Ulnar Collateral Ligament Damage: An Injury of the Young

Injuries affecting the medial elbow are common in overhead throwing sports such as baseball pitchers, and javelin throwers⁽¹⁾. The ulnar collateral ligament (UCL) is the primary stabilizer of the medial elbow joint and if injury presents, it can become a career-threatening injury in a throwing sport. Treatment can be conservative but, in some situations, reconstructive surgery is indicated.

Background

Patients who present with an injury to the UCL are typically adolescents or young adults - most likely due to the activities they participate in during this age range and the predisposing forces to this structure that are encountered. Researchers from the University of Florida, USA studied the age and injury severity in 136 young athletes ranging in ages from 11-22 years⁽¹⁾. Of these patients,101 were baseball pitchers, 12 played softball, eight American football, five javelin throwers, and the rest played ultimate Frisbee, volleyball, gymnastics and mixed martial arts. The mean age at the point of injury was 16.7 years. The authors found that the younger the patient, the more likely they were to be treated conservatively based on a lower degree of injury (based on the data as illustrated in the table below).

Age in years, indicating lower-level injuries in younger athletes, with more severe injuries in older age groups. Data extracted from Zaremski and colleagues⁽¹⁾.

The frequency of UCL injuries is becoming more and more pronounced within clinical practice. Over a 16-year period from 2000-2016136 patients were presented. Of these, five injuries were presented between 2000-2003, nine from 2004-2007, 50 from 2008-2012 and 72 from 2013-2016⁽¹⁾. The authors did suggest that the increased frequency of injury could be related to clinicians having increased awareness of injuries relating to the UCL, and lesser sprains being more accurately diagnosed as a UCL strain. However, it is also possible that due to strength and conditioning techniques, athletes are now throwing further, resulting in increased valgus forces.

Since lower grade strains tend to be experienced at a much younger age, it is conceivable to suggest that as athletes grow older, they may experience more severe strains to the UCL. Zaremski and colleagues stated that older more mature athletes can generate more force during the acceleration phase, with up to 50Nm being reported.

They have created a debate as to whether it is the increased force that is applied by the older athletes, or whether it’s the increased volume of throwing taking place at this age resulting in increased of total loading. It is plausible to state that both factors may well be responsible for the increased severity of UCL injury. In addition, if a patient has been a long-term baseball player who suffered an undiagnosed lower grade injury earlier in their life, this may result in a more severe injury later in adult life.

Anatomy and biomechanics

The UCL is a static stabilizer of the medial elbow joint alongside the joint capsule, whereas the elbow has dynamic stabilizers such as the flexor pronator muscle group (see Figure 1)⁽²⁾. These structures all assist in preventing valgus instability at the elbow. Cadaveric studies have shown that the UCL can increase in size through loading, with a mean thickness of 6.2mm in the throwing arm compared with 4.8mm in the non-throwing arm⁽²⁾.

The anterior bundle is the most commonly injured structure with the anterior fibres being the primary restricting factor against valgus forces between 30-90 degrees of elbow flexion⁽²⁾. By contrast, the posterior band of the anterior bundle stabilizes the fan-shaped structure against valgus forces from 90-120 degrees of elbow flexion. The length of the anterior bundle of the UCL ranges from 4.7cm to 5.4cm⁽²⁾The transverse ligament provides no resistance to valgus forces as it doesn’t cross the elbow joint. The anterior and posterior fibers originate at the medial epicondyle of the humerus and attach at the semilunar notch of the ulna⁽²⁾.