Getting the drop on Staphylococcus aureus: Semiquantitative Staphylococcus aureus nasal colony reduction in orthopedic surgery reduces surgical site infection.

BACKGROUND: Surgical site infection (SSI) is a frequent health care-associated infection. We aimed to reduce SSI risk after joint arthroplasty and spine surgery by reducing Staphylococcus aureus colonization burden with presurgery intranasal povidone-iodine (PVP-I) application in conjunction with skin antisepsis ("the intervention"). METHODS: Retrospective case-control study; postintervention cohort versus a historical cohort. Adults who underwent joint arthroplasty or spine surgery during February 2018 through October 2021 ("post-intervention cohort") included. In the analysis cases any patient who underwent surgery and developed SSI within 90 days postsurgery, controls had no SSI. Postintervention cohort data were compared with a similar retrospective 2016 to 2017 patient cohort that did not use intranasal PVP-I. RESULTS: The postintervention cohort comprised 688 consecutive patients aged 65y/o, 48.8% male, 28 cases, and 660 controls. Relatively more cases than controls had diabetes mellitus (P = .019). There was a 39.6% eradication rate of S aureus nasal colonization post intranasal PVP-I (P < .0001). SSI rate was higher in patients positive versus those negative for S aureus on a 24-hour postsurgery nasal culture (P < .0001). The deep SSI rate per 100 operations postintervention versus the historical cohort decreased for all surgical procedures. CONCLUSIONS: Semiquantitative S aureus nasal colony reduction using intranasal PVP-I is effective for decreasing SSI rate in joint arthroplasty and spine surgery. In patients with presurgery S aureus nasal colonization additional intranasal PVP-I postsurgery application should be considered.

Internal medicine physician embedded in an orthopedic service in a level 1 hospital: clinical impact.

BACKGROUND: The aim of our study was to evaluate the impact of an internist physician specialized in diabetes, appointed as an in-house physician in the orthopedic wards, on improving clinical outcomes and in particular 30-day mortality. METHODS: We analyzed a cohort of patients hospitalized more than 24 h in the orthopedic service. The analyses included a comparative analysis between the pre- and post-intervention time periods and an interrupted time series (ITS) analysis, which were conducted in stratification to three populations: whole population, patients with at least one chronic disease and/or older than 75 years of age and patients diagnosed with diabetes. The primary outcome was 30-day mortality following the hospitalization. RESULTS: A total of 11,546 patients were included in the study, of which 19% (2212) were hospitalized in the post intervention period. Although in the comparative analysis there was no significant change in 30-day mortality, in the ITS there was a decrease in the mortality trend during the post intervention period in the entire and chronic disease/elderly populations, compared to no change during the pre-intervention period: a post-intervention slope of - 0.14(p value < 0.001) and  - 0.11(p value = 0.03), respectively. Additionally, we found decrease in length of stay, increase in transfers to the internal medicine department with a negative trend, increase in HbA1c testing during the hospitalization and changes in diabetes drugs administration. CONCLUSION: The presence of an internist in the orthopedic wards is associated with health care improvement; decrease in the 30-day mortality trend, decrease in length of stay, increase in HbA1c testing during the hospitalization and an increase in diabetes drugs administration.

Clinical outcomes of critically ill multiple trauma patients with rib fractures. A prospective study with retrospective control.

INTRODUCTION: Rib fracture fixation is becoming more popular and widely accepted among trauma surgeons worldwide as the recommended treatment method for flail chest injury. Recent data demonstrate improved results when compared with non-operative treatment. Improved outcomes were reported regarding ICU stay, need for tracheostomy, length of hospital stay, ventilator-associated pneumonia (VAP), and even death. The objective of this study was to ascertain whether clinical respiratory para-meters are improved after rib fracture fixation procedure. MATERIAL AND METHODS: This is a prospective study using a retrospective cohort for control, which took place at the Soroka University Medical Centre, Israel. Inclusion criteria included all patients over 18 years of age with flail chest injury or multiple ribs fractures, who were admitted to the General Intensive Care Unit (GICU). Between October 2015 and December 2018, we identified 24 patients who had their rib fractures operatively fixed and compared them to 61 patients with flail chest and multiple rib fractures, who were admitted to our GICU between the years 2010 and 2015 and were treated non-opera-tively. In all the surgical cases operations were performed within 72 hours of arrival in accordance with our treatment algorithm. All fractures were fixed using specialised anatomic locking plates/nails. Demographic data were collected, and respiratory parameters before and after the surgery were recorded and analysed. RESULTS: We compared patients who had had their rib fractures fixed with a cohort group of patients who had been treated non-operatively in the past. No demographic differences were found between the 2 groups, nor were there any differences in their clinical trauma scoring, mechanical ventilation days, length of ICU stay, VAP, and death rates. The respiratory parameters (paO2/FiO2 ratio and chest wall compliance) were significantly higher during the 3 ensuing days after surgery and continued to improve in Group 1 (rib fixation group), in comparison to group 2 (non-operative) patients (P = 0.007 and P < 0.0001, respectively). The peak inspiratory pressure and PEEP para-meters were significantly lower in group 1 in comparison to group 2 during the 3 days, in favour of the operated group, with significant improvement noted over the 3 days post-surgery (P = 0.007 and P = 0.02, respectively). CONCLUSIONS: We suggest that surgical treatment of flail chest and multiple rib fractures has clinical benefit and improves respiratory parameters even in the presence of multiple trauma injuries.

The Influence of Achilles Tenotomy and Compliance with Foot Abduction Orthosis on the Relapse Rate of Ponseti Treatment for Idiopathic Clubfoot: A Regional Study.

The Ponseti method for treating idiopathic clubfoot is based on gradual manipulations and corrective plaster castings followed by a years-long period of use of a foot orthosis. The role of surgery is limited. The factors that may affect outcome and their influence are subject of controversy. The aim of the study is to systematically and objectively evaluate the results of Ponseti treatment in our region of Southern Israel and focus on the role of the Achilles tenotomy and compliance to foot orthosis as factors that may influence outcome. The use of Ponseti method was retrospectively studied (level of evidence IV) by searching computerized medical files and clinical photos. The severity of deformity was evaluated by Dimeglio score (D-score) at baseline and at last examination. During 2006-2014, 57 children with idiopathic clubfoot (total 90 feet) were enrolled. An Achilles tenotomy was performed in 55/90 (61.1%) of the feet. If the D-score was 15 or higher there was a 20% increase in the incidence of Achilles tenotomy. The parental compliance had a weak protective effect against relapse. The treatment of idiopathic clubfoot by the Ponseti method was successful and reliable, proving efficiency and universality of the method. A dominant predictor for relapse was not seen. An incidental observation was that extended time in cast may buffer the adverse effects of low compliance rate. Although the initial severity, or compliance to braces are important, there may be other factors that affect the outcome such as, accuracy of the casting technique, time in the cast, access to a dedicated clubfoot clinic, cooperation with nurses and pediatricians, economic status that allows purchase of new generation of braces, cultural perception, and education level of the patient population are some examples.

Do design variations in the artificial disc influence cervical spine biomechanics? A finite element investigation.

Various ball and socket-type designs of cervical artificial discs are in use or under investigation. Many artificial disc designs claim to restore the normal kinematics of the cervical spine. What differentiates one type of design from another design is currently not well understood. In this study, authors examined various clinically relevant parameters using a finite element model of C3-C7 cervical spine to study the effects of variations of ball and socket disc designs. Four variations of ball and socket-type artificial disc were placed at the C5-C6 level in an experimentally validated finite element model. Biomechanical effects of the shape (oval vs. spherical ball) and location (inferior vs. superior ball) were studied in detail. Range of motion, facet loading, implant stresses and capsule ligament strains were computed to investigate the influence of disc designs on resulting biomechanics. Motions at the implant level tended to increase following disc replacement. No major kinematic differences were observed among the disc designs tested. However, implant stresses were substantially higher in the spherical designs when compared to the oval designs. For both spherical and oval designs, the facet loads were lower for the designs with an inferior ball component. The capsule ligament strains were lower for the oval design with an inferior ball component. Overall, the oval design with an inferior ball component, produced motion, facet loads, implant stresses and capsule ligament strains closest to the intact spine, which may be key to long-term implant survival.

Are high-intensity zones and Modic changes mutually exclusive in symptomatic lumbar degenerative discs?

OBJECT: Modic changes (MCs) and high-intensity zones (HIZs) potentially serve as variably sensitive markers for discogenic chronic low-back pain (CLBP). No study has hitherto assessed the phenomenon of MC-HIZ coexistence at a single level, and the goal in this study was to assess the nature and frequency of this phenomenon. METHODS: One hundred twenty consecutive patients with discogenic CLBP in whom lumbar MR imaging studies had demonstrated an HIZ, an MC, or both were included. RESULTS: This cohort (120 consecutive patients with 193 degenerative discs) had discogenic CLBP in at least 1 lumbar level associated with either an HIZ (77 discs), an MC (67 discs), or both (16 patients); there were 55 coexistent non-HIZ/non-MC degenerative discs. Painful MC-HIZ coexistence at 1 level occurred in 6 patients (5 of whom were female). If HIZs and MCs were random, independent entities, then MC-HIZ coexistence at 1 level would have been expected in 67 x 77/193 (that is, 27) discs. The observed frequency was therefore significantly lower (chi(2) = 41, p < 0.001). There were no significant demographic differences between groups. The HIZ disc height (8 +/- 0.2 mm) was significantly greater than the MC (6.6 +/- 0.2 mm) or MC-HIZ (6.7 +/- 0.2 mm) disc heights (p < 0.001). CONCLUSIONS: In patients with discogenic CLBP associated with HIZ or MC lesions, MC-HIZ coexistence at 1 level was significantly rarer than expected even by chance; thus, despite both being manifestations of a seemingly common degenerative process, HIZ and MC more closely represent "either/or" phenomena. Because HIZ disc height was significantly greater, HIZs may develop earlier in the disc degenerative ontogeny. If any degenerative disc may only display an HIZ first, yet may ultimately display an MC instead, then HIZs must invariably regress as MCs supervene (or even vice versa). The MC-HIZ coexistence would therefore represent either a rare stable state (possibly more common in females) or a transitory state, as one lesion gradually replaces the other. Longitudinal studies would confirm or refute these hypotheses, although significantly larger sample sizes would be required.

Minimizing ferromagnetic artefact with metallic lumbar total disc arthroplasty devices at adjacent segments: technical note.

STUDY DESIGN: Technical report. OBJECTIVE: To minimize the gross artefact associated with a conventional metallic lumbar total disc arthroplasty (TDA) device on a conventional high field-strength (1.5 Tesla [T]) magnetic resonance imaging (MRI) scanner. SUMMARY OF BACKGROUND DATA: Gross artefact is often apparent with ferromagnetic metallic TDA devices on conventional high field-strength MRI scanners. Such artefact completely obliterates MRI assessment at the operated level, and usually obscures visualization of adjacent segments. Because adjacent segment preservation is a raison d'être of spinal TDA, clarity of imaging at this latter level is imperative. A failure to image adjacent segments may presage investigations, which are either invasive (e.g., myelography) or associated with significant radiation hazard (e.g., computed tomography), both with significantly less diagnostic sensitivity. This could negatively direct TDA choice with certain TDAs. METHODS: Progressive modifications to specific imaging parameter settings were sought on a conventional high field-strength (1.5T) closed-bore scanner to match the minimal artefact previously observed on a lower field-strength (0.3T) open scanner. Direct comparisons were made between each modified protocol image obtained initially using a phantom; however, routine postoperative MRIs were subsequently obtained in n = 40 patients following lumbar TDA insertion. RESULTS: Key parameter modifications were required in the receive bandwidth, the strength of the frequency encoding gradient, as well as in the echo train length. The use of higher specification "focused gradients" was also avoided. The overall effect was to reduce the slew rate of the gradients, which limited artefact due to a decrease in phase dispersion. Such appearances effectively matched with those previously obtained on the low field-strength (0.3T) open scanner in n = 40 patients. CONCLUSION: Relatively simple modifications to MRI parameter settings can be made on conventional high field-strength (1.5T) closed-bore scanners, which minimize metal artefact and enhance imaging of adjacent segments with ferromagnetic TDA devices. Such modifications effectively match appearances to those obtained with outmoded low field-strength (0.3T) open-bore scanners.

Lumbar total disc arthroplasty: coronal midline definition and optimal TDA placement.

It is a general principle with arthroplasty insertion that precise implant centering is critical for long term function and outcome. Whilst some authors have proclaimed that lumbar total disc arthroplasty (TDA) may be different, and that off -centre placement may be functionally well tolerated, these claims are premature: significantly worse clinical results have already been reported with poorly placed TDA at 2 years. Accurate TDA placement requires a precise and consistent definition of the desired coronal midline target (which is currently lacking), as well as a procedural mechanism to optimize placement at that target. We summarize our experience, as well as others', in achieving these two requirements. Long-term outcomes after lumbar TDA insertion should only be compared with results from fusion where TDAs have been implanted accurately.

Subsidence and malplacement with the Oblique Maverick Lumbar Disc Arthroplasty: technical note.

BACKGROUND: The A-Mav (Medtronic, Sofamor Danek, Memphis, TN) is a well-established lumbar total disc arthroplasty device. The O-Mav (Medtronic) is a more recent innovation designed to minimize the potential vascular complications associated with A-Mav insertion at L4/5. No study has hitherto studied the relative accuracy or safety of the two techniques. PURPOSE: To compare the accuracy of lumbar disc arthroplasty placement by using the anterior technique (A-Mav) with the oblique (O-Mav) technique. STUDY DESIGN: Technical report. PATIENT SAMPLE: Fourteen patients. OUTCOME MEASURES: Implant placement accuracy on high-resolution computed tomography scan. Comparative morbidity, mortality, blood loss, and operating time were also assessed. METHODS: Patients were considered for lumbar disc arthroplasty who had suffered chronic discogenic low back pain unresponsive to nonoperative management for at least 6 months. All patients were operated on at the L4/5 level. A-Mavs were inserted in 7 patients and O-Mavs in 7. Implant placement was analyzed postoperatively by using computer software on high-resolution computed tomography scan with respect to four parameters: (1) off-center malplacement, (2) axial rotational malplacement, (3) coronal tilt, and (4) vertebral body susbsidence. Comparative morbidity, mortality, blood loss, and operating time were also assessed. RESULTS: Subsidence, off-center malplacement, and rotational malplacement were significantly increased in O-Mavs compared with A-Mavs (4.3+/-0.6 mm vs. 1.6+/-0.6 mm, p=.008; 3.1+/-0.4 mm vs. 1.3+/-0.4 mm, p=.006; 6.5 degrees +/-1.2 degrees vs. 3.8 degrees +/-0.4 degrees , p=.046). No significant differences were found between O-Mavs and A-Mavs in tilt, operating time, blood loss, or morbidity and mortality. CONCLUSIONS: O-Mav insertion appears to be complicated by significantly greater vertebral body subsidence and malplacement than A-Mav insertion. A-Mav insertion therefore appears to be more accurate and less complicated yet equally as safe as O-Mav insertion.

The accuracy and validity of "routine" X-rays in estimating lumbar disc arthroplasty placement.

STUDY DESIGN: Original study. OBJECTIVE: To compare the accuracy of radiograph (XR) estimates of lumbar total disc arthroplasty placement with high-resolution computed tomography (CT). SUMMARY OF BACKGROUND DATA: Most lumbar disc arthroplasties are inserted and subsequently analyzed using anteroposterior and lateral XR: XR estimates are often correlated with clinical outcomes. No study has hitherto assessed the relative accuracy of XR estimates with CT. METHODS: Patients (N = 36) had recently undergone uncomplicated lumbar total disc arthroplasty for unresponsive discogenic back pain. Interpedicular midline malplacement and vertebral body penetration (VBP) were estimated after surgery, by "blinded" independent review, using computer software on both nonrotated XR and high-resolution CT at the same clinic attendance. RESULTS: Results were obtained in N = 36 patients. No significant differences were found between XR and CT in the mean +/- standard error estimation of either midline malplacement (1.7 +/- 0.2 mm vs. 1.8 +/- 0.2 mm, P = 0.86) or VBP (1.5 +/- 0.3 mm vs. 1.6 +/- 0.3 mm, P = 0.79). However, the correlation between XR and CT for midline malplacement appeared strong (r = 0.72, P < 0.001), whereas the correlation between XR and CT for VBP was poor (r = 0.23 P > 0.10). The standard deviation of XR-CT differences for VBP (2.2 mm) was almost twice that for midline malplacement (1.2 mm). XR-CT differences exceeded the 95% limit of agreement in 6% of midline placement estimates, and in 8% for VBP. CONCLUSION: Nonrotated XR permitted an accurate and valid estimate of midline malplacement relative to CT in most cases. However, the correlation was biased toward XR underestimation of CT-derived malplacement, and highly significant XR-CT differences occurred in 6% of estimates: early postoperative CT is therefore recommended to enhance the estimation of midline placement. XR-CT agreement for VBP was poor: CT is therefore indicated in all cases for this parameter. This is the first study to compare the accuracy of XR in estimating lumbar total disc arthroplasty placement with CT.

Significantly improved lumbar arthroplasty placement using image guidance: technical note.

STUDY DESIGN: Technical report. OBJECTIVE: To compare the accuracy of lumbar total disc arthroplasty placement using an image-guidance system (IGS) with conventional fluoroscopy. SUMMARY OF BACKGROUND DATA: Most disc arthroplasties are inserted and analyzed using fluoroscopy. One previous cadaveric study demonstrated beneficial, but insignificant, effects of IGS on total disc arthroplasty placement compared with conventional fluoroscopy. METHODS: Patients were considered for lumbar total disc arthroplasty who had chronic discogenic low back pain unresponsive to nonoperative management for at least 6 months. Total disc arthroplasty was performed in n = 6 with IGS and in n = 14 without IGS. Implant placement was analyzed after surgery using computer software on high-resolution CT with respect to 3 parameters: 1) off-center mal-placement, 2) axial rotational mal-placement, and 3) coronal tilt. RESULTS: Arthroplasties inserted with IGS were positioned with significantly greater accuracy than non-IGS arthroplasties with respect to all 3 parameters measured (off-center: 1.1 +/- 0.3 vs. 2.3 +/- 0.3 mm, P = 0.031; rotation: 88.8 degrees +/- 0.2 degrees vs. 87.1 degrees +/- 0.4 degrees; P = 0.0084; and tilt: 1.0 degrees +/- 0.5 degrees vs. 2.6 degrees +/- 0.3 degrees, P = 0.01). There was no significant difference in operating time between non-IGS controls (123 +/- 5 minutes) and IGS (139 +/- 10 minutes) groups (P = 0.129). CONCLUSION: This is the first clinical study to demonstrate significantly improved accuracy of lumbar total disc arthroplasty placement on CT using IGS compared with conventional fluoroscopy. IGS should be considered for routine use with lumbar total disc arthroplasty insertion.

Reverse transformation of Modic type 2 changes to Modic type 1 changes during sustained chronic low-back pain severity. Report of two cases and review of the literature.

Modic Type 2 (MT2) neuroimaging changes are considered stable or invariant over time and relatively quiescent, whereas Modic Type 1 (MT1) changes are considered unstable and more symptomatic. The authors report two cases in which MT2 changes were symptomatic and evidently unstable, and in which chronic low-back pain severity remained unaltered despite a MT2-MT1 reverse transformation. Two women (41 and 48 years old) both presented with chronic low-back pain. Magnetic resonance (MR) images demonstrated degenerating discs at L5-S1 associated with well-established MT2 changes in adjacent vertebrae. Repeated MR imaging in these two patients after 11 months and 7 years, respectively, revealed reverse transformation of the MT2 changes into more florid MT1 changes, despite unaltered chronic low-back pain severity. Following anterior discectomy and disc arthroplasty, immediate abolition of chronic low-back pain was achieved in both patients and sustained at 3-year follow up. Modic Type 2 changes are therefore neither as stable nor as quiescent as originally believed. Each type can change, with equal symptom-generating capacity. More representative imaging-pathological correlates are required to determine the precise nature of MT changes.

Finite element study of matched paired posterior disc implant and dynamic stabilizer (360° motion preservation system).

BACKGROUND: Anterior lumbar disc replacements are used to restore spinal alignment and kinematics of a degenerated segment. Compared to fusion of the segment, disc replacements may prevent adjacent segment degeneration. To resolve some of the deficiencies of anterior lumbar arthroplasty, such as the approach itself, difficulty of revision, and postoperative facet pain, 360° motion preservation systems based on posterior disc and posterior dynamic system (PDS) designs are being pursued. These systems are easier to revise and address all the pain generators in a motion segment, including the nerves, facets, and disc. However, biomechanics of the 360° posterior motion preservation system, including the contributions of the 2 subsystems (disc and PDS), are sparsely reported in the literature.nds. METHODS: An experimentally validated 3-dimensional finite element model of the ligamentous L3-S1 segment was used to investigate the differences in biomechanical behavior of the lumbar spine. A single-level 360° posterior motion preservation system and its individual components in various orientations were simulated and compared with an intact model. Appropriate posterior surgical procedures were simulated. The PDS, a curved device with male and female components, was attached to the pedicle screws. The finite element models were subjected to 400 N of follower load plus 10Nm moment in extension and flexion. RESULTS: The PDS restored flexion/extension motion to normal. The artificial disc led to increases in range of motion (ROM) compared with the intact model. ROM for the 360° system at the implanted and adjacent levels were similar to those of the respective intact levels. ROM was similar whether the discs were placed (a) both parallel to the midsagittal plane, (b) both angled 20° to the midsagittal plane, and (c) one at 20° and one parallel to the midsagittal plane. However, the stresses were slightly higher in the nonparallel disc configuration than in the parallel disc configuration, both in flexion and extension modes. CONCLUSIONS: Posterior disc replacement with PDS restored the kinematics of the spine at all levels to near normal. In addition, placing the discs in a nonparallel configuration with respect to the midsagittal plane does not affect the functionality of the discs compared with parallel placement. Posterior disc replacement alone is not sufficient to restore the segment biomechanics to normal levels. CLINICAL RELEVANCE: Finite element analysis results show that, unlike implants for fusion, PDS and posterior discs together (360° motion preservation system) are needed to preserve ROM. Such systems will prevent adjacent level degeneration and address pain from various spinal components, including facets.

Cement leakage in percutaneous vertebroplasty: effect of preinjection gelfoam embolization.

STUDY DESIGN: Prospective case series. OBJECTIVES: To determine the safety and feasibility of routine preinjection of gelfoam embolization during percutaneous vertebroplasty. SUMMARY OF BACKGROUND DATA: Percutaneous vertebroplasty has been used effectively in pain relief for vertebral fractures resulting from malignancy and osteoporosis. However, cement extrusion is a common problem and can lead to complications. Gelfoam embolization of venous channels before cement injection has not been widely used as a technique to prevent leakage. METHODS: Thirty-one patients who met the inclusion-exclusion criteria for the study underwent percutaneous vertebroplasty. Venography was first performed to determine the flow pattern in the vertebrae and confirm needle placement. Next, routine gelfoam embolization of venous channels was performed. This was followed by low-pressure, minimal-volume cement injection. The outcome measure of cement leakage was assessed after surgery using radiographs and CT scans. RESULTS: There were no complications. In the 31 patients, 61 levels of vertebroplasty were performed. Overall, there were 16 leaks out of 61 levels in 12 patients (26.2%). In osteoporotic fractures, there were 11 leaks in 49 levels, giving a leakage rate of 22.5%. There was only 1 epidural leak in this group (2%), and this was asymptomatic. Seven leakages were into the adjacent disc, 2 into the body, and 1 into the paravertebral tissues. In malignant fractures, there were 5 leakages out of 12 levels (41.7%). Of these, 2 were epidural leaks (16.7%), which were asymptomatic. CONCLUSIONS: Complications resulting from leakage are the most feared side effect of the procedure. This has resulted in only limited application of vertebroplasty in the United Kingdom. Routine gelfoam embolization together with careful technique has been shown to be a safe and feasible method during vertebroplasty.

Influence of facet and posterior muscle degeneration on clinical results of lumbar total disc replacement: two-year follow-up.

OBJECTIVE: There has been little analysis assessing the correlation between the clinical functional result of total disc replacement and the arthrosis of the posterior facets or the fatty degeneration of the spinal muscles. However, such knowledge is essential for understanding the long-term outcome of devices in functional terms. This prospective study reports the outcome of 64 Maverick (Medtronic) devices implanted between January 2002 and November 2003. RESULTS: Oswestry score preoperatively and at 2-year follow-up was 43.8 and 23.1, respectively (P < 0.05). Low back pain improved from a mean Visual Analog Scale (VAS) score of 7.6 +/- 1.7 preoperatively to 3.2 +/- 1.8 at 2 years. Mean VAS leg pain score decreased from 3.9 to 2.1 at 2 years (P < 0.05). Facet osteoarthritis grade 1 or 2 did not influence outcome (P = 0.82). On the other hand, muscle degeneration of grades 1 and 2 led to a better outcome than grades 3 and 4 (P = 0.006). CONCLUSIONS: This is the first study showing that a semiconstrained implant with a fixed posterior center of rotation can be implanted with grade 1 and 2 facet arthrosis with a good clinical outcome. This seems to confirm previous work showing that a posterior center of rotation lightens the load on the facets. This is also the first study to show a relationship between muscle fatty degeneration and clinical results since the greater the amount of fat, the less satisfactory the result. These promising midterm results must be confirmed by further studies.

Design rationale and biomechanics of Maverick Total Disc arthroplasty with early clinical results.

This paper reviews the design criteria, biomechanical and biological (wear and safety) testing of this chrome cobalt metal-on-metal, ball and socket design prosthesis. The surgical technique and early clinical results of the initial implantations are also reviewed. Initial results of 7 Maverick implantations showed all 7 patients attaining a 15 point Oswestry improvement within 3 months after implantation. This early result in a small sample is significantly quicker in recovery and improvement when compared to the historical control of the LT cage with Infuse IDE study. Longer term results and more careful study are needed of this interesting and optimistic finding.