gms | German Medical Science

54. Jahrestagung der Norddeutschen Orthopädenvereinigung e. V.

Norddeutsche Orthopädenvereinigung

16.06. bis 18.06.2005, Hamburg

In-vivo stability following high tibal osteotomy: a radio stereometric analysis (RSA)

Meeting Abstract

Suche in Medline nach

  • corresponding author D. Pape - Universitätskliniken des Saarlandes, Orthopädie, Homburg/Saar
  • O. Steimer - Homburg/Saar
  • D. Kohn - Homburg/Saar

Norddeutsche Orthopädenvereinigung. 54. Jahrestagung der Norddeutschen Orthopädenvereinigung e.V.. Hamburg, 16.-18.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05novP10

Die elektronische Version dieses Artikels ist vollständig und ist verfügbar unter: http://www.egms.de/de/meetings/nov2005/05nov061.shtml

Veröffentlicht: 13. Juni 2005

© 2005 Pape et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielf&aauml;ltigt, verbreitet und &oauml;ffentlich zug&aauml;nglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Introduction

In closed-wedge high-tibial osteotomies (HTO), closure of an osteotomy gap after resection of a bony wedge can be associated with a fracture of the medial cortex of the tibial head (MCT). A broken MCT can lead to lateral displacement of the distal tibial segment and early revarisation. In this study, serial RSA was used to determine the in vivo stability of rigid internal fixation after HTO over time in patients with varying degree of varus malalignment and correction.

Method

A prospective RSA study was undertaken to examine 15 consecutive patients (7 male, 8 female, mean age 55 years) with varus gonarthrosis grade 1-3 according to AHLBACK [1]. All patients were treated with HTO and internal fixation with an L-shaped rigid buttress plate. The aim of surgery was a slight overcorrection of the femorotibial angle to 8° of valgus. In all patients, a 10 mm cortical bridge of the medial cortex of the tibial head (MCT) was preserved during the cutting process. We intended to achieve a plastic deformation of the medial cortex of the tibial head to avoid fracture or fissure. Therefore, the osteotomy was gradually closed over ten minutes. For RSA examination, nine Tantalum markers (diameter of 0.8 mm) were implanted proximal and distal to the osteotomy into the cortex and the adjacent cancellous bone. Translations between tibial segments were calculated by repeated RSA examinations with the RSA-Kinematic software according to SELVIK [2].

Accuracy was defined as the extent to which, in the absence of a measurement error, the RSA values obtained represented relevant translations between the fixated tibial segments. The error of measurement was calculated by RSA double examinations in five patients with good osseous fusion seen in conventional x-rays 6 months after surgery using DAHLBERGS`s formula [3]. Values that exceeded 0.4 mm in the three axes of motion (transverse (x), vertical (y) and sagittal (z) axis, Table [Tab. 1]) were statistically evaluated since they were above the accuracy of the RSA setup. Patients were followed by serial RSA, conventional radiographs and clinical evaluation over a 12 months period.

Results

RSA variables showed micromotions [mm] of the distal tibial segment relative to the tibial plateau segment after completed HTO over time. Micromotions measured at 3 and 6 weeks after surgery represented further displacements in comparison to the preceding examination. Distal tibial translations were assigned positive values directing laterally (x-axis), cranially (y-axis) and anteriorly (z-axis).

In 9 of 15 succeeding patients, an average wedge size of 7.1 ° was resected leaving the MCT intact (group 1). In 6 of 15 of patients, the MCT was unintentionally fractured during surgery when an average 10.7° wedge was resected (group 2). In group 2, RSA revealed a 1.3 mm increase in lateral displacement of the distal tibial segment within three weeks after HTO. Twelve weeks after HTO, translations between tibial segments were below the accuracy of the RSA setup in 14 of 15 patients.

Discussion

Although we followed the manufacturer's recommendations closely and gradually closed the osteotomy gap over ten minutes, we were not able to achieve a plastic deformation of the MCT in some patients. The MCT fractured predominantly during the approximation of the tibial segments (in 4 of 6 group 2 patients) and less frequently while tightening the distal cortical screws (in 2 of 6 group 2 patients). Stratifying these clinical data by wedge size would suggest that five out of six patients with a wedge size of 10 degrees or greater sustained a fracture as compared to only one of nine patients with a wedge size of 8 degrees or less. These data indicate that the MCT`s capacity for plastic deformation might have been exceeded in osteotomies with larger wedge sizes leading to a fracture of the MCT in later stages of the operation. According to our RSA data, the fracture of the MCT in group 2 led to a significant increase in lateral displacement of the distal tibia within 3 weeks after HTO despite a rigid internal fixation. This might indicate a decreased fixation stability of the osteotomy site prior to bony fusion and emphasizes the importance of an intact MCT for retaining alignment until bony healing occurs. To draw practical conclusions relative to our findings we would recommend the described surgical technique in combination with the L-shaped buttress plate in cases with smaller wedge sizes (£ 8°) because we frequently found an intact MCT after surgery which offered a high fixation stability and allowed for a secure bone healing. In cases with larger wedge sizes (> 8°), a fracture of the MCT was frequent and the propensity for a lateral displacement of the distal tibia was increased.

In these cases we recommend an early and frequent clinical and radiological follow-up and a restriction of weight bearing up to 6 weeks with the leg kept in a splint.


References

1.
Ahlback 1968, Calcif Tissue Res
2.
Selvik 1983, Acta Radiol
3.
Dahlberg 1940, Interscience Publications