The most important finding of this study is that PCL injuries caused by high-energy trauma are commonly associated with additional injuries that are prone to severe complications, even in the short term. This study's highest number of cases were classified as Schenck 2 (n = 201, 48.1%), which entails cruciate ligament injury of the knee. The most common complication was stiffness of the knee. The majority of PCL injuries and associated injuries were treated via single-stage surgery. Car accidents were more likely to lead to two-stage surgeries when the injuries involved ligaments other than the PCL, indicating the complexity of such injuries. Younger age and staged operations showed trends toward increased complications.

Although PCL injuries are less common than ACL injuries, they are often involved in high-energy ligament injuries to the knee [6, 23, 24]. Mild to moderate PCL injuries can usually be treated without surgery, but in severe cases or cases involving significant knee instability, surgery may be necessary [17]. However, more research has yet to be conducted on high-energy PCL injuries, and this study aimed to fill that gap by investigating associated injuries and complications with a large number of patients over a sufficient follow-up period [9, 10, 17]. Due to our country's high population and traffic accident numbers, the primary aim was to obtain numerically valuable information about high-energy PCL injuries from national registry data.

One of the key findings of this study was that high-energy PCL injuries had a complication rate of 12%. Additionally, there was an 11.3% incidence of associated fractures in acute trauma settings. In a study by Salzler et al. utilizing the American Board of Orthopaedic Surgery database, the complication rates of PCL reconstruction were reported to be as high as 20% [25]. However, that study did not investigate the complications in a detailed manner. The complication rates observed in this study were similar to those found in patients with multiple-ligament injuries, given the association of high-energy PCL injuries with a heightened incidence of multiple-ligament injuries [26]. Moreover, complications arising from the fixation of associated fractures were not examined in this study, potentially contributing to an underestimation of the overall complication rate.

Male patients were approximately five times more likely to suffer from PCL injuries, as also evidenced by various studies that consistently reported similar results, suggesting that high-energy traumas are often associated with activities more commonly undertaken by male individuals [9, 12, 17, 18]. Pediatric PCL reconstructions in individuals under the age of 15 years were notably rare (n = 4), precluding a statistical comparison or in-depth evaluation for that specific age group. However, within our cohort's age group of ≤ 18 years, a propensity for complications was observed (p < 0.001). It was surprising that complication rates decreased as the age groups increased. We speculated that this trend could be linked to the more complex nature of injuries with higher energy levels at younger ages in this cohort. However, recent research has indicated the opposite trend in the general population [21]. The slight increase in multiple-ligament injuries in the age group of ≤ 18 years might have affected the complication rate in this group.

The most common injury mechanism was car accidents (70.2%), followed by falls from heights (16.6%) and motorcycle accidents (13.2%). The rates align with various epidemiological studies concerning car accidents [12]. Moreover, in densely populated regions, transportation-related accidents are prevalent. In certain Asian countries, motorcycle accidents constitute the majority of vehicle accident-related PCL injuries, with studies highlighting an increased incidence of isolated PCL injuries with motorcycles due to direct knee-ground contact [12]. While motorcycle use is not as common in our country as in Asian countries, except for the southern regions, car accidents constituted the primary source of high-energy traumas in this study, as in Western countries [24, 27, 28].

High-energy injury to the knee usually results in injuries to multiple ligaments besides the PCL. ACL injury was the most common accompanying injury (n = 170, 40.1%) in this cohort, as expected and as stated in similar publications. The ACL is seen as the most common accompanying ligament injury in cases of PCL injuries. Owesen et al. found at least one concomitant ligament injury in nearly two-thirds of operated PCL cases [10]. In another study by Caldas et al., two or more ligaments were involved in 85.9% of cases, including posteromedial and posterolateral corner injuries [18]. The high rate of multiple-ligament injuries in their high-energy PCL injury series was consistent with our study, as 75.7% of our patients had more than one ligament involved in their injuries. Although this study did not show an increase in the complication rates of the patients with multiple ligament injuries, Tucker et al. found an increased rate of complications in patients with multiple reconstructed ligaments compared to isolated PCL injuries. However, their cohort consisted of a military population that differed from the general population with higher-energy injuries and higher demands [29]. There is ongoing controversy about the definition of low- and high-energy injuries. Some authors have argued that even sports-related PCL injuries should be presented as multiple-ligament injuries. However, current reviews acknowledged the lower-energy nature of sports injuries and their predisposition to isolated PCL damage compared to high-velocity vehicle accidents or falls from heights [11, 30,31,32].

Fractures are one of the main factors that make treatment more complex and increase the risk of morbidity. As expected, the most common fractures were observed around the knee joint in this study. Thirty-one of 43 fractures needed operative fixation, but we did not provide detailed statistics because some occurred in anatomical regions unrelated to the PCL, such as pelvic girdle, phalanx, or talus fractures. However, 26 fractures, including bones such as the tibial plateau, distal femur, and patella, were located near the knee joint. The frequency of associated fractures in cases of PCL injury was described by Caldas et al. with a rate of 20.5%, nearly twice the rate of our cohort but a small number of patients [18]. Complications due to fracture treatment were not accounted for in this study.

The high-energy nature of the injuries was also reflected in their distribution according to the Schenck classification. The highest number of cases were classified as Schenck 2 (n = 201, 48.1%), which involves cruciate ligament injury of the knee. A significant number of more complex injuries also reflected the higher classes defined as Schenck 3M (n = 45 10.8%), 3L (n = 60 14.4%), and 4 (n = 13, 3.1%). Although some studies described higher complication rates for Schenck classes 3 and 4 [33], we did not find a statistical difference in complication rates between these groups (p = 0.693).

Similarly, comparing the mechanism of injury in terms of complication numbers did not reveal a statistical difference (p = 0.293). We did not observe compartment syndrome or vascular injury during or after the operations, but two patients admitted with knee dislocation had vascular injuries that required vascular repair, and they recovered without complications postoperatively. It was found that PCL operations performed for multiple-ligament injuries due to car accidents were more likely to have staged surgeries than those due to other causes (p = 0.014). This result seems logical as car accident victims usually present with more complicated injuries compared to the isolated ligament injuries caused by motorcycles [12]. The present study also showed an increase in complications with multi-stage operations in the group with multiple-ligament injuries, as expected (p = 0.009), which parallels the findings of previous studies as the complex and lengthy surgical procedures of patients with multiple-ligament injuries are reflected in an increase in complication rates [34].

In our study, the transtibial technique was predominantly used for PCL reconstruction. However, the tibial inlay technique is also a viable option [35, 36]. This technique allows for a direct approach to the tibial insertion of the PCL and can be particularly advantageous in specific clinical scenarios. Both the transtibial and tibial inlay techniques have been shown to produce equivalent results, supporting the choice of technique based on the surgeon's preference and the patient's specific anatomical and injury characteristics [35].

In our cohort, autografts were predominantly used for PCL reconstructions, with allografts used less frequently. This reflects findings from a systematic review showing no significant differences in outcomes between graft types [37]. The preference for autografts often stems from their availability, cost-effectiveness and fewer concerns about structural integrity after sterilization. However, allografts remain a viable option, particularly when reducing donor site morbidity or opting for less invasive approaches [37, 38]. Notably, no synthetic grafts like the Ligament Advanced Reinforcement System (LARS) synthetic graft were recorded in our registry data. LARS is known for potentially providing immediate stability with lower rates of failure and synovitis, although long-term data on its use in isolated PCL reconstructions remain sparse [38].

In our registry data, consistent findings from recent systematic reviews, the most commonly utilized grafts for PCL reconstructions were the hamstring and patellar tendon autografts [39]. These grafts are preferred due to their strong performance in terms of patient-reported outcomes and joint stability, aligning with global trends that recognize their efficacy and reliability for PCL reconstruction [39].

This study has limitations primarily due to its retrospective nature. The data were obtained from a national digital registry database, which is comprehensive in its radiological reports and operational notes but does not provide any patient feedback regarding clinical outcome scores. Incomplete data on fracture classification, graft types, and revision rates constitute a notable limitation of the study. Additionally, this study predominantly evaluated patients likely to benefit from PCL surgery, potentially limiting generalizability to those severely injured or unfit for surgery. Another weakness of the study was the lack of long-term follow-up, which limited further evaluation of the effects of complications on arthritis and revision rates.