This simple technique to compensate for bone defects on the medial tibial condyle during primary TKA using the AOBG has proven to be quite effective regarding higher graft healing rates and lower infection rate.
The use of methylmethacrylate cement, independently or with screws, is a good option to fill contained defects ≤5 mm; additionally, bone grafts or metal augments may be used to offer support for tibial components for bone defects ≥5 mm . Contained defects are ideal for impacted morselized bone grafts, which were found to be not recommended for repairing uncontained defects, because the cortical rim is considerable to ensure stability of the tibial component. In uncontained defects involving ≥50% of single tibial condyle, the use of structural allografts is recommended because they offer greater initial stability . However, many shortcomings have been associated with the use of structural allografts, such as risk of disease transmission, nonunion, collapse or resorption of the graft [4, 10]. Another consideration is that they often require a longer period of limited weight bearing to allow for union of the grafts with the host bone. In addition, Whittaker et al.  described how to use metal augments in uncontained defects with moderate and severe bone loss ≥50% and ≥5 mm of the tibial condyle. However, there are some disadvantages, including further resection of bone to create a proper off-the-shelf augment fit and elevated cost. In an attempt to overcome these shortcomings, autogenous bone graft has been used for uncontained defects with marked bone loss of the tibial condyle; it is an advantageous method that improves graft union rates and bone stock preservation [12,13,14].
One study evaluating prerequisites for complete graft incorporation in 24 primary or revision knees reported that pertinent coverage of the graft by the component can prevent resorption of unstressed graft which may contribute to failure by collapse . However, our study included one case of undersized tibial component on the cortical wall of the proximal tibia related to an our unintentional error during the initial learning curve. This suggests that limited coverage of the cortical wall of the proximal tibia may be related to early aseptic loosening especially with the standard tibial component. Nevertheless, we found no evidence of graft resorption or the need for revision surgery due to loosening of the tibial component. One reason for the better outcomes observed in the present study may be the use of autogenous bone obtained from posterior condylar bone or proximal tibial bone to augment bone defects on the medial tibial condyle, in cases where defect sizes are moderate with a depth of 5 to 20 mm in primary TKA, leading to a lower infection rate. However, the free-hand technique described earlier for the preparation of tibial bone defects may be somewhat technically demanding. Another factor that can explain the positive outcomes may be the soft tissue wall around the medial aspect of the proximal tibia, which can prevent the grafted bone from disintegrating after surgery. Furthermore, the AOBG can be harvested with little addition to the surgical time, and can be easily obtained without the additional fixatives, effectively creating the original shape of the medial tibial condyle in all cases by allowing the use of standard components for the primary system without tibial stem extenders. For additional fixatives, graft union rates have shown similar results across studies regardless of the presence of screws. One study classified tibial bone defects by their position and extent in 30 primary TKA cases without screw fixation treated with autogenous bone grafts. Nonunion between the graft and host bone occurred in one slant-peripheral-type case, resulting in 96.6% survivorship of autogenous bone grafts at 6.8 years . In contrast, another study evaluating an autologous bone graft procedure attached the proximal portion of the tibial resection using two cannulated cancellous screws; the authors found that the screws were responsible for rigid initial fixation with a high rate of bony union at 6.6 years, which helped maintain long-term alignment . Thus, we modified the surgical method to use temporary K wires instead of countersunk screws with more compression and less bone cement permeation under the graft. Additional surgical procedures, such as insertion of multiple screws may lead to fragmentation of the grafted bone, resulting in early failure of knee replacement .
We acknowledge the limitations of this article as it has a relatively small number of patients and short term follow-up study. However, it is not easy to find the appropriate indication of AOBG. In case of an uncontained, moderate, single condyle defect involving an area of 50% with a depth > 5 mm, surgeons may prefer use of allogenous bone or metal augments, because it does provide a simple way to reestablish the joint line without resecting the entire bone surface down to the level of the defect and offers the potential for early weight-bearing. Therefore, from a practical standpoint it is difficult to design and conduct randomized controlled trials comparing simple AOBG supplement technique and other techniques for a proximal tibia bone defect at the time of primary TKA.