Available online 9 April 2024, 111532

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The sustentaculum is essential for the stability of the subtalar joint.

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Orthopedic surgeons who fix the sustentaculum debate the superiority of two methods: (1) lateral plate (2) medial approach with a single screw.

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This study employed three different models to assess the ability of each method to resist the application of forces: formalin fixed cadaveric ankles, fresh-frozen cadavers with soft tissue, and synthetic ankles.

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Across all the models, there was no significant difference between the lateral plate and the medial approach with a single screw.

ABSTRACTBackground

Fixation of sustentaculum tali fractures is important to maintain the biomechanical function of the subtalar joint. A common method of fixation is securing the sustentacular fragment by way of a laterally based locking plate (LP). An alternative medial approach with a single screw (MS) has been proposed as an alternative method of fixation.

Methods

Five pairs of formalin-preserved cadaveric ankles with the subtalar joint and interosseous ligaments intact (“osseous cadavers”) and four pairs of fresh-frozen cadaveric ankles with soft-tissue preserved dissected from mid-tibia down (“soft tissue cadavers”) were used in the study. The left ankle was randomly assigned to one of the two fixation methods (LP or MS), while the right ankle was the opposite. These same steps for fixation were repeated for six synthetic ankle models. All models were loaded with an average body mass of 80 kg. Statistical differences between LP and MS stiffness were determined using a paired t-test in cadavers and un-paired t-tests in synthetic ankles.

Results

For osseous cadaveric ankles, LP demonstrated a mean stiffness of 232.95(SD: 59.96) N/mm, while MS was 239.72(SD:131.09) N/mm (p=0.9293). For soft tissue cadaveric ankles, LP mean stiffness was 133.58(SD:37.84) N/mm, while MS was 134.88(SD:20.75) N/mm (p=0.9578). For synthetic ankles, LP mean stiffness was 220.40(SD:81.93) N/mm, while MS was 261.50(SD:100.21) N/mm (p=0.6116).

Conclusions

Across all three models, there was no significant difference between LP and MS methods. Retrospective observational studies are recommended to assess patient outcomes from each of the methods.

Section snippetsINTRODUCTION

Calcaneal fractures are the most common tarsal fracture.[1] Of these fractures, the majority are high energy and approximately 75% are estimated to involve the articular surface.[1] The mechanism of injury for calcaneal fractures often involves an axial load.[2] The sustentaculum tali is a horizontal process located on the medial aspect of the distal calcaneus, supporting the medial talus during stance.[3] The sustentaculum tali has strong ligamentous attachments to the talus via the

Selection of Samples

Due to lack of previous literature on biomechanical testing of the LP and MS fixation methods, sample size was determined based on previous literature of biomechanical testing of cadaveric feet/ankles[9], [10], [11], [12] and synthetic feet/ankles[13], [14], [15]. What we term “osseous” cadaveric samples of the talus and calcaneus were harvested from formalin-preserved full body cadavers, with subtalar joint and interosseous ligaments. What we term “soft tissue” cadaveric samples were

RESULTS

Stiffness in axial loading based on the linear region in the force/ displacement graphs (Fig. 4) towards the end of the cycle were taken and recorded to calculate stiffness for each sample, for both types of cadaveric ankles and synthetic ankles (Table 2). For the osseous cadaveric ankle samples, the LP method demonstrated a mean stiffness of 232.95 N/mm with a standard deviation of 59.96 N/mm. The mean stiffness for osseous cadaveric ankles fixated using the MS method was 239.72 N/mm with a

DISCUSSION

Construct stiffness of the two methods of sustentacular fracture fixation, LP and MS, were found not to be significantly different in any of the cadaveric and synthetic ankle models. Cadaveric and synthetic ankle models had similar amounts of variability, regardless of construct type. This indicates that the typical variability of cadavers and synthetic ankles did not exercise an outsized influence.

For the osseous cadaveric and synthetic ankle models, the standard deviation of MS was larger

CONCLUSION

There is no significant difference between construct stiffness of the two primary methods of sustentaculum fracture fixation: medial to lateral screw fixation and lateral to medial plate fixation. Future retrospective observational studies are recommended to determine the clinical effectiveness of both methods of fixation.

Authors’ contributions

Writing of the manuscript – GRR, MMD

Performing osteotomies and fixation of implants – MS, SER, MMD

Surgical planning – BJY, DHW, MS, SER

Study Design – GRR, BJY, MS, DHW, SMT

Loading of Samples – SMT, GRR

Statistical Analysis – GRR

All authors have read and approved the final submitted manuscript.

CRediT authorship contribution statement

Gregory R. Roytman: . Motasem Salameh: Conceptualization, Investigation, Methodology, Writing – review & editing. Sarah E. Rizzo: . Meera M. Dhodapkar: . Steven M. Tommasini: . Daniel H. Wiznia: . Brad J. Yoo: .

Declaration of competing interest

None.

Source(s) of funding

Brad J. Yoo is supported by an AO Foundation Grant to provide research opportunities for Orthopedic trainees. Meera M. Dhodapkar is supported by the Richard K. Gershon, M.D. Fund at Yale University School of Medicine.

Meera M. Dhodapkar (Richard K. Gershon, M.D. Fund at Yale University School of Medicine)

Acknowledgements

We have no acknowledgements.

Reference (23)A. Beumer et al.A biomechanical evaluation of the tibiofibular and tibiotalar ligaments of the ankle

Foot Ankle Int

(2003)

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