Total knee replacement (TKR) is widely recognized as one of the most successful surgical procedures in orthopaedics, providing significant pain relief and functional improvement in patients with advanced degenerative arthritis of the knee joint. Advances in implant design, surgical technique, and perioperative management have significantly improved long-term outcomes of the procedure. Despite these improvements, postoperative complications such as instability remain an important cause of patient dissatisfaction and revision surgery.

Instability after TKR can occur due to several factors including improper ligament balancing, malalignment of prosthetic components, trauma, and progressive soft-tissue attenuation. Among these causes, coronal plane instability resulting from lateral collateral ligament insufficiency is relatively uncommon but can significantly affect knee biomechanics and prosthetic function. Previous studies have reported that ligament imbalance accounts for a considerable proportion of revision procedures following total knee arthroplasty [1][2].

The lateral collateral ligament (LCL), also known as the fibular collateral ligament, is a key stabilizing structure of the knee joint. It originates from the lateral femoral epicondyle and inserts onto the fibular head, forming an essential component of the posterolateral corner (PLC) of the knee [1]. Together with the popliteus tendon and popliteofibular ligament, the LCL contributes to resistance against varus stress, posterior tibial translation, and external rotation of the tibia [3]. Earlier biomechanical studies have also confirmed the important role of the posterolateral corner and cruciate ligaments in maintaining knee stability [4][5].

Biomechanical studies have demonstrated that the LCL is the primary restraint to varus stress in early knee flexion, particularly between 0˚ and 30˚ [6]. Injury to this ligament results in increased lateral compartment opening and abnormal load distribution across the knee joint. In the setting of total knee replacement, such instability may lead to increased stresses on the prosthetic components, potentially resulting in accelerated wear and early implant failure [7].

Anatomical studies have improved understanding of the posterolateral corner structures and their role in maintaining knee stability. LaPrade et al. described the detailed morphology of the posterolateral knee structures and emphasized the critical role of the fibular collateral ligament in maintaining varus stability [1]. Other anatomical investigations have further clarified the relationships between the LCL, iliotibial tract, and surrounding structures [2][7].

Management of instability following TKR traditionally involves revision arthroplasty using constrained or hinged prosthetic designs. Although effective in restoring mechanical stability, revision surgery is associated with greater surgical complexity, increased bone loss, and higher complication rates. Therefore, in selected cases where prosthetic components remain well aligned and securely fixed, reconstruction of the deficient ligament may provide a less invasive and joint-preserving treatment option.

Recent advances in surgical techniques for reconstruction of the posterolateral corner have emphasized anatomical reconstruction using tendon grafts. Several graft options have been described, including semitendinosus autograft, Achilles tendon allograft, and patellar tendon graft [8]-[10]. Among these, the semitendinosus tendon autograft has gained popularity due to its favourable biomechanical properties, adequate length, and minimal donor site morbidity.

The present study evaluates the clinical and radiological outcomes of lateral collateral ligament reconstruction using semitendinosus autograft in patients with symptomatic lateral instability following total knee replacement.

A total of 15 patients with symptomatic lateral instability following total knee replacement underwent lateral collateral ligament reconstruction using semitendinosus autograft during the study period. The mean age of the patients was 62 ± 6 years, and all patients were followed for a minimum period of six months postoperatively (Table 1). The mean follow-up duration was 8 ± 2 months (range, 6 - 12 months).

Table 1. Patient demographics.

Functional outcomes showed significant improvement following reconstruction (Table 2). The mean Knee Society Score improved from 56 ± 7 preoperatively to 84 ± 5 at the final follow-up, which was found to be statistically significant (p < 0.001).

Table 2.Clinical outcomes.

Similarly, knee range of motion improved from a mean preoperative value of 95˚ ± 12˚ to 105˚ ± 10˚ postoperatively, demonstrating a statistically significant improvement (p = 0.02).

Varus instability was corrected in 14 out of 15 patients, as confirmed by postoperative clinical examination and radiographic assessment. One patient demonstrated mild residual laxity; however, the patient remained functionally stable and did not require further surgical intervention.

Instability following total knee replacement remains one of the leading causes of patient dissatisfaction and revision surgery. While sagittal plane instability is more commonly encountered, coronal plane instability due to lateral collateral ligament insufficiency represents a relatively uncommon but clinically significant problem. Restoration of stability in such cases is essential to prevent abnormal load distribution, polyethylene wear, and early implant failure. Chronic posterolateral rotatory instability has long been recognized as an important cause of persistent functional instability and gait disturbance if untreated [14].

The posterolateral corner of the knee plays a crucial role in maintaining varus and rotational stability. It comprises key structures including the fibular collateral ligament, popliteus tendon, and popliteofibular ligament, which act synergistically to resist varus stress and external rotational forces. Previous anatomical and biomechanical studies have highlighted the importance of the fibular collateral ligament as the primary restraint to varus stress, particularly in early knee flexion angles [1][15].

Biomechanical investigations have demonstrated that disruption of the lateral collateral ligament leads to significant varus laxity and altered knee kinematics. Coobs et al. showed that anatomical reconstruction using a semitendinosus autograft can restore near-normal stability of the fibular collateral ligament, supporting the rationale for reconstruction in cases of isolated lateral instability [16].

In the setting of total knee arthroplasty, ligament imbalance may result from intraoperative factors, trauma, or progressive soft-tissue degeneration. When instability is caused primarily by soft-tissue insufficiency rather than implant-related factors, ligament reconstruction offers a joint-preserving alternative to revision arthroplasty. This approach avoids the morbidity associated with revision procedures, including bone loss, increased operative time, and higher complication rates.

In the present study, ligament reconstruction was performed in carefully selected patients with well-fixed and well-aligned prosthetic components, isolated lateral instability, and no evidence of infection or implant loosening. This selection strategy ensured that reconstruction was reserved for cases in which soft-tissue insufficiency was the primary cause of instability, thereby optimizing the likelihood of successful outcomes.

The findings of the present study are consistent with previous reports demonstrating improved stability following anatomical reconstruction of the posterolateral corner. LaPrade et al. reported favorable clinical outcomes following fibular collateral ligament reconstruction, while Geeslin et al. demonstrated improved functional outcomes in patients undergoing reconstruction for posterolateral instability [17][18]. Biomechanical studies have further shown that reconstruction using semitendinosus graft can restore near-normal knee stability [16]. Our results are in agreement with these findings, supporting the role of anatomical reconstruction in restoring knee stability and function.

Earlier literature has also shown that repair of posterolateral corner injuries is associated with higher failure rates compared with reconstruction. Levy et al. demonstrated superior outcomes with reconstruction techniques, which has led to a shift toward anatomical reconstruction as the preferred management strategy [19].

Radiological evaluation plays an important role in both diagnosis and postoperative assessment of instability. Stress radiography has been shown to be a reliable method for quantifying lateral joint opening and assessing posterolateral corner injuries [12]. In the present study, radiological outcomes correlated well with clinical findings, with correction of varus instability observed in the majority of patients.

Recent literature continues to support anatomical reconstruction techniques for posterolateral instability. Figueroa et al., in a contemporary review, emphasized the importance of restoring native knee biomechanics through anatomical reconstruction to achieve optimal clinical outcomes [20]. General epidemiological studies have also shown that knee soft-tissue injuries remain clinically relevant across active populations [21][22].

In our study, LCL reconstruction using semitendinosus autograft resulted in significant improvement in both knee stability and functional outcomes. The Knee Society Score improved significantly, and most patients demonstrated correction of varus laxity on both clinical examination and radiographic assessment. These findings suggest that ligament reconstruction is an effective treatment option in appropriately selected patients.

Importantly, this technique allowed preservation of the existing prosthetic components in all patients during short-term follow-up. While these results are encouraging, the role of ligament reconstruction as an alternative to revision arthroplasty requires further validation through larger studies with longer follow-up durations.

This study has several limitations, including a relatively small sample size, short follow-up duration, and lack of a control group. Additionally, variability in patient characteristics and primary TKR indications may influence outcomes. Future studies with larger cohorts and longer follow-up are necessary to assess the durability of reconstruction and its long-term clinical effectiveness.

LCL reconstruction using semitendinosus autograft is a safe and effective option for managing lateral instability following total knee replacement in carefully selected patients with well-aligned and stable prosthetic components. The procedure provides significant improvement in knee stability and functional outcomes in the short term. Further studies with longer follow-up are required to confirm its long-term effectiveness.