This article is found in the Journal of Plastic and Reconstructive Surgery Oct. 2011 issue. It is original bench-top research that demonstrates that a flexor tendon can be repaired without knots while remaining as strong as some traditional repairs.

1. HAND/PERIPHERAL NERVE
A Knotless Flexor Tendon Repair Technique
Using a Bidirectional Barbed Suture: An Ex
Vivo Comparison of Three Methods
W. Thomas McClellan, M.D.
Background: Flexor tendon repairs using conventional suture require knots
Matthew J. Schessler, M.D. that enlarge the cross-sectional area at the repair site. This enlargement in-
David S. Ruch, M.D. creases the force of finger flexion and jeopardizes the integrity of a nascent
L. Scott Levin, M.D. tendon repair during rehabilitation. The authors hypothesized that a knotless
Richard D. Goldner, M.D. flexor tendon repair using bidirectional barbed suture has similar strength and
Morgantown, W.Va.; Durham, N.C.; with reduced cross-sectional area compared with traditional techniques.
Philadelphia, Pa. Methods: Sixty-six fresh porcine flexor digitorum profundus tendons were di-
vided randomly into three groups. Tendons were transected and repaired with
one of the following techniques: two-strand Kessler technique, four-strand Sav-
age technique, or four-strand knotless technique. The cross-sectional area of
each tendon was calculated at the repair site before and after repair. All tendons
underwent mechanical testing to assess the 2-mm-gap formation force and
ultimate strength.
Results: The 2-mm-gap formation force and ultimate strength of the Savage and
knotless technique groups were not significantly different; however, both were
significantly greater than those of the Kessler repair group (p 0.05). The
repair-site cross-sectional area of tendons repaired with the knotless technique
was significantly smaller than that of tendons repaired with the Kessler or Savage
technique (p 0.01). Tendons repaired with the knotless technique also had
a significantly smaller change in repair-site cross-sectional area (p 0.01).
Conclusions: The authors demonstrate that knotless flexor tendon repair with
barbed suture has equivalent strength and reduced repair-site cross-sectional
area compared with traditional techniques. The smaller tendon profile may
decrease gliding resistance, thus reducing the risk for postsurgical tendon
rupture during rehabilitation. (Plast. Reconstr. Surg. 128: 322e, 2011.)
F
lexor tendon lacerations are devastating in- Tendon repairs have traditionally been per-
juries that hand surgeons all-too-commonly formed with permanent suture that requires knots
encounter. These injuries require surgical either inside or outside the tendon. Knots are the
repair to restore the patient’s function. Despite a weak point of the tendon repair,1,2 cause de-
plethora of research, the basis of primary flexor creased tendon apposition,3 and are operator de-
tendon repair has changed little since the 1970s. pendent. However, several studies show a positive
correlation between suture caliber and number of
knots with strength of repair.4 – 6
Early active motion rehabilitation protocols re-
From the Department of Surgery, Section of Plastic Surgery, quire strong tendon repairs. These protocols have
West Virginia University School of Medicine, the Department greatly improved patients’ function after surgical re-
of Orthopaedic Surgery, Duke University School of Medicine, pair of flexor tendon lacerations by decreasing ad-
and the Department of Orthopaedic Surgery, Hospital of the
hesions and increasing the repair’s strength.5,7 Sev-
University of Pennsylvania.
Received for publication August 6, 2010; accepted March 8,
2011.
Presented at Plastic Surgery 2010: 79th Annual Meeting of
the American Society of Plastic Surgeons, in Toronto, On- Disclosure: The authors have no financial interest
tario, Canada, October 1 through 5, 2010. in the products or surgical techniques employed in
Copyright ©2011 by the American Society of Plastic Surgeons this study.
DOI: 10.1097/PRS.0b013e3182268c1f
322e www.PRSJournal.com

2. Volume 128, Number 4 • Knotless Flexor Tendon Repair
eral studies indicate that friction created by Table 1. Brief Description of Tendon Repair Methods
tendons gliding against pulleys during active finger Group
flexion increases load.5,8,9 In addition, increased su-
ture caliber and number of knots increases tendon Group A B C
cross-sectional area, causing increased gliding No. of
resistance.4,10 This increased load endangers the nas- tendons 22 22 22
Repair Modified Modified
cent repair during active rehabilitation. Clearly, one technique Kessler Savage Knotless
must balance repair strength with the increased ten- No. of
don cross-sectional area within the tendon sheath. strands 2 4 4
Suture 3-0 Ethibond 3-0 Ethibond 0 barbed
We hypothesized that a four-strand knotless tendon
repair using a bidirectional barbed suture has com-
parable strength and reduced repair-site cross-sec-
tional area when compared with traditional flexor nonabsorbable, 3-0 braided polyester suture (Ethi-
tendon repairs. bond Excel; Ethicon, Inc., Somerville, N.J.), whereas
the knotless repair was performed using barbed,
nonabsorbable, 0-diameter monofilament polypro-
MATERIALS AND METHODS pylene suture (Quill SRS; Angiotech, Inc., Vancou-
Sixty-six fresh flexor digitorum profundus ten- ver, British Columbia, Canada). The 0-diameter su-
dons were obtained from adult pigs. These tendons ture was selected because of its similar strength to 3-0
have been used frequently in prior studies because polyester.17,18 A core suture purchase of 1 cm was
they are similar in structure and strength to a human used on all repairs.11,14
middle finger flexor tendon.11–15 The tendons were
examined for abnormalities such as synovitis and Knotless Repair Technique
degeneration, and were rejected if an abnormality
was present. Although a novel repair method, the knotless
technique incorporates elements of both the mod-
ified Kessler and the Savage methods. The knotless
Cross-Sectional Area Measurements method uses four strands and a locking grasp of the
Each tendon’s height and width were measured epitenon. A diagram of our technique is shown in
at the repair site and 1 cm proximal and distal to the Figure 1. The barbed repair first incorporates a
repair site using a Brown & Sharpe IP67 digital cal- straight pass through the tendon until the barbs
iper (part no. 00530300; Hexagon Metrology, Inc., catch the opposite side of the tendon. Then, the
North Kingstown, R.I.). The measurements were an- double-armed suture is passed back through the cen-
alyzed to ensure all tendons were a similar size. The tral core of the tendon to the transection site. The
cross-sectional area at each site was calculated using central core limbs of the barbed repair are then
the formula for area of an ellipse (area ab, where passed diagonally across the tendon twice and an
a equals one-half tendon height and b equals one- external bite of the epitenon is performed. The di-
half tendon width). Measurements were taken at all agonal passes serve two purposes. First, they increase
three sites before tendon transection and after re- the number of barbs within the tendon substance.
pair to determine prerepair and postrepair cross- Second, the diagonal passes allow for multiple grasps
sectional area. Blinded intrarater analysis was con- of the epitenon. Finally, the external bite locks the
ducted both before transection and after repair to suture onto itself and then a mirror stitch is applied to
ensure measurement consistency. the initial tendon. A running epitendinous suture was
not performed so that only the core suture strength was
Repair analyzed.
The tendons were divided randomly into three
repair groups (A, B, and C), transected, and then Biomechanical Testing
repaired as described in Table 1. After repair and surface area measurement,
All knots in groups A and B received six throws each tendon was secured into the clamps of a
to maximize effectiveness.1,16 The modified Kessler tensiometer (model 4411; Instron Corp., Canton,
technique was chosen to represent a two-strand Mass.) with a load cell of 500 N. The clamps have
grasping technique and the modified Savage tech- a broad surface that prevented tendon slippage
nique was chosen to represent a four-strand locking during testing. The upper clamp had a preload of
technique. One surgeon (W.T.M.) performed all 1.5 N and was advanced at a rate of 20 mm/minute
repairs under 3.5 loupe magnification. The mod- The preload and rate were selected because they
ified Kessler and Savage repairs were performed with best simulate forces acting on an immobilized ten-
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3. Plastic and Reconstructive Surgery • October 2011
Fig. 1. Diagram of the four-strand knotless flexor tendon repair technique.
don during active flexion.7,11,12,19,20 The linear dis- Table 2. Data from Mechanical Strength Testing of
traction was monitored with a video camera and Tendon Repairs Including 2-mm-Gap Formation
the digital caliper (previously noted) was placed Force, Ultimate Strength, and Mode of Failure
near the repaired tendon. The force and tendon
Tensile Strength (N) Failure Mode
displacement were recorded by Instron Series 9
software. The force that produced a 2-mm gap Repair 2-mm-Gap
between tendon halves at the repair site was re- Method Formation Ultimate Rupture Pullout
corded as the 2-mm-gap formation force. Linear Knotless 62.84 17.30 72.39 15.16 18 4
distraction continued until the sutures were pulled Savage 59.22 15.12 69.18 8.96 22 0
Kessler 23.45 5.32 32.03 5.36 17 5
out or ruptured. In all cases, the greatest force oc-
curring immediately before repair failure was re-
corded as the ultimate strength. The mode of repair Table 3. Comparison of Postrepair
failure was reported as pullout or rupture. An ob- Cross-Sectional Area*
server blinded to the tendon repair technique per-
Repair Site
formed all mechanical strength testing. Cross-Sectional Area (mm2)
RESULTS Repair Absolute Change
Technique Size (vs. native tendon)
Power analysis was performed to ensure a large
Knotless 24.4 7.10 4.58
enough sample size. For 0.80 power, seven tendons Savage 31.9 13.6 3.35
were needed in each group. The 2-mm-gap forma- Kessler 32.3 14.3 5.55
tion force, ultimate strength, and cross-sectional *The knotless technique had a significantly smaller tendon size and
area data were analyzed with one-way analysis of vari- change in cross-sectional area compared with the Kessler and Savage
techniques.
ance. A log transformation of the 2-mm-gap force
and ultimate strength data were taken before anal-
ysis of variance. Intergroup reliability was checked. 2-mm-gap formation force for tendons repaired by
Values of p 0.05 were considered significant. the Savage method was 59.22 N. Tendons repaired
The 2-mm-gap formation force results, ulti- with the modified Kessler method required 23.45
mate strength results, and mode of failure are N to form a 2-mm gap. The knotless and Savage
listed in Table 2, and changes in tendon dimen- methods demonstrated a significantly greater
sions are listed in Table 3. All values are reported 2-mm-gap formation force than the Kessler
as mean SD. Results are depicted graphically in method (p 0.05). However, no significant dif-
Figures 2 and 3. Mode of failure is reported as ference in 2-mm-gap formation force existed be-
either suture rupture or suture pullout. Rupture tween the knotless technique and the Savage
failure means the strands or knots broke. Pullout method.
failure means that the strands tore from the ten-
don without breaking. Ultimate Strength
The force causing ultimate failure is reported
2-mm-Gap Formation Force in Figure 2 and Table 2. Tendons repaired by the
Forces necessary to produce a 2-mm gap at the knotless method withstood 72.39 N before failing.
repair site are reported in Figure 2 and Table 2. The ultimate failure force for tendons repaired by
Tendons repaired by the knotless method pos- the Savage method was 69.18 N. Tendons repaired
sessed a 2-mm-gap formation force of 62.84 N. The by the modified Kessler method ultimately failed
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4. Volume 128, Number 4 • Knotless Flexor Tendon Repair
Fig. 2. Comparison of tensile strength among tendon repair techniques. Average
2-mm-gap formation force (yellow bars) and ultimate strength (blue bars) are
shown for each tendon repair technique. Knotless and Savage repairs were signif-
icantly stronger than the Kessler repairs (p 0.05). Knotless and Savage methods
were not significantly different in strength.
DISCUSSION
McKenzie first reported using a unidirectional
barbed steel wire to repair flexor tendons in
1967.21 His repair showed theoretical advantages
compared with traditional repair techniques, but
the use of a barbed suture repair was lost to the
literature until recently.22,23 Current barbed suture
technology has advanced radically. Barbed sutures
are bidirectional, with barbs spiraling around the
central core suture. Barbed suture can now be
Fig. 3. Comparison of postsurgical cross-sectional area among created using absorbable and nonabsorbable ma-
tendon repair techniques. Average cross-sectional area at the re- terials, unlike the original steel wire description.
pair site is shown for each repair technique. The knotless method Using these types of materials is advantageous for
had a significantly smaller cross-sectional area than the Savage or tendon repair.
Kessler method. According to Strickland, the ideal character-
istics of a primary flexor tendon repair include
secure and easily placed sutures to allow for early
at 32.03 N. The knotless and Savage methods dem- postsurgical mobilization, smooth apposition of
onstrated a significantly greater ultimate strength
the tendon sections, minimum gapping forces,
than the Kessler method (p 0.05). However, no
and minimal tendon vasculature disturbance.24,25
significant difference in ultimate strength was ob-
Trail et al. listed the ideal suture characteristics as
served between the knotless technique and the
having high tensile strength and being inexten-
Savage method.
sible, absorbable, and, most importantly, easy to
use.1,2 No current technique or suture meets all of
Cross-Sectional Area the criteria of Strickland and Trail et al.
The postrepair cross-sectional area for each Traditional flexor tendon repair techniques
tendon repair technique is reported in Figure 3. rely on knots either within the tendon or posi-
The change in tendon size with the knotless tech- tioned externally. When the knots lie within the
nique was significantly less than with the Savage tendon, they may also impede the tendon’s ulti-
and Kessler techniques (p 0.01). No significant mate healing potential because of interposition of
difference was observed in cross-sectional area the knot between the tendon halves.3,26 When us-
proximal or distal to the repair site among the ing a nonabsorbable suture, a permanent obstruc-
techniques (Fig. 4). tion is placed between the tendon ends. With a
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5. Plastic and Reconstructive Surgery • October 2011
Fig. 4. An unrepaired tendon (below) and a tendon repaired with the
knotless technique (above).
knotless repair, there is no knot interposition be- The knotless method does not decrease the
tween the tendon ends, so the potential exists for difficulty of flexor tendon repair or change its
better healing and increased long-term strength. indications. Further study of this four-stranded
Knots within the repair site do not affect the knotless technique should include cyclical loading
repair’s overall strength unless they are greater and angular tensile strength. Cyclical loading stud-
than 26 percent of the tendon’s cross-sectional ies would be important to determine the risk of
surface area.3 Although larger suture calibers im- barbed sutures slicing through the freshly re-
part greater strength to the tendon repair, they are paired tendon during early, active rehabilitation.
harder to manipulate and create larger knots.6,26 Angular tensile strength studies would more
Some authors have even recommended at least closely resemble forces acting on the tendon dur-
five throws to create a secure knot.1,16 In addition, ing rehabilitation.
increased foreign material within a repair site has Another weakness of our study is the lack of
been shown to decrease wound healing by stim- clinical data and outcomes from application in
ulating an inflammatory response.26 Although patients. In vivo studies should certainly be per-
large knots impart greater repair strength, they formed to assess repair healing and its environ-
are less than ideal because of their deleterious mental interactions in an animal model. Success-
effect on healing and increased tendon profile. ful application and outcomes in patients would
Bulky knots increase the tendon’s cross-sec- allow the knotless four-stranded technique to be
tional area, thus increasing gliding resistance dur- incorporated into clinical practice.
ing active flexion.4,10,27–29 Furthermore, this in-
creased load at the repair site can cause gap CONCLUSIONS
formation and failure.7,9,30
This report shows that our four-stranded knot-
Furthermore, knots have been shown to im- less technique yields a repair as strong as a con-
pede vasculature.29,31–33 This deprives the ten- temporary four-stranded method but with a
don of vital nourishment necessary to heal, caus- smaller cross-sectional area. Because our repair is
ing extrinsic neovascularization and adhesion as strong as current techniques and has a lower
formation.34 tendon profile, further ex vivo and in vivo studies
One way to prevent the problems caused by are warranted. Our knotless technique may im-
knots is to completely eliminate them. We report prove outcomes in patients with zone II flexor
a four-strand knotless flexor tendon repair tendon lacerations by allowing for more aggressive
method using a bidirectional barbed suture. Our rehabilitation with reduced risk of repair failure.
results show no significant difference in repair
strength between the four-strand knotless tech- W. Thomas McClellan, M.D.
nique and the criterion standard four-strand Sav- Morgantown Plastic Surgery Associates
age technique. Most importantly, the four-strand 1085 Van Voorhis Road, Suite 350
Morgantown, W.Va. 26505
knotless method creates a lower tendon profile at wtmcclellan@yahoo.com
the repair site. It is plausible that decreasing the
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