Cement brand and preparation effects cement-in-cement mantle shear strength.

Creating bi-laminar cement mantles as part of revision hip arthroplasty is well-documented but there is a lack of data concerning the effect of cement brand on the procedure. The aim of this study was to compare the shear strength of bi-laminar cement mantles using various combinations of two leading bone cement brands.Bi-laminar cement mantles were created using Simplex P with Tobramycin, and Palacos R+G: Simplex-Simplex (SS); Simplex-Palacos (SP); Palacos-Simplex (PS); and Palacos-Palacos (PP). Additionally, specimens were produced by rasping (R) the surface of the original mantle, or leaving it unrasped (U), leading to a total of eight groups (n = 10). Specimens were loaded in shear, at 0.1 mm/min, until failure, and the maximum shear strength calculated.The highest mean shear strength was found in the PSU and PSR groups (23.69 and 23.89 MPa respectively), and the lowest in the PPU group (14.70 MPa), which was significantly lower than all but two groups. Unrasped groups generally demonstrated greater standard error than rasped groups.In a further comparison to assess the effect of the new cement mantle brand, irrespective of the brand of the original mantle, Simplex significantly increased the shear strength compared to Palacos with equivalent preparation.It is recommended that the original mantle is rasped prior to injection of new cement, and that Simplex P with Tobramycin be used in preference to Palacos R+G irrespective of the existing cement type. Further research is needed to investigate more cement brands, and understand the underlying mechanisms relating to cement-in-cement procedures.

Surface replacement of the hip.

Attempts to resurface the hip joint date back to the 1930s. Throughout the last century many designs failed due to defective materials or fixation (or a combination). The metal-on-metal designs pioneered at the end of the century appeared to herald a new era, until difficulties associated with adverse reactions to metal debris were identified. Ultimately, a much narrower range of indications emerged - large, young males appear to be the ideal recipients. Implant design features and component orientation are crucial to the survivorship of these implants.

Empirical support for radiographic review: a follow-up study of total hip arthroplasty.

Routine post surgery surveillance of total hip arthroplasty (THA) is widely recommended to identify asymptomatic failure but inclusion of an x-ray adds to service costs. Evidence is needed to support orthopaedic opinion in order to identify what should be included in surveillance. An investigation was conducted to establish whether an x-ray is needed in addition to patient reported outcome measures. One hundred and fifty-four THA had been assessed at 3 years and were reviewed again at 6 to 9 years (mid-term) when radiographic signs of deterioration commonly appear. Data were explored for associations between radiographic changes and changes in the participants' Oxford Hip Score, age, EuroQol 5-D score or comorbidities. Hierarchical multiple regression analysis showed that the number of radiographic changes could not be predicted by any of the other variables. This supports the inclusion of an x-ray in THA surveillance and suggests that the state of the THA cannot be determined by the use of patient reported outcome measures alone. This has implications for future arthroplasty surveillance.

Evolution in hip resurfacing design and contemporary experience with an uncemented device.

The concepts of surface replacement of the hip and metal-on-metal articulation date back to the 1930s, and recent hip resurfacing designs have been more successful than their predecessors. Experience with the Cormet device followed initial collaboration with Mr. Derek McMinn. Both hybrid implants (a cementless cup and a cemented head) and entirely cementless implants, inserted with use of a variety of surgical approaches, yielded good results, with the cementless option increasing in popularity. The indications for hip resurfacing have become better understood, with the procedure considered most suitable for young and middle-aged males with a high activity profile. In addition, revision surgery, if necessary, has been associated in most cases with bone and soft-tissue conservation. Caution should be exercised when treating small individuals (especially females) and individuals with accompanying diagnoses other than osteoarthritis (such as hip dysplasia), for whom other bone-conserving options may be more appropriate to avoid an adverse reaction to metal debris. Correct implant placement during hip resurfacing is of critical importance.

Use of morphometry to quantify osteolysis after total hip arthroplasty.

BACKGROUND: Progressive osteolysis threatens the longevity of hip arthroplasties and radiographic review is recommended. Measurement of osteolytic lesions in a clinical setting has not been achieved easily in the past. Other radiologic investigations provide accurate information but cost and risk to the patient prohibit their use in routine review. QUESTIONS/PURPOSES: We developed a simple, reliable tool to be used in hip arthroplasty review to quantify osteolytic changes seen on plain film radiographs. METHODS: A morphometric grid was developed and tested on simulated and actual osteolytic lesions. Four health professionals measured lesions on each of two occasions. Intraclass correlation coefficients (ICC) for interobserver and intraobserver reliabilities were calculated and Bland-Altman plots were constructed for graphic analysis. RESULTS: The ICCs for interobserver reliability on the simulated and actual osteolytic lesions were in the range 0.90 to 0.96. The values for intraobserver (test-retest) reliability were 0.97 to 0.98. The Bland-Altman plots confirmed agreement and in each case, proximity of the mean to zero indicated no significant bias. CONCLUSIONS: The data show a morphometric grid is reliable for measuring osteolytic changes after hip arthroplasty. CLINICAL RELEVANCE: This tool has potential to improve monitoring processes for hip arthroplasty and to be useful in future research studies. Additional work is needed to test for validity and clinical importance of the measurements obtained.

A comparison of the validity and reliability of established bone stock loss classification systems and the proposal of a novel classification system.

The classification and management of aseptic loosening of total hip arthroplasty remains a distinct challenge to the modern orthopaedic surgeon. The aim of this study was to assess the inter-observer and intra-observer reliability of commonly used classification systems for the assessment of bone stock loss in revision hip surgery. Radiographs of 23 femoral and 32 acetabular components in 30 patients were assessed using the Paprosky, AAOS and Endo-Klinik classification systems. A novel classification system was introduced and also used to assess the radiographs. Assessment was undertaken by 3 surgeons on 2 separate occasions and the inter- and intra- observer reliability calculated. The novel classification system showed a good to very good intra-observer reliability for both femoral and acetabular components (0.77-1.0; p<0.001), performing better than the other systems assessed. The novel femoral system demonstrated moderate to good inter-observer agreement (0.46-0.73), performing as well as the Paprosky (0.63-0.80) and AAOS (0.63-0.68) femoral systems. The novel acetabular system demonstrated fair to moderate inter-observer reliability (0.35-0.51) performing better than the AAOS acetabular classification (0.07-0.10) and as well as the Paprosky acetabular classification system (0.59-0.60). We propose this novel system as an alternative method for assessing bone stock loss in revision hip surgery.

Leg length and offset following hip resurfacing and hip replacement.

We measured and compared critical parameters on antero-posterior radiographs from 28 patients who had undergone hybrid hip replacement (CPS/EPF), with 28 patients who had undergone cemented hip resurfacing (Cormet). All operations were performed by a single surgeon or under his supervision. We measured the femoral offset, acetabular offset, cup height and leg length on pre and post operative radiographs. The mean difference in femoral offset post-operatively was 3.52 mm (95% CI: -1.10 to 8.14 mm) in the hybrid group and -1.30 mm (95%CI: -2.88 to 0.29 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between these means was significant, test statistic t 2.025, p<0.05. This suggests that resurfacing restored the femoral offset more accurately than hybrid hip replacement. The mean difference in leg length post-operatively was 11.91 mm (95% CI: 8.21 to 15.62 mm) in the hybrid group and 4.87 mm (95% CI: 3.32 to 6.42 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between the means was significant, test statistic t 3.597, p<0.001. This suggests that resurfacing produced less change in leg length post-operatively than hybrid hip replacement. We found no statistically significant difference in ideal pre and post operative centre of rotation in the two groups. Proximal femoral anatomy was restored during hip resurfacing by resecting bone of a thickness determined by corresponding preoperative templating and implant thickness rather than relying on placement of the cutting ring at the head-neck junction. No femoral neck fractures occurred in the resurfacing group.

The effect of a modified posterior approach on blood flow to the femoral head during hip resurfacing.

The deep branch of the medial femoral circumflex artery is vulnerable to injury during posterior approaches to the hip. We modified the posterior approach during hip resurfacing in 10 patients by dividing the short external rotators 2 cm from their insertion into the femur. The cefuroxime concentrations in bone samples from the femoral heads were compared with results for the extended posterolateral approach from previous published work. There was no difference between the concentration of cefuroxime in bone when using the modified posterior approach (mean 5.6 mg/kg; CI 3.6 - 7.8) compared to the extended posterolateral approach (mean 5.6 mg/kg; CI 3.5 - 7.8; p=0.95). The similarity in femoral head perfusion between approaches suggests that the blood supply may be impaired further by capsulotomy and capsulectomy rather than by damage to the deep branch of the MFCA alone.

Biological organization of the extraocular muscles.

Extraocular muscle is fundamentally distinct from other skeletal muscles. Here, we review the biological organization of the extraocular muscles with the intent of understanding this novel muscle group in the context of oculomotor system function. The specific objectives of this review are threefold. The first objective is to understand the anatomic arrangement of the extraocular muscles and their compartmental or layered organization in the context of a new concept of orbital mechanics, the active pulley hypothesis. The second objective is to present an integrated view of the morphologic, cellular, and molecular differences between extraocular and the more traditional skeletal muscles. The third objective is to relate recent data from functional and molecular biology studies to the established extraocular muscle fiber types. Developmental mechanisms that may be responsible for the divergence of the eye muscles from a skeletal muscle prototype also are considered. Taken together, a multidisciplinary understanding of extraocular muscle biology in health and disease provides insights into oculomotor system function and malfunction. Moreover, because the eye muscles are selectively involved or spared in a variety of neuromuscular diseases, knowledge of their biology may improve current pathogenic models of and treatments for devastating systemic diseases.

The jaundiced gunn rat model of auditory neuropathy/dyssynchrony.

OBJECTIVE: High levels of bilirubin are neurotoxic and may result in deafness or auditory neuropathy/auditory dyssynchrony (AN/AD). The jaundiced (jj) Gunn rat animal model of kernicterus has electrophysiologic and neuroanatomic abnormalities of brainstem auditory nuclei with normal cochlear microphonic recordings. We examined morphologic changes in the cochlea, spiral ganglion, and auditory nerve and relate these findings to current understanding of AN/AD. METHODS: At 15 days of age, jj and nonjaundiced (Nj) littermates were injected with sulfadimethoxine (sulfa) and killed 3 days later by transcardial perfusion. Sections were cut through decalcified temporal bones, cochlear nerves, and auditory brainstem and processed for light and electron microscopy and immunohistochemical localization of calbindin-D and parvalbumin. RESULTS: Spiral ganglion neurons were severely degenerated with a paucity of myelinated axons in jj animals. Electron microscopy of the intramodilar auditory nerve revealed a lack of large caliber axons in jj-sulfa versus Nj-sulfa controls. Large diameter degenerating axons were characterized by an electron-dense atrophied axis cylinder resembling an axonopathy. CONCLUSIONS: Our findings of abnormal spiral ganglion cells and selective loss of large, myelinated auditory nerve fibers with no abnormalities in cochlear hair cells, support the sulfa-treated jj Gunn rat as a model for bilirubin induced AN/AD. The paucity of large caliber neurons undermines temporal coding of auditory information and neural synchrony and demonstrates that in addition to brainstem auditory nuclei, spiral ganglion neurons are selectively vulnerable to bilirubin toxicity.

Gentamicin concentrations in diagnostic aspirates from 25 patients with hip and knee arthroplasties.

BACKGROUND: There is little information on long-term release of antibiotics from impregnated bone cement. PATIENTS AND METHODS: We assayed joint fluids obtained for diagnostic purposes from 25 patients for the presence of gentamicin. All patients had presented with failing or painful joints up to 20 years following primary hip or knee arthroplasty, using gentamicin-impregnated cement. RESULTS: Gentamicin was detected in the joint fluids from 9 of 15 patients with knee prostheses and 4 of 10 patients with hip prostheses. The concentrations ranged from 0.06 mg/L to 0.85 mg/L with no significant differences in concentration between the patients with hip or knee prostheses, or the type of prosthesis. We found no relationship between the gentamicin concentration and the time after primary arthroplasty. INTERPRETATION: Although most concentrations were below the levels required to inhibit susceptible pathogens, we conclude that gentamicin release around failing implants may lead to false negative cultures in some patients and provide selective pressure for the emergence of resistance where infection is present in others.

Incidence of stereopsis after treatment of infantile esotropia with botulinum toxin A.

PURPOSE: The incidence of stereoscopic vision following surgery for infantile esotropia has been reported, but not from patients treated with simultaneous bimedial injection of botulinum toxin A. We previously reported other findings from 41 patients treated with botulinum toxin A before the age of 12 months. The purpose of this study was to report the incidence of stereopsis in these patients after long-term follow-up. PATIENTS AND METHODS: Data were acquired by recording the response to subjective stereoscopic testing during the postinjection follow-up period when reliable subjective responses could be obtained. At least 5 years had passed following injection, and the mean age of the patients was 8 years. RESULTS: Of the 41 patients, 11 were lost to follow-up, 10 had no stereopsis, 9 had gross stereopsis (according to Titmus fly tests), 1 had 800 seconds of stereoscopic vision, 2 had 400 seconds, 2 had 200 seconds, 1 had 60 seconds, and 5 had 40 seconds. CONCLUSIONS: In this study, two-thirds of the patients acquired stereopsis following simultaneous bimedial injection of botulinum toxin A for infantile esotropia. Stereopsis acquisition following injection of botulinum toxin A had a success rate comparable with that reported for surgically corrected infantile esotropia. Bimedial injection of botulinum toxin A accompanied by alternate patching prior to injection and diligent attention at ages ranging from 4 to 12 months is a simple and efficacious method for the management of infantile esotropia.

Demyelination of vestibular nerve axons in unilateral Ménière's disease.

We conducted a study to determine whether vestibular nerves in patients with unilateral Ménière's disease whose symptoms are refractory to medical management exhibit neuropathologic changes. We also endeavored to determine whether retrocochlear abnormalities are primary or secondary factors in the disease process. To these ends, we obtained vestibular nerve segments from five patients during retrosigmoid (posterior fossa) neurectomy, immediately fixed them, and processed them for light and electron microscopy. We found that all five segments exhibited moderate to severe demyelination with axonal sparing. Moreover, we noted that reactive astrocytes produced an extensive proliferation of fibrous processes and that the microglia assumed a phagocytic role. We conclude that the possible etiologies of demyelination include viral and/or immune-mediated factors similar to those seen in other demyelinating diseases, such as multiple sclerosis and Guillain-Barré syndrome. Our findings suggest that some forms of Ménière's disease that are refractory to traditional medical management might be the result of retrocochlear pathology that affects the neuroglial portion of the vestibular nerve.

Localization of biotinidase in the brain: implications for its role in hearing loss in biotinidase deficiency.

Biotinidase deficiency is an autosomal recessively inherited disorder characterized by neurological and cutaneous features, including sensorineural hearing loss. Although many of the features of the disorder are reversible following treatment with biotin, the hearing loss appears to be irreversible. To better characterize the nature of the hearing loss in this disorder, location of the expression and presence of biotinidase within the brain was examined using Northern blot analysis, in vitro hybridization of a cDNA panel, and immunohistochemical staining. Results indicate low, but detectable expression of biotinidase throughout the brain, but increased concentrations of biotinidase within the dorsal cochlear nucleus, ventral cochlear nucleus, and superior olivary complex of the brainstem, as well as, in the hair cells and spiral ganglion of the cochlea. These findings suggest that biotinidase and possibly biotin plays an important role in hearing.

Immunohistochemical localization of calcium-binding proteins in the brainstem vestibular nuclei of the jaundiced Gunn rat.

Vestibular gaze and postural abnormalities are major sequelae of neonatal hyperbilirubinemia. The sites and cellular effects of bilirubin toxicity in the brainstem vestibular pathway are not easily detected. Since altered intracellular calcium homeostasis may play a role in neuronal cell death, we hypothesized that altered expression of calcium-binding proteins may occur in brainstem vestibular nuclei of the classic animal model of bilirubin neurotoxicity. The expression of the calcium-binding proteins calbindin-D28k and parvalbumin in the brainstem vestibular pathways and cerebellum of homozygous recessive jaundiced (jj) Gunn rats was examined by light microscopy and immunohistochemistry at 18 days postnatally and compared to the findings obtained from age-matched non-jaundiced heterozygous (Nj) littermate controls. Jaundiced animals exhibited decreased parvalbumin immunoreactivity specifically in synaptic inputs to superior, medial, and inferior vestibular nuclei, and to oculomotor and trochlear nuclei, whereas the neurons retained their normal immunoreactivity. Jaundiced animals also demonstrated a decrease in calbindin expression in the lateral vestibular nuclei and a paucity of calbindin-immunoreactive synaptic endings on the somata of Deiters' neurons. The involved regions are related to the control of the vestibulo-ocular and vestibulospinal reflexes. Decreased expression of calcium-binding proteins in brainstem vestibular neurons may relate to the vestibulo-ocular and vestibulospinal dysfunction seen with clinical kernicterus, and may provide a sensitive new way to assess bilirubin toxicity in the vestibular system.