- This study retrospectively assessed whether CT-based planning helped restore the anatomy of the proximal humerus after stemless total shoulder arthroplasty in 100 consecutive patients
- The surgeon used three-dimensional reconstruction of the glenohumeral joint to plan the humeral head size and the angle of the humeral head cut; during surgery, the images were used as a visual guide in making a freehand cut
- Restoration of proximal humeral anatomy was not precise: the mean deviation between the pre- and postoperative humeral head center of rotation was 4.3 mm
- In some cases, "overstuffing" (medialization of the center of rotation of the humeral head cut) was the main reason for the poor anatomic restoration
- Still, in 75% of cases, the humeral head implant size selected intraoperatively was consistent with the planned size
Multiple biomechanical studies and two short-term clinical studies have indicated that poor restoration of proximal humeral anatomy (RPHA) after stemless total shoulder arthroplasty (TSA) is associated with poorer clinical outcomes.
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Florian Grubhofer, MD, former clinical fellow, and Jon J.P. Warner, MD, chief of the Shoulder Service in the Massachusetts General Hospital Department of Orthopaedic Surgery, and colleagues evaluated whether using a computerized CT-based three-dimensional tool to plan the humeral head cut and humeral head implant size could make RPHA more accurate.
In the Journal of Shoulder and Elbow Surgery, the team reports that preoperative use of the planning tool gave insight into proximal humeral anatomy, but applying that insight to surgery without guides or navigation did not improve RPHA.
The researchers retrospectively reviewed 100 consecutive patients who underwent stemless TSA for glenohumeral arthritis between November 2017 and October 2019. All patients had a preoperative CT scan. The images were imported into software that performed three-dimensional reconstruction of the glenohumeral joint.
The senior surgeon was the same in all cases and used the reconstructions for preoperative planning of the humeral head size and the angle of the humeral head cut. During surgery, the images were used as a visual guide in making a freehand cut.
For this study three reviewers measured and compared the anatomy of the proximal humerus on standardized pre- and postoperative shoulder radiographs.
Humeral Head Center of Rotation (COR)
The average deviation between the pre- and postoperative COR was 4.3 mm, and 65 patients showed a deviation ≥3 mm:
- Average medialization of the COR in relation to preoperative COR ("overstuffing"): 88% of the 65 patients
- Humeral head cut level higher than planned: 71%
- Humeral head size upsized intraoperatively: 17%
- Average lateralization of the COR: 12%
- Humeral head cut level lower than planned: 9%
- Humeral head size downsized intraoperatively: 3%
Risk Factors for Poor RPHA
Preoperative small humeral head diameter, low humeral head height and varus-oriented head–neck angle were risk factors for poor RPHA. In such humeri, the calcar region might be difficult to access.
Execution of Preoperative Plan
In 75% of cases, the humeral head implant size selected intraoperatively was consistent with the planned size. In 96% of cases, it was no more than one size larger or smaller.
Better Instrumentation May Be Worthwhile
Computerized CT-based preoperative planning in this study helped determine the humeral head implant size, which has the potential to reduce inventory and save money. However, proper planning of the head size did not help avoid overstuffing.
Intraoperatively, it was relatively difficult to estimate whether the level of the humeral head cut was correct.
The long-term consequences of poor RPHA after stemless TSA have not been well studied. However, it may be that patient outcomes will improve if proximal humeral anatomy is restored through the use of patient-specific instruments, intraoperative navigation aids or augmented reality-based guidance.
Learn more about the Shoulder Service at Mass General
Refer a patient to the Department of Orthopaedic Surgery