Quantification of rotator cuff tear geometry: the repair ratio as a guide for surgical repair in crescent and U-shaped tears

Surgical repair of symptomatic, retracted rotator cuff tears unresponsive to non-operative treatments requires closure of the tear without undue tension and reattaching the torn tendon to its former insertion site. In this study, the length of the torn tendon edge was hypothesized to be longer than the length of the humeral insertion site. The objective of this study was to quantify the discrepancy in length of the torn tendon edge and the length of the avulsed humeral insertion site. Full thickness, rotator cuff tears that were found in twelve fresh frozen cadaver shoulders was studied. The length of the torn tendon edge, the length of the avulsed humeral insertion site and the retraction were measured using digital calipers. Each tear involved the supraspinatus and the infraspinatus was additionally torn in six. The size of the tear was medium in eight and large in four. The length of the torn tendon edge was always longer than the length of the avulsed humeral insertion site. Retraction was 29.9 ± 9.3 mm (range 21–48 mm). The repair ratio, defined as the ratio of length of torn tendon edge to the length of avulsed humeral insertion site, was 2.6 ± 0.4 (range 2.1–3.5). As only the length of the torn tendon edge equal to the length of the avulsed humeral insertion site can be repaired to bone, a repair ratio more than one precludes a simple repair and an additional repair technique such as margin convergence would be necessary for the remaining unapproximated torn tendon edge in rotator cuff tears. Repair ratio may aid in selection of the surgical repair technique of these rotator cuff tears

Development of a new model for rotator cuff pathology: the rabbit subscapularis muscle

Background and purpose The New Zealand white rabbit subscapularis tendon passes under a bony arch to insert on the lesser tubercle of the humerus in a manner analogous to the supraspinatus tendon in humans. We assessed whether this unique anatomy may provide a new animal model of the shoulder to improve our understanding of rotator cuff pathology

Current biomechanical concepts for rotator cuff repair.

For the past few decades, the repair of rotator cuff tears has evolved significantly with advances in arthroscopy techniques, suture anchors and instrumentation. From the biomechanical perspective, the focus in arthroscopic repair has been on increasing fixation strength and restoration of the footprint contact characteristics to provide early rehabilitation and improve healing. To accomplish these objectives, various repair strategies and construct configurations have been developed for rotator cuff repair with the understanding that many factors contribute to the structural integrity of the repaired construct. These include repaired rotator cuff tendon-footprint motion, increased tendon-footprint contact area and pressure, and tissue quality of tendon and bone. In addition, the healing response may be compromised by intrinsic factors such as decreased vascularity, hypoxia, and fibrocartilaginous changes or aforementioned extrinsic compression factors. Furthermore, it is well documented that torn rotator cuff muscles have a tendency to atrophy and become subject to fatty infiltration which may affect the longevity of the repair. Despite all the aforementioned factors, initial fixation strength is an essential consideration in optimizing rotator cuff repair. Therefore, numerous biomechanical studies have focused on elucidating the strongest devices, knots, and repair configurations to improve contact characteristics for rotator cuff repair. In this review, the biomechanical concepts behind current rotator cuff repair techniques will be reviewed and discussed

Biomechanics of hyperflexion and kneeling before and after total knee arthroplasty.

The capacity to perform certain activities is frequently compromised after total knee arthroplasty (TKA) due to a functional decline resulting from decreased range of motion and a diminished ability to kneel. In this manuscript, the current biomechanical understanding of hyperflexion and kneeling before and after TKA will be discussed. Patellofemoral and tibiofemoral joint contact area, contact pressure, and kinematics were evaluated in cadaveric studies using a Tekscan pressure measuring system and Microscribe. Testing was performed on intact knees and following cruciate retaining and posterior stabilized TKA at knee flexion angles of 90°, 105°, 120°, and 135°. Three loading conditions were used to simulate squatting, double stance kneeling, and single stance kneeling. Following TKA with double stance kneeling, patellofemoral contact areas did not increase significantly at high knee flexion angle (135°). Kneeling resulted in tibial posterior translation and external rotation at all flexion angles. Moving from double to single stance kneeling tended to increase pressures in the cruciate retaining group, but decreased pressures in the posterior stabilized group. The cruciate retaining group had significantly larger contact areas than the posterior stabilized group, although no significant differences in pressures were observed comparing the two TKA designs (p < 0.05). If greater than 120° of postoperative knee range of motion can be achieved following TKA, then kneeling may be performed with less risk in the patellofemoral joint than was previously believed to be the case. However, kneeling may increase the likelihood of damage to cartilage and menisci in intact knees and after TKA increases in tibiofemoral contact area and pressures may lead to polyethyelene wear if performed on a chronic, repetitive basis

On the biomechanics of the patellofemoral joint and patellar resurfacing in total knee arthroplasty

The physiologic forces are essential for proper functioning and longevity of the patellofemoral joint. However, the abnormal forces in the patellofemoral joint are thought to have a strong correlation with patellar disorders in both the intact knees and the knees with total knee arthroplasty. Aims of this thesis were to develop biomechanical testing methods and devices to quantitatively assess the structural integrity of the patellofemoral joint as well as specific parameters for patellar resurfacing in total knee arthroplasty. To quantify the patellofemoral joint kinematics, contact areas, and contact pressures, custom patellofemoral joint testing jigs, a continuous video digitizing system and a three dimensional magnetic tracking system and a custom software for the Fuji pressure sensitive film were developed. Six biomechanical studies were performed. The first study showed that the increase in degree of fixed femur rotation resulted in a nonlinear increase in patellofemoral contact pressures on the contra-lateral facets of the patella in seven human cadaver knees. For total knee arthroplasty studies, anatomically based patellar resection criteria was first determined. This patellar resection criteria yielded a consistent and ideal resection for dome shaped patellar prosthesis in 36 patellae. Thereafter, using ten human cadaver knees, the effects of total knee arthroplasty was quantified. The results showed a significant decrease in the patellofemoral joint contact areas while the patellofemoral joint contact pressures increased well beyond the yield strength of ultra high molecular weight polyethylene following total knee arthroplasty. No statistically significant differences between preoperative and postoperative specimens were observed with respect to the patellofemoral joint kinematics. The effects of patellar component positioning were then determined in five human cadaver knees with total knee arthroplasty. The findings showed the central positioning of the patellar component resulted in the most optimal patellofemoral mechanics for dome shaped patellar prosthesis. The patellofemoral joint testing jig was then improved to simulate individual muscles of the quadriceps. We then determined the effects of anatomically based loading of the patellofemoral joint versus the traditional axial loading approach where a subtle yet significant differences in patellofemoral joint mechanics were quantified. Using this model, we demonstrated excessive edge loading of patellar components at higher knee flexion angles in two contemporary total knee arthroplasty systems with anatomic patellofemoral joints.Abnormal distribution of stresses resulting from improper kinematics of the patellofemoral joint has a strong correlation with patellar disorders in both the intact knees and the knees with total knee arthroplasty. Therefore, the greatest deficit in current knowledge of the patellofemoral joint biomechanics is still the understanding of the structure, function and the forces involved in the patellofemoral joint and its interactions with the extensor mechanism as well as the intra-articular patellofemoral joint contact pressures

Specimen-Specific Method for Quantifying Glenohumeral Joint Kinematics

Associate Editor Eric M. Darling oversaw the review of this article. Abstract—The existing glenohumeral joint kinematic protocols are highly effective for studying in vivo shoulder kinematics but are not anatomically specific enough to address the asymmetric changes in glenohumeral joint kinematics and do not provide clear anatomic definitions for landmarks and directions. Therefore, the objective of this study was to develop an anatomically relevant and specimenspecific three-dimensional glenohumeral joint kinematic method as a new standard definition protocol for the glenohumeral coordinate systems (CSs). The in situ kinematic data of the intra-capsular glenoid-based CS of the glenohumeral joint were mathematically determined from the kinematic data of the extra-capsular CSs measured with an intact capsule. To minimize irreproducibility arising from discrepanc