Patellofemoral Joint and Patellar Instability

For patellofemoral symptoms, assess contact and tracking at different flexion angles alongside strength and activity. The J sign, trochlear shape, patellar height, and rotational alignment provide different information. Anterior knee pain cannot be reduced to one anatomical measurement.

Distinguish what radiographs, CT, and MRI show. Interpret cartilage injury, trochlear dysplasia, soft-tissue injury, and associated alignment together. Treatment starts by considering imaging classifications with the patient’s function.

Anterior knee pain can arise from different problems, including patellofemoral cartilage changes, tendons or the fat pad, overload, and movement patterns. Document provoking situations such as stairs, squatting, or prolonged sitting, along with effusion, ROM, and tenderness, and distinguish pain from a history of actual dislocation or subluxation. Do not establish the cause from the Q-angle alone or use the imaging term chondromalacia to explain all pain.

Patellar stability depends on both soft tissues such as the MPFL and retinaculum and bony factors such as the trochlea, patellar height, and rotational and coronal limb structure. Observe the phase in which the patella enters the trochlea and tracking during flexion, and separate the assessment goals for recurrent dislocation from those for pain alone. Exercise assessment should address the hip and ankle, increases in loading, and actual movement, rather than focusing only on the quadriceps.

The MPFL is one structure restraining lateral patellar displacement. Planning reconstruction requires the dislocation history, anatomical risk factors, and cartilage assessment. Soft-tissue reconstruction alone does not resolve all bony or rotational risk factors.

Femoral attachment, graft length change, and tension matter. Overtensioning can affect pain and joint-surface loading. With open growth plates, attachment and tunnel planning need separate consideration. Do not use one imaging measurement alone as a surgical criterion.

MPFL reconstruction restores the restraining function of the medial soft tissues; it does not correct all bony risk factors. Assess trochlear dysplasia, patella alta, tubercle position, rotational deformity, and growth plates together. When comparing measurements such as TT–TG, check differences between CT and MRI and in knee position; a single threshold should not determine additional bony surgery.

Femoral attachment position and graft tension affect pressure and ROM during flexion. Overtensioning may cause medial overload or restricted flexion, so maximum tightness is not the goal. The ESSKA first-dislocation consensus emphasizes individualized decisions that consider recurrence risk, activity demands, and osteochondral lesions. Explain reconstruction and bony correction choices, strength of evidence, and the role of rehabilitation separately.

Patellofemoral problems after TKA are not explained solely by patellar resurfacing. Assess femoral component rotation and size, the joint line, patellar thickness and blood supply, and the extensor mechanism together.

When comparing routine resurfacing with non-resurfacing, evaluate pain, reoperation, fracture, and fixation problems as separate outcomes. For patellar fractures, implant fixation and continuity of the extensor mechanism are central to treatment decisions.

Patellar tracking in TKA is not solely a patellar problem. Femoral and tibial component rotation, size and position, the joint line, patellar resection and residual thickness, and extensor-mechanism tension all contribute. Before lateral release, review component position and resection and contact conditions to avoid missing the cause. Patellar thickness and bone quality are also needed to assess fracture and fixation risk.

When comparing resurfacing and non-resurfacing, distinguish anterior pain, secondary surgery, and fracture and fixation problems, and examine the design and follow-up duration. Pain in an already operated knee requires separate assessment of clunk, impingement, maltracking, infection, and loosening. In periprosthetic patellar fractures, component stability and continuity of the extensor mechanism are more important to treatment feasibility than the classification number alone.

Trochlear dysplasia describes abnormal depth and shape of the femoral groove that guides the patella. Soft-tissue restraints, including the MPFL, contribute substantially in early flexion; bony geometry becomes more influential as the patella enters the groove. Relate the timing of recurrent dislocation, apprehension, and the J-sign to the contribution of the groove to actual instability. Distinguish isolated anterior pain from repeated objective dislocation.

On a true lateral radiograph, examine the crossing sign, supratrochlear spur, and double contour; use axial MRI or CT to assess trochlear depth, inclination, and cartilage morphology. The Dejour classification communicates shape but does not automatically determine an operation. Radiographic rotation can distort lateral findings, and TT–TG distance and patellar height depend on measurement methods. Record bony prominence, delayed patellar engagement, and dislocation behavior separately.

MPFL reconstruction restores the medial soft-tissue restraint but does not directly reshape a prominent or shallow trochlea. Trochleoplasty changes bony geometry but does not resolve every accompanying abnormality of patellar height, tubercle lateralization, or rotation. Consider combined correction for severe dysplasia with recurrent instability; selected patients can also improve after isolated MPFL reconstruction. Include growth-plate status, cartilage injury, previous surgery, and rehabilitation feasibility in the same plan.

Interpret trochleoplasty outcomes separately for redislocation, pain and function, range of motion, and reoperation. Reduced dislocation can coexist with stiffness or persistent cartilage-related pain, so groove depth alone does not define success. Evidence for trochleoplasty solely for established arthritis or pain is limited. Follow-up should assess flexion recovery, anterior pain, and activity goals alongside stability testing.

Tibial tubercle osteotomy moves the patellar tendon attachment to change the extensor-mechanism force vector and patellofemoral contact. Medialization reduces a lateralized force vector; anteromedialization alters both alignment and contact-load distribution; distalization changes when a high patella engages the groove. These directions differ in purpose and adverse effects. First define whether the goal is control of recurrent instability or unloading of a focal cartilage lesion.

Include TT–TG distance, patellar height, the J-sign, trochlear morphology, and femoral and tibial rotation in planning. CT and MRI TT–TG values are not interchangeable, and flexion and rotation during imaging also matter. Determine whether a large TT–TG reflects tubercle lateralization, groove position, or rotational deformity. Assess the location and surrounding condition of cartilage damage to anticipate where contact will increase after transfer. A single number cannot determine the medial translation for every patient.

Actual anterior and medial translation during anteromedialization are jointly determined by osteotomy-plane inclination and fragment movement. Intraoperative estimates can overstate anterior translation compared with imaging, so document the plane and translation explicitly. Distalization can correct alta, but excessive correction producing patella baja may increase contact pressure in early flexion. Plan the need and magnitude of medialization, anteriorization, and distalization separately.

Tubercle transfer does not replace treatment of MPFL dysfunction, trochlear dysplasia, or rotational deformity; clarify the role of accompanying procedures. Protect fragment thickness, cortical continuity, and fixation, and monitor fracture, nonunion, and symptomatic screws. Progress weight-bearing and active extension according to osteotomy stability, concomitant cartilage treatment or ligament reconstruction, and union. Assess redislocation, pain, height indices, actual tracking, and reoperation as separate outcomes.