This report details a study on the biomechanical effects of using allograft wedges in medial opening wedge high tibial osteotomy (MOWHTO), particularly for large corrections. The findings indicate that incorporating allograft wedges significantly enhances the structural stability of the osteotomy, which is a crucial factor in achieving successful outcomes and preventing complications.
The Biomechanical Challenge of Large Corrections
High tibial osteotomy (HTO) is a well-established surgical procedure for correcting knee deformities and unloading the damaged compartment of the knee joint. While effective, large corrections, typically greater than 10 millimetres, create a substantial gap in the bone that can compromise stability. This can lead to complications such as hinge fractures, delayed union, or a loss of the intended correction. The decision of whether to fill this osteotomy gap with a graft has been a subject of debate within the orthopaedic community.
This study sought to provide a clear, evidence-based answer to this question by investigating the biomechanical effects of using allograft wedges in large-correction MOWHTO procedures. Allografts, which are bone grafts from a donor, are often used as an alternative to autografts (the patient’s own bone) to avoid the additional pain and morbidity associated with harvesting bone from another site.
Study Design and Key Findings
The research involved a series of controlled mechanical tests on synthetic tibia models. These models were subjected to MOWHTO with a significant correction angle to simulate a large-gap osteotomy. The models were divided into two groups: one where an allograft wedge was inserted into the osteotomy gap and a control group where the gap was left unfilled. All specimens were then fixed with a standard locking plate.
The constructs were put through both static compression and cyclical fatigue testing until failure. The results were compelling:
- Increased Stability: Under static compression, the models with allograft wedges withstood significantly higher peak forces before failing compared to the control group.
- Reduced Malrotation: The allograft group also showed less valgus malrotation (an excessive outward angulation of the knee) of the tibial head, indicating greater stability in the construct.
- Enhanced Consistency: During fatigue testing, the allograft group’s performance was more consistent, suggesting that the use of a graft leads to more predictable biomechanical results.
These findings highlight that allograft wedges provide crucial structural support to the osteotomy site, acting as a buttress that shares the load with the fixation plate. This added stability is particularly important in large corrections, where the forces on the healing bone are greatest.
Clinical Implications
The study’s conclusions have significant clinical relevance for orthopaedic surgeons. The use of an allograft wedge in a large-correction MOWHTO procedure can:
- Reduce the risk of failure: By providing mechanical support, the graft can help prevent complications such as lateral hinge fractures and loss of correction.
- Promote bone healing: The allograft acts as a scaffold for new bone to grow into, potentially accelerating the union of the osteotomy site.
- Provide predictable outcomes: The consistent biomechanical performance observed in the study suggests that allograft use can lead to more reliable surgical results.
This research reinforces the value of using bone graft augmentation, particularly in cases of larger corrections, as a critical step in optimising the healing environment and improving long-term outcomes for patients.
Professor Wilson’s Comments
“This is a lovely paper looking at the biomechanical effects of a bone wedge inserted into an osteotomy, part of the research carried out by James Belsey as part of his PhD. His work explored the biomechanics of osteotomy, particularly the role of bone wedges, as well as return to activity following osteotomy. He wrote several excellent papers, and this is one of them.
There are three main advantages to using a bone wedge during osteotomy:
1. Reduction in postoperative swelling:
The bone wedge acts like a cork in a bottle, preventing blood from leaking from the central canal of the bone. This has a remarkable effect in minimising postoperative swelling, which we observed dramatically in our early cases. The original idea actually came from Paul Gibb in Tunbridge Wells, who, to my knowledge, was the first to start using this approach. One of the theatre representatives mentioned it to me, and I quickly adopted the technique, making it standard practice for my patients in Basingstoke. It has since become a standard of care worldwide.
2. Immediate structural support and reduced pain:
The bone wedge provides immediate mechanical stability, which helps reduce micromotion at the osteotomy site. This stability, combined with reduced swelling, results in significantly less pain for patients following surgery.
3. Faster bone healing:
In approximately 50% of patients, these bone wedges incorporate early, leading to osteotomy union in less than six months. In comparison, standard osteotomy procedures performed without a bone wedge often required 12 to 18 months to achieve full union, as they relied on natural bone filling: a process that can take a very long time.
For these three reasons, I introduced this concept globally as standard care for HTO surgery, and it has now become accepted worldwide practice.”
For an in-depth look at the complete findings and methodology, the full research paper is available for your perusal.
Sources used in report overview:
- https://pubmed.ncbi.nlm.nih.gov/31075145/
- https://www.researchgate.net/publication/327098469_The_biomechanical_effects_of_allograft_wedges_used_for_large_corrections_during_high_tibial_osteotomy
- https://www.researchgate.net/publication/286488537_Is_Bone_Grafting_Necessary_in_Opening_Wedge_High_Tibial_Osteotomy_A_Meta-Analysis_of_Radiological_Outcomes
