Horizontal offset variation, correlation with neck shaft angle in primary and complex total hip arthroplasty.

AIMS AND

OBJECTIVES

The aim was to assess the individual variation in horizontal offset and neck shaft angle at templating before Total hip arthroplasty (THA). The horizontal offset was compared before and after THA. Restoration of the hip centre of rotation and horizontal offset restores the hip biomechanics.

METHODS

150 patients, including 103 males and 47 females who underwent unilateral THA, were pre-operatively templated. Pre-operative templating provides a roadmap for intra-operative execution and reconstruction assessment. The follow-up X-rays were used to assess restoration of the horizontal offset following THA.

RESULTS

The mean age was 43.51 years (range 14-73). Mean horizontal offset was 4.50 cm (range 2.58-7.0) (SD 0.67), and the mean neck shaft angle was 129.4 (SD 6.55), calculated using standard X-ray Pelvis AP radiographs on the PACS (Picture Archiving and Communication System). The neck shaft angle on the unaffected side varied from 103 to 142°. The post-operative horizontal offset was 3.4-6.0 (Mean 4.58, range 3.20-6.11, SD 0.73). Offset was restored ( ± 5 mm) in 107 hips (71.4 %), reduced (< less than 5 mm) in 17hips (11.3 %), and increased (> more than 5 mm) in 26 hips (17.3 %). 89.7 % (96 out of 107) of patients with horizontal offset restoration had excellent Harris hip scores. Short-neck femoral implants restored the horizontal offset in 18 out of 20 hips (90 %).

CONCLUSION

Our data indicates that there could be a variation in the horizontal offset that needs to be ascertained before THA. Offset restoration in our series was achieved with a single neck shaft angle femur component (135°) with multiple offset options. There was a predominant requirement for standard offset (124/150 hips, 82.7 %) and the short neck (20 out of 150, 13.3 %) options, with the high offset required in only 6 out of 150 (4 %).