gms | German Medical Science

Objectives: The use of custom 3D printed titanium implants is increasing in the complex revision scenario as these enable surgeons to treat massive acetabular defects.While initial migration can occur without eventual construct failure, if present on radiologic follow-up, it is advised that more frequent imaging is performed to monitor the patients until implant stabilization and ingrowth are achieved.

We aimed to assess component migration post acetabular reconstruction surgery by bone-to-bone registration of sequential CT imaging.

Our objectives were to:

1.

Assess implant position 3-year post surgery in comparison with the 1-year post-operative CT imaging;

2.

Assess clinical outcome.

Methods: This was a single-centre cohort study of 20 patients from a single surgeon. All patients had massive acetabular defects Paprosky type 3B and were treated with single-manufacturer 3D printed custom made acetabular cup including a dual mobility bearing type in all cases.

Using 3D software solutions, the CT images were rendered to produce 3D reconstructions of the patients' bony pelvis for relative comparison of the two imaging timepoints (1-year and 3-year post-operatively). Bone-to-bone registration allowed for the assessment of implant movement over time, this was studied in terms of difference in centre of rotation (CoR) in X (medial-lateral, ML), Y (inferior-superior, IS) and Z (anterior-posterior, AP) planes. Meticulous patient follow-up by the operating surgeon to monitor for complications was undertaken.

Outcome measures:

1.

The change in centre of rotation (CoR) between CT scans carried out 1-year and 3-year post-operatively.

2.

Clinical outcomes.

Results and conclusion: All 20 patients had Paprosky type-3B defects. Pelvic discontinuity was confirmed intraoperatively in 3 patients. The mean follow-up time was 71 months (range 52 to 93 months).

1. One year post-operatively, the deviation of CoR was a mean (± SD) of -0.1 ± 1.5 mm (min = -3.0 mm, max = 3.0 mm) inML plane, 1.5 (± 1.5) (min = 0 mm, max = 5 mm) in the IS plane and 1 (± 1.5) (min = -2.0 mm, max = 4 mm) in AP plane.

Three years post-operatively the deviation of CoR was a mean (± SD) of 0.3 ± 0.9 mm (min = 0 mm, max = 3 mm) in the ML plane, 0.7 (± 0.8) (min = 0 mm, max = 3 mm) in the IS plane and 0.5 (± 0.8) (min = 0 mm, max = 2 mm) in the AP plane. Overall, the migration was lower 3 years post-op compared to year 1 post-op in the three planes, significantly lower in the IS plane (inferior-superior direction), p = 0.0073.

2. The cumulative implant survivorship was 100% with 17 patients remaining at risk (3 patients died for reasons unrelated to the hip). The Oxford Hip Score improvedfrom a median of 8 (range, 2 to 21) preoperatively to 33 (range, 16 to 47) at the last follow-up, p = 0.0001.

Clinically well-fixed 3D printed custom implants used to reconstruct massive acetabular defects commonly exhibit small degrees of migration 1 year post-operatively. Surgeons and engineers should be aware when monitoring these patients.