Intracochlear pressure as an objective measure for perceived loudness with bone conduction implants

BACKGROUND

The generally accepted method to assess the functionality of novel bone conduction implants in a preclinical stage is to experimentally measure the vibratory response of the cochlear promontory. Yet, bone conduction of sound is a complex propagation phenomenon, depending on both frequency and amplitude, involving different conduction pathways.

OBJECTIVES

The aim of this study is to validate the use of intracochlear sound pressure (ICP) as an objective indicator for perceived loudness for bone conduction stimulation. It is investigated whether a correlation exists between intracochlear sound pressure measurements in cadaveric temporal bones and clinically obtained results using the outcome of a loudness balancing experiment.

METHODS

Ten normal hearing subjects were asked to balance the perceived loudness between air conducted (AC) sound and bone conducted (BC) sound by changing the AC stimulus. Mean balanced thresholds were calculated and used as stimulation levels in a cadaver trial (N = 4) where intracochlear sound pressure was measured during AC and BC stimulation to assess the correlation with the measured clinical data. The intracochlear pressure was measured at the relatively low stimulation amplitude of 80 dBHL using a lock-in amplification technique.

RESULTS

Applying AC and BC stimulation at equal perceived loudness on cadaveric heads yield a similar differential intracochlear pressure, with differences between AC and BC falling within the range of variability of normal hearing test subjects.

CONCLUSION

Comparing the perceived loudness at 80 dB HL for both AC and BC validates intracochlear pressure as an objective indicator of the cochlear drive. The measurement setup is more time-intensive than measuring the vibratory response of the cochlear promontory, yet it provides direct information on the level of the cochlear scalae.

Maintaining range of motion after cervical discectomy does not prevent adjacent segment degeneration

BACKGROUND

Motion preservation prostheses were introduced to prevent adjacent disc degeneration (ASD) and to diminish neck disability in the postsurgical follow-up. However, it is still a controversial issue, and the relationship between range of motion (ROM) and ASD has not been studied.

PURPOSE

To compare the correlation between ROM of the cervical spine and the presence of radiological ASD after anterior discectomy. Clinical outcome was also correlated to ROM and ASD.

STUDY DESIGN

Retrospective cohort study.

METHODS

In all, 253 patients who underwent anterior discectomy for cervical radiculopathy due to a herniated disc were analyzed for segmental and global cervical ROM and the presence of ASD both preoperatively, and 12 and 24 months postoperatively. Patients who were included in two randomized, double-blinded trials comparing anterior cervical discectomy with arthroplasty, anterior cervical discectomy with intervertebral cage, or anterior cervical discectomy without intervertebral cage for one level disc herniation were analyzed. ROM was defined by a custom-developed image analysis tool. ASD was defined by decrease in disc height and anterior osteophyte formation on X-rays. Clinical outcome was evaluated by means of the Neck Disability Index (NDI).

RESULTS

Two years postoperatively, no correlation was demonstrated between ROM and ASD. The incidence of ASD was comparable in the three groups, being 34% at baseline, and 58% at 2-year follow-up. Likewise, ASD progression was comparable in the three treatment arms. No correlation was demonstrated between ROM and NDI or ASD and NDI.

CONCLUSIONS

Since ROM is not correlated to ASD, and clinical outcome is not correlated to ROM either, the relevance of continued ROM at the target level seems absent.

A MEMS Condenser Microphone-Based Intracochlear Acoustic Receiver

GOAL

Intracochlear sound pressure (ICSP) measurements are limited by the small dimensions of the human inner ear and the requirements imposed by the liquid medium. A robust intracochlear acoustic receiver (ICAR) for repeated use with a simple data acquisition system that provides the required high sensitivity and small dimensions does not yet exist. The work described in this report aims to fill this gap and presents a new microelectromechanical systems (MEMS) condenser microphone (CMIC)-based ICAR concept suitable for ICSP measurements in human temporal bones.

METHODS

The ICAR head consisted of a passive protective diaphragm (PD) sealing the MEMS CMIC against the liquid medium, enabling insertion into the inner ear. The components of the MEMS CMIC-based ICAR were expressed by a lumped element model (LEM) and compared to the performance of successfully fabricated ICARs.

RESULTS

Good agreement was achieved between the LEM and the measurements with different sizes of the PD. The ICSP measurements in a human cadaver temporal bone yielded data in agreement with the literature.

CONCLUSION

Our results confirm that the presented MEMS CMIC-based ICAR is a promising technology for measuring ICSP in human temporal bones in the audible frequency range.

SIGNIFICANCE

A sensor for evaluation of the biomechanical hearing process by quantification of ICSP is presented. The concept has potential as an acoustic receiver in totally implantable cochlear implants.

10-year follow-up after implantation of the Bryan Cervical Disc Prosthesis

PURPOSE

Cervical arthroplasty is being used as an alternative for cervical fusion, but long-term follow-up results have rarely been reported. In this paper, we present 10-year follow-up results after implantation of the Bryan Cervical Disc Prosthesis in a single center.

METHODS

89 patients underwent implantation of a single-level Bryan Cervical Disc Prosthesis to treat radiculopathy and/or myelopathy. Clinical (Neurological Success, Neck Disability Index (NDI), Neck- and Arm-Pain, and SF-36) and radiological follow-up was prospectively organized up to 10 years after surgery. Adverse events and second surgeries were recorded and evaluated.

RESULTS

Ten-year follow-up data were available for 72 (81%) patients. Maintenance or improvement of the neurological state was seen in 89% of patients after 10-year follow-up. SF-36 PCS scores improved significantly at all follow-up points. SF-36 MCS improvement was significant at 4 and 6 year, but not at 8- and 10-year follow-up. Significant improvement for NDI, and Neck- and Arm-Pain scores was found for the subgroup of patients in whom these data were available. Mean angular motion of the prosthesis at 10-year follow-up was 8.6°. Mobility of the device, defined as >2° of angular motion, was reached in 81% of patients. During the study period, 21 patients (24%) developed new or recurrent radiculopathy or myelopathy, the majority of these being treated conservatively. Seven patients (8%) required 8 additional spine surgeries to treat persistent or recurrent symptoms. Of these, 2 patients (2%) were reoperated at the index level and at 5 (6%) an adjacent level.

CONCLUSION

In this study, favorable long-term clinical outcome after implantation of the Bryan Cervical Disc Prosthesis was seen, with the majority of prostheses remaining mobile after 10-year follow-up. However, still 6% of patients required adjacent level surgery.

Stochastic queueing-theory approach to human dynamics

Recently, numerous studies have shown that human dynamics cannot be described accurately by exponential laws. For instance, Barabási [Nature (London) 435, 207 (2005)] demonstrates that waiting times of tasks to be performed by a human are more suitably modeled by power laws. He presumes that these power laws are caused by a priority selection mechanism among the tasks. Priority models are well-developed in queueing theory (e.g., for telecommunication applications), and this paper demonstrates the (quasi-)immediate applicability of such a stochastic priority model to human dynamics. By calculating generating functions and by studying them in their dominant singularity, we prove that nonexponential tails result naturally. Contrary to popular belief, however, these are not necessarily triggered by the priority selection mechanism.

Longitudinal prospective long-term radiographic follow-up after treatment of single-level cervical disk disease with the Bryan Cervical Disc

BACKGROUND

Many short- and intermediate-term radiological and clinical studies on cervical arthroplasty with the Bryan Cervical Disc have been published, providing, most of the time, satisfactory results.

OBJECTIVE

To prospectively assess the intermediate and long-term radiographic characteristics of disk replacement surgery with the Bryan Cervical Disc and to correlate these results with clinical outcome.

METHODS

Range of motion was measured with a validated tool. Intervertebral disk degeneration was assessed with a quantitative scoring system. Heterotopic ossification was evaluated with a previously published scoring system. Device stability was investigated by measuring subsidence and anteroposterior migration. General clinical patient outcome was assessed with the Odom classification system.

RESULTS

Eighty-nine patients were initially included in this prospective long-term study. One patient was reoperated on at the index level and 4 were reoperated on at an adjacent level; those patients were not further analyzed. The mobility at the treated level was preserved in > or = 85% of our cases. The insertion of the prosthesis did not lead to an increase in mobility at the adjacent levels. The degeneration score increased at both adjacent levels. Heterotopic ossification was present in 34% to 39% of the patients, depending on the follow-up point. No cases of anteroposterior migration or subsidence were found. More than 82% of all patients had a good to excellent clinical outcome in the long run.

CONCLUSION

The device maintains preoperative motion at the index and adjacent levels, seems to protect against acceleration of adjacent-level degeneration as seen after anterior cervical discectomy and fusion, and remains securely anchored in the adjacent bone mass in the long run. Heterotopic ossification was frequently seen. The vast majority of all patients had a good to excellent clinical outcome.