Postoperative scarring is a common complication of knee replacement surgery, characterized by the excessive production of fibrous scar tissue resulting in loss of mobility, especially flexion and extension, due to the painful stiffness of the excessive scar tissue.

Arthrofibrosis, the well-known intra-articular scarring condition, is a debilitating complication after knee trauma or surgery [1], but a much less described condition is the entrapment of the extensor system, especially that of the patellar tendon.

In postsurgical arthrofibrosis, to the best of our knowledge, the involvement of the extensor tendons is not described, probably because it is less frequent in patients who undergo early rehabilitation [2]. Peritendinous fibrous scar bands can cause painful stiffness, especially during activities such as flexion, weight bearing, climbing, descending stairs, and squatting.

In this study, even a few degrees of limitation of knee flexion, and to an even greater extent, of knee extension, can alter gait and severely limit daily activities. Furthermore, these limitations involve, especially in the long-term postural compensations that could trigger other painful conditions [3].

Reference imaging to investigate tissue proliferation include MRI and ultrasound [4,5]. For MRI, metal suppression sequences are required to reduce artifacts and improve image quality and definition, which are not always available. In addition to being less expensive and easier to access, ultrasonography, especially with dynamic assessments [6], can be the imaging of choice for this condition, not only for diagnostic purposes but alsofor interventional treatment.

Scar tissue on an ultrasound may appear as a circumferential fibrous hyperechoic sleeve, either focally in a single area of the tendon, or between the tendon and superficial tissues, or between the tendon and Hoffa’s fat pad, or nodular with anisotropy for disorganized orientation of the fibers, as shown in this case (Figure 1, with purple). In the granulation tissue, it is possible to find a focal increase in the peritendinous vascularization with Power Doppler (PD), at the edge of the newly formed tissue. In the case presented, the PD signal was negative, probably reflecting an advanced and densely packed fibrotic tissue.

The dynamic ultrasound evaluation of the patellar tendon is performed with the patient seated on the bed and with the legs down and positioning the probe in the long axis on the tendon, and then proceeding with active, active-assisted, or passive flexion-extension movements. In the presence of cicatricial bridles, we will notice an anomalous sliding of the tendon, with the traction of the surrounding tissues up to, in the most serious cases, an absence of sliding.

In the early stages, hydrodissection may be sufficient to release the tendon, but when scar tissue is too dense or too adherent to be resolved through this procedure, percutaneous ultrasound-guided release of the patellar tendon may be the appropriate treatment choice. After hydrodissection of the space between the tendon/paratenon interspace with a fast-acting local anesthetic (lidocaine 1% in dextrose 5% 8 mL total volume) (Figure 1), we use the sharp bevel of an 18 G needle to proceed with the release of the tendon. With the probe positioned in the short axis on the patellar tendon, we introduce the needle in-plane and proceed to the resection of the scar tissue with firm but controlled lateral movements (Video 1), until complete release, which is easily evaluated with dynamic scans. With this procedure, the scar fibers are cut and loosened, freeing the tendon from the surrounding planes, but they are not aspirated, as with percutaneous tendon tenotomy (e.g., Tenex).

Figure 1. Hydrodissection of the Patellar Tendon
Hydrodissection with local anesthetic of the patellar tendon in short axis and in-plane needle visualization. The hydrodissection procedure, by
opening the peritendinous space, allows a better visualization of the scar tissue (purple).

Video 1. Summary and Procedural Video
The video is available at: https://doi.org/10.29760/APJP.202306/
PP.0002.

The procedure is outpatient and painless, and does not require immobilization; on the contrary, it must be followed by mobilization exercises to avoid possible recurrences. it is also possible to inject hyaluronic acid in the peritendinous space to limit any further adhesions.

Generally, recovery is rapid, with a constant and progressive improvement of both the echostructure of the tendon and its functionality, with a normal sliding on the dynamic scan (Figures 2 and 3). Although it was not used in this case, elastography could be used as an additional diagnostic and monitoring test. The peritendinous scar tissue is shown with increased stiffness, with the recovery of the normal pattern after the procedure [7].

In conclusion, ultrasound-guided patellar tendon release is an effective, safe, and low-cost procedure for postsurgical scar management in knee replacement or patellar tendon surgery, which we can add to our arsenal of minimally invasive ultrasound-guided techniques.

Figure 2. One Week Follow Up
One week after ultrasound-guided tendon release. Improvement in
echostructure of the patellar tendon with residual hypoechoic thick-
ened area at the treatment site (arrow) .

Figure 3. Four Week Follow Up
Four week after ultrasound-guided tendon release with complete recovery of functionality and tendon echostructure, no sign of recurring adhe-
sions. Proximal (A) and distal (B) scan of the patellar tendon.