1. PATELLOFEMORAL TRACKING IN T.K.A Dr . P.nagendra Postgraduate M.S.Ortho

2. - ANATOMY - primary function : - to increase the lever arm of extensor mechanism - Thus improving efficacy of quadriceps contraction - HOW - patella displaces the force vectors of quadriceps - and patellar tendons away from the centre of rotation of knee 3. The length of the lever arm varies as a function of : Geometry of trochlea Varying patellofemoral contact areas Varying center of rotation of knee Greatest at 20 flexion Force required for extension increase significantly in last 20 of extension 4. - PATELLOFEMORAL STABILITY - Articular surface geometry - Soft tissue restraints - Q angle : by hvid - Angle between the extended anatomical axis of femur and the line between the center of patella and the tibial tuberosity - Quadriceps acts in line with anatomical axis of femur ( V.medialis obliquus acts to medialise patella in terminal extension ) 5. LARGER Q angle : - greater tendency for lateral subluxation - Patella doesnt contact the trochlea in early flexion , lateral subluxation in this range is prevented by V.medialis obliquus - As flexion increses bony & prosthetic constraints play dominant role . 6. Patella experiences joint reaction force Depends on angle of flexion & magnitude of forces transmitted Forces of 2 3 times body weight : in daily activities 7 8 times body weight : squatting In normal knee resisted by thick articular cartilage Variations in area of contact: inf. Surface first contacts 20 flexion Mid-portion 60 flexion Superior portion 90 flexion Extreme flexion( > 120 ) only medially & laterally , quadriceps tendon articulates with trochlea 7. This has significant effect on prosthetic patellofemoral joint eccentric loading leads to shear forces in the patellar component & prosthesis bone interface - failure of metal backed patellar components , polythene wear & component loosening. - Normal tibia internally rotates during flexion - to centralize the tibial tubercle or diminish Q angle 8. . REASONS FOR PATELLAR SUBLUXATION - Nine malalignments - Femoral component - internal rotation - Medial displacement - Valgus reorient or displace the trochlear groove to increase the Q angle 9. Anterior displacement or femoral component oversizing - both displace the trochlea, and hence the patella, anteriorly, tightening the lateral retinaculum- increasing the tendency toward lateral subluxation. 10. Tibial component malalignment Internal rotation Medial displacement Valgus displace the tibial tubercle laterally increasing the Q angle lateral subluxation 11. Patellar component malalignment Under resection of patella displaces the ligament attachment more anterior tightening the lateral retinaculum lateral subluxation Lateral displacement of patellar component displaces the center of articulation laterally increasing the Q angle 12. under resection of patella 13. There is no patellar subluxation in the majority of the knees presenting for replacement. Therefore, if there is patellar subluxation at the end of the procedure,it is more logical to look for a cause rather than simply jump to a lateral retinacular release. 14. PATELLAR PREPARATION - Resurfacing the patella commonly performed though not routinely in TKA - restoration of the native patellar thickness -most desirable. - Increasing patellar thickness - detrimental effects anterior knee pain and decreased knee flexion. - diminished patellar thickness increased incidence of patellar fractures - recommendation - restore or slightly diminish patellar thickness when possible 15. Patellar osteotomy - should be symmetric - line of bony resection - from the margin of the medial facet to the margin of the lateral facet. resection - accurately performed using a reciprocal saw and eyeball technique Medialised postion on patellar undersurface is recommended Present designs have three peripheral pegs Guide systems allow for proper positioning of these peg holes in a superomedial position Use all polyethylene component designs 16. Cement is routinely used for fixation - bone surface prepared with thorough lavage - cement is applied in a doughy state. - no attempt is made to pressurize the cement during application. - A patellar clamp is utilized to secure the patellar - component while the cement is hardening and excess cement is removed. After all components are well fixed, the knee is reduced. modified no thumbs technique to evaluate patellar tracking 17. Finally, the peripatellar soft tissues including the synovium and fat pad are evaluated. Typically the synovial tissue in the area along the undersurface of the distal quadriceps is excised. This tissue has been implicated in the occasionally encountered patellar clunk syndrome, and it is important to remove it at the time of patellar resurfacing 18. PATELLAR CLUNK SYNDROME : A fibrous nodule forms on the posterior surface of the quadriceps tendon just above the superior pole of the patella . -This nodule can become entrapped in the intercondylar notch of the femoral prosthesis and cause the knee to pop or clunk at approximately 30 to 45 degrees of knee flexion as the knee is actively extended 19. Proximal placement of the patellar button so that it overhangs the cut surface of the patella is possible cause recommended treatment - arthroscopic dbridement Arthrotomy and nodule excision - recurrence after arthroscopic treatment or in the setting of loose or malpositioned patellar components that may require revision. Insall recommended a limited synovectomy of the posterior surface of the quadriceps tendon as a prophylactic measure 20. Patellofemoral instability, fracture, loosening, component wear or failure, patellar clunk syndrome, and patellar ligament and quadriceps tendon disruption all been associated with technical errors in the performance of patellar resurfacing. 21. The Intraoperative Assessment of Patellar Tracking Satisfactory tracking of the patellofemoral joint is essential to the success of total knee arthroplasty with or without patellar resurfacing. Preoperative assessment - X rays merchant view reveals thickness & symmetry of native patella ( aids in orienting patellar osteotomy) & presence of patellar tilt/ subluxation. - Note is made of HIGH POINT efforts are made at slightly medialising or atleast reproducing the high point 22. - lateral view may reveal patella baja (more extensile exposure by utilizing a quadriceps snip or tibial tubercle osteotomy) The full length standing and anteroposterior views of the knee are used to evaluate limb alignment INTRAOPERATIVE ASSESSMENT Begins After bone cuts and soft tissue releases have been performed. Trial components assembled and stability and overall limb alignment are verified. Attention is then turned to patellar tracking. 23. patella baja 24. Preferred Technique placement of a towel clip through the medial edge of the quadriceps tendon 8 cm proximal to the superior pole of the patella. - Gentle traction - in line with the pull of the quadriceps musculature- to eliminate slack in the extensor mechanism. knee slowly flexed & behavior of the patellofemoral articulation is observed - Acceptable tracking -contact of the patellar component with both the medial and lateral femoral condyles with no tendency for patellar tilt or subluxation . Particular attention - 60 to 90 degrees of flexion 25. - Alternatie technique : 1.RULE OF NO THUMB ( by scott ) - Most widely used if the patella tracks well without closing the capsule and without the surgeon holding the patella, then no lateral release is needed. Should the patella demonstrate a tendency to subluxate without counteracting pressure from the thumb, then a lateral retinacular release is recommended. - rule of no thumb tends to overestimate the need for lateral release. 26. 2. ONE STITCH TEST A single suture is placed adjacent to the patella to close the capsule and the knee is brought into deep flexion. suture cuts out of the capsule - lateral release is indicated. - performed again after the lateral release to verify appropriate tracking of the patella . variant of one-stitch test : single towel clip to reapproximate the capsule. one towel clip above the patella & one below the patella, to simulate the soft tissue tension attained with formal capsular closure. 27. Significance of patellar tracking problem : intraoperative patellar-tracking problem at the time of trial reduction should serve as a red flag to the surgeon - Focused review of the position and orientation of all three components of the TKA. - after review has been completed and appropriate component position is verified should lateral retinacular release be carried out. 28. Patellar symmetry : Goal symmetrical patellar remnant Normal patella assymmetric , medial facet thicker than lateral facet Thus unequal amounts has to be removed Manual palpation of patellar remnant excellent method for assessment PATELLAR BUTTON POSITION Goal high point slightly medial 29. LATERAL RETINACULAR RELEASE Step wise approach Begins with release of patellofemoral ligament all inside technique advantages - avoidance of large lateral cutaneous flap -adequate postoperative joint seal - post op haemarthrosis well contained -superficial wound infection occur, a direct connection to the joint is not present. -allows preservation of superior lateral geniculate artery 30. First step localization of sup. Lat. Geniculate A. (artery located within a mean of 1.5 mm from the superior pole of patella ) A one-fourth inch penrose drain is then placed around the vessel so gentle superior and inferior traction can be performed as needed The lateral release is then performed approximately 1 to 2 cm from the lateral patella margin Using gentle inferior traction on the vessels, the release is extended superiorly Gentle superior traction is then applied and the release is carried distally to the level of the joint. 31. - An oblique incision can be used in the lateral retinaculum to avoid the inferior lateral genicular artery. Closure done carefully to ensure adequate closure, & measure continued acceptable patella tracking. Motion should be checked throughout the closure 32. Problems related to lateral retinacular release increased postoperative pain wound-healing complications, delayed rehabilitation and compromised patellar blood supply.