Comparison of concomitant injuries and patient-reported outcome in patients that have undergone both primary and revision ACL reconstruction—a national registry study

Patients registered in the Swedish National Knee Ligament Registry (SNKLR) that had undergone ACL revision and also had a registered primary ACL were assessed for eligibility. Patients aged 13 to 49 years who received hamstring tendon (HT) autografts at the primary ACL reconstruction were eligible for inclusion. Hamstring tendon autografts are used in over 90% of all primary ACL reconstructions in Sweden [12], and another reason for limiting inclusion to HT autograft at primary ACL reconstruction was to obtain a homogenous study population with regard to graft choice at baseline. The graft choice at ACL revision was however not considered in the eligibility process as it was part of the study purpose to assess whether graft choice at ACL revision affected the outcome. Additionally, included patients needed to have available data for the Knee Injury and Osteoarthritis Outcome Score (KOOS) on at least one occasion (preoperative or 1 year) at both the primary and revision ACL reconstruction. Patients were excluded if they had a contralateral ACL reconstruction registered or underwent a contralateral ACL reconstruction within 2 years of the ACL revision since bilateral ACL reconstruction previously has been shown to result in inferior KOOS compared with unilateral ACL reconstruction [8] and, thus, could have affected the analysis. Finally, patients who had sustained a concomitant fracture, nerve, or vascular injury at either ACL reconstruction were excluded.

The SNKLR was established in 2005 and serves as a nationwide database with high coverage and compliance, including more than 90% of all ACL reconstructions performed annually in Sweden [13]. The surgeon-reported section includes reports of patient-, injury-, and surgery-related factors. All surgical procedures and intra-operative findings are documented. If a patient requires additional surgery, such as an ACL revision, this is registered as a separate entry which is linked to the patient’s primary surgery. The patient-reported part includes prospectively collected data in terms of the European Quality of Life-5 Dimensions (EQ-5D) and the KOOS, which are assessed at standardized timepoints following each ACL reconstruction. A detailed description of data collection has previously been reported [9].

Variables related to the following categories were extracted for the primary and revision ACL reconstruction: patient demographics, surgery-related factors, and intra-operatively identified concomitant injuries. Patient demographics included patient sex, age, and activity that led to injury/revision. The activity variable in the SNKLR includes sport and work-related activities, as well as activities of daily living (ADL). For this study, the most frequently reported sporting activities were reported separately, and the remainder were categorized as “other.” For surgery-related factors, the time from primary ACL reconstruction to ACL revision, graft type, and graft fixation were reported. The presence of intra-operatively identified concomitant injuries included meniscal, cartilage, and other ligament injuries. Injuries to the menisci were separated for medial and lateral injury and data on whether surgical treatment was performed (resection or repair) were extracted. The presence of cartilage injury was reported as yes or no and was further assessed for location (patella, femoral condyles, tibial plateaus, and trochlea) and severity according to the International Cartilage Repair Society (ICRS). The ICRS grading is based on cartilage lesion depth and ranges from 0 to 4. An ICRS of 0 represents normal cartilage, ICRS 1-2 involve less than 50% of the cartilage thickness, and ICRS 3-4 involve more than 50% of the cartilage thickness [14]. Concomitant injuries to other ligaments included the surgeon reporting a presence (Yes/No) of medial or lateral collateral ligament injury (MCL or LCL), posterior cruciate ligament (PCL) injury, and posterolateral corner (PLC) injury at time of ACL reconstruction.

The patient-reported outcome measurement used was the KOOS. The KOOS comprises five subscales—pain, knee-related symptoms, ADL, function in sports and recreation, and knee-related quality of life (QoL). The maximum score on each subscale is 100, which indicates no knee problems, while a score of zero represents the worst possible state [15]. The KOOS₄ is an average score (ranging between 0 and 100) of four subscales, where the ADL subscale has been excluded [16]. The KOOS₄ has been developed as a modification of the original KOOS to avoid a ceiling effect, since an ACL injury rarely causes problems in the ADL. For the purpose of this study, separate analyses were carried out for the KOOS₄ and each KOOS subscale, preoperatively and 1 year after primary and revision ACL reconstruction. The KOOS₄, KOOS sports and recreation, and KOOS QoL were regarded as the main outcomes in the predictive analysis of one-year outcome post-ACL revision. This was chosen since the KOOS sports and recreation subscale and the QoL subscales have been shown to be the most responsive subscales [17].

Statistical analyses were performed using the SAS statistical analysis system (SAS/STAT, version 14.2, 2016; SAS Institute Inc., Cary, North Carolina, USA). Descriptive statistics were reported as the mean and standard deviation (SD) and the median and range for continuous variables and as the count and proportion for categorical variables. The sign test was applied to analyze the change in the prevalence, treatment, and severity of concomitant injuries from primary to revision ACL reconstruction. Specifically, the sign test was used to analyze the difference in the proportion of patients with an increase or a decrease for each investigated concomitant injury from primary to revision ACL reconstruction. For injuries and performance of surgical treatments that were reported as “yes” or “no,” a decrease was defined as a change from “yes” at the primary ACL reconstruction to “no” at the ACL revision and an increase was defined as a change from “no” to “yes.” The severity of cartilage injuries ranged from “no injury or ICRS 0” to ICRS 4 and a decrease or increase referred to a patient changing one or more grades in either direction from primary to revision ACL reconstruction. The KOOS subscales and the KOOS₄ were analyzed as continuous variables and the preoperative and 1-year KOOS for primary and revision ACL reconstruction were compared over time using Wilcoxon signed rank test. In order to find predictors of the 1-year outcome after ACL revision, univariable linear regression models were used with the KOOS sports and recreation, KOOS QoL, and KOOS₄ as dependent variables in separate analyses. The distribution of the residuals of the dependent variables was inspected in a histogram and fulfilled the assumption of normal distribution. Independent variables for the analyses and the way specific variables were analyzed are presented in Table 1. Subsequently, a forward stepwise multivariable linear regression was performed. Predictors that reached a p value of < 0.10 in the univariable analysis were entered in the forward stepwise multivariable regression model. The results of the regression models were presented with β-coefficients, 95% confidence intervals (CI), and p values. All significance tests were two-sided and conducted at the 5% significance level.

Concomitant knee joint injuries at primary and revision ACL reconstruction are presented in Table 3. Meniscal injuries decreased at ACL revision (p < 0.001), as the reported meniscal status changed from injured at primary ACL reconstruction to uninjured at ACL revision in 277 patients (27.3%), while 183 patients (18.0%) had their first registered meniscal injury at ACL revision. There was no change in the number of medial meniscal injuries between primary and revision ACL reconstruction, while the lateral meniscal injuries decreased (p < 0.001). The prevalence of cartilage injuries increased from primary to revision ACL reconstruction (p < 0.001), as 23.0% of the cohort were identified with a cartilage injury at ACL revision that was not present at primary ACL reconstruction. There was a decrease in reported MCL injuries at ACL revision compared with primary ACL reconstruction (3.3% versus 1.2%, p = 0.003). Concomitant PLC injuries increased significantly between the surgeries (p = 0.002) and were present in three patients (0.3%) at primary ACL reconstruction compared with 16 patients (1.6%) at ACL revision.

Table 4 presents the ICRS grades for and locations of cartilage injuries and comparisons between primary and revision ACL reconstruction. A total of 263 patients (26.1%) had an increase in the reported ICRS grade at ACL revision compared with primary ACL reconstruction, while 75 patients (7.4%) had an improvement in ICRS grade (p < 0.001). At ACL revision, 93 patients (9.2%) presented with a grade 3–4 cartilage injury compared with 35 patients (3.5%) at the primary ACL reconstruction. The most common location of cartilage injuries was the femoral condyles, where 231 patients (22.9%) had a worsening in ICSR grade between primary and ACL revision and 77 patients (7.6%) had an improvement in ICRS grade (p < 0.001).

The comparisons of the KOOS are presented in Table 5. The preoperative KOOS for the ACL revision was significantly higher across all the subscales except the ADL and QoL, compared with the preoperative KOOS at primary ACL reconstruction. Conversely, the 1-year postoperative KOOS was significantly inferior after the ACL revision compared with the primary ACL reconstruction on all subscales except the QoL. The largest difference in the mean 1-year KOOS between primary and revision ACL reconstruction was in the sports and recreation subscale (5.2 points, SD 32.2, p = 0.002), followed by the pain subscale (3.1 points, SD 20.1, p = 0.003).

A significantly larger improvement from the preoperative KOOS to the 1-year KOOS was found with the primary ACL reconstruction compared with the ACL revision in the subscales of pain, symptoms and sports and recreation. The improvement in the sports and recreation subscale was 7.1 points (SD 46.9) lower with the ACL revision compared with the primary ACL reconstruction (p = 0.024). The difference in the symptoms subscale was 4.5 points (p = 0.011) and in the pain subscale 3.2 points (SD 28.2, p = 0.033).

A total of 482 patients had reported data for the 1-year follow-up after ACL revision and were included in the predictive analysis of the 1-year KOOS after ACL revision. Higher age at primary ACL reconstruction predicted a poorer outcome for KOOS sports and recreation and KOOS₄ in the univariable analysis (per 10-year increment in age). No other variable from the primary ACL reconstruction was a significant predictor of the one-year KOOS after ACL revision (data presented in Appendix).

With regard to the sports and recreation subscale, the following factors at ACL revision were significant negative predictors in the univariable analysis (p < 0.05); higher age, the use of allograft, a concomitant cartilage injury, a higher ICRS grade of cartilage injury (any location), an LCL injury, and a PLC injury, with β values ranging from − 35.23 (95% CI − 57.69; − 12.76) for a PLC injury to − 5.14 (95% CI − 8.55; − 1.73) for every 10-year increase in age. In the multivariable model, significant predictors were higher ICRS of any cartilage injury (β = − 4.55 [95% CI − 8.67; − 0.44], p = 0.030) and the presence of a PLC injury (β = − 29.20 [95% CI − 50.71; − 6.69], p = 0.011) at the time of ACL revision. Specifically, every one-step increment in ICRS category (ICRS 0, ICRS 1-2, ICRS 3-4) predicted 4.55 points poorer KOOS sports and recreation. Additionally, higher age at primary ACL reconstruction was a significant predictor of a poorer outcome in the multivariable model, resulting in a 4.69-point lower score for every 10-year increment in age (β = − 4.69 [95% CI − 8.38; − 1.01], p = 0.013). The multivariable model had an adjusted R² of 0.041 (Fig. 2).

For the QoL subscale, significant negative predictors at the time of ACL revision in the univariable analysis were the use of allograft, a concomitant cartilage injury, a higher ICRS grade of cartilage injury (any location), and a PLC injury, with β values ranging from − 30.13 (95% CI − 49.54; − 10.72) for a PLC injury to − 3.79 (95% CI − 7.26; − 0.31) for a one-unit increment in ICRS grade. Of these, the use of allograft (β = − 12.69 [95% CI − 21.84; − 3.55], p = 0.0066) and a concomitant PLC injury (β = − 25.21 [95% CI − 44.77; − 5.65], p = 0.012) were found to predict poorer QoL in the multivariable analysis (adjusted R² = 0.030) (Fig. 3).

The univariable analysis of the KOOS₄ identified the following negative predictors at the time of ACL revision; higher age, the use of allograft, a concomitant cartilage injury, a higher ICRS grade of cartilage injury (any location), an LCL injury, a PCL injury, and a PLC injury, with β values ranging from − 28.62 (95% CI − 45.19; − 12.04) for a PLC injury to − 2.63 (95% CI − 5.17; − 0.09) for higher age per 10 years. Significant predictors in the multivariable model were the use of allograft (β = − 11.40 [95% CI − 19.24; − 3.57], p = 0.0044) and a PLC injury (β = − 24.20 [95% CI − 40.96; − 7.43], p = 0.0048). The multivariable model had an adjusted R² of 0.036 (Fig. 4).

Treatment for cartilage injuries was not analyzed as a predictor of outcome since the majority of the cartilage injuries were left in situ (data not shown).