Lateral retinaculum is an important stabilizer of patella, and the role of lateral retinacular release (LRR) for patellar instability is controversial.¹

Like the medial patellar retinaculum, the lateral retinaculum contributes to the stability of the patella.²

LRR can be performed as an isolated procedure or as an associated procedure. Isolated LRR should not be used for the management of patellar instability.

LRR of the patella was first described in the modern literature in 1974.³ This technique consisted of an “isolated extra-articular release of the lateral patellar retinaculum and capsule.”

One year later, a technique for LRR was published, as “section of the lateral patellar ligament,” in French literature.⁴ The objective of this surgical technique was to treat a radioclinical entity described as the “syndrome of external hyperpressure of the patella.”⁵

Currently, isolated LRR is indicated only for lateral patellar hypercompression syndrome.

Since the original description, LRR has been widely used as an adjunct procedure or as a treatment for varied conditions. These conditions include lateral patellar instability, anterior knee pain, patellar chondromalacia, patellofemoral osteoarthritis, excessive lateral hypercompression syndrome, and total knee arthroplasty.⁶,⁷,⁸,⁹,¹⁰,¹¹ This liberal application to such a wide range of conditions was in part because of the reported low complication rates and the perception that LRR was a “minor surgery.”

With widespread use of the LRR for expanded indications, there came bad results and complications.¹² Currently, the number of LRRs performed has drastically decreased as a result of these reported complications. It is also acknowledged that to diminish complications, over-release of the lateral retinaculum must be avoided.¹³

Lengthening of the lateral retinaculum, rather than complete release, has been shown to reduce complications such as medial patellar instability and quadriceps atrophy.

Although lateral retinacular (LR) lengthening has received increased attention recently, this procedure is not a new technique.¹⁴ LR lengthening has been shown to result in less medial instability, less quadriceps atrophy, and a better clinical outcome at 2 years compared with retinacular release.¹⁵ This may be explained by the controlled preservation of the lateral patellar musclecapsuloligamentous continuity after lengthening.¹

The LR structures, from superficial to deep, have been described as (1) the fibrous expansion of the vastus lateralis muscle, (2) the superficial oblique retinaculum that originates from the iliotibial band and interdigitates with the longitudinal fibers of the vastus lateralis, (3) the deep transverse retinaculum bordered superiorly by the epicondylopatellar ligament and inferiorly by the patellotibial ligament, and (4) the capsulosynovial layer¹⁶ (Figure 12.1).

Patellar motion results from the sum of the passive and active loads that act on it. The patellar ligament inferiorly and the retinacula medially and laterally are passive restraints. The quadriceps muscle is an active component that predominantly provides a superior-posterior vector, depending on the amount of knee flexion. The iliotibial band also contributes as an active lateral force to some extent. Medial and lateral forces are balanced in a normal knee, and the patella glides appropriately in the trochlea.

Alteration in this medial-lateral equilibrium can lead to pain and instability.¹⁷ It has been demonstrated that the vastus lateralis muscle is a significant biomechanical extensor of the knee and that the vastus medialis obliquus muscle is primarily a dynamic medial stabilizer of the patella that counteracts the lateral pull of the vastus lateralis muscle.¹⁸

Similarly, the vastus lateralis muscle functions to laterally stabilize the patella against the vastus medialis obliquus muscle, as shown by Montgomery et al.¹⁹ Ishibashi et al²⁰ showed that the LR tension increases with knee flexion to reach its maximum at 120° flexion.

The stability of the patella depends on the maintenance of balance between the geometry of the bone-cartilage surfaces, the integrity of the ligamentous structures, and the action of the muscular components.

For patellar instability, addressing the LR alone cannot restore the normal orientation of the malaligned extensor mechanism. The most important factor in the assessment of these patients is the evaluation of the medial patellar restraints. This can be done using passive patellar glide, measured either manually or with instrumented laxity testing, and should be compared with the opposite side.²¹ Several authors have recommended lateral procedures (release or lengthening) as an adjunct to proximal and/or distal patellar alignment procedures such as medial retinacular reefing, medial patellofemoral ligament (MPFL) reconstruction or medial tibial tubercle transfer.²⁰,²¹,²²,²³

Table 12.1 lists the indications and contraindications for LRR.

History of the onset of pain, symptoms of subluxation, specific injuries, or painful positions or activities have to be recorded.

It is important to differentiate pain from arthritis and pain caused by instability.¹,²⁴

Core weakness, increased valgus alignment, generalized ligamentous laxity, increased foot pronation, and increased femoral anteversion have all shown to contribute to anterior knee pain and patellar instability.

The muscle balance between the vastus medialis obliquus and the vastus lateralis is important because a significant imbalance can lead to dynamic patellar instability. One significant clinical sign is the J-sign, illustrated in Figure 12.2. This describes lateral subluxation of the patella in terminal knee extension as a result of the nonlinear path of the patella.

Patellar mobility is another major factor that needs to be evaluated. The assessment of medial/lateral patella glide²¹,²⁵ as well as patellar tilt allows to determine whether the peripatellar soft-tissue restraints may be insufficient or too tight and predispose the patella to lateral subluxation. If medial translation is less than one quadrant or if the patella cannot be lifted from lateral femoral condyle over the neutral (horizontal) plane with the knee in extension, then LRR or lateral
lengthening should be considered in addition to proximal/distal alignment procedure.

The assessment of the overall extensor alignment can be performed by assessing the Q-angle,²⁶ illustrated in Figure 12.3. A lateralized insertion of the patellar tendon results in overall increased lateral force on the patella.

Patients’ ligamentous laxity should be assessed, and those with increased laxity (generalized hyperlaxity) as assessed with Beighton score or similar criteria should not be considered for LRR or lateral lengthening.

Once the clinical diagnosis of patellar instability is made, imaging modalities may then help to corroborate the clinical findings.

In more than 96% of cases of patellar instability, the radiographic evaluation would detect at least one of the four characteristic features—patellar height, patellar tilt, trochlear dysplasia, and increased tibial tubercle-trochlear groove distance.²⁴ In this chapter, the focus would be on the imaging modalities that would influence the decision to perform a lateral release or lengthening.

The important examinations to evaluate for patellar tilt are the skyline radiographic view and the computed tomography (CT) scan.

The skyline view of the patella in 30° flexion would show either laterally subluxed or laterally tilted patella (Figure 12.4).

The patellar tilt can be assessed on a CT scan knee in extension without quadriceps contraction (Figure 12.5), by measuring the angle subtended by a line through the transverse axis of the patella and a line tangential to the posterior aspect of the posterior condyles. Values greater than 20° of lateral tilt are considered abnormal.