Biomechanical analysis of an interbody cage with three integrated cancellous lag screws in a two-level cervical spine fusion construct: an in vitro study.

BACKGROUND CONTEXT: Despite an increase in the clinical use of no-profile anchored interbody cages (AIC) for anterior cervical discectomy and fusion (ACDF) procedures, there is little published biomechanical data describing its stabilizing effect relative to the traditional anterior plating technique over two contiguous levels. PURPOSE: To biomechanically compare the acute stability conferred by a stand-alone interbody fusion device with three integrated fixation screws ("anchored cage") with a traditional six-hole rigid anterior plate in a two contiguous levels (C4-C5+C5-C6) fusion construct. We hypothesized that the anchored cage would confer comparable segmental rigidity to the cage and anterior plate construct. STUDY DESIGN: A biomechanical laboratory study using cadaveric human cervical spines. METHODS: Seven (n=7) cadaveric human cervical spines (C3-C7) were subjected to quasistatic, pure-moment loading (±1.5 Nm) in flexion-extension (flex/ext), right/left lateral bending (RB/LB), and right/left axial rotation (RR/LR) for the following test conditions: intact; after discectomy and insertion of the AIC at C4-C5 and C5-C6 with anchoring screws engaged; after the removal of the integrated anchoring screws and instrumentation of an anterior locking plate (ALP) over both levels; and cage-only (CO) configuration with screws and anterior plate removed. Intervertebral range of motion (ROM) at the instrumented levels was the primary biomechanical outcome. RESULTS: Flex/ext, RB/LB, and RR/LR ROMs were significantly reduced (p<.001) over both levels by AIC and ALP constructs relative to the CO construct. Significant reduction in flex/ext motion was achieved with the ALP (6.8±3.7) relative to the AIC (10.2°±4.6°) (p=.041) construct. No significant differences were seen in ROM reductions over the two levels between the AIC and APL groups in lateral bending or axial rotation (p>.826). CONCLUSIONS: The anchored cage fusion construct conferred similar acute biomechanical stability in lateral bending and axial rotation ROMs relative to rigid anterior plating. We identified a statistically significant reduction (Δ=3.4°, combined over two levels) in sagittal plane ROM conferred by the ALP relative to the AIC construct. Our biomechanical findings may support the clinical use of no-profile integrated interbody devices over two contiguous levels in ACDF.

Biomechanics of an integrated interbody device versus ACDF anterior locking plate in a single-level cervical spine fusion construct.

BACKGROUND CONTEXT: No profile, integrated interbody cages are designed to act as implants for cervical spine fusion, which obviates the need for additional internal fixation, combining the functionality of an interbody device and the stabilizing benefits of an anterior cervical plate. Biomechanical data are needed to determine if integrated interbody constructs afford similar stability to anterior plating in single-level cervical spine fusion constructs. PURPOSE: The purpose of this study was to biomechanically quantify the acute stabilizing effect conferred by a single low-profile device design with three integrated screws ("anchored cage"), and compare the range of motion reductions to those conferred by a standard four-hole rigid anterior plate following instrumentation at the C5-C6 level. We hypothesized that the anchored cage would confer comparable postoperative segmental rigidity to the cage and anterior plate construct. STUDY DESIGN: Biomechanical laboratory study of human cadaveric spines. METHODS: Seven human cadaveric cervical spines (C3-C7) were biomechanically evaluated using a nondestructive, nonconstraining, pure-moment loading protocol with loads applied in flexion, extension, lateral bending (right+left), and axial rotation (left+right) for the intact and instrumented conditions. Range of motion (ROM) at the instrumented level was the primary biomechanical outcome. Spines were loaded quasi-statically up to 1.5 N-m in 0.5 N-m increments and ROM at the C5-C6 index level was recorded. Each specimen was tested in the following conditions: 1. Intact 2. Discectomy+anchored cage (STA) 3. Anchored cage (screws removed)+anterior locking plate (ALP) 4. Anchored cage only, without screws or plates (CO) RESULTS: ROM at the C5-C6 level was not statistically different in any motion plane between the STA and ALP treatment conditions (p>.407). STA demonstrated significant reductions in flexion/extension, lateral bending, and axial rotation ROM when compared with the CO condition (p<.022). CONCLUSIONS: In this in vitro biomechanical study, the anchored cage with three integrated screws afforded biomechanical stability comparable to that of the standard interbody cage+anterior plate cervical spine fusion approach. Due to its low profile design, this anchored cage device may avoid morbidities associated with standard anterior plating, such as dysphagia.

Hip resurfacing arthroplasty in severely obese patients.

We conducted a study of outcomes of modern hip resurfacing arthroplasty (HRA) in severely obese patients. Patients who had undergone HRA and been followed for a minimum of 2 years were divided into 2 groups, those with body mass index under 35 (control, 366 hips) and those with body mass index of 35 or above (study, 63 hips). At mean follow-up of 41 months, there was no significant difference between the groups with respect to postoperative Harris Hip Scores, complication rates, and need for revision. Six revision surgeries were required in the control group (98.4% survival), and 2 were required in the study group (96.8% survival). These results suggest that severely obese patients should be considered candidates for HRA.

Regeneration of a discoid meniscus after arthroscopic saucerization.

We report the case of a 5-year-old girl who presented to the clinic with recurrent knee pain after meniscal repair and saucerization at age 3. The finding of a regenerated discoid meniscus was confirmed arthroscopically and radiographically. To our knowledge, this is the first report in the literature to confirm regeneration of a discoid meniscus after saucerization. The case has significant implications for management of pediatric discoid meniscus tears and patient counseling, and is encouraging in terms of the potential for repair and regeneration of meniscal tissue, particularly in the very young pediatric population.

Complications following distal biceps repair.

PURPOSE: Distal biceps rupture is a relatively uncommon injury. Surgical repair is performed in patients who seek increased flexion and supination strength over that which results from nonoperative treatment. The purpose of this study was to evaluate complications associated with surgical repair of the distal biceps tendon in a large series of patients. METHODS: We retrospectively reviewed 198 consecutive patients with distal biceps ruptures treated with surgical repair, and evaluated time from injury to repair, surgical technique, and complications. RESULTS: A total of 72 patients (36%) developed complications; 6 patients underwent additional surgery. Minor complications included lateral antebrachial cutaneous nerve paresthesia (26%), radial sensory nerve paresthesia (6%), and superficial infection (2%). Major complications included posterior interosseous nerve injury (4%), symptomatic heterotropic ossification (3%), and re-rupture (2%). CONCLUSIONS: Minor complications were common after distal biceps tendon repair; however, most were sensory nerve injuries that resolved with time. Major complications were infrequent, and few patients required revision surgery. Complications were more common after distal biceps tendon repair performed more than 28 days after rupture. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Prevention of VTE Following total hip and knee arthroplasty in Hemophilia patients.

The often debilitating condition of hemophilic arthropathy is treated with elective total joint arthroplasty. Little has been published addressing the role of thromboembolic prophylaxis in the hemophilic patient population following total hip arthroplasty (THA) and total knee arthroplasty (TKA). Although the American College of Chest Physicians and the American Academy of Orthopaedic Surgeons have set guidelines for thromboembolic prophylaxis in the general population, no such standard of care is in place for hemophilic patients. While the risk of thrombosis in hemophilic patients following THA and TKA is thought to be lower, cases have been reported of pulmonary embolism and deep vein thrombosis (DVT) in hemophilic patients.

Articulated hip distraction: a treatment option for femoral head avascular necrosis in adolescence.

PURPOSE: To describe the clinical outcomes of adolescent patients treated with articulated hip distraction (AHD) for avascular necrosis (AVN) of the femoral head. Outcomes were examined in order to better understand the usefulness of and indications for performing hip arthrodiastasis in this patient population. METHODS: : Retrospective review was performed on 31 hips with femoral head AVN treated with AHD. Mean age at treatment was 14.7 years. Preoperative and follow-up pain and physical limitations, as well as follow-up range of motion, were assessed. RESULTS: Follow-up assessment was obtained at 18.7 years. Time of follow-up was 57.4 months after distraction. The etiologies of AVN were the following: 10 slipped capital femoral epiphysis (SCFE), 5 idiopathic AVN, 3 with hip dysplasia, and 12 others. There was a significant difference in pain preoperatively and postoperatively (P<0.001), most patients (78.6%, n=22) had less pain after the treatment. Multivariate regression model demonstrated that patients with SCFE were likely to have less improvement in pain than patients with other etiologies (odds ratio, 22.7; P=0.035). All patients had activity limitations before the treatment; at the postoperative assessment, half of our patients (n=14) reported no limitations in their regular daily activities. Eight patients had minor complications with the fixator. At follow-up, 5 patients (17.2%) converted to total hip replacement or arthrodesis. Survival rates were 90.6% at 5 years, 77.7% at 10 years, and 38.8% at 15 years. CONCLUSIONS: Hip distraction arthroplasty in adolescent patients with symptomatic AVN reduces the amount of pain and limitation in daily activities at a follow-up of 4.7 years. Arthrodiastasis is not the final solution to AVN. With longer follow-up, patient's symptoms increases. Patients with AVN secondary to SCFE do not seem to benefit from this procedure as much as other patients do. Articulated hip distraction is a safe and appropriate procedure to perform in these patients. The procedure might be able to delay definitive surgical procedures at an early age, restoring function and improving the patient's quality of life.

Molecular pathways regulating the self-renewal of hematopoietic stem cells.

Hematopoietic stem cells (HSC) self-renew throughout life, but the molecular mechanisms by which this process occurs and is regulated are imprecisely understood. We review the published data from overexpression and knockout studies describing genes that influence stem cell self-renewal, including transcription factors, cell cycle regulators, and genes that influence chromosome structure. One model suggesting how some of these disparate classes of molecular regulators might be integrated is presented, focusing on the role of G1/S progression in the developmental switch toward stem cell self-renewal vs differentiation. Experimental exploration of this model and other related hypotheses will hopefully lead to a more complete description of HSC self-renewal and its regulation, both in normal physiology and in applied therapeutics.