Between July 2009 and February 2014, 127 patients with isolated ACL ruptures underwent DIS repair within median 11 days (minimum 0, maximum 21 days) from injury at an academic institution (single-center).

Inclusion criteria were defined as: > 18 years of age, closed growth plates, diagnosed with an isolated proximal ACL rupture based on MRI and in intraoperative findings, performance of surgery within 21 days from the day of injury and a minimum postoperative period of 60 months.

Exclusion criteria were multi-ligamentous injuries (MCL tears grade 1 were not excluded) and additional injuries to the same leg, like fractures.

As shown in Figs. 1 and 2, a total of 102 cases fulfilled the inclusion criteria. Out of those, 15 cases were excluded due to the rupture location and 10 patients were lost to follow up. Thirty-one patients had a re-rupture and/or revision within 5 years. Of the remaining patients, 47 were available for clinical follow-up, 24 were available telephonically and answered our questionnaires without clinical examination. Patient demographics are shown in Table 1.

Fig. 1
figure 1

Flowchart illustrating patient inclusion

Fig. 2
figure 2

Arthroscopic picture of the collagen matrix ACL augmentation in a right knee

Table 1 Patient demographics

Surgical technique

DIS Surgery was performed as previously described by Kohl et al. [18].

In most cases, there was a concomitant meniscal tear found. Based on individual need meniscal surgery was performed, as displayed in Table 1. DIS repair was augmented with a collagen fleece and/or PRF in 45/102 patients.

Two very similar fabrics of collagen matrices were used (Novocart, B. Braun Medical AG, Melsungen, Germany (n = 24) and Chondro-Gide, Geistlich Pharma AG, Wolhusen Switzerland (n = 14)). PRF was applied inside the Collagen sheathing in three cases. Single PRF was used in seven cases.

The following technique described formerly by Evangelopoulos et al. [8] was used for the Collagen Typ I/III membrane wrapping. In brief, the membrane was cut in oval shape and three PDS 3.0 sutures were placed (proximal, distal-medial, distal-lateral) at the edge of the collagen sheath. The prepared collagen was wrapped to the ruptured side at the anterior surface of the ACL. The proximal suture was tightened by a trans-osseous fixation along with the arming of the ACL. The distal sutures were shuttled through 2.4-mm k-wire holes at the anteromedial and anterolateral surfaces of the proximal tibia and tightened over the bony bridge between those holes. Figure 2 shows an arthroscopic picture of the augmentation technique.

PRP was extracted from patient blood samples as recommended for AngelTM System (Arthrex Inc., Naples, Florida, US). The combination with Arthrex activAT offers the opportunity to prepare autologous thrombin to process the PRP into PRF. The autologous PRF was applied inside the Collagen sheathing. In the seven cases no collagen coverage was used, it was applied directly to the rupture site.

Postoperatively, full weight bearing was allowed for the patients with isolated ACL ruptures and those with partial meniscectomy, using a brace for the first week. Due to meniscus refixation, partial weight bearing was requested in 65 cases for 6 weeks. After 2 weeks strength training and after 9 weeks sports training was started.

Outcome measures

The minimum interval for final follow up was 60 months, median 72 (60–117) months. Patient reported outcome measures (PROMS) were collected for subjective assessment. All 102 patients answered Tegner, Lysholm and IKDC (subjective) questionnaires. Two groups were built, analogous to Ahmad et al. [1], one consisting of the patients with a Tegner activity level up to six and the other with Tegner 7 or more. This grouping showed a nearly balanced distribution of 40/102 versus 62/102. Furthermore, it characterizes the cutoff between recreational and competitive sports and a Tegner activity scale > 6 has been identified as a risk factor for failure [19].

In 47 patients available for physical examination the IKDC objective score (Group 1–4) was additionally determined. In these patients, joint stability was evaluated clinically and range of motion (ROM) was measured in degrees with a goniometer. Antero-posterior (a.p.) translation was examined at 20° flexion using the KT-1000 device, calculating the mean of three repetitive measures, respectively compared to the uninjured side.

Endpoint definition of failure

Failure as endpoint was defined as traumatic re-rupture or conversion to ACL reconstruction within the follow-up interval.

Statistical analysis

SPSS statistics was used for data analysis (IBM SPSS Statistics, Version 25 for Windows). According to a Kolmogorov-Smirnov-Test data was not normally distributed and is therefore given as median with range. Simple descriptive statistics were used to answer the study questions. A Wilcoxon signed-rank test was used to compare ordinal data and a student’s t-test to compare quantitative data. The significance level was set at p < 0.05. Kaplan-Meier survival analysis and Log Rank test were performed, results are given in estimated survival and standard error (S.E.). Binominal logistic regression was used to identify factors influencing failure.

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