The lesion of 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. The surgical treatment of detachment or excision of the central portion of the tendon and drilling of the inferior pole of the patellar has little basis if the pathology is one of chronic tension overload. The study was performed to analyse the relationship of patellar position during knee flexion in this condition by radiography and magnetic resonance imaging (MRI).We studied 22 patients presenting with chronic severe (grade 2, 3 or 4) patellar tendonitis. Patients were assessed clinically and radiographically in flexion and extension. Various MRI views were obtained in the position of knee flexion and extension. The radiographs were analysed to determine the morphology of the inferior pole of the patellar and the spatial relationship during flexion. The imaging methods were then compared with a matched control group with meniscal tears as demonstrated on MRI appearances.The results demonstrated that there was no significant difference in the morphology of the inferior pole in terms of patellofemoral tilt, congruence angle, index or patellar tilt during knee flexion. The inferior pole did appear to be more prominent or pointed in the affected patients, and the patella was sited in a lower position as compared with the control group. The MRI appearances demonstrated the characteristic area of inflammation clearly in 21 of 23 cases yet in none of the control group. The appearances were most apparent on the T2 sequences. The insertion of the patellar tendon was into rather than over the inferior pole in 17 of the 22 cases in the tendonitis group compared with 5 of 22 cases with meniscal tears. In five cases the inflammatory changes were more apparent in the position of knee flexion than extension.This study has characterized and categorized the morphology, radiography and MRI appearances in this condition. The results suggest that the microtrauma and degeneration may be a result of impingement against the inferior pole in flexion rather than tensile failure. This newly described pathogenesis would correlate with and be supported by the standard effective surgical treatment.DiscussionQuestion. In 244 patients only two or three required surgery, is this stress overload or is it a direct trauma from impingement?Answer. Not a stress overload because excision is beneficial.Question. What do you actually do? Do you strip or do you remove tissue?Answer. Recent study has shown that the lesion is deep in the patellar tendon.Question. How soon do they get back to sport?Answer. To swimming 3-4 weeks; competitive sport 6-8 weeks.Question. What about injecting the patellar tendon or surrounding area?Answer from Alex Cargill. I have seen a rupture of the patellar tendon after only a couple of injections.