Factors affecting stress shielding and osteolysis after reverse shoulder arthroplasty: A multicenter study in a Japanese population.

BACKGROUND: Stress shielding and osteolysis around the humeral stem after reverse shoulder arthroplasty causes loosening and periprosthetic fractures and reduces bone stock during revision surgery. In Japanese patients, who have relatively small bodies, different characteristics may exist regarding the occurrence of these changes compared with the characteristics of Westerners, who have relatively larger frames. The purpose of this multicenter study was to investigate the incidence and clarify the predictors of stress shielding and osteolysis in Japanese individuals who underwent reverse shoulder arthroplasty. METHODS: The occurrence of stress shielding and osteolysis was investigated in 135 shoulders that had undergone reverse shoulder arthroplasty at least 2 years prior in five Japanese hospitals. During post-surgical follow-up, which was conducted every 3 months, the locations of the stress shielding occurrences, such as cortical thinning and osteopenia (which primarily occurred in zones 1, 2, and 7, where 1 is the greater tuberosity and 7 is the calcar part), spot weld, and condensation lines, were recorded. Cases without any abnormal findings on radiographs obtained up to ≥2 years after surgery were regarded as having no abnormalities. Finally, the predictors of cortical thinning and proximal humeral osteolysis were assessed using univariate and multivariate regression analyses. RESULTS: Cortical thinning and osteopenia occurred in 68 shoulders, a condensation line occurred in 37 shoulders, and spot weld occurred in 23 shoulders. In particular, greater tuberosity and calcar osteolysis occurred in 40 and 47 shoulders, respectively. Long stem, cementless stem, and a larger proximal filling ratio were independent predictors of cortical thinning and osteopenia, whereas a cementless stem, larger metaphysis diameter, and a larger proximal filling ratio were associated with proximal humeral osteolysis. CONCLUSIONS: The predictors of stress shielding and osteolysis included the use of long stems, cementless stems, larger proximal filling ratios, and larger metaphysis diameters. LEVEL OF EVIDENCE: retrospective comparative study (Level III).

Rotator cuff regeneration using a bioabsorbable material with bone marrow-derived mesenchymal stem cells in a rabbit model.

BACKGROUND: Rotator cuff regeneration using tissue engineering techniques is a challenging treatment in elderly patients with irreparable rotator cuff tears. HYPOTHESIS: A polyglycolic acid sheet scaffold with seeded mesenchymal stem cells (MSCs) may enhance the expression of type I collagen products and increase the mechanical strength of the regenerated tendon in vivo. STUDY DESIGN: Controlled laboratory study. METHODS: A surgically created defect of infraspinatus tendons of rabbits was reconstructed with 2 different materials, a polyglycolic acid (PGA) sheet alone (PGA group) (n = 34) and a PGA sheet seeded with autologously cultured MSCs (MSC group) (n = 34). The authors created a tendon defect model without embedding any graft as the control model (control group) (n = 34). The rabbits were sacrificed at 4, 8, and 16 weeks after the operation and then were histologically evaluated. The rabbits were also biomechanically evaluated by measuring the ultimate failure loads and Young's modulus at 4 and 16 weeks following implantation. RESULTS: In the MSC group, the fibrocartilage layers and Sharpey fibers were found regularly in the insertion site at 8 weeks compared with the PGA group. In control group, thin membranes with many fibroblasts arranged in an irregular pattern linked the end of the torn cuff to the bone without any Sharpey fibers and type I collagen. A large volume of type I collagen was found in comparison with type III collagen at 16 weeks in the MSC group, whereas type III collagen was more prevalent than type I in the PGA group. The tendon maturing score in the MSC group had higher values than the PGA and control groups at 8 and 16 weeks (mean values were 21.0 ± 0.89, 24.0 ± 2.53 in the MSC group; 16.7 ± 2.25, 21.3 ± 2.42 in the PGA group; and 10.2 ± 0.98, 12.2 ± 1.72 in the control group, respectively) (P < .05). The results of the mechanical analysis revealed that the regenerated tendons in the MSC group had better tensile strength than in the PGA and control groups at 16 weeks (mean values were 3.04 ± 0.54 in the MSC group, 2.38 ± 0.63 in the PGA group, and 1.58 ± 0.13 in the control group) (P < .05). CONCLUSION: Bone marrow-derived MSCs were able to regenerate tendon-bone insertions and the tendon belly, including the production of type I collagen, and increased the mechanical strength of the regenerated rotator cuff tendon. CLINICAL RELEVANCE: Rotator cuff regeneration using MSCs is a promising treatment for massive rotator cuff defects.

Flow cytometric discrimination of mesenchymal progenitor cells from bone marrow-adherent cell populations using CD34/44/45(-) and Sca-1(+) markers.

BACKGROUND: Cultured bone marrow adherent cells (BMACs) have been commonly used as stem cells in bone and cartilage regeneration therapy. However, BMACs are actually a heterogeneous cell population, and clinicians might have previously transplanted more fibroblasts or other cells than actual stem cells. The purposes of this study were to (1) isolate immature mesenchymal stem cells with CD34/44/45 and Sca-1 surface-antigen patterns from BMACs using flow-activated cell sorting and (2) investigate their differentiation potential. METHODS: Bone marrow cells were extracted from the mouse femur and cultured. Adherent cells could be identified approximately 3 days after seeding, and nonadherent cells were removed with the medium when it was changed. BMAC samples were cultured for 3, 7, 10, 14, 21, 28, 35, and 42 days after the first seeding. We directly isolated CD34/44/45(-)Sca-1(+) mesenchymal progenitor cells (MPC1) and CD34/45(-)/44(+) Sca-1(+) mesenchymal progenitor cells (MPC2) from BMACs based on their cell surface marker patterns using a fluorescence-activated cell sorter. These subgroups - MPC1, MPC2, and the residual cells in BMACs (non-MPC population: RCs) - were then induced to differentiate into bone, cartilage, and fat using a plate culture. The cultures were examined after histochemical staining on day 14. RESULTS: In a plate culture, the MPC1 population had higher potential to differentiate into osteoblasts, chondrocytes, and lipocytes; whereas MPC2 and RCs differentiated into only two lineages: osteoblasts and lipocytes. The incidence of these multipotential cells was less than 5% among the cultured BMACs. MPC1 proliferated up to 17-fold within 3-4 weeks after separation from floating cells and did not increase thereafter. CONCLUSIONS: BMACs are conventionally thought to differentiate into cartilage only in pellet culture, but we showed that MPC1 produced cartilage-like extracellular matrix in plate culture. MPC1, which are more immature cells than MPC2 and RCs, were multipotential progenitors that showed unique cartilage-differentiation potential. MPC1 had less ability to proliferate in BMAC culture, but they might have higher potential for chondrogenic differentiation.

Changes of the mineralization pattern in the subchondral bone plate of the glenoid cavity in the shoulder joints of the throwing athletes.

The distribution of mineralization in the subchondral bone plate (DMSB) is used as a parameter for individual stress distribution of shoulder joints. We have analyzed 28 shoulder joints of throwing athletes by DMSB of the glenoid with computed tomography osteoabsorptiometry and described their mineralization patterns. The throwing motion imposes a heavy rotational load on the shoulder joint, and this, in turn, may lead to excessive translation of the humeral head on the glenoid. This could explain why the two most frequent density maxima were localized to the anterior and posterior portions of the glenoid. Our finding of a frequent bicentric density distribution of the shoulder joints of throwing athletes should be useful in any future analysis of the relationship between the DMSB and the bone morphology of the glenoid.

The HU knot: a new sliding knot for arthroscopic surgery.

Sliding knots are commonly used in arthroscopic knot tying. The Surgical knot as a hand-tied knot is very secure. We found that the Surgical knot could be used as a sliding knot. We have modified the Surgical knot to include a self-locking loop. A new sliding knot for arthroscopic surgery, the HU knot, is described. By tensioning the loop strand, the self-locking loop creates a snug knot without sliding backward. The HU knot provides great security.

The cellular origin of cartilage-like tissue after periosteal transplantation of full-thickness articular cartilage defects: an experimental study using transgenic rats expressing green fluorescent protein.

BACKGROUND: Periosteal transplantation is commonly used for the treatment of articular cartilage defects. However, the cellular origin of the regenerated tissue after periosteal transplantation has not been well defined. The objective of this study was to investigate the cellular origin of the regenerated tissue after periosteal transplantation. METHOD: Free periosteum was harvested from the tibia of 10-week-old adolescent enhanced green fluorescent protein (GFP-) expressing transgenic Sprague Dawley (SD) rats and was transplanted to full-thickness articular cartilage defects of the patellar groove in normal 10-week-old adolescent SD rats. The periosteum was sutured to the defect with the cambium layer facing the joint cavity. 8 SD rats were killed at 4 weeks and 8 SD rats were killed at 8 weeks after surgery. The repaired tissue was assessed histologically and histochemically. GFP-positive cells derived from the donor periosteum could easily be detected in the repaired tissue by use of a fluorescent microscope. RESULTS: At both 4 and 8 weeks after transplantation, the entire area of the defects had been repaired, with the regenerated tissue being well stained histologically with safranin-O. Most cells in the whole area of the regenerated tissue were GFP-positive, indicating that very few of the cells were GFP-negative cells originating from the recipient rats. INTERPRETATION: This experiment demonstrates that most cells in regenerated tissue after periosteal transplantation using adolescent animals do not originate from recipient cells but from the periosteal cells of the donor.

Allogeneic bone marrow-derived mesenchymal stromal cells promote the regeneration of injured skeletal muscle without differentiation into myofibers.

Half-stratum laceration was performed on the tibialis anterior muscle of Sprague-Dawley (SD) rats as a skeletal muscle injury model. Bone marrow-derived mesenchymal stromal cells (BMMSCs), which were derived from enhanced green fluorescent protein (GFP) transgenic SD rats, were transplanted into the injured site. Tensile strength produced by nerve stimulation was measured for functional evaluation before sacrifice. Specimens of the tibialis anterior muscles were stained with hematoxylin and eosin, and immunohistochemically stained for histological evaluation. Our results showed that transplanted BMMSCs promoted maturation of myofibers histologically and made the injured muscle acquire almost normal muscle power functionally by 1 month after transplantation. However, the results of immunohistochemical staining could not prove that transplanted BMMSCs differentiated into or fused to skeletal myofibers, although it showed that transplanted BMMSCs seemed to differentiate into muscle precursor cells. Therefore, our results indicated that BMMSCs contributed to the regeneration of skeletal muscle by mechanisms other than fusion to myofibers after differentiation.