While reverse shoulder arthroplasty (RSA) corrects vertical muscle imbalance, it cannot restore the horizontal imbalance seen in cuff-deficient shoulders with combined loss of active elevation and external rotation (CLEER). We report the medium-term results of the modified latissimus dorsi/teres major tendon transfer (L'Episcopo procedure) associated with RSA, performed via a single deltopectoral approach. Sixteen CLEER patients underwent the procedure and were followed up at a mean of 49 months (range, 36–70). All patients had lost spatial control of their arm, were unable to maintain neutral rotation, and had abnormal infraspinatus and teres minor muscles on imaging. Outcome measures included Constant score (CS), Subjective Shoulder Value (SSV), and ADLER score (activities of daily living requiring external rotation).Purpose
Method
Tendons and ligaments are similar in composition but differ in function. Simple anatomical definitions do not reflect the fact individual tendons and ligaments have unique properties due to their adaptation to a specific role. The patellar tendon is a structure of particular clinical interest. A null hypothesis was declared stating that the patellar tendon is not significantly different in terms of matrix composition and collagen fibril diameter to other tendons. The lateral and medial collateral ligaments (LCL, MCL), anterior and posterior cruciate ligaments (ACL, PCL), together with the long digital extensor, superfi-cial digital extensor and patellar tendons (LDET, SDFT, PT) were harvested from 3 cadaveric ovine hindlimbs. The extracellular matrix was assessed in terms of water, collagen and total sulphated glycosaminoglycan (GAG) content. The organisation of the collagen component was determined by an ultrastructural analysis of collagen fibril diameter distributions using electron microscopy, together with values for the collagen fibril index (CFI) and mass-average diameter (MAD). There were significant differences between ligaments and tendons. The PT had a bimodal collagen fibril diameter distribution with CFI72.9%, MAD 202nm, water content 53.1%, GAG content 2.3 g/mg and collagen content 73.7%, which was not significantly different from the other tendons. The results of this study support the null hypothesis suggesting that the patellar tendon is similar to other tendons and demonstrate that tendons have different characteristics to ligaments.
The skeletal system exhibits functional adaptation. For bone the mechanotransduction mechanisms have been well elucidated; in contrast, the response of tendon to its mechanical environment is much more poorly understood despite tendon disorders being commonly encountered in clinical practice. This study presents a novel approach to developing an isolated tendon system in vivo. This model is used to test the hypothesis that stress-shielding, and subsequent restressing, causes significant biomechanical changes. We propose a control mechanism that governs this process. A custom-built external fixator was used to functionally isolate the ovine patellar tendon(PT). In group 1 animals(n=5) the right PT was stress-shielded for 6 weeks. This was achieved by drawing the patella towards the tibial tubercle, thus slackening the PT. In group 2 (n=5) the PT was stress-shielded for 6 weeks. The external fixator was then removed and the PT physiologically loaded for a further 6 weeks. In each case, the PT subsequently underwent tensile testing and measurement of length(L) and cross-sectional area(CSA). The untreated left PTs acted as controls (n=10). 6 weeks of stress-shielding significantly decreased material and structural properties of tendon compared to controls (elastic modulus(E) 76.2%, ultimate tensile strength(UTS) 69.3%, stiffness(S) 79.2%, ultimate load(UL) 68.5%, strain energy(SE) 60.7%; p<
0.05). Ultimate strain(US), L and CSA were not significantly changed. 6 weeks of subsequent functional loading (Group 2) caused some improvement in material properties, but greater recovery in structural properties (E 79.8%, UTS 91.8%, S 96.7%, UL 92.7%, SE 96.5%). CSA was significantly greater than Group 1 tendons at 114% of control value. Previous models of tendon remodelling have relied on either joint immobilization or direct surgical procedures. This model allows close control of the tendon’s mechanical environment whilst allowing normal joint movement and avoiding surgical insult to the tendon itself. The hypothesis that stress-shielding, and subsequent restressing, causes significant biomechanical changes has been upheld. We propose that the biomechanical changes observed are governed by a strain homeostasis feedback mechanism.
