Biomedical Engineering Reference
In-Depth Information
or more during which a balance is achieved between new tissue
biosynthesis and degradation (16).
In patients with normal wound healing, investigators found
persistent fi broblast activity similar to the proliferation phase at
4 months and that most scars fade at about 7 months, but a con-
siderable proportion had persistent redness at 12 months (17,18).
As stated by Roseborough et al. (6), the most important fac-
tors that are known to contribute to the degree of scar forma-
tion are the extent and duration of infl ammation, the degree
of mechanical tension on the wound, and the genetic pheno-
type of the patient. Control of infl ammation is paramount in
the prevention of excessive scarring. That includes prevention
of infection, removal of foreign bodies in the wound, preven-
tion of mechanical abrasion or irritation of the wound, and
maintenance of a moist environment. However, the failure of
anti-infl ammatory therapies to improve fi broproliferative dis-
eases such as pulmonary fi brosis suggests that factors other
than infl ammation may be critical (17). Areas of investigation
include direct inhibition of cytokine elaboration, fi broblast
proliferation, and ECM deposition (19).
The complexity of the wound healing process dictates that a
multifaceted approach is used in the prevention of scarring as
well as in improving the cosmetic appearance of scars. Those
facets include (
i
) surgical—use of appropriate surgical princi-
ples in primary procedures as well as in revisions of scars;
(
ii
) medical—use of topical and intralesional (IL) medications
that may infl uence the wound healing cascade or decrease
infl ammation; (
iii
) laser intervention—use of various lasers to
improve the color, texture, and contours of scars.
The fi rst report of treatment of hypertrophic scars and keloids
with a laser was by Ginsbach and Kuhnel (20) about argon laser
treatment of keloids in 1978. Hulsbergen-Henning et al. (21)
reported temporary improvement in keloids treated with the
argon laser, but Apfelberg et al. (22) reported no improvement
in 13 keloids treated with the argon laser. Proposed mechanisms
of action have been coagulation of capillaries leading to local-
ized tissue anoxia (20) and heat conduction causing dermal
shrinkage (21).
The CO
2
laser has also been reported as useful in the man-
agement of keloids. Used as a continuous wave beam for exci-
sion of keloids, Bailin (23) reported success in 1982, which he
attributed to its nontraumatic and anti-infl ammatory proper-
ties. However, others were not able to confi rm his fi ndings, and
recurrences as high as 90% were reported (22,24,25).
The use of a high-energy, short-pulsed (<1 ms) CO
2
laser
was much more successful. Bernstein et al. (26) reported in
1998 their results of using CO
2
lasers with these characteristics
to treat 24 patients with postsurgical hypertrophic and keloidal
scars as well as six patients with traumatic, acne, or varicella
scars. All 30 patients showed greater than 50% improvement.
The erbium laser (Er:YAG, 2940 nm) has a coeffi cient of
absorption for water that is 16 times greater than that of the
CO
2
laser. This results in enhanced tissue vaporization and
much less residual thermal damage (27,28). It is interesting
that Bailin (23) considered the CO
2
laser to be nontraumatic
and anti-infl ammatory. It is the senior author's observation
(REF) that thermal injury is very infl ammatory and this needs
to be carefully controlled. The ablative effects of the erbium
laser are much less infl ammatory but also do not result in
hemostasis, which make its use problematic. However, the
combined use of pulsed CO
2
followed by pulsed erbium can
result in a much less infl ammatory wound. Used in this man-
ner a hypertrophic scar or sharply defi ned atrophic scar can be
carefully sculpted to achieve a smoother surface (27,28).
The principles of selective photothermolysis (29) revolu-
tionized the fi eld of cutaneous laser surgery. By adhering to
these principles, the short-pulsed CO
2
laser can be used with
minimal residual thermal damage. It is this characteristic that
makes the UltraPulse CO
2
laser appropriate for use in some
cases of hypertrophic scarring and keloids.
The use of these same principles with the 585-nm pulsed
dye laser (PDL) resulted in a successful treatment of atrophic,
hypertrophic, and keloid scars. Alster et al. (30) reported
improvement in erythema, skin texture, and fl attening of
hypertrophic portions of scars. Ten scars received fi ve treat-
ments over a 10-month period. These scars had been present
for 15-120 months prior to treatment. PDL treatment of
14 erythematous hypertrophic scars present for a minimum of
2 years resulted in 57% and 83% improvement after one and
two treatments (31). Treatment parameters were a pulse
duration of 0.45 ms and a fl uence of 6.5-7.25 J/cm
2
with a
5-mm spot size. Dierickx et al. (32) found similar results using
the PDL to treat erythematous hypertrophic scars. Goldman
and Fitzpatrick (33) treated 48 hypertrophic and erythema-
tous scars. Thirty-seven were treated with PDL alone, while
eleven received concomitant IL corticosteroid [triamcinolone
acetonide (TAC), 5-10 mg/mL]. Those scars treated with both
modalities achieved greater resolution than those receiving
only PDL treatment. An average of 4.4 treatments was needed
for objective clinical improvement. Alster and Williams (34)
used 585-nm PDL treatment to one-half of median sternot-
omy hypertrophic scars, using the untreated half as a control.
They compared optical profi lometry, clinical, histological, and
symptomatic responses. Signifi cant improvement was seen in
all parameters in the treated half versus the control half.
Manuskiatti and Fitzpatrick (35) reported that 585-nm PDL
using a pulse width of 0.45 ms was more effective in decreasing
scar size and improving scar pliability than a pulse of 40 ms.
Wittenberg et al. (36) and Alster (37) reported randomized
controlled trials combining silicone gel sheeting (36) and IL
steroid injections (37) with PDL versus PDL alone. Both trials
found PDL to be effective, but no added benefi t with combin-
ing the second modality (38). This conclusion has not been
supported by other studies, which will be reviewed in other
sections of this chapter.
Nonoverlapping laser pulses with fl uences of 6.0-7.5 J/cm
2
using a 7-mm spot or 4.5-5.5 J/cm
2
with a 10-mm spot have
been recommended for treatment of hypertrophic scars and
keloids. In the experience of the senior author (REF), these
parameters work well, when used with a 6- or 10-ms pulse
width. Tanzi and Alster (39) found that two to six treatment
sessions may be needed to successfully improve scar resolu-
tion, which includes scar color, height, pliability, and texture.
Alster and McMeekin (40) reported improvement in facial
acne scars after treatment with the 585-nm PDL and Alster
and Nanni (41) reported improvement in hypertrophic burn
scar using this same laser.
A review (42) of the use of the PDL for nonvascular lesions
revealed several reports showing better clinical improvement
using low-to-moderate fl uences that do not cause purpura.
