Distal Femur Fractures

Introduction

The distal femur fracture occupies an intermediate position between the diaphyseal femoral shaft fracture and the intra-articular knee injury, with anatomical and biomechanical considerations distinct from either. The distal femur fracture has a bimodal age distribution: high-energy injuries in young adults (motorcycle, motor vehicle, fall from height) and low-energy fragility fractures in elderly osteoporotic patients (often around an existing total knee arthroplasty as a periprosthetic fracture). The proximity to the knee joint, the wide metaphyseal-diaphyseal transition with thin cortices, and the substantial soft-tissue envelope all combine to produce fractures that are challenging to reduce and to fix securely, with a long history of disappointing outcomes from inadequate fixation methods. The advent of locked plating in the 1990s and 2000s and the parallel development of retrograde intramedullary nailing have substantially improved outcomes, although nonunion and malunion remain meaningful problems and the active debate concerns the relative merits of these two principal constructs. This chapter draws on Rockwood and Green’s Fractures in Adults, AO Principles of Fracture Management, Apley & Solomon’s, and Miller’s Review of Orthopaedics.

Surgical Anatomy

The distal femur comprises the region from approximately 9 to 15 cm proximal to the joint line to the articular surface. The bone transitions in this region from the relatively narrow cylindrical diaphysis to the wide flared metaphysis, with substantially thinner cortices and predominantly cancellous bone — a transition that contributes to the heightened risk of comminution and the technical difficulty of fixation. The medial and lateral femoral condyles form the distal articular surface, with the intercondylar notch between them; the trochlea at the anterior aspect articulates with the patella. The anatomical axis of the distal femur is approximately 7 to 9 degrees of valgus relative to the mechanical axis, a relationship that must be restored in operative reduction to avoid varus or valgus malunion that produces secondary knee arthritis. The distal femoral joint line in the coronal plane is in approximately 3 degrees of valgus relative to the femoral mechanical axis; the sagittal alignment has approximately 5 degrees of flexion relative to the diaphyseal axis. These parameters are the targets of reduction. The neurovascular structures in the distal femoral region include the superficial femoral artery descending through the adductor canal and emerging into the popliteal space as the popliteal artery, the superficial femoral vein running with the artery, and the sciatic nerve descending through the posterior thigh and dividing into the common peroneal and tibial branches just proximal to the popliteal fossa. The popliteal vessels lie directly posterior to the distal femoral metaphysis and are vulnerable in fractures with significant posterior displacement; vascular injury must be excluded by careful examination of distal pulses and, when in doubt, CT angiography or formal angiography.

The deforming forces on the distal femur fracture are predictable: the gastrocnemius insertions on the posterior aspect of the condyles pull the distal fragment posteriorly (extension) and proximally (shortening); the hamstrings add to the proximal pull; the adductor magnus adducts the proximal fragment; and the iliotibial band and vastus lateralis can add to lateral displacement. The classical resulting deformity is shortening, varus, and extension of the distal fragment (relative to the proximal — or alternatively, the proximal fragment displaces anteriorly and proximally), although the precise direction depends on the fracture pattern and adjacent fragment behaviors.

Classification

The AO/OTA classification (region 33) structures distal femur fractures by articular involvement: Type A (extra-articular): The fracture does not involve the articular surface. A1 simple metaphyseal, A2 metaphyseal with wedge fragment, A3 multifragmentary metaphyseal. Type B (partial articular): One condyle is fractured but a portion of the articular surface remains in continuity with the diaphysis. B1 lateral condyle sagittal (Hoffa fragment when in the coronal plane), B2 medial condyle sagittal, B3 frontal/coronal (Hoffa-type fracture in the coronal plane). Type C (complete articular): Both condyles are separated from the diaphysis, with the articular surface itself often comminuted. C1 simple intra-articular and metaphyseal, C2 simple articular with multifragmentary metaphyseal, C3 multifragmentary articular and metaphyseal. The Hoffa fracture (Albert Hoffa, 1904) deserves specific mention: it is a coronal-plane fracture of the femoral condyle (most commonly the lateral) producing a posterior osteochondral fragment. The injury is missed on standard AP and lateral views; CT is essential for diagnosis and operative planning. Treatment is open reduction with anterior- to-posterior screw fixation through a small arthrotomy. The historical Neer classification is largely superseded by the AO/OTA system. The Müller classification of supracondylar fractures (with extracondylar, intercondylar, and intracondylar variations) preceded the AO/OTA system and provides similar conceptual organization.

Clinical Assessment

The clinical presentation depends on energy: the high-energy distal femur fracture in a young adult presents with gross deformity, swelling, pain, and often associated injuries; the low-energy fragility fracture in the elderly may present with subtler findings of pain and inability to bear weight after a fall. The examination assesses neurovascular status of the lower leg with particular attention to distal pulses (the popliteal vessels are at risk in posteriorly displaced fractures), motor and sensory function of the peroneal and tibial divisions of the sciatic nerve, and the

integrity of the soft-tissue envelope (with attention to open wounds, contamination, and impending skin compromise). Compartment syndrome of the thigh or proximal leg should be considered, particularly in high-energy injuries; the leg compartments are at greater risk than the thigh, but both should be assessed. Imaging consists of standard AP and lateral radiographs of the entire femur (including the hip and knee), with additional traction views often helpful in defining the fracture morphology before CT. CT is the standard for operative planning in any intra-articular fracture, providing detailed assessment of articular fragments, Hoffa fragments, and the orientation of fracture lines. The CT angiography is added when vascular injury is suspected.

Treatment — Locked Plating

Lateral Locked Plating Lateral locked plating is the predominant operative technique for distal femur fractures and has produced the substantial improvement in outcomes that has characterized this region over the past two decades. The construct uses a precontoured anatomic locking plate (Less Invasive Stabilization System, LISS, or distal femoral locking plate) applied to the lateral aspect of the distal femur with multiple converging locking screws into the distal condylar fragment plus shaft fixation. The mechanical principle is fixed-angle bridge plating: the locking screws create a stable construct in the distal fragment that maintains the fixed angle relationships even in osteoporotic bone, allowing the plate to function as an “internal external fixator” in spanning the metaphyseal comminution. The construct is intended to permit controlled motion at the fracture site (allowing callus formation) while resisting the typical varus and recurvatum deforming forces. The technical considerations include: Reduction is the critical first step. The classical malreduction is varus and recurvatum (apex anterior) because of the deforming forces; specific attention to restoring valgus alignment and to extending the distal fragment is required. Indirect reduction techniques using traction, percutaneous reduction tools, and provisional K-wire fixation are typically used; open reduction through a lateral or anterolateral approach (developing the interval between the vastus lateralis and the iliotibial band) is reserved for intra-articular fractures requiring direct articular reduction. Articular reduction in type C fractures is performed first, with lag screws securing the articular block before plate application. The Hoffa fragment, when present, requires specific attention with separate anterior-to-posterior screw fixation through a small arthrotomy. Plate length should be substantial — at least 6 to 8 cortical screws in the proximal (diaphyseal) segment — to spread the load and provide adequate working length. The

“working length” concept — the distance between the most distal proximal screw and the most proximal screw of the distal fragment — is critical to construct flexibility and load distribution. Screw distribution in the distal fragment should provide multiple converging screws into the condylar bone, with attention to avoiding screws that penetrate the joint or the intercondylar notch. The complications of lateral locked plating include valgus or varus malreduction, nonunion (5 to 15 percent in series — substantially higher than for femoral shaft fractures, reflecting the metaphyseal comminution and the cantilever construct), implant failure with plate breakage at the working zone, and hardware-related symptoms. The “too stiff” plate construct has been recognized as a concern — excessive construct stiffness may inhibit the callus formation that is the principal healing mechanism in bridge plating, contributing to delayed union and implant failure. Strategies to address this include far cortical locking screws (with their threaded engagement only in the far cortex, permitting controlled near cortical motion) and longer working lengths. Medial Plate Augmentation The medial plate (added to the lateral construct for severely comminuted patterns or in osteoporotic bone) has gained traction as a means of reducing failure rates. The construct provides a “second column” of fixation that converts the cantilever loading on the lateral plate into a more balanced two-column construct. The technique uses a medial approach (typically posteromedial to avoid the saphenous nerve) and a smaller plate applied along the medial condyle. The evidence for routine medial augmentation is mixed; selective use in unstable patterns or in patients at risk for failure is generally accepted.

Treatment — Retrograde Intramedullary Nailing

Indications and Construct Retrograde intramedullary nailing through the intercondylar notch provides an alternative to lateral plating for distal femur fractures, particularly those without significant articular comminution. The technique entry point is just anterior to the PCL insertion in the intercondylar notch, accessed through a small parapatellar arthrotomy or a transpatellar tendon approach. The retrograde nail provides a load-sharing intramedullary construct with mechanical advantages in certain patterns — particularly the relatively simple extra-articular fracture (AO 33-A) and the partial articular fracture without significant comminution (33-B with stable condyle fixation). The nail has the disadvantage of more limited fixation in the distal condylar fragment compared with locked plating, and the entry through the knee joint introduces concerns about septic arthritis if infection develops and about residual knee pain.

Technique The technique parallels femoral shaft retrograde nailing (see Topic Trauma-23), with several specific considerations for distal femur fractures: Entry point is critical and is just anterior to the PCL insertion, with attention to placement in the line of the femoral mechanical axis to avoid valgus or varus malalignment driven by the entry. Reduction is performed before nail insertion, with the same considerations as locked plating regarding varus, recurvatum, and rotation. The articular reduction in type B and selected type C patterns is performed first with separate fixation. Nail size depends on the canal; distal femur fractures typically use 10 to 12 mm nails. Distal locking through the femoral condyles provides distal fixation. Multiple distal locking screws (typically 3 to 4) provide rotational stability and resistance to extension or flexion forces. Newer nail designs with multiplanar distal locking improve fixation in the distal fragment. Plate vs Nail — The Active Debate The choice between lateral locked plating and retrograde intramedullary nailing for distal femur fractures has been investigated through several randomized trials and meta- analyses. The general consensus is: Extra-articular fractures (AO 33-A): Either construct produces similar outcomes; retrograde nail may have advantages of load sharing and smaller exposure. Partial articular fractures (AO 33-B) with simple condyle pattern: Either construct is appropriate, with the choice depending on surgeon preference and the specific articular pattern. Complete articular fractures (AO 33-C) with simple condylar component: Locked plating provides better articular fixation; retrograde nailing requires preliminary articular reconstruction with separate fixation. Complete articular fractures with significant comminution (33-C2, 33-C3): Locked plating, often with medial augmentation, is the standard. Periprosthetic fractures around total knee arthroplasty: Discussed below; choice depends on the femoral component design and the position of the fracture.

Periprosthetic Distal Femur Fractures

Periprosthetic distal femur fractures around total knee arthroplasty are a rapidly growing category, reflecting the aging arthroplasty population. The Su classification organizes these fractures by their position relative to the femoral component (see Topic Trauma-8 for the broader periprosthetic discussion). The principal management decisions are:

Type I (proximal to the femoral component): Treated as a standard distal femur fracture with locked plating or retrograde nailing. Type II (at the level of the femoral component, extending proximally): Locked plating is typically preferred, although retrograde nailing may be feasible depending on the component design. Type III (extending into the component): Often requires revision arthroplasty if the femoral component is loose; if the component remains well-fixed and the fracture is reducible, fixation around the component may be possible. The choice of nail or plate is affected by the femoral component design — open-box “nail- compatible” components permit retrograde nailing without component revision, while closed-box designs preclude it. The Vancouver classification principles (well-fixed component versus loose component) apply: well-fixed implants are retained with fracture fixation around them; loose implants require revision.

Specific Considerations

Hoffa Fracture The Hoffa fracture (coronal plane fracture of the lateral or medial femoral condyle) is a distinct entity that deserves specific attention. The classical mechanism is a direct blow to the flexed knee or an axial load through the tibia in the flexed knee position. The fracture line is in the coronal plane of the condyle, producing a posterior fragment that is missed on standard AP and lateral radiographs. The fracture is best identified on CT, with the coronal plane reconstructions demonstrating the typical pattern. Treatment is open reduction and internal fixation through a small anterior or anterolateral arthrotomy, with anterior-to-posterior screw fixation (headless compression screws) buried below the articular surface. The Hoffa fragment, if missed, produces persistent knee pain and progressive arthritis from the displaced articular surface; recognition is therefore important.

Nonunion Nonunion of the distal femur is a recognized concern, occurring in 5 to 15 percent of fractures depending on the construct, the fracture pattern, and patient factors. The contributing factors include excessive construct stiffness (the “too stiff” plate phenomenon), inadequate fixation length in the proximal segment, significant initial bone loss, smoking, NSAIDs, and patient comorbidities. Treatment involves revision fixation with autograft, often with the addition of medial plate augmentation or conversion to longer plates with improved working length. Geriatric Distal Femur Fracture The geriatric distal femur fracture, often in osteoporotic bone and often as a periprosthetic fracture, has emerged as a significant clinical entity with high mortality (comparable to hip fracture in some series, approximately 25 percent at one year) and substantial functional

limitations. The principles of prompt surgical fixation (within 24 to 48 hours), early mobilization with weight bearing as tolerated, multidisciplinary geriatric co-management, VTE prophylaxis, and secondary fracture prevention all apply. The functional outcomes are less predictable than for hip fracture, with substantial loss of pre-fracture functional level common.

Pediatric Distal Femur Fractures Pediatric distal femur fractures include the distal femoral physeal injuries (Salter-Harris classification) and metaphyseal fractures. Salter-Harris type II is the most common, but type III and IV injuries involving the joint surface require anatomical reduction (often operative) to prevent growth disturbance and articular incongruity. The distal femoral physis contributes approximately 9 to 10 mm of growth annually (the majority of lower extremity growth in children) and growth arrest produces substantial length and angular deformity. Treatment of physeal injuries follows the Salter-Harris principles with attention to the high rate of growth arrest (approximately 25 percent) even in well-treated injuries; long-term follow-up for growth abnormalities is essential. Distal Femur Fracture with Vascular Injury Distal femur fractures with associated vascular injury (popliteal artery or vein) require coordinated orthopedic and vascular surgical management. The fracture is typically stabilized first (with rapid external fixation or temporary nail/plate) to provide a stable platform for the vascular repair; the vascular repair is then performed; and definitive fracture fixation can follow if not already accomplished. The “limb salvage versus amputation” decision in severe injuries with combined orthopedic and vascular involvement is informed by the Mangled Extremity Severity Score (MESS) and related instruments.

Rehabilitation and Outcomes

The rehabilitation after distal femur fracture fixation emphasizes early protected weight bearing (often toe-touch or 25 percent partial weight bearing for 6 to 8 weeks, progressing to full weight bearing as tolerated by 10 to 12 weeks) and early knee range of motion. The risk of knee stiffness is substantial because of the proximity to the joint, the surgical exposure, and the prolonged period of partial weight bearing. Continuous passive motion (CPM) machines, formal physiotherapy, and early aggressive motion protocols are used to mitigate stiffness; manipulation under anesthesia or arthroscopic lysis of adhesions may be needed in severe stiffness. The functional outcomes depend on multiple factors: quality of articular reduction (the most important predictor in C-type fractures), maintenance of mechanical axis (varus malalignment of more than 5 degrees produces medial compartment arthritis; valgus malalignment more than 7 degrees produces lateral arthritis), maintenance of knee range of motion (a flexion arc less than 90 to 110 degrees produces functional impairment), and the patient’s pre-fracture functional level.

Summary and Take-Home Points

The distal femur fracture combines the challenges of metaphyseal-diaphyseal transition fixation with the proximity to the knee joint and the substantial deforming forces of the gastrocnemius and adductor magnus muscles. The AO/OTA classification (33) organizes fractures by articular involvement (A extra-articular, B partial articular, C complete articular). The Hoffa fracture, a coronal-plane condylar fracture, is missed on plain radiographs and requires CT for diagnosis. The two principal operative constructs are lateral locked plating (the predominant technique, with bridge-plating principles applied to a fixed-angle precontoured implant) and retrograde intramedullary nailing (an alternative with load-sharing advantages for selected patterns). The choice between them depends on the fracture pattern, articular involvement, presence of a periprosthetic implant, and surgeon preference. Medial plate augmentation may improve outcomes in osteoporotic or severely comminuted patterns. The too stiff construct concept has informed contemporary practice toward longer working lengths and selective use of far cortical locking screws. The principles of anatomical reduction with attention to mechanical axis, valgus alignment, rotation, and articular surface, rigid fixation appropriate to the pattern, early protected motion and weight bearing, and systemic management of comorbidities are central to good outcomes. The complications of nonunion (managed by revision fixation with autograft, often with medial augmentation), malunion (managed by corrective osteotomy), and knee stiffness (mitigated by early motion protocols and managed by manipulation or arthroscopic release if severe) form the principal long-term concerns. The chapter that follows addresses the patella and the proximal tibia, completing the immediate knee region of the trauma section.