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PubMed1997

[Adjusting the geometry of implantable hearing aid components to human temporal bone. I: Electromechanical transducer].

Prerequisite to implantation of a piezoelectrical transducer of an implantable hearing aid is a shape allowing its implantation into human mastoid and middle ear. To approach this problem, a consecutive series of six transducer prototypes was created in an iterative process. Their functional geometry was evaluated in 50 human temporal bones. A shape for a functioning transducer was found which will enable implantation in 78% of the cases examined (confidence interval: 61.5%-89.2%). It will allow simultaneous implantation of the transducer into the mastoid and microphone, which is situated transmastoidal in the posterior wall of the ear canal. Furthermore, the transducer may be coupled to the ossicular chain or the perilymph.

Cochlear Implantation↗
PubMed1997

[Adjusting the geometry of implantable hearing aid components to human temporal bone. II: Microphone].

Recently, an implantable hearing aid for rehabilitation of sensorineural hearing loss has been developed. One component of the device is the microphone for implantation into the posterior canal wall. The membrane of the microphone can be covered by skin, cartilage, or fascia, avoiding reduction in sound transmission at the same time. In the study presented here, the microphone was implanted into 50 cadaver specimens of human temporal bone. Localization of the microphone was determined by the anatomical situation of the facial nerve. The microphone and the piezoelectric transducer could be implanted in 78% of the temporal bones after total mastoidectomy. In the final version of the microphone, the size was 4.5 mm and total weight 400 mg.

Cochlear Implantation↗
PubMed1997

[Intraoperative evaluation of signal transduction of prototypes of implantable hearing aid transducers in the human].

During routine middle ear surgery prototypes of implantable piezoelectric hearing aid transducers were coupled to the ossicular chain of 28 patients. Pure tone thresholds in a broad frequency range (250 Hz-8 kHz) and perception of music were the basis of psychoacoustic evaluation of the transfer properties of the prototypes in this human study. The piezoelectric transducer reached an equivalent transducer sound-pressure level of up to 145 dB SPL and frequencies of 10 kHz. The dynamics for music reached 32 dB, which was identical with the results of the preoperative investigations using hi-fi headsets (33 dB). The low nonlinear distortions of around 0.1% and the frequency range up to 10 kHz are reflected in the positive evaluation of sound quality by 84% of the patients involved. The study is the basis for realizing a piezoelectric transducer designed for routine clinical implantations. The transducer is thought to be part of a totally implantable future hearing aid for rehabilitation of moderate and severe sensory neural hearing loss predominantly in the middle and high frequency range.

Adult↗
PubMed1997

[An implantable hearing aid for inner ear hearing loss. Short-term implantation of microphone and transducer].

A microphone constructed for implantation in the posterior wall of the auditory canal and a piezoelectric transducer serving as the main components of an implantable hearing aid were temporally implanted in five patients during middle ear surgery under local anesthesia. The microphone was positioned beneath the skin of the auditory canal such that it completely covered the microphone membrane. The vibratory element of the transducer was coupled to the malleus in four patients with normal ossicular chains and directly to the stapes in one patient with missing incus. The microphone and transducer were electrically connected with an external battery-driven signal amplifier. Speech material and music were presented in the operation room at a sound level of 65 dB SPL under free-field conditions. The patients had to estimate the quality of speech, music, and their own voice as well as the effects of bone-conducting noises. All patients were able to hear with the system. An intraoperative talk without vision contact was possible without any problems, as was understanding of numerals ("Freiburger Zahlentest"). Perception of music was judged as "clear and undistorted with all broadband component." The estimation was also valid for one patient with a sensorineural hearing loss. One patient declared the music to be "a little of unnatural." Bone-conducted sound was estimated as normal in two patients, better than without an implant in one patient with sensorineural hearing loss, and "somewhat metallic" in another patient. Hearing the own voice was considered "normal" in two cases "monotonous" in one case, and "a little bit roaring" in another case. An amplification factor that can be technically realized in an implantable hearing aid was necessary for one of the patients with sensorineural hearing loss to perceive music at a pleasant volume. On the basis of this study, essential requirements for the construction of a fully implantable hearing aid are fulfilled.

Adult↗
PubMed1998

[Measuring vibration properties of middle ear implants with the mechanical middle ear model. Initial results].

With the aid of a mechanical middle ear model (MMM) the sound transmission properties of different middle ear implants were investigated. Input of the MMM involved a broad-band signal from 100 to 5000 Hz that was supplied by a miniaturized loudspeaker. Displacement of an artificial stapes footplate was measured by a fiberoptic probe. The transfer functions of four different total ossicular replacement prostheses (TORPs) of different materials and shapes were compared. Three of the devices revealed similar transfer functions which corresponded to the typical curve of the normal middle ear. One of the prostheses demonstrated a high-frequency deterioration of approximately 5 dB. This effect was explained by a 3- to 6-times higher mass of the implant when compared to the others. Altogether, the weight of the prosthesis seems to have the most marked impact on sound transmission to the inner ear, whereas stiffness of the implant itself is less crucial as long as it can be regarded as a rigid body.

Acoustic Impedance Tests↗
PubMed2004

[Endoprostheses of the knee joint].

Due to the advances in prosthesis design and standardisation of implant techniques, the maintenance of implants in arthroplasty of the knee joint has enormously increased during the past few years. Various arthroplastic designs enable an adjustment towards the patient's individual indiction and anatomy. For one-compartmental arthrosis, monocondylous prosthesis can be implanted using microinvasive operation techniques. Prerequisite for mere joint resurfacing is an intact lateral ligament apparatus, whereas the the symmetrical ligament balancing is essential for long-term analgesia, joint stability and good flexion. Aseptic loosening, discreet infections, instabilities and patellar problems are common reasons for painful knee arthroplastics.

Arthroplasty, Replacement, Knee↗
PubMed2005

[What is the influence of the approach to intraoperative measurement of the knee joint on total knee arthroplasty? A navigation-controlled study on a cadaver knee].

Correct postoperative leg alignment and stability of the total knee prosthesis over the full range of movement is one critical factor for successful TKA. The anatomic approach is still the subject of controversy. The aim of our study was to elucidate the influence of the surgical approach on the ligament balancing and the anterioposterior limb axis.On five cadaver knees we studied the influence of the subvastus, midvastus, medial parapatellar, rectus snip, and tuberosity osteotomy approaches on the anterioposterior leg axis in extension and the rotation of the femoral component in flexion. Measurements were performed and documented by CT-free Ci-Navigation-System. Ligament tension was measured with a tensor device. We found that the subvastus approach leads to less widening of the medial compartment than all other approaches in extension. In 90 degrees flexion we found a similar influence. The consecutive release from subvastus to midvastus to medial parapatellar approach leads to a further opening of 0.5-1 degrees valgus in extension as well as in flexion. An everted patella amplifies this influence. The surgeon has to be aware of the impact on the ligament situation in regard to the anatomic approach when ligament balancing and soft tissue releases are carried out. Patella eversion should be avoided when managing soft tissues.

Arthroplasty, Replacement, Knee↗
PubMed2005

[Prosthetic care of proximal femur fractures].

The endoprosthetic replacement of the hip joint or its components in fractures of the proximal femur is a standard method. Indications for replacement are strongly dislocated intracapsular femoral neck fractures in elderly patients, fractures with an existing arthritis of the hip joint, and profound osteoporosis. Improved perioperative management and more gentle anesthetic techniques have helped to reduce perioperative mortality from nearly 50% to 11.5% over the last 40 years. As routine treatment options, the bipolar endoprosthesis without replacement of the acetabular joint surface and total hip replacement in case of degenerative arthritis of the acetabular joint surface are commonly used. The mere replacement of the femoral head with a simple femoral head prosthesis should be reserved for exceptional cases. For the implantation of a hip joint prosthesis and its uncomplicated post-treatment and long-term durability, careful preoperative planning is essential together with the selection of a suitable implant, its optimal bony fixation, avoidance of intra-operative complications and restoration of the anatomical landmarks such as the centre of rotation of the hip joint, the offset of the prosthetic shaft as well as leg length. Despite the high standard of endoprosthetics in Germany, the results are still improvable in comparison to other countries. Measures which preserve the joint as well as the bone will be increasingly important in prophylaxis of further complications. In addition, more attention should be paid to the prophylaxis of falls and a sufficiently guide-lined therapy of osteoporosis for the prophylaxis of fractures of the elderly.

Arthroplasty, Replacement, Hip↗
PubMed2006

[Shaft lengthening in hip replacement: experimental studies on bending stiffness].

BACKGROUND: Cortical atrophy of the proximal femur can be seen after wearing a total hip prosthesis for several years because loads are borne distally at the prosthesis tip. To achieve stable prosthesis implantation on the one hand and proximal bone regeneration on the other hand in hip revision arthroplasty, lengthening of the shaft component distributes loading forces to the femoral shaft first. It concentrates them to the proximal femur later through a higher elasticity. METHODS: In a three-point bending study the bending stiffness of an elastic slotted hip prosthesis shaft lengthening (HSL) was compared with that of the Synthes universal femoral nail (MN) and the unslotted HSL. RESULTS: The slotting of the elastic HSL has a significant influence on its bending stiffness; it lies 1,287 N/mm (76%) over that of the MN, but 1,855 N/mm (38%) under that of the unslotted HSL. Altogether the slotted HSL is rather more comparable to the MN than to the unslotted HSL regarding its bending conduct. CONCLUSION: The results confirm the elasticity of the slotted HSL in the style of conventional intramedullary nailing and encourage-above all in the context of previous clinical studies-its further use.

Biomechanical Phenomena↗
PubMed2006

[Shoulder prostheses].

The design of shoulder prostheses has been developed through four generations which mirror adaptation to our increasing knowledge of the biomechanics of the shoulder joint. Modern shoulder prostheses are adapted to the size, inclination, posterior offset, and retrotorsion of the shoulder. The main reasons for implantation of a shoulder prosthesis are primary osteoarthritis, posttraumatic and rheumatoid arthritis, avascular necrosis, instability arthritis and cuff defect arthropathy. Typical implants are cup prostheses for surface replacement, anatomical stem prostheses, and reverse prostheses. Total prostheses are functionally better as soon as the arthritis involves the glenoid, whereas hemiprostheses should be preferred as long as the glenoid is intact. The stem is mostly cemented, whereas in younger patients with good bone quality a cementless stem may be used. Cemented glenoids may be considered as standard.

Arthritis, Rheumatoid↗
PubMed1997

[Computer-assisted robotics in hip endoprosthesis implantation].

The most important prerequisite for permanent fixation of an implant is primary stability. Osteointegration of the implant is a major goal in cementless total hip replacement (THR). This means direct contact between bone and implant leading to fixation of the implant in the bone without the interference of fibrous tissue. In addition to the design of the implant, the structure of the implant surface and the material of the implant, the specific operational technique plays a major role in permanent fixation. Only the conical fixation of femoral implants guarantees high primary stability in cementless THR. The type of fixation of the implant in the femoral cavity and the resulting load transfer from implant to bone has a decisive effect on the durability of the prostheses. In order to achieve optimal primary fixation of the implant, robot-assisted implantation of the cementless implant has been performed at the Berufsgenossenschaftliche Unfallklinik Frankfurt am Main since the summer of 1994. After preoperative planning at a three-dimensional graphic work station these data are transferred to the robot, which transforms the preoperative planning by milling the femoral cavity with the highest precision. So far this type of surgery has been performed on 300 patients. The encouraging postoperative results prompted us to install the second system of Robodoc at the Berufsgenossenschaftliche Unfallklinik Frankfurt.

Arthroplasty, Replacement, Hip↗
PubMed2004

[New developments for the surgical treatment of shoulder problems].

Tremendous advancement has been made in the surgical treatment of the shoulder within the last years. Arthroscopic techniques for treatment of rotator cuff lesions, instability problems and biceps tendon lesions are today established because of significant improvement of instruments, suture materials and anchor techniques. The 4th generation of shoulder prosthesis systems guarantee today anatomical and biomechanical advantages with significant functional improvement for the patient.

Arthroplasty, Replacement↗
PubMed2005

[Implantation of the AMS 800 artificial sphincter system in a woman via a paraurethral access].

The procedure described demonstrates the feasibility of reliable implantation of an artificial sphincter system in female patients via a paraurethral access between the urethral orifice and the clitoris following radical cystectomy with continent, orthotopic urinary diversion and postoperatively developed urinary stress-incontinence. The technique presented avoids the more invasive transperitoneal or transvaginal approaches which jeopardize the neobladder-neck and increase the risk for infections or fistulas.

Female↗
PubMed2004

[Damage analysis illustrated by two cases of broken ceramic inserts. Recommendations for avoiding breakages caused by handling].

Due to modular design today's total hip endoprostheses provide the choice of different bearing surfaces. Particle-induced osteolysis is the major reason for implant failure. Therefore, minimization of wear rates is the essential factor for the improvement of long-term function of the implants. The bearing couple ceramic-on-ceramic offers a linear wear rate of about 0.005 mm/year. That is an essential prerequisite for successful treatment of young and active patients. Ceramic femoral heads and taper fixation became standard. After some problems in the 1970s, manufacturers achieved all kinds of improvements. Surgeons learned how to handle ceramic femoral heads correctly. Nowadays ceramic heads are reliable implants. Ceramic inserts have been used since the mid-1990s. Some acetabular systems with ceramic inserts are used in clinical studies, some are approved. Complications with ceramic inserts are rare, e.g., fracturing or chipping off. Mostly those problems are due to mishandling. In this study some clinical failures are analyzed. Recommendations how to improve the handling of ceramic inserts are proposed and discussed.

Acetabulum↗
PubMed2005

[Procedures for treatment of joint mechanics impairment in the rotating Endo-model knee prosthesis].

In cases of mechanical damage of the Endo model rotating knee prosthesis, it is not necessary to change the complete prosthesis. Isolated replacement of the mechanics is possible. We changed a sled prosthesis of a 66-year-old patient to a rotating knee prosthesis because of ligament instability. After the patient fell and traumatized the operated knee, she experienced pain during weight bearing and instability. Because clinical and fluoroscopic examinations verified instability of the prosthesis, we decided to change the mechanics of the rotating knee prosthesis. In conclusion, mechanical damage of a rotating knee prosthesis is a rare complication. Operative treatment is easy to manage if replacement parts and instruments to change the mechanics have been organized preoperatively.

Aged↗
PubMed2005

[Prosthetic surgery for the rheumatoid hand].

In rheumatoid arthritis the complex biomechanics of the hand is impaired due to elongation of ligaments and displacement of tendons. This results in eccentric transfer of high loads to the arthritic joints. This pathological load transmission remains frequently after joint replacement. This is the main reason for the high failure rate after arthroplasty in the hand. Therefore, most of the endoprostheses are no longer in use. As long as techniques for reliable reconstruction of the periarticular structures have not been established, silicon arthroplasty will remain the golden standard. Arthroplasty of the wrist and the PIP joints is seldom performed. After arthrodesis of these joints, the function of the hand is sufficient and complications are seldom. Midterm results after resectional arthroplasty of the CMC-I joint show less complications and results comparable with silicon arthroplasty.

Arthritis, Rheumatoid↗