Deformity correction and extremity lengthening in the lower leg: comparison of clinical outcomes with two external surgical procedures

In lengthening osteotomies carried out from 1992 to 2008 at our university center, a total of 95 patients received treatment in the lower leg using two different external fixators—the Taylor Spatial Frame (TSF) and the classic Ilizarov ring fixator (IRF). The criteria for inclusion in the study consisted of distraction by at least 20 mm without simultaneous varus or valgus osteotomies of more than 10° at the tibia. Patients with less than 20 mm of planned lengthening and more than 10° of planned axial adjustment were excluded in order to rule out cases mainly involving only gradual adjustment. The rate of patients who were lost to follow-up was 48%. Due to the long periods between the operation and the follow-up examination, changes of residence meant that only limited tracing of patients was possible—particularly those who were treated in the 1990s. Although it is compulsory in Germany for residents to be registered at Residents’ Registration Offices, no inquiries for official assistance in tracing patients were made of these offices, due to the high costs expected to result after multiple changes of residence. The number of patients in the follow-up is 43, with 53 lengthened segments. Thirty-three segments were treated with the TSF, 20 with the IRF. The patients’ mean age at the time of surgery was 13.5 years (range 2–54 years). There were 14 female patients (24 segments) and 19 male patients (29 segments). The follow-up examinations took place over periods of 2–15 years postoperatively, between the fall of 2010 and 2012. A distinction was made between acquired and congenital entities. Monofocal and bifocal osteotomies were carried out in all of the groups. There were 13 monofocal and 20 bifocal osteotomies in the TSF group, eight monofocal and 12 bifocal osteotomies in the IRF group. With monofocal osteotomies, no distinction was made in this study between proximal and distal osteotomy. The mean preoperative leg length difference in all groups taken together was 56.25 mm, with 53.67 mm in the TSF group, 58.8 mm in the IRF group.

The leg length differences and centre of rotation and angulation (CORA) were measured preoperatively by taking leg axis views with the patient standing and corresponding lateral radiographs (Rödl et al. 2003; Seide et al. 1999; Feldman et al. 2003). In addition, the distal medial/lateral femoral angle, the proximal medial/lateral tibial angle, the distal tibial angle and the mechanical axis deviation (MAD) were measured. With TSF, preoperative planning included establishment of the reference fragment (Feldman et al. 2003). The position of the tibia relative to the reference ring (Seide et al. 1999) was used to define the mounting parameters.

With the IRF distraction was increased at 1 mm/d and with tight radiographic check-ups. The mean period in days to the start of distraction was 10 days in all of the groups. Fortnightly follow-up checks with a clinical examination and radiography were carried out, and leg axis views with the patient standing were taken every 3 months to assess the regenerate bone and to measure the articular angle and leg length difference in each patient.

With approval from the hospital’s review board and with written informed consent from the patients before the follow-up examination, a standardized questionnaire assessing the postoperative physical and mental state of health was sent to each patient in advance of the reassessment. The Short-Form Health Survey-36 (SF-36) questionnaire was used, with an evaluation of 36 questions consisting of a total of eight components and statements about patients’ perception of their physical and mental health. The questionnaire’s eight categories take into account physical functioning, physical role functioning, bodily pain, general health perceptions, vitality, social functioning, emotional role functioning, and mental health. A scoring scheme for the individual categories can be used to provide a physical summary score and a mental summary score, allowing a subjective assessment of the patient’s state of health. The results are standardized into an integral score with points from 0 to 100, with a high score representing a better subjectively perceived overall state of health.

The follow-up comprised an examination in accordance with various objective scores for each joint. For the knee joint, the Knee Society score as described by Insall et al. (1989) was used, which is also divided into an objective clinical section (the knee score) and a subjective functional section (the function score). The knee score takes into account the aspects of pain, range of motion in degrees, and ligament stability, with 0–100 points being possible.

The Tegner activity score (Tegner and Lysholm 1985) is used to assess postoperative physical activity. Assessment of the upper ankle joint (UAJ) and lower ankle joint (LAJ) was objectivized using the Weber score as an instrument. It features six categories, each including the three subjective dimensions of pain, walking distance, and activity at work and the three objective dimensions of radiographic diagnosis and clinical examination of the UAJ and LAJ using the neutral-0 method. The value 0 indicates the best possible result. Motor function in the extremity during plantar flexion, dorsal flexion, inversion, and supination is assessed using the Motor Score, divided into six levels of 0–5 points. The neurological status comprised the Neuropathy Symptom Score (NSS) and Neuropathy Deficit Score (NDS). The NSS covers the type of symptoms (stinging, numbness, paresthesias, faint feeling, cramp, pain), the location of the symptoms (foot, lower leg), exacerbation depending on the time of day and symptomatic improvement depending on exertion. The NDS assesses reflex status in the Achilles tendon, vibration sensitivity at the metacarpophalangeal joint of the great toe, pain on the back of the foot, and temperature sensitivity in both feet.

After the follow-up examination, all of the examination results obtained during and after completion of the fixator wearing period, as well as the current results, were correlated with the Paley criteria for problems, obstacles, and complications (Paley 1990). Problems in this context consist of difficulties during the distraction phase or consolidation phase that can be managed conservatively up to the time of fixator removal. Obstacles are events requiring secondary surgical intervention or an intervention under anesthesia, or an unplanned additional hospitalization lasting more than 24 h, which are resolved by the time the treatment is completed. Complications are defined as difficulties that it has not been possible to correct before removal of the fixator, although all possible conservative and surgical measures aimed at correcting them have been exhausted. An additional distinction is made between mild complications followed by successful conservative treatment after fixator removal and severe complications with persistent symptoms or surgery being required or with complete failure to achieve the goal of treatment (e.g., amputation, persistent leg length differences, limited everyday mobility).

All of the data were recorded using Microsoft Office Excel 2010 and were processed using descriptive statistics with IBM SPSS Statistics, version 21.0. For statistical calculations, the normal distribution of the groups was checked using the Kolmogorov–Smirnov test. If a normal distribution was present, the t test was then used to calculate significance with a confidence interval of 95%. When the variables were not normally distributed, the Mann–Whitney test for comparisons between two groups was used.