Intramedullary nailing of femoral shaft fractures. Part I

Effect of Interlocking Mode on the Outcomes of Exchange Nailing for the Treatment of Aseptic Femoral Shaft Nonunion

Background

Exchange nailing is a standard treatment for femoral shaft nonunion after intramedullary nailing. However, substantial uncertainty and controversy remain regarding the mode of interlocking fixation. This study aimed to compare the success rate and time to union of exchange nailing based on interlocking modes.

Methods

We retrospectively analyzed all consecutive patients who underwent exchange nailing for aseptic femoral shaft nonunion between February 2000 and February 2021. Patients who underwent exchange nailing using the dynamically locked mode and statically locked mode constituted the dynamic group and static group, respectively. We compared the success rates of the index surgery and the time to union between the groups and measured the extent of interlocking screw migration on the dynamic oblong hole in the dynamic group.

Results

The dynamic group and static group comprised 17 patients and 18 patients, respectively. All patients in the dynamic group achieved bone union, whereas 5 patients in the static group did not and underwent additional intervention. The success rate of the index surgery was significantly higher in the dynamic group than in the static group (100% vs. 72.2%, p = 0.045). Four of the 5 failed unions in the static group achieved bone union after dynamization. The median time to union was significantly shorter in the dynamic group than in the static group (6.0 months [range, 4.0-6.0] vs. 12.0 months [range, 3.7-21.7], p = 0.035). In the dynamic group, 3 of 17 patients exhibited interlocking screw migration ranging from 1.1 to 4.1 mm.

Conclusions

Exchange nailing with dynamic mode yields a higher success rate and shorter time to union in aseptic femoral shaft nonunion than that with static mode, without the risk of excessive shortening.

Histopathological examination of bone debris from reaming of interlocking intra-medullary nail fixation of long bone fractures with concomitant head injury

BACKGROUD/AIM

The aim of study was to test, for the presence of osteoblasts in the reaming debris of intramedullary nailing of femoral and tibial fracture in patients with and without severe head injury.

METHODS

Two groups of patients were studied. Group A (n = 32) had long bone fractures in addition to having head injuries. Group B (n = 35) had only long bone fractures. The fractures in the 2 groups of patients was treated by inter medullary nailing. Osteoblasts in the debris of the inter medullary nailing was compared between the 2 groups of patients.

RESULTS

The results demonstrated that histopathological specimens from reaming debris of fractured femur and tibia in patients with head injury showed osteoblasts in (82.9%) and in (27.5%) of patients with isolated long bone fractures (p < 0.001).

CONCLUSION

Healing indicators in diaphyseal fractures and concomitant head injury confirm fast and adequate healing in these patients and the presence of plenty of osteoblasts in their reaming debris may reflect a proof of accelerated fracture healing environment.

Perceptions and realities for distal freehand interlocking of intramedullary nails

There is a perception that distal freehand interlocking (DFHI) of intramedullary nails can be difficult and time consuming. This study consists of a survey of surgeons' practices for DFHI screws and their reasons for not using this technique. A survey was sent to 1400 orthopaedic surgeons who were asked to agree or disagree with statements regarding the difficulty and indications for the usage of distal freehand interlocking screws. The results were analyzed by practice demographics, resident availability, and completion of an orthopaedic trauma fellowship. Overall, 316 surgeons (22.6%) responded to the survey. Fellowship trained surgeons were 60% less likely to find DFHI difficult when compared to nonfellowship surgeons and surgeons with residents were 76% less likely to perceive DFHI as difficult than surgeons without residents. In all groups, 40-43% of surgeons used distal interlocking based on their comfort with the technique and not the fracture pattern. Distal freehand interlocking is perceived as difficult by community orthopaedic surgeons without residents and surgeons who have not done an orthopaedic trauma fellowship. Forty percent of surgeons based their usage of DFHI screws on their comfort with the technique and not the fracture pattern.

Distal interlocking screw placement in the femur: free-hand versus electromagnetic assisted technique (sureshot)

OBJECTIVES

To compare the free-hand (FH) technique of placing interlocking screws to a commercially available electromagnetic (EM) targeting system in terms of operating time, radiation dose, and accuracy of screw placement.

METHODS

Between September 2011 and July 2012, we prospectively randomized 100 consecutive femur shaft fractures in 99 patients requiring intramedullary nails to either FH using fluoroscopy (n = 43) or EM targeting (n = 38; Sureshot).

SETTING

Single Level 1 University Hospital Trauma Center.

MAIN OUTCOME MEASUREMENTS

The 2 groups were assessed for distal locking with respect to time, radiation, and accuracy.

RESULTS

Eight-one fractures had data accurately recorded (38 EM/43 FH). The average total operative time was 50 minutes (range, 25-88 minutes; SD, 13.9 minutes) for the FH group and 57 minutes (range, 40-103 minutes; SD, 16.12 minutes) for the EM group. The average time for distal locking was 10 minutes (range, 4-16 minutes; SD, 3.56 minutes) with FH and 11 minutes (range, 6-28 minutes; SD, 10.24 minutes) with EM. Average radiation dose for distal locking was significantly less (P < 0.0001) for EM at 230.54 μGy (range, 51-660 μGy; SD, 0.17 μGy) compared with 690.27 μGy (range, 200-2310 μGy; SD, 0.52 μGy) for FH. There were 2 misplaced drill bits in FH and 3 in EM. This was not statistically significant (P = 0.888).

CONCLUSIONS

The electromagnetic targeting device (Sureshot) significantly reduced radiation exposure during placement of distal interlocking screws, without sacrificing operative time, and was equivalent in accuracy when compared with the FH technique.

LEVEL OF EVIDENCE

Therapeutic level II.

Relevance of deep decortication and vascularization in a case of post-traumatic femoral non-union treated with grafts, platelet gel and bone marrow stromal cells

PURPOSE

A male patient suffering from non-union of the femoral diaphysis after a traumatic fracture was treated with deep decortication and grafted with lyophilized bone, platelet gel (PG) and autologous bone marrow stromal cells (BMSCs). After 40 days from surgery, he was re-operated, due to fracture secondary displacement, caused by inappropriate load during sports activity. In addition to radiographs, two bone biopsies were retrieved: this allowed for a histological evaluation of the early response of host bone to the graft. To our knowledge, there is no report describing such early tissue response.

METHODS

A clinical-radiographic evaluation of the patient and a histomorphometric analysis of the bone biopsies were performed.

RESULTS

An early reparative bone formation was observed adjacent to the osteointegrated graft. Non-resorbed bone chips and large islands of non-vital bone particles, surrounded by fibrous tissue, were observed in a zone of sclerotic diaphyseal bone, that is the process was delayed despite decortication.

CONCLUSIONS

These findings support the concept, until now evidenced only by imaging, that bone chips added with PG and BMSCs are effective in shortening the healing time in fracture non-union. The clinical relevance of deep decortication and vascularization is emphasized.

LEVEL OF EVIDENCE

Therapeutic studies-investigating the results of treatment, Level V.

Risk of injury to the superior gluteal nerve when using a proximal incision for insertion of a piriformis-entry reamed femoral intramedullary nail: a cadaveric study

BACKGROUND

This cadaveric study evaluated the risk of injury to the superior gluteal nerve when a proximal incision site is used for insertion of an antegrade, reamed femoral intramedullary nail into the piriformis fossa. Based on prior anatomical studies, our hypothesis is that the use of a proximal incision site for intramedullary nail insertion will consistently injure the superior gluteal nerve.

METHODS

A reamed femoral intramedullary nail was inserted through a piriformis fossa entry site in six pairs of fresh-frozen cadaver femora. The specimens were randomized to two groups: reaming of the femoral canal with or without a protective sleeve. Damage to the superior gluteal nerve was evaluated by means of layered dissection of specimens. Damage to any part(s) of the superior gluteal nerve was recorded, and the distances between the path of the instrumentation and nail and the branches of the superior gluteal nerve were measured.

RESULTS

A "spray" nerve pattern of the superior gluteal nerve was present in all twelve specimens. The average distance and standard deviation between the most superior branch of the superior gluteal nerve and the instrumentation and nail path was 17.75 ± 8.58 mm. The average distance between the most inferior branch of the superior gluteal nerve and the instrumentation and nail path was 22.39 ± 10.52 mm. There were no significant differences between the two groups. There were no injuries to any part of the superior gluteal nerve regardless of whether or not a protective sleeve was used.

CONCLUSIONS

This anatomic study demonstrated that the superior gluteal nerve is not at risk for injury when a proximal incision site is used to place a reamed intramedullary nail into the piriformis fossa.

Surgical technique: static intramedullary nailing of the femur and tibia without intraoperative fluoroscopy

BACKGROUND

On a recent mission directed at definitive care for victims of the Haitian earthquake, the orthopaedic team developed a technique for freehand distal locking of femoral and tibial nails without intraoperative fluoroscopy or proximally mounted targeting jigs.

DESCRIPTION OF TECHNIQUE

After performing open antegrade or retrograde nailing by standard techniques, the freehand lock must be obtained before doing standard outrigger locking. This allows the surgeon to control the nail and deliver the locking hole in the nail to a unicortical drill hole in the femur. Before nail insertion, the distance of the desired locking hole is measured from the outrigger in a standard way such that it can be reproduced after the nail is inserted. Through a unicortical drill hole, the nail is palpated with the tip of a Kirschner wire and systematic maneuvers allow the Kirschner wire to palpate and fall into the locking hole. The Kirschner wire is tapped across the second cortex before drilling. The screw is inserted, and the ball-tipped insertion guidewire is placed back into the nail to palpate the crossing screw confirming position.

PATIENTS AND METHODS

We treated 16 patients with 18 long bone fractures using the described technique. We assessed patients clinically and radiographically immediately postoperatively.

RESULTS

A total of 19 blind freehand interlocks were attempted, and 17 were successful as assessed by direct intraoperative observations and by postoperative radiographs.

CONCLUSIONS

We describe a simple technique for performing static locked intramedullary nailing of the femur and tibia without fluoroscopy. This technique was successful in most cases and is intended for use with any nailing system only when fluoroscopy or specialized systems for nailing without fluoroscopy are not available.

Femoral-shaft fractures and nonunions treated with intramedullary nails: the role of dynamisation

Dynamisation of a previously interlocked intramedullary nail is believed to stimulate an osteogenic response due to increased load across the fracture site. The purpose of this study was to retrospectively investigate fracture patterns that could tolerate dynamisation without the risk of major complications. Thirty patients (24 males) with an average age of 33 years (17-90) were studied. As many as 21 suffered from a fresh femoral fracture, whereas the remaining nine patients suffered from femoral nonunions. Four patterns of osseous lesion were recognised in terms of mechanical stability under a dynamic nail and biological activity at the fracture/nonunion site: stable/hypertrophic, stable/atrophic, unstable/hypertrophic and unstable/atrophic osseous lesions. Complete union (within 6 months) occurred in 21 patients. Six fractures united within the 7th-11th post-dynamisation month and, in the remaining three cases, a nonunion developed. Significant femur shortening (>20 mm) was noticed in four patients and rotational malalignment in one patient. Logistic regression analysis revealed high odds ratio (OR=70, 95% confidence interval (CI) 2.5-1998) for the unstable/atrophic pattern of osseous lesion to develop major complications. In the unstable/atrophic pattern of osseous lesion, dynamisation should never be done, as it could lead to significant complications.

Intramedullary femoral nailing through the trochanteric fossa versus greater trochanter tip: a randomized controlled study with in-depth functional outcome results

PURPOSE

In a level 1 university trauma center, an explorative randomized controlled study was performed to compare soft tissue damage and functional outcome after antegrade femoral nailing through a trochanteric fossa (also known as piriform fossa) entry point to a greater trochanter entry point in patients with a femoral shaft fracture.

MATERIALS AND METHODS

Nineteen patients were enrolled and randomly assigned to two nail insertion groups; ten patients were treated with an Unreamed Femoral Nail(®) (UFN, Synthes(®), Solothurn, Switzerland) inserted at the trochanteric fossa and nine patients were treated with an Antegrade Femoral Nail(®) (AFN, Synthes(®), Solothurn, Switzerland) inserted at the tip of the greater trochanter. The main outcome measures were pain, gait, nerve and muscle function, along with endurance. Magnetic resonance imaging (MRI), electromyography (EMG), and Cybex isokinetic testings were performed at, respectively, 2 and 6 weeks and at a minimum of 12 months after surgery.

RESULTS

The MRI and EMG showed, in both groups, signs of iatrogenic abductor musculature lesions (four in the UFN group and four in the AFN group) and superior gluteal nerve injury (five in the UFN group and four in the AFN group). The isokinetic measurements and the patient-reported outcomes showed moderate reduction in abduction strength and endurance, as well as functional impairment with slight to moderate interference with daily life in both groups, with no appreciable differences between the groups.

CONCLUSIONS

Anatomical localization of the entry point seems to be important for per-operative soft tissue damage and subsequent functional impairment. However, the results of this study did not show appreciable differences between femoral nailing through the greater trochanter tip and nailing through the trochanteric fossa.

Computer-assisted three-dimensional correlation between the femoral neck-shaft angle and the optimal entry point for antegrade nailing

Optimal entry point for antegrade femoral intramedullary nailing (IMN) remains controversial in the current medical literature. The definition of an ideal entry point for femoral IMN would implicate a tenseless introduction of the implant into the canal with anatomical alignment of the bone fragments. This study was undertaken in order to investigate possible existing relationships between the true 3D geometric parameters of the femur and the location of the optimum entry point. A sample population of 22 cadaveric femurs was used (mean age=51.09+/-14.82 years). Computed-tomography sections every 0.5mm for the entire length of femurs were produced. These sections were subsequently reconstructed to generate solid computer models of the external anatomy and medullary canal of each femur. Solid models of all femurs were subjected to a series of geometrical manipulations and computations using standard computer-aided-design tools. In the sagittal plane, the optimum entry point always lied a few millimeters behind the femoral neck axis (mean=3.5+/-1.5mm). In the coronal plane the optimum entry point lied at a location dependent on the femoral neck-shaft angle. Linear regression on the data showed that the optimal entry point is clearly correlated to the true 3D femoral neck-shaft angle (R(2)=0.7310) and the projected femoral neck-shaft angle (R(2)=0.6289). Anatomical parameters of the proximal femur, such as the varus-valgus angulation, are key factors in the determination of optimal entry point for nailing. The clinical relevance of the results is that in varus hips (neck-shaft angle <or=120 degrees) the correct entry point should be positioned over the trochanter tip and the use stiff nails is advised. In cases of hips with neck-shaft angle between 120 degrees and 130 degrees , the optimal entry point lies just medially to the trochanter tip (at the piriformis fossa) and the use of stiff implants is safe. In hips with neck-shaft angle over 130 degrees the anatomical axis of the canal is medially to the base of the neck, in a "restricted area". In these cases the entry point should be located at the insertion of the piriformis muscle and the application of more malleable implants that could easily follow the medullary canal should be considered.

Intramedullary nailing for the treatment of aseptic femoral shaft non-unions after plating failure: effectiveness and timing

This retrospective, multicentre study aimed to evaluate reamed intramedullary nailing (IMN) for the treatment of 30 cases of aseptic femoral shaft non-union after plating failure. Following nailing, 29 non-unions had healed by a mean 7.93 months. In one case a hypertrophic non-union required renailing after 8 months, using a nail of greater diameter, and united within five further months. Healing times were not related to whether the fracture was open or closed, the type non-union or the type of fracture. The delay from the initial plating to intramedullary nailing had a statistically significant effect on healing time and final outcome. This treatment is cost effective and should be implemented as soon as the non-union is diagnosed.

Case report: Patella baja after retrograde femoral nail insertion

Patella baja is a rare condition that can result from conditions involving trauma around the knee. Risk factors are believed to include scar tissue formation in the retropatellar fat pad, extensor mechanism dysfunction, and immobilization in extension. Early recognition and aggressive treatment are critical components in minimizing long-term disability. We present a case report of a woman with a fracture of the femoral diaphysis who underwent retrograde placement of an intramedullary nail. Subsequent followup revealed development of patella baja with resultant disability. The diagnosis was made late and the treatment was ineffective. Although patella baja has been reported in trauma around the knee, causative factors include retrograde femoral nailing. We believe early recognition and institution of treatment are important.

Lateral insertion points in antegrade femoral nailing and their influence on femoral bone strains

OBJECTIVES

Insertion of rigid uniplane bent femoral nails through the piriform fossa has been reported to cause neurovascular complications. New nails were designed for more lateral entry points. However, these may be associated with a higher risk of iatrogenic fractures. This study investigated if two differently bent nails with more lateral entry points induce higher cortical bone strains than a uniplane bent nail introduced through the piriform fossa.

METHODS

Three groups of 8 cadaveric femurs were instrumented using the following nail systems and entry points: Cannulated Femoral Nail, piriform fossa; Antegrade Femoral Nail, trochanteric tip; and helical nail, lateral of the trochanteric tip. During insertion, the maximum principal bone strains were recorded at 9 locations at the proximal femur and the diaphysis. The occurrence of iatrogenic fractures or fissures was documented.

RESULTS

The highest strains recorded were between 2000 and 4500 mum/m and mainly located at the posterior aspect of the greater trochanter and at the medial side of the entry point. In most of these cases fissures or fractures occurred, the number of which was higher for the trochanteric tip group as compared with the other groups. This was thought to be due to the thin cortical walls as a result of the larger reamer diameter in this group. Low strains (below 2000 microm/m) occurred at the medial cortex where the laterally inserted nails were expected to impinge.

CONCLUSIONS

Bone strains at the medial impingement location were low for all nails. Entry portals with thin cortical walls due to, for example, larger reamer diameters and a small greater trochanter seem to be more susceptible to insertion accuracy, which may influence strain and fissure or fracture occurrence. Furthermore, we do not recommend determination of the entry point of laterally inserted nails based solely on anatomic landmarks of the greater trochanter because this may influence insertion accuracy. This implies that biplanar imaging is important for accurate and safe insertion of laterally started nails.

Femoral head avascular necrosis after interlocking nail of a femoral shaft fracture in a male adult: a case report

Reamed interlocking nail through the piriformis fossa remains the golden standard for treatment of femoral shaft fracture. Fracture healing rates are 95-99%, and infection rates less than 1% (Clawson et al. in J Bone Joint Surg (Am) 53:681-692, 1971; Winquist et al. in J Bone Joint Surg (Am) 66:529-539, 1984; Brumback et al. in J Bone Joint Surg (Am) 70:1453-1462, 1988). Previous reports recognize avascular necrosis of the femoral head as a complication of antegrade interlocking nail in the adolescent (Beaty et al. in J Pediatr Orthop 14:178-183, 1994; Mileski et al. in J Bone Joint Surg (Am) 76:1706-1708, 1994; O'Malley et al. in J Pediatr Orthop 15:21-23, 1995; Buckaloo et al. in J Southern Orthop Assoc 6(2):97-100, 1997). This report describes a male adult who developed avascular necrosis of the femoral head after an open antegrade interlocking nail of a proximal third femoral shaft fracture. To our knowledge, there is no similar report in the English medical literature.

Femoral nailing-related coagulopathy determined by first-hit magnitude: an animal study

We asked whether coagulopathy worsened during femoral intramedullary nailing in the presence of lung contusion and hemorrhagic shock and whether reamed or unreamed nailing influenced these results. In 30 Merino sheep, we induced hemorrhagic shock and/or standardized lung contusion followed by femoral nailing. Six groups of five each were assigned as follows: thoracotomy control groups treated with reamed or unreamed nailing, lung contusion groups treated with reamed or unreamed nailing, and shock and lung contusion groups treated with reamed or unreamed nailing. After lung contusion alone (first hit), the serum values of antithrombin III, factor V, and fibrinogen were considerably altered after reamed and unreamed femoral nailing (second hit) 4 hours postoperatively. In the lung contusion and shock groups, we found a substantial reduction for all serum coagulative parameters between baseline and fixation after reamed and unreamed nailing. The magnitude of the first hit is increased if hemorrhagic shock is added to a lung contusion determined by hemostatic reactions. The magnitude of the injury appears equally important as the type of subsequent surgery and should be considered in planning for fracture fixation in patients at high risk for complications.

Expandable intramedullary nailing for tibial and femoral fractures: a preliminary analysis of perioperative complications

OBJECTIVE

To report the results of using the expandable nailing system in the treatment of femoral and tibial shaft fractures.

DESIGN

Prospective, cohort series.

SETTING

Two level-1 university trauma centers.

PARTICIPANTS

Forty-eight patients with acute, traumatic diaphyseal fractures of the tibia or femur.

INTERVENTION

Internal fixation of lower extremity long bone fractures using expandable intramedullary nailing.

MAIN OUTCOME MEASUREMENTS

Perioperative complications and time to healing.

RESULTS

Forty-nine long bone fractures were treated: 22 femoral fractures (OTA classification: 4 type A1, 6 A2, 7 A3, 1 B1, and 4 B2) and 27 tibial fractures (OTA classification: 4 type A1, 11 A2, 9 A3, 0 B1, and 3 B2). There were 13 open fractures and 37 closed fractures. Healing occurred in 37 (75%) fractures without additional interventions. There were 2 tibial delayed unions and 1 femoral and 1 tibial nonunion. Five tibial shaft fractures and 6 femoral fractures shortened by 1.0 cm or more postoperatively. In 3 tibias and 4 femurs, shortening occurred after fractures judged to be length-stable became unstable because of fracture propagation during nail expansion. Five tibias and 3 femurs were converted to standard locked nails because of shortening. The average time to healing, excluding nonunion, was 15 weeks in the tibia and 16 weeks in the femur. The expandable nail resulted in an unplanned reoperation in 12 cases (25%).

CONCLUSION

We found a high complication rate because of shortening, which was independent of fracture classification. Consequently, we cannot recommend the use of an unlocked, expandable nail in diaphyseal fractures of the femur or tibia.

Fracture Strain and Stability with Additional Locking Screws in Intramedullary Nailing: A Biomechanical Study

BACKGROUND

We studied the effect of additional locking screws on fracture strain and stability in tibial intramedullary nailing.

METHODS

We drilled an additional diaphyseal locking hole into 8-mm solid tibial nails 185 mm from the proximal end of the nail, and locked it proximally and distally. An osteotomy was produced 4.5 cm distal to the additional hole, and the construct loaded axially, in flexion, extension, and torsion. The nails were also tested for their fatigue strength.

RESULTS

With the additional locking screw, strain increased proximally during loading in neutral and flexion. Strain decreased on loading in extension. The extra locking screw decreased strain close to the osteotomy site in all loading positions. A significant reduction in angular motion at the osteotomy site occurred with the addition of the extra locking screw. The nails survived the fatigue test, although the stress increased around the additional locking hole

CONCLUSIONS

Nails with additional locking options, by altering strain and motion at the fracture site, may have the clinical potential to affect fracture healing.

Case reports: A subtrochanteric femur fracture with long intramedullary femorotibial nail for knee arthrodesis

We present a case report of a patient who had a transverse subtrochanteric femur fracture develop 2 months after uneventful placement of a long femorotibial intramedullary nail for knee arthrodesis. To date, diaphyseal fracture of a femur already stabilized with an intramedullary nail has not been reported. The possible etiology for this unusual complication is discussed.

Clinical evaluation of a true percutaneous technique for antegrade femoral nailing

From July 1997 to March 2001, 209 consecutive patients with 215 femoral shaft fractures amenable to antegrade femoral nailing were enrolled. A true percutaneous insertion technique was performed using a stab wound incision. One hundred ninety-seven (92%) fractures achieved primary union with anatomic or near anatomic alignment. Eighteen (8%) healing problems and two deep infections (1%) responded to repeat interventions. There was one iatrogenic complication related to an anterior starting point. External blood loss was minimal (generally <100 cc). Incisions averaged 16 mm and healed uneventfully. At one-year follow-up only 10% of patients had hip abductor pain. The percutaneous technique appears to be a safe and effective alternative to the standard technique. Hip pain at one year appears decreased compared to reports using a traditional approach.

Trochanteric nail insertion for the treatment of femoral shaft fractures

OBJECTIVES

This study was designed to evaluate whether the use of a new femoral nail, specifically designed to be inserted through the greater trochanter, could eliminate the complications previously seen with insertion of straight nails through this entry portal for the treatment of femoral shaft fractures.

DESIGN

Prospective, clinical trial.

SETTING

Three level I trauma centers.

PATIENTS

Sixty-one consecutive patients with femoral shaft fractures (50 closed and 11 open fractures) treated with antegrade nailing with insertion through the greater trochanter.

INTERVENTION

All patients were treated in the supine position with a TAN nail (Trigen System, Smith & Nephew, Memphis, TN) inserted through the greater trochanter.

MAIN OUTCOME MEASURE

Union, alignment, complications, and hip function.

RESULTS

Forty-six of 57 (81%) surviving patients were available for follow-up at a minimum of 12 (range, 12-25) months. Union occurred in all but 1 fracture after the index procedure. No patient sustained iatrogenic fracture comminution, and there were no angular malunions. Pain was reported as slight in 6 patients and moderate in 2. Visual and videotaped gate analysis, performed on 24 patients, revealed symmetrical walking in 21.

CONCLUSIONS

This study demonstrates that antegrade nailing of femoral shaft fractures with a specially designed nail inserted through a trochanteric starting point provides predictably high union rates and low rates of complications. Ease of entry and utility in patients with a large body habitus are advantages over conventional piriformis fossa entry techniques. Nailing through the greater trochanter with the patient supine is presently our treatment of choice for patients with femoral shaft fractures.

Human reaming debris: a source of multipotent stem cells

The biological characteristics of human reaming debris (HRD) generated in the course of surgical treatment of long bone diaphyseal fractures and nonunions are still a matter of dispute. Therefore, the objective of the present investigation has been to characterize the intrinsic properties of human reaming debris in vitro. Samples of reaming debris harvested from 12 patients with closed diaphyseal fractures were examined ultrastucturally and were cultured under standard conditions. After a lag phase of 4-7 days, cells started to grow out from small bone fragments and established a confluent monolayer within 20-22 days. The cells were characterized according to morphology, proliferation capacity, cell surface antigen profile, and differentiation repertoire. The results reveal that human reaming debris is a source of multipotent stem cells which are able to grow and proliferate in vitro. The cells differentiate along the osteogenic pathway after induction and can be directed toward a neuronal phenotype, as has been shown morphologically and by the expression of neuronal markers after DMSO induction. These findings have prompted interest in the use of reaming debris-derived stem cells in cell and bone replacement therapies.

A corrective osteotomy for post-traumatic malrotation and shortening of the femur

Malrotation following femoral nailing is problematic. We describe a new one-stage technique which utilises three components; a cortico-periosteal sleeve, a "dialled-in"correction of rotation and a peg-shaped osteotomy. Seven patients were treated. The mean correction of malrotation was within 5 degrees of the normal side and the mean correction of length was within 8 mm of the normal side. Clinical union was achieved on average by 6 months (range 4-8 months). The only complication was locking screw breakage in one case. The cortico-periosteal sleeve avoids the need for bone graft, surgery is facilitated by the use of "dialled-in" correction of rotation and a peg to correct length.

Outcome after intramedullary nailing of femoral shaft fractures

BACKGROUND

The results of intramedullary nailing of femoral shaft fractures from Australian institutions have not been widely reported. This study examines a consecutive group of patients treated at a major metropolitan trauma centre and reports on the injury statistics and outcome data, and compares this to previously reported results from the literature.

METHODS

A total of 101 fractures in 97 consecutive adult patients were included in the study. Nine patients were excluded. At a minimum of 6 months post injury, 54 patients were interviewed by telephone and 35 patients presented for clinical review and underwent physical examination, computed tomography (CT) scanogram of the lower limbs and Short Form 36 questionnaires.

RESULTS

Road trauma accounted for 81% of injuries and 15% of fractures were open. Of the 54 patients reviewed, 13 (23%) required further surgery for delayed or non-union. Of the 35 who presented for physical examination, there was poor correlation between perceived leg length discrepancy and measured leg length discrepancy on examination or scanogram. Presence of a limp correlated with measured leg length discrepancy of more than 1 cm but did not correlate with rotational abnormality measured on CT scanogram. Pain at the hip, thigh or knee was present in 60% of patients. The Short Form 36 scores for physical functioning, role--physical, bodily pain, general health and vitality were all significantly lower than population norms with P values ranging from <0.001-0.05. Subgroup analysis comparing isolated femur fracture to multi-trauma patients for all five of these parameters revealed significant differences only in the multi-trauma group.

CONCLUSION

The incidence of pain, limp, leg length discrepancy and delayed or non-union is higher in this study than in previously reported results of intramedullary nailing for femoral shaft fractures. This may be due to differences in the patient population, the skill level of the operating surgeon, or incomplete follow up.

Antegrade femoral nailing: an anatomical determination of the correct entry point

Operative problems in the application of femoral locking nails are frequently related to an unfavourable entry point at the greater trochanter. Especially in more distally located fractures the nail is forced to follow the cortex abutted medullary canal. A wrong defined entry point either in the medio-lateral or dorso-ventral direction inevitably leads to tension between nail and femur. Forceful insertion in this situation may cause disastrous iatrogenic comminution at the fracture side or additional fractures at the proximal femur. To avoid tension between nail and femur the best suited entry point must be defined according to the natural medullary cavity. In 16 human cadaver femora, the natural medullary cavity was opened and after cleaning filled with a radio-opaque substance (barium sulphate). Twelve radiographs where taken from each bone starting with the anterior-posterior view and then turning the bone axially in steps of 15 degrees. From these radiographs, the ideal entry point at the greater trochanter was calculated. In 88% of the specimen the ideal entry point for a straight nail was found constantly at the medial border of the greater trochanter overlaying the tendinous insertion of the piriformis muscle. The axis of the medullary cavity was in average 2.1cm anterior to the dorsal border of the greater trochanter. In a second step the ideal entry point for bend nails was calculated. According to this calculation a bend nail with a radius of 100 cm needs an entry point 0.7 mm anterior to the dorsal edge of the greater trochanter. Overlaying the hook like shape of the posterior part of the trochanter.

Treatment of femoral shaft fractures with a titanium intramedullary nail

Ninety-nine femoral shaft fractures were treated with locked intramedullary nails made from titanium alloy. One of the distal interlocking screws failed in six fractures (6%) and both screws failed in two fractures (2%). Delayed union was associated with all of the eight fractures that had locking screw failure. Young, heavier patients who had nails of small diameter had an increased risk of screw failure. Additional surgery was needed when both screws failed. The authors still use this nail, but currently prefer to ream the medullary canal more so that larger nails can be inserted. Decisions concerning weightbearing are made on an individual basis for each patient, and currently full weightbearing is delayed for young, active, and heavy patients. Two distal interlocking screws should be inserted for treatment of femoral shaft fracture when a Ti locked intramedullary nail is used.

Associated injuries complicating the management of acetabular fractures: review and case studies

The treatment of acetabular fractures has evolved considerably in the past three decades. Associated injuries to the femoral head, proximal femur, or femoral shaft can complicate the initial management of the acetabular fracture, and mandate a careful treatment strategy for optimal treatment of both the acetabular fracture and associated injury. These injuries may have a large impact on the clinical outcome. The surgeon must consider surgical approaches, timing, and alternative modes of fixation. A discussion with case illustrations is provided.

Subtrochanteric femur fractures

Fractures in the subtrochanteric zone of the proximal femur present complex treatment challenges. These treatment difficulties are related to the anatomic and biomechanic features that are unique to this area. These fractures occur in older patients from low-energy trauma and in younger patients with high-energy trauma, with separate diagnostic and treatment significance. Intramedullary fixation with standard centromedullary nails, as well as cephalomedullary nails, are commonly employed as fixation methods to treat this fracture. The techniques and results of this will be reviewed.

Extending fixation beyond the working length of an intramedullary nail with a linked intramedullary and extramedullary fixation in complex femoral fractures; a brief series

We report the use of a fixed-angle side-plate device linked to an intramedullary nail in the femur with the interlocking screws applied through the plate. The 95 degrees device extends the effective length of the nail and increases the stability of the fixation. This technique is one of various adaptations that can be recommended to stabilise a complex combination of femoral fractures. This is a report of four such patients.

Repair of diaphyseal femoral fractures in cats using interlocking intramedullary nails: 12 cases (1996-2000)

OBJECTIVE

To determine the outcome of femoral fractures repaired with 4.0- and 4.7-mm interlocking intramedullary nails in cats.

DESIGN

Retrospective study.

ANIMALS

12 cats with diaphyseal femoral fractures.

PROCEDURE

Records of all cats in which the 4.0- and 4.7-mm interlocking nail system was used for repair of diaphyseal femoral fractures at the Animal Medical Center and Florida Veterinary Specialists between 1996 and 2000 were reviewed. Information included signalment, type of fracture, size of the implant, details of the surgery, intra- and postoperative complications, fracture healing, and clinical outcome.

RESULTS

Femoral fractures in 12 cats were repaired. Eleven of the fractures were comminuted, with 2 of these being open. Clinical outcome was excellent in 7 cats, good in 3, and fair in 1. One resulted in a nonunion. Complications included screw breakage (1 cat) and fracture distal to the nail (1). Fracture distal to the nail occurred from a second trauma.

CONCLUSION AND CLINICAL RELEVANCE

Use of the interlocking nail has been limited in cats because of the small diameter of the medullary canal. Use of the 4.0-mm nail will allow for greater application of this implant in small patients. Results of this study indicate that the 4.0- and 4.7-mm interlocking nails can be used to repair simple or comminuted diaphyseal femoral fractures in cats.

Treatment of femoral shaft aseptic nonunion associated with plating failure: emphasis on the situation of screw breakage

BACKGROUND

Femoral shaft aseptic nonunions associated with plating failure resulting from screw breakage are rare, and the treatment is complex and yet to be defined. The aim of this prospective study was to develop a better technique for the treatment of this complication.

METHODS

Eight consecutive adult patients who sustained femoral shaft aseptic nonunions associated with plating failure resulting from screw breakage were treated. The procedure involved skeletal traction in the femoral condyle, removal of the broken screws after making a bony window in the lateral cortex, with or without lengthening the femur, stabilization with a static locked nail, and finally, corticocancellous bone grafting. Postoperatively, ambulation with protected weight bearing was encouraged as early as possible.

RESULTS

All eight patients were followed up for at least 1 year (range, 1.1-4.7 years), and seven nonunions healed. The median union period was 4 months (range, 3-6 months). One patient had a persistent nonunion, and the locked nail broke at 6 months. The nonunion healed 4 months after closed revision with a new locked nail.

CONCLUSION

The described technique has both theoretical and clinical merits. All abnormalities can be corrected concomitantly. The success rate is high and the complication rate is low. Whenever possible, therefore, it may be used to treat all indicated cases of nonunion.

Potential of increased risk of neurovascular injury using proximal interlocking screws of retrograde femoral nails in patients with acetabular fractures

OBJECTIVES

Neurologic and vascular structures are at risk of iatrogenic injury from proximal interlocking screw insertion after retrograde nailing. This risk may increase in the presence of acetabular fractures because of the displacement of soft tissues resulting from hematoma. The purpose of this study was to establish and compare the relative safe zones (RSZs) for interlocking screw insertion in adults with and without concomitant acetabular fractures.

MATERIALS AND METHODS

Thirty pelvic computed tomography scans of patients with acute unilateral acetabular fracture and magnetic resonance imaging scans of five healthy legs were used to evaluate the course of the femoral sheath, neurovascular complex, and the sciatic nerve as they course through the proximal thigh in sixty-five limbs.

RESULTS

The anatomy of the neurovascular structures on the fractured side was statistically different from that of the normal side. On the normal side, the RSZ at the lesser trochanteric level was identified from +7 degrees medial to +20 degrees lateral to the sagittal axis (27-degree angle zone) for anteroposterior screw placement. These values for the fractured side, respectively, changed to +1 degrees and +14 degrees (13-degree angle zone), a 52 percent decrease. The RSZ for lateral-medial screw placement was 28 degrees anterior to 39 degrees posterior to the coronal axis (67-degree angle zone) for the normal side, which changed, respectively, to 32 degrees and 41 degrees (73-degree angle zone) for the fractured side. At the level of the lesser trochanter, rotation in the femoral shaft was mimicked only in part (approximately 50 percent) by the neurovascular structures.

CONCLUSION

Lateral-medial screw insertion is safer than anteroposterior insertion. Anteroposterior screw insertion becomes even more critical if the acetabulum is fractured. Femoral external rotation after rod insertion, but before screw insertion, will enlarge the safe zones.

Initial rotational stability of distal tibial fractures nailed without proximal locking: the importance of fracture type and degree of cortical contact

Although distally locked (dynamic) nailing is generally recommended for fractures below the isthmus of the tibia in the presence of adequate proximal nail-bone contact, rotational stability in the above situation appears to be a major concern and can increase the risk of malunion. However, there is no published experimental evidence to quantify this mechanical parameter or to relate factors such as the fracture pattern with the final clinical outcome. This in-vitro biomechanical experimental study was set out to measure the initial rotational stability of dynamically nailed fractures of the distal tibial diaphysis. Using a composite tibial model, three non-comminuted types (spiral, oblique and transverse) and various comminuted patterns (comminution, 0-85%) of dynamically nailed fractures of the distal tibial diaphysis were tested. Using a special rig to simultaneously apply axial and torsional loading measurements of torsional stiffness and the previously described "spring-back angle" were carried out. Our results showed that in terms of torsional stiffness and the "spring-back" angle oblique fractures are the most stable followed by transverse and spiral fractures. Furthermore, when testing of the above parameters against the degree of comminution was carried out, a significant reduction of rotational stability was evident with comminution of 50% or above. It is concluded that oblique fractures of the distal tibial third that can be reduced with at least 50% cortical apposition present the optimal rotational stability following dynamic nailing.

Unreamed femoral nailing

Sixty one femoral fractures treated with ACE unreamed titanium nail (AIM femoral nail, ACE Medical, Los Angeles, CA) were studied. Ten patients died before bony union and three were lost to follow up. Forty eight fractures were followed up for an average of 11.2 months (4-31 months). All fractures united except one in which plating and bone grafting was performed at 6 months due to failure of progression of union. The mean time to bony union was 6.2 months. There was no implant failure but one distal interlocking bolt broke at 6 weeks. No incidence of adult respiratory distress syndrome (ARDS) was observed. Malunion was seen in one patient whereas three cases had shortening of more than 2 cm. Our results show that unreamed femoral nailing using titanium nail is a safe and effective procedure for the treatment of femoral shaft fractures.

Prospective comparison of retrograde and antegrade femoral intramedullary nailing

OBJECTIVE

To prospectively compare the results, function, and complications of antegrade and retrograde femoral nailing for femoral shaft fractures.

DESIGN

Prospective, randomized.

SETTING

Urban Level 1 trauma center.

PATIENTS

One hundred consecutive femoral shaft fractures. Fifty-four nails inserted retrograde and forty-six inserted antegrade.

INTERVENTION

Ten-millimeter antegrade or retrograde nail inserted for a femoral shaft fracture after reaming.

OUTCOME MEASUREMENTS

A comparison of the outcomes after antegrade and retrograde nailing of the femur. Data were collected for analysis on comminution, set-up and starting point times, open grade, location of fracture, injury severity score, body mass index, time to union, knee pain and motion, hip and thigh pain, and nail to intramedullary canal diameter difference. A linear regression model was employed.

RESULTS

Knee motion was 120 degrees in all but one knee in each group. The antegrade nailed femurs healed faster than those treated retrograde (A = 14.4, R = 18.1 weeks, p = 0.0496). More patients required dynamization for union in the retrograde insertion group (17 percent versus 5 percent, p = 0.10, NS). In a linear regression model, a nail-to-canal-diameter difference and retrograde nailing had an association with an increased time to union. Knee pain was equal in both groups; however, thigh pain was higher in the antegrade group (p = 0.0108). All of the antegrade nailed femurs healed (100 percent), and 98 percent (one nonunion) of the retrograde femurs healed after secondary procedures.

CONCLUSIONS

Both antegrade and retrograde nailing yielded high union rates. Each insertion technique has its own advantages and disadvantages. The two insertion modes appear to be relatively equal for the treatment of femoral shaft fractures.

Long-term residual musculoskeletal deficits after femoral shaft fractures treated with intramedullary nailing

BACKGROUND

Locked intramedullary (IM) nailing has been recognized as one of the most reliable methods for treatment of femoral shaft fractures. Although IM nails are routinely used in the treatment of these fractures, the long-term effects of retained IM nails are unknown.

METHODS

Seventeen patients with radiographically documented healed fracture of femoral diaphysis after locked IM nailing technique were evaluated at a follow-up of at least 18 months postoperatively. All patients had returned to their preinjury level of function and activity before the study. The bone mineral densities (BMD) of the injured and contralateral femora were measured using dual energy x-ray absorptiometry (DEXA). BMD of symmetrical regions in the femoral neck and medial and lateral femoral cortex of the implanted and contralateral femora were compared. Postinjury muscle function was assessed from measurement of the isometric strength of six separate muscle groups (quadriceps, hamstrings, hip extensors, hip flexors, hip abductors, and hip adductors) in treated and control extremities.

RESULTS

The average BMD of the femoral neck region of instrumented femora was 9% less than in contralateral control. Within the medial cortex, BMD of the control femora was an average of 20% greater than in the implanted side. In the lateral cortex, the difference averaged 13%. The isometric dynamometric data demonstrated a statistically significant reduction in the strength of the quadriceps of the instrumented extremities as compared with the contralateral ones. There was no significant difference in the strength of the hamstrings, hip extensors, hip flexors, abductors, or adductors. In the control extremities, the average torque generated by isometric contraction of the quadriceps was 3.45+/-1.35 times greater than by the hamstrings. Torque in extension/flexion and abduction/adduction was also observed.

CONCLUSION

Our data suggest that limbs with long-term retained IM nails experience a significant reduction in the femur BMD and quadriceps muscle strength. These findings may not be simply related to the implant, and further study is warranted to determine the causes of these changes.

Failure of exchange reamed intramedullary nails for ununited femoral shaft fractures

OBJECTIVE

To determine the effectiveness of exchange reamed nails for treatment of aseptic femoral delayed unions and nonunions.

DESIGN

Retrospective chart review.

PATIENTS

Nineteen patients admitted to the Carolinas Medical Center Level I trauma center from 1990 to 1996 for repair of femoral shaft fracture nonunion following contemporary locked nailing performed at least six months previously. These patients showed no radiographic evidence of progression of fracture healing for three months and had clinical symptoms of nonunion.

INTERVENTION

Exchange reamed nails to treat ununited femoral shaft fracture.

MAIN OUTCOME MEASUREMENTS

Radiographic and clinical evidence of union of the fracture or of the necessity for additional procedures.

RESULTS

In 53 percent of the patients the secondary procedure resulted in fracture union, whereas in 47 percent, one or more additional procedures were required. Eight of the nine fractures that did not unite with exchange nailing united after a subsequent procedure (bone grafting, compression plating, or nail dynamization). Neither the type of nonunion, the location of the shaft fracture, the use of static versus dynamic cross-locking, nor the use of tobacco products was statistically predictive of the need for additional procedures.

CONCLUSIONS

Reevaluation of routine exchange nailing as the recommended treatment for aseptic femoral delayed union or nonunion may be required. A significant number of patients who undergo reamed exchange nailing will require additional procedures to achieve fracture healing.

Success of exchange reamed intramedullary nailing for femoral shaft nonunion or delayed union

OBJECTIVES

To investigate the success of exchange reamed femoral nailing in the treatment of femoral nonunion after intramedullary (IM) nailing, and to analyze factors that may contribute to failure of exchange reamed femoral nailing.

DESIGN

Retrospective consecutive clinical series.

SETTING

Level I trauma center and tertiary university hospital.

PATIENTS

Twenty-three patients were identified whose radiographs failed to show progression of healing for four months after treatment with a reamed IM femoral nail. Nineteen patients had undergone primary IM nailing of an acute femoral shaft fracture, one patient had been converted to an IM nail after initially being treated in an external fixator, and three patients had previously undergone an unsuccessful exchange reamed nailing.

INTERVENTION

All patients were treated by exchange reamed femoral nailing. The diameter of the new nail was one to three millimeters larger than that of the previous nail (the majority were two millimeters larger). The intramedullary canal was overreamed by one millimeter more than the diameter of the nail. Most of the nails were statically locked, and care was taken to avoid distraction of the nonunion site by reverse impaction after distal interlocking was performed or by applying compression with a femoral distractor.

MAIN OUTCOME MEASUREMENTS

Radiographic evaluation of union was determined by the presence of healing on at least three of four cortices. Factors reviewed included the patient's age, smoking history, mechanism of injury, associated injuries, whether the initial fracture was open or closed, the pattern and location of the fracture, the type of nonunion, the increase in nail diameter, whether the nail was dynamically or statically locked, and the results of any intraoperative cultures.

RESULTS

Tobacco use was found to have a detrimental impact on the success of exchange reamed nailing. All eight of the nonsmokers healed after exchange reamed nailing, whereas only ten of the fifteen smokers (66.7 percent) healed after exchange reamed nailing. Overall, exchange reamed femoral nailing was successful in eighteen cases (78.3 percent). Three patients achieved union with additional procedures. Intramedullary cultures were positive in five cases; all of these achieved successful union.

CONCLUSIONS

Exchange reamed nailing remains the treatment of choice for most femoral diaphyseal nonunions. Exchange reamed IM nailing has low morbidity, may obviate the need for additional bone grafting, and allows full weight-bearing and active rehabilitation. Tobacco use appears to have an adverse effect on nonunion healing after exchange reamed femoral nailing.

Treatment of fractures of femur and tibia with the telescopic locking nail: design of a new implant and the first clinical results

BACKGROUND

This study was carried out to evaluate the first clinical experiences with the telescopic locking nail (TLN). The TLN is a newly developed universal locking nail system for both femur and tibia that permits cyclic dynamic loading at the fracture site while weightbearing. The nail can also be used for static interlocking or for compression of the fracture elements. The nail is strong enough to permit immediate weightbearing, and the diameter of 9 mm allows unreamed introduction in many cases.

MATERIALS

Seventy-one consecutive patients were treated with the TLN, 24 patients with femoral and 47 patients with tibial fracture or nonunion.

RESULTS

Functional outcome, complication rate, and union rate were comparable to other interlocking nail systems.

CONCLUSION

Its distinctive biomechanical properties and its universal application in both femur and tibia make the TLN a sophisticated, yet in practice simple, new asset in the practice of intramedullary nailing.

Effects of torsional rigidity on fracture healing: strength and mineralization in rat femora

OBJECTIVE

To assess the effects of torsional rigidity and dynamization on fracture healing in a medullary nailed rat femoral model.

STUDY DESIGN

Randomized study in male Wistar rats with a diaphyseal osteotomy/fracture.

METHODS

Reamed cannulated nailing was performed in sixty rats. One group (twenty rats) received unlocked nails (UL group) and another group received nails with proximal and distal locking that was dynamized after twenty days (DL group). The third group was statically locked (SL group). A fourth group of twenty rats served as the control group. After randomization, the femurs of ten rats in each group at six and twelve weeks were studied clinically, radiologically, and biomechanically, and bone mineralization was measured by dual-energy x-ray absorptiometry (DEXA).

RESULTS

Radiographs in two planes revealed clearly visible fractures at six weeks, and at twelve weeks bridging callus was apparent in all three treatment groups. The callus area in the UL group was significantly larger at six weeks than in the other groups, and at twelve weeks the UL and DL groups had larger callus areas than the SL group. Biomechanically, UL nails had reduced maximum bending load at six and twelve weeks, while DL nails had increased fracture energy at six weeks compared with SL nails. Bone mineral content and bone mineral density in the callus segment and diaphysis were increased with DL nails at six weeks.

CONCLUSION

This animal study indicates that (a) interlocked nailing has a beneficial effect on bone healing and (b) although dynamization may have a beneficial effect on the quality of early bone healing, (c) dynamization does not increase the rate of bony union. The clinical implication is that routine early dynamization of locked femoral fractures may not be indicated, reserving dynamization to cases of delayed union.

A comparison of mechanical strength of the femoral neck following locked intramedullary nailing using oblique versus transverse proximal screws

OBJECTIVE

The objective of the present study was to determine whether the 130-degree oblique or transverse proximal locking technique significantly enhances or diminishes the strength of the intramedullary nail-to-bone construct in a "stancelike" loading configuration.

DESIGN

Six paired fresh frozen femora were randomized to locked intramedullary nailing with either the 130-degree proximal locking technique or the transverse locking technique and tested in axial compressive loading. Torsion, shear, and impact loading were not tested.

PATIENTS/PARTICIPANTS

Six paired adult fresh frozen cadavers.

INTERVENTION

An unreamed eleven-millimeter by thirty-eight-centimeter intramedullary nail was placed under direct visualization in each femur. Proximal locking was randomly performed on each pair with either two transverse screws or a single oblique screw. Each femur was loaded to failure at a rate of 50.8 millimeters per minute (two inches per minute) by using an Instron tensiometer. Radiographs after nail insertion and after failure were obtained.

MAIN OUTCOME MEASURES

Load to fracture and fracture pattern.

RESULTS

A significant difference between load to fracture was observed across femora of different donors (p < 0.001). No significant difference was observed in paired femora from the same donor when using either 130-degree or transverse proximal locking (p > 0.05). This result was based on nonanatomical axial loading that approximated loading during stance, without hip abductor loads to help stabilize the femur.

CONCLUSION

Neither technique preferentially predisposed the construct to failure for the loading pattern tested. The mode of failure was the same in all cases, with failure beginning at the nail insertion site.