Bone 34 (2004) 845 – 848 www.elsevier.com/locate/bone
Predicting duration of Ilizarov frame treatment for tibial lengthening A.F. Dinah * Musgrave Park Hospital, Belfast, Northern Ireland, UK St. Helier Hospital, Carshalton Surrey, UK Accepted 29 January 2004
Abstract Aim: To predict duration of treatment for tibial lengthening, as a function of target length increase. Method: Review of case notes and radiographs of patients undergoing Ilizarov method of tibial distraction osteogenesis. Results: In the 27 cases suitable for analysis, the median age was 29.9 years (13.3 to 72.6 years), and the median distraction was 3.5 cm (1.0 to 7.2 cm). A positive linear relationship (r = 0.7) was demonstrated between the distraction length (x, in cm) and the frame duration ( y, in days), according to the equation y = 54x + 94. A negative hyperbolic relationship was also demonstrated between rate of bone healing and distraction length (r = 0.6), with distractions over 3.0 cm healing significantly faster than shorter ones (P < 0.03). D 2004 Elsevier Inc. All rights reserved. Keywords: Ilizarov frame; Distraction osteogenesis; Callotasis; Duration
Introduction Distraction osteogenesis (or callotasis) is a useful technique for regaining bone length lost from acute traumatic conditions or for lengthening congenitally short bones. Its applications vary from the craniofacial to the appendicular skeleton. Ilizarov  enumerated several biological principles to optimize bone healing: stable fixation, percutaneous metaphyseal corticotomy without damage to the medullary cavity, latent period before starting distraction, and a distraction rate of 1 mm/day (in four divided adjustments). After the latency and distraction phases, the third and usually the longest phase of the treatment is the consolidation of the regenerate. When counseling patients about the treatment, a common question is the length of time the frame has to be worn for. The duration of the distraction phase (1 mm/day) depends on the length to be regained, and the consolidation phase depends on the rate of bone healing. Classically, the metaphysis has been the preferred corticotomy site because of its superior osteogenic potential . There is also evidence that rate of healing is affected by the length of distraction [3,4]. The aim of this study was to determine
* 2 Bordesley Road, Morden, Surrey SM4 5LR, UK. E-mail address: [email protected]
8756-3282/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.bone.2004.01.026
whether the frame time could be predicted from the distraction length in cases of uncomplicated tibial lengthening.
Patients and methods All patients undergoing distraction osteogenesis of the tibia with an Ilizarov frame between 1999 and 2001 were identified from a dedicated Ilizarov database maintained prospectively by the Ilizarov team for audit purposes. The case notes and radiographs were also retrieved and examined. Skeletally immature patients were excluded, as they have greater bone healing potential than adults [5– 7]. Those undergoing bone transport and those requiring major alterations or frame revision during the distraction process were also excluded. All patients had standard application of a fine-wire circular frame. A proximal subperiosteal corticotomy was performed percutaneously with a Gigli saw. In cases requiring segmental excision of areas of non- or malunion, or abnormal bone, this was done as an open procedure, with acute shortening at the excision site, and then corticotomy (with subsequent distraction) at a more proximal site. Patients were encouraged to mobilize fully weight-bearing as soon as possible, with appropriate physiotherapy. Distraction started on the fifth to seventh postoperative day, at a rate of a quarter turn four times daily,
A.F. Dinah / Bone 34 (2004) 845–848
Fig. 1. Scatter plot (r = 0.7) and linear regression line ( y = 54x + 94).
that is, 1 mm/day. Patients were discharged home once distraction had started and reviewed with updated radiographs every 2 weeks in the outpatient clinic. Once the required length had been achieved, adjustments were stopped, and the regenerate was allowed to consolidate with the frame in situ. During the consolidation phase, patients were reviewed at about 6-week intervals with radiographs. According to clinical and radiologic assessment of the regenerate, the frame was initially dynamized (i.e., loosened), then gradually deconstructed, allowing the regenerate to transmit more weight. The frame was finally removed when the regenerate was judged to be sufficiently mature by the presence of three out of four cortices on anteroposterior and lateral radiographs . For each patient, the duration of frame treatment and total length gained were determined from the Ilizarov database, with cross-referencing from the case notes, and radiographs. For each set of data, the corresponding
healing index  (ratio of increase in length to time to frame removal, in days/cm) was calculated. If there was missing information or discrepancies, the patient was excluded from analysis. Scatter plots of frame duration against distraction length (Fig. 1) and healing index against distraction length (Fig. 2) were constructed, and linear regression was used to investigate mathematical relationship between the variables.
Results Twenty-seven tibias in 24 patients (19 males and 5 females) were suitable for analysis. Variables were found to have a nonnormal distribution with a positive skew. The median age was 29.9 years (range, 13.3 to 72.6 years). The median distraction was 3.5 cm (range, 1.0 to 7.2 cm), equivalent to 8.6% of bone length (range, 2.5% to 20.8%).
Fig. 2. Scatter plot of healing index versus distraction length showing a negative hyperbolic relation (r = 0.6).
A.F. Dinah / Bone 34 (2004) 845–848 Table 1 Regression analysis for ‘duration versus distraction’ line (r = 0.7)
95% confidence limits Lower
In 19 tibias, the underlying bony disorder was chronic posttraumatic non- or mal-union; there were seven cases of acute posttraumatic shortening and one case of congenital lower limb shortening (not dwarfism). The recorded complication rate was 44%, as follows: incomplete initial corticotomy (five cases, requiring repeat corticotomy under general anesthesia), residual deformity at corticotomy or regenerate sites (three cases, requiring further treatment), wound breakdown at segmental excision sites (two cases), infected wire requiring removal (one case), and fracture after frame removal (one case). There were no cases of nonunion. A scatter plot of ‘duration versus distraction’ (Fig. 1) shows a positive linear relationship with r = 0.7. The equation y = 54x + 94 describes the approximate relation between frame duration ( y, in days) and distraction (x, in cm). The 95% confidence intervals for the gradient and intercept are detailed in Table 1. A scatter plot of ‘healing index versus distraction’ is shown in Fig. 2. Nonlinear regression reveals a negative hyperbolic relationship (r = 0.6); that is, healing index decreases exponentially with increasing length of distraction. Indeed, short distractions (up to 3.0 cm) have a significantly greater healing index than longer distractions (P < 0.03), as shown in Table 2.
Discussion Duration of treatment is significant for the patient who has to live with the cumbersome frame. The longer the frame is on, the higher the risks of complications, such as pin-site infection. Thus, the surgeon must minimize the duration of treatment, without compromising its safety and success. Moreover, the patient must be counseled appropriately, so as to have reasonable expectations of the duration of treatment. The expected trend of longer frame times for longer distraction gaps is borne out by the scatter plot and linear regression model (Fig. 1). The gradient of the line gives a mean healing index of 54 days/cm for the whole group. As expected, this is higher than the healing index previously reported when using the Ilizarov method in younger age groups  or in children . Extrapolating the line to the vertical axis gives a frame time of about 94 days for a simple corticotomy with no distraction. This ‘minimum consolidation time’ is consistent with clinical experience of healing time of about 3 months
for an uncomplicated, low-energy tibial fracture treated in an Ilizarov frame. However, the 95% confidence intervals for both gradient and intercept are wide (Table 1), implying that there is substantial variation between individual patients. Indeed, the sample was a heterogeneous one, and unfortunately, the small number of subjects did not allow meaningful multiple regression analysis to control for other variables such as age, smoking status, underlying disorder, percutaneous osteotomy or open excision, etc. Such a linear model can therefore only serve as a guide to patient and surgeon as to the duration of frame treatment. The fact that distraction length also influences the healing index has been previously mentioned by Fischgrund et al.  and a 3.0-cm cut-off recently described by Sakurakichi et al. . This finding has been reproduced in this study, as shown in Fig. 2 and Table 2. The variation may be due to differential contributions of distraction and consolidation phases to the overall frame time. For small distractions (e.g., up to 3 cm), the minimum consolidation time contributes relatively more to the total frame time, inflating it disproportionately with respect to the distraction. As the distraction time increases, the consolidation time contributes relatively less to the total frame time— this results in a lower healing index for longer distractions. Thus, any comment on healing index—or rate of bone healing—needs to be qualified by the distraction length. Currently, the decision of when to remove the frame is based on clinical and radiologic findings. For example, the presence of three out of four cortices on anteroposterior and lateral radiographs of the regenerate is deemed evidence of adequate regenerate consolidation . Bone density studies have shown that at the time of frame removal, the regenerate has reached about 70% of the bone mineral content of the contralateral normal limb . In one study , the investigators routinely used a cast to protect the regenerate after frame removal and had a regenerate fracture rate of 3.0%. In this study, a cast was not used routinely after frame removal, and there was only one case of fracture after removal of the frame (3.7%). The optimal time for full consolidation remains elusive, although there have been attempts using quantitative computed tomography , ultrasonic assessment , and more recently, 99Tc-DP scintigraphy . For the present time, however, clinical and radiographic features play the
Table 2 Effect of distraction length on healing index Distraction
Number Healing index (days/cm)
Up to 3.0 cm
13 57.3 – 171.0 102.0*
14 40.0 – 102.0 77.2*
* Significant difference (Mann – Whitney U test: P < 0.03).
A.F. Dinah / Bone 34 (2004) 845–848
major part in deciding when to remove the frame. The linear model described in this study may have a place in preoperative patient counseling, providing an approximation of the amount of time to which a patient can expect to be managed with an external frame.
Acknowledgment I am grateful for the help and support of the Ilizarov team at the above institution, in particular, Mr. Michael Laverick, MD FRCS.
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