Abstract
Introduction
A decrease of 15% in femoral off-set (FO) was reported to generate a weakness of the abductor muscle after THA, which may increase the risk of limping and dislocation. However, this value was defined under experimental conditions using a CYBEX machine, which does not correspond to daily life activities. To our best knowledge, there is no reported study about the effect of the FO alteration on the gait, following THA.
Materials and Methods
To assess the functional consequences of an alteration in the FO, a prospective comparative study was carried out and it included patients who underwent THA for primary osteoarthritis.
In order to select only patients with an isolated FO alteration, the three-dimensional hip anatomy was analysed preoperatively and post-operatively with CT-scans using HipPlan Software. Three groups were defined according to the FO alteration: 15% decrease, restored and 15% increase. The exclusion criteria were: the presence of an arthroplasty or of an associated pathology on the contra-lateral or the same limb, a spine disease and a non-restoration of the other hip parameters (center of rotation, limb length). 26 patients were included: 12 restored, 9 decreased FO and 5 increased FO. The patients were composed of 20 women and 6 men with an average age of 67.7 ± 9 years. All the patients were assessed clinically, pre-operatively and 1 year after surgery with 4 scores: the Poste Merle d'Aubigné score, the Harris score, the womac score and the quality of life score SF12.
A gait analysis was performed at 1 year follow-up using an ambulatory device (Physilog (3)) under normal walking conditions. The patients were asked to walk at their usual normal speed for 30 metres in a standardized corridor: Each limb was compared to the contra-lateral healthy limb.
Results
Contrarily to the restored and the increased groups, there was in the decreased group a significant asymmetry between the operated limb and the healthy side with a decreased knee range of motion (8°, p<0.004) and a lower maximal swing speed. (30°/s, p<0.01) (Figure). There was no significant difference in the clinical scores between the three groups. However, there was a significant decrease in hip adduction in the decreased FO group
Discussion
The main finding of this study was that an isolated decrease in FO after THA generated an alteration of the gait with a lower swing speed and a decreased knee range of motion when walking. A 15% decrease in FO was proved to induce a gait asymmetry in the sagittal plane. This should be kept in mind for THA planning because X-rays underestimate the FO of up to 20%. This is why; the authors use now routinely CT-scan in order to perform a three-dimensional pre-operative planning for THA.
There was no significant difference between the groups regarding the clinical scores. These scores may be not adapted for an accurate clinical assessment after THA for young and active patients who have highly demanding physical activities.
