Development of a new implant for high tibial osteotomy: comparison "in vitro" with the Brunner & Weber fixation method

Abstracts

Os autores desenvolveram um novo implante para osteotomia proximal de tíbia como alternativa para tratamento da osteoartrose do joelho com deformidade em varo . O objetivo do trabalho foi desenvolver uma placa para fixação simples, de fácil manejo, e menor custo, propiciando baixa morbidade em relação aos métodos existentes, e compará-la com o método idealizado por BRUNNER e WEBER (1982)² que utilizaram a placa semitubular. Os testes mecânicos foram realizados em máquina universal de ensaios do Laboratório de Bioengenharia da Faculdade de Medicina de Ribeirão Preto, Campus Universitário, Universidade de São Paulo. Nos parâmetros analisados como limite de proporcionalidade, módulo de elasticidade observaram-se valores diferentes entre as duas placas mostrando que o novo implante apresentou resistência e estabilidade superior à placa semitubular quando submetidos a testes de flexão.

Joelho; osteotomia proximal de tíbia; fixação

ARTIGO ORIGINAL

Development of a new implant for high tibial osteotomy: comparison "in vitro" with the Brunner & Weber fixation method^*

Constantino Jorge Calapodopulos^I; Cleber Antonio Jansen Paccola^II

^IProfessor Adjunto, FMTM – Faculdade de Medicina do Triângulo Mineiro, Uberaba – MG.

^IIProfessor Titular do Deptº de Cirurgia, Ortopedia e Traumatologia, Faculdade de Medicina de Ribeirão Preto-USP

SUMMARY

The author compares this new plate with other type of fixation described by Weber that employed a semitubular plate based on tension band principle.

The mecanical tests were perfomed in a universal test machine of the "Laboratório de Bioengenharia da Faculdade de Medicina de Ribeirão Preto, Campus Universitário, Universidade de São Paulo".

A three-point-flexion test established was employed dislocation.The weak point in the semitubular plate model ocurred mainly where it was bent at is external hole, displaying hole enlargement at loads of less than 30 N.m.

The author choosed the 3-points flexion test, which provides a qualitative indication of the material resistivity.

The conclusion was that the new implant showed stability and resistance superior to the semitubular plate when submitted to flexion tests.

Key words - Knee; high tibial osteotomy; fixation

INTRODUCTION

A description of the tibial proximal osteotomy (OPT) to treat monocompartment arthrosis of the knee was mentioned in Merle D'aubigne's investigations, around 1948.

The osteotomy region, initially infratuberositas, was modified due to bone consolidation problems. Wedge osteotomy, proximal to the tibial tuberosity is now preferred. It was described by GARIEPY⁵ in 1964 and widely divulged and used by COVENTRY³ in 1965, due to its simplicity, becoming a synonym of osteoarthrosis treatment.

The first OPT results, published by JACKSON and WAUGH (1961)⁸ of deformity correction in knees with arthrosis, evidenced that pain lessened in the operated on cases.

Several authors studied the clinical value of this surgery and analyzed its results, relating them to age, sex, degree of deformity and psychological status of the patient, complications which appeared after JACKSON and WAUGH's studies (1961)⁸, alternatives to the surgical technique, as the one described as "ball and socket", the more proximal possible and below the tibial tuberosity.

BRUNNER and WEBER (1982)² devised a fixation system where a semitubular AO type plate was used associated to a tirante screw. This method became widely known and was largely used; no external support was necessary and allowed early moving and load.

Using the dome supratuberosal osteotomy, temporary fixation with two Steinmann pins for a better intraoperative alignment and afterwards definitive fixation with Conventry staples, SUNDARAM et al.¹³, in 1986, reported good functional results.

Among our colleagues, we mention the work of Paccola et al. (1990)¹⁰, using internal fixation in high tibial osteotomy with semitubular plate, the BRUNNER & WEBER (1982)² method. A series of complications were analyzed, and probably in view of these problems we started to investigate alternatives, developing our implant material with the tension band method devised by BRUNNER & WEBER (1982)².

The comparative study between staple fixation and type AO buttress plate fixation, evidenced a small number of complications in the operated on cases according to HEE et al. (1996)⁶.

Recent proposals of treatment were devised by AKIZUKI et al. (1997)¹, combining articular abrasion by arthroscopy and tibial proximal osteotomy in the knee with monocompartiment osteoarthrosis, and fixation with conventional implants.

MATERIAL AND METHODS

Several prototypes were developed, giving rise to a new trapezoidal implant, manufactured by Quinelato®, its apex pointing to the distal region when positioned in the osteotomy. It is 25 mm wide, 28 mm long, its superior part presents two circular equidistant holes, and another oval hole in the inferior region of its vertex, to allow oblique positioning of the 4.5 mm cortical screw. The upper orifices fix the osteotomized tibial proximal fragment and the inferior oval hole the distal part of the tibia.

All this tension band type fixation process was carried out in the Bioengineering Laboratory, Ribeirão Preto College of Medicine.

The model chosen for the test was made with intermediate consistency wood, Angelim gender (Platycyamus regnelli). The introduction of the semitubular plate in the sample specimen was effected through a transfixant orifice about 10 mm diameter allowing the semitubular plate introduction. The models were shaped to acquire the form of a 50 mm diameter and 150 mm long cylinder. The cortical screws were introduced in the plate orifices made with a 3.2 mm drill and electric perforator and mortised with the instruments for cortical 4.5 mm AO screws. The two assembled models showed quite significant resistance, in flexion and in rotation, evidencing differences between the two fixation systems. Flexion mechanical tests were carried out in the Bioengineering Laboratory universal machine using a 200 N final load.

The semitubular plate and the new implant material

The semitubular plates and the new implant used to fix in the osteotomies and in the mechanical tests, were manufactured by Schoubell Industrial Ltda. Quinelato®, Rio Claro, São Paulo. The screws for cortical also with special size, superior to 70 mm lenght and 4.5 mm diameter, were produced by the same company. They were manufactured with 316-L stainless steel. The semitubular plate was manufactured identically to the AO plate with 4 orifices, while the new plate obeyed its own specifications.

The "new implant" presented a trapezoidal form, 25 mm wide, 28 mm long with two round 5 mm orifices, the centers equidistant 10 mm. The third oval inferior orifice, allowed the placement of 4.5 mm screws in variable angles up to 60º inclination in relation to the greater axle of the plate, transversally 20º to 25º to the plate (Figure 1).

Preparation of the models for the test.

The conventional semitubular plate was introduced in the test cylinder by means of an orifice made with a 10 mm drill reproducing the internal diameter of the semitubular plate, facilitating its implantation with a wood impactor, causing no alterations in the tubular structure, leaving externally the equivalent to one hole (15 mm, approximately) afterwards distally folded in an approximately 45º angle with the model axle.

Assembly and fixation of the two implants in the wooden models

Fixation tested in this study was based in the "tirante de tensão" principle, according to PAUWELS' (1980)¹² column scheme and developed by BRUNNER and WEBER (1982)² using in particular the angled semitubular plate to fix the tibial osteotomy.

Eighteen models were made to test the implants (9 semitubular plates and 9 new plates). The models were made with massive wood. Tubular or hollow wood models were also made. The experimental groups were divided as follows:

Semitubular plate (9 specimens) massive (3 specimens) hollow (6 specimens) New plate (9 specimens) massive (3 specimens) hollow (6 specimens)

Mechanical tests

The mechanical tests were carried out in a universal test machine in the Bioengineering Laboratory, Ribeirão Preto College of Medicine, Campus of the University, University of São Paulo. The machine was coupled to a 200 N load cell (KRATOS), interconnected with the extensometry bridge system, 1.2 mm/min constant speed. The deformations were registered by a 0.01 mm precision Mitotoyo comparing watch.

Flexion test

The same supports were used in all flexion tests. A 52 N pre-load was used. Force readings were done at each 0.005 m deformation of the sample specimen and 9 tests were made for each plate.

To carry out the analysis, we adopted the “bi-supported beam” model (TIMOSHENKO and GOODIER, 1970)14 similar to the evaluation method used in the tests, representing the material resistance theory.

Analysis of the data

Flexion tests in three points produced flexion moment versus displacement graphs. The curves force x deformation presented an initial rectilinear phase of displacement, an intermediate phase of accomodation, and a subsequent phase of progressive variation of displacement, a very clear behavior.

The parameters used to comparatively evaluate the data were the values obtained testing both plates; graphs were obtained with readings from the extensiometry source at each 0.005 mm deformation and organized in an Excel (7.0, Microsoft 1977) personal computer program.

RESULTS

General considerations

In the semitubular plate assembly, we observed that the fixation flaw site was located externally where the plate had been folded in order that the tirante screw could be placed; deformation was observed with a lower than 30 N x m load, increasing the screw orifice width and the rupture of the material below this perforation.

In the "new implant" assembly widening of the screw orifice has also occurred, evidencing that, in the two models, this was the point of the synthesis greater solicitation. In the new plate, the model remained stable until the end of the test, plastic deformation occurring only after an approximately 120 N x m load.

The analysis of the curves inclinations and of the maximum moment in two segments, superior and inferior, and in the point where all the curves passed, showed significant differences represented in the figures and respective diagrams.

Flexion moment x deformation curves

The values for flexion moment and deformation obtained during the tests are grouped in the graph comparing the two tests (Fig. 2)

Flexion tests in the wooden specimens.

In the first system using the semitubular plate two critical points were observed; one at the orifice where the screw passed, at the point the plate was folded, and the other in the wood below the plate. In the second system, the new implant, the critical point was observed in the screw tirante entrance orifice.

In the flexion test results, the maximum moment endured by the "new implant" was significantly higher than in the semitubular plate group of tests.

Tables 1, 2 and 3 present the linear regression, the forces (maximum moment) in 150.10^–5 meters deformation, and the rigidity module (EJ) analyses, respectively.

DISCUSSION

Knee osteoarthrosis predominantly in the medial knee compartment presenting varus deformity is a relatively frequent pathology in patients between the fifties and sixties. The ideal patient to be treated with the realignment procedure using OTP is the one clinically diagnosed with mild and moderate arthrosis (COVENTRY, 1965)³.

Osteotomy is the surgical technique of choice to all age groups but mainly to less than 65 year-old patients with medial compartment degeneration and loss of articular cartilage, with small bone collapse COVENTRY ( 1965)³.

COVENTRY and BOWMAN (1982)⁴ determined with precision the indication and the techniques in OPT, propitiating the best results to younger than 70 year-old patients with varus deformities in minor knees and predominance of the unicompartment disease.

Recent studies have shown the importance to develop more rigid synthesis systems to fix the bone in high tibial osteotomy. It is also clear the intimate relationship between the final mechanical axle and the knee function, outlining the concept that a slightly excessive correction is better than the subcorrection to obtain good results (HSU, 1989)⁷. This gives support to the fact that the "new implant" type of assembly promotes greater post-operative stability, allowing early walking and maintaining the ideal correction angle of the deformity.

MINIACI et al. (1989)⁹ also developed a fixation system, a modification of the Weber method, using an AO semitubular plate with 5 holes, three of them externally to the bone, folded such as to allow the placement of two screws providing the system perfect stability and propitiating lower mobidity to the operated on cases.

PACCOLA et al. (1990)¹⁰ evaluated this system investigating the semitubular plate behavior as a fixation element in tibial osteotomies. These authors observed that the frequent complication using the semitubular plate occurred in the proximal layer of bone between the osteotomy and the insertion of the plate in the epiphysis that could rupture, producing progressive loss of the surgical correction initial alignment. Another important observation taken into consideration refers to bone incorporation in the semitubular plate holes making its late removal difficult.

The developed plate allows the observation of some basic principles in osteosynthesis, as providing mechanical stability with no impairment to the bone biology, sufficient stability to allow early mobility, resistance to deforming forces, propitiating the knee early functional activity (PACCOLA, 1997)¹¹. In the mechanical tests, wood fracture in the region below the folded semitubular plate was reported by PACCOLA et al.¹⁰; the bone is ruptured losing correction, and this was not observed with the new implant assembly. In practice, this can represent less correction of the valgism angle. We emphasize, also, the importance of the tirante screw placement in the two wooden walls. This could represent the weak point of the system, as compared to the screw in only one wall (PACCOLA et al, 1990)¹⁰.

This was observed in the tests, evidencing that in the compact wooden models, resistance has always been higher, since the tirante screw had a larger contact area (tests 1, 2 and 3) and the fixation with the hollow model (test 6) evidenced lack of good fixation in the cylinder distal wall (Table 4).

The results do not agree with HEE's (1996)⁶ work, where he compared staple fixation to AO buttress plate fixation, two mechanically different methods concerning stability. The results were analyzed using the Student's "t" in the two compared groups, semitubular plate and new plate, and p < 0.05 was considered a statistically significant value. In the first group, we analyzed the maximum moment between two points of deformation 50.10^–5 and 250.10^–5 meters (Table 1). The values were p = 0.012 and p = 0.026 for the compact model and for the hollow model, respectively. In another analysis we determined a linear deformation referential point, defined in 150.10^-5 m and the forces were evaluated at this point (Table 2). We obtained p = 0.05 and p = 0.0001 for the compact and hollow models, respectively. Finally, we analyzed the rigidity equivalent Module for all tests and obtained p = 0.001. The three analyses (Tables 1, 2 and 3) have shown statistically very significant (p < 0.05) differences between the two groups.

CONCLUSIONS

Considering the technique devised by Brunner & Weber and using cylinders of massive and hollow wood as test models, assembled with the two kinds of plate, the semitubular and the new implant, we concluded:

1. Assembly with the semitubular plate evidenced stability inferior to the assembly with the new implant, considering their different mechanical behaviors when submitted to flexion efforts.

REFERÊNCIAS

• 1. AKIZUKI, S. ; YSUKAWA, Y. ; TAKIZAWA, T.. Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic with knees eburnation? A prospective study of high osteotomy with abrasion arthroplasty versus high tibial osteotomy alone. Arthroscopy 13:9-17, 1997.
• 2. BRUNNER, Ch. F.; WEBER, B.G. Special tecniques in internal fixation : Springer Verlag, Berlin 1982. p.232-240.
• 3. COVENTRY, M.B. Osteotomy of the upper portion of the tíbia for degeneration arthritis of the knee: a preliminary reportt. J. Bone Joint Surg, 47-A:984-989, 1965.
• 4. COVENTRY, M.B.; BOWMAN, P.W. Long-term results of upper tibial osteotomy for degenerative arthritis of the knee. Acta Med. Belg., 48:139-156, 1982.
• 5. GARIEPY, R. Genu varum treated by high tibial osteotomy. J. Bone Joint Surg., 46:783-784, 1964.
• 6. HEE, H.T.; LOW, C.H.; SEOW, K.H.; TAN, S.K. Comparing staple fixation to buttress plate fixation in high tibial osteotomy. Ann. Acad. Med. Singapure, 25:233-235, 1996.
• 7. HSU, R.W. The study of Maquet dome high tibial osteotomy. Arthroscopic-assisted analysis. Clin. Orthop., 193: 280-285, 1989.
• 8. JACKSON, J.P.; WAUGH, W.: Tibial osteotomy for osteoarthritis of the knee. J Bone Joint Surg , 43-B: 746-751, 1961.
• 9. MINIACI, A.; BALLMER, F.T.; BALLMER, P.M.; JAKOB, R.P. Proximal tibial osteotomy. Clin. Orthop. Rel. Res., 246:250-259, 1989.
• 10. PACCOLA, C.A.J.; LEMOS, E.R.S.; KUNIOKA, C.T.; VAZ JUNIOR, A.J. Fixação interna para osteotomia valgizante alta da tíbia. Rev. Bras.Ortop., 25:303-310, 1990.
• 11. PACCOLA , C. A .J .: comunicação pessoal ,1997.
• 12. PAUWELS, F: Biomechanics of the locomotor apparatus.Springer, Berlin Heidelberg New York, 1980.
• 13. SUNDARAM, N.A.; HALLETT, J.P.; SULLIVAN, M.F. Dome osteotomy of the tíbia for osteoarthritis of the knee. J. Bone Joint Surg, 68-B:782-786, 1986.
• 14. TIMOSHENKO, S.P.; GOODIER , J.N.: Teory of elasticity . 3º ed., Ed. Mc Graw-Hill, chap. 1, 2 and 3, 1970.

*

Tese de doutorado (resumo) apres, à Faculdade de Medicina de Ribeirão Preto – USP - SP, para obtenção do título de doutor em Ortopedia e Traumatologia.

Publication Dates

• Publication in this collection
  28 June 2006
• Date of issue
  Dec 2000