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The varus-valgus stability of M knees with unicompartmental osteoarthritis was studied in vivo at the time of total knee replacement. Intact osteoarthritic knees had an average of 11.0" of varus-valgus motion. Removal of osteophytes from the osteoarthritic compartment significantly increased the motion to 13.1" (P < 0.05), while subsequent removal of osteophytes from the nonosteoarthritic compartment further increased motion to 14.7" ( P < 0.025). In primarily unicompartmental osteoarthritis, marginal osteophytes appear to stabilize osteoarthritic knees, but can cause fixed deformity.

Strain in the anteromedial fibers of the anterior cruciate ligament [ACL(am)] was studied in six cadaver knees. ACL(am) strain was measured in five knees during the application of isometric quadriceps forces alone and simultaneously applied isometric quadriceps and hamstrings forces at 10 degrees increments from 0 degrees to 90 degrees of knee flexion. ACL(am) strain during muscle loading was measured with respect to the ACL(am) strain measured with the knee in its resting position (neutral or near neutral position). A sixth knee was used to investigate the reproducibility of the resting position and quadriceps-induced ACL(am) strains. The strains induced in the ACL(am) by the quadriceps were significantly greater than 0 at knee flexion angles from 0 to 40 degrees and not significantly different from 0 for 50 to 90 degrees. The ACL(am) strains induced by simultaneously applied hamstrings and quadriceps forces were not significantly different from 0 at any of the knee flexion angles tested. Simultaneously applied hamstrings and quadriceps forces significantly reduced ACL(am) strain at 10, 20, and 90 degrees of knee flexion compared to the ACL(am) strain induced by quadriceps forces alone. The hamstrings are potentially capable of both significantly reducing and negating quadriceps-induced ACL(am) strain at 10 and 20 degrees of knee flexion.

The biomechanical effectiveness of an extraarticular ACL reconstruction, an intraarticular ACL reconstruction, and the combination of these on both anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. The extraarticular reconstruction consisted of the Müller anterolateral femorotibial ligament iliotibial band tenodesis, and the intraarticular reconstruction used the middle third of the patellar tendon in the manner of Clancy. The extraarticular reconstruction was found to overconstrain internal tibial rotation of the ACL excised knee between 30 degrees and 90 degrees (P less than 0.05). While the isolated extraarticular reconstruction did not return normal anterior stability to the ACL deficient knee (P less than 0.05), it did significantly reduce the anterior laxity of the ACL deficient knee between 30 degrees and 90 degrees of knee flexion (P less than 0.05). For the combined reconstruction, the intraarticular procedure was performed and then only enough tension was applied to the extraarticular reconstruction to take up slack in the tenodesis without shifting the rotatory position of the tibia from that produced by the intraarticular procedure alone. Neither the intraarticular reconstruction nor the combined procedure resulted in any significant shifts from normal (P less than 0.05) in the rotatory position of the unloaded tibia; during loading neither resulted in rotational displacements significantly different from normal; and both of these procedures reduced the increased anterior laxity of the ACL deficient knee to a level not statistically different from normal. Because the extraarticular reconstruction shared the load when performed with the intraarticular reconstruction as part of a combined procedure, we concluded that it would be useful as an adjunctive procedure in appropriate clinical situations.

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We tested the effect of intraarticular reconstructions of the anterior cruciate ligament alone and in combination with extraarticular reconstructions in 10 cadaveric knees. These knees had anterior cruciate ligament deficiency alone or in combination with anterolateral capsuloligamentous deficiencies. In the knees with combined injury, intraarticular reconstruction returned anterior stability to levels not significantly different from levels found for the knees deficient in the anterior cruciate ligament alone and treated with this procedure. After intraarticular reconstruction, rotational stability of the knee with combined injuries failed to return to the levels seen in the knee with isolated anterior cruciate ligament deficiencies that underwent the same treatment. When a tenodesis with either 0 N or 22 N of tension was added to the intraarticular reconstruction in the knee with combined injuries, we found that excessive internal rotation significantly decreased at all angles of flexion, except at full extension with 0 N of tension. In addition, the extraarticular reconstruction with 22 N of tension in the tenodesis overconstrained the knee in internal rotation between 30 degrees and 90 degrees of knee flexion. The tenodesis with 0 N of tension overconstrained the knee at only 60 degrees and 90 degrees of flexion. These results suggest extraarticular reconstruction as an adjunct to the intraarticular operation for the knee with anterior cruciate ligament and anterolateral structural injuries. The results also suggest that the surgeon can affect anterior and rotational laxity by adjusting the tension in the tenodesis.

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