1
Comparison of Revision Rates in Autograft and Allograft
2
Anterior Cruciate Ligament Reconstruction
3
4
Purpose: The purpose of this study is to compare the rates of revision after allograft and
5
autograft Anterior Cruciate Ligament (ACL) Reconstruction.
6
7
Methods: All ACL Reconstructions performed by a single surgeon (TSP) between
8
1/1/00 and 12/31/06 were identified by retrospective chart review. 231 patients met the
9
inclusion criteria and 181 patients were available for follow-up. 142 patients underwent
10
bone-patella tendon-bone autograft reconstruction (BTB-auto), 31 patients underwent
11
bone-patella tendon-bone allograft reconstruction (BTB-allo) and 8 patients underwent
12
Achilles tendon allograft reconstruction (Ach-allo). Patients were contacted to determine
13
whether their ACL Reconstruction had been revised. In addition, subjective IKDC and
14
Tegner scores were obtained.
15
16
Results: At a mean follow up of 49 months (11-91 months), revision rates were .7%
17
(1/142) in the BTB-auto group, 9.7% (3/31) in the BTB-allo group and 37.5% (3/8) in the
18
Ach-allo group. This difference reached statistical significance when comparing the
19
BTB-auto and BTB-allo groups (p=.02), as well as when comparing the BTB-auto and
20
Ach-allo groups (p=.0004). The difference in revision rates between the BTB-allo and
21
Ach-allo groups did not reach statistical significance (p=.09). Subjective IKDC scores
22
of non-revised (surviving) grafts in the BTB-auto group, BTB-allo group, and Ach-allo
1
23
group were 98.3, 95.2 and 86 respectively (p<.0001). Tegner scores of non-revised grafts
24
in the BTB-auto group, BTB-allo group, and Ach-allo group were 6.2, 6.5 and 5.6
25
respectively (p=.02).
26
27
Conclusions: ACL reconstruction with the use of bone-patella tendon-bone allografts
28
and Achilles tendon allografts is associated with a higher revision rate when compared to
29
bone-patella tendon autograft reconstruction. In addition, when comparing surviving
30
grafts, the subjective IKDC scores and Tegner scores are lower in the Achilles tendon
31
allograft group.
32
33
Clinical Relevance: Surgeons should be aware of the higher revision rate associated
34
with allograft ACL reconstruction when counseling patients on graft options.
35
36
Level of Evidence: III
37
38
Key Words: ACL, Allograft, Achilles, Revision, Autograft, Failure
39
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45
2
46
Ruptures of the Anterior Cruciate Ligament (ACL) continue to be a common and
47
significant source of disability amongst athletes. Throughout the past century, great
48
strides have been made in our understanding of the ACL and our ability to reconstruct it
49
surgically. Most of this progress has come in the form of improved surgical techniques
50
resulting from the development and advancement of arthroscopic surgery as well as a
51
better understanding of the anatomy of the ACL. Surgeons continue to explore ways to
52
improve ACL reconstruction and allow athletes a less painful recovery with a quicker
53
return to function. Some have advocated the use of allografts to achieve these goals and
54
to avoid the peri-operative morbidity associated with the harvesting of autograft tissue.
55
56
Despite the obvious advantages of allografts, there are also many potential
57
disadvantages associated with their use. Allografts carry the risks of viral disease
58
transmission, bacterial contamination and immune reaction.1, 2 Outside of these risks
59
inherent to the use of cadaveric tissue, there is also some evidence that allografts take
60
longer to incorporate, revascularize and remodel than autograft tissue.3-9 This longer
61
period of incorporation and remodeling may, in turn, cause allografts to have weaker
62
structural properties than autografts and potentially lead to a higher rate of failure.10-12 It
63
currently remains unclear whether the potential benefits from the use of allografts in ACL
64
reconstruction outweigh the risks. This study seeks to shed light on this dilemma by
65
comparing the failure rates of autograft and allograft ACL reconstruction. Specifically,
66
we seek to determine and compare the rates of failure for both autograft and allograft
67
ACL reconstructions performed by a single surgeon. We hypothesize, that the failure
68
rate of allograft ACL reconstruction is higher than that for autograft ACL reconstruction.
3
69
70
71
METHODS
72
73
Patient Evaluation
74
75
All primary ACL reconstructions performed by a single surgeon (TSP) from 9/1/2000 to
76
5/31/07 were identified. 231 patients were identified of which 50 patients could not be
77
contacted and were considered lost to follow-up. Of the 181 patients remaining in the
78
study, 142 patients underwent bone-patella tendon-bone autograft reconstruction (BTB-
79
auto), 31 patients underwent bone-patella tendon-bone allograft reconstruction (BTB-
80
allo) and 8 patients underwent Achilles tendon allograft reconstruction (Ach-allo).
81
Patients were contacted to determine whether their ACL reconstruction had been revised.
82
In addition, subjective IKDC and Tegner scores were obtained. Demographic data for
83
the 3 groups was compared (Table 1). Mean follow-up for the groups was 49 months
84
(11-91 months).
85
86
Surgical Technique
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88
Bone-patella tendon-bone autograft
89
A longitudinal incision was made over the medial aspect of the patella tendon exposing
90
the patella, patella tendon and tibial tubercle. A double-bladed #10 scalpel was used to
91
harvest a 10mm wide patella tendon graft. Patella and tibial bone plugs were harvested
4
92
with an oscillating saw at a length of 20-25 mm and a depth of 8-10 mm. Grafts were
93
prepared and fashioned on the back table while routine arthroscopy was performed along
94
with any concomitant meniscal or articular cartilage treatment. A femoral tunnel was
95
created at the 2 o’clock position (Left knee) or 10 o’clock position (Right knee). The
96
femoral tunnel was reamed to a depth to match the patella bone plug (20-25 mm) and
97
reamed to a diameter to accommodate the patella bone plug (9-10mm). The patella bone
98
plug was then advanced into place and secured with a 7 X 23 mm bioabsorbable
99
interference screw (Arthrex, Naples, FL). The tibial bone plug was then fixed with the
100
knee in 0-10 degrees of flexion using a 9 X 23 or 10 X 23 mm bioabsorbable interference
101
screw (Arthrex, Naples, FL).
102
103
Bone-patella tendon-bone allograft
104
Allografts were inspected and thawed to room temperature in a warm saline bath. They
105
were subsequently prepared and secured with identical technique to the bone-patella-bone
106
autograft group described above. All of the grafts were fresh frozen and 14 of the 31
107
grafts (45%) had undergone low dose irradiation (.8-1.5 MRad).
108
109
Achilles tendon allograft
110
Allografts were inspected and thawed to room temperature in a warm saline bath. The
111
calcaneal bone block was prepared to a length of 20-25mm, a width of 10 mm and a
112
depth of 8-10 mm. A double-bladed #10 scalpel was used to prepare the tendon to a
113
width of 10 mm. The soft tissue end of the grafts was whip-stitched with #2 non-
114
absorbable suture. The graft was fixed to the femoral tunnel with a 7 X 23 mm
5
115
bioabsorbable interference screw (Arthrex, Naples, FL) and the tendinous portion of the
116
graft was fixed to the tibial tunnel with a 10mm bioabsorbable delta taper screw (Arthrex,
117
Naples, FL). Graft fixation was performed with the knee in 0-10 degrees of flexion. All
118
of the Achilles grafts were fresh frozen and had undergone low dose irradiation (.8-1.5
119
MRad).
120
121
Rehabilitation
122
123
Immediate weight bearing as tolerated was allowed with crutches to be used for comfort.
124
All knees were placed in a hinged knee brace locked in extension until sufficient
125
quadriceps control was demonstrated. Early rehabilitation focused on regaining motion
126
and incorporated mostly closed chained exercises. Sports specific activity was
127
introduced at 4 months and a full return to sports was allowed at 6 months if sufficient
128
strength and one leg hop were demonstrated. All three groups underwent the same
129
rehabilitation protocol.
130
131
Statistical Methods
132
133
Revision rates between the three groups were compared using the Fisher test. A series of
134
one way ANOVA tests were used to compare IKDC scores and Tegner scores between
135
the groups. Statistical significance was set at p < .05. Tukey post-hoc analysis was
136
performed to determine specific differences between groups (GraphPad Prism Software,
137
version 5.01).
6
138
139
140
RESULTS
141
142
Revision Rates (Figure 1)
143
144
The primary endpoint of this study was the performance of revision ACL surgery. At a
145
mean follow up of 49 months (11-91 months), revision rates were .7% (1/142) in the
146
BTB-auto group, 9.7% (3/31) in the BTB-allo group and 37.5% (3/8) in the Ach-allo
147
group. This difference reached statistical significance when comparing the BTB-auto and
148
BTB-allo groups (p=.02), as well as when comparing the BTB-auto and Ach-allo groups
149
(p=.0004). The difference in revision rates between the BTB-allo and Ach-allo groups
150
did not reach statistical significance (p=.09). The single revised graft in the BTB-auto
151
group represented an acute traumatic re-rupture. Two of the 3 revisions in the BTB-allo
152
group represented acute traumatic re-ruptures while the other was a graft that was
153
symptomatically lax without any acute event. One of the 3 revisions in the Ach-allo
154
groups represented an acute traumatic re-rupture while the other two were lax grafts
155
resulting in instability without any particular acute event.
156
157
Outcome Scores (Figures 2 and 3)
158
159
Subjective IKDC scores of non-revised (surviving) grafts in the BTB-auto group, BTB-
160
allo group, and Ach-allo group were 98.3, 95.2 and 86 respectively (Table 2).
7
161
Statistically significant differences were found between all three groups (p<.0001).
162
Tegner scores of non-revised grafts in the BTB-auto group, BTB-allo group, and Ach-
163
allo group were 6.2, 6.5 and 5.6 respectively (Table 2). A statistically significant
164
difference group difference was found and Tukey post-hoc analysis demonstrated a
165
difference between the BTB-allo and Ach-allo groups (p=.02).
166
167
DISCUSSION
168
169
The use of allografts during ACL reconstruction remains a popular choice amongst
170
patients and surgeons. There are clearly many advantages to using an allograft:
171
decreased morbidity from tissue harvest, less pain and improved cosmesis.2, 13, 14
172
However, there are also many potential disadvantages: risk of disease transmission, cost,
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immune reaction and slower incorporation of the graft.1, 2, 9, 11, 15-21
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175
Concern over slower incorporation, revascularization and remodeling of allograft
176
tissue has been well documented in the orthopaedic literature.22 Jackson et al. performed
177
allograft ACL reconstruction on 11 goats using freeze dried bone-ACL-bone allograft.
178
At 1 year the grafts demonstrated histological properties of a normal ligament and
179
complete incorporation of the bone blocks. However, they also demonstrated inferior
180
biomechanical properties versus the native ACL.21 Zhang et al. performed bilateral ACL
181
reconstructions on dogs, with one knee receiving an allograft and the other an autograft.
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They found inferior incorporation in the allograft group at 6 months post-operatively.23 A
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recent sheep retrieval study also demonstrated delayed remodeling and inferior
8
184
biomechanical properties when comparing allografts to autografts at 1 year post-
185
operatively.16 There are few human studies addressing the concerns over incorporation,
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remodeling and revascularization of allograft ACLs. Muramatsu et al. examined the MRI
187
characteristics of allograft versus autograft bone-patella tendon-bone ACL reconstruction
188
in humans. They found a slower onset and rate of revascularization of the allografts
189
when compared to the autografts.24 Malinin et al. examined ACL allografts that were
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retrieved at the time of future arthroplasty.9 They found that at two years post-
191
implantation, the central portions of the graft remained acellular and complete
192
incorporation did not occur. If allografts do not incorporate and remodel as well as
193
autografts, they may be more susceptible to re-rupture during physical therapy or when
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patients return to physical activity. There have been several reports of increased failure
195
rates with the use of allograft tissue during ACL reconstruction.12, 25, 26 Most of these
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reports are case series or case reports. The data is somewhat conflicting as there are also
197
many studies demonstrating equal rates of success with the use of allografts.3, 27-30 This
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study represents an attempt to compare a single surgeon’s experience and results with
199
both autograft and allograft ACL reconstruction using similar fixation techniques. As
200
such, it provides particularly useful insight into the ongoing controversy surrounding the
201
use of allografts.
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203
In this study we find that the use of allografts during ACL reconstruction is
204
associated with a higher risk of revision ACL surgery. This was found to be true with
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both bone-patella tendon-bone allografts and Achilles tendon allografts. The reason
206
behind the higher rate of revision surgery was not the subject of this study and remains
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unclear. Certainly, many possibilities exist. The slower rate of incorporation,
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remodeling and revascularization of the allograft tissue may lead to a higher rate of re-
209
rupture as many authors have previously speculated. While this seems like a logical
210
explanation, other possibilities must be considered. The sterilization techniques used
211
(e.g. irradiation) may affect the structural properties of the allograft tissue thereby
212
causing more failures.31-34 Alternatively, it may be that patients feel better soon after
213
surgery allowing them to rehab more aggressively than desirable and leading to failure.
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Differences in fixation may also account for some of these failures. This would not
215
explain the differences found in this study between the BTB-auto and BTB-allo groups
216
but could potentially be a cause of increased failures in the Ach-allo group. Inferior
217
fixation associated with Achilles tendon grafts has been clearly demonstrated.35 While
218
the exact etiology of the difference in failure rates between autograft and allograft ACL
219
reconstruction remains unclear, it appears relatively certain from this study that there is a
220
lower incidence of revision ACL reconstruction when autograft tissue is used.
221
222
This study has several weaknesses. This is a retrospective study and as such is
223
subject to the weaknesses and potential bias that accompanies any retrospective study. In
224
addition, the demographics of the 3 groups (BTB-auto, BTB-allo, Ach-allo) were not
225
identical. While the 3 groups had equivalent pre-operative IKDC and Tegner scores, they
226
were of different ages. The Ach-allo group represented a population that was
227
significantly younger than the other groups. This was due to the author’s preference to
228
use Achilles allografts on patients with open physes. This is a potential source of bias
229
and must be considered. However, the findings of increased IKDC and Tegner scores
10
230
and a lower revision rate was also found when comparing the BTB-auto and BTB-allo
231
groups, which have comparable ages. With these weaknesses in mind, this study also has
232
several strengths. It compares the results of a single surgeon and thereby eliminates the
233
problems of comparing results of allografts done by one surgeon with the results of
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autografts done by another surgeon. Also, the techniques and fixation used in the BTB-
235
auto and BTB-allo groups are identical, allowing a fair direct comparison. Lastly, this
236
study involves a large sample size and thereby allows small differences in revision rates
237
and outcome scores to be detected.
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239
Despite the findings of this study, it is unwise to abandon the use of allograft
240
tissue during ACL reconstruction. There may be instances when allograft tissue is a
241
better option than the use of autograft. There are certainly instances in revision and
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multi-ligament surgery where standard autograft options may not be available. It is also
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still the authors’ practice to use allograft tissue in patients who have limited athletic
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aspirations and desire a quick return to their daily activities. In other words, allografts
245
may be a reasonable option for the middle-aged executive who desires to ski several
246
times a year, but a less desirable option for the competitive college basketball player with
247
professional aspirations.
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In summary, we have demonstrated a higher rate of revision ACL reconstruction
250
associated with the use of allograft during the primary ACL reconstruction. Surgeons
251
should be aware of these findings and counsel patients appropriately when discussing
252
graft options prior to ACL reconstruction.
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Table 1
Mean Age
Female
(years)
Male (%)
(%)
BTB-auto
30.2*
74 (51%)
71 (49%)
BTB-allo
35.5*
17 (55%)
14 (45%)
Ach-allo
16.6*
4 (50%)
4 (50%)
*Differences in mean age reached statistical significance between all
groups
389
390
391
392
Table 1: Patient demographics by type of graft
Table 2
IKDC
post
pre
post
BTB-auto
43.9
98.3
2.2
6.2
BTB-allo
42.7
95.2
2.5
6.5
Ach-allo
44.1
86.0
2.2
5.6
0.08
0.02*
p value
0.62
<.0001*
*Denotes statistically significant
difference
393
394
Tegner
pre
c
Table 2: Subjective IKDC and Tegner scores pre and post ACL reconstruction
395
396
397
Figure 1: Revision Rates
15
398
399
Figure 2: Subjective IKDC Scores
400
401
Figure 3: Tegner Scores
16