Early tibial subchondral bone texture changes after arthroscopic partial meniscectomy in knees without radiographic OA: A prospective cohort study.

Arthroscopic partial meniscectomy (APM) may lead to changes in underlying trabecular bone (TB) structure potentially promoting the development of knee joint osteoarthritis. Our aim was to investigate if there are early changes occurring in tibial subchondral TB texture in the leg undergoing medial APM compared with the unoperated non-injured contra-lateral leg. The bone texture was measured as the medial-to-lateral ratio of fractal dimensions (FD) calculated for regions selected on weight-bearing anteroposterior tibiofemoral x-rays. Twenty-one subjects before and 12 months after APM were included from 374 patients scheduled for unilateral medial APM. The medial-to-lateral ratio was calculated for horizontal, vertical, and roughest FDs respectively. Higher FD means higher bone roughness. Each FD was calculated over a range of scales using a variance orientation transform method. Mean values of medial-to-lateral horizontal FD calculated for APM knees at follow-up were higher than those at baseline. For unoperated knees the values were lower. The difference in the horizontal FD change from baseline to follow-up between APM and contra-lateral legs was 0.028 (95% CI, 0.004-0.052). The bone roughness changes may reflect the increase in peak knee adduction moment (KAM) and KAM impulse during walking reported for the same cohort in a previous study. They may also reflect early signs of osteoarthritis development and thus, we speculate that individuals with increased bone texture roughness ratio after APM might be at higher risk of knee osteoarthritis development.

Physical activity patterns and function 3 months after arthroscopic partial meniscectomy.

OBJECTIVES: To compare physical activity levels, subject-reported function, and knee strength in 21 arthroscopic partial meniscectomy (APM) patients (age 45.7 (6.06) years, BMI 27.3 (5.96) female 60%) 3 months post-surgery with 21 healthy controls (age 43.6 (5.71) years, BMI 24.5(4.2) female 60%) matched at the cohort level for age, gender and BMI. DESIGN: Case control study. METHODS: Physical activity intensity, number of steps, and minutes spent in activity were objectively quantified using an accelerometer-based activity monitor worn for 7 days. The Knee Injury and Osteoarthritis Outcome Score (KOOS) and concentric quadriceps strength were used to evaluate function post-surgery. Differences in activity levels and functional outcomes between the APM and control participants were assessed using t-tests, while multiple linear regression was used to quantify the best predictors of physical activity. RESULTS: APM patients engaged in a similar duration of activity to controls (469.0 (128.39)min vs. 497.1 (109.9)min), and take a similar number of steps per day (9227 (2977) vs. 10,383 (3501), but performed their activity at lower levels of intensity than controls. Time spent in moderate (r(2)=0.19) and hard (r(2)=0.145) intensity physical activity was best predicted by the Symptoms sub-scale of the KOOS for both controls and APM patients. CONCLUSIONS: APM patients participate in similar levels of activity at lower intensities, but with reduced activity at higher intensities which is related to the presence of symptoms of knee osteoarthritis.

A dissimilarity-based multiple classifier system for trabecular bone texture in detection and prediction of progression of knee osteoarthritis.

There is a growing need for classification systems that can accurately detect and predict knee osteoarthritis (OA) from plain radiographs. For this purpose, a system based on a support vector machine (SVM) classifier and distances measured between trabecular bone (TB) texture images was developed and tested in previous work. Unlike other systems, it allows an image classification without the calculation and selection of numerous texture features, and it is invariant to a range of imaging conditions encountered in a routine X-ray screening of knees. Although the system exhibited 85.4% classification accuracy in OA detection, which was higher than those obtained from other systems, its performance could be further improved. To achieve this, a dissimilarity-based multiple classifier (DMC) system is developed in this study. The system measures distances between TB texture images and generates a diverse ensemble of classifiers using prototype selection, bootstrapping of training set and heterogeneous classifiers. A measure of competence is used to select accurate (i.e. better-than-random) classifiers from the ensemble, which are then combined through the majority voting rule. To evaluate the newly developed system in OA detection (prediction of OA progression), TB texture images selected on standardised radiographs of healthy and OA (non-progressive and progressive OA) knees were used. The results obtained showed that the DMC system has higher classification accuracies for the detection (90.51% with 87.65% specificity and 93.33% sensitivity) and prediction (80% with 82.00% specificity and 77.97% sensitivity) than other systems, indicating its potential as a decision-support tool for the assessment of radiographic knee OA.

Trabecular bone texture detected by plain radiography and variance orientation transform method is different between knees with and without cartilage defects.

The objective of this work is to evaluate differences in trabecular bone (TB) texture between subjects with and without tibiofemoral cartilage defects using a variance orientation transform (VOT) method. A case-control study was performed in subjects without radiographic knee osteoarthritis (OA) (K&L grade <2) matched on sex, BMI, age, knee compartment, and meniscectomy where cases (n = 28) had cartilage defects (grade ≥2) and controls (n = 28) had no cartilage defects (grade <2). Cartilage defects were assessed from MRI using validated methods. The VOT was applied to TB regions selected on medial and lateral compartments in knee X-rays and fractal signatures (FS) in the horizontal (FS(H) ) and vertical (FS(V) ) directions, and along the roughest part of TB (FS(Sta) ) and texture aspect ratio signatures (StrS), at different trabecular image sizes (0.30-0.70 mm) were calculated. Compared with controls, FS(V) for cases were higher (p < 0.011) at image sizes 0.30-0.40 mm and 0.45-0.55 mm in the medial compartment. In the lateral compartment, FS(H) and FS(Sta) for cases were higher (p < 0.028) than those for controls at 0.30-0.40 mm and 0.45-0.55 mm, while FS(V) was higher (p < 0.02) at 0.30-0.40 mm. TB texture roughness was greater in subjects with cartilage defects than in subjects without, suggesting thinning and fenestration of TB occur early in OA and that the VOT identifies changes in TB in knees with early cartilage damage. No differences in StrS (p > 0.05) were found.

Knee strength and knee adduction moments following arthroscopic partial meniscectomy.

PURPOSE: This study investigated the relationship between muscular strength about the knee and knee joint moments during gait in patients who had undergone arthroscopic partial meniscectomy (APM). METHODS: One hundred and two APM patients and 42 age-matched nonoperated controls underwent strength testing and three-dimensional gait analysis. Patients were divided into weak and normal subgroups and compared with controls for spatiotemporal, kinematic, and kinetic gait parameters. RESULTS: Spatiotemporal parameters, kinematics, and sagittal plane kinetics were similar between APM patients and controls. The APM group displayed weaker concentric knee extension and flexion strength compared with controls. The weak APM subgroup had an increased average and peak knee adduction moments over stance compared with the APM subgroup with normal strength levels and controls. The normal strength APM subgroup had a larger peak knee adduction moment in early stance compared with controls. CONCLUSION: Achieving normal lower limb muscle strength following APM appears important to resume normal frontal plane loading of the knee while walking.

Knee joint biomechanics following arthroscopic partial meniscectomy.

We investigated spatiotemporal data, joint kinematics, and joint kinetics during gait in a group of subjects who had recently undergone arthroscopic partial meniscectomy and compared the results to those of healthy controls. Gait analysis was performed on 105 pain-free meniscectomy patients and 47 controls, walking at a self-selected speed. The meniscectomy population was comparable to controls in spatiotemporal parameters and knee kinematics. However, they had reduced range of motion (ROM) and lower peak moments in the sagittal plane on the operated limb compared to the nonoperated limb. Compared to controls, the meniscectomy patients had significantly larger knee adduction moments over stance, even after accounting for their greater body weight. These differences likely increase articular loads on the medial compartment of the tibiofemoral joint and may contribute to the high risk of knee osteoarthritis following arthroscopic meniscal surgery.

Comparative stability of perpendicular versus parallel double-locking plating systems in osteoporotic comminuted distal humerus fractures.

In distal humerus fractures, the restoration of stability is important to allow early mobilization and hence more favorable functional outcomes. In this article, we compare the biomechanical stability of perpendicular and parallel locking plating systems for the internal fixation of AO Type C2 distal humerus fractures in osteoporotic bone. Fractures were simulated in paired cadaveric bones and fixed using either the perpendicular 3.5 mm LCP distal humerus plating system (Synthes; Sydney, Australia) or the parallel Mayo Clinic Congruent elbow plate system (Acumed; Hillsboro, OR), using locking screws in both systems. Both systems were then tested for their stiffness (in compression and internal/external rotation), plastic deformation, and failure in torsion. Comparatively, the parallel locking plate system provided a significantly higher stability in compression (p = 0.005) and external rotation (p = 0.006), and a greater ability (p = 0.005) to resist axial plastic deformation. Stability for both constructs appeared to be dependent on bone quality, however the stability of the perpendicular system was generally more sensitive to bone mineral density, indicating a possible need for additional independent interfragmentary screws. A disadvantage of the parallel locking plate system was wear debris produced by its tapping system. In summary, the biomechanical findings of this study suggest that both locking plate systems allow early mobilization of the elbow in patients with osteoporotic bone following fixation of a comminuted distal humerus fracture. However, the parallel locking system showed improved stability compared with the perpendicular locking system, and therefore may be more indicated.

Open wedge high tibial osteotomy: biomechanical investigation of the modified Arthrex Osteotomy Plate (Puddu Plate) and the TomoFix Plate.

OBJECTIVE: To determine the biomechanical properties of different fixation methods for high tibial medial opening wedge osteotomy in order to determine appropriate surgical and rehabilitation guidelines. DESIGN: A biomechanical testing examined the construct stiffness and the fixation strength of two different plates. BACKGROUND: Although medial opening wedge techniques for high tibial osteotomies have become popular in recent years, biomechanical data of frequently used implants is lacking. METHODS: A 15-mm medial opening gap was stabilized in each of eight medium composite tibial bones either with the modified Arthrex Osteotomy Plate (Puddu Plate) or the TomoFix Plate. RESULTS: Both constructs failed under compression and torsion at the lateral cortex and occurred at higher maximal forces by using the TomoFix Plate. After fracture of the lateral cortex the axial stiffness was reduced by 47% and the torsional rigidity by 54% for the TomoFix. For the Puddu Plate these reductions were 66% and 78%, respectively. The differences between the two groups were significant in all conducted tests (P < 0.05). CONCLUSIONS: This study indicates that an unharmed lateral hinge largely dictates the stability after high tibial osteotomy. If the lateral cortex is injured, the TomoFix plate provides superior stability in both compression and torsion compared to the Puddu Plate. In the latter case additional fixation might be considered. RELEVANCE: These biomechanical tests helped to identify clinical situations in which the mechanical attributes of the plates would prove advantageous.

Oblique screws at the plate ends increase the fixation strength in synthetic bone test medium.

OBJECTIVE: To test the hypothesis that oblique screws at the ends of a plate provide increased strength of fixation as compared to standard screw insertion. DESIGN: Biomechanical laboratory study in synthetic bone test medium. METHODS: Narrow 4.5-mm stainless steel low-contoured dynamic compression plates were anchored with cortical screws to blocks of polyurethane foam. The fixation strength in cantilever bending (gap closing mode) and torsion was quantified using a material testing system. Different constructs were tested to investigate the effect of the screw orientation at the end of the plate (straight versus oblique at 30 degrees), the plate, and bridging length as well as the number of screws. RESULTS: An oblique screw at the plate end produced an increased strength of fixation in all tests; however, the difference was more significant in shorter plates and in constructs with no screw omission adjacent to the fracture site. Both longer plates and increased bridging length produced a significantly stronger construct able to withstand higher compression loads. Under torsional loading, the fixation strength was mainly dependent on the number of screws. CONCLUSIONS: The current data suggest that when using a conventional plating technique, plate length is the most important factor in withstanding forces in cantilever bending. With regard to resisting torsional load, the number of screws is the most important factor. Furthermore, oblique screws at the ends of a plate increase fixation strength.

Biomechanical testing of the LCP--how can stability in locked internal fixators be controlled?

New plating techniques, such as non-contact plates, have been introduced in acknowledgment of the importance of biological factors in internal fixation. Knowledge of the fixation stability provided by these new plates is very limited and clarification is still necessary to determine how the mechanical stability, e.g. fracture motion, and the risk of implant failure can best be controlled. The results of a study based on in vitro experiments with composite bone cylinders and finite element analysis using the Locking Compression Plate (LCP) for diaphyseal fractures are presented and recommendations for clinical practice are given. Several factors were shown to influence stability both in compression and torsion. Axial stiffness and torsional rigidity was mainly influenced by the working length, e.g. the distance of the first screw to the fracture site. By omitting one screw hole on either side of the fracture, the construct became almost twice as flexible in both compression and torsion. The number of screws also significantly affected the stability, however, more than three screws per fragment did little to increase axial stiffness; nor did four screws increase torsional rigidity. The position of the third screw in the fragment significantly affected axial stiffness, but not torsional rigidity. The closer an additional screw is positioned towards the fracture gap, the stiffer the construct becomes under compression. The rigidity under torsional load was determined by the number of screws only. Another factor affecting construct stability was the distance of the plate to the bone. Increasing this distance resulted in decreased construct stability. Finally, a shorter plate with an equal number of screws caused a reduction in axial stiffness but not in torsional rigidity. Static compression tests showed that increasing the working length, e.g. omitting the screws immediately adjacent to the fracture on both sides, significantly diminished the load causing plastic deformation of the plate. If bone contact was not present at the fracture site due to comminution, a greater working length also led to earlier failure in dynamic loading tests. For simple fractures with a small fracture gap and bone contact under dynamic load, the number of cycles until failure was greater than one million for all tested constructs. Plate failures invariably occurred through the DCP hole where the highest von Mises stresses were found in the finite element analysis (FEA). This stress was reduced in constructions with bone contact by increasing the bridging length. On the other hand, additional screws increased the implant stress since higher loads were needed to achieve bone contact. Based on the present results, the following clinical recommendations can be made for the locked internal fixator in bridging technique as part of a minimally invasive percutaneous osteosynthesis (MIPO): for fractures of the lower extremity, two or three screws on either side of the fracture should be sufficient. For fractures of the humerus or forearm, three to four screws on either side should be used as rotational forces predominate in these bones. In simple fractures with a small interfragmentary gap, one or two holes should be omitted on each side of the fracture to initiate spontaneous fracture healing, including the generation of callus formations. In fractures with a large fracture gap such as comminuted fractures, we advise placement of the innermost screws as close as practicable to the fracture. Furthermore, the distance between the plate and the bone ought to be kept small and long plates should be used to provide sufficient axial stiffness.

Factors affecting polyethylene wear in total knee arthroplasty.

A complication of total knee arthroplasty (TKA) is fatigue-type wear, which can destroy a tibial inlay in <10 years. This deleterious wear mechanism occurs during cyclic loading if the yield stress of polyethylene is exceeded. Because increased stress on and within the polyethylene inlay is associated with increased wear, it is important to reduce the inlay stress by either activity restrictions or conformity changes of design. All stress parameters are more sensitive to conformity changes (eg, design changes) than to load changes (eg, activity restrictions). However, the reduction of stress on and within the polyethylene through increased conformity will increase the stress at the tibial fixation interfaces. An attempt was made to solve this problem with the introduction of mobile-bearing designs. Many mobile-bearing designs exist with good long-term results. One important difference among the various designs is the amount of flexion range with full conformity between the femoral component and the tibial inlay. Although a single radius design reduces polyethylene stress throughout the flexion range, it may be disadvantageous for a revision design to intraoperatively adapt to different degrees of constraint. Aseptic loosening and osteolysis due to small abrasive and adhesive wear particles have also been reported as a cause of failure. The design and material parameters affecting polyethylene wear in TKAs, as well as the potential detrimental effects of wear particle size, are the key issues in defining the life of a TKA.