|Abstract / Summary
Knee axis corrective open-wedge high tibial osteotomy is a well established treatment of unicompartmental knee osteoarthritis in the young and active patients.
The studies in the present thesis focus on the healing of the bone gap that is created with the open-wedge technique.
Currently, limited weight bearing is usually prescribed in the first postoperative weeks (usually six weeks), regardless of implant and bone grafting material. Recently, osteotomy stability has improved with new implant design, and the short term outcome seems to have improved. But it is still unknown if different bone grafting materials provides further benefits regarding osteotomy stability, healing and clinical outcome of the procedure.
The aim of the studies in this PhD thesis therefore was to examine the influence on stability, healing and clinical outcome, of different bone grafting materials as supplement to internal fixation in the open-wedge osteotomy technique.
Specifically we investigated the effect of injectable calcium phosphate cement (ICPC) compared to no graft, in a biomechanical study, since ICPC offers high initial compressive strength and osteoconduction, and in a randomized clinical study we compared ICPC with two types of bone autograft: Local bone autograft and iliac crest bone autograft.
We conducted two studies: a biomechanical study, and a randomized controlled study.
Biomechanical study: The study investigated the, in vitro, primary stability of the open-wedge construct with and without ICPC as supplement to internal fixation. The study showed that ICPC improved the stiffness and stability of the construct, and protected the construct from increasing damage during cyclic loading, and increased the load-to failure significantly. It was also found that the construct even without reinforcement of ICPC seemed strong enough to withstand the approximated loads found during walking.
Randomized controlled study: In the study 45 patients were randomized to the three different bone grafting materials: ICPC, local bone autograft and iliac crest bone autograft. The patients were followed for two years with investigation of stability, measured with roentgenstereometric analysis (RSA), clinical outcome measured with the knee injury and osteoarthritis outcome score (KOOS), and graft healing evaluated after one year by histomorphometric analysis.
RSA showed that only minor migration of the proximal tibia took place after osteotomy in the study period regardless of bone grafting material. All three groups migrated the most during the first three months, after which migration declined.
The ICPC group had less improvement in all clinical subscores (Knee and Osteoarthritis Outcome Score) at almost all time points, though no statistically significant differences were found, apart from the quality of life assessment after two years, where statistically significant differences were found between local graft and ICPC.
Histomorphometric analysis revealed that the two bone autograft groups healed to the same quality based on bone volume fractions and trabecular thickness. On the other hand ICPC remodeled slowly and induced a mixed soft tissue response with both bone and soft tissue ongrowth which might delay the remodelling process.
In conclusion we found that ICPC stabilized the construct in vitro and to some extent in vivo. Clinically ICPC seemed to perform less well than the other groups especially at the end of the follow-up period. A reason for this could be that ICPC only remodels slowly and induces a varying soft tissue response which perhaps also is the reason why the ICPC group doesn’t perform better regarding migration. The findings warn of the use of ICPC as a bone grafting material in open-wedge HTO and verify that local autograft is safe to use in moderate sized osteotomies.