MECHANICAL COMPARISON OF CYCLIC LOADING IN FIVE DIFFERENT FIRST METATARSAL SHAFT OSTEOTOMIES
January 1st, 2002
Jorge I. Acevedo, MD; V. James Sammarco, MD; Henry R. Boucher, MD;
Brent G. Parks, MSc; Lew C. Schon, MD; Mark S. Myerson, MD
ABSTRACT
The purposes of the current study were: 1) to analyze the relative fatigue endurance of five different first metatarsal shaft osteotomies (proximal crescentic, proximal chevron, Ludloff, Mau, and Scarf), as performed on sawbone models using the most common fixation techniques (part I); and 2) to compare the two more commonly used techniques (per part I results) in matched-pair cadaver specimens (part II). In part I, the proximal chevron and Mau osteotomies were significantly more stable (P 0.005) than all other osteotomies except the Ludloff. In part II, there was no significant difference in fatigue endurance between the proximal chevron and Ludloff osteotomies.
Key Words: metatarsal, osteotomy, hallux valgus, biomechanics, fatigue failure
INTRODUCTION
Many procedures have been developed for the correction of moderate to severe hallux valgus deformities with large intermetatarsal angles.1,3,15,17,18,20,28 For angular deformities, proximal first metatarsal shaft osteotomies afford more correction than do distal osteotomies.12 The more common proximal osteotomies are the proximal crescentic,18 proximal chevron,28 oblique shaft (Ludloff),17 reverse oblique shaft (Mau),20 and rotational “Z” (Scarf) osteotomies.1 The proximal crescentic and proximal chevron osteotomies have become the standard for the correction of metatarsus primus varus.8,18,19,21,28,34 Among the European and podiatric communities, the Ludloff, Mau oblique, and Scarf osteotomies have more recently gained popularity. At our institution, the Ludloff osteotomy is currently the most commonly used osteotomy.
Stability of all of these osteotomies is critical to allow osseous union and to prevent malunion. Regardless of adequate fixation of the first metatarsal osteotomy, dorsal angulation has been reported to occur in up to 82% of patients undergoing the procedure.26 Although this angulation may occur as an intraoperative technical failure, postoperative dorsiflexion can similarly occur as a result of early weightbearing on a relatively unstable osteotomy.26,33-35 Dorsiflexion malunion may subsequently lead to the development of new transfer lesions of the lesser toes or persistence of existing lesions.8,24,30,35
Previous biomechanical studies have compared first metatarsal osteotomies regarding bending stiffness and ultimate (catastrophic) failure loads.14,21,22,25,31 Although catastrophic failure is possible, the postoperative clinical situation does not involve a single-cycle overload unless there is associated trauma. Such studies, however, provide maximum failure levels that may be useful in selecting applied fatigue loads.
To our knowledge, there have been no published biomechanical studies evaluating the relative fatigue strengths of metatarsal shaft osteotomies. The purposes of the current study were to analyze the relative fatigue endurance of five different first metatarsal shaft osteotomies, as performed on sawbone models using the most common fixation techniques (part I), and to compare the two more commonly used techniques (based on the results of part I) in matched-pair cadaver specimens (part II).
PART I. SAWBONE COMPARISON
Materials and Methods
Specimen preparation. Seventy-four sawbone models (Pacific Research, Vashon, WA) were used to mechanically test five different first metatarsal shaft osteotomies. After instrumentation, each sawbone model was secured in an MTS Mini Bionix load frame (MTS Systems, Corp. Eden Prairie, MN). Pilot tests (in three-point bending) conducted on seven random specimens confirmed the reproducibility of the sawbone model. Fifteen osteotomies were tested in the sawbone models to determine an average static failure load (the static failure load is used as a baseline on which to base the maximum load for the fatigue tests). We then compared the relative fatigue endurance of five osteotomies on 52 models (11 crescentic, 11 chevron, 12 Ludloff, nine Mau, and nine Scarf), and the number of cycles to failure was recorded for each specimen.
Proximal crescentic osteotomy. The proximal crescentic osteotomy was performed with the technique described by Mann et al.18 (Fig. 1a). A 3.5-mm glide hole was predrilled at a 45° angle to the dorsal cortex, 1 cm distal to the planned osteotomy site. A curved saw blade (Zimmer, Warsaw, IN) was then used to make the osteotomy 1 cm distal to the metatarsocuneiform joint with the concavity facing proximally. After rotating the metatarsal, the proximal hole was drilled with a 2.5-mm drill bit and the osteotomy was secured with a 4.0-mm cancellous lag screw.
Proximal chevron osteotomy. This osteotomy28 was made with a microsagittal saw at an angle of approximately 80° at the apex, and the cut was directed distally 1.5 cm from the tarsometatarsal joint (Fig. 1b). Before completing the osteotomy, the apex was marked and predrilled with a 0.062-inch K-wire. The distal fragment was then shifted 5 mm laterally and held in position with a guidewire for a 3.5-mm cannulated screw. The guidewire was overdrilled with a 2.7-mm drill bit, followed by insertion of the 3.5-mm cortical screw directed plantar to dorsal.
Ludloff oblique osteotomy. The Ludloff oblique osteotomy17 was performed approximately 5 mm from the metatarsocuneiform joint, extending distally and plantarly, and ending 1 cm proximal to the sesamoid complex (Fig. 1c). Only the dorsal two-thirds of the cut was performed initially to allow for the placement of a 3.5-mm cannulated positioning screw (using the same technique as described above) directed dorsal to plantar in the metatarsal. After placing, but not totally seating, the position screw, the osteotomy was completed and rotated 8°. A second 3.5-mm cortical screw was inserted from plantar to dorsal, 1 cm distal to the first screw.
Mau oblique osteotomy. This osteotomy20 was performed similarly to the Ludloff oblique osteotomy, except that it was directed from the dorsal aspect of the distal metatarsal neck and angled plantarly toward the proximal metatarsal base (Fig. 1d). As in the Ludloff procedure, the dorsal two-thirds of the osteotomy was performed first, and two 3.5-mm cortical screws were placed 1 cm apart for fixation.
Scarf osteotomy. The Scarf osteotomy1 is a horizontally directed displacement Z-osteotomy performed at the diaphyseal level (Fig. 1e). Two 0.045-inch K-wires were placed medial to lateral at the apex of the proximal and distal limbs of the Z. The distal limb was then cut through the dorsal cortex at a 45° angle to the horizontal limb, and the proximal limb was directed plantarly at a similar angle. The horizontal cut was approximately 3 cm in length and was angled 20° plantarly. The dorsal fragment was then translated laterally one-half of the metatarsal width and secured with two 3.5-mm cannulated cortical screws.
Data Analysis
Testware SX (MTS Systems Corp.) was used for data collection, and statistical analysis was performed with the SPSS statistics program (SPSS Inc., Plover, WI). The Kruskal-Wallis one-way ANOVA test was used for statistical analysis of the sawbone fatigue data. A Bonfiori modification was applied that set the level of significance at P 0.005.
Results
Cycles to failure. The mean number of cycles to failure for the five osteotomies tested were: Mau, 1062.6 ± 389.5; proximal chevron, 2215.7 ± 192.2; Ludloff, 389.4 ± 313.0; proximal crescentic, 38.6 ± 21.6; and Scarf, 12.0 ± 2.9 (Table I). Statistical analysis revealed the proximal crescentic osteotomy to be significantly weaker in fatigue (P < 0.005) than the Mau or the proximal chevron osteotomies (Table II). The proximal chevron and Mau osteotomies were significantly (P < 0.005) more resistant to fatigue than all the other osteotomies except for the Ludloff osteotomy. The Scarf osteotomy was the least resistant to fatigue of all osteotomies tested. The data of three of the sawbone models (one each in the proximal chevron, Ludloff, and proximal crescentic osteotomy groups) were eliminated because their values were greater than two standard deviations from the mean.
Failure modes. In the sawbone models, the predominant modes of failure were: Mau osteotomy, fracture at the screw site; proximal chevron and Ludloff osteotomies, fracture at the screw site and gapping; proximal crescentic osteotomy, gapping; and Scarf osteotomy, fracture through the apex of the proximal limb and gapping. Increased gapping caused most failures (27/52) overall (Table I).
PART II. CADAVER COMPARISON
Materials and Methods
Mechanical Testing. Based on the results of part I, the two more commonly performed techniques were compared. We chose to test the Chevron and the Ludloff osteotomies in a cadaver model. Although the Mau had superior strength compared to the Ludloff, the Mau osteotomy does not give the level of correction that the Ludloff osteomy provides. The Mau provides the same level of correction provided by distal osteotomies. We used eight matched pairs of fresh-frozen cadaver lower extremities to mechanically test the chevron and Ludloff osteotomies. To account for further variability among cadaver specimens, bone mineral density was measured (Hologic QDR 1000/W, Bedford, MA) and the values were compared.
Three 0.062-inch K-wires were placed dorsolateral to central, dorsomedial to plantolateral, and plantolateral to dorsal apex (one each) to allow fixation of the metatarsocuneiform joint and to provide anchoring sites for the specimens. No wires crossed the osteotomy sites. Each specimen was then placed in a 2-inch diameter polyvinyl chloride tube with polyester resin. The samples were positioned so that the osteotomy and fixation screws were not incorporated in the resin. An extensometer was then positioned into predrilled holes on the plantar aspect of the proximal and distal fragments of the metatarsal base. The specimen was inclined at a 15° angle on the MTS load frame to simulate the anatomic position (Fig. 2).
Fatigue testing was performed at a load equivalent to 90% of the static failure load of the weakest construct, which correlated with the average peak pressures observed under the first metatarsal during normal walking (280 kPa) (range, 96-615 kPa).5,16 A cyclic cantilever-bend load was applied at a frequency of 3 Hz, the number of cycles to failure was recorded, and failure was defined as bony fracture, screw pull-out, or a gap > 2 mm across the osteotomy site. A run-out limit was set at 300,000 cycles, based on the frequency of loading for an average, physiologically normal, adult lower limb. This was approximated to be 5,000 to 7,000 times per day,5,16 i.e., approximately 50,000 cycles per week and 300,000 cycles over 6 weeks, the time estimated for healing of the osteotomy to occur.
Data Analysis
A Student t-test was used to determine statistical significance, and the level of significance was set at P 0.05.
Results
Of the 16 specimens, 11 ran-out to 300,000 cycles (Table III). The average number of cycles to failure was 244,345 (range, 12-300,000 cycles) and 191,331 (range, 8-300,000 cycles) for the chevron and Ludloff osteotomies, respectively. Bone density values averaged 0.43 g/cm2 (range, 0.16-0.59 g/cm2) and 0.43 g/cm2 (range, 0.17-0.57 g/cm2) for the chevron and Ludloff osteotomies, respectively. Pair number seven was substantially more osteoporotic than the others demonstrating an average density of 0.16 g/cm2, and failure occurred at 12 cycles in the proximal chevron osteotomy and at 8 cycles in the Ludloff osteotomy. With the numbers available for study, we found no statistically significant difference between the matched pairs of cadaver specimens in fatigue endurance (P = 0.36) or bone density (P = 0.98) (Table III).
DISCUSSION
Numerous metatarsal shaft osteotomies have been recommended for the correction of moderate to severe metatarsus primus varus. Currently, the more commonly used procedures are the proximal crescentic, proximal chevron, Ludloff, Scarf, and Mau osteotomies. Although there are several factors that must be considered in the selection of an osteotomy, stability of the construct is paramount to prevent complications such as malunion.
Several studies have noted dorsal angulation and subsequent transfer metatarsalgia as a complication after first metatarsal osteotomy.8,24,30,34,35 In 1991, Pearson et al.26 reported an average 7.1° dorsal angulation in 82% of patients undergoing proximal crescentic osteotomies. Malunion in these patients was frequently not evident on early postoperative radiographs, but was seen 3 to 4 months later. Mann et al.18 noted the incidence of dorsal angulation to be 28% with no new transfer lesions, but 10.4% of pre-existing lesions remained symptomatic. Easley et al.8 noted 17% malunion and two new transfer lesions after proximal crescentic osteotomy. In the latter study, as well as in the series by Sammarco et al.28, no cases of dorsal malunion were observed after proximal chevron osteotomy. Trnka et al.35 observed dorsal angulation and new transfer lesions in 25 and 40% of their closing wedge osteotomies, respectively. Additionally, several studies have suggested a reduced incidence of dorsal malunion and a reduction in development of new transfer lesions with the Mau and Ludloff osteotomies.24,29 Although the Scarf osteotomy has been advocated in the United States and Europe for its intrinsic stability, we could find no clinical study documenting a lower incidence of transfer lesions or dorsal angulation.1,22,30
Regardless of the variable malunion rates reported in clinical studies, all the biomechanical studies evaluating stability of first metatarsal osteotomies have involved static failure testing.14,21,22,25,30,31 In the postoperative scenario, this is analogous to a single-cycle catastrophic failure. Shereff et al.31 were the first to provide a comprehensive analysis of several different fixation constructs. They tested four distal types and one proximal type of osteotomy, and regardless of fixation technique, proximal basilar osteotomies were found to be more unstable than distal osteotomies. This makes sense mechanically because there is a substantially shorter lever arm for the distal osteotomies. Lian et al.14 further evaluated construct geometry and compared static bending failure moments of the proximal crescentic osteotomy with those of the proximal chevron and Ludloff (oblique) osteotomies. The proximal crescentic osteotomy proved to be less stable than either the proximal chevron or Ludloff osteotomy, but only the latter was significantly different (P < 0.05). In another study comparing load-to-failure thresholds, the proximal chevron osteotomy was found to be significantly more stable (P < 0.05) than the proximal crescentic osteotomy.21 In the most comprehensive study of proximal osteotomies, Parks et al.25 found that the Mau, Ludloff, Scarf, and biplanar closing wedge osteotomies (with plantar-plate fixation) were significantly more stable than the proximal chevron and crescentic osteotomies.
Although those studies provide useful baseline data, they cannot be extrapolated to predict fatigue, the most likely mode of failure, in the clinical setting. Unlike the results of static testing, we found the Scarf osteotomy to be significantly weaker (P < 0.005) in fatigue than all other constructs except for the proximal crescentic osteotomy. As with previously reported static failure patterns,22,25 fracture occurred through the dorsal extension of the proximal plantar cut (Fig. 4). This stress riser, on the tension side of the metatarsal, appeared to be a more critical factor when loading in the cyclic mode. In the current study, the proximal chevron osteotomy was relatively more stable than that shown by Parks et al.25 in static studies. However, this difference was most likely the result of screw positioning rather than the actual mode of testing. In the study by Parks et al.,25 screws were placed from dorsal and distal to plantar and proximal, respectively, as opposed to parts I and II of the current study, in which the screw was placed in a plantar to dorsal direction. However, as reported in the static studies, we found that the Mau and Ludloff osteotomies were resistant to fatigue and that the proximal crescentic osteotomy was relatively not fatigue resistant.
Should postoperative weightbearing be allowed after a metatarsal shaft osteotomy? A review of the literature reveals a myriad of recommendations ranging from full weightbearing in a postoperative shoe to non-weightbearing with cast immobilization.8,14,18,31,35 The reported peak pressures under the first metatarsal during walking vary from 96 to 615 kPa.2,4,6,7,9-11,23,27,35
For part II of our study, we chose 90% of the average reported peak loads: 280 kPa (range, 96-615 kPa). Based on our results, the proximal chevron and Ludloff osteotomies were found to be capable of withstanding this average peak load for the required duration. Except for osteotomies performed in extremely osteoporotic bone, the proximal chevron osteotomy tolerated at least 3 weeks (154,750 cycles) of normal weightbearing loads and in most cases (86%) tolerated up to 6 weeks (300,000 cycles) of normal weightbearing. Although the Ludloff osteotomy can tolerate an equivalent of 6 weeks of weightbearing in most cases, this osteotomy may be more experience-dependent and can therefore fail much earlier in some cases. One Ludloff construct, with a slightly vertical cut, failed at an equivalent of 4 days, whereas another, with a relatively more vertical cut, failed almost catastrophically at an equivalent of ten minutes. Regardless of whether the Ludloff or proximal chevron osteotomy is used, both will be unsuccessful in poor bone quality if unprotected from normal peak pressures.
The current study has several potential limitations. In part I, the sawbone models did not simulate the viscoelastic properties of bone. However, our pilot study with static testing of these sawbones confirmed reproducibility among samples. Previous mechanical studies similarly suggest the reliability of sawbones for determining relative stability even though absolute values are not clinically relevant.13,32 Cadaver testing of five different constructs would have introduced even greater variability in size, shape, and density of specimens. Fatigue testing adds another source of variability owing to its sensitivity to experimental variables.16 Furthermore, the use of cadaver feet stripped of soft tissues and fixation at the metatarsocuneiform joint does not accurately simulate the normal forces surrounding the metatarsal.
In addition, certain approximations were necessary. The peak load (280 kPa) represented 90% of the average peak loads reported in the literature. Had the full load been used, samples would have failed in one cycle. In the current study, we wanted to evaluate cyclic loading in patients not bearing full weight initially. Although the theoretical clinical load under the first metatarsal may be more than 600 kPa,11 most of the pedobarographic studies2,4,7,9,10,27,35 demonstrate much smaller loads. In our clinical experience, most patients do not ambulate with normal metatarsal loads for the initial 2 to 3 weeks postoperatively, even if full weightbearing is allowed. Moreover, the predefined run-out limit of 300,000 cycles was based on approximations for an average, physiologically normal, adult lower limb.5,16 In a 6-week period, the frequency of clinical loading would inevitably vary among different patients.
In summary, our experience, as well as that reported in the literature, is that failure of metatarsal shaft osteotomies and subsequent malunion occurs most frequently in a fatigue mode from repetitive loading. According to our sawbone model comparison, the proximal chevron osteotomy with a plantar to dorsal screw and the Mau osteotomy were mechanically superior in fatigue testing. However, cyclic tests with matched cadaver samples are needed to make any clinical recommendations. Failure in the Ludloff osteotomy was more technique-dependent than that in the proximal chevron osteotomy. Based on average daily frequency of loading approximations, immediate weightbearing after a proximal chevron or Ludloff osteotomy may be tolerated. However, for a patient with poor bone quality or one who requires a more vertically oriented Ludloff osteotomy, protective weightbearing is recommended.
REFERENCES
1. Barouk, L. S.: Scarf osteotomy of the first metatarsal in the treatment of hallux valgus. Foot Dis., 2:35-48, 1995.
2. Baumhauer, J. F., Wervey, R., McWilliams, J., Harris, G. F., and Shereff, M. J.: A comparison study of plantar foot pressure in a standardized shoe, total contact cast, and prefabricated pneumatic walking brace. Foot Ankle Int., 18:26-33, 1997.
3. Borton, D. C., and Stephens, M. M.: Basal metatarsal osteotomy for hallux valgus. J. Bone Joint Surg., 76B:204-209, 1994.
4. Brown, M., Rudicel, S., and Esquenazi, A.: Measurement of dynamic pressures at the shoe-foot interface during normal walking with various foot orthoses using the FSCAN system. Foot Ankle Int., 17:152-156, 1996.
5. Brumback, R. J., Toal, T. R., Jr., Murphy-Zane, M. S., Novak, V. P., and Belkoff, S. M.: Immediate weight-bearing after treatment of a comminuted fracture of the femoral shaft with a statically locked intramedullary nail. J. Bone Joint Surg., 81A:1538-1544, 1999.
6. Cavanagh, P. R., Rodgers, M. M., and Iiboshi, A.: Pressure distribution under symptom-free feet during barefoot standing. Foot Ankle, 7:262-276, 1987.
7. Duckworth, T., Betts, R. P., Franks, C. I., and Burke, J.: The measurement of pressures under the foot. Foot Ankle, 3:130-141, 1982.
8. Easley, M. E., Kiebzak, G. M., Davis, W. H., and Anderson, R. B.: Prospective, randomized comparison of proximal crescentic and proximal chevron osteotomies for correction of hallux valgus deformity. Foot Ankle Int., 17:307-316, 1996.
9. Hennig, E. M., and Rosenbaum, D.: Pressure distribution patterns under the feet of children in comparison with adults. Foot Ankle, 11:306-311, 1991.
10. Hughes, J., Clark, P., Linge, K., and Klenerman, L.: A comparison of two studies of the pressure distribution under the feet of normal subjects using different equipment. Foot Ankle, 14:514-519, 1993.
11. Hutton, W. C., and Dhanendran, M.: The mechanics of normal and hallux valgus feet--a quantitative study. Clin. Orthop., 157:7-13, 1981.
12. Kummer, F. J.: Mathematical analysis of first metatarsal osteotomies. Foot Ankle, 9:281-289, 1989.
13. Landsman, A. S., and Chang, T. J.: Can synthetic bone models approximate the mechanical properties of cadaveric first metatarsal bone? J. Foot Ankle Surg., 37:122-127, 1998.
14. Lian, G. J., Markolf, K., and Cracchiolo, A., III: Strength of fixation constructs for basilar osteotomies of the first metatarsal. Foot Ankle, 13:509-514, 1992.
15. Lippert, F. G., III, and McDermott, J. E.: Crescentic osteotomy for hallux valgus: a biomechanical study of variables affecting the final position of the first metatarsal. Foot Ankle, 11:204-207, 1991.
16. Litsky, A. S., and Spector, M.: Biomaterials. In Simon, S. R. (ed.), Orthopaedic Basic Science, American Academy of Orthopaedic Surgeons, 1994, pp. 447-486.
17. Ludloff, K.: Die beseitigung des hallux valgus durch die schrage planta-dorsale osteotomie des metatarsus I. Arch Klin Chir, 110:364-387, 1918.
18. Mann, R. A., Rudicel, S., and Graves, S. C.: Repair of hallux valgus with a distal soft-tissue procedure and proximal metatarsal osteotomy. A long-term follow-up. J. Bone Joint Surg., 74A:124-129, 1992.
19. Markbreiter, L. A., and Thompson, F. M.: Proximal metatarsal osteotomy in hallux valgus correction: a comparison of crescentic and chevron procedures. Foot Ankle Int., 18:71-76, 1997.
20. Mau, C., and Lauber, H. J.: Die operative Behandlung des Hallux valgus (Nachuntersuchungen). Deutsche Zeit. Orthop., 197:361-377, 1926.
21. McCluskey, L. C., Johnson, J. E., Wynarsky, G. T., and Harris, G. F.: Comparison of stability of proximal crescentic metatarsal osteotomy and proximal horizontal "V" osteotomy. Foot Ankle Int., 15:263-270, 1994.
22. Miller, J. M., Stuck, R., Sartori, M., Patwardhan, A., Cane, R., et al: The inverted Z bunionectomy: quantitative analysis of the scarf and inverted scarf bunionectomy osteotomies in fresh cadaveric matched pair specimens. J. Foot Ankle Surg., 33:455-462, 1994.
23. Minns, R. J., and Craxford, A. D.: Pressure under the forefoot in rheumatoid arthritis. A comparison of static and dynamic methods of assessment. Clin. Orthop., 187:235-242, 1984.
24. Neese, D. J., Zelichowski, J. E., and Patton, G. W.: Mau osteotomy: an alternative procedure to the closing abductory base wedge osteotomy. J. Foot Surg., 28:352-362, 1989.
25. Parks, B. G., Trnka, H.-J., Nyska, M., and Myerson, M. S.: Mechanical comparison of six different first metatarsal shaft osteotomies and the influence of osteotomy type on postoperative immobilization. Presented at the 15th Annual Summer Meeting of the American Orthopaedic Foot and Ankle Society, Fajardo (PR), July 10, 1999.
26. Pearson, S. W., Kitaoka, H. B., Cracchiolo, A., III, and Leventen, E. O.: Results and complications following a proximal curved osteotomy of the hallux metatarsal. Contemp. Orthop., 23:127-132, 1991.
27. Rose, N. E., Feiwell, L. A., and Cracchiolo, A., III: A method for measuring foot pressures using a high resolution, computerized insole sensor: the effect of heel wedges on plantar pressure distribution and center of force. Foot Ankle, 13:263-270, 1992.
28. Sammarco, G. J., Brainard, B. J., and Sammarco, V. J.: Bunion correction using proximal Chevron osteotomy. Foot Ankle, 14:8-14, 1993.
29. Saxena, A., and McCammon, D. : The Ludloff osteotomy: a critical analysis. J. Foot Ankle Surg., 36:100-105; disc. 159-160, 1997.
30. Schwartz, N., and Groves, E. R.: Long-term follow-up of internal threaded Kirschner-wire fixation of the scarf bunionectomy. J. Foot Surg., 26:313-316, 1987.
31. Shereff, M. J., Sobel, M. A., and Kummer, F. J.: The stability of fixation of first metatarsal osteotomies. Foot Ankle, 11:208-211, 1991.
32. Szivek, J. A., Thomas, M., and Benjamin, J. B.: Characterization of a synthetic foam as a model for human cancellous bone. J. Appl. Biomater., 4:269-272, 1993.
33. Thompson, F. M.: Complications of hallux valgus surgery and salvage. Orthopedics, 13:1059-1067, 1990.
34. Thordarson, D. B., and Leventen, E. O.: Hallux valgus correction with proximal metatarsal osteotomy: two- year follow-up. Foot Ankle, 13:321-326, 1992.
35. Trnka, H.-J., Muhlbauer, M., Zembsch, A., Hungerford, M., Ritschl, P., et al: Basal closing wedge osteotomy for correction of metatarsus primus varus: 10- to 22- year follow-up. Foot Ankle Int., 20:171-177, 1999.
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