What is the best treatment approach for a patient with an avulsion fracture of the patella involving an 8mm fragment after total knee replacement (TKR)?

Treatment of Avulsion Fracture of Patella with 8mm Fragment After Total Knee Replacement

For an 8mm patellar avulsion fracture after TKR, treatment depends critically on extensor mechanism integrity and implant stability: if the extensor mechanism is intact and the patellar component is stable, pursue nonoperative management with excellent outcomes expected; if either is disrupted, operative intervention is required despite higher complication rates.

Classification-Based Treatment Algorithm

The management of post-TKR patellar fractures follows a three-criteria classification system that determines treatment approach 1:

Type I: Stable Implant + Intact Extensor Mechanism

• This is the most favorable scenario and likely applies to your 8mm avulsion fragment if the patient can actively extend the knee against gravity 1
• Nonoperative treatment is highly successful with minimal complications 1
• Only 1 of 37 cases treated nonoperatively required late surgical intervention 1
• Immobilization followed by early mobilization as pain permits 2

Type II: Disrupted Extensor Mechanism (Regardless of Implant Status)

• Operative treatment is mandatory if the patient cannot actively extend the knee or has an extensor lag 1, 2
• Warning: Operative treatment carries a 50% complication rate and 45% reoperation rate in this scenario 1
• Displaced fractures with extensor lag have poor results even with surgery 2
• Consider fragment excision for distal pole fractures with patellar tendon disruption 2

Type III: Loose Patellar Component (Regardless of Extensor Mechanism)

• Operative treatment required for component revision 1
• 45% complication rate and 20% reoperation rate 1
• Component loosening requires revision to prevent progression to global joint failure 3

Initial Diagnostic Evaluation

Obtain standard radiographs immediately, including weight-bearing axial views to assess fragment displacement and patellar tracking 3, 4, 5:

• Anteroposterior, lateral, and axial (sunrise) views are essential 5
• Weight-bearing axial radiographs better assess patellofemoral kinematics 3
• CT with metal artifact reduction techniques if radiographs are inconclusive 3, 5
• Assess for patellar maltracking, as transverse fractures are associated with this complication 3

Clinical Assessment Priorities

Perform active straight leg raise test to determine extensor mechanism integrity—this single finding determines your entire treatment pathway 1, 2:

• Ability to actively extend knee against gravity = intact mechanism = nonoperative treatment 1
• Extensor lag or inability to extend = disrupted mechanism = operative treatment required 1, 2
• Palpate for patellar component stability and assess for effusion 1

Fragment Size Considerations

Your 8mm fragment requires specific attention 6, 7:

• Small osseous fragments may underrepresent the actual cartilaginous component size 7
• Fragment size alone does not dictate treatment—mechanism integrity is paramount 1
• If operative fixation is chosen, basket plate fixation maintains patellar height better than fragment resection 6
• Pole resection results in patella baja in 77% of cases with significantly worse functional outcomes 6

Operative Techniques (When Required)

If surgery is necessary, internal fixation with basket plate or tension band wiring is preferred over fragment excision to preserve patellar height 6, 8:

• Basket plate fixation allows immediate mobilization and early weight-bearing 6
• Average patellofemoral score: 94.1 points with fixation vs. 81.2 points with resection 6
• Modified tension band wiring is most commonly used for patellar fractures 8
• Two parallel cannulated lag screws with tension band provide superior stability 8
• Patellectomy should be considered only as salvage for failed treatments 8, 2

Critical Pitfalls to Avoid

Do not assume nonoperative treatment is safe without confirming extensor mechanism integrity—this is the most common error 1, 2:

• Displaced fractures without extensor lag can be treated nonoperatively successfully 2
• Postoperative immobilization after pole resection leads to patella baja and poor outcomes 6
• Male patients have 2.5× higher fracture risk (1.01% vs 0.40%) 1
• Many patellar fractures post-TKR are asymptomatic, highlighting need for radiographic surveillance 3
• Patellofemoral instability occurs in 1-12% of TKA patients, often from component malrotation 3, 4

Rehabilitation Approach

Early mobilization is recommended regardless of treatment method, though timing differs 6, 8:

• Nonoperative: Begin range of motion as pain permits with protected weight-bearing 2
• Operative with basket plate: Immediate mobilization and early weight-bearing 6
• Operative with pole resection: Requires postoperative immobilization period 6

Expected Outcomes

Nonoperative treatment of Type I fractures (stable implant, intact mechanism) has >97% success rate, while operative treatment for Types II and III carries 20-50% complication rates 1:

• Type I nonoperative: 1 of 37 required late intervention 1
• Type II operative: 6 of 11 had complications, 5 of 11 required reoperation 1
• Type III operative: 9 of 20 had complications, 4 of 20 required reoperation 1
• Preservation of patellar height correlates directly with functional outcome 6