Summary

: In this cohort, 62% of the patients had radiographic healing by 4 month, with 2/4 tibial fractures occurring after 2 months.

Abstract

Introduction

Distalization of the tibial tubercle (TT) is a common procedure to treat patella instability when patella alta is present. Close apposition of the distal TT to the anterior tibial shaft (TS) is ideal for timely bone healing. The purpose of this study was:
1) to evaluate technical/demographic factors that could influence bone healing
2) to document the average healing time of the distal TT-TS interface (defined as the gap)
3) to evaluate frequency of bone resorption at the gap
4) to determine if gap size is related to complications of tibia fracture/delayed union

Methods

All patients who underwent distalization of TT for surgical treatment of patella alta were reviewed. Demographic data included age, sex, smoking status, BMI. Distal gap was measured on intra-operative fluoroscopy (initial bone gap) and followed on post-operative sagittal radiographs. The distal gap was measured consistently by the same person using a calibrated system converting flouro images to mm measurements. Bone resorption at the distal bony gap was defined as >2 mm increase in the gap between intra-operative and follow-up films (bone resorption gap).

Results

101 patients underwent distal TT osteotomy (2009-2015). There were 73 females/28 males with mean (range): age 21 y.o. (13-45), BMI 26.2 (17-44). Smokers: 10 current smokers/89 non-smokers/2 unknown.

88% had X-rays that allowed assessment within 4 month; 62% had radiographic healing at the distal TT-TS. Time to heal was not significantly correlated with sex, BMI or smoking status, though the smoking group was too small to make meaningful comparisons.

The initial gap was [mean (range)]: 1.51mm (0-8.4); all but 2 patients <3.3mm. If initial gap > 3mm, distalization distance was >8mm. 11 (11%) had an increase in their distal bony gap > 2mm (resorption gap range 2- 7.8mm) without radiographic evidence of motion in tubercle screw fixation. The thickness of the distal TT computed as a % of the total tibial width was mean 31% (range 22-37%).

There were 4 tibial fractures, none statistically related to initial gap distance, mm of distalization, or thickness of the distal osteotomy as a % of total tibial width. 7 patients had gap resorption >3mm, 2 of which went on to have a tibia fracture. Fracture time from surgery was between 1 and 6 months.

Initial gap or resorption gap was not related to the # of screws; all but 3 patients had 2 bicortical screw placement confirmed on X-ray.

Discussion

Though there are many technical aspects of TT distalization, this large cohort could identify no demographic or surgical factors directly related to risk of tibia fracture or bone healing except gap resorption >3mm at TT-TS interface. Initial gap is associated with distalization distance.

At 4 months complete radiographic healing was present in 62%, with 2/4 fractures happening after 2 months. This can be helpful in counseling our patients in anticipated post-operative recovery to pounding activities. Bone resorption at the distal TT-TS interface is recognized post-operatively (11%), is not statistically correlated with timely healing, but may be a risk factor for tibial shaft fracture.