Surgical Repair of Fractured Portion of Patella: What to Expect

Comprehensive Introduction and Patho-Epidemiology

The patella, representing the largest sesamoid bone in the human body, serves as the critical fulcrum of the knee extensor mechanism. Embedded within the quadriceps tendon proximally and the patellar ligament distally, it provides an essential mechanical advantage by displacing the extensor apparatus anteriorly, thereby maximizing the lever arm of the quadriceps muscle group. Fractures of the patella, therefore, possess the profound potential to catastrophically disrupt the extensor mechanism, rendering the patient unable to achieve or maintain active terminal knee extension. Beyond its biomechanical role in extension, the patella constitutes a vital component of the patellofemoral articulation. Consequently, fractures extending through the articular surface compromise the congruity of the joint, precipitating altered contact mechanics and establishing a deleterious cascade toward post-traumatic osteoarthritis. The fundamental objective of operative management is the dual restoration of extensor continuity and precise anatomic reduction of the articular surface to mitigate these long-term morbidities.

Epidemiologically, patellar fractures account for approximately 1% of all skeletal injuries, presenting across a bimodal age distribution that reflects distinct mechanisms of injury. High-energy trauma, such as motor vehicle collisions resulting in direct dashboard impaction against a flexed knee, predominantly afflicts younger demographics. Conversely, low-energy mechanisms, including simple falls from a standing height, are frequently observed in the elderly population, often exacerbated by underlying osteopenia or osteoporosis. The pathogenesis of these fractures is intrinsically linked to the vector and magnitude of the applied force. Direct trauma typically generates comminuted or stellate fracture patterns, with the specific location of the fracture line often correlating intimately with the degree of knee flexion at the moment of impact. This occurs because the contact area between the patellar articular surface and the femoral trochlea translates proximally as the knee transitions from extension into deep flexion.

Indirect forces represent a secondary, yet equally critical, mechanism of patellar failure. These injuries classically occur when an eccentric, violent contraction of the quadriceps muscle complex is opposed by an unexpected, rapid flexion of the knee joint—such as stumbling on a staircase and attempting to arrest the fall. The tensile forces generated during such an event frequently exceed the ultimate tensile strength of the bone, yielding transverse fracture patterns that are typically less comminuted but highly displaced due to the unopposed proximal retraction by the rectus femoris and vastus intermedius. In many clinical scenarios, a combination of both direct and indirect forces contributes to the final fracture morphology, complicating both classification and subsequent surgical reconstruction.

The natural history of patellar fractures is heavily dictated by the initial displacement, the degree of articular comminution, and the integrity of the medial and lateral retinacular expansions. Even with meticulous surgical intervention, patients frequently exhibit persistent deficits in extensor strength and total arc of motion compared to the contralateral limb. Furthermore, the incidence of patellofemoral osteoarthritis is markedly elevated following these injuries. This degenerative progression is multifactorial, stemming not only from residual articular incongruity and step-offs but also from the initial chondrocyte apoptosis triggered by the traumatic impact itself. Therefore, the surgeon must approach these injuries with a profound respect for the delicate interplay between osseous anatomy, soft tissue envelope integrity, and joint biomechanics.

Detailed Surgical Anatomy and Biomechanics

A comprehensive mastery of patellar osteology and its surrounding soft tissue envelope is non-negotiable for the reconstructive orthopedic surgeon. The articular surface of the patella is broadly divided into medial and lateral facets by a prominent vertical ridge. The lateral facet is typically larger and concave, perfectly complementing the lateral femoral condyle, whereas the medial facet exhibits substantial morphological variability. These primary facets are further subdivided by subtle horizontal ridges into superior, middle, and inferior thirds. Additionally, a distinct "odd facet" resides at the extreme medial margin of the articular surface, engaging the medial femoral condyle only during deep knee flexion (beyond 135 degrees). Crucially, the distal pole (apex) of the patella is entirely extra-articular, serving exclusively as the broad origin for the patellar tendon.

The soft tissue architecture surrounding the patella is complex and highly functional. The superior pole receives the insertion of the quadriceps tendon, which is composed of distinct anatomical layers: the superficial rectus femoris, the intermediate vastus medialis and lateralis, and the deep vastus intermedius. The most superficial fibers of this tendon continue distally over the anterior surface of the patella, blending seamlessly with the periosteum and the origin of the patellar tendon. Flanking the patella are the medial and lateral retinacula, robust structures formed by the aponeurotic expansions of the vastus medialis and lateralis, reinforced by contributions from the fascia lata. These retinacular expansions bypass the patella to insert directly onto the proximal tibia, functioning as secondary, independent extensors of the knee. If the retinaculum remains intact following a patellar fracture, the patient may paradoxically maintain the ability to actively extend the knee despite a complete transverse fracture of the bone.

The vascular anatomy of the patella is characterized by a rich extraosseous anastomotic ring—the peripatellar plexus—supplied primarily by the superior and inferior genicular arteries, as well as the anterior tibial recurrent artery. However, the intraosseous blood supply is notably precarious. The dominant arterial inflow enters the distal pole of the patella and courses in a distal-to-proximal direction. Consequently, transverse fractures, particularly those located at the superior pole or mid-body, possess a theoretical risk of disrupting this vascular supply, predisposing the proximal fragment to avascular necrosis (AVN) or delayed union. While clinically significant AVN is relatively uncommon, this anatomical quirk necessitates meticulous handling of the soft tissue envelope during surgical exposure to preserve the delicate peripatellar plexus.

Biomechanically, the patella functions as a highly efficient pulley. By displacing the line of action of the quadriceps tendon anteriorly, it significantly increases the moment arm of the extensor mechanism. This mechanical advantage is most critical during the terminal 15 to 20 degrees of extension, a phase where the quadriceps muscle is operating at a profound physiological disadvantage due to its shortened length on the Blix curve. Due to the relatively small contact area between the patella and the trochlea, combined with the massive compressive joint reaction forces generated during activities such as squatting or stair climbing (often exceeding seven times body weight), the patellofemoral joint experiences the highest contact stresses of any major weight-bearing articulation in the human body. Surgical reconstruction must therefore not only restore the moment arm but also withstand these immense cyclic loads during rehabilitation.

Exhaustive Indications and Contraindications

The clinical evaluation of a suspected patellar fracture demands a systematic and rigorous approach. The patient history is paramount in differentiating high-energy direct trauma, which carries a higher suspicion for concomitant intra-articular or soft tissue injuries, from low-energy indirect tension failures. On physical examination, a palpable defect or step-off within the anterior knee is frequently appreciated, accompanied by a rapid-onset hemarthrosis. However, the surgeon must remain vigilant: a massive retinacular disruption may decompress the joint capsule, allowing the hematoma to extravasate into the subcutaneous tissues of the thigh and leg, thereby masking a tense effusion. The hallmark functional test is the assessment of active terminal knee extension or the presence of an extensor lag. In cases where severe pain precludes reliable motor testing, the intra-articular injection of a local anesthetic, following the aspiration of the hemarthrosis, can dramatically facilitate the examination. The presence of fat macroglobules within the aspirated hematoma is pathognomonic for an intra-articular fracture.

Standard radiographic evaluation mandates, at minimum, an anteroposterior (AP), a true lateral, and an axial (skyline or Merchant) view of the knee. The lateral radiograph is arguably the most critical for assessing the degree of fracture displacement, articular step-off, and the height of the patella. The Insall-Salvati ratio—calculated by dividing the length of the patellar tendon by the greatest diagonal length of the patella—should approximate 1.0. A ratio significantly less than 1.0 (patella alta) in the setting of trauma may indicate a disruption of the patellar tendon or a pediatric sleeve fracture. The Merchant view, obtained with the knee flexed to 45 degrees and the x-ray beam angled at 30 degrees to the horizontal, provides unparalleled visualization of the patellofemoral articulation and vertical fracture patterns that may be occult on standard AP imaging.

A critical diagnostic pitfall is the misidentification of a bipartite patella as an acute fracture. Bipartite patellae, resulting from the failure of secondary ossification centers to fuse, are present in approximately 2% to 3% of the population, are bilateral in up to 40% of cases, and are overwhelmingly located at the superolateral pole. Radiographically, they exhibit smooth, sclerotic cortical margins, in stark contrast to the sharp, uncorticated edges characteristic of acute traumatic fractures. Advanced imaging, such as Computed Tomography (CT), is rarely required for isolated transverse fractures but becomes invaluable for preoperative planning in the setting of severe comminution, osteochondral shearing injuries, or when assessing distal femur and tibial plateau involvement in high-energy polytrauma.

The decision to proceed with operative versus nonoperative management hinges upon strict morphological and functional criteria. Nonoperative management is exclusively reserved for fractures demonstrating an intact extensor mechanism (the ability to perform a straight leg raise), less than 2 mm of articular step-off, and less than 3 mm of fracture fragment separation. Operative intervention is indicated for all fractures failing to meet these criteria, as well as all open fractures, which demand urgent surgical debridement.

Indications and Contraindications Table

Pre-Operative Planning, Templating, and Patient Positioning

Surgical timing is dictated by the physiological status of the patient and the condition of the local soft tissue envelope. While open fractures necessitate emergent operative debridement within hours of presentation, closed fractures can be managed on a delayed basis (typically within 3 to 7 days). This delay allows for the optimization of medical comorbidities and the resolution of acute soft tissue swelling. The patella is covered by a notoriously thin fascial and subcutaneous layer; operating through severely compromised, blistered, or edematous skin drastically increases the risk of postoperative wound dehiscence and deep infection. During the preoperative waiting period, the limb should be immobilized in full extension with copious padding to prevent pressure necrosis, particularly over the heel and the fibular head.

Preoperative planning involves a meticulous review of all radiographic studies to anticipate the fracture morphology and select the appropriate fixation construct. The surgeon must mentally template the trajectory of Kirschner wires (K-wires) or cannulated screws, ensuring they will be positioned entirely within bone and parallel to the articular surface. For highly comminuted fractures, the surgeon must ensure the availability of supplemental fixation modalities, including mini-fragment screws, cerclage wires, and potentially non-absorbable heavy sutures for inferior pole repairs.

Once in the operating theater, an Examination Under Anesthesia (EUA) is a mandatory preliminary step. The acute pain and muscle guarding present in the emergency department often preclude a reliable assessment of ligamentous stability. With the patient fully relaxed, the surgeon must perform Lachman, posterior drawer, varus, and valgus stress testing to rule out concomitant cruciate or collateral ligament disruptions, which are occasionally seen in dashboard impact injuries. Identifying these injuries preoperatively allows the surgical team to address them concurrently or plan for staged reconstruction.

Patient positioning is straightforward but requires attention to detail. The patient is placed supine on a fully radiolucent operating table to accommodate unrestricted intraoperative fluoroscopy. A sterile tourniquet is highly recommended to maintain a bloodless surgical field, but its placement is critical. The tourniquet must be positioned as proximally as possible on the thigh. Crucially, before inflating the tourniquet, the knee must be flexed to at least 90 degrees, and the quadriceps muscle bulk should be manually drawn distally. If the tourniquet is inflated while the knee is extended, it will tether the quadriceps mechanism proximally, creating immense resistance when the surgeon attempts to pull the superior patellar fragment distally to achieve fracture reduction.

Step-by-Step Surgical Approach and Fixation Technique

The surgical approach to the patella must balance the need for extensile exposure with the preservation of the delicate anterior soft tissue envelope. While transverse incisions parallel to Langer’s lines offer superior cosmesis and minimize the risk of neuroma formation from the infrapatellar branch of the saphenous nerve, a midline longitudinal incision remains the gold standard in orthopedic trauma. The longitudinal approach is infinitely extensile, allowing proximal extension for quadriceps tendon repair and distal extension to the tibial tubercle should the extensor mechanism require augmentation. Furthermore, a longitudinal incision does not compromise future surgical approaches, a critical consideration given the high incidence of post-traumatic osteoarthritis that may eventually necessitate a total knee arthroplasty.

Deep dissection is carried straight down through the subcutaneous tissues and the prepatellar bursa to directly expose the fracture site. The creation of large subcutaneous flaps must be strictly avoided to preserve the vascularity of the overlying skin. Upon opening the bursa, the surgeon will encounter a dense fracture hematoma, which must be meticulously evacuated using copious saline irrigation and small curettes. The fracture edges are debrided of interposed soft tissue, and the medial and lateral retinacular tears are identified, cleared of debris, and tagged with heavy non-absorbable sutures for later repair. The joint is thoroughly irrigated to remove any loose osteochondral fragments.

Fracture reduction is achieved by extending the knee to relax the extensor mechanism. Pointed reduction forceps (Weber clamps) are applied to the proximal and distal fragments. The accuracy of the reduction is verified by directly palpating the articular surface through the traumatic rents in the retinaculum using a Freer elevator or a gloved finger. If the retinaculum is intact, intraoperative fluoroscopy or a limited arthrotomy may be required to confirm articular congruity. Small, devitalized articular fragments devoid of subchondral bone may be excised, whereas depressed osteochondral fragments must be gently elevated and supported with cancellous bone graft if necessary.

The cornerstone of patellar fracture management is the tension band wiring technique, a biomechanical principle championed by the AO Foundation. This construct is designed to convert the tensile forces generated by the quadriceps across the anterior surface of the patella into compressive forces at the articular surface during knee flexion. Once provisional reduction is achieved, two parallel 1.6-mm or 2.0-mm K-wires are driven longitudinally across the fracture site. These wires should be positioned approximately 5 mm deep to the anterior cortical surface; placing them too anteriorly risks hardware prominence, while placing them too deeply (near the articular surface) negates the biomechanical advantage of the tension band and risks intra-articular penetration.

A 1.0-mm (18-gauge) stainless steel cerclage wire is then passed behind the protruding ends of the K-wires at both the superior and inferior poles. A highly effective technical pearl is to pass a 14- or 16-gauge intravenous angiocatheter through the quadriceps and patellar tendon insertions, utilizing the catheter as a conduit to smoothly shuttle the cerclage wire without entrapping intervening soft tissue. The wire is configured in a figure-of-eight pattern over the anterior surface of the patella. Tensioning is performed using a symmetric two-loop technique, twisting the wire simultaneously on the medial and lateral sides to ensure uniform compression across the fracture gap. The K-wires are then cut, bent 180 degrees, and impacted deep into the superior pole to prevent migration, while the inferior ends are trimmed to leave a minimal prominence. Finally, the retinacular tears are meticulously repaired with robust interrupted sutures, as restoring the retinaculum is as biomechanically crucial as the osseous fixation itself.

Complications, Incidence Rates, and Salvage Management

Despite meticulous surgical technique, the operative management of patellar fractures is fraught with a high incidence of postoperative complications, driven primarily by the subcutaneous nature of the bone and the immense mechanical forces subjected to the fixation construct. The most ubiquitous complication is symptomatic hardware prominence. Because the anterior aspect of the patella is devoid of muscle coverage, the twisted knots of the cerclage wire and the bent ends of the K-wires frequently cause severe irritation to the overlying skin and prepatellar bursa, particularly when the patient attempts to kneel. Literature suggests that up to 30% to 50% of patients will ultimately require a secondary surgical procedure for hardware removal once radiographic union is achieved (typically after 6 to 12 months).

Wound healing complications and surgical site infections (SSIs) represent a devastating clinical scenario. Superficial infections can often be managed with targeted oral antibiotics and local wound care. However, deep infections that penetrate the joint capsule constitute a septic arthritis, an orthopedic emergency. Deep infections require immediate operative irrigation and debridement. If the fracture is completely stable, the hardware may be retained while the patient undergoes a prolonged course of intravenous antibiotics. If the fixation is loose or the fracture is infected and non-united, the hardware must be explanted, the bone debrided, and external fixation or prolonged immobilization utilized until the infection is eradicated.

Loss of fixation and subsequent nonunion or malunion occur in approximately 2% to 6% of cases. This failure is typically multifactorial, stemming from technical errors (e.g., asymmetric tensioning, K-wires placed too close to the articular surface), severe unrecognized comminution, or patient non-compliance with postoperative weight-bearing and range-of-motion restrictions. Salvage management for a failed tension band construct depends on the remaining bone stock. Options include revision open reduction and internal fixation (ORIF) utilizing augmented techniques such as cannulated screws with a tension band wire passed through the screws, or plating systems specifically designed for the patella. In cases of catastrophic failure with non-reconstructable comminution, a partial or total patellectomy may be the only viable salvage option, though this leaves the patient with profound, permanent extensor weakness.

Complications and Incidence Rates Table

Phased Post-Operative Rehabilitation Protocols

The postoperative rehabilitation following patellar ORIF requires a delicate balancing act: the therapist must protect the surgical construct from catastrophic tensile failure while simultaneously initiating early motion to prevent debilitating arthrofibrosis. The protocol is heavily dependent on the surgeon’s intraoperative assessment of fixation stability and the quality of the patient's bone.

Phase I: Immediate Post-Operative Protection (Weeks 0 - 2)
Immediately following surgery, the limb is placed in a hinged knee brace locked in full extension. This neutralizes the tensile forces of the quadriceps. Weight-bearing is generally permitted as tolerated (WBAT), provided the knee remains locked in extension, as the axial load of standing does not significantly stress the fracture construct. The primary goals of this phase are wound healing, edema control through cryotherapy and elevation, and the prevention of deep vein thrombosis. Patients are instructed to perform isometric quadriceps sets and straight leg raises to prevent profound muscular atrophy, provided these do not induce severe pain at the fracture site.

Phase II: Early Controlled Motion (Weeks 2 - 6)
Once the surgical incisions have healed and the sutures are removed, the hinged brace is unlocked to permit a progressive, protected range of motion. A standard progression allows 0 to 45 degrees of flexion for weeks 2 to 4, advancing to