Standard total knee arthroplasty is initiated with "measured resection" in which the bone that is resected is the same dimension as the prosthesis. In general, exposure is not a problem as these usually have good flexion. Once the measured resections are completed, osteophytes are carefully removed from all segments of the knee. We carefully remove osteophytes from the posterior femoral condyles and circumferentially around the tibial plateau with a curved osteotome and curette (Fig. 5.4). The knee is then evaluated for the space in flexion compared to the space in extension. There will be a wide variation in the discrepancy depending on the amount of deformity, rigidity of fixation, and age of the patient.
To equilibrate the flexion-extension space, a soft tissue release is carried out in stages, checking the extension gap after each step.5-7 First, a periosteal elevator is used to elevate the capsule from the posterior femur (Fig. 5.5). Both the anterior and posterior cruciate attachments from the intercondylar notch of the femur are removed (Fig. 5.6) and the soft tissue capsular attachments in the posterior femur are dissected from the posterior femur (Fig. 5.7). The extension gap is again measured, and if more release is required, the dissection is carried more proximal releasing the gastrocnemius muscle origins from the femur. Again the extension gap is evaluated. If more release is required, we carefully dissect the medial and lateral corners approaching the posterior aspects of the medial and lateral collateral ligaments. We avoid resecting the collateral ligament attachments, although some authors completely skeletalize the distal femur. After all of the posterior capsule, gastrocnemius muscular origins, and posterior
corners have been resected along with the posterior aspects of the collateral ligaments, if the extension gap remains too tight, we will then resect more bone from the distal femur. The additional bone resection of the distal femur is done last because it significantly affects the joint mechanics by migrating the joint line proximally.
The soft tissue dissection of the posterior aspect of the joint and modest proximal migration of the joint line will correct most of the deformity and resolve the flexion-extension gap inequality. If the joint is still too tight in extension and/or too loose in flexion, the choice of a prosthesis with a high central trial spike, such as a total condylar III prosthesis, can be utilized in order to protect the knee from instability and subluxation. The inability to achieve full correction usually occurs in extremely disabled patients who have significant preoperative polyarticular deformity and who will not be achieving normal activity in the postoperative period. Therefore this will not be a major functional compromise.
At the end of surgery we like to have almost all of the deformity corrected. With the lesser flexion contractures we expect the knee to come to full extension. With flexion contractures greater than 70 degrees a few degrees of flexion may remain at surgery.8 In general, we work to avoid residual flexion contracture at the end of surgery.
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