Not often associated with disabling injury in baseball, the muscles of the groin—collectively known as the hip adductors (and here on out called 'adductors')—nonetheless can become painful and uncomfortable when strained or torn. A collection of seven muscles that originate from the pelvis that insert into the inner aspect of the femur and tibia, they are responsible for stabilizing the pelvis and moving the leg towards the midline of the body (adduction), which is where they get their name. Broadly, they are active especially when changing direction during running and in kicking.
|Muscles of the groin: adductor brevis, adductor magnus, adductor longus, adductor minimus, pectineus, and gracilis. Obturator externus not shown. Image courtesy of Wikimedia Commons.|
With regards to the mechanism of injury, tension is placed on the adductors when they are contracted. When this tension is excessive from repetition or high forces being applied in a short amount of time, one or more of the muscles can tear. Tears can range from a small partial tear with few muscle fibers torn with minimal pain and loss of function, to a complete rupture of one or more muscles, resulting in severe pain and marked loss of function. While there is no universally accepted grading system for muscle strains and tears, the most widely accepted system includes a grade 1 to a grade 4 strain, classified as follows:
- Grade 1: a small number of muscle fibers are torn; some pain/tenderness but with full function.
- Grade 2: a moderate number of muscle fibers are torn with moderate loss of function. Tenderness with swelling, possible hematoma and palpable defect.
- Grade 3: a large number of fibers torn with significant tenderness, swelling, hematoma and partial detraction of muscle. Increased loss of muscle function.
- Grade 4: all muscle fibers are ruptured resulting in major loss of function, substantial retraction of muscle and corresponding pain, swelling, and hematoma.
From a pitching biomechanics perspective (and with Norris being a rightander taken into consideration in the following descriptions), the right adductors play a large role in the windup, providing balance at the top of leg kick as well as initiating transfer of power to the upper body by stabilizing the lower extremity and pelvis when the right foot is planted. Through the latter phases of the pitching motion—through stride, arm cocking, arm acceleration, arm deceleration, and follow-through—the right adductors draw the thigh toward midline, pulling the back leg through the delivery and in turn, rotating the hips towards the plate as the pitcher releases the pitch. An electromyography study of the lower extremity in pitching showed that the adductors are the main source of energy that is eventually transferred to the upper extremities, while also contributing to the stabilization of the torso and deceleration of the shoulder and arm in follow-through. As such, insults to the adductors, creating discomfort and a decreased range of motion, can manifest themselves further downstream biomechanically, resulting in shorter stride lengths, leading to poor command of pitches (leaving pitches up in the strike zone) as well as increased stresses put upon the shoulder joint during deceleration and follow-through.
Thankfully for Norris and the Orioles, the groin injury sustained appears to be mild and will resolve with time and the use of one or all of the many physiotheraputic approaches to recovery, including RICE, massage, ultrasound, and stretching. More recent treatment approaches using platelet-rich plasma injections to the offending area are inconclusive, but anecdotally show some acceleration and improvement of the healing process, which can be protracted in lower grade strains. Given the mildness of the injury, Norris should return to the mound without much issue; however, given his history of right upper leg injuries, care will be taken to monitor the righthander's leg health and strength in order to prevent injury re-aggravation.
References: Dines, J. S. (2012). Sports medicine of baseball. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.