Introduction

Little is known about the surgical timing of ACL surgery, and available data were mainly created many years ago. One concern about acute ACL reconstruction immediately after injury is a consecutive deficit in range of motion (ROM) of the involved knee joint. Orthopaedic surgeons prefer to delay ACL reconstruction for at least 6 weeks following injury with the assumption to avoid arthrofibrosis, but studies investigating that issue report controversial results [1, 4, 14, 18, 24, 28, 30, 36, 39]. It is well known that a delay of ACL reconstruction in patients with a symptomatic unstable knee is accompanied by a significantly increased risk of chondral and meniscal damages [2, 3, 7, 8, 12, 13, 22, 23, 34]. It has further been shown that an early ACL reconstruction is more cost-effective than a delayed surgery after an early preoperative rehabilitation [29, 37]. Besides the economic factors and the significantly increased risk of further damages to the ACL deficient knee, an early treatment is of special interest to competitive athletes to avoid an unnecessary delay between injury and return to sports.

In the literature, there is no consistent definition of acute and chronic resulting in non-homogenous data regarding the outcome of early ACL reconstruction [10]. Recently published studies investigating cytokine levels in the knee joint following ACL injury might help to understand the inflammation cascade and adapt the definition of acute, subacute and chronic from the biochemical point of view [5, 20]. For example, transforming growth factor beta (TGF-ß), which stimulates cell proliferation, increases continuously after ACL injury but does not reach its maximum within the first week [15].

Previous studies investigating the influence of surgical timing used predefined time frames for acute and delayed ACL reconstruction [4, 18, 39, 41]. Instead, the state of inflammation of the involved knee joint (i.e. intra-articular effusion, ROM, quadriceps inhibition) may play a role when discriminating between acute and delayed surgical timing.

Therefore, the purpose of this study was to investigate the outcome of acute ACL reconstruction within 48 h after injury compared to delayed ACL reconstruction during the “inflammation-free” interval, defined as the time point where patients had a ROM of at least 90° of flexion and not more than 5° of extension deficit and no or only moderate effusion and pain. Despite early postoperative rehabilitation protocols and the lack of clear definition of acute and delayed surgery, it was hypothesized that an acute ACL reconstruction results in inferior patient reported outcomes and higher frequency of range of motion deficits.

Materials and methods

Two hundred and six consecutive patients with an ACL tear were included in this prospective non-randomized clinical trial. Inclusion criteria for the study were: (1) Preoperative magnetic resonance imaging (MRI) and physical examination showing an ACL injury with or without concomitant meniscal tear, (2) Written informed consent to participate in the study. Exclusion criteria were: (1) ACL re-ruptures, (2) Refusal to participate in the study, (3) Concomitant grade II and III medial collateral ligament and lateral collateral ligament injuries as well as posterior cruciate ligament injuries, (4) Concomitant fractures, (5) prior meniscal surgery and (6) neurological or cardiovascular disorders.

According to the interval between injury and first presentation in the office, patients were consecutively assigned to the study groups between January 2010 and December 2011 until a number of 50 patients with isolated ACL tears and 30 patients with combined ACL and meniscal tears for both, the acute and delayed surgical groups were achieved (Table 1). For patients who contacted the office within 48 h after injury, met the inclusion criteria and were willing to undergo immediate surgery, acute ACL reconstruction was performed. All other patients were assigned to the delayed reconstruction group, with surgical intervention during the inflammation-free interval and after an early rehabilitation protocol. Knee joints with a range of motion (ROM) of at least 90° of flexion and not more than 5° of extension deficit and no or only moderate effusion and pain were considered as inflammation free.

Table 1 Study groups
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During the study period, 46 additional patients who underwent acute or delayed ACL reconstruction in combination with partial meniscectomy were recorded to investigate the influence of surgical timing on the frequency of meniscus resection. However, these patients were not considered for the subjective and objective follow-up examinations because clinical follow-up on these patients was not available.

Surgical technique

In each patient, an anatomical single-bundle ACL reconstruction (Fig. 1) with autologous hamstring tendon grafts (minimum graft diameter in this study: 7.0 mm) was performed by one of three experienced knee surgeons (C.F., C.H., P.G.). The femoral bone tunnel was carried out through an anteromedial portal in maximum knee flexion and was placed in the centre of the native footprint. For tibial bone tunnel placement, the ACL stump and the anterior horn of the lateral meniscus were used as landmarks. For femoral graft fixation, an extracortical button with a continuous loop was used. On the tibial side, the graft was fixed using a bioabsorbable interference screw and an additional extracortical fixation via a cortical bone bridge or a small fragment screw with the knee in 20° of flexion.

Fig. 1
figure 1

Intraoperative images of an anatomic ACL reconstruction on a left knee. In image a, b, c the guide wire was placed within the femoral and tibial footprint. After insertion of the femoral guide wire, the remnant has been removed (b). Image d shows the passed hamstring tendon graft with fibres of the tibial ACL stump on its distal part

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For those patients with a repairable meniscus tear [25, 27, 32, 42], an all-inside meniscus repair was performed with the Fast-Fix® device (Smith & Nephew, Andover, Massachusetts).

Rehabilitation

All patients underwent a standardized rehabilitation protocol. Patients wore a brace with flexion restriction at 90° for the first 4 weeks after surgery. In cases of additional meniscus repair, flexion was restricted at 60° for the first 4 weeks. During this period, only partial toe-touch weight bearing was allowed. Physical therapy was initialized on the first postoperative day with special focus on knee extension. Isometric and closed chain exercises were started after one week. Bicycling was allowed after 3 weeks, and running and sport-specific exercises were started 3 months postoperatively. After 4 to 5 months, patients underwent a standardized ACL test battery to identify individual deficiencies to adapt the rehabilitation protocol [17]. At 8 months after surgery, the subjects performed the same test battery to determine the return to strenuous and competitive sports [16].

Patient evaluation

Demographic data were obtained at baseline and included patient age, gender, injured side, time from injury to surgery and concomitant injuries.

Standard radiographs and MRI were obtained for all patients to rule out any additional bony injuries and to evaluate ligamentous, cartilaginous and meniscal injuries.

Lysholm score, Tegner activity level and the visual analogue scale (VAS) for pain were obtained preoperatively, and patients were asked to refer to the status prior to the ACL injury. Preoperative examination was completed with a physical examination, including ROM, Lachman, anterior drawer and pivot shift testing. Grading of the ROM, Lachman, anterior drawer and pivot shift test was in accordance to the International Knee Documentation Committee (IKDC). Additionally, the objective IKDC score was obtained preoperatively.

Follow-up examinations were performed at 6, 12 and 24 months postoperatively by one of three experienced orthopaedic surgeons (C.F., C.H., P.G.). At all follow-up visits, patients underwent a full physical examination and objective IKDC knee examination form as well as the Lysholm score, Tegner activity level and VAS for pain were obtained.

Additionally, ROM values, ACL graft failures, contralateral ACL ruptures and meniscal repair failures with necessity of revision meniscus surgery were recorded during the 24-month study period. Patients with ACL graft rupture or contralateral ACL tear were not considered for the upcoming follow-up evaluations from the time point where the re-tear occurred.

Approval from the institutional review board of the Medical University of Innsbruck, Austria (AN2015-0050 346/4.28) was obtained. All included patients gave their written informed consent to participate in the study.

Statistical analysis

A post hoc power analysis using G*Power 3.1.9.2 (Franz Paul, Kiel, Germany) was used to determine the power of the present study. Based on passive range of motion deficits at final follow-up, an effect size of 0.42 was calculated. With the corresponding effect size and an α of 0.05, a power of 0.93 was achieved.

For statistical analysis, SPSS® 20.0 (IBM SPSS Statistics, New York, USA) for Mac was used. Quantitative parameters are expressed as means ± one standard deviation (SD) and the 95 % confidence interval (CI). To evaluate differences between the two surgical timing groups regarding ACL and meniscus re-rupture, partial meniscus resection, contralateral ACL tear, and IKDC and physical examination results, respectively, the Pearson Chi-squared test was used. The Mann–Whitney U test was performed to analyse the results of Lysholm score, Tegner activity level and VAS for pain. With the Friedman test, subjective outcomes over time within the groups were evaluated. The significance level was set at p < 0.05.

Results

Demographic data of the study groups are displayed in Tables 2 and 3. The only significant difference between the different groups was the gender distribution in the combined ACL reconstruction and meniscal repair group (p = 0.032). Only one patient was lost to follow-up in the delayed isolated ACL reconstruction group.

Table 2 Patient demographics at baseline (isolated ACL tear)
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Table 3 Patient demographics at baseline (combined ACL tear and meniscus tears)
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Patient reported outcomes

Figure 2 shows the Lysholm scores during the follow-up period of all patients who underwent isolated ACL reconstruction and combined ACL reconstruction and meniscus repair. There was no statistical significant difference at any time point between the acute and delayed treatment groups (n.s.). The same results were observed for the VAS for pain and the Tegner activity level, respectively. At final follow-up, the Tegner activity level for patients with an isolated ACL tear was 6.7 ± 1.3 SD (CI 6.3–7.1) in the acute and 6.3 ± 1.4 SD (CI 5.9–6.8) in the delayed group (n.s.). For patients, who had an ACL reconstruction and meniscus repair, the Tegner score at 24 months was 6.6 ± 1.3 (CI 6.0–7.2) in the acute group and 6.3 ± 1.5 (CI 5.8–6.9) (n.s.).

Fig. 2
figure 2

The left chart displays the Lysholm score in patients who underwent isolated ACL surgery, whereas the right chart shows the combined ACL reconstruction and meniscus repair group. No significant difference between an acute and delayed treatment was found at any time point

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Objective IKDC and manual laxity measurements

The overall objective IKDC as well as manual laxity measurements did not display any significant differences between acute and delayed treated subjects at any follow-up time (n.s.), regardless of the performed procedure.

Passive range of motion

Tables 4 and 5 display the distribution of range of motion scores according to the objective IKDC at 6, 12 and 24 months in the study groups. No subject treated with an acute or delayed isolated ACL reconstruction had a flexion or extension loss of more than 15° and 5° at any time point, respectively. No statistical significant difference was detectable between acute and delayed treated patients with an isolated ACL tear.

Table 4 ROM according to the IKDC (isolated ACL reconstruction)
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Table 5 ROM according to the IKDC (combined ACL reconstruction and meniscal repair)
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Statistically significant more patients who underwent delayed combined ACL reconstruction and meniscus repair had a lack of extension grade B according to the IKDC at 12 months following surgery (p = 0.043). However, at 6 and 24 months, the passive ROM was comparable between the acute and delayed combined ACL reconstructions and meniscus repairs.

Regardless of the injury pattern, arthroscopic removal of a cyclops lesion was necessary in 5 (6.3 %) patients in the acute groups and in 2 (2.5 %) subjects who underwent a delayed procedure (n.s.).

Graft rupture, contralateral ACL injury and meniscus repair failure

All patients with either graft rupture or meniscus repair failure reported a new trauma. Of those patients who underwent isolated ACL reconstruction, 12 % in the acute group and 4 % in the delayed group sustained a graft rupture during the study period. However, the difference was not significant (n.s.). In the combined ACL reconstruction and meniscus repair groups, the graft rupture rate was 16.7 % in the acute and 3.3 % in the delayed group (n.s.).

The incidence of contralateral ACL injuries did not differ statistically significant between acutely and delayed treated patients (isolated ACL reconstruction: 2 versus 4 %; combined ACL reconstruction and meniscus repair: 3.3 versus 6.7 %).

Although meniscus repair failures were higher in the acute group, no statistical significant difference was detected (23.3 vs. 16.7 %; n.s.).

Surgical timing and partial meniscectomy

Patients who underwent combined ACL reconstruction and partial meniscectomy were significantly older than those who underwent ACL reconstruction and meniscus repair (p < 0.001). However, the rate of partial meniscus resections did not differ between acute and delayed treated patients (n.s.)

Discussion

The most important finding of this study was that acute ACL reconstruction lead to improved outcomes in patients with a combined ACL and meniscus surgery in terms of restoration of ROM at 12 months disproving the hypothesis. In this study, acute surgery resulted in a clinical relevant extension and flexion loss for only 4.9 % of patients with an isolated ACL reconstruction and 4.2 % of patients with combined ACL reconstruction and meniscus repair. No significant difference regarding ROM between acute surgery within 48 h and a delayed surgery during in the inflammation-free interval was observed. Previous studies found that timing of ACL surgery does not influence postoperative ROM, when the surgery was performed within the first 2 weeks after injury or delayed for more than 3 to 6 weeks [6, 18, 31]. These findings are in contrast to other studies, where an acute ACL reconstruction was highly correlated with loss of ROM in up to 37 % of the cases [14, 35, 39, 45]. Interestingly, all of these studies were performed in the early 1990s or are a retrospective review of patients operated during that time [30].Therefore, those reported high rates of decreased ROM might be accounted for by a restrictive postoperative rehabilitation protocol as well as the non-anatomical ACL reconstruction that was typically performed during the 1990’s [18]. Van Griensven et al. [44] stated in their review article that an accelerated rehabilitation results in superior outcomes, including restoration of full ROM, compared to a more restricted protocol. In fact, more recent studies did not find any significant differences regarding ROM following acute or subacute ACL reconstruction [18, 24, 36, 41].

No evidenced based threshold to classify injuries as acute or chronic does exist in the literature. Commonly, acute is considered if the ACL tear is not older than 6 weeks. But, 23 % of the studies investigating the influence on surgical timing classified ACL injuries as chronic even if the surgery was not performed within 6 weeks [10]. Therefore, it is nearly impossible to compare the studies and to create evidence out of them. One possibility to differ between acute and chronic is the measurement of cytokine levels in the synovial fluid after ACL injury. It is well known that pro-inflammatory cytokine levels increase continuously over the first days following an ACL tear with a primary catabolic response [5, 9, 15, 20]. In this study, acute was considered as surgery within 48 h after ACL injury, whereas a delayed procedure was performed during the inflammation-free interval, regardless of the time point. This is reasonable since different studies reported a preferable outcome, when the knee shows no major signs of inflammation [24, 28, 30, 38].

From the literature, it is known that a delay of ACL reconstruction between 3 and 6 months leads to an increased risk of further or additional meniscal and cartilage damage [2, 3, 23, 33, 48]. Granan et al. [12] found that each month of delayed ACL reconstruction results in an increased odds ratio of further cartilage and meniscal damage of 1. Brambilla et al. [7] could demonstrate that a delay of ACL reconstruction is associated with a 0.6 % higher risk per month for further joint injury. Additional to the risk of further damages to the knee, it is obvious that especially athletes try to avoid an unnecessary delay regarding return to sports due to a delayed ACL surgery.

The ACL graft failure rate in this study was higher for the acute surgical groups. However, no statistical significance was detected between the two surgical time points. In general, ACL re-rupture rates vary in literature but are around 4–5 % depending on the follow-up period [11, 19, 21, 46]. These values are much lower than in this study. One explanation might be that the study population consists of highly active patients. Webster et al. [46] found an odds ratio of 3.9 for ACL re-injuries, when patients returned to cutting or pivoting sports following ACL reconstruction. In fact, in a recently published work of Sikka et al., the ACL re-rupture rate in professional hockey players was 8.5 % [40] and thus higher compared to other studies. Hunter et al. [18] found an increased re-operation rate in patients who underwent ACL reconstruction within 3 weeks of injury from 0 to 8 %. In the present study, arthroscopic removal of a cyclops was necessary in 6.3 and 2.5 % of the patients in the acute group and delayed group, respectively.

Lastly, it should be mentioned that an early ACL reconstruction is more cost-effective than a delayed surgery after an early preoperative rehabilitation [29, 37].

Although, it is known that meniscus repair failures are lower when performed during ACL reconstruction [26], in this study, re-injury of the repaired meniscus was observed in up to 23.3 %. These results are differing from reported failure rates between 5.5 and 14 % [43, 47]. The reason for the high meniscus re-rupture rates in this study might be due to the highly active study population with reported adequate trauma causing the re-injury. According to the current literature, the reparability of a meniscus tear depends significantly on the time elapsed between injury and surgery. This is especially true, when surgery is performed 6 months after the initial injury [23, 33, 48]. However, the present study could not find a significant difference with respect to meniscus repair and meniscus partial resection between acute and delayed treated patients. This might be due the fact that most patients in the delayed group underwent ACL reconstruction within 3 months following injury.

This study has limitations. The sample size might be too small to detect significant differences regarding ACL re-tear rates. Further, no randomization was performed. On the other hand, strengths of the study are the strict definition of the time points for surgical intervention based on the time from injury to surgery in the acute group and on the status of the knee joint in the delayed group. Further, the loss to follow-up rate was negligible (n = 1).

Conclusion

This study demonstrates that the outcome of an ACL reconstruction does not depend on surgical timing. Acute ACL reconstruction within 48 h can be performed in highly active patients and competitive athletes to avoid an unnecessary delay for return to full activity.