|Year : 2019 | Volume
| Issue : 2 | Page : 62-70
Blocking screws for intramedullary nail guidance
Keir A Ross1, Michael E Steinhaus2, S Robert Rozbruch2, Austin T Fragomen2
1 Department of Orthopaedic Surgery, New York University Langone Health, New York, NY, USA
2 Department of Orthopaedic Surgery, Limb Lengthening and Complex Reconstruction Service, Hospital for Special, New York, NY, USA
|Date of Submission||08-Sep-2019|
|Date of Decision||28-Oct-2019|
|Date of Acceptance||28-Nov-2019|
|Date of Web Publication||31-Dec-2019|
Dr. Keir A Ross
Department of Orthopaedic Surgery, New York University Langone Health, 301 E 17th Street, Suite 1402, New York, NY 10003
Source of Support: None, Conflict of Interest: None
Intramedullary nails (IMNs) are commonly used for fracture fixation of the femur and tibia, and internal lengthening nails (ILNs) can be used for deformity correction and limb lengthening. While this form of fixation has demonstrated substantial success, one major limitation is imperfect reduction and malalignment, particularly when used for fractures or osteotomies in the metaphysis. One means of overcoming this challenge is through the use of blocking screws, given their ability to guide the path of the nail, decrease the width of the medullary canal, and maintain reduction. In this literature review, indications, techniques, outcomes, and complications are reported. Searches of PubMed and The Cochrane Collaboration were performed. Technique articles and single case reports were not reviewed. All other English studies reporting outcomes of IMN or ILN fixation of the femur or tibia with concomitant use of blocking screws were reviewed. Blocking screws have been used successfully in the lower extremity for both trauma and in deformity surgery. Key techniques are placing the screws in the concavity and perpendicular to the plane of deformity, with adequate distance from the planned path of the nail and from the fracture or osteotomy site. Current data suggest high rates of union with adequate alignment and a low complication rate, although most studies are small, retrospective case series. Blocking screws appear to be a reasonable strategy for achieving fixation in difficulty, metaphyseal segments. Further, well-designed prospective studies should be carried out to make more definitive conclusions.
Keywords: Blocking screw, deformity, femur, fracture, lengthening, Poller screw, tibia
|How to cite this article:|
Ross KA, Steinhaus ME, Rozbruch S R, Fragomen AT. Blocking screws for intramedullary nail guidance. J Limb Lengthen Reconstr 2019;5:62-70
| Introduction|| |
Intramedullary nail (IMN) fixation has become a common method for the treatment of tibia and femur fractures with high rates of union. Where open surgical plate fixation was the standard for treatment of metaphyseal fractures, IMN fixation has been increasingly implemented to control short proximal or distal fragments despite increased rates of malalignment with these fractures. External fixator assisted nailing has been utilized to provided added stability and can be used for concomitant deformity correction or lengthening. This lengthening over a nail technique allows for deformity correction but decreases required time in the external fixator., Meanwhile, the introduction of reliable intramedullary internal lengthening nails (ILN) for gradual bone lengthening with or without concomitant deformity correction has gained recent attention. As with the use of IMN in metaphyseal fractures, ILNs often provide inadequate stability of metaphyseal osteotomies during distraction., This has been attributed to the discordance between nail diameter and the metaphyseal canal, which results in lack of contact between the nail and cortex, allowing translation of the nail and angular deformity of the bone fragment , [Figure 1].
|Figure 1: Lateral intraoperative fluoroscopy of a tibial intramedullary nail placed following osteotomy with no blocking screws in place. The nail is in contact with the cortices posteriorly (blue arrows) but is 6 mm away from the anterior cortex (blue demarcation) which may allow angular deformity and translation|
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First described by Krettek et al., “Poller” or blocking screws are one means of combating this challenge. Placed adjacent to the path of the nail, the blocking screw acts to guide the nail down a trajectory; helping to prevent deformity in fracture fixation or to hold the appropriate alignment in deformity correction. These screws assist in establishing and maintaining reduction by decreasing the width of the medullary canal and increasing stiffness of the bone-implant construct.,
The objective of this study was to provide an evidence-based review of the current indications, technique, and outcomes of blocking screws with IMN and ILN fixation in the lower extremity. The current study reviews clinical and radiographic outcomes as well as complications of blocking screw use for acute fracture reduction and in concert with osteotomy for deformity correction with or without lengthening in both the femur and tibia.
| Methods|| |
Searches of PubMed and The Cochrane Collaboration were performed with “((((blocking OR blocking screw) OR poller) OR poller screw)) AND ((((tibia OR tibial OR femur OR femoral)) AND (((((nail OR intramedullary OR intramedullary nail OR internal lengthening OR internal lengthening nail OR lengthening over nail OR fixator OR fixator assisted)).” Technique articles and single case reports were excluded. All other English studies reporting outcomes of IMN or ILN fixation of the femur or tibia with concomitant use of blocking screws were reviewed.
| Indications|| |
One major indication for the use of blocking screws is acute fracture fixation, particularly in the setting of metaphyseal fractures with short segments.,,,,,,,,,,,,,, Often proximal tibia fractures are fixed using a semi-extended position with suprapatellar approach in order to ensure a proximal start point and prevent flexion at the fracture site. Blocking screws have also been used in fractures of the proximal and distal tibia, and the proximal, mid-shaft, and distal femur to improve reduction.,,,,,,,,,,,,,, In their original study, Krettek et al. assessed the use of blocking screws in metaphyseal tibia fractures. Subsequent studies assessed the use of blocking screws in metaphyseal fractures of the femur and tibia.,,,
Outside of acute fracture fixation, blocking screws have been employed for malunion in both the tibia and femur following prior surgical fixation [Figure 2]a and [Figure 2]b.,,
|Figure 2: Anterior-posterior radiograph of a femoral shaft fracture with an intramedullary nail and cerclage wires (a). Valgus deformity is present. A blocking screw in the concavity of the deformity can allow for correction as demonstrated on anterior-posterior intraoperative fluoroscopy (b). In general, screws should be placed in the concave side of the short fragment|
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More recently, multiple studies have evaluated the benefit of blocking screws for deformity correction and limb lengthening, demonstrating high degrees of deformity correction in relation to preoperative planning.,,
| Technique and Key Concepts|| |
In metaphyseal fractures or osteotomies, the major consideration is translation of the short fragment secondary to increased medullary canal width, resulting in malalignment. Blocking screws not only guide the nail down the appropriate path, but also decrease the width of the medullary canal to prevent nail translation, helping to maintain alignment and stability  [Figure 2]b. Screws placed correctly enable three-point fixation: the nail insertion site, the canal isthmus, and the blocking screw.,, Importantly, overreaming or use of an under-sized nail will jeopardize fit. Screw placement prior to canal reaming is an effective way to ensure reaming of the appropriate nail path.,,, Blocking screws must be strong enough to withstand and counteract the forces of the reamer. For this reason, Muthusamy et al. have recommended fully-threaded 5.0 mm IMN interlocking screws for blocking. However, there is no data specifically assessing the most appropriate screw size or thread diameter. A smaller 4.0 mm screw is also reasonable and may be needed to allow adequate space for the reamer and nail when the screw is placed sufficiently close to the nail. For ILN cases, blocking screws can be inserted prior to reaming, with the same intension, or after reaming and nail insertion with the goal of preventing deformity during lengthening.
The location of the blocking screws is instrumental to their success. Some have proposed the screws should be at least 2 cm away from the osteotomy or fracture to avoid propagating a fracture., When placing blocking screws before reaming, screws can be placed at least 1–2 mm from the planned path of the nail to accommodate for the larger diameter reamer and to ensure the nail will take the intended path. This is particular to the case of ILN surgery with flexible reamers which requires 2 mm of overreaming. Leaving 1–2 mm of space also avoids any interference with the distraction process. Rigid, line-to-line reamers may call for no space between the nail and the screw. It is preferable to place the screw closer to the nail than too far away since the later condition will not prevent deformity. Screws should be placed perpendicular to the plane of the existing deformity or any deformity expected from a correction. For example, if attempting to avoid a varus/valgus deformity, blocking screws should be placed in the anterior-posterior plane., For oblique fractures, Hannah et al. described that a blocking screw can be placed in the acute angle formed by the long axis of the bone and the fracture line, on the metaphyseal side. In general, screws should be placed in the concave side of the short fragment.,,, More recently, Muthusamy et al. introduced the “reverse rule of thumbs,” in which the surgeon imagines manually correcting the deformity by holding the bone in both hands with the thumbs on the convex side of the deformity and the index fingers on the concave side farther from the apex. The blocking screws are placed on the opposite side of the nail from the thumbs and index fingers  [Figure 3]a and [Figure 3]b.
|Figure 3: Digital illustrations of the “reverse rule of thumbs” for both a pediatric femur deformity (a) and tibial shaft deformity in a skeletally mature patient (b). While diaphyseal blocking screws are less commonly utilized, the concept for both metaphyseal and diaphyseal screw placement is demonstrated|
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An additional challenge is assessing the appropriate number of blocking screws to be utilized. Not all screws suggested by the “reverse rule of thumbs” need to be placed [Figure 4]a, [Figure 4]b, [Figure 4]c.
|Figure 4: Anterior-posterior radiographs of the distal femur demonstrating laterally placed blocking screws to prevent valgus deformity (a and b). Lateral radiograph of the distal femur with a posterior screw placed prior to reaming and nail passage to prevent procurvatum (c)|
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| Outcomes|| |
Acute fracture fixation of the tibia
The data related to blocking screw use during fracture fixation are primarily limited to small case series, utilizing a variety of outcome measures, making it difficult to compare data across studies [Table 1]. In the first description of blocking screws, Krettek et al. prospectively studied 21 metaphyseal fractures of the tibia that underwent IMN fixation with blocking screws. All fractures healed at a mean of 5.4 months postoperatively and 89% had excellent-satisfactory outcomes. A mean varus-valgus and antecurvatum-recurvatum alignment of −1.0° and 1.6°, respectively, was reported. The cohort included acute fractures and delayed and malunion, suggesting that blocking screws may also be a viable strategy in revisions. Ricci et al. prospectively followed 11 patients that underwent IMN with blocking screws for proximal third tibia fractures. In all 11 patients, there was <5° of angulation and 10/11 achieved union. Kulkarni et al. assessed the use of blocking screws in 75 proximal tibial fractures. This series included 60 acute fractures, 10 delayed unions, and 5 malunions. For 69 cases, mean time to union was 4.2 months. Five cases required bone graft to achieve union, and there was one case of malunion after intervention. Seventy-four of 75 patients had <5° of varus/valgus malalignment. Sixty-five patients exhibited no deformity postoperatively and there were excellent/good clinical outcomes in 64 patients. There was no subgroup analysis or discussion of the malunion/nonunion group revised with blocking screws. Maniscalco et al. employed blocking screws in 56 tibial shaft fractures, noting no cases of delayed union. Fractures healed at a mean of 16 weeks postoperatively, there were three malunions, and one case that healed with significant shortening. Finally, Moongilpatti et al. reported on the use of blocking screws in distal tibial metaphyseal fractures treated with statically locked IMN. In 20 patients, there were good/excellent outcomes in 90%, with improvement in varus-valgus alignment from 10.3° to 1.7° and in the coronal plane from 8.0° to 0.2°.
|Table 1: Studies reporting outcomes of intramedullary nail or internal lengthening nail fixation with the use of concomitant blocking screws|
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Acute fracture fixation of the femur
Various authors have reported the use of blocking screws from the proximal-to-distal femur. Seyhan et al. reported the results of 45 subtrochanteric fractures that underwent IMN fixation with one of three forms of intraoperative reduction, including 22 clamp-assisted, 11 with cable cerclage, and 12 with blocking screws. Mean operative and fluoroscopy time was significantly longer in the blocking screw group compared to the other groups. After 1 year follow-up, the clamp-assisted reduction group had a significantly longer time to full weight bearing (4 weeks) and a lower mean Harris Hip Score (83). Postoperative alignment, time to union, and complications or need for other interventions were not significantly different between the three groups. Mean time to union was 21 weeks, 19 weeks, and 15 weeks for the clamp, cerclage, and blocking screw groups, respectively. Although comparisons are made in this study, the lack of randomization makes it difficult to do so, as the authors state that the cable cerclage method is only used “when absolutely required” and that blocking screws were used in cases when clamp-assisted reduction failed. An additional study by Amin et al. assessed the use of blocking screws in the setting of subtrochanteric fractures. At a mean follow-up of 8.5 months, all fractures had achieved bony union and all patients had returned to preinjury levels of activity.
Several authors have also described the successful use of concomitant blocking screws with retrograde IMN fixation of distal femur fractures.,, There were no studies identified comparing antegrade to retrograde nailing or comparing nails with varying degrees of curvature. Ostrum and colleagues described the results of eight retrograde femoral IMNs with concomitant blocking screws, noting that all fractures healed without secondary surgeries, malunion, or nonunion. Gavaskar and Chowdary reported a similar series of 11 patients that underwent retrograde IMN with blocking screws for distal femur fractures and found that all fractures united at a mean of 14 months without any cases of malunion, screw breaking, or screw bending. Seyhan et al. reported successful results of IMN with blocking screws in six distal metaphyseal and nine diaphyseometaphyseal fractures, noting that all patients achieved adequate reduction and union (mean time to union, 12.6 weeks) without significant complications. There was one case of delayed union at 32 weeks. Union was eventually achieved without further surgical intervention. Finally, in a retrospective cohort study comparing 46 cases of retrograde IMN fixation of infraisthmal femur fractures with blocking screws to 70 infrainsthmal femur fractures that underwent the same fixation without blocking screws, Van Dyke et al. showed no significant difference in union rate (61% and 77%, respectively), time to union (21.1 and 21.8 weeks, respectively), or final sagittal/coronal alignment. Nevertheless, given the retrospective nature of this study, there is likely an element of selection bias. It is possible, for example, that those in the blocking screw group had a more difficult reduction, greater deformity, or wider intramedullary canal, making it difficult to draw conclusions from these results.
Based on early data, blocking screws appear to be an effective means of achieving acceptable alignment of both metaphyseal and diaphyseal fractures of the tibia and femur., There are few studies with comparison groups and outcome measures are inconsistent, making it difficult to determine if blocking screws significantly improve rates of union. However, the low complication rate and high rate of union with minimal angulation in the currently available data is encouraging.
Delayed union and malunion
Common methods for addressing nonunion after IMN include dynamization, exchanging for a larger nail, bone grafting, plating around the nail, and nail removal with subsequent plating., While the majority of studies on blocking screws are in the setting of acute fracture, few have reported on their use in conjunction with exchange nailing in revision for delayed or malunion. When a fracture is malaligned and not healing, then treatment needs to include not only the principles of rereaming and inserting a larger nail but also the correction of the deformity to restore alignment. The original study by Krettek et al., for example, included three cases of delayed union and five cases of malunion that had undergone previous IMN. Blocking screws were employed within 28 days of index surgery and demonstrated success, with valgus deformity improving from −8.1° to −0.2° and improvement in the sagittal plane from −1.8° to 1.0° after revision.
Two studies specifically looked at the addition of blocking screws to address nonunion., In a prospective study of exchange nailing with blocking screws for seven tibial and five femoral diaphyseal aseptic nonunions after IM nailing, Gao et al. report union and resolution of symptoms in all patients at an average of 7.8 months. All patients were pain-free at an average 1.5-year follow-up. Kim et al. described the use of blocking screws or additional interlock screws with exchange nailing to address infraisthmal femoral nonunion, reporting union for all 18 patients at an average of 7.5 months, with full weight-bearing and resolution of symptoms for all patients by 3 months without complications. These studies demonstrated that exchange nailing with the addition of blocking screws may be a reasonable strategy for addressing delayed, non-, or malunion with good efficacy and little risk, although further studies to compare other strategies such as nail dynamization, bone grafting, and nail removal with plating are needed to determine the optimal technique.
Limb lengthening and deformity correction
Blocking screws have also been employed for limb lengthening and deformity correction with various ILNs, including magnetic and motorized.,,,,,, There are limited studies that analyze blocking screws as a variable for outcome in the setting of deformity correction and limb lengthening using an ILN. Furmetz et al. retrospectively analyzed the results of 31 patients (19 femurs and 12 tibias) treated with ILNs for correction of a mean 3.5 cm leg length discrepancy. Blocking screws were used in 15 of those patients. All patients reached preplanned distraction length. Those that did not require blocking screws had an averaged planned hip–knee angle correction of 1.7° and mechanical axis correction of 6.3 mm, whereas patients that did receive blocking screws had an average planned correction of 3.2° and mechanical axis correction of 9.3 mm (P < 0.05). Deviation from the planned correction was not different between groups. Despite this greater baseline difference, the authors reported similar final outcomes with regard to correction, demonstrating efficacy of the blocking screws. The authors noted delayed bone formation in 11 of 31 patients. This included six patients in the blocking screw group and five in the group without blocking screws, exculpating the screws as a source of impaired osteogenesis.
Iobst et al. reviewed 27 patients with femoral deformity and limb length inequality treated by distal femoral osteotomy with acute reduction, fixator-assisted nailing, and gradual lengthening. The magnetic ILN was used in all cases with a mean correction of 7° of varus or valgus angulation. In 9/10 (90%) patients, where 2 or more blocking screws were used, the final alignment was optimal. In 13/17 (76%) patients, where 1 or no blocking screw was used, the final alignment was optimal with 24% of patients having a mechanical axis deviation of >10 mm from the target. Although this study lacked the power to show significance, the authors suggest that blocking screws are quite effective at controlling limb alignment immediately postsurgery and maintaining this alignment through the lengthening process.
Park et al. have also described the use of blocking screws in conjunction with external fixation over a nail or the lengthening over nail technique. The authors report the results of 346 cases of tibial lengthening using the lengthening over nail technique. The purposes of the study were to assess the amount of valgus deviation during lengthening and the factors that were associated with valgus deviation. Factors studied included demographic factors, presence of a blocking screw, diameter and length of the nail, length of the nail in the distal segment after completion of distraction, final lengthening, and BMI. Valgus deviation was present during lengthening as evidenced by a mean increase in medial proximal tibial angle from 86° to 90°. Based on their multivariate regression model, the only factor associated with decreased valgus deviation was the use of a blocking screw.
| Complications|| |
To our knowledge, there are no studies specifically designed to analyze the complications of blockings screws. Based on the limited data from primarily retrospective studies, complication rates of blocking screws appear to be low.,,,,,,,,,,,,, Multiple studies have reported 100% union rates with no complications related specifically to the blocking screws.,,,,,,, The current authors are aware of only one case, in which the blocking screws directly resulted in complication. In this instance, a new fracture line was seen during nail implantation, although the union was still achieved within 8 weeks and adequate alignment was maintained. Stedtfeld et al. detailed the results of nine heterogeneous cases including fractures of the tibia, femur, and humerus. These authors further elaborated that they anecdotally had used blocking screws for fixation of 48 long bone fractures which all went on to bony union. They reported only one case of irritation of the anterior tibial tendon, but no complications related to the blocking screws. In the above noted study of 75 tibial fractures by Kulkarni et al., there were no cases of screw or nail breaks and only one case of malunion in the cohort at final follow-up; however, anterior knee pain was present in 8 cases (9%) and 47 patients (63%) later had their screws or nails removed.
The heterogeneity of the cohorts and types of complications studied in the literature makes it impractical to formulate meaningful overall rates of nonunion, malunion, screw or nail break, or other complications. Many studies report low complication rates, and there appears to be very few cases in which blocking screws result in nail break or in which the screws themselves propagate additional fracture. However, a blocking screw that is too aggressively placed in the path of the nail can result in splitting of the bone during nail insertion. Careful preoperative planning of the nail and screw diameter and the nail trajectory and screw placement are required.
| Conclusions|| |
IMN fixation is a widely popular method for fixation of both femoral and tibial fractures and has been increasingly utilized for deformity correction and limb lengthening. However, in the setting of certain fracture patterns or osteotomy sites (typically metaphyseal), obtaining and maintaining adequate alignment can be difficult. Current literature suggests that blocking screws may be an effective strategy for guiding the nail to obtain adequate alignment and increase the stiffness of the bone-implant construct with a low complication rate. It is also important to note other factors affecting reduction and alignment during IMN fixation that was outside of the scope of this article and were, therefore, not addressed. These factors include the approach used for nail placement such as suprapatellar versus parapatellar for tibial IMN and the type of nail and its radius of curvature in the case of femoral IMN. A number of the studies reviewed above did not specifically report pre-to-postoperative alignment correction, postoperative alignment alone, or the specific rates of malunion. Reporting nonunion rates does provide some insight into lack of inferiority compared to IMN alone, but the current review was limited by these factors none the less. Blocking screws are used primarily to prevent malalignment, and rates of nonunion are likely more affected by other previously reported factors such as infection and gapping and the fracture site. In addition, other commonly used techniques such as fixator-assisted nailing should be considered, and studies comparing this technique to blocking screws are required. While blocking screws appear effective for challenging fractures and osteotomies, the current literature contains small, retrospective studies, and further studies with larger enrollment are needed to compare the efficacy of blockings screws with IMN to other fixation strategies before definitive conclusions can be affirmed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]