Femoral fit in ABG-II hip stems, influence on clinical outcome and bone remodeling: a radiographic study

In a consecutive series of 64 patients with an ABG-II stem, we analyzed whether the tightness of the fit of the prosthesis affected bone remodeling and if there was a relation between clinical and radiological results.

Radiographic analysis of bone remodeling in different Gruen zones was done. Bone density changes were graded as present or absent in the AP and lateral radiographs as compared with the previous sets of radiographs. Bone remodeling was compared to literature values of the ABG-I stem. Three stem levels were defined. The proximal level was set at the upper border of the lesser trochanter, the mid-stem level at halfway the stem and the distal level 1 cm above the tip of the prosthesis. Femoral fit was defined as tight when the ratio of the fit was >/=0.8 and as non-tight if the fit was <0.8. The incidence of thigh pain was scored using the Merle d'Aubigne (MdA) hip score.

Proximal bone resorption in Gruen zone 1 was 26.6% and in zone 7, 34.4% compared to 48 and 45% for the ABG-I stem after 5 years. No correlation was found between femoral fit and radiological changes. Proximal and distal fit was significantly lower for patients with thigh pain than without thigh pain. Patients with a non-tight proximal fit produced significantly more varus (17/30 = 56.7%) than patients with a tight proximal fit (2/34 = 5.9%; P < 0.01).

Femoral fit in ABG-II does not predict certain radiological changes, but less proximal bone resorption confirms the design changes from ABG-I to ABG-II. A non-tight proximal fit is correlated with varus position of the stem. Thigh pain is correlated with a poor fit and fill of the femoral stem.