Radiological and M.R.I. Analysis of the Morphology of Patellar Tendonitis

Mr D P Johnson, Dr I Watt and Dr C Wakeley

Patellar tendonitis is thought to be due to a chronic overload of the tendon which results in repetitive microscopic damage and inflammation within the upper central aspect of the patellar tendon resulting in histological focal degeneration. This study was performed to analyse the morphology of the patella in this condition by conventional radiology and by MRI.

The analysis consisted of 22 patients presenting with chronic severe (Grade 2,3, or 4) patellar tendonitis. Patients were assessed clinically and radiologically in flexion and extension. The radiographs were analysed to determine the morphology of the inferior pole of the patellar and the spatial relationship during flexion. Various MRI imaging modalities were obtained in the position of knee flexion and extension. The imaging modalities were analysed to determine the optimal method. The results were then compared to a matched control group of patients.

The results demonstrated that there was no significant difference in the morphology of the patella in terms of patello-femoral tilt, congruence angle, or patella index. The inferior pole of the patella did not prove to be significantly elongated in the affected patients. There was a significant increase in the length of the patellar tendon in affected individuals. The MRI appearances demonstrated the inflammation characteristically in the deep superior and central part of the tendon. The appearances were most apparent on the saggital T2 sequences. There was also a significant increase in the thickness of the upper patellar tendon as compared to the control group. It was apparent that the majority of the patellar tendon did not insert into the inferior pole of the patella but continues over the anterior cortex. Thus in the position of knee flexion the inferior pole was seen to impinge on the characteristically inflamed region of the tendon.

This study has characterised and categorised the morphology, radiology and MRI appearances in this condition. The results suggest that the micro-trauma and degeneration may be a result of impingement against the inferior pole in flexion rather than the tensile failure. This newly described pathogenesis would correlate with and be supported by the effectiveness of surgical release of the central portion of the tendon.

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