Treatment of Patellar Fractures in TKA

Archival Presentation Notice: This article modernizes the multimedia presentation “Treatment of Patellar Fractures in TKA” originally presented by Kevin L. Garvin, MD (University of Nebraska Medical Center) at the International Congress for Joint Reconstruction (ICJR). The historical Flash lecture has been reconstructed into the synchronized video slide presentation above, with the original file preserved in the digital archives (patella_fractures_icjr_dec_2008_final.swf).

1. High-Yield Summary

• Clinical Significance: Periprosthetic patellar fractures represent the most frequent fracture complication following total knee arthroplasty (TKA), occurring in 0.2% to 5.4% of cases, with markedly higher prevalence in resurfaced patellae.
• Governing Decision Benchmark: Management is strictly dictated by two anatomical parameters: integrity of the knee extensor mechanism and stability (fixation) of the prosthetic patellar component.
• The Nonoperative Gold Standard (Type I): Fractures with an intact extensor mechanism and well-fixed component (Ortiguera-Berry Type I) should be managed nonoperatively with extension bracing; nonoperative management achieves successful outcomes in >85% of patients despite frequent asymptomatic fibrous nonunion.
• Operative High-Risk Profile (Type II & III): Surgical intervention is reserved for extensor mechanism disruption (Type II) or symptomatic loose components (Type III), but carries an overall complication rate exceeding 40% to 50% across clinical series.
• Bone Stock Threshold: In loose components with residual bone stock <10 mm (Type IIIb), attempting repeat resurfacing leads to recurrent failure; component excision and patelloplasty (resection arthroplasty) is the definitive salvage procedure of choice.

2. Anatomy & Vascularity

The patella functions as a vital biomechanical fulcrum that increases the quadriceps lever arm across the knee joint. Its arterial blood supply and osseous architecture are particularly vulnerable during surgical exposure and prosthetic preparation in total knee arthroplasty.

Vascular Anatomy & The Peripatellar Anastomotic Ring

The blood supply of the patella is derived from a complex anastomotic peripatellar arterial ring formed by six principal genicular vessels: the superior medial genicular artery, superior lateral genicular artery, inferior medial genicular artery, inferior lateral genicular artery, descending genicular artery (highest genicular), and anterior tibial recurrent artery. Intrinsic osseous vascularity penetrates via anterior nutrient foramina and polar vascular networks.

Standard medial parapatellar arthrotomy routinely transects the medial genicular arterial branches. If a concomitant lateral retinacular release is performed to optimize tracking, the superior lateral genicular artery is frequently divided. When combined with extensive excision of the infrapatellar fat pad, the patella becomes virtually devascularized, predisposing the remaining bony bed to avascular necrosis, microfracture, and delayed healing.

Neurovascular Danger Zones & Internervous Planes

• Infrapatellar Branch of the Saphenous Nerve: Traverses the anteromedial joint capsule; transection during medial incision causes anterolateral numbness and can produce painful postoperative neuromas.
• Common Peroneal (Fibular) Nerve: Located adjacent to the biceps femoris tendon posterolaterally; at risk during over-aggressive lateral retinacular release or posterior capsular releases for fixed valgus deformities.
• Popliteal Neurovascular Bundle: Separated from the posterior joint capsule by the oblique popliteal ligament; endangered during posterior capsular stripping or transosseous drill pin placement directed posteriorly.
• Surgical Planes: Medial parapatellar approach utilizes the interval between the vastus medialis obliquus (VMO) and quadriceps tendon, continuing distally through the medial patellar retinaculum into the medial border of the patellar tendon.

3. Pathogenesis & Risk Factors

Periprosthetic patellar fractures result from an interplay of patient biological characteristics, implant biomechanics, and technical surgical errors.

Surgical and Technical Etiologies

• Patellar Bone Over-Resection: Leaving a residual bony bed thinner than 12 mm to 15 mm (or resecting >50% of original native patellar composite thickness) exponentially increases mechanical hoop stress and bending failure.
• Asymmetric Resection: Non-coplanar or uneven bone resection produces an unseated, tilted patellar component (“patellar rocking”), generating localized eccentric contact pressures and point stress risers.
• Implant Fixation Geometry: Large central single-peg implants require broad central reaming, which induces thermal osteonecrosis and creates a massive focal stress riser. Modern designs utilize three smaller peripheral fixation lugs that distribute compressive loads more uniformly.
• Component Rotational Malalignment: Internal rotation of the femoral component or tibial tray shifts the trochlear groove medially, increasing the functional Q-angle. This causes severe lateral patellar tilt, subluxation, and excessive shear stress on the lateral facet during flexion.
• Anterior Knee Overstuffing: Placing an oversized femoral component or failing to resect sufficient anterior femoral bone increases joint line elevation and patellofemoral compressive reaction forces during deep flexion.
• Iatrogenic Perforation: Breaching the anterior cortical envelope with fixation drill bits or reamers significantly reduces torsional and bending strength.

Patient and Host Factors

Systemic osteoporosis, inflammatory arthropathies (rheumatoid arthritis), chronic corticosteroid administration, high body mass index (BMI), male gender (attributable to higher quadriceps force vectors), and strenuous post-arthroplasty physical activities all correlate with an elevated risk of stress failure.

4. Natural History & Epidemiology

The reported incidence of periprosthetic patellar fractures ranges from 0.2% to 1.5% in unresurfaced patellae and up to 3.0% to 5.4% in resurfaced primary TKAs. In revision knee arthroplasty cohorts, the incidence can exceed 10%.

The chronological presentation exhibits a bimodal distribution. Early fractures (occurring within the first 6 to 12 months postoperatively) typically reflect technical surgical errors, including devascularization necrosis, cortical notching, or severe over-resection. Late fractures (occurring 2 to 5+ years postoperatively) more commonly stem from chronic eccentric maltracking, polyethylene wear, focal osteolysis, or minor traumatic falls during active weight-bearing.

Untreated displaced fractures with extensor disruption progress to debilitating quadriceps insufficiency, knee instability, severe flexion contracture, and loss of independent ambulation. Conversely, undisplaced fractures with intact extensor mechanisms frequently undergo stable fibrous union without loss of knee function, remaining completely asymptomatic over long-term follow-up.

5. Clinical Presentation

History

Patients present via two distinct pathways: an acute traumatic event or an insidious, atraumatic progression.

• Acute Traumatic Mechanism: Direct low-energy impact on the flexed knee (such as a ground-level fall) or sudden violent eccentric quadriceps contraction while navigating stairs, stepping off a curb, or rising from a chair. Patients often report an audible “pop” followed by immediate inability to bear weight.
• Atraumatic / Insidious Presentation: Up to one-third of periprosthetic patellar fractures are identified incidentally on routine surveillance radiographs in patients who report mild, non-specific anterior knee pain or mechanical crepitus without functional impairment.
• Instability & Catching: Complaints of sudden knee giving way, subluxation sensations, or mechanical locking indicate either extensor discontinuity or displaced loose implant/cement fragments entering the tibiofemoral articulation.

Physical Exam

• Active Straight Leg Raise (SLR) Test: The essential diagnostic examination maneuver. The patient is asked to actively elevate the extended leg against gravity from the supine position. Inability to perform an active SLR or the presence of an extensor lag >15° to 20° establishes rupture of the extensor mechanism.
• Palpable Extensor Gap: A distinct transverse sulcus or gap is palpable between bone fragments or at the quadriceps/patellar tendon junction.
• Joint Effusion & Hemarthrosis: Marked knee effusion is typically present. Arthrocentesis reveals frank hemarthrosis; the presence of visible fat marrow globules confirms an acute intra-articular fracture hematoma.
• Implant Stability & Patellar Tracking: Palpation of the patellar button through the retinaculum; assessment for paradoxical mobility, gross crepitation, or lateral tilt in early flexion.
• Infection Exclusion Assessment: Strict clinical evaluation for signs of erythema, local warmth, wound drainage, or sinus tracts; any suspicion demands formal synovial aspiration.

6. Imaging and Diagnostic Studies

Plain Radiography

The standard imaging workup comprises three essential radiographic views:

• Standing Anteroposterior (AP) View: Evaluates overall limb coronal alignment, tibiofemoral joint space, and gross displacement of major fracture fragments.
• True Lateral View (in 20° to 30° Flexion): The cornerstone view for evaluating vertical displacement, separation distance between superior and inferior poles, cement-bone radiolucency >2 mm, patellar height (patella baja vs. alta), and residual osseous thickness behind the prosthetic button.
• Axial / Skyline (Merchant) View: Critical for detecting vertical, sagittal, and marginal fracture lines that are invisible on lateral projections, as well as patellar tilt, subluxation, and component seating.

Advanced Imaging

Computed Tomography (CT) with metal artifact reduction software (MARS) is indicated for complex comminuted fracture configurations, precise quantification of remaining osseous volume, and rotational profiling of the femoral and tibial components. Rotational assessment must evaluate the femoral posterior condylar angle (relative to the transepicondylar axis) and the tibial baseplate rotation (relative to the medial third of the tibial tubercle) to identify rotational malalignment driving patellar shear.

Laboratory Evaluation

Serum erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are mandatory in every patient evaluated for periprosthetic fracture. If inflammatory markers are elevated or if radiographic loosening is evident, diagnostic synovial fluid aspiration (cell count, leukocyte differential, alpha-defensin, and aerobic/anaerobic cultures) must be performed to definitively rule out occult periprosthetic joint infection (PJI) prior to any surgical undertaking.

7. Classification

The definitive, universally accepted classification system is the Ortiguera & Berry Classification (Mayo Clinic / JBJS Am 2002), which stratifies fractures based on the two parameters that dictate clinical management: extensor mechanism integrity and implant fixation stability.

An alternative historical classification is the Goldberg Classification: Type I encompasses fractures not involving the cement-bone interface or implant; Type II involves loosening of the patellar component; Type III encompasses superior pole (IIIa) or inferior pole (IIIb) fractures with extensor disruption; and Type IV represents fracture-dislocations.

8. Treatment

Nonoperative Management

Nonoperative care is the first-line treatment of choice for all Ortiguera-Berry Type I fractures (intact extensor mechanism with a well-fixed, stable patellar component), regardless of fracture displacement on radiographs.

• Immobilization Protocol: Rigid knee immobilization in full extension using a lightweight cylinder cast or a hinged knee brace locked at 0° for 4 to 6 weeks.
• Weight-Bearing Parameters: Immediate weight-bearing as tolerated with assistive devices (crutches or walker) is permitted while locked in full extension.
• Progression Phase: At 4 to 6 weeks post-injury, follow-up radiographs are obtained. If fragments remain stable and no component migration has occurred, progressive active-assisted flexion is initiated under physical therapy guidance, with weaning from the brace over the subsequent 4 weeks.
• Objective Failure Criteria: Secondary displacement accompanied by progressive extensor lag (>15°), component loosening, or progressive mechanical locking warrants conversion to operative intervention.

Operative Management & Surgical Decision Tree

Surgical intervention is indicated exclusively for extensor mechanism failure (Type II) or symptomatic loose components (Type III). The surgical approach must balance mechanical stabilization against the extreme risk of devascularization.

Type II Management: Extensor Disruption with Stable Implant

Internal fixation is performed using modified tension band wiring with two parallel 4.0 mm cannulated cancellous screws and an 18-gauge wire or braided cable passed through the screw lumens in a figure-of-eight configuration. Alternatively, low-profile variable-angle locking mesh plates provide multi-planar screw purchase in osteopenic bone.

Polar avulsions require transosseous suture fixation through bone tunnels or heavy non-absorbable suture anchors. Because native tissue quality is poor, synthetic mesh (monofilament polypropylene/Marlex tape) or Achilles tendon/extensor mechanism allograft augmentation should be utilized to protect the repair.

Type IIIa Management: Loose Component with Adequate Bone Stock (>10–12 mm)

The loose component and all fragmented cement must be extracted, and the fibrous pseudomembrane debrided down to bleeding viable bone. If the bone bed has >10–12 mm thickness with solid cortical support, revision resurfacing may be performed using an all-polyethylene biconvex or inset component, or a modern highly porous trabecular metal augment. Alternatively, if extensor continuity is intact, patelloplasty without re-implantation is strongly preferred to eliminate the risk of recurrent loosening.

Type IIIb Management: Loose Component with Inadequate Bone Stock (<10 mm)

Attempting to cement a revision button onto a compromised, paper-thin shell (<10 mm) results in immediate failure, catastrophic refracture, and cement extrusion. The loose implant is removed, fragmented osseous edges are contoured smooth with a high-speed burr, and the residual shell is covered with a local synovial or retinacular soft tissue flap to articulate against the femoral trochlea (patellar resection arthroplasty / patelloplasty). If the remaining bone is severely comminuted or avascular, fragments are excised, followed by formal reconstruction of the extensor mechanism.

Addressing Component Malalignment

If pre-operative CT imaging confirms severe internal rotation of the femoral or tibial component driving patellar shear, addressing the patella in isolation is doomed to failure. Revision of the malrotated femoral or tibial component is mandatory to restore a neutral patellofemoral tracking vector.

9. Outcome

Clinical outcomes following periprosthetic patellar fractures diverge dramatically depending on whether operative or nonoperative pathways are pursued.

• Nonoperative Results (Type I): Patients managed nonoperatively consistently demonstrate favorable outcomes, with >85% to 90% achieving satisfactory functional results, preservation of Knee Society Scores (KSS >80), and restoration of baseline active knee range of motion. Notably, up to 50% of these patients develop an asymptomatic fibrous nonunion on long-term radiographic surveillance; however, fibrous union does not impair quadriceps strength or clinical satisfaction.
• Surgical Intervention Outcomes (Type II & III): Surgical management carries a formidable complication profile across the orthopaedic literature, with complication rates ranging from 42% to 54%. Reoperation rates for hardware failure, persistent nonunion, infection, and recurrent extensor rupture reach 40% to 50%.
• Functional Extensor Restoration: Following operative repair of extensor mechanism disruption, active extension against gravity is restored in the majority of patients, but a residual extensor lag of 5° to 15° and an average loss of 15° to 20° of terminal flexion are common long-term sequelae.
• Resection Arthroplasty Durability: Patellar resection arthroplasty (patelloplasty) yields superior survivorship and significantly fewer reoperations compared to revision component fixation in compromised bone beds, providing durable pain relief despite modest persistent anterior knee aching during stair climbing.

10. Complications

11. Pearls and Pitfalls

Technical Pearls

• The 12 mm Rule: During primary arthroplasty, always measure remaining bone thickness with a caliper after cutting; never leave less than 12 mm to 15 mm of residual patellar bone.
• Vascular Stewardship: Preserve the lateral superior genicular artery whenever possible; perform lateral retinacular release from inside-out, ensuring that electrocautery stays >1.5 cm away from the superior lateral patellar border.
• CT Rotational Profiling Before Surgery: Always obtain a MARS CT scan to evaluate femoral and tibial component rotation before revising a fractured patella; fixing the extensor mechanism in the presence of uncorrected internal rotation guarantees hardware failure or refracture.
• Embrace Patelloplasty: If the component is loose and bone stock is marginal (<10 mm), resist the temptation to re-resurface. Debride the cement, smooth the bony bed with a high-speed burr into a flat or gently concave contour, and allow it to articulate directly against the femoral shield.
• Tension Band Rigidity: When repairing Type II transverse fractures, use cannulated screws with cable passed through the center; this creates a composite construct that resists both tensile distraction and rotational toggle.

Critical Pitfalls

• Operating on Asymptomatic Type I Fractures: Attempting open reduction and internal fixation on a non-displaced fracture with an intact extensor mechanism converts a predictable nonoperative success into a high-risk surgical procedure with a 40%+ complication rate.
• Ignoring Occult Infection: Assuming that an isolated loose patellar button or fracture is purely mechanical without checking ESR, CRP, and performing arthrocentesis.
• Re-Resurfacing Paper-Thin Bone: Forcing cement pressurization onto a thin, avascular shell leads to thermal necrosis, immediate re-loosening, and catastrophic loss of the entire anterior bone envelope.

12. Controversy

Several clinical dilemmas continue to stimulate active debate within adult reconstruction:

• Routine Resurfacing vs. Retention in Primary TKA: While patellar resurfacing eliminates anterior knee pain in a subset of patients, it creates the specific risk of periprosthetic patellar fracture. Proponents of selective retention argue that unresurfaced patellae have a near-zero fracture incidence, whereas proponents of universal resurfacing point to lower overall secondary surgery rates for persistent anterior pain.
• Management of Asymptomatic Fibrous Nonunion: When a Type I fracture heals with an asymptomatic fibrous nonunion on radiographs, debate exists regarding activity restrictions. Long-term registry data suggest that patients can return to unrestricted low-impact activity without fear of catastrophic late collapse.
• Synthetic Mesh vs. Fresh-Frozen Allograft for Extensor Reconstruction: Monofilament polypropylene (Marlex) mesh offers immediate availability, zero disease transmission risk, and lower cost. Fresh-frozen extensor mechanism allografts (incorporating tibial tubercle bone block) provide biological tendon tissue but suffer from progressive late stretching, extensor lag recurrence, and higher deep infection rates.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Ortiguera CJ, Berry DJ. Patellar fracture after total knee arthroplasty. J Bone Joint Surg Am. 2002. doi:10.2106/00004623-200204000-00004 [Level IV: Therapeutic Case Series / Classification System]
• Parvizi J, Kim KI, Oliashirazi A et al. Periprosthetic patellar fractures. Clin Orthop Relat Res. 2006. doi:10.1097/01.blo.0000218722.83601.18 [Level II: Comparative Cohort Study]
• Chalidis BE, Tsiridis E, Tragas AA et al. Management of periprosthetic patellar fractures. A systematic review of literature. Injury. 2007. doi:10.1016/j.injury.2007.02.054 [Level I: Systematic Review / Meta-Analysis]
• Windsor RE, Scuderi GR, Insall JN. Patellar fractures in total knee arthroplasty. J Arthroplasty. 1989. doi:10.1016/s0883-5403(89)80009-9 [Level IV: Retrospective Case Series]
• Ducharme MT, Selemon NA, Bedard NA et al. Classification and Outcomes of 214 Periprosthetic Patellar Fractures in Primary Total Knee Arthroplasty. J Arthroplasty. 2026. doi:10.1016/j.arth.2026.05.003 [Level IV: Multicenter Retrospective Cohort Study]

15. Master Class Pro-Tip

When approaching a periprosthetic patellar fracture, the surgeon’s greatest virtue is restraint. If the patient can actively straight-leg raise against gravity and the component shows no divergence from the bone on lateral and axial radiographs, nonoperative immobilization in extension produces reliable, pain-free outcomes in over 85% of cases—even in the presence of wide radiographic nonunion. Conversely, when surgery is forced by extensor rupture or component loosening, never sacrifice vascularity for radiographic reduction. If the residual patellar bone is thinner than 10 mm, abandon all thoughts of revision re-cementing: perform an uncompromised patellar resection arthroplasty (patelloplasty) by contouring the residual shell with a high-speed burr and interposing viable soft tissue. A stable, pain-free fibrous articulation against the femoral trochlea vastly outperforms the catastrophic cycle of re-cementation, thermal necrosis, and recurrent mechanical failure.

Master Class Surgical Pearl: Patellar Bone Preservation, Vascular Stewardship, and Conservative Restraint in TKA