A comparative study of bone to bone repair and bone to tendon healing in patella–patellar tendon complex in rabbits

Objectives. To study the healing quality of bone to bone and bone to tendon repair in a patella–patellar tendon complex. Design. In vivo animal experiment in 60 mature 32-week-old female rabbits. Background. Injuries of patella–patellar tendon complex are not uncommon. However, no studies are available to compare the healing quality between bone to bone and bone to tendon surgical reconstructions used for repair of patella–patellar tendon complex. Methods. A standard transverse osteotomy was performed at the distal one-third of patella of one hindlimb. Both patellar fragments were reattached for bone to bone group while the patellar tendon was reattached to the remaining patella after removing the distal one-third of patella for bone to tendon group. Patella–patellar tendon complex was harvested at 8, 12 and 24 weeks postoperatively for biomechanical and histological evaluations, with n=8 and n=2 at each healing time points in both groups. The contralateral knee served as a control. Results. No significant differences in the failure loads were found between two groups. However, greater ultimate stress was found in bone to bone group as compared with bone to tendon group at week 8 and 24 (both P<0.05). On average, the ultimate stress of the bone to tendon and bone to bone group only reached 20.6(4.2)% and 28.6(6.7)% of the control values at week 24, respectively. The discrepancy between findings in failure load and failure stress might be explained by an overall larger cross-sectional area of the healing interface in bone to tendon group as compared with bone to bone group. Histology revealed that the bone to bone healing was via endochondral ossification at the healing interface. In bone to tendon group, extensive scar tissue was formed to overbridge the healing interface and remodeled with healing over time. The structural integration at the tendon and bony healing interface was poor and no typical intermitted fibrocartilage zone as seen in normal bone to tendon junction was formed. Conclusion. Failure load of bone to bone and bone to tendon healing interface did not differ during repair of patella–patellar tendon complex. However, the healing interface of bone to bone repair in terms of material properties as reflected by failure stress was superior to that of the bone to tendon healing.