Planning

We support the “open meeting” principle of surgical planning a week before the event. The clinical picture, functional score, MRI or CT arthrogram are considered with the arthroscopy report from cartilage biopsy.

Instruments

Notchplasty gouge, pituitary rongeurs, and ring curettes are useful additions to the standard arthroscopy set (see also Chapters 9C and 9D).

Surgical Technique

This is an arthroscopic procedure performed under general anesthesia with a thigh tourniquet. First, a thorough examination under anesthetic is performed. The whole knee joint is inspected arthroscopically and the defect evaluated.

Meniscal tears, loose bodies, or internal derangement amenable to arthroscopic treatment is dealt with.

The biopsy for MACI is similar to other ACI techniques and may be taken from the median ridge at the level of the sulcus terminalis, the distal trochlea in the intercondylar region, or the surface of a fresh osteochondral fragment (see also Chapters 9C and 9D).

Using the small notchplasty gouge, a suitable-sized volume of cartilage is “scored” as deep as the subchondral plate. Using the gouge or ring curette, the biopsy is partially levered away from the subchondral plate of bone and finally grasped with pituitary rongeurs, immediately placed in culture medium (Fig. 9E-1), and transported to the laboratory for cell multiplication preparation.

FIGURE 9E-1 Using a gouge or a ring curette, a cartilage biopsy is partially levered away from the subchondral plate from the upper medial femoral condyle and grasped with pituitary rongeurs, immediately placed in culture medium, and transported to the laboratory for cell isolation and culture expansion.

We favor using a notchplasty gouge to partly dissect a biopsy from the median ridge as deep as the subchondral plate and as peripheral as possible from an area of normal cartilage. The biopsy should include the deep proliferative layer of cells.

Tension in the lateral retinaculum makes lateral ridge harvest more difficult and probably best done with pituitary forceps.

Briggs et al.⁷ have demonstrated that surface cartilage of osteochondral fragments produces chondrocytes of good quality.

MACI Implantation

For open MACI implantation, the patient is positioned supine with a midthigh tourniquet and foot braces to position the knee in 90 and 120 degrees of flexion, respectively. A side support helps to control the leg in flexion.

Incisions

The medial parapatellar incision is the most frequently used approach to the knee, as most cartilage defects occur on the medial femoral condyle (MFC).

A 5-cm incision is usually enough for isolated MFC defects, but this approach can be extended to gain access to the patellofemoral joint and lateral compartment. The standard incision starts just distal and medial to the proximal pole of the patella and runs distally to the tibial joint line parallel and medial to the patellar tendon.

The capsule is incised in line with the skin incision, and some of Hoffa’s fat pad may be removed if required.

Jackson-Burrows condyle-shaped retractors are useful, but adequate access to the defects is most commonly achieved with a simple West’s self-retaining retractor.

The incision is extensile proximally between rectus femoris and vastus medialis, with a medial bias. Femoral nerve branches to these muscles arise proximally and are not normally at risk.

Observe

The infrapatellar branch of the saphenous nerve can be damaged by distal extension, and this can occasionally lead to dysesthesia.

Although proximal extension and lateral displacement of the patella can be used to repair lateral femoral condylar damage in a patient with multiple defects, isolated lateral defects are best approached through a lateral parapatellar approach.

An incision from midpatella passing distally and further lateral in an oblique direction facilitates access to posterior femoral condylar and tibial lesions. The posterior tibial lesions are more readily dealt with arthroscopically.

A more vertical lateral parapatellar incision can be combined with a lateral release proximally and a tibial tubercle transfer distally. The deep dissection involves lateral retinaculum and joint capsule with no significant structures at risk. The capsule and retinaculum may be dissected separately and form a single repair following lateral release.

Recipient Bed Preparation

The defect is cleaned down to the subchondral plate and peripherally until stable vertical walls of normal cartilage surround the recipient site, removing all areas of damaged tissue and fibrocartilage. This is achieved with sharp curettes, a scalpel, and bone nibblers.

Eburnated bone and internal osteophytes should be removed with a small burr.

Very deep defects of 1 cm or more may be grafted with autogenous bone, milled allograft bone, or bone substitute. We prefer autogenous bone, which may be harvested from the distal femur or proximal tibia.

Hemostasis is achieved by pressure with epinephrine-soaked compresses or by the double fibrin glue technique. A thin layer of fibrin glue is used to seal off the area of hemorrhage, which when set forms a foundation for the definitive graft.

Templating the Defect

Templates or free hand membrane preparation are both acceptable and which method is used is determined by the skills and preference of the surgeon (Fig. 9E-2).

FIGURE 9E-2 Templates are created using aluminum foil and other inelastic materials. Templates or free hand membrane preparation are both acceptable, and which method is used is determined by the skills and preference of the surgeon.

Matched “cookie cutter” instruments are available to make oval defects and a matched membrane. Templates have been created using aluminum foil and other inelastic materials. The graft itself is more mobile and stretches during implantation. If a template is made, it can be used to mark a pattern or as a definitive guide. I have not found templates useful, and they are impractical in arthroscopic MACI.

The recipient bed is dried, and a trial fit of the membrane is done before implantation.

Implantation

The graft is oriented; there is a rough side and a smooth side (Fig. 9E-3). The cells are seeded on the rough side.

FIGURE 9E-3 The graft is oriented; there is a rough side and a smooth side. The rough side is where the cells are growing. This cell-seeded side should face the bone during implantation.

The recipient bed is completely covered with a very thin layer of fibrin glue. The membrane is inserted into the bed and pressurized with a transparent Silastic catheter; this provides even pressure throughout the bed.

Ideally, the rough (seeded) surface of the membrane should cover the whole of the recipient bed and at the periphery face out toward the vertical walls of normal cartilage to enable integration with adjacent cartilage.

The MACI graft is kept under mild pressure for 30 seconds and then allowed to cure for 2 minutes (Fig. 9E-4, A-B). The knee is then put through a full range of movement to check that the membrane is stable before the wound is closed. If the membrane is unstable, then strategic stitches and repeat application of fibrin glue is required. The wound should not be closed until you are sure that the membrane is perfectly stable. This is a critical step, and to ignore it would invite delamination of the membrane.

FIGURE 9E-4 A, The cell-seeded membrane has been implanted. The rough (seeded) surface of the membrane should cover the whole of the recipient bed and at the periphery face out toward the vertical walls of normal cartilage to enable integration with adjacent cartilage. B, The MACI graft is kept under mild pressure for 30 seconds and then allowed to cure for 2 minutes.

Ancillary sutures are more frequently needed in larger defects. Internal osteophytes should be removed with nibblers or a small burr. Eburnated bone may be “freshened up” with a burr.

Stitches are useful when there is an intact vertical wall to the perimeter of the defect, but when the defect is uncontained, it may be necessary to use resorbable Vicryl pins if sutures cannot be anchored in host cartilage or where access is too difficult. Pins should be strategically placed to hide the pinheads and prevent impingement on the articulating surface. We have tried to graft two opposing surfaces by this technique without success, as one membrane will displace the other.

The wounds are closed in layers, taking care to accurately close the synovial layer separately with a fine (2.0) Vicryl suture to prevent the friction of an uneven surface over the graft.

Indications

Simple single defects of the femoral condyles and tibial plateau can be treated arthroscopically, but the trochlear groove and patella are less accessible and best treated with a traditional open procedure.

Instruments

The arthroscopy set (Fig. 9E-5) should include atraumatic grasping forceps, ring- and standard curettes, a shaver, epinephrine-soaked compresses, transparent urinary catheters, a valveless arthroscopic cannula (Fig. 9E-6), neuro sucker, fibrin glue, and spinal needles. Ringer’s lactate irrigation fluid is preferred, although definitive implantation is done dry.

FIGURE 9E-5 The set for arthroscopic MACI implantation including different atraumatic grasping forceps, ring- and standard curettes, shaver, epinephrine-soaked compresses, transparent urinary catheters, neuro sucker, fibrin glue, and spinal needles.

FIGURE 9E-6 A valveless arthroscopic cannula used for the introduction of the MACI implant into the articular joint.

The patient is placed prepared in a low thigh tourniquet with a brace.

Anteromedial and anterolateral portals are used initially to prepare the defect as the knee is irrigated with Ringer’s lactate fluid.

First, the cartilage defect is prepared to accept the MACI graft. The edges of the defect must be debrided to ensure a well-defined, contained defect. All areas of fibro-cartilage and loose hyaline cartilage are removed with the aid of a curette and power shaver.

A stable shoulder of hyaline cartilage with a base of subchondral bone is achieved (Figs. 9E-7 and 9E-8). The resultant defect is then measured with the end of an arthroscopy probe in several planes (Figs. 9E-7 and 9E-8). These measurements are then used to shape the membrane of the MACI graft.

FIGURE 9E-7 A stable shoulder of hyaline cartilage with a base of subchondral bone has been achieved, and the cartilage defect is then measured with the end of an arthroscopy probe in several planes.

FIGURE 9E-8 Note the vertical walls that have been achieved during debridement plus a clean, bare subchondral bone surface.

Dots are placed onto the edges of the graft with a sterile colored marker to assist with orientation once the graft is inside the knee. Once the graft has been prepared, all irrigation fluid is drained from the knee converting to dry arthroscopy to facilitate implantation of the graft.

An arthroscopic sucker is used to fully dry the bed of the defect. An epinephrine-soaked compress is pressed onto the bed to further dry it and to try and prevent bleeding from the base. In the occurrence of any bleeding from the graft bed, fibrin glue can be used in a thin layer and allowed to set before proceeding with graft implantation.

The prepared graft is introduced into the knee (Fig. 9E-9, A) via a large bore valveless arthroscopic cannula (ConMed Linvatec, Largo, Florida). The graft is positioned in the defect using a probe; care must be taken to ensure the membrane is the right way up and correctly oriented (Fig. 9E-9, B).

FIGURE 9E-9 A, The MACI membrane is introduced with a grasper into the joint through the valveless arthroscopic cannula to be implanted into the defect. B, The graft is positioned in the defect using a probe. The MACI membrane has been marked with ink to ensure the membrane is the right way up and correctly oriented.

Graft size is then re-assessed to ensure it fits the defect exactly without overlap onto the surrounding healthy cartilage. The graft may need further trimming out of the knee at this point. The large cannula facilitates multiple atraumatic passes into and out of the knee for fine-tuning the shape of the graft.

The graft is then folded away from the defect to allow fibrin glue to be introduced to fix the graft (Fig. 9E-10a). A small amount of fibrin glue is introduced into the defect via a 19-gauge needle via the anteromedial portal (Fig. 9E-10, A). Even spread of the glue is achieved using the end of a probe (Fig. 9E-10, B).

FIGURE 9E-10 A, The graft is partly lifted up from the defect to allow fibrin glue to be injected on the bony surface to fix the graft. B, Fibrin glue is introduced into the defect via a 19-gauge needle via an anteromedial portal. The graft is folded over the glue and smoothed into place again with the probe.

The graft is then replaced over the glue and smoothed into place again with the probe (Fig. 9E-10, B).

Even pressure is applied to the graft for 30 seconds with the balloon end of a transparent Silastic urinary catheter (Fig. 9E-11). The catheter balloon is nonstick, and graft position can be checked as the glue sets.

FIGURE 9E-11 Even pressure is applied to the graft for 30 seconds with a balloon end of a transparent Silastic urinary catheter.

The redundant tip of the catheter is trimmed. The tip of the catheter is passed through the medial portal beyond the graft to orient the balloon over the defect and graft.

The balloon is then inflated with saline instilled into the end of the catheter outside of the knee (Fig. 9E-11). Even pressure is achieved over the graft as the balloon tamponades against the defect and the other surfaces of the knee. After 30 seconds the balloon is deflated and the catheter is removed (Fig. 9E-12).

FIGURE 9E-12 The MACI graft is now securely fixated with glue combined with 2 minutes of pressure from the applied balloon. The knee is put through a range of movement for several cycles to ensure the graft remains fixed.

A further 2 minutes is allowed for the glue to cure, then the knee is put through a range of movement for several cycles to ensure the graft remains fixed. The arthroscopy portals are then closed in standard fashion without drainage.

No local anesthetic is instilled into the knee.