The Uncommon Common Finger Injuries
When discussing sports injuries of the thumb, the typical conversation involves skier’s or gamekeeper’s thumb. These injuries involve damage to the ulnar collateral ligament (UCL), and may be acute or chronic. Much of the literature involves anatomical evaluation, clinical exam findings, radiological imaging findings, and treatment for these injuries as these encompass the most common type of injuries to the thumb in athletes (Hung 2020). An analogous, surprisingly common, and relatively underreported injury in athletes is the injury to the radial collateral ligament (RCL) of the thumb. It has been reported that up to 20% of Emergency Department visits due to trauma involve finger injuries (Clark et al). The literature in comparison to UCL injuries is limited regarding management of RCL injuries; however, it is imperative that a non-operative sports medicine provider is aware of the proper identification, management, and return to play protocol for this injury given the high risk of sequelae of improperly treated injuries.
As with any musculoskeletal injury, it is critical to understand the anatomy of the involved joint and surrounding soft tissue structures to adequately treat patients. The RCL originates from the dorsal metacarpal head, goes across the proximal interphalangeal (IP) joint, and runs obliquely to insert on the adjoined metacarpal head on the palmar aspect of the bone making it the primary restraint against radial deviation of the joint (Theumann et al). Accompanying the RCL, is an accessary collateral ligament which attaches volarly on the palmar plate (Theumann et al). These ligaments have a width range of 4-8 mm and are approximately 12 mm in length (Dy et al). The ligaments provide a static strength against hypermobility of the joint in radial deviation and also can send signals to nearby muscles to activate to protect the joint/ligament in a situation of increased stretch or strain (Rozmaryn et al). The collateral ligaments are stretched in finger flexion and relaxed in extension; whereas, the accessary ligaments are stretched in finger extension and relaxed in finger flexion (Roxmaryn et al).
Sports place athletes at higher risk for damaging these intrinsic ligaments of the thumb such as the RCL given increased chance of high velocity strain from various activities. As previously mentioned, soccer, football, and skiing put increased risk on the UCL of the thumb; whereas, the RCL is likely at higher risk during sports such as basketball although any injury mechanism causing traumatic force on the RCL could cause a disruption. As with any ligament that is damaged, there are varying degrees of injury from grade 1 strain, to partial tear (grade 2), to complete tear (grade3), and in most severe cases a complete tear with frank dislocation (Bahr 2012).
When evaluating an athlete with a thumb injury, it is important to obtain radiographs to evaluate for obvious fractures and subluxed or dislocated joint (Awh, 2020). A dislocated joint should be as quickly as possible reduced and splinted in anatomical position. Clinical stability should also be evaluated by placing the involved thumb joint (the proximal IP joint in this case) under stabilized radial and ulnar deviation to evaluate the RCL and UCL, respectively (Awh 2020). Palpation and range of motion of the involved joint as well as the joint above and below the injury- IE the distal IP joint and carpometacarpal joint is imperative. It should also be tested clinically if the flexors and extensors of the thumb are intact. The addition of musculoskeletal ultrasound can be utilized on the day of the evaluation to further provide information on ligament integrity and stability. However, consideration for MRI imaging should also be considered for complete gold standard evaluation of the tendons, ligaments, volar plate, and bony anatomy (Awh 2020).
Image 1. Example of RCL and UCL ultrasound (adopted from Indian Journal of Radiology and Imaging)
Diagnostic ultrasound can provide quick, reliable, same-day information about the severity of the injury. Ultrasound can visualize the radial collateral ligament and identify an acute strain which would show intact ligament with swelling versus a chronic strain which would show reactive hyperemia (Singh 2017). A partial tear would show disruption of ligament fibers but some fibers still intact, whereas a complete tear would show full disruption of the ligament with significant swelling (Singh, 2017). Additionally, dynamic testing can be performed to evaluate joint stability further and provide more real-time clinical information(Singh, 2017). Unlike UCL injuries, the possibility of a stener-type lesion where the injured ligament becomes entrapped in the adductor pollicis aponeurosis preventing healing is generally not seen (Mahajan 2013). The ability to pick up a Stener lesion on ultrasound is based off practitioner skills but has been reported in the literature to be in the range of 81%-100% (Arend 2014).
After a complete evaluation, which at minimum includes radiographs supplemented with US and/or MRI to evaluate for joint stability, fractures, and integrity of the surrounding soft tissues, an educated decision can be made to recommend treatment options. In cases where the joint is stable and the ligament is either strained or only partially torn, non-operative treatment can be initiated. If non-operative treatment is used, casting or custom splinting may need to be done for 8-12 weeks followed by physical therapy (Doyle, 1989). Longer treatment is needed for partial tears of the ligament than a sprain or injury involving a fracture without displacement. It is imperative to understand the surgical criteria for these types of injuries which include the following: majorly displaced fractures, fractures involving the joint, complete tears of the radial collateral ligament, open fractures, stener-type lesions (although rare in RCL injuries), and frank joint instability (Kang, 2007). Additionally, it must be taken into consideration the goals of the patient when considering surgical versus non-surgical management.
In summary, radial collateral ligament injuries are a type of injury that the sports medicine provider will have to deal with in their career. Knowing the relevant anatomy, pathophysiology, and clinical evaluation and management is key in order to private timely treatment for the athlete. Without appropriate management, the patient could have sequelae such as chronic pain and instability of the joint. Additionally, the addition of musculoskeletal ultrasound to the primary evaluation can add invaluable information and assistance with management.
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