This study evaluates high power low frequency ultrasound transmitted via a flat vibrating probe tip as an alternative technology for meniscal debridement in the knee. A limitation of this technology is thermal damage in residual meniscal tissue.

To compare tissue removal rate and thermal damage for a radiofrequency ablation device and an experimental ultrasound ablation device.

Twelve bovine meniscal specimens were treated in an identical fashion with (a) a 3.75mm 50° bipolar radiofrequency wand, Arthrocare Super Multivac 50 Arthrowand (Arthrocare Corporation, Sunnyvale, CA), operated in a free-hand manner in accordance with manufacturers instructions (n=6), and (b) an experimental flat-tipped 3mm 20kHz ultrasound probe, suspended vertically in a 500N force-controlled experimental rig (n=6).

Tissue removal rate (TRR), zone of thermal necrosis and zone of thermal alteration were calculated. Histological sections were prepared for each sample (H&E). Independent samples t-test was used to compare TRR, zone of thermal necrosis and zone of thermal alteration. Statistical analysis was performed using PASW Statistics (v.18, IBM SPSS Statistics, Chicago, IL, U.S.A.).

The mean TRR for meniscal debridement by the radiofrequency device was 5.59±1.1mg/s. This compared with a mean TRR of 4.74±1.4mg/s for debridement with the ultrasound device at settings (p=0.259, NS). Mean depth of tissue removal using the radiofrequency device was 2.21±0.26mm compared to 3.75±0.25mm (p< 0.001, ?²=0.09). Using the radiofrequency device, the mean depth of zone of thermal alteration was 1282±436µm, compared with 710±251µm for the force-controlled ultrasound device (p=0.29, ?²=0.42). For the radiofrequency device, the mean depth of zone of thermal necrosis was 64±41µm versus 97±44µm for the ultrasound device (p=0.239, NS). We observed a trend towards an increased zone of thermal necrosis and a reduced zone of thermal alteration for the ultrasound device, when compared with the radiofrequency device.

Ultrasonic debridement shows comparable thermal damage to existing radiofrequency meniscal debridement technology.

Background

There is minimal published data regarding the long-term functional outcome in pyogenic spinal infection. Previous studies have used heterogeneous, unreliable and non-validated measure instruments, or neurological outcome alone, yielding data that is difficult to interpret. We aim to assess long-term adverse outcome using standardised measures, Oswestry disability index (ODI) and MOS short form-36 (SF-36).