by Elizabeth Hofheinz, M.P.H., M.Ed., December 18, 2019
Question? Who has a deep-dive machine that can give you real-time 3D images of how the shoulder moves kinematically? Only a few facilities in the world—including the University of Pittsburgh Orthopaedic Biodynamics Lab, which publishes more orthopaedic research using this technology than all of the other facilities combined. This unusual tool allows researchers to closely and precisely examine the symphony of movement patterns in the shoulder.
Albert Lin, M.D., Associate Professor and Associate Chief of the Division of Sports Medicine at The University of Pittsburgh, is a shoulder expert who spends countless hours in that lab. He told OSN, “In order to examine how the shoulder functions in real time we use a 3D reconstructive model from CT scans that informs us how the shoulder is moving kinematically. This equipment also allows us to look into a shoulder pre- and post-operatively in order to determine what can be altered to get someone closer to a normal state of functioning.”
Along with William Anderst, Ph.D., Director of the Biodynamics Lab, Dr. Lin received an NIH grant to investigate how the shoulder moves after a reverse total shoulder surgery. “Knowing the details here are particularly important because this is a nonanatomic procedure meant for longstanding and irreparable rotator cuff problems. This surgery has revolutionized our ability to treat things for which we had no good prior solutions. The issue when dealing with non-anatomic reconstructive surgery, is that there are numerous variables (different sizes, different possible angles/positions). While there are some biomechanical studies on the best configuration for these situations, there remains intense debate regarding the optimal positioning of implants.”
“We are the first to be able to look at those variables and how they act in real time. And we have the ability to say, ‘If we change variable X does it change variable Y and does a particular variable get us closer to normal shoulder kinematics?’ These are patients with at least one or two years of followup, and the data is solid. It takes us beyond extrapolation from biomechanical studies performed on cadavers.”
Asked about the novelty of this work, Dr. Lin told OSN, “The technology is sophisticated, and we are fortunate to be one of only a few labs to have such capability. It requires biplanar xrays so that you can watch someone move. Then we are able to take those xrays and configure them with a CT model of the patient to see how the shoulder moves in 3D. This requires a substantial amount of programming thus we have several engineers and research assistants in the lab. Believe it or not, to capture data on just one patient, one motion, takes from 6-8 hours!”
Although some might say that the rotator cuff has been studied ad infinitum, Dr. Lin believes there are holes in our knowledge of this muscle group. “There are those people who develop tears for no reason and some of these patients have massive, irreparable tears involving more than two or three tendons yet have relatively normal joint mechanics and no significant deficit of strength. Others have the same presentation—no trauma—same number of tendons torn and are significantly debilitated, and I don’t think shoulder experts know why.”
“I suspect that it has to do with the bony and insertional anatomy and compensatory function. It may be that some of these patients have favorable anatomy that allow compensation, while another subgroup of patients do not. It may be a very specific subgroup of people that suffers from significant dysfunction. Perhaps in this subgroup of patients the remaining muscles are not attached in a way that makes them functionally useful. If we can identify why people in certain subgroups are faring better with massive tears than others, then perhaps we could devise treatments that are less invasive that restore patients closer to those who are functionally well compensated. Or we could identify these patients in advance, being more aggressive in repairing the rotator cuff before we have problems that are irreparable and where the person ends up requiring a more invasive surgery with greater risks of complications.”
Not shying away from controversial topics, Dr. Lin and his team are also examining superior capsular reconstruction, a joint salvaging procedure used in the treatment of massive irreparable rotator cuff tears. “This procedure is appealing to general orthopedic surgeons because everything is done arthroscopically and minimally invasively…and it doesn’t have the same level of surgical risks as other reconstructive procedures. When you have a massive, irreparable rotator cuff tear, the ball slides up and joint kinematics are altered; with this procedure you attach graft to the socket and on the other side you attach it to the ball, the goal being to keep the ball centered. Several cadaveric biomechanic studies have demonstrated this. So the procedure in a sense is supposed to recreate the function of the rotator cuff which is to keep the ball centered so that the shoulder can function normally.”
“This procedure was initially described in Japan with autograft from the hip; it was being done because it wasn’t possible to do a reverse replacement. The researchers reported excellent two-year clinical and MRI results, but if you look at the U.S. literature compared to that in Japan, you see that the healing rates are much lower—50-60% of all American patients heal fully as compared to 90% of Japanese patients. There may be several reasons for this including the use of autograft in Japan and the preference for allograft in the U.S.”
“For our related study we are looking at patient reported outcomes (PROSs), MRI follow-up, as well as shoulder kinematics following surgery. Our PRO and MRI findings are in line with what has been reported in the literature, i.e., PROs are significantly improved following surgery for almost all patients regardless of graft healing status. We are also finding that about 50-60% of our patients have full healing of their grafts, while a substantial portion demonstrate only partial healing. Also interesting is that no one has been able to prove that the graft keeps the head in place during shoulder motion. I believe we are the first to look at actual movement in a real patient during real functional activity; we are seeing that joint kinematics following surgery are not predictable, at least for our small study. At the end of the day these are expensive procedures involving graft and anchors so it is critical to know if this is really what we should be doing and if the costs of surgery are justified.”
Finally, says Dr. Lin, he is also working with the Orthopaedics Robotics Laboratory at the University of Pittsburgh using a robotics model for shoulder research. “One project involves simulating a clinical scenario in which a shoulder is dislocated. This work, which was just published in the Journal of Biomechanics, describes how we established a model to predictably recreate an injury sustained in a real life dislocation, and allows us to help differentiate what happens to tissue around the shoulder when there is one dislocation versus multiple. One of our goals is to find better ways of repairing the shoulder, including the capsule and the labrum.”
“Although arthroscopic shoulder stabilization surgery has been around for more than twenty years and the technology has improved, recurrence rates are still approximately 15%. Despite the fact that anchors and procedures have improved, the recurrence rates remain the same. The reason may be that there are areas of injury that are not addressed with current techniques, and we are finding with our dislocation models that we can very specifically identify the areas of capsular injury, the magnitude and direction of injuries which differ from patient to patient, as well as differ with the number of dislocations. Surgeons tend to focus on the front of the shoulder with a one size fits all type of surgery, but we are asking, ‘Why can’t these surgeries be individualized anatomically to every shoulder, every patient? Maybe we can decrease recurrence rates if we know exactly what to address in each individual patient.’”
Shoulders everywhere should be grateful that Dr. Albert Lin never stops questioning…
