Eric C. McCarty, R. David Rabalais, and Kenneth G. Swan, Jr.
DEFINITION
Articular cartilage lesions are focal, usually isolated, cartilage defects that may be either symptomatic or incidentally found.
Osteochondritis dissecans is an osteochondral lesion that occurs in adolescents and, therefore, may have different management ramifications from lesions in adults.
Lesions can be partialor full-thickness, down to subchondral bone.
Lesions can be secondary to trauma or atraumatic, as is the case for osteochondritis dissecans.
Cases with a traumatic etiology may have associated ligamentous or meniscal injury.
Small full-thickness chondral defects may heal adequately with mechanically inferior fibrocartilage (primarily type I collagen), but larger defects often require cartilage transplant surgery to replace the damaged chondral surface.
ANATOMY
Articular cartilage is composed primarily of type II collagen.
Chondrocytes that produce the extracellular matrix are of mesenchymal stem cell origin.
Osteochondral lesions may occur in all three compartments of the knee.
Chondral defects after a patellar dislocation may be found on the medial patellar facet or lateral trochlea.
Classically, osteochondritis dissecans occurs at the lateral aspect of the medial femoral condyle.
PATHOGENESIS
Osteochondral lesions may be traumatic or may have no known history of trauma.
Traumatic lesions may be caused by compaction, as with an anterior cruciate ligament tear and lateral-based osteochondral injury, or by a shearing mechanism, as seen with patellar dislocations.
Atraumatic lesions may be found in young persons, as is the case with osteochondritis dissecans, or in elderly persons, as seen with degenerative lesions.
The etiology of ostoechondritis dissecans is uncertain. Traumatic, inflammatory, developmental, and ischemic causes have all been proposed but not proven.
NATURAL HISTORY
Few controlled, prospective outcome studies have been published.
The natural history for juveniles with nondisplaced osteochondritis dissecans is very favorable.
Those diagnosed as adults have a less favorable prognosis. In one study, 81% of patients had tricompartmental gonarthrosis at an average of 33 years follow-up.5
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients with focal osteochondral lesions typically are active and young, ranging in age from adolescence to middle age.
Often, the history does not include a specific traumatic episode. History and physical findings can be subtle.
Presentation is variable; it may mimic meniscal pathology, with intermittent pain and swelling.
Condylar defects may present with high-impact loading complaints, whereas patellofemoral defects may produce anterior knee pain–type complaints, with stairs and prolonged sitting causing symptoms.
Patients with large cartilage lesions who are candidates for osteochondral allograft transplant surgery may have a history of previous knee surgery and previous attempts at cartilage regeneration by other methods (eg, microfracture, autologous chondrocyte implantation, osteochondral autograft transplant).
Physical findings can be nonspecific and may include joint effusion and painful range of motion.
Tenderness at the defect, on either the condyle, patellar facets, or trochlea, may be elicited.
In the case of patellofemoral defects, patellar mobility and apprehension must be assessed.
Ligament integrity must be determined.
Mechanical alignment must be assessed, and appropriate imaging studies obtained.
Failure to identify and address ligamentous deficiency or mechanical malalignment will lead to compromise of restorative cartilage procedures.
Physical examination of the knee should note the following.
Chronic or recurrent effusion associated with, although not predictive of, a chondral lesion
Pain at extremes of range of motion (ie, forced flexion or forced extension) may indicate mensical pathology. An extension block may indicate a displaced meniscus tear. Osteochondral defects may cause decreased flexion via effusion, or may have normal range of motion.
An isolated lesion may have point tenderness, although it often is difficult to palpate.
Increased patellar mobility may indicate generalized ligamentous laxity, increasing suspicion for patellar instabililty.
Mechanical axis views are obtained if there is any hint of malalignment based on gait and stance analysis.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Anteroposterior, lateral, and sunrise views are mandatory to determine overall knee condition, rule out diffuse degenerative arthritis, and assess patellar position within the trochlea.
FIG 1 • T2-weighted coronal (A), T1-weighted sagittal (B), and T2-weighted sagittal (C) MRI scans of a right knee with a medial femoral condyle osteochondral defect. D. Arthroscopic view of a large osteochondral defect. Full assessment of the lesion was not completed until the defect was débrided to stable rim.
Large chondral defects may not be visible on plain radiographs, or may have a small radiodense bone fragment attached.
“Notch views” may better define more central lesions.
Long-leg mechanical axis views are mandatory in patients with malalignment on physical examination, and should be considered in all candidates for osteochondral autograft transfer.
MRI is the best modality to determine the presence, size, and location of cartilage lesions, as well as to determine the integrity of menisci and ligaments (FIG 1A–C).
Arthroscopy remains the gold standard for evaluation of articular cartilage lesions (FIG 1D).
DIFFERENTIAL DIAGNOSIS
Meniscal tear
Degenerative arthritis
Patellar instability
Bone contusion
Avascular necrosis
Undiagnosed ligamentous injury
NONOPERATIVE MANAGEMENT
Patients with asymptomatic osteochondral lesions (often found incidentally on standard knee arthroscopy) may be candidates for nonoperative treatment.
Long-term studies may indicate an increased risk for degenerative arthritis with conservative management,5 but no randomized controlled studies exist.
Nonoperative treatment should consist of physical therapy to obtain or maintain painless, full range of motion.
Aggravating impact activities should be avoided.
Patients may participate in sports as tolerated.
Unloader braces or shoe wedges may help alleviate mild symptoms.
SURGICAL MANAGEMENT
Osteochondral allograft transplantation often is a two-stage procedure.
The magnitude of the lesion and occasionally the diagnosis itself often are not appreciated until first-look arthroscopy (FIG 2).
Size and location of the cartilage lesion is determined.
Lesions 1 cm in diameter or larger are considered for allograft transplant. Smaller lesions may be amenable to microfracture or autograft cartilage transplant with single or mutliple plugs.
FIG 2 • Patient positioning, with tourniquet, using a lateral post and foot rest.
The remainder of the knee is inspected to ensure this is not a diffuse cartilage process, and to examine the integrity of the cruciate ligaments and mensici.
Preoperative Planning
Mechanical alignment must be assessed and, if necessary, osteotomy planned for.
Templated radiographs are obtained for appropriate allograft sizing, based on the medial–lateral dimension of the lesion.
The patient must be informed that there is no way to predict when an appropriate-sized donor will become available, and that a moderate waiting period (weeks to months) may be required before surgery can be done.
Fresh osteochondral allografts are used. Frozen chondral grafts are unacceptable.
Allografts are harvested within 24 hours of donor death and can be preserved for up to 4 days at 4° C.
Chondrocyte viability likely declines after 5 days, but prolonged storage—up to 21 days—currently is acceptable.6
After 28 days, chondrocyte viability is unacceptably diminished.4
Tissue matching and immunologic suppression are unnecessary with osteochondral grafts.
Donors are screened with a multifactorial process promoted by the American Association of Tissue Banks to minimize the risk of disease transmission.
Positioning
We prefer to have the patient supine, keeping the foot of the table up.
A lateral post and sliding footrest or taped sandbag allow for 90-degree flexion positioning of the knee.
The surgeon should be able to flex the knee to 120 degrees if needed.
A tourniquet is placed but is inflated only if visualization is compromised by intra-articular bleeding.
Approach
The approach depends on the location of the defect.
The defect typically is on the medial or lateral femoral condyle, requiring a longitudinal parapatellar tendon arthrotomy.
Large trochlear or patellar defects amenable to osteochondral allograft transplation (rare) may require a larger parapatellar incision and eversion of the patella.
TECHNIQUES
FEMORAL CONDYLE OSTEOCHONDRAL ALLOGRAFT TRANSPLANT
Diagnostic Arthroscopy
A brief diagnostic arthroscopy is peformed to fully assess or reassess the condylar defect (TECH FIG 1A) as well as to examine for additional knee pathology and any changes from the original arthroscopy.
TECH FIG 1 • A. Arthroscopic view of a large osteochondral defect. B. Open view of a large osteochondral defect.
A standard parapatellar arthrotomy is carried out to expose the defect on the affected side of the knee. It is lateral for a lateral femoral condylar defect and medial for a medial femoral condylar defect (TECH FIG 1B).
Sizing
The size of the defect is determined using a cannulated cylindrical sizing device.
A circumferential mark is placed around the sizer to outline the margins of the defect to be grafted (TECH FIG 2A).
Occasionally, a chondral defect is large or irregularly shaped, and requires more than one allograft. The resultant graft may be in the form of a “snowman,” with two or even three differently sized circular grafts stacked on top of one another.
A central guide pin is placed through the sizer into bone to a depth of 2 to 3 cm. The sizer is then removed (TECH FIG 2B).
A reference mark is placed at the superior (12 o'clock) position of the recipient site.
Recipient Site Preparation
The recipient site is prepared by first scoring the periphery of the lesion (TECH FIG 3A).
Next, a counterbore or reamer is used to drill the defect to a depth of 8 to 10 mm circumferentially, to bleeding subchondral bone (TECH FIG 3B).
Following that, the recipient bed should be drilled with a small (1.6 to 2.0 mm) drill bit to stimulate additional vascular response (TECH FIG 3C).
The recipient site depth is then measured in four positions, as on the face of a clock: 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock. This may be done using a standard paper ruler, or by a measuring device supplied by the equipment company (TECH FIG 3D).
TECH FIG 2 • A. Sizing of osteochondral defect. B. Placement of a central pin through the center of the sizer into the center of the defect after circumferential marking of the sizer on the condyle.
The depth of the recipient site may not be precisely consistent throughout its circumference. Donor modification will allow for fine tuning.
Donor Preparation
The same sizer used for defect sizing is used to template the allograft hemicondyle on the back table. Careful comparison of defect location (eg, relative to femoral notch) and donor position is imperative to ensure optimal donor–recipient fit (TECH FIG 4A,B).
We use the Arthrex Osteochondral Allograft Transfer System (OATS) Workstation (Naples, FL) to help secure the donor graft. This instrument allows for multiple degrees of freedom while positioning and contouring the graft (TECH FIG 4C).
The angle of harvest of the donor tissue must match the angle at which the recipient site was reamed (TECH FIG 4D).
Next, the donor osteochondral plug(s) is harvested. The Arthrex system makes it possible to completely drill through the donor condyle, which is held in place with the OATS Workstation. The relevant donor graft tissue is then carefully removed from the harvester drill (TECH FIG 4E,F).
Graft Harvest
The graft depth is now measured and marked to the precise degree that the recipient bed was measured, in the same four quadrants.
The graft is held using allograft holding forceps, similar to the manner in which the patella is prepared during total knee arthroplasty. The graft cut is made using a power saw, with care taken to match the cut to the previously made depth measurements. The osteochondral portion of the graft should be held within the forceps, so as not to drop the relevant portion of the graft once the cut is completed (TECH FIG 5A–C).
TECH FIG 3 • A. Scoring of peripheral cartilage. Note placement of the 12 o'clock reference mark. B. Counterbore reaming of a defect, over the central pin, to a depth of 8 to 10 mm. C. Recipient site reamed to subchondral bone and drilled with 2.0-mm drill bit to enhance subchondral bleeding. D. Measuring of defect depth.
TECH FIG 4 • A. Comparing donor hemicondyle to recipient condyle, to specifically localize donor site. B. Schematic of intraoperative donor–recipient matching. C,D. Donor graft workstation. E.Perpendicular drilling of donor condyle. F. Precontoured donor plug.
TECH FIG 5 • A. Donor plug. B. Sawing of excess subchondral bone to exact depth of four quadrants of recipient site. C. Diagram of sawing excess bone at precise quadrant levels. D. Contouring of osteochondral plug. E.Fully contoured and “bulletized” osteochondral plug.
The bony end of the graft's edges should be slightly rounded, or “bulletized,” to ease insertion of the graft into the recipient socket (TECH FIG 5D,E).
Delivery
Before graft insertion, the recipient bed may be further prepared by using a dilator to widen the socket by 0.5 mm and to smooth the socket surfaces. (This step is optional.)
The graft is then inserted manually, after lining up the 12 o'clock recipient and donor reference marks (TECH FIG 6A). If the press-fit method is inadequate, an appropriately sized tamp is used to gently tap the graft into position (TECH FIG 6B).
Additional fixation usually is unnecessary (TECH FIG 6C–E).
TECH FIG 6 • A. Manual graft insertion. B. Diagram of insertion using graft delivery tube. C. Final graft, open. D. Final graft, as seen through the arthroscope. E. Three month follow-up, with a secondlook arthroscopy.
POSTOPERATIVE CARE
Patients typically are discharged home from same-day surgery.
An ice cuff about the knee helps alleviate postoperative pain and swelling.
Bracing is not indicated for isolated OATS.
Continuous passive motion is begun on day 1 and progressed to full as tolerated; typically 0 to 60 degrees on postoperative day 1, then increased by 5 degrees per day; however, there are no passive range-of-motion restrictions.
Patients are given strict non–weight-bearing instructions.
Our preference is strict non–weight bearing for 8 weeks, followed by partial weight bearing for another 4 weeks.
Patients may be expected to return to full activities by 6 to 8 months.
OUTCOMES
Gross et al2 reported on 60 fresh femoral osteochondral allografts at an average of 10 years and 65 fresh tibial plateau osteochondral allografts at 11.8 years (average) with 84% good/excellent results and 86% good/excellent results, respectively, for posttraumatic defects.
Kaplan-Meier survivorship analysis determined 95% survival at 5 years, 85% at 10 years, and 74% at 15 years for femoral grafts.
Tibial allografts were reported to have 95% survivorship at 5 years, 80% at 10 years, and 65% at 15 years.
We determined no negative outcome with meniscal transplant or limb realignment surgery.
Shasha et al7 reported the results of 60 fresh femoral allografts for varying etiologies (ie, posttraumatic, osteoarthritis, osteonecrosis, osteochondritis dissecans) with an average follow-up of 10 years.
Survivorship data revealed 95% survivorship at 5 years, 85% at 10 years, and 74% at 15 years, with 84% good/ excellent results and 12 graft failures.
Bakay et al1 reported 22 good/excellent results in 33 patients at 2 years follow-up with cryopreserved or cryoprotected osteochondral allografts in the femur, tibial plateau, and patella.
Jamali et al3 reported the results of 20 fresh osteochondral allografts in the patellofemoral joint at 94 months follow-up with 12 good/excellent results and 5 failures.
Kaplan-Meier survivorship data determined 67% survivorship at 10 years.
COMPLICATIONS
Infection
Stiffness
Thromboembolic events
Reflex sympathetic dystrophy
Graft dislodgment/failure
REFERENCES
1. Bakay A, Csonge L, Papp G, et al. Osteochondral resurfacing of the knee joint with allograft: clinical analysis of 33 cases. Int Orthop 1998;22:277–281.
2. Gross AE, Shasha N, Aubin P. Long-term follow-up of the use of fresh osteochondral allografts for post-traumatic knee defect. Clin Orthop Rel Res 2005;435:79–87.
3. Jamali AA, Emmerson BC, Chung C, et al. Fresh osteochondral allografts. Clin Orthop Rel Res 2005;437:176–185.
4. Kwan MK, Wayne JS, Woo SL, et al. Histological and biomechanical assessment of articular cartilage from stored osteochondral shell allografts. J Orthop Res 1989;7:637–644.
5. Linden B, Malmo S. Osteochondritis dissecans of the femoral condyles. J Bone Joint Surg Am 1977;59:769–776.
6. Shahgaldi BF, Amis A, Heatley FW. Repair of cartilage lesions using biological implants. A comparative histological and biomechanical study in goats. J Bone Joint Surg 1991;73B:57–65.
7. Shasha N, Aubin PP, Cheah HK, et al. Long-term clinical experience with fresh osteochondral allografts for articular knee defects in high demand patients. Cell and Tissue Banking 2002;3:175–182.