Abstract

Background

Intraoperative posterior cruciate ligament (PCL) avulsion fracture of tibial is an uncommon but serious complication during primary cruciate retaining (CR) total knee arthroplasty (TKA). However, the clinical outcomes and patient-reported outcome (PRO) of the reduction of PCL avulsion fracture of tibial have rarely been informed. The objective of this research was to investigate the prevalence and middle-term clinical outcomes of this kind of fracture during primary CR TKA and to identify the potential risk factors.

Methods

A retrospective cohort study from January 2014 to January 2016, 56 patients who experienced PCL avulsion fracture of tibial and intraoperative reduction during primary CR TKA as PCL avulsion group, matched in a 4:1 ratio of 224 patients who underwent primary CR TKA as control group for comparison. All patients were followed up at least 4 years. Patients’ demographics, before surgery and last follow-up after surgery including range of motion (ROM), Knee Society Score (KSS), Forgotten joint score (FJS) were assessed in the two groups, Logistic regression to identify the potential risk factors.

Results

In our series of 1216 patients who underwent CR TKA during the retrospective period, 56 patients (4.6%) experienced PCL avulsion fracture of tibial. There were no noteworthy differences in demographic, ROM, KSS, FJS scores of the patients between the two groups. In PCL avulsion fracture group, no patients experienced revision due to the knee instability. Logistic regression analysis showed that older age (P = 0.032) and female gender (P = 0.041) were the risk factors of PCL avulsion fracture of tibial.

Conclusions

The incidence of PCL avulsion fracture of tibial is 4.6%, older patients and female gender may be the two risk factors of PCL avulsion fracture. The reduction of PCL avulsion fracture during CR TKA can achieve an excellent middle-term clinical and PRO outcomes compared with the control group, and without increased the risk of complications.

Background

Osteoarthritis (OA) is a chronic joint disease that affects more than 100 million people in the world [1]. Knee joint is the most frequently affected joint and total knee arthroplasty (TKA) is an effective surgical method for the treatment of end-stage knee OA [2].

TKA can relieve knee pain, improve knee function, restore lower limb alignment, and improve the patients’ quality of life. The recovery of knee movement and stability during exercise are the two main clinical manifestations after TKA [3]. During primary TKA, two principal designs are used: cruciate-retaining (CR) TKA and PCL-substituting (PS) TKA. The debate over the results of CR and PS TKA did not show any difference in the overall results [4]. However, CR TKA has been widely used because it improves the knee's ability to exercise, preserves the knee's proprioception, and increases the knee's range of motion (ROM) and stability during knee extension and flexion [4, 5].

The objective of primary CR TKA is to maintain normal function of posterior cruciate ligament (PCL) and make PCL as a significant part in proper CR TKA too. A well-function PCL in CR TKA is thought to drive more physiological knee kinematics and provide proprioceptive feedback by decreasing paradoxical roll forward and allowing the femur to execute a controlled rollback during flexion [6, 7, 8]. A large number of different techniques have been introduced in CR TKA to protect PCL from injury, one study have described the use of bone island technology to protect PCL and to preserve as much PCL as possible, which is the initial reason for using CR-knee prosthesis [9].

During the CR TKA, we need to carefully evaluate the gap balance between knee extension and flexion, as well as the tension of PCL in order to avoid knee stiffness and instability after surgery. When performing a trial reduction and the flexion gap is tight, PCL avulsion fracture of tibial may be easy to occur. This kind of fracture is usually an incomplete fracture, which does not need to be converted to PS TKA during operation, and can change the tight of flexion gap, finally, achieve the gap balance and retain the complete PCL. However, whether reduce the PCL avulsion fracture or not in CR TKA is still controversial. One study analyzed the incidence of tibial side PCL avulsion fracture during primary CR TKA, and there was no attempt to reduce the avulsion fracture and achieved good postoperative results [10]. However, We think that if the avulsion fracture is not reduced, it may lead to the non-healing fracture, or even the knee instability and the failure of the operation.

Significantly, few studies have investigated the reduction of PCL avulsion fracture of tibial during primary CR TKA.The purpose of this research is to investigate the incidence and potential risk factors of PCL avulsion fracture and assess the middle-term clinical outcomes and patient-reported outcome (PRO) of reduce this kind of fracture during primary CR TKA.

Methods

Institutional Review Board approval was obtained before the study commenced. A retrospective cohort study from January 2014 to January 2016, 56 patients who experienced PCL avulsion fracture of tibial and intraoperative reduction during primary CR TKA with a mobile bearing implant (LINK, Germany, Gemini MK II) as PCL avulsion group, matched in a 4:1 ratio of 224 patients who underwent the same primary CR TKA as control group for comparison. All patients were followed up at least 4 years. Inclusion criteria were ① flexion-contracture deformity < 20°; ② varus deformity < 30°; ③ no patient had any knee instability or laxity in the sagittal plane detected during clinical examination before surgery. Patients with valgus knees or stiff were excluded.

In this research a single high-volume surgeon accomplished all surgeries, using a measured resection technique during all primary CR TKAs. Patients demographics, including age, gender, body mass index (BMI) and follow-up time were examined. Before surgery and at last follow-up after surgery including range of motion (ROM), Knee Society Scores (KSS, including clinical and functional scores of the knee) [11], Forgotten joint score (FJS) [12] were compared between the two groups. Fracture healing was evaluated by X-ray radiographs.

In addition, in order to determine whether age, gender, BMI, preoperative ROM and component sizes of patients were the potential risk factors of PCL avulsion fracture of tibial, we used the Logistic regression to analysis the correlation.

Results

There were 1216 CR TKAs accomplished by the same surgeon in our department between January 2014 to January 2016. And during the primary CR TKA, 56 patients suffered tibial side PCL avulsion fracture, the incidence is 4.6 %.  In control group, three patients were lost during follow-up because of uncooperative. In PCL avulsion fracture group, the mean follow-up time was 4.1±0.3 years, whereas in control group, there were 4.2±0.4 years of the mean follow. The PCL avulsion fracture group consisted of 12 males and 44 females, and in control group there were 78 males and 143 females (Table 1).

Before surgery and at last follow-up after surgery, no significant differences were found in the mean knee ROM between PCL avulsion fracture group and the control group (P = 0.495). At last follow-up, there were 92.4 and 93.6 points of the clinical knee scores respectively, and there were 85.1 and 87.1 points of the functional knee scores in the two groups respectively, all with no noteworthy differences between the two groups (P = 0.248, P = 0.066)(Table 2).

However, the ROM and KSS score were remarkably improved after surgery.

No significant statistical differences were found between the two groups in regard to FJS score at last follow-up.

The results of  Logistic regression analysis are summarized in Table 3. It demonstrated that older patients and female gender may be the two risk factors of PCL avulsion fracture.

The x-ray examination showed that all the avulsion fractures of  patients were well reduced and all healed after 3 months of surgery (Fig.4). After the reduction of avulsion fracture, the healing rate is 100%. No patients experienced knee instability after surgery during clinical examination. At last follow-up, no patients walked with an assisting device, and none of the patients underwent the revision arthroplasty.

Discussion

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.

Conclusions

Our research shows that the incidence of PCL avulsion fracture of tibial is 4.6%, older patients and female gender may be the two risk factors of PCL avulsion fracture. And the method of using a high-strength line through the tibial osteotomy surface to reduce and fix the PCL avulsion fracture, which has achieved excellent performance in terms of middle-term clinical and PRO outcomes as the primary CR TKA without increasing the risk of complications.

Abbreviations

PCL: posterior cruciate ligament; CR: cruciate retaining; TKA: total knee arthroplasty; PRO: patient-reported outcome; ROM: range of motion; KSS: knee society score; FJS: forgotten joint score; OA: osteoarthritis; PS: PCL-substituting; BMI: body mass index; ERAS: enhance recovery after surgery.

Declarations

Ethics approval

This study was approved by the Third Hospital of Hebei Medical University and followed the Declaration of Helsinki. Informed consent was received from all patients.

Consent for publication

Not applicable.

Availability of data and materials

The detailed data and materials of this study were available from the corresponding author through emails on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

Not applicable.

Authors' contributions

FW designed the study. WL, JHN, and YKD performed the experimental work. HXZ, JZ, WL evaluated the data. WL wrote the manuscript. All authors read and approved the final manuscript.

Acknowledgments

The authors thank all colleagues in the department of orthopedic surgery of the third hospital of Hebei medical university.

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