Our study found that the incidence of avulsion fracture in primary cruciate-retaining TKA is relatively high, and older age and female gender are the two risk factors. Our reinsertion and reduction technique is a reliable treatment for PCL avulsion fracture. By using the technique, acceptable PCL function is maintained, which provides sufficient stability to the knee during movement.
There are few studies that investigate patient-reported outcomes of PCL reduction in primary cruciate-retaining TKA. Kim et al  showed that the incidence of tibial-sided PCL avulsion fractures was 1.7%, and female gender was the only risk factor. However, they did not reduce the PCL avulsion fracture and the function of PCL was assessed based on the comparison between the pre- and post-operative range of motion of the knee. In our comparison cohort study, we assessed the function of PCL based on both the objective scores (Knee Society Scores) and subjective scores (FJS). Those multiple assessments enable the creation of a more comprehensive understanding of PCL function, ultimately leading to more accurate and appropriate clinical conclusions.
In our experience, PCL avulsion fractures may occur when an en bloc tibial resection is performed. The fractures may be related to a high (12 mm thickness) tibial osteotomy as required by the instructions for fitting the prosthesis. Older age and female gender are two risk factors, because osteoporosis affects mostly older women. We believe that this technique is more applicable to incomplete PCL avulsion fracture, and as the repair has not been biomechanical tested, but yet is being used for a very important function to ensure PCL stability post-operatively. When the flexion gap is too tight or PCL reinsertion is difficult, soft tissue release is appropriate, and soft tissue balance was confirmed using a tensor/balancer device as described by Sasanuma et al . In addition, we used posterior stabilized prosthesis that provided greater stability of the knee in flexion.
Both the anterior cruciate ligament and PCL play important roles in maintaining optimal knee stability. In our study, resecting the anterior cruciate ligament may cause instability of the affected knee joint, but PCL has also been recognized as the limiting factor for the posterior translation of the tibia when the knee flexion is greater than 30° [6, 12]. Patients can tolerate the loss of PCL at rest, but this kinematic change often leads to severe knee dysfunction . Some studies showed that preservation of PCL probably promoted patient proprioception, leading to an increased patient satisfaction and knee feeling more ‘normal’ after TKA [12, 14]. This finding corresponds to the FJS in our study. The FJS is a newly developed scoring system in recent years, which is often used to measure patients’ ability of forgetting joint replacement or joint awareness in daily life. In daily activities, people often don’t realize their healthy joints, so we take the lack of awareness of normal healthy joints (forgotten joints) as the standard to assess the outcomes after TKA . The FJS is affected by many factors, but we found that reduction of PCL avulsion fracture in primary TKA achieved acceptable FJS after 4 years. Therefore, we believe that reinsertion of PCL allows the femur to carry out a controlled rollback when the knee is flexed, in line with normal knee kinematics. The PCL maintains the stability of the knee, contributes to good gap balance, and helps to maintain good proprioception .
The proper tension of PCL is an important success factor in cruciate-retaining TKA . Excessive release of the ligaments may result in worse outcomes [16-19]. In many cases, the PCL insertion may be damaged during the tibial cut, which raises a question about how much the PCL is actually preserved [16, 20-24]. Some surgeons argued that a posterior-stabilized TKA with a spine-cam mechanism is an alternative when the PCL is sacrificed. Moreover, whether the PCL should be preserved has been discussed for nearly 30 years. Either a cruciate-retaining TKA or a posterior-stabilized TKA has its advantages and disadvantages of process, clinical outcomes, kinematics, and lifespan [9,24,25]. In a human cadaveric study, Kennedy et al  compared the kinematics of the knees after tibial resection with vs without preservation of the intact PCL, anterior lateral bundle, and posterior medial bundle. They found that the anterior lateral bundle and posterior medial bundle were the main stabilizers of the knee joint and serve primarily to resist the posterior translation of the tibia. Consequently, the surgeons should do their best to prevent PCL avulsion fractures in cruciate-retaining TKA.
Our research has several limitations. The retrospective study has a potential bias and weaknesses. The small number of PCL avulsion fracture decreases the power of the research. Surgeon preference, experience, and ability may influence ascertaining the effects of TKA. The follow-up period of 4 years is insufficient to fully assess the outcomes of PCL reduction.