The influence of anterior displacement of the tibial tuberosity on patellofemoral biomechanics

Methods to assess patellofemoral joint stress: A systematic review

Changes in patellofemoral joint (PFJ) stress are related to the development and course of PFJ dysfunctions. Different methods for PFJ stress calculation have been used, making the comparison of PFJ stress values across different studies difficult. The purpose of this study was to systematically review the methods for PFJ stress calculation and highlight the differences among the methods. A systematic literature search was conducted in Medline, Embase, CINAHL, SPORTDiscus and Web of Science databases. Included studies examined PFJ stress in subjects with or without musculoskeletal conditions. Of 12,670 identified studies, 53 were included, with a total of 1134 subjects evaluated. The main differences among the methods to calculate PFJ stress were: i) method to calculate PFJ contact area; ii) method to calculate a constant (coefficient k) that defines the relation between quadriceps force and PFJ reaction force; iii) the inclusion of adjustments for sagittal plane forces. Considerable variability in PFJ stress results was observed. The greatest PFJ stress value was 55.03 MPa during a dance jump and the lowest value was 1.9 MPa during walking at the speed of 1.4 m/s. Most studies applied methods which use data from previous studies. However, methods which use data from their own participants for most parts of the calculation might be preferred to minimize potential errors. When direct measures are not possible, a standard method could be applied to facilitate comparisons among studies.

Biphasic Analysis of Cartilage Stresses in the Patellofemoral Joint

The objective of this study was to examine the state of stress within the solid matrix of articular cartilage in the patellofemoral joint, using anatomically faithful biphasic models of the articular layers, with the joint subjected to physiologic muscle force magnitudes. Finite element models of five joints were created from human cadaver knees. Biphasic sliding contact analyses were performed using FEBio software to analyze the response of the joint from 30 to 60 degrees of knee flexion. Results demonstrated that the collagen matrix always sustains tensile stresses, despite the fact that the articular layers are loaded in compression. The principal direction of maximum solid stresses was consistent with the known orientation of collagen fibrils in cartilage. The magnitudes of these tensile stresses under muscle forces representative of activities of daily living were well below tensile failure stresses reported in the prior literature. Results also hinted that solid matrix stresses were higher in the patellar versus femoral superficial zone. These anatomically correct finite element models predicted outcomes consistent with our understanding of structure-function relationships in articular cartilage, while also producing solid matrix stress estimates not observable from experiments alone, yet highly relevant to our understanding of tissue degeneration.

Triple positioning of tibial tubercle osteotomy for patellofemoral disorders

BACKGROUND AND PURPOSE

Patellofemoral disorders are often associated with patellofemoral malalignment. Tibial tubercle transfer is an effective method to correct the patellofemoral malalignment. This study evaluated the long-term results of triple positioning of tibial tubercle osteotomy for refractory patellofemoral disorders with 10-year follow-up.

PATIENTS AND METHODS

Fifty-six patients with 62 knees underwent triple positioning of tibial tubercle osteotomy for refractory patellofemoral disorders. All patients received standard rehabilitation protocol postoperatively. The average length of follow-up was 128.5±9.8 months (range 116 to 149). The evaluations included pain score, Kujala patellofemoral score, Lysholm score and radiograph of the knee.

RESULTS

The overall clinical results were excellent in 41.9%, good in 37%, fair in 12.9% and poor in 5% at 1 year; and 29% excellent, 41% good, 18.3% fair and 9.3% poor at 10 years. Satisfactory results were 78.9% and 70.9%, and unsatisfactory results 21.1% and 29.1% at 1 year and 10 years respectively. There was no correlation of clinical outcomes with age, sex, body weight and height and preoperative pain score. However, there was a positive correlation of clinical outcomes with the improvement of the congruence angle on postoperative X-rays of the knee, and a negative correlation of clinical outcome with the severity of articular cartilage damage assessed in arthroscopy. The complications included 1 non-union and 1 infection with non-union.

CONCLUSION

Triple positioning of tibial tubercle osteotomy is effective and long lasting in patients with patellofemoral disorders with 70.9% satisfactory results at 10-year follow-up.

LEVEL OF EVIDENCE

IV (refer to instructions for detailed description on the level of evidence).

The influence of reduced hamstring length on patellofemoral joint stress during squatting in healthy male adults

Increased patellofemoral joint (PFJ) stress has been implicated in the development of PFJ pathologies. Previous studies have identified a relationship between reduced hamstring length and patellofemoral pain syndrome. Hamstring stretching is also recommended in the management thereof. However, the relationship between reduced hamstring length and PFJ stress has not been explored in vivo during activities that load the PFJ, such as squatting. The objective of this study was to determine if persons with reduced hamstring length demonstrate increased PFJ stress during squatting compared with individuals without reduced hamstring length. Eight participants with, and eight participants without, reduced hamstring length were assessed to determine their PFJ contact area using magnetic resonance imaging, and their PFJ reaction force during squatting using motion analysis. Data collected were entered into a biomechanical model to calculate medial, lateral and total PFJ stress. It was found that participants with reduced hamstring length had significantly greater total (393.39 Pa/kg vs. 213.01 Pa/kg) and lateral (311.23 Pa/kg vs. 142.55 Pa/kg) PFJ stress at 60 degrees knee flexion during squat descent and ascent (427.75 Pa/kg vs. 255.64 Pa/kg and 337.75 Pa/kg vs. 170.63 Pa/kg, respectively). This was due to significantly increased PFJ reaction force at 60 degrees knee flexion during squat descent (12.18 N/kg vs. 7.21 N/kg) and ascent (13.03 N/kg vs. 8.72 N/kg), and lower medial PFJ contact area at 60 degrees knee flexion (88 mm(2) vs. 160 mm(2)). The results of this study demonstrate a relationship between reduced hamstring length and increased PFJ stress during squatting due to increased PFJ reaction force and reduced medial PFJ contact area.

Factors affecting the outcome of distal realignment for patellofemoral disorders of the knee

This study correlated the risk factors with the clinical outcome of distal realignment for patellofemoral disorders in 48 patients with 53 knees with 25 to 96 months follow-up. The indications for surgery included pain and disability due to patellofemoral disorders with failure of at least 6 months of conservative treatments. The evaluations included pain scores, Lysholm functional scores and radiographs of the knee. The overall results were satisfactory in 47 knees (88.7%) and unsatisfactory in six knees (11.3%). There was no correlation of the clinical results with age, sex, body weight and body height, preoperative pain scores and Lysholm scores. However, the clinical outcome correlated with the severity of articular damage and the correction of patellar malalignment. Error in patient selection and inadequate surgical technique were attributable to poor outcomes.

Patient-driven control of FES-supported standing up: a simulation study

To control movements aided by functional electrical stimulation (FES) in paraplegic patients, stimulation of the paralyzed lower limbs might be adjusted in response to voluntary upper body effort. Recently, Donaldson and Yu proposed a theoretical approach, called "control by handle reactions of leg muscle stimulation" (CHRELMS), in which stimulation of the lower limbs depends on upper body effort, i.e., body posture and recorded hand reactions, and is aimed to minimize arm forces during standing up and standing. An alternative strategy is presented in this paper, which accounts for voluntary upper body effort as well, but does not require estimation of hand reactions. The objective of this study is to test both strategies by applying them to a generic two-dimensional (2-D) neuromusculoskeletal model. The model takes into account the major properties of muscle and segmental dynamics during FES-supported standing-up movements of a paraplegic patient. In comparison to standing up without FES-support, both closed-loop strategies yield satisfying standing-up movements although no reference information (e.g., a desired trajectory) is required. Arm forces can be significantly reduced. Using the model to optimize the controller, time-consuming and strenuous trial-and-error experimentation could be avoided. However, final experimental studies are planned to verify the presented strategies.