In this research, during the primary CR TKA, a retrospective cohort study between the PCL avulsion fracture group and the control group in terms of middle-term outcomes was conducted; the incidence of tibial side PCL avulsion fracture is 4.6%, and the most significant discovery of this study was that the reduction of tibial side PCL avulsion fracture achieved an excellent performance in terms of middle-term clinical and PRO outcomes as the primary CR TKA without increased risk of complications, older patients and female gender may be the two risk factors of PCL avulsion fracture, and the fracture healing rate is 100%.
There were few studies to investigate the middle-term clinical and PRO outcomes of patients with the reduction of PCL avulsion fracture of tibial during primary CR TKA. Besides, our research shows that this technology indicated an excellent outcome. We believe that using a high-strength line to reduce this incomplete avulsion fracture which enables slight movements of the bone fragments, accord to the principles of biofixation [13], and can not only help balance the flexion gap, but also ensure the stability of the flexion gap, avoid the conversion to PS TKA during the operation, and help patients to enhance recovery after surgery (ERAS).
Many scholars have realized that PCL is the main stable structure of the knee joint, and it has also been recognized as the limiting factor for the posterior translation of the tibia when the knee flexion is greater than 30 degrees [9]. Although people can tolerate the loss of PCL at rest, during activities, the kinematics of the knee changes, and often leads to severe knee dysfunction [14].
It is frequently thought that a PS TKA with a spine-cam mechanism has to be used to replace the PCL function when the PCL is sacrificed. And some authors have recommended that keeping the PCL in TKA promotes proprioception, leads to an increased satisfaction in patients, and obtains a more ‘normal’ feeling after TKA [15, 16]. This finding corresponds to our study of FJS, in our study, we found that no significant statistical differences between the two groups in regard to FJS score at last follow-up, the patients with the reduction of PCL avulsion fracture obtain the same “normal” feeling after TKA compared to the control group. 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 surgery [12]. We believe that restoring the position of PCL allows the femur to carry out a controlled rollback when flexion of the knee, in line with the knee biokinetics, maintains the stability of the knee, achieves good gap balance, and regains good proprioception [17].
The success of TKA is decided by several key elements, including the reestablishment of kinematics through the ligament balance and reconstruct the joint line. Several methods have been described to balance the ligaments and releasing the PCL completely may result worse outcomes [18, 19, 20, 21]. Some studies have drawn attention that most PCL insertions may be destroyed during tibia cutting, and which raises questions about how much PCL actually saves in a CR TKA [18, 22–26]. Eric Kim et al [10] studied the incidence and risk factors of PCL avulsion during CR TKA, they found the incidence is 1.7% and female gender was the only risk factor. This study only compared pre and post-operative ROMs to support their conclusions, but did not mention how the post-operative clinical outcomes of unreduced the PCL avulsion fracture was. In our study, we not only reflected the postoperative results of patients after reduction fractures in objective scores (KSS), but also in the subjective scores (FJS) of patients we also proved that reduction fracture may be a better choice.
In our study, the incidence of tibial side PCL avulsion fracture is 4.6%, relatively higher, We thought this may be related to the 12 mm thick piece of tibial bone osteotomy and the 5°-10°of retroverted angle required by our type of prosthesis, in addition, our sample size is relatively small, which may be one of the reasons for the difference. And, we found older patients and female gender may be the two risk factors of PCL avulsion fracture, we believe this may be due to more osteoporotic bones in women as older [10]; however, further research is needed before making a definitive statement.
During the primary TKA whether the PCL should be preserved has been discussed for nearly 30 years. A large number of researches have informed of the clinical outcomes, kinematics and life-span of CR TKA and PS TKA. However, each type of implant has its advantages and disadvantages [27–29]. The tension of PCL is a very important factor in a successful CR TKA [29]. Kennedy et al. keep the intact posterior cruciate ligament retained, anterior lateral bundle, posterior medial bundle and complete PCL-sectioned in human cadaveric knees to compare the kinematics[30]. They found that the anterior lateral bundle and posterior medial bundle play an important part in resisting the posterior of the tibial translation. Consequently, we believe that it is necessary to reduce PCL avulsion fracture in CR TKA, because it can not only help balance the flexion gap, but also ensure the stability of the flexion gap, avoid the conversion to PS TKA during the operation, and help patients to ERAS. In addition, our study achieved the same excellent middle-term clinical and PRO outcomes as the control group without increased the risk of complications.
Our research has several limitations. First, it is a retrospective study, which has its potential bias and weaknesses. The number of PCL avulsion fracture of tibial was rare, which decreases the power of the research. Second, in this study the follow-up time is short, so the long-term outcomes of the reduction this kind of avulsion fracture are still uncertain.