Let's begin with a brief anatomy and biomechanics lesson.
The ulnar collateral ligament — more frequently referred to as the UCL — is a robust and triangular sheet of tissue that helps support the inner elbow against valgus stress. The elbow experiences the most valgus stress during a baseball game when the arm is driven forward at high rates of speed while throwing a ball.
Damage to the UCL occurs when the torque produced as the arm is thrust forward — the technical term is internal rotation — is more significant than what the structure can compensate. Injury can occur chronically as well as acutely and is generally described as a sprain. The degree of damage is graded on a scale of 1-3. Grade 1 sprains are usually minor injuries that heal within a week or two. Grade 2 sprains — also referred to as partial tears — cause instability in the joint as some 50% of the ligament fibers have been damaged; the most frequently reported symptoms are pain and swelling. The recovery timeline for grade 2 sprains generally extends into months. Grade 3 sprains — or ruptures — result in significant instability and require Tommy John surgery to address.
Grade 2 sprains are where the best route of treatment is murkiest. As the UCL is technically an extension of the joint capsule — a larger sheet of tissue that envelops a joint and provides stability and nourishment — it has a relatively good blood supply, meaning it is technically capable of healing on its own without surgery. (Side note: This is why ACL injuries require surgery in most instances. Although the ACL is inside the knee, it is technically separate from the joint capsule, and, thus, has almost no blood supply.)
However, the UCL does not have the same blood supply throughout its structure. A recent study found evidence to suggest that the blood supply is best nearer where it connects to the upper arm bone — proximal — and decreases as the ligament extends to the forearm — distal. This finding may suggest that grade 2 sprains of the UCL that occur proximally are more likely to heal without surgery than those that are distal (or, read another way, Tommy John surgeries that treat proximal tears are more likely to be "successful" than their distal counterparts.) (Another side note: Interestingly, a study conducted in 2020 found data to suggest the opposite, though it should be noted that the study had a small sample size and was retrospective; both factors limit the findings' strength.)
Rest and anti-inflammatory medication are most often the first two steps in treating a grade 2 UCL sprains followed by physical therapy to improve range of motion and increase the strength of the surrounding muscles. While the UCL provides static stability for the inner elbow (i.e., its fibers don't contract and act as a brace), the forearm musculature provides dynamic stability (i.e., its fibers do contract and pull the inner elbow together). Having strong forearm muscles is vital for protecting the healing UCL.
Another treatment often reported after an athlete is diagnosed with a UCL sprain is platelet-rich plasma (PRP).
The theory behind PRP is sound. The process involves drawing blood into a test tube, spinning it around rapidly in a centrifuge to separate the blood into plasma and red blood cells, sucking the plasma into a syringe, and injecting the plasma into the injured tissue. Plasma contains a variety of cells and other substances, one of which are platelets. Platelets help form the foundation on which new tissue grows and secret substances that help aid the healing process.
The results surrounding PRP injections and return to play in baseball are … inconclusive, at best. Read one study, and you may come away believing that they work exceptionally well. Read another, and you may think they're just a bunch of hocus pocus. The fact of the matter is this: Despite being relatively well studied, there is little evidence, at this point, to suggest that PRP injections are the medical savior they were once considered to be.
So, back to the original question. Why should Maeda and the Twins even pursue a second opinion?
Well, the short answer is "Why not?" If the injury Maeda suffered is a UCL sprain, and if he ultimately undergoes surgery, he'll miss the entirety of the 2022 season anyway. Waiting another week or two to gather more information won't prevent him from playing next year.
The longer answer is that the most appropriate course of treatment may or may not be surgery, depending on various factors, including grade, location, and, frankly, a specific doctor's training and treatment philosophy. Again, if Maeda is dealing with UCL damage and if it is partial and proximal, it may have a chance to heal on its own.
Also, and this bears repeating, what's the harm in trying conservative rehabilitation and waiting on surgery? Best case scenario: Maeda can pitch again in relatively short order and definitely be next season. Worst case scenario: Maeda has to undergo surgery, which, again, would keep him out of 2022 anyway.
At this stage, there is minimal downside for the Twins and Maeda in gathering as much information as possible. The team isn't going to the playoffs, he's under contract next year, and he's one of the more critical pitching pieces in the Twins' system.
I'll pose the question again. Why should Maeda and the Twins seek a second opinion? Because it's the right thing to do.