Conservative treatment

Unlike other knee ligaments, the sMCL has significant healing potential. However, the location of the tear (proximal or distal) and the presence of associated ligamentous injuries determine a broad spectrum of injury combinations that require tailored management.

First, distal sMCL injuries have shown lower healing capacity when compared with proximal sMCL tears. This is related to the lower vascularization of the distal sMCL and the potential entrapment of other soft tissues, such as the pes anserine, between the two portions of the torn ligament.

Conservative treatment is usually performed in case of isolate grade I, grade II, and most proximal isolated grade III MCL injuries. Nonoperative treatment focuses on immobilization, followed by guided range of motion (ROM) and strengthening. For grade I and grade II MCL injuries with no valgus instability, the use of a knee brace is not mandatory, and patients can usually return to sport after a few weeks (10 days for grade I and 2–4 weeks for grade II MCL injuries). For grade III MCL injuries, the protocol is more controversial, and the duration of brace treatment, the knee degrees of early immobilization, and the weight-bearing protocol are all aspects intensely debated in the literature.

A recently published consensus paper provided a conservative protocol that helps to standardize the nonoperative approach to isolated high-grade MCL and combined ACL–MCL injuries [45].

•Duration of bracing treatment: 6 weeks

•ROM: In the first 2 weeks, the knee should be immobilized in full extension or 10° of knee flexion. From week 2 to week 4, a knee ROM from 0° to 60° could be allowed, with an increase to 0–90° during weeks 5 and 6 post injury. However, it is essential to reevaluate the patients during this period to adjust this protocol to avoid knee stiffness.

•Weight-bearing: Full weight-bearing may be allowed in varus or straight knees, while partial weight-bearing should be recommended in valgus-aligned knees.

Orthobiologic augmentation for conservative MCL treatment

Owing to the high incidence of MCL tear and the potential for healing given by the absence of the contact with synovial fluid and the profuse vascular supply, some authors have hypothesized a possible role for orthobiologics in the treatment of partial MCL injuries [62]. However, regarding MCL tears, the available literature is limited to case reports and animal studies with contradictory findings. In a first animal model of MCL injuries, including 30 rabbits treated with one platelet-rich plasma (PRP) injection, the authors found accelerated ligament healing and an increased tensile strength of the MCL at 3 and 6 weeks, when compared with a control group, thus suggesting a potential for PRP injections in expediting the recovery process of acute MCL injury [63].

An opposite conclusion was reported in a similar study performed on rats. The authors reported no difference in granulation tissue, histological scores, and biomechanical properties between PRP-treated animals and the control [64]. A more recent study performed on more than 180 knees of rabbits not only found no differences in the vascularity and the ligament tissue maturity score between PRP injections, a control group treated with saline, and a sham surgery group but also highlighted possible adverse effects of the PRP treatment in an acute setting. The authors showed that MCL treated with multiple PRP injections had less biomechanical load and stiffness when compared with the control group, thus demonstrating that high doses of PRP could reduce the quality of the repaired tissue [65].

To summarize, literature on the use of orthobiologics in MCL injuries is scarce and limited to animal models, and clear evidence does not support this biological augmentation use.

Surgical treatment

Surgical treatment is advised for high-grade tears with multiligament injury, chronic instability, failed conservative treatment, or specific acute conditions such as Stener-like lesion, MCL bony avulsion, or irreducible knee dislocations [25, 66].

While in the latter situations, there is more consensus on the need for surgical intervention and the operative techniques (MCL refixation with screws and washer or suture anchor) are similar, there is much controversy in surgical indication, timing, and type of MCL reconstruction in the other clinical scenarios. The following sections aim to provide a biomechanical rationale and a summary of the clinical outcomes of the most used medial-side surgical techniques. Table 3 shows the most common clinical scenarios with MCL lesions and the suggested treatment. Figure 8 reports a concise summary of the different surgical options for MCL treatment. 

Fig. 8

Treatment options in MCL surgical interventions

Table 3 Summary of the most common clinical scenarios with an associated medial-side injury and their proposed treatment Surgical techniques: POL advancement or the “Hughston technique”

Hughston and Eilers described in 1973 the detailed anatomy of the posteromedial structure and reported a surgical technique aimed at repairing all the torn ligaments using periosteal sutures and primary direct repair [67]. This technique aims to perform a capsular and POL plication over the MCL to restore the natural soft tissue tension, which contrasts with the modern surgical approach, which usually requires a former MCL and/or POL reconstruction with grafts.

This technique takes advantage of some anatomical features of the posteromedial corner: the proximal part of the sMCL, differently from the distal, shows a considerable amount of soft tissue adherences to the medial femoral condyle that could directly disperse the tension [17]. The observation that the sMCL is proximally anchored to soft tissues represents the anatomical rationale for performing a plication of the POL and PM capsule over the MCL for the treatment chronic medial [17]. Moreover, from a biomechanical point of view, in vitro study showed that there is significant load sharing between the sMCL and the POL [26, 29]. Therefore, restoring the tension of these two ligaments could potentially increase the stability against valgus and rotational laxity [45] This surgical technique has been recently rediscovered and described by Offerhaus et al. [68]. A longitudinal incision from the medial epicondyle to the medial joint line is performed. After skin and subcutaneous dissection, the sartorius fascia was opened to expose the sMCL and the POL. Three to five horizontal mattress sutures are passed through the POL and the MCL in the pants-over-vest fashion. Sutures are tied at 90° of flexion after applying slight varus stress (Figure 9).

Fig. 9

Schematic demonstration of the “Hughston” POL advancement over the sMCL. Three to five horizontal mattress sutures are performed, in a pants-over-vest fashion, to retension together these two structures

This procedure could be performed either isolated or in association with a former single-bundle MCL reconstruction. The indications for the “Hughston” technique include chronic proximal high-grade MCL tear with persistent valgus instability, chronic valgus instability associated with primary or revision ACL reconstruction, and multiligament knee injuries (MLKI) with medial-side involvement if this technique is performed in association with MCL reconstruction.

While historically this procedure showed excellent outcomes in terms of valgus stability and failure rate when performed either for isolated MCL tear or in associated ACL–MCL injuries [69], more recent studies found fair results in the setting of ACL revision and medial instability [70]. In this research including 53 patients with valgus instability undergoing ACL revision, performing an MCL reconstruction was superior to MCL plication in terms of anterior and valgus stability, failure rate, and clinical outcomes [70]. As described above, the “Hughston” technique could also be indicated in high-grade medial-side injuries if associated with single-bundle MCL reconstruction.

In a recent biomechanical study, the “Hughston” technique associated with single-bundle MCL reconstruction was compared with the anatomical LaPrade technique using two free grafts for the reconstruction of the sMCL and POL. Interestingly, while there were no differences in the restoration of the internal rotation, the “Hughston” techniques with a single graft more closely resembled the intact state in valgus stability and knee external rotation at low degrees of flexion when compared with the double-stranded MCL reconstruction [71]. However, a recent prospective multicenter randomized controlled trial found no difference in terms of clinical outcomes and objective stability in two groups of patients treated with single MCL reconstruction with MCL plication and a control group of double-bundle MCL reconstruction [72]. Overall, the “Hughston technique” presents several advantages, including its simplicity, cost-effectiveness, and the absence of a free graft, and therefore could be employed with the correct indication in the treatment of combined ACL–MCL injuries.

Surgical techniques: “augmentation” with synthetic ligament of the MCL

MCL “augmentation” refers to a surgical technique reinforcing primary ligament repair [73]. For MCL injuries, those techniques are usually performed with synthetic grafts such as high-resistant tape [74]. The “augmentation” techniques could be considered as an alternative to single-bundle MCL reconstruction, with some potential advantages, including the lack of donor-site morbidity and the preservation of native MCL proprioception while aiding the ligament healing process [75].

A biomechanical study showed that a high-resistance tape augmentation construct was able to resist cyclic loading and showed a valgus load to failure comparable to a native MCL [76]. Meanwhile, in another cadaveric study in a combined ACL reconstruction and MCL repair model, the repaired MCL augmented with highly resistant tape better restored valgus and external rotation laxity when compared with MCL suture repair alone [77]. However, clinical literature is limited to a few studies.

A retrospective analysis of 16 patients who underwent ACL reconstruction and MCL ligament repair augmentation showed excellent clinical results and objective knee stability without any failures or surgical complication [78]. Similarly, a recent analysis of 64 elite athletes who underwent MCL reconstruction augmented with synthetic tape reported an 88% return to sport rate, with 97% of the patients playing at the same or higher Tegner level. This study also underlined the efficacy and safety of synthetic ligaments when employed for extraarticular reconstruction [79].

Similarly, in a series of 23 professional athletes suffering a “Stener-like” lesion of the MCL treated in the acute setting, all the patients could return to sports after a mean of 17 weeks, and all the patients were still practicing the sports at 2 years of follow-up. Notable, the patients developed complications requiring the removal of the synthetic ligament, but the knee function was not affected [80].

Surgical techniques: “single-bundle” sMCL reconstruction

Anatomic “single-bundle” sMCL reconstruction techniques have been developed with the aim of recreating the native proximal and distal insertion of the sMCL and to mimic its biomechanical function (Fig. 10) [81]. Several techniques have been described that differ in terms of grafts (with hamstring being the most popular, followed by allografts and quadriceps tendon) and fixation methods (including suture anchors, interference screws, and cortical screws and spiked washers) [82,83,84]. The advantages of these techniques compared with “double-bundle” techniques is the possibility to perform smaller skin incision, reduced surgical time, and less hardware and possibility of tunnel collision when performed in the multiligament setting [85]. A “single-bundle” sMCL reconstruction could be performed in chronic medial-side injuries with predominant valgus instability and as an augmentation procedure in the setting of sMCL repair. It is, however, now fully demonstrated that the long lever arm of a single-bundle construct determines a biomechanically inferior result compared with the double-bundle reconstruction techniques [86]. In a recent biomechanical study comparing five different MCL reconstruction techniques, an isolated sMCL graft was the only one failing to control the external rotation and the combined AMRI pattern [86]

Fig. 10

Illustration of an isolated “single-bundle” superficial MCL reconstruction (sMCL) in a right knee. A free graft is employed to recreate the native proximal and distal sMCL insertions

Single-bundle sMCL reconstruction techniques can be considered for selected cases of medial-side instability, but only if there is predominant or sole valgus instability. A careful assessment of anteromedial instability should be performed, and alternative techniques should be employed if rotational issues are suspected.

Surgical techniques: semi-anatomic “double-bundle” sMCL and POL reconstruction

A double-bundle technique could be employed in cases of higher valgus instability, injury to the posteromedial corner, or knee hyperextension after an MCL tear. Some of these techniques, called “semi-anatomic,” are not aimed at precisely recreating the insertion of the sMCL and POL, but present some advantages, including the reconstruction of two different structures with only one autograft and the need for only one femoral tunnel [87].

Among those techniques, the “Lind” or Danish technique is one of the most commonly performed. The semitendinosus allograft of the patients is harvested, preserving the tibial insertion, and is then secured at the level of the proximal sMCL insertion to recreate the sMCL, and distally to the tibia to reproduce the POL [87] (Fig. 11). In a study of 61 patients suffering isolate high-grade valgus instability or MLKI treated with the “Lind” technique, the authors reported, at minimum 2 years of follow-up, excellent clinical and radiological outcomes with 98% normal or nearly normal (grade A or B), and for overall International Knee Documentation Committee (IKDC) score, a 91% rate of patient satisfaction and steady improvement in patient-reported outcomes.

Another author performed a similar reconstruction technique using free Achilles allograft to avoid hamstring tendon harvesting [88]. In this study of 56 patients with isolated or combined high-grade valgus instability, the medial side gapping under Telos stress x-rays was reduced from 10.1 to 2.9 in the postoperative period. Moreover, the percentage of patients with persistent AMRI dropped from 68% to 9%. It is important to note that four patients reported a significant loss of knee extension (more than 6°), and two patients reported a loss of more than 25° of flexion compared with the contralateral knee, thus underlying the risk of knee stiffness of this technique.

Fig. 11

Illustration of a semi-anatomic “double-bundle” sMCL and POL reconstruction in a right knee. The semitendinosus tendon is harvested, preserving the distal insertion, and the graft is then secured into a tunnel in the proximal sMCL and the tibial POL insertion

Surgical techniques: anatomic “double-bundle” sMCL and POL reconstruction

This technique, as described by Laprade et al. [89], involves meticulous reconstruction of the proximal and distal portion of the sMCL and the POL (Fig. 12). The particular emphasis on reproducing the original insertion site of those ligaments instills confidence in the precision of the procedure.

In the original study, the authors included 28 patients with high-grade medial-side injury, including both acute and chronic cases. Their short-term results showed an excellent improvement of all the patient-reported outcome measures (PROMs) and objective knee stability at valgus stress x-rays from 6.2 mm preoperatively to 1.3 mm postoperatively. In a more recent paper, Lee et al. investigated the outcome of the same technique at more than 5 years of follow-up in another case series of 23 patients. Similarly, the authors reported satisfactory results with an average Lysholm score of 90 points and a side-to-side difference of 1.2 mm at the postoperative stress X-ray. Moreover, preoperatively, 17 patients showed clinical signs of AMRI, but none presented the same instability pattern at the last follow-up [90].

The advantages of this technique include the high stability and low rate of knee stiffness, complications, and failures reported in these few clinical studies. However, with a more comprehensive understanding of medial-side anatomy and biomechanics, some authors have started to question this technique, considering that the dMCL is not reconstructed and injuries to the POL are quite rare compared with other structures [7, 31, 33] Moreover, the POL has limited, if any, role in controlling external rotation. Therefore, if AMRI is present, there could be concerns regarding rotational stability in combined injuries.

Fig. 12

Illustration of an anatomic “double-bundle” superficial MCL reconstruction (sMCL) and POL reconstruction in a right knee. Two separate free grafts are necessary to recreate the native proximal and distal insertions of the sMCL and the POL

Surgical techniques: “new in vitro evidence”

As described above, the concept of AMRI has been recently redefined, and new biomechanical evidence has emerged. It is now clear that an isolated sMCL reconstruction can provide some restraint against valgus load, but owing to a long lever arm and graft orientation, it will poorly control rotational instability. To address this, several new techniques have been developed and biomechanically tested to evaluate their role in controlling AMRI.

The “triple-stranded” MCL reconstruction technique (Fig. 13A) is a surgical method that includes three different grafts aimed at reproducing the sMCL, the POL, and the dMCL [27]. In a controlled laboratory study of a complete medial-side lesion, this technique showed superior results compared with the anatomic double-bundle technique in terms of valgus stability and control of external rotation. The authors concluded that an anteromedial dMCL graft could also help to unload an ACL graft in a combined ACL–MCL setting. However, it is important to locate the sMCL graft exactly at the medial epicondyle (and not posteriorly) to restore valgus stability across the entire range of movement.

Fig. 13

Illustration of a “triple stranded” MCL complex reconstruction (A), short isometric construct (SIC; B), and combined sMCL and anteromedial retinaculum reconstruction (C)

The single-strand “short isometric construct” (SIC) is an additional technique recently described (Fig. 13, B). This technique involves the use of a synthetic graft placed at the center of the medial epicondyle and 2 cm distal to the joint line on the tibia. This short construct has potential advantages, including increased stiffness, avoidance of hamstring irritation, and resistance against rotational stress. In a recent cadaveric study, SIC outperformed isolated sMCL and dMCL reconstruction in terms of valgus and rotational stability [14].

Finally, a third technique aimed at creating an extraarticular anteromedial graft has been described and evaluated in a cadaveric setting (Fig. 13C) [22, 91]. In both studies, the AM procedure showed excellent results in controlling external rotation and simulated AMRI, as well as providing a protective effect on the ACL graft.

In summary, there has been a significant advance in medial surgical techniques in recent years, with basic science evidence showing excellent biomechanical performance for these procedures. However, clinical studies are needed to confirm the indications and outcomes of these techniques in the clinical setting.