Seth Levitz | PubMed Health

PubMed2005

Retrograde (volar) scaphoid screw insertion-a quantitative computed tomographic analysis.

PURPOSE: The benefit of placing the screw tip in the center of the proximal pole of the scaphoid is supported by clinical and biomechanical data. In this investigation we attempted to quantify guidelines for optimal screw insertion into the scaphoid through a volar percutaneous approach using measurements from computed tomography images. METHODS: The parameters of safe insertion of a 3.0-mm cannulated-headed screw (Synthes, Paoli, PA) using a volar (retrograde) insertion technique were measured using quantitative computer analysis of computed tomography images of 15 unfractured scaphoids. In the coronal plane the average screw length for the most radial, most ulnar, and intermediate paths for safe screw insertion and the radial clearance of the trapezium were measured. In the sagittal planes defined by these screw paths the length of the screw, the length and depth of the concavity on the volar surface of the scaphoid, and the distance between a line corresponding to the center of the screw path and the volar surface of the trapezium were measured. RESULTS: Significant differences (1-way analysis of variance) were measured for the average screw lengths for different screw insertion paths in both the coronal and sagittal planes (with the shortest screw lengths observed for the most ulnar starting points) and for the volar clearance of the trapezium, which was greater for a radial screw path. The intermediate screw path-a measure of optimal screw insertion-passed radial to the radial edge of the trapezium in 10 of 15 patients (67%) with an average clearance of 3.9 mm (range, 1.1-7.9 mm) in those patients. The depth of the concavity on the volar surface of the scaphoid averaged 1.6, 2.0, and 2.5 mm in the 3 sagittal planes. CONCLUSIONS: Screw fixation of the scaphoid through a volar approach is hindered by the trapezium, risks cutout through the concavity in the volar surface of the scaphoid, and is most likely to violate the dorsoulnar aspect of the radiocarpal articular surface of the scaphoid if the screw is too long. A relatively radial starting point facilitates placement of the screw tip in the center of the proximal pole and helps avoid the trapezium but drilling or partial excision of the trapezium often may be necessary for optimal screw placement.

Adolescent↗

PubMed2005

Both scanning plane and observer affect measurements of scaphoid deformity.

PURPOSE: The influence of angular deformity of the scaphoid on wrist function and arthrosis is debated and the reliability of the described quantitative measurements of deformity has been questioned. We hypothesized that the inherent imprecision with which computed tomography scanning planes are selected introduces another source of variability in measurements of scaphoid deformity, further diminishing their reliability. METHODS: Sagittal plane images of 15 computed tomograms of normal scaphoids were evaluated in 3 different reconstruction planes. Four observers measured the lateral intrascaphoid angle, the dorsal cortical angle, and the height-to-length ratio of the 45 images in random order and then measured them again in a distinct random order 2 weeks later. The variability of each observer's measurements (intraobserver reliability) was evaluated with Pearson correlation coefficients. The agreement of the measurements made by the 4 observers (interobserver reliability) and the agreement of the measurements of the same bone in different reconstruction planes (interplane reliability) were evaluated using interclass correlation coefficients. RESULTS: The intraobserver reliability was poor for 27 of 36 comparisons. The interobserver reliability of the dorsal cortical angle and the intrascaphoid angle was poor for all reconstruction planes. The interobserver reliability of the height-to-length ratio was good for 2 planes and poor for the third plane. The interplane reliability was poor for 7 of 12 comparisons, with no single measurement technique remaining consistent for all observers across reconstruction planes. CONCLUSIONS: Quantitative measurements of scaphoid deformity have very limited reliability for individual observers, between different observers, and depending on the plane in which the image of the scaphoid is produced. Even the most reliable measure of deformity (height-to-length ratio) was not consistent between reconstruction planes. Unless more reliable scanning and measurement techniques are developed ideas about the effect of scaphoid deformity on wrist function will remain to a large degree speculative.

Adolescent↗