Primary Knee Replacement: Management and Alternatives

Medscape Orthopaedics & Sports Medicine eJourn. 2000;4(2) 

In This Article

Surgical Technical Tips for Primary Total Knee Replacements

Dr. Michael Ries, of the University of California in San Francisco, discussed externally rotating the femoral component in total knee replacements. Although external rotation of the femoral component does balance the flexion space, there are potential problems that may occur, such as notching of the anterior lateral cortex and incongruity in rotation of the knee in extension. It was suggested that an implant with asymmetrical posterior condyles be used, so that it filled the trapezoidal flexion space without resulting in external rotation of the implant.

Both Dr. Ries and Dr. Laskin discussed long-term results using this type of implant. They experienced a lateral release rate of only 2%; all of these patients had pre-existing patellar subluxation. Dr. Laskin expanded on this by describing a study that evaluated the configuration of the flexion space postoperatively. The results demonstrated that in approximately 96% of cases, the space was adequately filled by this trapezoidal type of implant. It was determined that the presence of congruity of these knees both in flexion and in extension was an important factor and that this method of balancing the flexion space had many advantages over the traditional method of externally rotating the femoral component.

Dr. Laskin also discussed balancing the flexion and extension spaces and the surgical techniques needed to do this. He described the surgical technique of measured femoral resection and measured tibial resection combined with flexion and extension space balancing. At the completion of this surgical procedure, the flexion and extension spaces must be completely filled by their respective implants and should be equal in size or within 1 to 2 mm of each other in size. In situations where the flexion space is found to be smaller than the extension space with the trial implants in place, the flexion space should be enlarged by downsizing the AP diameter of the femoral component used. In situations where the flexion space is larger than the extension space, he recommended resecting a bit more femur and inserting a thicker implant to fill both the larger flexion and extension spaces.

Dr. Whiteside presented a paper on surgical tips to increase range of motion during knee replacement, such as (1) ensuring proper tracking of the patella by avoiding overstuffing of the patella femoral groove, and (2) removal of the posterior femoral osteophytes.

These osteophytes can limit both flexion and extension of the knee. They are easily removed by a curved osteotome passed around the posterior femoral condyles after the condyles themselves have been resected.

Several speakers described how to elevate some of the soft tissue from the posterior aspect of the femoral condyles, even in those knees that do not have osteophytes. This maneuver alone tends to increase the potential flexion space posteriorly and will allow further flexion.

Dr. Whiteside expressed his belief that posterior sloping of the tibial component increases flexion as well. Likewise, avoidance of oversizing of the femoral component was important to optimize flexion.

Dr. Cecil Rorabeck presented techniques to expose the tight knee, especially during revisions. His algorithm calls for performing a lateral release; if this is ineffective, a rectus snip should be attempted. If the patella still cannot be everted for adequate exposure, a formalized quadriceps turndown or a tibial tubercle osteotomy should be attempted.

Dr. Rorabeck said that he would perform the tibial tubercle osteotomy rather than the formalized quadriceps turndown because of the lower complication rate. Also, with a formalized quadriceps turndown, there is the potential for avascular changes in the patella. He described the method of subsequent fixation of the tubercle osteotomy using 3 double-stranded metal wires, one going through the tubercle fragment and 2 going around it.

Correction of Soft Tissue Deformities. The final 3 papers related to the correction of soft tissue deformities during total knee replacement. Dr. Jan Victor of Brugge, Belgium, discussed the varus knee and the necessity for a sequential release of the structures that were tight. For those knees with a varus contracture in extension, the tight structures that would require release included the semimembranosis tendon, the posterior oblique ligament, and the posterior medial capsule.

Dr. Victor stated that, at times, there will be laxity on the lateral structures of the knee associated with the tight varus deformity. The choices in this situation are to accept the lateral laxity, continue to release the medial side, elongate it to the length of the lateral laxed structures, or advance the lateral structures to tighten them. He suggested that one should accept some mild laxity of the lateral structures in a severe varus knee after the main portion of the contracture is released.

Dr. Kelly Vince of the University of Southern California described his approach to the valgus knee and the selective releases that he performed for this. Although the valgus deformity was accentuated by the hypoplasia of the lateral femoral condyle both distally and posteriorly, he suggested that the disabling pathology was on the medial side, because that was the area that required advancement or tightening. Therefore, he suggests using the standard medium parapatellar approach for valgus knees rather than the lateral parapatellar approach. He was also concerned that use of the lateral parapatellar approach could jeopardize the extensive mechanism, because it required elevation of a portion of the patella tendon for a patella diversion. He expressed concern that closure was less secure with this approach when compared with the standard medium parapatellar approach.

After the correct static alignment is achieved, he suggested continuing a few degrees beyond neutral for the extremely severe valgus knee. Because the posterior condyles are often asymmetrically eroded, he believes that they are a poor landmark to use for femoral component rotation. He releases the ligaments by placing the knee in extension, placing 2 laminar spreaders to distract the knee, and then selectively releasing, with a pointed 11 blade, those tight structures that can be palpated. A lateral parapatellar release should be used if the patella is maltracking before surgery. However, the mere presence of a valgus deformity should not lead to an increased incidence of lateral release procedures.

The final paper of this session was presented by Dr. Johan Bellemans. He discussed the various methods used to release flexion contracture, including posterior stripping of the femur, removal of osteophytes, and balancing of the medial and lateral soft tissues. He stressed the importance of releasing tissues on the medial and lateral side that are tight in extension, namely the posterior oblique ligament and the semitendinosis on the medial side and the iliotibial band and posterior lateral capsule on the lateral side. He suggested that overresection of the distal femur should not be used unless soft tissue balancing is not successful.