Radiographic preoperative templating of extra-offset cemented THA implants: How reliable is it and how does it affect survival?

Introduction: Securing femoral offset should in theory improve hip stability and abductor muscles moment arms. As problems arise mainly in case of originally increased offset (> 40 mm), a range of extra-offset stems is available; the exact impact in terms of fixation, however, is not known. Hypothesis: Extra-offset stems should more reliably reestablish original femoral offsets exceeding 40 mm than standard femoral components, limiting instability risk without possible adverse effect on fixation. Objective: To compare the ability of five commonly available femoral stem designs to restitute offset exceeding 40 mm, and to assess function and cement fixation at a minimum 6 years' follow-up in a stem conceived to reproduce such offset. Patients and methods: A continuous series of 74 total hip replacements (THR) in hips with increased (> 40 mm) femoral offset was studied. All underwent preoperative X-ray templating on Imagika (TM) software to assess offset reproduction by five models of stem: four standard, and one Lubinus SP2 (TM) extra-offset stem. A retrospective clinical and X-ray study was conducted with a minimum 6 years' follow-up on the Lubinus SP2 (TM) 117 degrees stems used to try to reproduce offset in the 74 THRs. Results: Apart from the increased (> 40 mm) offset, the cervicodiaphyseal angle was consistently < 135 degrees, < 130 degrees in 60 femurs (81%) and < 125 degrees in 45 (60%). Planning showed the four standard stems to induce (> 5 mm femoral offset reduction in 50-83% of cases, versus only 25% with the Lubinus SP2 (TM) 117 degrees). All 74 hips received Lubinus SP2 (TM) 117 degrees stems: at a mean 78 months FU (range, 70-94 mo), their mean Postel-Merle d'Aubigne score was 17 +/- 1.8 (range, 13-18). Five of the 74 THRs underwent surgical revision: three cases of loosening, in which the stem was replaced, and two of instability, without change of stem. Loosening was not related to offset reproduction quality; two of the three cases were due to initial cementing defect, and the third occurred in a femur with previous history of two osteotomies. There were four cases of dislocation (5.4%: two primary, which were not operated on, and two recurrent, managed by acetabular revision), despite good reproduction of the preoperative offset in three of the four cases. Mean 7-year implant survivorship was 95.1% (+/- 4.8). Discussion and conclusion: The anatomic form of the Lubinus (TM) SP2 117 degrees should in theory provide a uniform cement mantle. Survivorship, however, is less good than for regular offset versions (126 degrees or 135 degrees). On the other hand, it does reproduce anatomy in case of > 40 mm offset, providing extra offset of more than 51 mm. The slightly shorter survivorship requires more long-term surveillance. Level of evidence: Level IV, retrospective study. (C) 2010 Elsevier Masson SAS. All rights reserved.