1 Introduction

Total knee arthroplasty (TKA), also known as total replacement (TKR), is a surgical procedure that resurfaces the damaged knee joint with artificial metal and plastic components.¹ TKA is one of the most cost-effective and consistently successful surgeries performed in orthopedics.² TKA is recommended as a viable treatment option when conservative treatments fail to provide relief.³ It is a standard treatment for advanced severe knee arthritis or other degenerative joint diseases at the end stage of advanced knee arthritis, particularly in cases where patients suffer from severe pain, restricted mobility, and knee instability, typically.^2,4–6 The primary goals are to relieve pain, improve mobility, and restore knee function. Studies have shown that TKA can significantly improve quality of life, reduce pain, and enhance functional abilities in most patients. However, a small percentage of patients may remain dissatisfied or experience persistent pain after the procedure, which can be associated with factors like depression or surgical complications.²

An experienced specialist with high skill levels should perform the surgical process to ensure precise and appropriate alignment of prosthesis components and achieve ligamentous balance to minimize complications.⁴ Treatment options for MCL injuries during TKA vary depending on the type and severity. They range from conservative approaches, such as bracing and physiotherapy, to more invasive procedures, including ligament repair or reconstruction. The severity of the injury influences the choice of treatment, the patient's overall health, and the surgeon's expertise and preferences 7–10.

Despite TKA success, intra-operative complications during TKA are rare but can occur.⁵ In general, the most common reported complications following TKA include bleeding, wound-related complications such as wound infection, deep joint infection, periprosthetic fracture, nerve injuries, stiffness, medial collateral ligament (MCL) injury, extensor mechanism disruption, limb length discrepancy, heterotopic ossification, instability and dislocation, thromboembolic diseases, and vascular injuries.^11–13 Intraoperative complications, such as MCL injuries, are a significant concern for surgeons. The MCL plays a crucial role in maintaining the stability of the knee joint, and its injury during TKA can complicate the postoperative recovery and overall outcome.

This study aims to assess the prevalence of intraoperative MCL injuries in TKA patients, evaluate the effectiveness of various therapeutic interventions, and analyze postoperative outcomes in terms of pain, knee stability, and functional recovery. By addressing these aspects, the findings will help inform surgical strategies and contribute to optimizing patient outcomes in TKA complicated by intraoperative MCL injury.

2 Methods

3 Results

3.3

3.3 Therapeutic outcomes

The mean pain score decreased from 90 preoperatively to 3.8 postoperatively, indicating a statistically significant improvement in knee pain (p-value <0.001). The mean IKDC score increased from 28.2 preoperatively to 77.8 postoperatively, indicating a statistically significant improvement in knee function (p-value <0.001). No significant association was found between the IKDC score in intraoperative MCL injury and patient gender (p-value = 0.806) (Table 3).

Table 3 Evaluation of the IKDC and pain scores based on before and after TKA.

Scores	Variables	Range	Mean (SD)	P-value
Pain score	Before TKA	70–100	90 (±9.5)	<0.001
	After TKA	0–20	8.3 (±7.1)	<0.001
IKDC score	Before TKA	24.8–34.6	28.8 (±3.4)	<0.001
	After TKA	70.3–83	78.7 (±3.4)	<0.001
IKDC score	Male	76–78.4	77.2 (±1.69)	0.806
	Female	70.3–83	77.9 (±3.72)	0.806

The correlation coefficient between the mean IKDC score and patient age was 0.001 (p-value = 0.998), indicating no statistically significant relationship between these variables (Fig. 1).

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Fig. 1 International Knee Documentation Committee (IKDC) score scatter diagram according to age.

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A comparison of the mean IKDC scores post-TKA between patients with treatment following intraoperative MCL injury (77.78) and patients without intraoperative MCL injury (80.00) revealed that MCL injury, when treated, had no significant effect on the IKDC score (P-value = 0.141) (Fig. 2).

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Fig. 2 Comparison chart of IKDC score before and after TKA in patients with and without MCL injury.

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4 Discussion

The current study aimed to assess the prevalence and therapeutic outcomes of intraoperative MCL injury in subjects undergoing TKA. The findings of this study indicate that while intraoperative MCL injury occurs in a small percentage (2.35 %) of TKA patients, predominantly in females, it does not significantly impact long-term functional outcomes when appropriately managed. Despite the higher incidence in females, there was no statistically significant relationship between gender and MCL injury risk. Therapeutic outcomes were favorable, with substantial reductions in pain levels and notable improvements in knee function, as evidenced by the significant increases in postoperative IKDC scores (p < 0.001). Importantly, a one-year follow-up revealed no knee instability, complications, or dependence on assistive devices, underscoring the effectiveness of the interventions for MCL injury. These results suggest that with proper intraoperative management, MCL injuries do not compromise TKA outcomes, supporting TKA's overall efficacy and safety even in cases complicated by MCL injury.

MCL injury during primary TKA can lead to coronal plane instability, affecting knee function and prosthesis longevity, potentially requiring revision with more constrained prostheses.^23,24 However, these prostheses pose challenges, including increased stress on interfaces, accelerated wear, and the need for more extensive bone resection, which can weaken fixation and complicate future revisions. Additionally, constrained prostheses are more costly and less available in certain regions, making surgeons cautious about their use. Therefore, most surgeons prefer more conservative management options instead of immediately opting for constrained prostheses.^25–29

Previous research on MCL injuries during TKA has primarily focused on cruciate-retaining (CR) prostheses.^30,31 For example, studies by Leopold et al.³⁰ and Wang et al.³¹ highlighted that the PCL serves as a secondary medial stabilizer in the coronal plane, potentially affecting the outcomes with such prostheses. Only one study by Lee & Lotke in 2018³² reported superior functional results in the MCL repair group compared to those using prostheses with canisters.

The prevalence of MCL injury in TKA in the present study was 2.35 %, whereas the prevalence of MCL injury in knee arthroplasty in various studies has been reported to range from 0.2 % to 7.2 %.^{30,31,33–35}

In our study, although 10 out of the 12 patients (83.3 %) who experienced injury were female, statistically, no significant difference was observed compared to the control group. Therefore, we did not obtain sufficient evidence to confirm a relationship between gender and MCL injury in this study, despite this result aligning with other studies in the field.^{30–32,34,36} However, Bohl et al.³⁵ reported a statistically significant higher frequency of MCL injury among females in their study.

In the present study, the technique of tendon pull-out in bone tunnels was used for fixing the graft or MCL to the bone, which imposes no additional cost burden on the patient and yields acceptable functional outcomes; however, in a study by Wang et al.,³¹ it was noted that although the cost of reconstruction with autograft hamstring is much lower than that of more constrained prostheses, using screws for graft fixation in bone incurs a fee of $1000, and if allograft is used, the cost increases by up to $2000 due to the need for fixation.

In our study, most MCL injuries (83.3 %) occurred at the osseous avulsion site, with only a minority (16.7 %) being mid-substance injuries. This contrasts sharply with the findings of Wang et al.,³¹ who reported that 70.6 % of their MCL injuries were mid-substance, attributing these to direct contact with oscillating saw blades during tibial cuts or the use of sharp instruments while elevating the medial side of the proximal tibia. Leopold et al.³⁰ also observed a predominance of mid-substance injuries and explained the causes similarly. The discrepancy in injury patterns between our study and others highlights the impact of surgical techniques and protective measures. For instance, Bohl et al.³⁵ reported a nearly equal distribution of mid-substance (53 %) and avulsion injuries (47 %). This balanced distribution further underscores the variability in MCL injury patterns based on different operative practices.

In this study, we utilized the subjective IKDC index to assess the Knee function in the study and control groups. The mean IKDC index of patients with MCL injury before surgery was 28.8, which increased to 77.8 after surgery. Although these results were lower than the control group (80.1), there was no statistically significant difference. In previous studies, all reported significant improvement in knee functional scores. For instance, Leopold et al. reported an improvement from 47 to 93 in the functional index, although they did not compare it with a control group. Wang et al.³¹ also reported an improvement in knee functional index (84.7). They indicated this index score is lower than the control group's (87.9). The difference is considerable but not statistically significant (p-value = 0.08). Therefore, it can be stated that the results of their study are consistent with the present study.

In this study, no cases of knee joint stiffness were observed contrary to the use of braces for six weeks postoperatively. However, Bohun et al.³⁵ reported joint stiffness in over 10 % of patients, defining it as flexion less than 90°. They assumed that this reduction in flexion was due to the use of knee braces for six weeks post-surgery. Leopold et al.³⁰ similarly their study, used braces for rehabilitation for six weeks postoperatively and reported one case of joint stiffness. It is worth mentioning, however, that some researchers, such as Dragosloveanu et al.,³⁴ state that successful MCL repair or reconstruction requires rigid ligament fixation and a less constrained PS prosthesis with polyethylene. In such cases, there is no need for brace use in postoperative rehabilitation stages, and they have also reported excellent study outcomes.

Whiteside et al.³⁷ demonstrated that releasing different bands of the MCL during knee surgery affects the medial joint gap at various degrees of knee flexion. This release is typically performed using techniques like pie crusting or tendon punctures. Excessive release can lead to complete disruption of the superficial MCL. Even without pie crusting, high pressure during ligament balancing may cause MCL tears, especially at its tibial attachment, a known complication in TKA surgeries. Loss of MCL tension due to tears increases the gap between the femoral condyles and tibial surface during knee movement, promoting more rotational movement around the lateral axis.³⁷

Surgeons and researchers have proposed various methods, including repair with sutures and screws, ligament reconstruction, and prosthetic replacement with more constrained models, to address MCL injuries during TKA surgery.³⁶ Despite the MCL's potential for self-healing when torn from the bone, some studies suggest lower healing potential and reduced strength after recovery in ligamentous injuries.³¹ PCL-retaining prostheses are commonly used in studies investigating conservative treatment during knee arthroplasty for MCL injury. However, this approach may introduce confounding effects due to the PCL's role as a secondary stabilizer against valgus forces.³⁸

The study had a few limitations. Firstly, the sample size was small due to the low rate of complications during TKA operations. However, our sample size is similar to other studies in this field. Secondly, we did not examine clinical results in subgroups of MCL injury based on the location of the injury due to the limited number of cases in these subgroups. Lastly, the follow-up period for the patients was only one year, and it was impossible to follow up with the patients to check the stability of the results in the future, considering that the study started in 2016.

5 Conclusion

In conclusion, the current study demonstrates that intraoperative MCL injury, although occurring in a small percentage of TKA patients, does not significantly affect long-term functional outcomes when properly managed. The favorable therapeutic outcomes, including significant pain reduction and improvement in knee function, as well as the absence of knee instability, complications, or need for assistive devices at one-year follow-up, highlight the effectiveness of appropriate interventions. These findings suggest that MCL injuries during TKA do not compromise the overall success of the procedure, reinforcing the safety and efficacy of TKA even in the presence of such complications.

Consent to participate

Returning informed consent was obtained from the participants of this study. All participants participated in the survey knowingly and with consent.

Ethics

This study was approved by the Ethics Committee of Hamadan University of Medical Sciences (UMSHA), with the number IR.umsha.rec.1399.616. It was performed according to the ethical standards in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.

Funding

This study did not receive any funding.

Author contribution

This statement is to certify that all authors have seen and approved the manuscript being submitted, have contributed significantly to the work, attest to the validity and legitimacy of the data and its interpretation, and agree to its submission to the Journal of Orthopaedic Reports.