[Measurement of femoral head diameter: a clinical study]

Abstract

PURPOSE OF THE STUDY To present the results of a clinical study concerned with the evaluation of femoral head size based on intra-operative measurement during hip hemiarthroplasty. MATERIAL AND METHODS The group studied comprised 801 patients who underwent hip hemiarthroplasty for femoral neck fracture in the period from 1997 to 2007. There were 638 women (79.7 %) and 282 men (20.3 %); the average age was 82.2 years (women, 82.2; men, 81.4). The procedure was indicated in elderly patients and was carried out under general anaesthesia or with spinal anaesthesia from the Kocher - Langenbeck approach. The diameter of a femoral head with preserved cartilage was measured with a sliding meter or circular template. The size of each cervico-capital prosthesis used for hip hemiarthroplasty was noted in the written operative report and subsequently appeared in the patients' database. These prospectively collected data were retrospectively evaluated. Statistical analysis of the categorical data was done by the Chi-square test of independence in a contingency table, using the Epi Info software package. The level of significance was 5 %. RESULTS The group included a significantly higher number of women than that of men (p<0.001). The diameter of implanted cervico- capital prostheses ranged from 38 mm to 60 mm, with a range of 38-58 mm in women and 42-60 mm in men. The cervico-capital prostheses most frequently implanted in women had 42 mm and 44-48 mm in diameter, and this was statistically significant (p=0.019 and p<0.001, respectively); in men the prostheses most frequently used were 50-56 mm in diameter (p<0.001). The average size of the cervico-capital prosthesis for the whole group was 47.3 mm in diameter; in women it was 46.3 mm and in men 51.1 mm (difference, 4.8 mm). DISCUSSION The femoral heads measured were only those used in elderly patients, which is the chief shortcomming of our study that is, however, in agreement with the common indication scheme for hip hemiarthroplasty. In addition, in case the diameter was an odd number, a prosthesis having an even number in diameter was eventually used according to the manufacturers' offer. This too can be regarded as a partial disadvantage of the method used. However, the large size of our patient group allowed for a normal Gaussian distribution and thus the effect of odd and even dimensions on the measurement results was reduced to a minimum. The advantage of the study is that the measuring of diameters of femoral heads including cartilage provided real values in contrast to the results based on anatomical specimens usually lacking any cartilage. The values obtained in the study are in agreement with the current relevant literature of the early 20th century. CONCLUSIONS Based on the measurements of femoral head size in hip hemiarthroplasty it can be concluded that the average size of the femoral head is markedly larger in men than in women. During the 11-year period the marginal femoral head sizes, which are regularly on offer, were used only occasionally. Therefore, the range of sizes currently available can be considered sufficient for orthopaedic surgery. Key words: femoral head size, hip hemiarthroplasty, femoral neck fracture.