These authors tested the hypothesis that preoperative 3D planning helps achieve normal proximal humeral anatomy after stemless TSA (see this link).
One hundred consecutive stemless TSA (67 males, 51 right shoulder, mean age of 62 ±9.4 years) were radiographically assessed using pre- and postoperative standardized AP radiographs.
The proximal humeral anatomy was characterized with the so-called circle method.
They measured deviation from the premorbid center of rotation (COR); more than 3mm was considered as minimal clinical important difference. Additionally, pre- and postoperative humeral head diameter (HHD), head neck angle (HNA) and humeral head height (HHH) were measured.
The mean distance from of the premorbid to the implanted head COR was 4.3mm ± 3.1mm. Thirty five shoulders (35%) showed a deviation of less than 3mm (mean 1.9, ±1.1) and 65 shoulders (65%) a deviation of ≥3mm (mean 8.0 ± 3.7).
The medial deviation of the humeral head COR of ≥3mm in relation to premorbid COR was considered as over overstuffing. A poorly performed humeral head cut was the main reason for overstuffing which was seen in 88% of the cases with inaccurate poor anatomic reconstruction. Preoperative small HHD, low HHH and varus angulated HNA are risk factors for poor anatomic reconstruction after stemless TSA.The level of the humeral head cut was responsible for overstuffing in the 46 of the 57 overstuffed cases. The preoperative HHD, HHH and the HNA were significantly larger, higher and more in valgus angulation in the group with accurate compared to the 24 group with poor restoration of premorbid anatomy.
The authors concluded that restoration of proximal humeral anatomy after stemless TSA using CT-based 3D planning was not precise.
The concept of overstuffing was introduced in 1994 in the book, "Practical Evaluation and Management of the Shoulder" (see this link). This text pointed out that in shoulder arthritis the glenohumeral capsule and ligaments are often contracted, limiting the range of motion of the joint. To avoid persistent stiffness after shoulder arthroplasty, the surgeon must perform adequate capsular releases and select components that put too much prosthesis volume in the joint so that it is tightened or "overstuffed".
Overstuffing can result from a relatively too thick humeral component
In performing a total shoulder arthroplasty, achieving a balance between mobility and stability is a much higher priority than "restoration of proximal humeral anatomy"; for example in tight shoulders it may require the use of thinner than "normal" humeral components. Our approach to total shoulder arthroplasty is shown in this link. Our practice is to focus more on soft tissue balancing (using the 40, 50, 60 rules as shown below), than on trying to replicate the "normal" center of humeral rotation.
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