Ultrasonic evaluation of acute impact injury of articular cartilage in vitro.

OBJECTIVE: The aim of the study was to investigate whether high frequency ultrasound technique, originally designed for arthroscopic use can be utilized to detect traumatic cartilage injuries. METHODS: A total of four intact osteochondral plugs were prepared from eight patellas for parallel comparison (total of 32 plugs). The plugs were injured by dropping an impactor on them from heights of 2.5 cm, 5.0 cm, 10.0 cm and 15.0 cm (corresponding to impact energies of 0.12, 0.25 0.50 and 0.74 J, respectively), in a custom made dropping tower. The samples were imaged with a high frequency (40 MHz) ultrasound device before and after the injury. Reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB) and ultrasound roughness index (URI) were determined for each sample. RESULTS: Injuries invisible to the naked eye could be sensitively detected via the decreased values of the ultrasound reflection parameters (P < 0.05). Furthermore, a decreasing trend was detected in the values of R and IRC as the momentum of the impactor increased. The values of AIB were significantly lower for samples injured by dropping the impactor on the cartilage from heights of 2.5 cm and 15 cm but the URI values were similar in intact and injured cartilage. Histological analysis of the cartilage samples revealed that the injured cartilage exhibited depletion of the cartilage surface proteoglycans but the structure of collagen network was almost normal. CONCLUSIONS: Quantitative ultrasound imaging enables the detection of minor visually non-detectable cartilage injuries. As the present technique is feasible for arthroscopic use it might have clinical value in the evaluation of cartilage lesions during arthroscopy e.g., after tear of the anterior cruciate ligament.