Chondrocyte transplantation

CHONDROCYTE TRANSPLANTATION TOM

MINAS,

MD, FRCS(C),

MS, and LARS

PETERSON,

MD, PHD

Autologous chondrocyte transplantation (ACT) provides a durable hyaline repair tissue in correctly selected indications. Autologous chondrocyte transplantation is indicated for full-thickness, weight-bearing condyle injuries and injuries to the trochlea of the femur. ACT results in reproducibly satisfactory results with return to high-level activities including sports in over 90% of the patients. Second-look arthroscopies demonstrate tissue fills wth biopsies showing hyaline-like cartilage repair. Hyaline cartilage repair is critical because this has been shown clinically to give long standing results with follow-up at 2 to 9 years. As technical refinements improve, and rehabilitation protocols, results for injuries to the patellar and the tibia will improve. At this time the response to treating bipolar focal chondral injuries is unknown and not recommended. KEY WORDS: autologous chondrocyte transplantation (ACT), knee and cartilage repair

Symptomatic fulMhickness chondral lesions in the knee pose a difficult management issue for orthopedists and patients alike. Symptomatic relief may be temporarily improved by arthroscopic lavage and debridement; however, this does not treat the problem or provide a long-term cure. 1,2 Similarly, marrow stimulation techniques aimed at intrinsic cells to provide fibrocartilage repair tissue has inferior mechanical properties to hyaline cartilage. This repair tissue often succumbs to mechanical stresses with premature degeneration, delamination, or intraarticular osteophyte formation and breakdown? The consistency with which an effective repair tissue of durable quality develops by drilling, arthroscopic abrasion arthroplasty, or microfracture technique, is unpredictable. Larger lesions, similarly, require a durable high-demand repair tissue not possible by these techniques. Osteochondra]L autografts or allografts require converting a chondral lesion into an osteochondral injury to affect articular repair. This might affect the ultimate function of the bone cartilage functional unit. This article will discuss the role of autologous chondrocyte transplantation (ACT) for the treatment of fullthickness cartilage injuries of the knee. Since the initial publication on fffis topic 4 there has been a renewed interest in the treatment and research of this clinical problem. This earlier published study indicated good and excellent results in 14 of 16 patients treated on the weight-bearing femoral condyles. 4 Only 2 of 7 treated patients with patellar lesions had similar results. Since then, the authors have performed over 500 procedures and there have been over 800 procedures performed worldwide. More than 90% of the time, patients with treatment of the weightbearing femoral condyle have been able to consistently

From the Department of Orthopedics, Brigham and Women's Hospital, and the New England Baptist Hospital, Boston, MA; and the Gothenburg Medical Center, Gothenburg University, V&stra Frol0nda. Sweden. Address reprint requeststo Tom Minas. MD, FRCS(C), MS, Department of Orthopedics, Brigham and Women's Hospital, 75 Francis St, Boston, MA02115. Copyright © 1997 by W.B. SaundersCornpany 1048-6666/97/0704-0002505.00/0

return to sports. Follow-up arthroscopy and biopsies have shown hyaline-like cartilage repair tissue. INDICATIONS Autologous chondrocyte transplantation is indicated for a symptomatic full-thickness weight-bearing chondral injury of the femoral articular surface in a physiologically young patient who is compliant with the rehabilitation protocol. The results of chondral injuries of the patella and tibia are not as consistently high as those of the femoral weight-bearing condyles and trochlea. Osteochondritis dissecans (OCD) has also been treated successfully. This is a procedure for treatment of symptomatic unipolar grade III or grade IV Outerbridge classification injuries, with no greater than the reciprocal articular surface having grade I to II Outerbridge classification chondromalacia, s It is not a treatment for osteoarthritis, ie, bipolar chondral injuries. Hence, preoperative weight-bearing radiographic evidence of joint space narrowing, osteophyte formation, subchondral bony sclerosis or cyst formation is a useful screening tool for selecting patients for treatment (Fig 1). Although helpful for soft tissue evaluation of meniscal or ligamentous injuries, magnetic resonance imaging (MRI) scanning does not at present have a high enough sensitivity and specificity to determine the extent of a chondral injury or subtle chondromalacic changes (Fig 2). The benchmark for assessment for determining whether a symptomatic patient is a candidate for (ACT) is arthroscopy with a normal radiograph. TECHNIQUE AND ARTHROSCOPIC ASSESSMENT Arthroscopic assessment of the joint and possible biopsy for articular cartilage culturing requires a careful and systematic evaluation of the articular surfaces with an arthroscopic probe to demonstrate and determine the extent of grade III and IV chondromalacia (CM) of the symptomatic lesion (Fig 3). The opposing tibial articular surface must be probed throughout to ensure that the meniscus is intact, the articular surface is healthy with no

Operative Techniques in Orthopaedics, Vol 7, No 4 (October), 1997: pp 323-333

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Fig 1. (A) Subtle lateral compartment joint space narrowing. (B) Thinning of the entire lateral tibial plateau.

more than superficial fissuring (grade II CM). Whether it is a contained or an uncontained lesion, the femoral condyle lesion should be assessed for its anterior to posterior length. The quality and thickness of the surrounding articular cartilage should also be assessed. This will determine whether healthy cartilage will be available for periosteum suturing or whether an uncontained chondral injury will require suturing through synovium or small drill holes through the bone. The posterior extent of the lesion is critical as this must be technically accessed at the time of open arthrotomy for periosteal suturing. If a lesion is considered appropriate then a biopsy site for

cartilage procurement must be selected. The most commonly chosen site for biopsy is the superior medial edge of the trochlea, adjacent to the medial patella (odd) facet (Fig 4). In this wa~ a biopsy site will not be producing a reciprocal symptomatic injury as there will be no opposing articular surface to make its contact. The patello-femoral joint must be assessed carefully. If there is an overhanging patellar facet on the medial side, often the superior lateral facet may be harvested. If both facets are overhanging then the lateral intercondylar notch may be prepared by examining the knee in full extension and flexion to determine whether the patella enters into the trochlea to the intercon-

Fig 2. (A) Coronal MRI image at region of full-thickness chondral injury, missing the chondral defect. (B) Medial femoral condyle.

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Fig 3. (A) Ideal candidate for ACT. Full-thickness unipolar medial femoral condyle weight-bearing injury, contained. (B) Usefulness of hyperflexing knee during arthroscopy to determine second focal weight-bearing lesion, medial femoral condyle. (C) Reciprocal bipolar full-thickness chondral injuries, medial joint compartment. Unacceptable candidate for ACT.

dylar notch or at a weight-bearing site (Fig 5). A final site is the superior transverse trochlea margin, adjacent to the supracondylar synovium, that may be biopsied through a separate superior portal. At the time of open implantation the synovium may then be advanced through sutures over the biopsy site through the articular cartilage. Approximately 200 to 300 mg of articular cartilage are required for enzymatic digestion for cell culturing. This is a cartilage surface about 5 m m wide by I cm in length (Fig 5D) and contains approximately 200,000 to 300,000 cells which may be enzymatically digested and grown to several million. Biopsy instruments may include ring curette or sharp gouges. It is often helpful to incise and score the area of biopsy in advance of attempting to remove it. A whittling, side-to-side motion of the gouge or curette will then more accurately remove the desired cartilage without an unwanted slip. Full-thickness cartilage down to bone should be biopsied. It is helpful to leave an end of the articular biopsy attached so that it may be grabbed with an arthroscopic grasper and torn off. This avoids an unwanted loose body in the joint that then would have to be captured. After in vitro expansion of cells some 2 to 5 weeks later, a suitable number and volume of cells will be grown to accommodate the defect size that is required. At this time, second stage open implantation may occur. CONDROCYTE TRANSPLANTATION

ADDRESSING CONCOMITANT OR PREDISPOSING FACTORS TO CHONDRAL INJURY Several predisposing factors to chondral injury must be assessed so that these may be either corrected in a staged or concomitant fashion with ACT. Tibio femoral and patellofemoral malalignment, ligamentous or bone insufficiency must all be assessed before definitive cartilage cell reimplantation. When varus or valgus malalignment is present with a medial or lateral condyle injury, then a corrective osteotomy is paramount to the success of the chondral transplantation. This can be done either in a staged or concomitant fashion. However, it is imperative that if done concomitantly, a stable fixation be obtained at the time of osteotomy surgery so that continuous passive motion and early active range motion may be pursued immediately postoperatively. Otherwise, a staged reconstruction should be performed. Similarly, chondral injury in the face of cruciate insufficiency may jeopardize a newly regenerating cartilage graft. Staged or concomitant surgery should be performed with the goals of an earlier rehabilitation for motion, quadriceps tone, and protected weight bearing. In the case of bony deficiency such as an osteochondral fracture or OCD the depth of the bony lesions should be assessed preoperatively through radiography or tomogra325

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Fig 4. (A) Superior medial trochlear ridge, appropriate for chondral biopsy. (B) Uncovered lateral superior ridge appropriate for chondral biopsy. (C) Ring curette technique of harvesting chondral biopsy. (D) Arthroscopic appearance of ring curette technique showing intact distal portion, appropriate for grasping without developing a loose body (E). (Illustration by Amy Waits, Ink Worx Illustration.)

phy. OCD defects, on average, are 6 to 8 m m deep including cartilage and bone. These often will do well without bone grafting and with chondrocyte transplantation only. However, defects that are greater than i to 2 cm deep clearly need preliminary bone grafting and healing before cartilage resurfacing.

Surgical Transplantationof Autologous Chondrocytes The steps in open implantation include arthrotomy defect preparation, periosteum procurement, periosteum fixation, periosteum water-tight integrity testing, autologous fibrin glue sealant, chondrocyte implantation, w o u n d closure, and rehabilitation. For a unicondylar injury, a medial or lateral parapatellar arthrotomy is used. This is usually performed through a midline incision or a longitudinal parapatellar incision. Adequate exposure is crucial for good periosteum suturing technique; several retractors are often required to obtain this goal. Posterior lesions on the femur will often require hyperflexion of the knee, occasionally require dissection of

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the meniscus in a subperiosteal fashion with coronary ligament incision, and midline intermeniscal ligament takedown. A repair of the coronary and intermeniscal ligaments at the end of the procedure is necessary. For multiple lesions, a traditional medial parapatellar arthrotomy is often required with subluxation or dislocation of the patella with hyperflexion. Defect preparation is critical (Fig 6). Radical debridement of all fissured and undermined articular cartilage surrounding the full-thickness chondral injury to healthy contained cartilage is desirable. Oval or curvilinear excisions with a No. 15 blade are made by incising the articular cartilage vertically down to the subchondral bone plate without penetrating the bone. Small ring or dosed curettes and periosteal elevators are used to debride the degenerating articular cartilage back to healthy host cartilage. Mainraining an intact subchondral bone plate without subchondral bone bleeding is important. It is essential not to perforate the subchondral bone plate so that a mixed stem cell population does not populate the chondral defect in MINAS AND PETERSON

Fig 5. (A) Lateral intercondylar notch biopsy site, sharply incising desired region, (B) Arthroscopic appearance of "notch" biopsy of cartilage for culturing. (C) Gouge has removed cartilage leaving distal portion attached for easy removal with grasping forceps. (D) Sterile transport of 200 to 300 mg of autologous cartilage in tissue culture medium. (Illustration by Amy Waits, Ink Worx Illustration.)

Fig 6. (A) Area depicted for radical cartilage debridement, removing undermined and degenerating cartilage margins. (Note intact subchondral bone without violation of the subchondral plate.) (B) Defect bed noting vertical chondral borders, appropriate for suturing. (C) Measuring or templating chondral defect to determine periosteal sizing. This defect is oversized at 2mm in length and width. (Illustration by Amy WaRs, Ink Worx Illustration.) CONDROCYTETRANSPLANTATION

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Fig 7. (A) Periosteum procurement site, distal to pes anserinus insertion on medial subcutaneus tibial border. (B) Periosteal harvest maintaining cambium deep layer intact through well-controlled, gentle harvest technique. (Illustration by Amy Waits, Ink Worx Illustration.)

addition to th°e end-differentiated chondrocytes that have been grown in vitro. A contained lesion is desired and it is better to leave a minimally chondromalacic cartilage border than to remove it and create an uncontained lesion that would require suturing to synovium or small holes through bone drills. Once a healthy defect bed is prepared, it is then measured in its length and width or, if it is irregularly shaped, templated with sterile tracing paper (sterile glove packaging paper works well). A sterile marker can be used to template the defect and it can then be cut out to fit the defect perfectly. This can then be oversized as a template on the periosteal site when it is prepared to approximately 2 mm in both length and width. (There is retraction of the periosteum as it is procured.) Alternatively, this can be measured and marked with a marker directly onto the periosteum if it is an uncomplicated shape and cut directly (Fig 6). The easiest and most suitable location for periosteum procurement is from the proximal medial tibia, distal to the pes anserinus insertion on the subcutaneous border (Fig 7). At this site there is subcutaneous fat, a very thin fascial 328

layer, and the periosteum is easily accessed. Once defect size has been assessed and templated, a second incision is made approximately a finger width distal to the pes anserinus insertion, in the center of the medial subcutaneus border of the tibia. Subcutaneous fat is incised initially and scissor dissection will then avail the shiny white proximal tibial periosteum. It is useful to use a wet sponge to sweep away loose areolar tissue. Electric cautery should not be used around periosteum as this will necrose the periosteum with the very sensitive cambium layer of cells on its deep surface. The template is then placed on the periosteum, or alternatively it is marked with a ruler and a sterile marking pen. A sharp No. 15 blade is then used to incise the periosteum sharply, down to bone. A small sharp periosteal elevator is then useful in very gently advancing the periosteum from its bony bed and preventing it from under-rolling so that it does not rip. Nontoothed forceps will aid in helping to pull the periosteum upwards as it is gently removed from the tibia. A gentle push/pull type of motion of the periosteal elevator from side to side across MINAS AND PETERSON

Fig 8, (A) Medial femoral condyle defect appearance after open arthrotomy, (B) Defect appearance after radical debridement of degenerating articular cartilage, (C) Cell implantation under periosteal patch (Note the ink mark on superficial periosteum to maintain correct orientation,)

the periosteum will help its removal (Fig 7). It is helpful to mark the outside of the periosteum on the superficial surface so that it is not inadvertently placed upside down when implanted. At this time the defect site is inspected and the tourniquet can be either let down to assess bleeding of the subchondral bone plate or let down at the end of the procedure if the surgeon is confident that the bone bed appears not to be violated. If there is any bleeding of the bony bed, this Call usually be stopped by using a combination of thrombin and epinephrine soaked in a neural patty which is applied to the defect and gently pressed for several minutes. On removal, if there continues to be some bleeding, a small drop of fibrin glue will usually suffice to make the defect dry. There are three goals of periosteum fixation: (1) to provide a water tight membrane that acts as a mechanical seaL (2) to act as a semipermeable membrane for intraarticular synovial nutrition to chondrocytes, and (3) to maintain a viable periosteal cambium layer of cells so that interactive growth factors between chondrocytes and periosteum may enhance chondrocyte growth. To this end, it is important to handle the periosteum delicately so that it is not perforated but is kept moist so that it does not undergo shrinkage or cambium cell death. Its orientation is always maintained so that a cambium layer is facing in towards the subchondral bone plate as noted by a pen mark on the superficial aspect (Fig 8). Periosteum may then be placed gently onto the defect in the appropriate orientation. Nontoothed forceps are used to handle the periesteum by its edges only. Suturing is usually done with a 6.0 suture on a P-1 cutting needle CONDROCYTE TRANSPLANTATION

which has been immersed in sterile mineral oil or glycerine (Fig 9). Approximately 8 inches of length is usually adequate and the remainder of the suture is cut and discarded. Suturing is done in an interrupted and alternating fashion. Sutures are placed through the periosteum and then the articular surface, the knots being tied on the side of the periosteum so they remain below the level of the adjacent cartilage so as not to unravel with motion and to evert the periosteal edge so that it may act as a washer seal on the edge of the vertical articular cartilage defect. Hence, one may obtain a water-tight seal by suture technique alone in most cases. When alternatively suturing corners, the analogy of tightening up a drum skin is followed. In this way the patch is tensioned adequately throughout the entire defect and the most superior aspect of the periosteal patch is left open to accept saline to check edge integrity and for chondrocyte transplantation. Use interval sutures of approxirnally 3 to 6 m m in length that protrude through the articular surface at least 3 ram. Periosteum water-tight integrity testing is assessed by using a plastic 18 gauge 2 inch angiocath with a tuberculin syringe filled with saline (Fig 9D). The angiocath is placed deep to the periosteum into the defect. By gently filling the defect with saline, a meniscus should rise to the opening if the defect is water tight. Any leakage can easily be seen around the perimeter of the repair site. An additional suture may be required to aid in obtaining water integrity. The saline is then reaspirated out from the defect and if water integrity cannot be obtained simply by suture technique, then a fibrin sealant is used. For autologous fibrin sealant the patient must preopera329

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Fig 9. (A) Periosteal suturing to obtain flush membrane cartilage border with knots tied on the periosteal surface to evert periosteal edges and prevent knots from unraveling with the use of continuous passive motion. (B-C) Alternating suture techniques to equally tighten periosteal patch with interrupted sutures at a distance of 3 to 5 mm to obtain water tightness. (D) Saline injection test to assess periosteal integrity to water tightness. (Illustration by Amy Waits, Ink Worx Illustration.)

tively donate one unit of whole blood. This is then spun off for a pack of red blood cells as well as a supernatant that is concentrated by a double-spin freeze thaw technique to produce cryoprecipitate. This takes 14 days of preparation before surgery. Following double-freeze thaw technique, a concentration of approximately of 80 to 100 mg per deciliter fibrinogen can be obtained. The fibrinogen or cryoprecipitate is then activated with bovine thrombin and calcium (Fig 10). A double-barreled syringe is required for this. In one barrel the cryoprecipitate is placed, and in the other barrel, a 50/50 mixture of 10% calcium chloride with a super concentrated bovine thrombin is placed. Fibrinogen is cleaved into active fibrin, which then is deposited along the margins of the defect, sealing them. Commercially available Tisseal R (Immuno AG, Vienna, Austria) made from pooled human serum is available in Europe but not the USA. After sealing the defect, water integrity is once more

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tested. The angiocath is placed underneath the periosteum to ensure that the periosteum is not inadvertently sealed to the subchondral bone. The saline is then aspirated out from the defect bed, and the defect is now ready to accept chondrocyte implantation. The chondrocyte suspension is then sterilely aspirated in a tuberculin syringe through a 18 gauge or larger needle (smaller gauges will damage the cells), the needle is then removed and switched to a flexible 18 gauge 2 inch angiocath (Fig 11). Next, the cells are very gently delivered through the superior opening of the periosteal defect margin down to the base of the defect; as the angiocath is withdrawn cells are injected until a meniscus comes to the surface. When the defect is filled with cells, several sutures are used to close the remaining defect and it is then sealed with fibrin glue. The procedure is now completed. Drains are not used within the joint so as to not damage the periosteal patch or suck out the cells from the defect. When a drain is needed,

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Fig 10. Autologous fibrin glue or Tisseal R (Immuno AG) adhesive sealant to ensure peripheral water tightness. (Illustration by Amy Waits, Ink Work Illustration.)

it should be without suction. The wound is then closed in layers and a soft dressing is applied to the knee.

REHABILITATION AFTER CARE Prophylactic intervenous cephalosporin antibiotics are used for 24 to 48 hours after surgery. There are three main goals of the postoperative period: (1) to enhance chondrocyte regeneration and decrease the likelihood of intraarticular adhesions with aggressive range of motion exercises, (2) protect weight bearing for 6 to 12 weeks after surgery to prevent the likelihood of periosteal overload and central degeneration or delamination of the graft, and (3) perform isometric muscle exercises to regain muscle tone and prevent atrophy. Continuous passive motion (CPM) is instituted as soon as cell attachment has occurred after 6 hours or the next day. With weight-bearing femoral condyles, CPM is increased to regain as full range of motion as the patient tolerates with a very slow cycle setting of approximately 2 minutes. CPM is used for approximately 6 to 8 hours daily for up to 6 weeks postoperatively. This is based on experimental work 6 showing an enhancement of the quality of repair tissue caused by this modality as well as

CONDROCYTE TRANSPLANTATION

clinical work 7 showing an increase in repair tissue fill with use of CPM 6 to 8 hours per day for 6 to 8 weeks postoperatively. At this time exact quantity and duration of CPM for ACT has not been determined. It is clear, however, that patients are comfortable while on the machine and that it does decrease the likelihood of intraarticular adhesions by motion. CPM for defects of the trochlea is less aggressive. Initially, CPM is used with a maximum range of 0 to 40 degrees. The remainder of the motion is obtained by the patient dangling his leg over the edge of the bed to regain further motion. CPM from 40 to 70 degrees is not recommended as maximal patellofemoral contact forces occur in this range. Weight-bearing for the femoral condyles is protected at touch weight-bearing status on crutches for 6 weeks postoperatively. Thereafter, weight-bearing is increased to full body weight by 12 weeks postoperatively. This is done as follows: one-third body weight in weeks 7 and 8, two-thirds body weight in weeks 9 and 10, and full body weight on crutches in weeks 11 and 12. Thereafter, the patient is instructed to use one crutch in the opposite arm and switch to a cane when he is comfortable. Each patient's progress is individualized and guided by symptoms. If weight-bearing discomfort, catching, locking, or swelling of the knee occur, then the weight-bearing status and activity level are decreased as tolerated by the patient. These symptoms may indicate that the graft is undergoing overload, with stimulation of the subchondral bone, resulting in pain for the patient. It is usually 4 to 4.5 months before patients have discarded their canes and are walking relatively comfortably with a small effusion. Larger lesions take longer to recover from. At this time, nonimpact activities such as long-distance walking, cycling, swimming, and cross-country skiing are encouraged. Running is not permitted until graft hardness is similar to adjacent cartilage (approximately 9 to 12 months later; Fig 12). Such cartilage hardening in larger lesions make take as long as 18 months, and in OCD it may take 18 to 24 months. Lesions of the trochlea require more time in the rehabilitation and healing process. Weight-bearing status is allowed at full weight bearing with a knee immobilizer from the onset because the weight-bearing condyles are not affected. Isometric straight leg lifts are instituted immediately. Rehabilitation to maintain decreased patellofemoral contact pressures is encouraged. At 6 to 8 weeks following surgery, walking backwards on a treadmill is encouraged: Straight leg lifts, active flexion, and passive extension are encouraged for the first 6 weeks. Effusion is more common with trochlea repairs for up to 6 months after surgery. Stationary bicycling with low resistance is allowed. Kneeling, squatting, and so on is not permitted until 12 to 18 months following surgery, at which time graft hardness is similar to adjacent cartilage. With regards to strengthening, rehabilitation of femoral condyle and trochlea lesions permit straight leg raising from the onset. Stationary bicycling is permitted for rehabilitating femoral condyle lesions as early as 3 to 4 weeks postoperatively. Rehabilitation of femoral weight-bearing lesions starts with isokinetic open-chain quad strengthening and open hamstring strengthened 6 to 8 weeks postop-

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Fig 11. (A) Gentle cell pellet suspension by aspiration and reinjection of supernatant tissue culture media with large bore needle, (B) Chondrocyte cell suspension injected deep to periosteal patch. (Illustration by Amy Waits, Ink Worx Illustration.)

eratively. If catching, swelling, a n d / o r pain are noted then activity should be decreased accordingly. Strengthening for trochlea lesions should involve short arc quadriceps strengthening from 0 to 30 degrees of flexion and closed-chain strengthening from the same 0 to

30 degrees range of motion. Open-chain isotonic quadriceps strengthening should not be permitted for 9 months after trochlear surgery according to symptoms.

RESULTS

Fig 12. Second-look arthroscopic appearance of medial femoral condyle defect 6 months after ACT. (Note rubbery indentability of chondral graft 6 months after implantation.)

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To date clinical results are dependent on the type of lesion treated and the concomitant procedures addressed. At the 1997 American Academy of Orthopedic Surgeons Annual Meeting, held in San Francisco in Februar3~ data on the first 100 consecutive patients treated in Sweden were presented. The overall results of isolated femoral condyle lesions and isolated femoral condyle lesions with anterior cruciate ligament (ACL) reconstruction showed a clinical improvement of 88%, and with OCD it was close to 90%. Follow-up ranged from 2 to 9 years, with an average follow-up of 3 years and 11 months, s (These results are being prepared for peer review publication at this time.) Outcomes measured with the Short Form 36 (SF-36), Knee Society Score (KSS), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, as well as patient satisfaction scores, showed clinically and statistically significant results within the first 12 months of chondrocyte implantation and a patient satisfaction rate of 95%. 9

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COMPLICATIONS

CONCLUSIONS

There have been no intraarticular joint infections following ACT to date. Minor superficial w o u n d infections may occur as well as complications related to open arthrotomy. The most common problems following ACT are incomplete periosteal graft incorporation to host cartilage and hypertrophic graft edge response. Clinically, this usually manifests at the stage of a proliferative hypertrophic periosteal healing response. This is between 3 and 7 months after surgery. Patients may present with new onset catching from a previously smooth tracking knee with symptoms of pain and effusion. If this should occur, activity level should be decreased and arthroscopic evaluation is recommended. At the time of arthroscopy, if a graft edge has not incorporated and is catching as a loose flap, it is best treated by sharp excision of the periosteal edge that has not healed, with removal. Removal with an arthroscopic Shaver may jeopardize the graft as it is still quite soft at this time. Similarly, well-incorporated graft edges with periosteal edge hypertrophy are best treated by sharp serrated scissors, used to make them flush with the adjacent articular surface and trimming down with a protected shaver blade device such as a turbo whisker. If the worst case scenario is present when a large portion of the graft has delaminated with the remaining portion intact and adherent to the underlying bone, an open suture repair is not recommended. Instead, arthroscopic sharp incision of the graft that has not attached to the subchondral bone should be performed with removal of the loose flap, leaving behind the integrated chondral graft. Intraarticular adhesions are uncomm o n except in the case of large grafts being taken from femoral periosteum. This may enhance intraarticular fibrosis. If this occurs, adhesions are best released with arthroscopic electrocauter3~ or gentle shaving, and a gentle manipulation after the intraarticular adhesions are released and the grafts visualized to ensure that there are no adhesions to the grafts that may cause delamination at the time of manipulation. Periosteal problems may occur as often as 10% to 20% of the time, sometimes requiring intervention. In most cases, the catching response settles and the patient remains asymptomatic, This likely represents graft remodelling by the patient's activity level alone without delamination.

Articular cartilage once injured does not heal. This has been known for over 200 years. 1° ACT provides a durable hyaline repair tissue in correctly selected patients and is indicated for full thickness, weight-bearing condyle injuries, and injuries to the trochlea of the femur. ACT results in reproducibly satisfactory results with return t o highlevel activities including sports in over 90% of the patients. Second-look arthroscopies reveal tissue fills with biopsies showing hyaline-like cartilage repair. Hyaline cartilage repair is critical as this has been shown clinically to give long-standing results with follow-up at 2 to 9 years. As technical refinements and rehabilitation protocols improve, results for injuries to the patella and the tibia will improve. At this time, the response for treating bipolar focal chondral injuries is u n k n o w n and cannot be recommended.

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REFERENCES 1. Jackson RW: Arthroscopic treatment of degenerative arthritis, in McGinty JB (ed): Operative Arthroscopy. New York NY, Raven, 1991, pp 319-323 2. Hubbard MJS: Articular debridement versus washout for degeneration of medial femoral condyle. J Bone Joint Surg [Br] 78:217-219,1996 3. Nehrer S, Speetor M, Minas T: Tissue retrieved from revised articular cartilage repair procedures reflects mechanisms of failure. Presented at the Annual Meeting of the American Academy of Orthopedic Surgeons, San Francisco, CA, February 12-15, 1997 4. Brittberg M, Lindahl A, Nilsson A, et al: Treatment of deep cartilage defects in the knee with autologous chondrocyte implantation. New Engl J Med 331:889-895, 1994 5. Outerbridge RE: The etiology of chondromalacia patellae. J Bone Joint Surg [Br] 43:752-767, 1961 6. O'Driscoll SW, Keeley FW, Salter RB, et ah Durability of regenerated articular cartilage produced by free autogneous periosteal grafts in major full-thickness defects in joint surfaces under the influence of continuous passive motion. J Bone Joint Surg [Am] 70:595-606, 1988 7. Rodrigo JJ, Steadman RJ, Fulst0ne HA: Improvement of h~ll-thickness chondral defect healing in the human knee after debridement and microfracture using continuous passive motion. Am J Knee Surg 7:109-116, 1994 8. Peterson L: Articular cartilage regeneration: Chondrocyte transplantation and other technologies (symposium). Presented at the Annual Meeting of the American Academy of Orthopedic Surgeons, San Francisco, CA, February 12-15, 1997 9. Minas T: Articular cartilage regeneration: Chondrocyte transplantation and other technologies (symposium). Presented at the Annual Meeting of the American Academy of Orthopedic Surgeons, San Francisco, CA, February 12-15, 1997 10. Hunter W: Of the structure and disease of articulating cartilage. Philos Trans R Soc Lond B Biol Sci 42:514-521,1743

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