Background Total knee arthroplasty (TKA) is an effective treatment for end stage knee osteoarthritis but the postoperative rehabilitaion period can be as long as one year1. During this period, patients may have increased risk of osteoporotic hip fracture after a fall2. Currently, there is a lack of literature reporting the effect of hip fracture on functional outcome in TKA.
Objectives This study aims to investigate: 1) the incidence of osteoporotic hip fracture within one year after undergoing TKA; and 2) the influence of hip fracture on functional outcome in TKA.
Methods Between March 1999 and February 2012, 2456 male patients and 10,452 female patients underwent a primary TKA at a tertiary hospital. Within one year after TKA, 25 patients had an ipsilateral hip fracture after a fall. A propensity score matching algorithm was used to select a 3:1 control group without hip fracture, with adjustment for potential confounders of functional outcome in TKA such as patients' age, gender and Body Mass Index. The operated knee was assessed using the Knee Society Function Score (KSFS), Knee Society Knee Score (KSKS) and Oxford Knee Score (OKS) at two years after TKA; while the general health of the patients was evaluated using the Physical Component Score (PCS) and Mental Component Score (MCS) of SF-36®. The Student's unpaired t-test was used to compare the two groups for continuous variables.
Results The incidence of hip fracture within one year after undergoing TKA was 0.16% (4 out of 2456) among male patients and 0.20% (21 out of 10,452) for female patients. The average age of these 25 patients was 71 ± 8 years old. There were 15 patients with neck of femur fractures and 10 patients with intertrochanteric fractures. Among them, 7 had a fall within 3 months after TKA and 6 each between 4–6 months, 7–9 months as well as 10–12 months after TKA. At two years after TKA, the KSFS was 50 ± 24 in the hip fracture group versus 68 ± 21 in the control group (p=0.002); while the KSKS was 83 ± 12 and 87 ± 8 respectively (p=0.090). Similarly, the OKS was 36 ± 7 in the hip fracture group versus 41 ± 5 in the control group (p<0.001). The PCS was 37 ± 12 in the hip fracture group versus 47 ± 11 in the control group (p<0.001); while the MCS was 55 ± 10 and 54 ± 11 respectively (p=0.662).
Conclusions In the country where the authors practise, the incidence of hip fracture after a fall was 0.16% for males and 0.44% for females among the general population. The incidence of hip fracture within one year after undergoing TKA among male patients was comparable to the general population, however it was two fold lower than the general population for female patients. Nonetheless, those patients who had an osteoporotic hip fracture during the rehabilitation period after TKA had poorer function at two years follow up, with significantly lower KSFS, OKS and PCS. The authors recommend additional caution against hip fracture within one year after TKA.
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Disclosure of Interest None declared