Keywords
internal brace - scapholunate instability - scapholunate reconstruction - suture tape
- internal brace augmentation
Scapholunate (SL) joint instability is one of the most common injuries of the wrist
joint and may result from a fall or high energy mechanism on the outstretched hand.
If unrecognized, the injury may lead to functional impairment and posttraumatic arthritis.[1]
[2]
[3]
Since its initial description,[4] a myriad of different surgical techniques have been devised with varied success.
These include capsular shrinkage, dorsal capsulodesis, reduction-association with
a screw of the scapholunate joint (RASL), scapholunate axis method (SLAM), bone ligament
bone grafts, and a variety of tendon reconstruction.[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12] Many of these constructs require prolonged immobilization with Kirschner (K) wire
stabilization, which may break, become infected, or require a secondary procedure
for their removal. In addition, the outcomes of scapholunate reconstructions can be
unpredictable. Possible explanations for this varied outcome may be related to the
use of soft tissue reconstructions for irreducible injuries and reconstruction of
only the dorsal SL ligament. Indeed, the sectioning studies by Berger[13] noted that, while the dorsal SL ligament has a yield strength of close to 300 N,
the palmar region provides 120 N of breaking strength. To try and correct the torsional
instability that may result from dorsal only repairs, recent techniques have been
described that address both dorsal and volar SL ligaments.[14]
[15]
The purpose of this study was to compare the biomechanical strength of a 360-degree
tenodesis to one augmented with an internal brace (suture tape) in a cadaveric model
and determine whether the stability achieved reaches normative yield strength of native
SL ligament.
Materials and Methods
We obtained 12 paired fresh frozen cadaveric wrists, average age 50.5 years (range:
41–65) for testing ([Table 1]). Preprocedural imaging demonstrated no evidence of carpal malalignment, preexisting
wrist arthritis, or previous surgery. To test the yield strength of the reconstructions,
and to remove any confounding variables provided by secondary stabilizers of the carpus,[16]
[17]
[18] each of the 24 specimens was disarticulated from the radiocarpal joint, the SL ligament
sectioned and randomized to 360-degree tenodesis reconstruction group or the 360-degree
tenodesis with an internal brace. All procedures were performed by the senior surgeon.
A 0.035 inch K wire was placed from dorsal to volar through the center of the lunate
and proximal scaphoid and confirmed on fluoroscopic imaging. Once the desired central
trajectory had been confirmed, a 2.5 mm cannulated drill hole was made within the
scaphoid and a 3.0 mm hole made within the lunate. A 15 cm palmaris longus graft was
procured and whip stitched at either end using a 4–0 fiberloop suture. Using a tendon
passer, the tendon graft was passed from dorsal to volar through the lunate, volar
to dorsal through the scaphoid, and dorsal to volar through the lunate ([Fig. 1]). In this way, a 360-degree tenodesis had been performed. Maximum tension was placed
by the surgeon pulling onto the tails of the graft to aid in reduction of the SL and
the wrist ranged in flexion to extension to remove any creep from the construct. Two
3 × 8 mm biotenodesis screws were then placed within the scaphoid and lunate to secure
the graft and the tendon tails cut flush ([Fig. 2]). Within the internal brace cohort, a similar procedure was performed. A 1.3 mm
suture tape was then passed from dorsal to volar through the cannulation of the biotenodesis
screws within the scaphoid and lunate and tied palmarly. The purpose of central passage
through the screw holes was to prevent the suture tape from cutting through the cortical
bone, if placed directly through the bone tunnels ([Figs. 3] and [4]).
Fig. 1 Cadaveric specimen showing reconstruction of the dorsal and volar scapholunate (SL)
ligament.
Fig. 2 Dorsal scapholunate ligament reconstruction with biotenodesis screw fixation.
Fig. 3 Dorsal aspect of scapholunate (SL) reconstruction with internal brace with the proximal
carpal row disarticulated prior to biomechanical testing.
Fig. 4 Volar aspect of scapholunate (SL) reconstruction with internal brace with the proximal
carpal row disarticulated prior to biomechanical testing.
Table 1
360 tenodesis reconstruction/360 tenodesis with suture tape internal brace fixation
|
360 tenodesis reconstruction
|
360 tenodesis with suture tape internal brace
|
|
Sample
|
Stiffness (N/mm)
|
Maximum load (N)
|
Mode of failure
|
Stiffness (N/mm)
|
Maximum load (N)
|
Mode of failure
|
|
1
|
46.57
|
159.28
|
Graft tore through bone tunnel
|
42.16
|
300.05
|
Suture knot failure
|
|
2
|
24.75
|
132.91
|
Anchor failure of graft
|
56.9
|
98.10
|
Suture knot failure
|
|
3
|
36.07
|
113.72
|
Anchor failure of graft
|
31.1
|
218.97
|
Anchor failure of graft
|
|
4
|
24.34
|
87.51
|
Graft slippage
|
67.14
|
252.83
|
Anchor failure of graft
|
|
5
|
51.07
|
266.07
|
Graft slippage with some tearing into bone tunnel
|
38.94
|
334.65
|
Anchor failure of graft
|
|
6
|
77.87
|
366.38
|
Graft slippage with some tearing into bone tunnel
|
57.28
|
339.86
|
Suture knot failure
|
|
7
|
20.40
|
61.06
|
Graft slippage with some tearing into bone tunnel
|
29.30
|
409.13
|
Graft and suture tape failure
|
|
8
|
17.70
|
104.37
|
Graft tore through bone tunnel
|
46.9
|
186.81
|
Bone tunnel failure
|
|
9
|
17.80
|
112.52
|
Graft slippage
|
36.4
|
347.16
|
Failure of biotenodesis screw
|
|
10
|
24.50
|
84.57
|
Graft slippage
|
24.3
|
322.05
|
Graft slippage with some tearing into bone tunnel
|
|
11
|
33.30
|
176.54
|
Graft slippage
|
42.4
|
426.44
|
Graft slippage with some tearing into bone tunnel
|
|
12
|
9.93
|
58.39
|
Graft slippage
|
30.3
|
165.57
|
Graft slippage with some tearing into bone tunnel
|
|
Mean
|
32.03
|
143.61
|
|
41.3
|
283.47
|
|
|
SD
|
18.81
|
90.54
|
|
13.08
|
100.25
|
|
Abbreviation: SD, standard deviation.
To prepare for biomechanical testing, the scaphoid, lunate, and triquetrum were removed
en bloc and a vertically orientated K wire was placed through the scaphoid and lunate,
with care taken to avoid the scapholunate ligament reconstruction. Specimens were
then potted in 1.5 inch polyvinyl chloride (PVC) piping and mounted into an Instron
machine and preloaded to 5 N. An axial distraction load was then applied at a rate
of 0.1 mm/s until failure of the reconstruction. The mode of and maximum load to failure
were recorded for each sample.
One way analysis of variance with a Tukey significant difference post hoc analysis
was performed with p < 0.05 for stiffness by group and maximum breaking strength (maximum load) by group,
for all specimens.
Results
Specimens that underwent loading after 360-degree tenodesis only demonstrated a breaking
strength of 143.61 ± 90.54 N. A total of 8 samples of 12 failed via tendon graft slippage
at the bone screw interface ([Table 1]). Constructs that were augmented with an internal brace (suture tape) had a breaking
strength of 283.47 ± 100.25 N (p ≤ 0.002; [Table 1]). Common modes of failure included graft slippage or knot breakage of the suture
tape ([Table 1]).
Discussion
The treatment of scapholunate instability continues to vex surgeons. The injury pattern
ranges from a minor sprain to gross disruption of the ligament with altered carpal
kinematics. Many techniques have been proposed and are based upon controlling the
scaphoid that assumes a position of flexion and pronation.[1]
[6]
[7]
[8]
[10]
[13]
[14]
[15]
[17]
[19]
[20]
[21]
[22]
[23] Berger's detailed anatomic prosections noted that the SL ligament comprised of a
dorsal, membranous, and volar region. The palmar ligament had a yield strength of
120 N compared with that of the dorsal ligament, which exhibited a breaking strength
of 300 N. Given this, traditional techniques had concentrated on reconstructing the
dorsal ligament only. Garcia-Elias et al[1] reported on the outcomes of the triligament tenodesis technique in 38 patients at
an average follow-up of 46 months. Twenty-eight patients reported no pain and 29 returned
to their original occupation. Of note, 18% of patients developed mild signs of arthritis.
Patients were immobilized for a prolonged period of time and required a secondary
procedure for K wire removal at an average of 8 weeks, postoperatively.
As load is transferred across the SL joint, the morphology of the SL ligament remains
important to resist torsional and translational moments. Indeed, one of the reasons
why there may be unpredictable outcomes in traditional dorsal ligament reconstruction
techniques is the failure to repair the volar ligament. Albeit not as strong as the
dorsal segment, it may aid in resisting rotation across the joint.[13] As such, there has been an increasing interest to address the volar SL ranging from
volar capsulodesis[23] to circumferential grafts around the scaphoid and lunate.[24] As reported by Chee et al,[14] a strip of the flexor carpi radialis (FCR) tendon can be passed from volar to dorsal
through the scaphoid and dorsal to volar through the triquetrum in an antipronation
tenodesis to correct carpal malalignment. Ho et al[24] described an arthroscopic-assisted technique of reconstructing the volar and dorsal
SL ligament using a palmaris longus graft. Seventeen patients with chronic SL instability
were treated and followed-up on average for 48 months. Eleven of 17 patients reported
no pain, the average SL gap was 2.9 mm and 13 patients returned to their preinjury
job level. There was one case of scaphoid ischemia that did not progress or become
symptomatic. Similar results have been reported by Henry following volar and dorsal
SLIL repair with immobilization for 10 to 12 weeks.[15] Pin removal occurred at 8 weeks, postoperatively.
Many of the treatments for SL instability involve prolonged casting and K wire augmentation.
Mathoulin et al[25] described results of arthroscopic dorsal capsuloligamentous repair with mean follow-up
of 11.4 months in 36 patients. Patients were immobilized via cast fixation for 8 weeks,
when K wires were removed (16 cases) and physical therapy protocol was initiated.
Patient grip strength on average increased to 92% of unaffected side with significant
reduction in VAS (visual analogue scale) score (mean VAS score = 0.5/10).
The concept of the 360-degree tenodesis is to provide resistance to load along multiple
axial planes. Compared with tenodesis only the addition of suture tape internal bracing
resulted in construct yield strengths similar to the native dorsal SL ligament.[13]
[20]
[26] Given this inherent immediate stability, we feel it may permit earlier range of
motion in patients without the need for prolonged immobilization, under the care of
a certified hand therapist to monitor function. In addition, given its inherent strength,
K wires may not be needed as the suture tape may prevent the creep of the tendon graft,
when load is initially applied to it. Taleisnik described two forms of SL instability:
type 1, in which the ulnar is anatomically located within the ulnar facet of the distal
radius; and type 2, whereby there is ulnar translocation of the lunate.[11] An additional advantage of this procedure is the ability of the palmar tail of the
tendon graft and suture tape to be secured to the volar rim of the distal radius to
reconstruct the long radiolunate ligament and provide a restraint to carpal translocation.
As with most biomechanical studies, there are inherent limitations to replicating
the natural forces that would be present in vivo. The model tested the breaking strength
of the fixation methods and did not factor in the strength of the soft tissues after
their healing response. It is unknown whether the tendon grafts would have stretched
out over time for which the internal brace provides immediate stability. There is
variability in the cadavers including their bone quality. To mitigate this, we used
12 matched pairs of cadavers. Lastly, the number of specimens tested may have accounted
for a type 2 error in the tenodesis and internal brace construct. Notwithstanding
these limitations, the 360-degree tenodesis with suture tape internal brace provides
immediate stability of the SL joint akin to native SL ligament strengths, permits
earlier range of motion with encouraging early clinical results, and can provide a
checkrein to ulnar translocation of the carpus.
The proposed 360-degree tenodesis technique presented in this paper aims to permitting
immediate construct stability that replicates native SL yield strength. The augmentation
with the suture tape internal brace may be better suited to resist immediate loads
and diastasis of the SL joint, while at the same time possibly obviating the need
for K wire stabilization.
