Patellar tendon ossification is a rare occurrence. Whenever reported, it is usually associated with conditions such as conservatively treated sleeve fractures of tibial tuberosity [1], total patellectomy during arthroplasty [2], intramedullary nailing of tibial fractures [3], anterior cruciate ligament reconstruction with patellar tendon autograft [4], and knee injury without fracture [5].

We report here a case of comminuted displaced inferior pole fracture of the patella that was treated with partial patellectomy. During the follow-up period the patellar tendon healed with ossification. To the best of our knowledge, this is the first reported clinical case of patellar tendon ossification occurring after partial patellectomy. The purpose of this report is to point out this rare complication of patellar tendon rupture.

The ideal treatment of inferior pole fractures of the patella remains a controversial issue. The options include internal fixation of the pole fragment and resection of the avulsed fragment with repair of the patellar tendon to the patella [6]. In experimental studies [7, 8], enlargement of the remaining patella and patellar tendon calcification after partial patellectomy were demonstrated in rabbits at about 24 weeks after surgeries were performed on them.

However, in clinical studies where the results of partial patellectomy were reported, incidences of extensive patellar tendon ossification were not detected [9, 10]. Saltzman et al. [9] reported that patellar length and the area of retained fragment were found to be enlarged in varying degrees in some patients. They concluded that this was different from the calcification or ossification phenomenon that could be seen at the extensor mechanism after a total patellectomy or the development of an osseous spur where the patellar tendon was reattached.

In our patient, the tendon was ruptured neither from the repaired bone-tendon junction nor throughout the length of the ossified tendon, but rather from an unexpected part, which is the tibial tubercle. An explanation for this may be the contraction of the quadriceps muscle that led to the rupture at the distal, weaker, nonossified ligamentous part of the ossified tendon. Cerclage wire might put additional pressure on the distal attachment of the tendon that was supplementing the rupture.

The only other report of ossified patellar tendon rupture to be found in the literature was by Yoon et al. [11] who described a case in which the ossified tendon ruptured in a z-like fashion from the proximal medial aspect to the distal lateral aspect. This differs from our patient's condition in that he had a prior partial patellectomy and the ossified tendon avulsed completely from its insertion into the tibial tubercle alone.

Surgeons must be cautious about patellar tendon ossification after partial patellectomy because this can lead to patellar tendon rupture.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.