This study evaluates the incidence of radiographic knee osteoarthritis in comparison to the contralateral knee, 10 years after a bone-tendon bone (BTB) patellar autograft ACL reconstruction. The long term effect of ACL reconstruction requires documentation to provide surgeons with a rationale for treatment protocols. This may help surgeons to prognosticate long term effects and educate patients regarding future use of their knees. ACL reconstruction techniques and the rehabilitation programs have evolved rapidly in the past decade. These changes were made with the objective to improve function and ROM post-operatively. These recent changes require additional research to clarify the long term prognosis of the current surgical and rehabilitation techniques. For this reason Lohmander proposed a national register of reconstructive procedures for ACL reconstruction .
With a satisfaction VAS of 8.5, the patients are content with the post-operative result of the ACL reconstruction compared to the contralateral side.
Concerning the IKDC grade, Irrgang  stated that it may be better to consider knees of grade A and B as one group and those of grade C and D as another. This helps to delineate the abnormal results found in grades C or D. In our study 86% of the patients are in the first group (IKDC A and B) at 10 year follow-up. According to Jomha et al.  there is no relationship between the IKDC grade and the post-operative levels of activity. This suggests that even people with stable and symptom free knees do not necessarily return to pre-trauma activities and those changes in individual preferences may account for some modifications in level of activity.
Documenting pre- and post-injury sports activity is an important part of the patient evaluation because disability for sports after ACL injury is the principle reason that patients request ACL reconstruction . One problem with evaluation of knee function, symptoms and activity is that different scores influence each other. The Lysholm score in the present study revealed a mean value of 91 points, but if the ACL reconstructed knee is not challenged by demanding activity, cutting and pivoting sports performance, the score may appear too high, and will reflect the actual function of the knee as well as the satisfaction of the patient. The Lysholm score has never been validated for the purpose of following ACL laxity in spite of its widespread use and that it has problems with a ceiling effect.
We found only a slight decline in activity and sports performance, as specified in a drop in Tegner score from 6.8 to 6.0. In patients who decreased three levels this was all due to non-knee-related reasons. After the follow-up the patients are 10 years older and logically most patients are less active and perform less sport.
Clinical evaluation of anterior displacement and anterior endpoint with the Lachman test has been used to diagnose the ACL disruption with test sensitivity ranging from 73% to 99% [38–40]. There remains a controversy about the usefulness of the KT-1000 as a device to measure the anterior-posterior displacement and to diagnose an ACL disruption. Daniel  postulates that there is a 98% probability that a KT unstable knee had an ACL disruption. To avoid false measurements, careful instrument positioning/placement, patella stabilisation, and patient relaxation is required [41, 42]. In our study we found that 45% of the patients had a greater anterior-posterior displacement on the operated knee than on the contralateral knee at 10 years follow-up.
The surgical procedure for reconstruction of the ACL may be of importance regarding the risk of eventually developing knee OA. The major factor with the potential to diminish this risk is improvement and maintenance of joint stability, resulting in a lower frequency of repeat injuries, especially of the meniscus. In this study no correlation between the remaining instability measured by the KT-1000 arthrometer and the grade of OA 10 years after the ACL construction was observed.
On the other hand, operative trauma with haemarthrosis, and the occasional necessity for repeated operations, may increase the risk of developing OA. Another factor of possible importance might be the required tension of the graft and the post-operative rehabilitation programme. It has been shown that over-tensioning of the graft can cause changes in knee joint kinematics that may lead to knee OA in the long term [43, 44]. Post-operative arthrofibrosis with decreased ROM may also increase the risk for knee deterioration especially in the patellofemoral joint.
The association between meniscectomy and OA has been well documented [45–49]. Medial meniscectomy is more often associated with severe radiologically demonstrable degenerative changes than lateral meniscectomy . Meniscectomy diminishes the joint contact surface area and increases stresses on the tibia . A number of studies have shown that protection of the injured meniscus at the time of ACL reconstruction may be the best chance of slowing down or preventing osteoarthritis in the knee [51, 52]. Leaving meniscal tears untreated has not been found to cause any clinical symptoms after ACL reconstruction with a medial follow-up of 2.6 years .
Several studies have demonstrated that a higher age at injury or onset of symptoms after knee injury is associated with an increased progression rate of OA [21, 54–57]. Yet, several of these reports fail to present adequate data on the age of the patients at time of the injury. In this study a subgroup analysis to evaluate differences in outcomes measurements for different ages at time of ACL rupture was not realistic
Endogenous factors may be contributing to the development of OA and will cause further variation in the frequency of post-traumatic OA after ACL reconstruction. It was shown that patients with meniscectomy who had an endogeneous risk factor for primary OA, reflected by distal interphalangeal OA had a higher frequency of knee OA than patients without this sign . Other endogenous risk factors may be present in the form of genetic variability in the structure of the gene of cartilage type II collagen [59, 60].
Osteochondral lesions and osteoarthritis in young patients are often caused by chronic knee instability and varus or valgus malalignment. These knees can be sufficiently treated by osteotomy and cruciate ligament reconstruction at the same time, suggesting that unicompartimental decompression and treatment of instability is a causal and cost-effective therapy delaying the progression of osteoarthritis and minimizing clinical symptoms [49, 61]. People with abnormal joint anatomy or alignment, previous joint injury or surgery, joint instability or above average body weight also appear to be at a greater risk of developing osteoarthritis .
An increase in frequency of joint changes with increasing time after the injury has been noted in several reports [23, 26, 46, 56, 63, 64] while others have failed to confirm this observation [21, 54, 65]. This variability may be explained by the fact that not all cases of knee OA progress [66, 67]. It may also due to the heterogeneous study groups and the use of outcome measurements of low precision and reproducibility.
Many reports have noted different frequencies of OA, depending of which criteria were used to define the presence of OA on radiographics. To undermine this problem we used two scales to classify the post-traumatic OA of the knee. Clearly the method used to evaluate the radiographic OA has a significant influence on the apparent outcome of the study. Using two radiographic scales yielded no different conclusions. Daniel described radiographic OA changes (own classification) in 50% of the ACL-injured knees after 5 years. These changes were even more frequent in surgically than conservatively treated patients . Since many studies use different radiographic scales, different clinical outcome measurements and different follow-up periods the results of the studies are difficult to compare .
In this study ACL reconstruction was not able to prevent radiological knee OA despite the fact that the patients with the most severe osteoarthritis, the patients who received a knee arthroplasty, were excluded in this study. This seems substantiated in the meta-analysis of 33 studies by the apparent inability of repair or reconstruction of the ACL to delay the progression of OA after knee injury . The question remains whether continued activity on the same or slightly lower sports level is recommended after ACL injury. Roos  and Sommerlath  found a higher OA rate in very active patients. However the cause and effect relationship is unclear and therefore no conclusion can be drawn about the outcome for an individual who changes activity.
As already proposed by Daniel [1
] five possible explanations for the development of OA in the reconstructed knee are:
Greater injury in the reconstructed knee before surgery than in the patients who did not choose reconstruction
Joint injury occurring at the time of surgery
The joint's response to stress deprivation after surgery 
Prolonged joint inflammation after surgery [72, 73]
Abnormal joint mechanics after surgery 
Our study had several limitations such as the retrospective character of our study; almost all studies that evaluate the development of knee OA after knee ligament surgery are retrospective because of the complexity of the injured knees with different types of tears in stable and unstable knees that make prospective trials difficult to perform. Twenty of the 28 patients had associated meniscal injuries. For the exact incidence of knee OA after ACL reconstruction surgery the results have to be compared with knee OA after meniscectomy in patients with intact ligaments and after isolated injuries to ligaments other than the ACL. The osteoarthritis in the ACL reconstructed can be due to the already mentioned associated intra-articular injuries but the osteoarthritis can also be developed in the period between trauma and reconstruction due to an unstable environment.
The surgery was performed by only one orthopaedic surgeon at our hospital which limits the extrapolation of the findings to other orthopaedics departments. The group of patients is relatively small and we did not mention the injury mechanism.
The strength or our study includes the long term follow-up, the use of validated outcome measures, the use of patient based and objective measurements, the comparison with the non- injured contralateral knee, the fact that the patients were operated in a relatively short interval of time, the patients were evaluated by an independent unbiased investigator, the evaluation of the standardised radiographics is done without the knowledge of patient identity. We agree with Lohmander that the time is right for a national register of reconstructive procedures for ACL reconstruction. This could assist in the identification of suitable procedures and ensure good quality .