Forefoot Function after Hallux Valgus Surgery: A Systematic Review and Meta-Analysis on Plantar Load Measurement

Abstract

While hallux valgus (HV) surgeries are useful for correcting skeletal alignment problems, their effects on plantar load, which reflects forefoot functions, are less understood. The objective of this study is to conduct a systematic review and meta-analysis on the plantar load change after HV surgeries. A systematic search of Web of Science, Scopus, PubMed, CENTRAL, EMBASE, and CINAHL was performed. Studies that assessed the pre- and post-operative plantar pressure of HV patients undergoing surgeries and reported load-related parameters over the hallux, medial metatarsal, and/or central metatarsal regions were included. Studies were appraised by using the modified NIH quality assessment tool for before-after study. Studies suitable for meta-analysis were pooled with the random-effects model, using the standardized mean difference of the before-after parameters as an effect measure. Twenty-six studies containing 857 HV patients and 973 feet were included for the systematic review. Meta-analysis was conducted on 20 of them, and most studies did not favor HV surgeries. Overall, HV surgeries reduced the plantar load over the hallux region (SMD -0.71, 95% CI, -1.15 to -0.26), indicating that forefoot function worsened after surgeries. For the other five outcomes, the overall estimates were not statistically significant, indicating that surgeries did not improve them either. There was substantial heterogeneity among the studies, which in most cases could not be resolved by pre-planned subgroup analyses by surgical classification, year of publication, median age of patients, and length of follow-up. Sensitivity analysis removing lower-quality studies showed that the load integrals (impulse) over the central metatarsal region significantly increased (SMD 0.27, 95% CI, 0 to 0.53), indicating that surgeries increased the risk of transfer metatarsalgia. There is no solid evidence that HV surgeries could improve forefoot functions from a biomechanical point perspective. Currently available evidence even suggests that surgeries might reduce the plantar load over the hallux and adversely affect push-off function. The reasons behind and the effectiveness of alternative surgical methods warrant further investigation.

Keywords: bunion; hallux abducto valgus; metatarsus primus varus; pedobarography; postoperative evaluation.

Figure 1

Pathomechanism of HV and transfer metatarsalgia: (a) The first ray plays an important role in push-off functions. The blue line illustrates the center of pressure trajectory during gait; (b) since the first metatarsal is less stable without any muscle insertions, it might deviate medially, conforming with the direction of the push-off load. The black arrows represent the directions of muscle force. The blue arrows represent the deformity directions of the bones [7]. The hallux and the sesamoids are hold in position by the muscle and plantar aponeurosis. Therefore, the hallux looks laterally deviated relative to the first metatarsal, while the sesamoids beneath the first metatarsal head are gradually exposed and disanchored. Plantarflexors, abductors, and stabilizing muscles of the first ray would become lateral to the longitudinal axis of the first ray and distribute deforming forces [7]. The problem aggravates with higher exposure and loading of the forefoot, such as wearing high-heeled shoes [26]; (c) when the muscles and the sesamoids that served as the fulcrum are deranged, the load-carrying capability and push-off functions are compromised and compensated by other forefoot regions, resulting in transfer metatarsalgia. The blue line represents the lateralized center of pressure trajectory; (d) the bone alignment and sesamoid positions shall be corrected after HV surgeries, but whether the center or pressure trajectory and thus load-carrying capability of the first ray could be restored is in doubt.

Figure 2

Preferred Reported Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart for systematic review. CINAHL: Cumulated Index to Nursing and Allied Health Literature; SE: Standard Error.

Figure 3

Meta-analysis on the overall effects of surgeries on plantar load over hallux region (increase means better). STP: soft tissue procedure [24,25,32,33,33,34,35,36,38,41,42,43,44,46,49,50,53,54,54].

Figure 4

Meta-analysis on the overall effects of surgeries on plantar load over medial metatarsal region (increase means better) [24,25,32,33,34,35,36,37,38,41,42,44,46,49,50,53,54].

Figure 5

Meta-analysis on the overall effects of surgeries on plantar load over central metatarsal region (decrease means better) [25,32,33,34,35,35,36,37,38,41,42,44,46,49,50,53,54].