Bone marrow stem cells (BMSCs) represent a collection of different cell types exhibiting stem cell characteristics but with notable heterogeneity. Among these, Skeletal Stem Cells (SSCs) represent a distinct matrix subgroup within BMSC and demonstrate a specialized capacity to facilitate bone formation, recruit chondrocytes, and contribute to hematopoiesis. SSCs play a pivotal role in orchestrating the functions of skeletal organs. Local ischemia has a significant impact on cell survival and function. We hypothesize that bone ischemia induces alterations in the differentiation potential of SSCs, consequently influencing changes in bone structure.

We mechanically dissected tissue from the necrotic segment in the femoral head and more normal appearing areas from the femoral neck of specimens from 5 patients diagnosed with osteonecrosis of the femoral head (ONFH). These tissues were enzymatically broken down into individual cell suspensions. Utilizing fluorescence-activated cell sorting (FACS) based on specific surface markers indicative of human skeletal stem cells (hSSC), namely CD45- CD235a- CD31- TIE2- Podoplanin (PDPN)+ CD146- CD73+ CD164+, we isolated a distinct cell population. Subsequent in vitro evaluations, focusing on clonogenicity, osteogenesis, and chondrogenesis were conducted to assess the functional prowess of these SSCs. Moreover, we introduced BMP2 at a concentration of 50ng/ml to SSCs extracted from necrotic regions to potentially reinstate their osteogenic capabilities.

We effectively isolated SSCs from both Necrotic and Non-necrotic Zones. We observed an augmented clonal formation capacity and chondrogenesis ability of SSCs isolated from the necrotic region, accompanied by a significant decline in osteogenic ability (P＜0.01), an effect not reversible even with the addition of BMP2.

Ischemia adversely affects the proliferation and function of SSCs, resulting in a diminished osteogenic capacity and an insensitivity to BMP2, ultimately leading to structural alterations in bone tissue.

Summary

The presence or absence of crimp within the anterior cruciate ligament (ACL) sub-bundle anatomy was correlated with knee flexion angle changes and provided a measure of differential loading within its sub-bundle microstructure.

Attempts have been made to develop standardise guidelines for knee implant wear testing of polyethylene (PE). The current ISO-14243-3 standard recommends the use “calf serum”, without giving ranges on the specific protein constituents and characteristics. In the present study, three types of frequently used calf sera with various protein constituents (albumin, globulins) were utilised. The effect of osmolality and hyaluronic acid (HA) was also assessed. An attempt was made to identify synovial fluid (SF) characteristics that may be responsible for the boundary lubrication in the joint with the goal to develop a more clinically relevant lubricant.

Twenty samples of SF were drawn from twenty patients and analyzed. Specific protein constituents and osmolality were then compared to three calf sera used for wear testing. Test One (six million cycles (Mc)): Bovine calf serum (BCS), newborn calf serum (NCS) and alpha-calf serum (ACS) were diluted with distilled water (DW). Test two (5.5Mc): ACS with an osmolality of 312 ± 1.00 mmol/kg (closest to clinical osmolality; diluted with phosphate buffered saline, PBS) and 145 ± 2.00 mmol/kg (diluted with DW) were consecutively tested. HA was added at a concentration of 1.5g/l. Modular total knee replacements of cruciate retaining design (GUR 1050, 10mm PE insert) were used.

ACS diluted with PBS appeared to be of closest specific protein constituents and osmolality when compared to SF. The wear rate for BCS was 21.81 ± 2.48 mg/Mc, 17.05 ± 3.25 mg/Mc for NCS, and 13.44 ± 0.79 mg/Mc for ACS (p < 0.016). Decreased osmolality amplified the PE wear by a factor of 2.3 (p = 0.020). Adding HA increased the PE wear by a factor of two (p = 0.002).

There was significant difference in PE wear rates between the three calf-sera. BCS and NBC did not have clinically relevant levels of specific protein constituents. This study strongly suggests that current standards for total knee wear testing should be revised to enable more controlled wear testing under more clinically relevant conditions. It is suggested to be of particular importance when new bearing materials, such as cross-linked PE’s, are evaluated and proposed for clinical application.