Introduction
Patient-reported outcome measurements (PROMs) are utilized to highlight the patient’s opinion of treatment outcome [
23]. For instance, PROMs are commonly used after anterior cruciate ligament (ACL) reconstruction where the Knee injury and Osteoarthritis Outcome Score (KOOS) is one of the most frequently reported ones in the literature [
10,
20]. In the KOOS, it has been suggested that a functional recovery for patients after ACL reconstruction can be defined as the lower threshold for the 95% CI of healthy 18- to 34-year-old males [
2,
16]. Moreover, a treatment failure has been suggested to be a KOOS QoL score of <44 [
9].
Previous studies including the KOOS have found that approximately 20–30% of patients after ACL reconstruction achieve a functional recovery or treatment failure, respectively [
2,
9,
12]. One of these studies conducted by Barenius et al. [
2] investigated patient-related and surgery-related factors to predict functional recovery and treatment failure in a cohort of patients with ACL reconstruction between 2005 and 2008. With regard to treatment outcome, the authors found that previous surgery on the menisci and a patellar graft were predictors of treatment failure and negative predictors of functional recovery after ACL reconstruction. In addition, a medial meniscus suture or resection at the time of reconstruction was predictive of treatment failure. Since this study was conducted, surgical procedures have evolved, where the use of anatomic reconstruction techniques has increased and has produced improved results in both biomechanical and clinical studies, compared with the older non-anatomic techniques [
13,
26]. To evaluate anatomic ACL reconstructions, a tool, the anatomic anterior cruciate ligament reconstruction scoring checklist (AARSC), has recently been published [
5,
25]. With new opportunities to perform and evaluate ACL reconstructive surgery, it remains to investigate whether detailed knowledge of the surgical procedures, with special emphasis on anatomic reconstruction, is able to predict patient-related outcome after ACL reconstruction.
The purpose of this study was therefore to investigate whether a detailed knowledge of surgical procedures was able to predict which patients have good and poor subjective knee function 2 years after ACL surgery in the Swedish National Knee Ligament Register (SNKLR). Specifically, the aim was to investigate whether the surgical technique of single-bundle ACL reconstruction, the visualization of anatomic surgical factors and the presence or absence of concomitant injuries at primary ACL reconstruction were able to predict patient-reported success and failure. The hypothesis of this study was that anatomic single-bundle surgical procedures would be predictive of patient-reported success. Increased knowledge of which patients do well or worse after treatment may in the future potentially help in terms of selecting appropriate for each individual patient.
Discussion
The main finding was that the absence of concomitant injury to the meniscus and articular cartilage predicted patient-reported success. In addition, the presence of a concomitant injury to cartilage was a predictor of patient-reported failure. Moreover, the surgical technique in single-bundle ACL reconstruction did not predict patient-reported success or failure in the KOOS4 at 2 years.
Injuries to the ACL are common and a reconstruction is one of the most commonly performed outpatient orthopaedic surgeries. Although there is general agreement that it is important to provide axial and rotational stability in the course of surgical reconstruction, the optimal method for doing so remains controversial. It has been suggested that non-anatomically placed grafts are exposed to fewer forces compared with anatomically placed grafts [
13]. The non-anatomically placed grafts may also result in residual rotational laxity of the knee, creating persisting instability [
6]. This instability may cause the patient to adapt his/her behaviour and activity level, which could potentially affect subjective knee function. Nevertheless, it has been suggested that PROMs provide an indirect measurement of functional stability [
24], but the present results may imply that the KOOS is suboptimal and is unable to detect any difference in knee kinematics affected by surgical technique in the short term. Additionally, the KOOS does not include any subscale or question related to perceived instability and the outcome could be too coarse to detect surgery-related differences in the knee. It is also possible to question whether the items in the KOOS are at all relevant when it comes to evaluating surgical outcome after ACL reconstruction. On the other hand, objective measurements of knee stability, such as a quantifiable pivot shift test, may be more appropriate for evaluating surgical technique and identifying small differences in knee-joint kinematics after using different ACL reconstruction techniques. However, no data on objective measurements of knee stability are kept at follow-up in the SNKLR.
Single-surgical factors, such as the identification of landmarks, footprints and both ridges, in addition to transtibial or transportal drilling, did not predict patient-reported outcome 2 years after ACL reconstruction in this cohort. Similarly, with regard to single-surgical factors, Duffee et al. [
7] compared the transtibial and transportal drilling techniques and reported no association between femoral tunnel drilling and KOOS Sport and KOOS Quality of Life. However, the authors reported that patients who underwent ACL reconstruction where a transtibial technique was used to drill the femoral tunnel had significantly higher odds of undergoing repeat ipsilateral knee surgery compared with those in whom the femoral tunnel had been drilled using an anteromedial portal technique. The authors dichotomized repeat ipsilateral knee surgery after primary ACL reconstruction as “Yes” or “No”, including revision ACL surgery, meniscus and cartilage treatment.
In this study, no analysis of concomitant injuries with regard to drilling technique was performed. However, it was shown that an articular cartilage injury at ACL reconstruction significantly affected patient-reported success and failure 2 years after reconstruction. The absence of an articular cartilage injury was a predictor of patient-reported success, but, in comparison, the presence of an articular cartilage injury was a predictor of patient-reported failure. It is possible to question whether the dichotomization of concomitant injuries, such as articular cartilage injury “Yes” or “No” in our study, may be insufficient when it comes to truly predicting patient-reported outcome after ACL reconstruction. Additionally, the treatment of cartilage or meniscus injury was not controlled for in this study. It might therefore might be possible that these injuries predicted a patient-reported failure only because they were not treated, or adequately treated, and not by the presence of the injury itself. Partly confirming this, Cox et al. [
3] showed that grade 3 and 4 articular cartilage lesions in various regions at index ACL reconstruction predicted poorer subjective knee function in the KOOS and International Knee Documentation Committee 6 years after surgery. Nevertheless, a concomitant injury to the articular cartilage appears to have a negative effect on patient-reported outcome [
3,
14,
21]. This is a concern in terms of future degenerative changes, osteoarthritis and long-term outcome among these patients [
15,
19]. In the future, it is recommended that the emphasis should be placed on treatment strategies aimed at restoring biomechanical function and delaying degenerative changes. Cox et al. [
3] also found that medial meniscus injury and treatment at ACL reconstruction negatively affected patient-reported outcome 2 years after surgery. In our cohort, the absence of a meniscus was predictive of patient-reported success, but no effect was found for patient-reported failure. Interestingly, Barenius et al. [
2], who investigated functional recovery and treatment failure after ACL reconstruction, found no effect of meniscus injury alone at the time of reconstruction in the KOOS 2 years after surgery. However, in their cohort, also from the SNKLR, a medial meniscus injury that required surgery was a predictor of treatment failure. Taken together, the results appear to provide further evidence of the improved patient-reported outcome in the short term when the meniscus is preserved at ACL reconstruction [
2,
3,
21,
22].
The most distinctive potential limitation of this study was the incomplete response to the questionnaire sent out to the surgeons and any recall bias. Nevertheless, the retrospective collection of detailed surgical data was necessary to obtain information relating to items in the AARCS. At present, the data kept in the SNKLR alone are insufficient to evaluate anatomic ACL reconstruction. Assuming correct answers from the questionnaire, the surgeons can still erroneously recall dates at which a certain technique was adopted. To minimize recall bias, responders were asked only to answer the questions if they were sure of the date, by specifying specific years and not months, on which they adopted or abandoned the surgical technique in question. Moreover, all patients who underwent surgery during time periods when the surgeon was “in between” surgical techniques were not included [
5]. There were also a large number of patients in the SNKLR with incomplete data and which therefore were excluded from the study. A non-response analysis of the SNKLR has been done showing that the register is valid despite the suboptimal number of patients responding at follow-up [
18]; however, it cannot be ruled out that the incomplete data may have bias the results. Further limitations of the present study are that rehabilitation and pre-injury sports participation had not been controlled for. A higher pre-injury level of activity has been shown to increase the likelihood of treatment failure after ACL reconstruction [
2]. In contrast, elite athletes have a higher rate of return to sport after surgery [
1]. In addition, Grindem at el. [
11] showed that patients who recover muscle strength and hop performance after ACL reconstruction are substantially less likely to sustain a re-injury to the ACL. Consequently, the incomplete data from muscle function and activity level may be confounders of our results. However, this is the first study to investigate whether anatomic single-bundle ACL reconstruction is able to predict patient-reported outcome 2 years after surgery. This study used the top and bottom quantiles of KOOS
4 responses in the SNKLR, defined as patient-reported success and failure. Whether the corresponding KOOS
4 for patient-reported success and failure correlates to the patients’ perception of treatment is not known. Recently, Ingelsrud et al. [
12] investigated the proportion of patients who reported acceptable symptoms or treatment failure. Moreover, they also defined the corresponding KOOS values for each subscale of the patients’ perception of treatment outcome. The KOOS
4 was not investigated, however, with regard to each subscale of the KOOS not including ADL, patients who reported acceptable symptoms had scores between 76 and 91 and patients who reported treatment failure had values between 31 and 58. The range presented for acceptable symptoms and treatment failure is extensive, but it does include the mean KOOS
4 values for our cohort and may therefore by comparable. However, the possibility cannot be ruled out that the KOOS could be too coarse to enable the use of predefined percentiles to determine patient-reported success and failure.
The strengths of the study include the large sample size in which the data were gathered from the National Knee Ligament Register covering a whole country, which implies that the results are highly generalizable across different hospital settings. The study highlights the fact that, in clinical practice, PROMs such as the KOOS may be insufficient to evaluate the surgical techniques used in single-bundle ACL reconstruction. Additionally, the results provide further evidence that concomitant injuries to the articular cartilage and menisci at ACL reconstruction affect subjective knee function and a detailed knowledge of the treatment of these concomitant injuries with respect to the timing of ACL reconstruction is needed.