Predictors of Graft Failure After Primary Medial Patellofemoral Ligament Reconstruction

Knee torsion predicts the preoperative J-sign grade in patients with recurrent patellar dislocation : a prospective study

Aims

The aim of this study was to determine the values for knee torsion in healthy knees, and explore predictive thresholds of torsion in grades of the J-sign in patients with recurrent dislocation of the patella.

Methods

A five-year prospective study was conducted involving healthy volunteers and patients with recurrent dislocation of the patella. The knees of the patients were categorized into four groups (J-sign -, J-sign 1+, J-sign 2+, and J-sign 3+) based on visual examination of the patellar maltracking. The torsion of the knee and other bony abnormalities were obtained from routine hip-knee-ankle CT scans. The ranges of the thresholds were determined from the 95% CI of the mean for each group. The predictive thresholds for each grade of J-sign were identified from receiver operating characteristic (ROC) and predictive probability curves.

Results

The study included 44 knees (in 22 healthy volunteers) and 255 knees in 234 patients with recurrent dislocation of the patella. In the J-sign -/1+, J-sign 2+, and J-sign 3+ groups, there were 87 (29.1%), 85 (28.4%), and 83 (27.8%) knees, respectively. Age, sex, and laterality were comparable among the groups. There were significant differences in the mean torsion between the groups: healthy knees 1.4° (-8.8° to 5.4°); J-sign 1+ 6.9° (SD 4.3°); J-sign 2+ 9.2° (SD 4.8°) and J-sign 3+ knees 13.9° (SD 5.4°) (p < 0.001). The ranges of the thresholds for the four groups based on the 95% CI of the means were: < 5.5°, 7.2° to 8.1°, and 10.2° to 12.8°, respectively. Ordered regression revealed a 25.4% increased probability of advancing to a higher J-sign grade for every 1° increase in torsion (adjusted odds ratio (OR) 1.254 (95% CI 1.182 to 1.331); p < 0.001). It was shown in the ROC curves that the presence of torsion effectively differentiated between normal and positive J-sign knees (area under curve (AUC) 0.92; sensitivity 0.76; specificity 1; cut-off 5.5°). Analysis of the ROC and predictive probability curves identified threshold values for the three abnormal J-signs at 7° and 12°, showing an excellent discriminatory performance (pall post-hoc < 0.01).

Conclusion

A threshold of 5° to 6° of torsion in the knee is associated with patellar maltracking in extension. In patients with recurrent dislocation of the patella, there is a one-grade increase in J-sign for approximately every 4° increase in torsion. The 7° and 12° of torsion represent the thresholds for the preoperative J-sign -/1+, J-sign 2+, and J sign 3+, respectively. Routine bilateral lower limb CT scans are therefore required if surgery is to be considered in the knees of patients with recurrent dislocation of the patella who have a positive J-sign.

Recurrent patellar dislocation patients with high-grade J-sign have multiple structural bone abnormalities in the lower limbs

PURPOSE

To explore the relationship between preoperative J-sign grading and structural bone abnormalities in patients with recurrent patellar dislocation (RPD).

METHODS

A retrospective study was conducted on RPD patients over 5 years. Patients were categorised based on J-sign grade into low (J- and J1+), moderate (J2+) and high groups (J3+). Trochlear dysplasia (TD) and osseous structures (femoral anteversion angle [FAA], knee torsion, tibial tuberosity-trochlear groove [TT-TG] distance, Caton-Deschamps index) were assessed and grouped according to risk factor thresholds. The χ2 test was used to compare composition ratio differences of structural bone abnormalities among the groups.

RESULTS

A total of 256 patients were included, with 206 (80.5%) females. The distribution of J-sign grade was as follows: 89 knees (34.8%) of low grade, 86 moderate (33.6%) and 81 high (31.6%). Among the five structural bone abnormalities, TD was the most common with a prevalence of 78.5%, followed by increased TT-TG at 47.4%. Excessive tibiofemoral rotation had the lowest occurrence at 28.9%. There were 173 (67.6%) patients who had two or more abnormalities, while 45 (17.6%) had four to five bony abnormalities. Among patients with any bony abnormality, the proportion of high-grade J-sign surpassed 40%. Patients with moderate and high-grade J-sign had more increased FAA and more pronounced patella alta (all p < 0.001). The proportion of excessive knee torsion and TD increased with increasing each J-sign grade, with the more notable tendency in knee torsion (high vs. moderate vs. low-grade: 61% vs. 22% vs 7%, p < 0.001). Furthermore, the higher J-sign grade was also associated with more combined bony abnormalities (p < 0.001). In the high-grade J-sign group, 90.2% of the knees had two or more bony risk factors and 40.7% had four or more, which were significantly higher than the moderate and low-grade J-sign groups (40.7% vs. 11.6% vs. 2.2%, p < 0.001).

CONCLUSION

In patients with a high-grade J-sign, over 90% of the lower limbs had two or more structural bone risk factors, and more than 40% had four or more. These proportions were significantly higher compared to knees with low-grade and moderate J-sign. In clinical practice, when treating high-grade patellar mal-tracking, it is important to focus on and correct these strongly correlated abnormal bone structures.

LEVEL OF EVIDENCE

Level III.

Increased TT-TG distance caused by excessive tibiofemoral rotation predicts poor clinical outcomes after tibial tubercle osteotomy in recurrent patellar dislocation

PURPOSE

To compare clinical outcome between recurrent patellar dislocation (RPD) with or without actual tibial tubercle lateralisation (TTL) after medial patellofemoral ligament reconstruction (MPFL-R) combined with tibial tubercle transfer.

METHODS

From 2015 to 2018, a total of 172 knees with RPD and a tibial tubercle-trochlear groove (TT-TG) distance of > 20 mm were treated with MPFL-R combined with tibial tubercle transfer. Patients were divided into the lateralisation group (TT-PCL > 24 mm, n = 74) and the nonlateralisation group (TT-PCL ≤ 24 mm, n = 60) based on the presence or absence of actual TTL (TT-PCL > 24 mm). Clinical outcomes were assessed postoperatively at a minimum of 2 years. Second-look arthroscopic evaluations were available for 84 knees to assess cartilage damage.

RESULTS

A total of 134 knees with a median follow-up time of 32 months were included. Tibiofemoral rotation (TFR) was significantly higher in the nonlateralisation group than in the lateralisation group (15.4° vs. 9.4°, P < 0.001). At the final follow-up, the nonlateralisation group had significantly lower Kujala (78.2 vs. 86.4, P = 0.001) and Lysholm (80.3 vs. 88.2, P = 0.003) scores than the lateralisation group. At the time of the second-look arthroscopic assessment, 38.9% of the patients in the nonlateralisation group showed cartilage worsening in the medial patellar facet that was significantly higher than that in the lateralisation group (38.9% vs. 12.5%, P = 0.015).

CONCLUSION

Patients with RPD and an increased TT-TG distance of > 20 mm but without actual tibial tubercle lateralisation benefit less from tibial tubercle transfer than patients with actual tibial tubercle lateralisation, which may be related to the significantly higher tibiofemoral rotation angle of the former.

LEVEL OF EVIDENCE

III.

Patellar malalignment: A common disorder associated with knee pain

Pain-associated knee joint disorders are common in daily life. Practically, knee pain should be divided into the origin from the isolated tibiofemoral (TF), isolated patellofemoral (PF) joint, or a combination thereof. The TF joint controls the actions of level walking, while the PF joint controls knee flexion-extension. Owing to its sufficient inherent stability, non-traumatic disorders of the isolated TF joint in young individuals are uncommon. In contrast, because of its insufficient inherent stability, non-traumatic disorders of the isolated PF joint are common in young individuals. Patellar malalignment (PM) associated with knee pain is common in all age groups, and the most common predisposing factor is imbalanced peripatellar soft-tissue tension. The outward forces acting on the patella are caused by pulling from the quadriceps femoris during knee flexion to extension (manifested by the quadriceps angle [Q-angle]), and sliding backward of the iliotibial band (ITB) during knee extension to flexion. Once the muscle power of the vastus medialis (especially the vastus medialis obliquus [VMO]) decreases, which lowers the counteracting effect against outward forces, the patella displaces or rotates laterally. The reduced contact surface between the patella and the femoral condyle significantly increases the compressive pressure and injures the articular cartilage. Subsequently, progressive PF degeneration occurs. Although other factors may also cause PM, they are relatively uncommon. In principle, nonsurgical treatment of PM should be considered first, while surgical treatment should follow established indications. Some nonsurgical techniques are currently widely used that feature high satisfaction rates. Surgical techniques are continuously being developed, and their success rates have gradually improved. This study aimed to review the current literature for relevant studies and report related publications of the author's institution to emphasize the universality and importance of PM management. Conceptually, simply focusing on problems of the TF joint cannot treat all knee disorders.