Background and indications: Tendinosis is cHaracterized histologically by tissue degeneration with failed reparative response and an absence of inflammatory cells.^1,2 In the patellar tendon, it is referred to as jumpers knee.^3,4 Tendinosis is associated with a relative expansion of tendinous tissue, longitudinal and collagen fibers, and a loss of clear demarcation between adjacent collagen bundles. In normal tendons, stainable ground subsTance (extracellular matrix) is absent and vasculature is not conspicuous. Tenocytes are also generally inconspicuous, and fibroblasts and myofibroblasts are absent. This is in stark contrast to patients with symptomatic tendinopathy where there is obvious discontinuity and disorganized collagen fibers with associated increased the amount of mucoid ground subsTance. Ultrasonography can assess the thickness of tendons and their echogenicity.

Patellar tendinopathy can be recalcitrant to treatment.⁵ Because of the tensile loads placed on the patellar tendon, corticosteroids injections within the tendon or tendon attachments are contraindicated. However, new therapies are emerging, including sclerotherapy,⁶ prolotherapy,⁷ platelet-rich plasma (PRP) injections,^{8, 9and 10} and the use of growth factors¹¹ and other cells^12,13 to promote healing.

Anatomy: The patella functions as a classic sesamoid bone improving mechanical leverage for the quadriceps mechanism.¹⁴ The patellar tendon extends from the inferior patellar pole to the tibial tubercle and is arranged in fascicles contributing to the course fibular appearance on ultrasound (Figs. 69.1 and 69.2). The anterior fascicles are typically longer than the posterior. The anterior attachments are longer because they are more proximal to the patella and attach more distally to the tibia than the corresponding posterior fascicles (see Fig. 69.1). The distal attachment of the patellar tendon at the tibial tubercle is crescent-shaped, and thus, the lateral fibers are more proximal than distal (see Fig. 69.1). The posterior aspect consists of both an articular zone and a nonarticular zone, which are devoid of tendon attachments and covered by a synovial fold of tissue. During flexion of the knee, the patellar tendon length is under the pull of the quadriceps tendon. For the same amount of elongation, the shorter fascicles of the posterior ridge strain more than the longer anterior fascicles. The shorter posterior attachments are more vulnerable to develop overuse damage and tendinopathy. This can be seen on a physical examination where the posterior aspect of the patellar tendon attachments are usually more sensitive on a physical examination and thus should be a target for injection. In order to palpate these fibers, it requires the practitioner to lift the inferior pole of the patella up in order to gain access for palpation (see Fig. 69.2).

Transducer: 7.5 to 15 MHz linear transducer.

Transducer orientation: Transducer placed in plane with the patellar tendon as seen in Figure 69.3.