Osteotomy Correction Angle Cut-off Points Can Guide the Operation to Prevent a Significant Decrease in Patella Height

OBJECTIVE

Patients who undergo a biplanar ascending medial open-wedge high tibial osteotomy with an excessive correction angle might experience patella infera and even knee pain after surgery. The purpose of this study was to identify the cut-off points for the degree of knee varus correction of open-wedge high tibial osteotomy, which is related to the symptomatic patellar position change.

METHODS

This retrospective study included 124 patients (mean age 61.69 ± 6.28 years; 78 women, 46 men) with varying degrees of varus knee osteoarthritis. All patients had undergone standard biplanar medial open-wedge high tibial osteotomy. They were divided into nine groups according to the change in hip-knee-ankle angle. Plain radiographs and three-dimensional CT images were obtained preoperatively and 18 months postoperatively. Patellar height was assessed using the Caton-Deschamps index, the Insall-Salvati index, and the Blackburne-Peel index. The patellofemoral index and patellar tilt were used to evaluate the degree of horizontal displacement of the patella. The varus correction, medial-proximal tibial angles, joint line convergence angles, and hip-knee-ankle angles were also measured. The subjective score was evaluated using the Western Ontario and McMaster Universities osteoarthritis index (WOMAC).

RESULTS

There were significant changes in patella indexes in each group after surgery, among which there was no significant difference in patellar height changes for Groups A to F (p > 0.05), which were significantly lower than those in Group G, H, and I (p < 0.001). The patellar tilt and patellofemoral index also followed the same trend. The improvement in WOMAC scores for Groups G, H, and I was also significantly less for Groups A to F (p < 0.001).

CONCLUSION

The patellar height, patellar tilt, and patellofemoral index all changed significantly in parallel with increasing degrees of osteotomy correction. The cut-off points for correction angle are 12.5° to 13.4°. When the correction angle is larger than this range, the patellar position can be significantly affected. Postoperative patellofemoral joint pain may be related to the changes in patella position.

The Dynamic Effect of Anterior Cruciate Ligament Deficiency on Patellar Height

BACKGROUND

The anterior tibial translation (ATT) in case of Anterior Cruciate Ligament (ACL) tear can lead to dynamic alterations of the extensor apparatus biomechanics. The aim of this study is to evaluate the dynamic effect of isolated ACL deficiency on patellar height. The hypothesis is that the ATT of ACL-insufficient knees dynamically reduces patellar height.

METHODS

Skeletally mature patients who underwent ACL reconstruction using hamstring graft between January and December 2018 were included in this study. The Posterior Tibial Slope (PTS), Caton-Deschamps (CDI), modified Insall-Salvati (MISI), and Blackburne-Peel (BPI) indices were calculated in standard lateral and TELOS X-rays. The mean of the measurements calculated between two observers was used to compare these parameters.

RESULTS

95 patients (M: 57; F: 38; 95 knees) were included in the study with a mean age of 31.8 years (16-56 years old). Significant patellar height reduction (CDI: 0.11 [- 0.32; 0.31]; MISI: 0.09 [- 0.66; 0.30]) was reported in TELOS compared with standard lateral knee radiography (p < 0.001). 20.0% of the study knees reported an abnormal CDI and 84.2% (16/19 knees) of them reduced this index to within normal limits in TELOS. 20.0% of the knees with mild patella alta reduced CDI in TELOS but always remained above 1.2.

CONCLUSIONS

The abnormal ATT in case of ACL-deficient knees results in a lowering effect of the patella in TELOS X-rays. In patients with ACL tear and anterior pain the reconstructive ligament surgery should be performed to avoid also chronic anterior knee pain.

LEVEL OF EVIDENCE

Basic Science Study (Case Series).

CLINICAL RELEVANCE

The decrease in patellar height in stress-X-rays compared with standard lateral knee radiography in ACL deficient knees, should be considered as a possible contributing cause of anterior pain in these patients.