The Birmingham Hip Resurfacing (Smith & Nephew London, UK) is the most popular hip resurfacing (HR) in the UK. However, it is now subject to two Medical Device Alerts (MDA) from the Medicines and Healthcare products Regulatory Agency (MHRA). A cross-sectional survey of primary metal-on-metal hip procedures recorded on the National Joint Registry for England, Wales and Northern Ireland (NJR) until 5th November 2013 was performed. Cost-analysis was based on an algorithm for surveillance of HR at a tertiary referral centre and followed previous MHRA guidance. NIHR NHS Treatment costs were used. The local protocol encompassed: patient outcome scoring (Oxford hip score), blood metal ion measurement (cobalt, chromium), cross-sectional imaging (MRI) and discussion at an internet-enabled multidisciplinary team meeting (iMDT) in addition to routine hip surveillance.Introduction
Patients/Materials & Methods
Failure of metal on metal (MOM) total hip arthroplasty (THA) and resurfacing arthroplasty (HRA) due to development of adverse local tissue reaction (ALTRs) is a significant problem. The prevalence of ALTRs in asymptomatic MOM arthroplasty patients is highly variable. The purpose of this prospective, longitudinal study was to: 1) determine MRI ALTR prevalence in patients with HRA; 2) determine if patients with HRA have a greater rate of MRI ALTRs compared to control patients with ceramic on poly (COP) THA; and 3) evaluate changes in patient reported outcomes between these implant designs. Following IRB approval with informed consent, self-reported asymptomatic primary COP and HRA patients greater than one year post arthroplasty were evaluated with 4 annual (TP1–4) MRIs using a standardized protocol and serum ion level testing. Morphologic and susceptibility reduced images were acquired for each hip and evaluated for synovial thickness, volume, capsule dehiscence and the presence of ALTR. Patient reported outcomes were evaluated by Hip Disability and Osteoarthritis Outcome Scores (HOOS). Analyses were performed to detect differences of synovial thickness and volume, and HOOS subgroups between and within bearing surfaces at each time point and over time, and to compare the time to and the risk of developing MRI ALTR. Analyses were adjusted for age, gender, and length of implantation.Introduction
Methods
Patients from a randomised trial on resurfacing
hip arthroplasty (RHA) (n = 36, 19 males; median age 57 years, 24
to 65) comparing a conventional 28 mm metal-on-metal total hip arthroplasty
(MoM THA) (n = 28, 17 males; median age 59 years, 37 to 65) and
a matched control group of asymptomatic patients with a 32 mm ceramic-on-polyethylene
(CoP) THA (n = 33, 18 males; median age 63 years, 38 to 71) were
cross-sectionally screened with metal artefact reducing sequence-MRI
(MARS-MRI) for pseudotumour formation at a median of 55 months (23
to 72) post-operatively. MRIs were scored by consensus according
to three different classification systems for pseudotumour formation. Clinical scores were available for all patients and metal ion
levels for MoM bearing patients. Periprosthetic lesions with a median volume of 16 mL (1.5 to
35.9) were diagnosed in six patients in the RHA group (17%), one
in the MoM THA group (4%) and six in the CoP group (18%). The classification
systems revealed no clear differences between the groups. Solid
lesions (n = 3) were exclusively encountered in the RHA group. Two patients
in the RHA group and one in the MoM THA group underwent a revision
for pseudotumour formation. There was no statistically significant
relationship between clinical scoring, metal ion levels and periprosthetic
lesions in any of the groups. Periprosthetic fluid collections are seen on MARS-MRI after conventional
CoP THA and RHA and may reflect a soft-tissue collection or effusion. Currently available MRI classification systems seem to score
these collections as pseudotumours, causing an-overestimatation
of the incidence of pseudotumours. Cite this article:
It is accepted that resurfacing hip replacement
preserves the bone mineral density (BMD) of the femur better than total
hip replacement (THR). However, no studies have investigated any
possible difference on the acetabular side. Between April 2007 and March 2009, 39 patients were randomised
into two groups to receive either a resurfacing or a THR and were
followed for two years. One patient’s resurfacing subsequently failed,
leaving 19 patients in each group. Resurfaced replacements maintained proximal femoral BMD and,
compared with THR, had an increased bone mineral density in Gruen
zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95%
confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6%
(95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD
of the medial femoral neck and increased that in the lateral zones
between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6). On the acetabular side, BMD was similar in every zone at each
point in time. The mean BMD of all acetabular regions in the resurfaced
group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total
hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863).
A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8
to 9.0) of BMD was found above the acetabular component in W1 and
10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial
to the implant in W2 for resurfaced replacements and THRs respectively.
Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to
12.7) in W3 but the BMD inferior to the acetabular component was
maintained in both groups. These results suggest that the ability of a resurfacing hip replacement
to preserve BMD only applies to the femoral side.
