How to Perform Radiographic-Guided Needle Placement Into the Collateral Ligaments of the Distal Interphalangel Joint

1. Introduction

The diagnosis of abnormalities in the collateral ligaments of the distal interphalangeal (DIP) joint distal to the coronary band is occurring with increased frequency. This is likely due to the use of magnetic resonance imaging (MRI) as a diagnostic tool in cases with foot lameness. Collateral ligament (CL) injury proximal and immediately distal to the coronary band can be diagnosed using ultrasound.¹  Osseous lesions of the distal phalanx at the CL insertions can be diagnosed on radiographs. However, visualization of abnormalities in the CLs of the DIP joint at the level of the insertion on the distal phalanx can only be diagnosed with MRI or computed tomography (CT).²  Lesions identified in the CLs of the DIP joint diagnosed on MR images consist of core lesions with fiber disruption, diffuse injury without fiber disruption, margin tears, and complete ligament disruption.^3,4

Intralesional therapy, such as platelet-rich plasma (PRP) and stem cells, is one of the possible treatment options in cases with a diagnosis of softtissue injury. Imaging modalities can be used to facilitate needle placement for injection of therapeutic agents. Soft tissue is best visualized with MR and ultrasound (US). Therefore, these modalities are often selected to facilitate needle placement into soft-tissue lesions. CT can be used in a soft-tissue window in conjunction with osseous landmarks for needle placement into soft-tissue injuries.⁵  MRI and CT require general anesthesia, whereas US and radiography can be performed in the standing horse. Radiography is commonly used to facilitate needle placement when reliable bony landmarks are available, such as injection of the navicular bursa using the navicular bone flexor surface as a landmark.⁶ 

The CLs of the DIP joint insert on the fossae of the distal phalanx. The fossae of the distal phalanx can be reliably identified on radiographs and recognized on multiple views. The purpose of this paper is to provide a description of how to use radiography to facilitate needle placement into the distal aspect of the CLs of the DIP joint for injection of intralesion therapy.
 

2. Materials and Methods

This technique is performed after diagnosis of a lesion in the distal aspect of the CLs of the DIP joint using high- or low-field MRI. The MR images are used to determine the desired site of needle placement based on relative distance from the margins of the fossa and whether the lesion is dorsal, palmar, or centrally located within the ligament. A 3.5-in, 18-gauge needle placed into the fossa can be performed with the horse standing or under general anesthesia. It can also be performed in conjunction with an MRI exam or other procedure. This report will provide a description of the procedure in a standing sedated horse, but it can certainly be adapted to a patient under general anesthesia.

3. Patient Preparation

Before performing the procedure, an abaxial nerve block is performed, and the hair is clipped from the injection site. During the procedure, sedation is used at the discretion of the veterinarian to prevent movement of the limbs. To approximate the location of the CLs for clipping, the coronary band can be palpated for areas of dense tissue at the 10:00 and 2:00 positions on the dorsal aspect of the foot. If the CLs are not palpable because of diffuse swelling, US can be used to locate them. A region of approximately 10 cm extending from the coronary band centered over the CL of interest is clipped. Properly placing a needle in the CL fossa is dependent on being able to identify the fossa margins on radiographs. Three radiographic views that are useful in locating the CL fossae include the lateromedial (LM), horizontal or weight-bearing dorsopalmar (DP), and dorso 60° proximal palmarodistal (D60°P) views (Fig. 1). Therefore, the horse will need to be positioned with both front feet on foot blocks to allow proper radiographs to be taken after the needle is placed.

When taking radiographs, it is important that proper safety precautions be taken and protective equipment be worn. In general, sequential radiographs are taken with continued needle advancement toward the fossa. We use a LM view followed by a horizontal DP view and then a D60°P view. However, the sequence of radiographs could be adjusted as needed. When first learning this technique, it is helpful to estimate the required proximal to distal angle of the needle before beginning needle placement. Before taking radiographs, a capped spinal needle can be positioned at the estimated proper angle and then held in place with tape (Fig. 2A). A lateral radiograph can be taken to view the needle placement in relation to the fossa.
 

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