Patella Baja or dropped patella

Josephine

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Patella baja and total knee arthroplasty (TKA): etiology, diagnosis, and management.
Surg Technol Int. 2004;12:231-8. authors: Chonko DJ1, Lombardi AV Jr, Berend KR.
http://www.ncbi.nlm.nih.gov/pubmed/15455331

Patella baja can be divided into congenital, acquired, or a combination of the two, is commonly encountered in total knee arthroplasty (TKA).

Congenital patella baja refers to a patella distal in relationship to the femoral trochlea and present since an early age.

patella-baja-and-alta.png


Acquired patella baja may occur secondary to distal positioning of the patella relative to the femoral trochlea or shortening of the patellar tendon, as a result of trauma or surgery.

Patella baja also can occur postoperatively as a result of scarring and shortening of the patellar tendon, scarring of the patellar tendon to the anterior aspect of the tibia, or both.

Another cause of acquired patella baja seen commonly in TKA is elevation of the joint line, referred to as pseudo-patella baja. The patella remains in a normal position relative to the femoral trochlea; however, the distance between the patella and tibia is narrowed. Pseudo-patella baja can be a result of tibial or femoral over-resection, which necessitates a larger polyethylene insert.

Alterations of the patello-tibial distance can occur during TKA by excessive soft-tissue release that requires elevation of the joint to regain stability and placement of the patellar polyethylene component distally on the patella.

Prevention is the easiest way to avoid potential problems with patella baja during TKA; however, the surgeon is often confronted with this situation during total knee revisions. Failure to address patella baja can lead to decreased range of motion (ROM), extensor lag, impingement of the patella against the tibial polyethylene or tibial plate, anterior knee pain, increased energy expenditure and rupture of the patellar or quadriceps tendons.

Treatment of patella baja first depends on determining the cause and distinguishing between patella baja and pseudo-patella baja.

Corrective measures include re-establishing the joint line by use of
distal femoral augments (shims)
tibial tubercle osteotomy with proximal displacement
lengthening of the patellar tendon
shaving of the anterior portion of the tibial polyethylene spacer
placement of the patellar implant in a direction toward the head position​
 

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