Introduction and Background

This chapter details the surgical technique for the implantation of TRUFIT CB plugs. This process involves creating perpendicular access to the articular surface via an arthroscopic or open approach, thereby creating a flush surface with one or two plugs. The technique can be expanded to allow implantation of multiple plugs.

The TRUFIT plug (Smith & Nephew, Andover, Massachusetts, United States) has been designed as a multiphase implant with tailored degradation (Fig. 4D-1). The implant is composed of a polylactic acid (PLA), polylactic glycolide (PLG), and polyglycolic acid (PGA) copolymer, with calcium sulphate, PGA fibers, and surfactant.^1,2,3 The bilayer design provides cartilage and bone phases, and initially the cartilage phase is softer and malleable enough to be physically contoured to joint curvature. The plug acts as a porous scaffold that provides structural support while allowing the growth of new healing tissue. The calcium sulphate resorbs in the first several months, and the remaining polymer dissolves over a 12- to 36-month period, allowing for complete filling of the defect by repair tissue.³

FIGURE 4D-1 The TRUFIT CB (cartilage/bone graft substitute) plug.

Indications/Contraindications

TRUFIT plugs are indicated for the repair of full-thickness articular cartilage or osteochondral lesions.⁵ The optimal lesion size is less than 2 cm² to ensure that the plugs are well shouldered by normal surrounding articular cartilage. However, the indication is extended for longitudinal patterns of defects in the articular surface when plugs can be inserted in a line. TRUFIT plugs are not indicated for larger areas where they would be positioned in a circle or group unless a 2 mm or more bone bridge is maintained between plugs.

Surgical Positioning

Surgery is performed under general or local anesthesia, and the patient is positioned supine on the operating table with a side post applied.

For femoral condyle lesions, the knee is positioned over the edge of the table against the side post and the angle of knee flexion is controlled by pushing the leg against the side of the table (Fig. 4D-2). This makes repositioning of the leg easier than the alternative of positioning the knee at 90 degrees on the table against a foot piece, which holds the knee more rigidly.

FIGURE 4D-2 Patient positioned with leg supported against a side post.

For lesions on the trochlea, the leg is positioned nearly straight on the operating table and is supported over a removable sterile bolster (Fig. 4D-3), such as a sandbag or a 3L irrigation fluid bag in a sterile Mayo cover, for example.

FIGURE 4D-3 Patient positioned with the knee flexed over a bolster.

Surgical Approach

Regarding the surgical approach, a decision has to be made as to where the lesion is and whether the surgeon is choosing an arthroscopic or a mini-open approach. When considering arthroscopic or a mini-open approach, there are various scenarios that make it more difficult for an arthroscopic technique. It may be quicker to make a small open arthrotomy rather than persevere arthroscopically, and it is certainly easier to visualize the surface to obtain a perpendicular approach.

Arthroscopic surgery, however, allows much better postoperative comfort for the patient and will produce a more cosmetic scar. A mini-open approach should be considered when there have been multiple previous operations, as this will create a more rigid envelope around the knee, restricting movement of the instruments. Space to approach the lateral femoral condyle with the knee in flexion is much tighter than on the medial side, and this makes it much more difficult when inserting two or more plugs.

The central trochlea is also more difficult to approach arthroscopically and again takes a fair amount of levering on the patella. In addition, some knees are simply tight and do not allow easy access. Arthroscopic portals are established to optimize the approach for arthroscopic repair, remembering that the overriding principle is to obtain perpendicular access for the TRUKOR instruments:

Surgical Technique

The technique for implanting the TRUFIT plugs is illustrated and detailed in Figures 4D-5 through 4D-14. The instrumentation comes in three parts. The reusable drill bits and sizing instruments are presented in a sterile box (Fig. 4D-4, A). All that is needed beyond these items and the standard arthroscopic instruments is a mallet. The sizers are used to determine the defect size and are matched to the size of the disposable TRUKOR drill sleeve (Fig. 4D-4, B) and TRUFIT CB plug kit (Fig. 4D-4,C).

FIGURE 4D-5 Sizing lesion on the medial femoral condyle of a right knee.

FIGURE 4D-6 Round-ended obturator is inserted into the chosen TRUKOR drill sleeve to facilitate insertion of the sharp sleeve into the knee.

FIGURE 4D-7 Once against the defect, the obturator is backed out and the drill sleeve is seated on to the articular surface, with care taken to keep it perpendicular.

FIGURE 4D-8 To check the alignment of the drill sleeve, it must be checked from at least two angles: A, initial view cartilage damage, B, mapping defect with 9-mm sizer, and, C, checking that the 9-mm sizer covers most of the area. D, The sleeve is gently impacted to the 2-mm line, and this line is then viewed from two or three directions to confirm perpendicular entry. E, Final depth at 12 mm maximum.

FIGURE 4D-9 The obturator is then fully removed and the drill sleeve impacted into the bone for 8 to 10 mm, using a mallet.

FIGURE 4D-10 The TRUKOR hand drill is inserted and drilled into the bone using firm pressure and twisting.

FIGURE 4D-11 Both the drill and the drill sleeve are then removed simultaneously.

FIGURE 4D-12 The TRUFIT delivery device is opened and the measuring tamp is inserted into the outer sleeve in the direction of the arrow until contact with the preloaded implant is made.

FIGURE 4D-13 The excess of the protruding plug is then cut, using the sharp, supplied knife.

FIGURE 4D-14 The plug is then delivered into the knee within the delivery device and press-fit into the defect, by pushing on the measuring tamp, either manually or by lightly tapping the plug with a mallet.

FIGURE 4D-4 A, Instrument set containing sizers that can be used for impacting the plugs and drill bits that attach to reusable handle. B, Disposable TRUKOR drill sleeve. C, The TRUFIT plug is preloaded in a delivery device, which is packaged with a measuring tamp and a trimming knife.

The initial part of the operation is to explore the defect and then map the sizes of the required plugs.

It is important to remove excessive synovium and the prominent areas of the fat pad, as this will make it much easier to insert the instrumentation later.

With good fluid input, it is possible to distend the joint enough to maintain the clear view and keep clear access for the instruments.

A full diagnostic arthroscopy needs to be performed, and the true edge of the defect is probed with the hook to ensure there is no remaining unstable cartilage. Once a plan of the plug insertions has been made, the chosen drill sleeve and plug kit are opened.

The main principles of the technique are to do the following:

It is not necessary to fully cover the whole defect, and the area surrounding the plugs can fill in with fibrocartilage.

Specific Steps of the Technique

Step 1

The lesion is probed and sized, taking into account the extent of the unstable cartilage. (Fig. 4D-5)

Step 2

The round-ended obturator is inserted into the chosen TRUKOR drill sleeve to facilitate insertion of the sharp sleeve into the knee (Fig. 4D-6).

Step 3

Once against the defect, the obturator is backed out and the drill sleeve is seated onto the articular surface, taking care to keep it perpendicular. Keeping the obturator in the tube prevents sudden loss of fluid pressure and allows the joint to remain distended (Fig. 4D-7).

Step 4

To check the alignment of the drill sleeve, it must be checked from at least two angles. Figure 4D-8, A, initial view of the cartilage damage. Figure 4D-8, B, mapping defect with a 9-mm sizer. Figure 4D-8, C, checking that the 9-mm sizer covers most of the area. Figure 4D-8, D, the sleeve is gently impacted to the 2-mm line, and this line is then viewed from two or three directions to confirm perpendicular entry. Figure 4D-8, E, the final depth is at 12 mm maximum. (Fig. 4D-8, A-E)

Step 5

The obturator is then fully removed and the drill sleeve impacted into the bone for 8 to 10 mm, using a mallet. Throughout the impaction, care is taken to ensure the sleeve is maintained perpendicular to the approach (Fig. 4D-9).

Step 6

The TRUKOR hand drill is inserted and drilled into the bone using firm pressure and twisting. A power drill is not usually required, as the drill bit is so sharp (Fig. 4D-10).

Step 7

Both the drill and the drill sleeve are then removed simultaneously. The drill captures the excised bone to leave a clean defect, and it is not usually necessary to clear the defect of any debris (Fig. 4D-11).

Step 8

The TRUFIT delivery device is opened and the measuring tamp is inserted into the outer sleeve in the direction of the arrow until contact with the preloaded implant is made (Fig. 4D-12).

At this point, the implant should not extend beyond the delivery device.

The measuring tap end is inserted through the skin, into the knee and the defect.

The outer sleeve is slid down until the lip of the outer sleeve is placed snugly against the surface of the articular surface. This automatically adjusts the implant to the correct position for trimming.

Firm pressure is applied to the sizing tube over the plug to ensure that the plug does not move and the tube is removed.

Tip: It is important to ensure that the tamp is fully bottomed out by pushing on the extruded plug. Bear in mind that the outer sleeve needs to be referenced off the intended height of the articular cartilage, not the bottom of the defect; otherwise a false level is achieved.

Step 9

The excess of the protruding plug is then cut, using the sharp, supplied knife. Using the lip of the delivery device as a guide, it is best to use a firm downward motion rather than a sawing action (Fig. 4D-13).

Tip: Leave a slightly oblique cut with a 1-mm step at one side, as this will allow the plug to bottom out early and will prevent overinsertion.

Step 10

The plug is then delivered into the knee within the delivery device and press-fit into the defect, by pushing on the measuring tamp, either manually or by lightly tapping the plug with a mallet (Fig. 4D-14).

To achieve a flush surface, either the tamp or the metal sizing rod can be used.

Tip: If one edge of the plug is slightly proud, then a smaller metal sizing rod can be used as this can be manipulated to round off the surface prominence.

Step 11

In Figure 4D-15, A-C, Photographs of the same operation as in Figure 4D-8 show insertion of the plug and final impaction into place using the plastic tamp and the metal sizing rod. Note that the arthroscope is oriented more tangentially along the articular surface than the more usual view of looking down onto it.

FIGURE 4D-15 A to C Photographs of the same operation as in Figure 4D-8 showing insertion of the plug and final impaction into place using the plastic tamp and the metal sizing rod.

Final positioning is checked by orienting the scope in a different direction to ensure that no edge has lifted up. The knee is cycled and again checked for any impingement from the edge.

Pearls and Pitfalls

FIGURE 4D-16 The assistant has a key role in helping to orient the arthroscope, so that a good perpendicular view is obtained while the surgeon holds the coring device steady in, A, the knee, B, during assessment of the depth, and, C, on implantation.

Rehabilitation

The overriding principle is that the surface needs to be protected from weight bearing for a short period of time after implantation.

On the femoral condyle, partial weight bearing is required for the first 4 weeks, whereas on the trochlea, full weight bearing is allowed with the aid of a brace, which prevents loading of the patellofemoral joint.

About 0° to 20° is allowed on walking for the first four weeks, but in sitting or non–weight bearing, a full range of movement is allowed.

Early full range of movement is encouraged for all areas of repair using either a continuous passive motion machine (CPM) or a static bicycle with 500 revolutions, three times a day. Significant loading of the joint surface should be avoided for at least 3 months and return to sport allowed as symptoms progress over the subsequent 3 to 6 months.

Results

It has been shown that functional scores improved over 12 to 18 months after implantation in a small series of 24 patients.⁴ Analysis of sequential MRI imaging has shown recovery of the subchondral laminar and gradual remodeling of the bone while the thickness of the articular cartilage is maintained during the differentiation with no or minimal loss of thickness.⁴