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Ultrastructural Collagen Fibril Alterations in the Patellar Tendon 6 Years After Harvesting Its Central Third

Michael Svensson, MD^*, Tomas Movin, MD, PhD, Lars Rostgård-Christensen, MD, Eva Blomén, PhD, Kjell Hultenby, PhD and Jüri Kartus, MD, PhD^*,||

From the ^* Department of Orthopaedics, Norra Älvsborg/Uddevalla Hospital, Trollhättan and Uddevalla, Sweden, Department of Orthopaedics, Karolinska University Hospital/Huddinge, Karolinska Institutet, Stockholm, Sweden, Department of Diagnostic Radiology, Norra Älvsborg/Uddevalla Hospital, Trollhättan and Uddevalla, Sweden, and Department of Pathology, Karolinska University Hospital/Huddinge, Karolinska Institutet, Stockholm, Sweden

^|| Address correspondence to Jüri Kartus, MD, PhD, Department of Orthopaedics, NÄL County Hospital, SE-461 85 Trollhättan, Sweden (e-mail: juri.kartus{at}vgregion.se).

Background: Clinically, donor site problems are common, even in the long term after anterior cruciate ligament reconstruction using patellar tendon autograft. However, there is a lack of knowledge in terms of the mid- and long-term ultrastructural appearance of the previously harvested tendon in humans.

Hypothesis: The patellar tendon does not regain normal ultrastructure 6 years after harvesting its central third and leaving the defect open.

Study Design: Case-control study; Level of evidence, 3.

Methods: Thirteen patients were included in the study. Biopsy specimens were obtained from the central and lateral thirds of the patellar tendon under ultrasound guidance 71 months (range, 68–73 months) after the reconstruction. Ten biopsy specimens from other subjects with asymptomatic patellar tendons served as controls. The sections were evaluated using transmission electron microscopy. Longitudinal sections were used for morphological evaluation, and the fibril diameter was measured on the transverse sections and grouped into 5 diameter classes.

Results: All control specimens were found to have a compact extracellular matrix with regularly oriented collagen fibrils. Specimens from the lateral part of the harvested tendons displayed a more heterogeneous extracellular matrix. In 3 specimens, the extracellular matrix was different from that of the control specimens. Specimens from the central part of the harvested tendons displayed an even more heterogeneous extracellular matrix, with 8 specimens judged as heterogeneous. The fibril diameter in control specimens displayed the most heterogeneous pattern, and all 5 fibril classes were present. All fibril classes were found in the lateral biopsy specimens from the previously harvested tendons, but the 2 smallest fibril classes (0–30 and 31–60 nm) were significantly more dominant compared with control specimens (P < .0001). In the central specimens from the previously harvested tendons, only the 3 smallest size classes were found (P < .0001 vs controls).

Conclusion: Six years after harvesting its central third and leaving the defect open, the patellar tendon revealed a "more heterogeneous matrix" with changes in ultrastructural morphology and relative fibril diameter distribution compared with normal control tendon.

Key Words: anterior cruciate ligament (ACL) • patellar tendon • surgery • ultrastructure • transmission electron microscopy