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PATELLAR TRACKING
Tibio-femoral dynamics
Patellar motion is highly dependent upon tibio-femoral motion and may be highly abnormal even before
TKA is attempted. Chronic retinacular contracture can lead to poor patellar tracking, restricted flexion, pain
and wear.
Iatrogenic factors
There has been an extensive and well-documented history of failure to adequately address patellar tracking.
Even in recent analyses, over 15 percent of patellae have been shown to track abnormally. Iatrogenic
factors including mal-positioning of components have been important in the past, but recent improvements
in the understanding of trochlear shape and positioning have helped greatly. Too thick a patella, oblique
patellar cuts and mal-positioned buttons can lead to pain and impingements. Overstuffing of the extensor
compartment can arise from anterior femoral positioning and oversizing.
Deformity and contracture
However, even when tibio-femoral joint dynamics have been optimised there remains a cohort of patients
of about 6% in an average knee arthroplasty practice, who will require some degree of soft tissue balancing
of the extensor mechanism. This is particularly so in cases where the primary abnormality has been within
the extensor mechanism and has led on to contracture of the lateral retinacular structures and collapse of
lateral patellar or lateral femoral bone.
Assessment of tracking and its correction
Intra-operative testing should always include temporary partial closure of the medial parapatellar incision
and stress testing of the whole knee construct while carefully observing patellar tracking including with the
tibia externally rotated. Staged lateral release can be performed using various techniques such as ‘piecrusting’
and ‘inside-to-out’ cuts. It is the authors preference however to use a staged , ‘proximal-to-distal’,
‘outside-to-in’ method in order to minimise risk of damage to the geniculate vessels and keep the knee
cavity sealed from the subcutaneous plane. Once again, surgical navigation can assist with quantification of
the severity of the problem and the efficacy of correction. Medial plication may be required, but must not
be used in isolation against tight lateral structures.
Summary
• Be aware of morphological variation in the knee and severe deformities
• Optimise all component positions
• Test and adjust tibio-femoral dynamics
• Then test patella tracking
• As a last resort, re-balance the soft tissues of the PFJ.
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