MCL Management in Combined ACL–MCL Injuries: An Evolving Treatment Strategy

Kyle Borque, MD, UNITED STATES James R. Robinson, MBBS, FRCS(Tr & Orth), MS, UNITED KINGDOM Mitzi S Laughlin, PhD, UNITED STATES Kurt Paul Spindler, MD, UNITED STATES Pedro Martins Farinha, MD, PORTUGAL Vítor Hugo Pinheiro, MD, MSc, PORTUGAL Andy Williams, MBBS, FRCS(Orth), FFSEM(UK), UNITED KINGDOM

ISAKOS eNewsletters   Current Perspective 2026   Not yet rated

Introduction

The anterior cruciate ligament (ACL) is rarely injured in isolation. In most cases, damage occurs in combination with injury to other stabilizing structures of the knee. Over the past several decades, clinicians and researchers have increasingly recognized the importance of identifying and addressing concomitant injuries to structures such as the menisci, the posterolateral corner (PLC), and, more recently, the anterolateral complex, in an effort to reduce the rate of ACL graft failure and improve long-term outcomes.

The medial ligament complex includes the superficial medial collateral ligament (sMLC), the deep MCL (dMCL), and the posterior oblique ligament (POL). Injuries, particularly to the dMCL and sMCL, occur frequently with ACL rupture, yet their significance is often overlooked by surgeons because of the well-documented intrinsic healing potential of the MCL.

Unfortunately, this intrinsic healing potential has led many surgeons to assume that medial-side injuries always heal. This is not the case. In the setting of combined ACL–MCL injuries, persistent valgus or rotatory laxity may remain despite appropriate conservative treatment. When the medial structures fail to heal adequately, the resulting instability significantly increases the loads that are placed on the ACL graft. Both biomechanical and clinical studies have demonstrated that even subtle injuries to these medial structures can have a meaningful impact on knee stability and graft survival.

Recent clinical data have highlighted the consequences of failing to adequately address medial-side laxity. Svantesson et al. observed significantly higher rates of ACL graft failure when concomitant MCL injuries were managed non-surgically rather than being surgically treated at the time of ACL reconstruction⁴. Alm et al. focused on a cohort of revision ACL reconstructions and noted that pre-operative medial laxity was the largest predictor of subsequent failure, with a 17-fold increase in relative risk. They also found that although surgery on the medial side reduced the risk of failure, patients with pre-operative medial laxity still had a higher risk compared to those without it.⁵ These findings highlight the importance of addressing medial sided laxity when present.

The ongoing controversy surrounding how best to manage MCL injuries in the setting of ACL reconstruction was recently highlighted in a debate at the 2025 International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) meeting in Munich.⁶ The discussion underscored the dispute between advocates of non-operative management, who emphasize the MCL’s inherent healing potential and the risks of stiffness and arthrofibrosis, and proponents of surgical intervention, who emphasize the importance of preventing residual valgus and rotatory laxity that could jeopardize the ACL graft. The present article builds upon that debate, presenting the rationale, evidence, and evolving perspectives that inform both treatment philosophies.

Non-Operative Focus

The MCL has a robust intrinsic healing capacity due to its rich vascular supply and extra-articular location. As a result, many isolated or low-grade MCL injuries are treated successfully with non-operative management, often healing without significant residual laxity or clinical sequelae. Non-operative treatment of the MCL remains the cornerstone for most injuries, particularly partial (grade I–II) tears and isolated lesions without valgus opening in full extension. Standard-of-care treatment involves bracing to protect against valgus stress, controlled early motion to prevent stiffness, and a progressive rehabilitation program aimed at restoring range of motion and quadriceps strength. Numerous studies have demonstrated excellent outcomes with this approach, including restoration of stability and return to sport within 2 to 3 months, for patients with isolated injuries.

For combined ACL–MCL injuries, many surgeons adopt a staged approach in which the MCL is first treated non-operatively to allow healing, followed by delayed ACL reconstruction once valgus stability is restored.³ This approach capitalizes on the MCL’s healing potential while minimizing the risk of limitation of knee motion that has historically been associated with simultaneous ACL and MCL reconstruction.

The MOON group² analyzed >3,000 primary ACL reconstructions and found that concomitant grade-III MCL injuries were relatively uncommon, occurring in approximately 1% of cases. This resulted in a small comparative cohort consisting of 16 patients who underwent MCL repair and 11 who were managed non-operatively. No patient in that series underwent acute MCL reconstruction. When comparing those treatment groups, it is important to note that they were not directly comparable, as patients selected for MCL repair demonstrated lower baseline patient-reported outcome measures (PROMs), potentially reflecting a more-severe initial injury pattern. Despite these baseline differences, both groups showed meaningful improvement in most PROMs at the 2-year follow-up, suggesting that acceptable outcomes can be achieved with either approach when appropriately selected. However, several secondary findings warrant consideration. The rate of arthrofibrosis requiring reoperation was higher in the repair group (19%) compared with the non-operative group (9%). Activity scores before injury were similar between the groups, but, by 2 years, activity levels remained lower in the repair cohort. Collectively, these findings suggest that while MCL surgery can restore stability in selected cases, it may be associated with higher rates of stiffness and somewhat lower postoperative activity levels compared with non-operative management.⁴ For these reasons, many surgeons will attempt to allow the medial structures to heal with a period of bracing, only performing surgery on the MCL reconstruction in those cases in which the MCL does not heal.

These results highlight the delicate balance between restoring medial stability and avoiding postoperative stiffness, an issue that lies at the heart of the ongoing debate regarding operative treatment of the medial ligament complex.⁵ This consideration has driven the evolution of more anatomic and selective surgical techniques aimed at addressing both valgus and anteromedial rotatory instability while minimizing complications.

Operative Focus

Slocum and Larson, in their seminal article on rotatory instability in 1968, stated that ‘‘Although long recognized as a clinical entity, rotatory instability has too often been overlooked by inexperienced surgeons.” They went on to posit that too much focus was being paid to valgus instability and not enough to anteromedial rotatory instability.¹ It has taken surgeons five decades to truly heed their advice.

Valgus laxity and anteromedial rotatory instability (AMRI) are both known to impose increased stresses on an ACL graft.² Recent studies showing higher ACL graft failure rates in the setting of persistent medial-side laxity have generated renewed interest in both treatment paradigms and surgical techniques for addressing medial-side injuries.³ Despite this, historical outcomes of combined ACL–MCL surgery have been inconsistent or poor. We hypothesize that these suboptimal results may stem from surgical techniques that emphasized reconstruction or repair of the superficial MCL and posterior oblique ligament (POL) while neglecting the deep MCL, an omission that may leave AMRI insufficiently addressed.

Recent studies have refined our understanding of medial-side knee injuries, demonstrating that combined ACL–MCL injuries most commonly involve the superficial and deep MCL fibers, with POL involvement occurring in only 11% of cases and never in isolation³. These findings challenge earlier assumptions that the POL is frequently injured and emphasize the importance of accurately identifying which medial structures are truly compromised. This highlights the rarity of needing to surgically address the POL. This paradigm shift has renewed interest in surgical techniques that restore both valgus and anteromedial rotatory stability by restoring the function of the dMCL to better control tibial external rotation. Two recent reconstruction techniques have shown improved restoration of native knee kinematics and reduced strain on ACL grafts in biomechanical models.⁴

In 2022, Kittl and colleagues⁴ proposed a technique that addresses both the sMCL and the dMCL. A flat sMCL reconstruction replicates the broad, anatomic morphology of the native ligament, which exhibits reciprocal tensioning patterns during knee flexion and extension. Additionally, an anteromedial reconstruction is performed to replicate the dMCL function in controlling tibial external rotation. The sMCL is reconstructed with a semitendinosus tendon that is dual-tensioned. The anterior fibers are tensioned at 50° of flexion while the posterior fibers are tensioned at 20° of flexion, allowing the sMCL reconstruction to mimic the physiologic behavior of the native sMCL. Anteromedial reconstruction is then performed to address residual AMRI, which persists with the isolated sMCL reconstruction.

Subsequently, Borque and colleagues⁵ developed a short isometric construct (SIC) technique to restore valgus and rotational stability in knees with combined sMCL and dMCL injuries using a single graft (Figure 1). A synthetic graft is placed in an isometric position connecting the medial femoral condyle to a point on the tibia that is halfway between the anterior and posterior borders of the sMCL, approximately 2 cm distal to the joint line. Biomechanically, the success of the SIC lies in its true isometric positioning, which minimizes changes in graft length during flexion. In addition, its short working length allows it to control both valgus and tibial external rotation (AMRI) with a single graft⁵.

Although simultaneous ACL–MCL reconstruction was once associated with postoperative stiffness and inferior outcomes, modern fixation methods, refined graft placement, and updated rehabilitation protocols seek to mitigate these concerns. Early clinical evidence now suggests that addressing both ligaments in a single setting, particularly in the presence of high-grade valgus laxity or AMRI, may improve joint stability and decrease the risk of ACL graft failure compared with isolated ACL reconstruction.⁶

Summary and Future Perspectives

Management of combined ACL–MCL injuries requires deliberate attention to the medial side at the time of ACL reconstruction, as it is not acceptable to simply assume that the medial ligament complex has healed. The authors emphasize that the vast majority of acute ACL–MCL injuries should initially be treated in a hinged knee brace to promote biologic healing of the medial structures prior to ACL reconstruction. Even with appropriate early management, it is essential to reassess the medial side after bracing to confirm that healing has indeed occurred. This verification step is critical, not optional. Careful evaluation is even more important in chronic injuries or revision ACL reconstructions, where the medial ligaments will frequently appear normal on MRI and no longer possess meaningful healing potential. Therefore, the decision to surgically address the medial structures must be made at the time of ACL reconstruction based on objective, reproducible findings. The authors propose the following indications for medial-sided surgery during ACL reconstruction:

1. If there is valgus laxity in full extension and at 30°, the sMCL and POL are injured and require stabilization. However, laxity in full knee extension is relatively rare in combined ACL/MCL injuries.
2. If there is grade II or III opening to valgus stress at 30° of flexion, a SIC (Figure 1) or sMCL and anteromedial reconstruction should be performed.
3. If there is a positive dial test or a positive Slocum test, a SIC or sMCL and anteromedial reconstruction should be performed.

Figure 1. Medial view of a right knee demonstrating insertion points of the deep MCL (red), superficial MCL (green), and short isometric construct (blue) reconstructions relative to the medial epicondyle (ME) and tibial plateau.

References

1. Svantesson E, Hamrin Senorski E, Alentorn-Geli E, et al. Increased risk of ACL revision with non-surgical treatment of a concomitant medial collateral ligament injury: A study on 19,457 patients from the Swedish National Knee Ligament Registry. Knee Surg Sports Traumatol Arthrosc. 2019;27(8):2450-2459. doi:10.1007/s00167-018-5237-3
2. Westermann RW, Spindler KP, Huston LJ, et al. Outcomes of grade III medial collateral ligament injuries treated concurrently with anterior cruciate ligament reconstruction: A multicenter study. Arthrosc J Arthrosc Relat Surg. 2019;35(5):1466-1472. doi:10.1016/j.arthro.2018.10.138
3. Willinger L, Balendra G, Pai V, et al. High incidence of superficial and deep medial collateral ligament injuries in “isolated” anterior cruciate ligament ruptures: A long overlooked injury. Knee Surg Sports Traumatol Arthrosc. 2022;30(1):167-175. doi:10.1007/s00167-021-06514-x
4. Behrendt P, Herbst E, Robinson JR, et al. The control of anteromedial rotatory instability is improved with combined flat sMCL and anteromedial reconstruction. Am J Sports Med. 2022;50(8):2093-2101. doi:10.1177/03635465221096464
5. Borque KA, Han S, Dunbar NJ, et al. Single-strand ‘short isometric construct’ medial collateral ligament reconstruction restores valgus and rotational stability while isolated deep MCL and superficial MCL reconstruction do not. Am J Sports Med. 2024;52:968-976. doi:10.1177/03635465231224477

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