Tissue engineering approaches to rotator cuff tendon deficiency

Biomechanical comparison of 3 latissimus dorsi transfer sites for reverse total shoulder arthroplasty in the absence of teres minor

BACKGROUND

Reverse total shoulder arthroplasty is often performed to treat rotator cuff tear arthropathy with irreparable rotator cuff tears. Patients with full-thickness tears involving the posterior cuff and teres minor specifically lose active external rotation of the humerus, limiting activities of daily living. A latissimus dorsi transfer has been described as one potential solution, but few studies have compared different latissimus dorsi transfer sites. This study assesses the biomechanics of 3 latissimus dorsi transfer sites, examining external rotation, deltoid muscle forces, and force across the glenoid for specific activities.

METHODS

The Newcastle Shoulder Model was modified to include a Delta III reverse shoulder arthroplasty and was used to model the effects of 3 latissimus dorsi transfer sites-anterior, posterolateral, and posterodistal-in the setting of teres minor deficiency. The latissimus dorsi was represented by 5 muscle elements approximating anatomic fascicle divisions. Kinematic data sets representing common activities were input into the model, allowing calculation of muscle forces and glenoid loads.

RESULTS

Each of the 3 latissimus dorsi transfer sites demonstrated a change of moment arm from internal to external rotation with increased magnitude. Average maximum deltoid muscle forces and glenoid loading across all motions decreased for each of the 3 transfer sites, with the greatest decreased force noted for the posterior deltoid. This decrease in deltoid force and glenoid loading was significantly greater with the anterior and posterolateral transfer sites, relative to the posterodistal site.

DISCUSSION

Latissimus dorsi transfer to all 3 sites in the setting of reverse total shoulder arthroplasty and posterior rotator cuff deficiency resulted in large external rotation moment arms. The transferred latissimus dorsi shared the external rotation load and resulted in decreased deltoid forces and glenoid loading with very small differences between the 3 transfer sites. The posterodistal location reduced deltoid force and glenoid loading to a lower degree compared with other sites, but it also showed that it did not alter the tendon length compared with the native shoulder.

Cell-based tissue engineering augments tendon-to-bone healing in a rat supraspinatus model

Rotator cuff pathology causes substantial pain/disability and health care costs. Cell-based tissue engineering offers promise for improved outcomes in tendon to bone healing. Cells from the tendon-bone interface were used here to amplify surgical defect healing in a rat model. Cells from tendon-to-bone interface of the rotator cuff were seeded in sponges and implanted into critical rotator cuff defects: Group I, control; II, surgical defect only; III, suture-repaired defect; IV, surgical defect, repair with sponge only; V, surgical defect, repair with sponge with cells. Three, 6-, and 12-week results were assessed for histologic features. At 3 weeks, histologic indices in Group V were significantly increased versus other treatment groups. Group V (12 weeks) showed significantly improved collagen organization versus other treatment groups; there was no difference in collagen organization in Group I versus V. In summary, increased cellularity, inflammation, vascularity, and collagen organization were present at 3 weeks; increased collagen organization at 12 weeks in Group V provides evidence for improved healing with cells. Data further support the utility of tendon-bone interface cells in rotator cuff healing.

Advancing regenerative surgery in orthopaedic sports medicine: the critical role of the surgeon

The constant desire to improve outcomes in orthopaedic sports medicine requires us to continuously consider the challenges faced in the surgical repair or reconstruction of soft tissue and cartilaginous injury. In many cases, surgical efforts targeted at restoring normal anatomy and functional status are ultimately impaired by the biological aspect of the natural history of these injuries, which acts as an obstacle to a satisfactory repair process after surgery. The clinical management of sports injuries and the delivery of appropriate surgical intervention are continuously evolving, and it is likely that the principles of regenerative medicine will have an increasing effect in this specialized field of orthopaedic practice going forward. Ongoing advances in arthroscopy and related surgical techniques should facilitate this process. In contrast to the concept of engineered replacement of entire tissues, it is probable that the earliest effect of regenerative strategies seen in clinical practice will involve biological augmentation of current operative techniques via a synergistic process that might be best considered "regenerative surgery." This article provides an overview of the principles of regenerative surgery in cartilage repair and related areas of orthopaedic surgery sports medicine. The possibilities and challenges of a gradual yet potential paradigm shift in treatment through the increased use of biological augmentation are considered. The translational process and critical role to be played by the specialist surgeon are also addressed. We conclude that increased understanding of the potential and challenges of regenerative surgery should allow those specializing in orthopaedic surgery sports medicine to lead the way in advancing the frontiers of biological strategies to enhance modern clinical care in an evidence-based manner.

Cell- and gene-based approaches to tendon regeneration

Repair of rotator cuff tears in experimental models has been significantly improved by the use of enhanced biologic approaches, including platelet-rich plasma, bone marrow aspirate, growth factor supplements, and cell- and gene-modified cell therapy. Despite added complexity, cell-based therapies form an important part of enhanced repair, and combinations of carrier vehicles, growth factors, and implanted cells provide the best opportunity for robust repair. Bone marrow-derived mesenchymal stem cells provide a stimulus for repair in flexor tendons, but application in rotator cuff repair has not shown universally positive results. The use of scaffolds such as platelet-rich plasma, fibrin, and synthetic vehicles and the use of gene priming for stem cell differentiation and local anabolic and anti-inflammatory impact have both provided essential components for enhanced tendon and tendon-to-bone repair in rotator cuff disruption. Application of these research techniques in human rotator cuff injury has generally been limited to autologous platelet-rich plasma, bone marrow concentrate, or bone marrow aspirates combined with scaffold materials. Cultured mesenchymal progenitor therapy and gene-enhanced function have not yet reached clinical trials in humans. Research in several animal species indicates that the concept of gene-primed stem cells, particularly embryonic stem cells, combined with effective culture conditions, transduction with long-term integrating vectors carrying anabolic growth factors, and development of cells conditioned by use of RNA interference gene therapy to resist matrix metalloproteinase degradation, may constitute potential advances in rotator cuff repair. This review summarizes cell- and gene-enhanced cell research for tendon repair and provides future directions for rotator cuff repair using biologic composites.

Translation of science to surgery

Orthopaedic surgery is in an exciting transitional period as modern surgical interventions, implants and scientific developments are providing new therapeutic options. As advances in basic science and technology improve our understanding of the pathology and repair of musculoskeletal tissue, traditional operations may be replaced by newer, less invasive procedures which are more appropriately targeted at the underlying pathophysiology. However, evidence-based practice will remain a basic requirement of care. Orthopaedic surgeons can and should remain at the forefront of the development of novel therapeutic interventions and their application. Progression of the potential of bench research into an improved array of orthopaedic treatments in an effective yet safe manner will require the development of a subgroup of specialists with extended training in research to play an important role in bridging the gap between laboratory science and clinical practice. International regulations regarding the introduction of new biological treatments will place an additional burden on the mechanisms of this translational process, and orthopaedic surgeons who are trained in science, surgery and the regulatory environment will be essential. Training and supporting individuals with these skills requires special consideration and discussion by the orthopaedic community.

In this paper we review some traditional approaches to the integration of orthopaedic science and surgery, the therapeutic potential of current regenerative biomedical science for cartilage repair and ways in which we may develop surgeons with the skills required to translate scientific discovery into effective and properly assessed orthopaedic treatments.