Effects of mechanical factors on the fracture healing process

An interdisciplinary study based on animal experiments, cell culture studies, and finite element models is presented. In a sheep model, the influence of the osteotomy gap size and interfragmentary motion on the healing success was investigated. Increasing gap sizes delayed the healing process. Increasing movement stimulated callus formation but not tissue quality. Typical distributions of intramembranous bone, endochondral ossification, and connective tissue in the fracture gap are quantified. The comparison of the mechanical data determined by a finite element model with the histologic images allowed the attribution of certain mechanical conditions to the type of tissue differentiation. Intramembranous bone formation was found for strains smaller than approximately 5% and small hydrostatic pressure (< 0.15 MPa). Strains less than 15% and hydrostatic pressure more than 0.15 MPa stimulated endochondral ossification. Larger strains led to connective tissue. Cell culture studies on the influence of strain on osteoblasts supported these findings. Proliferation and transforming growth factor beta production was increased for strains up to 5% but decreased for larger strains. Osteoblasts under larger strains (> 4%) turned away from the principal strain axis and avoided larger deformations. It is hypothesized that gap size and the amount of strain and hydrostatic pressure along the calcified surface in the fracture gap are the fundamental mechanical factors involved in bone healing.

Hallux valgus: demographics, etiology, and radiographic assessment

BACKGROUND

The purpose of the study was to preoperatively evaluate the demographics, etiology, and radiographic findings associated with moderate and severe hallux valgus deformities in adult patients (over 20 years of age) treated operatively over a 33-month period in a single surgeon's practice.

METHODS

Patients treated for a hallux valgus deformity between September, 1999, and May, 2002, were identified. Patients who had mild deformities (hallux valgus angle < 20 degrees), concurrent degenerative arthritis of the first metatarsophalangeal joint, inflammatory arthritis, recurrent deformities, or congruent deformities were excluded. When enrolled, all patients filled out a standardized questionnaire and had a routine examination that included standard radiographs, range of motion testing, and first ray mobility measurement. A chart review and evaluation of preoperative radiographs were completed on all eligible patients.

RESULTS

One-hundred and three of 108 (96%) patients (122 feet) with a diagnosis of moderate or severe hallux valgus (hallux valgus angle of 20 degrees or more)(70) qualified for the study. The onset of the hallux valgus deformity peaked during the third decade although the distribution of occurrence was almost equal from the second through fifth decades. Twenty-eight of 122 feet (23%) developed a deformity at an age of 20 years or younger. Eighty-six (83%) of patients had a positive family history for hallux valgus deformities and 87 (84%) patients had bilateral bunions. 15% of patients in the present series had moderate or severe pes planus based on a positive Harris mat study. Only 11% (14 feet) had evidence of an Achilles or gastrocnemius tendon contracture. Radiographic analysis found that 86 of 122 feet (71%) had an oval or curved metatarsophalangeal joint. Thirty-nine feet (32%) had moderate or severe metatarsus adductus. A long first metatarsal was common in patients with hallux valgus (110 of 122 feet; 71%); the mean increased length of the first metatarsal when compared to the second was 2.4 mm. While uncommon, the incidence of an os intermetatarsum was 7% and a proximal first metatarsal facet was 7%. The mean preoperative first ray mobility as measured with Klaue's device was 7.2 mm. 16 of 22 (13%) feet were observed to have increased first ray mobility before surgery.

CONCLUSIONS

The magnitude of the hallux valgus deformity was not associated with Achilles or gastrocnemius tendon tightness, increased first ray mobility, bilaterality or pes planus. Neither the magnitude of the preoperative angular deformity nor increasing age had any association with the magnitude of the first metatarsophalangeal joint range of motion. Constricting shoes and occupation were implicated by 35 (34%) patients as a cause of the bunions. A familial history of bunions, bilateral involvement, female gender, a long first metatarsal, and an oval or curved metatarsophalangeal joint articular surface were common findings. Increased first ray mobility and plantar gapping of the first metatarsocuneiform joint were more common in patients with hallux valgus than in the general population (when compared with historical controls).

Risk factors for recurrent stress fractures in athletes

Our aim was to identify factors predisposing athletes to multiple stress fractures, with the emphasis on biomechanical factors. Our hypothesis was that certain anatomic factors of the ankle are associated with risk of multiple stress fractures of the lower extremities in athletes. Thirty-one athletes (19 men and 12 women) with at least three separate stress fractures each, and a control group of 15 athletes without fractures completed a questionnaire focusing on putative risk factors for stress fractures, such as nutrition, training history, and hormonal history in women. Bone mineral density was measured by dual-energy x-ray absorptiometry in the lumbar spine and proximal femur. Biomechanical features such as foot structure, pronation and supination of the ankle, dorsiflexion of the ankle, forefoot varus and valgus, leg-length inequality, range of hip rotation, simple and choice reaction times, and balance in standing were measured. There was an average of 3.7 (range, 3 to 6) fractures in each athlete, totaling 114 fractures. The fracture site was the tibia or fibula in 70% of the fractures in men and the foot and ankle in 50% of the fractures in women. Most of the patients were runners (61%); the mean weekly running mileage was 117 km. Biomechanical factors associated with multiple stress fractures were high longitudinal arch of the foot, leg-length inequality, and excessive forefoot varus. Nearly half of the female patients (40%) reported menstrual irregularities. Runners with high weekly training mileage were found to be at risk of recurrent stress fractures of the lower extremities.

Plantar soft tissue loading under the medial metatarsals in the standing diabetic foot

Diabetes mellitus (type 2) is the most frequent cause of non-traumatic lower-limb amputations. The major cause of impairment to the feet of diabetics is persistent hyperglycemia, potentially leading to peripheral neuropathy as well as to pathological changes in plantar soft tissue, which stiffen its structure and diminish its ability to effectively distribute foot-ground contact loads. In this study, a computational model of the foot structure in the standing position was utilized to evaluate stress distributions in plantar soft tissue under the medial metatarsal heads of simulated diabetic versus normal feet. The model comprises five anatomic planar cross-sections in the directions of the foot rays, which were solved for internal stresses under static ankle joint reaction (300 N) and triceps surae muscle forces (150 N) using the finite element method. Tissues were assumed to be homogenous, isotropic and elastic materials, with nonlinear stress-strain relations for the ligaments, fascia and plantar tissue. The model revealed significant tension stress concentrations (90-150 KPa) in the plantar pad of the simulated diabetic forefoot: they were four times the normal maximum stress under the first metatarsal head and almost eight times the normal maximum stress under the second metatarsal head. It was shown that with increased severity of stiffening of the plantar pad, as related to glucose-exposure, peak forefoot contact stresses may rise by 38 and 50% under the first and second metatarsal heads, respectively. The increase in averaged (von Mises) internal stresses within the plantar soft tissue is even more pronounced, and may rise by 82 and 307% for the tissue under the first and second metatarsal heads, respectively. These results, which conform to experimental data gathered over the last two decades, suggest that the process of injury in diabetic feet is very likely to initiate not on the skin surface, but in deeper tissue layers, and the tissues underlying the distal bony prominences of the medial metatarsals are the most vulnerable ones.

Local tissue properties in bone healing: influence of size and stability of the osteotomy gap

To characterize the site-specific mechanical and histological properties in fracture repair and to relate these properties to the initial mechanical situation, an experimental fracture model was used in the metatarsus of 42 sheep. The mechanical situation of a transverse osteotomy was described by three gap sizes (1, 2, or 6 mm) and two amounts of strain (7 or 31%). An external fixator that allowed a defined axial movement provided control of these settings. Nine weeks following surgery, the healing area was dissected and tensile and compressive properties were measured in subregions of the fracture gap and the periosteal callus. The central, sagittal section was used for quantitative histology. We found the quality of the tissue along the osteotomy line to be most important for regaining mechanical stability. Increasing the size of osteotomy gaps resulted in poorer mechanical and histological qualities, and the repair process was less complete. Interfragmentary strain did not significantly influence the repair process. The smaller strain levels had already stimulated the secondary repair process, and this stimulatory effect could not be further enhanced by increasing the amount of strain. Our finding that large gaps between bone segments were not as well healed as were smaller gaps suggests that it is advantageous to avoid large gaps in fracture treatment.

Strains in the metatarsals during the stance phase of gait: implications for stress fractures

BACKGROUND

Stress fractures of the metatarsals are common overuse injuries in athletes and military cadets, yet their etiology remains unclear. In vitro, high bone strains have been associated with the accumulation of microdamage and shortened fatigue life. It is therefore postulated that stress fractures in vivo are caused by elevated strains, which lead to the accumulation of excessive damage. We used a cadaver model to test the hypothesis that strains in the metatarsals increase with simulated muscle fatigue and plantar fasciotomy.

METHODS

A dynamic gait simulator was used to load fifteen cadaveric feet during the entire stance phase of gait under conditions simulating normal walking, walking with fatigue of the auxiliary plantar flexors, and walking after a plantar fasciotomy. Strains were measured, with use of axial strain-gauges, in the dorsal, medial, and lateral aspects of the diaphysis of the second and fifth metatarsals as well as in the proximal metaphysis of the fifth metatarsal.

RESULTS

When the feet were loaded under normal walking conditions, the mean peak strain in the dorsal aspect of the second metatarsal (-1897 microstrain) was more than twice that in the medial aspect of the fifth metatarsal (-908 microstrain). Simulated muscle fatigue significantly increased peak strain in the second metatarsal and decreased peak strain in the fifth metatarsal. Release of the plantar fascia caused significant alterations in strain in both metatarsal bones; these alterations were greater than those caused by muscle fatigue. After the plantar fasciotomy, the mean peak strain in the dorsal aspect of the second metatarsal (-3797 microstrain) was twice that under normal walking conditions.

CONCLUSIONS

The peak axial strain in the diaphysis of the second metatarsal is significantly (p < 0.0001) higher than that in the diaphysis of the fifth metatarsal during normal gait. The plantar fascia and the auxiliary plantar flexors are important for maintaining normal strains in the metatarsals during gait.

The influence of muscle fatigue on electromyogram and plantar pressure patterns as an explanation for the incidence of metatarsal stress fractures

BACKGROUND

Stress fractures are common overuse injuries in runners and appear most frequently in the metatarsals.

PURPOSE

To investigate fatigue-related changes in surface electromyographic activity patterns and plantar pressure patterns during treadmill running as potential causative factors for metatarsal stress fractures.

STUDY DESIGN

Prospective cohort study with repeated measurements.

METHODS

Thirty experienced runners volunteered to participate in a maximally exhaustive run above the anaerobic threshold. Surface electromyographic activity was monitored for 14 muscles, and plantar pressures were measured using an in-shoe monitoring system. Fatigue was documented with blood lactate measurements.

RESULTS

The results demonstrated an increased maximal force (5%, P < .01), peak pressure (12%, P < .001), and impulse (9%, P < .01) under the second and third metatarsal head and under the medial midfoot (force = 7%, P < .05; pressure = 6%, P < .05; impulse = 17%, P < .01) toward the end of the fatiguing run. Contact area and contact time were only slightly affected. The mean electromyographic activity was significantly reduced in the medial gastrocnemius (-9%, P < .01), lateral gastrocnemius (-12%, P < .01), and soleus (-9%, P < .001) muscles.

CONCLUSION

The demonstrated alteration of the rollover process with an increased forefoot loading may help to explain the incidence of stress fractures of the metatarsals under fatiguing loading conditions.

The Weil osteotomy of the lesser metatarsals: a clinical and pedobarographic follow-up study

The clinical results with pedobarographic analysis were assessed in 32 patients (59 metatarsals) who underwent a distal metatarsal shortening (Weil) osteotomy for either intractable plantar keratoses or chronically dislocated lesser metatarsal phalangeal joints. All patients had increased pressure under the involved metatarsal heads. Thirty three of the 59 metatarsophalangeal (MTP) joints were chronically dislocated. At an average follow-up of 30 months, patients rated the result as excellent or good for 32 of the 37 feet (86%). The mean preoperative AOFAS score was 59 (maximum 100), which improved to 81 post-operatively. This difference is significant: p = 0.00001 (with t-test). Comparison of the pre and post-operative pedobarographic measurements showed a significant decreased load under the affected metatarsal heads (p = 0.05). A complete disappearance of the callus was noted under 44 operated metatarsals (75%) and partial disappearance under 12 metatarsals (20%). Two symptomatic transfer lesions occurred under an adjacent metatarsal head. Recurrent dislocations occurred in 5 joints (15%). While metatarsophalangeal joint range of motion was significantly diminished, toe strength was maintained. Average metatarsal shortening was 5.9 mm with no nonunions, delayed unions, or malunions. The Weil shortening osteotomy is a simple and reliable procedure which can effectively reduce the load under the lesser metatarsophalangeal joints and is helpful for the reduction of dorsally dislocated MTP joints.

Mobility of the first tarsometatarsal joint in relation to hallux valgus deformity: anatomical and biomechanical aspects

Hypermobility of the first tarsometatarsal (TMT 1) joint is suggested to be an important factor in the cause and progression of hallux valgus deformity. Hypermobility of the TMT 1 joint is tested clinically in the sagittal plane, but an important deformation also exists in the transversal plane: metatarsus primus varus. This in vitro study was undertaken to investigate the relation between the mobility of the TMT 1 joint in these two planes and to investigate the correlation of the mobility with morphological variables. A second aim was to study the possible stabilizing effect of the tibialis anterior muscle, flexor hallucis longus muscle, and peroneus longus muscle on the TMT 1 joint. Nine embalmed human specimens were tested under standardized conditions. A 30-N force was applied to the head of the first metatarsal (MT 1) to pull in either the dorsal or medial direction. To simulate muscle force, 21 N was applied to the three tendons: all seven possible combinations of muscle action were tested in each plane of motion. Angular displacements were measured using 2-dimensional LED video registration. TMT 1 mobility is a relevant factor in MT 1 mobility in the sagittal and transversal planes, the peroneus longus has a stabilizing effect on this joint, and the effect of the flexor hallucis longus on this joint is different in both planes. When considering a Lapidus procedure for surgically correcting a hallux valgus, the mobility of MT 1 in the transversal plane should also be assessed, but so far no objective clinical test in this plane has been described.

First ray dorsal mobility in relation to hallux valgus deformity and first intermetatarsal angle

The hypermobile first ray has been implicated as contributing to the cause and progression of hallux valgus deformity. Deformity of the hallux is often accompanied by an enlarged first intermetatarsal (IM 1-2) angle. It has been hypothesized that subjects having an abnormally large IM 1-2 angle have laxity of the first ray. Objectives of this study were to compare dorsal mobility of the first ray in subjects with hallux valgus to asymptomatic controls, and to investigate the relationship between dorsal mobility and the IM 1-2 angle. Fourteen subjects (age 23-81) with hallux valgus were matched by gender and age to control subjects. The IM 1-2 angle was measured from radiographs. A load-cell device measured dorsal mobility of the first ray under a standard load of 55 N. Pearson's correlation coefficient identified a marginal correlation (r = .51) between IM 1-2 angle and dorsal mobility. An independent t-test showed a statistically (P < 0.01) larger amount of dorsal mobility in the group of subjects having hallux valgus. Mobility of the first ray was increased in subjects with hallux valgus and a large IM 1-2 angle may be an indicator of increased dorsal mobility.

Chevron osteotomy fixed with absorbable polyglycolide pins

Seventy-eight chevron osteotomies augmented by internal fixation with self-reinforced polyglycolide pins, 2 mm in diameter, were performed in 60 patients suffering from a painful hallux valgus. The mean metatarsophalangeal angle was 31 degrees, and there was a metatarsus primus varus varying from 10 degrees to 20 degrees. The average follow-up time was 14 (range, 12 to 31) months. No postoperative redisplacement or disturbance of healing of the osteotomy was observed, but recurrence of hallux valgus occurred in 8 feet (10%), each initially with a moderate to severe hallux valgus. Some pain at the first metatarsophalangeal joint during physical activity remained in 12 feet (15%). There was a mean shortening of 2.5 mm of the first metatarsal bone, and the most significant shortening was associated with pain in the forefoot. The metatarsophalangeal joint motion was not decreased. The subjective overall result was excellent or good in 75% of the patients. Because of the biodegradability of the implants used, no secondary procedures to remove the implants were necessary.

The biomechanics of the first metatarsal bone in hallux valgus: a preliminary study utilizing a weight bearing extremity CT

BACKGROUND

Hallux valgus is a common but aetiologically not perfectly understood condition. Imaging in hallux valgus is based on weight bearing plain radiographs or in exceptional cases on non-weight bearing computerized tomography (CT)-studies.

METHODS

A portable extremity CT was used to study the forefoot with focus on first metatarsal bone in ten hallux valgus patients and five asymptomatic controls at rest and at weight bearing. Two-dimensional (2D) or three-dimensional (3D) hallux valgus angles, intermetatarsal angles and various other parameters were measured on CT data and the measurements between study groups were compared. The measured angles were also compared to angles measured on plain radiographs.

RESULTS

2D or 3D angles from CT data sets can be used to evaluate hallux valgus. In hallux valgus, when compared with normal asymptomatic foot, the first metatarsal bone is medially deviated (intermetatarsal angle is wider), the width of the forefoot is increased and the proximal phalanx pronates. Between the study groups there was a statistically significant difference of the measured 3D hallux valgus angles at weight bearing but not at rest suggesting the importance of weight bearing CT studies when evaluating hallux valgus.

CONCLUSIONS

To our knowledge, this is the first time weight bearing CT data is presented when evaluating hallux valgus, offering a true alternative to plain radiographs. The relationships of bones of the forefoot, including rotational changes, can be reliably measured using this imaging method.

Biomechanics of the first ray. Part II: Metatarsus primus varus as a cause of hypermobility. A three-dimensional kinematic analysis in a cadaver model

Variation in functional stability of the first metatarsocuneiform joint was analyzed between transverse plane deviated (adducted) and corrected first metatarsal positions in a closed kinetic chain model. Six fresh frozen cadaver specimens with intact ankles and feet were fitted with a custom fabricated titanium metatarsal jig, which allowed for manipulation of the first metatarsal in the transverse plane. Specimens were mounted into a custom-made acrylic load frame and axially loaded to 400 N. Radiowave three-dimensional tracking transducers were attached to the following osseous segments: first metatarsal head and base, medial cuneiform, and second metatarsal. A dorsally directed load was applied to the first metatarsal segment and resultant movements were measured. Repeated testing was performed on a transverse deviated and corrected first metatarsal positions with the hallux plantargrade and maximally dorsiflexed to engage the windlass mechanism. With the windlass mechanism engaged and first metatarsal corrected, a 26% increase in first ray plantarflexion occurred from a deviated to a corrected first metatarsal position (p < or = .05). This suggests that the windlass mechanism is more efficient when the first metatarsal, sesamoid apparatus, and hallux position are properly aligned with the orientation of the plantar aponeurosis. Clinically, this may explain the correlation of first ray hypermobility with the progression of bunion severity. Our study validates the earlier work of Hicks and adds additional insight into the functional stability in the medial column of the foot.

Proximal metatarsal osteotomies: a comparative geometric analysis conducted on sawbone models

We evaluated the change in position of the first metatarsal head using a three-dimensional digitizer on sawbone models. Crescentic, closing wedge, oblique shaft (Ludloff 8 degrees and 16 degrees), reverse oblique shaft (Mau 8 degrees and 16 degrees), rotational "Z" (Scarf), and proximal chevron osteotomies were performed and secured using 3-mm screws. The 16 degrees Ludloff provided the most lateral shift (9.5 mm) and angular correction (14.5 degrees) but also produced the most elevation (1.4 mm) and shortening (2.9 mm). The 8 degrees Ludloff provided lateral and angular corrections similar to those of the crescentic and closing wedge osteotomies with less elevation and shortening. Because the displacement osteotomies (Scarf, proximal chevron) provided less angular correction, the same lateral displacement, and less shortening than the basilar angular osteotomies, based upon this model they can be more reliably used for a patient with a mild to moderate deformity, a short first metatarsal, or an intermediate deformity with a large distal metatarsal articular angle. These results can serve as recommendations for selecting the optimal osteotomy with which to correct a deformation.

Critical evaluation of the modified Lapidus procedure

The modified Lapidus procedure has been used for treatment of hallux abducto valgus for many years, yet only a handful of reports evaluate procedure outcome. The purpose of this investigation was twofold: 1) to provide a retrospective outcome analysis of the modified Lapidus procedure using subjective and objective criteria, and 2) to evaluate procedure outcome in patient populations with differing functional demands: athletes, active patients, and sedentary patients. Thirty-four patients (42 feet) had the modified Lapidus procedure performed by the senior author (R.T.B.) over a 7-year period. Nine patients were lost to follow-up leaving 25 patients (32 feet) for study inclusion. Twenty-three females and two males with average age 44.4 years (range 15-71 years) were evaluated at an average follow-up time of 39 months (range 13-91 months). Evaluation consisted of subjective questionnaire, physical examination, and radiographic assessment. Subjective evaluation revealed that 78% of patients rated surgery "completely" or "very" effective. Athletes demonstrated lower return to preoperative activity levels (30%) than did active patients (86%) and sedentary patients (75%), but this was not statistically significant. Seventy-seven percent of athletes rated surgery "completely" or "very" effective. Postoperative intermetatarsal angle averaged 8.2 degrees (range -2 to 15) and first metatarsophalangeal joint dorsiflexion averaged 62.6 degrees (range 20- 90 degrees). Intermetatarsal angle correction to 10 degrees or less and postoperative first metatarso-phalangeal joint dorsiflexion 45 degrees or greater correlated with improved subjective results. The modified Lapidus procedure is an effective procedure in patients with hypermobility of the first metatarsocuneiform joint. Success is dependent on patient selection, meticulous surgical technique and comprehensive postoperative management.

Radiographic features that enable assessment of first metatarsal rotation: the role of pronation in hallux valgus

This study describes a method of detecting first metatarsal pronation on the basis of the movement of the inferior tuberosity of the base of 20 cadaveric first metatarsals at 0 degrees, 10 degrees, 20 degrees and 30 degrees pronation. On pronation, the inferior tuberosity of the base of the first metatarsal moved lateral to the mid-line axis. At 10 degrees, the tuberosity pointed to the junction of the inner third and outer two-thirds of a line between the midpoint and lateral tubercle of the base. At 20 degrees, it pointed to the junction of the inner two-thirds and outer third of that line. At 30 degrees, it pointed to the outer margin of the lateral third. Using these features, the amount of first metatarsal pronation in 100 consecutive weight-bearing views of feet was recorded and plotted against the corresponding intermetatarsal angles in those feet. Four of 43 patients with an intermetatarsal angle of less than 9 degrees had pronation greater than 10 degrees, 48 of 57 patients with an intermetatarsal angle greater than 9 degrees had pronation greater than 10 degrees (P < 0.001). As intermetatarsal angles increase, the amount of first metatarsal pronation increases (r = 0.69). Pronation and varus deviation of the first metatarsal are linked; both alter the tendon balance maintaining proximal phalanx alignment and lead to the development of hallux valgus.

Intramedullary screw fixation of Jones fractures: a biomechanical study

The management of proximal fifth metatarsal ("Jones") fractures in athletes has become increasingly more aggressive, despite a lack of biomechanical data in the literature. A cadaver biomechanical study was conducted to evaluate the strength of intramedullary fixation of simulated Jones fractures loaded to failure via three-point bending on a Materials Testing System machine. In a series of eight intact fifth metatarsal control specimens, the force to failure (fracture) was measured for comparison with repaired specimens. Acute fractures were simulated in 10 pairs of feet via osteotomy at the typical fracture location and were fixed with either a 4.5-mm malleolar screw or a 4.5-mm partially threaded, cancellous, cannulated screw, both placed using conventional intramedullary techniques. Force at initial displacement averaged 73.9 N (SD, 64.7 N) for the malleolar screws and 72.5 N (SD, 42.3 N) for the cannulated screws. Force at complete displacement averaged 519.3 N (SD, 226.2 N) for the malleolar screws and 608.4 N (SD, 179.7 N) for the cannulated screws. The force to failure of the intact specimens was significantly greater than the initial and complete forces to failure for the fixed specimens (P < 0.05, independent measures analysis of variance). There was no statistical difference between the average forces at initial displacement or at complete displacement in the fixed metatarsal specimens for the two different types of screws, but the forces at complete displacement for each screw type were significantly greater than the forces at initial displacement (P < 0.05). On the basis of literature review and data generated from this study, it is apparent that the forces necessary to cause displacement of the stabilized Jones fracture are above what would be transmitted within the lateral midfoot during normal weightbearing. The choice of screw and intramedullary technique of fixation is a matter of surgeon preference, because the choice of screw makes no biomechanical difference.

Dorsiflexion metatarsal osteotomy for treatment of recalcitrant diabetic neuropathic ulcers

Twenty diabetic patients underwent 22 dorsiflexion metatarsal osteotomies for treatment of chronic persistent or recurrent neuropathic forefoot ulcers. Mean duration of nonoperative treatment was 13 months. The procedure consisted of irrigation and debridement of the ulcer followed by basilar closing wedge metatarsal osteotomy performed through a dorsal approach. At follow-up, complete ulcer healing was noted in 21 cases (95%) at an average of 40 days postoperatively. Complications occurred in 15 cases (68%). The main problems encountered postoperatively were acute Charcot disease (32%) and deep wound infections (14%). Transfer lesions under adjacent metatarsal heads developed in two cases (9%). One ulcer (5%) failed to heal secondary to vascular insufficiency and eventually required a below the knee amputation after a failed revascularization attempt. Loss of screw fixation occurred in one patient (5%) but acceptable metatarsal alignment was maintained and the ulcer healed uneventfully. There were no cases of ulcer recurrence. The results of this study suggest that dorsiflexion metatarsal osteotomy is a reliable salvage procedure for the treatment of recalcitrant neuropathic forefoot ulcers that have failed an adequate trial of nonoperative treatment. This procedure is associated with a high complication rate, as would be expected in this patient population.

Plantar pressures determinants in mild Hallux Valgus

While podobarometric techniques have been applied to the study of pressures in Hallux Valgus (HV), little is known about its clinical and radiological determinants. So, the aim of the present study was to determine the plantar pressure pattern in participants with mild HV, comparing to a control group, and their clinical and anthropometric determinants. Biofoot/IBV(®) in-shoe system was used to evaluate 79 participants with mild HV. Computerized measurements of the 1st intermetatarsal angle (IMA) and the hallux abductus angle (HAA) were made on antero-posterior radiographs. The clinical outcome was assessed using the AOFAS score. The dependent baropodometric variables and the independent clinical and anthropometric variables were subjected to a multiple regression analysis. In both groups, the highest average pressure was in the 2nd metatarsal head (MTH). The mean pressure under the Hallux was significantly higher in HV group (controls, 146.5±92.5kPa; HV, 328.5±113.2kPa; p<0.001). An 18.6% of average pressure under the 1st MTH was accounted for pain, first ray alignment and total AOFAS score. Variations of the HAA explained 26.8% of the mean Hallux pressure. Women with mild HV present with pathologically increased pressure under the Hallux, which is caused by the altered alignment of the first ray. Pain and clinical result were associated with the pressure under the 1st MTH and the remaining variables were only moderate predictors of dynamic plantar pressures.

Strength of fixation constructs for basilar osteotomies of the first metatarsal

Twenty-four pairs of fresh-frozen human feet had a proximal osteotomy of the first metatarsal that was fixed using either screws, staples, or K wires. Each metatarsal was excised and the specimen was loaded to failure in a cantilever beam configuration by applying a superiorly directed force to the metatarsal head using an MTS servohydraulic test machine. Specimens with a crescentic osteotomy that were fixed using a single screw demonstrated higher mean failure moments than pairs that were fixed with four staples or two K wires; staples were the weakest construct. All specimens fixed with staples failed by bending of the staples without bony fracture; all K wire constructs but one failed by wire bending. Chevron and crescentic osteotomies fixed with a single screw demonstrated equal bending strengths; the bending strength of an oblique osteotomy fixed with two screws was 82% greater than for a crescentic osteotomy fixed with a single screw. Basilar osteotomies of the first metatarsal are useful in correcting metatarsus primus varus often associated with hallux valgus pathology. Fixation strength is an important consideration since weightbearing forces on the head of the first metatarsal acting at a distance from the osteotomy site subject the construct to a dorsiflexion bending moment, as simulated in our tests. Our results show that screw fixation is the strongest method for stabilizing a basilar osteotomy. Based upon the relatively low bending strengths of the staple and K wire constructs, we would not recommend these forms of fixation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone strain and microcracks at stress fracture sites in human metatarsals

Microcracks in bone have been implicated in the development of stress fractures. The goal of this study was to evaluate bone strain and microcracks at locations where stress fractures are common (second metatarsal diaphysis) and rare (fifth metatarsal diaphysis) in an attempt to increase our understanding of the pathogenesis of stress fractures. A dynamic gait simulator was used to simulate normal walking with cadaver feet. The feet were loaded over the entire stance phase of gait and diaphyseal strains were recorded in second and fifth metatarsals. Microcrack density (Cr.Dn) and surface density (Cr.S.Dn) were determined in metatarsal cross sections from the contralateral feet. Bone strain was significantly higher in second metatarsals (-1897 +/- 613 microstrain) than in fifth metatarsals (-908 +/- 503 microstrain). However, second metatarsal Cr.Dn (0.23 +/- 0.15 #/mm(2)) was not significantly different from fifth metatarsal Cr.Dn (0.35 +/- 0.19 #/mm(2)). There was also no significant difference between Cr.S.Dn in second (17.64 +/- 10.99 microm/mm(2)) and fifth (26.70 +/- 15.53 microm/mm(2)) metatarsals. There were no significant relationships between the microcrack parameters and peak strain in either metatarsal. Cracks that occurred in trabecular struts (92 +/- 33 microm) were significantly longer than those found ending at cement lines (71 +/- 15 microm) and within osteons (57 +/- 16 microm). There were no significant relationships between the microcrack parameters and age in either metatarsal. Peak strain was more than twofold greater in second metatarsals than in fifth metatarsals for simulations of normal walking; however, microcrack parameters were unable to explain the greater incidence of second metatarsal stress fractures.

Nonlinear finite element analysis for musculoskeletal biomechanics of medial and lateral plantar longitudinal arch of Virtual Chinese Human after plantar ligamentous structure failures

BACKGROUND

Musculoskeletal diseases of the foot such as stress fractures, tendonitis and subsequent pain are commonly associated with elevated stresses/strains of abnormal plantar arch after plantar ligamentous structure failures. The goal of this study was to develop anatomically detailed, finite element models of the medial and lateral plantar longitudinal arch, and to investigate bone and muscle stresses resulting from plantar fasciotomy and major plantar ligament injuries.

METHODS

Nonlinear finite element models of the second ray and the fifth ray of plantar longitudinal arches were constructed on the basis of CT and MR images of Virtual Chinese Human "female No. 1". The models assumed a balanced standing load configuration. Three different degrees of passive intrinsic muscle tensions (weak, moderate, or severe) were used in conjunction with simulations of plantar fasciotomy and major plantar ligament injury.

FINDINGS

Plantar fasciotomy caused von Mises stress increases in the bones and plantar ligaments while major plantar ligament injuries caused stress increases in the bones, flexor tendons, and plantar fascia. Increasing intrinsic muscle passive tensions decreased stress/strain levels in the medial and lateral arch, and adjusted abnormal tension/compression stress flows of both arches to close to the normal biomechanical states.

INTERPRETATION

This study shows that plantar longitudinal arches are concordant combination of bony structures, intrinsic muscles, plantar fascia and ligaments. After plantar ligamentous structure failures, intrinsic muscles have to contribute to stabilize the plantar arches. This mechanism may reduce the risk of developing stress fractures, tendonitis and pain syndrome.

Hypermobility of the first ray: a critical review of the literature

The authors provide a detailed review of the available literature regarding first ray sagittal plane direction and range of motion with special emphasis on whether or not hypermobility of the first ray can truly be supported as a definable clinical entity. They also describe a novel clinical test for assessing sagittal plane instability of the first ray. The authors believe that this test, when combined with previously defined clinical tests, helps to identify those few patients that would benefit from an arthrodesis procedure of the medial pillar of the foot for the treatment of the hallux valgus deformity.

Metatarsal strains are sufficient to cause fatigue fracture during cyclic overloading

Human in vivo tibial strains during vigorous walking have not been found to exceed 1200 microstrains. These values are below those found in ex vivo studies (>3000 microstrains) to cause cortical bone fatigue failure, suggesting that an intermediate bone remodeling response may be associated with tibial stress fractures. Metatarsal stress fractures, however, often develop before there is time for such a response to occur. Simultaneous in vivo axial strains were measured at the mid diaphysis of the second metatarsal and the tibia in two subjects. Peak axial metatarsal compression strains and strain rates were significantly higher than those of the tibia during treadmill walking and jogging both barefoot and with running shoes and during simple calisthenics. During barefoot treadmill walking metatarsal compression strains were greater than 2500 microstrains. During one- and two-leg vertical jumps and broad jumping, both metatarsal compression and tension strains were >3000 microstrains. Compression and tension strains in the metatarsus unlike those of the tibia may be sufficiently high even during moderate exertional activities to cause fatigue failure of bone secondary to the number of loading cycles without an intermediate bone remodeling response.