Exogenous collagen-enhanced recruitment of mesenchymal stem cells during rabbit articular cartilage repair

Background?Despite the well-known effect of type-I collagen in promoting cartilage repair, the mechanism still remains unknown. In this study we investigated this mechanism using a rabbit model of cartilage defects.

Animals and methods?5-mm-diameter full-thickness defects were created on both patellar grooves of 53 Japanese white rabbits (approximately 13 weeks old). The left defect was filled with collagen gel and the right defect was left empty. The rabbits were killed and examined morphometrically until the twenty-fourth postoperative week, by (1) evaluation of matrix production, (2) enumeration of the total number of cells engaged in cartilage repair, (3) enumeration of the proliferating cells, (4) localization of mesenchymal stem cells, and (v) localization of apoptotic cells.

Results?We found that type-I collagen enhances cell recruitment, and thereby increases the number of proliferating cells. A considerable proportion of the proliferating cells were identified as bone marrow-derived mesenchymal stem cells. However, type-I collagen does not prevent the chondrocyte precursors from undergoing apoptotic disengagement from the chondrogenic lineage.

Interpretation?Type-I collagen promotes cartilage repair by enhancing recruitment of bone marrowderived mesenchymal stem cells. Additional use of agent(s) that sustain mesenchymal stem cells along the chondrogenic path of differentiation may constitute an appropriate environment for cartilage repair.     

Implantation of perichondrium-derived chondrocytes in physeal defects of rabbit tibiae

Background Various cells and scaffolds have been used experimentally as interposition materials after physeal bar resection to treat partial physeal growth arrest. However, results of these cell therapies are unpredictable.

Methods We investigated the chondrogenic differentiation of rabbit perichondrial cells in vitro. We also investigated radiographic and histological changes after implantation of the perichondrium-derived chondrocytes, embedded in fibrin beads, into defects created in the medial aspect of the proximal tibial physis of 26 8-week-old New Zealand White rabbits. Physeal defects of the contralateral tibiae were left intact without any treatment, or were treated with fibrin beads not containing cells.

Results The perichondrial cells cultured in the alginate- fibrin beads were positive in immunohistochemical staining for S-100 protein and the extracellular area was stained with Safranin-O. RNase protection assay showed that the expression of type II collagen and aggrecan continued In the cell and bead-treated tibiae, varus deformity was reduced significantly and tibial length was maintained longer than that of the contralateral tibia. Histologically, cartilage clusters of varying size with intervening micro-bony trabeculae were found in the cell and bead-treated tibiae. The lateral, remaining physis in the untreated tibiae showed altered histology.

Interpretation Implantation of fibrin beads containing perichondrium-derived chondrocytes into the physeal defect helps to prevent angular deformation and shortening of long bone, but not completely. Physeal bony bar formation adversely affects the growth of the remaining physis from early stages onward.     

The effect of recombinant human bone morphogenetic protein-2 on the osteogenic potential of rat mesenchymal stem cells after several passages

Background Since the osteogenic potential of bone marrow derived mesenchymal stem cells (BMSCs) becomes reduced with passage, establishment of culture condition that permit the rapid expansion of BMSCs while retaining their potential for differentiation is needed for clinical application. Bone morphogenetic proteins stimulate osteogenic differentiation in mesenchymal progenitor cells as well as increase stem cell numbers. Thus, we analyzed the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the osteogenic potential of rat BMSCs over several passages.

Material and methods Osteogenic differentiation in vitro was evaluated in terms of the alkaline phosphatase (ALP) activity and the osteocalcin (OC) concentration in the supernatants, and the expression of ALP and OC mRNA in the cultured cells. For in-vivo osteogenesis, BMSCs cultured with and without rhBMP-2 through all passages were implanted into athymic mice.

Results  The levels of osteogenic markers were significantly higher in the cells of the BMP(+) group than in the cells of the BMP(-) group, although they decreased with passage irrespective of whether or not rhBMP-2 was added. Similar to the in-vitro experiments, there was a greater degree of bone and cartilage tissue formation in the BMP(+) group over all passages.

Interpretation  From our results, osteogenic potential can be maintained even in BMSCs that have been passaged several times in the presence of rhBMP-2. These cells are capable of inducing and participating in bone formation and can be used for clinical applications.     

High-resolution/high-contrast MRI of human articular cartilage lesions

Background Magnetic resonance microscopy (MRM) is an important experimental tool in the identification of early cartilage lesions.

Methods Normal and degenerated cartilage samples were imaged at 11.74 T using a standard spin echo sequence. Quantitative MR measurements for T₁, T₂, and ADC were obtained and mapping for T₂ and ADC was performed. The bi-exponential model for T₂ relaxation was also explored. Histology was carried out for comparison with MR images.

Results MR images of cartilage samples displaying early stages of degeneration were positively correlated to their histological appearance in 23-μm high-resolu-tion images and also with much shorter imaging times at 47-μm resolution. T₂ maps enable delineation of the actual cartilage zones, distinguishing the super?cial zone in particular. The bi-exponential model can reflect cartilage components at different stages of degeneration.

Interpretation At 11.74 T, with 23-μm resolution or with 47-μm resolution and shorter imaging times, MRM provides images that allow visualization of early stages of cartilage degeneration, including super?cial ?brillation. This has not been shown previously. The images also allow quantitative measurements (T₁, T₂, and ADC) in each cartilage region, which can be indicative of different stages of cartilage degeneration.     

Excellent results with femoral revision surgery using an extensively hydroxyapatite-coated stem: 59 patients followed for 10-16 years

Background The outcome of femoral component revision with either cemented or proximally coated stems has been disappointing, but revision with extensively coated stems has been promising. We report long-term outcome of a grit-blasted titanium stem entirely plasma sprayed with hydroxyapatite (HA), in femoral revision surgery.

Patients and methods During 1988 to 1993, we performed 66 femoral revisions in 65 patients (49 women) aged mean 58 (28-86) years. 3 patients died before the 10-year follow-up and 4 did not come for the follow-up examination because they had no hip problems, as confirmed by telephone and by a written reply. 1 of these, however, was previously controlled at 10 years. Thus, 59 patients (60 hips) were followed by clinical and radiographic analysis for 10-16 years after femoral stem revision.

Results 1 stem was re-revised due to mechanical failure, and none were revised because of infection. We noticed a low degree of proximal bone loss and a low incidence of distal bone hypertrophy. These observations indicate no significant net transfer of stress proximally to distally, and a somewhat physiological weight distribution from the stem to the femoral bone. The bone changes confirmed a well-fixed femoral component in asymptomatic patients.

Interpretation Our findings indicate good long-term results with a fully HA-coated stem in femoral revision surgery. ▪     

Expression of the PTH/PTHrP receptor in chondrogenic cells during the repair of full-thickness defects of articular cartilage

OBJECTIVE: We studied the accumulation of parathyroid hormone (PTH)/PTHrP receptor-positive mesenchymal cells using double immunohistochemistry and examined whether this correlated with the subsequent regeneration of 3-mm-diameter full-thickness defects of articular cartilage. MATERIALS AND METHODS: Cylindrical full-thickness articular cartilage defects (3 mm) were artificially created in the femoral trochlea of male adolescent Japanese white rabbits (n = 210) with a hand-drill. Recombinant human PTH(1-84) was then administered into the defect cavities with an osmotic pump for either 2 or 4 weeks post-injury. Following PTH treatment, the repair processes in the cartilage defects were histologically examined. Double immunostaining analyses for the PTH/PTH-related peptide (PTHrP) receptor and proliferating cell nuclear antigen (PCNA) in the regenerating tissues were then performed. RESULTS: Activation of PTH/PTHrP receptor signaling by hPTH(1-84) results in the inhibition of chondrogenic differentiation in full-thickness articular cartilage defects. At the conclusion of the 2-week PTH treatment, the defect cavities were filled with undifferentiated mesenchymal cells, which were similar to the controls. In addition, almost all of these cells localized at the center of the injuries were both PTH/PTHrP receptor- and PCNA-positive. In contrast, after prolonged PTH treatment for 4 weeks, there was no indication of a cartilaginous repair response and cells that had migrated to the defect cavities were found to have irreversibly lost expression of the PTH/PTHrP receptor. CONCLUSIONS: The chondrogenic capacity of cells that had migrated to the area of these defect cavities is closely associated with their ability to express the PTH/PTHrP receptor. Moreover, these cells maintain their chondrogenic potential within only a limited time-span of 2 weeks.     

Platelet-rich plasma accelerated surgical angio-genesis in vascular-implanted necrotic bone: an experimental study in rabbits

Background Platelets contain many kinds of growth factors with the ability to accelerate angiogenesis. We analyzed whether a single injection of platelet-rich plasma (PRP) would accelerate surgical angiogenesis in necrotic bone implanted with vascular tissue.

Methods We used 24 Japanese White rabbits. PRP was refined from autologous blood by separation twice with centrifugation. A removed iliac bone was frozen in liquid nitrogen to ensure complete cellular necrosis. A narrow hole was made in the bone and the saphenous vascular bundle was passed through the hole. The bone was wrapped after injection of either 1 mL (1) PRP, or (2) saline solution into the hole, and was placed subcu-taneously in the thigh. In both groups, angiogenesis was compared 1 week and 2 weeks after surgery.

Result Angiogenesis was observed along the implanted vascular bundle in both groups. At 1 and 2 weeks after surgery, both the vessel density and the average length of newly formed vessels of the experimental group were significantly greater than in the control group. Both the vessel density and the length were greater after 2 weeks than after 1 week.

Interpretation A single injection of PRP accelerates surgical angiogenesis in vascular-implanted necrotic bone.     

The figure-of-four axis as a reference to determine stem rotation in hip arthroplasty. What does it really measure? A cadaver study

Background and purpose Implantation of the femoral component at 10-15° of anteversion is recommended in THA. Surgical guidelines suggest that the lower leg be positioned horizontally or vertically with the knee flexed to 90° (figure of four). By constructing a perpendicular axis (a “figure-of-four” axis) to the lower leg, anteversion of the stem is approximated. We assessed whether the figure-of-four axis is a reliable intraoperative tool to approximate the retrocondylar line as a reference for stem version.

Methods Cadavers (21 in total) were placed supine on an operating table and the lower legs were aligned to the horizontal plane. Cannulated titanium screws were inserted perpendicular to the lower leg into the medial epicondyle, representing the figure-of-four axis. The femoral neck axes, retrocondylar lines, and the figure-of-four axes were determined using CT images of the specimen.

Results The anteversion of the femoral neck was median 9.8 (4.5-15.1) degrees (interquartile range). The figure-of-four axis deviated by 0.5 (-2.1-2) degrees, whereas the median difference in the axis in relation to the femoral neck axis was 9.5 (-13.6 to -2) degrees.

Interpretation The figure-of-four axis, being nearly parallel to the retrocondylar line, is a valid indirect method for determination of stem version intraoperatively in patients without varus/valgus deviations of the knee.     

Continuous bone loss around a tapered uncemented femoral stem: a long-term evaluation with DEXA

Background Periprosthetic bone loss is a well-docu-mented phenomenon after uncemented total hip arthroplasty (THA); however, little is known about how bone mineral density (BMD) changes after 2 years.

Patients and methods 14 patients with hip arthrosis (group A) were operated with a proximally porous- and hydroxyapatite-coated stem and followed for 10 years with DEXA, radiographs and Harris hip score (HHS). Another group of 14 patients (group B) was evaluated at 6 and 14 years using the same prosthesis and protocol.

Results No stem was revised and all stems were well-Fixed. At final follow-up, HHS was 97 points in group A after 10 years and 94 points in group B after 14 years. Bone mineral changes in group A were greatest in Gruen zones 1 and 7, where the losses were 31% and 26%, respectively, after 2 years on the operated side. The decrease in BMD continued after 2 years and in Gruen zone 7 it was faster than the rate of bone loss on the control side. In group B, the annual change in BMD on the operated side was not significantly different from the bone loss in group A.

Interpretation Up to 14 years after implantation of a tapered uncemented stem, the BMD in the calcar region continues to decrease faster than would be expected from normal ageing.     

Conversion from failed hemiarthroplasty to total hip arthroplasty: a Norwegian Arthroplasty Register analysis of 595 hips with previous femoral neck fractures

Background and purpose Conversion total hip replacement (THR) is a common procedure after failed hemiarthroplasty, but there have been few reports describing the long-term outcome of this procedure.

Patients and methods Between 1987 and 2004, 595 THRs were reported to the Norwegian Arthroplasty Register as conversion THR for failed hemiarthroplasty after a femoral neck fracture in patients aged 60 years and older. 122 operations left the femoral stem intact, whereas 473 were converted with exchange of the femoral stem.

Results We found a lower risk of failure (revision surgery for any reason) for the conversion procedures with stem exchange (RR = 0.4; 95% CI: 0.25-0.81) than for the conversion procedures that retained the femoral stem. For the 473 conversion arthroplasties with exchange of the stem, we found no difference in risk of failure compared to all revision stems in the register, either for the complete prosthesis (RR = 0.8; CI: 0.50- 1.20) or for the stem (RR = 0.9; CI: 0.53-1.59). However, for the 122 conversion procedures in which the femoral stem was retained, we found a significantly increased risk of failure for both the complete prosthesis (RR = 4.6; CI: 2.8-7.6) and for the acetabular cup (RR = 4.8; CI: 2.3-10) compared to primary hip arthroplasties.

Interpretation Our findings indicate that the seemingly easy operation of implanting an acetabular cup to convert a hemiarthroplasty to a total hip arthroplasty is an uncertain procedure and that the threshold for replacing the stem should be low.     

Serum total acid phosphatase for monitoring the clinical course of giant cell tumors of bone--26 patients with 5 local recurrences

Background Giant cell tumor of bone (GCT) is a bone-destroying tumor that sometimes recurs locally after treatment. A recent study showed increased levels of serum total acid phosphatase (TACP).

Methods We assessed TACP in the serum of 26 patients with primary GCT, and in 5 of them who developed a local recurrence.

Results We found a correlation between TACP level in serum and tumor size. TACP levels that were elevated preoperatively in patients with GCT became normalized after surgery, but increased in 3 of the 5 patients with local recurrence.

Interpretation TACP could be used as a tumor marker for monitoring response to treatment of GCT.     

Systemic zoledronate precoating of a bone graft reduces bone resorption during remodeling

Background Cartilage degeneration often occurs after osteosynthesis of a devascularized intermediary fragment in a joint fracture, in mosaicplasty or in whole-joint toe-to-finger transplantation. Hypothetically, the degeneration is secondary to a collapse of the transferred subchondral bone as it remodels during high mechanical load. Bisphosphonates are used to reduce resorption of necrotic bone. We tested a systemic pretreatment before harvesting the graft in order to protect the bone and cartilage against collapse and secondary arthrosis.

Methods Rats were given one zoledronate injection and bone grafts were harvested. The grafts were frozen, thawed and placed into bone chambers, and implanted into another batch of rats. Graft resorption and new bone formation was measured by histomorphometric analysis and compared with untreated grafts.

Results In the remodeled area of the controls, the graft was almost totally resorbed and replaced by bone marrow. In the zoledronate-treated specimens, the graft remained and the graft trabeculas were lined with new bone. By histomorphometry, the total amount of bone (graft plus new bone) within the remodeled area was 16% in the zoledronate-treated grafts and 5% in the controls (p = 0.003).

Interpretation A bone graft can be pretreated with bisphosphonate and remain protected against resorption once implanted again. ▪     

Comparison of analog and digital preoperative planning in total hip and knee arthroplasties. A prospective study of 173 hips and 65 total knees

Introduction Digital correction of the magnification factor is expected to yield more accurate and reliable preoperative plans. We hypothesized that digital templating would be more accurate than manual templating for total hip and knee arthroplasties.

Patients and methods Firstly, we established the interobserver and intraobserver reliability of the templating procedure. The accuracy and reliability of digital and analog plans were measured in a series of 238 interventions, which were all planned using both techniques.

Results Interobserver reliability was good for the planning of knee arthroplasties (κ-values 0.63-0.75), but not more than moderate for the planning of hip arthroplasties (κ-values 0.22-0.54). Analog plans of knee arthroplasties systematically underestimated the component sizes (1.1 size on average), while the digital procedure proved to be accurate (0.1-0.4 size too small on average). The following figures show percentage of cases receiving a correct implant, allowing an error of one size. Digital templating of the hip arthroplasty was less frequently correct (cemented cup and stem: 72% and 79%; uncemented cup and stem: 52% and 66%) than analog planning (cemented cup and stem: 73% and 89%; uncemented cup and stem: 64% and 52%).

Interpretation Planning of component sizes for total knee arthroplasties is an accurate procedure when performed digitally. Our digital preoperative plans which were performed by someone other than the surgeon were less accurate than the analog plans prepared by the surgeon.     

Socket wall addition device in the treatment of recurrent hip prosthesis dislocation: good outcome in 12 patients followed for 4.5 (1-9) years

Background Recurrent dislocation in total hip replacement is difficult to treat and causes severe morbidity.

Patients and methods 12 patients suffering dislocations were reoperated with a socket wall addition device (anti-luxation ring) for the Lubinus SPII prosthesis, and were followed up after a mean of 4.5 (1-9) years with regard to redislocation, function and radiographic loos-ening.

Results 1 of the patients suffered a redislocation after almost 7 years of use. There was no loosening during the follow-up time. A Harris hip score of 87 (60-100), a health-related quality of life (EQ-5D) index of 0.8 (0.6-1.0) and total range of motion of 145° (125-165) indicate that the patients had a level of function comparable to that of age-matched hip surgery patients with no com-plications.

Interpretation The anti-luxation ring shows promising mid-term results and seems to provide an alternative to more extensive revision surgery for selected patients. ▪     

Effect of bone marrow grafting on the titanium porous-coated implant in bilateral total knee arthroplasty

Background and purpose Poor bone ingrowth into the porous coating of tibial components has been reported. We hypothesized that iliac marrow grafting might be useful to enhance bone ingrowth into a porous-coated implant. The first part of this study was to examine the presence of fibroblast colony-forming units (CFUF) containing osteogenic precursor cells in tibial bone marrow and iliac bone marrow. The second aim was to compare the clinical and radiographic results after bilateral total knee arthroplasty (TKA) with and without autologous bone marrow transplantation to the bone-implant interface.

Methods Simultaneous bilateral TKA was performed in 21 patients with osteoarthritis. Aspirated iliac bone marrow was transplanted to the interface of one randomly selected porous-coated tibial component in each patient, and contralateral knees served as controls. All of the 21 patients were followed for 5 years.

Results The average number of CFU-F was significantly lower in tibial marrow than in iliac marrow (p = 0.008). The final fluoroscopically-guided radiographs revealed a decrease in the number of knees with radiolucent lines after marrow grafting compared to those without grafting (p = 0.004).

Interpretation Iliac bone marrow is useful as a bone grafting material to enhance the biological fixation in porous-coated implants.     

Osteoarticular infections in HIV-infected patients: 23 cases among 1,515 HIV-infected patients

Background The reported incidence of osteoarticular infections in HIV-infected patients has varied in the literature.

Patients and methods We determined the incidence and characteristics of osteoarticular infections reported in a database of 1,515 HIV-infected patients between 1983 and 2003.

Results 23 HIV-infected patients were identified with an osteoarticular infection, 11 of whom had a spondylodiscitis. 16 were intravenous drug abusers; this was identified as a risk factor for developing an osteoarticular infection. The most common agent was Staphylococcus aureus. 6 patients required surgical intervention and in a worst-case scenario more than one-fifth had recurrence of their infection.

Conclusion Development of an osteoarticular infection is a rare complication in this group of HIV-infected patients, but a remarkably high number of infections of the spine were seen.     

In vitro comparison of Refobacin-Palacos R with Refobacin Bone Cement and Palacos R + G

Background Refobacin Palacos R (RPR) is no longer produced and Palacos R + G (PRG) and Refobacin Bone Cement R (RBC) have been introduced to supersede it. We performed an in vitro study to ascertain whether the handling and mechanical properties of the more recent cement preparations are different to those of their predecessor.

Methods The 3 cements were tested to ISO 5833 and German DIN 53435 standards. In addition, their gentamicin elution, shrinkage, viscosity, and handling characteristics were studied.

Results All 3 cements had comparable mechanical properties exceeding the ISO 5833 and DIN 53435 standards. They eluted similar amounts of gentamicin and had comparable shrinkage. In the batches tested, RBC showed statistically significantly longer handling curves. Both PRG and RBC had statistically significantly lower viscosities as they cured compared to their predecessor.

Interpretation Surgeons must be aware that both successor cements do not appear to have handling curves and viscoelastic properties identical to those of RPR.     

Inflammatory response in 85 patients with loosened hip prostheses: a prospective study comparing inflammatory markers in patients with aseptic and septic prosthetic loosening

Background The most common complications of prosthetic hip joints are aseptic mechanical failure and infection. Delayed low-grade infections are seen most often, and they are also most difficult to distinguish from aseptic mechanical failures.

Methods We conducted a prospective study to compare inflammatory markers in patients diagnosed with aseptic or septic prosthetic loosening. The diagnostic criteria were based on the decisions of experienced orthopedic surgeons and microbiological analysis of periprosthetic tissue samples taken perioperatively.

Results Coagulase-negative staphylococci were the commonest pathogens in the infected patients. Pre- or perioperative elevation of C-reactive protein and erythrocyte sedimentation rate were significantly greater in the infection group, as were white blood cell count and levels of cytokines in synovial fluid. The patterns of infiltration of inflammatory cells in periprosthetic tissue were also significantly different between the groups.

Interpretation A combination of clinical judgment and multiple tissue samples constitutes a good platform for distinguishing between septic and aseptic loosening of prostheses. Moreover, the combined use of several laboratory and histopathological markers of inflammation, especially infiltration of polymorphonuclear cells, further helps the diagnosis.