Bioabsorbable vs. titanium screws for first tarsometatarsal joint arthrodesis: An in-vitro study.

BACKGROUND

The TMT-1 joint arthrodesis is a common repair for severe hallux valgus. Two crossing interfragmental screws, usually titanium or steel, and a locking plate or a plate with a compression screw are the most common fixation methods for first TMT joint arthrodesis. The qualities of an ideal fixation material include adequate strength and rigidity, biocompatibility, lack of interference with bone healing, lack of visibility and palpability, and a low risk of surgical removal. We sought to determine whether bioabsorbable cannulated screws would perform as well as titanium screws in anatomical models.

METHODS

Identical anatomical TMT-1 arthrodesis was created with a saw by making a straight cut in 30 anatomical models (Sawbone®). The bioabsorbable and titanium screws were placed one at a time in exactly the same location in each model according to careful measurements. All 30 models were analyzed with a material testing machine (MTS Insight 30, Eden Prairie, USA). Each model was oriented 15° to the platform to simulate its position to the ground during mid-stance.

RESULTS

In the single-cycle load-to-failure test, the mean yield load was 61.4 N ± 5.7 N (range, 50.1 N-70.3 N) in the bioabsorbable screw group and 81.2 N ± 12 N (range, 61.7 N-113.4 N) in the titanium screw group (P < .001). The respective values for the stiffness of the fixation were 8.1 N/mm ± 0.8 N/mm (range, 6.7 N/mm to 9.1 N/mm) and 9.7 N/mm ± 1.8 N/mm (range, 6.9 N/mm to 12.6 N/mm) for the bioabsorbable and titanium groups (P = .004). The mean maximum failure loads in the bioabsorbable group were 85.1 N ± 8.5 N (range, 67.1 N-97.2 N) and in the titanium group 120.6 N ± 13.2 N (range, 96.7 N-136.7 N), respectively (P < .001). Analysis of the failure models shows bioabsorbable fixation failures caused by bending occur more often than in the titanium group.

CONCLUSION

In biomechanical testing, titanium screws were stronger than bioabsorbable screws in the TMT-1 arthrodesis model tested, although bioabsorbable cannulated screws may be an alternative to titanium screws in the fixation Lapidus procedure.