Impact Of Positive Malalignment Sign On Knee CT On Postoperative Clinical Prognosis Of Patients With Patellar Dislocation

OBJECTIVES:（1）To investigate whether positive malalignment sign on coronal CT is a risk factor for prognosis after patellar dislocation surgery,and whether positive malalignment sign has an effect on the rate of recurrent patellar dislocation or patellar instability,knee function score,and return-to-sport ability after medial patellofemoral ligament（MPFL）reconstruction.（2）To verify that positive malalignment sign correlates with increased femoral anteversion and to investigate whether positive malalignment sign correlates with other risk factors(such as trochlear dysplasia,tibial tuberosity-trochlear groove（TT-TG）distance,and patellar tilt angle.METHODS: 37 patients included were divided into a test group and a control group according to positive and negative malalignment signs,with 22 patients in the test group and 15 patients in the control group.Patients in both groups underwent arthroscopic single bundle MPFL reconstruction with lateral retinacular release.The rates of recurrent patellar dislocation or patellar instability at 9 months after surgery were compared between the two groups.The Lysholm and Kujala knee function scores at 3,6,and 9 months after surgery,the International Knee Documentation Committee（IKDC）subjective knee scores and the Tegner return-to-sport score at 9 months after surgery were compared between the two groups.The preoperative femoral anteversion,TT-TG distance,patellar tilt angle,and trochlear dysplasia were compared between the two groups.RESULTS: No significant differences were seen in Lysholm,Kujala,and IKDC scores between the test and control groups at 3,6,and 9 months after surgery（P > 0.05）;3patients in the test group had recurrent patellar dislocation or patellar instability at 9months after surgery,and no patients in the control group had recurrent patellar dislocation or patellar instability,with no statistical differences between the two groups（P > 0.05）.At 9 months after surgery,17 patients in the test group returned to sports,with a return-to-sport rate of 77.3%;13 patients in the control group returned to sports,with a return-to-sport rate of 86.7%.The median Tegner return-to-sport score at 9months after surgery was 5（2-6）in the trial group compared with 6（2-7）in the control group（P < 0.05）.The total positive rate of malalignment sign was 59.5%.The mean femoral anteversion was 27.59° ± 6.76° in the positive malalignment sign group,which was higher than that of 20.13° ± 4.58° in the control group（P<0.05）.There were 20 patients with severe trochlear dysplasia in the test group and 8 patients with severe trochlear dysplasia in the control group,and the proportion of patients with severe trochlear dysplasia in the test group was greater than that in the control group（P< 0.05）.No significant differences were seen in TT-TG distance and patellar tilt angle angle between groups.CONCLUSION: Positive malalignment sign had no significant effect on functional scores and recurrent patellar dislocation or patellar instability after surgery,but positive malalignment sign was associated with poorer return-to-sport in patients at 9 months after surgery.We verified that positive malalignment sign was associated with increased femoral anteversion and found that positive malalignment sign was associated with severe trochlear dysplasia,but not with TT-TG distance or patellar tilt angle.In patients with positive malalignment sign,the presence of an increased femoral anteversion and severe trochlear dysplasia can be determined early and patients can be evaluated for a possible decrease in postoperative return-to-sport.In patients with positive misalignment signs,clinicians may need to treat them with a combination of osteotomy.