Non-operative treatment of posterior cruciate ligament (PCL) tears result in a reported 36-88% increase in knee arthrosis over time, and 80% of patients report persistent pain. Operative treatment of PCL tears, however, has had mixed results.

In Dr. Wang's study, eight humans knees were tested using a robotic system under intact, PCL-resected, and PCL-reconstructed conditions. Anterior-posterior tibial translation and internal-external tibial rotation were measured at 0, 30, 60, 90, and 120 of knee flexion with posterior drawer and simulated muscle loading. PCL reconstruction reduced posterior tibial translation and external rotation compared to PCL resected knees at high flexion angles, but this was not statistically significant. PCL reconstruction also did not consistently reduce posterior tibial translation and external rotation under simulated muscle loading. Peak patellofemoral pressures increased at high flexion angles and were not restored with PCL reconstruction. Dr. Wang concluded that the posterior drawer test may not be an adequate indicator of complex knee kinematics.

Dr. Boland commended Dr. Wang on a well-designed study and raised interesting areas for future study. In particular, he encouraged the authors to study the effects of PCL reconstruction on tibial contact pressures and the effect of medial/lateral placement of the tibial tunnel on anterior-posterior laxity.
 

Dr. Joshi discussed the effectiveness of two different calcium phosphate bone cement preparations used with electrical stimulation and bone graft substitutes in the rabbit spinal fusion model. Five groups of 12 rabbits underwent L5-L6 posterolateral fusion using autograft or one of four calcium phosphate bone cement preparations. Animals were sacrificed at eight weeks, and the specimens were assessed for fusion by manual palpation, radiographs, and histological analysis. Dr. Joshi's study revealed that fusion rates using calcium phosphate granules, bone marrow aspirate, and electrical stimulation were similar to that of autograft.

Dr. White commended Dr. Joshi for a study that may ultimately lead to a substitute for iliac crest bone graft, given the morbidity associated with autologous bone graft harvest. Dr. White suggested that further studies examine the rate of fusion for calcium phosphate granules, bone marrow aspirate and electrical stimulation compared to autograft and ways to enhance fusion rates.
 

Dr. Lewandrowski investigated the spatial distribution of fiber-forming collagens in the annulus fibrosis in longitudinal and horizontal sections of human lumbar intervertebral discs. A comparative analysis of immunohistochemistry and histology of adjacent discs was performed. Dr. Lewandrowski discovered that Type I collagen was predominantly seen in the outer lamellae of the inner zone of the annulus fibrosis. Longitudinal sections revealed Type I collagen was distributed in a wedge shaped pattern. Horizontal sections revealed Type I collagen in ring shape, wider anteriorly than posteriorly. Type II collagen was seen in the inner zone, but not in the outer zone. Type III collagen was found in a similar distribution to Type II collagen, especially in pericellular areas of spondylosis.

Dr. Glazer commended Dr. Lewandroski on elucidating the spatial distribution of collagen in vertebral discs. Given the small number of specimens and elderly age of the specimens, Dr. Glazer noted that age-related or degenerative changes may have affected the results of this analysis. Further study of collagen distribution in specimens from younger donors was suggested.