Review of “The Impact of Three-Dimensional Humeral Head Planning and Standard Transfer Instrumentation on Reconstruction of Native Humeral Anatomy for Anatomic Total Shoulder Arthroplasty.”

Review of “The Impact of Three-Dimensional Humeral Head Planning and Standard Transfer Instrumentation on Reconstruction of Native Humeral Anatomy for Anatomic Total Shoulder Arthroplasty.” Werner BC et al. J Shoulder Elbow Surg (2024). Article in Press.

Introduction

While the use of pre-operative 3D CT-based planning for total shoulder arthroplasty (TSA) has increased in popularity, the studies have primarily has focused on the glenoid component. This study investigates the impact of humeral head planning on the surgical execution of the humeral cut and prosthesis positioning, specifically with regards to the restoration of ideal center of rotation (COR).

Study Design

The study design was a basic science laboratory cadaveric study. The humerus and rotator cuff tendons were 3D printed from CT scans selected based on their standard deviation from the mean humeral diameter using a large database reference. Three fellowship-trained shoulder surgeons participated in preparation of the specimens using standardized technique. Sets of five humeri were 3D printed for each phase and constructed in materials selected to mimic anatomically realistic specimens.

The study was organized into three phases.

1. In phase 1, surgeons performed humeral neck cuts without preoperative humeral planning.
2. In phase 2, humeral planning was performed prior to any cuts; although no guides or transfer instrumentation were used.
3. Phase 3 used the same steps as phase 2 with the addition of a neck-shaft angle guide and digital calipers. The difference between the prosthetic COR and ideal COR, measured in medial-lateral (M-L) and anterior-posterior (A-P), was calculated, as was the 3D change in COR. The percentage of patients with a varus neck shaft angles (NSA) were compared for each phase. The difference between planned and actual cut thickness were also compared between phases.

Key Findings

The results of the study demonstrated that for M-L COR and 3D COR, the use of preoperative planning alone (Phase 2) and preoperative planning with standardized instrumentation (Phase 3) resulted in significantly more anatomic restoration of ideal COR. For NSA, there was a decrease of cases in varus and deviations from planned cut height noted with each successive phase.

Clinical Implications

From a clinical standpoint, recent literature on humeral planning has focused on implant concordance without addressing how planning impacts intra-operative surgeons’ performance. This study demonstrates that preoperative humeral planning improves restoration of ideal COR, with or without the use of standard instrumentation—although the latter appears to have an additive effect with the use of a neck-shaft angle cut guide and calipers. Limitations of this study include the inherent limitations of 3D printed models, the exclusion of deformed humeral heads and version as variables, and inter-observer variability in technique between the surgeons.

Conclusion

Ultimately, this study makes a strong case that pre-operative planning and instrumentation iteratively improves humeral cut performance.  However, humeral component placement is only one aspect of soft tissue tensioning in shoulder arthroplasty, and while accurate positioning is clearly the goal, further study is needed to determine the extent to which these improvements results in superior clinical outcomes.