Objective:
The toe vascularized joint transfer (VJT) plays certain role in reconstruction of a damaged proximal interphalangeal joint (PIPJ). The general outcomes of VJT have been improved with a simultaneous extensor reconstruction, but suboptimal outcomes were observed in our series. A diverse preoperative condition might affect the results. In this study, we developed a prognostic prediction model and tested the correlation with inferior outcomes after receiving VJT.

Material and methods:
In this study, 68 vascularized joint transfers of 64 patients with an average follow-up of 30 months were reviewed and tested. In our pilot study, we identified risk factors including replanted fingers, extensor tendon injury, and direct joint surface involvement correlated with the functional range of motion after VJT, with the correlation coefficient in a proportion of 2: 1: -1 respectively. Accordingly, we constructed a prognostic predicting model by assigning 2 points for prior replantation surgery of finger, 1 point for prior extensor tendon injury, and -1 point for prior PIPJ surface injury. Inferior outcome of VJT was defined by a result less than the average percentage of use (POU), which is the final active range of motion (ROM) of the PIPJ comparing to the original passive ROM of the toe. We accessed the association of prognostic score with the presence of inferior outcome. Receiver operating characteristic (ROC) curve were generated to evaluate diagnostic value of the prognostic score for inferior VJT outcome prediction.

Results:
The results from ROC curve showed the area under curve (AUC) of the prognostic score for inferior VJT functional outcome was 0.806. The optimal cutoff value for the prognostic score was 1.5, with a Youden index of 0.483, a sensitivity of 55.2%, and a specificity of 93.1%. Patients with the prognostic score less than 1.5 had greater POU comparing to patients with the score greater than 1.5 (78.9% vs. 46.1%, p < 0.0001).

Conclusions:
Recipient site condition prior to VJT plays important role in determine the functional outcome of PIPJ. We constructed a risk predicting scoring system by accessing the risks which had significant impact on functional outcome. The scoring system might predict functional outcome of the VJT in our series. The major limitation of the prognostic prediction model is the study from a retrospective review. A prospective study will be needed to test the reliability of the model.

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