for an ideal size and shape through the arthroscopic portal. Other syringe tips may be difficult to modify in this manner. While addressing osteochondral lesions of the medial femoral condyle, the surgeon should avoid multiple accessory portals by placing the anteromedial portal at the appropriate knee flexion angle to access the lesion. Use of a freer elevator to define 70% of the margin of the osteochondral injury before mobilizing the osteochondral fragment will safely retain the hinge. Visualization of bleeding bone is necessary after debridement and marrow stimulation (drilling or microfracture) to improve healing. An 18-gauge needle may be used percutaneously to assist in hinge manipulation (i.e., to hold the hinge open during debridement and graft introduction) while avoiding the creation of an additional portal. The surgeon should consider using fluoroscopy to confirm the location of the physis during proximal tibial autologous bone graft harvesting. Morcellation of the harvested autograft into a thick paste will allow for easy application through the tuberculin syringe. A fine paste may cause extravasation into the joint. Reduction of the fragment after bone grafting can be supplemented with leg extension to gently compress the osteochondral fragment. Thinner osteochondral fragments with minimal viable osseous surface may require metallic compression screws. Bioabsorbable screws in this instance may not have the compressive strength needed for these lesions. Titanium and bioabsorbable screws allow for magnetic resonance imaging to assess osteochondral lesions. A computed tomography scan may be useful after the use of any screw type to assess bony union. Pitfalls Use of an arthroscopic probe to mobilize and hinge the osteochondral fragment may cause fragmentation and increased iatrogenic damage to the fragile fragment. Loss of an intact hinge will add substantial difficulty to the arthroscopic procedure and should be avoided. K-wires may be used to hold the lesion in a hinged position during preparation and bone grafting if the hinge is lost. Converting to a mini-open incision may be needed in such cases. Lesions with an established posterior open margin may present difficulties for anterior opening and maintenance of a hinge required for an arthroscopic approach. These posteriorly detached lesions may require an open approach. Inadequate debridement of the fibrous subchondral tissue will prevent or delay healing. For larger lesions, injection of autograft without interval inspection, packing, and distribution of graft may cause inadequate coverage and overstuffing of the defect. Compression screw fixation on either the anterior or posterior surface may cause a seesaw effect. This can be avoided with alternating sinking screws during compression.

The bone graft and bone marrow aspirate are combined in a specimen cup and undergo morcellation with a curette, rongeur, or tamp. The tuberculin syringe is modified for use as a delivery tube by removing the tip with a No. 10 blade while being held stable against a surgical towel on the back table (Video 1). The syringe is packed to the top with the plunger withdrawn to the entire distal tubing to be filled. The proximal tibial incision is thoroughly irrigated and closed in a layered fashion.

The arthroscope is used to visualize the delivery of the bone graft. The arthroscopic fluid remains at a standard pressure setting during administration. A hinged lesion may be held open with a percutaneously directed 18-gauge needle to allow introduction of the graft syringe below the hinge. Under direct visualization, the bone graft is delivered into the lesion after the introduction of the modified tuberculin syringe through the corresponding arthroscopic portal overlying the condylar lesion (Fig 1, Video 1). The graft is applied by depressing the plunger. A freer or probe may be used, following in the same portal, to spread the graft throughout the defect. This allows for controlled arthroscopic delivery of bone graft. Extension of the knee assists in reduction and compression of the graft within the defect, and excess graft may be removed with a freer as needed to ensure anatomic reduction. Once the fragment is reduced, compressive fixation is achieved immediately. The adequate reduction of the chondral surface is visualized arthroscopically throughout (Fig 2). Bioabsorbable compression screws are most often used, although metallic screws may be preferable for thinner fragments. Other possible forms of fixation include threaded guide pins or suture.

Fig 1.

(A) Arthroscopic delivery of autograft to site of lesion using modified tuberculin syringe. (B) Introduction of syringe through standard arthroscopic portal.

Fig 2.

(A) Arthroscopic reduction of osteochondral fragment and (B) fixation of osteochondral lesion using bioabsorbable screw.

After grafting and fixation, the patient remains non–weight bearing for 3 months or until there is evidence of healing. Full non–weight-bearing range of motion, isometrics, and light strengthening are recommended. If radiographic healing of the lesion is indeterminate, repeat magnetic resonance imaging or diagnostic arthroscopy may be undertaken at 3 to 6 months.

In our experience, osteochondral injuries take 3 to 6 months to heal after the procedure. Nine consecutive patients have undergone this procedure (5 female and 4 male patients) at a mean age of 14.9 years. The mean surgical time was 130 minutes, with a mean estimated blood loss of 16 mL. There were no intraoperative events or complications associated with the donor site, including fracture, pain, infection, or wound dehiscence. All patients regained full range of motion by 2 months after the procedure. To date, 1 of 9 patients has required a revision procedure.

Discussion

Recently published clinical practice guidelines have reached consensus recommendations that both symptomatic skeletally immature and skeletally mature patients with salvageable unstable or displaced osteochondral lesions be offered the option of surgical treatment.⁵ Despite numerous descriptions of treatment methods for osteochondral lesions of the knee, both operative and nonoperative, no consensus has been reached on the optimal surgical technique for managing this clinical entity.^4,5 Historically, authors have advocated that repair of salvageable osteochondral lesions is preferred over lesion excision. Numerous methods of lesion fixation have been associated with successful clinical outcomes.

The addition of biologic supplementation to osteochondral fixation in the form of autologous bone graft has been reported in multiple studies.^2,6 Traditionally, an arthrotomy has been used to deliver autologous bone graft to the lesion site.^2,6 With advancements in arthroscopy, methods for less invasive treatment of orthopaedic disease are being developed. Wong and Yip⁷ detailed the use of a chest tube and metal trocar to introduce bone graft into the femoral tunnel during revision anterior cruciate ligament reconstruction. Said et al.⁸ described the alternative use of a unique set of specific instruments (osteochondral autograft transfer system [OATS]) to deliver bone graft to bone tunnels also in the setting of revision anterior cruciate ligament reconstruction. Descriptions of arthroscopic techniques for delivering autologous bone graft to osteochondral lesions of the knee are limited in the current literature.

The advantages of the described arthroscopic technique include the use of a modified tuberculin syringe by a simple, accurate, and reliable method to deliver bone graft to an osteochondral lesion in a minimally invasive fashion. The harvest site within the operative field allows the procurement of gold standard grafting material in a safe, relatively low-cost manner with minimal morbidity. The syringe rigidity allows manipulation of the angle of delivery, and the transparent tubing allows direct arthroscopic visualization of the delivery of graft to the lesion site. In addition, the tuberculin syringe is typically inexpensive and readily available. A limitation is the lack of direct reduction and visualization, which requires—in this technique—advanced arthroscopic skills. The risks include harvest-site morbidity, physeal damage in the skeletally immature patient, bone graft extravasation during application, and overstuffing of the defect.

Supplementary Data

Video 1

Technique for arthroscopic delivery of cancellous tibial autograft for unstable osteochondral lesions.