The Technique and Results of
Microfracture for the Treatment of
Articular Cartilage Defects in the Knee
Thomas J. Gill, M.D.
Visiting Assistant Professor
Harvard Medical School
Department of Orthopedic Surgery
Massachusetts General Hospital
15 Parkman Street
Boston, MA
02114
617-726-7797
617-726-3438 (FAX)
J. Richard Steadman, M.D.
Steadman Hawkins Clinic
181 W. Meadow Drive
Vail, CO
81657
Microfracture
Surgical Technique
The
patient is placed in the supine position on the operating table. Standard
arthroscopic portals are established. A tourniquet is not routinely used. Prior
to addressing the chondral defect, a careful arthroscopic assessment of the
entire joint is performed. Associated pathology such as a meniscal tear or
loose body is addressed prior to performing the microfracture.
The chondral surfaces are then
examined. Care is taken to exam all chondral surfaces, including the posterior
aspects of the medial and lateral femoral condyle, and the medial and lateral
facet of the patella. If any superficial chondral changes are noted, a probe is used to assess the firmness
and stability of the tissue. Any unstable chondral flaps are sharply debrided
using an arthroscopic shaver or currette. Typically, the size of the resulting
defect is significantly larger than originally noted. However, articular
cartialge has no ability to heal to the underlying subchondral bone once it has
delaminated, and an attempt should generally not be made to preserve this
tissue. Such an attempt would jeopardize the ability of the repair tissue to
heal to the surrounding articular cartilage.
A currette is then used to
debride the calcified cartilage layer from the base of the full-thickness
defect. Removal of the calcified cartilage layer greatly enhances the percentage
of the defect that is filled. This is presumably due to providing a better
surface for the “superclot” to adhere to, while allowing improved
chondral nutrition through subchondral diffusion. The calcified zone is
separated from the tangential, transitional and radial zones by the tidemark.
In the immature animal, the basal layers of cartilage are partially nourished
by diffusion from the vasculature of the subchondral bone. In the adult, little
if any nutrient is able to diffuse across the tidemark due to heavy deposition
of apatites in the calcified zone (2,3). The calcified zone also functions as
an efficient barrier to cellular invasion. This has been used to explain the
apparent immunity of cartilage transplants to the allograft rejection process
(i.e. mechanical rather than immunologic) (1). Removal of this calcified zone
not only may allow a better bed for adhesion of the fibrin clot, but may
improve the nutrition of the repair tissue by expediting the diffusion of
nutrients from the subchondral circulation.
A shaver is not generally used
to remove the calcified cartilage layer except on a sclerotic tibial surface.
It is more difficult to control the amount of bone removed when using a
motorized shaver, and the subchondral bone is more likely to be violated. If
this occurs, it can have a destabilizing effect on the overall alignment of the
knee.
A
surgical awl (Linvatec, Largo, FL) is used to make multiple small holes
(“microfractures”) in the exposed bone of the chondral defect. The
holes are spaced 1-2mm apart. Care is taken not to connect the holes.
Microfracture is initiated on the most peripheral aspects of the chondral
defect. This area must be carefully addressed in order to aid the healing of
the repair tissue to the surrounding stable articular surface. The
microfracture method is preferred because it creates less thermal injury than
drilling, is able to access difficult areas of the articular surface, and
provides controlled depth penetration. Upon completion, a rough surface is generated
for adherence of the ensuing blod clot containing the undifferentiated
mesenchymal cells from the subchondral bone. Once the microfracture is
complete, the pressure on the arthroscopic pump is decreased. Marrow bleeding
is observed emanating from the small holes and filling the defect.
Perhaps equally important as the surgical
technique is the post-operative management. Unlike the typical rehabilitation
following debridement and drilling procedures, patients are kept at protected
weight-bearing for six to eight weeks. Additionally, they are sent home with a
continuous passive motion (CPM) machine for eight weeks (4). If CPM is not
available for any reason, they are instructed to perform a full knee range of
motion 1500 times per day.
Post-operative weight-bearing
status depends on the location of the lesion. Patellar and trochlear groove
lesions may be weight-bearing as tolerated in a hinged-brace from 0-30 degrees.
This restricted flexion while weight-bearing prevents excessive pressure in the
patellofemoral joint, since the patella does not engage the trochlear groove
until after 30 degrees of flexion. The brace may be removed while the patient
is not weight-bearing. A CPM machine is initiated from 10-90 degrees for at
least 8-10 hours per day (generally at night). If they are unable to use a CPM
machine, they are instructed to cycle their knee over the edge of a table 1500
times per day.
If the chondral defect is in
the medial or lateral compartment, the patient is kept strictly touch-down
weight bearing (15% weight bearing), with a similar CPM protocol to that used
in patellofemoral lesions. The CPM machine is set at one cycle per minute,
using the largest ROM that the patient finds comfortable. If the lesions are in
non-weight bearing regions of the compartments, weight-bearing may begin as
early as six weeks post-operatively, depending on the size of the affected
area.
Following
the six to eight week period of protected weight-bearing, patients are
instructed to begin active ROM exercises and progress to full-weight bearing.
No cutting, twisting or jumping sports are allowed until at least four months
post-operatively.
At the present time, there is no universally accepted system for measuring the outcome of treatment for chondral defects. Systems such the IKDC are better suited to ligament reconstruction surgery, while the HSS and WOMAC scores are more appropriate for the evaluation of arthritis surgery. The International Cartilage Repair Society has recently proposed a comprehensive system for objective outcome assessment. However, it is rather complex and difficult to use clinically.
The authors have proposed a simple, patient-based scoring system for the evaluation of patients with chondral defects (Fig. 1). A classification of chondral defects was also developed in order to help standardize comparisons between various types of treatments, while giving prognostic information regarding the clinical result of the treatment for a given lesion (Fig. 2).
The first study on the
long-term results of microfracture for traumatic chondral defects was recently
completed by the authors at the Steadman Hawkins Sports Medicine Foundation.
Over one hundred patients were reviewed who had a microfracture for a
full-thickness chondral defect. The average follow-up was six years. Using a
scoring system designed specifically for the treatment of chondral defects (Fig.
1), patients were objectively assessed evaluated based on their pre- and
post-operative examinations.
Microfracture resulted in
statistically significant improvement (p<0.05) in pain, swelling, and all
functional parameters studied. The ability to walk two miles and descend stairs
demonstrated significant improvement. The ability to perform activities of
daily living, strenuous work and strenuous sports also demonstrated significant
improvement. Of note, improvement in symptoms of pain and swelling continued to
be seen until two years post-operatively. Maximum functional improvement was
not achieved until two to three years post-operatively.
Eighty-six
percent of patients rated their knee as feeling normal to nearly normal
following their microfracture. Only 14% of patients had their level of sports
participation reduced following microfracture.
There was no statistically
significant difference in outcome between patellofemoral lesions, medial
compartment lesions, and lateral compartment lesions. Larger lesions tended to
have more pain at final follow-up than smaller lesions, though this was not
statistically significant. Chondral defects treated within three months of
injury had significantly less pain and better scores for their activities of
daily living than defects treated greater than three months from injury,
regardless of lesion size.
Unlike other techniques of chondral re-surfacing such as autologous chondrocyte transplantation or mosaicplasty, microfracture can be used for the treatment of degenerative chondral lesions. The use of microfracture for the treatment of degenerative lesions in eighty patients over the age of fifty years with osteoarthrosis of the knee was also studied by Gill and Steadman (unpublished data). Outcome analysis was performed using the IKDC scoring system as an objective assessment of the long-term clinical results.
There
was a significant improvement in outcome with regard to subjective complaints
of pain and swelling. Microfracture resulted in a statistically significant
improvement in the ability to walk two miles, run, climb stairs, perform
strenuous work, perform strenuous sports, and perform activities of daily
living. Maximum functional improvement was not achieved until two to three
years post-operatively.
Seven microfractures were
classified as a failure due to the need for a subsequent procedure, including
five total knee arthroplasties. Risk factors for a poor result included
chronicity of the lesions and severity of pre-operative joint space narrowing.
Alignment also played a significant role in outcome following microfracture.
The microfracture technique is cost-effective, not technically challenging, and highly efficacious procedure. It is available to all surgeons who perform arthroscopy of the knee. It is a reasonable first approach to the treatment of chondral defects, since it does not “burn any bridges” with regard to future procedures such as a mosaic-plasty or autologous chondrocyte transplant should the microfracture fail.
Fig. 1
Chondral Defect
Scoring System
Subjective
(60)
Pain (20)
20 - none
15 - mild, activity related
10 - moderate, activity related
5 - unable to perform sports
0 - pain at rest
Ability to
perform sport / work (20)
10 - no restrictions
5 - mild
decrease in performance
0 - unable to
compete / work at same level
Swelling (10)
10 - none
5 - sports /
activity related
0 - with
ADL’s
Locking
10 - none
0 - intermittent
locking
Objective (40)
Range of Motion
(10)
10 - full ROM compared to opposite knee
5 - lacks 5-10
degrees flexion and/or extension
0 - lacks >
10 degrees flexion and/or extension
Effusion (10)
10 - none
5 - mild
0 - moderate to
severe
Ability to
Perform Knee Bends (10)
10 - without difficulty
5 - mild
discomfort
0 - unable
Pain with Varus
/ Valgus stress on ROM (10)
10 - none
5 - mild
0 - moderate to
severe
Fig. 2
Classification
of Traumatic Chondral Defects
I - partial thickness A
- Acute (< 12 weeks from injury)
II - full-thickness, less than 400 mm2 B - Chronic (> 12
weeks from injury)
III -
full-thickness, greater than 400 mm2
Classification Prognosis Treatment
I-A Excellent None; debridement
I-B Excellent None; debridement
II-A Excellent / Good Microfracture;
6-8 weeks CPM / TDWB
II-B Excellent
/ Good Microfracture;
8 weeks CPM / TDWB
III-A Good Microfracture;
6-8 weeks CPM / TDWB
III-B Good
/ Fair Microfracture; 8
week CPM / TDWB
1. Brown KLB, Cruess RL: Bone and cartilage
transplantation in orthopaedic surgery.
J Bone Joint Surg 64-A: 270-279, 1982
2. Mankin HJ: The articular cartilages: a
review. AAOS Instructional Course
Lectures, 204-224, 1969
3. Mankin HJ: The reaction of articular
cartilage to injury and osteoarthritis.
New Eng J Med 291: 1285-1292, 1974
4. Rodrigo J, Steadman JR. Improvement of full-thickness chondral
defect healing in the human knee after debridement and microfracture using
continuous passive motion. Am J Knee Surg 1994; 7:109-116.