Dislocation continues to be a significant problem in THA. Instability due to improper reconstruction of the abductors can be a contributing factor.

Eight hundred primary THA’s were performed over the past four years utilizing a proximal “Dual Press™” cementless porous coated modular stem. This design allows for a large selection of proximal bodies that enable the restoration of proper soft tissue tension and joint biomechanics after the stem is inserted.

Data on stem, neck and head centers were available for 600 of these cases. Head center locations were tabulated and compared to data from the literature.

The head center location data clearly showed that a wide variety of offsets and lengths are required to properly balance the soft tissues. Further, when the data were sorted by distal stem diameter, there is little correlation between head center location and stem size. All were performed utilizing the posterior approach and used without bone cement. 3 fractured stems, 2 dislocations, 14 intra-op fractures, no significant leg length inequalities (+/− 5mm), and 10% indexed to a position other than neutral.

Restoration of joint mechanics was possible using this proximal modular “Dual Press” stem due to the intra-operative versatility offered in regards to head center location when compared to monoblock stems. The data suggest that hip reconstruction benefits from the availability of many head centers for every stem size. The authors conclude that this proximal modular design provides for a more intra-operative accurate approach for reconstructing the biomechanics of the hip.