Abstract
Introduction
The achieved anteversion of uncemented stems is to a large extent limited by the internal anatomy of the bone. A better understanding of this has recently become an unmet need because of the increased use of uncemented stems.
We aimed to assess plan compliance in six degrees of freedom to evaluate the accuracy of PSI and guides for stem positioning in primary THAs.
Materials and Methods
We prospectively collected 3D plans generated from preoperative CTs of 30 consecutive THAs (17 left and 13 right hips), in 29 patients with OA, consisting of 16 males and 13 females (median age 68 years, range 46–83 years). A single CT-based planning system and cementless type of implant were used.
Post operatively, all patients had a CT scan which was reconstructed using state-of-the-art software solution: the plan and CT reconstruction models were
Outcome measures: 1) discrepancy between planned and achieved stem orientation angles Fig.2&3; 2) clinical outcome.
Results
1) The mean (±SD) discrepancy was low for: Varus-valgus −1.1 ± 1.4 deg (IQR −2.2 – 0.3 deg); Anterior-posterior 0.1 ± 1.6 deg (IQR −0.7 – 1.3 deg).
The discrepancy was higher for femoral version −1.4 ± 8.2 deg (IQR −8.3 – 7.2 deg). 3D-CT planning correctly predicted sizes in 93% of the femoral components.
2) There was no intra-operative fracture, no case showed evidence of early periprosthetic osseous injury.
Discussion
Surgeons and engineers should be cautious with their expectation of achieving the planned femoral stem version of an uncemented femoral stem from the pre-operative 3D-CT plan.
Conclusion
This is the first study to 3D-mensionally evaluate 3D-printed patient-specific instrumentation and guides for achieved femoral stem component orientation vis-à-vis to the plan. The tools allow accurate implant orientation, however there is still potential for improvement.
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