The purpose of this study was to clarify the effect of delay of the reattachment of the supraspinatus tendon into a bony trough to the strength of the repaired tendon-bone complex. The supraspinatus tendon of rabbits were transected and reattached into bony troughs at the greater tuberosity immediately and six weeks after transection. The tensile strength of the tendon-bone complex, harvested twelve weeks after reattachment, were measured.

The tensile strength showed no difference between immediate and delayed reattached shoulders. Six weeks delay of supraspinatus tendon repair seems not to weaken the tensile strength of repaired tendon-bone complex.

The purpose of this study was to clarify the effect of timing of surgery on the strength of the supraspinatus tendon-bone complex after the reimplantation of the tendon into a bony trough.

In eight rabbits, the supraspinatus tendon was transected and reinserted into a bony trough at the greater tuberosity (early reattachment group). In seven rabbits, the supraspinatus tendon was reinserted six weeks after transection (delayed reattachment group). In both groups, the rabbits were sacrificed twelve weeks after reattachment, and the tensile strength of the tendon-bone complex was measured. The contralateral shoulders served as controls.

None of the operated tendons failed at the site of reimplantation. The ratio of tensile strength of the operated tendon-bone complex to the controls showed no difference between two groups (Immediate reattachment group: 79.9± 1 S.E. 16.5%, delayed reattachment group: 80.4± 12.6%, P> 0.05).

This is the first experimental study to compare the tensile strength of supraspinatus tendon-bone complex repaired after different time intervals.

Stress-shielded tendon & bone tend to decrease their tensile strength. Given the six weeks duration of detachment, a weaker tensile strength of delayed reattachment group was expected than of the early reattachment group. The fact that both groups did not show a difference might be due to the recovery of tensile strength of tendon & bone in twelve weeks after reattachment.

Six weeks delay of repair of supraspinatus tendon does not weaken the tensile strength of repaired tendon-bone complex.

Fundings This study has been supported in part by a grant from the American Shoulder and Elbow Surgeons.

Aims: The purpose of this in-vitro study is to understand the mechanical behaviour of a fracture plate incorporating biodegradable inserts. Methods: A new, innovative fracture plate design incorporating biodegradable inserts was tested. These plates allow for micromotion during the union phase, which allows for increased healing. Resorption of the inserts over time works to decrease stress shielding during the remodelling phase. Two separate bone models were used to simulate a fracture during both the union phase of healing and the remodelling phase. This plate, termed an axially compressible plate (ACP) was mounted to the bone models in four different conþgurations. On the model simulating the union phase, stiffness and micromotion were measured using an LVDT for bending and an extensometer for compression. With the model simulating the remodelling phase, strain was measured on the bone model using a strain gage mounted directly below the plate midpoint.

Conclusions: The results show that during the union phase, the ACP should allow for micromotion, which increases with successive loss of inserts. Results also show that during the remodelling phase, the loss of inserts increases the amount of strain in bone and thus decreases stress shielding.