Knee Arthroplasty and Risk of Hip Fracture A Popu

Authors: Arief Lalmohamed Frans Opdam Nigel K Arden Daniel PrietoAlhambra Tjeerd van Staa Hubertus G M Leufkens Frank de Vries

Publish Date: 2011/12/18

Volume: 90, Issue: 2, Pages: 144-150

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Abstract

The majority of knee arthroplasties KAs are performed in patients with osteoarthritis OA Although bone mass may be increased in these patients subjects with knee OA may have an increased risk of hip fracture possibly due to an increased severity of falls However in patients with KAs risk of hip fracture has not been studied extensively We evaluated the association between KAs and hip fracture risk in a populationbased case–control study using the Dutch PHARMO Record Linkage System 1991–2002 n = 33104 Cases were patients with a first admission for hip fracture controls were matched by age gender and geographic location Neither group had a previous history of fracture Time since first KA was calculated Analyses were adjusted for disease and drug history A 54 increased hip fracture risk was found in patients who underwent KA adjusted adj OR = 154 95 CI 119–200 We found a strong effect modification by age in these patients the youngest patients aged 18–70 years were at more increased risk for hip fracture adj OR = 276 95 CI 116–659 while we could not detect a statistical increase in patients aged 80 years Furthermore the association tended to be greater during the first few years after surgery although it did not reach statistical significance We found that KAs are associated with a 54 increased risk of hip fracture in particular among adult patients aged 71 years old Fracture risk assessment could be considered in patients who are about to undergo a KAThe department of Pharmacoepidemiology and Clinical Pharmacology employing authors Arief Lalmohamed Tjeerd van Staa Hubertus GM Leufkens and Frank de Vries have received unrestricted funding for pharmacoepidemiological research from GlaxoSmithKline the privatepublic funded Top Institute Pharma wwwtipharmanl includes cofunding from universities government and industry the Dutch Medicines Evaluation Board and the Dutch Ministry of Health Tjeerd van Staa also works for the General Practice Research Database GPRD UK GPRD is owned by the UK Department of Health and operates within the Medicines and Healthcare products Regulatory Agency MHRA GPRD is funded by the MHRA Medical Research Council various universities contract research organisations and pharmaceutical companies The other authors have stated that they have no conflict of interestKnee arthroplasties KAs are effective interventions with low mortality rates and few severe adverse outcomes 1 The surgery is primarily performed in patients with primary osteoarthritis OA and rheumatoid arthritis In Finland 81 of patients who underwent KA were diagnosed with OA 48607 surgeries between 1980 and 2003 2 In Sweden 87 of the interventions were in patients with OA and 10 in patients with rheumatoid arthritis 3Risk of hip fracture may be either decreased or increased in patients with KA or OA In frail elderly patients KA may protect against hip fracture by reducing the occurrence of falls On the other hand within the first month after KA muscle strength is often decreased 4 which can elevate fracture riskThere is more evidence about the association of knee OA and fracture Observational studies have provided conflicting results regarding the risk of hip fracture in patients with OA A decreased risk of fractures compared to control patients has been reported by several epidemiological studies 5 6 7 This may be due to an increased bone mineral density BMD even at sites distant to the OA site 8 Review of histomorphometric and densitometric studies at OA sites of the hip and knee revealed that cartilage fibrillation could not be differentiated from bony changes even in the earliest stages of OA Moreover microfractures of subchondral trabecular bone were less frequently observed in patients with OA compared to controls 5 Epidemiological studies have revealed that in cases of generalized OA there are qualitative and quantitative differences including hypermineralization and increased content of growth factors suggesting a more generalized bone alteration 5 In contrast a UK study showed an increased risk of fracture in patients with knee OA 9 which may have been the result of an increased severity of falls in these patients The aim of this study was to evaluate the association between KA and the risk of hip fractureA case–control study was performed using the Dutch PHARMO Record Linkage System RLS database wwwpharmonl 10 The database contains pharmacy dispensing data including dispensed drug type of prescriber dispensing date amount dispensed and written dosage instructions of about 1 million Dutch residents linked to a nationwide hospital discharge register Diagnoses are coded according to the International Classification of Diseases 9th revision ICD9 Patients are included irrespective of health insurance or socioeconomic status and represent about 7 of the general population The PHARMO RLS database has a high level of completeness as shown in several independent validation studies 11Cases were defined as patients who had sustained their first hip fracture during the 10year study period 1 January 1991 to 31 December 2002 at least 18 years of age Up to four controls were selected for each case matched by year of birth gender and geographic location Control patients were registered in the database and had no record for a hip fracture hospitalization Cases were assigned the date of hip fracture hospitalization as their index date Controls were assigned the same index date as their case In a sensitivity analysis we restricted the study population to subjects who were at least 50 years of age at the index dateHistory of primary KA before index date was determined using ICD9 surgical procedure code 8154 Time since onset “recency” of the KA was determined by calculating the time between the index date and the earliest hospital admission for the KA We created a proxy for unilateral/bilateral KA by stratifying KA patients into 1 subjects with one primary KA record before the index date and 2 those with multiple primary KA records before the index date

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