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Complications and Adverse Events of a Randomized Clinical Trial Comparing 3 Graft Types for ACL Reconstruction

Mohtadi, Nicholas MD, MSc; Barber, Rhamona BKin, CAT(C); Chan, Denise MBT, MSc; Paolucci, Elizabeth Oddone PhD

Clinical Journal of Sport Medicine: May 2016 - Volume 26 - Issue 3 - p 182–189
doi: 10.1097/JSM.0000000000000202
Original Research

Objective: Complications/adverse events of anterior cruciate ligament (ACL) surgery are underreported, despite pooled level 1 data in systematic reviews. All adverse events/complications occurring within a 2-year postoperative period after primary ACL reconstruction, as part of a large randomized clinical trial (RCT), were identified and described.

Design: Prospective, double-blind randomized clinical trial. Patients and the independent trained examiner were blinded to treatment allocation.

Setting: University-based orthopedic referral practice.

Patients: Three hundred thirty patients (14-50 years; 183 males) with isolated ACL deficiency were intraoperatively randomized to ACL reconstruction with 1 autograft type. Graft harvest and arthroscopic portal incisions were identical.

Intervention: Patients were equally distributed to patellar tendon (PT), quadruple-stranded hamstring tendon (HT), and double-bundle (DB) hamstring autograft ACL reconstruction.

Main Outcome Measures: Adverse events/complications were patient reported, documented, and diagnoses confirmed.

Results: Two major complications occurred: pulmonary embolism and septic arthritis. Twenty-four patients (7.3%) required repeat surgery, including 25 separate operations: PT = 7 (6.4%), HT = 9 (8.2%), and DB = 8 (7.3%). Repeat surgery was performed for meniscal tears (3.6%; n = 12), intra-articular scarring (2.7%; n = 9), chondral pathology (0.6%; n = 2), and wound dehiscence (0.3%; n = 1). Other complications included wound problems, sensory nerve damage, muscle tendon injury, tibial periostitis, and suspected meniscal tears and chondral lesions. Overall, more complications occurred in the HT/DB groups (PT = 24; HT = 31; DB = 45), but more PT patients complained of moderate or severe kneeling pain (PT = 17; HT = 9; DB = 4) at 2 years.

Conclusions: Overall, ACL reconstructive surgery is safe. Major complications were uncommon. Secondary surgery was necessary 7.3% of the time for complications/adverse events (excluding graft reinjury or revisions) within the first 2 years.

Level of Evidence: Level 1 (therapeutic studies).

Clinical Relevance: This article reports on the complications/adverse events that were prospectively identified up to 2 years postoperatively, in a defined patient population participating in a large double-blind randomized clinical trial comparing PT, single-bundle hamstring, and DB hamstring reconstructions for ACL rupture.

*Sport Medicine Centre, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada; and

Departments of Surgery and Community Health Sciences, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.

Corresponding Author: Nicholas Mohtadi, MD, MSc, FRCSC, University of Calgary Sport Medicine Centre, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada (

N.M. and D.C. are currently receiving a research grant from the Workers' Compensation Board, Alberta, and received prior funding from the Calgary Orthopaedic Research and Education Fund (COREF). The remaining authors report no conflicts of interest.

Received July 11, 2014

Accepted December 02, 2014

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“Patient safety is the cornerstone of high-quality health care.”1 Therefore, it is not only necessary to understand the outcomes of surgical procedures but also the adverse events and complications associated with them. There is a disproportionate risk of bias toward the publication of positive results in the literature for orthopedic and general surgery.2–6 Negative outcomes or statistically insignificant results that are underrepresented in the literature may have clinical implications on patient quality of care and safety.7 In addition, small or nonsignificant results are less likely to be published.6 In randomized clinical trials, reporting is focused on the primary and secondary outcomes, and there is a recognized concern regarding the reporting of adverse events and complications.8 Consequently, these adverse events and complications associated with anterior cruciate ligament (ACL) reconstruction are not included in systematic reviews or meta-analyses and are often based on level 3 or level 4 evidence.6 Published systematic reviews of ACL reconstructive surgery consistently underreport complications and adverse events. A Cochrane systematic review of 17 randomized and quasi-randomized clinical trials concluded that there was insufficient evidence with respect to adverse events and complications to determine a difference between single-bundle and double-bundle (DB) ACL reconstructions.9 Results on infection could only be pooled from 9 of the 17 included studies in the systematic review, with fewer studies available for their pooled analyses of hardware problems (4 studies), cyclops lesions (2 studies), and graft failure (6 studies).9 A recently published randomized clinical trial, which was not included in the systematic review, only provided numbers of patients requiring a second-look arthroscopy for meniscus/cartilage, loose bodies, or notchplasty, and stated that there were no cases of septic arthritis or revision ACL reconstruction within the 2-year follow-up period.10

There are many other adverse events and complications associated with ACL reconstruction, which may not have been monitored in the published randomized clinical trials, and therefore, not reported. Additional complications of ACL reconstruction that have been reported in case series and retrospective literature include wound dehiscence, septic arthritis,11–15 deep vein thrombosis,16,17 and pulmonary embolism.18 Reported adverse events may also include meniscal and chondral pathology, graft reruptures requiring revision surgery, graft failures, contralateral ruptures, graft hypertrophy/cyclops lesions/arthrofibrosis,19–21 kneeling pain,22 hamstring strain/rupture,23 infections,24,25 and nerve injury.26,27 Csintalan et al28 reported the risk factors and incidence of nonrevision reoperations for meniscal and cartilage problems, hardware removal, and arthrofibrosis, based on information collected in an ACL reconstruction registry over a 6-year period. Hettrich et al29 reported an 18.9% rate for repeat surgery in a multicentre cohort of 905 ACL reconstruction patients at 6-year follow-up, including ACL revisions (7.7%), and procedures for cartilage problems (3.9%), arthrofibrosis (5.4%), anterior debridement/cyclops (4.2%), deep infections (0.5%), and hardware issues (2.4%). However, the patient population in this database study is inconsistent and included primary and revision index ACL reconstructions, autograft, and/or allograft graft types, and multiple ACL graft sources (patellar, hamstring, tibialis anterior, Achilles tendon).29 The Scandinavian ACL Registry provides another source of prospective data on a large number of cases of ACL reconstruction in Denmark, Norway, and Sweden.30,31 However, reporting is largely voluntary and is not detailed enough to capture the adverse events and complications, such as those recorded in a well-designed RCT.

A large double-blinded randomized clinical trial comparing patients who received a patellar tendon (PT), single-bundle semitendinosus/gracilis tendon, and DB hamstring tendon (HT) ACL reconstruction was just completed.32 The purpose of this article was to prospectively identify and report on all complications and adverse events that occurred within the 2-year postoperative period.

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All 330 eligible patients (mean age: 28.5 years; 183 males/147 females; range, 14-50 years) of the double-blind randomized clinical trial met the defined inclusion criteria for the study.32 Patients were randomized using computer-generated allocation concealment methodology, with stratification by injury chronicity (acute ≤3 months) to one of the 3 anatomically positioned reconstructive surgical autograft options: (1) PT, (2) quadruple-stranded HT, or (3) DB using HTs.32 All patients received the same incisions, irrespective of group allocation. Detailed surgical protocols for each ACL reconstruction technique were previously described.32 Only patients with a significant meniscal repair were braced postoperatively, at which time knee immobilizers and restricted weight-bearing were recommended for 2 to 4 weeks. Patients and the independent trained examiner were blinded to treatment allocation until the 2-year follow-up period. Patients were evaluated by the independent trained examiner and orthopedic surgeon at all scheduled study visits at 2 weeks, 3 and 6 months, and 1 and 2 years postoperatively.

Patients experiencing any unexpected or unusual problems with their knee contacted the independent trained examiner directly by phone or e-mail. A careful history was subsequently taken over the phone to determine whether the problem would be considered an adverse event/complication requiring a specific visit to the clinic. Patients with potential complications/adverse events were seen in the clinic by the principal investigator/orthopedic surgeon and/or the independent trained assessor. This visit included a detailed history and physical examination to evaluate the patient's concern. Patients presenting with urgent or emergent concerns were seen in the hospital emergency department and subsequently diagnosed and managed accordingly. All life-threatening complications were emergently addressed and immediately reported to the institutional ethics board. Additional adverse events or complications were identified at the regularly scheduled follow-up visits. Kneeling pain, an outcome that was defined a priori, was specifically assessed as a potential adverse event by having the patients kneel down on the same hard surface (ie, the clinic floor). This was measured at baseline, 1 and 2 years, and reported by the patients on a scale of none, mild, moderate, or severe. All patients experiencing an adverse event or complication were followed until the issue was completely resolved or appropriately managed. This included follow-up phone calls, regularly scheduled visits and additional visits for those patients requiring specific treatment. Blinding of the patient and independent trained examiner to group allocation was maintained at all times where possible.

Interventions included prescription medicine (antibiotics, anti-inflammatories, and blood thinners), ultrasound, x-ray, arthroscopic surgery, and nonsurgical rehabilitative treatment. Treatment recommendations were based on individual patient needs and diagnoses. In cases where study patients experienced 1 or more different events, each issue was identified, addressed, and recorded separately.

Any deviations from the standard surgical protocol were routinely documented in the operating room.32 All deviations were verbally identified by the principal investigator/orthopedic surgeon and subsequently recorded by the research assistant on intraoperative report forms, while present in the operating room. This information was used to correlate with any reported postoperative complications or adverse events.

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Statistical Analysis

Descriptive statistics were performed on all occurrences that occurred within the first 2 years postoperatively from the primary ACL reconstruction procedure. Comparisons were made between the 3 surgical techniques and where appropriate χ2 analysis to compare the proportions of events. A 5% significance level and IBM-SPSS Statistics 20 software (SPSS, Chicago, Illinois) were used for all analyses.

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Ethical Considerations

The prospective double-blind randomized clinical trial (NCT00529958) was approved by the University of Calgary Conjoint Health Research Ethics Board (CHREB). All serious adverse events were reported to the CHREB within the required time frame.

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As previously described, the demographic characteristics, baseline meniscal and cartilage conditions, and disease-specific quality-of-life (QOL) outcome of the study population are provided in Tables 1–3, respectively.32







There were a total of 100 reported complications/adverse events that occurred in 88 patients (26.7%) during the initial 2-year postoperative period. Table 4 lists the frequency of these complications/adverse events, including 95% confidence intervals (CIs) for the occurrence rate. There were a total of 24 complications/adverse events with PT reconstructions, 32 with HT reconstructions and 44 with DB reconstructions (Table 4). Twelve patients had 2 complications and the remainder had only 1 complication. Other complications include reports suggestive of unconfirmed meniscal tears and chondral lesions, persistent effusions, and inflammation, but no complaints referable to hardware/implant issues (Table 4). The frequency of patients reporting kneeling pain was not included in Table 4 and has been reported separately (Table 8).



Twenty-five surgical procedures were performed in 24 different patients (PT = 7; HT = 9; DB = 8). There was no statistically significant difference between the ACL reconstruction groups. Table 5 shows the 12 patients (3.6%) who had repeat surgery for meniscal tears. Eleven of the 12 patients had a medial meniscal repair at the time of index surgery. The proportions of failed meniscal repairs were not significantly different between treatment groups (P = 0.581). Table 6 describes the 9 (2.7%) patients who had repeat surgery for problems related to intra-articular scarring. The other 4 operations were for the septic arthritis (0.3%), a wound dehiscence (0.3%), and 2 (0.6%) patients with problems related to chondral lesions requiring repeat arthroscopy.





One life-threatening massive pulmonary embolism was identified at 2 weeks post-DB ACL reconstruction. This 22-year-old male patient presented to the emergency department with complaints of shortness of breath, chest pain, dizziness, and an associated cough with hemoptysis. He was treated successfully with anticoagulation and an IVC filter with no long-term sequelae. He was investigated for a specific clotting disorder, but none was found. His 2-year ACL-QOL outcome score was 89/100, indicating an excellent result. One deep vein thrombosis, identified at 18 days postoperatively, was treated successfully with anticoagulant therapy with no clinical sequelae. This patient had a DB reconstruction with a 2-year ACL-QOL score of 88/100. One severe complication of septic arthritis, detected at 1 month postoperatively, was treated with arthroscopic washout, IV antibiotics, and successful preservation of the graft. Coagulase-negative Staphylococcus was the identified organism. This patient had an HT ACL reconstruction and ended up with a 2-year ACL-QOL outcome score of 92/100.

Seven patients (2.1%) had tibial periostitis diagnosed as pain, swelling, redness, and tenderness isolated to the medial surface of the tibia and distinct from pain in the knee. All patients presented within 2 weeks of the surgery. These patients were all treated successfully with nonsteroidal anti-inflammatory drugs (NSAIDs).

There was 1 (0.3%) deep wound infection, treated successfully with IV and oral antibiotics. Five patients (1.5%) had superficial wound infections that were treated with oral antibiotics.

There were 8 patients (2.4%) who had sensory nerve problems. Five (1.5%) were related to the graft harvest/portal incisions and 3 (0.9%) as a result of a medial meniscal repair. All of these nerve problems were resolved to the patient's satisfaction with local management except for 1 that resulted in long-term dysesthesia that was not acceptable to the patient.

Hamstring injuries on the ipsilateral side occurred in 19 patients (5.8%). Eighteen patients experienced a hamstring strain and 1 patient experienced a traumatic single HT tear (Table 7). Overall, there was an 8.2% incidence of hamstring injury in patients who had semitendinosus/gracilis tendons harvested. The 1 complete hamstring tear occurred as a result of a major traumatic event in a patient who had a PT reconstruction.



Moderate or severe kneeling pain at baseline was not statistically significant between the 3 groups. However, there was a trend toward less kneeling pain in the DB group compared with both the PT and HT groups (P = 0.07) (Table 8). At 2-year postoperative follow-up, a greater number of patients in the PT group experienced moderate or severe kneeling pain compared with the HT or DB groups. This was statistically significant between the PT and DB groups (P = 0.001), approached statistical significance between PT and HT (P = 0.054), and was not significantly different between the HT and DB groups (P = 0.122). Overall, the incidence of moderate or severe kneeling pain was 30/305 (9.8%).



Anterior cruciate ligament graft ruptures and reinjuries have been previously reported and accounted for an additional 10 operations in 9 patients performed within the 2-year postoperative time period.32 Overall 32/330 (9.7%) of patients had at least 1 reoperation for a complication/adverse event staging arthroscopy and/or revision on the reconstructed side within the first 2 years of the index ACL reconstruction. Three of these patients had 2 separate procedures.

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Complications and adverse events after ACL reconstructive surgery have been reported sparingly according to multiple systematic reviews and meta-analyses.9,33–36 This study included 330 patients who were involved in a randomized clinical trial to compare 3 reconstructive techniques. All patients were followed prospectively and with the expressed purpose of identifying any possible complication or adverse event. None of the adverse events or complications resulted in “unblinding” of the independent examiner, who documented all outcome information.

Overall, the complication or adverse event was reported in 88 patients (26.7%) with 32 (9.7%; 95% CI, 6.8-13.5) patients requiring a reoperation within the first 2 years. This represents a higher reoperation rate than published by Lyman, who reported a reoperation rate of 6.5% at 1 year,37 and lower than van Dijck et al,38 who reported a rate of 26.7% at a longer follow-up of 7.4 years.

There were only 2 major emergency complications (pulmonary embolism and septic arthritis). Despite these life-threatening and joint-threatening complications, both were treated effectively with no long-term consequences, confirming that ACL reconstructive surgery is a safe procedure.

The most common adverse event encountered within the first 2 years was related to meniscal problems (25 patients; 7.6%); half of these required repeat surgery. Eleven of the 12 patients had previous medial meniscal repairs. This represents a meniscal repair “failure” of less than 10%. The other patient had a previously healed meniscus that re-tore. The remaining unconfirmed meniscal problems did not require any surgical treatment. There were no lateral meniscal repair failures in the first 2 years after index reconstruction.

The next most common complication was related to intra-articular scarring. This included patients with arthrofibosis, cyclops lesions, and graft hypertrophy causing impingement at 2.7% (95% CI, 1.34-5.3). Graft impingement could be directly related to tunnel placement, but all patients had grafts positioned to ensure that full extension was achieved and confirmed intraoperatively. There was no statistically significant difference between PT, HT, or DB reconstructions with respect to this complication. One patient had their repeat surgery 5 days beyond the 2-year cutoff point, but the actual procedure was delayed for logistical scheduling reasons, and therefore, this patient was included. The Multicenter Orthopaedic Outcomes Network (MOON) reported a rate of arthrofibrosis procedures at 5.4%.29 They did not distinguish whether this was generalized scarring, localized cyclops formation, or graft hypertrophy.

Hamstring strains were exclusively in patients who had hamstring autografts (ie, HT and DB groups). This would suggest that hamstring weakness is a concern and that patients should be informed regarding this potential problem. One patient developed pain related to patellar tendinopathy in both knees, requiring local treatment and eccentric exercise over several months.

A unique finding of this trial was with respect to kneeling pain (Table 8). There was a significant difference between the PT group compared with the DB groups at 2 years. There was a trend toward significance comparing the PT and HT groups. However, all groups had less reported kneeling pain compared with baseline numbers. The DB group started with less kneeling pain at baseline compared with the HT and PT groups. By 2 years, only 4/104 DB patients still reported moderate or severe kneeling pain. The explanation for these findings is elusive but may reflect the fact that a DB reconstruction requires more dissection intra-articularly to help in visualization and extra-articularly for exposure. This extradissection may have resulted in sensory nerve damage, particularly in the fat pad, and therefore less pain on kneeling.39

No patients had any complaints referable to either the tibial or femoral fixation. This is in contrast to the literature.28,29 There were no patellar fractures associated with the PT reconstructions. However, it was routine to place any available bone from the harvesting as an autogenous graft into the patellar defect.

Reinjuries and reruptures of the ACL graft have been reported as a separate publication along with the evaluation of knee range of motion.32,40 There were no relationships between any specific complications related to documented deviations of the surgical protocol, although the small numbers would make a specific analysis meaningless. Sensory nerve disturbances occurred in 2.4% (n = 8) of patients, but this was only a significant issue in 2 patients. These patients required topical treatment with NSAID cream and corticosteroid injections. One patient had dysesthesia that was unresolved.

There were limitations to this study. One minor limitation may be that the 2-year follow-up period is insufficient to determine the long-term effects of some adverse events, such as meniscal reinjuries, and osteoarthritis. However, it is anticipated that the long-term outcomes of these adverse events will be reported when the 5-year and 10-year follow-up data for this RCT become available. Also, some of the reported complications and adverse events were not confirmed with specific investigations or reoperations. However, the intent of this article was to report everything that occurred in this large randomized trial, so that surgeons can be made aware of potential similar concerns in their patients. This was considered to be of great importance, given the published literature does not currently provide any detailed reports of a comparable nature.

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Overall ACL reconstructive surgery is safe with major complications being uncommon. Secondary surgery was necessary for 7.3% of patients for complications or adverse events (excluding graft re-injury or revisions) within the first 2 years. Meniscal problems were common at 7.6%, with half requiring repeat arthroscopy. Hamstring injury was much more common in the HT and DB groups. Nearly, 10% of patients had kneeling pain, which was higher in the PT group. Scar-related problems requiring surgical treatment occurred in 2.7% of patients. Major complications of pulmonary embolism and septic arthritis were uncommon and were treated effectively with no consequences. The majority of complications and adverse events were minor and required simple nonsurgical treatment.

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anterior cruciate ligament; quality-of-life; randomized clinical trial; patellar tendon; quadruple hamstring tendon; double-bundle; autograft; complications; adverse events

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