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Response to the Letter From Drs Chiu and Yau
132
The Journal of Arthroplasty Vol. 20 No. 1 January 2005
tightness in extension, resulting in significant correction of varus deformity. Dixon et al suggested that if the gap in the extension were still trapezoidal after an appropriate bone cut and medial soft tissue release, b...the trial components were removed and a tibial tray was selected one size smaller than traditionally selected...[The] downsized tray was then lateralized to the lateral tibial cortical margin and the remaining medial tibial overhang was removed flush with the medial edge of the tibial tray....Q If we interpret this correctly, the femoral rotation is first set with the cuts made as guided by the transepicondylar axis and the flexion gap symmetry. The resection of the uncapped medial tibial plateau is done after such bone cuts. Although the described technique can convert a trapezoidal extension gap into a rectangular one, we are worried that the femoral rotation, which has been set before resection of the uncapped bone, may be adversely affected. In other words, the once-rectangular flexion gap may become trapezoidal with the resection of the uncapped medial bone. It is not uncommon to see stretching out of the lateral collateral ligament in a knee with a varus deformity of the severity as shown in Fig. 2 of the article. We find that in such a situation, releasing the medial collateral ligament alone may not be enough. In our institution, we would consider using a varus-valgus constraint prosthesis if there is a significant stretching out of the lateral collateral ligament. It would appear that Dixon et al balanced all their patients’ knees by using only the techniques they described and standard knee prostheses. However, readers would find it helpful had Dixon et al elaborated on the tips and tricks of dealing with an elongated lateral collateral ligament. Downsizing the tibial tray includes reducing both the mediolateral and anteroposterior dimensions of the prosthesis. Therefore, the tibial tray may not sit over the remaining cortical rim. We worry that such inadequate bone support medially and, perhaps, posteriorly may increase the risk of tibial component loosening. The fact that Dixon et al found no loosening after an average follow-up period of 3.5 years is encouraging. However, the authors did not mention whether any extra measure such as a stem extension was used routinely to enhance tibial fixation, although Fig. 2 in the article shows that a cemented stemmed tibial component was used. Although the indication for stem use could have been the tibial defect and subsequent use of the metal wedge augmentation, the stem might have helped dissipate the stress and thus might have accounted for the absence of mechanical failure. Kwong Yuen Chiu, MD, Wai Pan Yau, MD, Department of Orthopedics and Traumatology Queen Mary Hospital University of Hong Kong Hong Kong n 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.arth.2004.10.003
In Reply: We thank Drs Chiu and Yau for their thoughtful comments. We are in close agreement with their observations. Regarding a concomitant flexion contracture, we find that removal of the uncapped posteromedial tibial bone (often largely posterior tibial osteophytes) helps to correct a flexion contracture as well as a varus deformity by the same mechanism. Drs Chiu and Yau correctly point out that the resection technique affects the flexion gap as well as the extension gap. For this reason, we try to balance a severe varus knee in extension before establishing a rectangular gap in flexion. In the less common case where the resection technique is used after femoral rotation has been established, the medial side of the flexion gap, of course, is the side that is affected. A thicker insert will be necessary to stabilize the medial side. Fortunately, the lateral tissues in most knees are pliable enough to accept this thicker insert and no formal adjustment of the lateral tissues is necessary. We agree that residual lateral laxity can be a potential problem in the severe varus knee. In our experience, it is not clinically significant if 2 criteria are present. First, the mechanical axis of the knee has to have been corrected to neutral or slight valgus. Second, when the knee is allowed to rest in full extension, the imbalance does not allow the lateral side to passively gap open. In other words, the residual lateral laxity can only be demonstrated by actively applying a varus stress. If these 2 criteria are not present, more medial release and a thicker insert are necessary. Alternatively, as suggested by Drs Chiu and Yau, a varus/valgus-constrained articulation may be used in the very elderly or sedentary patient. Finally, we are not concerned with the threat of tibial loosening because of the downsizing alone. We believe in maximally capping the available tibial bone without prosthetic overhang to maximize the distribution of weight-bearing forces across the fixation interface. We think of maximizing the percentage of available bone that is capped, not of achieving bcortical contact.Q We will use extended stems (usually cemented) in association with augments and/or any residual medial deficiency because of poor bone quality (such as bone cysts that required curettage and grafting). Richard D. Scott, MD, Department of Orthopaedic Surgery Brigham and Womens Hospital Boston, Massachusetts n 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.arth.2004.10.004
The Journal of Arthroplasty Vol. 20 No. 1 January 2005
tightness in extension, resulting in significant correction of varus deformity. Dixon et al suggested that if the gap in the extension were still trapezoidal after an appropriate bone cut and medial soft tissue release, b...the trial components were removed and a tibial tray was selected one size smaller than traditionally selected...[The] downsized tray was then lateralized to the lateral tibial cortical margin and the remaining medial tibial overhang was removed flush with the medial edge of the tibial tray....Q If we interpret this correctly, the femoral rotation is first set with the cuts made as guided by the transepicondylar axis and the flexion gap symmetry. The resection of the uncapped medial tibial plateau is done after such bone cuts. Although the described technique can convert a trapezoidal extension gap into a rectangular one, we are worried that the femoral rotation, which has been set before resection of the uncapped bone, may be adversely affected. In other words, the once-rectangular flexion gap may become trapezoidal with the resection of the uncapped medial bone. It is not uncommon to see stretching out of the lateral collateral ligament in a knee with a varus deformity of the severity as shown in Fig. 2 of the article. We find that in such a situation, releasing the medial collateral ligament alone may not be enough. In our institution, we would consider using a varus-valgus constraint prosthesis if there is a significant stretching out of the lateral collateral ligament. It would appear that Dixon et al balanced all their patients’ knees by using only the techniques they described and standard knee prostheses. However, readers would find it helpful had Dixon et al elaborated on the tips and tricks of dealing with an elongated lateral collateral ligament. Downsizing the tibial tray includes reducing both the mediolateral and anteroposterior dimensions of the prosthesis. Therefore, the tibial tray may not sit over the remaining cortical rim. We worry that such inadequate bone support medially and, perhaps, posteriorly may increase the risk of tibial component loosening. The fact that Dixon et al found no loosening after an average follow-up period of 3.5 years is encouraging. However, the authors did not mention whether any extra measure such as a stem extension was used routinely to enhance tibial fixation, although Fig. 2 in the article shows that a cemented stemmed tibial component was used. Although the indication for stem use could have been the tibial defect and subsequent use of the metal wedge augmentation, the stem might have helped dissipate the stress and thus might have accounted for the absence of mechanical failure. Kwong Yuen Chiu, MD, Wai Pan Yau, MD, Department of Orthopedics and Traumatology Queen Mary Hospital University of Hong Kong Hong Kong n 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.arth.2004.10.003
In Reply: We thank Drs Chiu and Yau for their thoughtful comments. We are in close agreement with their observations. Regarding a concomitant flexion contracture, we find that removal of the uncapped posteromedial tibial bone (often largely posterior tibial osteophytes) helps to correct a flexion contracture as well as a varus deformity by the same mechanism. Drs Chiu and Yau correctly point out that the resection technique affects the flexion gap as well as the extension gap. For this reason, we try to balance a severe varus knee in extension before establishing a rectangular gap in flexion. In the less common case where the resection technique is used after femoral rotation has been established, the medial side of the flexion gap, of course, is the side that is affected. A thicker insert will be necessary to stabilize the medial side. Fortunately, the lateral tissues in most knees are pliable enough to accept this thicker insert and no formal adjustment of the lateral tissues is necessary. We agree that residual lateral laxity can be a potential problem in the severe varus knee. In our experience, it is not clinically significant if 2 criteria are present. First, the mechanical axis of the knee has to have been corrected to neutral or slight valgus. Second, when the knee is allowed to rest in full extension, the imbalance does not allow the lateral side to passively gap open. In other words, the residual lateral laxity can only be demonstrated by actively applying a varus stress. If these 2 criteria are not present, more medial release and a thicker insert are necessary. Alternatively, as suggested by Drs Chiu and Yau, a varus/valgus-constrained articulation may be used in the very elderly or sedentary patient. Finally, we are not concerned with the threat of tibial loosening because of the downsizing alone. We believe in maximally capping the available tibial bone without prosthetic overhang to maximize the distribution of weight-bearing forces across the fixation interface. We think of maximizing the percentage of available bone that is capped, not of achieving bcortical contact.Q We will use extended stems (usually cemented) in association with augments and/or any residual medial deficiency because of poor bone quality (such as bone cysts that required curettage and grafting). Richard D. Scott, MD, Department of Orthopaedic Surgery Brigham and Womens Hospital Boston, Massachusetts n 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.arth.2004.10.004