Prevalence of osteoporosis in patients awaiting total hip arthroplasty

Objective: To evaluate the prevalence of osteoporosis in patients awaiting total hip arthroplasty. Method: Twenty-nine patients diagnosed with hip osteoarthritis awaiting primary total arthroplasty of the hip answered WOMAC questionnaire, VAS and questions about habits, osteoporosis and related diseases. Bone mineral densitometry of the lumbar spine and hips and laboratory tests (complete blood count and examination of calcium metabolism) were performed. Weight and height were measured to calculate body mass index (BMI). The evaluated quantitative characteristics were compared between patients with and without osteoporosis using the Mann-Whitney tests. Results: Thirteen men and 16 women with a mean age of 61.5 years old, WOMAC 51.4; EVA 6.4 and BMI 27.6 were evaluated. The prevalence of osteoporosis was 20.7%, and 37.9% had osteopenia. Patients with osteoporosis were older than patients without osteoporosis (p=0.006). The mean bone mineral density of the femoral neck without hip osteoarthritis was lower than the affected side (p=0.007). Thirty-five percent of patients did not know what osteoporosis is. Of these, 30% had osteopenia or osteoporosis. Conclusion: osteoarthritis and osteoporosis may coexist and the population waiting for total hip arthroplasty should be considered at risk for the presence of osteoporosis. Level of Evidence III, Observational Study.


INTRODUCTION
Osteoarthritis (OA) and osteoporosis are two age-related conditions, both common in post-menopause women. 1,2 The relationship between the two diseases remains unclear, even after more than 40 years since the first description of an apparent inverse relationship. 3 According to some authors the incidence of osteoporosis is inversely correlated with the incidence of OA, 4.5 , i.e., the presence of OA would protect against osteoporosis. Recent evidence, however, point to a bone loss in patients with OA, [6][7][8] even in the early stages of disease. 9 Total hip arthroplasty (THA) is one of the most successful surgical procedures in orthopedics, considered by some as the "surgery of the century". 10 More than one million arthroplasties are performed annually worldwide, and projections indicate that this number will double in the next decade. 11 Cementless techniques are increasingly used, but have never been systematically evaluated for its use in osteoporotic patients. It is known that poor bone quality may affect the initial stability of non-cemented implants. 12 Osteoporosis can lead to four possible complications of cementless THA: increased migration (subsidence) of the rod, delay in osteointegration, increased risk of periprosthetic fracture and risk of late failure. 2 The presence of osteoporosis in patients with OA of the hip has, therefore, important implications both in disease progression, as from a surgical point of view, due to the potential of adversely influence the result of THA. 6 Thus, patients at risk for developing osteoporosis should be investigated. This study aims to assess the prevalence of osteoporosis in patients awaiting total hip arthroplasty.

Statistical Analysis
Statistical analysis was performed using Excel 2003 software (Microsoft Corporation, Redmond -WA, USA) and SPSS 20.0 (IBM, New York -NY, USA). The tests were done at 5% significance level. The qualitative characteristics evaluated with absolute and relative frequencies and quantitative measures using summary measurements were first described (mean, standard deviation, median, minimum and maximum). The diagnosis of osteoporosis was defined in patients with bone mineral density values less than 2.5 standard deviation peak values in young adults (T <-2.5 score) at any location. Osteopenia was defined in patients with bone mineral density values between -1 and -2.5 standard deviation peak values in young adults at any location, as defined by the World Health Organization (WHO). The prevalence of osteoporosis was described according to each qualitative characteristic assessed and checked for association with the use of Fisher's exact test or likelihood ratio test when the characteristics has more than two categories. The assessed quantitative characteristics were described according to the presence of osteoporosis and compared between patients with and without osteoporosis using Mann-Whitney tests. Bone mineral density at the femoral neck and total femur were described in the hip side with and without osteoarthritis and sides were compared by generalized estimating equations with symmetric component correlation matrix between the sides assuming normal distribution of BMD as a function of identity link.

RESULTS
Of the 50 patients enrolled, 29 performed all the exams and were included in the final statistical analysis. Table 1 shows the characteristics of the study population. The prevalence of osteoporosis in this patient was 20.7% (six patients) and of osteopenia was 37.9% (11 patients). The prevalence of inadequate serum levels of vitamin D was also high. Only 16.6% of patients had levels considered normal (>30 ng/ml). The prevalence of vitamin D insufficiency (serum level between 20 and 30 ng/ml) was 45.8% and the prevalence of vitamin D deficiency (<20 ng/ml) was 37.5%. Thirty-five percent of patients did not know what osteoporosis was. Table 2 shows that the mean age of the patients was 61.5 years old (St. Dev 15.2 years old), with mean VAS higher than 5 and WOMAC scale above the mean scale value (51.4 points). Table 3 shows that there was no statistically significant association between the presence of osteoporosis with the qualitative characteristics of the patients (p>0.05). Table 4 shows that patients with hip osteoarthritis who had osteoporosis were statistically significant older than patients without osteoporosis (p=0.006), the other parameters were similar between patients with and without osteoporosis (p>0, 05). Table 5 shows that mean BMD of the femur neck of the hip without osteoarthritis side was lower than side with osteoarthritis (p=0.007).

DISCUSSION
The number of arthroplasties performed annually is increasing, 11 and tends to increase, since our population is growing older. 16 Osteoarthritis patients who require joint replacement are predominantly elderly women, a population at high risk for developing osteoporosis. This is the first study to evaluate the relationship between osteoporosis and osteoarthritis in the Brazilian population.
The main finding of this work are in accordance with the world literature, showing a prevalence of osteoporosis of 20.7% in patients awaiting THA, which is compatible to the prevalence found in the general population. 17 These findings support the conclusion that osteoporosis and osteoarthritis can be found in the same patient, confirming recent data from the literature. Our results are similar to those found by Glowacki et al., 1 who performed similar preoperative analysis of 68 postmenopausal women scheduled for undergoing THA, which found hidden osteoporosis in 25% of patients. Makinen et al. 7 found a prevalence of 28% of osteoporosis and osteopenia in 45% of patients scheduled for THA, besides a 36% prevalence of vitamin D deficiency. These two studies evaluated a population formed only by women, which explains the higher prevalence of osteopenia and osteoporosis they found. Our study, however, included 44% of men who, in general, have lower prevalence of osteoporosis. Another important finding was the difference between the values of bone mineral density of the osteoarthritic hip and contralateral hip, with higher densities in the sick hip. This can be explained by the presence of bone sclerosis in the affected joint. This finding may also explain the lower prevalence of femoral neck fractures in patients with hip osteoarthritis. 18 Lingard et al. 6 found a 23% prevalence of osteoporosis among