## 4 Discussion
As stated by [PERSON] et al., a shortening of greater than 6 mm is outside the safe zone. Within this review, all studies reported a mean shortening of greater than 6 mm pre-operation, further demonstrating the importance of length restoration within salvage MTP arthrodeis [13]. When comparing the success of graft groups that reported kinematic results, the foot and ankle autograft group had the larger improvement in HV angle (\(-5.4^{\circ}\) (\(n=12\))) when compared to the non-foot and ankle autograft group (\(-1.2^{\circ}\)\(\pm\) 1.3 (\(n=20\))). This change in HV angle is reflective of the difference in HV before and after surgery. As HV angle is a direct predictor of hallux valgus severity, the foot and ankle autograft had a greater impact on improving MTP alignment than non-foot and ankle autografts [30]. Ideally, this change in angulation would be related to the deviation from the planned outcome, as some salvage procedures may optimally require a smaller decrease in HV angle to be deemed a successful correction. However, as the articles that differentiate by graft type did not report planned outcomes, improvements in angulation had to be compared qualitatively based upon pre-operative alignment. For IMA angle, both autograft groups had similar improvements in alignment, with non-foot and ankle autografts having a slightly larger improvement (\(-1.9^{\circ}\) (\(n=12\))) than autografts taken from within the foot and ankle (\(-1.1^{\circ}\) (\(n=12\))). This similarity in IMA measurements is expected due to the nature of the IMA measurement. IMA was measured from the base of the first and second metatarasal; any change distally should not have much effect. While there was not enough high-level evidence to perform proper statistical analysis on these two kinematic angles, qualitatively on an absolute scale, foot and ankle autograft performed better at realigning the hallux towards more normal HV angulation compared to the non-foot and ankle autograft group, while also having similar results for IMA. As foot and ankle autograft can be taken without the need for a separate surgical site, it could potentially be a cheaper and more optimal way of correcting kinematic alignment in salvage MTP arthrodeis. Previous reviews did not comment on these kinematic measurements, and additional investigation into the effect of allograft on kinematic alignment should be explored in future studies. As for first ray lengthening, foot and ankle autograft had a negligible effect on length restoration (average decrease of 0.1 cm, \(p=0.42\)). As only one group used strictly foot and ankle autograft (no supplementing with crushed allograft), more investigation into this technique is needed to further understand its effect on length restoration. The non-foot and ankle autograft group had a mean length restoration of 4.4 \(\pm\) 0.1 mm (\(n=33\), 73.3% reported), whereas the allograft group had a mean length restoration of 7.6 \(\pm\) 3.5 mm (\(n=49\), 100% reported). Interestingly, both subgroups reported similar graft lengths used for length restoration (allograft = 10.5 (\(n=38\), one article)): non-foot and ankle autograft (10.0 \(\pm\) 1.0 (\(n=37\), 82.2% reported)). As allograft had a greater length restoration, it can be inferred that allograft likely has greater bony integration. This could be due to allograft often being supplemented with additional orthobiologics as seen in the study by [PERSON] et al., and the increased bony integration capabilities were also reflected union rates [24]. The two studies that used allograft for length restoration had the highest success rates at 94.70% and 90.90% [21; 24]. However, as the studies included in our review were low-levelevidence, a proper comparison study between allograft and non-foot and ankle autograft is needed to fully understand which graft is best for length restoration. To update previously reported clinical outcomes, our review had similar results for successful union and the AOFAS post-operative score [16]. [PERSON] et al.