Early Results of the Less Invasive Stabilization System for
Mechanically Unstable Fractures of the Distal Femur (AO/OTA
Types A2, A3, C2, and C3)
Mark Weight, MD and Cory Collinge, MD
Objectives:Historically, mechanically unstable fractures of the dis-tal femur have been difficult to treat. Problems such as varus collapse, malunion, and nonunion frequently resulted before fixed-angle plates and indirect reduction techniques were popularized. More recently, the Less Invasive Stabilization System®, or LISS (Synthes, Paoli, PA), has been designed to combine these 2 approaches with the in-tended goals of achieving adequate stable fixation and early healing. Early clinical results for the femoral Less Invasive Stabilization Sys-tem® have been promising. The purpose of this study is to evaluate the clinical results of patients with high energy, mechanically un-stable fractures of the distal femur treated with the Less Invasive Sta-bilization System®.
Design:Retrospective analysis of a treatment protocol, consecutive patient series.
Setting:Busy level II trauma center.
Patients /Participants:Twenty-six patients with 27 high-energy AO/OTA types A2, A3, C2, and C3 fractures of the distal femur. Intervention:Treatment with indirect fracture reduction and in-ternal distal femoral fixation using the Less Invasive Stabilization System®.
Main Outcome Measurements:Clinical and radiographic as-sessment.
Results:Twenty-one patients with 22 fractures were available for evaluation at an average 19 months postinjury (range 12–35 months). The mechanism of injury included 12 motor vehicle collisions, 4 high falls, 5 motorcycle crashes, and 1 bicyclist struck by a car. Twenty patients had associated injuries. Six fractures were open. All fractures were comminuted; according to the AO/OTA fracture classification
there were 4 A2, 3 A3, 12 C2, and 3 C3 fractures. All fractures healed without secondary surgeries at a mean of 13 weeks (range 7–16 weeks). There were no cases of failed fixation, implant breakage, or infection. Average joint line orientation relative to the femoral shaft axis (valgus) measured 99° on postoperative radiographs and 99° on final radiographs. A comparison of postoperative to healed final ra-diographs for each femur demonstrated no case with greater than a 3° difference in either varus or valgus. Complications included 1 mal-union where the fracture was fixed in 8° of valgus and 2 cases of external rotation between 10° and 15°. Painful hardware occurred in 4 patients, of which 3 underwent implant removal. The average knee range of motion was 5° to 114°.
Conclusions:The Less Invasive Stabilization System® allows for stable fixation and facilitates early healing in mechanically unstable high-energy fractures of the distal femur. There were no patients with fixation failure, varus collapse, or nonunion in this “at-risk” popula-tion. This treatment safely allows for immediate postoperative initia-tion of joint mobility and the progression of weight bearing with early radiographic signs of healing.
Key Words: minimally invasive plating, biologic plating, fracture fixation, femur, supracondylar femur
(J Orthop Trauma 2004;18:503–508)
H
istorically, the treatment of distal femur fractures has not produced a high percentage of excellent clinical results. Thin cortices, osteoporosis, a wide intramedullary canal, and fracture comminution have made stable fixation of these inju-ries difficult to achieve and maintain with traditional operative methods. In the 1970s and early 1980s, these injuries were ap-proached with open reduction and internal fixation using es-tablished methods and standard implants. After early attempts at surgical treatment, however, relatively high complication rates were found that adversely affected clinical results.1–9 Problems including infection, nonunion or delayed union, mal-union, the need for bone graft, and stiffness due to delayed mobility were common.2,7–12Additionally, use of traditional methods to treat mechanically unstable distal femoral fractures resulted in problems with healing and failure of fixation result-ing in varus collapse.1,5,11–17Subsequently, alternativemeth-Accepted for publication April 28, 2004.
From the Harris Methodist Hospital-Fort Worth and Fort Worth Affiliated Hospitals/John Peter Smith Orthopaedic Surgery Residency, Fort Worth, TX.
The implants discussed in this manuscript have been 510K approved by the US Federal Drug Administration.
No direct financial or other support has been provided to the authors from the makers of the implants discussed in this manuscript.
Reprints: Cory Collinge, MD, 800 5th Street, Suite 500, Fort Worth, TX 76104 (e-mail: [email protected]).
ods for comminuted or unstable fractures of the distal femur were proposed, including double plating,13,18,19use of plates for endosteal substitution,1,20–22 and anatomically contoured plates.
In the 1980s, advances in fracture care were applied to these difficult injuries and clinical results improved. First, in-direct reduction and improved maintenance of the fracture bi-ology was popularized by Mast et al and others.1,23,24Second, improvements in implant design occurred, leading to fixed-angle plates such as the 95° angle blade plate and dynamic condylar screw. These fixed-angle implants impart a measure of stability to plate fixation in this area not previously avail-able: in particular, they resist relative shortening of the medial side that may result in varus deformity. When these 2 treat-ments were employed together, dramatically improved rates of bone healing and fewer complications of treatment were found compared with historical controls.2
Recently, “locked plating” systems have been devel-oped, where screws are inserted that attach to the plate forming a multiple fixed-angle construct. Some of these systems are designed to apply the implants in a minimally invasive fashion that may diminish problems with fracture healing and infec-tion.21–23,25–28 Additionally, the Less Invasive Stabilization System®, or LISS (Synthes USA, Paoli, PA), functions as an
“internal fixator,”as the implant is designed not to compress the periosteum, thus potentially allowing maintenance of the vascularity to the injured bone (Fig. 1). Early clinical results for the distal femoral LISS have been promising.19,29,30 To
date, however, no study has specifically looked at the results of high-energy, mechanically unstable fractures of the distal fe-mur (AO/OTA types A2, A3, C2, and C3)31treated with LISS. The purpose of this study is to evaluate early clinical and ra-diographic results of patients treated for these high-energy, mechanically unstable fractures of the distal femur (AO/OTA A2, A3, C2, and C3)31using the distal femoral LISS.
METHODS
Twenty-six patients identified from our trauma registry with 27 mechanically unstable distal femur fractures (AO/OTA 33-A2, A3, C2, and C3)31that were treated with LISS between August 1999 and October 2002. All fractures were treated by a single fellowship-trained orthopaedic trauma surgeon at a busy level II trauma facility. Treatment of patients with these injuries included a protocol of early fracture fixation using either LISS definitively or spanning of the fracture and knee joint with a temporizing external fixator. Open fractures, fractures with articular comminution, and polytraumatized pa-tients were treated in a staged fashion. Definitive treatment included open reduction of any intra-articular fractures, indi-rect reduction of metaphyseal and metadiaphyseal fractures, and minimally invasive plate application and fixation.
Operative treatment of the patients included in this re-port is as follows. Patients were positioned supine on a radio-lucent operating table. A wide surgical prep of the entire lower extremity was performed, and prophylactic antibiotics were administered. If an external fixator was in place, it was care-fully cleansed with iodine soap and paint and handled as little as possible throughout the case. Alcohol moistened sponges were placed around the pin sites and held in place with elastic gauze. A 5 to 10 cm skin incision was made along the lateral aspect of the distal femur and the iliotibial band fibers were incised in line with the skin. Displaced articular injuries were addressed first with reduction and application of 1 or 2 small fragment lag screws placed anterior to the expected site of plate placement. The surgical tactic was altered for commi-nuted articular fractures to include a lateral parapatellar ap-proach to the joint to allow for improved access for articular reconstruction.
Indirect reduction of the metaphyseal or metadiaphyseal fractures was achieved by a combination of methods. The ex-ternal fixator (Stryker-Howmedica-Osteonics, Mahwah, NJ),
FIGURE 1.Case example of a typical distal femur fracture treated in this series. A, Injury radiographs demonstrating high-energy distal femur fracture. B, Postoperative radiographs after minimally invasive treatment with LISS. C, Radiographs of healed fracture at 5.5 months.
if present, or a femoral distractor (Synthes USA) was used to gain length and was universally helpful in reduction. A well-placed knee roll was used in all cases to aid in obtaining and maintaining reduction in flexion–extension. Additional tools used for indirect reduction included the “whirlybird”device from the LISS set, Kirschner wire joysticks, or gentle manipu-lation of the condylar fragment using a large periarticular clamp (DePuy-Ace, Warsaw, IN).
Using the radiolucent arm as a handle, the plate was in-serted above the periosteum of the lateral femur in a submus-cular tunnel beneath the vastus lateralis. The plate is designed to fit the anatomy of the distal femur and was applied such that the plate was nestled up next to the metaphyseal flare and lat-eral condyle of the distal femur by sliding it proximally and distally. The plate was centered on bone both proximally and distally and oriented flush with the lateral femoral condyle. A large periarticular clamp was used distally to gently hold the bone to the plate, which typically aided in the sagittal plane fracture reduction. All of these fractures had some level of comminution, and, in many cases, approximation of the“ nor-mal”anatomy was necessary. The opposite uninjured femur was useful as a template in many of these cases, as bony land-marks on the injured side were obscured by fracture. Great effort was then expended toward critically assessing the frac-ture alignment in varus-valgus, flexion–extension, as well as rotation, prior to application of definitive fixation, a basic prin-ciple when using indirect reduction methods. Quality imaging was used, including an anterior-posterior (AP) view to assess varus-valgus, and a true lateral view to assess plate placement and flexion–extension. Restoration of limb alignment in rota-tion was assessed clinically as compared to the contralateral side on preoperative examination.
The successful use of the LISS system for the treatment of complicated fractures is technique dependent, and a learn-ing curve exists. Once the LISS plate was inserted, a mini-open approach was performed at the proximal end of the plate to ensure that the plate was centered on the lateral side of the femur bone. A locking bolt in the most proximal screw hole was then inserted into the most proximal screw hole; this added stability to the aiming arm by“rectangularizing”the construct. Any gross adjustment of fracture reduction was done before provisional fixation was applied, using K-wires through the cannulated stabilization bolts. The“whirlybird”push-pull de-vice was applied to bring the shaft of the femur toward the plate, fine tune the varus-valgus alignment, and augment sta-bility of the provisional construct. At this time, great effort was again made to carefully scrutinize the fracture reduction in all planes before application of definitive fixation.
Self-drilling locking screws (5 mm) were first placed for fixation into the condylar segment, and then into the shaft por-tion after drilling and measuring with K-wires. Considerable effort was made to apply K-wires and screws parallel to the
joint surface as assessed on the AP imaging as a guide for re-storing alignment. All screws were inserted in a unicortical fashion. They were placed using irrigation to cool the self-drilling screws in an effort to prevent potential problems with bony necrosis and loss of fixation. Once adequate fixation was achieved, the guide system was removed and the wounds irri-gated, dried, and closed. External fixators were only removed after all plating wounds were closed and sterilely dressed.
Postoperatively, knee motion was initiated in patients on day 1 or 2 using physical therapy while they were awake. For those patients remaining intubated or in the intensive care unit, a continuous passive motion machine (CPM) in patients was used. Progressive weight bearing was encouraged once there was radiographic evidence of callus formation. Clinical and radiographic examinations were performed until the fracture was healed, and patients more than 12 months postinjury were called back in and examined. Records and radiographs were reviewed for demographics, fracture type, postoperative align-ment, time to fracture healing (3 cortices bridged), and com-plications. Final clinical and radiographic evaluation was per-formed for knee range of motion, limb rotation, fracture heal-ing, and final radiographic alignment. Final radiographic alignment was assessed using standing bilateral AP and lateral views of the distal femurs on long cassettes. Alignment in varus-valgus was assessed on long AP views with the patient standing, using the intramedullary line of the femur relative to that of the distal femoral articular surface. Flexion–extension was evaluated on the lateral view by comparing the lines of the posterior (or anterior) cortical bone. Limb rotation was as-sessed with the patient prone and the knee flexed; this was compared to the contralateral side.
RESULTS
Of 26 patients, 2 died and 3 were lost to follow-up, leav-ing 21 patients with 22 fractures available for study. Of these 21 patients, the average age was 44 years (17–71 years) and follow-up averaged 18 months (range 12–35 months). Four-teen men and 7 women were available for inclusion. There was a high-energy mechanism of injury in all cases, including 12 motor vehicle collisions, 5 motorcycle crashes, 2 falls from a height greater than 10 feet, a parachuting accident (bilateral), and 1 bicyclist struck by a car. According to the AO/OTA frac-ture classification, there were 4 A2, 3 A3, 12 C2, and 3 C3 fractures (Fig. 2).31Only 1 patient had significant bone loss. Fifteen of 22 fractures extended proximally into the femoral diaphysis. Six fractures were open and were classified as 1 grade I, 1 grade II, and 4 grade III open fractures according to the system of Gustilo and Anderson.32There were 2 peripros-thetic fractures, one in an active 71-year-old man with a total hip arthroplasty and the other in an active 71-year-old woman above a knee arthroplasty. Neither had profound signs of teopenia radiographically nor were they being treated for
os-teoporosis. Fourteen of 22 fractures were initially treated with a knee spanning external fixator, and definitive surgery was delayed until the patient and/or soft tissues had recovered enough to“safely”undergo surgery (mean 5 days, range 2–18 days).
All fractures healed without secondary surgery. The mean time to healing was 13 weeks (range 7–16 weeks). There were no cases of failed fixation, nonunion, or infection, and no bone grafts were required. The mean time to full weight bear-ing was 11.5 weeks (range 8–15 weeks).
Average joint line orientation relative to the femoral shaft axis measured 99°(valgus) on postoperative radiographs and 99°on final radiographs.9No patient measured a
differ-ence of more than 3°from postoperation to final radiographs. The average anatomic axis of the contralateral side measured 97°. Only 1 of 22 fractures had greater than a 5°alteration of alignment in varus-valgus or flexion–extension, a case found to be fixed in 8°of valgus relative to the other side. Two pa-tients were found to have external rotation deformity of 10°to 15°relative to the contralateral side, but one of these had trauma to the contralateral femur. None had greater than a 15°
difference in limb rotation from side to side.
Four patients had symptomatic instrumentation at the lateral distal femur. Three had complete relief after implant removal, and 1 has surgery scheduled. Two patients underwent late knee ligament reconstruction, one for a symptomatic an-terior cruciate deficiency and the other for an unstable postero-lateral corner injury. No other secondary surgeries were per-formed. The average range of motion was 5°to 114°
(exten-sion range −2°–22°, flexion range 55°–145°). One patient with a C3 fracture pattern and associated severe ligamentous knee injury developed Brooker grade IV heterotopic ossification and marked knee stiffness. Excluding this patient, the average range of motion was 3° to 119°. Extra-articular fractures or AO/OTA type A fractures had a mean arc of motion from 2° to 130°, whereas intra-articular injuries or AO/OTA type C had an arc of motion of 7° to 102° (P< 0.01). The average knee range of motion for patients with open fractures was 3° to 117°.
DISCUSSION
Minimally invasive plating techniques have been devel-oped as a method of fracture fixation where additional soft tis-sue trauma is minimized and the fracture biology is left intact. The goals of these techniques are to restore the important anatomy, provide stable fixation, and to promote early fracture healing. This method of treatment has been applied to fractures of the distal femur,19,21,22,29,30as well as other complex lower extremity injuries from the hip to the pilon.1,21,22,25,26,28The use of fixed-angle implants has also shown benefits in the treatment of complex lower extremity injuries, including the distal femur.10,20,21,24Recently, LISS was developed with the rationale of combining the biologic advantages of a minimally invasive insertion technique with the mechanical advantages of a multiple fixed-angle device. Previous studies have dem-onstrated successful early results and relatively low complica-tion rates using this treatment method for fractures of the distal femur.19,29,30The goal of this report was to specifically evalu-ate the results of LISS in mechanically unstable high-energy fractures of the distal femur where the stability of the fixation construct and preservation of fracture biology may be critical. All 22 high-energy, mechanically unstable fractures of the distal femur treated in this study group healed after the index procedure at an average of 13 weeks. There were no cases of fixation failure or implant breakage, and no fracture required bone grafting. Little information is available as to the results of treatments for high-energy injuries of the distal fe-mur or those with mechanically unstable fractures that may be especially prone to healing or alignment problems and dimished clinical results. Two distinct patterns of distal femur in-jury have been recognized,2,12,15,19,20,24,29those in young pa-tients resulting from high-energy trauma and those in elderly osteoporotic patients suffering low-energy injuries. To date, previous reports have made no clinical distinction between these 2 distinct types of injury, and results have been grouped together for analysis.2–8,14–16,18–21,24,27,29,30
Historically, treatment failures have been relatively common, and complication rates have been high for these in-juries.2–7Early attempts at open anatomic reduction and rigid internal fixation with traditional plates had significant prob-lems, with delayed or nonunion occurring in 29% to 38% of fractures5,33 and infection rates of 7% to 20%.3,27,34 These FIGURE 2.AO/OTA classification demonstrating mechanically
problems likely reflect the effects of further trauma on the sur-rounding soft tissues during the wide dissection required for the technique. Dramatically improved results have been re-ported in similar injuries using more biologic approaches and improved implants.20,23,24 Reports by Bolhofner et al20 and Ostrum and Geel24in treating distal femur fractures with
tech-niques of indirect fracture reduction and internal fixation using 95° fixed-angle devices revealed markedly improved results compared with previous methods. They found early union in 93% to 100% of fractures and infections in only 0% to 2% of cases. The authors do, however, acknowledge certain limita-tions of their surgical technique, including the demanding na-ture of correct implant insertion and that it may not be suitable for all injuries. Early reports on distal femur fractures treated with similar principles using LISS have shown promising re-sults as well. Schutz et al described their early rere-sults from multiple European centers30; they found early healing in 37 of 40 patients (93%) treated for fractures with the distal femoral LISS. Kregor et al reported early union in 58 of 61 patients (95%) with distal femur fractures treated similarly with LISS.29The authors attribute successful early healing to vigi-lant maintenance of the fracture biology and strict adherence to the fixation principles of LISS.
We have found that using indirect fracture reduction and fixation with LISS provides ample fixation to maintain frac-ture alignment in these high-energy and mechanically unstable fractures. In this series, the authors found no problems with fixation failure, varus collapse, or other changes in alignment postoperatively for injuries “at risk,” and radiographic align-ment remained unchanged from operative fixation to final healed radiographs. Although earlier series demonstrated ex-cellent fixation in the relatively osteopenic distal or “condylar” segment,19,29,30 Schandelmaier et al found 4 patients whose
fixation failed due to proximal screw pullout in their series of patients with a combination of low-energy and high-energy injuries.19Our results demonstrated no problems with either proximal or distal fixation. This may be attributed to the dis-semination of information regarding the “learning curve” for this system and technique. Proximal failure due to eccentric placement of the plate on the lateral femur may result in inad-equate purchase of the unicortical screws; this problem has been well recognized and may be avoided relatively eas-ily.19,29,30
Three of 22 fractures treated resulted in malunion found in this series. One patient experienced an 8° valgus deformity, and 2 others were found with mild deformities in external ro-tation. All were operatively fixed in these positions early in this series. Persistent deformity has been noted as the most common risk in minimally invasive fracture surgery, with rates as high as 32% or 44%.19,21,22,28The question no longer ap-pears to be will the fracture heal or will it heal straight, but will we fix it straight? Most of the preliminary reports where mal-union rates were extremely high described techniques that
were still evolving at the time.21,22,25,26Although the risk for malunion is real, improved results should be expected if care-ful vigilance toward achieving alignment intraoperatively is observed.
Limitations of this study include all of the shortcomings inherent to its retrospective nature. Also, there is no alternative treatment or control group included in this study with which to compare these results. There are 2 main strengths of this study. First, it is a consecutive series by a single surgeon who had the opportunity to consider and benefit from the “learning curve” of others. Strict adherence to the mechanical, biologic, and technical principles of LISS were upheld. Thus, these mostly positive clinical results should be reproducible by other ortho-paedic surgeons. Second, the data analyzed only pertain to a limited type of patient, which are those who have experienced high-energy trauma resulting in comminuted or mechanically unstable fractures. These are patients that may reap the most benefit from these treatment methods, that is, a minimally in-vasive approach and use of fixed-angle implants.
CONCLUSIONS
A multiple fixed-angle and minimally invasive plating system such as LISS provides adequate stable fixation and fa-cilitates early healing in mechanically unstable, high-energy fractures of the distal femur. There were no nonunions or pa-tients who required bone grafting in this series of 22 similar fractures. There were no problems with fixation failure, varus collapse, or other postoperative changes in alignment in this “at risk” population. Radiographic alignment remained un-changed from operative fixation to final healed radiographs. It appears that LISS achieves the goals of stable fixation and early healing in these mechanically unstable injuries. It must be remembered that careful intraoperative attention should be given to restoring alignment in all planes.
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