IntroductionAccurate and comprehensive anthropometric data for the lumbar spine vertebrae, a frequent site for implantation surgery, are incomplete at present. Information on the precise dimensions of the lower lumbar vertebrae is, however, essential, for the rational design and development of spinal implants and instrumentation such as pedicle screws and, in particular, with the evolution towards robotic surgery. Previous studies have depended on direct measurements from plain X-ray films [9,12,13,23], or from computed tomographic (CT) scans [8,11,26,34,36]. A few reports have involved the analysis of cadaveric specimens [1,7,24,27,29]. The value of the data has depended on the number of samples and the accuracy of Abstract The precise dimensions of the lumbar vertebrae and discs are critical for the production of appropriate spinal implants. Unfortunately, existing databases of vertebral and intervertebral dimensions are limited either in accuracy, study population or parameters recorded. The objective of this study is to provide a large and accurate database of lumbar spinal characteristics from 126 digitised computed tomographic (CT) images, reviewed using the Picture Archiving Communication System (PACS) coupled with its internal measuring instrumentation. These CT images were obtained from patients with low back pain attending the spinal clinic at the Hammersmith Hospitals NHS Trust. Measurements of various aspects of vertebral dimensions and geometry were recorded, including vertebral and intervertebral disc height. The results from this study indicated that the depth and width of the vertebral endplate increased from the third to the fifth lumbar vertebra. Anterior vertebral height remained the same from the third to the fifth vertebra, but the posterior vertebral height decreased. Mean disc height in the lower lumbar segments was 11.6 ± 1.8 mm for the L3/4 disc, 11.3 ± 2.1 mm for the L4/5, and 10.7 ± 2.1 mm for the L5/S1 level. The average circumference of the lower endplate of the fourth lumbar vertebra was 141 mm and the average surface area was 1492 mm 2 . An increasing pedicle width from a mean of 9.6 ± 2.2 mm at L3 through to 16.2 ± 2.8 mm at L5 was noted. A comprehensive database of vertebral and intervertebral dimensions was generated from 378 lumbar vertebrae from 126 patients measured with a precise digital technique. These results are invaluable in establishing an anthropometric model of the human lumbar spine, and provide useful data for anatomical research. In addition this is important information for the scientific planning of spinal surgery and for the design of spinal implants.

Front crawl swimmers often restrict the number of breaths they take during a race because of the possible adverse effects of the breathing action on resistance or stroke mechanics. The aim of this study was to determine whether differences exist in the kinematics of the trunk and upper extremity used during preferred-side breathing and breath-holding front crawl swimming. Six male swimmers performed trials at their 200 m race pace under breathing and breath-holding conditions. The underwater arm stroke was filmed from the front and side using video cameras suspended over periscope systems. Video recordings were digitized at 50 Hz and the three-dimensional coordinates of the upper extremity obtained using a direct linear transformation algorithm. Body roll angles were obtained by digitizing video recordings of a balsa wood fin attached to the swimmers' backs. The swimmers performed the breathing action without any decrement in stroke length (mean +/- s: breathing 2.24 +/- 0.27 m; breath-holding 2.15 +/- 0.22 m). Stroke widths were similar in the breathing (0.28 +/- 0.07 m) and breath-holding (0.27 +/- 0.07 m) trials, despite swimmers rolling further when taking a breath (66 +/- 5 degrees) than when not (57 +/- 4 degrees). The timing of the four underwater phases of the stroke was also unaffected by the breathing action, with swimmers rolling back towards the neutral position during the insweep phase. In conclusion, the results suggest that front crawl swimmers can perform the breathing action without it interfering with their basic stroke parameters. The insweep phase of the stroke assists body roll and not vice versa as suggested in previous studies.

SUMMARY During the period 1950-81, 678 cases of primary hyperparathyroidism were surgically treated at University College Hospital, London. The causes were a single adenoma in 575, two adenomas in 25, carcinoma in 20 (two of which had coexistent adenomas), chief cell hyperplasia in 56, and water clear cell hyperplasia in two. Histological diagnosis is not difficult except in some cases of carcinoma and in a few in which differentiation between recurrent hyperplasia and recurrent carcinoma is exceptionally difficult. In this paper we review all the cases of primary carcinoma of the parathyroid seen during this period to define those pathological, features of value in the diagnosis.Two cardinal features for diagnosis of carcinoma at any site are local invasion and metastasis. In time, consistent association of certain macroscopic and histological features in a particular organ with this behaviour pattern may be used to diagnose carcinoma before infiltration and metastases have occurred. This approach has presented some difficulty with carcinoma of the parathyroid because it is uncommon and few people have the opportunity to study adequate numbers themselves. Moreover, metastasis is rare in carcinoma of the parathyroid. Further, although local recurrence may indicate a carcinoma, it may also occur because hyperplasia of all four parathyroids has been insufficiently resected. Again, although the typical adenoma and the typical carcinoma are quite distinct in their features, some tumours are difficult to categorise.In the AFIP Fascicle in 1952' the importance of mitoses, a trabecular architecture, adherence to surrounding tissues, and to some extent capsular invasion and the extension of fibrous trabeculae from the capsule into the tumour were emphasised in the diagnosis of carcinoma. In the revised Fascicle in 1978,2 in addition to these features, the grey-tan colour, the hard consistency, and the lobulated cut surface of many carcinomas were emphasised.2 The presence of mitoses within parenchymal cells was considered the single most valuable microscopic criterion, while cellular atypia and variation were not.

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Laser ablation of bone and ligament for nerve root decompression using the Ho: YAG laser may offer substantial advantages, but the risk of serious complication may only be avoided if the technique is combined with saline irrigation.