gms | German Medical Science

Objectives: Managing acetabular bone loss in revision THA poses challenges due to factors like osteolysis and component migration.

Bone impaction grafting is a versatile technique for managing acetabular bone loss, promoting long-term bone remodeling. Intraoperative volume measurement aids surgeons in selecting augments or allograft quantities. However, bone porosity may affect measurements, necessitating validation studies.

This study evaluates volume measurements using a digitalizer and compares them to CT-based volumes. The impact of bone porosity on intraoperative volume measurement is assessed using a plastic bone model. Validation is conducted on cadaveric acetabula and compared to theoretical volume calculations.

Methods: Porosity measurements were conducted on four polyurethane foam blocks with varying porosities (high porous HP, medium porous MP, low porous LP, and no porous NP) using standardized hemispheres created with a Trident^® acetabular hemispherical reamer (size 42 mm and 62 mm). Density was calculated by measuring the volume and weight of the blocks.

Cadaver measurements were carried out on four alcohol-glycerin-fixed cadavers using a direct anterior approach to access the hip joint. Point clouds were collected around the acetabular rim, and three digitalization repetitions were performed on seven reamed acetabula. Depth measurements were taken at three points on the acetabular rim.

Results and conclusion: The study aimed to validate a measurement system by comparing digitalized volume measurements with those derived from CT scans and theoretical calculations. For sawbone models, no significant difference was found between digitalized, CT-based, and theoretical volumes, except for one case where the digitalized volume lay between the other measurements.

The influence of bone porosity on measurements was evaluated using different porosity sawbone blocks. Results showed that in highly porous materials, digitalized volumes tended to overestimate, while in less porous materials, they underestimated theoretical volumes significantly. CT measurements also showed deviations in high porosity materials. This suggests that current digitalization systems, which use a single-size tip, may not adequately account for varying porosities.

Measurements of human acetabula did not significantly differ from theoretical volumes based on depth measurements, although measurement repetitions showed variability. Larger ball tips on digitalizers may improve accuracy.

In conclusion, bone porosity affects digitalization accuracy, suggesting the need for different digitalization tips for varying porosities. Digitalization could serve as an intraoperative tool for implant seat measurement and estimation of allograft amounts, but surgeons should be cautious of porosity effects. Further improvements in software and hardware could enhance measurement accuracy.