Displacement of the Posterior Horn of the Lateral Meniscus into Posterolateral Compartment: An Unusual Injury Pattern

We report a case of acute ACL injury with an unusual lateral meniscal tear pattern. The entire posterior horn of the lateral meniscus was avulsed from its attachments while remaining in continuity with the body of the meniscus. It was displaced posteriorly and laterally to the popliteus tendon so that it was not immediately visible at the time of arthroscopy. This type of displacement of the posterior horn of the lateral meniscus is difficult to identify at arthroscopy and has not previously been described in the literature to our knowledge. We recommend to surgeons who encounter an absent posterior horn of the lateral meniscus to consider this injury pattern

Heterogeneous distribution of phosphorus in olivine from otherwise well-equilibrated spinel peridotite xenoliths and its implications for the mantle geochemistry of lithium

The major- and trace-element abundances of the coexisting phases of four metasomatized spinel peridotite xenoliths from the Anakies locality (SE Australia) were determined by electron microprobe and laser-ablation ICP-MS. The compositions of all phases are remarkably homogeneous, with the exception of phosphorus (P), lithium (Li) and sodium (Na) in olivine. These three elements are enriched in large parts of most olivine crystals due to a second metasomatic episode. Apart from these elements, all phases are in mutual equilibrium with respect to both their major- and trace-element compositions. Li and Na show a strong correlation with P in olivine, although molar Li + Na are an order of magnitude less than molar P, indicating that the substitution mechanism of these elements is more complex than the simple charge-balanced coupled exchange IVSi 4+ + VI(FeMg) 2+ = IVP 5+ + VI(LiNa) +. We suggest that Li and Na are decorating octahedral-site cation vacancies formed by the original incorporation of P. Elemental maps revealed that the P zoning patterns are concentric in a few large olivine porphyroblasts, but form irregular patches in most crystals. This distribution of P is proposed to be the result of a two-stage process, whereby the initial concentric zoning, caused by its exceptionally sluggish diffusion after metasomatic influx, is broken up by extensive sub-solidus deformation and recrystallization, attesting to large grain-scale strains even within the lithosphere. Such strains must be an efficient means of ensuring trace-element equilibrium during partial melting. The association of Li with P in olivine may help to explain the variability of Li abundances in mantle minerals and to interpret Li diffusion experiments and Li isotopic fractionation

Arthroscopic meniscal repair with an absorbable screw: results and surgical technique

The results of a new method for arthroscopic all-inside meniscus repair using a biodegradable cannulated screw (Clearfix meniscal screw) were assessed in a medium-term follow-up prospective study. The Clearfix meniscal screw system consists of delivery cannulae, screw driver, and screw implants. After tear debridement, a screw is located on the driver and passed through the cannula to the insertion site, holding the two sides of the tear together under linear compression. Forty-eight patients (48 repairs) with a mean age of 32.7 years were included in the study. Ligament stabilizing procedures were done in 39 patients (81%) who had anterior cruciate ligament deficient knees. Only longitudinal lesions in the red/red or red/white zone were repaired. Follow-up averaged 19 months, with a range from 12 to 48 months. Patients were evaluated using clinical examination, the "Orthopaedische Arbeitsgemeinschaft Knie (OAK)" knee evaluation scheme and magnetic resonance imaging (MRI). Criteria for clinical success included absence of joint-line tenderness, absence of swelling and a negative McMurray test. Postoperatively, there were no complications directly associated with the device. Twelve of 48 repaired menisci (25%) were considered failures according to the above-mentioned criteria. According to the OAK knee evaluation scheme, 38 patients (79%) had an excellent or good result. MRI, however, showed persisting grade III or IV lesions in 35 patients (73%). Analysis showed that age, length of tear, and simultaneous anterior cruciate ligament reconstruction did not affect the clinical outcome. In contrast, risk factors for failure of meniscus repair are chronicity of injury, location of tear more than 3 mm from the meniscosynovial junction and meniscus side (medial)