Background

Femoroacetabular impingement due to a reduced femoral head-neck-offset or excessive acetabular coverage will lead to early cartilage lesions of the hip joint. The purpose of the present study was to analyze the relationship between the extent of bony deformity and the presence and extent of cartilage lesions in femoroacetabular impingement.

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: Whereas in traumatic avascular necrosis of the femoral head (ANFH) loss of the femoral head’s blood supply is due to a mechanical event, in non-traumatic AFNH it is the result of a wide variety of etiologies (e.g. alcoholism, hypercortisonism, etc.), which have in common that they lead to an intravascular complication with subsequent malperfusion of the femoral head. Additionally, for part of non-traumatic ANFH no causative factors are known, why they are called idiopathic. A mechanical cause for nontraumatic ANFH – as e.g. a repetitive trauma of the femoral head supplying deep branch of the medial femoral circumflex artery and its terminal branches by abutment of the femur against the acetabulum as in femoroacetabular impingement (FAI) – has not been discussed so far.

Methods: The anteroposterior and lateral radiographs of 118 hips in 77 patients, who were operated in our institution between January 1995 and December 2005 because of nontraumatic ANFH, were evaluated with respect to the configuration of the head-neck junction.

In a qualitative analysis the head-neck contour of all femora was assigned to one of the following four groups: regular waisting, mildly reduced waisting, reduced to distinctly reduced waisting or completely lacking waisting.

Results: In this retrospective analysis, for 44.1% of the hip joints hypercortisonism, for 40.7% alcoholism, for 12.7% hypercholesterinemia and for 11.0% no risk factors were found documented in the patients’ files. In AP and lateral radiographs a regular waisting was found in 60.2% and 9.3%, a mildly reduced waisting in 32.2% and 37.3%, a reduced waisting or distinctly reduced waisting in 7.6% and 35.6%, and a completely lacking waisting in 0% and 16.9%, respectively, and the mean angle alpha was 63° ± 18° and 67° ± 14°, respectively. On average, the (frontally projected) CCD angle was 133° ± 6°, the LCE angle 30° ± 7° and the acetabular index of the weightbearing zone 4° ± 5°.

Conclusion: Nötzli et al. found an angle alpha of 42° ± 2° for healthy individuals. A markedly increased angle alpha in both radiographic planes of the 118 investigated hips with nontraumatic ANFH was found, demonstrating a reduced shape of their head-neck junction in the anterior and lateral aspect. Together with the fact that no gross pathological deviations for the orientation of the femoral neck and the acetabulum were found, this may hint at cam-type FAI to occur in this hips and thus potentially at a mechanical (co-) factor in developing non-traumatic ANFH.

Introduction: There is rather broad consent that mildly slipped capital femoral epiphyses (SCFE) should be treated by in situ fixation with wires or dynamic screws. There is recent evidence, however, that even mild slips lead to early damage of the acetabular labrum and cartilage by abutment of a prominent femoral metaphysis. It is therefore proposed that treatment of mildly slipped capital femoral epiphyses should not only prevent further slipping of the epiphysis, but also address potential femoro-acetabular impingement (FAI) by restoring the anatomy of the proximal femur. To find proof for this newly proposed therapeutical approach, we reviewed all patients treated in our department ten to twenty years ago for unilateral slipped capital femoral epiphysis by in situ fixation without restoration of the anatomy of the proximal femur.

Methods: From forty-four patients treated between October 1984 and December 1995, twenty-eight could be contacted and eighteen reviewed. Development of FAI was documented by clinical examination (range of motion, “impingement provocation test”) and radiological evaluation (AP radiographs of the pelvis and lateral cross-table radiographs of both hips). Statistical analysis was performed with paired t test and Wilcoxon matched-pairs signed-ranks test in case of numerical data, and Fisher’s Exact Test and Chi-squared Test for Independence in case of ordinal data. The level of significance was set at p < 0.05.

Results: Comparing involved to non-involved hips, mean internal rotation and abduction differed significantly (15° ± 7.9° vs. 21° ± 7.9° (p < 0.01) and 37° ± 7.7° vs. 42° ± 6.7° (p < 0.01), respectively), but the “impingement provocation test” was found positive in only four vs. six hips (p = 0.71). Radiological examination showed significantly difference with respect to waisting of the femoral neck (p < 0.01) and bony appositions at the femoral head neck junction (p < 0.01). No regular waisting was found in all involved hips, whereas it was present in nine non-involved hips. A distinctly reduced or absent waisting was seen in twelve of the involved hips but in only four of the non-involved hips. Bony appositions were found in fourteen of the involved hips, but in only four of the non-involved hips. Furthermore the angle α according to Nötzli et al. (2002) showed a significant difference in its mean on AP radiographs (84° ± 10° vs. 60° ± 15°, p < 0.01), not so, however, in lateral cross-table radiographs (50° ± 8° vs. 48° ± 11°, p = 0.3).

Conclusion: From a clinical point of view, in situ fixation may be sufficient in treating mildly SCFE, whereas radiological data suggest that restoration of the anatomy of the head-neck junction of the proximal femur might be sensible to prevent or delay FAI and thus development of osteoarthritis of the respective hip joint.