Introduction

The rationale behind using carbon fiber as a biomaterial is as follows:

In 1987,¹ Minns et al. published a preliminary clinical experience in a new concept of biological resurfacing using carbon fiber implants in the form of pads or rods placed in defects within the knee that elicit a dense organized matrix of fibrous tissue that forms a new biological and functioning articular surface. No evidence of implant fragmentation has been seen since implantation in the 145 knees studied.¹

Carbon fiber arthroplasty appears to be appropriate in the surgical management of ICRS Grades 3 and 4 articular cartilage lesions in the painful knee.^2,3,4,5

FIGURE 4B-1 Carbon rod of 12.5 mm length; the average diameter is 3.2 mm. Porosity is about 50%.

FIGURE 4B-2 Carbon pad, approximately 4 mm thick in discs up to 22 mm in diameter. Porosity is about 85%.

FIGURE 4B-3 Carbon rods and pads implantation set.

With the arthroscope in the anterolateral portal, a special cannula with an obturator is inserted into an anteromedial portal.

The cannula is positioned in the defect, on the bony surface (Fig. 4B-4).

FIGURE 4B-4 The cannula is positioned in the defect, on the bony surface.

The obturator is removed. Through the cannula, a 3.2-mm drill bit is put and a hole is drilled until depth- stop (Fig. 4B-5).

FIGURE 4B-5 A 3.2-mm drill bit is put through the cannula, and a hole is drilled until depth-stop.

The holes should be drilled at a minimum distance of 8 to 10 mm apart to maintain a reliable interposing bone between the holes.

The drill is withdrawn and an insertion guide is put into the cannula. The guide should fit to the level of the stop (Fig. 4B-6)

FIGURE 4B-6 An insertion guide is testing the drilled hole.

The depth is controlled with a special thin obturator. The obturator should fit to the level of the stop, and there should be no difficulty in the insertion (Fig. 4B-7)

FIGURE 4B-7 The drilled depth is controlled with an obturator.

Finally, a rod is implanted through the insertion guide. The rod should slide in without any resistance (Fig. 4B-8). The top of the rod should be flush with the bony surface or slightly below. By no means should the top protrude above the bony surface.

FIGURE 4B-8 A carbon rod is gently put into the cannula and pushed until it stops. It should then be flush with bony surface or slightly below.

Carbon Pads (Needs Open Surgery)

The pads are mainly used for concave surfaces such as destroyed patellar surfaces.

The hard subchondral bone is opened by using a self-centering drill incorporating a 3-mm depth stop. Multiple holes are drilled (Fig. 4B-9).

FIGURE 4B-9 Multiple holes are drilled with the self-centering drill.

The bony bridges are broken down using a side cutter (Fig. 4B-10)

FIGURE 4B-10 The bony bridges are broken down using a side cutter

The subchondral bone is undercut using an under cutter (Fig. 4B-11).

FIGURE 4B-11 The subchondral bone is undercut using an under cutter

A caliper is used and placed into the defect with its tips in the undercut. The required size is read off the gauge (Fig. 4B-12).

FIGURE 4B-12 The required size of the pad is read off the caliper gauge when pushing its tips under the bony rim.

A circular cavity is formed of a suitable size to accommodate one of the ranges of carbon pads available. The carbon material can be cut with scissors to fit, and several of the pads may be used to fill the area.

The pad should be soaked in saline, and the edges of the pad are eased carefully under the bony rim of the defect (Fig. 4B-13). No extra fixation is needed.

FIGURE 4B-13 The pad is pushed into the defect, and its edges are placed under bony rims.

If the self-centering drill, side cutter, and under cutter are not available, the different stages can also be done using a 5-mm and a 3-mm burr. First the subchondral bone is removed to a depth of 3 mm with the 5-mm burr. The following undercut is made using the 3-mm burr into a depth of 2 mm (Fig. 4B-14).

FIGURE 4B-14 A bone pool is made in the subchondral bone with 3- and 5-mm burrs when a special carbon instrument set is not available.

Hybrid Repair

When a cartilage repair is partially insufficient at the borders to adjacent cartilage, one may use a carbon rod to induce a strong interpositional ingrowth of repair tissue. The author is using a carbon rod when autologous chondrocyte implantation (ACI), ACI repair tissue, or other induced repair tissue is showing insufficient repair with partial loosening of the grafted area. The loose area is then excised, and the bare area is debrided and treated by implantation of one or two rods. The strong induced fibrocartilaginous repair tissue will bridge the adjacent cartilage to the ACI repair tissue. (Fig. 4B-15).

FIGURE 4B-15 Treatment of a partial loosening of a grafted cartilage repair area. A carbon rod is put into a predrilled hole in the defect border zone area. The repair tissue from the implanted carbon rod will bridge and support the earlier graft to the adjacent cartilage.

Carbon Rod Revision

Carbon rods can easily be taken away if the overlaying repair has been destroyed and a new carbon rod may be needed.

Drill through the old rod. A black mass of carbon will protrude through the drill hole and can be swept away with a shaver, a “vacuum cleaning” effect. A new rod can then be implanted.

How do you manage a carbon fiber—treated joint when implanting to do a prosthetic joint total knee replacement? Do the required resections as usual. The surfaces will appear as surfaces with black spots of carbon at the level of the respected surface.

Leave those spots even but excise the carbon only if it sprouts out, and use a small ladle to clean the drill holes from carbon debris.

If the intent is to replace the patella surfaces with a plastic cup, do the normal resections, drill central holes for the central patella cup peg into the carbon, and use bone cement as it is normally used for arthroplasty fixation.

Pearls and Pitfalls

The technique is ideal to use in combination with other techniques such as autologous chondrocyte implantation (ACI).

Especially when there is a border insufficiency, the rods can augment and support the surroundings. As the technique is done transarthroscopically, the extra repair is done easily.

It is important that the carbon fibers are to be used implanted flush with the bony surface or preferably 1 mm below the bony surface, especially when treating kissing lesions and bipolar defects.

The biological response of carbon fiber in the knee was reported by Muckle and Minns,⁴ in which minimal synovitis was observed except in knees that also displayed an associated instability.

If there is no shouldering cartilage, just bare bone on both sides, “kissing lesions,” do not use the carbon implants.