Cup press fit in uncemented THA depends on sex, acetabular shape, and surgical technique

Abstract

Background: Uncemented press-fit cups provide bone fixation in primary THA, but the use of screws is sometimes necessary to achieve primary stability of the socket. However, it is unclear whether and when screws should be used.

Question/purposes: We analyzed the factors related to screw use with a press-fit uncemented cup and assessed whether screw use is associated with the same rates of loosening and revision as a press-fit technique.

Methods: We retrospectively reviewed 248 patients who underwent THA using the same prosthetic design. Eighty-eight hips had screws to achieve primary cup fixation (Group 1), and 189 did not (Group 2). Mean age was 50 years (range, 14-73 years). We analyzed factors related to the patient, acetabular type, and reconstruction of the rotation center of the hip. Minimum followup was 5 years (mean, 8.9 years; range, 5-12 years).

Results: We found higher screw use in women, patients with less physical activity, Acetabular Types A or C, and a distance from the center of the prosthetic femoral head to the normal center of rotation of more than 3 mm. There were four revisions in Group 1 and five in Group 2. Eight hips had radiographic loosening in Group 1 and nine in Group 2. Cups with a postoperative abduction angle of more than 50° had a higher risk for loosening.

Conclusions: Press fit was achieved less frequently in women and patients with Acetabular Types A or C and less physical activity; a closer distance to the normal center of rotation decreased screw use. Screw use to augment fixation achieved survival similar to that of a press-fit cup.

Level of evidence: Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.

Fig. 1

A graph shows Kaplan-Meier survivorship curves comparing the cumulative probability of not having a cup revision for any cause in patients with screws (Group 1) and without screws (Group 2). The survival rate for revision surgery for any cause at 12 years was 95.4% (95% CI, 91%–99%) in Group 1 and 97.8% (95% CI, 95%–99%) in Group 2 (p = 0.41). Cross lines represent censored hips.

Fig. 2

A graph shows Kaplan-Meier survivorship curves comparing the cumulative probability of not having radiographic aseptic cup loosening in patients with screws (Group 1) and without screws (Group 2). The probability of not having radiographic loosening at 12 years was 90.9% (95% CI, 84%–96%) in Group 1 and 95.1% (95% CI, 92%–98%) in Group 2 (p = 0.14). Cross lines represent censored hips.

Fig. 3

A graph shows Kaplan-Meier curves comparing the cumulative probability (with 95% CIs) of not having radiographic aseptic cup loosening in patients with a postoperative acetabular abduction angle of 50° or less and higher than 50°. The survival rate for radiographic loosening at 12 years was lower (p = 0.002) for cups with an acetabular abduction angle of higher than 50°. Cross lines represent censored hips.