3.12 Distal femur
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1 Introduction
Poor bone quality due to osteoporosis creates significant surgical challenges both in fracture reduction and stabilization of distal femoral fractures (DFFs) ( Case 1: Fig 3.12-1 ):
Fracture margins are often too fragile to manipulate directly without further breakage. Reduction clamps can penetrate the bone, making reduction and maintenance quite difficult.
Provisional fixation often fails.
Achieving stability, especially around the distal condylar area, is difficult.
Pronounced varus and anterior angulation malalignment in older patients cause implant-bone mismatch, reduce fixation strength in plating, and makes nailing cumbersome.
Surgeons need to be aware of these difficulties in reduction and fixation when they plan preoperatively. Pitfalls and technical tips to overcome these challenges will be discussed, together with illustrative cases.
CASE 1
Patient
A 73-year-old woman sustained a simple spiral distal femoral fracture (DFF) (AO/OTA 33A2.1) after getting up from the floor ( Fig 3.12-1a–b ). She lived alone in an apartment and walked with a cane.
Comorbidities
Osteoarthritis of both knees
Untreated osteoporosis
Treatment and outcome
The fracture was reduced with a collinear clamp, but the fracture gap was still visible. There was no further attempt to anatomically reduce the fracture due to concerns about further bone fractures ( Fig 3.12-1c–d ). The collinear clamp hindered plate positioning ( Fig 3.12-1e ). The fracture was preliminarily fixed with two positioning screws across the fracture site. Washers were used due to poor bone quality. The reduction was not anatomical ( Fig 3.12-1f–h ). Further reduction with the hammer was needed and further adjustment in the coronal plane was performed with the pulling device (whirly-bird) and the less invasive stabilization system ( Fig 3.12-1i–k ). The follow-up x-rays at 18 months after plating showed solid healing with abundant callus bridging, which means the screws did not have real purchase. All seven screw holes at the plate head were filled with locking head screws due to significant osteoporosis ( Fig 3.12-1l–m ).
Discussion
Standard minimally invasive plate osteosynthesis technique can be applied in the management of the osteoporotic DFF. It is necessary to create a balanced, flexible fixation construct with proper working length over the fracture span. Placing screws across the fracture level is not routinely recommended as it may hinder fracture-site motion and in turn fracture healing. The immediate intraoperative loss of reduction after insertion of two positioning screws illustrates technical problems at the osteoporotic metaphyseal bone.
2 Epidemiology and etiology
Distal femoral fractures represent about 3% of all femoral fractures. They occur in older adults mostly in osteoporotic bone after low-energy trauma and are more common in women (female:male ratio is 2:1). Mean age at fracture is 61 years, with patients older than 65 years in more than half of the cases [1].
3 Diagnostics and classification
AP and lateral x-rays of both femurs, including the adjacent joints, must be obtained in addition to well-dedicated views of the knee joint. Computed tomographic (CT) scans are indicated in the following scenarios:
Intraarticular fracture to assess articular involvement
Extraarticular fractures when they are mainly centered around the supracondylar area
The Unified Classification System (UCS) has gained popularity among surgeons in recent years. For more information on the UCS, see chapter 3.14 Periprosthetic fractures around the knee and Schütz and Perka [2].
4 Decision making
While there is little uncertainty about the necessity of the surgical fixation of DFF even in older patients, there are controversies about the procedure choice between plating and nailing.
Lateral locked plating has been the dominant fixation option for the past 20 years. Retrograde nailing has become more common recently because of improved design and better fixation options around the distal fragment. To improve distal fixation on osteoporotic bone, it is recommended to use the blade and angular stable locking system (ASLS) which enables surgeons to achieve an angular stable construct in osteoporotic bone. Some DFFs at the metadiaphyseal junction can be treated with antegrade nailing [2].
A nail can be inserted through incisions even smaller than those associated with minimally invasive plate osteosynthesis (MIPO) plating. This is especially true in morbidly obese patients. Nails are centrally located and therefore potentially load sharing with a better fatigue life under bending forces than lateral locked plating.
The decision making should be tailored to each fracture and each patient. It also depends on the surgeon′s experience and preference. In general, there are certain factors favoring locked plating:
In very distal fractures, a locking plate offers the insertion of more screws, ie, at least four to five are necessary, compared to the two to three locking bolts of a nail.
In osteoporotic bone, a plate with many locking screws (up to seven) in the distal bloc provides stronger anchorage than a nail with two or three locking bolts or one blade with one or two locking bolts. The risk of cut-through into the joint is less in a locking plate compared to a nail, where the protruding nail can damage intraarticular structures like the patellar intercondylar notch and/or the cruciate ligaments (see Case 4: Fig 3.12-4j–l ).
A torsional fracture pattern in osteopenic bone with a large medullary canal is better stabilized by a locked plate. A nail can toggle easily due to a loose fit in this large cavity, although the stability might be improved by using blocking screws at the correct position in the metaphysis.
A periprosthetic or periimplant fracture sometimes does not allow for the use of a nail and therefore requires a locking plate. In particular, an in situ proximal femoral nail or stem should be overlapped more than 7 cm with a distal femoral locked plate. A retrograde nail, nearly touching the proximal nail, should be avoided (see Case 6: Fig 3.12-6 ).
On the other hand, a more proximal fracture at the metadiaphyseal junction, a more oblique or transverse fracture pattern, and good bone quality are factors favoring a nail as primary implant of choice.
5 Preoperative planning
Patient positioning, specific reduction technique, and step-by-step description of the whole procedure should all be planned when either nailing or plating ( Case 2: Fig 3.12-2 ). Considerations include:
Selecting the proper length of the implants.
In periprosthetic fractures with possible loosening, revision prosthesis should be available.
The type of femoral component in total knee arthroplasty (TKA) should be carefully examined. Closed box-type femoral components preclude retrograde nailing and also limit the locking screw placement to the distal fragment in lateral locked plating. Variable angle locking function is typically beneficial in this situation.
In retrograde nailing, the size of the distal fragment should be carefully examined to estimate the number of interlocking screws/blades that can be placed.
In both plating and nailing, separate lag screws for the Hoffa and sagittal plane articular fractures should be placed carefully so as not to interfere with either locking screws for the plating or interlocking screws/blade in nailing.
The nail insertion depth is based upon the distal fragment size. Underinserting a nail can result in catastrophic articular destruction of the patellofemoral joint, and overinserting a nail may cause the interlocking screw to get too close to the facture site, leaving distal fixation suboptimal.
CASE 2
Patient
A 70-year-old physically fit and independent woman had a fall on an inclined road. She had undergone total knee replacement 3.5 years prior to injury and has taken oral bisphosphonates for the last 4 years.
Comorbidities
None
Treatment and outcome
The initial x-rays showed a Unified Classification System B1 stable prosthesis ( Fig 3.12-2a–b ). The anterior cortical wedge ( Fig 3.12-2b ) resulted in a secondary notching effect on the femoral component.
The patient was set up and both legs draped, which facilitated lateral imaging and assessment of rotational alignment ( Fig 3.12-2c ). A bump was placed under the distal femur to lessen the flexion deformity of the distal fragment and length was restored with gentle manual traction. Then, sagittal plane reduction was done with leverage technique using the Cobb elevator. The anterior cortical wedge was lifted simultaneously with the Cobb elevator ( Fig 3.12-2d–e ).
Once the sagittal plane alignment was reduced, proper plate length was determined to allow the plate to splint the entire femur and prevent a future fracture around the plate tip and the proximal femur. The plate was inserted through the lateral incision with assistance from the image intensifier. This provisional elastic plate positioning at both ends of the plate would later allow for minor adjustment in alignment and even plate positioning. The final adjustment in the coronal plane was done with a collinear clamp introduced through the separate incision in the middle. Then the locking screws were placed accordingly with working length and screw densities kept in mind.
To accommodate the trochanteric ridge, the plate was bent at the tip ( Fig 3.12-2f–i ). The plate position was checked and provisionally attached to the main fragments with K-wires through the drill sleeve, attached to the plate.
X-rays taken 2 years after plating showed soild healing with good alignment ( Fig 3.12-2j–k ) and with a balanced bridge plating construct with proper working length and screw density at the proximal fragment (4/9 = 0.44).
CASE 3
Patient
A 63-year-old woman slipped on a wet floor sustaining a distal femoral fracture. She has been treated for hypertension but was otherwise fit and independent.
Treatment and outcome
The initial x-rays showed a spiral fracture of the distal diaphysis extending into the metadiaphyseal level ( Fig 3.12-3a–b ).
The main spiral fracture was reduced, using a Weber clamp through a small incision which was made on the anterior surface at the level of the spiral fracture ( Fig 3.12-3c–e ).
The x-rays taken 9 months after nailing showed complete healing with callus bridging in good alignment. The angular stable locking systems (ASLSs) were used for distal interlocking. Placing of an ASLS to the dynamic hole may not be recommended routinely as there is no evidence to support this modification. The entire femur was successfully splinted in this patient to prevent future fractures around the hip joint ( Fig 3.12-3f–g ).
CASE 4
Patient
A 90-year-old woman was living independently in an apartment with stairs, able to ambulate independently without walking aids. When she fell after slipping on the wet ground, she sustained a distal femoral and two stable lumbar spinal fractures.
Comorbidities
Arterial hypertension
Vascular disease including bilateral moderate stenosis of carotid arteries
Previous osteoporotic fractures of both distal radii. Osteoporosis treated with vitamin D3 and calcium for more than 10 years and with bisphosphonates for 5 years.
Treatment and outcome
The patient sustained a distal torsional diaphyseal femoral fracture with a nondisplaced and possibly incomplete fissure line towards the intercondylar notch. A computed tomographic scan was not performed but would have been necessary to document the full extension of this fissure line ( Fig 3.12-4a–c ).
Intraoperative image intensification demonstrated a complete but nondisplaced fissure line into the joint. Prior to insertion of the central guide wire, a large reduction forceps was applied percutaneously to prevent a displacement of this fissure. The wire had to be placed correctly in the center of the intercondylar notch in both planes, which was in line with the femoral shaft ( Fig 3.12-4d–e ).
Retrograde nailing with a distal femoral nail was performed ( Fig 3.12-4f–g ). The nail was a bit short but seemed sufficient in this case due to quite thick cortical bone in the diaphysis. The more osteoporotic the bone, the longer the nail should be to prevent a future femoral fracture at the proximal end of the nail. Distal locking was performed with a locking bolt and a spiral blade, as recommended for osteoporotic bone. Importantly, the distal end of the nail was well below the cartilage surface of the intercondylar notch. This was visualized in the lateral view ( Fig 3.12-4i ), where the distance between the so-called Blumensaat′s line (red dotted line in Fig 3.12-4h–i ) and the nail should be at least 5–10 mm. It is important to get a true lateral view, which is best obtained intraoperatively under image intensification. Only then can the distance between the end of the nail and the bone surface be assessed properly. The postoperative x-rays are often not true lateral (as in this case) and therefore do not allow a perfect visualization of this important detail. In cases of severe osteoporosis, there is a risk of a slow ongoing cut-through process of the locking blade/bolt through the femoral metaphysis with secondary penetration of the nail into the knee joint.
The x-rays of a different 75-year-old woman ( Fig 3.12-4j–l ) show that the nail had moved distally by cut-through of the two locking bolts through the osteoporotic bone. The nail protruded into the intercondylar notch anteriorly (Blumensaat′s line, red dotted line in Fig 3.12-4k ) and damaged the cartilage of the patella (red dotted arrow in Fig 3.12-4l ). This complication could have been avoided by inserting the nail initially well below the Blumensaat′s line and by using a spiral blade distally with less risk of cut-through ( Fig 3.12-4i ).
The 4-month x-rays showed a healed situation and unchanged position of the nail and locking implants ( Fig 3.12-4m–n ). The patient was walking around pain free and nearly as well as before the injury. Further follow-up was not planned and implant removal was not advised.
6 Surgical techniques for reduction and fixation
In general, early definitive fixation as soon as medically optimized is preferable, as immobilization with skeletal traction in older patients frequently induces other complications such as deep vein thromboembolism, muscle wasting, pressure ulcers, and loss of functional status.
6.1 Reduction
In general, the authors aim for correct functional alignment (length, rotation, and axis in both planes). This can mostly be achieved in a minimally invasive fashion using different indirect and direct reduction tools and tricks.
In a simple fracture pattern, as is often the case in low-energy fractures in osteoporotic bone, the goal of functional alignment corresponds to a (near) anatomical reduction. Furthermore, we know from experience that simple fractures treated with an implant providing relative stability must be accurately reduced without larger interfragmentary gaps or distraction. This is true for bridge plating as well as for nailing. With a nail fitting well in the small intramedullary canal, this reduction occurs automatically by virtue of the nail itself. But since in most osteoporotic bones the medullary canal is much wider than the chosen nail (especially in fractures at the metadiaphyseal junction), the fracture must be reduced prior to nail or plate insertion. In long spiral or oblique fracture patterns, percutaneously applied cerclage wires and/or reduction forceps allow for minimally invasive (near) anatomical reduction, independent of the chosen implant (nail or plate) ( Case 1: Fig 3.12-1, Case 3: Fig 3.12-3 ). These maneuvers must be done gently and are usually combined with indirect reduction techniques such as manual traction on the leg and/or the use of distraction devices as femoral distractor or temporary external fixator.
In more complex fracture patterns, these tools do not help and the reduction is usually achieved over the implant itself. Details are mentioned in the following subchapters.
6.1.1 Flexion/extension
For correct alignment, the radiographic shape of the opposite leg is very helpful. Usually, if the leg is positioned horizontally, hyperextension occurs by pulling the gastrocnemius muscles on the distal femur. A roll under the knee (resulting in slight knee flexion) helps to prevent this malalignment. As in all minimally invasive plating procedures, the plate is first aligned in the periarticular (distal) part centrally on the bone and fixed with an initial screw. The next step is the alignment of the other plate end centrally onto the bone and, after correct length and rotation are confirmed, fixation of the plate to the bone either with a drill bit or K-wire (left in situ) or a definitive screw. With a second (preliminary) fixation distally (K-wire or drill bit), a relatively stable situation is achieved, which allows the surgeon to clinically check the flexion/extension accuracy by gently lifting the leg at the foot and extending the knee using the gravity. A straight knee then confirms the correct alignment in this lateral aspect. This has to be compared to the healthy opposite leg (to check for preexisting hyperextension). If a sagittal malalignment is detected, it can be corrected by rotating the distal articular bloc around the already inserted distal central interlocking screw. This can be achieved manually by bending or extending the fracture over a rolled towel until correct alignment is reached. Only then are further screws applied distally as well as proximally.
Aneja et al [4] described the following operative technique to address the problems in controlling the flexion deformity of the distal articular block with a Schanz screw placed in the sagittal plane. Once the articular reduction is done, the compression screws are placed bicortically and 0.5 mm apart in the sagittal plane. Following reconstruction of the articular block, a 4 mm Schanz pin is unicortically placed between the two bicortical screws in an anterior-to-posterior direction on the condylar segment. The Schanz pin is then levered up to correct the sagittal plane deformity. This creates a stronger lever arm construct that can be used to reduce the osteoporotic distal bone fragment with less risk of the Schanz pin wallowing out or even cut-out.
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