Aims

A fracture of the medial tibial plateau is a serious complication of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). The risk of these fractures is reportedly lower when using components with a longer keel-cortex distance (KCDs). The aim of this study was to examine how slight varus placement of the tibial component might affect the KCDs, and the rate of tibial plateau fracture, in a clinical setting.

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal.

Introduction: Monobutyrin (MB) has been shown to be a potent angiogenic factor for adipose tissue. It is one of the many compounds secreted from adipocytes adding to the knowledge that adipose tissue is not merely a storage unit but has an endocrine function. Adipocytes and osteoblasts share a common precursor. In osteoporosis the proportion of fat in bone increases. As both are present at a fracture site the addition of MB may enhance fracture healing by stimulating angiogenesis.

Method: 138 Sprague Dawley rodents were ovarect-omised at 12 weeks of age. After a further 24 weeks each animal underwent a right closed femoral fracture stabilized with a retrograde k-wire using a standard model (Walsh et al. 1997). Animals were randomised into control (empty or substrate only) or MB of varying concentrations (2.5μg, 7.5μg, 25μg, 75μg). A percutaneous injection of 0.2mls of each of the above was then injected into the fracture site. Animals were culled at 1, 3 and 6 week time points post surgery. The right and left femurs were dissected out and analyzed using radiographic, mechanical testing, micro computed tomography and histology endpoints. Statistical analysis was perfomed with SPSS for windows.

Results: All animals recovered well from the procedure and no adverse reactions were noted following the addition of MB. A progression to union was seen with time in all groups. Mechanical testing did not result in a statistical difference between groups, however the trend showed improved healing in the 7.5μg Monobutyrin group. Radiographic grading again showed no statistical difference however, interestingly micro CT data showed an increasing trend in both trabecular number and bone surface area to volume with increasing concentrations of MB.

The histology results implied a potential acceleration in the early stage of fracture healing in the high dose (75 μg) MB group. However progression to union following this initial early phase acceleration was delayed as callus volume increased rather than union according to micro CT and histological data.

Discussion: The ability to augment fracture healing has significant clinical implications considering the “greying of society”. This study investigated the possibility of improving fracture healing by incorporating the angiogenic factor, Monobutyrin in an estrogen deficient animal model. Although the results do not conclusively demonstrate an improvement in fracture healing, they do imply that MB does affect the early phase of fracture healing in the estrogen deficient model. This study is limited in that the effects of MB on fracture healing in a non-estrogen deficient model was not considered. The ideal release kinetics for Monobutyrin as well as other factors remains unknown.