Muscle cell-mediated gene delivery to the rotator cuff.

Rotator cuff lesions are one of the most common causes of upper extremity disability. Surgical therapy addresses mostly the extrinsic etiology, but not intrinsic factors such as aging, structural changes, low vascularity, and inflammatory processes. In this study, genetically engineered, highly purified muscle-derived cells (MDCs) were characterized and injected into the supraspinatus tendons of nude rats. The injected cells were monitored for 3 weeks. In vitro, the engineered, highly purified MDCs do not express vimentin; 98% of them are positive for the beta-galactosidase marker gene, and 99% hybridize with the specific pancentromeric mouse probe. beta-Galactosidase marker gene expression of the injected cells was detected up to 21 days. From day 7 after injection, the cell nuclei became spindle shaped, cells were integrated into the tendon collagen bundles, and the cells showed differentiation into vimentin-expressing fibroblastic cells. The results indicate that the rotator cuff tendon matrix and its original cellular components modulated the injected MDCs toward a fibroblastic phenotype. The compatibility and ability of MDCs to differentiate into other cell lineages, such as fibroblasts, might have high potential utility in tissue-engineering applications for tendon healing. This approach facilitates the application of muscle-derived progenitor cells and ex vivo gene therapy for the treatment of rotator cuff lesions.

The influence of chair height on lower limb mechanics during rising.

The mechanics of the lower limb were analyzed in young, adult normal subjects when rising from a seated position. Limb mechanics were described in terms of flexion-extension motion and moments at the hip, knee and ankle while rising from four seat heights corresponding to 65, 80, 100, and 115% of the subject's knee joint height. The results indicate that the maximum moment tending to flex the hip joint was higher than that occurring at the knee or ankle. The magnitude of the maximum flexion moment at the hip was not substantially influenced by chair height, changing by less than 12% between the highest and lowest chair heights. Conversely, the maximum knee flexion moments were found to be highly dependent on chair height and nearly doubled from the highest to the lowest position. The magnitude of the moments at the ankle did not change with chair height and were significantly lower than the magnitude of the moments found during normal walking. The magnitude of motion and moments at the hip were greater during chair-rising than during stair-climbing or walking. The range of motion required at the knee for the lower chair heights was also greater than was reported during stair-climbing studies. Thus, the combination of moments in joint angles during chair-rising are unique among common activities of daily living and should be considered in chair selection as well as in the guidelines for prosthetic devices.

The role of the long head of the biceps muscle and superior glenoid labrum in anterior stability of the shoulder.

The authors conducted a study to determine if the long head of the biceps muscle and its attachment at the superior glenoid labrum play a role in stability of the shoulder in an overhead position. Their study used a dynamic cadaveric shoulder model that simulated the forces of the rotator cuff and long head of biceps muscles as the glenohumeral joint was abducted and externally rotated. Their data suggest that the long head of the biceps muscle contributes to anterior stability of the glenohumeral joint by increasing the shoulder's resistance to torsional forces in the vulnerable abducted and externally rotated position. The biceps muscle also helps to diminish the stress placed on the inferior glenohumeral ligament. Detachment of the superior glenoid labrum is detrimental to anterior shoulder stability as it decreases the shoulder's resistance to torsion and places a greater magnitude of strain on the inferior glenohumeral ligament.

SLAP lesions: current concepts.

The presence and significance of superior glenoid labral tears have received increasing attention in the 1990s. The symptoms associated with labral tears can be quite disabling to competitive and recreational athletes alike. Recent basic science and clinical studies have contributed much to the understanding of these injuries, including their association with suprascapular nerve entrapment. This article reviews the current basic science and clinical understanding of SLAP (superior labrum anterior and posterior) lesions in order to guide clinicians and promote further investigation.

A clinical and comparative biomechanical evaluation of proximal femoral osteotomy fixation in children.

This study compared the biomechanical characteristics of a 90 degrees infant blade plate construct and anteriorly applied 120 degrees angled plate construct in response to an axial compression load. The blade plate construct stiffness was three times greater than the angled plate construct (238.9 vs 85.7 N/deg). Four degrees failure load was also significantly higher for the blade plate. Despite inferior biomechanical characteristics, the 120 degrees angled plate functioned very satisfactorily in a retrospective clinical review of 21 proximal femoral varus osteotomies. The authors conclude that the 120 degrees angled plate has practical benefits in terms of ease of insertion and intraoperative adjustability which may outweigh its biomechanical inferiority.