Sonographically Guided Anterior Cruciate Ligament Injection: Technique and Potential Use for the Treatment of Partial Anterior Cruciate Ligament Tear

Introduction

While surgical interventions for anterior cruciate ligament (ACL) injury continue to be advanced and perfected, the ability to percutaneously introduce novel biologic substrates to the site of pathology is an area of increasing interest. Essential to this topic has been the advancement of ultrasound in musculoskeletal medicine, as well as biologic therapies such as platelet rich plasma (PRP) and mesenchymal stem cells (MSCs). This chapter will outline how these technologies have converged and explain the indications, methods, and procedures of a sonographically guided injection of the ACL.

The use of ultrasound in musculoskeletal medicine has expanded at a rapid pace over recent years. This trend can be attributed in part to improvements in image resolution and lower equipment costs. In turn, novel diagnostic and therapeutic applications of ultrasound are continuously being discovered. The ACL has become a target of increasing sonographic investigation due to its frequency of injury and resultant functional impairment when disrupted. Currently, ultrasound applications toward the ACL reside in the realm of delivering therapeutic substrates, as further improvements in technology will be required to provide more diagnostic utility. Magnetic resonance imaging remains the gold standard in imaging the ACL, as it assists in evaluating for other possible injured structures and helps in preoperative planning.

Most tears of the ACL are complete disruptions of both the anteromedial and posterolateral bundles, and surgical reconstruction is a mainstay of treatment, especially in the competitive or recreational athlete. The treatment of partial tears of the ACL is less defined and a topic of frequent discussion. Pujol et al. performed a systematic literature review of 436 patients with partial ACL verified by arthroscopy. At a mean of 5.2 years postinjury, on average only 52% returned to sport at the previous level of activity, 54% reported at least intermittent pain with activity, 25% developed a positive pivot shift, and 8.1% required ACL subsequent reconstruction. From a histologic and cellular level, there are several factors that may blunt the healing ability of a partially torn ACL. First, exposure to the healing milieu of endogenous platelet-derived growth factors and stem cells is likely limited significantly due to poor intrinsic vascularity of the ligament. Additionally, the synovial fluid that bathes the ACL contains plasmin, an inhibitor of fibrin clotting matrix formation and further healing potential.

Concurrent with, yet independent of, the growth of ultrasound use in orthopaedics has been the emergence of biologic therapies such as PRP and MSCs. Detailed discussion of the biochemical and cellular mechanisms of action of these therapies is beyond the scope of this chapter; however the clinical effects in both animal and human models continue to show great promise. Even intra-articular injections of MSCs have displayed an ability to home in on injured ACL tissue. Several recent studies, however, have taken greater steps to place biologic therapies in closer proximity to the injured ACL. These have consisted of PRP-collagen scaffolds or gels, growth factor-embedded fibrin sealants, microfracture infiltration, and MSCs embedded in fibrin glue.

Injectable substrates have been highly utilized in the field of orthopaedics for many years. However, their accuracy and subsequent clinical efficacy can be limited by several factors, including injector expertise, patient body habitus, and anatomic location. That said, the use of ultrasound can significantly improve the consistency of delivering accurate injections while simultaneously allowing the clinician to verify correct placement in real time. This accuracy promotes the pairing of ultrasound-guided injections with novel biologic substrates, which may involve invasive procurement methods and increased expense to the patient. Additionally, when compared with arthroscopic, computed tomography–guided, and fluoroscopic-guided interventions, ultrasound-guided procedures have the advantage in terms of efficiency, lower cost, eliminating radiation exposure, and reduced risk of complications. Larger volumes of biologic substrates may also be used under ultrasound, as space-occupying contrast dye is not needed for needle placement verification. Until recently, literature regarding ultrasound-guided percutaneous needle placement at the ACL has been sparse. In 2013 Chen et al. were able to directly image the mid and distal ACL in 33 of 33 asymptomatic volunteers; however, the proximal ACL origin was not consistently identified. Smith et al. have performed the most recent study to date, and the only study using modern sonographic equipment to assess the accuracy of ultrasound-guided intraligamentous ACL injections.

A 12-3-MHz linear transducer was used to inject latex through a 22-g stainless steel needle into 10 cadaveric knees. The knees were positioned with 90 degrees of flexion and slight internal rotation in order to simultaneously create a tauter ACL, and to avoid obstruction of the ACL by the patella. The transducer was started in a coronal plane over the MCL and then translated over the anterior joint line, while keeping the tibiofemoral joint in sight and tilting the transducer toward the lateral aspect of the intercondylar notch. As the transducer assumed a more sagittal plane, just medial to the patellar tendon, the distal ACL was visualized as a relatively hypoechoic structure, 1–1.5 cm deep to the anterior tibial cortex. The depth was adjusted to 4–5 cm, and the cephalad end of the transducer was then rotated approximately 20–50 degrees laterally over the anticipated course of the ACL to its insertion on the medial portion of the lateral femoral condyle ( Fig. 98.1 ). To prepare for injection, the transducer was then translated cephalad, thus creating a soft tissue plane for needle entry cephalad to the superior tibial cortex. The distal two-thirds and sometimes proximal insertion of the ACL was then optimized by tilting the transducer in a slightly medial to lateral direction toward the lateral aspect of the intercondylar region ( Fig. 98.2 ). The needle was then inserted using an in-plane, caudad-to-cephalad, and anterior-to-posterior approach, with a long axis to the ACL. Orthogonal short axis imaging was then used to both confirm intraligamentous placement and allow for the advancement of the needle to the femoral ACL origin using out-of-plane needle imaging. All 10 injections successfully delivered latex to the proximal, midsubstance, and distal portions of the ACL, without being found in the menisci or PCL. It should be noted that this procedure may also be carried out using a curvilinear transducer, which may aid in visualizing the ACL in larger knees. Acknowledged limitations of this study include its unknown reproducibility when imaging partially torn ACLs, as all 10 of their specimens had ACLs that were relatively normal in appearance upon dissection. On a similar note, the extent or clinical significance of periligamentous leakage of the injectate during injections of the ACL is unknown.