The stability of fractures is key to successful treatment, enabling patients to perform early functional exercises to obtain better treatment results and reduce the incidence of traumatic arthritis.2 PT cannulated screws are broadly used to fix the ankle according to the size of the fracture block, although complications such as ankle pain secondary to loosened and backed-out screws occur in about 20% of patients, which may be largely related to the excessive lengths of PT cannulated screws. Preoperative CT can help clinicians determine the length and location of PT cannulated screws. As a commonly used clinical examination, CT cannot comprehensively show the density of cancellous bone in the distal end of the tibia. Simplifying the methods of measurement and improving its efficiency are crucial. More importantly, standardized methods of measurements increase the repeatability and reliability of these data, thus making it easy for clinicians to collect and compare parameters. However, to the best of our knowledge, there are still not enough related studies, and no clear quantitative indicators have been reported. Therefore, we analyzed specific levels of the medial malleolus on the coronal plane of CT images, which makes measurement simple, reliable, and repeatable.
Osteoporosis is an important factor affecting the internal fixation of fractures. It is correlated with an increased bone stiffness, deterioration of trabecular architecture, decreased bone mass and strength.20,21 Experts have already been paying attention to this factor. Some studies have demonstrated that information about bone quality can also be evaluated via HU measurements obtained from CT scans,16,22 while HU values of bones are positively correlated to their BMD.18,19 The results of this study indicate that HU values of the medial malleolus are clearly correlated with age. The area of the HU value greater than 130 HU in patients older than 60 years of age is notably lower than that in the other two groups of patients, indicating that the length of valid cancellous bone in the medial malleolus in this group is remarkably shorter. As a result, screws of excessive length would gain poor purchase in the sparse cancellous bone and could not obtain stable internal fixation. Therefore, age is a factor that clinicians should consider when performing internal fixation. When a patient is older than 60 years, a possibly shorter screw is recommended after ensuring that the thread has passed through the fracture line. A 35-mm screw would have stronger holding power and stability. L.parker et al11 in a cadaver study noted that shorter screws are recommended in osteoporotic bone so as to improve the purchase of the screw threads and compression at the fracture site. They also demonstrated that either a 45-mm fully threaded screw or a 30-mm partially threaded screw but not with a 45-mm partially threaded screw was more likely to purchase enough in the physeal scar, which we defined as valid cancellous bone.
Multiple studies have mentioned alternative strategies in fixing the medial malleolar fracture. 23–25 Christy M. King et al 26 and Jason D. Pollard et al 27 believed that fully threaded bicortical screw is an additional and acceptable treatment, especially in higher risk patient populations with poor bone stock and the 3.5 mm bicortical screws has greater pullout strength when compared with 4.0 mm partially threaded cancellous screws. Medial malleolar sled construct is also a good choice in fixation of horizontal medial malleolar fractures.10 However, partially threaded cancellous screws still provide many advantages such as lower expenses, easier and quicker placement. According to the AO/ASIF technique, partially threaded cancellous screws is recommended for fixation of medial malleolar fracture. Henrik C. Bäcker et al’s retrospective study indicated that unicortical screws fixation of the medial malleolar can achieve favorable clinical outcome with a low complication rate.28
The results of our study show that the length and ratio of valid cancellous bone in the posterior third of the medial malleolus is slightly larger than that in the anterior third and half of the medial malleolus. However, Femino et al.29 argued that the posterior colliculus is not a safe zone to implant lag screws because they may raise the possibility of irritating the tibialis posterior tendon. The anterior colliculus is the safe zone to place lag screws.
This study has the following drawbacks including the inherent nature of a retrospective review. Second, the number of cases for clinical follow-up was small in our study. A large-scale cohort study can better reveal the effectiveness and complications of this fixation method. Additionally, there was no comparison group. Third, although some studies have shown that HU values of bones are positively correlated to their BMD,18,19 most of them involved evaluations of HU values of the cervical spine and femur. No studies have analyzed the relationship between the HU value of the distal tibia and BMD. This may be a focus in future studies.