Negative correlation between extent of physeal ablation after percutaneous permanent physiodesis and postoperative growth: volume computer tomography and radiostereometric analysis of 37 physes in 27 patients.

BACKGROUND AND PURPOSE: Percutaneous physiodesis in the knee region is a well-established method for treating leg-length inequality. Longitudinal growth in the physis is believed to stop almost immediately after the operation. The extent of physis ablation required has never been investigated by any kind of tomography in humans. Using radiostereometric analysis (RSA), we determined when definite growth arrest occurred after surgery. We also studied the correlation between the extent of physis ablation and postoperative growth. Finally, we assessed any bone bridging across the physis. METHODS: 6, 12, and 30 weeks after surgery, we used RSA to measure longitudinal growth in 27 patients (37 physes) with a mean age of 13 years. CT scanning of the knee region was performed 12 weeks after surgery to measure the percentage of the ablated physis and to determine the distribution of bone bridges across the physis. RESULTS: RSA showed that growth rate was reduced to less than half of the expected rate after 6 weeks. During the next 6 weeks, the growth ceased completely. CT scans revealed a large variation in the extent of ablated physes (17-69%). In the ablated areas, tissues of various densities were mixed with mature bone. Bridges were found both laterally and medially across the physes in all of the patients. There was a negative correlation between the extent of ablation and total postoperative growth (rho = -0.37, p = 0.03). INTERPRETATION: Growth across the physis is effectively stopped by percutaneous physiodesis. RSA is well-suited for observation of this phenomenon. Volume CT scanning can be used to detect bone bridges that cross the physis and to calculate the extent of physis ablation.

Subsidence of callotasis zone in distraction osteogenesis after external fixator removal, measured by RSA.

BACKGROUND AND PURPOSE: In clinical practice, achieved lengthening of a callotasis zone should be maintained after the external fixator has been removed. The common understanding has been that the regenerated bone may subside. To investigate this, we used high-resolution radiostereometric analysis (RSA) with accurate measurement of the lengthening zone. PATIENTS AND METHODS: We assessed the longitudinal subsidence of a callotasis zone after removal of the external fixator in distraction osteogenesis in 16 patients who underwent 17 segmental lengthening operations on the tibia (n = 9) or femur (n = 8). Median lengthening was 32 (6-80) mm. RSA was performed at the end of the consolidation period before the external fixation device was removed, and this was later repeated at a median time of 11 (4-32) weeks after frame removal. RESULTS: A minimal median longitudinal change of 0.01 (-0.28 to 0.60) mm across the lengthening zone occurred in uncomplicated cases. INTERPRETATION: Our results indicate that no subsidence of clinical interest occurs after external frame removal.

Deformity correction during growth after partial physeal arrest.

The purpose of this study was to evaluate our treatment protocol for certain physeal injuries requiring complete epiphysiodesis of an injured physis, angular correction and lengthening with the Ilizarov method and overcorrection of length according to calculated loss of remaining growth. Five patients (age: 12 to 14 years) were operated with angular correction and lengthening in combination with complete epiphysiodesis. Angular deformities measured 12 degrees to 24 degrees and limb length discrepancies (LLD's) 15 to 60 mm. Mean overcorrection of length according to remaining growth of the affected physis was 12 mm (range: 7 to 15). All deformity parameters were fully corrected in all patients. Mechanical axis deviation (MAD) was within +/- 5 mm compared to the healthy side in 4 patients, 20 mm in one patient. Median LLD at maturity was 8 mm (range: 3 to 13). In cases of partial physeal arrest with severe symptomatic deformities, complete epiphysiodesis of the injured physis, angular correction and lengthening with the Ilizarov method with overcorrection of length according to estimated loss of remaining growth of the affected physis is a suitable method.

No difference in tibial lengthening index by use of Taylor spatial frame or Ilizarov external fixator.

BACKGROUND: Different methods and devices are used to perform lengthening and deformity reconstruction in the tibia. Recently, the Taylor spatial frame (TSF) has been introduced as a computer-assisted and versatile external ring fixator. Lengthening index (LI) and complications are important result parameters, and the aim of this study was to review our first 20 tibial segments operated with the TSF and to compare the results with our experience of using the traditional Ilizarov external fixator (IEF). PATIENTS AND METHODS: We lengthened 20 tibial segments in 20 patients with the TSF. The results were compared with those of 27 tibial segments from 27 patients that were lengthened with the IEF. All segments were operated on with monofocal osteotomies. RESULTS: In the overlapping zone of comparable lengthening distances between 2.4 and 6.0 cm, the LI of 2.4 and 1.8 months/cm was not significantly different between the TSF and IEF groups, respectively (p = 0.17). This non-significant difference was confirmed after adjustment for age. INTERPRETATION: We found no difference between the TSF and IEF frames regarding LI and complication rate. However, rotational, translational, and residual deformity correction is easier to perform with the TSF.

Optimum loading mode for axial stiffness testing in limb lengthening.

The axial stiffness of the regenerate is an indicator of bone healing after fracture or distraction osteogenesis. The axial stiffness may be assessed clinically by measuring the sharing of load between fixator and limb during loading. The aim of this study was to find out how to perform the stiffness test in order to minimize the influence of confounding factors to the test result. We investigated whether the test score was influenced by two factors: 1) the magnitude of the external load applied to the limb during the test; and 2) the patient's position during the test. The problem was approached by both a clinical study and by theoretical calculations. Thirty-three patients undergoing leg lengthening were tested regularly during the consolidation period. The stiffness test was executed with both high and low load, and in a standing and sitting position. There were significant differences in results between both the tests with high and low load, and between the standing and sitting tests. This indicated that both the magnitude of force and patient position during the test influenced the test result. Accordingly, these factors represent sources of error and must be taken into consideration when performing an axial stiffness test. The result of the theoretical calculations confirmed the result. We recommend performing the test while the patient is sitting, and to apply no more than 20% of the individual's body weight. It is also recommended that the same load be used in every test, when testing a patient several times during the treatment period.

Residual challenges after healing of congenital pseudarthrosis in the tibia.

The purpose of the current study was to evaluate the clinical results of the Ilizarov bone transport method in the treatment of congenital pseudarthrosis in the tibia. In seven patients operated on between 2.6 and 7.8 years of age, primary healing of the pseudarthrosis was achieved in all patients (after additional bone grafting in two patients). Within a followup of 6 to 8 years, major complications occurred in all patients. Five refractures occurred, and in one patient the refracture did not heal. At the last followup, axial deformities and an abnormal malalignment test with lateral mechanical axis deviation of 10 mm or greater was found in all patients. Three patients had leg length inequality of 20 mm or more. The Ilizarov bone transport method is useful in achieving primary healing in congenital pseudarthrosis of the tibia, but residual challenges with secondary reconstructive surgery caused by refracture and postoperative deformities must be expected.

High frequency distraction improves tissue adaptation during leg lengthening in humans.

The present study investigates the effect of distraction frequency on the development of tensile force in the tissues during lengthening. Two patients with bilateral Ilizarov leg lengthening underwent distraction with high frequency in one leg and low frequency in the other. The clinical situation represented a unique model for investigating the effect of distraction frequency, as each individual served as its own control. Both patients had double level lengthening. Distraction frequency at the proximal lengthening zone was 0.25 mm x 4 in the first leg and 1/1440 mm once every minute in the other. Total diurnal distraction at the proximal metaphysis was 1 mm in both legs. In addition, a distal metaphyseal distraction of 0.25 mm x 3 daily was performed on each leg. The tissue's mechanical response was monitored by measuring the tensile force at the proximal osteotomy. Both patients experienced a significant lower level of force during the high frequency lengthening. The lower level of force was concluded to be due to improved soft tissue adaptation, rather than reduced bone regeneration. Accordingly, high distraction frequency was considered favourable to low frequency, and is recommended in large lengthenings where high force levels are expected.

Reduced lengthening index by use of bifocal osteotomy in the tibia: comparison of monofocal and bifocal procedures with the Ilizarov external fixator.

We lengthened 63 tibial segments in 49 patients, performing a monofocal osteotomy on 31 segments and a bifocal osteotomy on 32 segments. In the monofocal osteotomy group, the average lengthening was 4.8 (2.4-7.1) cm with a lengthening index (LI) of 1.7 (0.9-4.4) months/cm. In the bifocal osteotomy group, the average lengthening was 7.4 (4.9-10.0) cm and with a LI of 1.0 (0.7-2.1) months/cm. The difference in LI between the groups was statistically significant, but more major complications, like persistent ankle joint contracture and pseudarthrosis in the callotasis lengthening zone, occurred with bifocal lengthening.

Tissue response during monofocal and bifocal leg lengthening in patients.

The purpose of this investigation was to compare the tissue response during mono- and bifocal limb lengthening. The study includes four patients undergoing leg lengthening. All patients started out bifocally with a total diurnal distraction of 1.75 mm, but proceeded monofocally with a rate of 1 mm a day when the distal distraction was terminated due to contractures or pain. The tissue response was monitored by registration of axial force in the distraction rods. The force increased linearly during bifocal lengthening, but culminated or decreased in the period of monofocal lengthening. Average tissue stiffness, defined as the immediate force increase due to each 0.25 mm distraction increment, was significantly higher in the bifocal lengthening phase. The force decay between each distraction was significantly lower during bifocal lengthening, thus indicating decreased tissue accommodation. Details in the force registrations indicated that the soft tissue, not the regenerate, was the main contributor to the tensile force. Conclusively, the tissues at the two osteotomy sites do not lengthen independently. Bifocal lengthening exposes the entire soft tissue to large loads, resulting in increased tissue stiffness and reduced ability to adapt to the increased length. Accordingly, bifocal leg lengthening requires special attention to soft tissue adaptation.