Light microscopic histology of quadriceps tendon ruptures

To assess histological changes and possible differences in the quadriceps of patients undergoing open repair of the tendon after spontaneous rupture, and subjects with no history of tendon pathology. Biopsies were harvested from the quadriceps tendon of 46 patients (34 men, 12 women) who had reported unilateral atraumatic quadriceps tendon rupture and had undergone surgical repair of the tendon. Samples were also harvested from both the tendons in 11 (N = 11 x 2) patients, nine males and two females, dying from cardiovascular disorders. For each tendon, three slides were randomly selected and examined under light microscopy, and assessed using a semiquantitative grading scale (range 0-21) which considers fibre structure, fibre arrangement, rounding of the nuclei, regional variations in cellularity, increased vascularity, decreased collagen stainability, and hyalinisation. The pathological sum-score averaged 19.2 +/- 3.7 in ruptured tendons and 5.6 +/- 2.0 in controls, and all variables considered were significantly different between the two groups, showing an association between tendon abnormalities and rupture (0.05 < P < 0.001). This study confirms that the presence of histological degenerative changes in torn quadriceps tendons increases the risk of rupture.