A comparative study of bone union and nonunion during distraction osteogenesis

BACKGROUND

The clinical characteristics of bone nonunion during distraction osteogenesis (DO) were rarely discussed. This study was employed to specify the difference between bone union and nonunion during DO.

METHODS

The patients with bone lengthening were recruited in our study. The bone union cases indicated the ones that remove the external fixator successfully, whereas the bone nonunion represented the bridging callus did not appear even after 9 months (an absence of bridging callus for at least three out of four cortices on plain radiographs) that needs autogenous bone transplantation. The differences in the pixel value ratio (PVR) growth of regenerated callus, lengthening index (LI), healing index (HI), external fixation index (EFI) and blood biochemical indexes between bone union and nonunion were analyzed.

RESULTS

A total of 8 bone nonunion and 27 bone union subjects were included in this study. The PVR growth in bone nonunion was significantly lower than that in bone union (0.19 ± 0.06 vs. 0.32 ± 0.16, P = 0.048). Interestingly, the HI and EFI in bone nonunion was significantly higher than that in bone union (62.0 ± 31.4 vs. 37.0 ± 27.4, P = 0.036; 75.0 ± 30.9 vs. 49.9 ± 16.1, P = 0.006). However, no significant difference with regard to LI was identified (0.76 ± 0.52 vs. 0.77 ± 0.32, P = 0.976). Moreover, the circulating level of urea and lymphocyte count in bone union was significantly lower than that in bone nonunion (4.31 ± 1.05 vs. 5.17 ± 1.06, P = 0.049; 2.08 ± 0.67 vs. 2.73 ± 0.54, P = 0.018). On the contrary, the circulating level of magnesium in bone union was significantly higher than that in bone nonunion (0.87 ± 0.07 vs. 0.80 ± 0.07, P = 0.014).

CONCLUSION

Compared to the bone union, the PVR growth was significantly lower, whereas the HI and EFI was significantly higher in the bone nonunion. Moreover, the circulating level of urea, magnesium and lymphocyte count was also different between these two. Therefore, the PVR, HI and EFI seems to be reliable and sensitive indicators to reflect the bone nonunion during DO, which might be considered in bone lengthening. Further prospective studies are still needed to elaborate the concerned issues.

Early Weight-bearing Accelerates Regenerate Bone Mineralisation: A Pilot Study Comparing Two Post-operative Weight-bearing Protocols Following Intramedullary Limb Lengthening Using the Pixel Value Ratio

Introduction

Limb lengthening is increasingly accomplished by internal lengthening nails. Previous versions of the magnetic lengthening nails made from titanium alloy allowed limited weight-bearing. In contrast, the newer nails made of stainless steel allow increased weight-bearing. An objective comparison of the rate of healing of the regenerate bone based on the weight-bearing capabilities of these two types of lengthening nails has not been evaluated. The hypothesis for the study is that earlier commencement of full weight-bearing in patients treated with the stainless steel STRYDE® nail will lead to faster healing of the regenerate bone during intramedullary limb lengthening compared with those treated with the titanium PRECICE® nail.

Materials and methods

Thirty patients, divided into two groups of 15 each, underwent antegrade intramedullary lengthening of the femur using a magnetic lengthening nail between May 2017 and November 2020. The pixel value ratio (PVR) obtained from serial digital radiographs was used to quantitatively determine the regenerate bone's mineralisation rate. We compared the rate of healing of the regenerate bone in both groups of patients using the PVR.

Results

Patients treated with the STRYDE® nail achieved unassisted full weight-bearing significantly earlier than patients treated with the PRECICE® nail (12 weeks vs 17 weeks for STRYDE® and PRECICE® nail-lengthened patients, respectively, p = 0.003). There was no difference in the PVR between both groups of patients at the time of full weight-bearing (p = 0.0857). However, patients treated with the STRYDE® nail attained a PVR of 1 significantly earlier than those treated with the PRECICE® nail (0.0317).

Conclusion

The STRYDE® nail provides an earlier return of function and full weight-bearing compared with the PRECICE® lengthening nail. Earlier commencement of weight-bearing ambulation leads to more rapid mineralisation of the regenerate bone in patients undergoing intramedullary limb lengthening.

How to cite this article

Bafor A, Duncan ME, Iobst CA, et al. Early Weight-bearing Accelerates Regenerate Bone Mineralisation: A Pilot Study Comparing Two Post-operative Weight-bearing Protocols Following Intramedullary Limb Lengthening Using the Pixel Value Ratio. Strategies Trauma Limb Reconstr 2022;17(3):148-152.

Bone reconstruction: Subjective evaluation and objective analysis based on conventional digital X-rays - a retrospective evaluation

BACKGROUND

Various approaches have been used to evaluate callus stiffness in distraction osteogenesis. This assessment becomes even more critical as inadequate corticalization and premature removal of the frame lead to bending, refracture, and loss of length. This study aimed to verify the objective Pixel Value Ratio (PVR) and define an evaluation scheme to assess callus tissue development during internal and external bone lengthening.

HYPOTHESIS

There are no differences between subjective parameters and objective evaluation for external and internal bone lengthening.

PATIENTS AND METHODS

We included 24 patients in this retrospective study, treated by distraction osteogenesis of the lower limb. Ten patients were treated with external ring fixators and 14 with intramedullary lengthening devices. The minimum distraction distance was 3cm. Callus tissue was evaluated with the PVR, using digital X-rays during and after treatment. We combined this method with subjective evaluation parameters, including the continuity, signal intensity, and the regeneration tissue's homogeneity, presented in the X-ray Evaluation System for Distraction Osteogenesis (XESDO).

RESULTS

The subjective evaluation showed an increase of continuity and signal-intensity between 4th postoperative weeks and complete healing with significant differences between the external and internal groups for homogeneity only after four weeks and for all parameters at 3C (p<0.05). The PVR showed an increase during consolidation with values between 0.7 and 1.0 for both groups with almost perfect interobserver agreement. Significant lower values were found in the anterior tibial cases.

CONCLUSION

PVR appears to be a practical tool for radiological evaluation of callus tissue development. In combination with the newly introduced XESDO and the surgeon's experience, these methods can be helpful for decisions during all phases of distraction osteogenesis. It is important for adapting alignment or distraction-rate, as various potential complications can be detected early. However, further studies are necessary to assess the image-based determination of callus tissue stability.

LEVEL OF EVIDENCE

III; cohort study.

Evaluating the Utility of the Pixel Value Ratio in the Determination of Time to Full Weight-bearing in Patients Undergoing Intramedullary Limb Lengthening

Introduction

Limb lengthening using intramedullary nails is an increasingly popular method of achieving limb length equalisation. Currently, the decision regarding when to commence full weight-bearing (FWB) remains largely subjective. Objective criteria for determining the proper timing of FWB would be helpful to limb lengthening surgeons. This study examines using the pixel value ratio (PVR) as an objective method to determine the time to FWB for patients being lengthened with an intramedullary nail.

Materials and methods

A retrospective chart review of 42 patients who underwent unilateral lengthening of the femur was undertaken. The PVR of all four cortices of the regenerate bone was monitored throughout the distraction and consolidation stages to determine the ratio at the time of FWB.

Results

Clinically and radiologically determined FWB was achieved at a mean time of 125.7 ± 30.1 days from surgery. The mean PVR at the time of FWB was 0.94. The medial cortex healed fastest with a mean PVR of 0.96, while the posterior cortex healed slowest with a mean PVR of 0.92.

Conclusion

The PVR is a quick and reliable method to objectively assess the state of healing of the regenerate bone during distraction osteogenesis. We observed that there were no adverse effects when subjects commenced FWB when three out of the four cortices had a PVR of at least 0.93.

How to cite this article

Bafor A, Duncan ME, Iobst CA. Evaluating the Utility of the Pixel Value Ratio in the Determination of Time to Full Weight-bearing in Patients Undergoing Intramedullary Limb Lengthening. Strategies Trauma Limb Reconstr 2020;15(2):74-78.