Physiologic load-bearing characteristics of autografts, allografts, and polymer-based scaffolds in a critical sized segmental defect of long bone: an experimental study

Background

To address the challenge of treating critical sized intercalary defects, we hypothesized that under physiologic cyclic loading, autografts, allografts, and scaffolds loaded with and without human mesenchymal stem cells (hMSCs) would have different biomechanical characteristics.

Methods

Using a rat femoral defect model, 46 rats were assigned to four groups, ie, autograft (n = 12), allograft (n = 10), scaffold (n = 13), and scaffold with hMSCs (n = 11). The scaffold groups used a 5 mm segment of scaffold composed of 80% poly-ε-caprolactone and 20% hydroxyapatite. Rats were sacrificed 4 months postoperatively, and the repairs were assessed radiographically and biomechanically.

Results

Autograft and allograft groups exhibited the most bridging callus, while the scaffold/hMSCs group had more callus than the scaffold repairs. Although signs of radiographic healing did not accurately reflect restoration of mechanical properties, addition of hMSCs on the scaffold enhanced bone formation. The scaffold alone group had significantly lower elastic and viscous stiffness and higher phase angles than other repairs and the contralateral controls. Addition of hMSCs increased the elastic and viscous stiffness of the repair, while decreasing the phase angle.

Conclusion

Further comparative analysis is needed to optimize clinical use of scaffolds and hMSCs for critical sized defect repairs. However, our results suggest that addition of hMSCs to scaffolds enhances mechanical simulation of native host bone.

Hamstrings and iliotibial band forces affect knee kinematics and contact pattern

Many clinical studies have emphasized the role of the hamstrings and the iliotibial band on knee mechanics, although few biomechanical studies have investigated it. This study therefore examined two hypotheses: (a) with loading of the hamstrings, the tibia translates posteriorly and rotates externally and the tibial contact pattern shifts anteriorly; furthermore, the changes in tibial kinematics alter patellar kinematics and contact; and (b) loading the iliotibial band alters the kinematics and contact pattern of the tibiofemoral joint similarly to loading the hamstrings, and loading the iliotibial band laterally translates the patella and its contact location. Five cadaveric knee specimens were tested with a specially designed knee-joint testing machine in an open-chain configuration. At various flexion angles, the knees were tested always with a quadriceps force but with and without a hamstrings force and with and without an iliotibial band force. The results support the first hypothesis. Hence, the hamstrings may be important anterior and rotational stabilizers of the tibia, a role similar to that of the anterior cruciate ligament. The results also support the second hypothesis, although the iliotibial band force had a smaller effect on the tibia than did the hamstrings force. Both forces also changed patellar kinematics and contact, demonstrating that these structures should also be considered during the clinical management of patellar disorders.

Differences in patellofemoral joint cartilage material properties and their significance to the etiology of cartilage surface fibrillation

OBJECTIVE

To determine if differences in biomechanical properties and biochemical composition exist between human patellar articular cartilage and the opposing femoral articular cartilage.

DESIGN

The biomechanical properties and biochemical composition of the articular cartilage of 17 knees from 13 donors were determined for four sites on the patella and three sites on the femur representing regions of contact at 30 degrees and 90 degrees of flexion. The material properties were determined by biphasic indentation testing, yielding the compressive aggregate modulus, HA, permeability, k, and Poisson's ratio, vs. The thickness of the cartilage at the indentation site, h, was also measured using a needle probe. Full-thickness samples of cartilage adjacent to each indentation site were used for wet weight, sulfated glycosaminoglycan content and hydroxyproline content determinations.

RESULTS

The patellar cartilage was found to have a lower compressive aggregate modulus by 30% (P < 0.001), higher permeability to fluid flow by 66% (P < 0.001) and greater thickness by 23% (P = 0.017) than that of the opposing femoral cartilage. The Poisson's ratios for both surfaces were found to be nearly zero. The water content of the patella was higher by 5% (P = 0.031) and the proteoglycan content lower by 19% (P = 0.030) than that of the femur. However, no differences were found between the collagen contents of the cartilages.

CONCLUSIONS

Significant differences were found between the intrinsic material properties of the patellar cartilage and those of the femoral-trochlear cartilage. This variability of cartilage material properties with the patellofemoral joint may help explain why patellar cartilage has been frequently observed clinically to exhibit earlier and more severe fibrillation changes than the opposing femoral cartilage.

Winner of the 1996 Cabaud Award. The effect of lifelong exercise on canine articular cartilage

The effect of long-term exercise on canine knees was studied to determine whether an increased level of lifelong weightbearing exercise causes degeneration, or changes that may lead to degeneration, of articular cartilage. Eleven dogs were exercised on a treadmill at 3 km/hr for 75 minutes 5 days a week for 527 weeks while carrying jackets weighing 130% of their body weight. Ten control dogs were allowed unrestricted activity in cages for the 550 weeks. At the completion of the study all knee joints were inspected for evidence of joint injury and degeneration. Articular cartilage surfaces from the medial tibial plateau were examined by light microscopy, the cartilage thickness was measured, and the intrinsic material properties were determined by mechanical testing. No joints had ligament or meniscal injuries, cartilage erosions, or osteophytes. Light microscopy did not demonstrate cartilage fibrillation or differences in safranin O staining of the tibial articular cartilages between the two groups. Furthermore, the tibial articular cartilage thickness and mechanical properties did not differ between the two groups. These results show that a lifetime of regular weightbearing exercise in dogs with normal joints did not cause alterations in the structure and mechanical properties of articular cartilage that might lead to joint degeneration.