Effect of shape and size of supraspinatus tears on rotator cuff strain distribution: an in vitro study.

BACKGROUND: The impact of the size and shape of a supraspinatus tear on the strain of the intact rotator cuff and the kinematics of the shoulder is still unknown. This, however, can be relevant when deciding whether surgical reconstruction is required to prevent an increase in a tendon defect. In this study, the effect of tear width and shape on rotator cuff strain and glenohumeral kinematics was evaluated during active abduction. METHODS: Twelve fresh-frozen cadaveric shoulders with intact rotator cuffs were used in this study. We created 50% and 100% wide (full-thickness) crescent-shaped (CS) tears (n = 6) and reverse L-shaped (rLS) tears (n = 6) in the supraspinatus tendon and measured strain and kinematics during active humeral elevation until 30°. RESULTS: Both tear shapes and sizes led to an increase in internal rotation, supraspinatus loading force, and superior translation of the humerus. For the 100% wide tear size, anterior translation was observed in the CS tear group, whereas in the rLS tear group, this translation occurred mainly in the posterior direction. Strain was higher in the infraspinatus during the first 25° of abduction in comparison with the supraspinatus tendon in both tear shape groups. An analysis of the anterior and posterior tear borders showed a higher strain concentration on the same side of the tear in the CS tear group with 50% and 100% wide tears. CONCLUSIONS: The influence of different tear shapes on translation in the anterior-posterior direction was evident as both CS and rLS tears led to an oppositely directed translation of the humeral head. The strain analysis showed a stress-shielding effect of the infraspinatus at the beginning of abduction. Therefore, special attention must be paid to correctly identify the tear extension and adequately reconstruct the rotator cuff footprint. Moreover, the constant location of maximum strain in the CS tear group may lead to an earlier progression than in the rLS tear group.

Experimental study of an implantable fiber-optic microphone on human cadavers.

In this paper, we present the results of an experimental study about a novel fiber optical vibrometer, aimed to be used as a totally implantable fiber-optic microphone for hearing aids. The sensor head, implanted inside the human cadaver middle ear, detects the amplitude of the incus vibrations, which are produced by an external acoustical source. The probe beam of coherent vertical cavity surface emitting laser (VCSEL) radiation is directed to the incus and the phase-modulated reflected beam is captured and demodulated. The problem of interferometric fading was solved using two quasi-quadrature signals, passively produced by the 3 × 3 single-mode fiber-optic coupler, processed by a special embedded algorithm. The implanted optoelectronic module works with very low-power consumption, performs real-time signal processing and outputs an analogue signal proportional to the incus vibration. The amplitude of the incus vibrations at different sound pressure levels (SPL) from 40 to 90 dB and at frequencies from 100 Hz to 10 kHz were measured by the implanted system. The system was evaluated on five cadaver skulls. The measured amplitudes were in the range of 1 pm to 5 nm, depending on the subjected skull and the applied sound pressure.