From the start of their career, each surgeon is launched on a personal learning curve for each procedure that they perform, progressively refining their approach. The surgeon is the method and this method evolves with experience. The great majority of our surgeries (thankfully) turn out well, thus the opportunity for learning lies in exploring the surgeon's adverse outcomes. One way to accomplish this is to compare a case of, for example, anatomic glenoid component failure to a matched set of aTSAs that did not have this type of failure, searching for surgeon-controlled variables that differed.
Here is an example of this type of intrapractice analysis. Four cases of acromial stress fractures after reverse shoulder arthroplasty (RSA) were each matched to four cases of RSA from the same surgeon's practice by age, sex, diagnosis, implant type, and year in which the surgery was performed.
Two of the cases were initially non-displaced Levy IIB fractures that went on to displace in spite of immobilization (FX1 and FX2). Two of the cases were Levy I fractures that healed with immobilization (FX3 and FX4).
For each case and for their respective controls, we documented 14 measures of component position that are easily determined on plain anteroposterior radiographs.
Radius of the glenosphere
Lateralization of the glenosphere center of rotation from the native glenoid bone.
Total thickness of the glenosphere (including baseplate and any augments) measured as the distance from the native glenoid bone to the lateral extent of the glenospherre.
Baseplate inferiorization measured as the distance between the center of the glenoid bone surface to the center of the baseplate.
Baseplate tilt measured as the angle between the supraspinatus fossa line (white) and the baseplate. Note that values greater than 90 degrees indicate superior tilt in relation to the supraspinatus fossa line.
Humeral distalization measured as the distance between the acromial tip and the superior-lateral tip of the tuberosity. The HD was measured before and after the RSA. The difference (Delta HD) was calculated.
Measured as the distance between the glenoid bone surface and the superior-lateral tip of the tuberosity.
Measured as the distance between the lateral aspect of the glenosphere and the superior-lateral tip of the tuberosity
Measured as the distance between the glenosphere center of rotation and the superior-lateral tip of the tuberosity.
Measured as the distance between the glenosphere center of rotation and the tip of the acromion.
The AC - CT difference and the AC/CT ratios were also determined.
Here is a series of plots of the 14 measurements for the two cases of displaced Levy IIB fractures (FX1 and FX2). In each of the plots, the red dot indicates the fracture case and the green dots indicate the four controls matched for age, sex, diagnosis, implant type, and year in which the surgery was performed.
Of particular interest in these two cases is the observation that the difference between the COR to acromion distance (AC) and the COR to tuberosity distance (CT) tended to be lower in the fracture cases than for the controls.
This relationship is not seen for the two Levy I fracture cases that healed witrh immobilization.
Because change in humeral distalization has been implicated as a risk factor for acromial fractures, Delta HD and AC-CT differences were compared among the two displaced Levy IIB fractures (FX1 and FX2), the two healed Levy I fractures (FX3 and FX 4), and their respective controls.
While these data only reflect four fracture cases and their respective controls in this surgeon's practice, they suggest that the AC to CT difference is a more important surgeon-controlled risk factor for displaced Levy IIB fractures than humeral distalization. Thus in patients with patient risk factors for acromial fractures, the surgeon may wish to strive for AC>CT (a greater distance from the center of rotation to the acromion than the distance from the center of rotation to the tuberosity).
More important than the results for these four cases is this methodolgy by which a surgeon can compare cases for any type of adverse outcome (e.g. glenoid component loosening, instability) to matched intrapractice controls with the goal of identifying potentially important surgeon-modifiable risk factors for future cases.
Always trying to get better
Sooty Grouse
Mt, Rainier
July 2025
Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link)
The total shoulder arthroplasty (see this link)
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).
