Introduction

Osteochondral fragments can occur in any synovial joint, but they are most commonly encountered in the knee. Typical etiologies include osteochondritis dissecans, trauma (such as the result of patellar dislocation), or nonunion of periarticular fracture.

Osteochondral fragments can also be created by the surgeon in the course of performing osteochondral autografts such as mosaicplasty and mega OATS (Chapters 5 and 6) or osteochondral allografting (Chapter 7).

This chapter reviews the most common methods of fragment fixation.

Indications for Internal Fixation

Few studies provide clear indications for surgical fixation of osteochondral fragments (Table 8-1). The underlying diagnosis has implications in the decision-making process, such as in the treatment of osteochondritis dissecans (OCD).

TABLE 8-1 Indications for Internal Fixation with Regard to Type of Osteochondral Fragment

OCD lesions in situ are much more likely to heal in skeletally immature patients than in adults. Conversely, fragments with lucency on radiographs or fluid on MRI between the fragment and bone bed are less likely to heal and may do better with fixation.

Acute displaced traumatic fragments should be operated in a timely fashion, as there is obviously no opportunity for healing and the fragment risks degeneration as it moves in the joint.

In cartilage repair procedures, the osteochondral graft may require fixation depending on the inherent stability, size, and location of the graft.

To our knowledge, no quantitative measures of graft stability are available to assist the surgeon in deciding when to perform adjunctive fixation.

Juvenile Osteochondritis Dissecans

This diagnosis is classified as an OCD lesion in a patient with open physes demonstrated on radiographic imagery, specifically of the distal femur. The most common patients are athletic, active adolescents.

Surgical indication for juvenile osteochondritis dissecans (jOCD) includes failure of 6 to 9 months of nonoperative treatment of a stable lesion, an unstable or detached lesion, or a symptomatic patient with imminent physeal closure within 6 months to a year.¹

Adult Osteochondritis Dissecans

Unlike jOCD, symptomatic adult OCD necessitates surgical intervention in most cases because of the progressive course, the inability of the fragment to heal on its own, and the fact that most adult lesions are unstable in nature.²

Arthroscopy is useful for determining size and stability of lesions. In situ lesions that are stable during arthroscopic probing can be treated with drilling or internal fixation. Flap lesions (unstable lesions) benefit most from internal fixation techniques.

Massive lesions, multiple fragmented lesions, and substantial craters often require procedures utilizing open bone grafting of the bed or osteochondral autografts and allografts when fixation is not possible or the fragment is not adequate for fixation.³

Traumatic Osteochondral Fragments

The most important decision making in treatment of traumatic osteochondral fragments is whether the fragment has adequate remaining bone to allow both fixation and osseous healing.

In adults there is little evidence that purely chondral fragments have the ability to heal to bone. Nonetheless, surgeons may choose to attempt to repair very thin or small osteochondral fragments with the understanding that there is a significant risk of failure.^4,5

One caveat of this approach (and, in fact, in treating any osteochondral fragment with internal fixation) is the avoidance iatrogenic injury to the joint by the fixation device should the fragment collapse or detach, leaving the fixation device proud or loose within the joint. Numerous case reports have documented articular cartilage injury and joint destruction by exposed or loose fixation devices.^3–7

Overview of Internal Fixation Devices

The goal of any chosen device should be rigid fixation and compression while establishing a position that is seated low enough as to not interfere with the surrounding articular cartilage (Table 8-2). The device should allow for early range of motion and should retain the ability to be removed, if necessary.⁸

TABLE 8-2 Internal Fixation Devices

Cannulated and Variable Pitch Screws

Several options exist with metal screws including cannulated screws and variable-pitch, headless screws. The most commonly referenced variable-pitch screw is the Herbert screw.^11–14 This type of screw allows for rigid fixation, as well as having an auto-compression effect. Another advantage to this screw is that the headless design allows it to be countersunk beneath the surface of the articular cartilage.

The disadvantage of the Herbert screw along with the other metal screws is that they may require an additional surgery for removal, and, if the fragment settles or breaks, the screw may become proud, leading to injury of the opposing articular surface. When possible, the surgeon attempts to place these devices in a manner that avoids the articular surface (Fig. 8-1).

FIGURE 8-1 Fixation of a large osteochondral shell allograft of the lateral femoral condyle with two 3.0 cannulated screws. Note the screws have been placed lateral to the articular surface.

Surgical Technique: Chondral Dart

Chondral darts or pins are best suited for providing resistance to shear of relatively stable fragments. They are not capable of providing significant fragment compression, if the surgeon deems this necessary. The low-profile nature is also suited to relatively small or thin fragments.

Darts can be inserted either arthroscopically or with an open procedure after bone grafting or placement of an allograft. The author’s experience is primarily using chondral darts for adjunctive fixation of osteochondral allografts (Chapter 7).

The instruments include a cannulated guide, drill, and insertion tamp, which are designed to allow for 2 mm of countersinking of the dart (Fig. 8-2).

FIGURE 8-2 Instruments for insertion of chondral dart (Arthrex, Naples, Florida), including cannulated guide, drill, insertion tamp, and dart holder.

In this case a partial talus shell allograft is to be placed.

After fashioning of the graft (Fig. 8-3) and the recipient site of the medial talus (Fig. 8-4), the graft fragment is seated (Fig. 8-5). Note the relative stability of this fragment because of the conformity of the tibiotalar joint and lateral support of the host talus.

FIGURE 8-3 Osteochondral shell allograft of the medial talus preceding insertion.

FIGURE 8-4 Intraoperative view of the ankle showing preparation of the medial talus for graft insertion. An external fixator is used to provide joint distraction.

FIGURE 8-5 Shell allograft in place. Note conformity and congruency, which confers relative stability, allowing for pin rather than screw fixation.

With the fragment in place, the cannulated guide is placed on the articular surface, and the drill is used to prepare the osseous channel for the dart (Fig. 8-6).

FIGURE 8-6 Drilling is performed through the cannulated guide. Depth is fixed at 20 mm.

While keeping the guide in place on the fragment, the chondral dart is loaded into the cannulated guide (Fig. 8-7) followed by the insertion tamp, which is gently impacted to seat the dart (Fig. 8-8). Care must be taken to maintain the cannulated guide at the same position and angle during both drilling and dart insertion.

FIGURE 8-7 The chondral dart is inserted into the cannulated guide. Care is taken to not move the guide from the site of fragment drilling.

FIGURE 8-8 The chondral dart is gently tamped into place. The dart is 18 mm in length, providing 2 mm of countersinking into the articular cartilage surface.

The stability of the fixation can be evaluated, and additional darts can be inserted as necessary. One advantage of darts and pins is the relatively small insertion defect footprint on the articular cartilage (Fig. 8-9).

FIGURE 8-9 The allograft in place with two chondral darts inserted. Note the small footprint in the articular surface at the site of dart insertion.

Surgical Technique: Biocompression Screw

Fixation devices that provide interfragmentary compression are ideal for fixation of osteochondritis dissecans fragments, when stability of fixation is critical or when there may be a mismatch between the fragment and the host bed requiring bone grafting.

Headed cannulated or variable pitch metal screws provide the best and most durable fixation, but absorbable compression screws may be adequate for many circumstances. For strength reasons, these absorbable screws are not cannulated, though the drill and tap may be.

Instruments include a tapered drill and tap (Fig. 8-10) and screwdriver for the implant insertion (Fig. 8-11). In this case example, the patient has an osteochondral lesion of the talus amenable to open grafting and fixation (Fig. 8-12).

FIGURE 8-10 Cannulated drill and tap for insertion of biocompression screw (Arthrex, Naples, Florida).

FIGURE 8-11 A 2.7-mm biocompression screw attached to a screwdriver. Note that the screw is tapered and the variable pitched.

FIGURE 8-12 Osteochondral lesion of the medial talus exposed through medial malleolar osteotomy.

The lesion is elevated to ensure there is adequate bone on the fragment for fixation and healing (Fig. 8-13), and the host bed is prepared by curettage, drilling, and bone grafting to improve the biological milieu (Fig. 8-14). Confirmation of the need for fixation with compression is made by determining fragment stability. It is preferable that the fragment is slightly proud (by addition of bone graft) to accommodate the effect of compression and remodeling of the bone graft and fragment (Fig. 8-15).

FIGURE 8-13 The lesion is elevated to inspect the osseous portion of the fragment and prepare the bone bed.

FIGURE 8-14 Cancellous bone grafting is performed to fill the lesion defect and improve potential for healing.

FIGURE 8-15 The osteochondral fragment is replaced and prepared for fixation.

Drilling and tapping through the fragment is performed, taking great care not to displace or damage the fragment with excessive torque (it may be worthwhile to place K-wires for temporary fixation while drilling, tapping, and inserting the compression screw).

The amount of countersinking can be adjusted by the depth of drilling and tapping. The biocompression screw is inserted carefully until the fragment is compressed and the screw is adequately countersunk (Figs. 8-16 and 8-17).

FIGURE 8-16 The biocompression screw is inserted after drilling and tapping. Note the additional K-wire placed for temporary fixation to prevent graft displacement during screw insertion.

FIGURE 8-17 The biocompression screw is fully inserted and countersunk. Note that the osteochondral fragment is now compressed and flush with the surrounding articular surface.

Headed screws require an additional step of removing cartilage and bone to allow countersinking of the screw head.

Summary

Numerous methods and devices are available for fixation of osteochondral fragments. Little objective data are available to guide the surgeon in decision making and choice of implant. Most common indications for fixation of osteochondral fragments include osteochondritis dissecans, acute traumatic injuries, and osteochondral graft fixation.

Principles of stable fixation should supersede the inherent desire to use minimal fixation in articular fragments, but surgeons should always be cognizant of the potential risk of loose or exposed fixation devices that can cause iatrogenic joint damage.