Purpose: To compare a computer-based program for measuring frontal plane leg alignment with a hand-measuring system.

Methods: Five patterns of frontal limb alignment, simulating full-length radiographs of healthy and malaligned limbs, were drawn in AutoCAD and exported as digital images. The patterns included variations in varus and valgus alignment and joint space slope. Copies of each pattern were given to 7 trained readers for analysis. The readers used a ruler and protractor to measure predefined angles and lengths following an established method which defines limb and joint margin landmarks to derive mechanical and anatomic (shaft) axes. Custom software was used to define the same landmarks on the digital copies of the patterns; the angles and lengths were calculated by the software, replicating the method above. A simple fixed calibration factor was used to convert the digital linear dimensions to their paper equivalent. The order of hand and computer analysis of the 5 patterns was randomized and each was repeated daily for 3 days. Measured angles included hip-knee-ankle (HKA), femoral condylar tangent-hip (CH), tibial plateau tangent-ankle (PA), condylar-plateau (joint orientation-CP) and angles between the femoral mechanical axis (FM), femoral shaft axis (FS), tibial mechanical axis (TM)and tibial shaft axis (TS). Repeated measures analysis of variance was performed to compare the methods, with a significance level set at p< 0.05.

Results: The analysis revealed differences between hand and computer measures in femoral lengths and apparent leg lengths (although these differences were less than 1 mm). Differences between methods were also obtained for CP and FM-FS angles (the differences in angles were less than 1 degree). The variance of the computer measures was the same as (19/55 measures) or significantly less than (35/55 measures) the hand measures, with the exception of angle CH on a single pattern. For all limb length measures and the angles HKA, FM-FS, FM-TS and FS-TS there were differences between the readers. There was no difference across days for any measure.

Conclusions: The analysis revealed similar results for limb alignment angles and for limb lengths between hand and computer methods. The computer application improved on the variance obtained with the hand measuring method, indicating a more precise system. Significant differences were found between readers, suggesting the need for standardization of methods for measuring alignment.

A method is described which provides standardised reproducible radiographic images of the lower limb. Anteroposterior and lateral radiographs are digitised and processed by computer to provide graphic/numeric displays of angles and linear measurements, relating the centre points of the hip, knee, and ankle. Two cases illustrate how surgical planning is facilitated when standardised data are available. These data confirm the close relationship between postoperative limb alignment and positioning of prosthetic elements.

Some arthritic knees with varus deformity show excessive valgus angulation of the femoral joint surface with proximal tibia vara. This causes a downward and medial inclination of the articular surfaces in the coronal plane. The patients we studied had a medial shift of the standing load-bearing axis, and arthritic changes mainly in the medial compartment. Some also had lateral tibial subluxation with twisting of the distal femur and proximal tibia in opposite directions. We assessed the articular geometry by precise radiographic analysis, and compared the results with those in normal volunteers and a group of osteoarthritic patients. The prevalence of this type of deformity in our osteoarthritic patients was 11.5%; its recognition allows the use of specific operative correction that may include double osteotomy or the precise orientation of prosthetic components.

We studied the morphology of the haversian canals in the osteopenic cortical bone of the medial femoral neck from patients with rheumatoid arthritis and compared the findings with those in patients with osteoarthritis and with uncomplicated coxa valga. In the rheumatoid bone, the diameters of the canals were larger and many more contained osteoclasts. Fewer haversian canals showed only lining cells than in the osteoarthritic or coxa valga patients. In bone from rheumatoid patients, especially in canals with osteoclasts, small blood vessels were frequently lined by tall endothelial cells with an infiltration of mononuclear cells. These morphological differences are discussed with reference to the possible mechanisms of loss of cortical bone in rheumatoid arthritis and other conditions.