Summary
Distalization of the tibial tubercle leads to a high rate of normalization of patellar height measurements, with 93% patella stabilization and improvement in functional outcomes.
Abstract
Introduction
Patella alta is a known anatomic risk factor for lateral patella dislocation (LPD). When present, reducing patella height by distalization of the tibial tubercle (TT) is recommended. The purpose of this study is to evaluate the clinical outcomes of TT distalization.
Methods
Data was collected retrospectively on consecutive patients who underwent TT distalization as part of patellar stabilization for recurrent lateral patella dislocation. All patients had concurrent medial patella ligament reconstruction, performed by a single surgeon between 2009-2015. Data collected included demographics, pre-and post-operative imaging measurements related to patella alta and trochlear dysplasia on MRI and plain radiographs, and outcomes including knee stiffness needing a manipulation, recurrent LPD, and patient reported outcomes.
Results
89 patients underwent TTO with distal transfer (DT) alone or with a medial transfer (MT) of the osteotomy. There were 21 (24%) males and 68 (76%) female. Mean (range): age 21 (13-45), BMI 25.8 (17-44.6). Pre-operative imaging characteristics were present as: crossing sign 93%, double contour sign 45%, supratrochlear spur 37%. Average (range) pre-operative imaging measurements were: IS ratio 1.5 (1.18-2.06), CD ratio 1.4 (1.05-1.93), lateral patella tilt 24.7º (1-53), TT-TG 18.6 mm (8-28), sulcus angle on MR 158º (123-180), PTI 29% (5-70).
19% (17/89) had an isolated DT. In 88% (80/89), DT was the primary surgical transfer direction with mm of DT > MT. When DT was <7mm, MT mm > DT (12%).
Post-operative average CD was 1.09 (0.92-1.67) which was statistically significantly different from pre-op (p< 0.00). The amount of distalization averaged 9.8mm (range 4 to 15). 76/89 (86%) achieved patella height normalization, with no post op baja present in any patients.
6 patients (7%) had frank recurrent dislocation, two within the first year (5, 8, 16,17,32,37 months): There were 5F/1M, average age 15. Postoperative patella height in the dislocation group averaged 1.11 (1.02 -1.25). All re-dislocators had high grade trochlear dysplasia as judged by sulcus angles (146º -172 º)
72% had post operative patient reported outcomes (KOOS), with Minimum Meaningful Difference (10 points) achieved between pre and post op scores in all categories, with the largest improvement in Sports (30 points) and Quality of Life (QOL) (30 points). Final KOOS was Pain (76), Symptoms (50), ADL’s (82), Sports (58), QOL (50)
Conclusion
Distalization of TT leads to a high rate of normalization of patellar height measurements, with 93% patella stabilization. Redislocation was not associated with residual patella alta; all redislocators had high grade trochlear dysplasia.
Patient reported outcomes show improvement in all categories, especially in sports and QOL. Despite functional gains, this population still demonstrates significant dysfunction as measured by KOOS, especially in symptoms and QOL.