J. Richard Steadman and William G. Rodkey
DEFINITION
Chondral defects in the knee are common.
The lesions may be partialor full-thickness (FIG 1), through all layers of the articular cartilage down to the level of the subchondral bone.
Chondral defects may be acute or chronic.
These articular cartilage lesions may present in a variety of clinical settings and at different ages.5–10
ANATOMY
The articular cartilage of the knee is 2 to 4 mm thick, depending on the location within the joint.
The articular cartilage is avascular tissue that is devoid of nerves and lymphatics.
Relatively few cells (chondrocytes) are present in the abundant extracellular matrix.
These factors are critical in the lack of a spontaneous or naturally occurring repair response after injury to articular cartilage.
FIG 1 • A. A full-thickness chondral defect through all layers of the articular cartilage is outlined (arrows). B. A full-thickness chondral lesion.
PATHOGENESIS
The shearing forces of the femur on the tibia as a single event may result in trauma to the articular cartilage (FIG 2), causing the cartilage to fracture, lacerate, and separate from the underlying subchondral bone or separate with a piece of the subchondral bone.
Chronic repetitive loading in excess of normal physiologic levels also may result in fatigue and failure of the chondral surface.
Single events usually occur in younger patients, whereas chronic degenerative lesions are seen more commonly in persons of middle age and older.5–10
Repetitive impacts can cause cartilage swelling, an increase in collagen fiber diameter, and an alteration in the relation between collagen and proteoglycans.
NATURAL HISTORY
Articular cartilage defects that extend for the full thickness to subchondral bone rarely heal without intervention.5–10
Some patients may not develop clinically significant problems from acute full-thickness chondral defects, but most eventually suffer from degenerative changes that can be debilitating.
FIG 2 • A shearing injury has resulted in a full-thickness chondral defect, as seen on this MRI scan. The dark arrow denotes the cartilage defect, and the light arrows show the limits of the subchondral bone edema secondary to the shearing injury. (Courtesy of Dr. Charles Ho, Vail, CO.)
Acute events may not result in full-thickness cartilage loss but, rather, may start a degenerative cascade that can lead to chronic full-thickness loss.
The degenerative cascade typically includes early softening and fibrillation (grade I); fissures and cracks in the surface of the cartilage (grade II); severe fissures and cracks with a “crab meat” appearance (grade III); and, finally, exposure of the subchondral bone (grade IV).
PATIENT HISTORY AND PHYSICAL FINDINGS
The physical diagnosis can be difficult to establish, especially if the chondral defect is isolated.
Chondral lesions can be located on the joint surfaces of the femur, tibia, or patella.
Point tenderness over a femoral condyle or tibial plateau is a useful finding, but is not diagnostic.
If compression of the patella elicits pain, a patellar or trochlear lesion may be indicated.
Joint effusion may be present, but it is not a consistent finding.
Catching or clicking may be present, especially if there is an elevated flap of cartilage.
Restricted range of motion (ROM) can be associated with many pathologic conditions of the knee, but the ROM should be documented as a baseline prior to any treatment.
Physical examinations should be performed, as follows:
The patella is palpated in superior-inferior and medial-lateral directions for evidence of effusion. About 50% of patients with chondral defects have an effusion.
The Lachman test is used to rule out ligamentous instability by applying anterior force to the tibia with the knee in 20 to 30 degrees of flexion.
The thumb and index finger are used to place digital pressure over all geographic areas of the knee to detect point tenderness; this finding is useful but is not in itself diagnostic.
A palpable or audible pop in combination with pain is considered a positive result to the McMurray's test, indicating a meniscus lesion rather than a chondral lesion.
IMAGING AND OTHER DIAGNOSTIC STUDIES
For diagnostic imaging, angular deformity and joint space narrowing are assessed using long standing radiographs.
Two methods for radiographic measurement of the biomechanical alignment of the weight-bearing axis of the knee are used in our facility:
The angle between the femur and tibia on anterorposterior (AP) views obtained with the patient standing
The weight-bearing mechanical axis drawn from the center of the femoral head to the center of the tibiotarsal joint on long (~51 inches/130 cm) standing radiographs (FIG 3A).
If the angle drawn between the tibia and femur shows more than 5 degrees of varus or valgus compared with the normal knee, this amount of axial malalignment would be a relative contraindication for microfracture.
We rely most often on the mechanical axis. It is preferable for the mechanical axis weight-bearing line to be in the central quarter of the tibial plateau of either the medial or lateral compartment.
FIG 3 • A. On this long standing radiographic view, the weight-bearing axis is seen to have shifted somewhat medially in the left knee, but it is significantly shifted in the right knee (green line). B. If the weight-bearing axis falls within the neutral 25% of either compartment (green area), the alignment of the knee would be considered normal. If the weight-bearing axis is between 25% and 50% (yellow area), a realignment procedure should be considered in conjunction with a microfracture chondroplasty. If the weight-bearing axis is greater than 50% (red area) in either compartment, then this would be an absolute contraindication to microfracture unless a realignment procedure was done first or in conjunction with the microfracture. C. MRI clearly shows an acute full-thickness chondral defect, the extent of which is noted by the white arrows. (C: Courtesy of Dr. Charles Ho, Vail, CO.)
If the mechanical axis weight-bearing line falls outside the quarter of the plateaus closest to the center (FIG 3B), either medial or lateral, this weight-bearing shift also would be a relative contraindication if left uncorrected. In such cases, a realignment procedure should be included as a part of the overall treatment regimen.
Standard AP, lateral, and weight-bearing radiographic views with knees flexed to 30 to 45 degrees also are obtained.
MRI that uses newer diagnostic sequences specific for articular cartilage is crucial to our diagnostic workup of patients with suspected chondral lesions (FIG 3C).
DIFFERENTIAL DIAGNOSIS
Meniscus tear
Loose bodies
Attached chondral flap
Symptomatic plica
Synovitis
Chondral bruising, with or without subchondral edema
NONOPERATIVE MANAGEMENT
Patients with acute chondral injuries are treated as soon as practical after the diagnosis is made, especially if the knee is being treated concurrently for meniscus or anterior cruciate ligament pathology.
Patients with chronic or degenerative chondral lesions often are treated nonoperatively (conservatively) for at least 12 weeks after a suspected chondral lesion is diagnosed clinically.
This treatment regimen includes activity modification, physical therapy, nonsteroidal anti-inflammatory drugs, viscosupplement injections, and possibly dietary supplements that may have cartilage-stimulating properties.
If nonoperative treatment is not successful, then surgical treatment is considered.
SURGICAL MANAGEMENT
Microfracture initially was designed for patients with posttraumatic articular cartilage lesions of the knee that had progressed to full-thickness chondral defects.
The microfracture technique still is most commonly indicated for full-thickness loss of articular cartilage in either a weight-bearing area between the femur and tibia or an area of contact between the patella and the trochlear groove.
Unstable cartilage that overlies the subchondral bone also is an indication for microfracture (FIG 4).
If a partial-thickness lesion is probed and the cartilage simply scrapes off down to bone, we consider this a full-thickness lesion.
FIG 4 • The probe (red arrow) shows that this chondral defect has areas of unstable cartilage (black arrows) that are fissured fully to subchondral bone. These unstable cartilage segments must be removed until a stable margin is achieved.
FIG 5 • For the definitive procedure, the distal portion of the table is lowered so that the foot is off the table and the knee is flexed 90 degrees.
Degenerative joint disease in a knee that has proper axial alignment is another common indication for microfracture.
These lesions all involve loss of articular cartilage at the bone–cartilage interface.
Preoperative Planning
All imaging studies are reviewed.
MRI scans are re-reviewed for presence of concomitant pathology.
Radiographs are carefully studied for fractures, loose bodies, axial alignment, and joint space narrowing.
The surgical plan should include addressing concomitant pathology concurrently, as appropriate.
Examination under anesthesia should be accomplished before skin preparation and draping.
Positioning
The patient is positioned supine.
Initially, for the diagnostic portion of the arthroscopy, the foot is on the table.
For the definitive procedure, the distal portion of the table is lowered so that the foot is off the table and the knee is flexed 90 degrees (FIG 5).
A lateral post is raised so that a varus force can be placed on the joint to increase visualization as necessary.
Approach
Our primary approach to chondral lesions is arthroscopic microfracture chondroplasty (Table 1).5–10
TECHNIQUES
DIAGNOSTIC ARTHROSCOPY
Three portals routinely are made about the knee for use of the inflow cannula, the arthroscope, and the working instruments (TECH FIG 1).
Typically, a tourniquet is not used during the microfracture procedure; rather, the arthroscopic fluid pump pressure is varied to control bleeding.
An initial, thorough diagnostic examination of the knee should be done.
All geographic areas of the knee must be inspected carefully, including the suprapatellar pouch, the medial and lateral gutters, the patellofemoral joint, the intercondylar notch and its contents, and the medial and lateral compartments, including the posterior horns of both menisci.
All other intra-articular procedures are done before microfracture.
This technique helps prevent loss of visualization when fat droplets and blood enter the knee from the microfracture holes.
Importantly, particular attention must be paid to soft tissues such as plicae and the lateral retinaculum that potentially could produce increased compression between cartilage surfaces.
TECH FIG 1 • Three portals routinely are made about the knee for use of the inflow cannula (yellow arrow), the arthroscope (black arrow), and the working instruments (green arrow indicates the approximate location where this portal will be made).
INITIAL PREPARATION
After careful assessment of the full-thickness articular cartilage lesion, the exposed bone is débrided of all remaining unstable cartilage.
A hand-held curved curette (TECH FIG 2A) and a full radius resector (TECH FIG 2B) are used to débride the cartilage.
It is critical to débride all loose or marginally attached cartilage from the surrounding rim of the lesion.
The calcified cartilage layer that remains as a cap to many lesions must be removed, preferably with a curette (TECH FIG 2C).
Thorough and complete removal of the calcified cartilage layer is extremely important, based on animal studies we have completed.1,2
Care should be taken to maintain the integrity of the subchondral plate by not débriding too deeply.
This prepared lesion, with a stable perpendicular edge of healthy, well-attached viable cartilage surrounding the defect (TECH FIG 2D), provides a pool that helps hold the marrow clot—”super clot”—as it forms.
TECH FIG 2 • A. A handheld, curved curette is used to remove unstable and damaged cartilage segments. B. A full-radius resector also may be used to remove unstable or damaged cartilage from the lesion in preparation for the microfracture procedure. C. The calcified cartilage layer that remains as a cap to many lesions must be removed, preferably by using a curette as noted by the blue arrow. D. This prepared lesion has a stable perpendicular edge of healthy, well-attached viable cartilage surrounding the defect, as noted by the green arrows. A properly prepared lesion provides a pool that helps hold the marrow clot—”super clot”—as it forms.
MICROFRACTURE
After preparation of the lesion, an arthroscopic awl is used to make multiple holes, or “microfractures,” in the exposed subchondral bone plate.
An awl with an angle that permits the tip to be perpendicular to the bone as it is advanced, typically 30 or 45 degrees, is used.
A 90-degree awl is available that should be used only on the patella or other soft bone. The 90-degree awl should be advanced only manually, not with a mallet.
The holes are made as close together as possible but not so close that one breaks into another, thus damaging the subchondral plate between them.
This technique usually results in microfracture holes that are approximately 3 to 4 mm apart.
When fat droplets can be seen coming from the marrow cavity, the appropriate depth (approximately 2–4 mm) has been reached.
Arthroscopic awls produce essentially no thermal necrosis of the bone compared with hand-driven or motorized drills.
Microfracture holes around the periphery of the defect should be made first, immediately adjacent to the healthy stable cartilage rim (TECH FIG 3A,B).
The process is completed by making the microfracture holes toward the center of the defect (TECH FIG 3C).
TECH FIG 3 • A. An awl is used with an angle that permits the tip to be perpendicular to the bone as it is advanced, typically 30 or 45 degrees. Microfracture holes are made around the periphery of the defect first, immediately adjacent to the healthy stable cartilage rim (purple arrow). B. The microfracture holes are made starting at the periphery of the prepared lesion, keeping the awl perpendicular to the bone. C. The microfracture process is completed by making the microfracture holes (red arrows) toward the center of the defect. The holes are as close together as possible, 3 to 4 mm apart, but without any hole breaking into another and disrupting the integrity of the subchondral bone plate.
ASSESSMENT
The treated lesion is assessed at the conclusion of the microfracture to ensure a sufficient number of holes have been made before reducing the arthroscopic irrigation fluid flow.
After the arthroscopic irrigation fluid pump pressure is reduced, the release of marrow fat droplets and blood from the microfracture holes into the subchondral bone is observed under direct visualization (TECH FIG 4).
The quantity of marrow contents flowing into the joint is judged to be adequate when marrow is observed emanating from all microfracture holes.
Finally, all instruments are removed from the knee and the joint is cleared of fluid.
TECH FIG 4 • Marrow elements, including blood and fat droplets, accessed by the subchondral bone microfracture can be seen coming from essentially all of the microfracture holes (white arrows) after the arthroscopic irrigation fluid pressure has been reduced.
ADDITIONAL CONSIDERATIONS
Intra-articular drains should not be used, because the goal is for the surgically induced marrow clot, rich in marrow elements, to form and to stabilize while covering the lesion.
Chronic degenerative chondral lesions commonly have extensive eburnated bone and bony sclerosis with thickening of the subchondral plate, thus making it difficult to do an adequate microfracture procedure (TECH FIG 5).
In these instances, and when the axial alignment and other indications for microfracture are met, first a few microfracture holes are made with the awls in various locations of the lesion to assess the thickness of the eburnated bone, and then a motorized burr is used to remove the sclerotic bone until punctate bleeding is seen.
TECH FIG 5 • Chronic degenerative chondral lesions commonly have extensive eburnated bone and bony sclerosis with thickening of the subchondral plate, making it difficult to do an adequate microfracture procedure. The black arrow points to a single microfracture hole that has been made to help assess the depth of eburnated or sclerotic bone that must be removed before performing the microfracture procedure.
After the bleeding appears uniformly over the surface of the lesion, a microfracture procedure can be performed as described.
We have observed noticeably improved results for these patients with chronic chondral lesions since we began using this technique. However, if the surrounding cartilage is too thin to establish a perpendicular rim to hold the marrow clot, we probably would not do a microfracture procedure in patients with degenerative lesions that have advanced to that degree.
POSTOPERATIVE CARE
We prescribe cold therapy for all patients postoperatively, and it is continued for 1 to 7 days.5–10
The specific post-microfracture rehabilitation protocol recommended depends on both the anatomic location and the size of the defect.3,4
If other intra-articular procedures are done concurrently with microfracture, such as anterior cruciate ligament reconstruction, we do not hesitate to alter the rehabilitation program as necessary.3
After microfracture of lesions on the weight-bearing surfaces of the femoral condyles or tibial plateaus, we initiate immediate motion with a continuous passive motion (CPM) machine in the recovery room.5–10
The initial ROM typically is 30 to 70 degrees, which is increased as tolerated in 10- to 20-degree increments until full passive ROM is achieved.
The machine usually is set at 1 cycle per minute, but the rate can be varied based on patient preference and comfort.
The goal is to have the patient in the CPM machine for 6 to 8 hours every 24 hours.
If the patient is unable to use the CPM machine, instructions are given for passive flexion and extension of the knee with 500 repetitions three times per day and encouragement to gain full passive ROM of the injured knee as soon as possible after surgery.
Crutch-assisted touchdown weight-bearing ambulation (10% of body weight) is prescribed for 6 to 8 weeks, depending on the size of the lesion.
Patients with lesions on the femoral condyles or tibial plateaus rarely use a brace during the initial postoperative period.
Patients begin therapy immediately after surgery with an emphasis on patellar mobility and ROM, with instructions to perform medial to lateral and superior to inferior movement of the patella as well as medial to lateral movement of the quadriceps and patellar tendons (FIG 6).
FIG 6 • We place great emphasis on patellar mobility and range of motion with instructions to perform medial to lateral and superior to inferior movement of the patella as well as medial to lateral movement of the quadriceps and patellar tendons as shown here.
This mobilization is crucial in preventing patellar tendon adhesions and associated increases in patellofemoral joint reaction forces.
ROM exercises (without ROM limitations), quadriceps sets, straight leg raises, hamstring stretching, and ankle pumps also are initiated the day of surgery.
Stationary biking without resistance and a deep water exercise program are initiated at 1 to 2 weeks postoperatively.
After 8 weeks of touchdown weight bearing, the patient is progressed to weight bearing as tolerated, typically weaning off crutches within 1 week.
Restoration of normal muscular function through the use of low-impact exercices is emphasized during weeks 9 through 16.
Depending on the clinical examination, the patient's size, the sport, and the size of the lesion, we usually recommend that patients not return to sports that involve pivoting, cutting, and jumping until at least 4 to 9 months after microfracture.
All patients treated by microfracture for patellofemoral lesions must use a brace set at 0 to 20 degrees for the first 8 weeks postoperatively to limit compression of the regenerating surfaces of the trochlea or patella, or both.
We allow passive motion with the brace removed, but otherwise the brace must be worn at all times.
Patients with patellofemoral lesions are placed into a continuous passive motion machine set at 0 to 50 degrees immediately postoperatively.
Apart from the ROM setting, parameters for the CPM are the same as for tibiofemoral lesions.
With this regimen, patients typically obtain a pain-free and full passive ROM soon after surgery.
Patients with lesions of the patellofemoral joint treated by microfracture are allowed to bear weight as tolerated in their brace 2 weeks after surgery.
After 8 weeks, we open the knee brace gradually before it is discontinued, and then patients are allowed to advance their training progressively.
Stationary biking without resistance is allowed 2 weeks postoperatively; resistance is added at 8 weeks after microfracture.
Starting 12 weeks after microfracture, the exercise program is the same as that used for femorotibial lesions.
OUTCOMES
With appropriate indications, surgical technique, and especially use of our prescribed rehabilitation program, the success rate of microfracture chondroplasty is approximately 90%.3–10
In a study that followed 72 patients (95% follow-up rate) for an average of 11 years (range, 7–17 years) following microfracture, results showed improvement in symptoms and function in all patients.5
Patient-reported pain and swelling decreased at postoperative year 1 and continued to decrease at year 2, and clinical improvements were maintained over the study period.
Age was the only independent predictor of functional (Lysholm) improvement, with patients over 35 years of age improving less than patients under 35; however, both groups showed improvement.
In National Football League (NFL) players treated with microfracture (FIG 7) between 1986 and 1997, 76% of players returned to play in the NFL the next football season.6
FIG 7 • A. A National Football League player presented with a severe defect of the femoral condyle that measured about 5 × 9 cm. This lesion was treated with the microfracture procedure as described here, and the patient was fully compliant with the rehabilitation protocol. B. Four months after the microfracture procedure a relook arthroscopy was carried out. The blue arrows show the margins of the lesion, which has been completely filled with repair tissue. C. Illustration of how new “repair” cartilage formed over the damaged area.
Those players played an average of 4.6 additional seasons in the NFL.
All players showed decreased symptoms and improvement in function.
Of those players who did not return to play, most had preexisting degenerative changes of the knee.
COMPLICATIONS
Mild transient pain, most often after microfracture in the patellofemoral joint
A grating or “gritty” sensation of the joint, especially when a patient discontinues use of the knee brace and begins normal weight bearing through a full ROM
“Catching” or “locking” as the apex of the patella rides over this lesion during joint motion
Recurrent effusion between 6 and 8 weeks after microfracture, most commonly when beginning to bear weight on the injured leg after microfracture of a defect on the femoral condyle
Decreased ROM due to secondary scarring
REFERENCES
1. Frisbie DD, Morisset S, Ho CP, et al. Effects of calcified cartilage on healing of chondral defects treated with microfracture in horses. Am J Sports Med 2006;34:1824–1831.
2. Frisbie DD, Oxford JT, Southwood L, et al. Early events in cartilage repair after subchondral bone microfracture. Clin Orthop 2003;407:215–227.
3. Hagerman GR, Atkins JA, Dillman C. Rehabilitation of chondral injuries and chronic degenerative arthritis of the knee in the athlete. Oper Tech Sports Med 1995;3:127–135.
4. Irrgang JJ, Pezzullo D. Rehabilitation following surgical procedures to address articular cartilage lesions of the knee. J Orthop Sports Phys Ther 1998;28:232–240.
5. Steadman JR, Briggs KK, Rodrigo JJ, et al. Outcomes of microfracture for traumatic chondral defects of the knee: average 11-year follow-up. Arthroscopy 2003;19:477–484.
6. Steadman JR, Miller BS, Karas SG, et al. The microfracture technique in the treatment of full-thickness chondral lesions of the knee in National Football League players. J Knee Surg 2003;16:83–86.
7. Steadman JR, Rodkey WG, Briggs KK. Microfracture chondroplasty: indications, techniques, and outcomes. Sports Med Arthrosc 2003;11:236–244.
8. Steadman JR, Rodkey WG, Briggs KK. Microfracture to treat fullthickness chondral defects. J Knee Surg 2002;15:170–176.
9. Steadman JR, Rodkey WG, Briggs KK, et al. Débridement and microfracture for full-thickness articular cartilage defects. In: Scott WN, ed. Insall & Scott Surgery of the Knee. Philadelphia: Churchill Livingstone Elsevier, 2006:359–366.
10. Steadman JR, Rodkey WG, Rodrigo JJ. “Microfracture”: surgical technique and rehabilitation to treat chondral defects. Clin Orthop 2001;391S:S362–S369.