Acute patellar ligament reconstruction with the synthetic LARS ligament as an internal stabilizer

Introduction

The acute rupture of the patellar ligament represents still an important challenge for the surgeon today. A rapid diagnosis and therapy are essential for an adequate rehabilitation of the patient since the patellar tendon is a key part of the knee extensor apparatus and is essential for walking and maintaining an upright position [1]. Anatomically, the patellar ligament is the continuation of the quadriceps tendon, and mainly composed of the rectus femoris component which passes over the anterior aspect of the patella and inserts itself on the tibial tuberosity. The anteroposterior thickness of the patellar ligament is about 5 - 7 mm and less than that of the quadriceps tendon [2] . The patellar ligament has an average size of 30 mm in width and 50 mm in length [3].

Being an integral part of the knee extensor system, the role of the patellar tendon is to transmit the contraction forces of the quadriceps to the leg. Studies have shown that the distribution of forces during knee flexion are changing. When the knee flexion goes beyond 45 degrees the forces on the patellar ligament are increasing and peak at 60 degrees. Conversely, for knee flexion angles less than 45 degrees, the forces are greater in the quadriceps tendon [4]. This biomechanical concept becomes very interesting when associated with the clinic, where most of the patellar ligament injuries are happening with the knee in flexion [5,6]. The main component of the patellar ligament is type 1 collagen and fibroblasts, distributed parallel in space which gives the ligament a considerable strength [7].

Patellar ligament rupture is the result of a trauma mostly associated with a weakened tendon or chronic tendinosis [7]. Furthermore, many systemic conditions can be associated with an overall weakening of the ligament and tendon structures [8]. All these pathologies correspond histologically to mucoid degeneration, tendon lipomatosis and calcifying tendinopathy. These pathological conditions must be considered when planning surgery. A macroscopically degenerated tendon will make direct repair very difficult but other surgical options, such as internal brace reconstruction, may be a good option, even in acute traumatic injuries.

The LARS ligament as internal stabilizer

In our experience, patellar ligament repair is always a challenge. In our practice, we have used many different techniques including direct repair (by direct suture, anchors or trans osseous fixation) or reconstruction with allo- or autografts. Our clinical results are comparable with those of the literature [9,10]. Sometimes, however, we are faced with cases, where the best-known techniques are not enough. Especially when the tissue conditions of the tendon are not very suitable for repair or if the functional demands of the patient are very high (athletics, elite sports). For these special cases after acute trauma , we use an artificial internal stabilizer for our patellar ligament reconstruction technique. The artificial LARS ligament (LARS company, Arc-sur-Tille) is composed of a woof of longitudinal synthetic fibers and a transversal warp consisting of a thread of textured polyethylene terephthalate (PET).

The synthetic Lars ligament PTR 30 consists of three separate portions (Fig.1):

• superior or proximal portion flattened, whose end contains a small stainless-steel barrette which aids in the primary fixation of the ligament
• middle portion corresponding to the patella tendon of small diameter and made of free fibers
• distal or inferior portion which is cylindrical and intended for tibial fixation

The ligament consists of 30 longitudinal fibers, not braided and therefore less sensitive to plastic deformation. The ligament shows a resistance of 1 500 N and an elasticity of 9 %[11].

Important preoperative considerations

We use this technique for all patients with acute and chronic rupture of the patellar tendon. Obviously, a careful preoperative evaluation must be made, especially about the presence of large wounds or other causes of contamination of the surgical site. A complete assessment of the ligament status of the knee must always be performed, for not to miss the diagnosis of multi-ligament lesions. A preoperative radiograph should be done to exclude patella fractures that could complicate surgery. An ultrasound evaluation will also be necessary to understand the type of the lesion (partial or complete injury, distal or proximal or intermediate lesion).

After the clinical and image evaluations, it will be very important to understand the functional needs of the patient and especially his motivation necessary for postoperative rehabilitation. Young patients, sports or professional athletes represent the type of patients ideal for this surgical technique. In our experience, we have also used this reconstruction technique with the artificial LARS ligament even for more complicated cases like failure of osteosynthesis after tibial tubercle osteotomy. TTO represents a very common surgical procedure for patella instabilities which might have complications that are not always easy to solve. In this specific case we often found a bone fragment which was no longer possible to be fixed for a new osteosynthesis with plates or screws, therefore we approached these cases like an acute avulsion of the patellar tendon from the tibia.

The surgical technique : tips and tricks

We will present our personal technique for the reconstruction of the patellar tendon, using two artificial ligaments (LARS, PRT 30) as internal stabilizers. The patient is in dorsal decubitus position with torniquet inflated during surgery. As antibiotic prophylaxis two grams of cefazolin is given to the patient intravenously, less than 60 minutes before the start of surgery. The surgical approach is made in flexion medial to the patella, from the superior edge of the patella to the anterior tibial tuberosity (Fig.2).

Soft tissue dissection is done up to the tendinous plane and the retinaculum and patellar ligament are exposed (Fig. 3).

Surgical debridement is performed on the distal stump of the patella ligament, to eliminate none viable tissue (Fig. 4).

Two tunnels are prepared in the patella, to allow a 4.5mm mesh to be passed from distal to proximal. The tunnels are parallel and must be fully in the bony structure. Two Lars ligaments are then passed from distal to proximal. The steel rod is flipped to the upper pole of the patella to act as an anchoring system (Fig. 5, 6).

Subsequently, two further tunnels are performed at the root of the anterior tibia tubercle. They should be on different levels in the anteroposterior plane. The distal part of each ligament is passed through the tunnel, so that it comes out on the opposite side (Fig. 7).

The stump of the distal patellar ligament is sutured end to end, to create a solid distal part which is strongly supported by the artificial ligaments.

The ligaments are finally fixed with 2 full threaded metal interference screws (5.2 x 30 mm) and excess ligament is cut (Fig. 8 A & B). The extensor system of the knee is now restored. Flexion and extension are tested introperatively. The subcutis and skin are closed with sutures and staples.

Post-operative management

After surgery the patient wears an extension immobilizer brace for 2 weeks with unrestricted load walking. After two weeks, the first medical follow-up with an radiograph is performed to verify the adequate wound healing and verify the correct position of the implants. Immobilization in extension is changed to an articulated orthosis that allows progressive knee flexion. Flexion is allowed progressively in 2 weeks interval from 30 to 60 and finally 90 degrees at the end of the sixth week. Physiotherapy should be started immediately after the operation. For the first 6 weeks the goal is the recovery of knee mobility and the drainage of edema. Then, protocols for the recovery of proprioception and muscle strengthening are followed. The complete resumption of sports, even those at risk, starts around the eighth/ninth postoperative month.

Considerations and Conclusion

The use of the LARS artificial ligament for the reconstruction of the patellar ligament seems to ideal from our experience for the cases we have discussed especially to increase resistance, biointegration and failures. The PET fibers used possess a high resistance to traction that increases with the number of longitudinal fibers used. Tests have been undertaken by the Institut Textile de France (ITF) demonstrated a total resistance to rupture equal to 1500 N for the 30 fibers ligament PTR 30, used in our surgery. Also, the rate of residual stretching is very low. A study conducted by the ITF after traction at 2 500 N indicates the same results immediately after testing and 24 hours later. Elongation was less or equal to 1.5 % regardless of fiber quantity in the ligament[12]. Regarding biointegration, a histological study demonstrated a complete cellular and connective tissue in growth in the LARS ligament and in vitro fibroblasts and osteoblast-like cells encapsulated the LARS ligament fibers [13]. Our post-operative results correspond to what was published in the literature, with excellent results for patellar ligament reconstruction [14,15,16]. This technique allowed our patients to initiate retesting early and quickly return to daily activities and favorite sports. In addition to the simple surgical technique, there are several advantages compared to other techniques described in the literature.

Main advantages of the LARS technique

• no donor site morbidity
• no presence of rejection or intolerance of the implant
• growth of fibroblasts around artificial ligaments[17]
• rapid mobilization and immediate weightbearing for walking
• possibility of repeating the reconstruction surgery if necessary [18, 19]
• no need for cerclage wiring