The findings of this study indicate that pronation may need to be considered in the operative correction of hallux valgus for restoration of normal anatomy.

BackgroundThis study sought to determine whether several metatarsophalangeal (MTP) fusion techniques require complete immobilization or if some level of weight-bearing could be recommended after surgery. A comparison of synthetic composite to actual bone was included in order to examine the validity of the testing conditions.MethodsFour MTP fusion modalities were tested in synthetic composite bone models: unlocked plating, locked plating, crossed lag screws, and an unlocked plate with a single lag screw. Stiffness was calculated and then used to find the two most rigid constructs; the load to failure was recorded. Stiffness and load to failure testing for the two more rigid constructs in paired cadaveric bones were followed.ResultsThe unlocked plate plus screw and crossed screw constructs were stiffest (p < 0.008). Loads to failure of the unlocked plate plus screw and crossed screws in synthetic bone were 131 and 101 N, respectively and in cadaveric bone were 154 and 94 N, respectively, which are less than the estimated 25% body weight required at the MTP joint. The plate plus screws were statistically more stiff than crossed screws (p = 0.008), but there was no statistical difference between synthetic and cadaveric bone in load to failure (p = 0.296).ConclusionsThe plate plus screw offered the greatest stiffness; the failure test showed that no construct could withstand weight-bearing as tolerated; and, synthetic composite models of the MTP joint did not provide the consistent results in stiffness and failure.

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The progression of the hallux valgus (HV) deformity demonstrates dorsiflexion and abduction; concomitant pronation has not received adequate documentation and the extent of pronation in the pathology is unknown even though correction of the deformity may need to address all three angles. To overcome the inability of standard radiographs to capture pronation, we have developed a means to assess the three dimensional deformity using CT scans. Our goal was to document the extent of pronation/supination both of the first phalanx with respect to the first metatarsal and of the first metatarsal with respect to the second metatarsal. Furthermore, we wanted to regress pronation against the intermetatarsal (IMA) angle of hallux valgus patients. Methods: Three-dimensional models were reconstructed from loaded and unloaded CT files of patients (10 HV, 10 normal). The orientations of specific bones, in anatomic directions, were determined by selecting landmarks on the surface of the phalanx and of the first and second metatarsals. The resulting calculations output a set of angles to determine the pronation/supination of the first metatarsal relative to the second and of the first phalanx relative to the first metatarsal. A regression analysis was conducted to extrapolate any relationship between adduction and pronation (known intermetatarsal and pronation). Results: The average pronation of the first metatarsal relative to the second metatarsal was 19.8 ± 7.1 and 28.3 ± 10.8 in the normal and HV groups respectively (p < 0.05). The influence of weightbearing demonstrated pronation angle differences that were greater in the normal group than in the HV group for both the IM pronation and the HV pronation (p < 0.05) (Figure 1). The differences in HV angles and IM angles between normal and HV patients were 22° and 7° respectively. The regression analysis of the pronation and intermetatarsal angle was not found to be significant, with a weak correlation (r2 = 0.26). Conclusion: The pronation of the first metatarsal relative to the second metatarsal between normal and HV patients is significantly different. While the first metatarsal had measurable pronation in patients with hallux valgus but that value was not predicted by the IMA. The findings of this study indicate pronation should be considered in any surgical technique that seeks to restore native configurations.

Category: Ankle Introduction/Purpose: Knowledge of cartilage pressure distribution in healthy ankle joints during gait is important for understanding the loading environment of articular cartilage and for providing a basis for comparison to evaluate how ankle pathology and surgical procedures affect cartilage loading. Finite element models of the ankle have been developed to examine in vitro loads at the tibiotalar joint during simulated standing in healthy and injured ankle joints [1, 2]. However, there are currently no in vivo studies of tibiotalar cartilage pressure during dynamic loading activities. The goal of this study was to develop a subject-specific finite element model of the tibiotalar joint to estimate contact pressure during walking and running. Methods: Informed consent was obtained from one healthy male, age 23 yrs., BMI 27 kg/m2). Synchronized biplane radiographs of the ankle were acquired at 100 and 150 frames per second during the support phase of overground walking and running, respectively, at a self-selected pace (1.5 m/s and 3.0 m/s, respectively). CT-based bone models of the tibia and talus were matched to the stereoradiographic images to precisely track the three-dimensional bone movement [3]. Six degrees-of-freedom joint kinematics were calculated for each bone model, and used to position bone models in the finite element analysis. Cartilage volumes for the distal tibia and proximal talus were created in Geomagic software by extruding the articulating bone surface. Bones were modeled as rigid bodies and cartilage was modeled as deformable bodies with uniform thickness of 1.3 mm [4-7]. Simulations were performed using FEBio software. The primary outcome parameter was peak cartilage pressure in the tibiotalar joint. Results: On average, peak tibiotalar cartilage pressure was approximately 25% greater during the midstance phase of running in comparison to walking (Figure 1). During walking, peak contact pressure occurred on the lateral-central region of the tibiotalar cartilage throughout the entire stance phase. During the early support phase of running, the location of peak contact pressure was also on the lateral-central region of the tibiotalar cartilage. During running push-off, pressure increased in the medial-central cartilage region and the overall peak cartilage pressure increased. Conclusion: A novel finding of this study is that the peak pressure in tibiotalar cartilage moves from the lateral to medial side of the joint during running, but remains on the lateral side throughout the support phase of walking. This suggests that the location and magnitude of the loads seen by tibiotalar joint cartilage are activity dependent, even in the healthy ankle joint. Future work will investigate cartilage loading in pathologic ankles before and after surgical intervention, as well as during other common athletic activities.