The Relationships between the Rotational Axes of the Distal Femur in the Arthritic Caucasian Knee: A Magnetic Resonance Imaging Analysis.

Four distal femoral axes have been described to aid in the accuracy of transverse plane component alignment in total knee arthroplasty (TKA). These include the surgical epicondylar axis (SEA), the posterior condylar axis (PCA), and the anteroposterior (AP) axis. Therefore, the primary purpose of this study is to identify the axial femoral relationship with the least variation in a Caucasian population awaiting TKA for osteoarthritis. Secondarily, we further plan to determine if these femoral axis relationships differ with respect to sex or preoperative coronal alignment. These anatomic relationships were measured using preoperative magnetic resonance imaging, which was performed within 2 months of the planned operation date for patient specific instrumentation templating. In terms of our primary outcome, the mean SEA/AP angle was 92.8 degrees (standard deviation [SD]: 2.5 degrees), the mean PCA/AP angle was 95.7 degrees (SD: 2.8 degrees), and the mean PCA/SEA angle was 3.4 degrees (SD: 1.8 degrees). Overall, the PCA/SEA relationship had the smallest variance, while the PCA/AP had the most variance for all comparisons. In terms of our secondary outcome, there was no statistical difference between femoral axis relationships based on preoperative coronal plane alignment. In terms of sex differences, the PCA/SEA was significantly higher in female knees compared with males. Females had a PCA/SEA relationship of 4.7 degrees (SD: 1.3 degrees) compared with 2.6 degrees (SD: 1.2 degrees) for males (p < 0.05). By using the PCA/AP axes, the AP axis was externally rotated by 96.7 degrees (SD: 2.3 degrees) in females, compared with 93.2 degrees (SD: 2.1 degrees) in males, from the PCA. In conclusion, our results demonstrate that the PCA/SEA relationship should be used to determine axial rotation in TKA as it shows the least variation. When using the PCA, approximately 5 degrees of external rotation for Caucasian women and 3 degrees of external rotation for the Caucasian men should be dialed into the femoral cutting block to restore anatomic axial rotation. Further evaluation is needed to determine to role of preoperative coronal alignment on distal femoral axial alignment.

Pre-operative analysis of lower limb coronal alignment - a comparison of supine MRI versus standing full-length alignment radiographs.

BACKGROUND: In this study we compare the results of pre-operative standing full-length alignment (SFLA) radiographs with supine MRI assessment of the lower limb alignment prior to MRI based patient specific total knee arthroplasty (TKA). METHODS: Imaging was performed in 45 knees (45 patients). Assessment of SFLA radiographs was performed by three independent assessors. Inter-observer correlation was high and so the mean values were calculated. This data was then compared to MRI alignment data used to create the patient specific cutting jigs. RESULTS: The range of alignment on SFLA radiographs ranged from +25° to -13° versus +20° to -11° with MRI. The mean difference between techniques was 2° (range 0-8°, SD ± 3°). Supine MRI under-estimated the degree of deformity in 31/45 (69%) cases. In 25/45 (56%) cases the supine MRI result was within ±2° of the value on SFLA radiographs, 31/45 (69%) were within ±3° and 38/45 (84%) within ±5°. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between imaging modalities (Spearman's r(2)=0.02, p=0.41). CONCLUSIONS: The findings from this study would indicate that supine MRI underestimates the degree of deformity at the knee joint, a conclusion which may be important for pre-operative planning or follow-up of corrective osteotomy or TKA.

Osteoinductive ability of human allograft formulations.

BACKGROUND: Bone graft materials are needed in periodontics that are osteoinductive, have good handling characteristics, and have physical properties that provide appropriate stiffness for the treatment site. Demineralized freeze-dried bone allograft (DFDBA), also called demineralized bone matrix (DBM), is osteoinductive but requires a carrier to meet the other clinical objectives, thereby decreasing the DBM content per volume of the bone graft material. The present study determined whether the DBM content of a carrier formulation is an important variable with respect to its effectiveness as an osteoinductive material. METHODS: The immunocompromised Nu/Nu mouse-muscle implantation assay of osteoinductivity was used to test human DBM formulated with hyaluronic acid (HY) and cancellous and cortical bone granules from the same donor: DBM alone (11 mg); DBM (11 mg):HY, 55:45, weight/weight (wt/wt); DBM (6.4 mg):HY, 32:68, wt/wt; DBM mixed with cortical and cancellous bone chips 1:4 (DBMC) (11 mg total, of which 2.2 mg was DBM); DBMC (11 mg):HY, 55:45, wt/wt; heat-treated DBM (11 mg); HY alone; and positive-control DBM (11 mg). Osteoinduction was scored using a qualitative scale and by histomorphometry. RESULTS: Results showed that all DBM was osteoinductive and the addition of HY did not change this as long as the amount of DBM used was held constant. The reduction in the absolute amount of DBM resulted in a reduced osteoinduction score, reduced ossicle area, and reduced new bone formation. The addition of HY also caused a decrease in the amount of residual non-vital bone particles, particularly when DBMC was implanted. Results were donor dependent. CONCLUSION: This study showed the importance of DBM content and donor variability in osteoinductivity of DBM formulations with improved handling and stiffness characteristics.

Platelet-derived growth factor inhibits demineralized bone matrix-induced intramuscular cartilage and bone formation. A study of immunocompromised mice.

BACKGROUND: Platelet-derived growth factor (PDGF) has been proposed as a therapeutic agent to promote bone-healing. The purpose of this study was to examine the effect of PDGF on the ability of human demineralized bone matrix to induce bone formation in a nude-mouse muscle-implantation model. We also examined whether platelet-rich plasma, which contains PDGF, also modulates osteoinduction in this model. METHODS: Human demineralized bone matrix, previously shown to be osteoinductive in the calf muscles of nude mice, was mixed with PDGF-BB (0, 0.1, 1, and 10 microg/10 mg of demineralized bone matrix) and was implanted bilaterally in the calf muscles of immunocompromised (nu/nu) mice (six mice in each group). Heat-inactivated demineralized bone matrix was used as a control. Tissue was harvested at fourteen, twenty-eight, and fifty-six days after implantation. Platelet-rich plasma was prepared from the blood of a healthy donor with use of the Harvest PRP preparation device, activated with thrombin, and mixed with active and inactive demineralized bone matrix. Fifty-six days post-implantation, tissues were harvested. Osteoinduction was assessed with use of a qualitative scoring system and with quantitative histomorphometry. RESULTS: Cartilage was present at fourteen days in all tissues that had received an implant, but the amount decreased as the PDGF concentration increased. PDGF reduced bone formation at twenty-eight days in a dose-dependent manner. This inhibitory effect was resolved by fifty-six days, except in tissues in which demineralized bone matrix and 10 microg of PDGF had been implanted. In sites treated with 10 microg of PDGF, the area of new bone was decreased and the area of bone marrow was reduced at twenty-eight and fifty-six days. PDGF also appeared to retard resorption of demineralized bone matrix in a dose-dependent manner. Platelet-rich plasma reduced osteoinduction by human demineralized bone matrix that had high osteoinductive activity and had no effect on osteoinduction by demineralized bone matrix with low activity. CONCLUSIONS: PDGF inhibits, in a dose-dependent manner, intramuscular osteoinduction and chondrogenesis by demineralized bone matrix in immunocompromised mice. Platelet-rich plasma also reduces the osteoinductivity of active demineralized bone matrix.