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Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor
G Model
JINJ-6230; No. of Pages 5 Injury, Int. J. Care Injured xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Injury journal homepage: www.elsevier.com/locate/injury
Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor Nael Hawi a,*, Mohamed Kenawey b, Martin Panzica a, Timo Stuebig a, Mohamed Omar a, Christian Krettek a, Emmanouil Liodakis a a b
Trauma Department, Hannover Medical School, Germany Orthopaedic Surgery Department, Sohag University, Egypt
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 14 May 2015
Introduction: Callus distraction of the femur using an intramedullary distractor has several advantages over the use of external fixators. However, difficulty in controlling the mechanical axis during lengthening may cause deformities and knee osteoarthritis. Purpose of the study is to answer the following questions: (1) is lengthening with an intramedullary device associated with a medial or lateral shift of the mechanical axis? (2) Which factors are associated with varisation/valgisation of the mechanical axis during lengthening? Materials and methods: We analysed pre-treatment and post-treatment radiographs from 20 patients who underwent unilateral femoral-lengthening procedures using intramedullary distractors. Patients with acute correction of pre-existing deformities or combined ipsilateral femoral and tibial lengthening were excluded. Mechanical axis deviations, osteotomy level, and nail–medullary canal ratio were recorded. Results: Compared to the preoperative axis, the mechanical axis shifted medially in 7 patients (varisation group) and laterally in 13 patients (valgisation group). The groups did not significantly differ regarding preoperative leg length discrepancy (LLD), mechanical axis alignment, LLD-cause and implants used. The nail–medullary canal ratio significantly differed between groups (p < 0.001), being <85% in the varisation group and >85% in the valgisation group. The distance between the lesser trochanter and the osteotomy site was significantly longer in the valgisation group (58.9 16.3 mm, middle third of the femur) compared to the varisation group (40.6 11.4 mm, proximal third of the femur; p = 0.02). Conclusion: The nail–medullary canal ratio should be considered during preoperative planning. To avoid a varisation effect—for example, in cases with pre-existing varus alignment—it would be advisable to perform an osteotomy at the middle third of the femur with implantation of a nail that fully covers the medullary canal at the osteotomy site. Level of evidence: Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence. ß 2015 Elsevier Ltd. All rights reserved.
Keywords: Telescopic nails Femoral lengthening Mechanical axis changes Level of osteotomy
Introduction
* Corresponding author at: Trauma Department, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. Tel.: +49 17615326964; fax: +49 5115325877. E-mail addresses: [email protected] (N. Hawi), [email protected] (M. Kenawey), [email protected] (M. Panzica), [email protected] (T. Stuebig), [email protected] (M. Omar), [email protected] (C. Krettek), [email protected] (E. Liodakis).
The last 20 years have seen much progress towards the development and establishment of totally implantable intramedullary lengthening nails in clinical practice [1–5]. This technique carries the main advantage of avoiding complications associated with external fixators, such as pin tract infections, neurovascular injuries, transfixation of soft tissues, and refractures [2,4,6–9]. Additional advantages include earlier rehabilitation, reduced pain, reduced risk of infection, earlier normal joint motion and activity level, and improved patient comfort [2–6,10,11].
http://dx.doi.org/10.1016/j.injury.2015.05.040 0020–1383/ß 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
G Model
JINJ-6230; No. of Pages 5 N. Hawi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx
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Despite these advantages, intramedullary lengthening is also associated with problems and complications. Implant availability and cost can pose problems. Additionally, mechanically activated lengthening nails—such as the Albizzia nail and the intramedullary skeletal kinetic distractor (ISKD)—have fallen out of favour due to difficulties with the ratchet mechanism and the inability to control the distraction rate [10,12,13]. Moreover, intramedullary lengthening occurs along the anatomical axis of the femur, which carries the theoretical risk of medially displacing the knee joint and therefore causing genu valgum deformity—a secondary effect that would become more evident with increasing lengthening magnitude [8,14]. There are currently no consistent recommendations concerning the level of femoral osteotomy. It can generally be assumed that the proximal third of the femur, as a metaphyseal area, should have better bony regeneration and healing characteristics [11]. On the other hand, the femur diameter is wider in the proximal part compared to in the middle third or isthmus [15]. The authors believe that mechanical axis changes during limb lengthening with an intramedullary device can be better controlled by an osteotomy at the most narrow area of the bone (isthmus) than by an osteotomy at the subtrochanteric area (proximal third). Purpose of the study is to answer the following questions: (1) is lengthening with an intramedullary device associated with a medial or lateral shift of the mechanical axis? (2) Which factors are associated with varisation/valgisation of the mechanical axis during lengthening? Materials and methods The present study was approved by the Institutional Review Board (2164–2014). We retrospectively reviewed the charts of all patients who underwent intramedullary femoral lengthening procedures at our institution (Hannover Medical School, Hannover, Germany) between July 2002 and August 2014. The study included all patients who had long-standing radiographs taken before and after femoral lengthening with an intramedullary distractor. Patients with acute correction of preexisting deformities or who underwent combined ipsilateral femoral and tibial lengthening were excluded. Patients were also excluded if they did not have weight-bearing radiographs taken before and after lengthening. To maintain the control of the femoral rotation and to eliminate the effect of a possible malrotation on the mechanical axis, as described by Gungenheim et al. [16], an external fixator with 2 parallel 5 mm Schanz screws in the proximal and distal part of the femur was used. The fixator was placed before the femoral osteotomy and was removed after proximal and distal locking of the nail. A total of 20 patients (11 males and 9 females) underwent isolated femoral lengthening and met our inclusion criteria. The mean age at the time of the lengthening procedure was 29 11 years. Causes of leg length discrepancy included congenital shortening (n = 8) and post-traumatic shortening (n = 12). The mean amount of lengthening achieved was 4.1 1.9 cm, with a mean distraction rate of 1.3 0.5 mm/day. Preoperatively, 12 patients had a varus alignment and 8 had a valgus alignment. An ISKD nail (Orthofix, Valley, Germany) was used in 18 patients, while a Precice nail (Ellipse Technologies, Irvine, USA) was used in 2 patients. The implant diameter was either 10.7 mm or 12.5 mm. A trochanteric entry point was used in 17 cases and a piriformis entry in 3 cases. The mean osteotomy level was 52.4 17 mm (range, 34–75 mm) distal to the lesser trochanter. The preoperative and post-healing long-standing lower extremity X-rays were used to verify the lower limb alignment changes using the system described by Paley et al. [17]. In each
Table 1 Patient demographics and perioperative characteristics. Age (years) Female-gender Leg length discrepancy (LLD) Cause of LLD – post-traumatic Preoperative axis-varus Osteotomy side (proximal third) Percentage of medullary canal occupied by nail Transport index (mm/day) ISKD nail Piriformis entry point
29 11 9 (45%) 4.1 1.9 12 (60%) 12 (60%) 8 (40%) 86 14 (%) 1.3 0.5 18 (90%) 3 (15%)
radiograph, we measured the mechanical femoro-tibial angle (mFTA) and the mechanical axis deviation (MAD). The direct postoperative X-rays were used to measure the percentage of the femoral medullar canal that was occupied by the nail at the osteotomy level. All measurements were performed digitally on a computer with the use of FDA-approved medical planning software (MediCAD version 2.0, Hectec, Altfraunhofen, Germany) [18]. Continuous variables were checked for normal distribution using the Shapiro–Wilk test, and presented as mean standard deviation (SD). Categorical variables were described as frequencies with percentages. Between-group differences were evaluated with the Mann–Whitney U test for non-parametric continuous data, while Pearson’s chi-square test was used for categorical values. A two-tailed p-value of 0.05 was considered to be statistically significant. The SPSS 22.0 program (SPSS Inc., Chicago, IL) was used for statistical analyses. Table 1 shows the preoperative characteristics of the patients. Results Table 2 summarises the postoperative data. The mechanical axis shifted medially in 7 patients (varisation group) and laterally in 13 patients (valgisation group). The overall absolute change of the mechanical femoro-tibial angle was 1.68 1.28 (range: 0.18– 4.28, 25th–75th percentile: 0.68–2.18). This change was 1.48 1.48 (range: 0.18–4.28, 25th–75th percentile: 0.58–2.48) for the varisation group, and 1.88 1.18 (range: 0.38–3.98, 25th–75th percentile: 0.68– 2.48) for the valgisation group (p = 0.588). Table 2 Postoperative data.
Age (years) mFTA (8) Limb length discrepancy (mm) Transport index (mm/day) Distance distal to Lesser Trochanter (mm) Medullary canal -nail ratio (%)
Varisation group
Valgisation group
p-Value
24.7 10.7 1.4 1.4 49.0 24.4 1.3 1.2 40.6 11.4
31.5 11.8 1.8 1.1 36.3 14.9 2.2 1.2 58.9 16.3
0.26 0.59 0.26 0.18 0.02
69.7 6.6
95.0 6.9
Cause of LLD Post-traumatic Congenital
4 (20%) 3 (15%)
8 (40%) 5 (25%)
1.0
Entry point Piriformis Trochanteric
2 (10%) 11 (55%)
1 (5%) 6 (30%)
1.0
Type of nail ISKD Precice
5 (25%) 0 (0%)
13 (75%) 2 (10%)
0.11
Preoperative alignment Varus Valgus
4 (20%) 3 (15%)
9 (45%) 4 (20%)
0.65
<0.001
Bold values show a statistical significance (p < 0.05).
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
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JINJ-6230; No. of Pages 5 N. Hawi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx
The two groups did not significantly differ regarding preoperative leg length discrepancy, alignment, cause of length discrepancy, and implants used. The percentage of the medullary canal occupied by the nail at the osteotomy level—i.e. the nail–medullary canal ratio—significantly differed between the two groups (69.7 6.6 for the varisation group vs. 95.0 6.9 for the valgisation group; p < 0.001). The nail–medullary canal ratio was <85% among all patients of the varisation group and >85% among all patients of the valgisation group. The distance between the lesser trochanter and the osteotomy site was also significantly longer in the valgisation group (58.9 16.3 mm, middle third of the femur) compared to the varisation group (40.6 11.4 mm, proximal third of the femur; p = 0.02). In all patients, the desired length was achieved with no implant-related complications. One patient had insufficient bone regeneration and healing was achieved by revision surgery with bone grafting. Discussion Although changes of the mechanical axis after femoral lengthening are often not big (<2.18 in 75% of the cases in our study), they can be clinically significant. Axial malalignment has previously been associated with knee osteoarthritis [19] and biomechanical studies show that even small changes of the hip– knee–ankle angle have a significant effect in the distribution of
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the medial and lateral femorotibial compartment pressures [20,21]. Predicting the direction of the mechanical axis changes during lengthening is especially relevant in cases with pre-existing deformities in order to correct smaller deformities and to avoid worsening them [3,8,10]. The present study has some limitations. First, small sample size is a universal problem among studies investigating uncommon procedures, such as intramedullary limb lengthening. Second, our results are based on a retrospective study design where errors due to confounding and bias are more common than in prospective studies. Last but not least, our analysis was limited to mechanical axis changes, and we did not consider long-term outcomes, such as incidences of osteoarthritis or other deformity-related symptoms. This study has also important strengths, including the data completeness and detailed clinical information. To the best of our knowledge, this is the first study to analyse the association between mechanical axis changes, nail diameter and osteotomy site. In the tibia, the anatomical and mechanical axes are usually identical. In contrast, the anatomical axis of the femur is inclined 78 to its mechanical axis [17,22]. From a geometrical point of view, femoral lengthening along the anatomical axis causes a lateral shift of the mechanical axis (valgisation) [8,11]. However, this is contradicted by the clinical reality, in which alignment changes are difficult to predict. In our study, the mechanical axis shifted medially (varisation) in 35% of the cases.
Fig. 1. Mechanical axis before and after femoral lengthening in patients with nail–medullary canal ratios of <85% (A) and of >85% (B).
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
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The main finding of the current study was that the nail– medullary canal ratio at the osteotomy level was a significant predictor of varisation or valgisation of the mechanical axis (Fig. 1). The tendency of the femur to become varus in the presence of a nail–medullary canal mismatch can be explained by analysing the muscular anatomy of the thigh. The proximal fragment is continuously abducted by the abductor muscle group that inserts on the proximal femur, while the distal fragment is constantly adducted by the distally inserted adductors [23]. Proximal fragment abduction combined with distal fragment adduction cause varus angulation at the fracture or osteotomy level, which can be accentuated by the nail–medullary mismatch [24]. In cases of particularly wide medullary canal, the restricted range of available implant diameters (biggest nail diameter: 12.7 mm) can be problematic. To avoid the effects of a nail– medullary canal mismatch, the width of the medullary canal can be functionally decreased using blocking (‘‘poller’’) screws. The poller screws should be placed on the concave side of the deformity between the cortex and nail [24]. Another important finding of the study is the effect of the osteotomy level on the post-lengthening alignment. Intramedullary lengthening through a proximal osteotomy in the wide subtrochanteric area was associated with a low nail–medullary canal ratio, and consequently, varisation. This can be explained by the funnel shape of the femur (wide proximal and narrow in the middle third). So even if the nail fits the narrow medullary canal diameter at the isthmus, nail–medullary canal mismatch cannot be avoided at the wider proximal femur. On the other hand, more distal osteotomies in the middle third of the femur lead to valgisation of the mechanical axis if the nail fits the medullary canal. In agreement with our present results, Paley et al. [8] previously described five cases of femoral lengthening with external fixators in which subtrochanteric osteotomies were associated with marked varus angulation. The degree of the varus angulation does not seem to be associated with the LLD to be corrected, but depends more on the nail–medullary canal mismatch. In our study, only two patients with a middle-third femoral osteotomy showed postoperative varus angulation. In both patients, the medullary canal was 14-mm wide and a 10.7-mm nail was used (nail– medullary canal ratio = 76%). Guichet et al. [10] investigated intramedullary lengthening using Albizzia nails, and found that the femoral alignment was well maintained with no change in the lateral distal femoral angle. However, direct assessment of the mechanical axis revealed that there was a valgus increase of an average of 1.048 1.38. The osteotomy was performed at the level of the diaphyseal region, which is narrow. Thus, these results are consistent with our present findings. Recently, Burghardt et al. [14] closely examined changes of the mechanical axis associated with isolated ISKD femoral lengthening. They found that 26 out of 27 limbs showed lateral deviation of the mechanical axis with lengthening, and that in 11 limbs this deviation was significant (>2 mm according to their definition). In these 11 limbs, the mean lateral shift of the mechanical axis was 2 mm per cm of lengthening. The average osteotomy level was 5.5 cm distal to the lesser trochanter, which is very close to the isthmus. Our present study could confirm these findings only among the patients in which the medullary canal was fully covered by the nail at the osteotomy level. In cases where the ratio was lower than 100%, the magnitude of varus or valgus deviation could not be accurately predicted, because of the additional variables influencing the axis, such as lengthening along the anatomical axis, and degree of nail–medullary canal mismatch.
Nail design and entry point do not seem to affect lower limb alignment. In this study, two different types of lengthening nails (ISKD and Precice) were used. For each nail, there is an option to choose between a piriformis and a trochanteric entry point depending on the preference of the surgeon. Both variables (ISKD vs. Precice nail and Piriformis vs. Trochanteric entry point) were evaluated. No association between these variables and changes of the mechanical axis alignment were found in this study.
Conclusion In conclusion, the direction of mechanical axis deviation during intramedullary femoral lengthening depends on the ratio between the nail diameter and the medullary canal diameter at the level of the osteotomy. To avoid a varisation effect—for example, in cases with pre-existing varus alignment—it would be advisable to perform an osteotomy at the middle third of the femur with implantation of a nail that fully covers the medullary canal at the osteotomy site. To avoid a valgisation effect, the osteotomy can be performed a few centimetres distal to lesser trochanter with a nail diameter that is equal to the medullary canal diameter at the middle third of the femur and smaller that the medullary canal diameter at the osteotomy level.
Conflict of interest Each author certifies that he has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The ethical committee of the Hannover Medical School approved the study (2164–2014). References [1] Betz A, Baumgart R, Schweiberer L. First fully implantable intramedullary system for callus distraction – intramedullary nail with programmable drive for leg lengthening and segment displacement. Principles and initial clinical results. Chirurg 1990;61:605–9. [2] Guichet JM, Casar RS. Mechanical characterization of a totally intramedullary gradual elongation nail. Clin Orthop Relat Res 1997;281–90. [3] Hankemeier S, Pape HC, Gosling T, Hufner T, Richter M, Krettek C. Improved comfort in lower limb lengthening with the intramedullary skeletal kinetic distractor. Principles and preliminary clinical experiences. Arch Orthop Trauma Surg 2004;124:129–33. [4] Cole JD, Justin D, Kasparis T, DeVlught D, Knobloch C. The intramedullary skeletal kinetic distractor (ISKD): first clinical results of a new intramedullary nail for lengthening of the femur and tibia. Injury 2001;32(Suppl. 4): SD129–39. [5] Simpson AH, Shalaby H, Keenan G. Femoral lengthening with the intramedullary skeletal kinetic distractor. J Bone Joint Surg Br 2009;91:955–61. [6] Baumgart R, Betz A, Schweiberer L. A fully implantable motorized intramedullary nail for limb lengthening and bone transport. Clin Orthop Relat Res 1997;135–43. [7] Paley D. Problems, obstacles, and complications of limb lengthening by the Ilizarov technique. Clin Orthop Relat Res 1990;81–104. [8] Paley D, Herzenberg JE, Paremain G, Bhave A. Femoral lengthening over an intramedullary nail. A matched-case comparison with Ilizarov femoral lengthening. J Bone Joint Surg Am 1997;79:1464–80. [9] Simpson AH, Cole AS, Kenwright J. Leg lengthening over an intramedullary nail. J Bone Joint Surg Br 1999;81:1041–5. [10] Guichet JM, Deromedis B, Donnan LT, Peretti G, Lascombes P, Bado F. Gradual femoral lengthening with the Albizzia intramedullary nail. J Bone Joint Surg Am 2003;85-A:838–48. [11] Hankemeier S, Gosling T, Pape HC, Wiebking U, Krettek C. Limb lengthening with the Intramedullary Skeletal Kinetic Distractor (ISKD). Oper Orthop Traumatol 2005;17:79–101. [12] Kenawey M, Krettek C, Liodakis E, Wiebking U, Hankemeier S. Leg lengthening using intramedullay skeletal kinetic distractor: results of 57 consecutive applications. Injury 2011;42:150–5. [13] Kenawey M, Krettek C, Liodakis E, Meller R, Hankemeier S. Insufficient bone regenerate after intramedullary femoral lengthening: risk factors and classification system. Clin Orthop Relat Res 2011;469:264–73.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
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JINJ-6230; No. of Pages 5 N. Hawi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx [14] Burghardt RD, Paley D, Specht SC, Herzenberg JE. The effect on mechanical axis deviation of femoral lengthening with an intramedullary telescopic nail. J Bone Joint Surg Br 2012;94:1241–5. [15] Dorr LD, Faugere MC, Mackel AM, Gruen TA, Bognar B, Malluche HH, et al. Structural and cellular assessment of bone quality of proximal femur. Bone 1993;14:231–42. [16] Gugenheim JJ, Probe RA, Brinker MR. The effects of femoral shaft malrotation on lower extremity anatomy. J Orthop Trauma 2004;18:658–64. [17] Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs, preoperative planning of multiapical frontal plane angular and bowing deformities of the femur and tibia. Clin Orthop Relat Res 1992;65–71. [18] Tetsworth KD, Paley D. Accuracy of correction of complex lower-extremity deformities by the Ilizarov method. Clin Orthop Relat Res 1994;102–10. [19] Cooke D, Scudamore A, Li J, Wyss U, Bryant T, Costigan P. Axial lower-limb alignment: comparison of knee geometry in normal volunteers and osteoarthritis patients. Osteoarthr Cartil 1997;5:39–47.
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[20] Agneskirchner JD, Hurschler C, Wrann CD, Lobenhoffer P. The effects of valgus medial opening wedge high tibial osteotomy on articular cartilage pressure of the knee: a biomechanical study. Arthroscopy 2007;23:852–61. [21] Suero EM, Sabbagh Y, Westphal R, Hawi N, Citak M, Wahl FM, et al. Effect of medial opening wedge high tibial osteotomy on intraarticular knee and ankle contact pressures. J Orthop Res 2015;33:598–604. [22] Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs, preoperative planning of uniapical angular deformities of the tibia or femur. Clin Orthop Relat Res 1992;48–64. [23] Haidukewych G, Langford J. Subtrochanteric fractures. In: Bucholz RW, CourtBrown CM, Heckman JD, Tornetta III P, editors. Rockwood and Green’s fractures in adults. 7th ed., Lippincott Williams & Wilkins; 2010. p. 1641–54. [24] Krettek C, Miclau T, Schandelmaier P, Stephan C, Mohlmann U, Tscherne H. The mechanical effect of blocking screws (‘‘Poller screws’’) in stabilizing tibia fractures with short proximal or distal fragments after insertion of smalldiameter intramedullary nails. J Orthop Trauma 1999;13:550–3.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
JINJ-6230; No. of Pages 5 Injury, Int. J. Care Injured xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Injury journal homepage: www.elsevier.com/locate/injury
Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor Nael Hawi a,*, Mohamed Kenawey b, Martin Panzica a, Timo Stuebig a, Mohamed Omar a, Christian Krettek a, Emmanouil Liodakis a a b
Trauma Department, Hannover Medical School, Germany Orthopaedic Surgery Department, Sohag University, Egypt
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 14 May 2015
Introduction: Callus distraction of the femur using an intramedullary distractor has several advantages over the use of external fixators. However, difficulty in controlling the mechanical axis during lengthening may cause deformities and knee osteoarthritis. Purpose of the study is to answer the following questions: (1) is lengthening with an intramedullary device associated with a medial or lateral shift of the mechanical axis? (2) Which factors are associated with varisation/valgisation of the mechanical axis during lengthening? Materials and methods: We analysed pre-treatment and post-treatment radiographs from 20 patients who underwent unilateral femoral-lengthening procedures using intramedullary distractors. Patients with acute correction of pre-existing deformities or combined ipsilateral femoral and tibial lengthening were excluded. Mechanical axis deviations, osteotomy level, and nail–medullary canal ratio were recorded. Results: Compared to the preoperative axis, the mechanical axis shifted medially in 7 patients (varisation group) and laterally in 13 patients (valgisation group). The groups did not significantly differ regarding preoperative leg length discrepancy (LLD), mechanical axis alignment, LLD-cause and implants used. The nail–medullary canal ratio significantly differed between groups (p < 0.001), being <85% in the varisation group and >85% in the valgisation group. The distance between the lesser trochanter and the osteotomy site was significantly longer in the valgisation group (58.9 16.3 mm, middle third of the femur) compared to the varisation group (40.6 11.4 mm, proximal third of the femur; p = 0.02). Conclusion: The nail–medullary canal ratio should be considered during preoperative planning. To avoid a varisation effect—for example, in cases with pre-existing varus alignment—it would be advisable to perform an osteotomy at the middle third of the femur with implantation of a nail that fully covers the medullary canal at the osteotomy site. Level of evidence: Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence. ß 2015 Elsevier Ltd. All rights reserved.
Keywords: Telescopic nails Femoral lengthening Mechanical axis changes Level of osteotomy
Introduction
* Corresponding author at: Trauma Department, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. Tel.: +49 17615326964; fax: +49 5115325877. E-mail addresses: [email protected] (N. Hawi), [email protected] (M. Kenawey), [email protected] (M. Panzica), [email protected] (T. Stuebig), [email protected] (M. Omar), [email protected] (C. Krettek), [email protected] (E. Liodakis).
The last 20 years have seen much progress towards the development and establishment of totally implantable intramedullary lengthening nails in clinical practice [1–5]. This technique carries the main advantage of avoiding complications associated with external fixators, such as pin tract infections, neurovascular injuries, transfixation of soft tissues, and refractures [2,4,6–9]. Additional advantages include earlier rehabilitation, reduced pain, reduced risk of infection, earlier normal joint motion and activity level, and improved patient comfort [2–6,10,11].
http://dx.doi.org/10.1016/j.injury.2015.05.040 0020–1383/ß 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
G Model
JINJ-6230; No. of Pages 5 N. Hawi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx
2
Despite these advantages, intramedullary lengthening is also associated with problems and complications. Implant availability and cost can pose problems. Additionally, mechanically activated lengthening nails—such as the Albizzia nail and the intramedullary skeletal kinetic distractor (ISKD)—have fallen out of favour due to difficulties with the ratchet mechanism and the inability to control the distraction rate [10,12,13]. Moreover, intramedullary lengthening occurs along the anatomical axis of the femur, which carries the theoretical risk of medially displacing the knee joint and therefore causing genu valgum deformity—a secondary effect that would become more evident with increasing lengthening magnitude [8,14]. There are currently no consistent recommendations concerning the level of femoral osteotomy. It can generally be assumed that the proximal third of the femur, as a metaphyseal area, should have better bony regeneration and healing characteristics [11]. On the other hand, the femur diameter is wider in the proximal part compared to in the middle third or isthmus [15]. The authors believe that mechanical axis changes during limb lengthening with an intramedullary device can be better controlled by an osteotomy at the most narrow area of the bone (isthmus) than by an osteotomy at the subtrochanteric area (proximal third). Purpose of the study is to answer the following questions: (1) is lengthening with an intramedullary device associated with a medial or lateral shift of the mechanical axis? (2) Which factors are associated with varisation/valgisation of the mechanical axis during lengthening? Materials and methods The present study was approved by the Institutional Review Board (2164–2014). We retrospectively reviewed the charts of all patients who underwent intramedullary femoral lengthening procedures at our institution (Hannover Medical School, Hannover, Germany) between July 2002 and August 2014. The study included all patients who had long-standing radiographs taken before and after femoral lengthening with an intramedullary distractor. Patients with acute correction of preexisting deformities or who underwent combined ipsilateral femoral and tibial lengthening were excluded. Patients were also excluded if they did not have weight-bearing radiographs taken before and after lengthening. To maintain the control of the femoral rotation and to eliminate the effect of a possible malrotation on the mechanical axis, as described by Gungenheim et al. [16], an external fixator with 2 parallel 5 mm Schanz screws in the proximal and distal part of the femur was used. The fixator was placed before the femoral osteotomy and was removed after proximal and distal locking of the nail. A total of 20 patients (11 males and 9 females) underwent isolated femoral lengthening and met our inclusion criteria. The mean age at the time of the lengthening procedure was 29 11 years. Causes of leg length discrepancy included congenital shortening (n = 8) and post-traumatic shortening (n = 12). The mean amount of lengthening achieved was 4.1 1.9 cm, with a mean distraction rate of 1.3 0.5 mm/day. Preoperatively, 12 patients had a varus alignment and 8 had a valgus alignment. An ISKD nail (Orthofix, Valley, Germany) was used in 18 patients, while a Precice nail (Ellipse Technologies, Irvine, USA) was used in 2 patients. The implant diameter was either 10.7 mm or 12.5 mm. A trochanteric entry point was used in 17 cases and a piriformis entry in 3 cases. The mean osteotomy level was 52.4 17 mm (range, 34–75 mm) distal to the lesser trochanter. The preoperative and post-healing long-standing lower extremity X-rays were used to verify the lower limb alignment changes using the system described by Paley et al. [17]. In each
Table 1 Patient demographics and perioperative characteristics. Age (years) Female-gender Leg length discrepancy (LLD) Cause of LLD – post-traumatic Preoperative axis-varus Osteotomy side (proximal third) Percentage of medullary canal occupied by nail Transport index (mm/day) ISKD nail Piriformis entry point
29 11 9 (45%) 4.1 1.9 12 (60%) 12 (60%) 8 (40%) 86 14 (%) 1.3 0.5 18 (90%) 3 (15%)
radiograph, we measured the mechanical femoro-tibial angle (mFTA) and the mechanical axis deviation (MAD). The direct postoperative X-rays were used to measure the percentage of the femoral medullar canal that was occupied by the nail at the osteotomy level. All measurements were performed digitally on a computer with the use of FDA-approved medical planning software (MediCAD version 2.0, Hectec, Altfraunhofen, Germany) [18]. Continuous variables were checked for normal distribution using the Shapiro–Wilk test, and presented as mean standard deviation (SD). Categorical variables were described as frequencies with percentages. Between-group differences were evaluated with the Mann–Whitney U test for non-parametric continuous data, while Pearson’s chi-square test was used for categorical values. A two-tailed p-value of 0.05 was considered to be statistically significant. The SPSS 22.0 program (SPSS Inc., Chicago, IL) was used for statistical analyses. Table 1 shows the preoperative characteristics of the patients. Results Table 2 summarises the postoperative data. The mechanical axis shifted medially in 7 patients (varisation group) and laterally in 13 patients (valgisation group). The overall absolute change of the mechanical femoro-tibial angle was 1.68 1.28 (range: 0.18– 4.28, 25th–75th percentile: 0.68–2.18). This change was 1.48 1.48 (range: 0.18–4.28, 25th–75th percentile: 0.58–2.48) for the varisation group, and 1.88 1.18 (range: 0.38–3.98, 25th–75th percentile: 0.68– 2.48) for the valgisation group (p = 0.588). Table 2 Postoperative data.
Age (years) mFTA (8) Limb length discrepancy (mm) Transport index (mm/day) Distance distal to Lesser Trochanter (mm) Medullary canal -nail ratio (%)
Varisation group
Valgisation group
p-Value
24.7 10.7 1.4 1.4 49.0 24.4 1.3 1.2 40.6 11.4
31.5 11.8 1.8 1.1 36.3 14.9 2.2 1.2 58.9 16.3
0.26 0.59 0.26 0.18 0.02
69.7 6.6
95.0 6.9
Cause of LLD Post-traumatic Congenital
4 (20%) 3 (15%)
8 (40%) 5 (25%)
1.0
Entry point Piriformis Trochanteric
2 (10%) 11 (55%)
1 (5%) 6 (30%)
1.0
Type of nail ISKD Precice
5 (25%) 0 (0%)
13 (75%) 2 (10%)
0.11
Preoperative alignment Varus Valgus
4 (20%) 3 (15%)
9 (45%) 4 (20%)
0.65
<0.001
Bold values show a statistical significance (p < 0.05).
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The two groups did not significantly differ regarding preoperative leg length discrepancy, alignment, cause of length discrepancy, and implants used. The percentage of the medullary canal occupied by the nail at the osteotomy level—i.e. the nail–medullary canal ratio—significantly differed between the two groups (69.7 6.6 for the varisation group vs. 95.0 6.9 for the valgisation group; p < 0.001). The nail–medullary canal ratio was <85% among all patients of the varisation group and >85% among all patients of the valgisation group. The distance between the lesser trochanter and the osteotomy site was also significantly longer in the valgisation group (58.9 16.3 mm, middle third of the femur) compared to the varisation group (40.6 11.4 mm, proximal third of the femur; p = 0.02). In all patients, the desired length was achieved with no implant-related complications. One patient had insufficient bone regeneration and healing was achieved by revision surgery with bone grafting. Discussion Although changes of the mechanical axis after femoral lengthening are often not big (<2.18 in 75% of the cases in our study), they can be clinically significant. Axial malalignment has previously been associated with knee osteoarthritis [19] and biomechanical studies show that even small changes of the hip– knee–ankle angle have a significant effect in the distribution of
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the medial and lateral femorotibial compartment pressures [20,21]. Predicting the direction of the mechanical axis changes during lengthening is especially relevant in cases with pre-existing deformities in order to correct smaller deformities and to avoid worsening them [3,8,10]. The present study has some limitations. First, small sample size is a universal problem among studies investigating uncommon procedures, such as intramedullary limb lengthening. Second, our results are based on a retrospective study design where errors due to confounding and bias are more common than in prospective studies. Last but not least, our analysis was limited to mechanical axis changes, and we did not consider long-term outcomes, such as incidences of osteoarthritis or other deformity-related symptoms. This study has also important strengths, including the data completeness and detailed clinical information. To the best of our knowledge, this is the first study to analyse the association between mechanical axis changes, nail diameter and osteotomy site. In the tibia, the anatomical and mechanical axes are usually identical. In contrast, the anatomical axis of the femur is inclined 78 to its mechanical axis [17,22]. From a geometrical point of view, femoral lengthening along the anatomical axis causes a lateral shift of the mechanical axis (valgisation) [8,11]. However, this is contradicted by the clinical reality, in which alignment changes are difficult to predict. In our study, the mechanical axis shifted medially (varisation) in 35% of the cases.
Fig. 1. Mechanical axis before and after femoral lengthening in patients with nail–medullary canal ratios of <85% (A) and of >85% (B).
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The main finding of the current study was that the nail– medullary canal ratio at the osteotomy level was a significant predictor of varisation or valgisation of the mechanical axis (Fig. 1). The tendency of the femur to become varus in the presence of a nail–medullary canal mismatch can be explained by analysing the muscular anatomy of the thigh. The proximal fragment is continuously abducted by the abductor muscle group that inserts on the proximal femur, while the distal fragment is constantly adducted by the distally inserted adductors [23]. Proximal fragment abduction combined with distal fragment adduction cause varus angulation at the fracture or osteotomy level, which can be accentuated by the nail–medullary mismatch [24]. In cases of particularly wide medullary canal, the restricted range of available implant diameters (biggest nail diameter: 12.7 mm) can be problematic. To avoid the effects of a nail– medullary canal mismatch, the width of the medullary canal can be functionally decreased using blocking (‘‘poller’’) screws. The poller screws should be placed on the concave side of the deformity between the cortex and nail [24]. Another important finding of the study is the effect of the osteotomy level on the post-lengthening alignment. Intramedullary lengthening through a proximal osteotomy in the wide subtrochanteric area was associated with a low nail–medullary canal ratio, and consequently, varisation. This can be explained by the funnel shape of the femur (wide proximal and narrow in the middle third). So even if the nail fits the narrow medullary canal diameter at the isthmus, nail–medullary canal mismatch cannot be avoided at the wider proximal femur. On the other hand, more distal osteotomies in the middle third of the femur lead to valgisation of the mechanical axis if the nail fits the medullary canal. In agreement with our present results, Paley et al. [8] previously described five cases of femoral lengthening with external fixators in which subtrochanteric osteotomies were associated with marked varus angulation. The degree of the varus angulation does not seem to be associated with the LLD to be corrected, but depends more on the nail–medullary canal mismatch. In our study, only two patients with a middle-third femoral osteotomy showed postoperative varus angulation. In both patients, the medullary canal was 14-mm wide and a 10.7-mm nail was used (nail– medullary canal ratio = 76%). Guichet et al. [10] investigated intramedullary lengthening using Albizzia nails, and found that the femoral alignment was well maintained with no change in the lateral distal femoral angle. However, direct assessment of the mechanical axis revealed that there was a valgus increase of an average of 1.048 1.38. The osteotomy was performed at the level of the diaphyseal region, which is narrow. Thus, these results are consistent with our present findings. Recently, Burghardt et al. [14] closely examined changes of the mechanical axis associated with isolated ISKD femoral lengthening. They found that 26 out of 27 limbs showed lateral deviation of the mechanical axis with lengthening, and that in 11 limbs this deviation was significant (>2 mm according to their definition). In these 11 limbs, the mean lateral shift of the mechanical axis was 2 mm per cm of lengthening. The average osteotomy level was 5.5 cm distal to the lesser trochanter, which is very close to the isthmus. Our present study could confirm these findings only among the patients in which the medullary canal was fully covered by the nail at the osteotomy level. In cases where the ratio was lower than 100%, the magnitude of varus or valgus deviation could not be accurately predicted, because of the additional variables influencing the axis, such as lengthening along the anatomical axis, and degree of nail–medullary canal mismatch.
Nail design and entry point do not seem to affect lower limb alignment. In this study, two different types of lengthening nails (ISKD and Precice) were used. For each nail, there is an option to choose between a piriformis and a trochanteric entry point depending on the preference of the surgeon. Both variables (ISKD vs. Precice nail and Piriformis vs. Trochanteric entry point) were evaluated. No association between these variables and changes of the mechanical axis alignment were found in this study.
Conclusion In conclusion, the direction of mechanical axis deviation during intramedullary femoral lengthening depends on the ratio between the nail diameter and the medullary canal diameter at the level of the osteotomy. To avoid a varisation effect—for example, in cases with pre-existing varus alignment—it would be advisable to perform an osteotomy at the middle third of the femur with implantation of a nail that fully covers the medullary canal at the osteotomy site. To avoid a valgisation effect, the osteotomy can be performed a few centimetres distal to lesser trochanter with a nail diameter that is equal to the medullary canal diameter at the middle third of the femur and smaller that the medullary canal diameter at the osteotomy level.
Conflict of interest Each author certifies that he has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The ethical committee of the Hannover Medical School approved the study (2164–2014). References [1] Betz A, Baumgart R, Schweiberer L. First fully implantable intramedullary system for callus distraction – intramedullary nail with programmable drive for leg lengthening and segment displacement. Principles and initial clinical results. Chirurg 1990;61:605–9. [2] Guichet JM, Casar RS. Mechanical characterization of a totally intramedullary gradual elongation nail. Clin Orthop Relat Res 1997;281–90. [3] Hankemeier S, Pape HC, Gosling T, Hufner T, Richter M, Krettek C. Improved comfort in lower limb lengthening with the intramedullary skeletal kinetic distractor. Principles and preliminary clinical experiences. Arch Orthop Trauma Surg 2004;124:129–33. [4] Cole JD, Justin D, Kasparis T, DeVlught D, Knobloch C. The intramedullary skeletal kinetic distractor (ISKD): first clinical results of a new intramedullary nail for lengthening of the femur and tibia. Injury 2001;32(Suppl. 4): SD129–39. [5] Simpson AH, Shalaby H, Keenan G. Femoral lengthening with the intramedullary skeletal kinetic distractor. J Bone Joint Surg Br 2009;91:955–61. [6] Baumgart R, Betz A, Schweiberer L. A fully implantable motorized intramedullary nail for limb lengthening and bone transport. Clin Orthop Relat Res 1997;135–43. [7] Paley D. Problems, obstacles, and complications of limb lengthening by the Ilizarov technique. Clin Orthop Relat Res 1990;81–104. [8] Paley D, Herzenberg JE, Paremain G, Bhave A. Femoral lengthening over an intramedullary nail. A matched-case comparison with Ilizarov femoral lengthening. J Bone Joint Surg Am 1997;79:1464–80. [9] Simpson AH, Cole AS, Kenwright J. Leg lengthening over an intramedullary nail. J Bone Joint Surg Br 1999;81:1041–5. [10] Guichet JM, Deromedis B, Donnan LT, Peretti G, Lascombes P, Bado F. Gradual femoral lengthening with the Albizzia intramedullary nail. J Bone Joint Surg Am 2003;85-A:838–48. [11] Hankemeier S, Gosling T, Pape HC, Wiebking U, Krettek C. Limb lengthening with the Intramedullary Skeletal Kinetic Distractor (ISKD). Oper Orthop Traumatol 2005;17:79–101. [12] Kenawey M, Krettek C, Liodakis E, Wiebking U, Hankemeier S. Leg lengthening using intramedullay skeletal kinetic distractor: results of 57 consecutive applications. Injury 2011;42:150–5. [13] Kenawey M, Krettek C, Liodakis E, Meller R, Hankemeier S. Insufficient bone regenerate after intramedullary femoral lengthening: risk factors and classification system. Clin Orthop Relat Res 2011;469:264–73.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040
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JINJ-6230; No. of Pages 5 N. Hawi et al. / Injury, Int. J. Care Injured xxx (2015) xxx–xxx [14] Burghardt RD, Paley D, Specht SC, Herzenberg JE. The effect on mechanical axis deviation of femoral lengthening with an intramedullary telescopic nail. J Bone Joint Surg Br 2012;94:1241–5. [15] Dorr LD, Faugere MC, Mackel AM, Gruen TA, Bognar B, Malluche HH, et al. Structural and cellular assessment of bone quality of proximal femur. Bone 1993;14:231–42. [16] Gugenheim JJ, Probe RA, Brinker MR. The effects of femoral shaft malrotation on lower extremity anatomy. J Orthop Trauma 2004;18:658–64. [17] Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs, preoperative planning of multiapical frontal plane angular and bowing deformities of the femur and tibia. Clin Orthop Relat Res 1992;65–71. [18] Tetsworth KD, Paley D. Accuracy of correction of complex lower-extremity deformities by the Ilizarov method. Clin Orthop Relat Res 1994;102–10. [19] Cooke D, Scudamore A, Li J, Wyss U, Bryant T, Costigan P. Axial lower-limb alignment: comparison of knee geometry in normal volunteers and osteoarthritis patients. Osteoarthr Cartil 1997;5:39–47.
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[20] Agneskirchner JD, Hurschler C, Wrann CD, Lobenhoffer P. The effects of valgus medial opening wedge high tibial osteotomy on articular cartilage pressure of the knee: a biomechanical study. Arthroscopy 2007;23:852–61. [21] Suero EM, Sabbagh Y, Westphal R, Hawi N, Citak M, Wahl FM, et al. Effect of medial opening wedge high tibial osteotomy on intraarticular knee and ankle contact pressures. J Orthop Res 2015;33:598–604. [22] Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs, preoperative planning of uniapical angular deformities of the tibia or femur. Clin Orthop Relat Res 1992;48–64. [23] Haidukewych G, Langford J. Subtrochanteric fractures. In: Bucholz RW, CourtBrown CM, Heckman JD, Tornetta III P, editors. Rockwood and Green’s fractures in adults. 7th ed., Lippincott Williams & Wilkins; 2010. p. 1641–54. [24] Krettek C, Miclau T, Schandelmaier P, Stephan C, Mohlmann U, Tscherne H. The mechanical effect of blocking screws (‘‘Poller screws’’) in stabilizing tibia fractures with short proximal or distal fragments after insertion of smalldiameter intramedullary nails. J Orthop Trauma 1999;13:550–3.
Please cite this article in press as: Hawi N, et al. Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor. Injury (2015), http://dx.doi.org/10.1016/j.injury.2015.05.040