Supplementary axial Kirschner wire fixation for crescentic and Ludloff proximal metatarsal osteotomies: a biomechanical study

BACKGROUND: Loss of reduction of proximal metatarsal osteotomies may result from poor bone quality, suboptimal fixation, and limitations inherent in the bony geometry of the osteotomy. This study evaluated the mechanical benefit of adding two supplementary Kirschner wires to the crescentic and Ludloff osteotomies. METHODS: Eleven and 10 matched pairs of cadaver foot specimens were used for the Ludloff and the proximal crescentic metatarsal osteotomies, respectively. Each metatarsal head specimen was then loaded to failure using a servohydraulic MTS Mini Bionix test frame (MTS Systems Corp, Eden Prairie, MN), and the failure gap was measured with an extensometer. To account for variable bone quality in the study specimens, the failure loads were normalized with the measured bone mineral density (BMD) values of the metatarsal specimens. A paired Student's t-test analysis was used to compare the failure loads between the specimens with the conventional osteotomies and the osteotomies supplemented with two axial Kirschner wires. RESULTS: The load-to-failure of the Ludloff osteotomy with two screws and with one proximal screw and two Kirschner wires was 858.5 N cm(2)/gm and 692.3 N cm(2)/gm, respectively (p > 0.05). The average load-to-failure of crescentic osteotomy with one screw and two axial Kirschner wires (458.8 N cm(2)/gm) was significantly higher than the strength of crescentic osteotomy fixed with one screw only (367.5 N cm(2)/gm) (p = 0.05). For the Ludloff osteotomy, 16 specimens (72.7%) failed by more than 2 mm of gapping. The crescentic osteotomy failures included 16 2-mm gap failures (80%). The Ludloff osteotomy showed a trend toward increased fixation stability as compared with both crescentic osteotomy constructs. CONCLUSION: The use of two supplemental axial Kirschner wires offers a simple and effective means to improve the initial mechanical stability of the proximal crescentic osteotomy and can be used in the standard Ludloff osteotomy to replace the second screw when screw purchase is poor without significant loss of fixation strength. The possible advantage of Kirschner wire flexibility in restoring position after gapping of the osteotomy site should be investigated.     

Stability of a cannulated screw versus a Kirschner wire for the proximal crescentic osteotomy of the first metatarsal: a biomechanical study.

The purpose of this study was to compare the stability of a Kirschner wire (K-wire) versus a single cannulated screw for fixation of the proximal crescentic first metatarsal osteotomy. Seven matched pairs of fresh-frozen human cadaver first metatarsal specimens were dissected out en bloc at the first metatarsal-medial cuneiform complex; right and left specimens were randomized as to fixation. In screw specimens, a cannulated screw was mounted from the proximal medial side of the metatarsal, traversing osteotomy and engaging the lateral diaphyseal cortical bone. In the corresponding specimen, a K-wire was placed from the distal medial metatarsal cortex oriented as close to the longitudinal metatarsal axis as possible. Using a materials testing machine, a continuous load was applied to the plantar aspect of the metatarsal head at a rate of 5 mm/min until a displacement of 10 mm was reached. The following parameters were measured: initial stiffness of the entire specimen, stiffness of the osteotomy, the force required to create a 1-mm displacement, the force required to create a 0.15-mm gap across the osteotomy, and the ultimate force to create the 10-mm displacement. Both specimen and osteotomy stiffness were found to be significantly higher for screw fixation versus the K-wire (P <.05). Although there was also a difference in the force-to-failure load in favor of screw fixation, this result was found not found to be statistically significant.     

Proximal crescentic metatarsal osteotomy: the effect of saw blade orientation on first ray elevation

BACKGROUND: Moderate and severe hallux valgus deformities generally require a proximal metatarsal osteotomy to correct a widened intermetatarsal angle. Although excellent results have been reported using the proximal crescentic osteotomy, concerns have been raised about the incidence of postoperative dorsal malunion, which may lead to transfer lesions. The objectives of this paper were to evaluate the influence of saw blade angulation on the final position of the first metatarsal and to test a new technique used to ensure proper orientation of the osteotomy. METHODS: For part I of the study, 26 Sawbones specimens with hallux valgus deformities were corrected using a proximal crescentic osteotomy with the saw blade position incrementally rotated in the coronal plane. The sagittal change in the final position of the metatarsal was quantified radiographically and correlated to the saw blade orientation. For part II of the study, a Kirschner wire was placed in a vertical position into the medial cuneiform to serve as a guide for the crescentic saw blade in 13 cadaver feet with hallux valgus. Metatarsus primus elevatus was measured after surgical correction. RESULTS: Part I of the study demonstrated a highly linear relationship (R2=0.95) between first metatarsal elevation and the orientation of the saw blade. Every 10-degree of saw blade angulation resulted in a 2-mm change in the sagittal position of the first metatarsal. In part II of the study, the average change in metatarsus primus elevation for the 13 specimens after surgical correction of the hallux valgus deformity was only 1.1 mm (range -3.9 to +4.9 mm). Eleven of the 13 specimens had less than 2.5 mm of elevatus. CONCLUSION: Dorsal malunion of the first metatarsal after proximal crescentic osteotomy is a recognized complication. The final position of the hallux metatarsal is influenced by the coronal plane orientation of the saw. A new technique is described to aid the surgeon in proper alignment of the saw and help prevent excessive first ray elevation.     

Strength of fixation of Ludloff metatarsal osteotomy utilizing three different types of Kirschner wires: a biomechanical study

Static biomechanical studies have demonstrated that the Ludloff shaft metatarsal osteotomy is significantly more stable than other commonly used proximal (basilar) osteotomies, such as the proximal crescentic and the proximal chevron. High average static bending failure moments have been recorded for the screw fixation Ludloff osteotomy construct. The objective of the current study was to find a reasonable alternative method of fixation in cases where a short osteotomy may not be amenable to adequate screw fixation and in cases where an inadvertent intraoperative fracture of the metatarsal occurs and subsequent screw fixation is precarious due to inadequate bone stock. A Ludloff osteotomy was performed on 24 matched pairs of cadaveric specimens to compare the strength of fixation of three different types of Kirschner wires (smooth, threaded, and SOC threaded). Biomechanical testing with plantar force was carried out, and failure load and stiffness were measured for each specimen. The current results indicate that the threaded pin construct provides adequate strength for fixation of the Ludloff osteotomy in the clinical setting.     

The effect of screw type on the biomechanical properties of SCARF and crescentic osteotomies of the first metatarsal

The basilar crescentic osteotomy is a popular method for correcting moderate to severe hallux valgus. However, inadvertent dorsiflexion of the osteotomy can result from intraoperative malposition or from malunion after fixation failure. The mechanical properties of osteotomies are dependent on the nature of the osteotomy and the type of fixation. This study examines the mechanical properties of the SCARF and crescentic osteotomies of the first metatarsal by using a cannulated asymmetric pitched screw or AO cancellous screws. Sixteen human cadaveric first metatarsal specimens were tested in plantar to dorsiflexion cantilever bending by using a mechanical testing machine. The data was compared with our recent work on the mechanical properties of the SCARF and crescentic osteotomies. Ultimate load and stiffness of the SCARF osteotomy were superior to the crescentic osteotomy but were not dependent on screw type. Screw type was a prominent factor in the stiffness but not in the strength of the crescentic osteotomy. The ultimate load and the stiffness of SCARF osteotomy fixed with the cannulated asymmetric pitched screws were not significantly different compared with AO screws (ultimate load, 124.6 N [SD = 56.8] v 105.3 N [SD = 57.0]; stiffness, 52.0 N/mm [SD = 48.0] v 31.8 N/mm [SD = 19.0]). Modes of failure were fracture of the cortical bone bridge between the screw hole and the osteotomy in all crescentic osteotomies and fracture of the proximal dorsal bridge in all SCARF osteotomies. The superior mechanical properties of the SCARF osteotomy, fixed with cannulated asymmetric pitched screws, make this a more secure construct, with less risk of malunion than the crescentic osteotomy. Stiffness is an important mechanical factor that helps distinguish the mechanical performance of different osteotomy techniques.     

Biomechanical Comparison of Internal Fixation Techniques for the Akin Osteotomy of the Proximal Phalanx

The Akin osteotomy is performed at the proximal phalanx for correction of an abducted great toe in a hallux abducto valgus deformity. Several internal fixation techniques have been widely advocated; however, their respective stabilities have not been compared. A biomechanical analysis was performed comparing 5 commonly used fixation techniques for the Akin osteotomy to determine the strongest method in simulated weightbearing in sawbone models. An Akin osteotomy was uniformly performed on 25 sawbones and fixated with 5 different internal fixation types, including a 2-hole locking plate and locking screws, a heat-sensitive memory staple (8 mm × 8 mm), a 28-gauge monofilament wire, 2.7-mm bicortical screws, and crossed 0.062-in. Kirschner wires. The results of simulated weightbearing load to failure rates with an Instron compression device demonstrated the following mean load to failures: crossed Kirschner wire, 57.05 N; 2-hole locking plate, 36.49 N; monofilament wire, 35.69 N; heat-sensitive memory staple, 34.32 N; and 2.7-mm bicortical screw, 13.66 N. Statistical analysis demonstrated the crossed Kirschner wire technique performed significantly better than the other fixation techniques (p < .007); the 4 other techniques were found not to be significantly different statistically (p = .041) from each another. Our study results suggest a crossing Kirschner wire construct significantly increases the stability of the Akin osteotomy in a sawbone model. This might be clinically extrapolated in an effort to improve patient outcomes because these osteotomies can undergo nonunion and malunion, resulting in postoperative pain and swelling.     

Biomechanical analysis of two fixation methods for proximal chevron osteotomy of the first metatarsal

Purpose

The proximal chevron osteotomy provides high correctional power. However, relatively high rates of dorsiflexion malunion of up to 17 % are reported for this procedure. This leads to insufficient weight bearing of the first ray and therefore to metatarsalgia. Recent biomechanical and clinical studies pointed out the importance of rigid fixation of proximal metatarsal osteotomies. Therefore, the aim of the present study was to compare biomechanical properties of fixation of proximal chevron osteotomies with variable locking plate and cancellous screw respectively.

Methods

Ten matched pairs of human fresh frozen cadaveric first metatarsals underwent proximal chevron osteotomy with either variable locking plate or cancellous screw fixation after obtaining bone mineral density. Biomechanical testing included repetitive plantar to dorsal loading from 0 to 31 N with the 858 Mini Bionix^® (MTS^® Systems Corporation, Eden Prairie, MN, USA). Dorsal angulation of the distal fragment was recorded.

Results

The variable locking plate construct reveals statistically superior results in terms of bending stiffness and dorsal angulation compared to the cancellous screw construct. There was a statistically significant correlation between bone mineral density and maximum tolerated load until construct failure occurred for the screw construct (r = 0.640, p = 0.406).

Conclusion

The results of the present study indicate that variable locking plate fixation shows superior biomechanical results to cancellous screw fixation for proximal chevron osteotomy. Additionally, screw construct failure was related to levels of low bone mineral density. Based on the results of the present study we recommend variable locking plate fixation for proximal chevron osteotomy, especially in osteoporotic bone.     

Relative Strength of Tailor’s Bunion Osteotomies and Fixation Techniques

A paucity of data is available on the mechanical strength of fifth metatarsal osteotomies. The present study was designed to provide that information. Five osteotomies were mechanically tested to failure using a materials testing machine and compared with an intact fifth metatarsal using a hollow saw bone model with a sample size of 10 for each construct. The osteotomies tested were the distal reverse chevron fixated with a Kirschner wire, the long plantar reverse chevron osteotomy fixated with 2 screws, a mid-diaphyseal sagittal plane osteotomy fixated with 2 screws, the mid-diaphyseal sagittal plane osteotomy fixated with 2 screws, and an additional cerclage wire and a transverse closing wedge osteotomy fixated with a box wire technique. Analysis of variance was performed, resulting in a statistically significant difference among the data at p <.0001. The Tukey-Kramer honestly significant difference with least significant differences was performed post hoc to separate out the pairs at a minimum α of 0.05. The chevron was statistically the strongest construct at 130 N, followed by the long plantar osteotomy at 78 N. The chevron compared well with the control at 114 N, and they both fractured at the proximal model to fixture interface. The other osteotomies were statistically and significantly weaker than both the chevron and the long plantar constructs, with no statistically significant difference among them at 36, 39, and 48 N. In conclusion, the chevron osteotomy was superior in strength to the sagittal and transverse plane osteotomies and similar in strength and failure to the intact model.     

Six first metatarsal shaft osteotomies: mechanical and immobilization comparisons

Because malunion (usually with dorsal elevation of the first metatarsal) has been reported after the treatment of severe hallux valgus deformities by proximal osteotomies, the current study was designed to compare the sagittal stability of six different metatarsal shaft osteotomies: the proximal crescentic, proximal chevron, Mau, Scarf, Ludloff, and biplanar closing wedge osteotomies. A plate was used in the biplanar closing wedge osteotomy; all others used screws for fixation. Ten fresh-frozen, human anatomic lower extremity specimens were used for each osteotomy. Failure loads were measured as units of force (newtons) and converted to pressure (kilopascals). Then the F-Scan system, which uses a thin insole to measure plantar pressure, was used to evaluate the pressure under the first metatarsal of seven volunteers using four types of shoes. According to the results, in patients with normal bone stock who are compliant, any of the four shoe types tested may be used after a Ludloff, Scarf, biplanar wedge (plantar screw fixation), or Mau osteotomy, but the wedge-based shoe should be used after a proximal crescentic or chevron osteotomy or for patients with severe osteopenic bone.     

First metatarsal-phalangeal joint arthrodesis: a biomechanical assessment of stability

BACKGROUND: First metatarsal phalangeal joint (MTP) arthrodesis is a commonly performed procedure for the treatment of hallux rigidus, severe and recurrent bunion deformities, rheumatoid arthritis and other less common disorders of the joint. There are different techniques of fixation of the joint to promote arthrodesis including oblique lag screw fixation, lag screw and dorsal plate fixation, crossed Kirschner wires, dorsal plate fixation alone and various types of external fixation. Ideally the fixation method should be reproducible, lead to a high rate of fusion, and have a low incidence of complications. METHODS: In the present study, we compared the strength of fixation of five commonly utilized techniques of first MTP joint arthrodesis. These were: 1. Surface excision with machined conical reaming and fixation with a 3.5 mm cortical interfragmentary lag screw. 2. Surface excision with machined conical reaming and fixation with crossed 0.062 Kirschner wires. 3. Surface excision with machined conical reaming and fixation with a 3.5 mm cortical lag screw and a four hole dorsal miniplate secured with 3.5 mm cortical screws. 4. Surface excision with machined conical reaming and fixation with a four hole dorsal miniplate secured with 3.5 mm cortical screws and no lag screw. 5. Planar surface excision and fixation with a single oblique 3.5 mm interfragmentary cortical lag screw. Testing was done on an Instron materials testing device loading the first MTP joint in dorsiflexion. Liquid metal strain gauges were placed over the joint and micromotion was detected with varying loads and cycles. RESULTS: The most stable technique was the combination of machined conical reaming and an oblique interfragmentary lag screw and dorsal plate. This was greater than two times stronger than an oblique lag screw alone. Dorsal plate alone and Kirschner wire fixation were the weakest techniques. CONCLUSIONS: First MTP fusion is a commonly performed procedure for the treatment of a variety of disorders of the first MTP joint. The most stable technique for obtaining fusion in this study was the combination of an oblique lag screw and a dorsal plate. This should lead to higher rates of arthrodesis.     

Clinical results with the Ludloff osteotomy for correction of adult hallux valgus

BACKGROUND: Biomechanically, the Ludloff osteotomy fixed with lag screw compression has been shown to be more rigid than proximal crescentic and other proximal first metatarsal osteotomies for correction of symptomatic hallux valgus with a moderate to severe increase in the first intermetatarsal angle. The Ludloff osteotomy may, therefore, have a lower incidence of dorsal malunion and transfer metatarsalgia than other proximal first metatarsal osteotomies, such as the crescentic or chevron. METHODS: We reviewed the results of 82 consecutive cases of moderate to severe hallux valgus deformities corrected with the Ludloff oblique metaphyseal-diaphyseal osteotomy of the first metatarsal combined with a distal soft-tissue procedure and medial eminence resection. RESULTS: Follow-up was possible in 70 cases (85%) at an average of 30 months (range, 18 to 42 months). Preoperatively, the mean hallux valgus and first intermetatarsal angles were 31 degrees and 16 degrees, respectively. Postoperatively, these values improved to an average of 11 degrees and 7 degrees. In the sagittal plane, the first metatarsal was plantarflexed by an average of 1 mm, and there were no symptomatic transfer lesions of the second metatarsal. The mean AOFAS hindfoot score improved from 54 to 91 points. Complications included prominent hardware requiring removal (5), hallux varus (4), delayed union (3), superficial infection (3), and neuralgia (3). CONCLUSIONS: The use of the Ludloff oblique first metatarsal osteotomy resulted in excellent correction of the first intermetatarsal angle in patients with moderate to severe hallux valgus. With the plane of the osteotomy and rigidity of fixation, immediate ambulation was possible with minimal risk of dorsiflexion malunion of the first metatarsal.     

尺骨上段合并鹰嘴骨折内固定的生物力学研究

目的比较克氏针张力带、重建钢板联合张力带及鹰嘴解剖钢板固定尺骨上段合并鹰嘴骨折3种方式的生物力学稳定性,为临床选择内固定提供理论依据。方法 8个自愿捐献的新鲜成人尸体肘关节标本,均为男性;年龄26～43岁,平均34.8岁。于尺骨上段及尺骨鹰嘴分别截骨制作尺骨上段合并鹰嘴骨折模型。每个标本分别采用克氏针张力带(A组)、重建钢板联合张力带(B组)及鹰嘴解剖钢板(C组)3种方式对骨折端固定。采用生物力学测试系统进行单轴压缩试验,记录载荷-位移曲线,内固定系统的稳定性采用骨折端压缩位移为2 mm时所加的载荷值进行评价。结果实验过程中未出现克氏针退出、钢板螺钉断裂、标本破坏,标本与夹具固定无松动。3组标本均表现为位移随载荷增加而逐渐增长,但B、C组的载荷-位移曲线斜率明显高于A组。当骨折端压缩位移为2 mm时,A、B、C组的所加载荷值分别为(218.6±66.9)、(560.3±116.1)、(577.2±137.6)N,B、C组所加载荷值均显著高于A组,差异有统计学意义(P<0.05);B、C组间差异无统计学意义(t=0.305,P=0.763)。结论尺骨上段合并鹰嘴骨折多为不稳定骨折,重建钢板联合张力带、鹰嘴解剖钢板固定均能满足要求,临床上可根据患者情况合理选用。克氏针张力带固定不够牢固,临床上应避免单独使用。     

Plantar-to-dorsal compared to dorsal-to-plantar screw fixation for proximal chevron osteotomy: a biomechanical analysis

BACKGROUND: A change in screw orientation in fixing the chevron proximal first metatarsal osteotomy was noted anecdotally to improve fixation strength. The authors hypothesized that plantar-to-dorsal screw orientation would be more stable than the conventional dorsal-to-plantar screw orientation for fixation of the chevron osteotomy. The purpose of this study was to determine if the load-to-failure and stiffness of the chevron type proximal first metatarsal osteotomy stabilized using plantar-to-dorsal screw fixation were greater than with the more conventional dorsal-to-plantar screw fixation method. METHODS: One foot from each of eight matched cadaver pairs was randomly assigned to one of two groups: 1) fixation with a dorsal-to-plantar lag screw or 2) fixation with a plantar-to-dorsal lag screw. A proximal chevron osteotomy was then created using standard technique and the metatarsal was fixed according to previously established method. The bone was potted in polyester resin, and the construct was fitted into a materials testing system machine in which load was applied to the plantar aspect of the metatarsal until failure. The two groups were compared using a two-tailed Student t test. RESULTS: The average load-to-failure and stiffness of the chevron osteotomy fixed with the plantar-to-dorsal lag screw were significantly greater (p < 0.05) than the group fixed with more conventional dorsal-to-plantar lag screws. CONCLUSION: Plantar-to-dorsal screw orientation was more stable than the conventional dorsal-to-plantar screw orientation for fixation of the proximal chevron osteotomy. Plantar-to-dorsal screw orientation should be considered when using the chevron proximal first metatarsal osteotomy.     

Plate fixation for crescentic metatarsal osteotomy in the treatment of hallux valgus: an eight-year followup study

BACKGROUND: Distal soft tissue realignment and crescentic metatarsal osteotomy is a popular procedure in the treatment of hallux valgus. The traditional technique of screw fixation for crescentic osteotomy is technically demanding, and the inferior stability of this construct has been described. We evaluated the long-term results of a modified fixation method. METHODS: Twenty-six patients (32 feet) undergoing this procedure were retrospectively reviewed. Five patients (six feet) were lost to followup. Mean age of the patients was 47 (14 to 74) years. The osteotomy was fixed with a 2.7 mm AO plate. Assessment of clinical and radiographic results was performed at a mean followup of 2.7 (1.3 to 7.2) years and 8.0 (6.1 to 12.0) years, respectively. RESULTS: The mean American Orthopaedic Foot and Ankle Society (AOFAS) score improved from 57.9 to 90.5 at 2.7 years of mean followup, whereas the patient satisfaction rate was 96%. The intermetatarsal angle (IMA) and hallux valgus angle (HVA) improved from the mean preoperative values of 16.1 degrees and 34.2 degrees to 9.5 degrees and 16.3 degrees. At eight years of mean followup, the mean AOFAS score and patient satisfaction rate remained at 88.5% and 92%. The mean IMA and mean HVA were 9.7 degrees and 17.0 degrees. Complications included one case of hallux varus (4%) and two cases of recurrence (8%). The osteotomy achieved union in all cases. CONCLUSIONS: Dorsal plate fixation of crescentic metatarsal osteotomy is a technically easier procedure. Equally good results can be achieved when compared with screw fixation methods, and the results can be maintained long-term.     

Fixation of the offset V osteotomy: Mechanical testing of 4 constructs

The purpose of this study was to assess 4 methods of fixation for the offset V osteotomy. Maximum load, failure energy, and stiffness were determined in a control group and in 4 different test models. There were 10 specimens for each group. The control group consisted of intact first ray sawbones. An offset V osteotomy was performed on each specimen in each of the 4 test groups. The osteotomies were fixated either with two 2.0-mm cortical screws, two 2.7-mm cortical screws, two 3.5-mm cortical screws, or one 2.7-mm cortical screw and a 0.045-in Kirschner wire, respectively. Each model was then loaded to failure with a computerized hydraulic-tensile testing machine. Results for maximum load to failure for all 4 fixation constructs showed a mean ranging from 113.0 to 144.0 N, a mean energy to failure ranging from 272.2 to 365.0 J, and a mean stiffness ranging from 21.3 to 27.0 N/mm. There were no statistically significant differences detected among the individual constructs. In the group fixated with 3.5-mm screws, there were statistically significant differences in all 3 parameters compared with the control group. In the groups fixated with 2.7-mm screws, 2.0-mm screws, and the 2.7-mm screw and Kirschner wire, there were statistically significant differences in the maximum load and the failure energy, but not in stiffness, when compared with the control group. These findings suggest that all 4 constructs provide similar mechanical properties when utilized for the fixation of the offset V osteotomy.     

Crossed screws versus dorsomedial locking plate with compression screw for first metatarsocuneiform arthrodesis: a cadaver study

BACKGROUND: We hypothesized that a dorsomedial locking plate with adjunct screw compression would provide superior rigidity compared to crossed screws for first metatarsocuneiform (MTC) arthrodesis. MATERIALS AND METHODS: In ten matched lower extremity pairs, specimens in each pair were randomly assigned to receive screw fixation or plate with screw fixation. Bone mineral density (BMD) was measured. For the crossed-screw construct, two 4.0-mm cannulated screws were used. One screw was inserted dorsal to plantar beginning from the first metatarsal 10 to 15 mm distal to the joint, and the second was inserted from the cuneiform 8 to10 mm proximal to the joint, medial to the first screw, into the first metatarsal. For the plate construct, a 4.0-mm cannulated compression screw was inserted from the dorsal cortex of the first metatarsal to the plantar aspect of the medial cuneiform. A locking plate was inserted dorsomedially across the MTC joint. Specimens were loaded in four-point bend configuration (displacement rate, 5 mm/min) until failure of the fixation or 3-mm deformation. An extensometer was used to measure deformation. RESULTS: There was no difference in load to failure or stiffness between the two groups. BMD was positively correlated with load to failure in the screw (r = 0.893, p = 0.001) and the plate (r = 0.858, p = 0.001) construct. CONCLUSION: The plate construct with compression screw did not show different rigidity as compared with the screw construct with the numbers available. CLINICAL RELEVANCE: Further investigation of a dorsomedial plate with adjunct screw compression may be warranted for first MTC arthrodesis.     

Stability of the offset V osteotomy: Effects of fixation, orientation, and surgical translocation in polyurethane foam models and preserved cadaveric specimens

Polyurethane foam models and cadaver specimens were used to examine the stability of the offset V first metatarsal osteotomy. Uniform osteotomies were performed in all specimens by using a specially designed jig. Specimens in the polyurethane foam model series (n = 10) varied with respect to fixation type, fixation orientation, and degree of lateral translocation of the osteotomy. All specimens were loaded to failure in an Instron testing machine (Instron, Canton, MA). The plantar wing-pin (Kirschner wire) osteotomy group showed statistically significantly greater stiffness (P =.0119) and load at failure (P =.0027) than the dorsal wing-pin group. Cadaveric offset V specimens received the same amount of capital fragment lateral translocation but had different fixation types and orientations. Using the identical protocol as the models, the cadaveric dorsal wing-screw group showed statistically significantly less displacement at failure than the plantar wing-screw, plantar wing-pin, and dorsal wing-pin groups (P =.0262). The dorsal wing-pin group with a synthetic tension band showed a statistically significant greater stiffness (P =.0054) and peak load at failure (P =.0004) compared with the dorsal wing-pin group without the tension band. The most stable offset V construct in the polyurethane foam model was the plantar wing-pin group. The preserved cadaveric specimens yielded different results. The cadaveric dorsal wing-pin group with the synthetic tension band showed superior stability compared with all other non-tension-band groups. These results indicate the importance of tension band effects provided by capsular and ligamentous structures, which are typically ignored in surgical optimization research.     

Compression screw fixation in proximal first metatarsal osteotomies for metatarsus primus varus: initial observations.

Many methods of fixation have been used after proximal abductory metatarsal osteotomies for the correction of metatarsus primus varus. The methods include external immobilization and the application of devices such as stainless steel wire, Kirschner wires, staples, and compression plates. We have combined external immobilization with compression screw fixation across the osteotomy site. Two different types of screws were used: 1) an AO screw 3.6 mm. wide and 26 to 28 mm. long and 2) a standard Woodruff screw 3.5 mm. wide and 31.8 to 44.4 mm long. Twenty-two procedures were reviewed. When we compared the results, we found the AO screw to be superior in the degree of rigid fixation which it provides, as judged by the extent of postoperative callus formation.     

Mechanical Comparison of Cortical Screw Fixation Versus Locking Plate Fixation in First Metatarsal Base Osteotomy

The oblique closing base wedge osteotomy has been used for surgical treatment of moderate to severe hallux valgus deformities with an intermetatarsal angle typically greater than 15°. Several postoperative complications have been identified that relate to failure of the fixation construct used to fixate the osteotomy, especially when that construct has been subjected to a vertical load. We performed a mechanical analysis comparing 2 constructs used to fixate oblique osteotomies of the first metatarsal using composite first metatarsals. An oblique base osteotomy was uniformly performed on 40 composite first metatarsals. Of the 40 specimens, 20 were fixated with a locking plate construct and 18 with a cortical screw construct, consisting of an anchor and compression screw (2 specimens from the latter group were excluded because of hinge fracture). Each specimen was loaded in a materials testing machine to measure the maximum load at construct failure when a vertical force was applied to the plantar aspect of the metatarsal head. The mean load to failure for the locking plate construct was significantly greater than the cortical screw construct (190.0 ± 70 N versus 110.3 ± 20.3 N, p < .001). Our study results have demonstrated that the locking plate construct was able to withstand a significantly greater vertical load before failure than was the 2-cortical screw construct in oblique osteotomies performed at the base of composite first metatarsals.     

Comparative mechanical testing of different geometric designs of distal first metatarsal osteotomies

BACKGROUND: The mechanical behavior of a newly described distal metatarsal osteotomy design in the shape of a reversed "L" was compared with the modified chevron and scarf osteotomies. METHODS: Experiments were performed using full-sized Sawbone models (Sawbones Europe AB, Malm?, Sweden) of the first ray. Three groups consisting of 10 scarf, 10 modified chevron, and 10 reversed L osteotomies were investigated. All distal fragments were displaced 5 mm laterally without angulation. The proximal fragment of each specimen was embedded in an epoxy resin cylinder and positioned at 15 degrees inclination to the ground. The distal fragment was loaded by a dorsally directed vertical force which was applied at the sesamoid location under the metatarsal head. Load and displacement at failure, work to failure, site of failure and contact areas were recorded for each osteotomy. RESULTS: Similar testing results were obtained in the reversed "L" and chevron osteotomies, while the scarf osteotomy needed almost 5 times less work to failure. In nine of 10 reversed "L" osteotomies and in all scarf osteotomies, the site of failure was at the proximal screw insertion site. The contact areas averaged 163 mm(2) for the reversed "L," 116 mm(2) for the chevron, and 270 mm(2) for the scarf osteotomy. CONCLUSIONS: The reversed L osteotomy is a promising design combining the advantages of both the chevron and scarf osteotomies. Further investigations need to be performed to confirm its clinical utility.