6.6.3 Femur, distal
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1 Introduction
Fractures of the distal femur represent about 6% of all femoral fractures.
Distal femoral fractures typically occur after high-energy trauma in younger patients or after low-energy trauma in the elderly with osteoporotic bone.
One-third of the younger patients have multiple-system trauma and only a fifth of cases occur as an isolated injury. There is usually considerable soft-tissue damage and almost 50% of high-energy, intraarticular distal femoral fractures are open injuries. With the increasing number of patients with knee joint replacement, the incidence of periprosthetic fractures has been increasing in recent years.
2 Evaluation and diagnosis
In elderly patients with osteoporosis, a low-energy injury causes simple spiral or oblique fractures. In contrast, young adults with high-energy trauma may have severe soft-tissue injuries, multifragmentary fractures; open fractures may have associated bone loss. Careful examination of the neurovascular status is essential. It may be necessary to verify with a Doppler ultrasound or more accurately with angiography to prove that the superficial femoral artery is not injured—it is at risk as it passes through the adductor canal to enter the popliteal fossa. Examination of knee ligament stability before osteosynthesis is painful and not helpful: it should be done after the fracture has been stabilized. If multiple injuries of the lower extremity are suspected, AP and lateral x-rays of femur and tibia, including the adjacent joints, must be taken as well as views centered on the knee joint. Traction x-rays are helpful if there is significant shortening or if a joint spanning external fixator is being placed. Computed tomographic (CT) scans with 2-D and 3-D reconstructions are recommended for intraarticular fractures. This is to assess articular fractures and depression, especially coronal fractures of the posterior condyles (Hoffa fractures) which can be missed with plain x-rays. This may significantly change preoperative planning [1]. Magnetic resonance imaging (MRI) can offer additional information about soft tissues but is not essential in treating acute injuries.
3 Anatomy
The shape of the distal femur, when viewed end on, is a trapezoid with the posterior part wider than the anterior part, creating about 25° of inclination on the medial surface and about 10° on the lateral surface ( Fig 6.6.3-1 ). The plate should lie flat on this lateral surface. A line that is drawn from the anterior aspect of the lateral femoral condyle to the anterior aspect of the medial femoral condyle (patello-femoral inclination) slopes posteriorly approximately 10°. These anatomical details are important when inserting any implants or plates. Knowledge of the normal radiographic joint line angle helps to assess alignment during an operation. The normal anatomical axis of the femoral shaft relative to the knee or the anatomical lateral distal femoral angle (LDFA) is 80–84° ( Fig 6.6.3-2 ). Measured contralateral LDFA can be used as a reference for the assessment of coronal alignment.
Femoral bowing varies in different ethnicities worldwide and this may cause an anatomical mismatch with preshaped distal femoral plates, especially in Asians. There is a consistent pattern of mismatch at the proximal part of the 11-hole locking compression plate distal femur (LCP-DF) that may cause valgus malalignment [2].
The quadriceps, hamstring, and adductor muscle groups cause significant shortening and varus displacement, especially when there are multiple fragments in the metaphysis (33A3, 33C2, and 33C3 fractures). The gastrocnemius muscle originates from the posterior aspect of both femoral condyles and its unopposed action causes a flexion deformity of the distal fragment. The typical deformity is one of shortening with the proximal fragment displaced anteriorly piercing the quadriceps (and sometimes the skin) while the distal fragment is flexed, in varus and rotated posteriorly ( Fig 6.6.3-3 ).
The joint capsule, cruciate ligaments, and the strong collateral ligaments originate from the femoral condyles and contribute to the function and stability of the knee joint. The cruciate ligaments are located in the intercondylar notch. Screw malposition may violate the intercondylar notch and damage the cruciate ligaments. This should be avoided, especially with the use of variable angle locking plates.
Due to the proximity of neurovascular structures, vascular injuries are found in about 3% and nerve injuries in about 1% of distal femoral fractures. Lesions of the menisci and osteochondral fractures can be observed in 8–12% of cases, while there are associated fractures of the patella in approximately 15% of cases. High-energy injuries can lead to severe cartilage damage of both the distal femur and the patella.
4 Classification
Distal femoral fractures follow the same classification as all periarticular fractures ( Fig 6.6.3-4 ).
5 Surgical indications
Standard treatment consists of surgical reduction and fixation with early rehabilitation.
Nonoperative treatment is only justified in impacted, nondisplaced, extraarticular (type A) distal femoral fractures or in patients who are deemed nonambulatory and inoperable. Splint care with a knee immobilizer is usually satisfactory in these cases. Operative indications include:
Any displaced distal femoral fracture
Intraarticular displacement of the distal femoral joint surface
Malalignment of the distal femur
The traditional concept of open reduction and internal fixation (ORIF) of distal femoral fractures which advocated an extended approach to the multifragmentary fracture zone at the metaphysis is not favored because of the high rate of nonunion and failure. The biological plating concept uses less traumatic approaches, with careful handling of the soft-tissue envelope and is now the gold standard.
It is still mandatory to perform precise reconstruction of the anatomy of the condyles and articular surface and to restore the correct limb axis and rotation.
This usually requires direct exposure of the knee joint through an appropriate surgical exposure.
6 Preoperative planning
6.1 Timing of surgery
In patients with polytrauma, open fractures with severe soft-tissue damage, vascular injuries, or under conditions that prevent an early definitive operation (eg, inexperienced staff), damage-control surgery is recommended. In such cases, a knee-spanning external fixator is a quick and effective method of stabilization ( Fig 6.6.3-5 ) [3]. Two Schanz screws with a rod are placed along the anteromedial aspect of the tibia. Manual traction is applied to restore the length and rotation. It should be noted that Schanz screws placed through the quadriceps before restoration of length will hinder a surgeon from restoring length. Then, two Schanz screws and the rod are placed on the anterior aspect of the femur, well away from the future surgical site. This will avoid later obstruction from bone loss or a Schanz screw(s) placed on the lateral side of the femur. Once the knee-spanning external fixator is placed, it will restore length, rotation and alignment and this will greatly facilitate definitive fixation.
Most of the open wounds are anterior and associated with a variable degree of quadriceps injury. Early administration of appropriate antibiotics followed by meticulous debridement and irrigation are important. Subsequent definitive fixation and early range of motion will help restore knee function.
6.2 Implant selection
Extraarticular fractures can be treated successfully with retrograde intramedullary nails or with plate constructs. In young adults with good bone quality, nonlocking implants provide favorable clinical outcomes. In elderly patients with osteoporosis or periprosthetic distal femoral fractures, locking plate systems become valuable for solid fixation in situations where there is limited bone stock in the distal fragment.
The basic principle in treating intraarticular distal femoral fractures is based upon the anatomical reduction of articular fragments under direct vision [4]. Fixation is achieved by compressing the fragments with lag screws. Position screws may be required when there is bone loss. The subsequent fixation of the articular block to the distal femur is done with additional implants, depending on the type of fracture ( Fig 6.6.3-6 ). For type B fractures with osteoporosis or vertical fracture lines, the stability of the lag screw fixation may be augmented by a plate with buttress function ( Fig 6.6.3-7 ).
6.3 Operating room set-up
Light manual traction is maintained on the limb during preparation to avoid excessive deformity at the fracture site. The whole leg is disinfected from the hip, including the foot, with the appropriate antiseptic. The limb is draped with a single-use U-drape or extremity drape. A stockinette covers the foot and lower leg and is fixed with a tape. The leg is draped to allow it to be freely moved ( Fig 6.6.3-8 ). The knee is slightly flexed over a roll of padding and the image intensifier is draped.
The operating room personnel and surgeons stand on the side of the affected limb. The image intensifier is positioned on the opposite side of the table, medial to the fracture with the display screen in full view of the surgical team and the radiographer ( Fig 6.6.3-9 ).
7 Surgery
7.1 Approaches
7.1.1 Patient positioning
When the knee joint is fully extended, the pull of the gastrocnemius muscle and of the adductor magnus muscle leads to genu recurvatum and shortening.
The patient is positioned supine with the knee flexed 30–45° over a knee support to relax the gastrocnemius ( Fig 6.6.3-10 ). Shortening is corrected by manual traction or a distractor. In cases of extensive fragmentation, careful preoperative planning using the contralateral side as a template is helpful.
In osteopenic bone and complex fractures, acceptance of some shortening by fracture impaction is sometimes preferable to fracture instability.
7.1.2 Approaches
The surgical approach used depends on whether the fracture is extraarticular or intraarticular. For extraarticular fractures, a standard lateral approach or modified standard lateral approach with a minimally invasive plate osteosynthesis (MIPO) technique is used. For intraarticular fractures, a lateral or medial parapatellar or medial subvastus approach is used. An open wound may dictate the surgical approach. Careful planning should be done during wound debridement so as not to interfere with the definitive treatment and the approach necessary for that procedure. Open fractures often have insufficient soft-tissue cover. If a tension-free closure of the skin is not feasible, the options include immediate local muscle flap and skin grafting or leaving the wound open (with appropriate dressings) and planning further debridement and soft-tissue reconstruction over the next 48–72 hours (see chapter 4.3)
Standard lateral approach
The approach allows anatomical reduction of the shaft and the metaphyseal area, with the disadvantages of extensive soft-tissue dissection. It can be used in simple fractures to obtain anatomical reduction and absolute stability. It is not recommended in multifragmentary fractures, which need to have preservation of the soft-tissue envelope around the fracture zone ( Fig 6.6.3-11 ).
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