EXTENSOR MECHANISM PROBLEMS IN TOTAL KNEE ARTHROPLASTY

1. EXTENSOR MECHANISM PROBLEMS IN TOTAL KNEE ARTHROPLASTY Scott M. Heithoff, DO Garden City Hospital

2. INTRODUCTION • Complications related to the extensor mechanism are the most frequent reason for reoperation in an aseptic TKA. • The prevalence of complications ranges from 1.5 to 12 percent. • Patient selection, operative technique, and implant design all influence the frequency of the complications.

3. POTENTIAL PROBLEMS WITH THE EXTENSOR MECHANISM • Patellofemoral Instability • Patellar Fractures • Patellar Component Loosening • Patellar Component Failure • Patellar Clunk Syndrome • Tendon Rupture

4. PATELLOFEMORAL INSTABILITY • The incidence of patellar subluxation following TKA has been reported to be as high as 29%. • Failure to obtain proper tracking can result in: • Patellofemoral pain and crepitus • Component wear • Component failure and loosening • Fracture

5. PATELLOFEMORAL INSTABILITY • Etiologies: • Excessive lateral retinaculum tightness • Weakness of VMO • Excessive valgus position of implants • Rotational malalignment of the femoral and/or tibial components • Patellar component problems • Disruption of capsular repair

6. PATELLOFEMORAL INSTABILITY – LATERAL RETINACULUM • Most common cause of instability is excessive tightness of the lateral retinaculum and associated weakness of the VMO. • Intraoperative assessment of patellar tracking is critical: • The tourniquet should be released to eliminate the tourniquet’s binding effect on the extensor mechanism. • If the patella subluxes laterally during flexion with the “no-thumb” technique, a lateral release should be performed.

7. PATELLOFEMORAL INSTABILITY –VALGUS POSTION OF IMPLANTS • Excessive postoperative limb alignment of greater than 10 degreed valgus has consistently correlated with patellofemoral problems. • This can be caused by either excessive valgus resection of the distal femur or proximal tibia. • The high valgus angle increases the Q-angle, thereby increasing the lateral force vector on the patella.

8. PATELLOFEMORAL INSTABILITY –ROTATIONAL MALALIGNMENT • Internal rotation or medial shift of the femoral component places the trochlear groove at a greater distance from the patella, leaving the patella laterally positioned. • A small amount of external rotation has been shown to improve tracking.

9. PATELLOFEMORAL INSTABILITY –ROTATIONAL MALALIGNMENT • Internal rotation of the tibia results in lateralization of the tibial tubercle and increase in the Q-angle.

10. PATELLOFEMORAL INSTABILITY –PATELLAR COMPONENT • Avoidance of asymmetric patellar resection. • Re-creating the original thickness with the patella-prosthetic composite. • Slight medialization of the patellar component

11. PATELLOFEMORAL INSTABILITY –MANAGEMENT • Conservative treatment (PT with strengthening of VMO) may be helpful, but only if components are in good position • Recognize problems intraoperativly and correct them before the patient is off the table: • Perform lateral release if needed • Avoid internal rotation of components • Avoid excessive valgus cuts

12. PATELLOFEMORAL INSTABILITY –MANAGEMENT • Revise components if malaligned • Proximal vs. distal reconstructive procedures • Generally, distal procedures should be avoided (tibial tubercle osteotomy) because of the the high failure and complication rate associated with it • Proximal procedures include: • Lateral release • VMO advancement

13. PATELLOFEMORAL INSTABILITY –MANAGEMENT • VMO advancement

14. PATELLAR FRACTURES • The prevalence of patellar fractures after TKA has ranged from 0.1% to 8.5%. • There are multiple factors implicated: • High demand (weight, activity) • Weak bone • Surgeon (excessive/inadequate resection, AVN from lateral release, component malaignment) • Trauma

15. PATELLAR FRACTURES • Risk Factors: • Excessive patellar resection (<15mm patellar thickness) • Minimal patellar resection – Increases patellofemoral joint reaction forces • Femoral components with excessive AP diameter • Asymmetric patellar resection • Large central peg

16. PATELLAR FRACTURES – GOLDBERG CLASSIFICATION • Type I – Fractures not involving the implant / cement composite or quadriceps mechanism • Type II – Fractures disrupting the quadriceps mechanism or the fixation of the implant

17. PATELLAR FRACTURES – GOLDBERG CLASSIFICATION • Type IIIA – Inferior pole fractures with patellar ligament rupture • Type IIIB – Non-displaced inferior pole fractures with intact patellar ligament • Type IV - Lateral fracture-dislocation of the patella

18. PATELLAR FRACTURES – TREATMENT • Depends on four things: • Integrity of the extensor mechanism • Stability of the patellar component • Degree of fracture displacement • Extent of bony comminution

19. PATELLAR FRACTURES – TREATMENT • Nonoperative Tx: • Intact extensor mechanism • Secure implant • <2 cm displacement • Minimal comminution • Knee Immobilizer or cylinder cast for 4-6 weeks with protected weight bearing, followed by progressive weight bearing.

20. PATELLAR FRACTURES – TREATMENT • Surgical options: • Secure Implant: • A partial patellectomy with repair of extensor mechanism provides a better result than attempts at ORIF • Loose Implant: • Removal of loose component, cement, and avascular pieces • Deficient bone stock precludes prosthetic reimplantation • Patelloplasty

21. PATELLAR COMPONENT LOOSENING • Uncommon – Incidence <2% in most studies • Causes: • Cementing into deficient bone • Component malposition • Patellar subluxation • AVN patella • Osteoporosis

22. PATELLAR COMPONENT LOOSENING –TREATMENT • Component revision – if bone stock allows • Component removal and patellar arthroplasty (smoothing of the remaining patella without resurfacing) • Patellectomy

23. PATELLAR COMPONENT FAILURE • Most complications have been associated with metal-backed designs. • Proposed advantages to metal-backed patella's: • Decreasing patellar surface strains • Lessening delamination by supporting the poly • Allows for cementless patellar component fixation • Failure of metal-backed designs: • Poly-metal plate dissociation • Peg-plate dissociation • Metal plate fracture

24. PATELLAR COMPONENTFAILURE • Poly-metal plate dissociation

25. PATELLAR CLUNK SYNDROME • Condition resulting from the development of a fibrous nodule at the junction of the posterior aspect of the quadriceps tendon and proximal pole of the patella. • With knee flexion, the nodule enters the intercondylar notch of the femoral prosthesis • As the knee is extended, the nodule becomes entrapped within the notch • At 30 to 45 deg, enough tension is placed on the fibrous nodule to cause it to clunk out of the notch

26. PATELLAR CLUNK SYNDROME

27. PATELLAR CLUNK SYNDROME • Etiologies: • Femoral components with a sharp anterior edge at the superior aspect of the intercondylar notch • Malpositioning of the patellar component beyond the proximal border of the patella • Postoperative scarring • Alterations of joint line, patellar height, or patellar thickness

28. PATELLAR CLUNK SYNDROME • Treatment: • Revision of components if positioned incorrectly • Debridement of fibrous nodule • Open • Arthroscopically

29. TENDON RUPTURE – QUADRICEPS TENDON • Rupture of the quadriceps or patellar tendon is an infrequent complication of TKA – 0.17% to 0.55% • Quadriceps tendon rupture is associated with lateral release – due to devascularization of the tendon or extension of the release to proximally • Treat with resection of the rupture zone back to healthy tissue, mobilization of the quadriceps, and preparation of the proximal patellar pole for tendon reattachment • A No. 5 nonabsorbable suture weaved through the quads and anchored to the patella via drill holes provides secure fixation

30. TENDON RUPTURE –PATELLAR TENDON • Etiologies: • Inadvertent intraoperative detachment from the tibial tubercle during exposure • Stiff knee with limited motion – use rectus snip • Patients with previous HTO • Residents • Late rupture due to impingement of the prosthesis on the tendon • Traumatic rupture

31. TENDON RUPTURE –PATELLAR TENDON • Intraoperative rupture: • The tendon can be repaired or reattached using No. 5 nonabsorbable suture, synthetic tape, screw or staple fixation. • Usually as long as the problem is recognized early and delt with accordingly, this may be all that is necessary. • If the repair in tenuous, autograft semitendinosis may be used.

32. TENDON RUPTURE –PATELLAR TENDON

33. TENDON RUPTURE –PATELLAR TENDON • Late ruptures: • Long standing ruptures can be complicated by contractures of the extensor mechanism • Allograft tendon is usually used in these circumstances • If all else fails, a knee arthrodesis can be used as a salvage procedure.

34. CONCLUSIONS • Patellofemoral complications are a frequent cause of revision surgery • To avoid most problems, put the components is correctly • Internal rotation is death • Don’t be afraid to use a lateral release • Don’t cut tendons!