Stiffness and laxity of the knee--the contributions of the supporting structures. A quantitative in vitro study.

Thirty-five normal cadaver knees were tested manually in six positions of the knee using apparatus designed to measure the moment-rotation responses for both varus-valgus angulation and torsion of the tibia, as well as the force-displacement responses for anterior-posterior movement of the tibia. The responses of all knees to all modes of loading were non-linear, reflecting increasing stiffness. With the knee at full extension, stiffness was maximum and laxity was minimum. Hence, it was in this position that changes in stability (laxity and stiffness) were best demonstrated when ligament structures were sectioned. Differences in laxity were observed between right and left knees of intact paired specimens. Torsional laxity and internal rotation stiffness were most affected by sectioning the medial collateral ligament, while external rotation stiffness was only affected by division of both the lateral collateral ligament and the posterior capsule. Varus-valgus laxity was relatively unaffected by removal of the menisci or section of the cruciate ligaments but increased greatly when either collateral ligament was cut. The medial collateral ligament was the main contributor to valgus stiffness, whereas the lateral collateral ligament had no measurable effect on varus stiffness. Anterior-posterior stability was affected to some extent by virtually every sectioning procedure. Isolated section of the anterior cruciate ligament produced the greatest increase in anterior-posterior laxity at full extension and section of the posterior cruciate, the greatest increase at 90 degrees of flexion. Large increases in anterior-posterior laxity were also observed when the medial collateral ligament and posterior capsule were sectioned in combination.

Experimental stabilization of segmental defects in the human femur. A torsional study.

One of each of thirty-five pairs of fresh intact femora were tested to failure in torsion, recording the dynamic torque, the absorbed energy, and the angle of rotation. These results were compared with the results obtained with the contralateral femur, reconstituted after removal of a segment. Intramedullary nails with polymethylmethacrylate cement, strips of titanium mesh with cement, bone plates with and without cement, and multiple Steinmann pins with cement were the reconstituting configurations. Bone plates were the strongest configuration; the failure torques in all cases were limited by the stress concentration effects of the holes in the bone used for screw fixation. The use of cement as an adjunct to single-plate fixation provided some additional strength. The torsional strength of femora fixed with Küntscher and Schneider nails was limited by failure of the cement and bone. The use of titanium mesh with polymethylmethacrylate was less effective, because this composite has a low torsional rigidity. The use of multiple Steinmann pins packed with polymethylmethacrylate in the medullary cavity should be discouraged because severe twisting and fragmentation of the surrounding acrylic will occur at low levels of torque.

Knee morphology as a guide to knee replacement.

The complexity of knee geometry requires correct prosthesis design and size selection for the recipient. This study analyzes the morphological relationships within the knee; 16 linear anatomical parameters were measured on 30 cadaveric knees. The marginal femoral condylar contour was geometrically described by two tangent radii. Standardized radiographic techniques were developed to obtain a modified tunnel and true lateral view of the knee. Subsequently, X-rays were taken from 11 cadaver knees to achieve reproducible magnification factors. From X-rays of 53 normal subjects, 11 comparable linear dimensions were measured. The linear dimensions and condylar contour measurements were analyzed for their interrelationships by computer techniques. The width of the femur was found to be dimensionally related (correlation coefficient significant at the one per cent level) to the measured parameters with the exception of the intercondylar notch and interspinous widths. Using regression analysis, nomograms were developed to predict the linear and marginal femoral contour dimensions from the femur width. The resulting standard deviations were low, ranging from 1.0 mm for ascertaining the tibial width to 3.5 mm for determination of the femoral width at the level of the intercondylar notch. The nomograms we developed will aid the surgeon in a more precise, preoperative, morphological evaluation and may be used as a guide for future knee prosthesis design.