Patellofemoral Landmark Studies

FRCS Level

What the Question Was

The patellofemoral literature divides cleanly into two questions that were pursued separately and have never been joined.

The mechanical question: what loads does the patella carry, over what contact area, and what moves it off track. The clinical question: why does the front of the knee hurt.

The first has good answers. The second does not, and the honest position is that the mechanical answers have not explained the symptom. 3.12.9 covers the pain problem.

A third question sits between them and is answerable: what makes a patella dislocate, as opposed to ache.

What Was Done

Ficat and Hungerford described patellofemoral disorders as a subject in their own right in the 1970s, including the cartilage changes seen at surgery.

Goodfellow and colleagues examined the patellofemoral joint's surface mechanics and cartilage behaviour in the same period, and separated surface degeneration from basal degeneration.

Huberti and Hayes measured patellofemoral contact pressure in the 1980s, across flexion and with the quadriceps line of pull altered.

Insall worked on patellar realignment and on the radiographic ratio used to describe patellar height, which gave the subject measurable parameters.

Dejour and colleagues classified trochlear dysplasia and described the tibial tubercle to trochlear groove distance in the 1990s, from imaging rather than from cadaveric work.

Farahmand and Amis measured the lateral stability of the patella across the flexion range and quantified the contribution of the soft tissue restraints.

Amis and colleagues examined the medial patellofemoral ligament's anatomy and its role in resisting lateral displacement, which underpins current reconstruction.

Powers and colleagues argued from motion analysis in the 2000s that the femur rotating beneath the patella matters as much as the patella moving on the femur.

What It Showed

Contact area moves proximally on the patella and grows with flexion, so contact pressure does not simply follow joint reaction force. 3.12.2 covers contact areas.

Patellofemoral joint reaction force in deep flexion is several times body weight, which is why stair descent and squatting provoke symptoms that level walking does not.

The medial patellofemoral ligament is the principal soft tissue restraint to lateral displacement in early flexion, and its contribution falls as the trochlea takes over. 3.12.5 covers it.

Trochlear dysplasia is the strongest structural predictor of recurrent dislocation, and it is a shape rather than a laxity. 3.12.8 covers instability.

Dynamic valgus and femoral internal rotation alter patellar tracking without any patellar abnormality, which moved the subject's attention up the limb. 3.12.7 covers it.

None of this explains patellofemoral pain. Measured maltracking and measured pain correlate weakly, and the subject has not closed that gap.

What It Changed

Instability and pain separated into different subjects with different workups, which is the single most useful change this literature produced.

Imaging parameters replaced impression in instability assessment, and surgical planning now rests on trochlear shape and tubercle position.

Medial patellofemoral ligament reconstruction replaced lateral release as the default operation for recurrent dislocation, on the basis of the restraint work.

Pain management moved towards hip and trunk control, driven by the dynamic valgus work rather than by any patellar finding.

Fellowship Level

What Was Done

The contact pressure work uses inserted sensors in cadaveric knees with simulated quadriceps pull, and both the insertion and the simulation introduce error.

Simulated quadriceps loading is usually a single line of pull, and the real quadriceps is four muscles with different directions and independent timing.

The imaging parameters are measured on static scans in extension or slight flexion, and the instability they predict happens dynamically in early flexion under load.

The motion analysis work carries the soft tissue artefact problem that limits all surface marker measurement, and patellar motion is particularly badly served by it. 3.16.7 covers the limitation.

What It Showed

Where the literature is strong: contact mechanics direction, the restraint hierarchy in early flexion, and dysplasia as a predictor of recurrence.

Where it is weak: every link between a measurement and the symptom of pain. The subject has a large literature of correlations and no established mechanism.

Where it is contested: whether tibial tubercle transfer adds anything to medial patellofemoral ligament reconstruction in a knee with a borderline tubercle position. 3.12.12 covers tubercle position.

The thresholds in common use for tubercle position and patellar height were derived on specific imaging protocols and are applied across protocols that measure them differently.

What to Read Now

Read a patellofemoral contact study for how the quadriceps was loaded, because a single line of pull limits what the result describes.

Check the imaging protocol behind any threshold before applying it, since the same number means different things on different sequences and positions.

Read the pain literature as correlation and say so, rather than restating a correlation as a mechanism.

Read instability and pain separately even when a paper treats them together.

Consultant Perspective

What It Changed

The decision this literature informs most often is what to do for anterior knee pain with measured maltracking, and the evidence genuinely does not settle it.

Arguing for a mechanical intervention: the contact pressure work shows that correcting tracking reduces local pressure, and some patients with clear structural abnormality do well.

Arguing against: the correlation between tracking and pain is weak, non-operative management of anterior knee pain succeeds in most patients given time, and an operation that corrects a measurement without addressing the symptom has added risk for nothing.

Weigh the patient's age and physiology, since skeletal maturity changes both the options and the natural history. Weigh comorbidities, including the widespread pain and sensitisation that frequently accompany this presentation. Weigh the demands on the knee, because deep flexion loading is where this joint declares itself. Weigh their psychological state seriously here rather than as a formality, since anterior knee pain is the knee presentation where distress and symptom severity are most closely linked. And elicit their ideas, concerns and expectations, because a patient who has been told their patella is out of place carries that explanation into every conversation afterwards.

Settle the balance explicitly, and record that the mechanical finding was not treated as the indication on its own.

What to Read Now

What a trainee should take from this chapter is that a well measured mechanical abnormality is not an indication, and the patellofemoral joint is where that lesson is cheapest to learn and most often ignored.

Read the instability literature for structural prediction and the pain literature for what it actually claims, which is less than it is usually quoted as claiming.

Be careful how a maltracking finding is communicated, since the explanation given to a patient becomes part of their problem and is hard to withdraw later.