Factors affecting squeaking in metal on metal hip resurfacings

We reviewed 380 hip resurfacings cases between December 1999 and Dec 2012. 11 cases (2.89%) squeaked postoperatively. Mean follow-up was 88.6 months (19-130 months). Mean time to squeak was 11.3 months (3-22 months). Ten (91%) cases were male and nine (81%) cases had a Birmingham hip resurfacing. Cases were matched for age, gender, BMI and implant to three controls. Radiographs were analysed using EBRA (Einzel-Bild-Roentgen-Analysis, University of Innsbruck, Austria) software to evaluate cup orientation. There was no significant difference between the mean inclination angle of the cups (p = 0.26) or the mean anteversion angle (p = 0.29). There was no difference in serum cobalt (p = 0.20) or serum chromium (p = 0.45) levels at latest follow-up. Three of the 11 (27.3%) cases had revision surgery at a mean follow-up of 101 months (72-117 months). Squeaking was not influenced by patient demographic parameters and resolved in all cases that did not undergo revision surgery. Males with a resurfacing head size <50 mm had significantly increased odds of squeaking when compared to controls (odds ratio = 26.6; 95% CI = 1.2-573.3; p<0.05). Based on our findings, we do not recommend that squeaking on its own should be an indication for revision of hip resurfacing components.

Squeaking: Current knowledge and how to avoid it

This review aims to update the reader with current thinking and research related to the well documented phenomenon of squeaking hip arthroplasties. The etiology of squeaking is multifactorial and still not well understood. We aim to share our own experience and views on the combination of factors we believe increases the likelihood of squeaking, along with mechanisms by which the sound may be generated. Recent published findings from other groups are summarized along with an appropriate management algorithm we recommend for this cohort of patients.

A review of squeaking hips

The incidence of squeaking in hip replacement varies for ceramic-on-ceramic and metal-on-metal bearings, and the implications are not fully understood. Contributing factors may include component malposition, edge loading, impingement, third-body particles, and loss of lubrication. However, squeaking is multifactorial, requiring a certain combination of interaction among patient, surgical, and implant factors. When squeaking is infrequent and function is not impaired, patients should avoid activities that precipitate the squeaking. Surgery is recommended for persistent or troublesome squeaking, severe malpositioning of components, failure of the implants (including fracture), impingement and subluxation, and pain. If necessary, the bearing can be changed during surgery to another ceramic-on-ceramic or to a ceramic-on-polyethylene bearing.

Femoral neck fractures after hip resurfacing

Femoral neck fracture is an important early complication after hip resurfacing. Our aims were firstly to determine the incidence of fracture in an independent series and secondly, in a case control study, to investigate potential risk factors. Fifteen femoral neck fractures occurred in a series of 842 procedures, representing an incidence of 1.8%. No relationship existed between age, sex, and fracture incidence. Mechanical factors such as notching, femoral neck lengthening, and varus alignment of the femoral component were found to have a similar incidence in both fracture and control groups. The proportion of patients that had at least 1 mechanical risk factor was not different between the 2 groups (fracture group, 50%; control group, 41%). Established avascular necrosis of the femoral head was evident in all retrieved femoral heads (n = 9) of patients who sustained postoperative fracture; in none of these patients was avascular necrosis the initial diagnosis. This study suggests that in our practice, mechanical factors, such as neck notching, neck lengthening, or varus angulations, are not the primary cause of femoral neck fractures.

The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements

Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking.

The 2007 Otto Aufranc Award. Ceramic-on-metal hip arthroplasties: a comparative in vitro and in vivo study

The performance of novel ceramic-on-metal bearing couples has been compared with metal-on-metal and ceramic-on-ceramic bearing couples in laboratory and short-term clinical studies. Laboratory studies compared ceramic-on-metal with metal-on-metal and ceramic-on-ceramic bearings with diameters of 28 and 36 mm under standard conditions and under adverse conditions with head loading on the rim of the cup. Clinical studies compared metal ion levels in ceramic-on-metal with metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings in a randomized prospective study. In the laboratory studies, friction, wear, and ion levels were lower in ceramic-on-metal bearings compared with metal-on-metal, with results similar to ceramic-on-ceramic couples. Under adverse conditions and rim loading, all bearings showed increased wear with lower wear and absence of stripe wear in ceramic-on-metal compared with metal-on-metal bearings. Short-term studies in 31 patients at 6 months revealed lower metal ion levels (cobalt and chromium) in those with ceramic-on-metal compared with metal-on-metal bearings.

An unfavourable outcome after periprosthetic fracture following metal-on-metal surface hip arthroplasty

We report a case of a varus malunited periprosthetic femoral neck fracture following metal-on-metal hip resurfacing operation. Failure to closely observe and poor compliance in the young and active group of patients may contribute to such an unfavourable outcome.

Metal-on-metal surface hip arthroplasty in patients with abnormal Coxanatomy: preliminary results

The purpose of this study was to evaluate early to intermediate results of metal-on-metal (MoM) hip resurfacing arthroplasty in patients with abnormal hip anatomy. We evaluated nine MoM hip resurfacing arthroplasty in eight patients with abnormal coxanatomy performed at a district general hospital in the UK between March 1999 and November 2002. One patient had undergone bilateral sequential hip resurfacing procedure. These patients were defined to have abnormal coxanatomy by virtue of previous dysplastic disease of hip in three cases, previous Legg-Calve-Perthes disease, multiple epiphyseal dysplasia, T cell acute lymphoblastic leukaemia, trauma and sepsis in one case each. The mean follow-up was 40.8 months. The mean age at primary operation was 35 years (range: minimum 21 years; maximum 44 years). There were six male and two female patients. There were six right-sided and three left-sided procedures. All patients had satisfactory outcomes. There were no deep infections, dislocations, or femoral neck fractures. Although this is a short series, MoM resurfaced hips with appropriate case selection can yield satisfactory short-term to intermediate-term results in the young and active patients with abnormal hip anatomy.

Deformation of press-fitted metallic resurfacing cups. Part 1: Experimental simulation

The interference press fit of a metallic one-piece acetabular cup employed for metal-on-metal hip resurfacing procedures was investigated experimentally under laboratory conditions in the present study, in particular regarding the cup deformation. Tests were carried out in cadavers as well as polyurethane foams of various grades with different elastic moduli to represent different cancellous bone qualities. The cadaver test was used to establish the most suitable configuration of the foam model representing realistic support and geometrical conditions at the pelvis. It was found that a spherical cavity, with two identical areas relieved on opposite sides, was capable of creating a two-point pinching action of the ischeal and ilial columns on the cup as the worst-case scenario. Furthermore, the cup deformation produced from such a two-point loading model with a grade 30 foam was similar to that measured from the cadaver test. Therefore, such a protocol was employed in subsequent experimental tests. For a given size of the outside diameter of the cup of 60 mm, the cup deflection was shown to be dependent largely on the cup wall thickness and the diametral interference between cup and prepared cavity at implantation. For a relatively thin cup with a wall thickness between 2.3 mm (equator) and 4 mm (pole) and with a modest nominal diametral interference of 1 mm, which corresponds to an actual interference of approximately 0.5 mm, the maximum diametral cup deflection (at the rim) was around 60 μm, compared with a diametral clearance of 80-120 μm between the femoral head and the acetabular cup, generally required for fluid-film lubrication and tribological performances. Stiffening of the cup, by both thickening and lateralizing by 1 mm, reduced the cup deformation to between 30 and 50 μm with actual diametral interferences between 0.5 and 1 mm.

Femoral neck fractures complicating metal-on-metal resurfaced hips: a report of 2 cases

Metal-on-metal hip resurfacing arthroplasty is increasingly popular for younger patients with advanced hip disease. Intra-operative or immediate postoperative femoral neck fracture after metal-on-metal hip resurfacing is a well-described technical complication, ranging from 0% to 1.5%. We report 2 cases of late femoral neck fracture occurring 8 and 15 months following the index operation, with a review of the literature. We recommend that patient selection should be of prime importance before embarking on metal-on-metal surface hip replacement to avoid such complications.