The role of skeletal sonography in limb lengthening procedures.HM Malde, SS Hemmadi, D Chadda, ML Parihar, PB Bhosale, RP Kedar
Dept of Orthopaedics, KEM Hospital, Parel, Bombay, Maharashtra.
Eleven patients (8 males, 3 females) undergoing limb-lengthening procedures were subjected to weekly conventional radiography along with fortnightly skeletal sonography of the distraction site, to assess the rate of new bone production and complications. The radiographs were assessed for: (i) distance between the distracted bone ends, (ii) presence of new bone formation at the distraction site, (iii) regeneration of the cortical outline and (iv) overlaying soft tissue abnormality. The sonographs were assessed for: (i) distance between the distracted bone ends, (ii) rate of new bone formation, (iii) density of the new bone produced, (iv) integrity and continuity of the cortical outline and (v) overlaying soft tissue abnormality. Our results indicate the superiority of sonography over conventional radiographs in: (i) detecting early new bone formation, (ii) establishing cortical and medullary canal remodelling, (iii) detecting soft tissue complications at the distraction site and (iv) determining the presence of fluid collection at the distraction site, in patients with delayed consolidation. Conventional radiographs were more accurate in determining the distance between the two distracted bone ends, and thus the degree of distraction achieved. Ideal assessments of events at the distraction site can be achieved by a combined assessment of conventional radiotherapy and skeletal sonography.
Keywords: Bone Lengthening, Bone Regeneration, physiology,External Fixators, Female, Follow-Up Studies, Human, Leg Length Inequality, etiology,surgery,ultrasonography,Male, Postoperative Complications, ultrasonography,
The assessment of bone production and complications following limb-lengthening procedures is currently done by a combination of clinical examination and conventional radiographs. We have, however, found sonography to be an extremely useful investigative tool in evaluating events at the distraction, site. Young et al, were the first to report a series of 12 patients in whom sonography was used following limb-lengthening to detect early new bone formation. We describe here our experience regarding the use of sonography following limb-lengthening procedures.
Our study group comprises of 11 patients (8 males, 3 females) who underwent limb-lengthening procedures using the AD tubular threaded external fixator system, for following reasons -: following infection (4), trauma (3), operation (2), burns (1) and in 1 patient there was congenital shortening of limb.
Weekly conventional radiographs of the operative sites were obtained following the limb-lengthening procedures, in all patients. These radiographs were assessed for: (i) length of the osteotomy effect, (ii) presence of new bone formation at the distraction site, (iii) cortical outline, whether restored, at the distraction site, and (iv) overlaying soft tissues.
Fortnightly sonography was performed with or without standoff pads, using sector, convex and linear array transducers with frequencies of 5.0 and 7.5 MHz (Sonoline AC, Siemens Medical Systems), in these patients, following the initiation of distraction. The sonographs were assessed for: (i) length of the osteotomy site, (ii) echotexture at the osteotomy site (to detect echogenic new bone), (iii) sound attenuation at the distraction site (to determine the density of new bone formation), (iv) cortical outline (to determine the integrity and continuity of the neocortex) and (v) overlaying soft tissue abnormality.
Conventional radiographs proved more accurate in determining the distance between the two distracted bone ends. Sonographic determination of this distance was found to be variable and dependent on the scanning plane employed.
Sonography proved superior to conventional radiography in detecting early new bone formation. Callus formation is typically seen on conventional radiographs as well-formed columns of bone arising from each bone surface. A radioluscent central band initially separates the newly formed bone. It took at least 8 weeks to convincingly demonstrate new bone by conventional radiography. The sonographic appearance of new bone consists of echogenic foci within the distraction site, which gradually become aligned along the long axis of the bone, and increase in size and number until they coalesce as echodense bone [Figure:1a] and [Figure:1b]. Sonography consistently revealed new bone formation within the distraction site by the end of the 2nd week.
Remodelling of cortex and medullary canal was also detected much earlier on sonograms (8-12 weeks) than on conventional radiographs (minimum 18 weeks). Active radiologic and sonographic supervision of the distraction site significantly reduced the number of complications. One patient developed grade 2, pin tract problems. Although this was not evident on conventional radiographs, sonograms readily showed a well-defined fluid collection in the subcutaneous tissues. One patient developed non-union at the distraction site. Conventional radiographs showed a non-specific lack of callus formation across the distraction site, but sonography revealed the presence of a fluid collection at the distraction site, responsible for the nonunion.
Failure to regularly follow-up for the radiographic and sonographic examination on the part of one patient led to premature consolidation at the distraction site. No patient developed malunion, refracture or osteomyelitis.
Overall, both studies were equally well-tolerated by all patients.
Current limb-lengthening techniques, which involve fracture of the limb and distraction of the fragments at a slow constant rate, have been successfully used to correct angular deformities resulting from congenital causes (eg. achondroplasia) or as a result of previous trauma. The success of these procedures depends on the successful production of new bone at the distraction site, which in turn depends upon the rate of distraction. If this rate is too slow in proportion to the amount of new bone formation, premature fusion at the distraction site will occur. If it is too fast, insufficient new bone formation will occur to allow healing of the distraction site. Because of the limitations of plain radiographs in detecting the small amount of new bone that forms at the distraction site in the early stages of healing, sonography has been advocated as the preferred modality for the same purpose. At the same time, conventional radiographs are necessary to allow assessment of alignment of bone fragments. They are also preferred to detect the complications of maialignment or angulation, malunion, refracture, joint deformity and pin osteolysis. Also since the duration of distraction depends upon the distance between the 2 distracted bone segments, this factor is better assessed by conventional radiographs.
We have successfully utilised a combination of conventional radiology and sonography to evaluate the changes occurring at and around the distraction site. Our study emphasizes the superiority of sonography over conventional radiology in (i) detecting early new bone formation (which markedly influences the rate of distraction), (ii) rapidly establishing cortical and medullary canal remodelling (which leads to early weight bearing), (iii) detecting soft tissue complications at the distraction site (which can then be promptly corrected without further complications), (iv) determining complications such as fluid collections at the distraction site in patients with delayed consolidation.
Ultrasound has been used for the early detection of osteomyelitis, An anecholic fluid collection adjacent to the bone dissecting in a subperiosteal or extra periosteal location may suggest osteomyelitis. However, any fluid (eg. inflammatory or haemmorhagic) next to bone would have a similar appearance at sonography and therefore the diagnosis may not be specific.
Conventional radiographs were found to be more accurate in determining the distance between the two distracted bone segments and thus the degree of distraction.
Hence we feel that a combination of radiographic and sonographic evaluation ensures successful limb-lengthening and minimises complications.
[Figure - 1], [Figure - 2]