Patella and Proximal Tibial Intra-Articular Fractures

Introduction

The patella and the proximal tibial articular surfaces are the two principal components of the bony skeleton at the knee, and their fractures share several thematic concerns despite their distinct anatomical roles. Both are intra-articular fractures requiring anatomical reduction to preserve joint function; both have a tendency toward post-traumatic osteoarthritis when imperfectly reduced; both demand attention to soft-tissue injury (the extensor mechanism for the patella, the meniscal and ligamentous structures for the tibial plateau); and both have evolved substantially in management over the past several decades as operative techniques have improved. The patella fracture is approached through the prism of extensor mechanism integrity — the principal functional question is whether the patient can extend the knee against gravity, which guides operative decision-making. The tibial plateau fracture is approached through the prism of articular congruity and limb mechanical axis — the principal functional concerns are the post-traumatic arthritis that follows from articular incongruity and the limb malalignment that follows from inadequate reduction of the metaphyseal component. 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.

Patella Anatomy and Biomechanics

The patella is the largest sesamoid bone in the body, formed in the substance of the quadriceps tendon and serving to increase the moment arm of the extensor mechanism by approximately 30 percent at full extension. The bone is roughly triangular with the apex distal and the base (and the bulk of the quadriceps insertion) proximal. The articular surface on the posterior aspect of the patella is divided by a vertical ridge into medial and lateral facets, with the odd facet at the extreme medial border articulating with the femoral condyle only in deep flexion. The patellar tendon extends from the inferior pole (apex) to the tibial tuberosity; the medial and lateral patellar retinacula are the lateral expansions of the extensor mechanism that maintain extensor continuity across the knee even with patellar disruption. The functional importance of the retinacula is critical: in patellar fracture with intact retinacula, the patient may retain the ability to extend the knee against gravity (partial extensor function); in patellar fracture with disrupted retinacula or with widely separated patellar fragments, active extension is lost. The blood supply to the patella is through an anastomotic ring of vessels around the periphery, with the principal contribution from the inferior pole through small arteries entering from the patellar tendon. This pattern produces a relative watershed in the central body of the patella that contributes to nonunion and avascular necrosis risk in transverse fractures, particularly with separation of the fragments.

Patella Fractures — Classification and Mechanism

Patella fractures account for approximately 1 percent of all skeletal injuries. The mechanism is typically a direct blow to the patella (fall on the knee, dashboard injury) or an eccentric contraction of the quadriceps against resistance (sudden eccentric load with the foot planted, producing a transverse fracture through tension forces). The classification is morphological: Transverse fracture: The most common pattern (50 to 80 percent of patellar fractures), typically located through the middle or distal third of the patella, with displacement of the upper fragment proximally by quadriceps pull and the lower fragment held by the patellar tendon. Vertical (longitudinal) fracture: Less common, with the fracture line in the sagittal plane. Generally less displaced because the fragments are not pulled apart by the muscle and tendon attachments. Comminuted (stellate): Multiple fragments, often from direct high-energy trauma. Osteochondral fracture: Pure cartilaginous or osteochondral fragments, often from patellar dislocation rather than from a discrete fracture mechanism. Polar fracture: Avulsion fracture of the upper pole (insertion of quadriceps tendon) or, more commonly, the lower pole (origin of patellar tendon). Sleeve fracture: A pediatric variant with avulsion of the cartilaginous sleeve from the inferior pole of the patella; can be missed on radiographs as the avulsed cartilage is non- ossified. The bipartite patella — a normal anatomic variant with an accessory ossification center, typically at the superolateral aspect — must not be confused with fracture. Bipartite patella has smooth corticated edges, is typically bilateral (60 percent), and is asymptomatic in most cases.

Clinical Assessment and Imaging of Patella Fractures

The clinical features include pain over the patella, tense effusion with palpable defect at the fracture site, ecchymosis, and the central functional question of active knee extension against gravity. The straight leg raise test assesses extensor mechanism continuity; inability to maintain active extension or to perform straight leg raise indicates extensor mechanism disruption. The palpable gap between the fracture fragments correlates with both the magnitude of displacement and the risk of extensor disruption. Imaging includes AP, lateral, and sunrise (Merchant or sky-line) views of the patella. The lateral view best demonstrates transverse fractures; the sunrise view best demonstrates vertical and osteochondral fractures. CT is reserved for complex comminuted patterns being considered for operative reconstruction. MRI is occasionally

useful for suspected pure cartilaginous injury or for the bipartite patella with suspicion of acute injury.

Treatment of Patella Fractures

Non-Operative Management Non-operative management is appropriate for non-displaced or minimally displaced fractures with intact extensor mechanism (intact retinacula, preserved active extension). The principal threshold is: • Less than 3 mm fragment displacement. • Less than 2 mm articular step-off. • Intact extensor mechanism (ability to perform straight leg raise). These patients are treated in a knee immobilizer or cylinder cast in extension for 4 to 6 weeks, with early progressive range of motion exercises beginning as the fracture stabilizes. Weight bearing is permitted as tolerated with the knee in extension. Outcomes are generally excellent. Operative Management Operative management is indicated for displaced fractures with disrupted extensor mechanism, articular step-off greater than 2 mm, comminuted fractures with significant displacement, open fractures, and osteochondral fractures requiring fragment management. The classical operative technique for transverse patellar fractures is tension-band wiring, using the same principle described for olecranon fractures (see Topic Trauma-15). Two parallel K-wires are passed longitudinally across the fracture from the proximal pole to the distal, and a figure-of-eight tension-band wire is placed in the anterior cortex of the patella, passing dorsal to the K-wires and crossing over the anterior surface. As the knee flexes, the tensile forces on the anterior cortex are converted by the tension-band into compressive forces at the articular (posterior) surface. The construct produces dynamic compression during knee flexion that promotes union. Complications of tension-band wiring include hardware prominence (extremely common, up to 30 to 50 percent of patients requiring hardware removal because of K-wire migration or wire-related symptoms), wire breakage, and loss of reduction. The technique remains the standard for non-comminuted transverse patellar fractures despite these limitations. Plate fixation of patellar fractures has gained traction for comminuted patterns where tension-band wiring is inadequate. Specialized mini-fragment plates (sometimes mesh plates) provide multipoint fixation of the small fragments and a stable construct. The technique is more demanding but produces lower hardware-related complication rates than tension-band wiring in selected patterns.

Cerclage wire fixation alone may be used for highly comminuted fractures where individual fragment fixation is impossible — a circumferential wire around the patella to hold the fragments together as they consolidate. Partial patellectomy with excision of a non-reconstructible polar fragment and tendon advancement is reserved for cases where reconstruction is not feasible. The inferior pole fragment can be excised with patellar tendon advancement; less commonly the superior pole fragment with quadriceps advancement. Outcomes after partial patellectomy are inferior to those of reconstruction; total patellectomy (now rarely performed) has substantially worse functional outcomes. The rehabilitation after patellar fracture fixation emphasizes early protected range of motion to prevent stiffness, with progressive extension and flexion exercises beginning within the first postoperative week. The knee is typically immobilized only when the fracture pattern or fixation construct demands it; for tension-band fixation, immediate motion is generally permitted, with cylinder cast or hinged knee brace used during ambulation.

Proximal Tibia (Tibial Plateau) Anatomy

The proximal tibia comprises the medial and lateral tibial plateaus (separated by the intercondylar eminence with the cruciate ligament insertions), the tibial tubercle (the patellar tendon insertion on the anterior aspect), and the fibular head articulation on the lateral aspect. The articular surfaces are not flat but have a slight slope: the medial plateau slopes posteriorly approximately 5 to 10 degrees, the lateral plateau slopes posteriorly approximately 5 to 10 degrees (the posterior tibial slope), and the lateral plateau is also slightly convex compared with the concave medial plateau. The mechanical alignment of the knee places approximately 60 percent of the load on the medial compartment in normal stance, with the relative load distributions changing during gait and activities. The medial cortical bone is denser than the lateral; consequently, the medial plateau fractures less commonly and through a more vertical mechanism, while the lateral plateau fractures more commonly and through a depression mechanism. The menisci (medial and lateral) overlie the plateaus and increase the effective articular contact area; they are critical structures for load distribution. The anterior and posterior cruciate ligaments insert on the intercondylar eminence; their bony insertions can be avulsed in fracture patterns. The collateral ligaments (medial and lateral) provide coronal-plane stability and are at risk in tibial plateau injuries. The vascular structures around the proximal tibia include the popliteal artery in the popliteal fossa, dividing into the anterior tibial, posterior tibial, and peroneal arteries; the anterior tibial artery crosses the interosseous membrane just distal to the proximal tibial-fibular joint to enter the anterior compartment of the leg. Vascular injury in tibial plateau fractures is uncommon but reported, particularly in Schatzker types IV through VI with significant displacement.

The common peroneal nerve courses around the neck of the fibula and is at risk in lateral approaches to the tibial plateau.

Tibial Plateau Fractures — Schatzker Classification

The Schatzker classification (Joseph Schatzker, 1979) is the standard system for tibial plateau fractures: Type I: Pure split (cleavage) fracture of the lateral plateau without depression. The mechanism is valgus force on a relatively normal-density bone (typically in young adults). The articular surface remains in continuity with the metaphysis, displaced laterally as a wedge. Type II: Split-depression fracture of the lateral plateau (combination of types I and III). The split component is similar to type I, with an additional depression of the lateral articular surface. The most common Schatzker type. Type III: Pure depression fracture of the lateral plateau without split. The articular surface is depressed into the metaphysis. The mechanism is axial loading in osteoporotic bone (often elderly patients). Subdivided into IIIa (lateral) and IIIb (central) depression. Type IV: Medial plateau fracture, with or without depression. The medial plateau is more resistant to fracture than the lateral; medial plateau fractures imply higher energy and are associated with higher rates of vascular injury, peroneal nerve injury, and meniscal injury. Subdivided into IVa (split alone) and IVb (split with depression). Type V: Bicondylar fracture, with both medial and lateral plateaus separated from the diaphysis. Type VI: Bicondylar fracture with metaphyseal-diaphyseal dissociation (the articular surface and the diaphysis are separated by a metaphyseal comminution zone). The most severe pattern, with the highest rates of associated injury. The AO/OTA classification (region 41) parallels the Schatzker with type A extra- articular, type B partial articular, and type C complete articular patterns.

Clinical Assessment and Imaging of Tibial Plateau Fractures

The clinical features include pain, swelling, effusion, and inability to bear weight, with the mechanism typically motor vehicle accident or fall from height (high-energy) or low- energy fall in osteoporotic patients. The examination evaluates: Soft-tissue envelope: The skin condition, blisters, abrasions, and open wounds determine the urgency and approach of operative intervention. The proximal medial tibia is a watershed area for skin and wound healing. Neurovascular examination: Distal pulses (anterior tibial, posterior tibial, dorsalis pedis); peroneal and tibial nerve function (with peroneal nerve at particular risk in type IV and lateral approaches).

Compartment syndrome: The leg compartments are at substantial risk in tibial plateau fractures, particularly high-energy patterns. Disproportionate pain, pain on passive stretch, sensory changes, and tense compartments are evaluated; intra-compartmental pressures are measured in equivocal cases. Ligamentous integrity: Approximately 50 percent of tibial plateau fractures have associated ligamentous injuries (MCL, LCL, ACL, PCL, posterolateral corner). The clinical examination of ligaments may be difficult acutely because of pain and swelling but should be repeated after reduction and again before definitive surgery. Meniscal injury: Lateral meniscal tears are particularly common in lateral plateau fractures; medial meniscal injuries occur with medial plateau fractures. Tears can occur as the femoral condyle drives into the depressed plateau. The imaging includes AP and lateral radiographs as the initial study. CT with 3D reconstruction is the standard for any fracture being considered for operative intervention, providing detailed assessment of articular involvement, depression, comminution, and posterior involvement. MRI is added to evaluate ligamentous and meniscal injuries; the dual modality CT plus MRI is often used in preoperative planning. CT angiography is added for suspected vascular injury, particularly in high-energy Schatzker IV through VI patterns.

Treatment of Tibial Plateau Fractures

Non-Operative Management Non-operative management is appropriate for non-displaced or minimally displaced fractures with articular step-off less than 2 to 5 mm (depending on the source and patient factors), maintained mechanical axis of the limb, and intact ligaments. Treatment is typically by knee immobilization in extension (hinged knee brace or, less commonly, cylinder cast) for 4 to 6 weeks with non-weight bearing or toe-touch weight bearing, followed by progressive weight bearing and range of motion. Outcomes are generally good for appropriate fracture patterns.

Operative Management Operative indications include articular step-off greater than 2 to 5 mm (with the threshold debated; many surgeons use 3 mm), depression of the articular surface, condylar widening, mechanical axis malalignment, open fracture, and associated ligamentous or meniscal injury requiring repair. The principles of operative fixation are: Anatomical articular reduction: Restoration of the articular surface with minimization of step-off and depression. The depression is typically addressed by elevation of the depressed segment through a metaphyseal window (“loosening” the impacted bone with a small osteotome), with packing of the resulting void with bone graft or bone graft substitute.

Restoration of mechanical axis: Correction of varus or valgus angulation produced by the fracture. Buttress fixation: Plate fixation along the lateral or medial cortex to support the articular segment after reduction. Modern locking plates have largely replaced non-locked buttress plates, particularly in osteoporotic bone. Augmentation of articular support: The depressed articular segment, after elevation, requires support to prevent re-collapse. Autogenous bone graft (from iliac crest or RIA), allograft, calcium phosphate cement, or other bone graft substitutes are used to fill the void. The calcium phosphate cement has the advantage of rapid mechanical strength gain (within hours), making it particularly attractive for the early weight-bearing patient. Specific Patterns Schatzker I: Open reduction and lag screw fixation, often with a buttress plate. Anatomical reduction of the split is the goal. Schatzker II (most common): Open reduction through a lateral approach. The depression is elevated through a metaphyseal window or by direct intra-articular approach; the split is reduced; bone graft fills the metaphyseal void; lateral buttress plate (locked or non-locked) is applied. The lateral meniscus is preserved (usually retracted by submeniscal arthrotomy) and repaired if torn. Schatzker III: Elevation of the depression through a metaphyseal window with bone grafting. Plate fixation may not be needed if the construct is stable, but a buttress plate is typically applied. Schatzker IV: Open reduction through a medial approach. Special attention to ligamentous evaluation and to the substantially higher rate of associated injuries. Buttress plating of the medial plateau is the standard. Schatzker V and VI: Bicondylar fractures requiring both medial and lateral fixation. The contemporary approach is dual approach with separate medial and lateral incisions (avoiding a single midline anterior incision because of skin necrosis risk), with separate medial and lateral plates. The monolateral fixator with delayed conversion has been used for severe injuries with extensive soft-tissue compromise — initial spanning external fixation across the knee with delayed conversion to internal fixation when the soft-tissue envelope permits. Knee Spanning External Fixation For the high-energy Schatzker V or VI with severe soft-tissue compromise (open fracture, severe contusion, blistering), the damage control approach with knee spanning external fixation is appropriate. The fixator is applied across the knee from femur to tibia, providing immediate stabilization and protection of the soft-tissue envelope; definitive internal fixation is delayed until the soft tissues permit (typically 7 to 21 days).

Summary and Take-Home Points

The patella fracture is fundamentally about extensor mechanism integrity — the central management question is whether the patient can actively extend the knee against gravity, which determines operative versus non-operative management. Non-displaced fractures with preserved extensor mechanism are managed by cylinder cast or knee immobilizer; displaced fractures or those with extensor mechanism disruption are managed by open reduction and tension-band wiring (the classical Weber-style construct), plate fixation (for comminuted patterns), or partial patellectomy with tendon advancement (for non- reconstructible polar fragments). Hardware-related complications are extremely common with tension-band wiring; modern plate fixation has reduced these rates in appropriate patterns. The tibial plateau fracture is classified by the Schatzker system (I split lateral, II split- depression lateral, III pure depression lateral, IV medial, V bicondylar, VI bicondylar with metaphyseal-diaphyseal dissociation). The AO/OTA system (41) provides a parallel framework. CT with 3D reconstruction is the standard for operative planning; MRI evaluates ligamentous and meniscal injuries; CT angiography evaluates vascular injury in high-energy patterns. The principles of tibial plateau fracture management include anatomical articular reduction with elevation of depressed segments through metaphyseal windows, bone grafting of the resulting voids (autograft, allograft, or calcium phosphate cement), buttress plating with locked plates providing fixed-angle support in osteoporotic bone, restoration of mechanical axis, and management of associated meniscal and ligamentous injuries. The Schatzker V and VI bicondylar patterns require dual approaches with separate medial and lateral incisions to avoid soft-tissue complications. The damage control approach with knee spanning external fixation is appropriate for severe injuries with soft-tissue compromise. The complications of post-traumatic arthritis (related to articular incongruity), knee stiffness (mitigated by early motion), nonunion of the articular component, and ongoing problems with ligamentous and meniscal injuries form the principal long-term concerns. The chapter that follows turns to knee dislocation and the associated severe ligamentous injuries that may follow.