Removal of well-fixed fixed femoral stems

The removal of a well-fixed prosthetic stem raises technical challenges. The objective is not only to remove the material, but also to prepare the implantation of a new prosthesis. Cemented stems are only very rarely unremovable; extraction of the cement mantle and plug raises the greatest difficulties. The main risk is cortex perforation, and a radiograph should be obtained at the slightest doubt. The removal of cementless stems carries a higher risk of fracture. Difficulties should be anticipated based on thorough familiarity with the implant design and on evaluations of implant fixation and bone stock. The intramedullary approach is usually sufficient to extract a cemented or cementless, well fixed, standard stem. Routine use of a transfemoral approach is warranted only in the following situations: revision surgery for infection, S-shaped stem, long stem, curvature or angulation of the femoral shaft, or unfeasible hip dislocation. However, the possibility that the intramedullary approach may need to be converted to a transfemoral approach should be anticipated. Thus, preoperative planning must include determination of the optimal length of a femoral osteotomy or femoral flap, should one be needed, and the surgeon must have access to all the revision implants and tools that might be needed for re-implantation. Experience with the various techniques is indispensable, as a well-performed extensive approach is associated with less morbidity than a fracture or trajectory error. There are three main techniques, which are described here: intramedullary extraction of a cementless stem, intramedullary extraction of a cemented stem, and transfemoral extraction through an extended trochanterotomy. The patients should receive detailed information on the difficulties of femoral stem removal and on the available solutions

Influence of fluid-flow direction on effective permeability of the vertebral end plate: an analytical model

Convective transports in the vertebral end plate (VEP) play a significant role in the homeostasis of the spine. A few studies hypothesised that the hydraulic resistance or effective permeability of the VEP could be dependant upon fluid-flow direction. Results were influenced by species, region of interest within the end plate and pathology. Some results were contradictory. We propose an analytical model based on steady-state Newtonian flows in capillary media to develop a phenomenological analysis of convective transport through the VEP. This dependence was established using a biquadratic analytical function involving porosities of subchondral bone, capillary bed and cartilage end plate. Discussion of results provided a theoretical justification for variable and/or contradictory experimental results concerning the amount of energy lost by fluid during its course through the end plate. Tissue porosities and, especially, those relative to the capillary bed could strongly influence the dependence of fluid energy loss on flow direction and could potentially modify tissue homeostasis related to the day and night cycle

Biomechanical study of ACL reconstruction grafts

There are no published studies describing the strength quadrupled gracilis tendon alone and quadrupled semitendinosus tendon alone in the configuration used for anterior cruciate ligament (ACL) reconstruction. The primary objective was to compare the mechanical properties of grafts used for ACL reconstruction during a tensile failure test. The secondary objective was to evaluate the effect of uniform suturing on graft strength. Fifteen pairs of knees were used. The mechanical properties of five types of ACL grafts were evaluated: patellar tendon (PT), sutured patellar tendon (sPT), both hamstring tendons (GST4), quadrupled semitendinosus (ST4), and quadrupled gracilis (G4). Validated methods were used to perform the tensile tests to failure and to record the results. Student's t-test was used to compare the various samples. The maximum load to failure was 630.8N (± 239.1) for the ST4, 473.5N (± 176.9) for the GST4, 413.3N (± 120.4) for the sPT, and 416.4N (± 187.7) for the G4 construct. Only the ST4 had a significantly higher failure load than the other grafts. The sPT had a higher failure load than the PT. The ST4 construct had the highest maximum load to failure of all the ACL graft types in the testing performed here. Uniform suturing of the grafts improved their ability to withstand tensile loading

Can the gracilis replace the anterior cruciate ligament in the knee? A biomechanical study

Purpose The purpose of this study was to determine whether a four-strand gracilis-only construct possesses the biomechanical properties needed to act as an anterior cruciate ligament (ACL) reconstruction graft. Methods This was a pilot study with 32 cadaver specimens. The biomechanical properties of three types of grafts were determined using validated tensile testing methods: patellar tendon (BTB), both hamstring tendons together (GST4) and gracilis alone (G4). Results The maximum load at failure of the G4 was 416.4 N (±187.7). The GST4 and BTB had a maximum load at failure of 473.5 N (±176.9) and 413.3 N (±120.4), respectively. The three groups had similar mean maximum load and stiffness values. The patellar tendon had significantly less elongation at failure than the other two graft types. Conclusions The biomechanical properties of a four-strand gracilis construct are comparable to the ones of standard grafts. This type of graft would be useful in the reconstruction of the anteromedial bundle in patients with partial ACL ruptures

Correlations between effective permeability and marrow contact channels surface of vertebral endplates

Homeostasis of the intervertebral disc relies on nutrient supply and waste clearance through the dense capillary network that is in contact with the cartilage endplate (CEP). We developed a micro-computerized tomography (micro-CT) method to quantify the marrow contact channel surface (MCCS) with the CEP and to validate the hypothesis according to which MCCS was correlated to the effective permeability of the vertebral endplate (VEP) and influenced by the mechanical stimuli. The influence of compression loading on local vascularization was investigated. Six 4-week-old skeletally immature pigs were instrumented with left pedicle screws and rod at both T5-T6 and L1-L2 levels to create asymmetrical spine tethers. After 3 months of growth, three cylindrical specimens of the VEP (one central and two lateral right and left) were obtained from both the instrumented and the control levels. We used a previously validated method for measuring permeability. Micro-CT analysis (resolution 12 mu m) yielded a gray-scale 2D-image of the discal end of each specimen converted into a binary 2D-image to derive the MCCS. Correlations between MCCS and effective permeability were assessed. Effective permeability and MCCS were significantly decreased compared to the control group especially on the tethered side (-41..5%, p = 0.004 and -52.5%, p = 0.0009, respectively). Correlations were significant and showed maximal value (r(2) = 0.430, p < 0.0001) on the tethered side involving maximal compressive loadings. Mechanical stimuli, due to unbalanced growth, altered the vascularization and the convective properties of the CEP. The cascade of mechanobiological events should offer perspectives for research on disc degeneration and attempted treatment. (C) 2010 Orthopaedic Research Society

Cadaveric study comparing the biomechanical properties of grafts used for knee anterolateral ligament reconstruction

Purpose: To measure the biomechanical properties (maximum load, stiffness, and elongation) of the anterolateral ligament (ALL), gracilis, and iliotibial band (ITB) within the same subject. METHODS: Thirteen unpaired knees were used (7 women, 6 men). The donors had a mean age at death of 54 years (range: 37 to 70 years). The mechanical properties of two types of ALL grafts were evaluated: ITB and two-strand gracilis. The mechanical properties of ALL were also measured. Validated methods were used to perform the tensile tests to failure and to record the results. Student's t-test was used to compare the various samples. RESULTS: The maximum load to failure was 141 N (±40.6) for the ALL, 200.7 N (±48.7) for the gracilis, and 161.1 N (±27.1) for the ITB. Only the gracilis had a significantly higher failure load than ITB and ALL (P = .001 and P = .03). The stiffness was 21 N mm-1 (±8.2) for the ALL, 131.7 N mm-1 (±43.7) for the gracilis, and 39.9 N mm-1 (±6) for the ITB. The elongation at failure was 6.2 mm (±3.2) for the ALL, 19.9 mm (±6.5) for the gracilis, and 20.8 mm (±14.7) for the ITB. CONCLUSIONS: The gracilis had the highest maximum load to failure. The ITB's mechanical properties most closely resemble those of the ALL. CLINICAL RELEVANCE: The biomechanical properties of each potential ALL graft can be factored in when deciding which type of graft to use

Influence of growth modulation on the effective permeability of the vertebral end plate. A porcine experimental scoliosis model

Background: Abnormal mechanical loading occurs in scoliosis as compared to normal spines. Intervertebral disc degeneration has been correlated with alteration of bone density in adjacent vertebral bodies. How vertebral end plate remodels in scoliosis and the consequences on disc homeostasis are not well understood. Permeability is a relevant physical measure to quantify mass transport in porous media. We hypothesized that effective permeability of the vertebral end plate was modified by growth modulation in a scoliosis animal model. Methods: Flexible asymmetric posterior instrumentation was undertaken on six healthy four-week-old pigs. Two sets of left pedicle screws were inserted and connected with a stainless steel cable. After two months, the apical intervertebral unit and three units located cranially and caudally, were harvested. One central and two lateral specimens were investigated using a previously validated method for measuring permeability. Findings: A three-dimensional deformity was obtained in all six animals with an average of 42 degrees right thoracic curve. 44 degrees lordosis and 21 degrees rotation. Permeability was significantly greater in the center of the end plates than in the periphery and it was decreased by -45% towards the apex of the deformity. Fluid flow direction did not play a significant role. No significant difference was found between the convex side and the concave side. Interpretation: The end plate is a crucial zone for diffusive and convective transport and we showed in a scoliosis animal model that a growth modulation may decrease its effective permeability. The proposed methodology and associated results could help to understand degenerative changes in human spine

Is the prognosis the same for periprosthetic joint infections due to Staphylococcus aureus versus coagulase-negative staphylococci? A retrospective study of 101 patients with 2-year minimum follow-up.

BACKGROUND: Staphylococcus aureus (SA) and Coagulase-negative staphylococci (CoNS) are often responsible for infections of total hip arthroplasty (THA) and total knee arthroplasty (TKA). One of the main differences between these two microorganisms is their virulence, with SA presumed to be more virulent; however, few studies have specifically investigated the impact of this virulence. This inspired us to carry out a retrospective study to evaluate whether the healing rate differed between SA and CoNS infections. HYPOTHESIS: We hypothesised that the healing rate is lower for SA prosthetic joint infections. MATERIALS AND METHODS: This was a retrospective study of 101 consecutive Staphylococcus infection cases that occurred between 2007 and 2011. There were 56 men and 45 women with an average age of 69 years (range 23-95). The infection was associated with TKA in 38 cases and THA in 63 cases. Thirty-two percent of patients had one or more comorbidities with infectious potential. In our cohort, there were 32 SA infections (31.7 %) and 69 CoNS infections (68.3 %) with 58 of the infections being methicillin-resistant (15 SA and 43 CoNS); there were 27 polymicrobial infections (26.7 %). RESULTS: With a minimum 24-month follow-up after the end of antibiotic treatment, the healing rate was 70.3 % overall (71 patients). The healing rate was 75 % in the SA group (24 patients) versus 68.1 % (47 patients) in the CoNS group (P = 0.42). CONCLUSION: Our hypothesis was not confirmed: the healing rate of SA prosthetic joint infections was not lower than that of CoNS infections. LEVEL OF EVIDENCE: III, retrospective case-control study

Laterality and grip strength influence hand bone micro-architecture in modern humans, an HRpQCT study

It is widely hypothesized that mechanical loading, specifically repetitive low-intensity tasks, influences the inner structure of cancellous bone. As such, there is likely a relationship between handedness and bone morphology. The aim of this study is to determine patterns in trabecular bone between dominant and non-dominant hands in modern humans. Seventeen healthy patients between 22 and 32 years old were included in the study. Radial carpal bones (lunate, capitate, scaphoid, trapezium, trapezoid, 1st, 2nd and 3rd metacarpals) were analyzed with high-resolution micro-computed tomography. Additionally, crush and pinch grip were recorded. Factorial analysis indicated that bone volume ratio, trabeculae number (Tb.N), bone surface to volume ratio (BS.BV), body weight, stature and crush grip were all positively correlated with principal components 1 and 2 explaining 78.7% of the variance. Volumetric and trabecular endostructural parameters (BV/TV, BS/BV or Tb.Th, Tb.N) explain the observed inter-individual variability better than anthropometric or clinical parameters. Factors analysis regressions showed correlations between these parameters and the dominant side for crush strength for the lunate (r2 = 0.640, P < 0.0001), trapezium (r2 = 0.836, P < 0.0001) and third metacarpal (r2 = 0.763). However, despite a significant lateralization in grip strength for all patients, the endostructural variability between dominant and non-dominant sides was limited in perspective to inter-individual differences. In conclusion, handedness is unlikely to generate trabecular patterns of asymmetry. It appears, however, that crush strength can be considered for endostructural analysis in the modern human wrist