The Flexion Gap Measured Balancing Technique In Total Knee Arthroplasty

Objective To study the tension difference between medial and lateral collateral ligaments of the knee joint and to investigate the influence of flexion gap balancing on the positioning angle of femoral external rotation.Methods The clinical data of patients who underwent mechanically aligned knee replacement with posterior cruciate-retaining highly congruent rotating-platform prostheses from December 2017 to December 2019 at our department were reviewed.A total of 108 cases(108 knees)were included after excluding those with non-vertical tibial plateau alignment in the full-length standing film of the lower limb after surgery,including 28 males and 80 females,with a mean age of(68.87 ± 7.70)years.All patients underwent preoperative computed tomography to measure the anatomical external rotation angle α between the femoral surgical transepicondylar axis and the posterior condylar line.After balancing the extension gap intraoperatively,the flexion gap balancer was used to locate the intercept line parallel to the tibial plateau when completely bracing the medial and lateral collateral ligaments,then another positioning line was made for the condylar clasp without external rotation.The intersection angle β of the two lines was calculated by the topological printing method,that is,the external rotation angle of the parallel cutting line to the posterior condyle line.Subsequently,the angle difference(δ)between β and α was calculated,which is the tension difference between the medial and lateral collateral ligaments.Results The average anatomical external rotation angle α was(3.07 ± 1.15)°,and the average external rotation angle β was(6.01 ± 1.02)° after completely bracing the collateral ligament.The mean δ was(2.93 ± 0.61)°.Conclusion The angle of the tension difference between the medial and lateral collateral ligaments was about 3°.When using the gap balancing technique,fully tightening the balancer would result in an average of 6° external rotation of the posterior femoral condyle.During the operation,the appropriate balancing position should be determined by combining the anatomical external rotation angle,measured resection technique,Whiteside line,and transepicondylar axis.Objective To compare the application difference and early clinical outcomes of the flexion gap equal point measured balancing technique and the 3°external rotation measured resection technique in total knee arthroplasty(TKA)with posterior cruciateretaining highly congruent rotating-platform prostheses.Methods From March 2018 to March 2020,patients who underwent mechanically aligned TKA with posterior cruciate-retaining highly congruent rotating-platform prostheses at our department were prospectively included.They were divided into two groups by random number table.55 patients(14 males and 41 females)undergoing TKA with flexion gap equal point measured balancing technique were included in the gap balancing group and another 55 cases(16 males and 39 females)undergoing TKA with measured resection technique were included in the measured resection group.A total of 110 cases(110 knees)in the two groups were ATTUNE CR RP prosthesis.In all cases,the angle between the femoral external rotation intercept line positioned by the balancer and the posterior condyle line was measured during surgery.The abnormalities,such as the excessive rollback of the prosthesis,lifting or loosening of the rotating platform liner during surgery were compared between the two groups.One year after surgery,the flexion Range of Motion(ROM),the Posterior Condylar Offset(PCO),the Visual Analogue Scale(VAS)for pain,the Oxford Knee Score(OKS),the Knee Society score(KSS),and the Knee Society Function Score(KSFS)were compared.Data within a group were compared using the Paired Samples t-test and data between the two groups were compared using the Independent Samples t-test.Results In the gap balancing group,the angle between the femoral external rotation intercept line located by the balancer and the posterior condyle line was(4.93 ± 0.98)°.The total incidence of intraoperative abnormalities in the gap balancing group was 10.9%,but that in the measured resection group was 41.8%.The difference was statistically significant(P < 0.001).Those abnormalities were well corrected by methods such as posterior cruciate ligament release.During the 1-year follow-up after surgery,no serious complications such as rotating platform liner dislocation,prosthesis loosening,infection,or venous thrombosis occurred in either group.The OKS,KSS,and KSFS were slightly higher in the gap balancing group than those in the measured resection group(P < 0.05 for all).There was no significant difference in PCO before and after surgery in the gap balancing group(P = 0.823),but the PCO was slightly decreased in the measured resection group after surgery(P < 0.001).The difference in VAS score between the two groups was not statistically significant(P > 0.05).The postoperative ROM in the gap balancing group was slightly higher than that in the measured resection group,and the difference was statistically significant(P < 0.001).Conclusion Compared to the traditional resection technique,the gap balancing technique can significantly reduce the occurrence of liner abnormality and rotation during surgery,more effectively improve ROM and knee function.The flexion gap equal point measured balancing technique can better maintain postoperative PCO.The measured resection technique with 3° external rotation often requires intraoperative release of the posterior cruciate ligament and thickening of the liner,resulting in a decrease in PCO.Releasing the posterior cruciate ligament can correct intraoperative liner abnormalities.