SUTURE-LESS AVASCULAR MENISCAL REPAIR: A PRELIMINARY ANIMAL STUDY
*Pollo, FE; *Jackson, RW; **Kane, RR; **Chang, HM; **Zhang, J; *Dieterichs, CP; *Riedel, S
* Baylor University Medical Center; Dallas, TX; ** Baylor University, Waco, TX
INTRODUCTION:
Meniscal injuries are the most common traumatic injury seen in both athletes
and non-athletes, and are second only to osteoarthritis as an etiology of knee
problems. Not surprisingly, meniscal injuries and meniscal deficiencies have
osteoarthritis as their most common sequelae. Many authors have demonstrated
that following total and partial menisectomy, degenerative changes within the
knee are both more likely and more pronounced, although slower to develop
and less severe after partial menisectomy.
To avoid degenerative changes in the knee joint, clinical researchers are
exploring options for healing injuries to the avascular zones in order to restore
the mechanical integrity of the meniscus. New research initiatives have
explored the use of rasping of the tear, gene therapy, various growth factors,
synovial pedicle flaps, fibrin glue, tissue welding, cyanoacrylate glue, collagen
scaffolds, hi-frequency current stimulation, and laser stimulation to promote
healing of meniscal tears.
Our group has some encouraging results with several photoactive dyes that
show promise as collagen-bonding agents for the repair of avascular meniscal
tears [1]. The purpose of this study was to evaluate the ability of two new
photoactive monomeric naphthalimides to repair a small stable lesion in the
avascular zone of the meniscus using a sheep animal model.
METHODS:
A total of ten adult male Barbados sheep were used for this study. Under
general anesthesia, the left knee joint was opened through a medial arthrotomy.
Once the medial meniscus was exposed, two similar lesions were produced
using a #15 scalpel blade. The lesions measured approximately 4 mm in width
and 1-2 mm in depth. One lesion was made in the posterior horn of the medial
meniscus and the other was made in the anterior horn. Both lesions were made
in the inner two-thirds of the meniscus (the avascular zone). The lesion in the
posterior horn was left alone and used as the control for that animal. The lesion
in the anterior horn was repaired using the photoactive laser technique which is
described below.
The laser system used in this study had a wavelength of 457 nm and
maximum output power of 350 milliWatts. The beam diameter for this study
was set at 4 mm, which produced a measured power density of 1.8 Watts/cm2
after some power loss from transmitting through the bottom of the glass test
tube.
After the meniscal lesions were made, approximately 1-2 milliliters of
naphthalimide was introduced into the anterior meniscal lesion using a
micropipette. The glass test tube containing the diode laser hand piece was held
over the lesion against the meniscus applying gentle pressure to the site, and the
lesion was irradiated for a period of 6 minutes. After the lasing procedure, the
joint was flushed with normal saline solution and closed in layers with
resorbable sutures. The animals were transported to a local farm for periods
ranging from 1 month to 3 months. Four animals were sacrificed at the end of 1
month and 6 animals were sacrificed at the end of 3 months. After the animal
was euthanized, the operated knee joint was opened and the medial meniscus
exposed for examination and photography. The medial meniscus was then
dissected free and placed in 10% buffered formalin for histology preparation,
which consisted of staining with hematoxylin/eosin (H&E) solution and
selected sections were stained using Masson’s trichrome and safranin-O-stain.
RESULTS:
Four of the ten sheep were sacrificed after 1 month. Macroscopically,
the four joints appeared normal, without any signs of infection or
synovitis. Upon probing, the unrepaired control lesions all demonstrated
no adhesion. The repaired lesions appeared to still be bonded and could
not be disturbed with minor probing, as could the control lesion.
The H&E stained histological specimens showed all control lesions
unrepaired, with no repair process present (Fig 1a). The experimental
specimens had a distinct area of ruptured meniscus ultrastructure,
consistent with the area of previous surgical intervention (Fig 1b).
However, the most distal ends of these areas appeared to have the most
closed tissue connection. On some sections the edges of the previous
surgical cut were bridged by an eosinophilic “amorphous” appearing
substance. The previous cleft within the fibrocartilaginous structure had
disappeared, and early formation of connective tissue fibers was
identified. However, trichrome stains performed on these sections could
not confirm the formation of mature collagen, and these areas only
appeared rich in proteoglycans.
Six sheep were sacrificed after 3 months. Again, macroscopically all
six joints appeared normal without any evidence of inflammation or
synovitis. Menisci from the three months group of animals sacrificed
again showed an inconsistent pattern of tissue bonding and remodeling
between sections from different animals. In animal menisci with
microscopic evidence of tissue bonding, the presence of eosinophilic
matrix in the formerly introduced cleft again was suggestive of early
tissue bonding and formation of connective tissue fibers and matrix.
However, there was no evidence of a consistent filling of these tissue
clefts with the eosinophilic matrix and no definitive (mature) collagen
formation was present.
Figure 1a (control)
Figure 1b (treated)
DISCUSSION:
These preliminary results demonstrate that this technique has
significant potential for bonding meniscal tissue in the avascular zone. In
both the 1 month and 3 month cohorts, gross mechanical examination of
each of the treated lesions revealed significant bonding while the control
lesions showed no healing at all. The majority of the tissue sections
demonstrated a eosinophilic matrix with formation of early, immature
connective tissue fibers. Indeed, some of these fibers did show some
crosslinking. These findings are interpreted as tissue bonding, and a
possible early healing response. However, the loss of cellularity in the
treated regions is of significant concern, and could in fact question the
theory of a healing response within the treated tissue. A true form of
healing and repair constitutes the presence of viable cells, cellular
proliferation, and the production of a viable matrix. Extreme
hypocellularity in the areas of interest is almost incompatible with a true
repair process or healing response of the tissue. In this instance, the
presence of an eosinophilic bonding matrix, as described in the histologic
sections, has to be considered a response to either laser effect or the dye
used in the specific animal. These preliminary results demonstrate the
potential usefulness of this photochemical bonding for the treatment of
avascular meniscal lesions. The observed problems such as decreased
cellularity and irregular bonds are currently being addressed by careful
compound and experimental design. Future investigations will focus on
demonstrating the formation of a ‘healthy’ bond using our experimental
model, as well as on the repair of more clinically relevant lesions using
arthroscopic techniques.
REFERENCES:
1. Jackson RW, et al., Repair of Articular Cartilage and Meniscal
Tears by 1,8-Naphthalimide Dyes: In Vivo Study. Arthroscopy
1997;13:392.
ACKNOWLEDGMENT:
We would like to acknowledge Genzyme BioSurgery for their support
of this study.
50th Annual Meeting of the Orthopaedic Research Society
Poster No: 1236