Biomechanical and Clinical Evaluation of a New Operative Technique

Transcription

1 27 Posterior Olecranon Plating Biomechanical and Clinical Evaluation of a New Operative Technique Nirmal C. Tejwani, M.D., Ian R. Garnham, F.R.C.S., Philip R. Wolinsky, M.D., Frederick J. Kummer, Ph.D., and Kenneth J. Koval, M.D. Abstract The purpose of this investigation was to compare the biomechanical analysis of a new plating technique for olecranon fractures to tension band wiring, and review early clinical results. Six matched pairs of cadaveric ulnae were used for the biomechanical analysis. A transverse osteotomy of the mid part of the olecranon was made. One ulna of each pair was stabilized using a tension band and the other with a posterior hook plate. The ulnae were mounted and loaded, and displacement at the osteotomy site recorded. Twenty patients treated with this new technique (14 fractures and 6 osteotomies) were reviewed at one year (range: 8 to 18 months) for infection, union rate, hardware related complaints, and removal. Statistical analysis showed significantly less displacement occurred at the osteotomy site in the plating group. Clinically, all patients had fracture union, and there were no hardware related problems. Posterior plating with this technique achieves greater stability compared to tension band wiring. Early clinical results indicate a low level of hardware related complications. Open reduction and internal fixation is the accepted method of treatment for displaced olecranon fractures. It allows early mobilization of the elbow joint and reduces postoperative elbow joint stiffness. Various methods of internal fixation have been used including tension band wiring, intramedullary screws (with and without a tension band), and screw and plate fixation. Nirmal C. Tejwani, M.D., Philip R. Wolinsky, M.D., Fred J. Kummer, Ph.D., and Kenneth J. Koval, M.D., are in the Department of Orthopaedic Surgery, NYU-Hospital for Joint Diseases, Bellevue Hospital, New York, New York. Ian R. Garnham, F.R.C.S., is in the Department of Orthopaedic Surgery, Royal London Hospital, Whitechapel, London, England. Reprint requests: N. C. Tejwani, M.D., 550, First Avenue, NBV 21W 37, New York, New York At present, tension band wiring is the widely accepted technique. A tension band converts the tensile forces at the fracture site that are created as a result of muscle action into compressive forces. In 1963, Weber and Vasey 1 introduced the concept of combining the tension band with Kirschner wires to increase the stability of the fixation. This technique was further modified by the AO group by placing the Kirschner wires obliquely to engage the anterior cortex of the ulna in order to increase the stability of the fracture fixation and to prevent the wires from backing out. A biomechanical analysis of this technique showed a significant increase in fracture stability when compared to the original Weber-Vasey technique. 2 While tension band wiring has been shown to be rigid under biomechanical testing, various investigators have reported a significant rate of complications, 3-9 most frequently hardware prominence. Helm and colleagues 8 reported that 82% of patients in their series needed removal of hardware following tension band wiring. Hume and Wiss 7 performed a randomized prospective trial with 41 patients with displaced olecranon fractures treated with either tension band wiring or plate fixation. Eight patients in the tension band group (42%) had symptomatic hardware, compared to one in the plate group. Several investigators have reported on their experience with plating of olecranon fractures. In 1951, Zuelzer 10 reported the successful use of a hook plate in one patient with a comminuted olecranon fracture. Weseley and associates 11 subsequently reported satisfactory results in 25 patients treated using with the Zuelzer plate technique. In 1973, Waddell and Howat 12 reported the use of a contoured posterior plate combined with an intramedullary screw in 6 patients. They recommended the use of this plating technique in comminuted fractures where tension band techniques were deemed unsuitable. A prospective randomized study comparing tension band wiring and posterior plating

2 28 Figure 1 Anteroposterior and lateral view of an olecranon fracture successfully treated with the posterior hook plate technique. for simple displaced olecranon fractures reported that the tension band group had a higher rate of symptomatic hardware, while the plate group had a higher rate of good clinical outcomes. 7 Many have investigated the biomechanical stability of variations on the tension band technique, but few have compared it to plating. Fyfe and coworkers 13 performed a biomechanical study assessing different methods of fracture fixation. They found that the AO tension band technique with two knots and two parallel K-wires (Weber-Vasey) was the most stable fixation. However the plating technique tested used unicortical screws and did not use a hook plate or an intramedullary screw. The high incidence of hardware problems associated with tension band wiring and the inability to use this technique for comminuted and oblique olecranon fractures prompted us to try a different technique. Our aim was to devise a construct that would be useful in all fracture types, allow compression in transverse fractures, be stronger than tension band wiring, and have significantly lower hardware loosening and removal. Figure 2 Tension band wiring in cadaver olecranon for biomechanical testing. We describe a technique of posterior plating combining the use of hook plate and an intramedullary screw; this fulfills all our criteria (Fig. 1). We report the findings of a biomechanical study that compared the rigidity of the fixation of this plating technique to the standard tension band wiring and discuss the outcome of an initial group of twenty patients treated with this technique. Materials and Methods Biomechanical Study Six matched pairs of embalmed human ulnae were prepared for analysis. One ulna from each matched pair was treated with AO tension band wiring and the other with a posterior hook plate. Tension Band Group Two parallel inch Kirschner wires were inserted obliquely into the proximal ulna so that they penetrated the anterior cortex of the ulna prior to the osteotomy. The Kirschner wires were then removed and a transverse osteotomy was made with a fine saw blade in the center of the trochlear fossa. A 20-gauge stainless steel wire was then passed through a 2 mm transverse drill hole 2 cm distal to the osteotomy and secured in a figure-ofeight with two tightening loops. All wires were tightened by the same surgeon (IRG) until he felt that sufficient tension had been achieved in the wire for osteotomy stabilization, thus simulating a clinical scenario. The Kirschner wires were then bent and impacted into the proximal ulna (Fig. 2). Plate Group A seven-hole one-third tubular plate was contoured to fit the posterior aspect of the proximal ulna prior to the osteotomy. The plate was flattened at one end and cut obliquely at the first hole to produce two prongs that are bent at right angles to create a hook. A cortical screw ( home run screw ) measuring 65 mm long and 3.5 mm in diameter was inserted intramedullary through the plate

3 29 Figure 3 Posterior hook plate with our technique in cadaver bone for biomechanical testing. across the fracture site but was not initially fully seated. A longer screw may be inserted depending on the fracture pattern. A cortical screw was inserted obliquely (angled distally) into the distal hole of the plate to pull the plate distally and effectively create compression at the fracture site. The intramedullary screw was then fully seated to further compress the fracture site. The third and final screw was inserted through the plate into the coronoid process to supplement the rigidity of the construction (Fig. 3). Each sample was then examined for deflection at the osteotomy site under different loading conditions. The ulnae were loaded by suspending a weight from the proximal ulna that produced the equivalent of a 45 Newton force. The weight was suspended from a string looped around a 2 mm diameter metal pin placed medial to lateral through the ulna proximal to the osteotomy site. The ulna was secured by ring clamps allowing the entire load to act across the osteotomy (Fig. 4). To obtain the measurements for deflection of the osteotomy gap after loading, metal pins were screwed into pre-drilled holes on either side of the osteotomy so that they would protrude anteriorly, and were stabilized with epoxy cement (Fig. 5). Results from earlier work, indicate that deflection at the site of the osteotomy is due to angulation of the proximal segment. 14 As such, the deflection at the osteotomy gap could be calculated using the length of the pins, the length of the osteotomy, and Figure 4 Cadaver olecranon with anterior wires to measure deflection at the osteotomy site. the displacement of the tips of the pins after loading. The first pair was initially loaded with the anterior surface of the ulna facing upward to simulate a flexion force at the elbow from the brachialis muscle. The specimens were then rotated 180 so that the posterior surface of the ulna faced upward and then were loaded to simulate the effect of the triceps muscle. Displacement measurements of the tips of the pins were taken with digital calipers after the application of each load. Cyclical loading was then applied ten times with the ulna mounted in both configurations and displacement measurements were made after the cycling was completed. The order of load application was alternated for each subsequent specimen. The results of the four loading scenarios were summarized for both fixation techniques and plotted as bar charts of the mean displacements. For each loading scenario the techniques were compared using a matched Student s t-test. Clinical Study Twenty patients who were treated using this plating technique were evaluated. The patient s charts and radiographs were reviewed, and the patients were evaluated at the time of their last follow-up. The fracture types, infection rate, time to bony union, and any symptoms resulting from the hardware were recorded. The average follow-up was one year (range: 8 to 18 months). Table 1 Mean Displacement at Osteotomy Site Initial Loading Cyclic Loading Displacement Displacement Brachialis Triceps Brachialis Triceps (N = 6) mm SD mm SD mm SD mm SD Posterior plate (0.052) (0.013) (0.11) (0.032) Tension band wiring 0.15 (0.085) 0.11 (0.08) (0.08) (0.11) p value < 0.05 < 0.05 < 0.05 < 0.005

4 30 Figure 5 Apparatus used for biomechanical testing and measurement (the same apparatus was used for testing both techniques). Figure 6 Lateral view of an olecranon osteotomy treated with the new plating technique. Results Biomechanical The mean displacements resulting from the applied loads for the two fixation techniques are shown in Table 1. Initial loading of the osteotomy in the plating group led to a mean displacement of mm and mm for the brachialis and triceps forces respectively, compared to a mean displacement of 0.15 mm and 0.11 mm in the tension band group. The difference in displacement between the two groups was found to be statistically significant for both the brachialis (p < 0.05) and triceps forces (p < 0.05). Cyclical loading led to an increased displacement at the osteotomy site in both groups. Again the amount of displacement was found to be lower in the posterior plate group when compared to the tension band group for both the brachialis force (p < 0.05) and the triceps force (p < 0.005). Clinical Of the 20 patients reviewed, 14 had been treated for olecranon fractures and six for stabilization of an olecranon osteotomy during fixation of a supracondylar/intercondylar fracture of the humerus (Fig. 6). Of the 14 fractures, six were comminuted and eight were transverse. There were 13 males and seven females with a mean age of 37.5 years (range: 19 to 77 years). The operated side was the right in 13 patients and the left in seven. Clinical and radiological follow-up at a mean of 12 months (range: 8 to 18 months) showed all the fractures to be united. None of the patients needed to have their hardware removed, and no patient had complaints related to the hardware. Discussion Our results show that significantly less displacement occurred at the olecranon osteotomy site when a posterior plate was used for stabilization when compared to a tension band. This was true for initial as well as cyclical loading of the osteotomy. Cyclical loading led to an increase in displacement in all groups, however it was less in the plate group. Our clinical group had a 100% union rate of the olecranon fractures or osteotomies, and to date none have had hardware related symptoms that required hardware removal. The ability to achieve static interfragmentary compression with this technique may lead to a lower rate of nonunion for olecranon osteotomies, the rate of which has been reported to be as high as 10%

5 31 The low profile of the plate and the fact that none of the screws backed out, was the reason that no patient needed a second operation for hardware removal. A one-third tubular plate was chosen, rather than a reconstruction plate, for its lower profile. We did not test for scenarios where a proximal ulna fracture may need a stronger implant, however this investigation was limited to olecranon fractures and this technique is best suited for these injuries. We recognize that the biomechanical study shows a very small range of displacement and this may not be clinically significant. Also, this study was performed on cadaveric bone with no soft tissue attachment, though the use of weights attempted to duplicate the forces across the fracture. The purpose of the biomechanical study was to prove that this technique could stand up to the rigors of elbow motion in a manner similar to tension band wiring. Clinically, the sample size of patients treated with this technique is small, however, these are early results and we continue to use this plating technique. The results of this study are significant in contrast to the historical literature and our experience of incidence of hardware related problems using the tension band technique. We feel that this technique is superior to the traditional methods for olecranon fractures in ease of use, universality for all fracture types, and low profile of the implant. For comminuted fractures, a longer plate may be used based on the extent of the fracture. Avoidance of a second operation will result in significant savings of health care resources and improved patient outcomes and care. These early, positive results have encouraged us to continue using this technique and we will be able to report on larger numbers with longer follow-up in the future. Conclusion We conclude that posterior plating achieves a more rigid construct than tension band wiring. This plating technique allows compression at the fracture site, which is an advantage when treating transverse non-comminuted olecranon fractures and osteotomies. The same technique can also be used for comminuted fractures without any significant modifications. The initial results from our clinical data indicate that this technique has a high union rate and a low incidence of hardware related complications. We believe this technique will lead to fewer reoperations for removal of symptomatic hardware than the current rate encountered when using the tension band wiring technique. References 1. Weber B, Vasey H: Osteosyntheses bei olecranonfraktur. ZunfallmedBerukskr 56:90-96, Prayson MJ, Williams JL, Marshall MP et al: Biomechanical comparison of fixation methods in transverse olecranon fractures. J Orthop Trauma 11(8): , Finsen V, Lingaas PS, Storro S: AO tension-band osteosynthesis of displaced olecranon fracture. Orthopaedics 23(10): , Romero JM, Miran A, Jensen CH: Complications and reoperation rate after tension-band wiring olecranon fractures. J Orthop Sci 5(4): , Macko D, Szabo RM: Complications of tension-band wiring of olecranon fractures. J Bone Joint Surg 67A(9): , Horne JG, Tanzer TL: Olecranon fractures: A review of 100 cases. J Trauma 21(6): , Hume MC, Wiss MD: Olecranon fractures: A clinical and radiographic comparison of tension band wiring and plate fixation. Clin Orthop 285: , Helm RH, Hornby R, Miller SWM: The complications of surgical treatment of displaced fractures of the olecranon. Injury 18(1):48-50, Mullet JH, Shannon F, Noel J, et al: K-wire position in tension band wiring of the olecranon: A comparison of two techniques. Injury 31(6): , Zuelzer WA: Fixation of small but important bone fragments with a hook-plate. J Bone Joint Surg 33A:430, Wesley MS, Barenfeld PA, Eisenstein AL: The use of the Zuelzer hook plate in fixation of olecranon fractures. J Bone Joint Surg 58A: , Waddell G, Howat TW: A technique of plating severe olecranon fractures. Injury 5(2): , Fyde IS, Mossad MM, Holdsworth BJ: Methods of fixation of olecranon fractures: An experimental mechanical study. J Bone Joint Surg 67B(3): , Henley MB: Intra-articular distal humeral fractures in adults. Orthop Clin North Am 18:11-23, Holdsworth BJ, Mossad MM: Fractures of the adult distal humerus: Elbow function after fixation. J Bone Joint Surg 72B: , Sodergard J, Sandelin J, Bostman O: Postoperative complications of distal humeral fractures. Acta Orthop Scand 63:85-89, 1992.