Traumatic reinjury to one's knee after anterior cruciate ligament (ACL) reconstruction is a devastating consequence. Fear of reinjury is a factor before returning to sport.1 In the absence of a traumatic event, graft “failures” may be characterized by continued symptoms of instability, or the presence of a grade 2+ Lachman test, positive pivot shift test, and ≥5 mm side-to-side-difference on the KT arthrometer.2,3 The International Knee Documentation Committee (IKDC) Abnormal (C) and Severely Abnormal (D) classifications for the overall IKDC score may also characterize failures.4 However, these “objective” signs do not always correlate with subjective outcomes or return to sport.1
A systematic review of 19 randomized and quasi-randomized trials comparing patellar and hamstring tendons (HTs) for ACL reconstruction identified 13 studies reporting graft reruptures and concluded no difference in rerupture rates between the grafts.5 However, the cause of rerupture in these trials was unclear; therefore, accurate traumatic rerupture and atraumatic graft failure rates could not be determined.5
Another systematic review of 19 studies comparing single- and double-bundle ACL reconstructions6 pooled results from 3 studies7–9 reporting data on traumatic ACL reruptures, which showed significantly lower rerupture rates with a double-bundle (0.8%) versus a single-bundle (5.4%) reconstruction, at 2 years postoperatively.6 Six studies7,10–14 reporting data on graft failures were pooled, showing no difference between single- and double-bundle reconstructions.6 However, the quality of evidence from these trials was insufficient to determine the relative effectiveness of double-bundle compared with single-bundle reconstructions.
Factors associated with graft rupture include the use of HT grafts,3 single-bundle reconstructions,7,9 younger age (<20 years15 and <25 years2,3), higher activity level and female patients,3,15–18 smaller hamstring autograft size (≤8 mm),15 and contact mechanism of the initial injury.17 One study of 612 patients with patellar or HT ACL reconstructions reported an overall rerupture rate of 6.4% and contralateral rupture rate of 5.7% at 5 years postoperatively.17 Contralateral rupture rates have been reported as high as 26% for patellar tendon (PT), compared with 12% for HT reconstructions.19 However, these rates were based on systematic reviews,4,20 retrospective studies,2 prospective cohort studies,21 and case series.17 Also, studies define atraumatic graft failures differently, or inadequately define reruptures, which may or may not include graft failures, complete, or partial ACL ruptures. Consequentially, traumatic graft rerupture and atraumatic graft failure rates are inaccurately reported or ambiguous to interpret.
A double-blind randomized clinical trial (RCT) was conducted to compare 3 autograft options for primary ACL reconstruction: PT, single-bundle semitendinosus/gracilis tendon (HT), and double-bundle HT (DB), at 2 years postoperatively.22 This article describes the traumatic graft reinjury (including complete reruptures and partial tears), atraumatic graft failure, and contralateral ACL tear rates observed in the RCT. It also evaluates the odds and predictive factors of traumatic rerupture and reinjury, atraumatic graft failure, and contralateral tears at a minimum of 2 years postoperatively.
Recruitment, Randomization, and Clinical Follow-up
The orthopedic research team screened all patients presenting with isolated ACL deficiency, to the University of Calgary Sport Medicine Centre between 2007 and 2010. Eligibility was determined using defined study inclusion and exclusion criteria (Table 1).
Three hundred thirty eligible patients (28.5 years; SD = 9.8) were randomized, with 110 patients/group (Figure 1) according to sample size calculations.22 Computer-generated [using IBM-SPSS Statistics 20 software (SPSS, Chicago, Illinois)] allocation was performed intraoperatively by the research assistant, using varied block sizes and stratification by injury chronicity (acute ≤3 months) to ACL reconstruction with 1 anatomically positioned autograft option: (1) PT, (2) quadruple-stranded HT, or (3) double-bundle using HTs (DB).
Operative techniques for each group were identical, as previously described22: 3 standard arthroscopic portals, a universal graft harvest incision (5-7 cm length, longitudinally orientated) positioned medial to the PT and distal to the medial arthroscopic portals, and use of an endoscopic 1-incision technique with EndoButton (Smith and Nephew Inc, Andover, Massachusetts) fixation on the femoral side and absorbable interference screw (Bioscrew; Conmed-Linvatec, Largo, Florida) fixation on the tibial side.22 In the PT and HT reconstruction groups, the femoral tunnels were made using a transtibial approach, except where it was not possible to place the guide pin in the center of the anatomic footprint. The femoral tunnels in the DB group were all drilled through the supplemental anterior–medial portal. All 3 groups received identical clinical follow-up and rehabilitation protocols.23
Patients and the independent trained examiner were blinded to treatment allocation until 2 years postoperatively. As previously reported,22 the independent examiner performed clinical and functional assessments and collected patient-reported outcomes, including the Tegner Activity Level,24 at baseline, 1 and 2 years postoperatively.
Patients reported complications/adverse events by phone, e-mail, in person, or at scheduled follow-up visits. All occurrences were documented and investigated, and diagnoses were confirmed. These patients were classified into complete traumatic reruptures, partial traumatic tears, or atraumatic graft failures. Patients suffering a tear on their opposite knee were classified as contralateral ACL tears.
Complete traumatic reruptures—defined as a consequence of an acute traumatic event resulting in a change in static stability since the most recent follow-up visit. This change was determined clinically by a definite loss of end point on Lachman testing, increased anterior translation (>3 mm) and a ≥grade 2 pivot shift. Complete traumatic reruptures were confirmed by magnetic resonance imaging (MRI) or diagnostic arthroscopy. Revision ACL reconstruction was recommended for all patients.
Partial traumatic tears—defined as a consequence of an acute traumatic event resulting in a suspected meniscal injury or graft tear on history, without the clinical characteristics of a complete rerupture, as defined above. A partial traumatic tear was confirmed by MRI or diagnostic arthroscopy. Revision ACL reconstruction was not recommended or required for these patients.
Atraumatic graft failures—defined in the absence of an acute traumatic event, with ≥grade 2 pivot shift and/or ≥6 mm side-to-side difference on the KT arthrometer at 2 years postoperatively.
Contralateral ACL tears—defined by a loss of end point on Lachman testing and evidence of a pivot shift, both of which occurred relative to baseline and previously scheduled follow-up examinations.
Demographic, surgical, and outcome information was compared at baseline. The χ2/Fisher exact statistics were used for categorical data; 1-way analyses of variance were used for continuous variables.
Separate analyses were performed on the proportions of complete traumatic reruptures, atraumatic failures and contralateral ACL tears. A combined analysis, “Traumatic Reinjuries,” of complete traumatic reruptures and partial traumatic tears, determined the clinical risk of reinjury. Proportions of complete traumatic reruptures, traumatic reinjuries, atraumatic graft failures, and contralateral ACL tears were calculated for patients above and below the median age of 27 years for the overall sample.
Changes in Anterior Cruciate Ligament Quality of Life (ACL-QOL) outcome scores over time were compared for patients with complete traumatic reruptures and contralateral ACL tears. ACL-QOL scores in patients with and without atraumatic graft failures were also compared using descriptive statistics.
An exploratory logistic regression analysis assessed 5 independent predictors, determined a priori, of complete traumatic reruptures, traumatic reinjuries, and contralateral ACL tears: chronicity, graft type, age at surgery, sex, and 2-year Tegner activity level, in a subgroup of patients aged ≤27 years and in the overall sample. For patients with complete traumatic reruptures and traumatic reinjuries, the Tegner activity levels reported at the time of rerupture or reinjury were used in the logistic regression analysis.
All patients were analyzed on an “intention-to-treat” basis. A 5% significance level and IBM-SPSS Statistics 20 software (SPSS) were used for all analyses.
This RCT (NCT00529958) was approved by the University of Calgary Conjoint Health Research Ethics Board.
Demographic (Table 2) and baseline meniscal and chondral conditions were not different between groups (Table 3). Three hundred twenty-two patients (97.6%) completed minimum 2-year follow-up. Three PT patients withdrew after 6 months; 5 patients were lost-to-follow-up (Figure 1).
Seventeen patients (5.2%) suffered a complete traumatic rerupture (Table 4) at a median 16.0 months (mean, 18.3 months) postoperatively. More reruptures occurred with HT and DB compared with PT reconstructions (Table 4). Seven (PT = 3, DB = 4) reruptures occurred before 12 months postoperatively. Of the 17 complete traumatic reruptures, 15 patients received revision surgery; 12 patients had 2-stage and 3 patients had 1-stage revisions. Two patients declined the recommended revision procedure and chose conservative management with bracing and rehabilitation.
The proportions of traumatic reinjuries (Table 4) significantly favored PT reconstructions (P = 0.047). Sixty-five percent (17/26) of traumatic reinjuries were male (P = 0.090; Table 5). The majority of reinjuries occurred during sport participation and 2 patients were reinjured while at work (Table 5). Only 4 involved direct contact with the knee, with the majority involving a twisting mechanism of injury.
Atraumatic graft failures were not different between groups (P = 0.747; Table 4). There were no differences between the number of males (n = 32) and females (n = 21) with an atraumatic graft failure (P = 0.431). Meniscal pathology was evaluated as a potential risk in predicting atraumatic graft failure, but there was no difference between the groups (the relative risk of an atraumatic graft failure with a previous meniscectomy was 1.00; P = 0.987).
Seventeen patients (5.2%) suffered a contralateral ACL tear at a minimum 2-year follow-up (Table 4). The incidence of contralateral ACL tears between groups was not significantly different (Table 4). Fifty-nine percent (10/17) of the patients with contralateral ACL tears were female (P = 0.096; Table 6). At the time of contralateral injury, all patients were performing at a Tegner level ≥5 in their sport/activity. Only 2 patients had a contralateral tear by direct contact while playing soccer. The remaining contralateral tears were noncontact and had typical mechanisms of injury (Table 6).
Minor deviations from the defined surgical protocol occurred in some patients with a traumatic reinjury (Table 7) and atraumatic graft failure (Table 8). The commonest departure, occurring in 11.8% of the patients (12 HT, 1 PT), required use of the anteromedial portal, rather than a transtibial approach, to drill the femoral tunnel in the anatomic footprint of the ACL. Of these 13 patients, 2 suffered a complete traumatic rerupture and 1 patient had a partial traumatic tear (Table 7). The incidence of traumatic reinjuries in these patients was not different than in patients who had the transtibial femoral tunnel drilling (P = 0.134). Similarly, in patients with atraumatic graft failures, there was no difference in those patients who had their femoral tunnel drilled through the anteromedial portal compared to those drilled through a transtibial approach (P = 0.156). Four patients required a minor fixation change: 2 patients needed metal interference screws (1 femur; 1 tibia) and 2 required supplemental staple fixation on the tibia due to soft bone and a lengthy PT. Adequate fixation was achieved for all cases with surgical deviations. In 2 patients, the double-bundle guide (once for the femur and once for the tibia) was not used because it did not reproduce the anatomy. Therefore, standard ACL guides were used. None of these deviations had any measurable effect on patient outcome.
In Figure 2, baseline ACL-QOL scores (mean = 28.8; SD = 12.5) improved for all patients following the index ACL reconstruction procedure (mean = 77.6; SD = 12.8). The scores decreased to a mean of 36.0 (SD = 15.6) at the time of traumatic rerupture, then improved after revision surgery (mean = 64.0; SD = 14.2). For patients with contralateral ACL tears (Figure 3), baseline ACL-QOL scores (mean = 29.8; SD = 14.4) improved following the index ACL reconstruction procedure (mean = 77.4; SD = 10.1). The scores decreased to a mean of 31.6 (SD = 10.5) at the time of contralateral injury, then improved after contralateral ACL reconstructive surgery (mean = 72.4; SD = 18.6).
Relative to all study patients, and a subgroup of patients without any traumatic reinjuries or graft failures, 2-year ACL-QOL scores for patients with atraumatic graft failures were not different (Table 9).
Overall, there were significantly more patients aged ≤27 years with complete traumatic reruptures and traumatic reinjuries than patients aged ≥28 years (Table 10).
Younger age was identified as a significant predictor in the overall population for complete traumatic reruptures (P = 0.02) and traumatic reinjuries (P = 0.04), having allowed for acuity, age, study group, sex, graft type, and Tegner activity level. This predictor accounted for 15% of the explanation in complete traumatic rerupture (Nagelkerke R2 = 0.150) and 16% of traumatic reinjury (Nagelkerke R2 = 0.160). In patients aged ≤27 years, younger age was also identified as the only significant predictor of complete traumatic reruptures (Nagelkerke R2 = 0.159; P = 0.02) and traumatic reinjuries (Nagelkerke R2 = 0.209; P = 0.01). None of the factors were significant in predicting atraumatic failures.
Table 11 shows the odds ratios for the remaining independent predictors included in the exploratory logistic regression analysis in patients aged ≤27 years. The odds of complete traumatic rerupture or traumatic reinjury were the highest for DB and lowest for the PT reconstructions; higher in males and in patients with a higher activity level. None of these odds ratios were statistically significant reflecting the relatively small number of reruptures and reinjuries.
There was no difference between the proportion of patients aged ≤27 years compared with patients aged ≥28 years with a contralateral ACL tear (Table 10). Exploratory logistic regression analyses did not identify any significant predictors of contralateral ACL tears; however, there was a trend toward higher odds of a contralateral tear in younger (P = 0.08) female (P = 0.09) patients. Females were 2.5 times more likely to have a contralateral tear than males.
This double-blind RCT comparing 3 different ACL reconstruction techniques demonstrated no overall differences with respect to disease-specific quality-of-life outcome.22 However, this article has shed light on the risks of reinjury and contralateral knee injury in this population of ACL-reconstructed patients.
All information was collected prospectively and by a blinded independent examiner. The existing literature is fraught with concerns about a lack of reporting of these events, risk of bias, and small numbers from which to make inferences.5,6
The overall incidences of a complete traumatic rerupture and a contralateral ACL tear were identical (5.2%). This might be considered an acceptable rate compared with other reports. Pinczewski et al21 reported an overall rerupture rate of 10.6%, but this study was carried forward for 10 years. Longer-term follow-up for the current trial is ongoing, and it remains to be seen if the incidence of reinjury will increase.
This is the first large randomized trial to evaluate 3 separate autograft techniques to have direct comparisons of risks of reruptures and reinjuries. In this trial, PT reconstructions had a lower risk of traumatic reinjury compared with HT or DB reconstructions. There are several explanations for these findings. This trial involved a single surgeon, and while avoiding any potential for between-surgeon differences, exposed a potential bias with respect to having better expertise with 1 technique over another. A single-surgeon trial also potentially limits the generalizability of the findings, but the direction of this potential bias is not determinable. However, as previously reported, the surgeon spent over 2 years learning the double-bundle technique and had over 20 years of experience in performing a high volume of ACL surgery (personal communication: Mohtadi N. Double-Bundle ACL Reconstruction: The Learning Curve. Fowlers' Fellows Meeting; 2008; Emerald Lake, BC, Canada). The same surgical assistant, with more than 20 years of experience in preparing over 5000 ACL grafts, prepared the grafts in this trial. Therefore, surgical technique variability was minimized and every effort was made to ensure that this bias did not affect outcome. It is possible to speculate that using hamstring autografts (HT and DB) weakens the dynamic control of the knee,25,26 thus putting the graft at greater risk. PT reconstructions may have the opposite or protective effect.
Recent trends regarding the drilling of the femoral tunnel from the anteromedial portal have been suggested as a possible reason for higher revision rates, based on the Danish ACL registry.27 However, overinterpretation of low fidelity information from a registry should be done with caution, compared with data collected in an RCT. No relationship with rerupture, reinjury, or atraumatic failure could be explained on this basis in this RCT.
Only 1 factor, younger age (≤27 years), independently explained the risk of traumatic reinjury in this population. Nevertheless, patients who were male, with an HT or DB reconstruction and a higher Tegner activity level, had higher odds of reinjury. The lack of statistical significance may be a reflection of statistical disequilibrium when comparing low numbers of reinjuries to the remaining uninjured patients. Contralateral ACL tears occurred with an equal occurrence overall (5.2%), but no significant risk factors were identified. There was a trend for younger female patients to suffer contralateral ACL tears, but these were not statistically significant. The higher rate in females is consistent with the higher risks typically seen in female athletes.
Relatively high percentages of patients (14%-18%) were defined with an atraumatic graft failure (Table 4). This designation (ie, ≥grade 2 pivot shift and/or ≥6 mm side-to-side difference) is equivalent to the Abnormal (C) and Severely Abnormal (D) IKDC grades, but only with respect to anterior translation and pivot shift examination.28 In a previous Cochrane review, IKDC Abnormal and Severely Abnormal categories were reported to be at 21% for PT and 25% for HT reconstructions.5 Lower rates were reported in a more recent Cochrane review, at 5.6% for DB and 10% for HT reconstructions.6 The literature reports great variability in these numbers, which may reflect the lack of consistency and blinding between examiners. Graft sizes ≤8 mm in HT reconstructions have also been associated with greater failure rates.15 The average HT graft size for the atraumatic graft failures in the current trial was 8.0 mm, which was similar to those without failures. ACL-QOL scores in patients with atraumatic graft failures were similar to those without reinjuries/failures, and to all study patients, suggesting that despite having loose knees, there is no correlation with quality-of-life outcome in patients defined with atraumatic graft failures.
Graft diameter could not explain the higher rates of reinjury in the HT and DB groups, with no statistically significant differences in graft sizes. The average diameter of the HT grafts was 8.4 mm in those patients with a traumatic rerupture and 8.0 mm in those without. Similarly, the average diameters of the anteromedial bundle and posterolateral bundles were 6.8 and 5.1 mm compared with 7.2 and 5.3 mm in patients with and without traumatic ruptures, respectively.
Revision ACL reconstruction was recommended for 17 patients (5.2%) in the first 2 years. The 2 patients refusing revision surgery or arthroscopic confirmation of the graft rupture may have introduced a diagnostic accuracy bias; however, their clinical characteristics were unambiguous and a publicly funded MRI was not indicated. These patients were unable to pay privately.
Through this randomized double-blind trial, reinjuries and static failures in a large group of patients could be prospectively documented. The authors identified, a priori, risk factors to examine the predictability of these events. The authors had clinical equipoise with no preconceived hypothesis of the technique that would be expected to have a better outcome. Blinding of the patients and the independent assessor also reduced the risk of bias.
Hamstring (HT) and double-bundle (DB) reconstructions had a significantly increased risk of traumatic reinjury at a minimum 2-year follow-up, compared with PT reconstructions. Revision surgery was recommended in 5.2% of patients. Younger age was the only significant predictive factor, irrespective of graft type. Trends for more traumatic reinjuries were seen in males with higher Tegner levels. Atraumatic graft failures were similar between groups. Contralateral ACL tears occurred in 5.2% of patients, with trends for higher risks in younger females.
The authors thank Jocelyn Fredine for assisting with patient follow-up and data collection, Niko Lagumen for assisting with intraoperative randomization and data collection, and the surgical staff at the Peter Lougheed Hospital.
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