ACL Injury and the Patellar Tendon: What the Evidence Says

A recent study from Aspetar Orthopaedic and Sports Medicine Hospital and the University of Jyväskylä sheds new light on a long-standing clinical question: how does an ACL injury affect the quality of the patellar tendon?

Using ultrasound tissue characterization (UTC), researchers assessed tendon structure in male athletes awaiting ACL reconstruction. The results challenge common assumptions about tendon degradation following knee trauma and highlight the complexity of symptoms that accompany ACL tears.

Study design and aims

The study, led by Carla S. Pereira and colleagues, evaluated 81 male athletes with unilateral ACL ruptures. Participants underwent detailed assessment of:

• Patellar tendon quality (via UTC)
• Quadriceps strength
• Knee extension range
• Pain and subjective stability
• Load exposure during rehabilitation

The goal was to compare injured and uninjured legs and examine whether reduced strength, extension loss, or knee pain influenced tendon quality.

Unexpected stability in tendon structure

Despite common impairments in ACL-injured athletes — including a 22% quadriceps strength deficit and a 2° extension loss — UTC scans revealed no significant difference in echo-type distribution between injured and uninjured patellar tendons.

This finding suggests that short-term offloading after ACL injury does not necessarily degrade tendon structure, and that increased load and time since injury may even improve tissue organization.

UTC Imaging: A closer look at tendon condition

As the researchers explain:

“One method of exploring tendon quality is ultrasound tissue characterization (UTC), which is a valid and reliable tool to assess healthy, pathological, and harvested tendons. The UTC grading system… categorizes tendon tissue from more to least organized (echo-types I–IV).”

In this study, UTC not only confirmed the structural integrity of most tendons but also detected abnormalities in a subset of participants:

• 16 of 81 athletes showed localized tendon disorganization (e.g. increased thickness or hypoechogenic areas)
• 5 of these abnormalities occurred in the injured leg only, 4 in the uninjured leg, and 7 bilaterally
• Some UTC scans revealed signs of Sinding-Larsen-Johansson and Osgood Schlatter diseases
• Only 2 of the 16 had anterior knee pain at the time of imaging

These findings emphasize UTC’s ability to pick up silent pathology, even when symptoms are absent.

Quadriceps strength: central but not isolated

The study found that quadriceps strength was moderately correlated with pain, knee extension, perceived stability, and load exposure. Yet this relationship was not uniform:

• 38 of 41 athletes with extension deficits also reported knee pain
• A minority (9 athletes) had no pain, full extension, and normal strength — despite their ACL tear
• These “copers” showed distinct rehab profiles, and 5 of them chose non-surgical management

These patterns highlight the need for personalized rehabilitation strategies. While most athletes showed protective behavior and limitations, a few demonstrated high tolerance and recovery without surgery.

Clinical implications

The study concludes:

“Clinicians might assume, when treating ACL-injured patients before surgery, that the injury itself, the presence of knee pain, reduced extension range, and quadriceps weakness will not significantly affect the quality of their patellar tendons.”

This has relevance for:

• Rehabilitation planning: don’t underload the tendon unnecessarily
• Graft decisions: patellar tendons may remain viable even after injury
• Progress tracking: UTC helps identify both normal and abnormal patterns

Furthermore, the uninjured leg can serve as a reliable reference point in future longitudinal studies.

Conclusion

This study underscores the importance of looking beyond symptoms when managing ACL injuries. Despite common deficits in strength and extension, patellar tendon quality can remain intact, particularly when athletes are progressively reloaded and actively rehabilitated.

UTC Imaging plays a key role in revealing these structural insights — supporting more precise and personalized care.

Reference

This summary is based on the open-access publication:

Pereira CS, Klauznicer J, Maree D, McAuliffe S, Farooq A, Whiteley R, Finni T.
Patellar tendon quality, strength and knee extension are impaired in ACL injured athletes: findings from quantitative imaging and functional assessments.
Frontiers in Sports and Active Living. 2023.

Click here for the full publication: https://pmc.ncbi.nlm.nih.gov/articles/PMC10624220/