Title : Predicting cup implantation safety- Focus on acetabular bone stock
Abstract:
Statement of the Problem: Implantation of the cup above or laterally to the level of the hip biomechanical center is considered to be a risk factor for the acetabular component's instability, so its implantation in the projection of the true acetabulum is desired but accompained with risk of medial wall perforation and neuvascular complications. Thus precised quantative assessment of medial wall bone stock in site of the planned acetabular component's bony bed during DDH is required.
Methodology & Theoretical Orientation: There were revealed a complex comparative MSCT- mophometric investigation of 32 normal hips and 65 hips with DDH Crowe I-III types. There were assessed medial wall bone width in projection of the lig. teres bed and planned acetabular component's bony bed centre according to the proposed MSCT- measuring technique; their correlation with indeces of femoral head's cranial migration, acetabular horizontal sphericity angle and centre-edge (Viberg's) angle. MannWhitney test, one-way analysis of variance and Spearman's rank correlation were used respectively.
Findings: Width of the acetabular medial wall in projection of the lig. teres / acetabular component's bony bed centre was defined as: 4,3 mm (3,3; 4,8) / 7,2 mm (6,2; 7,8) for normal hips, 9,95 mm (7,5; 11,6) /11,85 mm (9,8; 13,5) for Crowe I hips, 15 mm [(1,7; 17,3)/ 15,7 mm (13,5; 17,3) for Crowe II hips and 15,45 mm (13,7; 19,8) / 16,05 mm (12,8; 20,2) for Crowe III hips, respectively. Weak correlation of acetabular medial wall bone stock in projection of acetabular component's bony bed centre with femoral head's cranial migration indicates the invalidity of the Crowe's DDH staging for THR's needs and the necessity of independent measuring of the index during individual preoperative planning.
Conclusion & Significance: Positioning of the cup at the level of the hip's biomechanical centre requires its medialisation that can be achieved safely only with medial wall width not less then 12-15 mm in both localisations, otherwise it should be turned to cotypoplasty technique. Since conventional biplanar X-ray imaging is invalid for precise measuring of the aforementioned indeces due to superimpositioning, the proposed MSCT-morphometric technique could be of help in terms of individual safe implantation technique selection during THR preplanning for DDH.
