The change in position of the sciatic nerve during the posterior approach to the hip.

The aim of this cadaver study was to identify the change in position of the sciatic nerve during arthroplasty using the posterior surgical approach to the hip. We investigated the position of the nerve during this procedure by dissecting 11 formalin-treated cadavers (22 hips: 12 male, ten female). The distance between the sciatic nerve and the femoral neck was measured before and after dislocation of the hip, and in positions used during the preparation of the femur. The nerve moves closer to the femoral neck when the hip is flexed to > 30° and internally rotated to 90° (90° IR). The mean distance between the nerve and femoral neck was 43.1 mm (standard deviation (sd) 8.7) with the hip at 0° of flexion and 90° IR; this significantly decreased to a mean of 36.1 mm (sd 9.5), 28.8 mm (sd 9.8) and 19.1 mm (sd 9.7) at 30°, 60° and 90° of hip flexion respectively (p < 0.001). In two hips the nerve was in contact with the femoral neck when the hip was flexed to 90°. This study demonstrates that the sciatic nerve becomes closer to the operative field during hip arthroplasty using the posterior approach with progressive flexion of the hip.

A rapid and definitive test for Charcot-Marie-Tooth 1A and hereditary neuropathy with liability to pressure palsies using multiplexed real-time PCR.

Alterations in gene copy number have been shown to cause disease in humans. Two of the most common inherited peripheral neuropathies, Charcot-Marie-Tooth 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), are two such diseases resulting from alteration in gene copy number of the dosage sensitive peripheral myelin protein 22 (PMP22) gene. Many complicated and laborious diagnostic tests exist for the diagnosis of these diseases. The aim of our study was to develop the first quantitative multiplex real-time PCR assay for the diagnosis of CMT1A and HNPP. A total of 160 individuals who were known to have CMT1A, HNPP, or were normal from previous testing were assayed by our multiplex real-time PCR method. The results confirmed the previously determined gene copy number of all patient and control individuals tested. The range of ratio values between the disease and control groups were easily defined. The assay is accurate, simple, and cost effective and can detect a 50% change in gene copy number. This represents an ideal assay for any small diagnostic laboratory.

Frequency of spinocerebellar ataxia types 1, 2, 3, 6, and 7 in Australian patients with spinocerebellar ataxia.

The frequencies of various genetically defined spinocerebellar ataxias (SCAs) vary in different populations presumably due to founder effects. No data have been published on the Australian population. Although predominantly of Anglo-Celtic extraction, Australia has also received considerable influx from southeastern Europe and more recently eastern and southeastern Asia. We examined the frequency of mutations for SCA types 1, 2, 3, 6, and 7 in southeastern Australia. Of 88 pedigrees with multiple-affected members, SCA type 1 (SCA1) accounted for 16%, SCA2 for 6%, SCA3 for 12%, SCA6 for 17%, SCA7 for 2%, and 47% (41 pedigrees) were negative for each of SCA1, 2, 3, and 6. Twenty of the 41 negative pedigrees were also negative for dentatorubralpallidoluysian atrophy, and indeed dentatorubralpallidoluysian atrophy has not been reported in Australia. In addition, no pedigree information was available on a further four patients with SCA1, three patients with SCA2, three patients with SCA3, and three patients with SCA6. One SCA1 and two SCA2 patients had no other known affected family members. In total, of 63 pedigrees or individuals with positive tests, 30% were those with SCA1, 15% with SCA2, 22% with SCA3, 30% with SCA6, and 3% with SCA7. Judging by pedigree names, four of the nine SCA2 positive individuals/pedigrees were of Italian extraction, and four of the 14 SCA3 positive individuals/pedigrees were of Chinese descent, whereas only 1 of the 20 SCA1 positive individuals/pedigrees were non-Anglo-Celtic. These results are in accordance with the known ethnic composition of the Australian population and with gene frequencies in these constituent ethnic groups reported by others. The frequency of large-normal alleles for SCA1 and SCA3 in the population reflects the prevalence of these two diseases, supporting the hypothesis that disease alleles arise by expansion of large-normal alleles.