Introduction

Version abnormalities of the femur, either retroversion or excessive anteversion, cause pain and hip joint damage due to impingement or instability respectively. A retrospective clinical review was conducted on patients undergoing a subtrochanteric derotation osteotomy for either excessive anteversion or retroversion of the femur.

Introduction: The S-ROM^® modular hip system (DePuy, Warsaw, IN) has a cementless femoral component made of titanium alloy with a distally fluted and slotted stem. The stem mates with a sleeve that is implanted in the proximal femur. No reports exist in the literature of intraoperative difficulties in disengaging the sleeve-stem interface. Induced by the impossibility of intraop-eratively disconnecting the sleeve-stem interface in one patient leading to unintended revision of a well-fixed sleeve, we asked whether in vivo evidence for fretting or mechanically-assisted crevice corrosion of the mating surfaces could be found in retrieved components and whether its appearance is influenced by factors such as length of implantation.

Methods: The sleeve-stem combinations were retrieved from 1998 to 2008 as part of our IRB-approved implant retrieval system. Twenty-two sleeve-stem interfaces of S-ROM^® femoral components were located in our retrieval collection. Seven sleeve-stem combinations were still mated when retrieved; 2 were disengaged by hammering the sleeve away from the stem, the remaining 5 had to be cut longitudinally with a diamond saw to disengage the sleeve from the stem. All disengaged sleeves were also cut to expose their inner surfaces. The surfaces of the taper region and the corresponding inner surfaces of the split sleeves were inspected macroscopically and assigned to the following groups: severe corrosion; moderate surface changes; and few or no evidence of surface changes. Microscopic examination was used to grade fretting and corrosion using an established subjective scale (Goldberg et al., 2002). The surface of the taper and the sleeve was divided into 12 regions each and every region was evaluated separately. The mean score of all 24 regions was calculated and opposed to the implantation time of the respective femoral component. Statistical analysis of correlation between the mean score and implantation length was performed using the Pearson product moment correlation. Additionally, the surface of the taper regions of 6 specimens underwent detailed analysis with SEM and EDAX.

Results: In 3 of 22 sleeve-stem interfaces severe corrosion accounting for at least 80% of the surface area was detected. Furthermore, ten sleeve-stem interfaces showed moderate surface changes. Nine sleeve-stem interfaces showed few or no surface changes. There was no correlation between presence of corrosion and implantation length (r=0.13; p=0.56).

Conclusion: In 3 of 22 retrieved sleeve-stem interfaces severe corrosion was found at the stem-sleeve interface. Though apparently not the rule, failure to disengage the stem from the sleeve undermines an important advantage of this type of modularity in total hip replacement and suggests that alternative procedures should be anticipated when planning for revision surgery of such (or a similar) modular femoral component.

Introduction: Femoroacetabular impingement (FAI) is one of the main causes of hip osteoarthritis. Femoral retroversion has been reported as a cause of FAI and it is well established that a retroverted femur produces hip pain and alterations in the external and internal rotation balance. However, no studies of femoral retroversion in patients with FAI have been reported. Furthermore, since the lack of internal rotation is a common feature in patients with FAI, it could be possible that femoral version abnormalities are present in these patients. The purpose of this study is to describe the femoral version in a group of patients with FAI and to assess its relation in the development of hip osteoarthritis.

Methods: The history, x-rays and hip CT scans of 142 patients with FAI were reviewed. All patients presented persistent hip pain and were evaluated clinically between January 2006 and July 2008. We defined FAI when at least one of the following features were present:

an abnormal alpha angle (> 49°) measured on the elongated femoral neck x-ray,

We documented the type of FAI, the presence of acetabular dysplasia, coxa valga, coxa vara and the femoral version measured on the CT scan. The degree of osteoarthritis of the hip using the Tönnis classification was documented as well.

Results: Two hundred and sixty-five FAI hips from 142 patients (73 females and 69 males) were analyzed. The average age was 36.7 years. The mean femoral version was 11.4 ° (−14.1° to 47°). We found 43 hips (16.6%) of the femora were retroverted and 133 hips (50%) had either diminished anteversion (< 10°) or were retroverted. In 12 hips (0.05%) the only cause of FAI was the presence of a diminished anteversion or retroverted femur. The statistical analysis using the generalized estimating equations method including the right and left hips, shown that among these six predictors, both femoral retroversion (p=0.046) and coxa vara (p< 0.001) were statistically significant for the presence of osteoarthritis.

Conclusion: The presence of a retroverted femur seems to be a cofactor in the development of hip osteoarthritis in patients with FAI. The orthopedic surgeons should be aware of the high frequency of femoral retroversion when evaluating patients with hip impingement, in order to make the right diagnosis and treatment. It might be possible that this association between FAI and femoral retroversion is due to a common hip disease during skeletal maturation (i.e. SCFE) leading to two anatomical alterations at the proximal femur: reduced head-neck offset and retroverted femur.