FGF gene expression in injured tendons as a prognostic biomarker of 1-year patient outcome after Achilles tendon repair

Abstract

Purpose: Healing outcome after Achilles Tendon Rupture (ATR) is variable and unsatisfactory. Many ATR patients still exhibit pain, functional deficits and limitations in walking one-year post-surgery. The present study was designed to investigate the association between the expression of healing biomarkers and patient outcome after ATR.

Methods: Tendon biopsies were collected from 25 ATR patients during surgery. At 1-year post surgery, all patients completed questionnaires; Achilles tendon Total Rupture Score (ATRS) and Foot and Ankle Outcome Score (FAOS), and were tested for functional outcomes by heel-rise test. In biopsies, FGF, COL III, FN, COL I and MMP-9 mRNA levels were assessed by quantitative RT-PCR while protein expression was studied by immunohistochemistry (IHC).

Results: Our analysis confirmed the presence of FGF, COL III, FN, COL I and MMP-9 at mRNA and protein levels in tendon biopsies. FGF gene expression associated positively with improved total ATRS and better functional outcomes. Additionally, FGF mRNA levels were associated with less pain, less running limitations and less loss in physical activity. In addition, higher COL III mRNA expression was associated with more tendon strength.

Conclusion: Our findings indicate that FGF gene expression is associated with improved patient-reported outcome. FGF expression in surgical biopsies could potentially be used to assist the prognostic evaluation of patient outcome and may be used as a predictor for healing. However, further studies are needed to evaluate the role of FGF in Achilles tendon healing.

Level of evidence: II.

Keywords: Achilles tendon rupture; Biomarkers; Patient outcome; mRNA expression, immunohistochemistry.

Conflict of interest statement

There is no financial or other relationship that may cause a conflict of interest.

Figures

Fig. 1

Relative gene expression of Fibroblast growth factor (FGF), collagen III (COL III), fibronectin (FN), collagen I (COL I) and matrix metalloproteinase-9 (MMP-9) in biopsies collected from the injured and intact area of tendon. Values reported are mean ± SEM n = 12

Fig. 2

Correlation between FGF mRNA expression and total ATRS as measured by Spearman’s rank correlation coefficient. FGF mRNA expression was normalized and ATRS ranges from 0 to 100, with 100 = best outcome. n = 12

Fig. 3

Associations among biomarker mRNA expression and ATRS sub-scales. Correlations between a) FGF gene expression and pain, b) FGF gene expression and run, c) FGF gene expression and physical work activity and, d) COL III gene expression and strength measured by Spearman’s rank correlation coefficient. ATRS sub-scales ranges from 0 to 10, with 10 = best outcome. n = 12

Fig. 4

Associations among biomarker gene expression and HRT categories. Correlations between (a) FGF gene expression and LSI average height and, bFGF gene expression and LSI power measured by Spearman’s rank correlation coefficient. HRT categories ranges from 0 to 100, with 100 = best outcome. n = 12

Fig. 5

Associations among gene expression of aMMP-9 and FGF, bMMP-9 and COL I, cMMP-9 and FN and, dFN and COL measured by Spearman’s rank correlation coefficient. n = 12

Fig. 6

Photomicrographs of the injured and intact Achilles tendon stained with haematoxylin and eosin (a-d). All images are representatives from 5 patients. Original magnification is 10x (a and c) or 20X (b and d)

Fig. 7

Protein expression of FGF (a-c), COL III (d-f), FN (g-i), COL I (j-l), MMP-9 (m-o), negative control for horse anti mouse (p-r), and goat anti rabbit (s-u) secondary antibodies in Achilles tendon tissue biopsies. Light microscope images are representative of 5 patients. The first and third columns displays 20x magnification, while the second column depict 40x magnification from the black rectangles in the first column. The first 2 columns display the injured side while the third column shows the intact area