The effects of an early return to training on the bone-tendon junction post-acute micro-injury healing

Abstract

Bone-tendon junction (BTJ) overuse injuries are common athletic and occupational problems. BTJ injuries may sometimes be caused by resuming training too early after injury. To study the effects of post-injury resuming training within 48 hours on the acute injury healing process, as it is often the case for athletes. Twelve mature female rabbits were assigned to one of the following groups: acute injury (AI, n = 6), post-injury early return to training (PIERT, n = 6) and normal control (CON, n = 6). Tissue specimens were harvested at week 4. The radiological and histological characteristics of the AI and PIERT groups were compared among the groups. The trabecular thickness of the PIERT group was significantly different from those of the AI and CON group. A histological evaluation revealed poor collagen fibre alignment, extensive scar tissue and lowered cell density in the AI and PIERT groups compared with the CON group, but no significant differences were observed between the AI group and the PIERT group. The fibrocartilage zone and proteoglycan area in the PIERT group were significantly different from those in AI group. No differences were observed in the Total VOI volume (TV), Object volume (OBV), Percent object volume (BV/TV) and trabecular number (Tb.N) among the AI, PIERT and CON groups. In conclusion, a repeatable animal model of bone-tendon junction acute micro-damage by puncture was established. Resuming training in 48 hours did not significantly deteriorate the BTJ injury healing, but improved bone remodelling and increased fibrocartilage zone thickness. Key pointsAn easy and repeatable bone-tendon junction injury model was established in this study, it will provide a platform to the injury research.Post-injury resuming training in 48 hours did not delay the acute bone-tendon junction injury healing process, it provided a basic theory for the post-injury training.To find the proper post-injury training intensity will help athletes to train scientifically, it is the destination of our next research.

Keywords: Bone-tendon junction; Patella; early return to training; injury healing; quantitative loading.

Figure 1.

The plum-blossom needle vertically punctured the left-side surface and was then moved up to two other locations. The same process was then performed on the middle and right side. Finally, the needle was scratched from right to left at three levels.

Figure 2.

A sagittal section of the patella-patellar tendon junction for proteoglycan area quantification with the area coloured in red used for imaging analysis (Safranin O, 20×).

Figure 3.

A week 4 representative sagittal section of the patella-patellar tendon junction after injury and training. H&E-stained sections from the AI (A) and PIERT (B) groups indicated an indistinct cell profile, lowered cell density, and unclear tidemark, but the CON group (C) presented well-aligned collagen fibres and a clear tidemark. Polarised microscopy images demonstrated poorer collagen alignment in the AI group (D) and PIERT group (E) than in the CON group (F).

Figure 4.

Safranin O staining indicated an indistinct proteoglycan profile and reduced area in the AI group (A, D) and PIERT group (B, E) relative to the CON group (C, F). (10× for A, B, C and 20× for D, E, F).