The effect of femoral offset modification on gait after total hip arthroplasty

Background and purpose

A decrease of 15% in femoral offset (FO) has been reported to generate a weakness of the abductor muscle, but this has not been directly linked to an alteration of gait. Our hypothesis was that this 15% decrease in FO may also generate a clinically detectable alteration in the gait.

Patients and methods

We performed a prospective comparative study on 28 patients who underwent total hip arthroplasty (THA) for unilateral primary osteoarthritis. The 3D hip anatomy was analyzed preoperatively and postoperatively. 3 groups were defined according to the alteration in FO following surgery: a minimum decrease of 15% (9 patients), restored (14), and a minimum increase of 15% (5). A gait analysis was performed at 1-year follow-up using an ambulatory device. Each limb was compared to the contralateral healthy limb.

Results

In contrast to the “restored” group and the “increased” group, in the “decreased” group there was a statistically significant asymmetry between sides, with reduced range of motion and a lower maximal swing speed on the operated side.

Interpretation

A decrease in FO of 15% or more after THA leads to an alteration in the gait. We recommend 3-D preoperative planning because the FO may be underestimated by up to 20% on radiographs and it may therefore not be restored, with clinical consequences.The femoral offset (FO) and limb length have to be restored during total hip arthroplasty (THA) in order to improve the functional outcomes and to reduce the risk of limping, dislocation (McGrory et al. 1995, Downing et al. 2001, Bourne and Rorabeck 2002, Asayama et al. 2005, Kiyama et al. 2010), and edge loading (Sariali et al. 2010). The restoration of the FO also appears to be crucial to improve the long-term survival rates of THA. Sakalkale et al. (2001) reported that restoration of the FO reduces the wear in THA.With respect to the functional outcomes of THA, a decrease of 15% in FO has been reported to generate weakness of the abductor muscle (Asayama et al. 2005), but this has not been directly linked to an alteration of gait. Indeed, this threshold was defined under laboratory conditions using a CYBEX machine, which does not correspond to realistic activities of daily living. Our hypothesis was that a 15% decrease in the FO may also generate a clinically detectable alteration of gait.Many devices are available for analysis of gait, but most of them are constraining and cannot be used without laboratory conditions (Lamontagne et al. 2011). Some authors have proposed the use of devices for ambulatory gait analysis that can be used for long distances and under realistic daily living conditions (Aminian et al. 2004). For example, the Physilog device (Aminian et al. 2004) has been validated as an evaluation tool for the clinical assessment of patients before and after THA.We analyzed the consequences of an alteration in FO after THA for gait under realistic walking conditions.