Postoperative migration of short stem prosthesis of the hip joint

Hip replacement surgery is a popular procedure that provides predictable, long-lasting and good effects. The use of short stem prostheses helps preserve an intact medullary cavity and proximal diaphysis. It has been demonstrated that the use of short stem prostheses leads to better clinical results compared to standard stem prostheses. The study aimed to assess the migration of the stem of the Proxima hip prosthesis. Migration was defined as a change in the angle of stem position towards a varus deformity.

The study involved 164 patients (83 women, 81 men) who underwent hip replacement surgery with a total of 185 Proxima prostheses in the Cracow Rehabilitation Centre between 2007 and 2012.

Radiographic analysis included a series of three radiographs obtained for each patient on Day 0 and after 6 and 12 months. Stem migration towards a varus deformity was reported during the follow-up period. There was a correlation between the change in the angle of varus prosthesis alignment and the length of follow-up. The mean change of the varus angle was 8.21° after 12 months. There was a statistically significant difference in the angle of the varus prosthesis alignment between the sexes. After 12 months the total change was 6.82° in women and 9.65° in men. There was no significant correlation between a patient's BMI, age, the total length of the neck of the implant and the progression of the angle of varus prosthesis alignment.

1. The greatest displacement of the Proxima short stem implant towards a varus deformity is seen within the first 6 months following implantation. 2. The change of the angle of varus prosthesis alignment depends on the initial positioning of the prosthesis and the sex of the patient. 3. The change of the angle of varus prosthesis alignment is independent from the patient's age and BMI.