F. Alan Barber and David A. Coons
DEFINITION
Osteochondral autograft “plug” transfer is a technique for treating full-thickness, localized articular cartilage lesions with or without subchondral bone loss in a nonarthritic joint.
Cylinders or “plugs” of healthy cartilage, with their associated tidemark and subchondral bone, are harvested from one location in the joint and press-fit into same-length recipient holes prepared in the lesion to restore bone contour and the articular surface.
Multiple plugs may be tranferred to the same region, depending on the defect size.
ANATOMY
Articular cartilage has a complex structure and plays a vital role in normal and athletic activity. It transmits loads uniformly across the joint and provides a smooth, low-friction, gliding surface.
Articular cartilage is a smooth, viscoelastic, hypocellular structure with a low coefficient of friction (estimated to be 20% of the friction seen with ice on ice) and the ability to withstand significant recurring compressive loads.
The articular surfaces of diarthroidal joints are covered with hyaline cartilage.
Hyaline cartilage is composed of sparsely distributed chondrocytes in a large extracellular matrix made of about 80% water and 20% collagen.
Collagen fibers provide form and tensile strength; water gives it substance.
Type II collagen accounts for 95% of the total collagen present. The cellular component (chondrocytes) synthesizes and degrades proteoglycans and is the metabolically active portion of this structure.
Articular cartilage has four distinct zones: a superficial (tangential) zone; a middle (transitional) zone; a deep (radial) zone; and the calcified zone (FIG 1).
The superficial zone collagen fibers are oriented parallel to the joint surface and resist both compressive and shear forces. This zone is the thinnest and sometimes is called the gliding zone.
The surface layer, known as the lamina splendens, is cell free, and consists mainly of randomly oriented flat bundles of fine collagen fibrils.
Under that layer are more densely packed collagen fibers interspersed with elongated, oval chondrocytes oriented parallel to the articular surface.
This superficial zone acts as a barrier, limiting the penetration of large molecules into the deeper zone and preventing the loss of molecules from the cartilage into the synovial fluid.
The middle (transitional) zone collagen fibers are parallel to the plane of joint motion and resist compressive forces.
This zone has more proteoglycans and less water and collagen than the superficial zone.
The chondrocytes are more spherical with more cellular structures, suggesting a matrix synthesis function.
The deep (radial) zone fibers are perpendicular to the surface and resist both compressive and shear forces.
The collagen bundles are arranged in a formation known as the arcades of Benninghoff, in which the round chondrocytes are arranged in columns perpendicular to the joint surface.
The tidemark is located at the base of the deep zone and resists shear stress. It represents a zone of transition from the deep zone to the zone of calcified cartilage.
The calcified zone acts as an anchor between the articular cartilage and the subchondral bone.
It is the deepest zone and is a thin layer of calcified cartilage creating a boundary with the underlying subchondral bone.
The cells in this zone usually are smaller and are surrounded by a cartilaginous matrix.
PATHOGENESIS
Chondral damage can result from a variety of mechanisms, including a pivoting twisting fall, significant direct impacts on the knee, anterior cruciate ligament (ACL) tears, or a patellar dislocation (FIG 2).
FIG 1 • Articular cartilage has four distinct zones: superficial (tangential); middle (transitional); deep (radial); and calcified. (Modified from Browne JE, Branch TP. Surgical alternative for treatment of articular cartilage lesions. J Am Acad Orthop Surg 2000;8:180–189.)
FIG 2 • Chondral damage can result from a variety of mechanisms, including a pivoting twisting fall or significant direct impacts on the knee.
ACL injuries cause direct contusions to the articular surfaces and may lead to instability and localized, full-thickness articular cartilage defects.
Osteochondritis dissecans involves the separation of subchondral bone and cartilage from surrounding healthy tissues.
It most commonly occurs in the lateral aspect of the medial femoral condyle.
Traumatic osteochondral lesions include acute bone and cartilage loss due to fracture, crush, or shear injuries.
Sometimes, even without a clearly remembered traumatic event, the patient develops pain with weight bearing.
NATURAL HISTORY
Cartilage biopsy samples overlying bone bruises have shown degeneration, necrosis of the chondrocytes, and a loss of proteoglycan.
An experimental model suggests that a severe bone bruise and its associated chondral necrosis are precursors to degenerative changes.20
Instability secondary to ACL loss has been shown to contribute to the onset of osteoarthritis after ACL tears.21
Articular cartilage has limited regeneration potential.
PATIENT HISTORY AND PHYSICAL FINDINGS
Various mechanisms of injury are associated with full-thickness articular cartilage lesions, inncluding pivoting twisting falls, direct impacts, and patellar instability.
Full-thickness chondral lesions often are clinically silent and should be suspected in the setting of any traumatic hemarthrosis, especially with a ligament disruption.
Reports of pain localized to one compartment, a persistent dull aching pain worsening after activity, and pain most noticeable when falling asleep are common.
Running, stair climbing, rising from a chair, and squatting may aggravate the symptoms, as does sitting for a prolonged period.
Physical findings include joint line tenderness, effusion, crepitus, grinding, or catching.
Effusion is nonspecific but suggests intra-articular pathology.
Pain on direct palpation of the femoral condyles may indicate cartilage damage.
Decreased range of motion is nonspecific but often indicates pathology.
The Lachman test detects ACL instability that may lead to cartilage injury.
Malalignment of the tibia to the femur when standing may lead to abnormal chondral wear.
A positive patellar apprehension test signals damage to the medial patellofemoral ligament.
IMAGING AND OTHER DIAGNOSTIC STUDIES
A standard radiographic knee evaluation should be performed.
This includes standing anteroposterior (AP) views in full extension to identify angular changes and to compare joint space height.
A 45-degree flexion posteroanterior (PA) weight-bearing view may identify subtle joint space narrowing.
A non–weight-bearing lateral view obtained in 45-degree flexion in which the posterior femoral condyles overlap, an axial view of both patellae to help evaluate the patellar alignment, and an AP knee flexion view to outline the femoral intercondylar notch also should be obtained.
Osteochondritis dissecans lesions most commonly are found in the lateral aspect of the medial femoral condyle (FIG 3A) and are best demonstrated on an AP knee flexion view.
Long-leg hip-to-ankle films accurately determine varus or valgus alignment.
Proper MRI protocols have high sensitivity and specificity.
MRI has evolved into a proven tool to evaluate chondral surfaces and detect fulland partial-thickness lesions that may be clinically silent (FIG 3B,C).
FIG 3 • A. Osteochondritis dissecans involves subchondral bone and cartilage separation from the adjacent condyle and is found most commonly in the lateral aspect of the medial femoral condyle. B,C. MRI evaluation can detect full- or partial-thickness articular lesions and osteochondritis dissecans that may be clinically silent.
Clinically proven cartilage-sensitive sequences include T1-weighted gradient echo with fat suppression and fast spinecho sequences with and without fat suppression.
Many newer sequences offer promise but have not yet been validated.22
DIFFERENTIAL DIAGNOSIS
Partial- or full-thickness cartilage lesion
Osteonecrosis
Osteochondritis dissecans
Meniscal tear
Ligament injuries
NONOPERATIVE MANAGEMENT
Nonoperative treatment for full-thickness, discrete chondral lesions consists of physical therapy, anti-inflamatory medication, and activity modification to avoid high-impact or patelladestabilizing activities.
Bracing options include patellar stabilizing braces for patellofemoral instability and load-shifting braces that unload the injured compartment.
Unloading the compartment also can be accomplished by shoe inserts that provide an appropriate heel and sole wedge.
These efforts are more effective for medial femoral condyle lesions than lateral ones.
It is important to ensure that the patient understands that full-thickness lesions have little spontaneous healing capacity and that further degeneration is likely.
SURGICAL MANAGEMENT
The indications for osteochondral autograft transplantation include discrete, isolated, full-thickness articular cartilage lesions between 1.0 and 2.5 cm in diameter (FIG 4).
Acceptable results with larger defects have been reported, but not consistently.
If the depth of subchondral bone loss exceeds 6 mm, it will be necessary to adjust the harvested graft accordingly.
Contraindications include opposing full-thickness articular cartilage damage (“kissing” lesions), multiple-compartment full-thickness lesions, significant angular changes, history of joint infection, intra-articular fracture, and rheumatoid arthritis.
This technique is most commonly performed on the femoral condyle; however, osteochondral autograft transplantation of the trochlea, patella, tibial plateau, humerus, and talus has been reported.
The COR osteochondral repair system (Depuy Mitek, Raynham, MA) allows for the harvesting of a precisely sized osteochondral plug and transplantation into a precisely drilled defect. The technique illustrated here uses this system.
Other systems have been developed, including the osteochondral autologous transfer system (OATS; Arthrex, Naples, FL), and MosaicPlasty (Smith & Nephew Endoscopy, Andover, MA).
FIG 4 • The indications for osteochondral autograft transplantation include discrete, isolated, full-thickness articular cartilage lesions between 1.0 and 2.5 cm in diameter.
Preoperative Planning
The success of this procedure depends upon maintaining viable chondrocytes. Confocal microscopy studies demonstrate that greater pressure on the articular cartilage cells leads to cell death. Several technical issues are related to greater transplanted cell death. These include high impact pressure during insertion, proud grafts which are not advanced to the level of the adjacent native articular cartilage, and sunken grafts depressed 2 mm or more compared to the adjacent articular cartilage.
The ideal technique optimizes graft position and stability, provides for consistent graft length harvesting, and minimizes the forces required to insert the grafts.
Multiple procedures can be performed at the same time, including meniscal repair and ligament reconstruction.
Improved results occur with concomitant ACL reconstruction.18
Any ligament instability or malalignment should be corrected at the time of autografting to avoid increased failure rates.
All radiographs and MRI images should be reviewed before surgery to confirm whether the lesion can be treated arthroscopically or whether an arthrotomy is needed.
Perpendicular placement of the harvester and drill to the articular surface is required.
The COR transfer system has a unique “perpendicularity” guide which enhances the perpendicular harvest of the donor graft as well as the perpendicular orientation of the drilled recipient site.
Any allograft or synthetic materials that may be needed should be available in the operating room.
Although allograft tissue avoids concerns about harvest site morbidity, it is offset by the risks of transmitted disease and decreased chondrocyte viability17 as well as significant costs.
Positioning
Osteochondral autograft transfer in the knee is performed with the patient supine and the operative knee in an arthroscopic leg holder flexed off the table.
It is crucial to confirm that the knee can be flexed adequately to access the lesion before operative preparation and draping.
The contralateral leg should be well padded and positioned out of the operative field.
It may be necessary to drape the operative leg free of a leg holder to obtain enough knee flexion to access the lesion.
Approach
Arthroscopic osteochondral autograft transplantation can be techinically difficult, because of the need to achieve perpendicular access to the articular cartilage and adequate knee flexion.
The use of the intercondylar notch as a donor site allows for ready arthroscopic access and avoids the need for an arthrotomy such as is required when obtaining grafts from either the superior medial or lateral femoral condyles above the linea terminalis.
A thorough arthroscopic diagnostic knee evaluation should be performed first.
An arthrotomy can be performed for lesions that cannot be addressed adequately arthroscopically. A spinal needle can be used to determine the best angle for portal creation, ensuring a perpendicular approach to the harvest and defect sites.
Arthroscopic osteochondral autografting includes five steps: lesion evaluation and preparation, determination of the number of grafts needed, defect preparation, graft harvest, and graft delivery.
The other plug transfer systems have technique differences including the order in which the donor plugs are harvested and the relative length of the donor plug to the recipient hole.
The Mosaicplasty system required overdrilling of the recipient site by 2 mm creating room for debris and allowing the graft to “float” into place. The donor plug is harvested first before creating the recipient hole to avoid donor-recipient site mismatch.
The OATS system requires underdrilling of the recipient sites by 2 mm and requires a final “impaction” designed to improve graft stability but at the same time placing additional impact pressure on the graft articular cartilage. Here too the donor plug is harvested first before creating the recipient hole to avoid donor-recipient site mismatch.
TECHNIQUES
DIAGNOSTIC ARTHROSCOPY
During the diagnostic evaluation, a complete examination must be performed to rule out other pathology and confirm that no contraindications to the procedure exist.
It is necessary to look in the posterior recesses and underneath the menisci for chondral pieces.
Concomitant ligament surgery should be addressed after the transplantation.
An adequate synovectomy, especially of the fat pad, is needed to facilitate complete visualization of both the defect and harvest sites.
A spinal needle should be used to identify the correct portal placement for a perpendicular approach.
LESION EVALUATION AND PREPARATION
A 16-gauge needle can be used to plan the best (perpendicular) approach to both the defect and donor sites.
The defect is prepared by removing loose debris and freshening the edges with a curette or an arthroscopic knife to create perpendicular chondral walls (TECH FIG 1).
The subchondral bone should be cleared of any residual articular cartilage, but generalized bone bleeding should be avoided.
TECH FIG 1 • The defect is prepared by removing loose debris and freshening the edges with a curette or an arthroscopic knife to create perpendicular chondral walls.
DETERMINING NUMBER OF GRAFTS
The number of grafts required is planned using the probe to obtain a preliminary measurement of the defect's shape and dimensions (TECH FIG 2A).
When using more than 1 graft, a 2–3-mm bone bridge should be maintained between the recipient sites to ensure a good press fit.
The depth of the lesion should be estimated using the 2-mm marks on the harvester.
A series of grafts 6 mm in diameter fills the defect best.
Larger-plug harvesters are available but may require an arthrotomy and are more likely to encroach on weight-bearing areas at harvest sites.
Specifically, given that a 10-mm diameter lesion is an indication for grafting, harvesting a 10-mm graft defeats the purpose of using this grafting technique.
The plan should be to place the grafts starting at the periphery of the defect so that the articular cartilage matches the adjacent chondral edge after transplantation (TECH FIG 2B).
The depth of the defect also should be analyzed.
In most cases, the standard 10
–12-mm harvester depth is sufficient to fill the defect.
Osteochondritis dissecans lesions or those with significant bone loss may require the use of the variable depth harvester and placement of grafts that have cancellous sections standing above the crater base.
TECH FIG 2 • A. The number of grafts required is planned using the probe to obtain a preliminary measurerment of the defect shape and dimensions. B. Plugs of healthy cartilage and subchondral bone are harvested from one location and press-fit into the defect, restoring the articular surface. (B: Reprinted with permission from Barber FA. Chondral injuries in the knee. In: Johnson DH, Pedowitz RA, eds. Practical Orthopaedic Sports Medicine and Arthroscopy. Philadelphia: Lippincott Williams & Wilkins, 2007:752.)
DEFECT PREPARATION
Any residual articular cartilage is removed from the subchondral bone, but generalized bone bleeding should be avoided.
Drilling the recipient site before harvesting the donor autograft plugs allows the selection of the best match on the femoral surface between the donor grafts and the articular cartilage adjacent to the recipient sites.
Using the COR perpendicularity system reproducibly identifies the best orientation for drilling the recipient site and makes it feasible to drill the recipient site before harvesting the grafts.
Insert the drill guide with the perpendicularity rod through the portal and into position at the recipient site. With the drill guide positioned in a perpendicular orientation, turn the perpendicularity rod counterclockwise until it disengages and remove the rod.
The recipient sites in the defect are drilled with the corresponding size COR drill bit under direct arthroscopic visualization, keeping the drill perpendicular to the articular surface.
The projecting tooth at the drill tip keeps the drill from “walking” and allows for precise recipient site placement by creating a starter hole (TECH FIG 3).
The drill is advanced to the appropriate depth using the markings of 5 mm, 8 mm, 10 mm, 12 mm, 15 mm, and 20 mm found on the side of the drill. This line is compared to the adjacent articular cartilage. The fluted drill's concave sides remove bone during drilling and reduce both friction and heat.
In cases of subchondral bone loss, the depth should be used and the depth underdrilled to restore the contour and height of the articular surface.
This is accomplished by aligning the laser mark with the desired articular cartilage height.
The recipient holes can be drilled at the same time or sequentially after autograft insertion.
Care should be taken to maintain a bone bridge between recipient sites of 2 to 3 mm and to avoid recipient site convergence.
TECH FIG 3 • The recipient sites in the defect are drilled with the corresponding size COR (DePuy Mitek, Inc, Raynham, MA) drill bit under direct arthroscopic visualization, keeping the drill perpendicular to the articular surface.
GRAFT HARVEST
Potential harvest sites include the lateral and medial trochlea above the linea terminalis and the intercondylar notch.
In general, contact pressures are lower in the intercondylar notch and medial trochlea, but available harvest material is limited.1
Higher contact pressures are found in the lateral trochlea, but these decrease more posteriorly.
Harvesting 5-mm plugs from the lateral trochlea did not result in significant increases in stress concentration and loading in one study.7
We prefer to harvest from the superior and lateral intercondylar notch, because it commonly is obliterated in ACL reconstruction without subsequent morbidity and allows for an entirely arthroscopic procedure (TECH FIG 4A).
Once the number of plugs to be obtained is determined and the sites prepared, the harvester is inserted into the disposable cutter.
The retropatellar fat pad is completely débrided to improve visualization and avoid soft tissue entrapment.
The COR Harvester Delivery Guide comes with the cutting tool pre-assembled as a single unit. The perpendicularity rod should be inserted into this Harvester/Cutter assembly before insertion into the joint. The perpendicularity rod will function as an obturator and minimize both soft tissue capture and fluid loss as the assembly is inserted into the knee.
The Harvester Delivery Guide/Cutter/perpendicularity rod assembly is positioned on the donor site in preparation for the graft harvest. The perpendicularity rod is used to confirm the perpendicular position of the cutter and then removed.
The arthroscope is rotated to confirm this alignment from several angles.
Perpendicular grafts can be obtained readily with both arthroscopic and open approaches.4
Using a mallet and continuing to hold the harvester perpendicular to the articular cartilage in all planes, use a mallet to tap the Harvester Delivery Guide/Cutter to the desired depth based upon the 5-mm, 8-mm, 10-mm, 12-mm, 15-mm, and 20-mm markings on the side of the harvester (TECH FIG 4B).
A unique feature of the COR system is the cutter tooth on the harvester which underscores the cancellous bone at the distal end of the harvester tube allowing for a precise and consistent depth cut (TECH FIG 4C).
The T-handle of the harvester is rotated clockwise at least two full rotations, undercutting the distal bone and creating a precise harvest depth.
The plug is removed by gently twisting the T-handle while withdrawing the plug. Care should be taken to avoid toggling the donor hole.
On a firm surface, insert the Harvester Delivery Guide/ Cutter into the graft loader and push down firmly until it makes contact with the bottom of the loader. The harvested graft will be pushed from the cancellous bone side of the graft plug upwards into the Harvester/Delivery Guide and out of the cutter section (TECH FIG 5). A loud noise usually accompanies this transfer.
TECH FIG 4 • A. Harvest sites include the superior and lateral intercondylar notch, an area that is commonly removed in anterior cruciate ligament reconstruction notchplasty. B. Position the Harvester/Delivery Guide/Cutter with the perpendicularity guide on the selected donor site. After verifying the perpendicularity, remove the guide and then tap the harvester until the desired laser line depth has been reached. C. A unique feature of the COR system is the cutting tooth which underscores the cancellous bone at the distal end of the harvester tube and allows for a precise depth cut. (B,C: Courtesy of Depuy Mitek, Inc, Raynham, MA.)
The harvester is removed from the cutter. The graft plug remains inside the harvester until it is transplanted.
This transfer system eliminates any loads to the articular surface of the graft and eliminates the danger of chondrocyte damage in this step.
TECH FIG 5 • On a firm surface, insert the Harvester Delivery Guide/Cutter into the graft loader and push down firmly until it makes contact with the bottom of the loader. The harvested graft will be pushed from the cancellous bone side of the graft plug upwards into the Harvester/Delivery Guide and out of the cutter section.
GRAFT INSERTION
Once the harvester tube is disassembled from the cutter, it is placed in the clear plastic insertion tube with depth markings.
The plastic plunger is placed in the harvester delivery system before insertion of the delivery system into the joint.
The loaded harvester–clear plastic delivery guide system is then inserted into the knee. It may be necessary to enlarge the portal slightly to permit this passage.
The clear end of the delivery system, with the graft tip slightly projecting, is held perpendicularly at the recipient site outlet, and, aligning the articular cartilage of the autograft with the adjacent articular cartilage, implanted with gentle tapping until it is flush with the articular cartilage (TECH FIG 6).
The Universal tamp may be used to fine-tune the graft placement.
The 8 mm side is recommended for 4 mm and 6 mm grafts and the 12 mm side is recommended for 8 mm and 10 mm grafts.
TECH FIG 6 • The loaded harvester–clear plastic delivery guide system is held perpendicular to the articular cartilage and implanted with gentle tapping.
MULTIPLE GRAFT REPAIR
If more than one graft is needed to repair an articular cartilage defect, the Harvester/Delivery Guide and Cutter is reassembled and the process repeated until the defect is completely filled. A 2-mm to 3-mm bone bridge should be maintained between the drilled holes to allow for a secure graft press fit.
BACKFILLING
Filling the donor sites is recommended, especially for harvested plugs greater than 6 mm in diameter or if multiple plugs have been harvested from a single area.
Large-diameter and deep defects can cause excessive stress on the surrounding cartilage and lead to degeneration.13
Allograft or commercially available biodegradable material can be used as backfill material plugs (TECH FIG 7).
TECH FIG 7 • Grafting (back-filling) the donor sites is recommended, especially for harvested plugs greater than 6 mm in diameter or if multiple plugs are harvested from a single area.
POSTOPERATIVE CARE
Immediate range-of-motion exercises without a brace are begun.
Non–weight bearing is observed for 3 weeks, followed by progressive weight bearing during weeks 3 to 6 after surgery and then full weight bearing beginning at 6 weeks after surgery.
A progressive quadriceps strengthening program is then started.
Full athletic activity is permitted at 4 months.
OUTCOMES
Condylar lesions typically have excellent clnical results.
Multiple authors report excellent and good results ranging from 78% to 96% at a minimum of 2 years followup.2,6,8,18,19
Patellar or patellar and trochlear mosaicplasties have been reported to have good to excellent results in 79% of patients.9,23
Allograft has been shown to be an effective treatment for patellofemoral disease.14,23
Comparisons of osteochondral transplantation with microfracture, Pridie drilling, and abrasion arthroplasty have shown better results with osteochondral transplantation.6,10
Osteochondral transplantation consistently results in restoration of hyaline cartilage versus “hyaline-like” or fibrocartilage.2,3,6,12
Patients younger than 40 years of age have better results.6,11,18
COMPLICATIONS
Infection
Loose body if graft loosens
Graft reabsorption
Cartilage degeneration due to excessive pressure when seating the graft
Proud graft leading to excessive contact pressures, graft destruction, and possible “catching” sensation.
REFERENCES
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