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Gap Tension Affects the Rotation of Femoral Component in Total Knee Arthroplasty
e172
2013 ISAKOS ABSTRACTS
resection techniques proved equally reliable and accurate in determining femoral component rotation in TKA. There was a tendency towards more external rotation in the gapbalancing group. However, this difference was small (0.71 ) and not statistically significant. The number of outliers for the ‘adapted’ measured resection technique was much lower than reported in literature with ’classic’ measured resection. Paper #231: Gap Tension Affects the Rotation of Femoral Component in Total Knee Arthroplasty SAHNGHOON LEE, MD, PHD, KOREA PRESENTING AUTHOR SAE HYUNG CHUN, MD, KOREA JOON KYU LEE, MD, PHD, KOREA TAE WOO KIM, MD, KOREA SE HYUK IM, MD, KOREA SANG CHEOL SEONG, MD, PHD, KOREA MYUNG CHUL LEE, MD, PHD, KOREA $ Seoul National University College of Medicine, Seoul, Korea
SUMMARY The use of excessive tension of 30 lb with tensor device resulted in externally-rotated femoral component and frequent outliers. ABSTRACT DATA Introduction: In total knee arthroplasty (TKA), the femoral component rotation is a very important factor in the flexion stability and biomechanics of the knee joint. However, it is still unclear how much tension is appropriate when performing TKA. In this retrospective matched pair study, we analyzed the femoral component rotation in postoperative CT scan of 150 TKAs using gap technique of three different amounts of gap tension. Methods: One hundred and fifty primary knee osteoarthritis patients who underwent total knee arthroplasty and followed up for more than 2 years were included in this study. The patients were divided into the three groups according to the method of gap tensioning. The Group 1 was the patients who had undergone TKAs by conventional gap technique using their own gravity of lower leg. In the Group 2, a gap tensioning device which was set at 20 lb was used. In the Group 3, the tensioning device set at 30 lb was used. Each group composed of 50 TKAs and was matched each other by age, sex, body mass index (BMI), range of motion, severity of deformity, clinical and functional Knee Society score, Hospital for Special Surgery score and WOMAC score. The femoral component rotation was measured on the basis of clinical transepicondylar axis (TEA) on the postoperative CT scan and the outliers were evaluated whose femoral component rotation diverging from the epicondylar axis more than 3 degrees. Results: The mean femoral component rotation was -0.82 2.44 in Group 1, -0.40 2.22 in Group 2 and 1.37 2.70 in Group 3. The rotation in Group 3 was different from those in Group 1 and 2 (p¼0.001, p¼0.001), although there was no statistical difference between Group 1 and 2 (p>0.05). The outliers were more frequent in Group 3 (18% in Group 1, 18% in Group 2 and 36% in Group 3, chi2¼0.043).
Discussion and Conclusion: The femoral component rotated externally as the tension increased in TKA when the soft tissue gap tensioning technique was used in bone cutting, suggesting abnormal widening of lateral flexion gap was expected when the excess tension was applied. The use of tensor device set at 30lb resulted in externallyrotated femoral component and frequent outliers. It may be appropriate to use the gravity of the lower leg or the tensor device set at 20lb to obtain optimal femoral component rotation. Paper #232: Comparative Study of Radiological and Functional Outcome After TKA Using the Measured Resection and Balanced Gap Technique JONG-KEUN SEON, MD, KOREA PRESENTING AUTHOR $ Chonnam National University Hwasun Hospital, Hwasun-gun, Jeollanamdo, South Korea
SUMMARY Both measured resection and balanced gap techniques can achieve good stability. ABSTRACT DATA Introduction: Stability of total knee arthroplasty (TKA) is dependent on correct and precise rotation of the femoral component. Multiple differing surgical techniques are currently utilized to perform total knee arthroplasty. There are two techniques of achieving soft gap balancing in TKA; a measured resection technique and a balanced gap technique. In this prospective comparative study, the authors evaluated rotational alignments of femoral components and flexion stabilities after TKA performed using the measured resection or gap balanced technique and compared findings. In additional, functional outcomes obtained using the two techniques were compared after a minimum follow-up of 2 years. Methods: Seventy-two consecutive patients, who were awaiting unilateral TKAs, were allocated alternatively to either the TKA using measured resection or using balanced gap techniques. Eight patients were excluded from this study (2 patients due to refusal to participate in the study and 4 patients due to loss of follow-up). This left sixty-four TKAs (32 TKA by measured resection and 32 by balanced gap) with a minimum of 2 years. At final follow-up, valgus and varus laxities at 90 degrees of knee flexion were measured on radiographs taken under valgus-varus stress, and total flexion laxity was determined by summing valgus and varus laxities. In addition, the rotations of femoral components from the transepicondyalr axis were also measured on flexion radiographs. To compare clinical outcomes, range of motion, HSS scores, and WOMAC scores at final follow-up were evaluated and compared between two groups. Results: Mean varus laxities were 5.1 in the measured resection group and 5.7 in the balanced gap group, and mean valgus laxities were 4.0 and 3.6 , respectively without statistical significance. Mean total laxities were similar in the two groups (9.1 vs. 9.3, p¼0.89). However, mean femoral component rotations were significantly different in the two groups (measured resection; 0.4 external rotation from tran-sepicondylar axis and balanced gap; 2.1 external rotation (p¼0.003)). The average HSS
2013 ISAKOS ABSTRACTS
resection techniques proved equally reliable and accurate in determining femoral component rotation in TKA. There was a tendency towards more external rotation in the gapbalancing group. However, this difference was small (0.71 ) and not statistically significant. The number of outliers for the ‘adapted’ measured resection technique was much lower than reported in literature with ’classic’ measured resection. Paper #231: Gap Tension Affects the Rotation of Femoral Component in Total Knee Arthroplasty SAHNGHOON LEE, MD, PHD, KOREA PRESENTING AUTHOR SAE HYUNG CHUN, MD, KOREA JOON KYU LEE, MD, PHD, KOREA TAE WOO KIM, MD, KOREA SE HYUK IM, MD, KOREA SANG CHEOL SEONG, MD, PHD, KOREA MYUNG CHUL LEE, MD, PHD, KOREA $ Seoul National University College of Medicine, Seoul, Korea
SUMMARY The use of excessive tension of 30 lb with tensor device resulted in externally-rotated femoral component and frequent outliers. ABSTRACT DATA Introduction: In total knee arthroplasty (TKA), the femoral component rotation is a very important factor in the flexion stability and biomechanics of the knee joint. However, it is still unclear how much tension is appropriate when performing TKA. In this retrospective matched pair study, we analyzed the femoral component rotation in postoperative CT scan of 150 TKAs using gap technique of three different amounts of gap tension. Methods: One hundred and fifty primary knee osteoarthritis patients who underwent total knee arthroplasty and followed up for more than 2 years were included in this study. The patients were divided into the three groups according to the method of gap tensioning. The Group 1 was the patients who had undergone TKAs by conventional gap technique using their own gravity of lower leg. In the Group 2, a gap tensioning device which was set at 20 lb was used. In the Group 3, the tensioning device set at 30 lb was used. Each group composed of 50 TKAs and was matched each other by age, sex, body mass index (BMI), range of motion, severity of deformity, clinical and functional Knee Society score, Hospital for Special Surgery score and WOMAC score. The femoral component rotation was measured on the basis of clinical transepicondylar axis (TEA) on the postoperative CT scan and the outliers were evaluated whose femoral component rotation diverging from the epicondylar axis more than 3 degrees. Results: The mean femoral component rotation was -0.82 2.44 in Group 1, -0.40 2.22 in Group 2 and 1.37 2.70 in Group 3. The rotation in Group 3 was different from those in Group 1 and 2 (p¼0.001, p¼0.001), although there was no statistical difference between Group 1 and 2 (p>0.05). The outliers were more frequent in Group 3 (18% in Group 1, 18% in Group 2 and 36% in Group 3, chi2¼0.043).
Discussion and Conclusion: The femoral component rotated externally as the tension increased in TKA when the soft tissue gap tensioning technique was used in bone cutting, suggesting abnormal widening of lateral flexion gap was expected when the excess tension was applied. The use of tensor device set at 30lb resulted in externallyrotated femoral component and frequent outliers. It may be appropriate to use the gravity of the lower leg or the tensor device set at 20lb to obtain optimal femoral component rotation. Paper #232: Comparative Study of Radiological and Functional Outcome After TKA Using the Measured Resection and Balanced Gap Technique JONG-KEUN SEON, MD, KOREA PRESENTING AUTHOR $ Chonnam National University Hwasun Hospital, Hwasun-gun, Jeollanamdo, South Korea
SUMMARY Both measured resection and balanced gap techniques can achieve good stability. ABSTRACT DATA Introduction: Stability of total knee arthroplasty (TKA) is dependent on correct and precise rotation of the femoral component. Multiple differing surgical techniques are currently utilized to perform total knee arthroplasty. There are two techniques of achieving soft gap balancing in TKA; a measured resection technique and a balanced gap technique. In this prospective comparative study, the authors evaluated rotational alignments of femoral components and flexion stabilities after TKA performed using the measured resection or gap balanced technique and compared findings. In additional, functional outcomes obtained using the two techniques were compared after a minimum follow-up of 2 years. Methods: Seventy-two consecutive patients, who were awaiting unilateral TKAs, were allocated alternatively to either the TKA using measured resection or using balanced gap techniques. Eight patients were excluded from this study (2 patients due to refusal to participate in the study and 4 patients due to loss of follow-up). This left sixty-four TKAs (32 TKA by measured resection and 32 by balanced gap) with a minimum of 2 years. At final follow-up, valgus and varus laxities at 90 degrees of knee flexion were measured on radiographs taken under valgus-varus stress, and total flexion laxity was determined by summing valgus and varus laxities. In addition, the rotations of femoral components from the transepicondyalr axis were also measured on flexion radiographs. To compare clinical outcomes, range of motion, HSS scores, and WOMAC scores at final follow-up were evaluated and compared between two groups. Results: Mean varus laxities were 5.1 in the measured resection group and 5.7 in the balanced gap group, and mean valgus laxities were 4.0 and 3.6 , respectively without statistical significance. Mean total laxities were similar in the two groups (9.1 vs. 9.3, p¼0.89). However, mean femoral component rotations were significantly different in the two groups (measured resection; 0.4 external rotation from tran-sepicondylar axis and balanced gap; 2.1 external rotation (p¼0.003)). The average HSS