Arthroscopic Primary Repair of the Cruciate Ligaments

Introduction

Anterior cruciate ligament (ACL) tears are one of the most common injuries of the knee, with approximately 200,000 ruptures in the United States each year. On the contrary, only 3% of the injured knee ligaments are isolated posterior cruciate ligament (PCL) injuries because PCL tears more often occur in the setting of the multiligament injured knee (MLIK). The standard surgical treatment for ACL and PCL tears in younger and more active patients is reconstruction of the ligament, either with autograft or allograft tissue, and this has been shown to effectively restore knee stability. ^, However, in older and less active patients either reconstructive surgery or conservative treatment can be pursued. Although good functional outcomes have been reported after reconstruction of knee ligaments in the MLIK, this treatment is associated with some potential disadvantages that are mainly associated with the morbidity of the surgery and resultant stiffness, use of multiple grafts and the possibility of tunnel convergence. ^,

There has been a renewed interest in arthroscopic primary ACL and PCL repair because there are some potential benefits of repairing the ligament rather than reconstructing it. Arthroscopic primary repair is less invasive than reconstruction because it avoids potential donor site complications and a less complicated revision surgery, if needed, compared with reconstruction surgery. Furthermore, the native ligament is maintained, which preserves proprioception, and there is some early (experimental) evidence that primary repair ultimately might decrease the incidence of osteoarthritis. ^, Because of the high incidence of ACL injuries, ACL repair has been the main focus on the topic of primary knee ligament repair research over the last decade. Several studies have reported promising outcomes after primary ACL repair at short- to midterm follow-up with comparable failure rates, increased range of motion (ROM) and a trends towards fewer infections and complications compared with ACL reconstruction.

In this chapter we discuss the (1) indications and patient selection, (2) treatment algorithm, (3) surgical techniques, (4) rehabilitation, (5) outcomes of modern-day arthroscopic repair and (6) future directions of primary cruciate ligament repair.

History of Primary Repair

In 1897 Mayo Robson performed the first open primary repair of a proximal avulsed ACL and PCL tear. Over the ensuing decades, acute primary repair was further developed and ultimately became the mainstay surgical treatment with various studies reporting excellent short-term outcomes. ^, In 1976, however, Feagin and Curl noted significant deterioration of their short-term outcomes in a series of military cadets at midterm follow-up after open primary repair. Others corroborated these results by also reporting a deterioration in outcomes in patients with longer follow-up. ^, Meanwhile, several randomised and prospective studies noted better outcomes after ACL reconstruction, and this ultimately led to the abandonment of open primary repair and a shift towards reconstruction surgery. ^,

In 1991 Sherman et al. performed a subgroup analysis in an attempt to find an explanation for the deterioration of outcomes in some repair patients. They noted that better results after primary repair could be expected in patients with proximal tears with good tissue quality compared with midsubstance tears. Although their study showed promising outcomes in the selected group of patients with proximal tears and good tissue quality, the overall results were less than stellar. At this time, given the unpredictable nature of open ACL primary repair, reconstruction surgery had already become the new surgical standard, despite the potential advantages of ligament preservation.

In 2015 Taylor et al. performed a systematic review to determine whether there was still a role for primary repair in the surgical treatment algorithm for ACL tears. When reviewing the literature, the authors concluded that long-term stability was achieved in a subset of patients treated with repair. When looking closely at these results, more consistent results were found in patients with proximal tears with excellent tissue quality. Therefore, the authors concluded that these proximal tears might be eligible for primary repair.

The Rationale for Modern-Day Repair

Various modern developments have contributed to the renewed interest of primary repair. First, in contrast to the historic open repair approach for all types of tears, modern arthroscopic primary ACL repair is now performed only in appropriately selected patients. This is important because several studies have reported that it is the avulsion type tears that are the most likely to be successfully repaired. ^, The difference can be explained by the better healing capacity in these specific type of tears. On the other hand, the healing in midsubstance tears is limited, which can likely be explained by the fact that the fibrin clot is washed away by the synovial fluid.

Second, ligament preservation surgery is now performed using a minimally invasive arthroscopic approach with immediate mobilisation, whereas the repair procedure historically was performed using arthrotomy with postoperative casting. Performing open primary repair via arthrotomy was a more morbid procedure, especially in light of the postoperative straight-leg cast that was generally applied for 4 to 6 weeks after these surgeries, which most certainly contributed to the inconsistent and disappointing results found in most studies. One can therefore expect better outcomes and less postoperative stiffness after a modern surgical approach of arthroscopic repair.

Third, the development of additional suture augmentations means that better outcomes can be expected because augmentation of the repaired ligament has been shown to protect the repaired ligament during the healing phase. An experimental study in sheep found that, in a repair with suture, augmentation of the ligament provided more anteroposterior (AP) stability, tensile strength and stiffness compared with a repair without suture augmentation. Additionally, Vavken et al. noted that the strength of the ligament increased with 20% when additional suture augmentation was added to the repair.

Finally, postoperative management today focuses on early mobilisation, which is associated with better outcomes and shorter rehabilitation. Postoperative management in most historical studies, as mentioned, often consisted of joint immobilisation for a period of at 4 to 6 weeks with a long leg cast. This has been shown to lead to suboptimal results because prolonged immobilisation decreased ROM and increased postoperative pain and stiffness. ^,

Taking these factors into account, better outcomes can now be expected after arthroscopic primary repair than with the historic open repair approach. Certainly there are potential advantages with this technique compared with ACL reconstruction ( Table 12.1 ).

Table 12.1

Advantages and Disadvantages of Arthroscopic Primary Repair of Cruciate Ligaments

Advantages	Disadvantages
Minimally invasive surgical technique	Potentially higher failure rates in younger patients
No tunnels need to be drilled	Surgery is performed in the acute setting
No need for graft harvesting	No attempt to treat conservatively
Preservation of native tissue	Increased risk of postoperative stiffness
Maintaining proprioception	Not all injuries are deemed repairable
Regaining early range of motion
Potentially shorter rehabilitation time
Revision surgery similar to primary reconstruction
Less complicated compared with reconstruction
Experimental studies suggest lower incidence of osteoarthritis

Indications and Patient Selection

As learned from the historically disappointing studies, it is now well known that patient selection is critical for successful clinical outcomes at short- and longer-term follow-up for ACL repair. In this section patient selection, preoperative imaging, eligibility of repair and optimal timing of surgery are discussed.

Patient Selection

Patient selection for primary repair is mainly based on tear type and tissue quality. For the location of the tear, it is important that the length of distal tissue remnant is sufficient to reach its anatomical footprint. Tissue quality has to be sufficient to withhold intrasubstance suturing and tensioning towards the anatomical footprint. To understand the different tear types, Van der List et al. have proposed a classification system that is based on tear location as defined by the length of the distal remnant divided by the total length of the ligament and is displayed as the percentage of the intact distal remnant from the total ligament length. This includes proximal avulsion tears (type I), proximal tears (type II), midsubstance tears (type III), distal tears (type IV) and distal avulsion tears (type V) ( Fig. 12.1 ). This classification system can be applied to both cruciate ligaments ( Table 12.2 ), although the inter- and intraobserver reliability has only been established for ACL tears. As mentioned, patients are deemed eligible for primary repair when avulsion type tears are present, although it should be noted that distal soft tissue ACL avulsion tears are a rare entity.

Fig. 12.1, Three examples of sagittal magnetic resonance images of three different anterior cruciate ligament (ACL) tear types (arrow). (A) The ACL is torn proximally (type I). (B) The ACL is torn at the midsubstance (type III). (C) The ACL is torn distally (type V).

Table 12.2

Tear Types of the Cruciate Ligaments

Tear Location∗	Classification	Tear Type
>90%	Proximal avulsion	I
75%–90%	Proximal	II
25%–75%	Midsubstance	III
10%–25%	Distal	IV
<10%	Distal (bony) avulsion	V

∗Tear location is defined as the location where the ligament is torn and is calculated by dividing the distal remnant by the total (distal + proximal) remnant length. It is expressed as the relative length of the distal remnant that is used for repair (e.g. 50% tear means that the ligament is torn exactly in the middle, whereas a 90% tear means that the ligament is torn at 90% of the distal-proximal distance, thus that the tear is between 90% of distal remnant and 10% of femoral remnant).

Preoperative Imaging

Magnetic resonance imaging (MRI) has become the gold standard to determine an ACL tear with 100% sensitivity and 97% to 100% specifity. MRI is not only able to indicate whether ligaments are torn, but it can also distinguish between different tear types. In a 2017 study, Van der List et al. assessed the distribution of ACL tear types in 350 MRIs, of which 16% of all cases had type I, 23% type II, 52% type III, 1% type IV and 3% type V tears. Similar findings were found in children overall; however, for adolescent patients between 11 to 13 years old, 32% of patients had type I tears, 16% type II and 32% type III. Interestingly, 92% of all paediatric patients (younger than 11 years old) presented with a bony avulsion type V tear. Although MRI is reliable to determine tear location and tissue quality, the final assessment before primary repair will always be made intraoperatively.

Eligibility for Repair

With regard to the potential reparability of ACL tears, it is estimated that up to 40% of all tears could potentially be repaired based on the aforementioned MRI study (i.e., those with proximal tears, types I and II). The same authors reported in another MRI study that tear location and tissue quality could preoperatively predict the eligibility for a primary ACL repair. In their study they noted that repair patients more often had a type I tear (41% versus 4%, P < .001) with good tissue quality (89% versus 12%, P < .001) compared with reconstruction patients. Furthermore, it was noted that 90% of all type I tears and 88% of type II with good tissue quality were ultimately able to be repaired. These findings are supported by the historical work of Sherman et al. because similar incidences of proximal tears were noted in their study. In a cohort of 361 patients who were surgically treated between 2008 and 2018, 44% of all ACL tears were repaired, although it should be noted that this was performed by a surgeon experienced in knee ligament preservation surgery.

With regard to PCL tears, Twaddle et al. determined the eligibility of primary repair for all major knee ligament tears in MLIKs and noted that 51% of PCL tears were deemed repairable. These findings were supported by Goiney et al., who reported that 27 patients of their cohort of 50 MLIKs (54%) ultimately underwent primary PCL repair. Based on this MRI study, they noted that patients were more likely to be treated with repair if a distal remnant length of more than 41 mm was present. Similar to the literature, in the experience of the senior author it has also been noted that 62% of PCL tears were potentially repairable when surgery was performed within 6 weeks of injury.

Patients of all ages and activity levels can be treated with primary repair, although it seems that patients older than 35 years more often have proximal avulsion type tears compared with younger patients. We can only speculate on the reason for the possible associating between age and primary repair because this has not yet been examined extensively. Variance in injury mechanisms might explain the noted difference in repairability of ligaments between younger and older patients. Another possible reason might be that some mucoid degeneration in the proximal aspect of the ligament is due to the age-related decrease in vascularity that is seen in older patients, which weakens the ligament and potentially results in more common tearing of the ligament proximally compared with younger patients.

Timing of Surgery

Surgery is generally preferred in the acute setting (<4 weeks) because better tissue quality can be expected within the early phase as the ligament remnant can potentially retract after several weeks. In a 2019 case-control study in which patient characteristics were compared between a group of patients in whom primary repair was possible (i.e., those with proximal tears) and a group of patients whose injuries were deemed unrepairable (i.e., midsubstance tears or ligaments with poor tissue quality), the authors noted that patients were more likely to be treated with primary repair if surgery was performed within 4 weeks of injury in ACL tears (odds ratio (OR) 3.3, P < .001) compared with surgery more than 4 weeks after injury. Despite these findings, the possibility of primary repair will always depend on the length and quality of the tissue, and there are exceptions in the literature; even a chronic 11-year old proximal ACL tear that was scarred to the PCL was reported to have been successfully reattached to its femoral footprint.

Treatment Algorithm

As mentioned in the section on the rationale for modern-day repair, better outcomes after primary repair can be expected in cases when avulsion tear types are present. Therefore, all patients undergo the same treatment algorithm for all cruciate ligaments in the clinic of the senior author. All patients are preoperatively counselled that primary repair of the ACL or PCL will only be performed when (1) good to excellent tissue quality and (2) sufficient remnant length are present during the final intraoperative assessment. In cases of tears that are nonrepairable because of location (i.e., those with midsubstance tears) or tissue quality (i.e., retraction, resorption or significant fraying of the fibres), standard reconstruction will be performed either with autograft or allograft tissue depending on specific patient variables and preferences. Patients are treated using a personalised approach to preserve native tissue along with its proprioceptive function when feasible.

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